Switched capacitor circuit and capacitive digital-to-analog converter

Abstract

The present invention discloses a switched capacitor circuit and a capacitive digital-to-analog converter. The switched capacitor circuit includes an output capacitor, a first transmission switch, a first reference voltage generator, a second transmission switch, a second reference voltage generator, and a charge compensation circuit. A first terminal of the output capacitor is coupled to an output terminal of the switched capacitor circuit; a second terminal of the output capacitor is coupled to a reference node. The first transmission switch is coupled to the reference node. The first reference voltage generator is coupled to the first transmission switch. The second transmission switch is coupled to the reference node. The second reference voltage generator is coupled to the second transmission switch. The charge compensation circuit is coupled to the reference node.

Description

Technical Field

[0001] The present invention relates to a switched capacitor circuit, and more particularly to a switched capacitor circuit with a charge compensation solution. Background Art

[0002] Switched capacitor circuits are widely used in a variety of circuit systems to generate switched output voltages. By controlling the switches in the switched capacitor circuit to open or close, different input voltages can be coupled to the output terminal through the output capacitor of the switched capacitor circuit, allowing the output voltage to switch between different voltage levels. Generally, each input voltage is provided by a reference voltage generator, which supplies charge to charge or discharge the output capacitor, thereby driving the output voltage switching. Therefore, the output capability of the reference voltage generator determines the stable rate of voltage switching. To reduce the output voltage settling time, the reference voltage generator must have sufficient output capability. However, greater output capability often comes with increased power consumption. Therefore, the output capability requirement and power consumption issues become limitations in the design of reference voltage generators. Summary of the Invention

[0003] Therefore, the primary objective of the present invention is to provide a switched capacitor circuit with a charge compensation scheme. A charge compensation circuit is provided to supply charge to charge or discharge the output capacitor. This improves the settling rate of the switched capacitor circuit and reduces the burden on the output capability of the reference voltage generator, thereby simplifying the design of the reference voltage generator.

[0004] One embodiment of the present invention discloses a switched capacitor circuit, comprising an output capacitor, a first transmission switch, a first reference voltage generator, a second transmission switch, a second reference voltage generator, and a charge compensation circuit. The output capacitor comprises a first terminal and a second terminal, wherein the first terminal is coupled to an output terminal of the switched capacitor circuit, and the second terminal is coupled to a reference node. The first transmission switch is coupled to the reference node. The first reference voltage generator is coupled to the first transmission switch. The second transmission switch is coupled to the reference node. The second reference voltage generator is coupled to the second transmission switch. The charge compensation circuit is coupled to the reference node.

[0005] Another embodiment of the present invention discloses a capacitive digital-to-analog converter (DAC), comprising a plurality of switched capacitor circuits, each of which includes an output capacitor, a first transmission switch, a second transmission switch, and a charge compensation circuit. The output capacitor includes a first terminal and a second terminal, wherein the first terminal is coupled to an output terminal of the DAC and the second terminal is coupled to a reference node. The first transmission switch is coupled between the reference node and a first reference voltage generator. The second transmission switch is coupled between the reference node and a second reference voltage generator. The charge compensation circuit is coupled to the reference node. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Figure 1 Schematic diagram of a general switched capacitor circuit.

[0007] Figure 2 An exemplary waveform diagram of switched capacitor circuit operation.

[0008] Figure 3 and 4 FIG. 1 is a schematic diagram of a switched capacitor circuit according to an embodiment of the present invention.

[0009] Figure 5 and 6 FIG. 1 is a schematic diagram of an implementation of a switched capacitor circuit with a charge compensation circuit according to an embodiment of the present invention.

[0010] Figure 7 for Figure 5 and 6 Example waveform diagram of the switched capacitor circuit operation in .

[0011] Figure 8 and 9 FIG. 4 is a schematic diagram of another implementation of a switched capacitor circuit with a charge compensation circuit according to an embodiment of the present invention.

[0012] Figure 10 for Figure 8 and 9 Example waveform diagram of the switched capacitor circuit operation in .

[0013] Figure 11 and 12 FIG. 4 is a schematic diagram of another implementation of a switched capacitor circuit with a charge compensation circuit according to an embodiment of the present invention.

[0014] Figure 13 for Figure 11 and 12 Example waveform diagram of the switched capacitor circuit operation in .

[0015] Figure 14 and 15 FIG. 4 is a schematic diagram of another embodiment of a switched capacitor circuit with a charge compensation circuit according to an embodiment of the present invention.

[0016] Figure 16 Schematic diagram of a general capacitive digital-to-analog converter.

[0017] Figure 17 FIG. 1 is a schematic diagram of a capacitive digital-to-analog converter according to an embodiment of the present invention.

[0018] The description of the accompanying drawings is as follows:

[0019] 10, 30 switched capacitor circuit

[0020] 100 load circuit

[0021] C A 、C AN ~C A0 Output capacitor

[0022] S A 、S B 、S NA ~S 0A 、S NB ~S 0B Transmission switch

[0023] BUF A BUF B Reference voltage generator

[0024] V OUT Output voltage

[0025] N R Reference Node

[0026] V A 、V B Voltage

[0027] Q R , Q A , Q C Charge

[0028] T A 、T B 、T C 、T D Time point

[0029] 300 Charge Compensation Circuit

[0030] V DD 、V SS Supply voltage

[0031] CB Compensation capacitor

[0032] S1, S2, S3 compensation switches

[0033] I1, I2 current sources

[0034] 1600, 1700 Capacitive Digital-to-Analog Converters

[0035] S RESET Reset switch

[0036] V RESET Reset voltage DETAILED DESCRIPTION

[0037] Please refer to Figure 1 , Figure 1 FIG. 1 is a schematic diagram of a general switched capacitor circuit 10. Figure 1 As shown, the switched capacitor circuit 10 includes an output capacitor C A , Transmission switch S A and S B , and reference voltage generator BUF A and BUF B For the convenience of explanation, Figure 1 A load circuit 100 is also shown, which can be included in the switched capacitor circuit 10 or independent of the switched capacitor circuit 10. Generally speaking, the load circuit 100 refers to any circuit device or module that can operate by receiving the output switching voltage of the switched capacitor circuit 10.

[0038] In the switched capacitor circuit 10, the output capacitor C A Can be used to provide an output voltage V OUT The load circuit 100 is provided to realize various applications. Specifically, the output capacitor C A The first end of the output capacitor C is coupled to the output end of the switched capacitor circuit 10. A The second end is coupled to a reference node N R . Transmission switch S A and S B Through the reference node N R Coupled to the output capacitor C A , transmission switch S A and S B The other end is coupled to the reference voltage generator BUF A and BUF B . Transmission switch S A and S B It can be realized by a transmission gate, a transistor, or any circuit element or module. Each reference voltage generator BUFA and BUF B Both can be realized by an operational amplifier connected in a buffer manner, wherein the operational amplifier can be used to provide output capability (or driving capability) to output a specific voltage. In this example, the reference voltage generator BUF A and transmission switch S A Can be used to output a voltage V A , reference voltage generator BUF B and transmission switch S B Can be used to output a voltage V B .

[0039] Figure 2 is an exemplary waveform diagram of the operation of the switched capacitor circuit 10, which shows the operation of the transmission switch S A and S B The waveform of the control signal. In order to make the output capacitor C A The first end outputs the switched output voltage V OUT , which can control the output capacitance C A The second end passes through the reference node N R Alternating receiving voltage V A and V B By switching S A and S B Control, reference node N R The voltage V A Switch to voltage V B Or from the voltage V B Switch to voltage V A During the switching operation, the reference voltage generator BUF A and BUF B It can be used to compare the reference node N R Charge or discharge to charge and discharge the output capacitor C A of charge.

[0040] like Figure 2 As shown, for transmission switch S A and S B The control signal is a complementary signal, which ensures that the reference node N R At each time point, the voltage V A and V B In this example, the control signal at a high level can turn on (conduct) the corresponding switch, and at a low level can turn off (disconnect) the corresponding switch. At time point T A On, switch S A Close the switch S B Open, so that the reference node N R Receive voltage V BThen, at time T B On, switch S A Turn on the switch S B Close, so that the reference node N R Receive voltage V A Assuming the voltage V A Higher than the voltage V B , when the reference node N R From the lower voltage V B Switching to a higher voltage V A Time (such as from T A to T B ), used to adjust the output capacitor C A The charge can be completely charged by the reference voltage generator BUF A For example, if the reference voltage generator BUF A The amount of charge provided is Q R , and drive reference node N R From the voltage V B Rising to voltage V A The required charge is Q A , then the charge Q R Equal to Q A (i.e. Q R =Q A ).

[0041] From time point T B At time T C During the period, the switch S A and S B The state of the output capacitor C A The second end and reference node N R Maintained at voltage V A , no need to charge or discharge operations.

[0042] At time point T C On, switch S A Turn on the switch S B Close, so that the reference node N R Receive voltage V A Then, at time T D On, switch S A Close the switch S B Open, so that the reference node N R Receive voltage V B When the reference node N R From the higher voltage V A Switching to a lower voltage V B Time (such as from T C to T D), from the output capacitor C A The charge can be completely passed through the reference voltage generator BUF B For example, if the reference voltage generator BUF B The amount of charge released is Q R , and drive reference node N R From the voltage V A Drop to voltage V B The required charge is Q A , then the charge Q R Equal to Q A (i.e. Q R =Q A ).

[0043] At time point T A to T B and time point T C to T D During the switching process, the reference voltage generator BUF A Can supply the required charge to the output capacitor C A , and the reference voltage generator BUF B The output capacitor C A To achieve an output voltage V OUT The fast switching should accelerate the output capacitor C A Therefore, the reference voltage generator BUF A and BUF B It must have a stronger output capability so that the reference node N R The voltage of the reference voltage generator BUF can reach steady state more quickly during the switching process. A and BUF B The powerful output capability is often accompanied by large current consumption and high power requirements, and there are design difficulties.

[0044] Please refer to Figure 3 and 4 , Figure 3 and 4 FIG. 1 is a schematic diagram of a switched capacitor circuit 30 according to an embodiment of the present invention. Figure 3 and 4 As shown, the circuit structure of the switched capacitor circuit 30 is similar to Figure 1 The circuit structure of the switched capacitor circuit 10 is shown, so signals or components with similar functions are represented by the same symbols. The difference between the switched capacitor circuit 30 and the switched capacitor circuit 10 is that the switched capacitor circuit 30 further includes a charge compensation circuit 300. The charge compensation circuit 300 is coupled to the reference node N R , can be used to supply part of the charge to the output capacitor C Aor from the output capacitor C A Release part of the charge to reduce the reference voltage generator BUF A and BUF B The operation of the charge compensation circuit 300 can be based on the reference node N R Specifically, if the reference node N R To switch from a lower voltage (such as V B ) to a higher voltage (such as V A ), the charge compensation circuit 300 can compensate the output capacitor C A Charge and drive reference node N R The voltage of the reference node N R To get a higher voltage (such as V A ) to a lower voltage (such as V B ), the charge compensation circuit 300 can compensate the output capacitor C A Discharge and drive the reference node N R The voltage drops.

[0045] In one embodiment, the charge compensation circuit 300 may be coupled to a first power supply node for receiving a first supply voltage V DD , the first supply voltage V DD The charge compensation circuit 300 can also be coupled to a second power supply node for receiving a second supply voltage V SS , the second supply voltage V SS It can be a negative supply voltage or a ground voltage of the circuit system. Generally speaking, the first supply voltage V DD It can be the highest voltage in the circuit system, the second supply voltage V SS It can be the lowest voltage in the circuit system. Supply voltage V DD and V SS It is usually provided by the most powerful voltage source in the circuit system, and has the ability to quickly generate or absorb charge. Therefore, it is preferably used to quickly drive the switched capacitor circuit 30 to output the voltage V OUT Switch.

[0046] Figure 3 The charging operation of the charge compensation circuit 300 is shown. R To start from a lower voltage V B Switching to a higher voltage V A When (such as Figure 2 T shown A to T B ), can be used to provide a first supply voltage V DD The first power supply node and the reference node N RTherefore, the charge compensation circuit 300 can receive the charge from the first power supply node to compensate the output capacitor C A In this example, the charge from the first power supply node is Q C , since the driving reference node N R From the voltage V B Rising to voltage V A The required charge is Q A , therefore, the reference voltage generator BUF A Used to adjust the output capacitor C A The total charge required for charging is Q R Can be lowered to Q A Minus Q C (i.e. Q R =Q A -Q C ).

[0047] Figure 4 The discharge operation of the charge compensation circuit 300 is shown. R To get a higher voltage V A Switching to a lower voltage V B When (such as Figure 2 T shown C to T D ), can be used to provide a second supply voltage V SS The second power supply node and the reference node N R Therefore, the charge compensation circuit 300 can discharge the charge to the second power supply node to compensate the output capacitor C A Similarly, the amount of charge released to the second power supply node is Q C , since the driving reference node N R From the voltage V A Drop to voltage V B The required charge is Q A , therefore, the reference voltage generator BUF B Used to adjust the output capacitor C A The total charge required for discharge Q R Can be lowered to Q A Minus Q C (i.e. Q R =Q A -Q C ).

[0048] In this case, the reference voltage generator BUF can be reduced A and BUF B The amount of charge processed thereby reduces the reference voltage generator BUF Aand BUF B The demand for output capacity. Since the charge compensation circuit 300 can provide A The partial charge, therefore, in the reference voltage generator BUF A and BUF B Under the same output capacity, the output voltage V OUT In this way, the operating speed of the switched capacitor circuit 30 can be improved.

[0049] Please refer to Figure 5 and 6 , Figure 5 and 6 FIG. 1 is a schematic diagram of an embodiment of a switch capacitor circuit 30 having a charge compensation circuit 300 according to an embodiment of the present invention. Figure 5 and 6 As shown, the charge compensation circuit 300 may include a compensation capacitor C B And two compensation switches S1 and S2. Compensation capacitor C B The first end is coupled to the reference node N R , compensation capacitor C B The second end of is coupled to the compensation switches S1 and S2. The compensation switch S1 is also coupled to the first power supply node for receiving the first supply voltage V DD The compensation switch S2 is also coupled to the second power supply node for receiving the second supply voltage V SS .

[0050] Figure 7 for Figure 5 and 6 An exemplary waveform diagram of the operation of the switched capacitor circuit 30 in FIG. 1 shows the operation of the switching capacitor circuit 30 for transmitting the switch S A and S B And the waveform of the control signal of the compensation switch S1 and S2, wherein the control signal at a high level can turn on (conduct) the corresponding switch, and at a low level can turn off (disconnect) the corresponding switch. A and S B The detailed operation mode is similar to the transmission switch S in the above-mentioned switched capacitor circuit 10. A and S B The control signals for compensating switches S1 and S2 are complementary signals, which can ensure that the compensation capacitor C B At each time point, the supply voltage V DD and V SS In this example, the control signal of the compensation switch S1 is the same as the control signal of the transmission switch S A The control signal is the same, so when the transmission switch S AOpen and reference node N R From the reference voltage generator BUF A Receive voltage V A When the compensation switch S1 is turned on, the compensation capacitor C B Can receive the first supply voltage V DD Similarly, the control signal of the compensation switch S2 is the same as that of the transmission switch S B The control signal is the same, so when the transmission switch S B Open and reference node N R From the reference voltage generator BUF B Receive voltage V B When the compensation switch S2 is turned on, the compensation capacitor C B Can receive the second supply voltage V SS .

[0051] Please continue to refer to Figure 7 Matching Figure 5 As shown, Figure 5 FIG. 3 shows the charging operation of the charge compensation circuit 300. At time point T A On the other hand, the switch S1 is closed and the switch S2 is opened, so that the compensation capacitor C B The second end is coupled to the second power supply node to receive the second supply voltage V SS Then, at time T B On the other hand, the switch S1 is turned on and the switch S2 is turned off, so that the compensation capacitor C B The second end is coupled to the first power supply node to receive the first supply voltage V DD Therefore, from the time point T A to T B During the period, the reference node N R From the voltage V B Switch to voltage V A , while compensating the capacitor C B The second end is supplied from the second supply voltage V SS Switch to the first supply voltage V DD , compensation capacitor C B The voltage level at the terminal is increased to provide charge to drive the reference node N R The voltage rises.

[0052] In this case, the charge compensation circuit 300 can use the compensation capacitor C B The coupling to supply charge (ie Q C ) to the output capacitor C A The remaining charge is then fed from the reference voltage generator BUF A Therefore, the reference voltage generator BUF A The amount of charge required (i.e. Q R) can be reduced to drive the output capacitor C A The total charge required (i.e. Q A ) minus the compensation charge from the charge compensation circuit 300, i.e. Q R =Q A -Q C In this way, the reference voltage generator BUF A No need for larger output capacity, can reduce the reference voltage generator BUF A At the same time, due to the powerful output capability of the charge compensation circuit 300, the voltage stabilization rate of the switched capacitor circuit 30 can be improved.

[0053] In this example, the compensation capacitor C B The voltage of the second terminal is V SS Rising to the first supply voltage V DD According to the capacitance formula Q=C×ΔV, by compensating the capacitance C B The coupled charge (Q) is equal to the compensation capacitance C B The capacitance value (C) multiplied by the compensation capacitance C B The received voltage difference (ΔV). Therefore, based on the compensation capacitor C B The capacitance value and / or voltage change can effectively control the compensation capacitor C B For example, the charge amount Q supplied by the charge compensation circuit 300 is C Can be set close to the drive output capacitance C A The total charge required makes the reference voltage generator BUF A In another embodiment, the first supply voltage V DD and / or the second supply voltage V SS The charge compensation circuit 300 can be provided by a specific voltage generator having a preset voltage to control the charge compensation circuit 300 to output an appropriate amount of charge to the output capacitor C A In this case, the first supply voltage V DD and / or the second supply voltage V SS It does not need to be the highest or lowest voltage level in the circuit system.

[0054] Please continue to refer to Figure 7 Matching Figure 6 As shown, Figure 6 FIG. 3 shows the discharge operation of the charge compensation circuit 300. At time point T C On the other hand, the switch S1 is turned on and the switch S2 is turned off, so that the compensation capacitor C B The second end is coupled to the first power supply node to receive the first supply voltage V DD Then, at time T DWhen the switch S1 is closed and the switch S2 is opened, the compensation capacitor C B The second end is coupled to the second power supply node to receive the second supply voltage V SS Therefore, from the time point T C to T D During the period, the reference node N R From the voltage V A Switch to voltage V B , while compensating the capacitor C B The second end is supplied from the first voltage V DD Switch to the second supply voltage V SS , compensation capacitor C B The voltage level at the terminal drops to release the charge to drive the reference node N R The voltage drops.

[0055] In this case, the charge compensation circuit 300 can use the compensation capacitor C B The coupling from the output capacitor C A Absorbed charge (i.e. Q C ), the remaining charge then passes through the reference voltage generator BUF B Therefore, the reference voltage generator BUF is required. B The amount of charge released (i.e. Q R ) can be reduced to drive the output capacitor C A The total charge required (i.e. Q A ) minus the compensation charge absorbed by the charge compensation circuit 300, i.e., Q R =Q A -Q C In this way, the reference voltage generator BUF B No need for larger output capacity, can reduce the reference voltage generator BUF B At the same time, due to the powerful output capability of the charge compensation circuit 300, the voltage stabilization rate of the switched capacitor circuit 30 can be improved.

[0056] Please refer to Figure 8 and 9 , Figure 8 and 9 FIG. 1 is a schematic diagram of another embodiment of a switched capacitor circuit 30 having a charge compensation circuit 300 according to an embodiment of the present invention. Figure 8 and 9 As shown, in addition to the compensation capacitor C B In addition to the compensation switches S1 and S2, the charge compensation circuit 300 further includes a compensation switch S3 coupled to the reference node N R And compensation capacitor C B In this example, the compensation capacitor C BThe implementation of the compensation switches S1 and S2 and their charge flows is similar to Figure 5 and 6 The embodiments of the present invention are not described here in detail.

[0057] Figure 10 for Figure 8 and 9 An exemplary waveform diagram of the operation of the switched capacitor circuit 30 in FIG. 1 shows the operation of the switching capacitor circuit 30 for transmitting the switch S A and S B And the waveforms of the control signals of the compensation switches S1, S2 and S3, wherein the control signal at a high level can turn on (conduct) the corresponding switch, and at a low level can turn off (disconnect) the corresponding switch. A and S B The detailed operation of the compensation switches S1 and S2 is similar to that of the corresponding switches in the above-mentioned switched capacitor circuit, and will not be described in detail here.

[0058] like Figure 10 As shown, the compensation switch S3 can be used at the reference node N R The voltage on the switch is turned on to connect the compensation capacitor C B With output capacitor C A , at this time, the transmission switch S A and S B And the compensation switches S1 and S2 are both turned on, and the reference node N R The voltage from V B Switch to V A Or from V A Switch to V B When the compensation switch S3 is turned on, the output capacitor C A The required charge can be supplied by the compensation capacitor C B In addition, when these switches are not in transition and the reference node N R During the period when the voltage is kept constant, the compensation switch S3 can be closed.

[0059] As described above, the charge of the charge compensation circuit 300 can be supplied by the first supply voltage V DD Provided and released to the second supply voltage V SS Supply voltage V DD and V SS Usually comes from the global voltage source of the circuit system. This global voltage source can be used to supply voltage to the entire circuit system, so there is often power supply noise that is difficult to ignore. In order to prevent the power supply noise from passing through the compensation capacitor C B The coupling interferes with the reference node N R Preferably, a switch can be provided to isolate the power supply noise on the global voltage source. Therefore, the compensation switch S3 can be provided at the reference node NR The voltage of the switched capacitor circuit 30 is kept constant during the time it is turned off, thereby improving voltage stability.

[0060] Please refer to Figure 11 and 12 , Figure 11 and 12 FIG. 1 is a schematic diagram of another embodiment of a switch capacitor circuit 30 having a charge compensation circuit 300 according to an embodiment of the present invention. Figure 11 and 12 As shown, the charge compensation circuit 300 may include two compensation switches S1 and S2. The compensation switch S1 is coupled to the reference node N R and the first power supply node, for receiving a first supply voltage V DD , the compensation switch S2 is coupled to the reference node N R and the second power supply node, for receiving the second supply voltage V SS .

[0061] Figure 13 for Figure 11 and 12 An exemplary waveform diagram of the operation of the switched capacitor circuit 30 in FIG. 1 shows the operation of the switching capacitor circuit 30 for transmitting the switch S A and S B And the waveform of the control signal of the compensation switch S1 and S2, wherein the control signal at a high level can turn on (conduct) the corresponding switch, and at a low level can turn off (disconnect) the corresponding switch. A and S B The detailed operation mode is similar to the transmission switch S in the above-mentioned switched capacitor circuit 10. A and S B , I will not go into details here.

[0062] Please continue to refer to Figure 13 Matching Figure 11 As shown, Figure 11 FIG. 3 shows the charging operation of the charge compensation circuit 300. At time point T A On, switch S A Close the switch S B Open, so that the reference node N R The voltage is equal to V B At time point T B On, switch S A Turn on the switch S B Close, so that the reference node N R The voltage is equal to V A From time point T A to T B During the period, the reference node N RFrom the lower voltage V B Switching to a higher voltage V A , at this time the compensation switch S1 is turned on for a short period of time, and at the same time the transmission switch S A and S B are all turned off. In this case, the output capacitor C A The reference node N R Can be charged to the first supply voltage V DD Then, at time T B On, switch S A Open and switch S1 closed, reference node N R Coupled to the reference voltage generator BUF A To receive voltage V A .

[0063] In this case, the charge compensation circuit 300 can supply charge (ie, Q C ) to the output capacitor C A , so that the reference node N R Charged to the first supply voltage V DD Assume that the first supply voltage V DD Higher than the voltage V A , reference voltage generator BUF A The output capacitor C needs to be released A The charge to drive the reference node N R From the first supply voltage V DD Drop to voltage V A , the amount of charge released is equal to Q R Therefore, the reference voltage generator BUF is required A The amount of charge released is equal to the compensation charge supplied by the charge compensation circuit 300 minus the amount used to drive the reference node N R From the voltage V B To voltage V A The total charge required (i.e. Q A ), namely Q R =Q C -Q A If the voltage V A Close to the first supply voltage V DD When (that is, the charge Q A Close to Q C ), reference voltage generator BUF A No need for larger output capacity, can reduce the reference voltage generator BUF A At the same time, due to the powerful output capability of the charge compensation circuit 300, the voltage stabilization rate of the switched capacitor circuit 30 can be improved.

[0064] In another embodiment, if the time point T A and T B The pulse length of the compensation switch S1 is shorter, making the reference node N R After the compensation switch S1 is closed, the voltage is lower than the voltage V A When the charge compensation circuit 300 can only supply part of the charge to the output capacitor C A The remaining charge then passes through the reference voltage generator BUF A Provided that the reference node N R Reaching its target voltage V A In this way, the reference voltage generator BUF can also be reduced. A output capability requirements, thereby reducing the reference voltage generator BUF A At the same time, the voltage stabilization rate of the switched capacitor circuit 30 can still be improved.

[0065] Please continue to refer to Figure 13 Matching Figure 12 As shown, Figure 12 FIG. 3 shows the discharge operation of the charge compensation circuit 300. At time point T C On, switch S A Turn on the switch S B Close, so that the reference node N R The voltage is equal to V A At time point T D On, switch S A Close the switch S B Open, so that the reference node N R The voltage is equal to V B From time point T C to T D During the period, the reference node N R From the higher voltage V A Switching to a lower voltage V B At this time, the compensation switch S2 is turned on for a short period of time, and the transmission switch S A and S B are all turned off. In this case, the output capacitor C A The charge on the reference node N R Can be discharged to the second supply voltage V SS Then, at time T D On, switch S B Open and switch S2 closed, reference node N R Coupled to the reference voltage generator BUF B To receive voltage V B .

[0066] In this case, the charge compensation circuit 300 can release the output capacitance C A The charge (i.e. Q C ), so that the reference node N R Discharge to the second supply voltage V SS Assume that the second supply voltage V SS Lower than voltage V B , reference voltage generator BUF B Charge needs to be supplied to the output capacitor C A , to drive the reference node N R From the second supply voltage V SS Rising to voltage V B , the amount of charge supplied is equal to Q R Therefore, it is necessary to use the reference voltage generator BUF B The amount of charge supplied is equal to the amount of charge released by the charge compensation circuit 300 minus the amount of charge used to drive the reference node N R From the voltage V A To voltage V B The total charge required (i.e. Q A ), namely Q R =Q C -Q A If the voltage V B Close to the second supply voltage V SS When (that is, the charge Q A Close to Q C ), reference voltage generator BUF B No need for larger output capacity, can reduce the reference voltage generator BUF B At the same time, due to the powerful output capability of the charge compensation circuit 300, the voltage stabilization rate of the switched capacitor circuit 30 can be improved.

[0067] In another embodiment, if the time point T C and T D The pulse length of the compensation switch S2 is shorter, making the reference node N R After the compensation switch S2 is closed, the voltage is higher than the voltage V B When the charge compensation circuit 300 can only draw the charge from the output capacitor C A Release part of the charge, and the rest of the charge passes through the reference voltage generator BUF B Release, so that the reference node N R Reaching its target voltage V B In this way, the reference voltage generator BUF can also be reduced. B output capability requirements, thereby reducing the reference voltage generator BUF B At the same time, the voltage stabilization rate of the switched capacitor circuit 30 can still be improved.

[0068] Please refer to Figure 14 and 15 , Figure 14 and 15 FIG. 1 is a schematic diagram of another embodiment of a switch capacitor circuit 30 having a charge compensation circuit 300 according to an embodiment of the present invention. Figure 14 and 15 As shown, the charge compensation circuit 300 may include two compensation switches S1 and S2 and two current sources I1 and I2. The compensation switches S1 and S2 are coupled to the reference node N R The current source I1 is coupled between the compensation switch S1 and the first power supply node, and the current source I2 is coupled between the compensation switch S2 and the second power supply node.

[0069] about Figure 14 and 15 The waveform of the switched capacitor circuit 30 operation is similar to Figure 13 The waveform diagram shows the transmission switch S A and S B And the waveform of the control signal of the compensation switch S1 and S2. A and S B The detailed operation mode is similar to the transmission switch S in the above-mentioned switched capacitor circuit 10. A and S B , I will not go into details here.

[0070] Please continue to refer to Figure 13 Matching Figure 14 As shown, Figure 14 FIG. 3 shows the charging operation of the charge compensation circuit 300. At time point T A On, switch S A Close the switch S B Open, so that the reference node N R The voltage is equal to V B At time point T B On, switch S A Turn on the switch S B Close, so that the reference node N R The voltage is equal to V A From time point T A to T B During the period, the reference node N R From the lower voltage V B Switching to a higher voltage V A , at this time the compensation switch S1 is turned on for a short period of time, and at the same time the transmission switch S A and S B are all turned off. In this case, the output capacitor C AThe charge can be received from the current source I1, and the amount of charge received can be determined by the pulse length of the compensation switch S1. B On, switch S A Open and switch S1 closed, reference node N R Coupled to the reference voltage generator BUF A To receive voltage V A At this time, the current source I1 can be disconnected by turning off the switch S1 to avoid additional current consumption.

[0071] In this case, the charge compensation circuit 300 can use the current source I1 to compensate the output capacitor C A Charge to supply charge (i.e. Q C ) to the output capacitor C A The remaining charge is then fed from the reference voltage generator BUF A Therefore, the reference voltage generator BUF A The amount of charge required (i.e. Q R ) can be reduced to drive the output capacitor C A The total charge required (i.e. Q A ) minus the compensation charge from the charge compensation circuit 300, i.e. Q R =Q A -Q C In this way, the reference voltage generator BUF A No need for larger output capacity, can reduce the reference voltage generator BUF A At the same time, due to the powerful output capability of the charge compensation circuit 300, the voltage stabilization rate of the switched capacitor circuit 30 can be improved.

[0072] Please continue to refer to Figure 13 Matching Figure 15 As shown, Figure 15 FIG. 3 shows the discharge operation of the charge compensation circuit 300. At time point T C On, switch S A Turn on the switch S B Close, so that the reference node N R The voltage is equal to V A At time point T D On, switch S A Close the switch S B Open, so that the reference node N R The voltage is equal to V B From time point T C to T D During the period, the reference node N R From the higher voltage V A Switching to a lower voltage V BAt this time, the compensation switch S2 is turned on for a short period of time, and the transmission switch S A and S B are all turned off. In this case, the output capacitor C A The charge on the capacitor can be released through the current source I2. The amount of charge released can be determined by the pulse length of the compensation switch S2. D On, switch S B Open and switch S2 closed, reference node N R Coupled to the reference voltage generator BUF B To receive voltage V B At this time, the current source I2 can be disconnected by turning off the switch S2 to avoid additional current consumption.

[0073] In this case, the charge compensation circuit 300 can use the current source I2 to compensate the output capacitor C A discharge from the output capacitor C A Absorbed charge (i.e. Q C ), the remaining charge then passes through the reference voltage generator BUF B Therefore, the reference voltage generator BUF is required. B The amount of charge released (i.e. Q R ) can be reduced to drive the output capacitor C A The total charge required (i.e. Q A ) minus the compensation charge absorbed by the charge compensation circuit 300, i.e., Q R =Q A -Q C In this way, the reference voltage generator BUF B No need for larger output capacity, can reduce the reference voltage generator BUF B At the same time, due to the powerful output capability of the charge compensation circuit 300, the voltage stabilization rate of the switched capacitor circuit 30 can be improved.

[0074] Please refer to Figure 16 , Figure 16 FIG. 1 is a schematic diagram of a general capacitive digital-to-analog converter (capacitive DAC) 1600. Figure 16 As shown, the capacitive digital-to-analog converter 1600 may be composed of a plurality of switched capacitor circuits, wherein each switched capacitor circuit includes an output capacitor (C AN ~C A0 ) and two transmission switches (S NA ~S 0A 、S NB ~S 0B). The circuit structure of the switched capacitor circuit is similar to Figure 1 The switched capacitor circuit 10 is shown. Specifically, the output capacitor C AN ~C A0 The first end of the transmission switch S is commonly coupled to the output end of the capacitive digital-to-analog converter 1600. NA ~S 0A are coupled to the output capacitors C AN ~C A0 The second end and the reference voltage generator (omitted for simplicity) Figure 16 )Receive voltage V A A transmission switch S NB ~S 0B are coupled to the output capacitors C AN ~C A0 The second end and another reference voltage generator (omitted for simplicity) Figure 16 )Receive voltage V B Between the first and second input terminals of the transmission switch S NA ~S 0A and S NB ~S 0B The output capacitor C AN ~C A0 The second end can be at voltage V A and V B Switch between. With output capacitor C AN For example, when the switch S NA Turn on the switch S NB When turned off, the output capacitor C AN The second end can be used to receive the voltage V A ; When the switch S NA Close the switch S NB When turned on, the output capacitor C AN The second end can be used to receive the voltage V B The output terminal of the capacitive digital-to-analog converter 1600 can also be coupled to a reset terminal for resetting the capacitor through a reset switch S RESET Receive a reset voltage V RESET .

[0075] In the capacitive digital-to-analog converter 1600, the output capacitor C AN ~C A0 The capacitance values ​​of the output capacitors can be arranged according to the binary weights. That is, the capacitance value of each output capacitor is twice the capacitance value of its adjacent output capacitor (e.g., C AN =2×C A(N-1) 、C A(N-1) =2×C A(N-2) ,…,C A1=2×C A0 The input digital data can be converted into a control signal to control the transmission switch S NA ~S 0A and S NB ~S 0B , to switch the output capacitor C AN ~C A0 The voltage at the second terminal couples the charge to the output capacitor C AN ~C A0 The first terminal generates the output voltage V of the capacitive digital-to-analog converter 1600. OUT In this example, the charge used for voltage switching is entirely provided by the voltage V A and V B The reference voltage generators are used to supply or release the charge, and all switched capacitor circuits can share these two reference voltage generators. Because the reference voltage generators are used to drive a large number of switched capacitor circuits, and the output capacitors under the binary weight arrangement have a very large capacitance, the reference voltage generators must have very strong output capabilities to meet the charge requirements of the capacitive digital-to-analog converter 1600.

[0076] Please refer to Figure 17 , Figure 17 FIG is a schematic diagram of a capacitive digital-to-analog converter 1700 according to an embodiment of the present invention. Figure 17 As shown, the circuit structure of the capacitive digital-to-analog converter 1700 is similar to Figure 16 The circuit structure of the capacitance digital-to-analog converter 1600 is shown, so signals or components with similar functions are represented by the same symbols. The difference between the capacitance digital-to-analog converter 1700 and the capacitance digital-to-analog converter 1600 is that in the capacitance digital-to-analog converter 1700, each switched capacitor circuit further includes a charge compensation circuit. The charge compensation circuit is coupled to the corresponding output capacitor C AN ~C A0 The second end is used to compensate the output capacitor C AN ~C A0 Required charge.

[0077] During voltage switching operation, the charge compensation circuit can adjust the output capacitor C according to the voltage change. AN ~C A0 For example, when the output capacitor is charged or discharged from a lower voltage V B Switching to a higher voltage V A When the charge compensation circuit is used to supply the first supply voltage V DD The charge is used to charge the output capacitor; when the output capacitor is charged from the higher voltage V A Switching to a lower voltage V BWhen the charge compensation circuit is used to release the charge to the second supply voltage V SS To discharge the output capacitor. In this way, part of the charge can be provided by or released to the charge compensation circuit, which can reduce the output capacity requirement of the reference voltage generator, thereby making the reference voltage generator consume less power. In addition, due to the powerful output capacity of the charge compensation circuit, the voltage stability rate of the switched capacitor circuit can also be improved. It should be noted that the detailed implementation and operation of the switched capacitor circuit and its charge compensation circuit in the capacitive digital-to-analog converter 1700 are similar to Figure 3 and 4 The switched capacitor circuit shown and various embodiments of the charge compensation circuit described in this specification can be applied to the capacitive digital-to-analog converter 1700.

[0078] It is worth noting that the present invention is intended to provide a switched capacitor circuit having a charge compensation circuit that can be used to supply or release charge. Those skilled in the art may make modifications or changes accordingly, and are not limited to this. For example, in the above embodiment, the charge of the charge compensation circuit comes from the first supply voltage V DD and released to the second supply voltage V SS These supply voltages may be the highest or lowest voltage levels supplied by the global voltage source of the circuit system. In another embodiment, the supply voltage V DD and / or V SS Alternatively, the voltage may be generated by a specific voltage source or voltage generator and have any suitable voltage level. As long as the supply voltage can compensate for the required charge and the charge compensation circuit has sufficient driving capability, it can have any suitable voltage level. It should be noted that the steady-state voltage of the reference node is derived from the reference voltage generator, not determined by the charge compensation circuit.

[0079] Furthermore, in an embodiment of the present invention, a first terminal of the output capacitor is coupled to the output terminal of the switched capacitor circuit and the capacitive digital-to-analog converter, while a second terminal of the output capacitor is coupled to the reference node, the transmission switch, and the charge compensation circuit. In one exemplary embodiment, the top plate of the output capacitor can be designed as the first terminal, and the bottom plate of the output capacitor can be designed as the second terminal; alternatively, an embodiment can also be used in which the top plate of the output capacitor is designed as the second terminal, and the bottom plate of the output capacitor is designed as the first terminal.

[0080] In summary, the present invention provides a switched capacitor circuit having a charge compensation circuit that can be used to supply or release charge, wherein the switched capacitor circuit can be applied to a capacitive digital-to-analog converter or any other circuit module. The charge compensation circuit can supply or release charge to the output capacitor of the switched capacitor circuit, which is originally charged and discharged by the reference voltage generator, thereby reducing the burden on the reference voltage generator, thereby reducing the output capacity requirement of the reference voltage generator, and achieving the purpose of saving power for the reference voltage generator. In addition, due to the powerful driving capability of the charge compensation circuit, the voltage stabilization rate of the output capacitor can be increased, thereby improving the operating speed of the switched capacitor circuit and the capacitive digital-to-analog converter.

[0081] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A switched capacitor circuit, comprising: An output capacitor, including: a first terminal coupled to an output terminal of the switched capacitor circuit; and a second terminal coupled to a reference node; a first transmission switch coupled to the reference node; a first reference voltage generator coupled to the first transmission switch; a second transmission switch coupled to the reference node; a second reference voltage generator coupled to the second transmission switch; and a charge compensation circuit coupled to the reference node; Wherein, the charge compensation circuit includes: a first compensation switch coupled between the reference node and a first power supply node; and A second compensation switch is coupled between the reference node and a second power supply node.

2. The switched capacitor circuit according to claim 1, wherein: The charge compensation circuit is used to charge or discharge the output capacitor according to the voltage change on the reference node.

3. The switched capacitor circuit according to claim 1, wherein: The charge compensation circuit charges the output capacitor by receiving charges from the first power supply node.

4. The switched capacitor circuit according to claim 1, wherein: The charge compensation circuit discharges the output capacitor by releasing charge to the second power supply node.

5. The switched capacitor circuit according to claim 1, wherein: The charge compensation circuit is configured to charge the output capacitor when the reference node switches from a second voltage supplied by the second reference voltage generator to a first voltage supplied by the first reference voltage generator, wherein the first voltage is higher than the second voltage.

6. The switched capacitor circuit according to claim 1, wherein: The charge compensation circuit is configured to discharge the output capacitor when the reference node switches from a first voltage supplied by the first reference voltage generator to a second voltage supplied by the second reference voltage generator, wherein the second voltage is lower than the first voltage.

7. The switched capacitor circuit according to claim 1, wherein: The charge compensation circuit further includes: A compensation capacitor, comprising: a first terminal coupled to the reference node; and a second end; The first compensation switch is coupled to the second end of the compensation capacitor, and the second compensation switch is coupled to the second end of the compensation capacitor.

8. The switched capacitor circuit according to claim 1, wherein: When the first transmission switch is turned on and the reference node receives a first voltage from the first reference voltage generator, the first compensation switch is turned on to receive charges from the first power supply node.

9. The switched capacitor circuit according to claim 1, wherein: When the second transmission switch is turned on and the reference node receives a second voltage from the second reference voltage generator, the second compensation switch is turned on to release charge to the second power supply node.

10. The switched capacitor circuit according to claim 7, wherein: The charge compensation circuit further includes: A third compensation switch is coupled between the reference node and the compensation capacitor.

11. The switched capacitor circuit according to claim 10, wherein: The third compensation switch is turned on when the voltage on the reference node switches.

12. The switched capacitor circuit according to claim 1, wherein: When the reference node switches from a second voltage to a first voltage higher than the second voltage, the first compensation switch is turned on, so that the output capacitor receives charges from the first power supply node.

13. The switched capacitor circuit according to claim 1, wherein: When the reference node switches from a first voltage to a second voltage lower than the first voltage, the second compensation switch is turned on, so that the output capacitor releases charges to the second power supply node.

14. The switched capacitor circuit according to claim 1, wherein: The charge compensation circuit further includes: a first current source coupled between the first compensation switch and the first power supply node; and A second current source is coupled between the second compensation switch and the second power supply node.

15. The switched capacitor circuit according to claim 14, wherein: When the reference node switches from a second voltage to a first voltage higher than the second voltage, the first compensation switch is turned on, so that the output capacitor receives the charge from the first current source.

16. The switched capacitor circuit according to claim 14, wherein: When the reference node switches from a first voltage to a second voltage lower than the first voltage, the second compensation switch is turned on, so that the output capacitor releases charges to the second current source.

17. A capacitive digital-to-analog converter, comprising: A plurality of switched capacitor circuits, wherein each switched capacitor circuit comprises: An output capacitor, including: a first terminal coupled to an output terminal of the capacitive digital-to-analog converter; and a second terminal coupled to a reference node; a first transmission switch coupled between the reference node and a first reference voltage generator; a second transmission switch coupled between the reference node and a second reference voltage generator; and a charge compensation circuit coupled to the reference node; Wherein, the charge compensation circuit includes: a first compensation switch coupled between the reference node and a first power supply node; and A second compensation switch is coupled between the reference node and a second power supply node.

18. The capacitive digital-to-analog converter according to claim 17, wherein: The charge compensation circuit is used to charge or discharge the output capacitor according to the voltage change on the reference node.

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