Amplification circuit for improving common mode rejection ratio

Abstract

The invention discloses an amplifying circuit for improving a common-mode rejection ratio, relates to the field of sensor analog front-end circuits, and aims to improve the common-mode rejection ratio of a circuit system by suppressing common-mode signal change and differential-mode signals caused by the common-mode signal change. A capacitive coupling structure and a chopping stabilizing circuit are combined, so that the problems of an instrument amplifier with a three-operational-amplifier structure are solved, firstly, the amplifier drives a passive network, and the power consumption is reduced; secondly, the AC capacitor is connected in series to isolate a common-mode signal, so that the CMRR of the circuit is improved; thirdly, the chopping stabilizing circuit modulates the offset voltage and the common-mode signal change voltage to high frequency, the offset voltage and the common-mode signal change voltage are filtered by a filter, the circuit gain is improved, and meanwhile, the CMRR is also improved; and fourthly, the problems of residual offset and output ripple caused by the chopper circuit are reduced through the DSL and the RRL, so that saturation of a post-stage circuit is avoided.

Description

Technical Field

[0001] The invention relates to the field of sensor analog front-end circuits, and in particular to an amplifier circuit for improving a common-mode rejection ratio. Background Art

[0002] like Figure 1 As shown in the figure, in the application scenario of the sensor analog front-end circuit, the instrument amplifier with a three-op-amp structure is widely used. It consists of two stages. The first stage realizes high input impedance, high CMRR, and provides a certain gain. The second stage provides the main gain and realizes the conversion of the differential signal into a single-ended signal.

[0003] The main problem with the three-op-amp instrumentation amplifier is that all three amplifiers drive resistive loads, which results in high power consumption. In addition, in order to prevent the input signal offset voltage given by the front end from being too large, resulting in output voltage saturation, the gain cannot be set too high. In addition, the gain configuration of the second-stage amplifier is the ratio of resistors, which is affected by resistor mismatch and chip area constraints. Usually, the overall CMRR (Common-mode rejection ratio) is not high enough, unless laser trimming technology or special high-resistance resistor technology is used to reduce resistor mismatch. However, this increases costs and weakens the mass production competitiveness of the product. Summary of the invention

[0004] The purpose of the present invention is to provide an amplifier circuit with improved common mode rejection ratio, thereby solving the technical problems existing in the prior art.

[0005] The present invention is achieved through the following technical solutions:

[0006] An amplifier circuit for improving common mode rejection ratio, comprising: a fully differential transconductance amplifier module, a passive capacitor and resistor module, and a chopper stabilization module;

[0007] The fully differential transconductance amplifier module is used to convert the input differential voltage into an output current and amplify the output;

[0008] The passive capacitor and resistor module is arranged on the fully differential transconductance amplifier module, and is used to isolate the common mode voltage, determine the in-band gain through the capacitor, perform self-biasing through the resistor, and achieve high-pass angular frequency through the resistor and capacitor;

[0009] The chopper stabilization module is arranged on the fully differential transconductance amplifier module, and is used to implement the chopper modulation function by switching the switch through the clock signal, thereby improving the common mode suppression capability of the amplifier.

[0010] In a possible implementation, the fully differential transconductance amplification module includes a transconductance amplifier, and the transconductance amplifier is electrically connected to the passive capacitor and resistor module and the chopper stabilization module respectively.

[0011] In a possible implementation manner, the passive capacitor and resistor module includes a first AC capacitor, a second AC capacitor, a first parasitic capacitor, a second parasitic capacitor, a first feedback capacitor, a second feedback capacitor, a first feedback resistor, and a second feedback resistor;

[0012] The chopper stabilization module includes a first chopper circuit and a second chopper circuit;

[0013] One end of the first AC capacitor and one end of the second AC capacitor jointly receive a differential signal input from the outside, the other end of the first AC capacitor is respectively connected to one end of the first parasitic capacitor, the positive input end of the first chopping circuit and one end of the first feedback capacitor, the other end of the first parasitic capacitor is grounded, the other end of the second AC capacitor is respectively connected to one end of the second parasitic capacitor, the negative input end of the first chopping circuit and one end of the second feedback capacitor, the positive output end of the first chopping circuit is respectively connected to one end of the first feedback resistor and the in-phase input end of the transconductance amplifier, the other end of the first feedback resistor is respectively connected to the negative output end of the transconductance amplifier and the negative input end of the second chopping circuit, the negative output end of the second chopping circuit is connected to the other end of the first feedback capacitor; the negative output end of the first chopping circuit is respectively connected to one end of the second feedback resistor and the inverting input end of the transconductance amplifier, the other end of the second feedback resistor is respectively connected to the positive output end of the transconductance amplifier and the positive input end of the second chopping circuit, the positive output end of the second chopping circuit is connected to the other end of the second feedback capacitor; the two output ends of the second chopping circuit output signals.

[0014] In a possible implementation manner, the first chopping circuit and the second chopping circuit have the same structure and both include: a first transmission gate, a second transmission gate, a third transmission gate and a fourth transmission gate;

[0015] The input end of the first transmission gate serves as the negative input end of the chopper circuit and is connected to the input end of the fourth transmission gate; the input end of the second transmission gate serves as the positive input end of the chopper circuit and is connected to the input end of the third transmission gate; the output end of the third transmission gate serves as the negative output end of the chopper circuit, and the output end of the third transmission gate is connected to the output end of the first transmission gate; the output end of the fourth transmission gate serves as the positive output end of the chopper circuit, and the output end of the fourth transmission gate is connected to the output end of the second transmission gate.

[0016] In a possible implementation manner, the first transmission gate, the second transmission gate, the third transmission gate and the fourth transmission gate have the same structure and are all formed by connecting a P-channel and an N-channel enhancement type field effect transistor in parallel.

[0017] In a possible implementation manner, a DSL feedback loop and an RRL feedback loop are further included. The DSL feedback loop and the RRL feedback loop are both based on the output signal of the fully differential transconductance amplifier module to generate a feedback signal to the fully differential transconductance amplifier module.

[0018] In a possible implementation, the DSL feedback loop includes a first integrating amplifier, a first DSL chopping circuit, and a DSL amplifier connected in sequence; the input end of the first integrating amplifier is respectively connected to two output ends of the second chopping circuit, and the output end of the DSL amplifier is connected to the input end of the transconductance amplifier.

[0019] In one possible implementation, the RRL feedback loop includes a first capacitor, a first RRL chopper circuit, a second integrating amplifier and an RRL amplifier connected in sequence, the input end of the second integrating amplifier is connected to two output ends of the second chopper circuit through the first capacitor and the first RRL chopper circuit, and the output end of the RRL amplifier is connected to the input end of the transconductance amplifier.

[0020] In a possible implementation manner, a low-pass filter circuit is further included, and the low-pass filter circuit is arranged at the output end of the second chopper circuit in the chopper stabilization module to filter the output signal.

[0021] In a possible implementation, the low-pass filter circuit includes: a first filter resistor, a second filter resistor, and a third filter capacitor;

[0022] One end of the first filter resistor is connected to the negative output end of the second chopper circuit, one end of the second filter resistor is connected to the positive output end of the second chopper circuit, the other end of the first filter resistor and the other end of the second filter resistor are respectively connected to the two ends of the third filter capacitor, and the other end of the first filter resistor and the other end of the second filter resistor are provided as the output end of the amplifier circuit for improving the common mode rejection ratio.

[0023] The present invention provides an amplifier circuit for improving the common mode rejection ratio, which improves the common mode rejection ratio of the circuit system by suppressing the change of the common mode signal and the differential mode signal caused by the change of the common mode signal; adopts a combination of a capacitor coupling structure and a chopper stabilization circuit to solve several problems of the instrument amplifier with a three-op amp structure, firstly, the amplifier driving passive network is conducive to reducing power consumption; secondly, the series AC capacitor isolates the common mode signal, which helps to improve the CMRR of the circuit; thirdly, the chopper stabilization circuit modulates the offset voltage and the common mode signal change voltage to a high frequency, filters them out through a filter, improves the circuit gain, and also improves the CMRR; fourthly, the residual offset and output ripple problems caused by the chopper circuit are reduced through DSL and RRL, so that the subsequent circuit avoids saturation. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and should not be regarded as limiting the scope. For those of ordinary skill in the art, other relevant drawings can be obtained based on these drawings without creative work. In the drawings:

[0025] Figure 1 The present invention is provided as a schematic diagram of the prior art.

[0026] Figure 2 A schematic structural diagram of an amplifier circuit for improving the common mode rejection ratio provided by the present invention.

[0027] Figure 3 This is a schematic diagram of the structure of the capacitive coupling instrument amplifier provided by the present invention.

[0028] Figure 4 A schematic diagram of the circuit structure and switch timing of the chopper stabilization module provided by the present invention.

[0029] Figure 5 This is a schematic diagram of the structure of a DSL feedback loop provided by the present invention.

[0030] Figure 6 A schematic diagram of the structure of the RRL feedback loop provided by the present invention. DETAILED DESCRIPTION

[0031] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments and drawings. The exemplary embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0032] like Figure 2 As shown, an embodiment of the present invention provides an amplifier circuit for improving the common mode rejection ratio, comprising: a fully differential transconductance amplifier module, a passive capacitor and resistor module, and a chopper stabilization module;

[0033] The fully differential transconductance amplifier module is used to convert the input differential voltage into an output current and amplify the output;

[0034] The passive capacitor and resistor module is arranged on the fully differential transconductance amplifier module, and is used to isolate the common mode voltage, determine the in-band gain through the capacitor, perform self-biasing through the resistor, and achieve high-pass angular frequency through the resistor and capacitor;

[0035] The chopper stabilization module is arranged on the fully differential transconductance amplifier module, and is used to implement the chopper modulation function by switching the switch through the clock signal, thereby improving the common mode suppression capability of the amplifier.

[0036] The traditional three-op-amp structure is affected by the second-stage resistor mismatch and it is difficult to obtain a high CMRR value. By adopting the chopper-stabilized circuit with capacitor-coupled instrument amplifier solution of the invention, the common-mode to differential-mode gain at low frequencies is optimized, thereby greatly improving the overall CMRR.

[0037] In a possible implementation, the fully differential transconductance amplification module includes a transconductance amplifier OPA, and the transconductance amplifier OPA is electrically connected to the passive capacitor and resistor module and the chopper stabilization module respectively.

[0038] A fully differential operational transconductance amplifier (OTA) converts the input differential voltage into an output current and amplifies it. The fully differential structure is beneficial for suppressing noise.

[0039] like Figure 3 As shown, the present invention changes the architecture of the three-op-amp instrumentation amplifier and adopts an instrumentation amplifier solution with a chopper stabilization circuit to obtain a capacitively coupled instrumentation amplifier (CCIA).

[0040] In a possible implementation, the passive capacitor and resistor module includes a first AC capacitor CIN1, a second AC capacitor CIN2, a first parasitic capacitor CP1, a second parasitic capacitor CP2, a first feedback capacitor CF1, a second feedback capacitor CF2, a first feedback resistor RF1, and a second feedback resistor RF2;

[0041] The chopper stabilization module includes a first chopper circuit and a second chopper circuit;

[0042] One end of the first AC capacitor CIN1 and one end of the second AC capacitor CIN2 jointly receive a differential signal input from the outside, the other end of the first AC capacitor CIN1 is respectively connected to one end of the first parasitic capacitor CP1, the positive input end of the first chopper circuit and one end of the first feedback capacitor CF1, the other end of the first parasitic capacitor CP1 is grounded, the other end of the second AC capacitor CIN2 is respectively connected to one end of the second parasitic capacitor CP2, the negative input end of the first chopper circuit and one end of the second feedback capacitor CF2, the positive output end of the first chopper circuit is respectively connected to one end of the first feedback resistor RF1 and the in-phase input end of the transconductance amplifier OPA. The first chopper circuit is connected to the negative output terminal of the transconductance amplifier OPA and the negative input terminal of the second chopper circuit, and the negative output terminal of the second chopper circuit is connected to the other end of the first feedback capacitor CF1; the negative output terminal of the first chopper circuit is connected to one end of the second feedback resistor RF2 and the inverting input terminal of the transconductance amplifier OPA, and the other end of the second feedback resistor RF2 is connected to the positive output terminal of the transconductance amplifier OPA and the positive input terminal of the second chopper circuit, and the positive output terminal of the second chopper circuit is connected to the other end of the second feedback capacitor CF2; the two output terminals of the second chopper circuit output signals.

[0043] The in-band gain is determined by the capacitor ratio. The advantage of using capacitors to set the gain is that the capacitors have better matching and more stable gain. The AC capacitors in series can isolate the common-mode voltage and improve the CMRR. The feedback resistor has two functions: one is self-biasing, that is, the input common mode is biased with the output common mode, and the other is that the resistor and feedback capacitor achieve a high-pass angular frequency. The high-pass transfer function is conducive to filtering out flicker noise and offset voltage at low frequencies.

[0044] like Figure 4 As shown, the first chopping circuit and the second chopping circuit have the same structure, and both include: a first transmission gate, a second transmission gate, a third transmission gate and a fourth transmission gate;

[0045] The input end of the first transmission gate serves as the negative input end of the chopper circuit and is connected to the input end of the fourth transmission gate; the input end of the second transmission gate serves as the positive input end of the chopper circuit and is connected to the input end of the third transmission gate; the output end of the third transmission gate serves as the negative output end of the chopper circuit, and the output end of the third transmission gate is connected to the output end of the first transmission gate; the output end of the fourth transmission gate serves as the positive output end of the chopper circuit, and the output end of the fourth transmission gate is connected to the output end of the second transmission gate.

[0046] The chopper-stabilized circuit mainly uses four transmission gates to realize switching, and then switches the clock signal to realize the chopper modulation function. The chopper-stabilized circuit can significantly improve the common-mode rejection capability of the amplifier. The principle is that the common-mode input signal will not be modulated, but due to the limited CMRR of the amplifier itself, after passing through the OTA, the common-mode signal will be converted into a differential-mode signal, and then after passing through the second-stage chopper circuit, the differential-mode signal converted from the common-mode signal change is modulated to a high frequency.

[0047] In a possible implementation manner, the first transmission gate, the second transmission gate, the third transmission gate and the fourth transmission gate have the same structure and are all formed by connecting a P-channel and an N-channel enhancement type field effect transistor in parallel.

[0048] In a possible implementation, a DSL (DC servo loop) feedback loop and an RRL (Ripple Rejection Loop) feedback loop are also included. The DSL feedback loop and the RRL feedback loop are both based on the output signal of the fully differential transconductance amplifier module to generate feedback signals to the fully differential transconductance amplifier module.

[0049] In this embodiment, the main function of DSL is to control the residual offset introduced by chopping, and RRL is to filter the output ripple caused by chopping. The residual offset voltage and output ripple of chopping are eliminated through the DSL and RRL feedback loops, making the entire system more stable.

[0050] like Figure 5 As shown, the DSL feedback loop includes a first integrating amplifier, a first DSL chopping circuit and a DSL amplifier connected in sequence; the input end of the first integrating amplifier is respectively connected to the two output ends of the second chopping circuit, and the output end of the DSL amplifier is connected to the input end of the transconductance amplifier OPA.

[0051] like Figure 6 As shown, the RRL feedback loop includes a first capacitor CRRL, a first RRL chopper circuit, a second integrating amplifier and an RRL amplifier connected in sequence, the input end of the second integrating amplifier is connected to the two output ends of the second chopper circuit through the first capacitor CRRL and the first RRL chopper circuit, and the output end of the RRL amplifier is connected to the input end of the transconductance amplifier OPA.

[0052] In a possible implementation, a low-pass filter circuit is further included, and the low-pass filter circuit is arranged at the output end of the second chopper circuit in the chopper stabilization module to filter the output signal. The differential mode signal is removed by the low-pass filter circuit (LPF), thereby improving the overall CMRR.

[0053] In a possible implementation, the low-pass filter circuit includes: a first filter resistor RL1, a second filter resistor RL2, and a third filter capacitor CL;

[0054] One end of the first filter resistor RL1 is connected to the negative output end of the second chopper circuit, one end of the second filter resistor RL2 is connected to the positive output end of the second chopper circuit, the other end of the first filter resistor RL1 and the other end of the second filter resistor RL2 are respectively connected to the two ends of the third filter capacitor CL, and the other end of the first filter resistor RL1 and the other end of the second filter resistor RL2 are provided as the output end of the amplifier circuit for improving the common mode rejection ratio.

[0055] The present invention provides an amplifier circuit for improving the common mode rejection ratio, which improves the common mode rejection ratio of the circuit system by suppressing the change of the common mode signal and the differential mode signal caused by the change of the common mode signal; adopts a combination of a capacitor coupling structure and a chopper stabilization circuit to solve several problems of the instrument amplifier with a three-op amp structure, firstly, the amplifier driving passive network is conducive to reducing power consumption; secondly, the series AC capacitor isolates the common mode signal, which helps to improve the CMRR of the circuit; thirdly, the chopper stabilization circuit modulates the offset voltage and the common mode signal change voltage to a high frequency, filters them out through a filter, improves the circuit gain, and also improves the CMRR; fourthly, the residual offset and output ripple problems caused by the chopper circuit are reduced through DSL and RRL, so that the subsequent circuit avoids saturation.

[0056] The in-band gain of a capacitively-coupled instrumentation amplifier (CCIA) is determined by the capacitor ratio:

[0057]

[0058] Among them, C IN1 >>C F1 and C IN1 >>C P1 Now, considering the mismatch of resistors and capacitors and ignoring the effect of chopping, we can get the common-mode to differential-mode gain:

[0059]

[0060] Where f is the input signal frequency, is the relative mismatch of the feedback resistors, σ C The input capacitor C IN , feedback capacitor C FB and parasitic capacitance C P The equivalent capacitance mismatch can be expressed as:

[0061]

[0062] Among them, f HPF represents the high-pass corner frequency of CCIA, f Z is with f HPF The relevant angular frequencies are:

[0063]

[0064] According to the gain formula, the mismatch of the feedback resistor determines the low-frequency performance of the CMRR, and the mismatch of the capacitor determines the mid- and high-frequency performance of the CMRR.

[0065] Since the high-pass angle is generally low, the feedback resistor is generally very large. If a large resistor is used, the area will exceed the constraint. Therefore, the feedback resistor is generally a pseudo-resistor composed of a MOS tube. However, the resistance of the pseudo-resistor will change with the driving voltage. In addition, the resistance mismatch of the pseudo-resistor itself is also large. Now consider placing the pseudo-resistor in the chopper circuit to eliminate the influence of the pseudo-resistor resistance mismatch and thus improve CMRR. In this way, the optimized A c_d :

[0066]

[0067] In addition, the non-ideality of the chopper circuit will lead to incomplete elimination of the offset voltage, and the residual offset may saturate the subsequent circuit after post-stage amplification. The DSL structure can offset the input offset.

[0068] The voltage range that can be offset is V os,res :

[0069]

[0070] Among them, gm DSL is the transconductance of the DSL level, gm is the transconductance of the amplifier, VOUT INT is the maximum output voltage of the DSL feedback loop integrator.

[0071] Another non-ideal factor of chopper modulation is the output ripple caused by the primary modulation of the input offset. The RRL loop is eliminated to avoid integrator saturation.

[0072] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. An amplifier circuit for improving the common mode rejection ratio, It is characterized in that include: Fully differential transconductance amplifier module, passive capacitor and resistor module, and chopper stabilization module; The fully differential transconductance amplifier module is used to convert the input differential voltage into an output current and amplify the output; The passive capacitor and resistor module is arranged on the fully differential transconductance amplifier module, and is used to isolate the common mode voltage, determine the in-band gain through the capacitor, perform self-biasing through the resistor, and achieve high-pass angular frequency through the resistor and capacitor; The chopper stabilization module is arranged on the fully differential transconductance amplifier module, and is used to implement the chopper modulation function by switching the switch through the clock signal, thereby improving the common mode suppression capability of the amplifier.

2. The amplifier circuit for improving the common mode rejection ratio according to claim 1, It is characterized in that The fully differential transconductance amplification module includes a transconductance amplifier (OPA), and the transconductance amplifier (OPA) is electrically connected to the passive capacitor and resistor module and the chopper stabilization module respectively.

3. The amplifier circuit for improving the common mode rejection ratio according to claim 2, It is characterized in that The passive capacitor and resistor module includes a first AC capacitor (CIN1), a second AC capacitor (CIN2), a first parasitic capacitor (CP1), a second parasitic capacitor (CP2), a first feedback capacitor (CF1), a second feedback capacitor (CF2), a first feedback resistor (RF1) and a second feedback resistor (RF2); The chopper stabilization module includes a first chopper circuit and a second chopper circuit; One end of the first AC capacitor (CIN1) and one end of the second AC capacitor (CIN2) jointly receive a differential signal input from the outside, the other end of the first AC capacitor (CIN1) is respectively connected to one end of the first parasitic capacitor (CP1), the positive input end of the first chopper circuit and one end of the first feedback capacitor (CF1), the other end of the first parasitic capacitor (CP1) is grounded, the other end of the second AC capacitor (CIN2) is respectively connected to one end of the second parasitic capacitor (CP2), the negative input end of the first chopper circuit and one end of the second feedback capacitor (CF2), the positive output end of the first chopper circuit is respectively connected to one end of the first feedback resistor (RF1) and the positive output end of the transconductance amplifier (OPA) The first chopper circuit is connected to the negative input terminal of the transconductance amplifier (OPA), the other end of the first feedback resistor (RF1) is respectively connected to the negative output terminal of the transconductance amplifier (OPA) and the negative input terminal of the second chopper circuit, and the negative output terminal of the second chopper circuit is connected to the other end of the first feedback capacitor (CF1); the negative output terminal of the first chopper circuit is respectively connected to one end of the second feedback resistor (RF2) and the inverting input terminal of the transconductance amplifier (OPA), the other end of the second feedback resistor (RF2) is respectively connected to the positive output terminal of the transconductance amplifier (OPA) and the positive input terminal of the second chopper circuit, and the positive output terminal of the second chopper circuit is connected to the other end of the second feedback capacitor (CF2); the two output terminals of the second chopper circuit output signals.

4. The amplifier circuit for improving the common mode rejection ratio according to claim 3, It is characterized in that The first chopping circuit and the second chopping circuit have the same structure and both include: a first transmission gate, a second transmission gate, a third transmission gate and a fourth transmission gate; The input end of the first transmission gate serves as the negative input end of the chopper circuit and is connected to the input end of the fourth transmission gate; the input end of the second transmission gate serves as the positive input end of the chopper circuit and is connected to the input end of the third transmission gate; the output end of the third transmission gate serves as the negative output end of the chopper circuit, and the output end of the third transmission gate is connected to the output end of the first transmission gate; the output end of the fourth transmission gate serves as the positive output end of the chopper circuit, and the output end of the fourth transmission gate is connected to the output end of the second transmission gate.

5. The amplifier circuit for improving common mode rejection ratio according to claim 4, It is characterized in that The first transmission gate, the second transmission gate, the third transmission gate and the fourth transmission gate have the same structure and are all formed by connecting a P-channel and an N-channel enhancement type field effect transistor in parallel.

6. The amplifier circuit for improving common mode rejection ratio according to claim 3, It is characterized in that It also includes a DSL feedback loop and an RRL feedback loop. The DSL feedback loop and the RRL feedback loop are both based on the output signal of the full differential transconductance amplifier module to generate a feedback signal to the full differential transconductance amplifier module.

7. The amplifier circuit for improving common mode rejection ratio according to claim 5, It is characterized in that The DSL feedback loop includes a first integrating amplifier, a first DSL chopping circuit and a DSL amplifier connected in sequence; the input end of the first integrating amplifier is respectively connected to the two output ends of the second chopping circuit, and the output end of the DSL amplifier is connected to the input end of a transconductance amplifier (OPA).

8. The amplifier circuit for improving common mode rejection ratio according to claim 5, It is characterized in that The RRL feedback loop includes a first capacitor (CRRL), a first RRL chopper circuit, a second integrating amplifier and an RRL amplifier connected in sequence, the input end of the second integrating amplifier is connected to the two output ends of the second chopper circuit through the first capacitor (CRRL) and the first RRL chopper circuit, and the output end of the RRL amplifier is connected to the input end of the transconductance amplifier (OPA).

9. The amplifier circuit for improving common mode rejection ratio according to claim 3, It is characterized in that It also includes a low-pass filter circuit, which is arranged on the output end of the second chopper circuit in the chopper stabilization module to filter the output signal.

10. The amplifier circuit for improving common mode rejection ratio according to claim 8, It is characterized in that The low-pass filter circuit comprises: a first filter resistor (RL1), a second filter resistor (RL2) and a third filter capacitor (CL); One end of the first filter resistor (RL1) is connected to the negative output end of the second chopper circuit, one end of the second filter resistor (RL2) is connected to the positive output end of the second chopper circuit, the other end of the first filter resistor (RL1) and the other end of the second filter resistor (RL2) are respectively connected to the two ends of the third filter capacitor (CL), and the other end of the first filter resistor (RL1) and the other end of the second filter resistor (RL2) are provided as the output end of the amplifier circuit for improving the common mode rejection ratio.

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