Multiplying digital-to-analog converter

[0001] The present invention generally relates to a multiplying digital-to-analog converter (MDAC) of a pipeline analog-to-digital converter (pipeline ADC, also known as pipelined ADC).

[0002] Reference is made to FIG. 1, which is the circuit diagram of a multiplying digital-to-analog converter (MDAC). The MDAC 100 is a 1.5-bit MDAC, which has an input terminal Vinp, an input terminal Vinn, an output terminal Vp2, and an output terminal Vn2. The MDAC 100 includes an analog-to-digital converter (ADC) 110, a selection circuit 120, a sampling and amplifying circuit 130p, a sampling and amplifying circuit 130n, and an operational amplifier 140.

[0003] When the MDAC 100 is applied to a pipeline ADC (also known as pipelined ADC), the ADC 110 is the sub-ADC of the pipeline ADC. The ADC 110 is coupled to the input terminals Vinp and Vinn and configured to generate the selection signal SEL according to the input signals Vsp and Vsn. The input signal Vsp (=Vdc+dV) and the input signal Vsn (=Vdc−dV) may be a differential signal pair, where Vdc is the common-mode voltage of the two, and dV is the signal component.

[0004] The selection circuit 120 is coupled to the ADC 110 and configured to determine the reference voltages VR1 and VR2 according to the selection signal SEL from multiple preset voltages (including, but not limited to, the preset voltage Vx, the preset voltage Vy, and the common-mode voltage Vcm of the preset voltages Vx and Vy) and to provide the reference voltages VR1 and VR2 to the sampling and amplifying circuits 130p and 130n, respectively. The preset voltage Vx may be Vcm+Vz, and the preset voltage Vy may be Vcm−Vz, where Vz is a direct current (DC) voltage.

[0005] The sampling and amplifying circuits 130p and 130n each include two capacitors (including the capacitor C1a or the capacitor C1b) and six switches. The sampling and amplifying circuit 130p (sampling and amplifying circuit 130n) samples the input signal Vsp (input signal Vsn) in the sampling phase and amplifies the signal component dV of the input signal Vsp (input signal Vsn) in the amplifying phase according to the reference voltage VR1 (reference voltage VR2) and the reference voltage Vref. As the operational details of the MDAC 100 are well known to people having ordinary skill in the art, further elaboration is omitted for brevity here.

[0006] Reference is made to FIG. 2, which is the circuit diagram of the conventional MDAC. The MDAC 200 is a 2.5-bit MDAC, which includes an ADC 210, a selection circuit 220, a sampling and amplifying circuit 230p, a sampling and amplifying circuit 230n, and an operational amplifier 240.

[0007] The sampling and amplifying circuit 230p includes four capacitors (including a capacitor C1a, a capacitor C2a, and a capacitor C3a) and ten switches. The sampling and amplifying circuit 230n is the differential counterpart of the sampling and amplifying circuit 230p and also includes four capacitors and ten switches (not shown). In the amplification phase, the capacitors C1a, C2a, and C3a each receive one of the preset voltage Vx, the preset voltage Vy, and the common-mode voltage Vcm. As the operational details of the MDAC 200 are well known to people having ordinary skill in the art, further elaboration is omitted for brevity here.

[0008] Because the feedback factor of the MDACs 100 and 200 is not large enough (0.5 and 0.25, respectively), the area and power consumption of the operational amplifiers 140 and 240 are quite considerable, resulting in the circuit being uncompetitive.

[0009] Furthermore, due to the typically large capacitance value of the capacitors in the sampling and amplifying circuits 130p, 130n, 230p, and 230n, these capacitors are not easily driven by the reference voltage VR1, the reference voltage VR2, the preset voltage Vx, the preset voltage Vy, or the common-mode voltage Vcm. However, if the driving capability of the reference voltages VR1 and VR2 is enhanced to drive these capacitors, the overall power consumption of the MDAC 100 and the MDAC 200 will increase.

[0010] In view of the issues of the prior art, an object of the present invention is to provide a multiplying digital-to-analog converter (MDAC), so as to make an improvement to the prior art.

[0011] According to one aspect of the present invention, an MDAC is provided. The MDAC has a first input terminal, a second input terminal, a first output terminal, and a second output terminal. The first input terminal and the second input terminal respectively receive a first input signal and a second input signal. The first input signal is a common-mode voltage minus a signal component, and the second input signal is the common-mode voltage plus the signal component. The MDAC includes an analog-to-digital converter (ADC), a selection circuit, an operational amplifier, a first switched capacitor (SC) circuit, a second SC circuit, a first switch, a second switch, a first load capacitor, and a second load capacitor. The ADC is configured to generate a selection signal according to the first input signal and the second input signal. The selection circuit is coupled to the ADC and configured to generate a first reference voltage and a second reference voltage according to the selection signal. The operational amplifier has an input port and an output port. The first SC circuit is coupled to the first input terminal, the second input terminal, the input port, and the output port and configured to amplify the signal component. The second SC circuit is coupled to the first input terminal, the second input terminal, the input port, and the output port and configured to amplify the signal component. The first switch is coupled to the first output terminal and receives the second reference voltage. The second switch is coupled to the second output terminal and receives the first reference voltage. The first load capacitor is coupled to the output port and receives the second reference voltage through the first switch. The second load capacitor is coupled to the output port and receives the first reference voltage through the second switch.

[0012] The technical means embodied in the embodiments of the present invention can solve at least one of the problems of the prior art. Therefore, compared to the prior art, the present invention can effectively reduce the circuit area and power consumption.

[0013] These and other objectives of the present invention no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiments with reference to the various figures and drawings.

[0021] The following description is written by referring to terms of this technical field. If any term is defined in this specification, such term should be interpreted accordingly. In addition, the connection between objects or events in the below-described embodiments can be direct or indirect provided that these embodiments are practicable under such connection. Said “indirect” means that an intermediate object or a physical space exists between the objects, or an intermediate event or a time interval exists between the events.

[0022] The disclosure herein includes multiplying digital-to-analog converters (MDACs). On account of that some or all elements of the MDAC could be known, the detail of such elements is omitted provided that such detail has little to do with the features of this disclosure, and that this omission nowhere dissatisfies the specification and enablement requirements. A person having ordinary skill in the art can choose components or steps equivalent to those described in this specification to carry out the present invention, which means that the scope of this invention is not limited to the embodiments in the specification.

[0023] In the following description, signals are active-high, which means that signals are active at high levels and inactive at low levels, and that asserting/de-asserting a signal means setting the signal high/low. This is for the purpose of explanation, not for limiting the scope of the invention. In other words, in an alternative implementation, signals can be active-low, which means that signals are active at low levels and inactive at high levels, and that asserting/de-asserting a signal means setting the signal low/high. A level transition or a logic level transition means that a signal changes from an asserted (active) state to a de-asserted (inactive) state, or from a de-asserted (inactive) state to an asserted (active) state.

[0024] Reference is made to FIG. 3, which is a circuit diagram of an MDAC according to an embodiment of the present invention. The MDAC 300 has an input terminal Vin1 and an input terminal Vin2 and includes an analog-to-digital converter (ADC) 310, a selection circuit 320, an operational amplifier 330, a load capacitor CLp, a load capacitor CLn, a switched capacitor (SC) circuit 340p, an SC circuit 340n, a switch Ss4p, and a switch Ss4n. The SC circuit 340p is coupled or electrically connected to the input terminals Vin1 and Vin2 and includes a capacitor C1p, a switch Ss0p, a switch Ss1p, a switch Ss2p, and a switch Ss3p. The SC circuit 340n is coupled or electrically connected to the input terminals Vin1 and Vin2 and includes a capacitor C1n, a switch Ss0n, a switch Ss1n, a switch Ss2n, and a switch Ss3n.

[0025] The input terminals Vin1 and Vin2 receive the input signals Vsn and Vsp, respectively. The input signal Vsp (=Vdc+dV) and the input signal Vsn (=Vdc-dV) may be a differential signal pair, where Vdc is the common-mode voltage of the two, and dV is the signal component. The SC circuits 340p and 340n are used to amplify the signal component dV.

[0026] The two terminals of the capacitor C1p (capacitor C1n) are a node N1p (node N1n) and a node N2p (node N2n), respectively.

[0027] The operational amplifier 330 has an input port 332 and an output port 334. The input port 332 includes an input node Vp0 and an input node Vn0, which are respectively the inverting input terminal and the non-inverting input terminal of the operational amplifier 330. The output port 334 includes an output node Vp1 and an output node Vn1, which are respectively the non-inverting output terminal and the inverting output terminal of the operational amplifier 330. The signal (e.g., voltage) at the output node Vp1 (output node Vn1) is coupled or outputted to the output terminal Vp2 (output terminal Vn2) through the load capacitor CLp (load capacitor CLn). In some embodiments, the output terminals Vp2 and Vn2 can be the input terminals of a next stage circuit.

[0028] The SC circuit 340p is further coupled or electrically connected to the input port 332 (more specifically, the input node Vp0) and the output port 334 (more specifically, the output node Vp1). The SC circuit 340n is further coupled or electrically connected to the input port 332 (more specifically, the input node Vn0) and the output port 334 (more specifically, the output node Vn1).

[0029] The two terminals of the load capacitor CLp (load capacitor CLn) are the output port 334 (more specifically, the output node Vp1 (output node Vn1)) and the output terminal Vp2 (output terminal Vn2), respectively.

[0030] One terminal of the switch Ss0p (switch Ss0n) is coupled or electrically connected to the input terminal Vin1 (input terminal Vin2) (i.e., receiving the input signal Vsn (input signal Vsp)); the other terminal of the switch Ss0p (switch Ss0n) is coupled or electrically connected to the node N1p (node N1n).

[0031] One terminal of the switch Ss1p (switch Ss1n) is coupled or electrically connected to the input terminal Vin2 (input terminal Vin1); the other terminal of the switch Ss1p (switch Ss1n) is coupled or electrically connected to the node N2p (node N2n).

[0032] One terminal of the switch Ss2p (switch Ss2n) is coupled or electrically connected to the node N1p (node N1n); the other terminal of the switch Ss2p (switch Ss2n) is coupled or electrically connected to the input port 332 (more specifically, the input node Vp0 (input node Vn0)).

[0033] One terminal of the switch Ss3p (switch Ss3n) is coupled or electrically connected to the node N2p (node N2n); the other terminal of the switch Ss3p (switch Ss3n) is coupled or electrically connected to the output port 334 (more specifically, the output node Vp1 (output node Vn1)).

[0034] One terminal of the switch Ss4p (switch Ss4n) is coupled or electrically connected to the output terminal Vp2 (output terminal Vn2); the other terminal of the switch Ss4p (switch Ss4n) receives the reference voltage VR2 (reference voltage VR1) (i.e., coupled or electrically connected to the selection circuit 320).

[0035] When the MDAC 300 is applied to a pipeline analog-to-digital converter (pipeline ADC, also known as pipelined ADC), the ADC 310 is the sub-ADC of the pipeline ADC. The ADC 310 is coupled or electrically connected to the input terminals Vin1 and Vin2 and generates the selection signal SEL according to the input signals Vsp and Vsn.

[0036] The selection circuit 320 is coupled or electrically connected to the ADC 310. The functions of the ADC 310 and the selection circuit 320 are similar or substantially identical to those of the ADC 110 and the selection circuit 120, and therefore further elaboration is omitted for brevity here.

[0037] Reference is made to FIG. 4, which shows the waveform of the clocks of the present invention. The clocks CLK1, CLK2, and CLK3 are not at the first level (e.g., high level) at the same time.

[0038] When the clock CLK1 is at the first level (second level), the switches Ss0p, Ss0n, Ss1p, and Ss1n are turned on (turned off). When the clock CLK3 is at the first level (second level), the switches Ss2p, Ss2n, Ss3p, Ss3n, Ss4p, and Ss4n are turned on (turned off).

[0039] During the phase Φ1 (i.e., when the clock CLK1 is at the first level and the clocks CLK2 and CLK3 are at the second level (e.g., low level)), the switches Ss0p, Ss0n, Ss1p, and Ss1n are turned on, and the switches Ss2p, Ss2n, Ss3p, Ss3n, Ss4p, and Ss4n are turned off, so that the capacitors C1p and C1n sample the input signals Vsn and Vsp. When the phase Φ1 ends, the voltage Vxp across the capacitor C1p and the voltage Vxn across the capacitor C1n are 2 dV and −2 dV, respectively (in other words, |Vxp|=|Vxn|=2 dV).

[0040] During the phase Φb (i.e., when the clock CLK2 is at the first level, and the clocks CLK1 and CLK3 are at the second level), the ADC 310 generates the selection signal SEL, and the selection circuit 320 generates the reference voltages VR1 and VR2 according to the selection signal SEL.

[0041] During the phase Φ2 (i.e., when the clock CLK3 is at the first level, and the clocks CLK1 and CLK2 are at the second level), the switches Ss0p, Ss0n, Ss1p, and Ss1n are turned off, and the switches Ss2p, Ss2n, Ss3p, Ss3n, Ss4p, and Ss4n are turned on, so that the voltage Vxp across the capacitor C1p and the voltage Vxn across the capacitor C1n are applied to the output port 334 of the operational amplifier 330 (more specifically, the output node Vp1 and the output node Vn1), and the reference voltages VR2 and VR1 are applied to the output terminals Vp2 and Vn2, respectively.

[0042] It should be noted that the length of the phase Φ1 can be equal to or not equal to the length of the phase Φ2.

[0043] As is known from the above discussion to people having ordinary skill in the art, the effect achieved by the MDAC 300 is equivalent to the effect achieved by the MDAC 100, so the MDAC 300 is also a 1.5-bit MDAC. Because the feedback factor (1) of the MDAC 300 is twice the feedback factor (0.5) of the MDAC 100, the area and power consumption of the operational amplifier 330 can be effectively reduced. This advantage can greatly enhance the competitiveness of the MDAC 300.

[0044] In addition, please refer to both FIG. 1 and FIG. 3. The MDAC 100 uses four capacitors to sample the input signals Vsn and Vsp, while the MDAC 300 uses only two capacitors (the capacitors C1p and C1n) to sample the input signals Vsn and Vsp. That is to say, the MDAC of the present invention uses fewer sampling capacitors, which can reduce the circuit area and/or cost.

[0045] Reference is made to FIG. 5, which is a schematic diagram of the configurations of the reference voltages VR1 and VR2. The configuration of the reference voltages VR1 and VR2 of the MDAC 300 is the same as that of the MDAC 100. However, it should be noted that in the MDAC 100, the reference voltages VR1 and VR2 are applied to the inverting input terminal and the non-inverting input terminal of the operational amplifier 140, respectively, while in the MDAC 300, the reference voltages VR1 and VR2 are applied to the inverting output terminal and the non-inverting output terminal of the operational amplifier 330, respectively.

[0046] Reference is made to FIG. 6, which is the circuit diagram of an MDAC according to another embodiment of the present invention. The MDAC 600 is a 2.5-bit MDAC. In comparison with the MDAC 300, the MDAC 600 further includes an SC circuit 640p and an SC circuit 640n, and the ADC 310 and the selection circuit 320 are replaced by the ADC 610 and the selection circuit 620, respectively.

[0047] The function of the ADC 610 is similar to that of the ADC 210 from FIG. 2, so further elaboration is omitted for brevity here. The selection circuit 620 is coupled or electrically connected to the ADC 610, determines the reference voltages VR1, VR2, VR3, and VR4 according to the selection signal SEL from multiple preset voltages (including, but not limited to, the preset voltage Vx, the preset voltage Vy, the common-mode voltage Vcm, 2 times Vx (2 Vx), and 2 times Vy (2 Vy)), and provides the reference voltages VR1, VR2, VR3, and VR4 to the load capacitor CLn, the load capacitor CLp, the capacitor C2n, and the capacitor C2p, respectively. The design of the selection circuit 620 will be detailed below with reference to FIG. 7A and FIG. 7B.

[0048] The SC circuit 640p (SC circuit 640n) includes the capacitor C2p (capacitor C2n), the switch Ss5p (switch Ss5n), the switch Ss6p (switch Ss6n), the switch Ss7p (switch Ss7n), and the switch Ss8p (switch Ss8n).

[0049] The two terminals of the capacitor C2p (capacitor C2n) are a node N3p (node N3n) and a node N4p (node N4n), respectively.

[0050] One terminal of the switch Ss5p (switch Ss5n) is coupled or electrically connected to the input terminal Vin2 (input terminal Vin1); the other terminal of the switch Ss5p (switch Ss5n) is coupled or electrically connected to the node N3p (node N3n).

[0051] One terminal of the switch Ss6p (switch Ss6n) is coupled or electrically connected to the input terminal Vin1 (input terminal Vin2); the other terminal of the switch Ss6p (switch Ss6n) is coupled or electrically connected to the node N4p (node N4n).

[0052] One terminal of the switch Ss7p (switch Ss7n) is coupled or electrically connected to the node N3p (node N3n); the other terminal of the switch Ss7p (switch Ss7n) receives the reference voltage VR4 (reference voltage VR3) (i.e., coupled or electrically connected to the selection circuit 620).

[0053] One terminal of the switch Ss8p (switch Ss8n) is coupled or electrically connected to the node N4p (node N4n); the other terminal of the switch Ss8p (switch Ss8n) is coupled or electrically connected to the input port 332 (more specifically, the input node Vp0 (input node Vn0)).

[0054] Reference is made to both FIG. 4 and FIG. 6. When the clock CLK1 is at the first level (second level), the switches Ss5p, Ss5n, Ss6p, and Ss6n are turned on (turned off). When the clock CLK3 is at the first level (second level), the switches Ss7p, Ss7n, Ss8p, and Ss8n are turned on (turned off).

[0055] During the phase Φ1, the switches Ss5p, Ss5n, Ss6p, and Ss6n are turned on, and the switches Ss7p, Ss7n, Ss8p, and Ss8n are turned off, so that the capacitors C2p and C2n sample the input signals Vsp and Vsn. Similarly, when the phase Φ1 ends, the absolute value of the voltage Vyp across the capacitor C2p and the absolute value of the voltage Vyn across the capacitor C2n are both 2 dV (in other words, |Vyp|=|Vyn|=2 dV).

[0056] During the phase Φb, the ADC 610 generates the selection signal SEL, and the selection circuit 620 generates the reference voltages VR1, VR2, VR3, and VR4 according to the selection signal SEL.

[0057] During the phase Φ2, the switches Ss5p, Ss5n, Ss6p, and Ss6n are turned off, while the switches Ss7p, Ss7n, Ss8p, and Ss8n are turned on. This configuration connects the capacitors C1p and C2p in series, as well as the capacitors C1n and C2n in series. Consequently, the voltages across the capacitors C1p and C2p (each 2 dV, totaling 4 dV) and the voltages across the capacitors C1n and C2n (each −2 dV, totaling −4 dV) are applied to the output port 334 of the operational amplifier 330 (more specifically, to the output nodes Vp1 and Vn1).

[0058] Reference is made to FIG. 7A and FIG. 7B. FIG. 7A shows the configurations of the reference voltages in the MDAC 200 from FIG. 2 (it should be noted that the capacitors C1b, C2b, and C3b are included in the sampling and amplifying circuit 230n). FIG. 7B shows the configurations of the reference voltages in the MDAC 600 from FIG. 6. The configurations 1 to 7 in FIG. 7A correspond to the configurations 1 to 7 in FIG. 7B, respectively. Therefore, people having ordinary skill in the art can design and the selection circuit 620 according to FIG. 7A and FIG. 7B. For example, in reference to configuration 4, the capacitors C1a to C3a and the capacitors C1b to C3b in FIG. 2 receive the voltages Vx, Vx, Vcm, Vy, Vy, and Vcm, respectively; if the reference voltages VR1 to VR4 in FIG. 6 are set to Vy, Vx, Vy, and Vx, respectively, then the MDAC 600 in FIG. 6 is equivalent to the MDAC 200.

[0059] As is known from the above discussion to people having ordinary skill in the art, the effect achieved by the MDAC 600 is equivalent to the effect achieved by the MDAC 200. Because the feedback factor (0.5) of the MDAC 600 is twice the feedback factor (0.25) of the MDAC 200, the area and power consumption of the operational amplifier 330 can be effectively reduced. This advantage can greatly enhance the competitiveness of the MDAC 600.

[0060] In addition, please refer to both FIG. 2 and FIG. 6. The MDAC 200 uses eight capacitors to sample the input signals Vsn and Vsp (four capacitors in the sampling and amplifying circuit 230p, and the other four in the sampling and amplifying circuit 230n), while the MDAC 600 uses only four capacitors (capacitors C1p, C1n, C2p, and C2n) to sample the input signals Vsn and Vsp. That is to say, the MDAC of the present invention uses fewer sampling capacitors, which can reduce the circuit area and/or cost.

[0061] The 1.5-bit MDAC and the 2.5-bit MDAC are intended to illustrate the invention by way of example and not to limit the scope of the claimed invention. People having ordinary skill in the art may apply the present invention to MDACs of more bits (where the number of preset voltages increases accordingly) in accordance with the foregoing discussions.

[0062] Note that the shape, size, and ratio of any element in the disclosed figures are exemplary for understanding, not for limiting the scope of this invention.

[0063] The aforementioned descriptions represent merely the preferred embodiments of the present invention, without any intention to limit the scope of the present invention thereto. Various equivalent changes, alterations, or modifications based on the claims of the present invention are all consequently viewed as being embraced by the scope of the present invention.