Pseudo-envelope follower power management system with high frequency ripple current compensation

[0001] The present application claims priority to U.S. Provisional Patent Application No. 61/421,348, filed Dec. 9, 2010.

[0002] The present application claims priority to U.S. Provisional Patent Application No. 61/421,475, filed Dec. 9, 2010.

[0003] The present application claims priority to U.S. Provisional Patent Application No. 61/469,276, filed Mar. 30, 2011.

[0004] The present application claims priority to and is a continuation-in-part of U.S. patent application Ser. No. 13/089,917, filed Apr. 19, 2011, entitled “PSEUDO-ENVELOPE FOLLOWING POWER MANAGEMENT SYSTEM,” which claims priority to U.S. Provisional Patent Application No. 61/325,659, filed Apr. 19, 2010.

[0005] The present application claims priority to and is a continuation-in-part of U.S. patent application Ser. No. 13/218,400, filed Aug. 25, 2011, entitled “BOOST CHARGE-PUMP WITH FRACTIONAL RATIO AND OFFSET LOOP FOR SUPPLY MODULATION,” which claims priority to U.S. Provisional Patent Application No. 61/376,877, filed Aug. 25, 2010. U.S. patent application Ser. No. 13/218,400, is a continuation-in-part of U.S. patent application Ser. No. 13/089,917, filed Apr. 19, 2011, which claims priority to U.S. Provisional Patent Application No. 61/325,659, filed Apr. 19, 2010.

[0006] All of the applications listed above are hereby incorporated herein by reference in their entireties.

[0007] The embodiments described herein relate to a power management system for delivering current to a linear RF power amplifier. More particularly, the embodiments relate to the use of a pseudo-envelope tracker in a power management system of mobile communications equipment.

[0008] Next-generation mobile devices are morphing from voice-centric telephones to message and multimedia-based “smart” phones that offer attractive new features. As an example, smart phones offer robust multimedia features such as web-browsing, audio and video playback and streaming, email access and a rich gaming environment. But even as manufacturers race to deliver ever more feature rich mobile devices, the challenge of powering them looms large.

[0009] In particular, the impressive growth of high bandwidth applications for radio-frequency (RF) hand-held devices has led to increased demand for efficient power saving techniques to increase battery life. Because the power amplifier of the mobile device consumes a large percentage of the overall power budget of the mobile device, various power management systems have been proposed to increase the overall power efficiency of the power amplifier.

[0010] As an example, some power managements systems may use a V_RAMP power control voltage to control the voltage presented on a power amplifier collector of a linear RF power amplifier. As another example, other power management schemes may use a buck converter power supply and a class AB amplifier in tandem to provide power to the linear RF power amplifier.

[0011] Even so, there remains a need to further improve the power efficiency of mobile devices to provide extended battery life. As a result, there is a need to improve the power management system of mobile devices.

[0012] Embodiments disclosed in the detailed description relate to a pseudo-envelope follower power management system including a parallel amplifier and a switch mode power supply converter cooperatively coupled to generate a power supply voltage at a power supply output coupled to a linear RF power amplifier. The parallel amplifier output is in communication with the power amplifier supply output. The parallel amplifier governs operation of the switch mode power supply converter and regulates the power amplifier supply voltage base on a V_RAMP signal. The parallel amplifier circuit includes an open loop high frequency compensation assist circuit that generates a high frequency ripple compensation current based on an estimate of the high frequency ripple currents contained in a ripple current of the power inductor. The high frequency ripple compensation current is injected into the parallel amplifier circuit output to cancel out high frequency ripple currents at the power amplifier supply output

[0013] A first embodiment of pseudo-envelope follower power management system with high frequency ripple compensation includes a switch mode power supply converter and an open loop high frequency ripple compensation assist circuit. For example, the switch mode power supply converter may be configured to operate as a buck converter. As another example, the switch mode power supply converter may be configured to operate as a multi-level charge pump buck converter. The switch mode power supply may generate a switching output voltage and a switching voltage output estimate. The switching voltage output estimate may provide an early indication of a future voltage level of the switching output voltage. For example, in some embodiments, the switch mode power supply converter may also include programmable delay circuitry, a switcher control circuit, and a buffer scalar. The switcher control circuit may generate a digital switching voltage output signal that represents a state of the switcher control circuit used to control generation of the switching output voltage by the switch mode power supply converter. The programmable delay circuitry may receive the digital switching voltage output signal, and delay the digital switching voltage output signal by a programmable delay period to generate a delayed digital switching voltage output signal. The buffer scalar is configured to receive the delayed digital switching voltage output signal, and generate the switching voltage output estimate based on the delayed digital switching voltage output signal and a buffer scalar.

[0014] The open loop high frequency ripple compensation assist circuit is configured to receive the switching voltage output estimate and a V_RAMP signal. Based on the based on the switching voltage output estimate and the V_RAMP signal, the open loop high frequency ripple compensation assist circuit generates a high frequency ripple compensation current. The open loop high frequency ripple compensation assist circuit applies the high frequency ripple compensation current to a power amplifier supply output to reduce high frequency ripple current at the power amplifier supply output. The power amplifier supply output is configured to power a linear radio frequency power amplifier. The high frequency ripple compensation current is generated in a frequency band located substantially near a transmit to receive duplex offset for a band of operation in a communication network, where the frequency band of the high frequency ripple compensation current has a bandwidth substantially equal to a bandwidth of a receiver channel frequency band for the band of operation.

[0015] In some embodiments, the switch mode power supply converter further includes a programmable delay circuitry configured to delay generation of the switching voltage output estimate by a programmable delay period. The programmable delay period may be configured to temporally align the switching voltage output estimate and the V_RAMP signal to position a notch in a ripple rejection response of the power amplifier supply output near the transmit to receive duplex offset for the band of operation. In addition, the open loop high frequency ripple compensation assist circuit may generate a scaled high frequency ripple compensation current estimate based on the high frequency ripple compensation current, which can be used as part of a feedback signal to the switch mode power supply converter. As an example, the switch mode power supply converter may receive a feedback signal, wherein the feedback signal is based on the scaled high frequency ripple compensation current estimate, where the switch mode power supply converter adjusts the switching output voltage based on the feedback signal. In some embodiments, the pseudo-envelope follower power management system with high frequency ripple compensation further includes a parallel amplifier. The parallel amplifier receives the V_RAMP signal and a power amplifier supply voltage from the power amplifier supply output. Based on a difference between the V_RAMP signal and the power amplifier supply voltage, the parallel amplifier generates a parallel amplifier output current. The parallel amplifier applies the parallel amplifier output current to the power amplifier supply output to control the power amplifier supply voltage. In addition, the parallel amplifier may generate a scaled parallel amplifier output current estimate based on the parallel amplifier output current. The scaled parallel amplifier output current estimate may be combined with the scaled high frequency ripple compensation current estimate to create the feedback signal provided to the switch mode power supply converter.

[0016] Some embodiments of open loop high frequency ripple compensation assist circuit may include a filter network having a first node and a second node, a feedback network having a first node and a second node, and an operational amplifier including a non-inverting input, an inverting input, and an operational amplifier output. The first node of the filter network may be configured to receive the switching voltage output estimate. The second node of the filter network may be in communication with the inverting input of the operational amplifier. The first node of the feedback network may be in communication with the second node of the filter network and the inverting input of the operational amplifier. In addition, the second node of the feedback network may be in communication with the operational amplifier output. The operational amplifier may be configured to generate the high frequency ripple compensation current. The operational amplifier may also be configured to generate a scaled high frequency ripple compensation current estimate as a function of the high frequency ripple compensation current. The operational amplifier may include a first push-pull output stage in communication with the operational amplifier output, where the first push-pull output stage generates an operational amplifier output current. A bias capacitor having a bias capacitance and a bias resistor may be arranged in series between the operational amplifier output and a reference voltage. For example, the reference voltage may be ground. The first push-pull output stage may have a first stage transconductance. The bias capacitance may be configured such that the first stage transconductance of the first push-pull output stage is substantially equal to a transconductance of the bias resistor in a frequency band located substantially near a transmit to receive duplex offset for a band of operation in a communication network. The open loop high frequency ripple compensation assist circuit may also include an operational amplifier output isolation circuit including a high impedance input in communication with the operational amplifier output and an isolated feedback node in communication with the second node of the feedback network. The operational amplifier may also include a second push-pull output stage configured to generate the high frequency ripple compensation current, where the high frequency ripple compensation current is mirrored to the operational amplifier output current. The second push-pull output stage may include a programmable second output stage transconductance. The programmable second output stage transconductance second output stage transconductance may be a substantially linear function of a programmable transconductance parameter. The open loop high frequency ripple compensation assist circuit may adjust a magnitude of the high frequency ripple compensation current based on the programmable second output stage transconductance. The operational amplifier may also include a third push-pull output stage configured to generate the scaled high frequency ripple compensation current estimate as a function of the high frequency ripple compensation current based on a sense scaling factor.

[0017] The filter network may be associated with a first corner frequency of a filter response of the open loop ripple compensation assist circuit. The feedback network may be associated with a second corner frequency of the frequency response of the open loop ripple compensation assist circuit. In some cases, the first corner frequency has a programmable range between 3 MHz and 11.5 MHz and the second corner frequency has a programmable range between 3 MHz and 11.5 MHz. In other cases, the first corner frequency is substantially equal to 6 MHz, and the second corner frequency is substantially equal to 6 MHz.

[0018] Another example embodiment includes a method for reducing high frequency ripple currents at a power amplifier supply output. The method may include a first step of generating a switching output voltage and a switching voltage output estimate with a switch mode power supply converter, where the switching voltage output estimate provides an early indication of a future voltage level of the switching output voltage. The method may include the step of receiving the switching voltage output estimate and a V_RAMP signal at an open loop high frequency ripple compensation assist circuit. The method may include the step of generating a high frequency ripple compensation current based on the switching voltage output estimate and the V_RAMP signal. The method may include the step of applying the high frequency ripple compensation current to a power amplifier supply output to reduce high frequency ripple current at the power amplifier supply output. In some embodiments the generation of the high frequency ripple compensation current based on the switching voltage output estimate and the V_RAMP signal may include generating the high frequency ripple compensation current within in a frequency band located substantially near a transmit to receive duplex offset for a band of operation in a communication network. In addition, the frequency band of the high frequency ripple compensation current may have a bandwidth substantially equal to a bandwidth of a receiver channel frequency band for the band of operation. In some embodiments, generation of the switching voltage output estimate may include delaying generation of the switching voltage output estimate by a programmable delay period to temporally align the switching voltage output estimate and the V_RAMP signal to position a notch in a ripple rejection response of the power amplifier supply output near the transmit to receive duplex offset for the band of operation. In addition, the method may further include a step for generating a scaled high frequency ripple compensation current estimate based on the high frequency ripple compensation current. Based on the scaled high frequency ripple compensation current estimate, the method may form a feedback signal, which is provided to the switch mode power supply converter. The switch mode power supply converter may adjust the switching output voltage based on the feedback signal. In some embodiments, the switch mode power supply converter is configured to be a buck converter. Alternatively, in other embodiments, the switch mode power supply converter is configured to be a multi-level charge pump buck converter.

[0019] One example embodiment of the pseudo-envelope follower power management system may include a switch mode power supply converter and a parallel amplifier cooperatively coupled to provide a linear RF power amplifier supply to a linear RF power amplifier. The pseudo-envelope follower power management system may include a charge pump configured to power the parallel amplifier. The charge pump may generate a plurality of output voltage levels. The charge pump may be either a boost charge pump or a boost/buck charge pump. The pseudo-envelope follower power management system may include an offset voltage control circuit configured to provide feedback to the switch mode power supply converter to regulate an offset voltage developed across a coupling device that couples the output of the parallel amplifier to the linear RF power amplifier supply.

[0020] Another example embodiment of a power management system for a linear radio frequency power amplifier includes a switch mode power supply converter and a parallel amplifier operatively coupled to generate a linear radio frequency power amplifier supply output for a linear radio frequency power amplifier of a radio frequency device. The switch mode power supply converter may be configured to generate a plurality of switching voltage levels on a switching voltage output. The switching voltage output of the switch mode power supply converter may be coupled via a power inductor to the linear radio frequency power amplifier supply output. A bypass capacitor may be coupled between the linear radio frequency power amplifier supply output and ground such that the power inductor and bypass capacitor form a low pass filter for the switch mode power supply converter. The parallel amplifier may include a parallel amplifier output coupled, via a coupling device, to the linear radio frequency power amplifier supply output. As an example, the coupling device may be a coupling capacitor. The power management system may further include a charge pump configured to provide a charge pump parallel amplifier power supply output. The charge pump may include a first flying capacitor, a second flying capacitor, a plurality of switches operably coupled to form the charge pump parallel amplifier power supply output. The charge pump may be configured to selectively generate various output voltage levels, derived from a supply voltage, on the charge pump parallel amplifier power supply output. In addition, the charge pump parallel amplifier power supply output may be configured to provide an operational power supply voltage to the parallel amplifier.

[0021] Another example embodiment of a pseudo-envelope follower power management system may include a multi-level charge pump buck converter and a parallel amplifier configured to operate in tandem to generate a power amplifier supply voltage output for a linear RF power amplifier. The multi-level charge pump buck converter may include a supply input configured to receive a direct current (DC) voltage, and a switching voltage output. The switching voltage output is coupled to the power amplifier supply voltage output by a power inductor, where the power inductor couples to a bypass capacitor to form an output filter for the switching voltage output of the multi-level charge pump buck converter. The parallel amplifier may include a supply input configured to receive the direct current (DC) voltage, an amplifier output, a first control input configured to receive a V_RAMP signal, and a second control input configured to receive the power amplifier supply voltage. The amplifier output may be coupled to the power amplifier supply voltage by a coupling circuit. In some embodiments of the pseudo-envelope follower system, the coupling circuit may be an offset capacitor. In other embodiments of the pseudo-envelope follower system, the coupling circuit may be a wire trace such that the offset voltage between the amplifier output and the power amplifier supply voltage is zero volts.

[0022] In addition, the multi-level charge pump buck converter may generate a feed forward control signal configured to provide an indication of the output state of the switching voltage output to the parallel amplifier. In some embodiments, the switching voltage output is provided as the feed forward control signal. In other embodiments, the feed forward control signal is generated by a switcher control circuit and provides an indication of the switching voltage output based on the state of the switcher control circuit. The parallel amplifier may include a power amplifier output current estimate signal that provides an estimate of the output current of the parallel amplifier. In some embodiments of the pseudo-envelope follower system, the parallel amplifier may also generate a threshold offset signal. The threshold offset signal may be configured to estimate the magnitude of the offset voltage appearing across the coupling circuit.

[0023] The multi-level buck converter may include a supply input configured to receive a direct current (DC) voltage, a switching voltage output coupled to a power inductor, a switcher control circuit, a multi-level charge pump circuit having a control input, a charge pump supply input configured to receive the DC voltage, a series switch having a first switch terminal, a second switch terminal, and a series control terminal and a shunt switch having a first switch terminal, a second switch terminal, and a shunt control terminal. The first terminal of the series switch may be coupled to the supply input of the multi-level buck converter. The second terminal of the series switch may be coupled to the first terminal of the series switch to form a switching voltage output. The second terminal of the series switch may be coupled to ground. The boost charge pump circuit may include a charge pump control input, a charge pump supply input coupled to the supply input of the multi-level buck converter, and a charge pump output coupled to the supply input of the multi-level buck converter. The boost charge pump includes a plurality of switches and two flying capacitors that provide for three modes of operation. In a charging mode of operation, the flying capacitors are coupled in series between the charge pump supply input and ground, wherein the flying capacitors are switchably disconnected from the charge pump output. In a first boost mode of operation, the flying capacitors are arranged in parallel between the charge pump output and the charge pump supply input to generate a 1.5× the DC voltage output at the charge pump output. In a second boost mode of operation, the flying capacitors are arranged in series between the charge pump output and the charge pump supply input to generate a 2× the DC voltage output at the charge pump output. The multi-level buck converter may include four modes of operation. In a first mode of operation, the series switch is open, the boost charge pump is in the charging mode of operation, and the shunt switch is closed to generate zero volts at the switching voltage output. In a second mode of operation, the series switch is closed, the boost charge pump is in the charging mode of operation, and the shunt switch is open to generate the DC voltage output at the switching voltage output. In a third mode of operation, both the series switch and the shunt switch are open and the boost charge pump is in the first boost mode of operation to generate a 1.5× the DC voltage output at the switching mode output. In a fourth mode of operation, both the series switch and the shunt switch are open and the boost charge pump is in the second boost mode of operation to generate a 2× the DC voltage output at the switching mode output.

[0024] Those skilled in the art will appreciate the scope of the disclosure and realize additional aspects thereof after reading the following detailed description in association with the accompanying drawings.

[0148] The embodiments set forth below represent the necessary information to enable those skilled in the art to practice the disclosure and illustrate the best mode of practicing the disclosure. Upon reading the following description in light of the accompanying drawings, those skilled in the art will understand the concepts of the disclosure and will recognize applications of these concepts not particularly addressed herein. It should be understood that these concepts and applications fall within the scope of the disclosure and the accompanying claims.

[0149] Embodiments disclosed herein relate to a pseudo-envelope follower power management system including a parallel amplifier and a switch mode power supply converter cooperatively coupled to generate a power supply voltage at a power supply output coupled to a linear RF power amplifier. The parallel amplifier output is in communication with the power amplifier supply output. The parallel amplifier governs operation of the switch mode power supply converter and regulates the power amplifier supply voltage base on a V_RAMP signal. The parallel amplifier circuit includes an open loop high frequency compensation assist circuit that generates a high frequency ripple compensation current based on an estimate of the high frequency ripple currents contained in a ripple current of the power inductor. The high frequency ripple compensation current is injected into the parallel amplifier circuit output to cancel out high frequency ripple currents at the power amplifier supply output.

[0150] A first embodiment of the pseudo-envelope follower power management system with high frequency ripple compensation includes a switch mode power supply converter and an open loop high frequency ripple compensation assist circuit. For example, the switch mode power supply converter may be configured to operate as a buck converter. As another example, the switch mode power supply converter may be configured to operate as a multi-level charge pump buck converter. The switch mode power supply may generate a switching output voltage and a switching voltage output estimate. The switching voltage output estimate may provide an early indication of a future voltage level of the switching output voltage. For example, in some embodiments, the switch mode power supply converter may also include programmable delay circuitry, a switcher control circuit, and a buffer scalar. The switcher control circuit may generate a digital switching voltage output signal that represents a state of the switcher control circuit used to control generation of the switching output voltage by the switch mode power supply converter. The programmable delay circuitry may receive the digital switching voltage output signal, and delay the digital switching voltage output signal by a programmable delay period to generate a delayed digital switching voltage output signal. The buffer scalar is configured to receive the delayed digital switching voltage output signal, and generate the switching voltage output estimate based on the delayed digital switching voltage output signal and a buffer scalar.

[0151] The open loop high frequency ripple compensation assist circuit is configured to receive the switching voltage output estimate and a V_RAMP signal. Based on the switching voltage output estimate and the V_RAMP signal, the open loop high frequency ripple compensation assist circuit generates a high frequency ripple compensation current. The open loop high frequency ripple compensation assist circuit applies the high frequency ripple compensation current to a power amplifier supply output to reduce high frequency ripple current at the power amplifier supply output. The power amplifier supply output is configured to power a linear radio frequency power amplifier. The high frequency ripple compensation current is generated in a frequency band located substantially near a transmit to receive duplex offset for a band of operation in a communication network, where the frequency band of the high frequency ripple compensation current has a bandwidth substantially equal to a bandwidth of a receiver channel frequency band for the band of operation.

[0152] In some embodiments, the switch mode power supply converter further includes programmable delay circuitry configured to delay generation of the switching voltage output estimate by a programmable delay period. The programmable delay period may be configured to temporally align the switching voltage output estimate and the V_RAMP signal to position a notch in a ripple rejection response of the power amplifier supply output near the transmit to receive duplex offset for the band of operation. In addition, the open loop high frequency ripple compensation assist circuit may generate a scaled high frequency ripple compensation current estimate based on the high frequency ripple compensation current, which can be used as part of a feedback signal to the switch mode power supply converter. As an example, the switch mode power supply converter may receive a feedback signal, wherein the feedback signal is based on the scaled high frequency ripple compensation current estimate, where the switch mode power supply converter adjusts the switching output voltage based on the feedback signal. In some embodiments, the pseudo-envelope follower power management system with high frequency ripple compensation further includes a parallel amplifier. The parallel amplifier receives the V_RAMP signal and a power amplifier supply voltage from the power amplifier supply output. Based on a difference between the V_RAMP signal and the power amplifier supply voltage, the parallel amplifier generates a parallel amplifier output current. The parallel amplifier applies the parallel amplifier output current to the power amplifier supply output to control the power amplifier supply voltage. In addition, the parallel amplifier may generate a scaled parallel amplifier output current estimate based on the parallel amplifier output current. The scaled parallel amplifier output current estimate may be combined with the scaled high frequency ripple compensation current estimate to create the feedback signal provided to the switch mode power supply converter.

[0153] Some embodiments of the open loop high frequency ripple compensation assist circuit may include a filter network having a first node and a second node, a feedback network having a first node and a second node, and an operational amplifier including a non-inverting input, an inverting input, and an operational amplifier output. The first node of the filter network may be configured to receive the switching voltage output estimate. The second node of the filter network may be in communication with the inverting input of the operational amplifier. The first node of the feedback network may be in communication with the second node of the filter network and the inverting input of the operational amplifier. In addition, the second node of the feedback network may be in communication with the operational amplifier output. The operational amplifier may be configured to generate the high frequency ripple compensation current. The operational amplifier may also be configured to generate a scaled high frequency ripple compensation current estimate as a function of the high frequency ripple compensation current. The operational amplifier may include a first push-pull output stage in communication with the operational amplifier output, where the first push-pull output stage generates an operational amplifier output current. A bias capacitor having a bias capacitance and a bias resistor may be arranged in series between the operational amplifier output and a reference voltage. For example, the reference voltage may be ground. The first push-pull output stage may have a first stage transconductance. The bias capacitance may be configured such that the first stage transconductance of the first push-pull output stage is substantially equal to a transconductance of the bias resistor in a frequency band located substantially near a transmit to receive duplex offset for a band of operation in a communication network. The open loop high frequency ripple compensation assist circuit may also include an operational amplifier output isolation circuit including a high impedance input in communication with the operational amplifier output and an isolated feedback node in communication with the second node of the feedback network. The operational amplifier may also include a second push-pull output stage configured to generate the high frequency ripple compensation current, where the high frequency ripple compensation current is mirrored to the operational amplifier output current. The second push-pull output stage may include a programmable second output stage transconductance. The programmable second output stage transconductance second output stage transconductance may be a substantially linear function of a programmable transconductance parameter. The open loop high frequency ripple compensation assist circuit may adjust a magnitude of the high frequency ripple compensation current based on the programmable second output stage transconductance. The operational amplifier may also include a third push-pull output stage configured to generate the scaled high frequency ripple compensation current estimate as a function of the high frequency ripple compensation current based on a sense scaling factor.

[0154] The filter network may be associated with a first corner frequency of a filter response of the open loop high frequency ripple compensation assist circuit. The feedback network may be associated with a second corner frequency of the frequency response of the open loop high frequency ripple compensation assist circuit. In some cases, the first corner frequency has a programmable range between 3 MHz and 11.5 MHz and the second corner frequency has a programmable range between 3 MHz and 11.5 MHz. In other cases, the first corner frequency is substantially equal to 6 MHz, and the second corner frequency is substantially equal to 6 MHz.

[0155] Another example embodiment includes a method for reducing high frequency ripple currents at a power amplifier supply output. The method may include a first step of generating a switching output voltage and a switching voltage output estimate with a switch mode power supply converter, where the switching voltage output estimate provides an early indication of a future voltage level of the switching output voltage. The method may include the step of receiving the switching voltage output estimate and a V_RAMP signal at an open loop high frequency ripple compensation assist circuit. The method may include the step of generating a high frequency ripple compensation current based on the switching voltage output estimate and the V_RAMP signal. The method may include the step of applying the high frequency ripple compensation current to a power amplifier supply output to reduce high frequency ripple currents at the power amplifier supply output. In some embodiments, the generation of the high frequency ripple compensation current based on the switching voltage output estimate and the V_RAMP signal may include generating the high frequency ripple compensation current within in a frequency band located substantially near a transmit to receive duplex offset for a band of operation in a communication network. In addition, the frequency band of the high frequency ripple compensation current may have a bandwidth substantially equal to a bandwidth of a receiver channel frequency band for the band of operation. In some embodiments, generation of the switching voltage output estimate may include delaying generation of the switching voltage output estimate by a programmable delay period to temporally align the switching voltage output estimate and the V_RAMP signal to position a notch in a ripple rejection response of the power amplifier supply output near the transmit to receive duplex offset for the band of operation. In addition, the method may further include a step for generating a scaled high frequency ripple compensation current estimate based on the high frequency ripple compensation current. Based on the scaled high frequency ripple compensation current estimate, the method may form a feedback signal, which is provided to the switch mode power supply converter. The switch mode power supply converter may adjust the switching output voltage based on the feedback signal. In some embodiments, the switch mode power supply converter is configured to be a buck converter. Alternatively, in other embodiments, the switch mode power supply converter is configured to be a multi-level charge pump buck converter.

[0156] Embodiments disclosed herein further relate to a pseudo-envelope follower power management system used to manage the power delivered to a linear RF power amplifier. One example embodiment of the pseudo-envelope follower power management system may include a switch mode power supply converter and a parallel amplifier cooperatively coupled to provide a linear RF power amplifier supply to a linear RF power amplifier. The pseudo-envelope follower power management system may include a charge pump configured to power the parallel amplifier. The charge pump may generate a plurality of output voltage levels. The charge pump may be either a boost charge pump or a boost/buck charge pump. The pseudo-envelope follower power management system may include an offset voltage control circuit configured to provide feedback to the switch mode power supply converter to regulate an offset voltage developed across a coupling device that couples the output of the parallel amplifier to the linear RF power amplifier supply.

[0157] Another example embodiment of a power management system for a linear radio frequency power amplifier includes a switch mode power supply converter and a parallel amplifier operatively coupled to generate a linear radio frequency power amplifier supply output for a linear radio frequency power amplifier of a radio frequency device. The switch mode power supply converter may be configured to generate a plurality of switching voltage levels on a switching voltage output. The switching voltage output of the switch mode power supply converter may be coupled via a power inductor to the linear radio frequency power amplifier supply output. A bypass capacitor may be coupled between the linear radio frequency power amplifier supply output and ground such that the power inductor and bypass capacitor form a low pass filter for the switch mode power supply converter. The parallel amplifier may include a parallel amplifier output coupled, via a coupling device, to the linear radio frequency power amplifier supply output. As an example, the coupling device may be a coupling capacitor. The power management system may further include a charge pump configured to provide a charge pump parallel amplifier power supply output. The charge pump may include a first flying capacitor, a second flying capacitor, a plurality of switches operably coupled to form the charge pump parallel amplifier power supply output. The charge pump may be configured to selectively generate various output voltage levels, derived from a supply voltage, on the charge pump parallel amplifier power supply output. In addition, the charge pump parallel amplifier power supply output may be configured to provide an operational power supply voltage to the parallel amplifier.

[0158] Another example embodiment of a pseudo-envelope follower power management system may include a multi-level charge pump buck converter and a parallel amplifier configured to operate in tandem to generate a power amplifier supply voltage output for a linear RF power amplifier. The multi-level charge pump buck converter may include a supply input configured to receive a direct current (DC) voltage, and a switching voltage output. The switching voltage output is coupled to the power amplifier supply voltage output by a power inductor, where the power inductor couples to a bypass capacitor to form an output filter for the switching voltage output of the multi-level charge pump buck converter. The parallel amplifier may include a supply input configured to receive the direct current (DC) voltage, an amplifier output, a first control input configured to receive a V_RAMP signal, and a second control input configured to receive the power amplifier supply voltage. The amplifier output may be coupled to the power amplifier supply voltage by a coupling circuit. In some embodiments of the pseudo-envelope follower system, the coupling circuit may be an offset capacitor. In other embodiments of the pseudo-envelope follower system, the coupling circuit may be a wire trace such that the offset voltage between the amplifier output and the power amplifier supply voltage is zero volts.

[0159] In addition, the multi-level charge pump buck converter may generate a feed forward control signal configured to provide an indication of the output state of the switching voltage output to the parallel amplifier. In some embodiments, the switching voltage output is provided as the feed forward control signal. In other embodiments, the feed forward control signal is generated by a switcher control circuit and provides an indication of the switching voltage output based on the state of the switcher control circuit. The parallel amplifier may include a power amplifier output current estimate signal that provides an estimate of the output current of the parallel amplifier. In some embodiments of the pseudo-envelope follower system, the parallel amplifier may also generate a threshold offset signal. The threshold offset signal may be configured to estimate the magnitude of the offset voltage appearing across the coupling circuit.

[0160] The multi-level buck converter may include a supply input configured to receive a direct current (DC) voltage, a switching voltage output coupled to a power inductor, a switcher control circuit, a multi-level charge pump circuit having a control input, a charge pump supply input configured to receive the DC voltage, a series switch having a first switch terminal, a second switch terminal, and a series control terminal and a shunt switch having a first switch terminal, a second switch terminal, and a shunt control terminal. The first terminal of the series switch may be coupled to the supply input of the multi-level buck converter. The second terminal of the series switch may be coupled to the first terminal of the series switch to form a switching voltage output. The second terminal of the series switch may be coupled to ground. The boost charge pump circuit may include a charge pump control input, a charge pump supply input coupled to the supply input of the multi-level buck converter, and a charge pump output coupled to the supply input of the multi-level buck converter. The boost charge pump includes a plurality of switches and two flying capacitors that provide for three modes of operation. In a charging mode of operation, the flying capacitors are coupled in series between the charge pump supply input and ground, where the flying capacitors are switchably disconnected from the charge pump output. In a first boost mode of operation, the flying capacitors are arranged in parallel between the charge pump output and the charge pump supply input to generate a 1.5× the DC voltage output at the charge pump output. In a second boost mode of operation, the flying capacitors are arranged in series between the charge pump output and the charge pump supply input to generate a 2× the DC voltage output at the charge pump output. The multi-level buck converter may include four modes of operation. In a first mode of operation, the series switch is open, the boost charge pump is in the charging mode of operation, and the shunt switch is closed to generate zero volts at the switching voltage output. In a second mode of operation, the series switch is closed, the boost charge pump is in the charging mode of operation, and the shunt switch is open to generate the DC voltage output at the switching voltage output. In a third mode of operation, both the series switch and the shunt switch are open and the boost charge pump is in the first boost mode of operation to generate a 1.5× the DC voltage output at the switching mode output. In a fourth mode of operation, both the series switch and the shunt switch are open and the boost charge pump is in the second boost mode of operation to generate a 2× the DC voltage output at the switching mode output.

[0161] FIGS. 1A and 2A depict an example embodiment of pseudo-envelope follower power management system 10A including a multi-level charge pump buck converter 12, a parallel amplifier circuit 14, a power inductor 16, a coupling circuit 18, and a bypass capacitor 19. The bypass capacitor 19 has a bypass capacitor capacitance, C_BYPASS. The multi-level charge pump buck converter 12 and the parallel amplifier circuit 14 may be configured to operate in tandem to generate a power amplifier supply voltage, V_CC, at the power amplifier supply output 28 of the pseudo-envelope follower power management system 10A for a linear RF power amplifier 22. The power amplifier supply output 28 provides an output current, I_OUT, to the linear RF power amplifier 22. The linear RF power amplifier 22 may include a power amplifier input, P_IN, configured to receive a modulated RF signal and a power amplifier output, P_OUT, coupled to an output load, Z_LOAD. As an example, the output load, Z_LOAD, may be an antenna.

[0162] The multi-level charge pump buck converter 12 may include a supply input 24, (V_BAT), configured to receive a direct current (DC) voltage, V_BAT, from a battery 20 and a switching voltage output 26 configured to provide a switching voltage, V_SW. The switching voltage output 26 may be coupled to the power amplifier supply output 28 by the power inductor 16, where the power inductor 16 couples to a bypass capacitor 19 to form an output filter 29 for the switching voltage output 26 of the multi-level charge pump buck converter 12. The power inductor 16 provides an inductor current, I_SW—OUT, to the power amplifier supply output 28. The parallel amplifier circuit 14 may include a parallel amplifier supply input 30 configured to receive the direct current (DC) voltage, V_BAT, from the battery 20, a parallel amplifier output 32A, a first control input 34 configured to receive a V_RAMP signal, and a second control input configured to receive the power amplifier supply voltage, V_CC. The parallel amplifier output 32A of the parallel amplifier circuit 14 may be coupled to the power amplifier supply voltage V_CC, by a coupling circuit 18. The parallel amplifier output voltage, V_PARA—AMP, is provided by the parallel amplifier circuit 14.

[0163] As an example, the parallel amplifier circuit 14 may generate the parallel amplifier output voltage, V_PARA—AMP, based on the difference between the V_RAMP signal and the power amplifier supply voltage, V_CC. Thus, the V_RAMP signal may represent either an analog or digital signal that contains the required supply modulation information for a power amplifier collector of a linear RF power amplifier. Typically, the V_RAMP signal is provided to the parallel amplifier circuit 14 as a differential analog signal to provide common mode rejection against any noise or spurs that could appear on this signal. The V_RAMP signal may be a time domain signal, V_RAMP(t), generated by a transceiver or modem and used to transmit radio-frequency (RF) signals. For example, the V_RAMP signal may be generated by a digital baseband processing portion of the transceiver or modem, where the digital V_RAMP signal, V_{RAMP—DIGITAL}, is digital-to-analog converted to form the V_RAMP signal in the analog domain. In some embodiments, the “analog” V_RAMP signal is a differential signal. The transceiver or a modem may generate the V_RAMP signal based upon a known RF modulation Amp(t)*cos(2*pi*f_RF*t+Phase(t)). The V_RAMP signal may represent the target voltage for the power amplifier supply voltage, V_CC, to be generated at the power amplifier supply output 28 of the pseudo-envelope follower power management system 10A, where the pseudo-envelope follower power management system 10A provides the power amplifier supply voltage, V_CC, to the linear RF power amplifier 22. Also the V_RAMP signal may be generated from a detector coupled to the RF input power amplifier.

[0164] For example, the parallel amplifier circuit 14 includes a parallel amplifier output 32A that provides a parallel amplifier output voltage, V_PARA—AMP, to the coupling circuit 18. The parallel amplifier output 32A sources a parallel amplifier circuit output current, I_PAWA—OUT, to the coupling circuit 18. The parallel amplifier circuit 14, depicted in FIG. 1A and FIG. 1B, may provide a parallel amplifier circuit output current estimate 40, I_{PAWA—OUT—EST}, to the multi-level charge pump buck converter 12 as an estimate of the parallel amplifier circuit output current I_PAWA—OUT, of the parallel amplifier circuit 14. Thus, the parallel amplifier circuit output current estimate 40, I_{PAWA—OUT—EST}, represents an estimate of the parallel amplifier circuit output current I_PAWA—OUT, provided by the parallel amplifier circuit as a feedback signal to the multi-level charge pump buck converter 12. Based on the parallel amplifier circuit output current estimate 40, I_{PAWA—OUT—EST}, multi-level charge pump buck converter 12 may be configured to control the switching voltage, V_SW, provided at the switching voltage output 26 of the multi-level charge pump buck converter 12.

[0165] In some embodiments of the pseudo-envelope follower power management system 10A, depicted in FIG. 1A, and the pseudo-envelope follower power management system 10B, depicted in FIG. 1B, the coupling circuit 18 may be an offset capacitor, C_OFFSET. An offset voltage, V_OFFSET, may be developed across the coupling circuit 18. In other alternative embodiments, the coupling circuit may be a wire trace such that the offset voltage, V_OFFSET, between the parallel amplifier output voltage, V_PARA—AMP, and the power amplifier supply voltage output, V_CC, is zero volts. In still other embodiments, the coupling circuit may be a transformer.

[0166] As an example, a pseudo-envelope follower power management system 10A, depicted in FIG. 2A, is an example embodiment of the pseudo-envelope follower power management systems 10, depicted in FIG. 1A. Unlike the pseudo-envelope follower power management systems 10, depicted in FIG. 1A, the pseudo-envelope follower power management system 10A depicted in FIG. 2A includes an embodiment of the multi-level charge pump buck converter 12A and a parallel amplifier circuit 14A having parallel amplifier circuitry 32. The parallel amplifier circuitry 32 includes a parallel amplifier 35 and a parallel amplifier sense circuit 36. The parallel amplifier circuit 14A further includes a parallel amplifier output impedance compensation circuit 37 configured to receive a V_RAMP: signal and provide a compensated V_RAMP signal, V_RAMP—C, as an input to the parallel amplifier 35. The parallel amplifier circuit 14A further includes a parallel amplifier output impedance compensation circuit 37 configured to receive the V_RAMP signal and generate a compensated V_RAMP signal, V_RAMP—C, as a function of the V_RAMP signal. The parallel amplifier 35 generates a parallel amplifier output current, I_PARA—AMP, to produce a parallel amplifier output voltage, V_PARA—AMP, at the parallel amplifier output 32A based on the difference between the compensated V_RAMP signal, V_RAMP—C and the power amplifier supply voltage, V_CC, generated at power amplifier supply output 28. The parallel amplifier sense circuit 36 generates a scaled parallel amplifier output current estimate, I_{PARA—AMP—SENSE}, which is a fractional representation of the parallel amplifier output current, I_PARA—AMP, generated by the parallel amplifier 35. Alternatively, in those embodiments of the parallel amplifier circuit 14 that do not include the parallel amplifier output impedance compensation circuit 37, the parallel amplifier 35 generates the parallel amplifier output current, I_PARA—AMP, to product the parallel amplifier output voltage, V_PARA—AMP, based on the difference between the V_RAMP signal and the power amplifier supply voltage, V_CC. The parallel amplifier circuit 14A may further include an open loop assist circuit 39 configured to receive the feed forward control signal 38, V_SWITCHER, the scaled parallel amplifier output current estimate, I_{PARA—AMP—SENSE}, and the V_RAMP signal. In response to the feed forward control signal 38, V_SWITCHER, scaled parallel amplifier output current estimate, I_{PARA—AMP—SENSE}, and the V_RAMP signal, the open loop assist circuit 39 may be configured to generate an open loop assist current, I_ASSIST. The open loop assist current, I_ASSIST, may be provided to the parallel amplifier output 32A. The parallel amplifier output current, I_PARA—AMP, generated by the parallel amplifier 35 and the open loop assist circuit current, I_ASSIST, generated by the open loop assist circuit 39 may be combined to form the parallel amplifier circuit output current, I_PAWA—OUT, of the parallel amplifier circuit 14A. The parallel amplifier circuit 14A may further include a V_OFFSET loop circuit 41, configured to generate a threshold offset current 42, I_{THRESHOLD—OFFSET}. The threshold offset current 42, I_{THRESHOLD—OFFSET}, may be provided from the parallel amplifier circuit 14A as a feedback signal to the multi-level charge pump buck converter 12A. The V_OFFSET loop circuit 41 may be configured to provide a threshold offset current 42, I_{THRESHOLD—OFFSET}, as an estimate of the magnitude of the offset voltage, V_OFFSET, appearing across the coupling circuit 18. In those cases where the coupling circuit is a wire trace such that the offset voltage, V_OFFSET, is always zero volts, the parallel amplifier circuit 14A may not provide the threshold offset current 42, I_{THRESHOLD—OFFSET}, to the multi-level charge pump buck converter 12A. An embodiment of the V_OFFSET loop circuit 41 is depicted in FIG. 8. In addition, another embodiment of the V_OFFSET loop circuit 41A, depicted in FIG. 18A and FIG. 18C, represents an alternative embodiment the V_OFFSET loop circuit 41 depicted in FIGS. 2A, 2B, 8, 18A, and 18C. Moreover, as also described below, an alternative embodiment of a V_OFFSET loop circuit 41B, depicted FIG. 18B and FIG. 18D, represents an alternative embodiment of the V_OFFSET loop circuit 41 depicted in FIGS. 2A, 2B, 8, 18B, and 18D. In addition, another example is the pseudo-envelope follower power management system 10B, depicted in FIG. 2B, which is similar to the embodiment of the pseudo-envelope follower power management system 10B, depicted in FIG. 1B. The pseudo-envelope follower power management system 10B operationally and functionally similar in form and function to the pseudo-envelope follower power management system 10A, depicted in FIG. 2A. However, unlike the pseudo-envelope follower power management system 10A depicted in FIG. 2A, the pseudo-envelope follower power management system 10B includes a multi-level charge pump buck converter 12B configured to generate an estimated switching voltage output 38B, V_SW—EST, and a parallel amplifier circuit 14B configured to receive the estimated switching voltage output 38B, V_SW—EST, instead of the feed forward control signal 38, V_SWITCHER. Consequentially, as depicted in FIG. 2B, the open loop assist circuit 39 of the parallel amplifier circuit 14B in configured to use only the estimated switching voltage output 38B, V_SW—EST, instead of the feed forward control signal 38, V_SWITCHER.

[0167] The generation of the feed forward control signal 38, V_SWITCHER, depicted in FIGS. 1A and 2A, will now be explained with reference to FIG. 3A. As an example, the multi-level charge pump buck converters 12 and 12A may each be configured to generate a feed forward control signal 38, V_SWITCHER, to provide an indication of the output state of the switching voltage output 26 to the parallel amplifier circuit 14. As an example, FIG. 3A depicts an embodiment of the switcher control circuit 52, depicted in FIG. 2A, as a switcher control circuit 52A. In FIG. 3A, the feed forward control signal 38, V_SWITCHER, is provided by a switch 43. The switch 43 may be configured by the V_{SWITCHER—CONTROL} signal to provide either an indication of the switching voltage output, V_SW, from the threshold detector and control circuit 132A or a scaled version of the switching voltage output, V_SW, from the scalar circuit as the feed forward control signal 38, V_SWITCHER. The threshold detector and control circuit 132A may generate an estimated switching voltage output 38B, V_SW—EST, based on the state of the switcher control circuit 52A, where the estimated switching voltage output 38B, V_SW—EST, provides an indication of the switching voltage output, V_SW, based on the state of the switcher control circuit 52A. Due to propagation delay within the switcher control circuit 52A, the multilevel-charge pump circuit 56 and the switching circuit 58 of the multi-level charge pump buck converter 12A, the indication of the switching voltage output, V_SW, based on the state of the switcher control circuit 52A is a feed forward signal that indicates what the voltage level of the switching voltage output, V_SW, at the switching voltage output 26 will be based on the state of the switcher control circuit 52A instead of the current voltage level of the switching voltage output, V_SW, at the switching voltage output 26. Thus, the estimated switching voltage output 38B, V_SW—EST, may provide an early indication what the voltage level of the switching voltage output, V_SW, will be in the future instead of the present voltage level of the switching voltage output, V_SW, at the switching voltage output 26. In contrast, the scalar circuit may generate a scaled switching voltage output 38A, V_SW—SCALED, by scaling the switching voltage output 26, V_SW, where the scaled switching voltage output 38A, V_SW—SCALED, provides a scaled version of the switching voltage output, V_SW. Thus, the scaled switching voltage output 38A, V_SW—SCALED, is a scaled version of the voltage level currently at the switching voltage output 26 instead of a future voltage level. Accordingly, the switch 43 may be configured such that the feed forward control signal 38, V_SWITCHER, provides either the estimated switching voltage output 38B, V_SW—EST, or the scaled switching voltage output 38A, V_SW—SCALED, as the feed forward control signal 38, V_SWITCHER.

[0168] Another embodiment of the pseudo-envelope follower power management system 10B, as depicted in FIG. 1B, is described with reference to FIG. 3B. As depicted in FIG. 1B, the multi-level charge pump buck converter 12B may be configured to provide both a scaled switching voltage output 38A, V_SW—SCALED, and an estimated switching voltage output 38B, V_SW—EST, to the parallel amplifier circuit 14B. As still another example, the pseudo-envelope follower power management system 10B depicted in FIG. 2B may be configured to only provide the estimated switching voltage output 38B, V_SW—EST, as a feed forward signal to the parallel amplifier circuit 14B.

[0169] The generation of the parallel amplifier circuit output current estimate 40, I_{PAWA—OUT—EST}, depicted in FIGS. 1A and 1B will now be described with continuing reference to the embodiment of the parallel amplifier circuit 14A, depicted in FIG. 2A, and the embodiment of the parallel amplifier circuit 14B depicted in FIG. 2B. Embodiments of the parallel amplifier circuit 14A and the parallel amplifier circuit 14B, depicted in FIGS. 2A and 2B, may provide the parallel amplifier circuit output current estimate 40, I_{PAWA—OUT—EST}, where the parallel amplifier circuit output current estimate 40, I_{PAWA—OUT—EST}, includes a scaled parallel amplifier output current estimate, I_{PARA—AMP—SENSE}, and a scaled open loop assist circuit output current estimate, I_{ASSIST—SENSE}. The scaled parallel amplifier output current estimate, I_{PARA—AMP—SENSE}, is a scaled estimate of the parallel amplifier output current, I_PARA—AMP, generated by the parallel amplifier sense circuit 36 of the parallel amplifier circuitry 32. In some alternative embodiments, the parallel amplifier 35 may generate the scaled estimate of the parallel amplifier output current, I_{PARA—AMP—SENSE}, directly. The scaled open loop assist circuit current estimate, I_{ASSIST—SENSE}, is a scaled estimate of the open loop assist circuit current, I_ASSIST, generated by the open loop assist circuit 39. In other alternative embodiments of the parallel amplifier circuit 14 depicted in FIG. 1A and FIG. 1B, the parallel amplifier circuit 14 does not include the open loop assist circuit 39. In those embodiments of the parallel amplifier circuit 14 depicted in FIG. 1A and FIG. 1B that do not include the open loop assist circuit 39, the parallel amplifier circuit output current estimate 40, I_{PAWA—OUT—EST}, may only be based on the scaled parallel amplifier output current estimate, I_{PARA—AMP—SENSE}.

[0170] Returning to FIGS. 1A and 1B, the pseudo-envelope follower power management systems 10A and 10B may further include a control bus 44 coupled to a controller 50. The control bus 44 may be coupled to a control bus interface 46 of the multi-level charge pump buck converter 12 and the control bus interface 48 of the parallel amplifier circuit 14. The controller 50 may include various logical blocks, modules, and circuits. The controller 50 may be implemented or performed with a processor, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices. As an example, a combination of computing devices may include a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. The controller may further include or be embodied in hardware and in computer executable instructions that are stored in memory, and may reside, for example, in Random Access Memory (RAM), flash memory, Read Only Memory (ROM), Electrically Programmable ROM (EPROM), Electrically Erasable Programmable ROM (EEPROM), registers, hard disk, a removable disk, a CD-ROM, or any other form of computer readable medium known in the art. An exemplary storage medium may be coupled to the processor such that a processor can read information from, and write information to, the storage medium. In the alternative, the storage medium or a portion of the storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC.

[0171] FIGS. 2A and 2B depict a pseudo-envelope follower power management system 10A and a pseudo-envelope follower power management system 10B, respectively, that include embodiments of the multi-level charge pump buck converter 12A and the multi-level charge pump buck converter 12B. As depicted in FIGS. 2A and 2B, some embodiments of the multi-level charge pump buck converter 12 of FIGS. 1A and 1B may include an FLL circuit 54 configured to interoperate with a switcher control circuit 52, as depicted in FIGS. 2A and 2B. Alternatively, some embodiments of the multi-level charge pump buck converter 12A and the multi-level charge pump buck converter 12B may not include an FLL circuit 54 or be configured to operate with the FLL circuit 54 being disabled.

[0172] As further depicted in FIGS. 2A and 2B, some embodiments of the switcher control circuit 52 may be configured to control the operation of the multi-level charge pump circuit 56 and the switching circuit 58 to generate the switching voltage, V_SW, on the switching voltage output 26 of the multi-level charge pump buck converter 12A or the multi-level charge pump buck converter 12B, respectively. For example, the switcher control circuit 52 may use a charge pump mode control signal 60 to configure the operation of the multi-level charge pump circuit 56 to provide a charge pump output 64 to the switching circuit 58. Alternatively, the switcher control circuit 52 may generate a series switch control signal 66 to configure the switching circuit 58 to provide the switching voltage, V_SW, substantially equal to the DC voltage, V_BAT, from the battery 20 via a first switching element coupled between the supply input 24 and the switching voltage output 26. As another example, the switcher control circuit 52 may configure the switching circuit 58 to provide the switching voltage, V_SW, through a second switching element coupled to ground such that the switching voltage, V_SW, is substantially equal to ground.

[0173] In addition, the parallel amplifier circuit 14A, depicted in FIG. 2A, and the parallel amplifier circuit 14B, depicted in FIG. 2B, may be configured to provide the parallel amplifier circuit output current estimate 40, I_{PAWA—OUT—EST}, and the threshold offset current 42, I_{THRESHOLD—OFFSET}, to the switcher control circuit 52 in order to control the operation of the switcher control circuit 52. As discussed in detail below, some embodiments of the switcher control circuit 52 may be configured to receive and use the parallel amplifier circuit output current estimate 40, I_{PAWA—OUT—EST}, the threshold offset current 42, I_{THRESHOLD—OFFSET}, and/or a combination thereof to control the operation of the switcher control circuit 52.

[0174] For example, the switcher control circuit 52 may use the parallel amplifier circuit output current estimate 40, I_{PAWA—OUT—EST}, the threshold offset current 42, I_{THRESHOLD—OFFSET}, and/or a combination thereof to determine the magnitude of the voltage provided the switching voltage, V_SW, from the multi-level charge pump circuit 56.

[0175] Some embodiments of the switcher control circuit 52, depicted in FIG. 2A and FIG. 2B, may be configured to interoperate with an FLL circuit 54. As an example, FIG. 3A depicts an example embodiment of a switcher control circuit 52A configured to interoperate with an example embodiment of the FLL circuit 54, which is depicted as FLL circuit 54A. For the sake of clarity, and not by limitation, the description of the operation of the switcher control circuit 52A and the FLL circuit 54A will be done with continuing reference to the multi-level charge pump buck converter 12A, depicted in FIG. 2A.

[0176] As depicted in FIG. 3A, some embodiments of the multi-level charge pump buck converter 12A may include switcher control circuit 52A, an embodiment of the frequency lock loop frequency lock loop (FLL) circuit 54A, a multi-level charge pump circuit 56, and the switching circuit 58. The switcher control circuit 52A may be in communication with the frequency lock loop (FLL) circuit 54A. The frequency lock loop (FLL) circuit 54A may be in communication with a clock reference 139. The multi-level charge pump circuit 56 and the switching circuit 58 may be configured to receive the DC voltage, V_BAT, from the supply input 24 of the multi-level charge pump buck converter 12.

[0177] The clock reference 139 may provide a clock reference signal 139A to the frequency lock loop (FLL) circuit 54A. In addition, the switcher control circuit 52A may provide a logic level indication of the switching voltage output, V_{SW—EST—OUT}, to the frequency lock loop (FLL) circuit 54A. The logic level indication of the switching voltage output, V_{SW—EST—OUT}, is discussed relative to the logic circuit 148A of FIG. 4A. In some embodiments of the multi-level charge pump buck converter 12 of FIGS. 1A and 1B, the multi-level charge pump buck converter 12 may not include the frequency lock loop (FLL) circuit 54 and a clock reference 139, as depicted in FIGS. 3C and 3D.

[0178] The switcher control circuit 52A may be configured to receive the parallel amplifier circuit output current estimate 40, I_{PAWA—OUT—EST}, and the threshold offset current 42, I_{THRESHOLD—OFFSET}, from the parallel amplifier circuit 14A. The switcher control circuit 52A may provide a charge pump mode control signal 60 to the charge pump mode control input 62 of the multi-level charge pump circuit 56. Based upon the charge pump mode control signal 60, the multi-level charge pump circuit 56 may generate one of a plurality of output voltages or present an open circuit at the charge pump output 64. The switcher control circuit 52A may further provide a series switch control signal 66 and a shunt switch control signal 68 to the switching circuit 58.

[0179] The switching circuit 58 may include a series switch 70 and a shunt switch 72. The series switch 70 and the shunt switch 72 may be a solid state based switch such as a field effect transistor, an insulator-on-semiconductor based transistor, or a bipolar based transistor. The series switch 70 may include a first switch terminal 74, a second switch terminal 76, and a series switch control terminal 78 coupled to the series switch control signal 66. The shunt switch 72 may include a first switch terminal 80, a second switch terminal 82, and a shunt switch control terminal 83 coupled to the shunt switch control signal 68. The first switch terminal 74 of the series switch 70 may be coupled to the supply input 24, (V_BAT), of the multi-level charge pump buck converters 12 and 12A, as depicted in FIGS. 1A and 2A. The second switch terminal 76 of the series switch 70 may be coupled to the first switch terminal 80 of the shunt switch 72 and the charge pump output 64 to form the switching voltage output 26. The second switch terminal 82 of the shunt switch 72 may be coupled to ground.

[0180] As depicted in FIG. 7A, with continuing reference to FIGS. 1A, 2A and 3A, the multi-level charge pump circuit 56 may include a charge pump control circuit 84A, a plurality of switches including a first switch 86, a second switch 88, a third switch 90, a fourth switch 92, a fifth switch 94, a sixth switch 96 and a seventh switch 98, a first flying capacitor 100 having a first terminal 100A and a second terminal 100B, and a second flying capacitor 102 having a first terminal 102A and a second terminal 102B. As depicted in FIG. 7A, some alternative embodiments of the multi-level charge pump circuit 56 may further include an eighth switch 118 to advantageously provide an additional functional feature, described below. Each of the first switch 86, the second switch 88, the third switch 90, the fourth switch 92, the fifth switch 94, the sixth switch 96, the seventh switch 98, and the alternatively included eighth switch 118 may be a solid state based switch implemented with field effect transistors, insulator-on-semiconductor based transistors, or bipolar based transistors, or a combination thereof. Each of the first switch 86, the second switch 88, the third switch 90, the fourth switch 92, the fifth switch 94, the sixth switch 96, the seventh switch 98, and the alternatively included eighth switch 118 may be a solid state transmission gate. As another example, each of the first switch 86, the second switch 88, the third switch 90, the fourth switch 92, the fifth switch 94, the sixth switch 96, the seventh switch 98, and the alternatively included eighth switch 118 may be based on a GaN process. Alternatively, each of the first switch 86, the second switch 88, the third switch 90, the fourth switch 92, the fifth switch 94, the sixth switch 96, the seventh switch 98, and the alternatively included eighth switch 118 may be micro-electromechanical systems (MEMS) contact type switches.

[0181] The first switch 86 may be coupled between the first terminal 100A of the first flying capacitor 100 and the charge pump output 64. The first switch 86 may include a first switch control input configured to receive a first switch control signal 104 from the charge pump control circuit 84A, where the first switch control signal 104 operably opens and closes the first switch 86 based upon the charge pump mode control signal 60. The second switch 88 may be coupled between the first terminal 100A of the first flying capacitor 100 and the supply input 24, (V_BAT), of the multi-level charge pump buck converter 12. The second switch 88 may include a second switch control input configured to receive a second switch control signal 106 from the charge pump control circuit 84A, where the second switch control signal 106 operably opens and closes the second switch 88 based upon the charge pump mode control signal 60. The third switch 90 may be coupled between the second terminal 100B of the first flying capacitor 100 and the supply input 24, (V_BAT), of the multi-level charge pump buck converter 12. The third switch 90 may include a third switch control input configured to receive a third switch control signal 108 from the charge pump control circuit 84A, where the third switch control signal 108 operably opens and closes the third switch 90 based upon the charge pump mode control signal 60. The fourth switch 92 may be coupled between the second terminal 100B of the first flying capacitor 100 and the first terminal 102A of the second flying capacitor 102. The fourth switch 92 may include a fourth switch control input configured to receive a fourth switch control signal 110 from the charge pump control circuit 84A, where the fourth switch control signal 110 operably opens and closes the fourth switch 92 based upon the charge pump mode control signal 60. The fifth switch 94 may be coupled between the supply input 24, (V_BAT), of the multi-level charge pump buck converter 12 and the second terminal 102B of the second flying capacitor 102. The fifth switch 94 may include a fifth switch control input configured to receive a fifth switch control signal 112 from the charge pump control circuit 84A, where the fifth switch control signal 112 operably opens and closes the fifth switch 94 based upon the charge pump mode control signal 60. The sixth switch 96 may be coupled between the second terminal 102B of the second flying capacitor 102 and ground. The sixth switch 96 may include a sixth switch control input configured to receive a sixth switch control signal 114 from the charge pump control circuit 84A, where the sixth switch control signal 114 operably opens and closes the sixth switch 96 based upon the charge pump mode control signal 60. The seventh switch 98 may be coupled between the first terminal 102A of the second flying capacitor 102 and the charge pump output 64. The seventh switch 98 includes a seventh switch control input configured to receive a seventh switch control signal 116 from the charge pump control circuit 84A, where the seventh switch control signal 116 operably opens and closes the seventh switch 98 based upon the charge pump mode control signal 60.

[0182] Based upon the charge pump mode control signal 60 received at the charge pump control circuit 84A, the charge pump control circuit 84A may configure each of the first switch 86, the second switch 88, the third switch 90, the fourth switch 92, the fifth switch 94, the sixth switch 96, the seventh switch 98, and the alternatively included eighth switch 118 to place the first flying capacitor 100 and the second flying capacitor 102 in various arrangements in order to place the multi-level charge pump circuit 56 in various modes of operation. As an example, the multi-level charge pump circuit 56 may have a charging mode to charge the first flying capacitor 100 and the second flying capacitor 102, a first boost mode to provide 1.5×V_BAT at the charge pump output 64, and a second boost mode to provide 2×V_BAT at the charge pump output 64. Some alternative embodiments of the multi-level charge pump circuit 56 may further include an eighth switch 118, the operation of which is discussed below with respect to providing a first output mode of operation.

[0183] As an example, in response to receipt of the charge pump mode control signal 60 that indicates the multi-level charge pump circuit 56 should be in the charging mode of operation, the charge pump control circuit 84A configures the first flying capacitor 100 and the second flying capacitor 102 to be coupled in series between the supply input 24, (V_BAT), of the multi-level charge pump buck converter 12 and ground, where the first flying capacitor and the second flying capacitor may be switchably disconnected from the charge pump output 64. Assuming that the capacitance of the first flying capacitor 100 and the second flying capacitor 102 are equal, the first flying capacitor 100 and the second flying capacitor 102 each charge to a charged voltage of ½×V_BAT. The charge pump control circuit 84A configures the first switch 86 to be open, the second switch 88 to be closed, the third switch 90 to be open, the fourth switch 92 to be closed, the fifth switch 94 to be open, the sixth switch 96 to be closed, and the seventh switch 98 to be open. In those embodiments of the multi-level charge pump circuit 56 that further include the eighth switch 118, the eighth switch 118 may be configured to be open.

[0184] In response to receipt of the charge pump mode control signal 60 that indicates the multi-level charge pump circuit 56 should be in the first boost mode of operation, the charge pump control circuit 84A configures the first flying capacitor 100 and the second flying capacitor 102 to be arranged in parallel between the charge pump output 64 and the supply input 24, (V_BAT), to generate 1.5×V_BAT at the charge pump output. The charge pump control circuit 84A configures the first switch 86 to be closed, the second switch 88 to be open, the third switch 90 to be closed, the fourth switch 92 to be open, the fifth switch 94 to be closed, the sixth switch 96 to be open, and the seventh switch 98 to be closed. In those embodiments of the multi-level charge pump circuit 56 that further include the eighth switch 118, the eighth switch 118 may be configured to be open.

[0185] In response to receipt of the charge pump mode control signal 60 that indicates the multi-level charge pump circuit 56 should be in the second boost mode of operation, the charge pump control circuit 84A configures the first flying capacitor 100 and the second flying capacitor 102 to be arranged in series between the charge pump output 64 and the supply input 24, (V_BAT), to generate 2×V_BAT at the charge pump output 64. The charge pump control circuit 84A configures the first switch 86 to be closed, the second switch 88 to be open, the third switch 90 to be open, the fourth switch 92 to be closed, the fifth switch 94 to be closed, the sixth switch 96 to be open, and the seventh switch 98 to be open. In those embodiments of the multi-level charge pump circuit 56 that further include the eighth switch 118, the eighth switch 118 may be configured to be open.

[0186] As discussed above, some embodiments of the multi-level charge pump circuit 56 may further include an eighth switch 118 coupled between the second terminal 100B of the first flying capacitor 100 and ground in order to provide for a first output mode of operation. The eighth switch 118 may include an eighth switch control input configured to receive an eighth switch control signal 120 from the charge pump control circuit 84A, where the eighth switch control signal 120 operably opens and closes the eighth switch 118 based upon the charge pump mode control signal 60.

[0187] In the first output mode of operation, the multi-level charge pump circuit 56 may provide ½×V_BAT at the charge pump output 64. In response to receipt of the charge pump mode control signal 60 that indicates the multi-level charge pump circuit 56 should be in the first output mode of operation, the charge pump control circuit 84A configures the first flying capacitor 100 and the second flying capacitor 102 to be coupled in parallel between the charge pump output 64 and ground. The charge pump control circuit 84A configures the first switch 86 to be closed, the second switch 88 to be open, the third switch 90 to be open, the fourth switch 92 to be open, the fifth switch 94 to be open, the sixth switch 96 to be closed, the seventh switch 98 to be closed and the eighth switch 118 to be closed.

[0188] Otherwise, the charge pump control circuit 84A configures the eighth switch 118 to be open when the multi-level charge pump circuit 56 is in the charging mode of operation, the first boost mode of operation, or the second boost mode of operation.

[0189] FIG. 7B depicts an embodiment of a multi-level charge pump circuit 258, depicted in FIGS. 18A and 18B, as multi-level charge pump circuit 258A. The multi-level charge pump circuit 258A is similar to the multi-level charge pump circuit 56 except the multi-level charge pump circuit 258A further includes a ninth switch 119 configured to provide an internal charge pump node parallel amplifier supply 294 as an additional output. The ninth switch 119 may be similar to the plurality of switches including the first switch 86, the second switch 88, the third switch 90, the fourth switch 92, the fifth switch 94, the sixth 96, the seventh switch 98, and eighth switch 118 of FIG. 7A. In addition, the multi-level charge pump circuit 258A is similar to the multi-level charge pump circuit 56 except that the charge pump control circuit 84A is replaced by a charge pump control circuit 84B. Unlike the charge pump control circuit 84A, the charge pump control circuit 84B further includes a ninth switch control signal 121 configured to control the ninth switch 119.

[0190] The ninth switch 119 may include a ninth switch control input configured to receive a ninth switch control signal 121 from the charge pump control circuit 84B, where the ninth switch control signal 121 operably opens and closes the ninth switch 119 based upon the charge pump mode control signal 60. The ninth switch may be operably coupled between the first terminal 102A of the second flying capacitor 102 and the internal charge pump node parallel amplifier supply 294.

[0191] Operationally, the charge pump control circuit 84B functions similar to the operation of the charge pump control circuit 84A. As an example, the multi-level charge pump circuit 258A may have a charging mode to charge the first flying capacitor 100 and the second flying capacitor 102, a first boost mode to provide 1.5×V_BAT at the charge pump output 64, and a second boost mode to provide 2×V_BAT at the charge pump output 64. However, unlike the charge pump control circuit 84A, the charge pump control circuit 84B is configured to operably close the ninth switch 119 when the multi-level charge pump circuit 258A is configured to operate in either the first boost mode to provide 1.5×V_BAT at the charge pump output 64 or the second boost mode to provide 2×V_BAT at the charge pump output 64. Thus, when the ninth switch 119 is in a closed state during either the first boost mode of operation or the second boost mode of operation, the voltage appearing on the first terminal 102A of the second flying capacitor 102, is substantially equal to 1.5×V_BAT. Advantageously, the configuration of the multi-level charge pump circuit 258A provides the same voltage output level to the internal charge pump node parallel amplifier supply 294, which may improve the ripple noise on the power amplifier supply voltage V_CC.

[0192] FIG. 7C depicts another embodiment of a multi-level charge pump circuit 258, depicted in FIGS. 18A and 18B, as multi-level charge pump circuit 258B. The multi-level charge pump circuit 258B is similar to the multi-level charge pump circuit 258A of FIG. 7B except the ninth switch may be operably coupled between the first terminal 100A of the first flying capacitor 100 and the internal charge pump node parallel amplifier supply 294.

[0193] Operationally, the charge pump control circuit 84C functions similar to the operation of the charge pump control circuit 84B. As an example, like the multi-level charge pump circuit 258A, the multi-level charge pump circuit 258B may have a charging mode to charge the first flying capacitor 100 and the second flying capacitor 102, a first boost mode to provide 1.5×V_BAT at the charge pump output 64, and a second boost mode to provide 2×V_BAT at the charge pump output 64. In addition, like the charge pump control circuit 84B, the charge pump control circuit 84C is configured to operably close the ninth switch 119 when the multi-level charge pump circuit 258B is configured to operate in either the first boost mode to provide 1.5×V_BAT at the charge pump output 64 or the second boost mode to provide 2×V_BAT at the charge pump output 64. Thus, when the ninth switch 119 is in a closed state during either the first boost mode of operation or the second boost mode of operation, the voltage appearing on the first terminal 100A of the first flying capacitor 100 may depend upon whether the multi-level charge pump circuit 258B is configured to operate in the first boost mode or the second boost mode. For example, due to the topological location of the first flying capacitor, the voltage output level provided to the internal charge pump node parallel amplifier supply 294 may be 1.5×V_BAT when the multi-level charge pump circuit 258B is configured to operate in the first boost mode and 2.0×V_BAT when the multi-level charge pump circuit 258B is configured to operate in the second boost mode. As a result, advantageously, the multi-level charge pump circuit 258B may provide a higher power supply rail for the parallel amplifier 35 of FIGS. 18A and 18B. In particular, in the case where the parallel amplifier 35 of FIGS. 18A and 18B is a rechargeable parallel amplifier, similar to the rechargeable parallel amplifier 35E of FIG. 12E and the rechargeable parallel amplifier 35F of FIG. 12F, the saved charge voltage, V_AB on the charge conservation capacitor, C_AB, may be increased and result in a larger range of operation of the second output stage, as depicted in FIGS. 12E and 12F.

[0194] In those embodiments that further provide a first output threshold parameter (not shown), the first output threshold parameter may correspond to a first output mode of operation of the multi-level charge pump buck converter 12. In the first output mode of operation, both the series switch 70 and the shunt switch 72 are open and the multi-level charge pump circuit 56 is in the first output mode of operation to generate a ½×V_BAT at the switching voltage output 26.

[0195] Returning to FIG. 3A, for the sake of clarity and not by way of limitation, the following discussion of the operation of the circuits depicted in FIG. 3A will be done with continuing reference to the multi-level charge pump buck converter 12A depicted in FIG. 2A. As depicted in FIG. 3A, the switcher control circuit 52A may include a programmable threshold circuit 122 configured to receive a plurality of programmable threshold levels and one embodiment of a threshold detector and control circuit 132A. The programmable threshold levels may be received from a controller 50 via the control bus 44. As an example, in some embodiments, the controller 50 may provide a shunt level threshold parameter, a series level threshold parameter, a first boost level threshold parameter, and a second boost level threshold parameter. In another embodiment, the controller 50 may further provide a first output threshold parameter.

[0196] As an example, each of the threshold levels may correspond to one of a plurality of output modes of the multi-level charge pump buck converter 12A. As an example, the shunt level threshold parameter may correspond to a shunt output mode of operation. In a shunt output mode of operation of the multi-level charge pump buck converter 12A, the series switch 70 is open (not conducting), the multi-level charge pump circuit 56 is in the charging mode of operation, and the shunt switch 72 is closed (conducting) to generate zero volts at the switching voltage output 26. The shunt output mode of operation provides a conduct path for current to continue flowing through the power inductor 16 when the multi-level charge pump circuit 56 is in the charging mode of operation and the series switch 70 is open (not conducting). The series level threshold parameter may correspond to a shunt output mode of operation of the multi-level charge pump buck converter 12A. In a series output mode of operation, the series switch 70 is closed (conducting), the multi-level charge pump circuit 56 is in the charging mode of operation, and the shunt switch 72 is open to generate V_BAT at the switching voltage output 26. The first boost level threshold parameter may correspond to a first boost output mode of operation of the multi-level charge pump buck converter 12A. In the first boost output mode of operation, both the series switch 70 and the shunt switch 72 are open and the multi-level charge pump circuit 56 is in the first boost mode of operation to generate 1.5×V_BAT at the switching voltage output 26. The second boost level threshold parameter may correspond to a second boost output mode of operation of the multi-level charge pump buck converter 12A. In a second boost output mode of operation, both the series switch 70 and the shunt switch 72 are open and the multi-level charge pump circuit 56 is in the second boost mode of operation to generate a 2×V_BAT at the switching voltage output 26.

[0197] Based upon the shunt level threshold parameter, the series level threshold parameter, the first boost level threshold parameter, and the second boost level threshold parameter, the programmable threshold circuit 122 generates a shunt level threshold 124, a series level threshold 126, a first boost level threshold 128, and a second boost level threshold 130, respectively, which are provided to the threshold detector and control circuit 132A. In those embodiments that provide for a first output threshold parameter and a first output mode of operation of the multi-level charge pump circuit 56, the programmable threshold circuit 122 may further generate a first output threshold (not shown), which is provided to the threshold detector and control circuit 132A. As depicted in FIG. 3A, the shunt level threshold 124, the series level threshold 126, the first boost level threshold 128, the second boost level threshold 130 and the first output threshold may be represented by a current level for use with a current comparator. In alternative embodiments, programmable threshold circuit 122 may be configured to generate the shunt level threshold 124, the series level threshold 126, the first boost level threshold 128, the second boost level threshold 130 and the first output threshold as voltage levels to be used in conjunction with voltage comparator circuits.

[0198] The switcher control circuit 52A may also receive a mode switch control signal 131 from the controller 50. The mode switch control signal 131 may configure the threshold detector and control circuit 132A to operate the multi-level charge pump buck converter 12A in different modes of operation. As an example, the mode switch control signal 131 may configure operation of a state machine within the threshold detector and control circuit 132A that governs how the switching voltage output 26 transitions the switching voltage output 26 to provide different output levels. As a first example embodiment of a state machine within the threshold detector and control circuit 132A, the mode switch control signal 131 may configure the multi-level charge pump buck converter 12A to operate in a first mode of operation, depicted in FIG. 5A. As another example embodiment of a state machine within the threshold detector and control circuit 132A, the mode switch control signal 131 may configure the multi-level charge pump buck converter 12A to operate in a second mode of operation, depicted in FIG. 6A.

[0199] Continuing with FIG. 3A, the switcher control circuit 52A may further include a multiplier circuit 134 and a summing circuit 136. The multiplier circuit may be configured to receive the parallel amplifier circuit output current estimate 40, I_{PAWA—OUT—EST}, and a threshold scalar 137A from the threshold detector and control circuit 132A. The threshold scalar 137A may be provided by FLL circuit 54A, which is one embodiment of the frequency lock loop (FLL) circuit 54 depicted in FIG. 2A.

[0200] The FLL circuit 54A receives a clock reference signal 139A from a clock reference 139 and a logic level indication of the switching voltage output, V_{SW—EST—OUT}. The FLL circuit 54A extracts the operating frequency of the multi-level charge pump buck converter 12A based upon the logic level indication of the switching voltage output, V_{SW—EST—OUT}. Thereafter, the FLL circuit 54A compares the extracted operating frequency of the multi-level charge pump buck converter 12A to the clock reference signal 139A to generate the threshold scalar 137A. The magnitude of the threshold scalar 137A may be used to adjust the operating frequency of the multi-level charge pump buck converter 12A. In some embodiments (not shown), the FLL circuit 54A may provide the threshold scalar 137A directly to the multiplier circuit 134.

[0201] The multiplier circuit 134 may multiply the parallel amplifier circuit output current estimate 40, I_{PAWA—OUT—EST}, by the threshold scalar 137A to generate a scaled parallel amplifier output current estimate 138. The scaled parallel amplifier output current estimate 138 is provided to the summing circuit 136. The summing circuit 136 subtracts the threshold offset current 42, I_{THRESHOLD—OFFSET}, from the scaled parallel amplifier output current estimate 138 to generate a compensated parallel amplifier circuit output current estimate, I_PAWA—COMP, which may be used as a composite feedback signal for the first comparator 140, the second comparator 142, the third comparator 144, and the fourth comparator 146 as depicted, for example, in FIG. 4A. In those embodiments of the parallel amplifier circuit 14 that do not include the V_OFFSET loop circuit 41, the threshold offset current 42, I_{THRESHOLD—OFFSET}, and summing circuit 136 are omitted.

[0202] The scaled parallel amplifier output current estimate 138 may be used to control the operating frequency of the multi-level charge pump buck converter 12A by increasing or decreasing the magnitude of the parallel amplifier circuit output current estimate 40, I_{PAWA—OUT—EST}. As an example, the FLL circuit 54A may be configured to increase the magnitude of the threshold scalar 137A to increase the magnitude of the scaled parallel amplifier output current estimate 138. As the magnitude of the scaled parallel amplifier output current estimate 138 increases, the operating frequency of the multi-level charge pump buck converter 12A will tend to also increase, which will tend to increase the power inductor current, I_SW—OUT, delivered by the power inductor 16. The FLL circuit 54A may be further be configured to decrease the magnitude of the threshold scalar 137A to decrease the magnitude of the scaled parallel amplifier output current estimate 138. As the magnitude of the scaled parallel amplifier output current estimate 138 decreases, the magnitude of the scaled parallel amplifier output current estimate 138, will tend to decrease the operating frequency of the multi-level charge pump buck converter 12A. As the operating frequency of the multi-level charge pump buck converter 12A decreases, the power inductor current, I_SW—OUT, delivered by the power inductor 16, tends to decrease. The threshold offset current 42, I_{THRESHOLD—OFFSET}, may be used to control the offset voltage, V_OFFSET, which appears across the coupling circuit 18, depicted in FIG. 2A.

[0203] FIG. 8 depicts the V_OFFSET loop circuit 41 that generates the threshold offset current, I_{THRESHOLD—OFFSET}. Returning to FIG. 3A, as the threshold offset current, I_{THRESHOLD—OFFSET}, increases above zero current, the value magnitude of the compensated parallel amplifier circuit output current estimate, I_{PAWA—COMP—EST}, is reduced, which tends to lower the output frequency of the multi-level charge pump buck converter 12A. As the output frequency of the multi-level charge pump buck converter 12A is decreased, the power inductor current, I_SW—OUT, delivered by the power inductor 16 will also decrease. As the power inductor current, I_SW—OUT, delivered by the power inductor 16 decreases, the offset voltage, V_OFFSET, also decreases because the parallel amplifier circuit output current, I_PAWA—OUT, tends to become positive to compensate for the reduction of the power inductor current, I_SW—OUT. As the threshold offset current, I_{THRESHOLD—OFFSET}, decreases below zero current, the value magnitude of the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP, is increased, and as a result, the output frequency, also referred to as switching frequency, of the multi-level charge pump buck converter 12A tends to increase. As the output frequency of the multi-level charge pump buck converter 12A is increased, the power inductor current, I_SW—OUT, delivered by the power inductor 16 increases. As the power inductor current, I_SW—OUT, increases, the offset voltage, V_OFFSET, also tends to increase because the parallel amplifier circuit output current, I_PAWA—OUT, tends to become negative to absorb the increase of the power inductor current, I_SW—OUT.

[0204] As depicted in FIG. 4A, with continuing reference to FIGS. 2A and 3A, the threshold detector and control circuit 132A of the switcher control circuit 52A includes a first comparator 140, a second comparator 142, a third comparator 144, a fourth comparator 146, and a logic circuit 148A. The example embodiment of the logic circuit 148A may include a Field Programmable Gate Array (FPGA) or other programmable logic device, discrete gates or transistor logic, discrete hardware components, or any combination thereof. Some embodiments of the logic circuit 148A may be implemented in either a digital or analog processor. As depicted in FIG. 4A, the first comparator 140, the second comparator 142, the third comparator 144, and the fourth comparator 146 may be configured as current comparators. However, in some alternative embodiments, the first comparator 140, the second comparator 142, the third comparator 144, and the fourth comparator 146 may be configured as voltage comparator circuits, where the input currents provided as inputs to the positive terminal and the negative terminal of each respective one of the first comparator 140, the second comparator 142, the third comparator 144, and the fourth comparator 146 is first converted to a voltage level.

[0205] The first comparator 140 includes a positive terminal coupled to the shunt level threshold 124, a negative terminal coupled to the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP, and a first comparator output configured to generate a shunt level indication 150A, which is provided to the logic circuit 148A. When the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP, is greater than or equal to the shunt level threshold 124, the shunt level indication 150A is asserted by setting output of the first comparator 140 to a digital logic low state. When the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP, is less than the shunt level threshold 124, the shunt level indication 150A is de-asserted by setting output of the first comparator 140 to a digital logic high state. The second comparator 142 includes a positive terminal coupled to the series level threshold 126, a negative terminal coupled to the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP, and a second comparator output configured to generate a series level indication 152A, which is provided to the logic circuit 148A. When the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP, is greater than or equal to the series level threshold 126, the series level indication 152A is asserted by setting output of the second comparator 142 to a digital logic low state. When the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP, is less than the series level threshold 126, the series level indication 152A is de-asserted by setting output of the second comparator 150 to a digital logic high state. The third comparator 144 includes a positive terminal coupled to the first boost level threshold 128, a negative terminal coupled to the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP, and a third comparator output configured to generate a first boost level indication 154A, which is provided to the logic circuit 148A. When the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP, is greater than the first boost level threshold 128, the first boost level indication 154A is asserted by setting output of the third comparator 144 to a digital logic low state. When the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP, is less than the first boost level threshold 128, the first boost level indication 154A is de-asserted by setting output of the third comparator 144 to a digital logic high state. The fourth comparator 146 includes a positive terminal coupled to the second boost level threshold 130, a negative terminal coupled to the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP, and a fourth comparator output configured to generate a second boost level indication 156A, which is provided to the logic circuit 148A. When the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP, is greater than the second boost level threshold 130, the second boost level indication 156A is asserted by setting output of the fourth comparator 146 to a digital logic low state. When the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP, is less than the second boost level threshold 130, the second boost level indication 156A is de-asserted by setting output of the first comparator 146 to a digital logic high state.

[0206] The threshold detector and control circuit 132A may further include a first output buffer 158, a second output buffer 160, and a third output buffer 161. The logic circuit 148A may provide a charge pump mode control signal 60, a series switch control output 162, a provides a shunt switch control output 164, and a one or more switching voltage output cmos signal(s) 166, V_{SW—EST—CMOS—SIGNAL}(s). The logic circuit 148A generates the series switch control output 162 to drive the first output buffer 158, which provides the series switch control signal 66 to the series switch 70. The logic circuit 148A generates a shunt switch control output 164 to drive the second output buffer 160, which provides the shunt switch control signal 68 to the shunt switch 72. In addition, logic circuit 148A generates the one or more switching voltage output cmos signal(s) 166, V_{SW—EST—CMOS—SIGNAL}(s), to drive the third output buffer 161, which provide the estimated switching voltage output 38B, V_SW—EST. Each of the one or more switching voltage output cmos signal(s) 166, V_{SW—EST—CMOS—SIGNAL}(s), indicates a future output mode of the multi-level charge pump buck converter 12A. In other words, the one or more switching voltage output cmos signal(s) 166, V_{SW—EST—CMOS—SIGNAL}(s) are a feed forward signal that represents a state of the switcher control circuit 52A that will be used to configure the multi-level charge pump buck converter 12A to provide a future voltage level of the switching voltage, V_SW, at the switching voltage output 26. In other words, due to delays in the switcher control circuit 52A, the multi-level charge pump circuit 56, and the switching circuit 58, the one or more switching voltage output cmos signal(s) 166, V_{SW—EST—CMOS—SIGNAL}(s), may provide an early indication of what the switching voltage, V_SW, at the switching voltage output 26 will become before the voltage level at the switching voltage output 26 transitions to reflect the switching voltage, V_SW, indicated by the one or more switching voltage output cmos signal(s) 166, V_{SW—EST—CMOS—SIGNAL}(s). Based upon one or more switching voltage output cmos signal(s) 166, V_{SW—EST—CMOS—SIGNAL}(s), the third output buffer 161 generates the estimated switching voltage output 38B, V_SW—EST. The third output buffer 161 is supplied by the DC voltage, V_BAT, such that the output of the third output buffer 161 does not exceed the DC voltage, V_BAT.

[0207] FIG. 11A through FIG. 11F depict various waveforms that may be used to represent the estimated switching voltage output 38B, V_SW—EST. FIG. 11A depicts one embodiment of the estimated switching voltage output 38B, V_SW—EST, When the multi-level charge pump buck converter 12A is in either the series output mode, the first boost output mode, or the second boost output mode, the third output buffer 161 outputs a boost/series mode level. Alternatively, when the multi-level charge pump buck converter 12A is in the shunt output mode, the third output buffer 161 outputs a shunt mode level.

[0208] FIG. 11B depicts another embodiment of the estimated switching voltage output 38B, V_SW—EST. When the multi-level charge pump buck converter 12A is in the series output mode, the third output buffer 161 generates a series level. When the multi-level charge pump buck converter 12A is in either the first boost output mode or the second boost output mode, the third output buffer 161 outputs a boost mode level. Alternatively, when the multi-level charge pump buck converter 12A is in the shunt output mode, the third output buffer 161 outputs a shunt mode level.

[0209] FIG. 11C depicts another embodiment of the estimated switching voltage output 38B, V_SW—EST. When the multi-level charge pump buck converter 12A is in the series output mode, the third output buffer 161 generates a series level. When the multi-level charge pump buck converter 12A is in the first boost output mode the third output buffer 161 generates a first boost level. When the multi-level charge pump buck converter 12A is in the second boost output mode, the third output buffer 161 outputs a second boost mode level. Alternatively, when the multi-level charge pump buck converter 12A is in the shunt output mode, the third output buffer 161 outputs a shunt mode level.

[0210] FIG. 11D depicts another embodiment of the estimated switching voltage output 38B, V_SW—EST, for the case where the multi-level charge pump circuit 56 includes a first output mode of operation. When the multi-level charge pump buck converter 12A is in the first output mode of operation, the third output buffer 161 generates a first output level. When the multi-level charge pump buck converter 12A is in the series output mode, the third output buffer 161 generates a series level. When the multi-level charge pump buck converter 12A is in the first boost output mode, the third output buffer 161 generates a first boost level. When the multi-level charge pump buck converter 12A is in the second boost output mode, the third output buffer 161 outputs a second boost mode level. Alternatively, when the multi-level charge pump buck converter 12A is in the shunt output mode, the third output buffer 161 outputs a shunt level.

[0211] FIG. 11E depicts another embodiment of the estimated switching voltage output 38B, V_SW—EST, for the case where the multi-level charge pump circuit 56 includes a first output mode of operation. When the multi-level charge pump buck converter 12A is in the first output mode of operation, the third output buffer 161 generates a first output level. However, when the multi-level charge pump buck converter 12A is in either the series output mode, the first boost output mode, or the second boost output mode, the third output buffer 161 generates a boost/series level. Alternatively, when the multi-level charge pump buck converter 12A is in the shunt output mode, the third output buffer 161 outputs a shunt mode level.

[0212] FIG. 11F depicts another embodiment of the estimated switching voltage output 38B, V_SW—EST, for the case where the multi-level charge pump circuit 56 includes a first output mode of operation. When the multi-level charge pump buck converter 12A is in either the series output mode, the first boost mode, or the second boost mode, the third output buffer 161 generates a boost/series level. Alternatively, when the multi-level charge pump buck converter 12A is in either the first output mode of operation or the shunt output mode, the third output buffer 161 outputs a shunt level.

[0213] FIG. 8 depicts an embodiment of the V_OFFSET loop circuit 41, depicted in FIGS. 2A and 2B. The embodiment of the V_OFFSET loop circuit 41, depicted in FIG. 8, generates the threshold offset current 42, I_{THRESHOLD—OFFSET}, based upon a calculated value of the offset voltage, V_OFFSET, and a target offset voltage, V_{OFFSET—TARGET}. For the sake of simplicity, and without limitation, the operation of the V_OFFSET loop circuit 41, depicted in FIG. 8, will be done with continuing reference to FIG. 2A.

[0214] The target offset voltage, V_{OFFSET—TARGET}, may be based upon a parameter provided by the controller 50 to the parallel amplifier circuit 14.

[0215] The V_OFFSET loop circuit 41 includes a first subtractor circuit, a second subtractor circuit, and an integrator circuit. The first subtractor circuit may be configured to receive the power amplifier supply voltage, V_CC, and the parallel amplifier output voltage, V_PARA—AMP. The first subtractor circuit subtracts the parallel amplifier output voltage, V_PARA—AMP from the power amplifier supply voltage, V_CC, to generate the offset voltage, V_OFFSET, which appears across the coupling circuit 18, depicted in FIG. 2A. The second subtractor circuit receives the offset voltage, V_OFFSET, and the target offset voltage, V_{OFFSET—TARGET}. The second subtractor circuit subtracts the target offset voltage, V_{OFFSET—TARGET}, from the offset voltage, V_OFFSET, to generate an offset error voltage, V_{OFFSET—ERROR}, which is provided to the integrator circuit. The integrator circuit integrates the offset error voltage, V_{OFFSET—ERROR}, to generate the threshold offset current 42, I_{THRESHOLD—OFFSET}, which is provided to the multi-level charge pump buck converter 12A, depicted in FIG. 2A.

[0216] The operation of the logic circuit 148A of FIG. 4A will now be discussed with continuing reference to FIGS. 2A, 3A, 5A, 6A, and 7A. The logic circuit 148A may be digital or analog based logic configured for one or more state machines of the threshold detector and control circuit 132A. As an example embodiment, the logic circuit 148A (FIG. 4A) may have a first state machine corresponding to a first mode of operation of the multi-level charge pump buck converter 12A, depicted in FIG. 5A, and a second state machine corresponding to a second mode of operation of the multi-level charge pump buck converter 12A, depicted in FIG. 6A. Based on the mode switch control signal 131 received by the threshold detector and control circuit 132A, the threshold detector and control circuit 132A may configure the logic circuit 148A to use the first state machine to govern operation of the multi-level charge pump buck converter 12A using the first state machine of the logic circuit 148A, depicted in FIG. 5A. Alternatively, the threshold detector and control circuit 132A may configure the logic circuit 148A to use the second state machine to govern operation of the multi-level charge pump buck converter 12A using the second state machine of the logic circuit 148A, depicted in FIG. 6A.

[0217] As depicted in FIG. 4A, the logic circuit 148A may include a boost lockout counter 184 and a boost time counter 186. The boost time counter 186 may be used to keep track of the time that the multi-level charge pump buck converter 12A of FIG. 2A is in either the first boost output mode or the second output boost mode. When the multi-level charge pump buck converter 12A is in either the first boost output mode or the second boost output mode, the multi-level charge pump circuit 56 (FIG. 3A) is configured to be in either the first boost mode of operation or the second boost mode of operation, respectively. In one embodiment of the logic circuit 148A, when the logic circuit 148A determines that the multi-level charge pump buck converter 12A is in either the first boost output mode or the second output boost mode, the logic circuit 148A resets the counter output of the boost time counter 186 and enables the boost time counter 186 to begin counting up. The logic circuit 148A compares the counter output of the boost time counter 186 to a maximum boost time parameter, which may be provided by the controller 50. If the counter output of the boost time counter 186 is equal to or exceeds the maximum boost time parameter before the multi-level charge pump buck converter 12A is configured to return to either the shunt output mode of operation or the series output mode of operation, the logic circuit 148A asserts a minimum charge time indicator. However, if the multi-level charge pump buck converter 12A returns to either the series output mode of operation or the shunt output mode of operation while the counter output of the boost time counter 186 is less than the maximum boost time parameter, the logic circuit 148A de-asserts the minimum charge time indicator.

[0218] The boost lockout counter 184 may be a count-down timer that is used to ensure that the multi-level charge pump circuit 56 of FIGS. 2A and 3A remains in a charging mode of operation for a minimum charge time period after the multi-level charge pump circuit 56 has been in either the first boost mode of operation or the second boost mode of operation. This permits the first flying capacitor 100 and the second flying capacitor 102, of FIG. 7A, a sufficient amount of time to charge before the multi-level charge pump circuit 56 transitions again into either the first boost mode of operation or the second boost mode of operation. The minimum charge time period may be a parameter provided by the controller 50 via the control bus 44, as depicted in FIG. 1A. Operationally, after the multi-level charge pump buck converter 12A transitions from either the first boost output mode or the second boost output mode to either the shunt output mode of operation or the series output mode of operation, the logic circuit 148A determines whether the minimum charge time indicator is asserted. If the minimum charge time indicator is asserted, the logic circuit 148A sets the count value of the boost lockout counter 184 to an equal minimum charge time period and enables the boost lockout counter 184 to begin counting down. Once the boost lockout counter 184 counts down to zero, the logic circuit 148A is configured to de-assert the minimum charge time indicator.

[0219] Operation of the first state machine implemented in the logic circuit 148A, which is depicted in FIG. 5A, will now be described. The first state machine includes a shunt output mode 188A, a series output mode 190A, a first boost output mode 192A, and a second boost output mode 194A.

[0220] In the shunt output mode 188A, the logic circuit 148A (FIG. 4A) configures the series switch control output 162 such that the series switch 70 (FIG. 3A) is in an open state (not conducting). The logic circuit 148A also configures the shunt switch control output 164 such that the shunt switch 72 is in a closed state (conducting). In addition, the logic circuit 148A configures the charge pump mode control signal 60 to instruct the multi-level charge pump circuit 56 (FIG. 2A) to be in a charging mode of operation. As a result, the switching voltage output 26 of FIG. 3A is configured to provide a switching voltage, V_SW, substantially equal to ground. In response to assertion of the series level indication 152A, which indicates that the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP, is greater than or equal to the series level threshold 126, the logic circuit 148A configures the first state machine to transition to the series output mode 190A. Otherwise the state machine remains in the shunt output mode 188A.

[0221] In the series output mode 190A, the logic circuit 148A configures the series switch control output 162 such that the series switch 70 is in a closed state (conducting). The logic circuit 148A also configures the shunt switch control output 164 such that the shunt switch 72 is in an open state (not conducting). In addition, the logic circuit 148A configures the charge pump mode control signal 60 to instruct the multi-level charge pump circuit 56 to be in a charging mode of operation. As a result, the switching voltage output 26 of FIG. 3A is configured to provide a switching voltage, V_SW, substantially equal to the direct current (DC) voltage, V_BAT.

[0222] In response to de-assertion of the shunt level indication 150A (FIG. 4A), which indicates that the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP, is less than the shunt level threshold 124, the logic circuit 148A configures the first state machine to transition to the shunt output mode 188A (FIG. 5A). However, in response to assertion of the first boost level indication 154A, which indicates that the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP, is greater than or equal to the first boost level threshold 128, the logic circuit 148A configures the first state machine to transition to the desired voltage level of the power amplifier supply voltage V_CC, that correspond to the first boost output mode 192A. Otherwise, the first state machine remains in the series output mode 190A.

[0223] In the first boost output mode 192A, the logic circuit 148A (FIG. 4A) configures the series switch control output 162 such that the series switch 70 (FIG. 3A) is in an open state (not conducting). The logic circuit 148A also configures the shunt switch control output 164 such that the shunt switch 72 is in an open state (not conducting). In addition, the logic circuit 148A configures the charge pump mode control signal 60 to instruct the multi-level charge pump circuit 56 to be in a first boost mode of operation to provide 1.5×V_BAT at the charge pump output 64. As a result, the switching voltage output 26 of FIG. 3A is configured to provide a switching voltage, V_SW, substantially equal to 1.5×V_BAT. In response to de-assertion of the shunt level indication 150A (FIG. 4A), which indicates that the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP, is less than the shunt level threshold 124, the logic circuit 148A configures the first state machine to transition to the shunt output mode 188A (FIG. 5A). However, in response to assertion of the second boost level indication 156A, which indicates that the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP, is greater than or equal to the second boost level threshold 130, the logic circuit 148A configures the first state machine to transition to the second boost output mode 194A. Otherwise, the first state machine remains in the first boost output mode 192A.

[0224] In the second boost output mode 194A, the logic circuit 148A (FIG. 4A) configures the series switch control output 162 such that the series switch 70 (FIG. 3A) is in an open state (not conducting). The logic circuit 148A also configures the shunt switch control output 164 such that the shunt switch 72 is in an open state (not conducting). In addition, the logic circuit 148A configures the charge pump mode control signal 60 to instruct the multi-level charge pump circuit 56 to be in a second boost mode of operation to provide 2×V_BAT at the charge pump output 64. As a result, the switching voltage output 26 of FIG. 3A is configured to provide a switching voltage, V_SW, substantially equal to 2×V_BAT. In response to de-assertion of the shunt level indication 150A, which indicates that the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP, is less than the shunt level threshold 124, the first state machine transitions to the shunt output mode 188A. Otherwise, the state machine remains in the second boost output mode 194A.

[0225] Operation of the second state machine of the logic circuit 148A, which is depicted in FIG. 6A, will now be described. The second state machine includes a shunt output mode 196A, a series output mode 198A, a first boost output mode 200A, and a second boost output mode 202A. In addition, the second state machine uses the above-described boost lockout counter 184 and boost time counter 186 of the logic circuit 148A.

[0226] In the shunt output mode 196A, the logic circuit 148A (FIG. 4A) configures the series switch control output 162 such that the series switch 70 is in an open state (not conducting). The logic circuit 148A also configures the shunt switch control output 164 such that the shunt switch 72 is in a closed state (conducting). In addition, the logic circuit 148A configures the charge pump mode control signal 60 to instruct the multi-level charge pump circuit 56 (FIG. 3A) to be in a charging mode of operation. As a result, the switching voltage output 26 of FIG. 3A is configured to provide a switching voltage, V_SW, substantially equal to ground. If the boost lockout counter 184 is enabled, the boost lockout counter 184 continues to count down. In response to assertion of the series level indication 152A, which indicates that the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP, is greater than or equal to the series level threshold 126, the second state machine transitions to the series output mode 198A. Otherwise the second state machine remains in the shunt output mode 196A.

[0227] In the series output mode 198A, the logic circuit 148A (FIG. 4A) configures the series switch control output 162 such that the series switch 70 is in a closed state (conducting). The logic circuit 148A also configures the shunt switch control output 164 such that the shunt switch 72 is in an open state (not conducting). In addition, the logic circuit 148A configures the charge pump mode control signal 60 to instruct the multi-level charge pump circuit 56 to be in a charging mode of operation. As a result, the switching voltage output 26 of FIG. 3A is configured to provide a switching voltage, V_SW, substantially equal to the direct current (DC) voltage, V_BAT. If the boost lockout counter 184 is enabled, the boost lockout counter 184 continues to count down. In response to de-assertion of the shunt level indication 150A, which indicates that the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP, is less than the shunt level threshold 124, the logic circuit 148A configures the second state machine to transition to the shunt output mode 196A. However, in response to assertion of the first boost level indication 154D, which indicates that the compensated power amplifier circuit output current estimate, I_PAWA—COMP, is greater than or equal to the first boost level threshold 128, the logic circuit 148A determines whether both the minimum charge time indicator is de-asserted and the first boost level indication 154A is asserted. If the minimum charge time indicator is de-asserted and the first boost level indication 154A is asserted, the logic circuit 148A configures the second machine to transition to the first boost output mode 200A. Otherwise, the logic circuit 148A prevents the second state machine from transitioning to the first boost output mode 200A until the minimum time indicator is de-asserted. Once both the minimum charge time indicator is de-asserted and the first boost level indication 154A is asserted, the logic circuit 148A configures the second state machine to transition to the first boost output mode 200A, resets the counter output of the boost time counter 186, and enables the boost time counter 186 to begin counting up. Otherwise, the second state machine remains in the series output mode 198A.

[0228] In the first boost output mode 200A, the logic circuit 148A configures the series switch control output 162 such that the series switch 70 is in an open state (not conducting). The logic circuit 148A also configures the shunt switch control output 164 such that the shunt switch 72 is in an open state (not conducting). In addition, the logic circuit 148A configures the charge pump mode control signal 60 to instruct the multi-level charge pump circuit 56 to be in a first boost mode of operation to provide 1.5×V_BAT at the charge pump output 64. As a result, the switching voltage output 26 of FIG. 3A is configured to provide a switching voltage, V_SW, substantially equal to 1.5×V_BAT. In response to de-assertion of the first boost level indication 154A, which indicates that the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP, is less than the first boost level threshold 128, the logic circuit 148A configures the second state machine to transition to the series output mode 198A. If the count output of the boost time counter 186 exceeds the maximum boost time parameter, the logic circuit 148A asserts a minimum charge time indicator. In response to the minimum charge time indicator being asserted, the logic circuit 148A sets the count value of the boost lockout counter 184 and enables the boost lockout counter 184 to begin counting down. However, in response to assertion of the second boost level indication 156A, which indicates that the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP, is greater than or equal to the second boost level threshold 130, the logic circuit 148A configures the second state machine to transition to the second boost output mode 202A. Otherwise, the second state machine remains in the first boost output mode 200A.

[0229] In the second boost output mode 202A, the logic circuit 148A configures the series switch control output 162 such that the series switch 70 is in an open state (not conducting). The logic circuit 148A also configures the shunt switch control output 164 such that the shunt switch 72 is in an open state (not conducting). In addition, the logic circuit 148A configures the charge pump mode control signal 60 to instruct the multi-level charge pump circuit 56 (FIG. 3A) to be in a second boost mode of operation to provide 2×V_BAT at the charge pump output 64. As a result, the switching voltage output 26 of FIG. 3A is configured to provide a switching voltage, V_SW, substantially equal to 2×V_BAT.

[0230] In response to de-assertion of the first boost level indication 154A, which indicates that the compensated power amplifier circuit output current estimate, I_PAWA—COMP, is less than the first boost level threshold 128, the logic circuit 148A configures the second state machine to transition to the series output mode 198A. If the count output of the boost time counter 186 exceeds the maximum boost time parameter, the logic circuit 148A asserts a minimum charge time indicator. In response to the minimum charge time indicator being asserted, the logic circuit 148A sets the count value of the boost lockout counter 184 and enables the boost lockout counter 184 to begin counting down. Otherwise, the second state machine remains in the second boost output mode 202A.

[0231] The threshold and control circuit 132A further provides a logic level indication of the switching voltage output, V_{SW—EST—OUT}, which is a logic level representation of the switching voltage output, V_SW. The switching voltage output, V_{SW—EST—OUT}, may be based upon the V_{SW—EST—CMOS—SIGNAL}(s). In some embodiments of the threshold and control circuit 132A, the logic level indication of the switching voltage output, V_{SW—EST—OUT}, may be asserted when the multi-level charge pump buck converter 12A is in either the series output mode, the first boost output mode, or the second boost output mode. The logic level indication of the switching voltage output, V_{SW—EST—OUT}, is de-asserted when the multi-level charge pump buck converter 12A is in the shunt output mode.

[0232] FIG. 3B depicts another embodiment of switcher control circuit 52, the switcher control circuit 52B, and another embodiment of the FLL circuit 54 of the multi-level charge pump buck converter 12, FLL circuit 54B. The operation of the switcher control circuit 52B and the FLL circuit 54B will now be described.

[0233] Unlike the FLL circuit 54A depicted in FIG. 3A, the FLL circuit 54B outputs a threshold scalar′ 137B. Similar to the FLL circuit 54A, the FLL circuit 54B receives a clock reference signal 139A from a clock reference 139 and a logic level indication of the switching voltage output, V_{SW—EST—OUT}. The FLL circuit 54B extracts the operating frequency of the multi-level charge pump buck converter 12 based upon the logic level indication of the switching voltage output, V_{SW—EST—OUT}. Thereafter, the FLL circuit 54B compares the extracted operating frequency of the multi-level charge pump buck converter 12 to the clock reference signal 139A to generate the threshold scalar′ 137B. The magnitude of the threshold scalar′ 137B may be used to adjust the operating frequency of the multi-level charge pump buck converter 12. As will be discussed relative to the threshold detector and control circuit 132B of FIG. 4B, the FLL circuit 54B provides the threshold scalar′ 137B directly to a plurality of multiplier circuits, where the plurality of multiplier circuits includes a first multiplier circuit 168, a second multiplier circuit 170, a third multiplier circuit 172, and a fourth multiplier circuit 174. The first multiplier circuit 168, the second multiplier circuit 170, the third multiplier circuit 172, and the fourth multiplier circuit 174 may be used to scale the shunt level threshold 124, the series level threshold 126, the first boost level threshold 128, and the second boost level threshold 130, respectively to generate a scaled shunt level threshold 176, a scaled series level threshold 178, a scaled first boost level threshold 180, and a scaled second boost level threshold 182, of FIG. 4B. The scaled shunt level threshold 176, the scaled series level threshold 178, the scaled first boost level threshold 180, and the scaled second boost level threshold 182 may be used to control the operating frequency of the multi-level charge pump buck converter 12.

[0234] As an example, the FLL circuit 54B may be configured to decrease the magnitude of the threshold scalar′ 137B to decrease the magnitude of the scaled shunt level threshold 176, the scaled series level threshold 178, the scaled first boost level threshold 180, and the scaled second boost level threshold 182. As the magnitudes of the scaled shunt level threshold 176, the scaled series level threshold 178, the scaled first boost level threshold 180, and the scaled second boost level threshold 182 decrease, the operating frequency of the multi-level charge pump buck converter 12 will tend to increase, which will tend to increase the power inductor current, I_SW—OUT, delivered by the power inductor 16.

[0235] The FLL circuit 54B may be configured to increase the magnitude of the threshold scalar′ 137B to increase the magnitude of the scaled shunt level threshold 176, the scaled series level threshold 178, the scaled first boost level threshold 180, and the scaled second boost level threshold 182. As the scaled shunt level threshold 176, the scaled series level threshold 178, the scaled first boost level threshold 180, and the scaled second boost level threshold 182 are increased, the operating frequency of the multi-level charge pump buck converter 12 will tend to decrease, which will tend to decrease the power inductor current, I_SW—OUT, delivered by the power inductor 16.

[0236] Returning to FIG. 3B, unlike the switcher control circuit 52A of FIG. 3A, the switcher control circuit 52B includes a threshold detector and control circuit 132B. The switcher control circuit 52B omits the multiplier circuit 134. As will be discussed below relative to the threshold detector and control circuit 132B of FIG. 4B, the summing circuit 136, is placed in the threshold detector and control circuit 132B.

[0237] Also, similar to the switcher control circuit 52A, the switcher control circuit 52B may also receive a mode switch control signal 131 from the controller 50. The mode switch control signal 131 may configure the threshold detector and control circuit 132B to operate the multi-level charge pump buck converter in different modes of operation. As an example, the mode switch control signal 131 may configure operation of a state machine within the threshold detector and control circuit 132B that governs how the switching voltage output 26 transitions the switching voltage output 26 to provide different output levels. As a first example embodiment of a state machine within the threshold detector and control circuit 132B, the mode switch control signal 131 may configure the multi-level charge pump buck converter 12 to operate in a first mode of operation, depicted in FIG. 5B. As another example embodiment of a state machine within the threshold detector and control circuit 132A, the mode switch control signal 131 may configure the multi-level charge pump buck converter 12 to operate in a second mode of operation, depicted in FIG. 6B.

[0238] Referring to FIG. 4B, the FLL circuit 54B will now be discussed. Similar to FLL Circuit 54A of FIG. 3A, the FLL circuit 54B may be configured to receive a clock reference signal 139A from the clock reference 139 and a logic level indication of the switching voltage output, V_{SW—EST—OUT}, from the switcher control circuit 52B. The logic level indication of the switching voltage output, V_{SW—EST—OUT}, may be provided by the logic circuit 148B of the threshold detector and control circuit 132B. As discussed above, the logic level indication of the switching voltage output, V_{SW—EST—OUT}, is a logic level representation of the switching voltage output, V_SW.

[0239] The one embodiment of the threshold detector and control circuit 132B includes a first multiplier circuit 168, a second multiplier circuit 170, a third multiplier circuit 172, and a fourth multiplier circuit 174. The first multiplier circuit 168 may be configured to receive the shunt level threshold 124 and the receive threshold scalar′ 137B. The first multiplier circuit 168 multiplies the shunt level threshold 124 by the received threshold scalar′ 137B to generate a scaled shunt level threshold 176. The second multiplier circuit 170 may be configured to receive the series level threshold 126 and the threshold scalar′ 137B. The second multiplier circuit 170 multiplies the series level threshold 126 by the threshold scalar′ 137B to generate a scaled series level threshold 178. The third multiplier circuit 172 may be configured to receive the first boost level threshold 128 and the threshold scalar′ 137B. The third multiplier circuit 172 may multiplies the first boost level threshold 128 by the threshold scalar′ 137B to generate a scaled first boost level threshold 180. The fourth multiplier circuit 174 may be configured to receive the second boost level threshold 130 and the threshold scalar′ 137B. The fourth multiplier circuit 174 multiplies the second boost level threshold 130 by the threshold scalar′ 137B to generate the scaled second boost level threshold 182. The summing circuit 136 subtracts the threshold offset current 42, I_{THRESHOLD—OFFSET}, from the parallel amplifier circuit output current estimate 40, I_{PAWA—OUT—EST}, to generate a compensated parallel amplifier circuit output current estimate, I_PAWA—COMP′, which may be used as a composite feedback signal for the first comparator 140, the second comparator 142, the third comparator 144, and the fourth comparator 146. As discussed before, the threshold offset current 42, I_{THRESHOLD—OFFSET}, may be used to control the offset voltage, V_OFFSET, that is generated across the coupling circuit 18, as depicted in FIG. 2A. In the case where the coupling circuit 18 is a wire, such that the parallel amplifier output 32A is directly coupled to the power amplifier supply output 28, the V_OFFSET loop circuit 41 and the threshold offset current, I_{THRESHOLD—OFFSET}, are omitted such that I_PAWA—COMP′ is the same as parallel amplifier circuit output current estimate 40, I_{PAWA—OUT—EST}.

[0240] The first comparator 140 includes a positive terminal coupled to the scaled shunt level threshold 176, a negative terminal coupled to the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP′, and a first comparator output configured to generate a shunt level indication 150B, which is provided to the logic circuit 148B. When the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP′, is greater than or equal to the scaled shunt level threshold 176, the shunt level indication 150B is asserted by setting output of the first comparator 140 to a digital logic low state. When the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP′, is less than the scaled shunt level threshold 176, the shunt level indication 150B is de-asserted by setting output of the first comparator 140 to a digital logic high state. The second comparator 142 includes a positive terminal coupled to the scaled series level threshold 178, a negative terminal coupled to the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP′, and a second comparator output configured to generate a series level indication 152B, which is provided to the logic circuit 148B. When the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP′, is greater than or equal to the scaled series level threshold 178, the series level indication 152B is asserted by setting output of the second comparator 142 to a digital logic low state. When the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP′, is less than the scaled series level threshold 178, the series level indication 152B is de-asserted by setting output of the second comparator 142 to a digital logic high state. The third comparator 144 includes a positive terminal coupled to the scaled first boost level threshold 180, a negative terminal coupled to the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP′, and a third comparator output configured to generate a first boost level indication 154B, which is provided to the logic circuit 148B. When the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP′, is greater than the scaled first boost level threshold 180, the first boost level indication 154B is asserted by setting output of the third comparator 144 to a digital logic low state. When the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP′, is less than the scaled first boost level threshold 180, the first boost level indication 154B is de-asserted by setting output of the third comparator 144 to a digital logic high state. The fourth comparator 146 includes a positive terminal coupled to the scaled second boost level threshold 182, a negative terminal coupled to the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP′, and a fourth comparator output configured to generate a second boost level indication 156B, which is provided to the logic circuit 148B. When the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP′, is greater than the scaled second boost level threshold 182, the second boost level indication 156B is asserted by setting output of the fourth comparator 146 to a digital logic low state. When the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP′, is less than the scaled second boost level threshold 182, the second boost level indication 156B is de-asserted by setting output of the fourth comparator 146 to a digital logic high state.

[0241] The logic circuit 148B will now be discussed. The logic circuit 148B is similar to the logic circuit 148A of FIG. 4A. The example embodiment of the logic circuit 148B may include a Field Programmable Gate Array (FPGA) or other programmable logic device, discrete gates or transistor logic, discrete hardware components, or any combination thereof designed to perform. Some embodiments of the logic circuit 148B may be implemented in either a digital or analog processor. The logic circuit 148B generates the series switch control output 162, the shunt switch control output 164, the one or more switching voltage output cmos signal(s) 166, V_{SW—EST—CMOS—SIGNAL}(s), the charge pump mode control signal 60, and the logic level indication of the switching voltage output, V_{SW—EST—OUT} in a similar fashion as the logic circuit 148A, which has been previously discussed.

[0242] The operation of the logic circuit 148B will now be discussed with continuing reference to FIGS. 2A, 3B, 4B, 5B, 6B, and 7A. Similar to the logic circuit 148A of FIG. 4A, the logic circuit 148B may be digital or analog based logic configured for one or more state machines of the threshold detector and control circuit 132B. As an example embodiment, the logic circuit 148B (FIG. 4B) may have a first state machine corresponding to a first mode of operation, depicted in FIG. 5B and a second state machine corresponding to a second mode of operation, depicted in FIG. 6B. Based on the mode switch control signal 131, depicted in FIG. 3B, received by the threshold detector and control circuit 132B, the threshold detector and control circuit 132B may configure the logic circuit 148B to use the first state machine to govern operation of the multi-level charge pump buck converter using the first state machine of the logic circuit 148B, depicted in FIG. 5B. Alternatively, the threshold detector and control circuit 132B may configure the logic circuit 148B to use the second state machine to govern operation of the multi-level charge pump buck converter using the second state machine of the logic circuit 148B, depicted in FIG. 6B

[0243] Also similar to the logic circuit 148A, the logic circuit 148B may include a boost lockout counter 184 and a boost time counter 186. The boost time counter 186 may be used to keep track of the time that the multi-level charge pump buck converter 12A is in either the first boost output mode or the second boost output mode. When the multi-level charge pump buck converter 12A is in either the first boost output mode or the second boost output mode, the multi-level charge pump circuit 56 (FIG. 3B) is configured to be in either the first boost mode of operation or the second boost mode of operation, respectively. In one embodiment of the logic circuit 148B, when the logic circuit 148B determines that the multi-level charge pump buck converter 12A is in either the first boost output mode or the second boost output mode, the logic circuit 148B resets the counter output of the boost time counter 186 and enables the boost time counter 186 to begin counting up. The logic circuit 148B compares the counter output of the boost timer counter 186 to a maximum boost time parameter, which may be provided by the controller 50. If the counter output of the boost time counter 186 is equal to or exceeds the maximum boost time parameter before the multi-level charge pump buck converter 12A is configured to return to either the shunt output mode of operation or the series output mode of operation, the logic circuit 148B asserts a minimum charge time indicator. However, if the multi-level charge pump buck converter 12A returns to either the series output mode of operation or the shunt output mode of operation while the counter output of the boost time counter 186 is less than the maximum boost time parameter, the logic circuit 148B de-asserts the minimum charge time indicator.

[0244] Similar to the boost lockout counter 184 of the logic circuit 148A, the boost lockout counter 184 of the logic circuit 148B may be a count-down timer that is used to ensure that the multi-level charge pump circuit 56, depicted in FIG. 3B, remains in a charging mode of operation for a minimum charge time period after the multi-level charge pump circuit 56 has been in either the first boost mode of operation or the second boost mode of operation. This permits the first flying capacitor 100 and the second flying capacitor 102 of FIG. 7A a sufficient amount of time to charge before the multi-level charge pump circuit 56 transitions again into either the first boost mode of operation or the second boost mode of operation. Similar to the logic circuit 148A, the minimum charge time period may be a parameter provided by the controller 50 via the control bus 44 to the logic circuit 148B. Operationally, after the multi-level charge pump buck converter 12A transitions from either the first boost output mode or the second boost output mode to either the shunt output mode of operation or the series output mode of operation, the logic circuit 148B determines whether the minimum charge time indicator is asserted. If the minimum charge time indicator is asserted, the logic circuit 148B sets the count value of the boost lockout counter 184 to equal the minimum charge time period and enables the boost lockout counter 184 to begin counting down. Once the boost lockout counter 184 counts down to zero, the logic circuit 148B is configured to de-assert the minimum charge time indicator.

[0245] Operation of the first state machine implemented in the logic circuit 148B, depicted in FIG. 5B, will now be described. The first state machine includes a shunt output mode 188B, a series output mode 190B, a first boost output mode 192B, and a second boost output mode 194B.

[0246] In the shunt output mode 188B, the logic circuit 148B (FIG. 4B) configures the series switch control output 162 such that the series switch 70 (FIG. 3B) is in an open state (not conducting). The logic circuit 148B also configures the shunt switch control output 164 such that the shunt switch 72 is in a closed state (conducting). In addition, the logic circuit 148B configures the charge pump mode control signal 60 to instruct the multi-level charge pump circuit 56 (FIG. 3B) to be in a charging mode of operation. As a result, the switching voltage output 26 of FIG. 3B is configured to provide a switching voltage, V_SW, substantially equal to ground. In response to assertion of the series level indication 152B, which indicates that the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP′, is greater than or equal to the scaled series level threshold 178, the logic circuit 148B configures the first state machine to transition to the series output mode 190B. Otherwise the first state machine remains in the shunt output mode 188B.

[0247] In the series output mode 190B, the logic circuit 148B configures the series switch control output 162 such that the series switch 70 is in a closed state (conducting). The logic circuit 148B also configures the shunt switch control output 164 such that the shunt switch 72 is in an open state (not conducting). In addition, the logic circuit 148B configures the charge pump mode control signal 60 to instruct the multi-level charge pump circuit 56 to be in a charging mode of operation. As a result, the switching voltage output 26 of FIG. 3B is configured to provide a switching voltage, V_SW, substantially equal to the direct current (DC) voltage, V_BAT.

[0248] In response to de-assertion of the shunt level indication 150B (FIG. 4B), which indicates that the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP′, is less than the scaled shunt level threshold 176, the logic circuit 148B configures the first state machine to transition to the shunt output mode 188B (FIG. 5B). However, in response to assertion of the first boost level indication 154B which indicates that the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP′, is greater than or equal to the scaled first boost level threshold 180, the logic circuit 148B configures the first state machine to transition to the first boost output mode 192B. Otherwise, the first state machine remains in the series output mode 190B.

[0249] In the first boost output mode 192B, the logic circuit 148B (FIG. 4B) configures the series switch control output 162 such that the series switch 70 (FIG. 3B) is in an open state (not conducting). The logic circuit 148B also configures the shunt switch control output 164 such that the shunt switch 72 is in an open state (not conducting). In addition, the logic circuit 148B configures the charge pump mode control signal 60 to instruct the multi-level charge pump circuit 56 to be in a first boost mode of operation to provide 1.5×V_BAT at the charge pump output 64. As a result, the switching voltage output 26 of FIG. 3B is configured to provide a switching voltage, V_SW, substantially equal to 1.5×V_BAT. In response to de-assertion of the shunt level indication 150B (FIG. 4B), which indicates that the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP′, is less than the scaled shunt level threshold 176, the logic circuit 148B configures the first state machine to transition to the shunt output mode 188B (FIG. 5B). However, in response to assertion of the second boost level indication 156B, which indicates that the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP′, is greater than or equal to the scaled second boost level threshold 182, the logic circuit 148B configures the first state machine to transition to the second boost output mode 194B. Otherwise, the first state machine remains in the first boost output mode 192B.

[0250] In the second boost output mode 194B, the logic circuit 148B (FIG. 4B) configures the series switch control output 162 such that the series switch 70 (FIG. 3B) is in an open state (not conducting). The logic circuit 148B also configures the shunt switch control output 164 such that the shunt switch 72 is in an open state (not conducting). In addition, the logic circuit 148B configures the charge pump mode control signal 60 to instruct the multi-level charge pump circuit 56 to be in a second boost mode of operation to provide 2×V_BAT at the charge pump output 64. As a result, the switching voltage output 26 of FIG. 3B is configured to provide a switching voltage, V_SW, substantially equal to 2×V_BAT. In response to de-assertion of the shunt level indication 150B, which indicates that the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP′, is less than the scaled shunt level threshold 176, the first state machine transitions to the shunt output mode 188B. Otherwise, the first state machine remains in the second boost output mode 194B.

[0251] Operation of the second state machine of the logic circuit 148B (FIG. 3B), which is depicted in FIG. 6B, will now be described. The second state machine includes a shunt output mode 196B, a series output mode 198B, a first boost output mode 200B, and a second boost output mode 202B. In addition, the second state machine uses the above-described boost lockout counter 184 and boost time counter 186 of the logic circuit 148B.

[0252] In the shunt output mode 196B, the logic circuit 148B, depicted in FIG. 4B, configures the series switch control output 162 such that the series switch 70 is in an open state (not conducting). The logic circuit 148B also configures the shunt switch control output 164 such that the shunt switch 72 is in a closed state (conducting). In addition, the logic circuit 148B configures the charge pump mode control signal 60 to instruct the multi-level charge pump circuit 56, depicted in FIG. 2A, to be in a charging mode of operation. As a result, the switching voltage output 26 of FIG. 3B is configured to provide a switching voltage, V_SW, substantially equal to ground. If the boost lockout counter 184 is enabled, the boost lockout counter 184 continues to count down. In response to assertion of the series level indication 152B, which indicates that the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP′, is greater than or equal to the scaled series level threshold 178, the second state machine transitions to the series output mode 198B. Otherwise the second state machine remains in the shunt output mode 196B.

[0253] In the series output mode 198B, the logic circuit 148B (FIG. 4B) configures the series switch control output 162 such that the series switch 70 is in a closed state (conducting). The logic circuit 148B also configures the shunt switch control output 164 such that the shunt switch 72 is in an open state (not conducting). In addition, the logic circuit 148B configures the charge pump mode control signal 60 to instruct the multi-level charge pump circuit 56 to be in a charging mode of operation. As a result, the switching voltage output 26 of FIG. 3B is configured to provide a switching voltage, V_SW, substantially equal to the direct current (DC) voltage, V_BAT. If the boost lockout counter 184 is enabled, the boost lockout counter 184 continues to count down. In response to de-assertion of the shunt level indication 150B, which indicates that the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP′, is less than the scaled shunt level threshold 176, the logic circuit 148B configures the second state machine to transition to the shunt output mode 196B. However, in response to assertion of the first boost level indication 154B which indicates that the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP,′ is greater than or equal to the scaled first boost level threshold 180, the logic circuit 148B determines whether both the minimum charge time indicator is de-asserted and the first boost level indication 154B is asserted. If the minimum charge time indicator is de-asserted and the first boost level indication 154B is asserted, the logic circuit 148B configures the second machine to transition to the first boost output mode 200B. Otherwise, the logic circuit 148B prevents the second state machine from transitioning to the first boost output mode 200B until the minimum time indicator is de-asserted. Once both the minimum charge time indicator is de-asserted and the first boost level indication 154B is asserted, the logic circuit 148B configures the second state machine to transition to the first boost output mode 200B, resets the counter output of the boost time counter 186, and enables the boost time counter 186 to begin counting up. Otherwise, the second state machine remains in the series output mode 198B.

[0254] In the first boost output mode 200B, the logic circuit 148B configures the series switch control output 162 such that the series switch 70 is in an open state (not conducting). The logic circuit 148B also configures the shunt switch control output 164 such that the shunt switch 72 is in an open state (not conducting). In addition, the logic circuit 148B configures the charge pump mode control signal 60 to instruct the multi-level charge pump circuit 56 to be in a first boost mode of operation to provide 1.5×V_BAT at the charge pump output 64. As a result, the switching voltage output 26 of FIG. 3B is configured to provide a switching voltage, V_SW, substantially equal to 1.5×V_BAT. In response to de-assertion of the first boost level indication 154B, which indicates that the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP′, is less than the scaled first boost level threshold 180, the logic circuit 148B configures the second state machine to transition to the series output mode 198B. If the count output of the boost time counter 186 exceeds the maximum boost time parameter, the logic circuit 148B asserts a minimum charge time indicator. In response to the minimum charge time indicator being asserted, the logic circuit 148B sets the count value of the boost lockout counter 184 and enables the boost lockout counter 184 to begin counting down. However, in response to assertion of the second boost level indication 156B which indicates that the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP′, is greater than or equal to the scaled second boost level threshold 182, the logic circuit 148B configures the second state machine to transition to the second boost output mode 202B. Otherwise, the second state machine remains in the first boost output mode 200B.

[0255] In the second boost output mode 202B, the logic circuit 148B configures the series switch control output 162 such that the series switch 70 is in an open state (not conducting). The logic circuit 148B also configures the shunt switch control output 164 such that the shunt switch 72 is in an open state (not conducting). In addition, the logic circuit 148B configures the charge pump mode control signal 60 to instruct the multi-level charge pump circuit 56 to be in a second boost mode of operation to provide 2×V_BAT at the charge pump output 64. As a result, the switching voltage output 26 of FIG. 3B is configured to provide a switching voltage, V_SW, substantially equal to 2×V_BAT.

[0256] In response to de-assertion of the first boost level indication 154B which indicates that the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP′, is less than the scaled first boost level threshold 180, the logic circuit 148B configures the second state machine to transition to the series output mode 198B. If the count output of the boost time counter 186 exceeds the maximum boost time parameter, the logic circuit 148B asserts a minimum charge time indicator. In response to the minimum charge time indicator being asserted, the logic circuit 148B sets the count value of the boost lockout counter 184 and enables the boost lockout counter 184 to begin counting down. Otherwise, the second state machine remains in the second boost output mode 202B.

[0257] FIG. 3C depicts an embodiment of the pseudo-envelope follower power management system 10B of FIG. 1B that does not include a frequency lock loop (FLL) circuit. The embodiment of the pseudo-envelope follower power management system 10B that does not include a frequency lock loop (FLL) circuit may include a switcher control circuit 52C. The switcher controller circuit 52C may include a threshold detector and control circuit 132C, which is similar to the threshold detector and control circuit 132B of FIG. 3B. However, unlike threshold detector and control circuit 132B, the threshold detector and control circuit 132C may not be configured to provide the logic level indication of the switching voltage output, V_{SW—EST—OUT}, to an FLL circuit. Likewise, unlike threshold detector and control circuit 132B, the threshold detector and control circuit 132C may not be configured to receive a threshold scalar from an FLL circuit.

[0258] FIG. 4C depicts an embodiment of the threshold detector and control circuit 132C. Similar to the threshold detector and control circuit 132B of FIG. 4B, the threshold detector and control circuit 132C includes a summing circuit 136 configured to receive the threshold offset current 42, I_{THRESHOLD—OFFSET}, and the parallel amplifier circuit output current estimate 40, I_{PAWA—OUT—EST}, generated by the parallel amplifier circuit. The summing circuit 136 subtracts the threshold offset current 42, I_{THRESHOLD—OFFSET}, from the parallel amplifier circuit output current estimate 40, I_{PAWA—OUT—EST}, to generate a compensated parallel amplifier circuit output current estimate, I_PAWA—COMP′, which may be used as a composite feedback signal for the first comparator 140, the second comparator 142, the third comparator 144, and the fourth comparator 146. As discussed before, the threshold offset current 42, I_{THRESHOLD—OFFSET}, may be used to control the offset voltage, V_OFFSET, which is generated across the coupling circuit 18, as depicted in FIG. 1A. In the case where the coupling circuit 18 is a wire, such that the parallel amplifier output 32A is directly coupled to the power amplifier supply output 28, the V_OFFSET loop circuit 41 and the threshold offset current 42, I_{THRESHOLD—OFFSET}, are omitted such that I_PAWA—COMP′ is the same as the parallel amplifier circuit output current estimate 40, I_{PAWA—OUT—EST}.

[0259] As depicted in FIG. 4C, with continuing reference to FIGS. 1A and 3C, the threshold detector and control circuit 132C may include a first comparator 140, a second comparator 142, a third comparator 144, a fourth comparator 146, and a logic circuit 148C. The example embodiment of the logic circuit 148C may include a Field Programmable Gate Array (FPGA) or other programmable logic device, discrete gates or transistor logic, discrete hardware components, or any combination thereof designed to perform. Some embodiments of the logic circuit 148C may be implemented in either a digital or analog processor.

[0260] The first comparator 140 includes a positive terminal coupled to the shunt level threshold 124, a negative terminal coupled to the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP′, and a first comparator output configured to generate a shunt level indication 150C, which is provided to the logic circuit 148C. When the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP′, is greater than or equal to the shunt level threshold 124, the shunt level indication 150C is asserted by setting output of the first comparator 140 to a digital logic low state. When the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP′, is less than the shunt level threshold 124, the shunt level indication 150C is de-asserted by setting output of the first comparator 140 to a digital logic high state. The second comparator 142 includes a positive terminal coupled to the series level threshold 126, a negative terminal coupled to the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP,′ and a second comparator output configured to generate a series level indication 152C, which is provided to the logic circuit 148C. When the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP,′ is greater than or equal to the series level threshold 126, the series level indication 152C is asserted by setting output of the second comparator 142 to a digital logic low state. When the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP,′ is less than the series level threshold 126, the series level indication 152C is de-asserted by setting output of the second comparator 142 to a digital logic high state. The third comparator 144 includes a positive terminal coupled to the first boost level threshold 128, a negative terminal coupled to the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP′, and a third comparator output configured to generate a first boost level indication 154C which is provided to the logic circuit 148C. When the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP′, is greater than the first boost level threshold 128, the first boost level indication 154C is asserted by setting output of the third comparator 144 to a digital logic low state. When the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP,′ is less than the first boost level threshold 128, the first boost level indication 154C is de-asserted by setting output of the third comparator 144 to a digital logic high state. The fourth comparator 146 includes a positive terminal coupled to the second boost level threshold 130, a negative terminal coupled to the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP,′ and a fourth comparator output configured to generate a second boost level indication 156C, which is provided to the logic circuit 148C. When the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP,′ is greater than the second boost level threshold 130, the second boost level indication 156C is asserted by setting output of the fourth comparator 146 to a digital logic low state. When the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP,′ is less than the second boost level threshold 130, the second boost level indication 156C is de-asserted by setting output of the fourth comparator 146 to a digital logic high state.

[0261] Similar to the logic circuit 148A of FIG. 4A and the logic circuit 148B of FIG. 4B, the logic circuit 148C of FIG. 4C may be configured to generate a charge pump mode control signal 60, a series switch control output 162 provided to the first output buffer 158, a shunt switch control output 164 provided to the second output buffer 160, one or more switching voltage output cmos signal(s) 166, V_{SW—EST—CMOS—SIGNAL}(s), provided to the third output buffer 161, and an estimated switching voltage output 38B, V_SW—EST. As previously described, the series switch control output 162, a shunt switch control output 164, and the one or more switching voltage output cmos signal(s) 166, V_{SW—EST—CMOS—SIGNAL}(s), may be configured to operate with the first output buffer 158, the second output buffer 160, and the third output buffer 161 to generate the series switch control signal 66, the shunt switch control signal 68, and the estimated switching voltage output 38B, V_SW—EST, respectively. Similar to the logic circuit 148A of FIG. 4A and the logic circuit 148B of FIG. 4B, the logic circuit 148C may include a boost lockout counter 184 and a boost time counter 186. The operation of the boost lockout counter 184 and a boost time counter 186 of the logic circuit 148C is substantially similar to the operation of the boost lockout counter 184 and a boost time counter 186 of the logic circuit 148A and 148B of FIGS. 4A and 4B, respectively.

[0262] Similar to the threshold detector and control circuit 132A of FIG. 4A and the threshold detector and control circuit 132B of FIG. 4B, the threshold detector and control circuit 132C may be configured to receive a mode switch control signal 131 from the controller 50, as depicted in FIG. 3C, in order to configure the logic circuit 148C to operate the multi-level charge pump buck converter in different modes of operation. As an example, the mode switch control signal 131 may configure operation of a state machine within the threshold detector and control circuit 132C that governs how the switching voltage output 26 transitions the switching voltage output 26 to provide different output levels. As a first example embodiment of a state machine within the threshold detector and control circuit 132C, the mode switch control signal 131 may configure the multi-level charge pump buck converter 12 to operate in a first mode of operation, depicted in FIG. 5C. As another example embodiment of a state machine within the threshold detector and control circuit 132C, the mode switch control signal 131 may configure the multi-level charge pump buck converter 12 to operate in a second mode of operation, depicted in FIG. 6C.

[0263] The operation of the logic circuit 148C will now be discussed with continuing reference to FIGS. 2A, 3C, 4C, 5C, 6C, and 7A. Similar to the logic circuit 148A of FIG. 4A and the logic circuit 148B of FIG. 4B, the logic circuit 148C may be digital or analog based logic configured for one or more state machines of the threshold detector and control circuit 132C.

[0264] Operation of the first state machine implemented in the logic circuit 148C, depicted in FIG. 5C, will now be described. The first state machine includes a shunt output mode 188C, a series output mode 190C, a first boost output mode 192C, and a second boost output mode 194C.

[0265] In the shunt output mode 188C, the logic circuit 148C (FIG. 4C) configures the series switch control output 162 such that the series switch 70 (FIG. 3C) is in an open state (not conducting). The logic circuit 148C also configures the shunt switch control output 164 such that the shunt switch 72 is in a closed state (conducting). In addition, the logic circuit 148C configures the charge pump mode control signal 60 to instruct the multi-level charge pump circuit 56 (FIG. 3C) to be in a charging mode of operation. As a result, the switching voltage output 26 of FIG. 3C is configured to provide a switching voltage, V_SW, substantially equal to ground. In response to assertion of the series level indication 152C, which indicates that the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP′, is greater than or equal to the series level threshold 126, the logic circuit 148C configures the first state machine to transition to the series output mode 190C. Otherwise the state machine remains in the shunt output mode 188C.

[0266] In the series output mode 190C, the logic circuit 148C configures the series switch control output 162 such that the series switch 70 is in a closed state (conducting). The logic circuit 148C also configures the shunt switch control output 164 such that the shunt switch 72 is in an open state (not conducting). In addition, the logic circuit 148C configures the charge pump mode control signal 60 to instruct the multi-level charge pump circuit 56 to be in a charging mode of operation. As a result, the switching voltage output 26 of FIG. 3C is configured to provide a switching voltage, V_SW, substantially equal to the direct current (DC) voltage, V_BAT.

[0267] In response to de-assertion of the shunt level indication 150C (FIG. 4C), which indicates that the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP′, is less than the shunt level threshold 124, the logic circuit 148C configures the first state machine to transition to the shunt output mode 188C (FIG. 5C). However, in response to assertion of the first boost level indication 154C, which indicates that the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP′, is greater than or equal to the first boost level threshold 128, the logic circuit 148C configures the first state machine to transition to the first boost output mode 192C. Otherwise, the first state machine remains in the series output mode 190C.

[0268] In the first boost output mode 192C, the logic circuit 148C (FIG. 4C) configures the series switch control output 162 such that the series switch 70 (FIG. 3C) is in an open state (not conducting). The logic circuit 148C also configures the shunt switch control output 164 such that the shunt switch 72 is in an open state (not conducting). In addition, the logic circuit 148C configures the charge pump mode control signal 60 to instruct the multi-level charge pump circuit 56 to be in a first boost mode of operation to provide 1.5×V_BAT at the charge pump output 64. As a result, the switching voltage output 26 of FIG. 3C is configured to provide a switching voltage, V_SW, substantially equal to 1.5×V_BAT. In response to de-assertion of the shunt level indication 150C (FIG. 4C), which indicates that the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP′, is less than the shunt level threshold 124, the logic circuit 148C configures the first state machine to transition to the shunt output mode 188C (FIG. 5C). However, in response to assertion of the second boost level indication 156C, which indicates that the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP′, is greater than or equal to the second boost level threshold 130, the logic circuit 148C configures the first state machine to transition to the second boost output mode 194C. Otherwise, the first state machine remains in the first boost output mode 192C.

[0269] In the second boost output mode 194C, the logic circuit 148C (FIG. 4C) configures the series switch control output 162 such that the series switch 70 (FIG. 3C) is in an open state (not conducting). The logic circuit 148C also configures the shunt switch control output 164 such that the shunt switch 72 is in an open state (not conducting). In addition, the logic circuit 148C configures the charge pump mode control signal 60 to instruct the multi-level charge pump circuit 56 to be in a second boost mode of operation to provide 2×V_BAT at the charge pump output 64. As a result, the switching voltage output 26 of FIG. 3C is configured to provide a switching voltage, V_SW, substantially equal to 2×V_BAT. In response to de-assertion of the shunt level indication 150C, which indicates that the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP′, is less than the shunt level threshold 124, the first state machine transitions to the shunt output mode 188C. Otherwise, the state machine remains in the second boost output mode 194C.

[0270] Operation of the second state machine of the logic circuit 148C, depicted in FIG. 6C, will now be described. The second state machine includes a shunt output mode 196C, a series output mode 198C, a first boost output mode 200C, and a second boost output mode 202C. In addition, the second state machine uses the above-described boost lockout counter 184 and boost time counter 186 of the logic circuit 148C.

[0271] In the shunt output mode 196C, the logic circuit 148C (FIG. 4C) configures the series switch control output 162 such that the series switch 70 is in an open state (not conducting). The logic circuit 148C also configures the shunt switch control output 164 such that the shunt switch 72 is in a closed state (conducting). In addition, the logic circuit 148C configures the charge pump mode control signal 60 to instruct the multi-level charge pump circuit 56 (FIG. 3C) to be in a charging mode of operation. As a result, the switching voltage output 26 of FIG. 3C is configured to provide a switching voltage, V_SW, substantially equal to ground. If the boost lockout counter 184 is enabled, the boost lockout counter 184 continues to count down. In response to assertion of the series level indication 152C, which indicates that the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP′, is greater than or equal to the series level threshold 126, the second state machine transitions to the series output mode 198C. Otherwise the second state machine remains in the shunt output mode 196C.

[0272] In the series output mode 198C, the logic circuit 148C (FIG. 4C) configures the series switch control output 162 such that the series switch 70 is in a closed state (conducting). The logic circuit 148C also configures the shunt switch control output 164 such that the shunt switch 72 is in an open state (not conducting). In addition, the logic circuit 148C configures the charge pump mode control signal 60 to instruct the multi-level charge pump circuit 56 to be in a charging mode of operation. As a result, the switching voltage output 26 of FIG. 3C is configured to provide a switching voltage, V_SW, substantially equal to the direct current (DC) voltage, V_BAT. If the boost lockout counter 184 is enabled, the boost lockout counter 184 continues to count down. In response to de-assertion of the shunt level indication 150C, which indicates that the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP′, is less than the shunt level threshold 124, the logic circuit 148C configures the second state machine to transition to the shunt output mode 196C. However, in response to assertion of the first boost level indication 154C, which indicates that the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP′, is greater than or equal to the first boost level threshold 128, the logic circuit 148C determines whether both the minimum charge time indicator is de-asserted and the first boost level indication 154C is asserted. If the minimum charge time indicator is de-asserted and the first boost level indication 154C is asserted, the logic circuit 148C configures the second machine to transition to the first boost output mode 200C. Otherwise, the logic circuit 148C prevents the second state machine from transitioning to the first boost output mode 200C until the minimum time indicator is de-asserted. Once both the minimum charge time indicator is de-asserted and the first boost level indication 154C is asserted, the logic circuit 148C configures the second state machine to transition to the first boost output mode 200C, resets the counter output of the boost time counter 186, and enables the boost time counter 186 to begin counting up. Otherwise, the second state machine remains in the series output mode 198C.

[0273] In the first boost output mode 200C, the logic circuit 148C configures the series switch control output 162 such that the series switch 70 is in an open state (not conducting). The logic circuit 148C also configures the shunt switch control output 164 such that the shunt switch 72 is in an open state (not conducting). In addition, the logic circuit 148C configures the charge pump mode control signal 60 to instruct the multi-level charge pump circuit 56 (FIG. 3C) to be in a first boost mode of operation to provide 1.5×V_BAT at the charge pump output 64. As a result, the switching voltage output 26 of FIG. 3C is configured to provide a switching voltage, V_SW, substantially equal to 1.5×V_BAT. In response to de-assertion of the first boost level indication 154C, which indicates that the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP′, is less than the first boost level threshold 128, the logic circuit 148C configures the second state machine to transition to the series output mode 198C. If the count output of the boost time counter 186 exceeds the maximum boost time parameter, the logic circuit 148C asserts a minimum charge time indicator. In response to the minimum charge time indicator being asserted, the logic circuit 148C sets the count value of the boost lockout counter 184 and enables the boost lockout counter 184 to begin counting down. However, in response to assertion of the second boost level indication 156C, which indicates that the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP′, is greater than or equal to the second boost level threshold 130, the logic circuit 148C configures the second state machine to transition to the second boost output mode 202C. Otherwise, the second state machine remains in the first boost output mode 200C.

[0274] In the second boost output mode 202C, the logic circuit 148C configures the series switch control output 162 such that the series switch 70 (FIG. 3C) is in an open state (not conducting). The logic circuit 148C also configures the shunt switch control output 164 such that the shunt switch 72 (FIG. 3C) is in an open state (not conducting). In addition, the logic circuit 148C configures the charge pump mode control signal 60 to instruct the multi-level charge pump circuit 56 (FIG. 3C) to be in a second boost mode of operation to provide 2×V_BAT at the charge pump output 64. As a result, the switching voltage output 26 of FIG. 3C is configured to provide a switching voltage, V_SW, substantially equal to 2×V_BAT.

[0275] In response to de-assertion of the first boost level indication 154C, which indicates that the compensated parallel amplifier circuit output current estimate, I_PAWA—COMP′, is less than the first boost level threshold 128, the logic circuit 148C configures the second state machine to transition to the series output mode 198C. If the count output of the boost time counter 186 exceeds the maximum boost time parameter, the logic circuit 148C asserts a minimum charge time indicator. In response to the minimum charge time indicator being asserted, the logic circuit 148C sets the count value of the boost lockout counter 184 and enables the boost lockout counter 184 to begin counting down. Otherwise, the second state machine remains in the second boost output mode 202C.

[0276] The threshold and control circuit 132C further provides a logic level indication of the switching voltage output, V_{SW—EST—OUT}, which is a logic level representation of the switching voltage output, V_SW. The switching voltage output, V_{SW—EST—OUT}, may be based upon the V_{SW—EST—CMOS—SIGNAL}(s). In some embodiments of the threshold and control circuit 132C, the logic level indication of the switching voltage output, V_{SW—EST—OUT}, may be asserted when the multi-level charge pump buck converter 12A is in either the series output mode, the first boost output mode, or the second boost output mode. The logic level indication of the switching voltage output, V_{SW—EST—OUT}, is de-asserted when the multi-level charge pump buck converter 12A is in the shunt output mode of operation.

[0277] By way of example, and not by limitation, FIG. 3D depicts an embodiment of the pseudo-envelope follower power management system 10B of FIG. 1B that includes neither a frequency lock loop (FLL) circuit nor a V_OFFSET loop circuit 41. In addition, FIG. 3D depicts another embodiment of the pseudo-envelope follower power management system 10B of FIG. 1B where the coupling circuit 18 is a wire and the parallel amplifier output 32A of the parallel amplifier circuit 14 is directly coupled to the power amplifier supply output 28. Other embodiments of the pseudo-envelope follower power management system 10B of FIG. 1B that include the circuitry depicted in FIG. 3D may include a coupling circuit 18 that does not directly couple the output of the parallel amplifier output 32A to the power amplifier supply output 28, V_CC. In those cases, the circuitry depicted in FIG. 3D may be included in a parallel amplifier circuit 14, of FIG. 1A, that includes a V_OFFSET loop circuit 41.

[0278] FIG. 3D depicts an embodiment of the multi-level charge pump buck converter having a switcher control circuit 52D, which is similar to the switcher control circuit 52C depicted in FIG. 3C. However, unlike the switcher control circuit 52C, the switcher control circuit 52D includes a threshold detector and control circuit 132D that is not configured to receive the threshold offset current 42, I_{THRESHOLD—OFFSET}, from the parallel amplifier circuit 14.

[0279] Similar to the threshold detector and control circuit 132A of FIG. 4A, the threshold detector and control circuit 132B of FIG. 4B, and the threshold detector and control circuit 132C of FIG. 4C, the threshold detector and control circuit 132D of FIG. 4D may be configured to receive mode switch control signal 131, depicted in FIG. 3D, from the controller 50 in order to configure the logic circuit 148D to operate the multi-level charge pump buck converter in different modes of operation. As an example, the mode switch control signal 131 may configure operation of a state machine within the threshold detector and control circuit 132D that governs how the switching voltage output 26 transitions the switching voltage output 26 to provide different output levels. As a first example embodiment of a first state machine within the threshold detector and control circuit 132D, the mode switch control signal 131 may configure the multi-level charge pump buck converter 12 to operate in a first mode of operation, depicted in FIG. 5D. As another example embodiment a second state machine within the threshold detector and control circuit 132D, the mode switch control signal 131 may configure the multi-level charge pump buck converter 12 to operate in a second mode of operation, depicted in FIG. 6D.

[0280] One embodiment of the threshold detector and control circuit 132D is depicted in FIG. 4D. The threshold detector and control circuit 132D is similar to the threshold detector and control circuit 132A, depicted in FIG. 4A, except the logic circuit 148A is replace by a logic circuit 148D and the parallel amplifier circuit output current estimate, I_PAWA—COMP, is replaced by the parallel amplifier circuit output current estimate 40, I_{PAWA—OUT—EST}. As discussed above, the parallel amplifier circuit output current estimate 40, I_{PAWA—OUT—EST}, may include the scaled parallel amplifier output current estimate, I_{PARA—AMP—SENSE}, and the scaled open loop assist circuit output current estimate, I_{ASSIST—SENSE}. However, in some embodiments of the parallel amplifier circuit that do not include the open loop assist circuit 39, the parallel amplifier circuit output current estimate 40, I_{PAWA—OUT—EST}, only includes the scaled parallel amplifier output current estimate, I_{PARA—AMP—SENSE}, generated by the parallel amplifier sense circuit 36 of the parallel amplifier circuitry 32, as above described.

[0281] The threshold detector and control circuit 132D of FIG. 4D will be described with continuing reference to FIG. 3D. The threshold detector and control circuit 132D may include a first comparator 140, a second comparator 142, a third comparator 144, a fourth comparator 146, and a logic circuit 148D. The example embodiment of the logic circuit 148D may include a Field Programmable Gate Array (FPGA) or other programmable logic device, discrete gates or transistor logic, discrete hardware components, or any combination thereof designed to perform. Some embodiments of the logic circuit 148D may be implemented in either a digital or analog processor.

[0282] The first comparator 140 includes a positive terminal coupled to the shunt level threshold 124, a negative terminal coupled to the parallel amplifier circuit output current estimate 40, I_{PAWA—OUT—EST}, and a first comparator output is configured to generate a shunt level indication 150D, which is provided to the logic circuit 148D. When the parallel amplifier circuit output current estimate 40, I_{PAWA—OUT—EST}, is greater than or equal to the shunt level threshold 124, the shunt level indication 150D is asserted by setting output of the first comparator 140 to a digital logic low state. When the parallel amplifier circuit output current estimate 40, I_{PAWA—OUT—EST}, is less than the shunt level threshold 124, the shunt level indication 150D is de-asserted by setting output of the first comparator 140 to a digital logic high state. The second comparator 142 includes a positive terminal coupled to the series level threshold 126, a negative terminal coupled to the parallel amplifier circuit output current estimate 40, I_{PAWA—OUT—EST}, and a second comparator output is configured to generate a series level indication 152D, which is provided to the logic circuit 148D. When the parallel amplifier circuit output current estimate 40, I_{PAWA—OUT—EST}, is greater than or equal to the series level threshold 126, the series level indication 152D is asserted by setting output of the second comparator 142 to a digital logic low state. When the parallel amplifier circuit output current estimate 40, I_{PAWA—OUT—EST}, is less than the series level threshold 126, the series level indication 152D is de-asserted by setting output of the second comparator 142 to a digital logic high state. The third comparator 144 includes a positive terminal coupled to the first boost level threshold 128, a negative terminal coupled to the parallel amplifier circuit output current estimate 40, I_{PAWA—OUT—EST}, and a third comparator output is configured to generate a first boost level indication 154D, which is provided to the logic circuit 148D. When the parallel amplifier circuit output current estimate 40, I_{PAWA—OUT—EST}, is greater than the first boost level threshold 128, the first boost level indication 154D is asserted by setting output of the third comparator 144 to a digital logic low state. When the parallel amplifier circuit output current estimate 40, I_{PAWA—OUT—EST}, is less than the first boost level threshold 128, the first boost level indication 154D is de-asserted by setting output of the third comparator 144 to a digital logic high state. The fourth comparator 146 includes a positive terminal coupled to the second boost level threshold 130, a negative terminal coupled to the parallel amplifier circuit output current estimate 40, I_{PAWA—OUT—EST}, and a fourth comparator output is configured to generate a second boost level indication 156D, which is provided to the logic circuit 148D. When the parallel amplifier circuit output current estimate 40, I_{PAWA—OUT—EST}, is greater than the second boost level threshold 130, the second boost level indication 156D is asserted by setting output of the fourth comparator 146 to a digital logic low state. When the parallel amplifier circuit output current estimate 40, I_{PAWA—OUT—EST}, is less than the second boost level threshold 130, the second boost level indication 156D is de-asserted by setting output of the fourth comparator 146 to a digital logic high state.

[0283] Similar to the logic circuit 148A of FIG. 4A, the logic circuit 148B of FIG. 4B, and the logic circuit 148C of FIG. 4C, the logic circuit 148D may also be configured to generate charge pump mode control signal, a series switch control output 162 provided to the first output buffer 158, a shunt switch control output 164 provided to the second output buffer 160, one or more switching voltage output cmos signal(s) 166, V_{SW—EST—CMOS—SIGNAL}(s), provided to the third output buffer 161, and an estimated switching voltage output 38B, V_SW—EST. As previously described, the series switch control output 162, the shunt switch control output 164, and the one or more switching voltage output cmos signal(s) 166, V_{SW—EST—CMOS—SIGNAL}(s), may be configured to operate with the first output buffer 158, the second output buffer 160, and the third output buffer 161 to generate the series switch control signal 66, the shunt switch control signal 68, and the estimated switching voltage output 38B, V_SW—EST, respectively. Also similar to the logic circuit 148A of FIG. 4A, the logic circuit 148B of FIG. 4B, and the logic circuit 148C of FIG. 4C, the logic circuit 148D may include a boost lockout counter 184 and a boost time counter 186. The operation of the boost lockout counter 184 and the boost time counter 186 of the logic circuit 148D is substantially similar to the operation of the boost lockout counter 184 and the boost time counter 186 of the logic circuits 148A, 148B, and 148C of FIGS. 4A, 4B, and 4C, respectively.

[0284] The example embodiment of the logic circuit 148D may include a Field Programmable Gate Array (FPGA) or other programmable logic device, discrete gates or transistor logic, discrete hardware components, or any combination thereof designed to perform. Some embodiments of the logic circuit 148D may be implemented in either a digital or analog processor. In addition, the logic circuit 148D may include an embodiment of the first state machine and the second state machine of the threshold detector and control circuit 132D.

[0285] Operation of the first state machine implemented in the logic circuit 148D, depicted in FIG. 5D, will now be described. The first state machine includes a shunt output mode 188D, a series output mode 190D, a first boost output mode 192D, and a second boost output mode 194D.

[0286] In the shunt output mode 188D, the logic circuit 148D (FIG. 4D) configures the series switch control output 162 such that the series switch 70 (FIG. 3D) is in an open state (not conducting). The logic circuit 148D also configures the shunt switch control output 164 such that the shunt switch 72 (FIG. 3D) is in a closed state (conducting). In addition, the logic circuit 148D configures the charge pump mode control signal 60 to instruct the multi-level charge pump circuit 56 (FIG. 3D) to be in a charging mode of operation. As a result, the switching voltage output 26 of FIG. 3D is configured to provide a switching voltage, V_SW, substantially equal to ground. In response to assertion of the series level indication 152D, which indicates that the parallel amplifier circuit output current estimate 40, I_{PAWA—OUT—EST}, is greater than or equal to the series level threshold 126, the logic circuit 148D configures the first state machine to transition to the series output mode 190D. Otherwise the state machine remains in the shunt output mode 188D.

[0287] In the series output mode 190D, the logic circuit 148D configures the series switch control output 162 such that the series switch 70 (FIG. 3D) is in a closed state (conducting). The logic circuit 148D also configures the shunt switch control output 164 such that the shunt switch 72 (FIG. 3D) is in an open state (not conducting). In addition, the logic circuit 148D configures the charge pump mode control signal 60 to instruct the multi-level charge pump circuit 56 to be in a charging mode of operation. As a result, the switching voltage output 26 of FIG. 3D is configured to provide a switching voltage, V_SW, substantially equal to the direct current (DC) voltage, V_BAT.

[0288] In response to de-assertion of the shunt level indication 150D (FIG. 4D), which indicates that the power amplifier circuit output current estimate, I_{PAWA—OUT—EST}, is less than the shunt level threshold 124, the logic circuit 148D configures the first state machine to transition to the shunt output mode 188D (FIG. 5D). However, in response to assertion of the first boost level indication 154D, which indicates that the parallel amplifier circuit output current estimate 40, I_{PAWA—OUT—EST}, is greater than or equal to the first boost level threshold 128, the logic circuit 148D configures the first state machine to transition to the first boost output mode 192D. Otherwise, the first state machine remains in the series output mode 190D.

[0289] In the first boost output mode 192D, the logic circuit 148D (FIG. 4D) configures the series switch control output 162 such that the series switch 70 (FIG. 3D) is in an open state (not conducting). The logic circuit 148D also configures the shunt switch control output 164 such that the shunt switch 72 (FIG. 3D) is in an open state (not conducting). In addition, the logic circuit 148D configures the charge pump mode control signal 60 to instruct the multi-level charge pump circuit 56 to be in a first boost mode of operation to provide 1.5×V_BAT at the charge pump output 64. As a result, the switching voltage output 26 of FIG. 3D is configured to provide a switching voltage, V_SW, substantially equal to 1.5×V_BAT. In response to de-assertion of the shunt level indication 150D (FIG. 4D), which indicates that the parallel amplifier circuit output current estimate 40, I_{PAWA—OUT—EST}, is less than the shunt level threshold 124, the logic circuit 148D configures the first state machine to transition to the shunt output mode 188D (FIG. 5D). However, in response to assertion of the second boost level indication 156D, which indicates that the parallel amplifier circuit output current estimate 40, I_{PAWA—OUT—EST}, is greater than or equal to the second boost level threshold 130, the logic circuit 148D configures the first state machine to transition to the second boost output mode 194D. Otherwise, the first state machine remains in the first boost output mode 192D.

[0290] In the second boost output mode 194D, the logic circuit 148D (FIG. 4D) configures the series switch control output 162 such that the series switch 70 (FIG. 3D) is in an open state (not conducting). The logic circuit 148D also configures the shunt switch control output 164 such that the shunt switch 72 (FIG. 3D) is in an open state (not conducting). In addition, the logic circuit 148D configures the charge pump mode control signal 60 to instruct the multi-level charge pump circuit 56 to be in a second boost mode of operation to provide 2×V_BAT at the charge pump output 64. As a result, the switching voltage output 26 of FIG. 3D is configured to provide a switching voltage, V_SW, substantially equal to 2×V_BAT. In response to de-assertion of the shunt level indication 150D, which indicates that the parallel amplifier circuit output current estimate 40, I_{PAWA—OUT—EST}, is less than the shunt level threshold 124, the first state machine transitions to the shunt output mode 188D. Otherwise, the state machine remains in the second boost output mode 194D.

[0291] Operation of the second state machine of the logic circuit 148D, depicted in FIG. 6D, will now be described. The second state machine includes a shunt output mode 196D, a series output mode 198D, a first boost output mode 200D, and a second boost output mode 202D. In addition, the second state machine uses the above-described boost lockout counter 184 and boost time counter 186 of the logic circuit 148D.

[0292] In the shunt output mode 196D, the logic circuit 148D (FIG. 4D) configures the series switch control output 162 such that the series switch 70 (FIG. 3D) is in an open state (not conducting). The logic circuit 148D also configures the shunt switch control output 164 such that the shunt switch 72 (FIG. 3D) is in a closed state (conducting). In addition, the logic circuit 148D configures the charge pump mode control signal 60 to instruct the multi-level charge pump circuit 56 (FIG. 3D) to be in a charging mode of operation. As a result, the switching voltage output 26 of FIG. 3D is configured to provide a switching voltage, V_SW, substantially equal to ground. If the boost lockout counter 184 is enabled, the boost lockout counter 184 continues to count down. In response to assertion of the series level indication 152D, which indicates that the parallel amplifier circuit output current estimate 40, I_{PAWA—OUT—EST}, is greater than or equal to the series level threshold 126, the second state machine transitions to the series output mode 198D. Otherwise the second state machine remains in the shunt output mode 196D.

[0293] In the series output mode 198D, the logic circuit 148D (FIG. 4D) configures the series switch control output 162 such that the series switch 70 (FIG. 3D) is in a closed state (conducting). The logic circuit 148D also configures the shunt switch control output 164 such that the shunt switch 72 (FIG. 3D) is in an open state (not conducting). In addition, the logic circuit 148D configures the charge pump mode control signal 60 to instruct the multi-level charge pump circuit 56 to be in a charging mode of operation. As a result, the switching voltage output 26 of FIG. 3D is configured to provide a switching voltage, V_SW, substantially equal to the direct current (DC) voltage, V_BAT. If the boost lockout counter 184 is enabled, the boost lockout counter 184 continues to count down. In response to de-assertion of the shunt level indication 150D, which indicates that the parallel amplifier circuit output current estimate 40, I_{PAWA—OUT—EST}, is less than the shunt level threshold 124, the logic circuit 148D configures the second state machine to transition to the shunt output mode 196D. However, in response to assertion of the first boost level indication 154D, which indicates that parallel amplifier circuit output current estimate 40, I_{PAWA—OUT—EST}, is greater than or equal to the first boost level threshold 128, the logic circuit 148D determines whether both the minimum charge time indicator is de-asserted and the first boost level indication 154D is asserted. If the minimum charge time indicator is de-asserted and the first boost level indication 154D is asserted, the logic circuit 148D configures the second machine to transition to the first boost output mode 200D. Otherwise, the logic circuit 148D prevents the second state machine from transitioning to the first boost output mode 200D until the minimum time indicator is de-asserted. Once both the minimum charge time indicator is de-asserted and the first boost level indication 154D is asserted, the logic circuit 148D configures the second state machine to transition to the first boost output mode 200D, resets the counter output of the boost time counter 186, and enables the boost time counter 186 to begin counting up. Otherwise, the second state machine remains in the series output mode 198D.

[0294] In the first boost output mode 200D, the logic circuit 148D configures the series switch control output 162 such that the series switch 70 (FIG. 3D) is in an open state (not conducting). The logic circuit 148D also configures the shunt switch control output 164 such that the shunt switch 72 (FIG. 3D) is in an open state (not conducting). In addition, the logic circuit 148D configures the charge pump mode control signal 60 to instruct the multi-level charge pump circuit 56 to be in a first boost mode of operation to provide 1.5×V_BAT at the charge pump output 64. As a result, the switching voltage output 26 of FIG. 3D is configured to provide a switching voltage, V_SW, substantially equal to 1.5×V_BAT. In response to de-assertion of the first boost level indication 154D, which indicates that the parallel amplifier circuit output current estimate 40, I_{PAWA—OUT—EST}, is less than the first boost level threshold 128, the logic circuit 148D configures the second state machine to transition to the series output mode 198D. If the count output of the boost time counter 186 exceeds the maximum boost time parameter, the logic circuit 148D asserts a minimum charge time indicator. In response to the minimum charge time indicator being asserted, the logic circuit 148D sets the count value of the boost lockout counter 184 and enables the boost lockout counter 184 to begin counting down. However, in response to assertion of the second boost level indication 156D, which indicates that the parallel amplifier circuit output current estimate 40, I_{PAWA—OUT—EST}, is greater than or equal to the second boost level threshold 130, the logic circuit 148D configures the second state machine to transition to the second boost output mode 202D. Otherwise, the second state machine remains in the first boost output mode 200D.

[0295] In the second boost output mode 202D, the logic circuit 148D configures the series switch control output 162 such that the series switch 70 (FIG. 3D) is in an open state (not conducting). The logic circuit 148D also configures the shunt switch control output 164 such that the shunt switch 72 (FIG. 3D) is in an open state (not conducting). In addition, the logic circuit 148D configures the charge pump mode control signal 60 to instruct the multi-level charge pump circuit 56 (FIG. 3D) to be in a second boost mode of operation to provide 2×V_BAT at the charge pump output 64. As a result, the switching voltage output 26 of FIG. 3D is configured to provide a switching voltage, V_SW, substantially equal to 2×V_BAT.

[0296] In response to de-assertion of the first boost level indication 154D, which indicates that the parallel amplifier circuit output current estimate 40, I_{PAWA—OUT—EST}, is less than the first boost level threshold 128, the logic circuit 148D configures the second state machine to transition to the series output mode 198D. If the count output of the boost time counter 186 exceeds the maximum boost time parameter, the logic circuit 148D asserts a minimum charge time indicator. In response to the minimum charge time indicator being asserted, the logic circuit 148D sets the count value of the boost lockout counter 184 and enables the boost lockout counter 184 to begin counting down. Otherwise, the second state machine remains in the second boost output mode 202D.

[0297] With respect to the cases where the first state machine or the second state machine of the logic circuit 148A, the logic circuit 148B, the logic circuit 148C, and the logic circuit 148D depicted in the respective FIGS. 4A, 4B, 4C, and 4D, are configured to be in either the first boost output mode 192A, the first boost output mode 192B, the first boost output mode 192C, and the first boost output mode 192D, or the first boost output mode 200A, the first boost output mode 200B, the first boost output mode 200C, or the first boost output mode 200D, respectively, when the multi-level charge pump circuit 56 is configured to be in a first boost mode of operation, the first switch 86, the third switch 90, the fifth switch 94 and the seventh switch 98 of the multi-level charge pump circuit 56 are configured to be closed such that charge from the supply input 24, (V_BAT), the first flying capacitor 100 and the second flying capacitor 102, arranged in parallel, is provided directly to the switching voltage output 26 via the charge pump output 64 in order to provide substantially 1.5×V_BAT at the switching voltage output 26. The second switch 88, the fourth switch 92, and the sixth switch 96, and the eighth switch 118 of the multi-level charge pump are configured to be open.

[0298] Similarly, with respect to the cases where the first state machine or the second state machine of the logic circuit 148A, the logic circuit 148B, the logic circuit 148C, and logic circuit 148D depicted in the respective FIGS. 4A, 4B, 4C, and 4D, are configured to be in either the second boost output mode 194A, the second boost output mode 194B, the second boost output mode 194C, and the second boost output mode 194D, or the second boost output mode 202A, the second boost output mode 202B, the second boost output mode 202C, and the second boost output mode 202D, when the multi-level charge pump circuit 56 is configured to be in a second boost mode of operation, the first switch 86, the fourth switch 92, and the fifth switch 94 are configured to be closed such that charge from the supply input 24, (V_BAT), the first flying capacitor 100 and the second flying capacitor 102, arranged in series, is provided directly to the switching voltage output 26 via the charge pump output 64 in order to provide substantially 2×V_BAT at the switching voltage output 26. The second switch 88, the third switch 90, the sixth switch 96, and the seventh switch 98 of the multi-level charge pump circuit 56 are configured to be open. In those embodiments of the multi-level charge pump circuit 56 that further include the eighth switch 118, the eighth switch 118 may also be configured to be open.

[0299] Advantageously, this permits the multi-level charge pump circuit 56 to provide either substantially 1.5×V_BAT or substantially 2×V_BAT at the switching voltage output 26 without the need for a charge pump output capacitor. Moreover, while some embodiments of the multi-level charge pump circuit 56 may include more than two flying capacitors or inductive components to provide boost voltage levels, some embodiments of the multi-level charge pump circuit 56 only include the first flying capacitor 100 and the second flying capacitor 102. Even more advantageously, some embodiments of the multi-level charge pump circuit 56 that further include an eighth switch 118, may provide an additional first output mode of operation to provide substantially ½×V_BAT at the switching voltage output 26 using only the first flying capacitor 100 and the second flying capacitor 102.

[0300] Returning to FIG. 2A, an example embodiment of the parallel amplifier circuit 14A includes the parallel amplifier circuitry 32. The parallel amplifier circuitry 32 includes a parallel amplifier 35 and a parallel amplifier sense circuit 36. The parallel amplifier 35 generates the parallel amplifier output voltage, V_PARA—AMP, at the parallel amplifier output 32A based on the difference between the compensated V_RAMP signal, V_RAMP—C, and the power amplifier supply voltage, V_CC. In addition, the parallel amplifier 35 outputs a parallel amplifier output current, I_PARA—AMP. The parallel amplifier sense circuit 36 may include one or more current mirror circuits that are in communication with the parallel amplifier 35 depending upon the operational blocks included in the example embodiment of the parallel amplifier circuit 14A. Based upon the parallel amplifier output current, I_PARA—AMP, the parallel amplifier sense circuit 36 generates a scaled parallel amplifier output current estimate, I_{PARA—AMP—SENSE}, which provides an indication of the parallel amplifier output current, I_PARA—AMP. In those embodiments of the parallel amplifier circuit 14A that include an open loop assist circuit 39, the scaled parallel amplifier output current estimate, I_{PARA—AMP—SENSE}, is combined with the scaled open loop assist circuit output current estimate, I_{ASSIST—SENSE}, from the open loop assist circuit 39 to generate the parallel amplifier circuit output current estimate 40, I_{PAWA—OUT—EST}, which is provided to the multi-level charge pump buck converter 12A. However, in those embodiments of the parallel amplifier circuit 14A that do not include an open loop assist circuit 39, only the scaled parallel amplifier output current estimate, I_{PARA—AMP—SENSE}, may be provided as a contribution to form the parallel amplifier circuit output current estimate 40, I_{PAWA—OUT—EST}, provided to the multi-level charge pump buck converter 12A. In addition, as depicted in FIG. 2A, in those embodiments of the parallel amplifier circuit 14A that include a parallel amplifier output impedance compensation circuit 37, a copy of the scaled parallel amplifier output current estimate, I_{PARA—AMP—SENSE}, is provided to the parallel amplifier output impedance compensation circuit 37. However, in those embodiments of the parallel amplifier circuit 14A that do not include a parallel amplifier output impedance compensation circuit 37, the parallel amplifier sense circuit 36 is configured to only provide the scaled parallel amplifier output current estimate, I_{PARA—AMP—SENSE}, as a contribution to the formation of the parallel amplifier circuit output current estimate 40, I_{PAWA—OUT—EST}, provided to the multi-level charge pump buck converter 12A.

[0301] FIG. 12A depicts one embodiment of the parallel amplifier 35 as the parallel amplifier 35A. The parallel amplifier 35A depicts one embodiment of an AB class amplifier. The parallel amplifier 35A includes a parallel amplifier input voltage 204, a first amplifier, AMP_A, 206, the second amplifier 208, AMP_B, a first output stage 210, and an amplifier feedback node 212. The parallel amplifier input voltage 204 may be configured to receive either the V_RAMP signal or the compensated V_RAMP signal, V_RAMP—C.

[0302] The first amplifier 206, AMP_A, includes a positive input terminal 206A, a negative input terminal 206B, and an output terminal 206C. Regarding the first amplifier 206, AMP_A, the positive input terminal 206A may be coupled to the parallel amplifier input voltage 204. The negative input terminal 206B may be coupled to the amplifier feedback node 212, which is coupled to the power amplifier supply voltage, V_CC. A first resistor, R_A, and a first capacitor, C_A, are arranged in series between the output terminal 206C and the amplifier feedback node 212. The first resistor, R_A, and the first capacitor, C_A, are a feedback network used to extend the operating bandwidth by compensating for the dominant pole introduced by the bypass capacitor capacitance, C_BYPASS, of the bypass capacitor 19. The feedback network may be configured to extend the modulation bandwidth of the first amplifier 206, AMP_A, out to approximately 30 MHz. The first amplifier 206, AMP_A, generates a first amplifier output voltage, V_A, at the output terminal 206C based upon the difference between the parallel amplifier input voltage 204 appearing at the positive input terminal 206A and the power amplifier supply voltage, V_CC, appearing at the negative input terminal 206B.

[0303] Regarding the second amplifier 208, AMP_B, the positive input terminal 208A may be coupled to the parallel amplifier input voltage 204. The negative input terminal 208B may be coupled to the amplifier feedback node 212, which is coupled to the power amplifier supply voltage, V_CC. A second resistor, R_B, and a second capacitor, C_B, are arranged in series between the output terminal 208C and the amplifier feedback node 212. The second resistor, R_B, and the second capacitor, C_B, are a feedback network used to extend the operating bandwidth by compensating for the dominant pole introduced by the bypass capacitor capacitance, C_BYPASS, of the bypass capacitor 19. The feedback network may be configured to extend the modulation bandwidth of the second amplifier 208, AMP_B, out to approximately 30 MHz. The second amplifier 208, AMP_B, generates a second amplifier output voltage, V_B, at the output terminal 208C based upon the difference between the parallel amplifier input voltage 204 appearing at the positive input terminal 208A and the power amplifier supply voltage, V_CC, appearing at the negative input terminal 208B.

[0304] The first output stage 210 includes a first switching element, SW_1A, 214 and a second switching element, SW_1B, 216. As a non limiting example, some embodiments of the first switching element, SW_1A, 214 and the second switching element, SW_1B, 216, may be a solid state based switch such as a field effect transistor, an insulator-on-semiconductor based transistor, or a bipolar based transistor. These transistors may operate mainly in Class-AB mode, thus near to linear operation, even though the transistors are referred to as switches. In one example embodiment, the first switching element 214, SW_1A, may be a PFET device having a drain 214D, a gate 214G, and a source 214S. Likewise, the second switching element 216, SW_1B, may be an NFET device having a drain 216D, a gate 216G, and a source 216S.

[0305] The source 214S of the first switching element 214, SW_1A, may be coupled to the parallel amplifier supply input 30, (V_BAT), of the multi-level charge pump buck converter 12. The drain 214D of the first switching element 214, SW_1A, may be coupled to the drain 216D of the second switching element 216, SW_1B, to form a parallel amplifier output node 218 that provides the parallel amplifier output voltage, V_PARA—AMP, of the parallel amplifier 35A. The source 216S of the second switching element 216, SW_1B, may be coupled to ground.

[0306] The gate 214G of the first switching element 214, SW_1A, may be coupled to the output terminal 206C of the first amplifier 206, AMP_A, in order to receive the first amplifier output voltage, V_A. Similarly, the gate 216G of the second switching element 216, SW_1B, may be coupled to the output terminal 208C of the second amplifier 208, AMP_B, in order to receive the second amplifier output voltage, V_B.

[0307] The parallel amplifier 35A may be configured to source from the parallel amplifier output node 218 and sink current to the parallel amplifier output node 218 based upon the difference between the parallel amplifier input voltage 204 (either V_RAMP or V_RAMP—C) and the power amplifier supply voltage, V_CC. For example, when the power inductor current, I_SW—OUT, delivered by the power inductor 16 and the bypass capacitor current, I_BYPASS—CAP, delivered by the bypass capacitor capacitance, C_BYPASS, of the bypass capacitor 19 are insufficient to supply the output current, I_OUT, to the linear RF power amplifier 22, the parallel amplifier 35A turns on the first switching element 214, SW_1A, to provide additional current through the coupling capacitor 18A to the power amplifier supply output 28. However, when the power inductor current, I_SW—OUT, delivered by the power inductor 16, and the bypass capacitor current, I_BYPASS—CAP, from the bypass capacitor capacitance, C_BYPASS, of the bypass capacitor 19 exceed the desired level of output current, I_OUT, to be delivered to the linear RF power amplifier 22, the parallel amplifier 35A turns on the second switching element 216, SW_1B, to shunt the excess current provided to the power amplifier supply output 28 to ground.

[0308] In the case, as depicted in FIGS. 2A and 2B, where the parallel amplifier circuit 14A includes an open loop assist circuit 39 providing an open loop assist circuit current, I_ASSIST, the parallel amplifier 35A compensates for either an excess of current or the lack of current supplied to the power amplifier supply output 28. As an example, when the power inductor current, I_SW—OUT, the open loop assist current, I_ASSIST, and the bypass capacitor current, I_BYPASS—CAP, deliver less than the desired level of output current, I_OUT, to the linear RF power amplifier 22, the parallel amplifier 35 turns on the first switching element 214, SW_1A, to provide the additional current desired by the linear RF power amplifier 22. As another example, when the power inductor current, I_SW—OUT, the open loop assist current, I_ASSIST, and the bypass capacitor current, I_BYPASS—CAP, deliver excess current to the power amplifier supply output 28, the parallel amplifier 35A turns on the second switching element 216, SW_1B, such that the excess current is shunted to ground.

[0309] FIG. 12B depicts another embodiment of the parallel amplifier 35 as the rechargeable parallel amplifier 35B. Unlike the parallel amplifier 35A of FIG. 12A, the rechargeable parallel amplifier 35B includes a second output stage 220A, a charge conservation capacitor, C_AB, and an output control circuit 230A.

[0310] The second output stage 220A includes a first switching element 222, SW_2A, and a second switching element 224, SW_2B. As a non limiting example, some embodiments of the first switching element 222, SW_2A, and the second switching element 224, SW_2B, may be a solid state based switch such as a field effect transistor, an insulator-on-semiconductor transistor, or a bipolar based transistor. These transistors operate mainly in Class-AB mode, thus near to linear operation, even though the transistors are referred to as switches. In one example embodiment, the first switching element 222, SW_2A, may be a PFET device having a drain 222D, a gate 222G, and a source 222S. Likewise, the second switching element 224, SW_2B, may be an NFET device having a drain 224D, a gate 224G, and a source 224S.

[0311] The source 222S of the first switching element 222, SW_2A, may be coupled to the charge conservation capacitor, C_AB. The drain 222D of the first switching element 222, SW_2A, and the drain 224D of the second switching element 224, SW_2B, may be coupled to the parallel amplifier output node 218 to provide the parallel amplifier output voltage, V_PARA—AMP, of the rechargeable parallel amplifier 35B. The source 224S of the second switching element 224, SW_2B, may be coupled to the charge conservation capacitor, C_AB. As will be explained in further detail below, when the second switching element 224, SW_2B, of the second output stage 220A may be turned on to sink excess current provided to the power amplifier supply output 28, charge is stored on the charge conservation capacitor, C_AB, to generate a saved charge voltage, V_AB. Similarly, when insufficient current is provided to the power amplifier supply output 28, the first switching element 222, SW_2A, may be turned on to provide additional current to the power amplifier supply output 28 from the charge conservation capacitor, C_AB.

[0312] In order to operate in the linear mode of operation, the range of operation of the first switching element 222, SW_2A, and the second switching element 224, SW_2B, must take into consideration a minimum headroom voltage, V_HEADROOM, of each device. As an example, the first switching element 222, SW_2A, may operate in the linear mode provided the parallel amplifier output node 218 that provides the parallel amplifier output voltage, V_PARA—AMP, is less than the saved charge voltage, V_AB, minus the minimum headroom voltage, V_HEADROOM. Similarly, the second switching element 224, SW_2B, may operate in the linear mode provided the parallel amplifier output node 218 that provides the parallel amplifier output voltage, V_PARA—AMP, is greater than the saved charge voltage, V_AB, plus the minimum headroom voltage, V_HEADROOM.

[0313] The output control circuit 230A includes a V_A input, V_A—IN, a V_B input, V_B—IN, a V_AB input, V_AB—IN, and a V_PARA—AMP input, V_{PARA—AMP—IN}. The V_A input, V_A—IN, may be coupled to the output terminal 206C of the first amplifier 206, AMP_A, to receive the first amplifier output voltage, V_A. The V_B input, V_B—IN, may be coupled to the output terminal 208C of the second amplifier 208, AMP_B, to receive the second amplifier output voltage, V_B. The V_PARA—AMP input, V_{PARA—AMP—IN}, may be coupled to the parallel amplifier output node 218 to receive the parallel amplifier output voltage, V_PARA—AMP. The V_AB input, V_AB—IN, may be coupled to the saved charge voltage, V_AB.

[0314] The output control circuit 230A may include a first switch control output, V_SW1A, a second switch control output, V_SW2A, a third switch control output, V_SW2B, and a fourth switch control output, V_SW1B. The first switch control output, V_SW1A, may be coupled to the gate 214G of the first switching element 214, SW_1A. The second switch control output, V_SW2A, may be coupled to the gate 222G of the first switching element 222, SW_2A. The third switch control output, V_SW2B, may be coupled to the gate 224G of the second switching element 224, SW_2B. The fourth switch control output, V_SW1B, may be coupled to the gate 216G of the second switching element 216, SW_1B.

[0315] The output control circuit 230A selectively couples the V_A input, V_A—IN, to either the first switch control output, V_SW1A, or the second switch control output, V_SW2A, based upon the minimum headroom voltage, V_HEADROOM, the saved charge voltage, V_AB, and the parallel amplifier output voltage, V_PARA—AMP. For example, when the parallel amplifier output voltage, V_PARA—AMP, is greater than the saved charge voltage, V_AB, minus the minimum headroom voltage, V_HEADROOM, the output control circuit 230A couples the V_A input, V_A—IN, to the first switch control output, V_SW1A, of the first output stage 210 and sets the second switch control output, V_SW2A, to disable the second switching element 224, SW_2A, of the second output stage 220A. As an example, the output control circuit 230A may pull up the second switch control output, V_SW2A, to the saved charge voltage, V_AB. As a result, the first amplifier output voltage, V_A, is coupled to the gate 214G of the first switching element 214, SW_1A, of the first output stage 210.

[0316] However, when the parallel amplifier output voltage, V_PARA—AMP, is less than or equal to the saved charge voltage, V_AB, minus the minimum headroom voltage, V_HEADROOM, the output control circuit 230A couples the V_A input, V_A—IN, to the second switch control output, V_SW2A, and sets the first switch control output, V_{SW 1A}, to disable the first switching element 214, SW_1A, of the first output stage 210. As an example, the output control circuit 230A may pull up the first switch control output, V_SW1A, to the parallel amplifier supply input 30, (V_BAT). As a result, the first amplifier output voltage, V_A, is coupled to the gate 222G of the first switching element 222, SW_2A, of the second output stage 220A.

[0317] The output control circuit 230A also selectively couples the V_B input, V_B—IN, to either the third switch control output, V_SW2B, or the fourth switch control output, V_SW1B, based upon the minimum headroom voltage, V_HEADROOM, the saved charge voltage, V_AB, and the parallel amplifier output voltage, V_PARA—AMP. For example, when the parallel amplifier output voltage, V_PARA—AMP, is greater than the saved charge voltage, V_AB, plus the minimum headroom voltage, V_HEADROOM, the output control circuit 230A couples the V_B input, V_B—IN, to the third switch control output, V_SW2B, and sets the fourth switch control output, V_SW1B, to disable the second switching element 216, SW_1B. As an example, the output control circuit 230A may pull down the fourth switch control output, V_SW1B, to ground. As a result, the second amplifier output voltage, V_B, is coupled to the gate 224G of the second switching element 224, SW_2B, of the second output stage 220A.

[0318] However, when the parallel amplifier output voltage, V_PARA—AMP, is less than or equal to the saved charge voltage, V_AB, plus the minimum headroom voltage, V_HEADROOM, the output control circuit 230A couples the fourth switch control output, V_SW1B, to the V_B input, V_B—IN, and sets the third switch control output, V_SW2B, to disable the second switching element 224, SW_2B. As an example, the output control circuit 230A may pull down the third switch control output, V_SW2B, to ground.

[0319] FIG. 12C depicts another embodiment of the parallel amplifier 35 as the rechargeable parallel amplifier 35C. The rechargeable parallel amplifier 35C of FIG. 12C is similar to the rechargeable parallel amplifier 35B of FIG. 12B. However, unlike rechargeable parallel amplifier 35B, rechargeable parallel amplifier 35C includes an output control circuit 230B instead of the output control circuit 230A and a second output stage 220B instead of the second output stage 220A. The output control circuit 230B further includes a V_CC input, V_CC—IN, that is coupled to the power amplifier supply output 28 in order to receive the power amplifier supply voltage, V_CC. In addition, unlike rechargeable parallel amplifier 35B, in the rechargeable parallel amplifier 35C, the drain 224D of the second switching element 224, SW_2B, is coupled to the power amplifier supply output 28 instead of being coupled to the parallel amplifier output node 218, which is now labeled as the parallel amplifier output node 218C. Furthermore, as will be explained, the operation of the output control circuit 230B is different from the operation of output control circuit 230A in order to accommodate the coupling of the drain 224D of the second switching element, SW_2B, 224 to the power amplifier supply output 28.

[0320] Similar to the rechargeable parallel amplifier 35B, the rechargeable parallel amplifier 35C must also take into consideration the minimum headroom voltage, V_HEADROOM, of the first switching element 222, SW_2A, and the second switching element 224, SW_2B, in order to assure the first switching element 222, SW_2A, and the second switching element 224, SW_2B, operate in the linear mode. However, because the drain 224D of the second switching element 224, SW_2B is coupled to the power amplifier supply output 28, the power amplifier supply voltage, V_CC, must also be considered.

[0321] Similar to the rechargeable parallel amplifier 35B, the first switching element 222, SW_2A, of the rechargeable parallel amplifier 35C may operate in the linear mode provided the parallel amplifier output node 218C that provides the parallel amplifier output voltage, V_PARA—AMP, is less than the saved charge voltage, V_AB, minus the minimum headroom voltage, V_HEADROOM. However, unlike the rechargeable parallel amplifier 35B, the second switching element 224, SW_2B, of the rechargeable parallel amplifier 35C may operate in the linear mode provided the power amplifier supply voltage, V_CC, is greater than the saved charge voltage, V_AB, plus the minimum headroom voltage, V_HEADROOM. Because the power amplifier supply voltage, V_CC, tends to be higher than the parallel amplifier output voltage, V_PARA—AMP, the rechargeable parallel amplifier 35C may store additional charge on the charge conservation capacitor, C_AB, which increases the charge voltage, V_AB. As a result, the operating range of the first switching element 222, SW_2A, is also increased.

[0322] Similar to the output control circuit 230A of FIG. 12B, the output control circuit 230B of FIG. 12C selectively couples the V_A input, V_A—IN, to either the first switch control output, V_SW1A, or the second switch control output, V_SW2A, based upon the minimum headroom voltage, V_HEADROOM, the saved charge voltage, V_AB, and the parallel amplifier output voltage, V_PARA—AMP. For example, when parallel amplifier output voltage, V_PARA—AMP, is greater than the saved charge voltage, V_AB, minus the minimum headroom voltage, V_HEADROOM, the output control circuit 230B couples the V_A input, V_A—IN, to the first switch control output, V_SW1A, and sets the second switch control output, V_SW2A, to disable the first switching element 222, SW_2A, of the second output stage 220B. As an example, the output control circuit 230B may pull up the second switch control output, V_SW2A, to the saved charge voltage, V_AB. As a result, the first amplifier output voltage, V_A, is coupled to the gate 214G of the first switching element 214, SW_1A, of the first output stage 210C.

[0323] However, when the parallel amplifier output voltage, V_PARA—AMP, is less than or equal to the saved charge voltage, V_AB, minus the minimum headroom voltage, V_HEADROOM, the output control circuit 230B couples the V_A input, V_A—IN, to the second switch control output, V_SW2A, of the second output stage 220B and sets the first switch control output, V_SW1A, to disable the first switching element 214, SW_1A, of the first output stage 210C. As an example, the output control circuit 230B may pull up the first switch control output, V_SW1A, to the parallel amplifier supply input 30, (V_BAT). As a result, the first amplifier output voltage, V_A, is coupled to the gate 222G of the first switching element 222, SW_2A, of the second output stage 220B.

[0324] However, different from the output control circuit 230A, the output control circuit 230B also selectively couples the V_B input, V_B—IN, to either the third switch control output, V_SW2B, or the fourth switch control output, V_SW1B, based upon the minimum headroom voltage, V_HEADROOM, the saved charge voltage, V_AB, and the power amplifier supply voltage, V_CC. For example, when the power amplifier supply voltage, V_CC, is greater than the saved charge voltage, V_AB, plus the minimum headroom voltage, V_HEADROOM, the output control circuit 230B couples the V_B input, V_B—IN, to the third switch control output, V_SW2B, and sets the fourth switch control output, V_SW1B, to disable the second switching element 216, SW_1B. As an example, the output control circuit 230B may pull down the fourth switch control output, V_SW1B, to ground. As a result, the second amplifier output voltage, V_B, is coupled to the gate 224G of the second switching element 224, SW_2B, of the second output stage 220B.

[0325] However, when the power amplifier supply voltage, V_CC, is less than or equal to the saved charge voltage, V_AB, plus the minimum headroom voltage, V_HEADROOM, the output control circuit 230B couples the fourth switch control output, V_SW1B, to the V_B input, V_B—IN, and sets the third switch control output, V_SW2B, to disable the second switching element 224, SW_2B. As an example, the output control circuit 230B may pull down the third switch control output, V_SW2B, to ground. As a result, the second amplifier output voltage, V_B, is coupled to the gate 216G of the second switching element 216, SW_1B, of the first output stage 210C.

[0326] While the embodiments of the parallel amplifier 35A, the rechargeable parallel amplifier 35B, and the rechargeable parallel amplifier 35C of FIGS. 12A, FIG. 12B, and FIG. 12C, respectively, depict that the source 214S of the first switching element 214, SW_1A, of the first output stages 210 and 210C are coupled to parallel amplifier supply input 30, (V_BAT), this is by way of illustration and non-limiting. In some embodiments, the supply voltage provided to the parallel amplifier 35A, rechargeable parallel amplifier 35B, and the rechargeable parallel amplifier 35C of FIGS. 12A, FIG. 12B, and FIG. 12C, may be provided by a separate power supply not depicted herein. The separate power supply may provide other voltage levels to power or bias the respective parallel amplifier 35A, rechargeable parallel amplifier 35B, and the rechargeable parallel amplifier 35C. As a non-limiting example, the separate power supply may provide a parallel amplifier supply voltage substantially equal to 2×V_BAT. Accordingly, in these example embodiments of the parallel amplifier 35A, the rechargeable parallel amplifier 35B, and the rechargeable parallel amplifier 35C, source 214S of the first switching element 214, SW_1A, of the first output stage 210 may be coupled to the parallel amplifier supply voltage substantially equal to 2×V_BAT.

[0327] As an example, discussed relative to FIGS. 18A-D, FIG. 12D depicts one embodiment of a parallel amplifier 35D, similar to the parallel amplifier 35A, that is configured to use a parallel amplifier supply voltage, V_{SUPPLY—PARA—AMP}. In some embodiments, the parallel amplifier supply voltage, V_{SUPPLY—PARA—AMP}, may be configured to come from various power supply voltage generation circuits depending upon the needs of the linear RF power amplifier 22. As depicted in FIGS. 18A-D, the parallel amplifier supply voltage, V_{SUPPLY—PARA—AMP}, may be provided by a μC charge pump circuit 262 or by the multi-level charge pump circuit 258 of multi-level charge pump buck converter 12C. In addition, as discussed below, in some embodiments of the μC charge pump circuit 262, the μC charge pump circuit 262 generates a μC charge pump output voltage, V_μC—OUT, that may be configured to provide various voltage levels dependent upon the mode of operation of the μC charge pump circuit 262.

[0328] As depicted in FIG. 12D, unlike the parallel amplifier 35A of FIG. 12A, the parallel amplifier 35D may be configured to use the parallel amplifier supply voltage, V_{SUPPLY—PARA—AMP}, instead of the parallel amplifier supply input 30, (V_BAT), provided by the battery 20. The parallel amplifier supply voltage, V_{SUPPLY—PARA—AMP}, may be a discrete ratio of the parallel amplifier supply input 30, (V_BAT), provided by the battery 20. In other embodiments, however, the voltage level provided by the parallel amplifier supply voltage, V_{SUPPLY—PARA—AMP}, may be programmatically selected depending upon the operational conditions of the mobile device or pseudo-envelope follower power management system.

[0329] For example, as depicted in FIG. 12D, the source 214S of the first switching element 214, SW_1A, may be coupled to the parallel amplifier supply voltage, V_{SUPPLY—PARA—AMP}. Although not depicted in FIG. 12D, the circuitry associated with the first amplifier 206, AMP_A, and the second amplifier 208, AMP_B, may also be supplied by the parallel amplifier supply voltage, V_{SUPPLY—PARA—AMP}.

[0330] As another example, FIG. 12E depicts an embodiment of the rechargeable parallel amplifier 35E that is similar to the rechargeable parallel amplifier 35B depicted in FIG. 12B. Unlike the rechargeable parallel amplifier 35B, the rechargeable parallel amplifier 35E is configured to use the parallel amplifier supply voltage, V_{SUPPLY—PARA—AMP}, instead of the parallel amplifier supply input 30, (V_BAT), provided by the battery 20.

[0331] Accordingly, unlike the rechargeable parallel amplifier 35B, the rechargeable parallel amplifier 35E is configured such that the source 214S of the first switching element 214, SW_1A, is coupled to the parallel amplifier supply voltage, V_{SUPPLY—PARA—AMP}. Similar to the parallel amplifier 35D of FIG. 12D, the rechargeable parallel amplifier 35E may also be reconfigured to use the parallel amplifier supply voltage, V_{SUPPLY—PARA—AMP}, as the supply voltage of the first amplifier 206, AMP_A, the second amplifier 208, AMP_B, and the output control circuit 230A.

[0332] FIG. 12F depicts another embodiment of the rechargeable parallel amplifier 35C, of FIG. 12C, as a rechargeable parallel amplifier 35F. Similar to the parallel amplifier 35D, depicted in FIG. 12D, and the rechargeable parallel amplifier 35E, depicted in FIG. 12E, the rechargeable parallel amplifier 35F is configured to use the parallel amplifier supply voltage, V_{SUPPLY—PARA—AMP}, instead of the parallel amplifier supply input 30, (V_BAT), supplied by the battery 20. Also similar to the parallel amplifier 35D and the rechargeable parallel amplifier 35E, rechargeable parallel amplifier 35F may be configured such that the source 214S of the first switching element 214, SW_1A, may be coupled to the parallel amplifier supply voltage, V_{SUPPLY—PARA—AMP}, instead of the parallel amplifier supply input 30, (V_BAT). Also similar to the rechargeable parallel amplifier 35E, depicted in FIG. 12E, the first amplifier 206, AMP_A, the second amplifier 208, AMP_B, and the output control circuit 230B may also be further configured to use the parallel supply voltage, V_{SUPPLY—PARA—AMP}, as a supply source instead of the parallel amplifier supply input 30, (V_BAT).

[0333] Returning to FIG. 2A, the open loop assist circuit 39 will now be discussed. As discussed above, the parallel amplifier circuit output current, I_PAWA—OUT, may be a combination of the parallel amplifier output current I_PARA—AMP, and the open loop assist circuit, I_ASSIST. The open loop assist circuit 39 may be used to reduce the amount of current that the parallel amplifier 35 of the parallel amplifier circuitry 32 may need to source and sink in order to regulate the power amplifier supply voltage, V_CC. In particular, the parallel amplifier 35 may sink excess power inductor current, I_SW—OUT, which may generate a large voltage ripple on the power amplifier supply voltage, V_CC. The large voltage ripple on the power amplifier supply voltage, V_CC, can be due to the interaction of the power inductor current, I_SW—OUT, with the non-zero impedance of parallel amplifier 35 over frequency in the pass band of the pseudo-envelope follower power management system. The open loop assist current, I_ASSIST, provided by the open loop assist circuit 39 can be configured to reduce the parallel amplifier output current, I_PARA—AMP, sourced or sunk by the parallel amplifier 35, which may reduce the ripple voltage on the power amplifier supply voltage, V_CC, because the non-zero output impedance of the parallel amplifier 35 is convoluted with less current.

[0334] One embodiment of the open loop assist circuit 39 may be configured to receive an estimated power inductor inductance parameter, L_EST, and a minimum power amplifier turn on a voltage parameter, V_OFFSET—PA, an estimated bypass capacitor capacitance parameter, C_BYPASS—EST, and an estimated power amplifier transconductance parameter, K_I_OUT—EST.

[0335] The estimated power inductor inductance parameter, L_EST, may be either the measured or estimated inductance of the power inductor 16 between a specific range of frequencies. For example, the estimated power inductor inductance parameter, L_EST, may be either the measured or estimated inductance of the power inductor 16 between approximately 10 MHz and 30 MHz. The minimum power amplifier turn on voltage parameter, V_OFFSET—PA, may be either the measured or estimated value of the minimum supply voltage at which the linear RF power amplifier 22 will begin to operate. The estimated bypass capacitor capacitance parameter, C_BYPASS—EST, may be either the measured or estimate capacitance of the bypass capacitor capacitance, C_BYPASS, of the bypass capacitor 19 measured between a specific range of frequencies. For example, the estimated bypass capacitor capacitance parameter, C_BYPASS—EST, may be either the measured or estimated capacitance of the bypass capacitor capacitance, C_BYPASS, of the bypass capacitor 19 between approximately 10 MHz and 30 MHz. The estimated power amplifier transconductance parameter, K_I_OUT—EST, may be either the measured or estimated transconductance of the linear RF power amplifier 22. Transconductance of the linear RF power amplifier 22 may be 1/R_LOAD, where R_LOAD, is the estimated resistive load of the linear RF power amplifier 22. The estimated power amplifier transconductance parameter, K_I_OUT—EST, may be either the measured or estimated transconductance of the linear RF power amplifier 22 between a specific range of frequencies. For example, the estimated power amplifier transconductance parameter, K_I_OUT—EST, may be either the measured or estimated transconductance of the linear RF power amplifier 22 between approximately 10 MHz and 30 MHz.

[0336] The estimated power inductor inductance parameter, L_EST, the minimum power amplifier turn on voltage parameter, V_OFFSET—PA, the estimated bypass capacitor capacitance parameter, C_BYPASS—EST, and the estimated power amplifier transconductance parameter, K_I_OUT—EST may be provided by the controller 50 through the control bus 44, as depicted in FIGS. 1A and 1B. Typically, values of the estimated power inductor inductance parameter, L_EST, the minimum power amplifier turn on the voltage parameter, V_OFFSET—PA, the estimated bypass capacitor capacitance parameter, C_BYPASS—EST, and the estimated power amplifier transconductance parameter, K_I_OUT—EST, are obtained at calibration time of the pseudo-envelope follower system.

[0337] In addition, the open loop assist circuit 39 may be configured to receive the feed forward control signal 38, V_SWITCHER, from the multi-level charge pump buck converter 12. As discussed above, the feed forward control signal 38, V_SWITCHER, may be configured to provide either the scaled switching voltage output 38A, V_SW—SCALED, or the estimated switching voltage output 38B, V_SW—EST. The open loop assist circuit 39 may also be configured to receive the V_RAMP signal, from the first control input 34.

[0338] FIG. 9A depicts a more detailed block diagram of an embodiment of the open loop assist circuit 39 of FIG. 2A, which is depicted as an open loop assist circuit 39A. The open loop assist circuit 39A will be described with continuing reference to FIGS. 1A and 2A. The open loop assist circuit 39A includes an output current estimator 240, a bypass capacitor current estimator 242, a power inductor current estimator 244A, a summing circuit 246, and a controlled current source 248. The output current estimator 240 receives the V_RAMP signal, the estimated power amplifier transconductance parameter, K_I_OUT—EST, and the minimum power amplifier turn on voltage parameter, V_OFFSET—PA. The output current estimator 240 generates an output current estimate, I_OUT—EST, based upon the V_RAMP signal, the estimated power amplifier transconductance parameter, K_I_OUT—EST, and the minimum power amplifier turn on voltage parameter, V_OFFSET—PA. The output current estimate, I_OUT—EST, is an estimate of the output current, I_OUT, provided to the linear RF power amplifier 22.

[0339] In one embodiment, the output current estimator 240 calculates the difference between the V_RAMP signal and the minimum power amplifier turn on voltage parameter, V_OFFSET—PA, by subtracting the minimum power amplifier turn on voltage parameter, V_OFFSET—PA, from the V_RAMP signal, (V_RAMP−V_OFFSET—PA). Thereafter, the difference between the V_RAMP signal and the minimum power amplifier turn on voltage parameter, V_OFFSET—PA, is scaled by the estimated power amplifier transconductance parameter, K_I_OUT—EST, to generate the output current estimate, I_OUT—EST, where I_OUT—EST=K_I_OUT—EST*(V_RAMP−V_OFFSET—PA). Typical circuitry may include an operational amplifier to perform (V_RAMP−V_OFFSET—PA) and the voltage difference is applied to a transconductance amplifier, which the transconductance amplifier gain, Gm, is programmable and equal to K_I_OUT—EST.

[0340] The bypass capacitor current estimator 242 receives the V_RAMP signal and the estimated bypass capacitor capacitance parameter, C_BYPASS—EST. The bypass capacitor current estimator 242 generates a bypass capacitor current estimate, I_BYPASS—EST, based upon the V_RAMP signal and the estimated bypass capacitor capacitance parameter, C_BYPASS—EST. The bypass capacitor current estimate, I_BYPASS—EST, is an estimate of the bypass capacitor current, I_BYPASS—CAP, delivered by the bypass capacitor capacitance, C_BYPASS, of the bypass capacitor 19.

[0341] In one embodiment, the V_RAMP signal is differentiated to provide a V_RAMP rate of change signal, d(V_RAMP)/dT, which serves as an estimate of the rate of change of the voltage across the bypass capacitor 19. The V_RAMP rate of change signal, d(V_RAMP)/dT, may be an estimate of the rate of change of the V_RAMP signal over time. In some embodiments, the V_RAMP rate of change signal, d(V_RAMP)/dT, is generated by a high pass filter having a desired time constant. A simple high-pass filter followed by a gain circuit provides a frequency response below its corner frequency that have a +6 dB/octave slope thus equivalent to “s laplace transform” and thus creating a differentiator function below the corner frequency. The high-pass filter is typically made of a series capacitor and a shunt resistor. In some embodiments, the time constant of the high pass filter may be between the range of 8 nanoseconds and 16 nanoseconds.

[0342] The power inductor current estimator 244A receives the V_RAMP signal, the feed forward control signal 38, V_SWITCHER, and the estimated power inductor inductance parameter, L_EST. The power inductor current estimator 244A generates a power inductor current estimate, I_{SW—OUT—EST}, based upon the V_RAMP signal, the feed forward control signal 38, V_SWITCHER, and the estimated power inductor inductance parameter, L_EST. The power inductor current estimate, I_{SW—OUT—EST}, is an estimate of the power inductor current, I_SW—OUT, delivered by the power inductor 16.

[0343] In one embodiment of the power inductor current estimator 244A, the power inductor current estimator 244A subtracts the V_RAMP signal from the feed forward control signal 38, V_SWITCHER, to generate a difference voltage V_DIFFERENCE. The power inductor current estimator 244A may include an integrator circuit (not shown) that integrates the difference voltage V_DIFFERENCE to generate an accumulated difference signal. The power inductor current estimator 244A then scales an accumulated difference signal with a factor of 1/L_EST, to generate the power inductor current estimate, I_{SW—OUT—EST}. The bandwidth of the integrator circuit used to integrate the difference voltage V_DIFFERENCE may be between 5 MHz and 45 MHz. In some embodiments, the integrator slope may be programmable. For example, the controller 50 may adjust the gain of the transistors of the integrator circuit (not shown) of the power inductor current estimator 244A in order to adjust the integrator slope. Also, it is possible to use a low-pass filter followed by a gain which above the corner frequency the slope versus frequency is −6 dB/octave similar to “1/s Laplace transform” thus acting as an integrator in the frequencies above the corner frequency. The corner frequency can be set below 5 MHz and is made programmable.

[0344] In another embodiment of the power inductor current estimator 244A the power inductor current estimator 244A divides the accumulated difference signal by the estimated power inductor inductance parameter, L_EST, to generate the power inductor current estimate, I_{SW—OUT—EST}.

[0345] In still another embodiment of the power inductor current estimator 244A, the difference voltage, V_DIFFERENCE, is scaled by the factor of 1/L_EST, or divided by the estimated power inductor inductance parameter, L_EST, to generate a scaled difference signal, S_{DIFFERENCE—SCALED}, (not shown) prior to integration. The power inductor current estimator 244A then integrates a scaled difference signal, S_{DIFFERENCE—SCALED}, (not shown) to generate the power inductor current estimate, I_{SW—OUT—EST}. In yet another embodiment of the power inductor current estimator 244A, the power inductor current estimator 244A scales the V_RAMP signal and the feed forward control signal 38, V_SWITCHER, by the factor of 1/L_EST, or divides the V_RAMP signal and the feed forward control signal 38, V_SWITCHER, by the estimated power inductor inductance parameter, L_EST, prior to calculating the scaled difference signal, S_{DIFFERENCE—SCALED}, (not shown). Thereafter, the scaled difference signal, S_{DIFFERENCE—SCALED}, is integrated to generate the power inductor current estimate, I_{SW—OUT—EST}.

[0346] When the feed forward control signal 38, V_SWITCHER, is configured to provide the estimated switching voltage output 38B, V_SW—EST, to the open loop assist circuit 39, the power inductor current estimate, I_{SW—OUT—EST}, is generated based upon the estimated switching voltage output 38B, V_SW—EST. When the feed forward control signal 38, V_SWITCHER, is configured to provide the scaled switching voltage output 38A, V_SW—SCALED, to the open loop assist circuit 39, the power inductor current estimate, I_{SW—OUT—EST}, is generated based upon the switching voltage output, V_SW—SCALED, 38A.

[0347] The summing circuit 246 is configured to receive the output current estimate, I_OUT—EST, the bypass capacitor current estimate, I_BYPASS—EST, and power inductor current estimate, I_{SW—OUT—EST}. The summing circuit 246 subtracts the bypass capacitor current estimate, I_BYPASS—EST, and the power inductor current estimate, I_{SW—OUT—EST}, from the output current estimate, I_OUT—EST, to generate an estimate of the open loop assist current, I_ASSIST—EST. The open loop assist current, I_ASSIST—EST, is an estimate of the open loop assist current, I_ASSIST, provided by the open loop assist circuit 39A to the parallel amplifier output 32A in order to generate the parallel amplifier circuit output current, I_PAWA—OUT, from the parallel amplifier circuit 14.

[0348] The controlled current source 248 is a controlled current source that generates the open loop assist current, I_ASSIST, based upon the open loop assist current, I_ASSIST—EST. The open loop assist current can be activated when reduced voltage ripple reduction is required and can be disabled when voltage ripple reduction is not required such as when operating at lower power amplifier output power. The open loop assist current can be made of three separate controlled current sources, where each controlled current source is controlled by the power inductor current estimate, I_{SW—OUT—EST}, the bypass capacitor current estimate, I_BYPASS—EST, and the output current estimate, I_OUT—EST, respectively. Also, the open loop assist current, I_ASSIST, in phase may be time aligned with the parallel amplifier output current, I_PARA—AMP. For example, when the open loop assist current, I_ASSIST, is positive, parallel amplifier output current, I_PARA—AMP, may be positive and when the open loop assist current, I_ASSIST, is negative, the parallel amplifier output current, I_PARA—AMP, may also be negative as such there is no wasted currents, where the parallel amplifier output current, I_PARA—AMP, that is sourced is not sunk by the open loop assist circuit 39A.

[0349] FIG. 9B depicts another embodiment of the open loop assist circuit 39B. As depicted in FIG. 9B, the open loop assist circuit 39B is similar to the open loop assist circuit 39A except that the open loop assist circuit 39B receives the estimated switching voltage output 38B, V_SW—EST, as the feed forward control signal instead of the feed forward control signal 38, V_SWITCHER. Accordingly, the estimated switching voltage output 38B, V_SW—EST, includes a power inductor current estimator 244B instead of the power inductor current estimator 244A. The power inductor current estimator 244B is similar to the power inductor current estimator 244A except the power inductor current estimator 244B only receives estimated switching voltage output 38B, V_SW—EST, instead of the feed forward control signal 38, V_SWITCHER.

[0350] As a result, the power inductor current estimate, I_{SW—OUT—EST}, generated by the power inductor current estimator 244B is based upon the estimated switching voltage output 38B, V_SW—EST. As a result, the power inductor current estimator 244B is functionally like the power inductor current estimator 244A when the feed forward control signal 38, V_SWITCHER, provides the estimated switching voltage output 38B, V_SW—EST, as an output. Accordingly, the open loop assist circuit 39B operates in a manner that is similar to the operation of the open loop assist circuit 39A when the feed forward control signal 38, V_SWITCHER, provides the estimated switching voltage output 38B, V_SW—EST, to the open loop assist circuit 39A.

[0351] Returning to FIG. 2A, the parallel amplifier output impedance compensation circuit 37 will now be discussed. The combination of the multi-level charge pump buck converter 12 and the parallel amplifier 35 of the parallel amplifier circuitry 32 may not have a flat frequency response across the modulation bandwidth of the power amplifier supply voltage, V_CC, provided to the linear RF power amplifier 22. In particular, the desired modulation bandwidth of the power amplifier supply voltage, V_CC, is between 1.5 to 2.5 times the RF modulation bandwidth of the linear RF power amplifier 22. As an example, the Long Term Evolution LTE 3GPP standard of the RF modulation bandwidth may be up to 20 MHz. As a result, the desired modulation bandwidth of power amplifier supply voltage, V_CC, generated by the pseudo-envelope follower power management system 10A may be between 30 MHz to 40 MHz. In some embodiments of the pseudo-envelope follower power management system 10A, the desired modulation bandwidth of the power amplifier supply voltage, V_CC, may be approximately 35 MHz. However, at higher frequencies, the output impedance of the parallel amplifier 35 that regulates the power amplifier supply voltage, V_CC, may become inductive. The output impedance of the parallel amplifier 35 combines with the bypass capacitor capacitance, C_BYPASS, of the bypass capacitor 19 to roll off the modulation frequency response of the parallel amplifier 35. The roll off of the modulation frequency response of the parallel amplifier 35 may result in increased ripple voltage in the power amplifier supply voltage, V_CC, due to the inductor current, I_SW—OUT, provided by the power inductor 16. The parallel amplifier output impedance compensation circuit 37 may be configured to pre-compensate the V_RAMP signal in order to provide a compensated V_RAMP signal, V_RAMP—C, to the parallel amplifier 35 in order to flatten the modulation frequency response of the parallel amplifier 35.

[0352] The parallel amplifier output impedance compensation circuit 37 depicted in FIG. 2A is configured to receive the V_RAMP signal, an estimated bypass capacitor capacitance parameter, C_BYPASS—EST, and a parallel amplifier inductance estimate parameter, L_CORR—EST. The parallel amplifier inductance estimate parameter, L_CORR—EST, may be an estimated inductance of the parallel amplifier 35 between the frequencies 10 MHz and 30 MHz, which is measured during calibration. The parallel amplifier inductance estimate parameter, L_CORR—EST, may be provided by the controller 50 via the control bus 44 at configuration time.

[0353] FIG. 10 depicts an example embodiment of the parallel amplifier output impedance compensation circuit 37, depicted in FIG. 2A, as a parallel amplifier output impedance compensation circuit 37A. The parallel amplifier output impedance compensation circuit 37A may include a first differentiator circuit 250, a second differentiator 252, a frequency pre-distortion circuit 254, and a summing circuit 256.

[0354] The first differentiator circuit 250 receives the V_RAMP signal and the estimated bypass capacitor capacitance parameter, C_BYPASS—EST. Similar to the bypass capacitor current estimator 242 of FIGS. 9A and 9B, the first differentiator circuit 250 generates a bypass capacitor current estimate, I_BYPASS—EST, based upon the V_RAMP signal and the bypass capacitor capacitance parameter, C_BYPASS—EST. The bypass capacitor current estimate, I_BYPASS—EST, is an estimate of the bypass capacitor current, I_BYPASS—CAP, delivered by the bypass capacitor capacitance, C_BYPASS, of the bypass capacitor 19. In some embodiments of the parallel amplifier output impedance compensation circuit 37A, the parallel amplifier output impedance compensation circuit 37A uses the bypass capacitor current estimate, I_BYPASS—EST, provided by the bypass capacitor current estimator 242 and the first differentiator circuit 250 is omitted. In other embodiments of the parallel amplifier output impedance compensation circuit 37A, the time constant of the first differentiator circuit 250 may be different than the time constant of bypass capacitor current estimator 242 of the open loop assist circuit 39.

[0355] Similar to the bypass capacitor current estimator 242, in one embodiment of the first differentiator circuit 250, the V_RAMP signal is differentiated to provide a V_RAMP rate of change signal, d(V_RAMP)/dT, which serves as an estimate of the rate of change of the voltage across the bypass capacitor 19. The V_RAMP rate of change signal, d(V_RAMP)/dT, may be an estimate of the rate of change of the V_RAMP signal over time. In some embodiments, the V_RAMP rate of change signal, d(V_RAMP)/dT, is generated by a high pass filter (not shown) having a desired time constant. As an example, a simple high-pass filter followed by a gain stage may provide a frequency response below its corner frequency that has a +6 dB/octave slope, thus equivalent to the “s Laplace transform” and thus creating a differentiator function below the corner frequency. The high-pass filter (not shown) is typically made of a series capacitor and a shunt resistor. In some embodiments, the time constant of the high pass filter may be between the range of 8 nanoseconds and 16 nanoseconds.

[0356] The bypass capacitor current estimate, I_BYPASS—EST, and the scaled parallel amplifier output current estimate, I_{PARA—AMP—SENSE}, are combined to create a dynamic current, I_DYNAMIC, which is provided to the second differentiator circuit 252. The dynamic current, I_DYNAMIC, represents the dynamic portion of the power inductor current, I_SW—OUT, delivered by the power inductor 16. The second differentiator circuit 252 is to replicate the parallel amplifier output impedance frequency response, which exhibits an output impedance that increases at +6 dB/octave, like an inductor, at the frequency range where the switcher current is operating, up to a resonance frequency equal to 1/(2*pi*sqrt(L_CORR*C_BYPASS)).

[0357] The second differentiator circuit 252 is configured to receive the dynamic current, I_DYNAMIC, and the parallel amplifier inductance estimate parameter, L_CORR.

[0358] The second differentiator circuit 252 differentiates the dynamic current, I_DYNAMIC, to provide a dynamic current rate of change signal, d/(I_DYNAMIC)/dT. The dynamic current rate of change signal, d/(I_DYNAMIC)/dT, estimates change of the dynamic current, I_DYNAMIC, with respect to time. In some embodiments, the dynamic current rate of change signal, d(I_DYNAMIC)/dT, is generated by a low pass filter (not shown) having a desired time constant. The time constants of the second differentiator circuit 252 may be configured to optimize the modulation bandwidth of the parallel amplifier 35. The second differentiator can be made from a high-pass filter (not shown) followed by a gain to provide a frequency response below its corner frequency that has a +6 dB/octave slope thus equivalent to “s Laplace transform” and thus creating a differentiator function below the corner frequency. The high-pass filter is typically made of a series capacitor and a shunt resistor. The time constant of the high-pass filter may be between 8 nanoseconds and 16 nanoseconds. The second differentiator circuit 252 scales the dynamic current rate of change signal, d(I_DYNAMIC)/dT, by the parallel amplifier inductance estimate parameter, L_CORR, to generate a power amplifier supply ripple voltage estimate, V_RIPPLE, at the negative input of the summing circuit 256. The power amplifier supply ripple voltage estimate is an estimate of the ripple voltage component of the power amplifier supply voltage, V_CC, at the power amplifier supply output 28.

[0359] The frequency pre-distortion circuit 254 may be configured to receive the V_RAMP signal and output a peaked V_RAMP signal, V_{RAMP—PEAKED}. The frequency pre-distortion circuit 254 may be a programmable peaking filter that may be configured to compensate for the roll off of the modulation frequency response of the parallel amplifier 35. The frequency pre-distortion circuit 254 may include a frequency equalizer circuit that includes a programmable pole time constant, Tau_Pole, and a programmable zero time constant, Tau_Zero. The frequency pre-distortion circuit Laplace transfer function, V_RAMP—C/V_RAMP, may be approximately equal to [1+Tau_Zero*s]/[1+Tau_Pole*s]. The programmable pole time constant, Tau_Pole, and the programmable zero time constant, Tau_Zero, may be adjusted to increase the frequency response of the frequency pre-distortion circuit 254, V_RAMP—C/V_RAMP, in order to flatten the overall modulation frequency response of the pseudo-envelope follower power management system 10A. In some embodiments of the frequency pre-distortion circuit 254, the programmable pole time constant, Tau_Pole, is configured to about 0.4 microseconds, (1/2.5 MHz). The programmable zero time constant, Tau_Zero, may be configured to be about 0.192 microseconds, (1/5.8 MHz). As a result, the pseudo-envelope follower power management system transfer function, V_CC/V_RAMPS, may be flattened up to about 35 MHz.

[0360] FIG. 13 depicts an embodiment of a pseudo-envelope follower power management system 10G including a buck converter 13G and a parallel amplifier circuit 14G having an open loop assist circuit 39 and parallel amplifier circuitry 32. In some alternative embodiments of the pseudo-envelope follower power management system of FIG. 13, the parallel amplifier 35 may be a rechargeable parallel amplifier. As an example, the parallel amplifier 35 may be a rechargeable parallel amplifier similar to the embodiments of the rechargeable parallel amplifier depicted in FIGS. 12B-C and FIGS. 12E-F.