MULTI-MODE/MULTI-BAND POWER MANAGEMENT SYSTEM

[0001] This application claims the benefit of provisional patent application Ser. No. 61/376,787, filed Aug. 25, 2010, the disclosure of which is hereby incorporated herein by reference in its entirety.

[0002] The present disclosure relates to a power management system that is usable to control power supplying multi-mode/multi-band power amplifiers.

[0003] Multi-mode/multi-band power amplifiers (PAs) are designed to amplify radio frequency (RF) signals that may operate in second generation (2G) wireless access networks that use Gaussian minimum shift keying (GMSK) and enhanced data GSM evolution (EDGE) modulation protocols. Third generation (3G) wireless access networks that use high speed packet access (HSPA) and enhanced high speed packet access (HSPA+) modulation protocols may also be amplified by multi-mode/multi-band PAs. Further still, fourth generation (4G) wireless access networks that use long term evolution frequency division duplex (LTE FDD) and time division duplex (TDD) may also be amplified by multi-mode/multi-band PAs. Other dedicated transmit chain amplifiers are used to support extra bands that operate with a single mode. These dedicated transmit chain amplifiers are sometimes referred to as “bolt-on” PAs. For example, a bolt-on amplifier could be used to support 4G specific bands that are outside the bands that are compatible with an individual multi-mode/multi-band PA.

[0004] FIG. 1 is a block diagram of a related art power management system 10 for a multi-mode/multi-band PA 12 and bolt-on PAs 14, all of which are powered by a single power converter 16. The power converter 16 also includes a serial interface 18 that sends and receives data and receives commands for controlling the power management system 10. A typical serial interface is a mobile industry processor interface (MIPI) for communicating with a radio frequency front end (RFFE).

[0005] An output filter 20 is coupled between the power converter 16 and a power node 22 for both the multi-mode/multi-band PA 12 and the bolt-on PAs 14. The output filter 20 is an LC type filter that includes an inductor LGMSK/LINEAR that is coupled between the power converter 16 and the power node 22. Also, a capacitor CGMSK/LINEAR is coupled between the inductor LGMSK/LINEAR and ground GND.

[0006] The power management system 10 provides power to the multi-mode/multi-band PA 12 for a saturated amplifier mode used to amplify GMSK modulated signals. When GMSK signals are being amplified by the multi-mode/multi-band PA 12, a slow DC-DC mode of the power converter 16 provides a constant direct current (DC) voltage output. In order to meet GMSK requirements that limit a magnitude of ripple current flowing through the inductor LGMSK/LINEAR, an inductance value for the inductor LGMSK/LINEAR is relatively large, ranging from around 1 μH to 2 μH. Moreover, a capacitance value for the capacitor CGMSK/LINEAR is relative large, being around 2 μF in order to meet GMSK spectrum requirements. An integration of the ripple current flowing through the inductor LGMSK/LINEAR divided by the capacitance value of the capacitor CGMSK/LINEAR provides a value for an undesirable ripple voltage that appears across the power node 22 to ground GND. In order to reduce this undesirable ripple voltage, either a large inductance value for the inductor LGMSK/LINEAR is needed or a larger capacitance value for the capacitor CGMSK/LINEAR is needed. Alternately, a high switching frequency for the power converter 16 can be used.

[0007] The power management system 10 must also provide power to the multi-mode/multi-band PA 12 and the bolt-on PAs 14 when they are operated in a linear amplifier mode used to amplify signals for 3G and 4G operation. Since the linear amplifier mode is typically less efficient than the saturated amplifier mode, envelope tracking is employed wherein the power converter 16 outputs a supply voltage V_CC that is amplitude modulated in synchronization with the amplitude of a signal that is to be amplified by a PA of either the multi-mode/multi-band PA 12 or the bolt-on PAs 14. In this way, efficient operation of the multi-mode/multi-band PA 12 and the bolt-on PAs 14 is increased as the supply voltage follows the amplitude of the signal to be amplified. A power control signal known as V_RAMP received by the power converter 16 carries envelope tracking information that is used by a parallel amplifier 24 to control the amplitude modulation of the supply voltage V_CC, which is typically on the order of 3V peak-to-peak (pkpk).

[0008] A problem arises when operation in envelope tracking mode in that the parallel amplifier 24 will have to provide the relatively large voltage modulation of 3Vpkpk across the capacitor CGMSK/LINEAR that serves as a large decoupling capacitor during the saturated amplifier mode. The problem is that a relatively large modulation current I_BYPASS is demanded from the parallel amplifier 24 in order to satisfy the following relationship that assumes a 10 MHz modulation of the supply voltage V_CC.

I_BYPASS=CGMSK/LINEAR*dV_CC/dt=2 μF*3Vpkpk*10 MHz=60A

[0009] In actuality, the modulation current I_BYPASS is lower than 60A since the amplitude modulation provided by the parallel amplifier 24 is typically only around 1 MHz to 5 MHz. Nevertheless, the modulation current I_BYPASS remains unacceptably large.

[0010] FIG. 2 is a schematic diagram of a system model 26 that is usable to derive a transfer function for the power management system 10 of FIG. 1. The system model 26 includes a multi-level switcher 28 that is controlled by a source voltage V_CCI that is responsive to a power control signal V_RAMPS—C that equals the power control signal V_RAMP without pre-distortion. The system model 26 also includes a PA model 30 that represents a PA under the control of the power management system 10. A resistance R_PA in parallel with a current source I_PA models a response of the PA to an output current I_OUT(S). A voltage V_CCPA is developed across the PA in response to the output current I_OUT(S).

[0011] An output voltage V_CC0 represents an output voltage V_CC versus the power control signal V_RAMP when a switching current I_SW(S) output from the multi-level switcher 28 is equal to zero. A transfer function HEQ_(S)=V_CC0/V_RAMPS—C when the switching current I_SW(S) output from the multi-level switcher 28 is equal to zero. Extra decoupling capacitors located within the PA are represented in the PA model 30 as a decoupling capacitor C_PA. Extra parasitic inductance that results from layout routing of a power line from a V_CC node to the PA is represented by a parasitic inductor L_PA.

[0012] During operation in the envelope tracking mode for LTE, an inductor value for the inductor LGMSK/LINEAR (FIG. 1), and represented by L should be lowered to around 0.5 μH to allow the multi-level switcher 28 to quickly provide current through the inductor LGMSK/LINEAR. In this way, a slew rate limitation is avoided. For example, a current I_SW(S) through the inductor LGMSK/LINEAR, and represented by L has a current rate of change dl_SW/dt that is given by the following equation.

dl_SW/dt=(V_SW−V_CC)/(LGMSK/LINEAR)

[0013] As a result, the current rate of change dl_SW/dt is limited by an amount of available headroom V_SW−V_CC, which is usually increased by a value of inductance for the inductor LGMSK/LINEAR. A lower inductance value for LGMSK/LINEAR will result in a higher current rate of change dl_SW/dt. Thus, care must be taken not to lower the inductance value for LGMSK/LINEAR such that an instantaneous switching frequency of the switcher is required to be increased.

[0014] A more detailed analysis of the power management system 10 can be achieved by considering the various impedances that are represented in the system model 26. For example, an impedance Z1 is made up of the model inductor L that represents the impedance of the inductor LGMSK/LINEAR. An impedance Z2 represents optional filtering components and parasitic inductance between an output of the parallel amplifier 24 (FIG. 1) and a PA represented by the PA model 30. An impedance Z3 is primarily made up of the parasitic inductance L_PA in parallel with the decoupling capacitor C_PA coupled the resistance R_PA. An impedance Z_OUT represents the impedance of the parallel amplifier 24 in parallel with a decoupling capacitor located on the V_CC node.

[0015] The following equations are derived from the system model 26 shown in FIG. 2.

V_CC/V_CC0=(Z1/(Z1+Z_OUT))*(Z2+Z3)/(Z2+Z3+Z_OUT*Z1/(Z_OUT+Z1))

V_CCPA/V_CC0=(Z1/(Z1+Z_OUT))*(Z3/(Z2+Z3+Z_OUT*Z1/(Z_OUT+Z1))

V_CC/V_SW=(Z_OUT/(Z1+Z_OUT))*(Z2+Z3)/(Z2+Z3+Z_OUT*Z1/(Z_OUT+Z1))

V_CCPA/V_SW=(Z_OUT/(Z1+Z_OUT))*(Z3/(Z2+Z3+Z_OUT*Z1/(Z_OUT+Z1))

[0016] A computer simulation of the system model 26 starts with V_RAMPS—C set to zero, which forces V_CC0 equal to zero. In this way, the slow DCDC mode for saturated amplifier operation such as needed with GSMK is simulated. A typical inductance value for the impedance Z1 is set to about 1 μH, and a decoupling capacitance value for Z_OUT is set to around 2.2 μF for simulating the slow DCDC mode.

[0017] FIG. 3 is a frequency response graph for computer simulation results for the slow-DCDC mode that uses the relatively large inductance value of about 1 μH and the relatively large capacitance value of 2.2 μF. The frequency response graph confirms that there are conflicting needs to have a relatively large inductance value and a relatively large decoupling capacitance value for the slow DCDC mode, and a relatively small inductance value and a relatively small capacitance value for the envelope tracking mode. As a result of these conflicting needs, the related art power management system 10 (FIG. 1) cannot effectively supply power to the multi-mode/multi-band PA 12 (FIG. 1) and the bolt-on PAs 14 (FIG. 1) that includes PAs that operate in a saturated mode and that includes PAs that operate in a linear mode.

[0018] One related art attempt at solving this conflict is to have a pair of switched inductor and capacitor filter branches that have inductances and capacitances matched to the two different modes of operation. However, the related art switched inductor and capacitor filter branches include series electronic switches that have on state resistance values that lower the quality Q of any filtering provided by the switched inductor and capacitor filter branches. Thus the filtering achieved is not effective enough to pass spectrum requirements. Therefore, a need remains for a power management system that supplies power to a multi-mode/multi-band RF PA load that includes PAs that operate in a saturated mode and that includes PAs that operate in a linear mode.

[0019] The present disclosure provides a power management system for a radio frequency (RF) power amplifier (PA) load. In general, the power management system of the present disclosure supplies power to a multi-mode/multi-band RF PA load that includes PAs that operate in a saturated mode and that includes PAs that operate in a linear mode. When the RF PA load operates in the saturated mode, the power management system provides a slow DC-DC mode that supplies a relatively constant direct current (DC) voltage output that has selectable constant power levels. Alternately, when the RF PA load operates in the linear mode, the power management system takes advantage of envelope tracking of a transmit signal to be amplified or pseudo envelope following when the transmit signal is pre-distorted. For example, when the RF PA load is operating in the linear mode, the power management system provides a dynamic DC voltage that is amplitude modulated in synchronization with the amplitude of the transmit signal that is to be amplified by the RF PA load.

[0020] In one embodiment, the power management system includes a first switching power supply that is coupled to an electronic switch for selectively coupling the first switching power supply to the RF PA load. A second switching power supply is continually coupled to the RF PA load. A control system is provided for closing the electronic switch to supply the relatively constant DC voltage in addition to the dynamic DC voltage to the RF PA load in a first mode, and for opening the electronic switch wherein the relatively constant DC voltage from the first switching power supply is not supplied to the RF PA load in the second mode. In another embodiment, a first output filter is coupled between the first switching power supply and the electronic switch, and a second output filter is coupled between the second switching power supply and the RF PA load. In at least one embodiment, the first output filter and the second output filter are both LC type filters.

[0021] The first switching power supply is adapted to output the relatively constant DC voltage based upon an expected power output. Alternately, the second switching power supply outputs the dynamic DC voltage that is amplitude modulated in synchronization with the amplitude of a signal that is to be amplified by the RF PA load. As a result of the relatively constant DC voltage of the first switching power supply, the first output filter has relatively large inductance and capacitance values. In contrast, due to the relatively large and dynamic amplitude modulation of the dynamic DC voltage supplied by the second switching power supply, the inductance and capacitance values of the second output filter are relatively small.

[0022] Operation of the power management system of the present disclosure involves a step of closing the electronic switch to supply a constant DC voltage in addition to the dynamic DC voltage to the RF PA load operating in the first mode. Another step provides for opening the electronic switch to remove the relatively constant DC voltage from the RF PA load in the second mode. In one embodiment, the first mode is saturation mode and the second mode is linear mode.

[0023] Those skilled in the art will appreciate the scope of the present disclosure and realize additional aspects thereof after reading the following detailed description of the preferred embodiments in association with the accompanying drawing figures.

[0032] The embodiments set forth below represent the necessary information to enable those skilled in the art to practice the embodiments and illustrate the best mode of practicing the embodiments. Upon reading the following description in light of the accompanying drawing figures, 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.

[0033] FIG. 4 depicts a power management system 32 for supplying power to a power amplifier (PA) load 34 that includes PAs that operate in a saturated mode for one type of transmission and a linear mode for another type of transmission. As shown in FIG. 4, a multi-mode/multi-band PA 36 making up a portion of the RF PA load 34 is for amplifying RF signals that require either a PA operating in saturation mode or a PA operating in linear mode. For example, the multi-mode/multi-band PA 36 accepts second generation 2G high-band (HB) and low-band (LB) RF signals that require the PAs of the multi-mode/multi-band PA 36 to operate in a saturation mode. Gaussian minimum shift keying (GMSK) is a form of modulation used in 2G modulation schemes. Since data in GMSK modulation is based upon phase only, a PA with the multi-mode/multi-band PA 36 may be operated entirely in saturation mode. In contrast, 3G and 4G modulation schemes included in a long term evolution (LTE) standard rely on linear mode operation. Therefore, when transmission of LTE signals is required the PAs of the multi-mode/multi-band PA 36 may entirely operate in a linear mode. The linear mode of operation is also called for during RF signal transmissions that use the bolt on PAs 38 that are dedicated to special bands that are outside operational boundaries for the multi-mode/multi-band PA 36.

[0034] The power management system 32 includes a power converter 40 having a first switching power supply 42 with a output terminal 43 and a second switching power supply 44 with an output terminal 45. The first switching power supply 42 and the second switching power supply 44 are integrated into a single wafer die 46. In at least one embodiment, the first switching power supply 42 and the second switching power supply 44 are both a buck/boost type power supply that can be commanded to output a voltage that is less than a source voltage in a buck mode or output a voltage that is greater than the source voltage in a boost mode.

[0035] The power converter 40 also includes a digital interface 48 that sends and receives data and receives commands for controlling the power management system 32. In one embodiment, the digital interface 48 is a mobile industry processor interface (MIPI). The power converter 40 further includes differential terminals V_RAMP—P, and V_RAMP—N for receiving a power control signal known as V_RAMP. A parallel amplifier 49 responds to the power control signal V_RAMP applied to the differential terminals V_RAMP—P and V_RAMP—N by amplitude modulating the output voltage of the second switching power supply 44 in synchronization with the amplitude of a signal that is to be amplified by the RF PA load 34.

[0036] A first output filter 50 is coupled to the first switching power supply 42 via the output terminal 43. The first output filter 50 is an inductor-capacitor (LC) filter for reducing output ripple voltage that is a component of a constant DC voltage output from the first switching power supply 42. In one embodiment, the first output filter 50 includes a first inductor LGMSK1 coupled between the first switching power supply 42 and a first capacitor CGMSK1 coupled to a fixed voltage node such as ground GND. This embodiment also includes a second inductor LGMSK2 coupled between the first inductor LGMSK1 and a second capacitor CGMSK2 that is coupled to the fixed voltage node. Preferably, the first inductor LGMSK1 has an inductance value of several μH, while the first capacitor has a capacitance value of several μF. For example, the first inductor LGMSK1 typically has an inductance value on the order of 1 μH to 10 μH, and the first capacitor CGMSK1 typically has a capacitance value that ranges from about 1 μF to 10 μF. In contrast, the inductance value of the second inductor LGMSK2 and the capacitance value of the second capacitor CGMSK2 are significantly smaller. For example, the second inductor LGMSK2 typically has an inductance value that ranges from about 1 nH to 10 nH, and the second capacitor CGMSK2 typically has a capacitance value that ranges from about 1 nF to 10 nF.

[0037] An electronic switch 52 has a throw coupled to both the second capacitor CGMSK2 and the second inductor LGMSK2. A pole of the electronic switch 52 is coupled to a power supply node 54 of the PA load 34. The electronic switch 52 is switched on and off via a control signal that is output from the power converter 40. In one embodiment, the control signal for switching on and off the electronic switch 52 is transmitted to the power converter 40 over the digital interface 48. The electronic switch 52 can be realized in the form of a field effect transistor (FET), wherein the throw of the electronic switch is the source terminal of the FET, the control signal is coupled to the gate of the FET, and the drain of the FET serves as the pole of electronic switch 52.

[0038] A second output filter 56 coupled to the output terminal 45 of the second switching power supply is continuously coupled between the second switching power supply 44 and the power supply node 54 of the PA load 34. The second output filter 56 is an LC type filter for reducing output ripple voltage that is a component of a dynamic voltage output from the second switching power supply 44. In one embodiment, the second output filter 56 includes an inductor LLINEAR coupled between the second switching power supply 44 and the power supply node 54 of the PA load 34. A capacitor CLINEAR is coupled between the inductor LLINEAR and a fixed voltage node such as ground GND. Preferably, the inductor LLINEAR has an inductance value of a few nH, while the CLINEAR capacitor has a capacitance value of a few nF. For example, the inductor LLINEAR has an inductance value that ranges from about 1 nH to 10 nH, and the first capacitor CLINEAR has a capacitance value that ranges from about 1 nF to 10 nF.

[0039] In operation, and in anticipation of a transmission of an RF signal via a PA operating in saturation mode, the electronic switch 52 is closed in response to a command passed through the digital interface 48. In this way, a PA of the RF PA load 34 operating in saturation mode is supplied with the relatively constant DC voltage that is appropriate for a selected power level. For example, the power management system 32 may output a relatively constant DC voltage of 0.5V for a selected low power level, and the power management system 32 may output a relatively constant DC voltage of 5.0V for a selected high power level. In at least one embodiment, the selected power level for the PA operating in saturation mode is indicated via data transferred over the digital interface 48.

[0040] Alternately, in anticipation of a transmission of an RF signal via a linear mode, the electronic switch 52 is opened in response to a command passed through the digital interface 48. In this way, a PA of the RF PA load 34 operating in linear mode is supplied with a dynamic DC voltage that is amplitude modulated in synchronization with the amplitude of a signal that is to be amplified by the RF PA load 34 while the relatively constant DC voltage is not supplied to the RF PA load 34. In one embodiment, the power control signal V_RAMP is digitally extracted from an envelope signal at baseband. The envelope signal is used to amplitude modulate the RF signal to be amplified by the PA of the RF PA load 34 operating in linear mode.

[0041] An exemplary process of generating the power control signal V_RAMP begins with digitally sampling in-phase (I) and quadrature (Q) samples from the envelope signal. The digital I/O samples are also scaled by a gain value appropriate for a desired signal power level to be transmitted. The I/O samples can also be pre-distorted via values in a pre-distoration look-up table (LUT) in order to further linearize operation of the PA of the RF PA load 34 operating in linear mode. The I/O samples are ultimately converted from digital samples to an analog signal that makes up the power control signal V_RAMP, which in turn is applied to the terminals V_RAMP—P and V_RAMP—N as a differential signal. A positive attribute of this process of generating the V_RAMP signal is that this process allows for some latency time to perform additional digital processing since the envelope signal is sampled at baseband before the RF signal to be amplified arrives at a PA of the RF PA load 34. The above exemplary process of generating the power control signal V_RAMP is referred to as envelope following because the power control signal V_RAMP includes pre-distortion components. However, another process of generating the power control signal V_RAMP is known as envelope tracking if pre-distortion components are not included in the power control signal V_RAMP.

[0042] FIG. 5 is a block diagram of another embodiment of multi-mode/multi-band power management system 58 that is in accordance with the present disclosure. The multi-mode/multi-band power management system 58 adds an offset capacitor C_OFFSET to the output of the parallel amplifier 49. The offset capacitor C_OFFSET serves two roles. A first role for the offset capacitor C_OFFSET is to shift the average voltage at the power supply node 54 to a lower voltage. A second role for the offset capacitor C_OFFSET is to increase decoupling for the first switching power supply 42 during the slow DCDC mode while a PA of the RF PA load 34 is operating in saturation mode.

[0043] FIG. 6 is a block diagram of yet another embodiment of the multi-mode/multi-band power management system 60 that is in accordance with the present disclosure. In this embodiment, the bolt-on PAs 38 have separate power nodes for pre-amplifier stages and output power amplifier stages. The V_CC2 node supplies the output stages of the bolt-on PAs 38, while a V_CC1—μBB node supplies the pre-amplifier stages. The V_CC1—uBB node is coupled to the output of a micro-buck/boost switching power supply 62. The V_CC1—μBB node also supplies power to the parallel amplifier 49 to enhance the efficiency of the multi-mode/multi-band power management system 60. Thus, there is no need to add an extra micro-buck/boost switching power supply.

[0044] FIG. 7 depicts the basic architecture of user equipment (UE) in the form of a mobile terminal 64 that incorporates an embodiment of the power management system 32 of FIG. 4. In particular, the power management system 32 is usable to supply power to a power amplifier 66 in the mobile terminal 64. The mobile terminal 64 may include a receiver front end 68, a radio frequency (RF) transmitter section 70, an antenna 72, a multi-band duplexer/switch 74, a baseband processor 76, a control system 78, a frequency synthesizer 80, and an interface 82. The receiver front end 68 receives information bearing radio frequency signals from one or more remote transmitters provided by a base station (not shown). A low noise amplifier (LNA) 84 amplifies the signal. A filter circuit 86 minimizes broadband interference in the received signal, while down conversion and digitization circuitry 88 down converts the filtered, received signal to an intermediate or baseband frequency signal, which is then digitized into one or more digital streams. The receiver front end 68 typically uses one or more mixing frequencies generated by the frequency synthesizer 80. The baseband processor 76 processes the digitized received signal to extract the information or data bits conveyed in the received signal. This processing typically comprises demodulation, decoding, and error correction operations. As such, the baseband processor 76 is generally implemented in one or more digital signal processors (DSPs).

[0045] On the transmit side, the baseband processor 76 receives digitized data, which may represent voice, data, or control information, from the control system 78, which it encodes for transmission. In a case of envelope tracking, the baseband processor 76 extracts the I/O components of a baseband envelope signal in order to generate a differential V_RAMP signal that is applied to the V_RAMP—P and V_RAMP—N terminals of the power converter 40. Moreover, the encoded data is output to the RF transmitter section 70, where it is used by a modulator 90 to modulate a carrier signal that is at a desired transmit frequency. The power amplifier 66 amplifies the modulated carrier signal to a level appropriate for transmission, and delivers the amplified and modulated carrier signal to the antenna 72 through the a power amplifier 66. The control system 78 outputs a MIPI signal that provides instructions and data for the power management system 32 as needed. For example, the control system 78 may instruct the power converter 40 to close the electronic switch 52 in anticipation of a transmission event that will use a PA operating in saturation mode. Alternately, the control system 78 may instruct the power converter 40 to open the electronic switch 52 in anticipation of a transmission event that will use a PA operating in linear mode. In this case, the baseband processor provides to the power converter 40, the power control signal V_RAMP that is amplitude modulated in synchronization with the amplitude of a signal that is to be amplified by the RF PA load 34.

[0046] A user may interact with the mobile terminal 64 via the interface 82, which may include interface circuitry 92 associated with a microphone 94, a speaker 96, a keypad 98, and a display 100. The interface circuitry 92 typically includes analog-to-digital converters, digital-to-analog converters, amplifiers, and the like. Additionally, it may include a voice encoder/decoder, in which case it may communicate directly with the baseband processor 76. The microphone 94 will typically convert audio input, such as the user's voice, into an electrical signal, which is then digitized and passed directly or indirectly to the baseband processor 76. Audio information encoded in the received signal is recovered by the baseband processor 76, and converted by the interface circuitry 92 into an analog signal suitable for driving the speaker 96. The keypad 98 and the display 100 enable the user to interact with the mobile terminal 64, input numbers to be dialed, address book information, or the like, as well as monitor call progress information.

[0047] Those skilled in the art will recognize improvements and modifications to the preferred embodiments of the present disclosure. All such improvements and modifications are considered within the scope of the concepts disclosed herein and the claims that follow.