A biomedical front-end detection circuit with duty cycle adjustment positive feedback capacitor and a fixed access positive feedback capacitor value method thereof

Abstract

This invention relates to a biomedical front-end detection circuit with duty cycle adjustable positive feedback capacitor and a method for fixing the capacitance value of the positive feedback capacitor. The circuit includes a duty cycle adjustment signal generator, a fully differential gain circuit, a positive feedback capacitor loop, and a low-pass filter. The fully differential gain circuit amplifies physiological signals. The positive feedback capacitor loop is an array of positive feedback capacitors connected to the fully differential gain circuit, and the positive feedback capacitor array includes a high-order positive feedback capacitor and a low-order feedback capacitor. The low-pass filter circuit filters the high-frequency biological signals output by the fully differential gain circuit. The duty cycle adjustment signal generator generates a duty cycle adjustment signal and continuously adjusts the low-order feedback capacitor to generate the minimum equivalent capacitance value. The beneficial effect is that by adjusting the duty cycle of the positive feedback capacitor to obtain an adjustable minimum capacitance value, high gain and high input impedance calibration resolution are achieved.

Description

[Technical Field]

[0001] This invention relates to the field of integrated circuit technology, specifically to a biomedical front-end detection circuit with a duty cycle adjustable positive feedback capacitor and a method for fixing the capacitance value of the positive feedback capacitor. [Background Technology]

[0002] Common physiological signal detection circuits acquire physiological signals through electrodes. Since these electrodes are in direct contact with human skin, physiological activities can cause changes in the surface area or tension at the electrode-skin interface, leading to continuous variations in impedance. In multi-electrode systems, these impedance changes differ between electrodes, resulting in decreased common-mode rejection and significant motion artifacts, thus affecting system operation. The most common solution is to increase the input impedance of the front-end circuitry, thereby reducing the impact of electrode state changes on biosignal acquisition.

[0003] In biomedical front-end detection circuits, the most common technique for improving input impedance is based on positive feedback loop amplifier circuits. Through calibration algorithms, the positive feedback capacitor array connected to the circuit is brought as close as possible to the ideal calibration value, ultimately fixing the positive feedback capacitor value. The drawback of this technique is that its circuit gain and adjustable minimum capacitor value determine the final calibrable input impedance. For high-gain first-stage op-amps, achieving ultra-high front-end circuit input impedance requires a very small adjustable minimum capacitor value. For example, with an adjustable minimum capacitor value of 1 fF and a circuit gain of 10, the input impedance calibration resolution is 9 fF. However, when the circuit gain is 100, to achieve the same input impedance calibration resolution, the adjustable minimum capacitor value needs to be around 0.1 fF, which is virtually impossible to accurately produce with current integrated circuit manufacturing processes. This results in a higher circuit gain but lower front-end circuit input impedance calibration resolution, and a greater impact from impedance changes at the electrode-skin interface.

[0004] This invention addresses the technical problem that higher circuit gain in positive feedback loop-based amplifier circuits leads to lower input impedance calibration resolution in front-end circuits, and provides technical improvements to biomedical front-end detection circuits. [Summary of the Invention]

[0005] The purpose of this invention is to provide a biomedical front-end detection circuit that achieves high gain and high input impedance calibration resolution by obtaining an adjustable minimum capacitance value through adjusting the duty cycle of the positive feedback capacitor.

[0006] To achieve the above objectives, the present invention provides a biomedical front-end detection circuit with a duty cycle adjustable positive feedback capacitor, comprising a duty cycle adjustment signal generator, a fully differential gain circuit, a positive feedback capacitor loop, and a low-pass filter. The fully differential gain circuit amplifies physiological signals. The positive feedback capacitor loop is a positive feedback capacitor array connected to the fully differential gain circuit, and the positive feedback capacitor array includes a high-order positive feedback capacitor and a low-order feedback capacitor. The low-pass filter circuit filters the high-frequency biological signals output by the fully differential gain circuit. The duty cycle adjustment signal generator generates a duty cycle adjustment signal and continuously adjusts the low-order feedback capacitor to produce the minimum equivalent capacitance value, thereby achieving high gain for physiological signal detection and high input impedance calibration resolution.

[0007] Preferably, when the duty cycle adjustment signal is high, the least significant bit feedback capacitor is connected to the positive feedback loop of the fully differential gain circuit; when the duty cycle adjustment signal is low, the least significant bit feedback capacitor is connected to the negative feedback loop of the fully differential gain circuit.

[0008] Preferably, the fully differential gain circuit employs a low-noise, low-power fully differential operational amplifier for biosignal detection, including a first negative feedback capacitor connected between the positive input terminal and the negative output terminal of the fully differential operational amplifier, and a second negative feedback capacitor connected between the negative input terminal and the positive output terminal of the fully differential operational amplifier. It also includes a first negative feedback resistor connected between the positive input terminal and the negative output terminal of the fully differential operational amplifier, and a second negative feedback resistor electrically connected between the negative input terminal and the positive output terminal of the fully differential operational amplifier. Furthermore, it includes a first input capacitor connected to the positive input terminal of the fully differential operational amplifier, and a second input capacitor connected to the negative input terminal of the fully differential operational amplifier.

[0009] Preferably, the high-level positive feedback capacitor includes a first high-level positive feedback capacitor pool and a second high-level positive feedback capacitor pool, and the lowest-level feedback capacitor includes a first lowest-level feedback capacitor and a second lowest-level feedback capacitor; the capacitance values ​​of the first high-level positive feedback capacitor pool, the first lowest-level feedback capacitor, the second high-level positive feedback capacitor pool, and the second lowest-level feedback capacitor increase exponentially; one end of each capacitor in the first high-level positive feedback capacitor pool is connected to the positive input port of the fully differential operational amplifier, and the other end is connected to the positive output port of the fully differential operational amplifier; one end of the first lowest-level feedback capacitor is connected to the positive input port of the fully differential operational amplifier, and the other end is connected to the positive output port and the negative output port of the fully differential operational amplifier respectively via switches; when the duty cycle adjustment signal is high, the other end of the first lowest-level feedback capacitor... When the duty cycle adjustment signal is low, the other end of the first least significant feedback capacitor is connected to the negative output of the fully differential operational amplifier. In the second high-order positive feedback capacitor pool, one end of each capacitor is connected to the negative input port of the fully differential operational amplifier, and the other end is connected to the negative output port. The second least significant feedback capacitor is connected to the negative input port of the fully differential operational amplifier, and the other end is connected to both the negative and positive output ports via switches. When the duty cycle adjustment signal is high, the other end of the second least significant feedback capacitor is connected to the negative output of the fully differential operational amplifier; when the duty cycle adjustment signal is low, the other end of the second least significant feedback capacitor is connected to the positive output of the fully differential operational amplifier.

[0010] Preferably, the input terminal of the low-pass filter is connected to the output terminal of the fully differential gain circuit, and the output terminal of the low-pass filter is the output terminal of the biomedical front-end detection circuit.

[0011] Preferably, the aforementioned biomedical front-end detection circuit with duty cycle adjustable positive feedback capacitor is a gain circuit used to detect electrocardiogram and electroencephalogram physiological signals.

[0012] Another objective of this invention is to provide a method for obtaining an adjustable minimum capacitance value by adjusting the duty cycle of the positive feedback capacitor, thereby achieving a fixed positive feedback capacitor value for a biomedical front-end detection circuit with high gain and high input impedance calibration resolution.

[0013] To achieve the aforementioned objective, the present invention provides a method for fixing the capacitance value of a positive feedback capacitor in a biomedical front-end detection circuit with adjustable duty cycle. Based on the aforementioned biomedical front-end detection circuit with adjustable duty cycle, the method includes the following steps:

[0014] S1. A sinusoidal signal is used to simulate a high-frequency physiological signal and is input to the biomedical front-end detection circuit through electrodes to detect the output signal of the biomedical front-end detection circuit.

[0015] S2. The duty cycle adjustment signal generator does not generate a duty cycle adjustment signal, and the capacitance value of the high-level positive feedback capacitor is increased until the output signal of the biomedical front-end detection circuit oscillates.

[0016] S3. Keeping the high-level positive feedback capacitor value unchanged as described in step S2, the duty cycle adjustment signal generator generates a duty cycle adjustment signal to continuously adjust the equivalent capacitance value of the lowest-level feedback capacitor until the output signal of the biomedical front-end detection circuit is at the boundary point between stability and oscillation.

[0017] Preferably, the duty cycle adjustment signal is a square wave signal with a variable duty cycle, and the frequency of the duty cycle adjustment signal is greater than the bandwidth of the biomedical front-end detection circuit.

[0018] Preferably, the cutoff frequency of the low-pass filter is less than the frequency of the duty cycle adjustment signal.

[0019] Preferably, in step S3, when the output signal of the biomedical front-end detection circuit oscillates, the duty cycle of the duty cycle adjustment signal is decreased; when the output signal of the biomedical front-end detection circuit stabilizes, the duty cycle of the duty cycle adjustment signal is increased, until the biomedical front-end detection circuit is in a critical state of positive feedback compensation.

[0020] The present invention discloses a biomedical front-end detection circuit with duty cycle adjustable positive feedback capacitor and a method for fixing the value of the positive feedback capacitor, which has the following beneficial effects: By adjusting the duty cycle of the capacitor, the degree of positive feedback of the circuit can be continuously adjusted. The positive feedback capacitor of the circuit can be equivalent to a time capacitor. The equivalent capacitance value of this time capacitor is smaller than the actual capacitance value, which can realize small capacitance values ​​that cannot be produced due to process limitations. Moreover, the equivalent capacitance value can be controlled in the time domain, reducing the limitation of the minimum achievable capacitance value on input impedance calibration, realizing higher precision continuous adjustment of input impedance, and reducing the impact of changes in electrode state on biosignal acquisition. [Attached Image Description]

[0021] Figure 1 This is a schematic diagram of a biomedical front-end detection circuit structure with a duty cycle adjustable positive feedback capacitor.

[0022] Figure 2 This is a schematic diagram of the input-output signal relationship when a duty cycle adjustment signal is present in a biomedical front-end detection circuit with a duty cycle adjustable positive feedback capacitor.

[0023] Figure 3This is a schematic diagram of the duty cycle adjustment process of a positive feedback capacitor in a biomedical front-end detection circuit.

[0024] The reference numerals and components involved in the attached figures are as follows: 1. Fully differential gain circuit, 2. Adjustable duty cycle positive feedback capacitor loop, 3. Low-pass filter.

Detailed Implementation Methods

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0026] Example 1

[0027] This embodiment implements a biomedical front-end detection circuit with a duty cycle adjustable positive feedback capacitor. The front-end detection circuit is a gain circuit used to detect biosignals such as electrocardiograms (ECG) and electroencephalograms (EEGs). This circuit can continuously adjust the input impedance of the circuit by adjusting the duty cycle of the positive feedback capacitor connected to the circuit. The positive feedback capacitor can be considered equivalent to a time capacitor, meaning its capacitance value is related to the duty cycle of the capacitor connected to the circuit, and is equivalent to a time-domain continuous capacitance value. This circuit can reduce the limitation of the minimum achievable capacitor value on the input impedance, achieving more precise continuous adjustment of the input impedance.

[0028] Figure 1 This is a schematic diagram of a biomedical front-end detection circuit with a duty cycle adjustable positive feedback capacitor. (See attached diagram.) Figure 1 As shown, this embodiment discloses a biomedical front-end detection circuit with adjustable duty cycle positive feedback capacitor, including a fully differential gain circuit 1, an adjustable duty cycle positive feedback capacitor loop 2, and a low-pass filter 3. The fully differential gain circuit 1 amplifies the biological signal, and the adjustable duty cycle positive feedback capacitor loop 2 continuously adjusts the circuit's input impedance. When the duty cycle adjustment signal is high, the capacitor with the smallest capacitance value is connected to the positive feedback loop; when the duty cycle adjustment signal is low, the capacitor with the smallest capacitance value is connected to the negative feedback loop. The low-pass filter circuit 3 filters the high-frequency signal introduced by the duty cycle adjustment signal. The fully differential gain circuit 1 includes a fully differential operational amplifier, a capacitive negative feedback loop, a resistive negative feedback loop, and an input capacitor. The fully differential operational amplifier is a low-noise, low-power operational amplifier A used for biological signal detection. The capacitive negative feedback loop includes a first negative feedback capacitor C electrically connected between the positive input terminal and the negative output terminal of the fully differential operational amplifier. 2p And a second negative feedback capacitor C electrically connected between the negative input terminal and the positive output terminal.2n The resistive negative feedback loop includes a first negative feedback resistor RP electrically connected between the positive input terminal and the negative output terminal of the fully differential operational amplifier, and a second negative feedback resistor R electrically connected between the negative input terminal and the positive output terminal. n The input capacitor includes a first input capacitor C that connects the positive input terminal of the fully differential gain circuit to the positive input terminal of the fully differential operational amplifier. 1p And the second input capacitor C connecting the negative input terminal of the fully differential gain circuit and the negative input terminal of the fully differential operational amplifier. 1n Adjustable positive feedback capacitor loop 2 consists of the first positive feedback capacitor pool C. PFp [n:0] and the second positive feedback capacitor bank C PFn Composed of [n:0], where n represents the number of control bits in the capacitor array, and the capacitance value in the capacitor pool increases exponentially with the number of control bits; the first positive feedback capacitor pool contains C PFp [n:1] Each capacitor is connected to the positive output and positive input terminals of the fully differential gain circuit. The first positive feedback capacitor pool contains C... PFp [0] Each capacitor is connected to the positive and negative output terminals of the fully differential gain circuit via S1 and S2; C in the second positive feedback capacitor pool PFn [n:1] Each capacitor is connected to the negative output and negative input terminals of the fully differential gain circuit, and C in the second positive feedback capacitor pool PFn [0] Each capacitor is connected to the positive and negative output terminals of the fully differential gain circuit via S3 and S4; the C PFp [n:0] and C PFn All capacitors included in [n:0] are connected to the circuit by an external control signal; the input of low-pass filter 3 is connected to the output of the fully differential gain circuit, and the output of the low-pass filter is the output of the overall circuit.

[0029] Let C 1p and C 1n The capacitance value is C1, C 2p and C 2n With a capacitance value of C2, the amplification factor of the fully differential gain circuit is: Let C PFp and C PFn The capacitance value connected to the circuit is C. PF Assuming C in the circuit PFp and C PFn When connected to the circuit in the form of positive feedback, the overall circuit input impedance is: Where s represents the angular frequency, and assuming C in the circuit... PFp and C PFn When connected to the circuit in the form of negative feedback, the overall circuit input impedance is: Where s represents the angular frequency. For the traditional first case, when the input impedance is at its maximum, C1 = C... PF (A0-1), where C PF Adjustable, but accuracy is limited by circuit gain and the minimum adjustable capacitance value. This embodiment presents a biomedical front-end detection circuit with duty cycle adjustable positive feedback capacitor. The capacitor is switched between positive and negative feedback loops, and the equivalent input current from the signal source is I. IN1 and I IN2 The linear average. Assuming the duty cycle is D, meaning that within the period T of the duty cycle adjustment signal, the capacitor is connected to the positive feedback loop for D*T time and to the negative feedback loop for (1-D)*T time, then the equivalent input current of the entire circuit within the period T is I. IN =D*I IN1 +(1-D)*I IN2 =sV IN (C1-C PF (2DA0-A0-1), at this time the magnitude of the positive feedback capacitor connected to the circuit is equivalent to The input impedance of the circuit is related to the duty cycle D. This embodiment is a biomedical front-end detection circuit with a duty cycle adjustable positive feedback capacitor, using the minimum capacitance for switching, assuming C... PF With the positive feedback loop fixed, switching is performed using a capacitor with a value of ΔC. In this case, within period T, the equivalent input current of the entire circuit is I. IN =D*I′ IN1 +(1-D)*I′ IN2 =sV IN (C1-C PF (A0-1)-ΔC(2DA0-A0-1)), the magnitude of the minimum capacitance ΔC is equivalent to... This implementation presents a biomedical front-end detection circuit with a duty cycle adjustable positive feedback capacitor. By correlating the equivalent capacitance value of the capacitor with the duty cycle, a continuously adjustable capacitance value is indirectly achieved.

[0030] Figure 2 This is a schematic diagram illustrating the input-output signal relationship of a biomedical front-end detection circuit with a duty cycle adjustable positive feedback capacitor when the duty cycle adjustment signal is present. (See attached diagram.) Figure 2 As shown, this embodiment is a biomedical front-end detection circuit with a duty cycle adjustable positive feedback capacitor. Taking the input signal as a sine wave as an example, the output signal is still a sine wave after being amplified by the gain circuit. However, due to the existence of the duty cycle adjustment signal, the capacitor switches between positive and negative feedback connections, causing the output signal to fluctuate with the period T of the duty cycle adjustment signal in the two states. However, this does not affect the stability of the system. This fluctuation can be filtered out by a low-pass filter.

[0031] Figure 3 This is a schematic diagram illustrating the duty cycle adjustment process of a positive feedback capacitor in a biomedical front-end detection circuit. (See attached diagram.) Figure 3 As shown, this embodiment describes a biomedical front-end detection circuit with duty cycle adjustable positive feedback capacitor. The duty cycle adjustment process of the positive feedback capacitor achieves continuous capacitance value adjustment, using a time-domain duty cycle signal to adjust the equivalent capacitance value. The specific process is as follows: A sinusoidal signal is input to the electrode circuit, and the output signal is detected at the filter output terminal; firstly, C... PFp [n:0],C PFn All capacitors in [n:0] are not connected to the circuit. S1, S2, S3, and S4 remain open. The circuit output is a sine wave, but the gain observed at the filter output is less than A0. The specific gain value is determined by the voltage division between the input impedance and the electrode impedance. Then, increase C. PFp [n:0],C PFn The positive feedback capacitor value is connected in [n:0], and the output of the circuit is a sine wave. The gain observed from the filter output gradually increases. When C PFp [n:0],C PFn When the positive feedback capacitor value in the circuit connected to [n:0] exceeds a certain value, the output signal observed from the filter output terminal will suddenly change from a steady state to an oscillating state; at this time, keep C PFp [n:1],C PFn The positive feedback capacitor value in the circuit connected to [n:1] remains unchanged. The duty cycle of the duty cycle adjustment signal is increased from zero, and this signal controls the switching states of S1, S2, S3, and S4: when the duty cycle adjustment signal is high, S1 and S4 are closed, and S2 and S3 are open. PFp [0]、C PFn [0] All are connected to the circuit in the form of positive feedback. When the duty cycle adjustment signal is low, S1 and S4 are open, and S2 and S3 are closed. C PFp [0]、C PFn [0] are all connected to the circuit in the form of negative feedback. When the duty cycle adjustment signal has a low duty cycle, that is, when the high level state occupies a shorter time in one cycle, C PFp [0]、C PFn The equivalent positive feedback capacitor value of [0] is small, which can bring the circuit back to a stable state; when the duty cycle adjustment signal has a high duty cycle, that is, when the high level state occupies a large time in one cycle, C PFp [0]、C PFnThe equivalent positive feedback capacitance of [0] is relatively large, causing the circuit to oscillate. By continuously adjusting the duty cycle signal, the duty cycle signal at the boundary between stability and oscillation is found. At this point, the gain of the output signal observed from the filter output terminal is the largest, and the positive feedback circuit controlled by this duty cycle signal makes the entire system have the highest input impedance. It should be noted that the frequency of the duty cycle adjustment signal must be greater than the overall bandwidth of the circuit, and the interference it introduces will be filtered out by the low-pass filter.

[0032] Those skilled in the art will understand that all or part of the steps of the above embodiments can be implemented by hardware or by a program instructing related hardware. The program can be stored in a computer-readable storage medium, such as a magnetic disk, optical disk, read-only memory (ROM), or random access memory (RAM).

[0033] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements and additions without departing from the principle of the present invention, and these improvements and additions should also be considered within the scope of protection of the present invention.

Claims

1. A biomedical front-end detection circuit with a duty cycle adjustable positive feedback capacitor, characterized in that: The system includes a duty cycle adjustment signal generator, a fully differential gain circuit, a positive feedback capacitor loop, and a low-pass filter. The fully differential gain circuit amplifies physiological signals. The positive feedback capacitor loop is a positive feedback capacitor array connected to the fully differential gain circuit, and the positive feedback capacitor array includes a high-order positive feedback capacitor and a low-order feedback capacitor. The low-pass filter filters the high-frequency biological signals output by the fully differential gain circuit. The duty cycle adjustment signal generator generates a duty cycle adjustment signal and continuously adjusts the low-order feedback capacitor to generate the minimum equivalent capacitance value, achieving high gain for physiological signal detection and high calibration resolution for input impedance. When the duty cycle adjustment signal is high, the low-order feedback capacitor is connected to the positive feedback loop of the fully differential gain circuit; when the duty cycle adjustment signal is low, the low-order feedback capacitor is connected to the negative feedback loop of the fully differential gain circuit.

2. The biomedical front-end detection circuit with a duty cycle adjustable positive feedback capacitor according to claim 1, characterized in that: The fully differential gain circuit employs a low-noise, low-power fully differential operational amplifier for biosignal detection. It includes a first negative feedback capacitor connected between the positive input and negative output terminals of the fully differential operational amplifier, and a second negative feedback capacitor connected between the negative input and positive output terminals. It also includes a first negative feedback resistor connected between the positive input and negative output terminals of the fully differential operational amplifier, and a second negative feedback resistor electrically connected between the negative input and positive output terminals. Furthermore, it includes a first input capacitor connected to the positive input terminal of the fully differential operational amplifier, and a second input capacitor connected to the negative input terminal of the fully differential operational amplifier.

3. The biomedical front-end detection circuit with a duty cycle adjustable positive feedback capacitor according to claim 2, characterized in that: The high-level positive feedback capacitor includes a first high-level positive feedback capacitor pool and a second high-level positive feedback capacitor pool, and the lowest-level feedback capacitor includes a first lowest-level feedback capacitor and a second lowest-level feedback capacitor; the capacitance values ​​of the first high-level positive feedback capacitor pool, the first lowest-level feedback capacitor, the second high-level positive feedback capacitor pool, and the second lowest-level feedback capacitor increase exponentially; one end of each capacitor in the first high-level positive feedback capacitor pool is connected to the positive input port of the fully differential operational amplifier, and the other end is connected to the positive output port of the fully differential operational amplifier; one end of the first lowest-level feedback capacitor is connected to the positive input port of the fully differential operational amplifier, and the other end is connected to the positive output port and the negative output port of the fully differential operational amplifier respectively via switches; when the duty cycle adjustment signal is high, the other end of the first lowest-level feedback capacitor is connected to the positive input port of the fully differential operational amplifier. When the differential operational amplifier's positive output is on, and the duty cycle adjustment signal is low, the other end of the first least significant feedback capacitor is on the negative output of the fully differential operational amplifier. Each capacitor in the second high-signal positive feedback capacitor pool has one end connected to the negative input port of the fully differential operational amplifier and the other end connected to its negative output. One end of the second least significant feedback capacitor is connected to the negative input port of the fully differential operational amplifier, and the other end is connected to both the negative and positive outputs of the fully differential operational amplifier via switches. When the duty cycle adjustment signal is high, the other end of the second least significant feedback capacitor is on the negative output of the fully differential operational amplifier; when the duty cycle adjustment signal is low, the other end of the second least significant feedback capacitor is on the positive output of the fully differential operational amplifier.

4. The biomedical front-end detection circuit with a duty cycle adjustable positive feedback capacitor according to claim 3, characterized in that: The input terminal of the low-pass filter is connected to the output terminal of the fully differential gain circuit, and the output terminal of the low-pass filter is the output terminal of the biomedical front-end detection circuit.

5. A biomedical front-end detection circuit with a duty cycle adjustable positive feedback capacitor according to any one of claims 1 to 4, characterized in that: It is a gain circuit used to detect electrocardiogram and electroencephalogram (EEG) physiological signals.

6. A method for fixing the capacitance value of a positive feedback capacitor in a biomedical front-end detection circuit with adjustable duty cycle, based on the biomedical front-end detection circuit with adjustable duty cycle described in any one of claims 1 to 5, characterized in that... Includes the following steps: S1. A sinusoidal signal is used to simulate a high-frequency physiological signal and is input to the biomedical front-end detection circuit through electrodes to detect the output signal of the biomedical front-end detection circuit. S2. The duty cycle adjustment signal generator does not generate a duty cycle adjustment signal, and the capacitance value of the high-level positive feedback capacitor is increased until the output signal of the biomedical front-end detection circuit oscillates. S3. Keeping the high-level positive feedback capacitor value unchanged as described in step S2, the duty cycle adjustment signal generator generates a duty cycle adjustment signal to continuously adjust the equivalent capacitance value of the lowest-level feedback capacitor until the output signal of the biomedical front-end detection circuit is at the boundary point between stability and oscillation.

7. The method for fixing the capacitance value of the positive feedback capacitor in a biomedical front-end detection circuit with adjustable duty cycle as described in claim 6, characterized in that: The duty cycle adjustment signal is a square wave signal with a variable duty cycle, and the frequency of the duty cycle adjustment signal is greater than the bandwidth of the biomedical front-end detection circuit.

8. The method for fixing the capacitance value of a positive feedback capacitor in a biomedical front-end detection circuit with adjustable duty cycle as described in claim 7, characterized in that: The cutoff frequency of the low-pass filter is lower than the frequency of the duty cycle adjustment signal.

9. The method for fixing the capacitance value of a positive feedback capacitor in a biomedical front-end detection circuit with adjustable duty cycle as described in claim 8, characterized in that: Step S3: When the output signal of the biomedical front-end detection circuit oscillates, decrease the duty cycle of the duty cycle adjustment signal; when the output signal of the biomedical front-end detection circuit stabilizes, increase the duty cycle of the duty cycle adjustment signal until the biomedical front-end detection circuit is in a critical state of positive feedback compensation.

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