CN111464139A - Common-mode feedback circuit suitable for wide-swing fully-differential operational amplifier - Google Patents
Common-mode feedback circuit suitable for wide-swing fully-differential operational amplifier Download PDFInfo
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Abstract
A common mode feedback circuit suitable for a wide-swing fully-differential operational amplifier collects the common mode output of the wide-swing fully-differential operational amplifier through two groups of parallel resistor capacitors in a common mode signal collection module and injects the collected common mode output into a common mode amplification module to be compared with common mode reference voltage, and a feedback adjusting signal is generated in the common mode feedback module and fed back to a first-stage load current source tube gate end in the wide-swing fully-differential circuit, so that the output common mode of the wide-swing fully-differential circuit is stabilized through feedback; meanwhile, a feedforward adjusting signal generated in the common mode feedforward module is connected to a current source tube gate end of a source follower in the wide-swing fully-differential circuit, so that the output common mode of the wide-swing fully-differential circuit is stable. According to the invention, a new feed-forward path is introduced to provide an additional zero point for the whole common-mode response circuit, so that the whole phase margin performance of the wide-swing fully-differential operational amplifier is improved without influencing the common-mode response gain, and the stability of the wide-swing fully-differential operational amplifier is improved without influencing the output swing.
Description
Technical Field
The invention belongs to the technical field of analog integrated circuits, and relates to a common-mode feedback circuit which introduces a feedforward path through common-mode feedback to improve the stability of a wide-swing fully-differential operational amplifier.
Background
With the rapid development of the integrated circuit field and the continuous reduction of the process size, the design and manufacture of the integrated circuit tend to have high stability, high integration and low power consumption. The fully differential operational amplifier has a fully symmetric matching structure and strong common-mode rejection capability, so that the application requirements of low noise and high output swing can be met. Due to the influences of mismatch, parasitics and the like of devices in process manufacturing, the fully differential operational amplifier actually tested cannot achieve an ideal common mode rejection ratio. In many cases, the performance of the fully differential operational amplifier is reduced sharply due to the common mode variation, and finally the fully differential operational amplifier cannot work normally. Therefore, a common-mode feedback circuit is added to a practical circuit design to stabilize the common-mode signal of the fully-differential operational amplifier. However, the addition of the common mode feedback circuit in the fully differential operational amplifier inevitably brings extra power consumption, the common mode feedback circuit collects a common mode signal from the output end of the fully differential operational amplifier and easily affects the output swing of the fully differential operational amplifier, and meanwhile, the introduction of the extra circuit provides a higher challenge to the stability of the whole circuit. Therefore, how to stabilize the common-mode signal of the fully-differential operational amplifier and not greatly affect other performance indexes needs to be considered when designing the common-mode feedback circuit.
Traditional wide-swing fully-differential amplifier and common-mode feedbackThe circuit is shown in fig. 1, the conventional wide-swing fully-differential amplifier includes a first-stage pent-transistor amplifier 101, a second-stage common-source amplifier 102, a third-stage source follower 103, a miller compensation circuit 104, and a bias current source 105, and the conventional common-mode feedback circuit is 106. Wherein the input tube M of the first stage of the five-tube amplifier1、M2Gate terminal differential input signal VIP、VIN，M1、M2The drain end of the tube is an input tube M of which the output end of the first-stage operational amplifier is respectively connected with the second-stage common source amplifier7、M8The gate terminal of (1). Second-stage common-source amplifier M7、M8The tube is a second-stage signal input tube, the input tube M7、M8The grid ends of the first-stage operational amplifier are respectively connected with the output end M of the first-stage operational amplifier1、M2Discharge end of the tube, M7、M8The drain end of the tube is the output end of the second-stage common-source amplifier and is respectively connected with the third-stage source follower input tube M9、M10The gate terminal of (1). Third-stage source follower input tube M9、M10The grid ends of the first-stage common-source amplifier and the second-stage common-source amplifier are respectively connected with the output end M of the second-stage common-source amplifier7、M8Discharge end of the tube, M9、M10The source end of the tube is the output end V of the fully differential operational amplifierOP、VONAnd is also connected to the input of the common mode feedback circuit. Common mode feedback circuit is two sets of parallelly connected electric capacity CCMResistance RCMOutput end V of fully differential amplifier forming common mode acquisition circuitOP、VONAre respectively connected to a group of C in parallelCM、RCMOne end of (A), two groups of C connected in parallelCM、RCMThe other end is connected together to the MC1The gate end of the tube. Input tube MC2The grid end of the tube is connected with a common mode reference signal VREF，MC3The drain terminal of the tube is the output terminal of the common mode feedback circuit and is connected with the fully differential operational amplifier M3、M4The gate end of the tube.
The gain of the differential signal of the conventional wide-swing fully-differential operational amplifier is shown in formula (1):
ADM＝gm1gm7gm9RA2RA3ROUT(1)
in the formula, gm1、gm7、gm9Are respectively M1、M7、M9Transconductance of the tube, RA2、RA3、ROUTThe node resistance of the output node of the first-stage five-tube amplifier, the node resistance of the output node of the second-stage common-source amplifier and the node resistance of the output node of the third-stage source follower are respectively. The traditional wide-swing fully-differential amplifier has high gain, and the poles need to be separated by using Miller compensation to ensure that the phase margin is large enough to ensure the stability of the system. The output module of the source follower ensures that the output swing of the three-level amplifier can meet the design requirement after the three-level amplifier is connected into the common-mode feedback structure.
The traditional common-mode feedback structure does not affect the output swing of the fully differential amplifier, the output common mode is stable by introducing feedback regulation mismatch current into the three-stage amplifier, but higher requirements are provided for the overall common-mode response. Therefore, although the conventional common-mode feedback structure ensures a sufficiently high common-mode signal gain without affecting the swing, the position of the secondary point needs to be sufficiently high to ensure that the phase margin of the system is sufficiently high in the common-mode condition, which causes the design of the fully-differential operational amplifier to be greatly restricted and difficult to meet the requirement on the overall stability.
Disclosure of Invention
Aiming at overcoming the influence of mismatch of devices and difficult adjustment of poles on the stability of the whole system in the wide-swing fully-differential operational amplifier in the traditional common-mode feedback structure, the invention provides the common-mode feedback circuit suitable for the wide-swing fully-differential operational amplifier. Meanwhile, a feed-forward channel introduced by common-mode feedback cannot reduce the common-mode response gain of the wide-swing fully-differential operational amplifier, so that the overall stability of the wide-swing fully-differential operational amplifier is improved.
The technical scheme of the invention is as follows:
a common mode feedback circuit suitable for a wide-swing fully-differential operational amplifier comprises an output stage consisting of a multi-stage amplification structure and a source follower, and comprises a common mode signal acquisition module, a common mode amplification module, a common mode feedback module and a current bias module;
the common-mode signal acquisition module comprises a first resistor, a first capacitor, a second resistor and a second capacitor, the first resistor and the first capacitor are connected in parallel and then connected between the positive output end of the wide-swing fully-differential operational amplifier and the output end of the common-mode signal acquisition module, and the second resistor and the second capacitor are connected in parallel and then connected between the negative output end of the wide-swing fully-differential operational amplifier and the output end of the common-mode signal acquisition module;
the common mode amplification module comprises a first NMOS tube and a second NMOS tube, the grid electrode of the first NMOS tube is connected with the output end of the common mode signal acquisition module, the source electrode of the first NMOS tube is connected with the source electrode of the second NMOS tube and the output end of the current bias module, and the drain electrode of the first NMOS tube is used as the first output end of the common mode amplification module; the grid electrode of the second NMOS tube is connected with a common mode reference voltage, and the drain electrode of the second NMOS tube is used as a second output end of the common mode amplification module;
the common-mode feedback module comprises a first PMOS (P-channel metal oxide semiconductor) tube, the grid-drain short circuit of the first PMOS tube is connected with the first output end of the common-mode amplification module and the grid electrode of the load current tube of the first-stage amplification structure in the wide-swing fully-differential operational amplifier, and the source electrode of the first PMOS tube is connected with power supply voltage;
the common mode feedback circuit further comprises a common mode feedforward module, the common mode feedforward module comprises a second PMOS tube, the grid drain of the second PMOS tube is in short circuit connection with the second output end of the common mode amplification module and the grid electrode of the current source tube of the source follower in the output stage of the wide-swing fully differential operational amplifier, and the source electrode of the common mode feedforward module is connected with power supply voltage.
Specifically, the current bias module includes a third NMOS transistor, a gate of the third NMOS transistor is connected to a bias voltage, a drain of the third NMOS transistor is used as an output terminal of the current bias module, and a source of the third NMOS transistor is grounded.
Specifically, the wide-swing fully differential operational amplifier comprises a two-stage amplification structure, wherein the first-stage amplification structure comprises a third PMOS tube, a fourth NMOS tube, a fifth NMOS tube and a sixth NMOS tube,
the grid electrode of the fourth NMOS tube is used as the positive input end of the wide-swing fully-differential operational amplifier, the drain electrode of the fourth NMOS tube is connected with the drain electrode of the third PMOS tube and is used as the first output end of the first-stage amplification structure to be connected with the first input end of the second-stage amplification structure, and the source electrode of the fourth NMOS tube is connected with the source electrode of the fifth NMOS tube and the drain electrode of the sixth NMOS tube;
a grid electrode of the fifth NMOS tube is used as a negative input end of the wide-swing fully-differential operational amplifier, and a drain electrode of the fifth NMOS tube is connected with a drain electrode of the fourth PMOS tube and is used as a second output end of the first-stage amplification structure to be connected with a second input end of the second-stage amplification structure;
the grid electrode of the sixth NMOS tube is connected with bias voltage, and the source electrode of the sixth NMOS tube is grounded;
the third PMOS tube and the fourth PMOS tube are load current tubes of a first-stage amplification structure in the wide-swing fully-differential operational amplifier, the grid electrodes of the third PMOS tube and the fourth PMOS tube are both connected with the drain electrode of the first PMOS tube in the common-mode feedback module, and the source electrodes of the third PMOS tube and the fourth PMOS tube are both connected with power supply voltage.
Specifically, the output stage of the wide-swing fully differential operational amplifier comprises a fifth PMOS tube, a sixth PMOS tube, a seventh PMOS tube and an eighth PMOS tube,
the grid electrode of the fifth PMOS tube is connected with the first output end of the second-stage amplification structure, the source electrode of the fifth PMOS tube is connected with the drain electrode of the seventh PMOS tube and serves as the positive output end of the wide-swing fully-differential operational amplifier, and the drain electrode of the fifth PMOS tube is connected with the drain electrode of the sixth PMOS tube and is grounded;
the grid electrode of the sixth PMOS tube is connected with the second output end of the second-stage amplification structure, and the source electrode of the sixth PMOS tube is connected with the drain electrode of the eighth PMOS tube and is used as the negative output end of the wide-swing fully-differential operational amplifier;
the seventh PMOS tube and the eighth PMOS tube are current source tubes of a source follower in the output stage of the wide-swing fully-differential operational amplifier, the grid electrodes of the seventh PMOS tube and the eighth PMOS tube are both connected with the drain electrode of the second PMOS tube in the common-mode feed-forward module, and the source electrodes of the seventh PMOS tube and the eighth PMOS tube are both connected with power supply voltage.
The invention has the beneficial effects that: according to the invention, the common-mode signal acquisition module is used for sampling the common-mode output of the wide-swing fully-differential operational amplifier and comparing the common-mode output with the common-mode reference voltage in the common-mode amplification module, and a feedback adjustment signal is generated in the common-mode feedback module according to the output of the common-mode amplification module and is fed back to the gate end of the first-stage load current source tube of the wide-swing fully-differential circuit, so that the output common mode of the wide-swing fully-differential circuit is stabilized through feedback; meanwhile, the invention also provides a method for generating a feedforward adjusting signal according to the output of the common mode amplification module in the common mode feedforward module, and connecting the feedforward adjusting signal to the grid end of the current source tube of the third-stage source follower of the wide-swing fully-differential circuit, so that the output common mode of the wide-swing fully-differential circuit is stable; by introducing a new feed-forward path, an extra zero point is provided for the whole common-mode response circuit, so that the whole phase margin performance of the wide-swing fully-differential operational amplifier is improved, the common-mode response gain is not influenced, and the stability of the wide-swing fully-differential operational amplifier is improved under the condition of not influencing the output swing.
Drawings
Fig. 1 is a schematic diagram of a conventional wide-swing fully-differential amplifier and a common-mode feedback circuit.
Fig. 2 is a schematic structural diagram of a common mode feedback circuit suitable for a wide-swing fully-differential operational amplifier according to the present invention.
Fig. 3 is a schematic structural diagram of applying the common mode feedback circuit proposed by the present invention to a specific wide-swing fully-differential amplifier.
Fig. 4 is a schematic diagram of an amplifier common-mode signal transmission model of a common-mode feedback circuit suitable for a wide-swing fully-differential operational amplifier according to the present invention.
Fig. 5 is a simulation comparison diagram of the common-mode response of the conventional wide-swing fully-differential amplifier and the common-mode response of the wide-swing fully-differential amplifier after applying the common-mode feedback circuit provided by the present application.
Detailed Description
The invention is further illustrated by way of example with reference to the accompanying drawings.
The invention provides a common mode feedback circuit which is suitable for a wide-swing fully-differential operational amplifier comprising a multi-stage amplification structure and an output stage formed by a source follower. Fig. 2 is a schematic structural diagram of a common mode feedback circuit according to the present invention, which includes a common mode signal acquisition module 201, a common mode amplification module 202, a common mode feedback module 203, a common mode feedforward module 204, and a current bias module 205.
Wherein the common-mode signal acquisition module 201 is used for acquiring the common-mode output V of the wide-swing fully-differential operational amplifierCMComprises a first resistor RCM1A first capacitor CCM1A second resistor RCM2And a second capacitor CCM2First resistance RCM1And a first capacitor CCM1Is connected in parallel and then is connected with the positive output end V of the wide-swing full-differential operational amplifierOPAnd a second resistor R between the output end of the common-mode signal acquisition moduleCM2And a second capacitor CCM2Is connected in parallel and then is connected with a negative output end V of the wide-swing full-differential operational amplifierONAnd the output end of the common-mode signal acquisition module.
The common mode amplification module 202 receives the common mode signal and the common mode signal acquisition module 201 acquires the common mode output V of the wide-swing fully differential operational amplifierCMFor comparison with a common-mode reference voltage VREFIn comparison, as shown in fig. 2, the common mode amplifying module includes a first NMOS transistor MC1And a second NMOS transistor MC2First NMOS transistor MC1The grid of the common-mode signal acquisition module is connected with the common-mode output V of the wide-swing fully-differential operational amplifier output by the output end of the common-mode signal acquisition moduleCMThe source electrode of the NMOS transistor is connected with a second NMOS transistor MC2The drain of the source and current bias module 205 is connected to the common mode feedback module 203 as a first output terminal of the common mode amplification module 202; second NMOS transistor MC2Is connected to a common-mode reference voltage VREFAnd a drain thereof is connected to the common mode feed forward module 204 as a second output terminal of the common mode amplifying module 202.
The current bias module 205 is used forProviding a bias, as shown in fig. 2, which shows an implementation form of the current bias module 205, including a third NMOS transistor M14Third NMOS transistor M14Is connected to a bias voltage VBiasThe drain of the current bias module is connected to the first NMOS transistor MC of the common mode amplifier module 2021And a second NMOS transistor MC2And the source of (3) is grounded.
The common mode feedback module 203 comprises a first PMOS transistor MC3First PMOS transistor MC3The gate-drain end of the transistor is shorted as the feedback output end of the common mode feedback module 203, and is connected to the first output end of the common mode amplification module 202, i.e. the first NMOS transistor MC1The drain terminal of the first-stage amplifier is connected to the current source grid terminal of the first-stage amplification structure of the external wide-swing fully-differential amplifier, and the first PMOS tube MC3The source terminal of which is connected to the supply voltage.
The common mode feed-forward module 204 comprises a second PMOS transistor MC4Second PMOS transistor MC4Is connected to a second output terminal of the common mode amplifying module 202, i.e. the second NMOS transistor MC, as a feed-forward output terminal of the common mode feed-forward module 2042The drain terminal of the second PMOS tube MC is connected to the gate terminal of the current source tube of the source follower in the output stage of the external wide-swing fully-differential amplifier4The source terminal of which is connected to the supply voltage.
The third NMOS transistor M in the common mode feedback circuit provided by the invention14Is a current source tube, a first PMOS tube MC3And a second PMOS transistor MC4Is a load tube, a first NMOS tube MC1A second NMOS transistor MC2The tube is a signal input tube. The invention utilizes two groups of parallel resistor-capacitor pairs in the common-mode signal acquisition module 201 to output the common-mode output V of the wide-swing fully-differential operational amplifierCMCollecting, offsetting the differential signal output by the wide-swing fully-differential operational amplifier and extracting the output common-mode signal VCMThe first NMOS transistor MC is injected into the common mode amplifier 2021Grid of (1), common-mode output V of wide-swing fully-differential operational amplifierCMAnd the second NMOS transistor MC in the common mode amplifying module 2022Grid-end connected common mode reference voltage VREFComparing, the first PMOS transistor MC in the common mode feedback module 2033Drain terminal generationAnd feeding back a regulation signal and feeding back the regulation signal to a gate end of a first-stage load current source tube of the wide-swing fully-differential circuit, so as to realize the stabilization of the output common mode of the wide-swing fully-differential circuit through feedback. Meanwhile, the invention also provides a second PMOS tube MC in the common mode feedforward module 2044The drain terminal of the wide-swing fully-differential circuit generates a feedforward adjusting signal and is connected to the grid terminal of a current source tube of a third-stage source follower of the wide-swing fully-differential circuit, so that the output common mode of the wide-swing fully-differential circuit is stable; considering that the common-mode feedback needs to form a feedback path, the introduced feedforward path cannot change the characteristics of the feedback path so that the overall feedback is disabled, and the feedforward adjustment is usually realized by introducing an additional circuit. The invention introduces a new feedforward path according to the structure of the common mode feedback circuit, provides an additional zero point in the whole common mode response circuit, improves the whole phase margin performance of the wide-swing fully-differential operational amplifier, does not influence the common mode response gain, and improves the stability of the wide-swing fully-differential operational amplifier under the condition of not influencing the output swing.
The present invention is applicable to a wide swing fully differential operational amplifier including an output stage formed by a multi-stage amplification structure and a source follower, and an implementation form of applying the present invention to a three-stage operational amplifier structure is shown in fig. 3ZAnd a capacitor CC) And a bias current source (i.e. NMOS transistor M)13Converting a bias current IB into a bias voltage VBiasTo provide biasing for later stage circuitry). It should be noted that, in the present embodiment, the first-stage five-transistor amplifier and the second-stage common-source amplifier are taken as examples for description, but the multi-stage amplification structure with other structures and the wide-swing fully-differential operational amplifier with an output stage formed by a source follower are also applicable to the common-mode feedback circuit of the present invention.
As shown in fig. 3, the first stage of the amplifying structure in this embodiment is a five-transistor amplifier, which includes a third PMOS transistor M3And the fourth PMOS transistor M4And the fourth NMOS tube M1The fifth NMOS transistor M2And a sixth NMOS transistor M0Sixth NMOS transistor M0Is a current source tube, a third PMOS tube M3And a fourth PMOS transistor M4Is a load tube, a fourth NMOS tube M1And a fifth NMOS transistor M2Is a differential signal input tube. Fourth NMOS transistor M1The grid of the second PMOS transistor is used as the positive input end of the wide-swing fully-differential operational amplifier, and the drain of the second PMOS transistor is connected with a second PMOS transistor3The drain electrode of the first-stage amplifying structure is used as a first output end of the first-stage amplifying structure and is connected with a first input end of the second-stage amplifying structure, and the source electrode of the first-stage amplifying structure is connected with a fifth NMOS tube M2Source electrode of (1) and sixth NMOS transistor M0A drain electrode of (1); fifth NMOS transistor M2The grid of the second PMOS transistor is used as the negative input end of the wide-swing fully-differential operational amplifier, and the drain of the second PMOS transistor is connected with the fourth PMOS transistor M4The drain electrode is used as a second output end of the first-stage amplification structure and is connected with a second input end of the second-stage amplification structure; sixth NMOS transistor M0Is connected to a bias voltage VBiasThe source of the transistor is grounded; third PMOS transistor M3And a fourth PMOS transistor M4Is a load current tube of a first-stage amplification structure in a wide-swing fully-differential operational amplifier, and a third PMOS tube M3And a fourth PMOS transistor M4Are all connected to the first PMOS transistor MC in the common mode feedback module 2033And the sources of the drains are connected with a power supply voltage.
The second stage common source amplifier comprises an NMOS tube M5、M6And PMOS transistor M7、M8Wherein the NMOS tube M5、M6The transistor is a current source load transistor, a PMOS transistor M7、M8The tube is a signal input tube. Current source tube M5、M6Tube gate terminal bias voltage VBias，M5、M6The drain ends of the tubes are respectively connected with M7、M8Source end of tube, M5、M6The source end of the tube is grounded. Input pipe M7、M8The grid ends of the first-stage amplifying structure are respectively connected with a first output end and a second output end of the first-stage amplifying structure, namely a fourth NMOS tube M1And a fifth NMOS transistor M2Discharge end of the tube, M7、M8The source terminal of the tube is connected to the supply voltage, M7、M8The drain terminal of the transistor is the first output terminal and the second output terminal of the second-stage operational amplifier, which are respectively connected to the third-stage source followerInput tube M of device9、M10The gate terminal of (1).
The third stage source follower comprises a fifth PMOS tube M9Sixth PMOS transistor M10Seventh PMOS transistor M11And eighth PMOS transistor M12Seventh PMOS transistor M11And eighth PMOS transistor M12Is a current source load tube, a fifth PMOS tube M9And a sixth PMOS transistor M10Is a signal input tube. Fifth PMOS transistor M9The grid of the first stage amplifier is connected with the first output end M of the second stage amplifier7The drain end of the tube and the source electrode of the tube are connected with a seventh PMOS tube M11The drain electrode of the second PMOS transistor is used as the positive output end of the wide-swing fully differential operational amplifier, and the drain electrode of the second PMOS transistor is connected with a sixth PMOS tube M10The drain electrode of the transistor is grounded; sixth PMOS transistor M10Is connected with a second output end (M) of the second stage amplification structure8The drain end of the tube and the source electrode of the tube are connected with an eighth PMOS tube M12The drain electrode of the wide-swing fully-differential operational amplifier is used as a negative output end of the wide-swing fully-differential operational amplifier; seventh PMOS tube M11And eighth PMOS transistor M12A current source tube of a source follower in an output stage of the wide-swing fully-differential operational amplifier, a seventh PMOS tube M11And eighth PMOS transistor M12Are all connected to the second PMOS transistor MC in the common mode feed-forward module 2044And the sources of the drains are connected with a power supply voltage.
In this embodiment, a common mode feedback circuit is applied to a common mode signal transmission model in a wide-swing fully-differential operational amplifier, as shown in fig. 4, a signal flows from a common mode feedback input end under common mode response, and the common mode feedback and a three-stage amplifier form a first-stage transconductance 401 and a feedforward path 402 of the common mode signal transmission model. The common mode signal transmission model second-stage transconductance 403 and the third-stage transconductance 404 are third-stage and second-stage transconductance of a three-stage amplifier. Wherein C isgsFor the fifth PMOS tube M in the third-stage source follower9Sixth PMOS transistor M10Parasitic capacitance of gate and source, CPIs a first NMOS transistor MC1The parasitic capacitance of (1). The symmetrical structure of two sides of the fully differential operational amplifier under the common mode condition is equivalent to parallel connection, so that the node capacitance resistance and the transconductance of each stage are processed in parallel connection. The low-frequency gain of the common-mode signal of the wide-swing fully-differential operational amplifier is shown in formula (2):
ACM＝-1/2gmC1gm4gm8gm10RA2RA3RDROUT(2)
in the formula RDA first PMOS transistor MC at the output end of the common mode feedback circuit3Equivalent resistance of gmC1、gm4、gm8、gm10Are respectively a first NMOS tube MC1Transconductance and fourth PMOS tube M4Transconductance PMOS transistor M8Transconductance and sixth PMOS tube M10The common mode signal gain is typically greater than the differential signal gain. The transfer function in common mode is shown in equation (3):
in the formula ACMFor common mode gain at low frequencies, wZ1、wZ2、wZ3Zero point in common mode, wP1、wP2、wP3、wP4Being the poles in the common mode case. The pole zero in common mode is shown in equation (4):
in the formula gmA1、gmfRespectively, amplifier transconductance formed by connecting common mode feedback circuit output and three-stage amplifier current source, wherein gmA1＝1/2(gmC1RD2gm3,4)，gmf＝-1/2(gmC1RD2gm11,12) And Δ represents a higher order term. First resistor R for collecting common-mode signalCM1A first capacitor CCM1A second resistor RCM2And a second capacitor CCM2A zero pole pair, typically 4C, is introducedCM＞＞CPTherefore wP4≈wZ3And can be cancelled. w is aZ1,2Is a feed-forward path gmfAnd Miller compensation capacitance resistance CCAnd RZTwo zero points are introduced, compared with the traditional common zero pointThe mode feedback circuit can effectively improve the phase margin of the loop and improve the stability of the loop. The gain and amplitude-frequency characteristic curves of the common-mode response are shown in fig. 5 under the condition of no front feed-through circuit and the simulation result, and it can be seen that the stability of the system is obviously improved after the feed-forward circuit is added.
In summary, the present embodiment provides a novel common mode feedback circuit suitable for wide swing fully differential amplifier, which utilizes two sets of parallel resistor capacitors in the common mode signal acquisition module 201 to output the common mode output V of the wide swing fully differential operational amplifierCMThe first NMOS transistor MC is collected and injected into the common mode amplification module 2021Gate terminal of, common mode output V of wide swing fully differential operational amplifierCMAnd the second NMOS transistor MC in the common mode amplifying module 2022Fixed common mode reference voltage V of grid terminalREFComparing, the first PMOS transistor MC in the common mode feedback module 2033The drain terminal generates a feedback regulation signal and feeds the feedback regulation signal back to a first-stage load current source tube, namely a third PMOS tube M of the wide-swing fully-differential circuit3And a fourth PMOS transistor M4The gate terminal of (1). Third PMOS transistor M3And a fourth PMOS transistor M4And a first PMOS transistor MC3The current mirror relationship is adopted, so that the feedback current is input into the three-stage operational amplifier, and the common mode of the output end of the three-stage operational amplifier is stable by modulating the common mode signal of the output end by the current. Meanwhile, the invention also provides a second PMOS tube MC in the common mode feedforward module 2044The drain terminal outputs a feedforward adjusting signal to be connected to a current source tube of a third-stage source follower of the wide-swing fully-differential circuit, namely a seventh PMOS tube M11And eighth PMOS transistor M12The gate terminal of (a) directly couples the current signal to the output terminal to form a feed-forward path. Through the introduced feedforward path, an extra zero point is provided for the whole common mode response circuit, so that the whole phase margin performance of the wide-swing fully-differential operational amplifier is improved, meanwhile, the common mode response gain is not influenced, and the stability of the wide-swing fully-differential operational amplifier is improved under the condition that the output swing is not influenced.
Although the disclosure of the present invention in a common mode feedback circuit for wide swing fully differential operational amplifiers has been described in an exemplary manner, it should be understood by those skilled in the art that the invention is not limited thereto, and that the invention is not limited thereto.
Claims (4)
1. A common mode feedback circuit suitable for a wide-swing fully-differential operational amplifier comprises an output stage consisting of a multi-stage amplification structure and a source follower, and comprises a common mode signal acquisition module, a common mode amplification module, a common mode feedback module and a current bias module;
the common-mode signal acquisition module comprises a first resistor, a first capacitor, a second resistor and a second capacitor, the first resistor and the first capacitor are connected in parallel and then connected between the positive output end of the wide-swing fully-differential operational amplifier and the output end of the common-mode signal acquisition module, and the second resistor and the second capacitor are connected in parallel and then connected between the negative output end of the wide-swing fully-differential operational amplifier and the output end of the common-mode signal acquisition module;
the common mode amplification module comprises a first NMOS tube and a second NMOS tube, the grid electrode of the first NMOS tube is connected with the output end of the common mode signal acquisition module, the source electrode of the first NMOS tube is connected with the source electrode of the second NMOS tube and the output end of the current bias module, and the drain electrode of the first NMOS tube is used as the first output end of the common mode amplification module; the grid electrode of the second NMOS tube is connected with a common mode reference voltage, and the drain electrode of the second NMOS tube is used as a second output end of the common mode amplification module;
the common-mode feedback module comprises a first PMOS (P-channel metal oxide semiconductor) tube, the grid-drain short circuit of the first PMOS tube is connected with the first output end of the common-mode amplification module and the grid electrode of the load current tube of the first-stage amplification structure in the wide-swing fully-differential operational amplifier, and the source electrode of the first PMOS tube is connected with power supply voltage;
the common mode feedback circuit is characterized by further comprising a common mode feedforward module, the common mode feedforward module comprises a second PMOS (P-channel metal oxide semiconductor) tube, the grid drain of the second PMOS tube is in short circuit connection with the second output end of the common mode amplification module and the grid electrode of the current source tube of the source follower in the output stage of the wide-swing fully differential operational amplifier, and the source electrode of the common mode feedforward module is connected with power supply voltage.
2. The common-mode feedback circuit suitable for wide-swing fully-differential operational amplifier according to claim 1, wherein the current bias module comprises a third NMOS transistor, a gate of the third NMOS transistor is connected to a bias voltage, a drain of the third NMOS transistor is used as an output terminal of the current bias module, and a source of the third NMOS transistor is grounded.
3. The common-mode feedback circuit suitable for wide-swing fully-differential operational amplifier according to claim 1 or 2, wherein the wide-swing fully-differential operational amplifier comprises a two-stage amplification structure, wherein the first-stage amplification structure comprises a third PMOS transistor, a fourth NMOS transistor, a fifth NMOS transistor and a sixth NMOS transistor,
the grid electrode of the fourth NMOS tube is used as the positive input end of the wide-swing fully-differential operational amplifier, the drain electrode of the fourth NMOS tube is connected with the drain electrode of the third PMOS tube and is used as the first output end of the first-stage amplification structure to be connected with the first input end of the second-stage amplification structure, and the source electrode of the fourth NMOS tube is connected with the source electrode of the fifth NMOS tube and the drain electrode of the sixth NMOS tube;
a grid electrode of the fifth NMOS tube is used as a negative input end of the wide-swing fully-differential operational amplifier, and a drain electrode of the fifth NMOS tube is connected with a drain electrode of the fourth PMOS tube and is used as a second output end of the first-stage amplification structure to be connected with a second input end of the second-stage amplification structure;
the grid electrode of the sixth NMOS tube is connected with bias voltage, and the source electrode of the sixth NMOS tube is grounded;
the third PMOS tube and the fourth PMOS tube are load current tubes of a first-stage amplification structure in the wide-swing fully-differential operational amplifier, the grid electrodes of the third PMOS tube and the fourth PMOS tube are both connected with the drain electrode of the first PMOS tube in the common-mode feedback module, and the source electrodes of the third PMOS tube and the fourth PMOS tube are both connected with power supply voltage.
4. The common-mode feedback circuit suitable for wide-swing fully-differential operational amplifier according to claim 3, wherein the output stage of the wide-swing fully-differential operational amplifier comprises a fifth PMOS transistor, a sixth PMOS transistor, a seventh PMOS transistor and an eighth PMOS transistor,
the grid electrode of the fifth PMOS tube is connected with the first output end of the second-stage amplification structure, the source electrode of the fifth PMOS tube is connected with the drain electrode of the seventh PMOS tube and serves as the positive output end of the wide-swing fully-differential operational amplifier, and the drain electrode of the fifth PMOS tube is connected with the drain electrode of the sixth PMOS tube and is grounded;
the grid electrode of the sixth PMOS tube is connected with the second output end of the second-stage amplification structure, and the source electrode of the sixth PMOS tube is connected with the drain electrode of the eighth PMOS tube and is used as the negative output end of the wide-swing fully-differential operational amplifier;
the seventh PMOS tube and the eighth PMOS tube are current source tubes of a source follower in the output stage of the wide-swing fully-differential operational amplifier, the grid electrodes of the seventh PMOS tube and the eighth PMOS tube are both connected with the drain electrode of the second PMOS tube in the common-mode feed-forward module, and the source electrodes of the seventh PMOS tube and the eighth PMOS tube are both connected with power supply voltage.
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