CN117665397B - Capacitor complex impedance measurement method, circuit and device - Google Patents

Abstract

The invention belongs to the technical field of impedance measurement, and particularly relates to a capacitor complex impedance measurement method, circuit and device with self-adaptive parasitic capacitance compensation, wherein the method comprises the steps of inputting sinusoidal alternating current signal excitation into a measurement circuit, and carrying out output zeroing on the measurement circuit in an initial state so as to detect the complex impedance of a capacitor to be detected; shifting the phase of an input sinusoidal alternating current signal by 90 degrees or 0 degrees to generate a phase control signal after phase shifting; responding to the phase control signal and carrying out phase control rectification on the alternating current signal, filtering the alternating current signal subjected to phase control rectification, and converting the alternating current signal into direct current voltage for output; the measuring circuit provided by the invention can be used for measuring the complex impedance of the capacitive sensor, can also be used for measuring the variation of the complex impedance of the capacitive sensor, can automatically eliminate parasitic capacitance, achieves the purpose of precision measurement, and has the characteristics of large measuring range, high measuring precision and strong anti-interference capability.

Description

A method, circuit and device for measuring complex impedance of capacitor

Technical Field

The present invention belongs to the technical field of impedance measurement, and in particular relates to a method, circuit and device for measuring the complex impedance of a capacitor.

Background technique

Microcapacitance measurement technology has been widely used in various MEMS devices, capacitive sensors, and distributed capacitance between structures. Therefore, it can be used in military manufacturing, aerospace, vacuum measurement, biomedicine and other related fields. For capacitive sensor application scenarios such as capacitance tomography, the measurement of the complex impedance of the capacitor under AC excitation can obtain higher resolution imaging images or more target feature information.

At present, many measurement circuits have been invented based on the resonance method, CV conversion, charge and discharge measurement methods, but the complex impedance of the test capacitor is used. At the same time, the existence of parasitic capacitance or stray capacitance can be optimized through board-level design, usually by using input and output signal shielding and other measures to reduce the generation of parasitic capacitance, or through circuit scheme design optimization, usually designing a circuit with differential output, so that the common mode signal can be eliminated more easily. However, not all detection circuits use differential output, so the solution of designing a differential output circuit to eliminate parasitic capacitance has certain limitations, making it difficult to eliminate in these measurement methods. This also causes the measured capacitance to be larger than the theoretical calculation or simulation, which reduces the clarity of capacitance tomography. In addition, there are increasingly higher requirements for the cost, sensitivity, and parasitic effect suppression of the measurement circuit.

Summary of the invention

The purpose of the present invention is to provide a method, circuit and device for measuring the complex impedance of a capacitor to solve the problems raised in the background technology.

The present invention achieves the above-mentioned purpose through the following technical solutions:

In a first aspect, the present invention provides a method for measuring complex impedance of a capacitor, which is applicable to a measurement circuit including a capacitor to be detected, and the method comprises:

Inputting a sinusoidal AC signal excitation into the measuring circuit, and performing output zeroing on the measuring circuit in an initial state to detect the complex impedance of the capacitor to be detected;

The input sinusoidal AC signal is phase-shifted by 90° or 0° to generate a phase-shifted phase-controlled signal;

In response to the phase-controlled signal, the AC signal is subjected to phase-controlled rectification, and the AC signal after the phase-controlled rectification is filtered and converted into a DC voltage for output.

As a further optimization solution of the present invention, the initial state includes the initial moment when the measuring circuit is not connected to the capacitor to be detected, or the measuring circuit is connected to the capacitor to be detected and powered on.

As a further optimization scheme of the present invention, based on the real part and imaginary part of the complex number of the capacitor to be detected, when detecting the real part, the input sinusoidal AC signal is phase-shifted by 90°, and when detecting the imaginary part, the input sinusoidal AC signal is phase-shifted by 0°.

In a second aspect, the present invention provides a capacitor complex impedance measurement circuit for implementing the measurement method as described above, wherein the measurement circuit comprises a self-compensating calibration bridge circuit, a phase shift circuit and a phase-controlled rectifier circuit;

The self-compensating calibration bridge circuit is used to input a sinusoidal AC signal excitation into the measuring circuit, and to perform output zeroing on the measuring circuit when the self-compensating calibration bridge circuit is not connected to the capacitor to be detected, or when the self-compensating calibration bridge circuit is connected to the capacitor to be detected and powered on at the initial moment, so as to detect the complex impedance of the capacitor to be detected;

The phase shift circuit is used to shift the phase of the input sinusoidal AC signal by 90° or 0° to generate a phase-shifted phase-controlled signal;

The phase-controlled rectifier circuit is used to respond to the phase-controlled signal and perform phase-controlled rectification on the AC signal, and filter the AC signal after the phase-controlled rectification and convert it into a DC voltage for output.

As a further optimization scheme of the present invention, the self-compensation calibration bridge circuit comprises a first-stage reverse proportional circuit, an integration circuit and a feedback circuit with PI regulation;

The phase-controlled rectifier circuit includes a comparator, a second-stage reverse proportional circuit, an analog switch S1 , and a second-order low-pass filter circuit; the comparator is an operational amplifier. , the operational amplifier/> The inverting input terminal is connected to the phase shift circuit, the positive input terminal is connected to the electrical ground, and the operational amplifier/> The output end is connected to the signal output end of the analog switch S1 , and the signal output end of the switch S1 is connected to the second-order low-pass filter circuit. The signal is / > , the two input ends of the analog switch S1 are respectively connected to the integration circuit of the self-compensation calibration bridge circuit and the output end of the second-stage reverse proportional circuit;

The first stage reverse proportional circuit consists of an amplifier , resistance/> 、/> Composition, resistance/> One end is connected to electrical ground and the other end is connected to the amplifier/> The positive input terminal of the amplifier is connected to The inverting input terminal and resistor/> 、/> Connected, resistor/> Connected to the capacitor to be detected in the integration circuit, the resistor The other end of the amplifier The output terminal is connected to

The integration circuit consists of an operational amplifier Feedback resistor/> Composition, amplifier/> With resistor/> The first stage reverse proportional circuit and reference capacitor Connect in series with the capacitor to be detected and the automatic compensation capacitor/> In parallel, and then through the operational amplifier/> With feedback resistor/> The output signal of the integral circuit is composed of ;

The second stage reverse proportional circuit consists of an amplifier With resistor/> 、/> The output end of the integrating circuit is connected to a resistor. One end is connected to the resistor/> With amplifier/> The reverse input terminal and resistor/> Connected, resistor/> The other end is connected to the amplifier/> The output end of the amplifier is connected to The positive input terminal is connected to the electrical ground, and the output signal of the second stage inverse proportional circuit, that is, the amplifier / > The output signal at the output end is / > , the automatic compensation capacitor/> Programmable capacitor, capacitor to be detected includes leakage capacitor/> and leakage resistor/> ;

The feedback circuit with PI adjustment includes an FPGA single-chip computer system, an ADC acquisition circuit, and a PI controller. The ADC acquisition circuit is connected to the output end of the second-order low-pass filter circuit. After the ADC acquisition circuit collects information, it is transmitted to the single-chip computer system for processing and then transmitted to the PC end. The PC end then implements calibration of the variable capacitor CT through the PI controller. According to the output feedback of the phase-controlled rectifier circuit based on the comparator, the ADC collects the system output signal and performs PI adjustment value through the MCU controller to complete zeroing when the capacitor to be detected is not connected or the system is in the initial state of power-on.

As a further optimization solution of the present invention, in the phase shift circuit, when detecting the imaginary part of the capacitor to be detected When the phase shift circuit is a differential circuit, when the real part of the capacitance sensor is detected/> When phase shift is not required, the AC signal and the next stage operational amplifier /> is connected to the inverting input terminal of .

As a further optimization solution of the present invention, the normally open contact of the analog switch S1 is connected to the output end of the self-compensation calibration bridge circuit , the normally closed contact is connected to the output terminal /> , when the input end is the original excitation signal phase shifted 90°, the analog switch output signal/> After being rectified into DC by a second-order low-pass filter circuit, the imaginary part of the capacitor to be tested is detected at this time./> ; When the input end is the original excitation signal, the real part of the capacitor to be tested is detected at this time/> , where the input sinusoidal excitation signal is , A is the gain of the input sinusoidal excitation signal;

Among them, when detecting When the phase of the output signal of the phase shift circuit is 90° behind the excitation signal, the analog switch controlled by the comparator is The output signal is:

Then it is integrated through a second-order low-pass filter circuit. When the cut-off frequency of the second-order low-pass filter is much smaller than the excitation signal frequency, a DC signal can be obtained. , the DC output after signal integration in one cycle is approximately calculated as:

Detecting the imaginary part for:

When testing When the phase shift circuit is not required, the excitation signal directly passes through the analog switch controlled by the comparator. The output signal is:

Detection of real part for:

.

In a third aspect, the present invention provides a measuring device, comprising the measuring circuit in any possible implementation of the first aspect or the second aspect.

1. The beneficial effects of the present invention are:

The present invention proposes a measurement circuit which can be used to measure the complex impedance of a capacitance sensor and can also measure the change in the complex impedance of the capacitance sensor. The parasitic capacitance can be automatically eliminated to achieve the purpose of accurate measurement. The circuit has the characteristics of a large measurement range, high measurement accuracy and strong anti-interference ability.

2. The measurement circuit proposed in the present invention includes a self-compensating calibration bridge circuit, a phase-shifting circuit, and a phase-controlled rectifier circuit based on a comparator, which realizes the conversion of the complex impedance (or leakage capacitance, leakage resistance) of the capacitive sensor into a DC voltage for detection. It can be used to measure the complex impedance of the capacitive sensor, and can also measure the change in the complex impedance of the capacitive sensor. It can automatically eliminate parasitic capacitance to achieve the purpose of precision measurement.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic diagram of the execution flow of the measurement method in the present invention.

FIG. 2 is a system principle block diagram of the present invention.

FIG3 is a block diagram of the programmable capacitor principle of the present invention.

FIG. 4 is a circuit diagram of a phase shift circuit of the present invention for achieving a 90° phase shift of an input AC signal.

Detailed ways

The present application is further described in detail below in conjunction with the accompanying drawings. It is necessary to point out here that the following specific implementation methods are only used to further illustrate the present application and cannot be understood as limiting the scope of protection of the present application. Technical personnel in this field can make some non-essential improvements and adjustments to the present application based on the above application content.

Example 1

As shown in FIG. 1 , this embodiment provides a method for measuring complex impedance of a capacitor, which is applicable to a measurement circuit including a capacitor to be detected. The method includes:

S1. Input a sinusoidal AC signal excitation into the measurement circuit. Under the condition of input sinusoidal AC signal excitation, the detected complex impedance of the capacitance sensor is converted into a voltage signal. The output of the measurement circuit is zeroed in the initial state to detect the complex impedance of the capacitor to be detected. The parasitic capacitance can be automatically eliminated by the system zeroing operation.

Specifically, the initial state includes the initial moment when the measuring circuit is not connected to the capacitor to be detected, or when the measuring circuit is connected to the capacitor to be detected and powered on.

S2, shift the phase of the input sinusoidal AC signal by 90° or 0° to generate a phase-shifted phase-controlled signal;

Specifically, based on the real and imaginary parts of the complex number of the capacitor to be detected, when detecting the real part, the input sinusoidal AC signal is phase-shifted by 90°, and when detecting the imaginary part, the input sinusoidal AC signal is phase-shifted by 0°. A phase shift of 0° means that no phase shift is required.

S3, responding to the phase-controlled signal and performing phase-controlled rectification on the AC signal, filtering the AC signal after phase-controlled rectification and converting it into a DC voltage for output, wherein the filtering operation is implemented based on a low-pass filter circuit.

It can be understood that the above measurement method is applicable to sensors based on the measurement of complex impedance of capacitance or complex impedance change; it realizes converting the complex impedance (or leakage capacitance, leakage resistance) of the capacitance sensor into a DC voltage for detection, which can be used to measure the complex impedance of the capacitance sensor, or only measure the change in the complex impedance of the capacitance sensor, and can automatically eliminate parasitic capacitance to achieve the purpose of precision measurement.

Example 2

Based on the same inventive concept, a measurement circuit corresponding to the measurement method is also provided in this embodiment. Since the principle of solving the problem by the measurement circuit in the embodiment of the present disclosure is similar to the above-mentioned measurement method in the embodiment of the present disclosure, the implementation of the measurement circuit can refer to the implementation of the method, and the repeated parts will not be repeated.

As shown in FIG2-4 , this embodiment provides a capacitor complex impedance measurement circuit for implementing the above measurement method, wherein the measurement circuit includes a self-compensating calibration bridge circuit, a phase shift circuit, and a phase-controlled rectifier circuit;

The self-compensating calibration bridge circuit is used to input a sinusoidal AC signal excitation into the measuring circuit, and to adjust the output of the measuring circuit to zero when the self-compensating calibration bridge circuit is not connected to the capacitor to be detected, or when the self-compensating calibration bridge circuit is connected to the capacitor to be detected and powered on, so as to detect the complex impedance of the capacitor to be detected;

The phase shift circuit is used to shift the input sinusoidal AC signal by 90° or 0° to generate a phase-shifted phase-controlled signal;

The phase-controlled rectifier circuit is used to respond to the phase-controlled signal and perform phase-controlled rectification on the AC signal, filter the AC signal after the phase-controlled rectification, and then convert it into a DC voltage for output.

2 , as a further implementation, the self-compensation calibration bridge circuit includes a first-stage reverse proportional circuit, an integration circuit, and a feedback circuit with PI regulation;

The phase-controlled rectifier circuit includes a comparator, a second-stage reverse proportional circuit, an analog switch S1 , and a second-order low-pass filter circuit; the comparator is an operational amplifier. , operational amplifier/> The reverse input terminal is connected to the phase shift circuit, the positive input terminal is connected to the electrical ground, and the operational amplifier/> The output end is connected to the signal output end of the analog switch S1 , and the signal output end of the switch S1 is connected to the second-order low-pass filter circuit. The signal is / > , the two input ends of the analog switch S1 are respectively connected to the integration circuit of the self-compensation calibration bridge circuit and the output end of the second-stage reverse proportional circuit;

The first stage reverse proportional circuit consists of an amplifier , resistance/> 、/> 、/> Composition, resistance/> One end is connected to electrical ground and the other end is connected to the amplifier/> The positive input terminal of the amplifier is connected to The inverting input terminal and resistor/> 、/> Connected, resistor Connected to the capacitor to be detected in the integration circuit, the resistor The other end of the amplifier The output terminal is connected to

The integrator circuit consists of an operational amplifier With feedback resistor/> Composition, amplifier/> With resistor/> 、/> 、/> The first stage reverse proportional circuit and reference capacitor Connect in series with the capacitor to be detected and the automatic compensation capacitor/> In parallel, and then through the operational amplifier/> With feedback resistor/> The output signal of the integral circuit is composed of ;

The second stage reverse proportional circuit consists of an amplifier With resistor/> 、/> Composition, the output end of the integrator circuit and the resistor/> One end is connected to the resistor/> With amplifier/> The reverse input terminal and resistor/> Connected, resistor/> The other end is connected to the amplifier/> The output end of the amplifier is connected to The positive input terminal is connected to the electrical ground, and the output signal of the second stage inverse proportional circuit, that is, the amplifier / > The output signal at the output end is / > , automatic compensation capacitor/> is a programmable capacitor, and the capacitor to be detected includes a leakage capacitor/> and leakage resistor/> .

The feedback circuit with PI adjustment includes an FPGA single-chip computer system, an ADC acquisition circuit, and a PI controller. The ADC acquisition circuit is connected to the output end of the second-order low-pass filter circuit. After the ADC acquisition circuit collects information, it is transmitted to the single-chip computer system for processing and then transmitted to the PC end. The PC end then implements the calibration of the variable capacitor CT through the PI controller. According to the output feedback of the phase-controlled rectifier circuit based on the comparator, the ADC collects the information and performs PI adjustment on the system output signal through the MCU controller to complete the zeroing when the capacitor to be detected is not connected or the system is in the initial state of power-on.

Referring to FIG. 2 , the measurement circuit further includes: an FPGA single-chip computer system, an ADC acquisition circuit, and a PI controller.

According to the output feedback of the phase-controlled rectifier circuit based on the comparator, the ADC collects the system output signal through the MCU controller to perform PI adjustment. value, complete the detection of the capacitor to be detected or the system is zeroed in the initial state of power-on, and the input of the integration circuit passes through the amplifier/> With resistor/> 、/> 、/> The first stage reverse proportional circuit is composed of;

When the input sinusoidal excitation is , the integrator circuit output of the self-compensating calibration bridge circuit/> , and the integral circuit outputs the signal through the second stage reverse proportional circuit/> for:

In the formula, is the gain of the inverse proportional circuit, /> is the gain of the input sinusoidal excitation signal.

The ADC acquisition circuit is connected to the output end of the low-pass filter LPF. After the ADC acquisition circuit collects information, it is transmitted to the single-chip computer system, and then transmitted to the PC end after simple processing. The PC end then implements the calibration of the variable capacitor CT through the PI controller. When the capacitance sensor is not connected in the initial state, initialization zeroing is performed, so that the capacitance can be adaptively supplemented to eliminate the influence of parasitic capacitance; when the capacitance sensor is connected in the initial state and initialization zeroing is performed, at this time, the influence of parasitic capacitance can be eliminated and adaptive parasitic capacitance supplement can be performed, and the change of the capacitance sensor can also be directly detected, including the change of the imaginary part (leakage capacitance) of the capacitance sensor, and the change of the real part (leakage resistance) of the capacitance sensor.

As a further implementation, in the phase shift circuit, when the imaginary part of the capacitor to be detected is detected When the phase shift circuit is a differential circuit, when the real part of the capacitance sensor is detected/> When phase shift is not required, the AC signal and the next stage operational amplifier /> is connected to the inverting input terminal of .

As a further implementation, based on the above measurement circuit, the parasitic capacitance is automatically eliminated by implementing the following steps:

(1) Controlling the analog switch by comparing the phase shifter input with ground The on-off of the analog switch S1 is used to control the phase of the signal. The normally open contact of the analog switch S1 is connected to the output end of the self-compensation calibration bridge circuit. , the normally closed contact is connected to the output terminal /> , when the input end is the original excitation signal phase-shifted by 90°, the analog switch output signal/> After being rectified into DC by a second-order low-pass filter circuit, the imaginary part of the capacitor to be tested is detected at this time./> ; When the input end is the original excitation signal, the real part of the capacitor to be tested is detected at this time/> ; Among them, the input sinusoidal excitation signal is/> , A is the gain of the input sinusoidal excitation signal;

Among them, when detecting When the phase of the output signal of the phase shift circuit is 90° behind the excitation signal, the analog switch controlled by the comparator is The output signal is:

(2) After integration through a second-order low-pass filter circuit, a DC signal can be obtained when the cutoff frequency of the second-order low-pass filter is much smaller than the excitation signal frequency. , the DC output after signal integration in one cycle is approximately calculated as:

Detecting the imaginary part for:

When testing When the phase shift circuit is not required, the excitation signal directly passes through the analog switch controlled by the comparator. The output signal is:

(3) Then pass through the second-order low-pass filter circuit for integration. When the cutoff frequency of the second-order low-pass filter is much smaller than the excitation signal frequency, a DC signal can be obtained. , the DC output after signal integration in one cycle is approximately calculated as:

'

Detection of real part for:

.

Example 3

This embodiment provides a measuring device, which includes the measuring circuit as described above. For the specific description of the measuring device, reference can be made to the description of the measuring circuit, which will not be described in detail here.

It is understandable that other elements included in the measuring device are not limited in the embodiments of the present application.

Exemplarily, the measuring device is a chip, a sensor, or an electronic device, or an Internet of Things device, etc., which are not listed one by one in the embodiments of the present application.

The above embodiments may be implemented in whole or in part by software, hardware, firmware or any other combination thereof. When implemented by software, the above embodiments may be implemented in whole or in part in the form of a computer program product. The computer program product includes one or more computer instructions or computer programs. When the computer instructions or computer programs are loaded or executed on a computer, the process or function described in the embodiment of the present invention is generated in whole or in part. The computer may be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions may be stored in a computer-readable storage medium, or may be transmitted from one computer-readable storage medium to another computer-readable storage medium. For example, the computer instructions may be transmitted from one website, computer, server or data center to another website, computer, server or data center by wired means (e.g., infrared, wireless, microwave, etc.). The computer-readable storage medium may be any available medium that can be accessed by a computer or a data storage device such as a server or data center that includes one or more available media sets. The available medium may be a magnetic medium (e.g., a floppy disk, a hard disk, a tape), an optical medium (e.g., a DVD), or a semiconductor medium. The semiconductor medium may be a solid-state hard disk.

Those of ordinary skill in the art will appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of this application.

In addition, each functional module in each embodiment of the present application may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit.

If the function is implemented in the form of a software function module and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present application, or the part that contributes to the prior art or the part of the technical solution, can be embodied in the form of a software product, which is stored in a storage medium and includes several instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the method described in the embodiment of the present invention. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM), random access memory (RAM), disk or optical disk, etc., various media that can store program codes.

The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims (4)

1. A method for measuring complex impedance of a capacitor, characterized in that it is applicable to a measurement circuit including a capacitor to be detected, wherein the measurement circuit includes a self-compensating calibration bridge circuit, a phase shift circuit and a phase-controlled rectifier circuit, and the method includes: Inputting a sinusoidal AC signal excitation into the measuring circuit, and performing output zeroing on the measuring circuit in an initial state to detect the complex impedance of the capacitor to be detected; The input sinusoidal AC signal is phase-shifted by 90° or 0° to generate a phase-shifted phase-controlled signal; Responding to the phase-controlled signal and performing phase-controlled rectification on the AC signal, filtering the AC signal after the phase-controlled rectification and converting it into a DC voltage for output; Based on the real part and imaginary part of the complex number of the capacitor to be detected, the input sinusoidal AC signal is phase-shifted by 90° when the real part is detected, and the input sinusoidal AC signal is phase-shifted by 0° when the imaginary part is detected; The self-compensation calibration bridge circuit comprises a first-stage reverse proportional circuit, an integration circuit and a feedback circuit with PI regulation; The phase-controlled rectifier circuit includes a comparator, a second-stage reverse proportional circuit, an analog switch S1 , and a second-order low-pass filter circuit; the comparator is an operational amplifier. , the operational amplifier/> The inverting input terminal is connected to the phase shift circuit, the positive input terminal is connected to the electrical ground, and the operational amplifier/> The output end is connected to the signal output end of the analog switch S1 , and the signal output end of the switch S1 is connected to the second-order low-pass filter circuit. The signal is / > , the two input ends of the analog switch S1 are respectively connected to the integration circuit of the self-compensation calibration bridge circuit and the output end of the second-stage reverse proportional circuit; The first stage reverse proportional circuit consists of an amplifier , resistance/> 、/> 、/> Composition, resistance/> One end is connected to electrical ground and the other end is connected to the amplifier/> The positive input terminal of the amplifier is connected to The inverting input terminal and resistor/> 、/> Connected, resistor Connected to the capacitor to be detected in the integration circuit, the resistor The other end of the amplifier The output terminal is connected to The integration circuit consists of an operational amplifier With feedback resistor/> Composition, amplifier/> With resistor/> The first stage reverse proportional circuit and reference capacitor / > Connect in series with the capacitor to be detected and the automatic compensation capacitor/> In parallel, and then through the operational amplifier/> With feedback resistor/> The output signal of the integral circuit is composed of ; The second stage reverse proportional circuit consists of an amplifier With resistor/> 、/> The output end of the integrating circuit is connected to a resistor. One end is connected to the resistor/> With amplifier/> The reverse input terminal and resistor/> Connected, resistor/> The other end is connected to the amplifier/> The output end of the amplifier is connected to The positive input terminal is connected to the electrical ground, and the output signal of the second stage inverse proportional circuit, that is, the amplifier / > The output signal at the output end is / > , the automatic compensation capacitor/> is a programmable capacitor, and the capacitor to be detected includes a leakage capacitor/> and leakage resistor/> ; The feedback circuit with PI adjustment includes an FPGA single-chip computer system, an ADC acquisition circuit, and a PI controller. The ADC acquisition circuit is connected to the output end of the second-order low-pass filter circuit. After the ADC acquisition circuit collects information, it is transmitted to the single-chip computer system for processing and then transmitted to the PC end. The PC end then implements the calibration of the variable capacitor CT through the PI controller. According to the output feedback of the phase-controlled rectifier circuit based on the comparator, the ADC collects the system output signal through the MCU controller to perform PI adjustment value, and completes zeroing when the capacitor to be detected is not connected or the system is powered on in the initial state; In the phase shift circuit, when the imaginary part of the capacitor to be detected is detected When the phase shift circuit is a differential circuit, when the real part of the capacitance sensor is detected/> When phase shift is not required, the AC signal and the next stage operational amplifier /> is connected to the inverting input terminal of; The normally open contact of the analog switch S1 is connected to the output terminal of the self-compensation calibration bridge circuit , the normally closed contact is connected to the output terminal /> , when the input end is the original excitation signal phase shifted 90°, the analog switch output signal/> After being rectified into DC by a second-order low-pass filter circuit, the imaginary part of the capacitor to be tested is detected at this time./> ; When the input end is the original excitation signal, the real part of the capacitor to be tested is detected at this time/> ; Among them, the input sinusoidal excitation signal is/> , A is the gain of the input sinusoidal excitation signal; Among them, when detecting When the phase of the output signal of the phase shift circuit is 90° behind the excitation signal, the analog switch controlled by the comparator is The output signal is: Then it is integrated through a second-order low-pass filter circuit. When the cut-off frequency of the second-order low-pass filter is much smaller than the excitation signal frequency, a DC signal can be obtained. , the DC output after signal integration in one cycle is approximately calculated as: Detecting the imaginary part for: When testing When the phase shift circuit is not required, the excitation signal directly passes through the analog switch controlled by the comparator. The output signal is: Then it is integrated through a second-order low-pass filter circuit. When the cut-off frequency of the second-order low-pass filter is much smaller than the excitation signal frequency, a DC signal can be obtained. , the DC output after signal integration in one cycle is approximately calculated as: Detection of real part for: . 2. A method for measuring complex impedance of a capacitor according to claim 1, characterized in that the initial state includes the initial moment when the measurement circuit is not connected to the capacitor to be detected, or the measurement circuit is connected to the capacitor to be detected and powered on. 3. A capacitor complex impedance measurement circuit, used to implement the measurement method as claimed in claim 1, characterized in that the measurement circuit comprises a self-compensating calibration bridge circuit, a phase shift circuit and a phase-controlled rectifier circuit; The self-compensating calibration bridge circuit is used to input a sinusoidal AC signal excitation into the measuring circuit, and to perform output zeroing on the measuring circuit when the self-compensating calibration bridge circuit is not connected to the capacitor to be detected, or when the self-compensating calibration bridge circuit is connected to the capacitor to be detected and powered on at the initial moment, so as to detect the complex impedance of the capacitor to be detected; The phase shift circuit is used to shift the phase of the input sinusoidal AC signal by 90° or 0° to generate a phase-shifted phase-controlled signal; The phase-controlled rectifier circuit is used to respond to the phase-controlled signal and perform phase-controlled rectification on the AC signal, and then filter the AC signal after phase-controlled rectification and convert it into a DC voltage for output; The self-compensation calibration bridge circuit comprises a first-stage reverse proportional circuit, an integration circuit and a feedback circuit with PI regulation; The phase-controlled rectifier circuit includes a comparator, a second-stage reverse proportional circuit, an analog switch S1 , and a second-order low-pass filter circuit; the comparator is an operational amplifier. , the operational amplifier/> The inverting input terminal is connected to the phase shift circuit, the positive input terminal is connected to the electrical ground, and the operational amplifier/> The output end is connected to the signal output end of the analog switch S1 , and the signal output end of the switch S1 is connected to the second-order low-pass filter circuit. The signal is / > , the two input ends of the analog switch S1 are respectively connected to the integration circuit of the self-compensation calibration bridge circuit and the output end of the second-stage reverse proportional circuit; The first stage reverse proportional circuit consists of an amplifier , resistance/> 、/> 、/> Composition, resistance/> One end is connected to electrical ground and the other end is connected to the amplifier/> The positive input terminal of the amplifier is connected to The inverting input terminal and resistor/> 、/> Connected, resistor Connected to the capacitor to be detected in the integration circuit, the resistor The other end of the amplifier The output terminal is connected to The integration circuit consists of an operational amplifier With feedback resistor/> Composition, amplifier/> With resistor/> The first stage reverse proportional circuit and reference capacitor / > Connect in series with the capacitor to be detected and the automatic compensation capacitor/> In parallel, and then through the operational amplifier/> With feedback resistor/> The output signal of the integral circuit is composed of ; The second stage reverse proportional circuit consists of an amplifier With resistor/> 、/> The output terminal of the integrator circuit is connected to the resistor One end is connected to the resistor/> With amplifier/> The reverse input terminal and resistor/> Connected, resistor/> The other end is connected to the amplifier/> The output end of the amplifier is connected to The positive input terminal is connected to the electrical ground, and the output signal of the second stage inverse proportional circuit, that is, the amplifier / > The output signal at the output end is / > , the automatic compensation capacitor/> is a programmable capacitor, and the capacitor to be detected includes a leakage capacitor/> and leakage resistor/> ; The feedback circuit with PI adjustment includes an FPGA single-chip computer system, an ADC acquisition circuit, and a PI controller. The ADC acquisition circuit is connected to the output end of the second-order low-pass filter circuit. After the ADC acquisition circuit collects information, it is transmitted to the single-chip computer system for processing and then transmitted to the PC end. The PC end then implements the calibration of the variable capacitor CT through the PI controller. According to the output feedback of the phase-controlled rectifier circuit based on the comparator, the ADC collects the system output signal through the MCU controller to perform PI adjustment value, and completes zeroing when the capacitor to be detected is not connected or the system is powered on in the initial state; In the phase shift circuit, when the imaginary part of the capacitor to be detected is detected When the phase shift circuit is a differential circuit, when the real part of the capacitance sensor is detected/> When phase shift is not required, the AC signal and the next stage operational amplifier /> is connected to the inverting input terminal of . 4. A measuring device, comprising the measuring circuit as claimed in claim 3.