Automatic calibration analog front-end circuit based on embedded direct-current servo loop

Abstract

The invention relates to the technical field of integrated circuits, and provides an automatic calibration analog front-end circuit based on an embedded direct-current servo loop, and the circuit comprises a two-stage chopping operational amplifier which comprises a first-stage chopping operational amplifier and a second-stage chopping operational amplifier; according to the embedded direct-current servo loop, a transconductance stage is used for replacing a traditional coupling capacitor, and a voltage signal is converted into a current signal to be coupled to a first-stage chopping operational amplifier; the input end of the automatic calibration unit is connected with the output end of the secondary chopping operational amplifier, and the output end of the automatic calibration unit is connected with the transconductance stage of the embedded direct-current servo loop; the variable gain amplifier is connected with the output end of the secondary chopping operational amplifier; the invention discloses a common-mode detection circuit and a common-mode copy circuit. According to the analog front-end circuit, the framework of combining the embedded direct-current servo loop and the automatic calibration unit is introduced, so that the analog front-end circuit can adaptively suppress wide-range electrode direct-current imbalance on the basis of keeping low noise and high input impedance.

Description

Technical Field

[0001] This invention belongs to the field of integrated circuits, and particularly relates to an automatic calibration analog front-end circuit based on an embedded DC servo circuit. Background Technology

[0002] With the development of integrated circuit technology, portable long-term physiological electrical signal monitoring devices have become possible. The core of such devices lies in their ability to accurately capture weak physiological electrical signals, which are typically characterized by low frequency and small amplitude. Therefore, this places high demands on their detection circuitry: it must possess extremely low input reference noise and strong electrode DC offset voltage cancellation capabilities. Simultaneously, to meet the requirements of portability and long-term monitoring, circuit power consumption must also be kept at a low level. Furthermore, while dry electrode acquisition is convenient, it introduces significant electrode DC offset voltage and reduces the circuit's common-mode rejection ratio, further increasing the design difficulty of the front-end circuitry. As the primary link for signal entry into the system, the performance of the analog front-end circuitry directly determines the effectiveness and reliability of the entire system.

[0003] In summary, achieving a good balance between key performance indicators such as low noise, high DC offset tolerance, low power consumption, and high input impedance is the main technical challenge in analog front-end circuit design. Therefore, an innovative circuit architecture is needed to address these contradictions. Summary of the Invention

[0004] In view of the above-mentioned deficiencies of the prior art, the present invention proposes an automatic calibration analog front-end circuit based on an embedded DC servo circuit. The technical solution designed in this invention includes: A two-stage chopper operational amplifier includes a first-stage chopper operational amplifier and a second-stage chopper operational amplifier, which are used to amplify the input signal, respectively. An embedded DC servo circuit uses a transconductance stage instead of a traditional coupling capacitor to convert the voltage signal into a current signal and couple it to the first-stage chopper operational amplifier to suppress the DC offset voltage of the electrodes. An automatic calibration unit, whose input is connected to the output of the two-stage chopper operational amplifier and whose output is connected to the transconductance stage of the embedded DC servo circuit, is used to adaptively adjust the equivalent transconductance value of the transconductance stage. A variable gain amplifier, connected to the output of the second-stage chopper operational amplifier, is used to provide multiple programmable gain levels. The common-mode detection circuit and common-mode replication circuit are used to detect the common-mode level of the input signal and generate an internally stable common-mode reference voltage.

[0005] Preferably, the first-stage chopper operational amplifier adopts an input complementary cascode amplifier structure.

[0006] Preferably, the input complementary cascode amplifier structure includes: The non-inverting input terminal is connected to the gates of the first PMOS input transistor M1 and the first NMOS input transistor M2; The drain of the first PMOS input transistor M1 is connected to the source of the first cascode transistor M5, and the drain of the first NMOS input transistor M2 is connected to the source of the second cascode transistor M7. The drains of the first cascode transistor M5 and the second cascode transistor M7 together serve as the inverting output terminal of the first-stage chopper operational amplifier. The inverting input terminal is connected to the gates of the second PMOS input transistor M3 and the second NMOS input transistor M4; The drain of the second PMOS input transistor M3 is connected to the source of the third cascode transistor M6, and the drain of the second NMOS input transistor M4 is connected to the source of the fourth cascode transistor M8. The drains of the third cascode transistor M6 and the fourth cascode transistor M8 together serve as the non-inverting output terminal of the first-stage chopper operational amplifier.

[0007] Preferably, the transconductance stage of the embedded DC servo circuit includes at least three independently controllable parallel transconductance branches.

[0008] Preferably, by controlling the on / off combination of the parallel transconductance branches, the transconductance stage can be configured to have four different equivalent transconductance values, and the ratio of the four equivalent transconductance values ​​is 1:3:5:7.

[0009] Preferably, the transconductance stage positive input terminal includes a first pair of differential input transistors M11 and M12, a second pair of differential input transistors M15 and M18, and a first switch transistor M16 and a second switch transistor M17 connected in series with the drains of the second pair of differential input transistors, respectively. Wherein, the drains of the first pair of differential input transistors M11 and M12 serve as a pair of differential output nodes of the transconductance stage, and the drains of the second pair of differential input transistors M15 and M18 are selectively connected to the pair of differential output nodes through the first switch transistor M16 and the second switch transistor M17. The drains of the first pair of differential input transistors M11 and M16 are connected, and the drains of the first pair of differential input transistors M12 and M17 are connected, which are the inverting output terminals of the transconductance stage. The transconductance stage inverting input terminal includes a first pair of differential input transistors M13 and M14, a second pair of differential input transistors M19 and M22, and a first switching transistor M20 and a second switching transistor M21 connected in series with the drains of the second pair of differential input transistors, respectively. In this configuration, the drains of the first pair of differential input transistors M13 and M14 serve as a pair of differential output nodes of the transconductance stage. The drains of the second pair of differential input transistors M19 and M22 are selectively connected to the pair of differential output nodes through the first switch transistor M20 and the second switch transistor M21. The drains of the first pair of differential input transistors M13 and M20 are connected, and the drains of the first pair of differential input transistors M14 and M21 are connected, forming the positive output terminals of the transconductance stage.

[0010] Preferably, the automatic calibration unit includes: The voltage detection module is used to compare the differential output voltage of the second-stage chopper operational amplifier with a high reference voltage and a low reference voltage. A logic control module, connected to the voltage detection module, is used to generate and output a control signal to adjust the equivalent transconductance value of the transconductance stage when the differential output voltage exceeds the threshold range determined by the high reference voltage and the low reference voltage.

[0011] Preferably, the voltage detection module includes four comparators, wherein: The non-inverting input of the first comparator is connected to the non-inverting output of the second-stage chopper operational amplifier, and the inverting input is connected to the low reference voltage. The inverting input of the second comparator is connected to the non-inverting output of the second-stage chopper operational amplifier, and the non-inverting input is connected to the high reference voltage. The non-inverting input of the third comparator is connected to the inverting output of the second-stage chopper operational amplifier, and the inverting input is connected to the low reference voltage. The inverting input of the fourth comparator is connected to the inverting output of the second-stage chopper operational amplifier, and the non-inverting input is connected to the high reference voltage.

[0012] Preferably, the control signal output by the automatic calibration unit is connected to the gates of the first switch M16, the second switch M17, the third switch M20 and the fourth switch M21 in the transconductance stage, and is used to control the on / off state of the transconductance stage.

[0013] Preferably, the variable gain amplifier changes its gain by switching the capacitor array at its input, the capacitor array providing at least four different input capacitance values, corresponding to at least four programmable gain levels.

[0014] Beneficial effects: 1. This application significantly reduces the inherent input reference noise of the circuit by adopting a chopper amplifier with an input complementary cascode structure. At the same time, the embedded DC servo circuit combined with the automatic calibration mechanism can dynamically and accurately cancel a wide range of electrode DC offset voltages. Thus, while ensuring high-precision acquisition of weak physiological signals, it can effectively resist strong DC interference and improve the reliability of the system in practical applications. 2. The automatic calibration unit of this application monitors the output status in real time and intelligently adjusts the connection mode of the transconductance stage branch to change the magnitude of the equivalent transconductance value of the transconductance stage, so that the circuit has an adaptive anti-interference capability that can be adjusted as needed. This dynamic optimization mechanism avoids the performance overkill of traditional fixed parameter circuits under no interference or weak interference conditions, thereby achieving strong offset suppression capability while optimizing the power consumption efficiency of the overall circuit. 3. This application adopts a transconductance level ( Direct coupling replaces the traditional embedded servo solution using large-size coupling capacitors, which not only saves chip area and facilitates high integration, but also eliminates the additional noise and signal integrity risks caused by capacitors. Combined with auxiliary circuits, it further improves the equivalent input impedance, making this circuit particularly suitable for high-impedance dry electrode bioelectric signal acquisition scenarios. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the overall structure of the analog front-end circuit according to a preferred embodiment of the present invention; Figure 2 This is a schematic diagram of an embedded DC servo circuit structure according to a preferred embodiment of the present invention; Figure 3 This is a schematic diagram of the first-stage chopper operational amplifier circuit of a preferred embodiment of the present invention; Figure 4 This is a schematic diagram of the automatic calibration unit structure according to a preferred embodiment of the present invention; Figure 5 This is a schematic diagram of a variable gain amplifier structure according to a preferred embodiment of the present invention. Detailed Implementation

[0016] The embodiments of the present invention will be described in detail below. The embodiments described below are implemented based on the technical solution of the present invention, and detailed implementation methods and specific operation processes are given. However, the protection scope of the present invention is not limited to the embodiments described below.

[0017] This invention designs an automatic calibration analog front-end circuit based on an embedded DC servo circuit, such as... Figure 1-5 As shown, the technical solution specifically includes: A two-stage chopper operational amplifier includes a first-stage chopper operational amplifier and a second-stage chopper operational amplifier, which are used to amplify the input signal, respectively. An embedded DC servo circuit uses a transconductance stage instead of a traditional coupling capacitor to convert the voltage signal into a current signal and couple it to the first-stage chopper operational amplifier to suppress the DC offset voltage of the electrodes. An automatic calibration unit has its input connected to the output of a two-stage chopper operational amplifier and its output connected to the transconductance stage of an embedded DC servo circuit, used to adaptively adjust the equivalent transconductance value of the transconductance stage. A variable gain amplifier, which is connected to the output of a two-stage chopper operational amplifier, is used to provide multiple programmable gain levels. The common-mode detection circuit and common-mode replication circuit are used to detect the common-mode level of the input signal and generate an internally stable common-mode reference voltage.

[0018] Specifically, the input terminals of the analog front-end circuit are connected to electrodes, and the equivalent input impedance is increased through auxiliary circuits and positive feedback circuits. The auxiliary circuit uses precharge technology to improve the circuit's equivalent input impedance. Simultaneously, a chopping scheme is employed, and the first-stage operational amplifier uses an input complementary cascode amplifier structure to reduce the circuit's input reference noise and ensure the reliability of the acquired signal.

[0019] Preferably, the first-stage chopper operational amplifier adopts an input complementary cascode amplifier structure.

[0020] Preferably, the input complementary cascode amplifier structure includes: The non-inverting input terminal is connected to the gates of the first PMOS input transistor M1 and the first NMOS input transistor M2; The drain of the first PMOS input transistor M1 is connected to the source of the first cascode transistor M5, and the drain of the first NMOS input transistor M2 is connected to the source of the second cascode transistor M7. The drains of the first cascode transistor M5 and the second cascode transistor M7 together serve as the inverting output terminal of the first-stage chopper operational amplifier. The inverting input terminal is connected to the gates of the second PMOS input transistor M3 and the second NMOS input transistor M4; The drain of the second PMOS input transistor M3 is connected to the source of the third cascode transistor M6, and the drain of the second NMOS input transistor M4 is connected to the source of the fourth cascode transistor M8. The drains of the third cascode transistor M6 and the fourth cascode transistor M8 together serve as the non-inverting output terminal of the first-stage chopper operational amplifier.

[0021] Specifically, an input complementary cascode amplifier structure is used to reduce the noise contributed by the first-stage operational amplifier, while an embedded DC servo circuit is used to reduce the noise contributed by the DSL.

[0022] Preferably, the transconductance stage of the embedded DC servo circuit includes at least three independently controllable parallel transconductance branches.

[0023] Specifically, the analog front-end circuit adopts an embedded DC servo circuit and uses transconductance stages. Replace coupling capacitor The output voltage of the integrator in the DC servo circuit is transmitted through the transconductance. The current is converted into current, and then converted into voltage across the output resistor of the first-stage transconductance amplifier, thus achieving signal coupling. The embedded DC servo circuit connected to the transconductance stage of the first-stage operational amplifier consists of three branches, with four possible connection methods, and their transconductance ratios are 1:3:5:7.

[0024] Preferably, by controlling the on / off combination of the parallel transconductance branches, the transconductance level can be configured to have four different equivalent transconductance values, and the ratio of the four equivalent transconductance values ​​is 1:3:5:7.

[0025] Preferably, the non-phase input terminal of the transconductance stage includes a first pair of differential input transistors M11 and M12, a second pair of differential input transistors M15 and M18, and a first switch transistor M16 and a second switch transistor M17 connected in series with the drains of the second pair of differential input transistors, respectively. In this system, the drains of the first pair of differential input transistors M11 and M12 serve as a pair of differential output nodes in the transconductance stage. The drains of the second pair of differential input transistors M15 and M18 can be selectively connected to a pair of differential output nodes through the first switch transistor M16 and the second switch transistor M17. The drains of the first pair of differential input transistors M11 and M16 are connected, and the drains of the first pair of differential input transistors M12 and M17 are connected, which serve as the inverting output terminals of the transconductance stage. The transconductance stage inverting input terminal includes a first pair of differential input transistors M13 and M14, a second pair of differential input transistors M19 and M22, and a first switching transistor M20 and a second switching transistor M21 connected in series with the drains of the second pair of differential input transistors, respectively. In this system, the drains of the first pair of differential input transistors M13 and M14 serve as a pair of differential output nodes in the transconductance stage. The drains of the second pair of differential input transistors M19 and M22 can be selectively connected to a pair of differential output nodes through the first switch transistor M20 and the second switch transistor M21. The drains of the first pair of differential input transistors M13 and M20 are connected, and the drains of the first pair of differential input transistors M14 and M21 are connected, which are the positive output terminals of the transconductance stage.

[0026] Specifically, the non-inverting output terminal of chopper CH7 in the embedded DC servo circuit is connected to the transconductance stage. The gates of transistors M11, M12, M15, and M18 at the non-inverting input terminals are connected; the drains of transistors M15 and M18 are connected to the sources of switching transistors M16 and M17, which control their respective branches; the drains of transistors M11 and M16 are connected, and the drains of transistors M12 and M17 are connected, forming a transconductance stage. The inverting output terminal of the transistor; the drains of transistors M11 and M16 are connected to the drain of transistor M1 and the source of transistor M5 in the first-stage chopper amplifier; the drains of transistors M12 and M17 are connected to the drain of transistor M2 and the source of transistor M7 in the first-stage chopper amplifier; the inverting output terminal of chopper CH7 in the embedded DC servo circuit is connected to the transconductance stage. The gates of transistors M13, M14, M19, and M22 are connected to the inverting input terminals; the drains of transistors M19 and M21 are connected to the sources of the switching transistors M20 and M21 that control their respective branches; transistor M13 is connected to the drain of M20, and transistor M14 is connected to the drain of M21, forming a transconductance stage. The positive output terminal; the drains of transistors M13 and M20 are connected to the drain of transistor M3 and the source of transistor M6 in the first-stage chopper amplifier; the drains of transistors M14 and M21 are connected to the drain of transistor M4 and the source of transistor M8 in the first-stage chopper amplifier.

[0027] Preferably, the automatic calibration unit includes: The voltage detection module is used to compare the differential output voltage of the second-stage chopper operational amplifier with a high reference voltage and a low reference voltage. The logic control module, connected to the voltage detection module, generates and outputs a control signal to adjust the equivalent transconductance value of the transconductance stage when the differential output voltage exceeds the threshold range determined by the high reference voltage and the low reference voltage.

[0028] Specifically, the automatic calibration unit consists of four comparators, one D flip-flop, one 4-bit counter, and a majority voting circuit module. It determines the circuit's output state by comparing the input voltage with a set voltage threshold. When the amplifier output is saturated, it adjusts the transconductance stage connection of the DC servo circuit via the output enable signal EN until the circuit output returns to normal. The automatic calibration scheme is implemented by the automatic calibration unit by adjusting the transconductance stage connection of the embedded DC servo circuit. The automatic calibration unit controls the transconductance stage through the enable signal EN. The connection state of the parallel branches enhances the circuit's resistance to electrode DC offset voltage while minimizing the input reference noise contributed by the DC servo circuit. The automatic calibration unit uses a comparator to determine if the amplifier's output voltage is within the standard voltage range. When the output voltage exceeds the given standard voltage, the circuit output state is abnormal. The automatic calibration unit records the output state using a D flip-flop and generates an enable signal EN through a four-bit counter and majority voting circuit, thereby changing the transconductance stage of the DC servo circuit. The branch connection method changes the circuit's ability to resist DC interference voltage until the circuit output returns to normal.

[0029] Preferably, the voltage detection module includes four comparators, wherein: The non-inverting input of the first comparator is connected to the non-inverting output of the second-stage chopper operational amplifier, and the inverting input is connected to the low reference voltage. The inverting input of the second comparator is connected to the non-inverting output of the second-stage chopper operational amplifier, and the non-inverting input is connected to the high reference voltage. The non-inverting input of the third comparator is connected to the inverting output of the second-stage chopper operational amplifier, and the inverting input is connected to the low reference voltage. The inverting input of the fourth comparator is connected to the inverting output of the second-stage chopper operational amplifier, and the non-inverting input is connected to the high reference voltage.

[0030] Specifically, the non-inverting output of the second-stage chopper amplifier is connected to the non-inverting input of the comparator in the automatic calibration unit, and the inverting input of the comparator is set with a reference voltage. The non-inverting output of the second-stage chopper amplifier is simultaneously connected to the inverting output of another comparator, whose non-inverting input is set with a reference voltage. The non-inverting output of the second-stage chopper amplifier is connected to the inverting input of the comparator in the automatic calibration unit, and the inverting input of this comparator is set with a reference voltage. The inverting output of the second-stage chopper amplifier is simultaneously connected to the inverting output of another comparator, whose non-inverting input is set with a reference voltage. The automatic calibration unit uses a comparator to detect whether the output voltage of the second-stage chopper amplifier is within the specified reference voltage. and Between these stages, the output state of the second-stage chopper amplifier is detected and recorded by a flag detector consisting of a 4-input OR gate and a rising-edge triggered D flip-flop. This flag is then used to generate a signal `en` via a four-bit counter. The `en` signal passes through a majority voting circuit to eliminate logic errors that may be caused by the dead time, thus generating the control transconductance stage. The enable signal EN indicates the connection status of parallel branches.

[0031] Preferably, the control signal output by the automatic calibration unit is connected to the gates of the first switch M16, the second switch M17, the third switch M20 and the fourth switch M21 in the transconductance stage, and is used to control the on and off of the transconductance stage.

[0032] Specifically, the output of the automatic calibration unit is connected to the gates of switching transistors M16, M17, M20, and M21.

[0033] Preferably, the variable gain amplifier changes its gain by switching the capacitor array at its input, the capacitor array providing at least four different input capacitance values, corresponding to at least four programmable gain levels.

[0034] Specifically, the variable gain amplifier offers four gain options to accommodate different signal intensities. Its feedback capacitor is 1pF, and the input capacitor has four different sizes to choose from depending on the switching state. By selecting different input capacitor sizes, the gain of the variable gain amplifier is changed, thus meeting the acquisition requirements of signals with different amplitudes. The variable gain amplifier's gain is altered by controlling the switching transistor to change the input capacitor.

[0035] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. An automatic calibration analog front-end circuit based on an embedded DC servo circuit, characterized in that, include: A two-stage chopper operational amplifier includes a first-stage chopper operational amplifier and a second-stage chopper operational amplifier, which are used to amplify the input signal, respectively. An embedded DC servo circuit uses a transconductance stage instead of a traditional coupling capacitor to convert the voltage signal into a current signal and couple it to the first-stage chopper operational amplifier to suppress the DC offset voltage of the electrodes. An automatic calibration unit, whose input is connected to the output of the two-stage chopper operational amplifier and whose output is connected to the transconductance stage of the embedded DC servo circuit, is used to adaptively adjust the equivalent transconductance value of the transconductance stage. A variable gain amplifier, connected to the output of the second-stage chopper operational amplifier, is used to provide multiple programmable gain levels. The common-mode detection circuit and common-mode replication circuit are used to detect the common-mode level of the input signal and generate an internally stable common-mode reference voltage.

2. The automatic calibration analog front-end circuit based on an embedded DC servo circuit according to claim 1, characterized in that, The first-stage chopper operational amplifier adopts an input complementary cascode amplifier structure.

3. The automatic calibration analog front-end circuit based on an embedded DC servo circuit according to claim 2, characterized in that, The input complementary cascode amplifier structure includes: The non-inverting input terminal is connected to the gates of the first PMOS input transistor M1 and the first NMOS input transistor M2; The drain of the first PMOS input transistor M1 is connected to the source of the first cascode transistor M5, and the drain of the first NMOS input transistor M2 is connected to the source of the second cascode transistor M7. The drains of the first cascode transistor M5 and the second cascode transistor M7 together serve as the inverting output terminal of the first-stage chopper operational amplifier. The inverting input terminal is connected to the gates of the second PMOS input transistor M3 and the second NMOS input transistor M4; The drain of the second PMOS input transistor M3 is connected to the source of the third cascode transistor M6, and the drain of the second NMOS input transistor M4 is connected to the source of the fourth cascode transistor M8. The drains of the third cascode transistor M6 and the fourth cascode transistor M8 together serve as the non-inverting output terminal of the first-stage chopper operational amplifier.

4. The automatic calibration analog front-end circuit based on an embedded DC servo circuit according to claim 1, characterized in that, The transconductance stage of the embedded DC servo circuit includes at least three independently controllable parallel transconductance branches.

5. The automatic calibration analog front-end circuit based on an embedded DC servo circuit according to claim 4, characterized in that, By controlling the on / off combination of the parallel transconductance branches, the transconductance stage can be configured to have four different equivalent transconductance values, and the ratio of the four equivalent transconductance values ​​is 1:3:5:

7.

6. The automatic calibration analog front-end circuit based on an embedded DC servo circuit according to claim 1, characterized in that, The transconductance stage positive phase input terminal includes a first pair of differential input transistors M11 and M12, a second pair of differential input transistors M15 and M18, and a first switch transistor M16 and a second switch transistor M17 connected in series with the drains of the second pair of differential input transistors, respectively. Wherein, the drains of the first pair of differential input transistors M11 and M12 serve as a pair of differential output nodes of the transconductance stage, and the drains of the second pair of differential input transistors M15 and M18 are selectively connected to the pair of differential output nodes through the first switch transistor M16 and the second switch transistor M17. The drains of the first pair of differential input transistors M11 and M16 are connected, and the drains of the first pair of differential input transistors M12 and M17 are connected, which are the inverting output terminals of the transconductance stage. The transconductance stage inverting input terminal includes a first pair of differential input transistors M13 and M14, a second pair of differential input transistors M19 and M22, and a first switching transistor M20 and a second switching transistor M21 connected in series with the drains of the second pair of differential input transistors, respectively. In this configuration, the drains of the first pair of differential input transistors M13 and M14 serve as a pair of differential output nodes of the transconductance stage. The drains of the second pair of differential input transistors M19 and M22 are selectively connected to the pair of differential output nodes through the first switch transistor M20 and the second switch transistor M21. The drains of the first pair of differential input transistors M13 and M20 are connected, and the drains of the first pair of differential input transistors M14 and M21 are connected, forming the positive output terminals of the transconductance stage.

7. The automatic calibration analog front-end circuit based on an embedded DC servo circuit according to claim 1, characterized in that, The automatic calibration unit includes: The voltage detection module is used to compare the differential output voltage of the second-stage chopper operational amplifier with a high reference voltage and a low reference voltage. A logic control module, connected to the voltage detection module, is used to generate and output a control signal to adjust the equivalent transconductance value of the transconductance stage when the differential output voltage exceeds the threshold range determined by the high reference voltage and the low reference voltage.

8. The automatic calibration analog front-end circuit based on an embedded DC servo circuit according to claim 7, characterized in that, The voltage detection module includes four comparators, wherein: The non-inverting input of the first comparator is connected to the non-inverting output of the second-stage chopper operational amplifier, and the inverting input is connected to the low reference voltage. The inverting input of the second comparator is connected to the non-inverting output of the second-stage chopper operational amplifier, and the non-inverting input is connected to the high reference voltage. The non-inverting input of the third comparator is connected to the inverting output of the second-stage chopper operational amplifier, and the inverting input is connected to the low reference voltage. The inverting input of the fourth comparator is connected to the inverting output of the second-stage chopper operational amplifier, and the non-inverting input is connected to the high reference voltage.

9. The automatic calibration analog front-end circuit based on an embedded DC servo circuit according to claim 7, characterized in that, The control signal output by the automatic calibration unit is connected to the gates of the first switch M16, the second switch M17, the third switch M20, and the fourth switch M21 in the transconductance stage, and is used to control the on / off state of the transconductance stage.

10. The automatic calibration analog front-end circuit based on an embedded DC servo circuit according to claim 1, characterized in that, The variable gain amplifier changes its gain by switching the capacitor array at its input, which provides at least four different input capacitance values, corresponding to at least four programmable gain levels.

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