A high-precision and low-power AC impedance measurement circuit and method

Abstract

The present invention discloses a high-precision and low-power AC impedance measurement circuit and method. The circuit includes: a waveform generator; a first isolation buffer, whose positive input terminal is connected to the sine wave signal output terminal; a switching circuit, which is connected to the negative input terminal and the output terminal of the first isolation buffer; a to-be-measured impedance and a reference impedance, which are connected to the switching circuit; an operational amplifier, whose positive input terminal is connected to a reference voltage, and whose negative input terminal is connected to the to-be-measured impedance and the reference impedance; a sampling impedance, which is connected between the negative input terminal and the output terminal of the operational amplifier; a first selection switch, which is connected between a second isolation buffer and the to-be-measured impedance or the reference impedance; a second selection switch, which is connected between a third isolation buffer and the operational amplifier; a fully differential I / Q modulation rectifier, which is used for rectifying the received signal; a low-pass filter; an analog-to-digital converter; and an MCU / DSP module, which is used for calculating the modulus value and the phase angle of the to-be-measured impedance. The present invention can improve the measurement accuracy of the to-be-measured impedance and reduce the power consumption.

Description

Technical Field

[0001] The present invention relates to the technical field of AC impedance measurement, and particularly to a high-precision and low-power consumption AC impedance measurement circuit and method. Background Art

[0002] AC impedance measurement technology has extensive application requirements in the fields of electrochemistry, biomedicine, materials science, etc. By applying an AC signal to the object to be measured to measure its AC impedance information, the electrochemical characteristics, reaction mechanism, and related parameters of the system can be analyzed in depth.

[0003] Patent document CN105662411A discloses an AC impedance measurement circuit and method. By using a sinusoidal current excitation across the two ends of the human body to be measured, a corresponding sinusoidal voltage is generated across the two ends of the human body to be measured, and then after rectification and filtering, the equivalent impedance of the human body to be measured is calculated. This solution requires two external calibration resistors, and the non-linearity of the switch conduction impedance has a certain impact on the measurement performance, and it is not applicable to the measurement of the impedance model to be measured with a capacitor or a series connection of a capacitor and a resistor, and does not have the versatility of high-precision impedance measurement.

[0004] Patent document CN113796847A discloses an AC impedance measurement circuit with a calibration function. Similarly, a sine wave is used to excite a reference resistor and a resistor to be measured respectively to generate corresponding sine wave voltages. The sine wave voltage signals are quantized by an analog-to-digital converter (ADC) to obtain preliminary impedance information to be measured containing switch impedance. Then, through the measurement of different combinations of the switch circuit, the switch equivalent impedance is calculated, and then the switch equivalent impedance value is subtracted from the preliminary impedance measurement result to calculate the final impedance information to be measured. The measurement accuracy of the switch impedance in this solution depends on the matching accuracy of the switch, and the non-linearity of the switch impedance has an impact on the measurement performance. In addition, a large-bandwidth operational amplifier is required to adapt to the high-frequency AC excitation measurement scenario, and high precision, low power consumption, and low cost cannot be achieved.

[0005] Among them, the basic core principle of AC impedance measurement technology is an inverting amplifier circuit, which consists of an operational amplifier OPA, an impedance Zr or Zt, and an impedance Zb to form an inverting amplifier circuit. The impedance Zr or Zt is selected by switching through switches TGA and TGB. Ve is the AC excitation signal of the inverting amplifier circuit. The AC excitation signal can be a sine wave, a square wave, a triangular wave, a sawtooth wave, etc. Generally, a sine wave is selected as the AC excitation signal. Vx is the inverting input terminal of OPA, Vo is the output of the inverting amplifier circuit, and (Vo - Vx) is used as the analog signal representing the AC impedance information. Two corresponding voltage signals (Vo - Vx) r and (Vo - Vx) t are generated by exciting Zr + TGA and Zt + TGB with Ve respectively, and Zt = (Zr + TGA)·(Vo - Vx) is calculated according to the inverse proportional relationship between the corresponding voltage and the corresponding impedance.r / (Vo - Vx) t - The AC impedance information of TGB, where the measurement results include the switch impedances TGA and TGB, which affect the impedance measurement accuracy. In addition, due to the limited bandwidth of OPA, (Vo - Vx) r and (Vo - Vx) t contain different phase delay information and cannot be canceled out, ultimately resulting in errors in the calculation result of Zt. This error is particularly significant in high-frequency AC excitation application scenarios. To reduce this error, it is necessary to increase the bandwidth of OPA, which increases the power consumption of the system.

[0006] Therefore, there is an urgent need for an AC impedance measurement circuit and method with high precision, low power consumption, and low cost that can adapt to various frequencies. Summary of the Invention

[0007] The purpose of the present invention is to provide an AC impedance measurement circuit and method with high precision and low power consumption in view of the deficiencies of the prior art.

[0008] The purpose of the present invention is achieved through the following technical solutions: In the first aspect of the embodiments of the present invention, an AC impedance measurement circuit with high precision and low power consumption is provided, including:

[0009] A waveform generator, including a sine wave signal output terminal and a square wave signal output terminal;

[0010] A first isolation buffer, whose positive input terminal is connected to the sine wave signal output terminal;

[0011] A switch circuit, connected to the negative input terminal and the output terminal of the first isolation buffer;

[0012] The impedance to be measured and the reference impedance, connected to the switch circuit;

[0013] An operational amplifier, whose positive input terminal is connected to the reference voltage, and whose negative input terminal is connected to the impedance to be measured and the reference impedance;

[0014] A sampling impedance, connected between the negative input terminal and the output terminal of the operational amplifier;

[0015] A first selection switch and a second selection switch, one input terminal of the first selection switch is connected to the negative input terminal of the first isolation buffer, the other input terminal of the first selection switch and one input terminal of the second selection switch are connected to the negative input terminal of the operational amplifier, and the other input terminal of the second selection switch is connected to the output terminal of the operational amplifier;

[0016] A second isolation buffer and a third isolation buffer, whose positive input terminals are respectively connected to the output terminals of the first selection switch and the second selection switch, and whose negative input terminals are respectively connected to their corresponding output terminals;

[0017] Fully differential I / Q modulation rectifier, low-pass filter, analog-to-digital converter, and MCU / DSP module;

[0018] Among them, the switching circuit includes multiple switches. By controlling the multiple switches, a measured impedance or a reference impedance is connected between the first isolation buffer and the operational amplifier.

[0019] Further, the sine wave signal output terminal of the waveform generator is used to output a sine wave signal, and this sine wave signal is used as an AC excitation signal;

[0020] The square wave signal output terminal of the waveform generator is used to output a periodic square wave signal. This square wave signal has two mode signals, namely, an I demodulation mode signal for in-phase demodulation and a Q demodulation mode signal for quadrature demodulation, so as to extract the real part and the imaginary part components of the AC excitation voltage signal input to the fully differential I / Q modulation rectifier.

[0021] Further, the switching circuit includes a first switch, a second switch, a third switch, and a fourth switch. Among them, the first switch is connected between the output terminal of the first isolation buffer and the reference impedance; the second switch is connected between the output terminal of the first isolation buffer and the measured impedance; the third switch is connected between the negative input terminal of the first isolation buffer and the reference impedance; the fourth switch is connected between the negative input terminal of the first isolation buffer and the measured impedance.

[0022] Further, the switching circuit is controlled by a first control signal. When the first control signal is at a high level, the first switch and the third switch are turned on, so that a reference impedance is connected between the first isolation buffer and the operational amplifier, and this reference impedance is connected between the output terminal of the first isolation buffer and the negative input terminal of the operational amplifier; when the first control signal is at a low level, the second switch and the fourth switch are turned on, so that a measured impedance is connected between the first isolation buffer and the operational amplifier, and this measured impedance is connected between the output terminal of the first isolation buffer and the negative input terminal of the operational amplifier.

[0023] Further, the first selection switch and the second selection switch are controlled by a second control signal. When the second control signal is at a high level, the negative input terminal of the first isolation buffer and the positive input terminal of the second isolation buffer are turned on, and at the same time, the negative input terminal of the operational amplifier and the positive input terminal of the third isolation buffer are turned on; when the second control signal is at a low level, the negative input terminal of the operational amplifier and the positive input terminal of the second isolation buffer are turned on, and at the same time, the output terminal of the operational amplifier and the positive input terminal of the third isolation buffer are turned on.

[0024] Further, the fully differential I / Q modulation rectifier includes a first input terminal and a second input terminal for receiving the output signals of the second isolation buffer and the third isolation buffer, a third input terminal for receiving the square wave signal generated by the waveform generator, and a first output terminal and a second output terminal for outputting the rectified signals;

[0025] The fully differential I / Q modulation rectifier controls the I demodulation mode of in-phase demodulation or the Q demodulation mode of quadrature demodulation through the received square wave signal generated by the waveform generator. When the square wave signal is at a high level, the first input terminal and the first output terminal of the fully differential I / Q modulation rectifier are turned on, and the second input terminal and the second output terminal of the fully differential I / Q modulation rectifier are turned on; when the square wave signal is at a low level, the first input terminal and the second output terminal of the fully differential I / Q modulation rectifier are turned on, and the second input terminal and the first output terminal of the fully differential I / Q modulation rectifier are turned on.

[0026] Further, the low-pass filter is used to filter the rectified signal;

[0027] The analog-to-digital converter is used to quantize the filtered signal into a DC signal;

[0028] The MCU / DSP module is used to calculate the modulus and phase angle of the impedance to be measured based on the quantized signal data.

[0029] In a second aspect of the embodiments of the present invention, an AC impedance measurement method is provided, which is implemented based on the above-mentioned high-precision and low-power AC impedance measurement circuit. The method includes the following steps:

[0030] (1) Set the modulus of the reference impedance, and the type, amplitude, and frequency of the sine wave signal generated by the waveform generator;

[0031] (2) Control the voltage signal fed into the fully differential I / Q modulation rectifier by controlling the first control signal of the switch circuit and the second control signals of the first selection switch and the second selection switch; control the conversion result output by the analog-to-digital converter by controlling the demodulation mode of the square wave signal to obtain the conversion results D1I and D1Q, the conversion results D2I and D2Q, the conversion results D3I and D3Q, and the conversion results D4I and D4Q; wherein, the square wave signal is output from the square wave signal output terminal of the waveform generator and received by the third input terminal of the fully differential I / Q modulation rectifier;

[0032] (3) The MCU / DSP module calculates and caches the magnitude |Vr(s)| and phase angle ∠Vr(s) of the voltage signal across the reference impedance based on the conversion results D1I and D1Q, calculates and caches the magnitude |Vb1(s)| and phase angle ∠Vb1(s) of the voltage signal across the sampling impedance based on the conversion results D2I and D2Q, calculates and caches the magnitude |Vt(s)| and phase angle ∠Vt(s) of the voltage signal across the impedance under test based on the conversion results D3I and D3Q, and calculates and caches the magnitude |Vb2(s)| and phase angle ∠Vb2(s) of the voltage signal across the sampling impedance based on the conversion results D4I and D4Q;

[0033] (4) The MCU / DSP module calculates the magnitude and phase angle of the impedance under test based on the magnitude |Vr(s)| and phase angle ∠Vr(s) of the voltage signal across the reference impedance, the magnitude |Vb1(s)| and phase angle ∠Vb1(s) of the voltage signal across the sampling impedance, the magnitude |Vt(s)| and phase angle ∠Vt(s) of the voltage signal across the impedance under test, and the magnitude |Vb2(s)| and phase angle ∠Vb2(s) of the voltage signal across the sampling impedance cached therein.

[0034] Further, the step (2) specifically includes the following sub-steps:

[0035] (2.1) Set the first control signal of the switch circuit to high level, and set the second control signals of the first selection switch and the second selection switch to high level to send the voltage signal across the reference impedance into the fully differential I / Q modulation rectifier; set the square wave signal to I demodulation mode and Q demodulation mode respectively to obtain the conversion results D1I and D1Q output by the analog-to-digital converter;

[0036] (2.2) Set the first control signal of the switch circuit to high level, and set the second control signals of the first selection switch and the second selection switch to low level to send the voltage signal across the sampling impedance into the fully differential I / Q modulation rectifier; set the square wave signal to I demodulation mode and Q demodulation mode respectively to obtain the conversion results D2I and D2Q output by the analog-to-digital converter;

[0037] (2.3) Set the first control signal of the switch circuit to low level, and set the second control signals of the first selection switch and the second selection switch to high level to send the voltage signal across the impedance under test into the fully differential I / Q modulation rectifier; set the square wave signal to I demodulation mode and Q demodulation mode respectively to obtain the conversion results D3I and D3Q output by the analog-to-digital converter;

[0038] (2.4) Set the first control signal of the switch circuit to low level, and set the second control signals of the first selection switch and the second selection switch to low level, so as to send the voltage signal across the sampling impedance into the fully differential I / Q modulation rectifier; set the square wave signal to the I demodulation mode and the Q demodulation mode respectively, so as to obtain the conversion results D4I and D4Q output by the analog-to-digital converter.

[0039] Further, the modulus and phase angle of the voltage signal across the reference impedance are calculated by the following formulas respectively:

[0040]

[0041]

[0042] The modulus and phase angle of the voltage signal across the sampling impedance are calculated by the following formulas respectively:

[0043]

[0044]

[0045] The modulus and phase angle of the voltage signal across the impedance to be measured are calculated by the following formulas respectively:

[0046]

[0047]

[0048] The modulus and phase angle of the voltage signal across the sampling impedance are calculated by the following formulas respectively:

[0049]

[0050]

[0051] In the formulas, represents the arctangent value;

[0052] The formulas for calculating the modulus and phase angle of the impedance to be measured are as follows:

[0053]

[0054]

[0055] In the formulas, represents the modulus of the impedance to be measured Zt, Represents the phase angle of the impedance Zt to be measured.

[0056] The beneficial effects of the present invention are as follows: Through the feedback selection of the excitation signal node, the present invention avoids the AC signal to be quantized by the ADC from containing switch impedance information, and eliminates the influence of the switch impedance and its nonlinearity on the measurement accuracy; By measuring the input signal and output signal of the reverse amplifier circuit under different signal path settings, and using a specific mathematical operation algorithm for each measured signal, the present invention eliminates the influence of the limited bandwidth of the operational amplifier OPA in the measurement system, obtains accurate impedance information to be measured, avoids using a large bandwidth OPA, realizes low power consumption, and at the same time makes the measurement system have strong PVT immunity; The present invention can reduce the requirements for the performance of each module of the high-precision AC impedance measurement circuit, adapt to the accurate measurement of AC impedance at various frequencies, realize high-precision impedance measurement insensitive to PVT (Process, Voltage, Temperature), improve the immunity of the measurement system to PVT, realize the measurement of high-precision AC impedance with low cost and low power consumption, and at the same time simplify the measurement system and reduce the power consumption of the measurement system. Brief Description of the Drawings

[0057] Figure 1 Is the system architecture diagram of the high-precision and low-power AC impedance measurement circuit according to the embodiment of the present invention;

[0058] Figure 2 Is the timing relationship diagram of the AC excitation signal Ve generated by the waveform generator and the control signal PS of the fully differential I / Q modulation rectifier according to the embodiment of the present invention;

[0059] Figure 3 Is the architecture diagram of the fully differential I / Q modulation rectifier circuit according to the embodiment of the present invention;

[0060] Figure 4 Is the flowchart of the AC impedance measurement method according to the embodiment of the present invention. Detailed Embodiments

[0061] Here, the exemplary embodiments will be described in detail, and the examples are shown in the drawings. When the following description refers to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. On the contrary, they are only examples of devices and methods consistent with some aspects of the present invention as detailed in the appended claims.

[0062] The terms used in this invention are for the purpose of describing particular embodiments only and are not intended to limit the invention. The singular forms “a”, “said” and “the” used in this invention and the appended claims are also intended to include the plural forms unless the context clearly dictates otherwise. It should also be understood that the term “and / or” as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items.

[0063] It should be understood that although the terms first, second, third, etc. may be used herein to describe various information, such information should not be limited to these terms. These terms are only used to distinguish information of the same type from each other. For example, without departing from the scope of this invention, the first information may also be referred to as the second information, and similarly, the second information may also be referred to as the first information. Depending on the context, the word “if” as used herein may be interpreted as “when” or “while” or “in response to a determination”.

[0064] The present invention will be described in detail below with reference to the accompanying drawings. Without conflict, the features in the following embodiments and implementation manners can be combined with each other.

[0065] See Figure 1 , the high-precision and low-power AC impedance measurement circuit of the present invention specifically includes: a waveform generator, a first isolation buffer BUF0, a switch circuit MUX, a to-be-measured impedance Zt, a reference impedance Zr, a sampling impedance Zb, an operational amplifier OPA, a first selection switch S1, a second selection switch S2, a second isolation buffer BUF1, a third isolation buffer BUF2, a fully differential I / Q modulation rectifier, a low-pass filter LPF, an analog-to-digital converter ADC, and an MCU / DSP (Microcontroller Unit / Digital Signal Processors) module.

[0066] As Figure 1As shown, the waveform generator includes a sine wave signal output terminal for outputting a sine wave signal Ve, and a square wave signal output terminal for outputting a periodic square wave signal PS; the positive input terminal of the first isolation buffer BUF0 is connected to the sine wave signal output terminal of the waveform generator; the switch circuit MUX is connected to the negative input terminal and the output terminal of the first isolation buffer BUF0; the impedance under test Zt and the reference impedance Zr are connected to the switch circuit; the positive input terminal of the operational amplifier OPA is connected to the reference voltage (common mode voltage) VCM, and the negative input terminal of the operational amplifier OPA is connected to the impedance under test Zt and the reference impedance Zr; the sampling impedance Zb is connected between the negative input terminal and the output terminal of the operational amplifier; one input terminal of the first selection switch S1 is connected to the negative input terminal of the first isolation buffer BUF0, the other input terminal of the first selection switch S1 and one input terminal of the second selection switch S2 are connected to the negative input terminal of the operational amplifier OPA, and the other input terminal of the second selection switch S2 is connected to the output terminal of the operational amplifier OPA; the positive input terminals of the second isolation buffer BUF1 and the third isolation buffer BUF2 are respectively connected to the output terminals of the first selection switch S1 and the second selection switch S2, that is, the positive input terminal of the second isolation buffer BUF1 is connected to the output terminal of the first selection switch S1, the positive input terminal of the third isolation buffer BUF2 is connected to the output terminal of the second selection switch S2, the negative input terminal of the second isolation buffer BUF1 is connected to the output terminal of the second isolation buffer BUF1, and the negative input terminal of the third isolation buffer BUF2 is connected to the output terminal of the third isolation buffer BUF2; the fully differential I / Q modulation rectifier includes three input terminals VA1, VA2, VA3 and two output terminals VB1, VB2, wherein the first input terminal VA1 and the second input terminal VA2 are respectively used to receive the signals output by the output terminals of the second isolation buffer BUF1 and the third isolation buffer BUF2, the third input terminal VA3 is respectively used to receive the square wave signal PS generated by the waveform generator, and the first output terminal VB1 and the second output terminal VB2 are respectively used to output the rectified signals; the low-pass filter LPF is used to filter the rectified signals; the analog-to-digital converter ADC is used to perform DC signal quantization on the filtered signals; the MCU / DSP module is used to calculate the modulus and phase angle of the impedance under test Zt based on the quantized signal data. Among them, the switch circuit MUX includes multiple switches, and by controlling the multiple switches, the impedance under test Zt or the reference impedance Zr is connected between the first isolation buffer BUF0 and the operational amplifier OPA.

[0067] Further, the sine wave signal output terminal of the waveform generator is used to output a sine wave signal Ve, and this sine wave signal Ve is used as the AC excitation signal Ve; the square wave signal output terminal of the waveform generator is used to output a periodic square wave signal PS, and there are two mode signals for this square wave signal PS, namely the I demodulation mode signal for in-phase demodulation and the Q demodulation mode signal for quadrature demodulation, so as to extract the real part and imaginary part components of the AC excitation voltage signal input to the fully differential I / Q modulation rectifier. The relationship between the Ve signal and the PS signal output by the waveform generator is as Figure 2 shown.

[0068] Further, the switch circuit MUX includes a first switch TG1A, a second switch TG2A, a third switch TG1B, and a fourth switch TG2B. Among them, the first switch TG1A is connected between the output terminal of the first isolation buffer BUF0 and the reference impedance Zr; the second switch TG2A is connected between the output terminal of the first isolation buffer BUF0 and the impedance under test Zt; the third switch TG1B is connected between the negative input terminal of the first isolation buffer BUF0 and the reference impedance Zr; the fourth switch TG2B is connected between the negative input terminal of the first isolation buffer BUF0 and the impedance under test Zt, as Figure 1 shown.

[0069] Further, the switch circuit MUX is controlled by a first control signal SEL1. When the first control signal SEL1 is at a high level, that is, SEL1 = 1, the first switch TG1A and the third switch TG1B are turned on, so that the reference impedance Zr is connected between the first isolation buffer BUF0 and the operational amplifier OPA, and this reference impedance Zr is connected between the output terminal of the first isolation buffer BUF0 and the negative input terminal of the operational amplifier OPA; when the first control signal SEL1 is at a low level, that is, SEL1 = 0, the second switch TG2A and the fourth switch TG2B are turned on, so that the impedance under test Zt is connected between the first isolation buffer BUF0 and the operational amplifier OPA, and this impedance under test Zt is connected between the output terminal of the first isolation buffer BUF0 and the negative input terminal of the operational amplifier OPA.

[0070] Further, the operational amplifier OPA is a finite bandwidth operational amplifier with a single pole within the bandwidth, and its model can be regarded as BW / s, where BW represents the bandwidth of the operational amplifier OPA, and s represents the frequency domain variable in the system transfer function. In this embodiment, s is used to represent the single pole.

[0071] Further, the first selection switch S1 and the second selection switch S2 are single-pole double-throw switches, which are controlled by the second control signal SEL2. When the second control signal SEL2 is at a high level, i.e., SEL2 = 1, the negative input terminal of the first isolation buffer BUF0 and the positive input terminal of the second isolation buffer BUF1 are conducted, and at the same time, the negative input terminal of the operational amplifier OPA and the positive input terminal of the third isolation buffer BUF2 are conducted; when the second control signal SEL2 is at a low level, i.e., SEL2 = 0, the negative input terminal of the operational amplifier OPA and the positive input terminal of the second isolation buffer BUF1 are conducted, and at the same time, the output terminal of the operational amplifier OPA and the positive input terminal of the third isolation buffer BUF2 are conducted, as Figure 1 shown.

[0072] Further, the fully differential I / Q modulation rectifier controls the I demodulation mode of in-phase demodulation or the Q demodulation mode of quadrature demodulation through the square wave signal PS generated by the received waveform generator. When the square wave signal PS is at a high level, i.e., PS = 1, the first input terminal VA1 and the first output terminal VB1 of the fully differential I / Q modulation rectifier are conducted, and the second input terminal VA2 and the second output terminal VB2 of the fully differential I / Q modulation rectifier are conducted. At this time, VB1 = VA1, VB2 = VA2; when the square wave signal PS is at a low level, i.e., PS = 0, the first input terminal VA1 and the second output terminal VB2 of the fully differential I / Q modulation rectifier are conducted, and the second input terminal VA2 and the first output terminal VB1 of the fully differential I / Q modulation rectifier are conducted, as Figure 3 shown. At this time, VB1 = VA2, VB2 = VA1, so that the rectification of the input signal (VA1 - VA2) can be realized. The four signals (Vi1 - Vx1), (Vx1 - Vo1), (Vi2 - Vx2), and (Vx2 - Vo2) mentioned later will be rectified twice by the fully differential I / Q modulation rectifier with PS = 1 and PS = 0 respectively and quantized by the analog-to-digital converter ADC.

[0073] Specifically, the fully differential I / Q modulation rectifier controls the I demodulation mode or the Q demodulation mode through the received square wave signal PS, and can be specifically realized by two selection switches (i.e., the third selection switch and the fourth selection switch).

[0074] Exemplarily, the third selection switch and the fourth selection switch are double-pole double-throw switches, as Figure 3As shown, both input terminals of the third selection switch are connected to the first input terminal VA1 of the fully differential I / Q modulation rectifier, both input terminals of the fourth selection switch are connected to the second input terminal VA2 of the fully differential I / Q modulation rectifier, one output terminal of the third selection switch and one output terminal of the fourth selection switch are connected to the first output terminal VB1 of the fully differential I / Q modulation rectifier, and the other output terminal of the third selection switch and the other output terminal of the fourth selection switch are connected to the second output terminal VB2 of the fully differential I / Q modulation rectifier.

[0075] Exemplarily, the third selection switch and the fourth selection switch can also be single-pole double-throw switches. The input terminal of the third selection switch is connected to the first input terminal VA1 of the fully differential I / Q modulation rectifier, and the two output terminals of the third selection switch are respectively connected to the first output terminal VB1 and the second output terminal VB2 of the fully differential I / Q modulation rectifier. The input terminal of the fourth selection switch is connected to the second input terminal VA2 of the fully differential I / Q modulation rectifier, and the two output terminals of the fourth selection switch are respectively connected to the first output terminal VB1 and the second output terminal VB2 of the fully differential I / Q modulation rectifier.

[0076] In this embodiment, as Figure 1 shown, the sine wave signal output terminal of the waveform generator generates an AC excitation signal Ve. Through the switch circuit MUX, the reference impedance Zr and the impedance under test Zt are respectively selected for AC voltage signal excitation. At the same time, the reference impedance Zr or the impedance under test Zt, the operational amplifier OPA, and the sampling impedance Zb form an inverting amplifier circuit. The voltage signals (Vi - Vx) at both ends of the reference impedance Zr and the voltage signal (Vx - Vo) at both ends of the sampling impedance Zb are the main measurement signal objects of the AC impedance measurement circuit. According to different selections of the MUX channel of the switch circuit, there are two groups of different signals for both (Vi - Vx) and (Vx - Vo), which are specifically controlled by the first control signal SEL1.

[0077] Specifically, when the first control signal SEL1 of the switch circuit MUX = 1, the first switch TG1A and the third switch TG1B are selected to conduct. The inverting amplifier circuit is composed of the reference impedance Zr, the sampling impedance Zb, and the operational amplifier OPA. The voltage signal at both ends of the reference impedance Zr is (Vi1 - Vx1), and the voltage signal at both ends of the sampling impedance Zb is (Vx1 - Vo1). That is, when SELI = 1, the first switch TG1A and the third switch TG1B conduct, and the AC excitation signal Ve is excited to the reference impedance Zr. A Vi1 excitation signal is generated on the reference impedance Zr, and Vx1 and Vo1 signals are respectively generated at the negative input terminal and the output terminal of the operational amplifier OPA. The voltage signals at both ends of the reference impedance Zr and the voltage signals at both ends of the sampling impedance Zb can be obtained, and their calculation formulas are respectively:

[0078] (1)

[0079] (2)

[0080] In the formula, represents the voltage signal across the reference impedance Zr, represents the voltage signal across the sampling impedance Zb, represents the excitation signal Vi1 generated at the input of the reference impedance Zr, represents the signal Vx1 generated at the negative input of the operational amplifier OPA, represents the signal Vo1 generated at the output of the operational amplifier OPA, represents the excitation voltage at the input of the reference impedance Zr, represents the bandwidth of the operational amplifier OPA, represents the frequency-domain variable in the system transfer function, is the feedback coefficient of the inverting amplifier circuit involving the reference impedance Zr, , represents the reference impedance Zr, represents the sampling impedance Zb.

[0081] When the first control signal SEL1 of the switch circuit MUX = 0, the second switch TG2A and the fourth switch TG2B are selected to conduct. The inverting amplifier circuit is composed of the impedance under test Zt, the sampling impedance Zb, and the operational amplifier OPA. The voltage signal across the impedance under test Zt is (Vi2 - Vx2), and the voltage signal across the sampling impedance Zb is (Vx2 - Vo2). That is, when SEL1 = 0, the second switch TG2A and the fourth switch TG2B conduct, and the AC excitation signal Ve is applied to the impedance under test Zt. The excitation signal Vi2 is generated on the impedance under test Zt, and the signals Vx2 and Vo2 are generated at the negative input and the output of the operational amplifier OPA respectively. The voltage signal across the impedance under test Zt and the voltage signal across the sampling impedance Zb can be obtained, and their calculation formulas are respectively:

[0082] (3)

[0083] (4)

[0084] In the formula, represents the voltage signal across the impedance under test Zt, represents the voltage signal across the sampling impedance Zb, represents the excitation signal Vi2 generated at the input of the impedance under test Zt, represents the signal Vx2 generated at the negative input of the operational amplifier OPA, Represents the Vo2 signal generated at the output terminal of the operational amplifier OPA, represents the excitation voltage at the input terminal of the impedance Zt to be measured, is the feedback coefficient of the inverting amplifier circuit in which the impedance Zt to be measured is involved, , represents the impedance Zt to be measured.

[0085] The above four signals (Vi1 - Vx1), (Vx1 - Vo1), (Vi2 - Vx2), and (Vx2 - Vo2) are respectively input into the second isolation buffer BUF1 and the third isolation buffer BUF2 through the first selection switch S1 and the second selection switch S2. The signals output by the second isolation buffer BUF1 and the third isolation buffer BUF2 respectively enter the fully differential I / Q modulation rectifier for I / Q two-mode rectification, and the rectified signals are transferred to the low-pass filter LPF for filtering. The filtered signals then enter the analog-to-digital converter ADC for DC signal quantization. The four signals (Vi1 - Vx1), (Vx1 - Vo1), (Vi2 - Vx2), and (Vx2 - Vo2) contain the feedback coefficient of the inverting amplifier circuit and the finite bandwidth BW factor of the operational amplifier OPA. Other modules such as the first isolation buffer BUF0, the second isolation buffer BUF1, the third isolation buffer BUF2, the fully differential I / Q modulation rectifier, the low-pass filter LPF, and the analog-to-digital converter ADC on the signal path of the AC impedance measurement circuit all have module delays (i.e., signal phase shifts). However, the cumulative value of this phase shift is the same during the quantization process of the four signals (Vi1 - Vx1), (Vx1 - Vo1), (Vi2 - Vx2), and (Vx2 - Vo2), which can be equivalent to H(s). Therefore, the four signals can be respectively equivalent to , , , and are analyzed by equivalent ideal analog-to-digital converter ADC quantization without delay. Considering the influence of the feedback coefficient of the inverting amplifier circuit and the finite bandwidth BW of the operational amplifier OPA, the four signals are further correspondingly equivalent to:

[0086] (5)

[0087] (6)

[0088] (7)

[0089] (8)

[0090] According to the above formula (1) and formula (2) or formula (5) and formula (6) for calculation, we can obtain:

[0091] (9)

[0092] The right side of Equation (9) in is eliminated, that is, it has nothing to do with the limited bandwidth of the operational amplifier OPA. Similarly, according to the above formulas (3) and (4) or formulas (7) and (8) for calculation, the formula (10) that has nothing to do with the limited bandwidth of the operational amplifier OPA can be obtained:

[0093] (10)

[0094] In the formula, represents the voltage signal across the impedance Zt to be measured, represents the voltage signal across the sampling impedance Zb, represents the impedance Zt to be measured. From the calculations of formulas (9) and (10), the impedance Zt to be measured can be obtained:

[0095] (11)

[0096] In the formula, is the known reference impedance. Vb1(s), Vr(s), Vb2(s), and Vt(s) can be rectified through full-differential I / Q (in-phase / quadrature) modulation and then quantized by the analog-to-digital converter ADC. After quantization, the real and imaginary components of each AC voltage are extracted respectively, and then the real and imaginary parts of the impedance Zt to be measured can be calculated, that is, the modulus value and phase angle information of the impedance Zt to be measured are calculated, and the results are not affected by negative impacts brought by factors such as switch impedance and the limited bandwidth of the operational amplifier OPA. That is, the quantized signal data is sent into the MCU / DSP module for mathematical operations to calculate the modulus value and phase angle of the impedance Zt to be measured, which are respectively expressed as:

[0097] (12)

[0098] (13)

[0099] In the formula, represents the modulus value of the impedance Zt to be measured, represents the phase angle of the impedance Zt to be measured.

[0100] It should be understood that the MCU / DSP module can obtain the corresponding modulus value and phase angle results through a specified software algorithm. Formula (11) is the expression of the impedance Zt to be measured in the complex frequency domain, which contains real and imaginary components. The modulus value of the impedance = square root of (square of the real part + square of the imaginary part), and the phase angle of the impedance = arctangent value (imaginary part / real part). Thus, the modulus value and phase angle can be obtained, as shown in formulas (12) and (13).

[0101] As a specific implementation example for further describing the AC impedance measurement method shown in Formula (12) and Formula (13), Figure 4 The process and algorithm for measuring the AC impedance Zt in combination with the circuit system are shown.

[0102] Specifically, the AC impedance measurement method specifically includes the following steps:

[0103] (1) Set the modulus value |Zr| of the reference impedance Zr, and the type, amplitude, and frequency of the sine wave signal Ve generated by the waveform generator.

[0104] (2) Control the voltage signal fed into the fully differential I / Q modulation rectifier through the first control signal SEL1 of the control switch circuit MUX, the first selection switch S1, and the second control signal SEL2 of the second selection switch S2; control the demodulation mode of the square wave signal to control the conversion result output by the analog-to-digital converter ADC, so as to obtain the conversion results D1I and D1Q, the conversion results D2I and D2Q, the conversion results D3I and D3Q, and the conversion results D4I and D4Q.

[0105] (3) The MCU / DSP module calculates and caches the modulus value |Vr(s)| and phase angle ∠Vr(s) of the voltage signal across the reference impedance according to the conversion results D1I and D1Q, calculates and caches the modulus value |Vb1(s)| and phase angle ∠Vb1(s) of the voltage signal across the sampling impedance according to the conversion results D2I and D2Q, calculates and caches the modulus value |Vt(s)| and phase angle ∠Vt(s) of the voltage signal across the impedance to be measured according to the conversion results D3I and D3Q, and calculates and caches the modulus value |Vb2(s)| and phase angle ∠Vb2(s) of the voltage signal across the sampling impedance according to the conversion results D4I and D4Q.

[0106] (4) The MCU / DSP module calculates the modulus value and phase angle of the impedance to be measured according to the cached modulus value |Vr(s)| and phase angle ∠Vr(s) of the voltage signal across the reference impedance, the modulus value |Vb1(s)| and phase angle ∠Vb1(s) of the voltage signal across the sampling impedance, the modulus value |Vt(s)| and phase angle ∠Vt(s) of the voltage signal across the impedance to be measured, and the modulus value |Vb2(s)| and phase angle ∠Vb2(s) of the voltage signal across the sampling impedance.

[0107] Taking Figure 4 the process shown as an example, the AC impedance measurement method described in the present invention is described. This AC impedance measurement method is implemented based on the high-precision and low-power AC impedance measurement circuit of the above embodiment, and specifically includes the following steps:

[0108] (1) Set the modulus value of the reference impedance Zr , and the type, amplitude, and frequency of the sine wave signal Ve generated by the waveform generator.

[0109] (2) Set the first control signal SEL1 of the switch circuit MUX to high level 1 to turn on the first switch TG1A and the third switch TG1B, and use the sine wave signal Ve output from the sine wave signal output terminal of the waveform generator to excite the reference impedance Zr.

[0110] (3) Set the second control signal SEL2 of the first selection switch S1 and the second selection switch S2 to high level 1 to turn on the negative input terminal of the first isolation buffer BUF0 and the positive input terminal of the second isolation buffer BUF1, as well as the negative input terminal of the operational amplifier OPA and the positive input terminal of the third isolation buffer BUF2.

[0111] (4) Send the voltage signal (Vi1 - Vx1) across the reference impedance Zr to the fully differential I / Q modulation rectifier. First, set the square wave signal PS to the I demodulation mode and record the conversion result D1I output by the analog-to-digital converter ADC at this time; then set the square wave signal PS to the Q demodulation mode and record the conversion result D1Q output by the analog-to-digital converter ADC at this time. Among them, the square wave signal PS is output from the square wave signal output terminal of the waveform generator and received by the third input terminal VA3 of the fully differential I / Q modulation rectifier.

[0112] (5) Send the conversion results D1I and D1Q obtained in step (4) to the MCU / DSP module to calculate and cache the modulus of the voltage signal across the reference impedance Zr and the phase angle .

[0113] Further, the calculation formulas for the modulus and the phase angle of the voltage signal across the reference impedance Zr are respectively:

[0114] (14)

[0115] (15)

[0116] (6) Set the second control signal SEL2 of the first selection switch S1 and the second selection switch S2 to low level 0 to turn on the negative input terminal of the operational amplifier OPA and the positive input terminal of the second isolation buffer BUF1, as well as the output terminal of the operational amplifier OPA and the positive input terminal of the third isolation buffer BUF2.

[0117] (7) Send the voltage signal (Vx1 - Vo1) across the sampling impedance Zb to the fully differential I / Q modulation rectifier. First, set the square wave signal PS to the I demodulation mode and record the conversion result D2I output by the analog-to-digital converter ADC at this time; then set the square wave signal PS to the Q demodulation mode and record the conversion result D2Q output by the analog-to-digital converter ADC at this time.

[0118] (8) Feed the conversion results D2I and D2Q obtained in step (7) into the MCU / DSP module to calculate and cache the modulus of the voltage signal across the sampling impedance Zb. and the phase angle .

[0119] Furthermore, the formulas for calculating the modulus and the phase angle of the voltage signal across the sampling impedance Zb are respectively:

[0120] (16)

[0121] (17)

[0122] (9) Set the first control signal SEL1 of the switch circuit MUX to low level 0 to turn on the second switch TG2A and the fourth switch TG2B, and use the sine wave signal Ve output from the sine wave signal output terminal of the waveform generator to excite the impedance under test Zt.

[0123] (10) Repeat step (3), that is, set the second control signal SEL2 of the first selection switch S1 and the second selection switch S2 to high level 1 to turn on the negative input terminal of the first isolation buffer BUF0 and the positive input terminal of the second isolation buffer BUF1, as well as the negative input terminal of the operational amplifier OPA and the positive input terminal of the third isolation buffer BUF2.

[0124] (11) Feed the voltage signal (Vi2 - Vx2) across the impedance under test Zt into the fully differential I / Q modulation rectifier. First, set the square wave signal PS to the I demodulation mode and record the conversion result D3I output by the analog-to-digital converter ADC at this time; then set the square wave signal PS to the Q demodulation mode and record the conversion result D3Q output by the analog-to-digital converter ADC at this time.

[0125] (12) Feed the conversion results D3I and D3Q obtained in step (11) into the MCU / DSP module to calculate and cache the modulus and the phase angle of the voltage signal across the impedance under test Zt.

[0126] Furthermore, the formulas for calculating the modulus and the phase angle of the voltage signal across the impedance under test Zt are respectively:

[0127] (18)

[0128] (19)

[0129] (13) Repeat step (6), that is, set the second control signal SEL2 of the first selection switch S1 and the second selection switch S2 to low level 0, turn on the negative input terminal of the operational amplifier OPA and the positive input terminal of the second isolation buffer BUF1, and the output terminal of the operational amplifier OPA and the positive input terminal of the third isolation buffer BUF2.

[0130] (14) Send the voltage signal (Vx2 - Vo2) across the sampling impedance Zb into the fully differential I / Q modulation rectifier. First, set the square wave signal PS to the I demodulation mode, and record the conversion result D4I output by the analog-to-digital converter ADC at this time; then set the square wave signal PS to the Q demodulation mode, and record the conversion result D4Q output by the analog-to-digital converter ADC at this time.

[0131] (15) Send the conversion results D4I and D4Q obtained in step (14) into the MCU / DSP module to calculate and cache the modulus of the voltage signal across the sampling impedance Zb and the phase angle .

[0132] Further, the modulus of the voltage signal across the sampling impedance Zb and the phase angle are calculated by the following formulas respectively:

[0133] (20)

[0134] (21)

[0135] (16) According to the modulus of the voltage signal across the reference impedance Zr cached in the MCU / DSP module and the phase angle , the modulus of the voltage signal across the sampling impedance Zb and the phase angle , the modulus of the voltage signal across the impedance under test Zt and the phase angle and the modulus of the voltage signal across the sampling impedance Zb and the phase angle calculate the modulus of the impedance under test Zt and the phase angle .

[0136] Further, the modulus of the impedance under test Zt and the phase angle are calculated by the following formulas respectively:

[0137] (22)

[0138] (23)

[0139] In the formula, since the modulus value of the reference impedance Zr is preset in step (1) , and its phase angle is 0, formula (13) is transformed into formula (23).

[0140] In summary, the present invention extracts the common influence factor of the input signal and the output signal in the inverting amplifier circuit for the limited bandwidth of the operational amplifier OPA, quantifies the input signal and the output signal respectively, and cancels the common influence factor of the two through a corresponding algorithm, so as to obtain the information of the impedance to be measured Zt that is only related to the reference impedance Zr and is independent of the switch impedance, the bandwidth of the operational amplifier OPA, the amplitude and phase shift of the excitation signal. The present invention avoids the AC signal to be quantized by the analog-to-digital converter ADC containing switch impedance information through the feedback selection of the excitation signal node, and eliminates the influence of the switch impedance and its nonlinearity on the measurement accuracy; the present invention measures the input signal and the output signal of the inverting amplifier circuit under different signal path settings, and adopts a specific mathematical operation algorithm for each measured signal to eliminate the influence of the limited bandwidth of the operational amplifier OPA in the measurement system, obtains accurate impedance information to be measured, avoids using an operational amplifier OPA with a large bandwidth, realizes low power consumption, and at the same time makes the measurement system have strong PVT immunity; the present invention can reduce the requirements for the performance of each module of the high-precision AC impedance measurement circuit, adapt to the accurate measurement of AC impedance at various frequencies, realize high-precision impedance measurement that is insensitive to PVT (Process, Voltage, Temperature), improve the PVT immunity of the measurement system, realize the measurement of high-precision AC impedance with low cost and low power consumption, and at the same time simplify the measurement system and reduce the power consumption of the measurement system.

[0141] It should be noted that in this article, the term "comprising", "including" or any other variant thereof is intended to cover a non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or further includes elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "including a..." does not exclude the existence of additional identical elements in the process, method, article or device including that element.

[0142] The embodiments of the present invention have been described above in conjunction with the accompanying drawings, but the present invention is not limited to the above specific embodiments. The above specific embodiments are merely illustrative and not restrictive. Under the inspiration of the present invention, those of ordinary skill in the art can also make many forms without departing from the purpose of the present invention and the scope protected by the claims, and these all belong to the protection scope of the present invention.

Claims

1. An AC impedance measurement circuit with high precision and low power consumption, characterized in that, Comprising: A waveform generator, including a sine wave signal output terminal and a square wave signal output terminal; A first isolation buffer, whose positive input terminal is connected to the sine wave signal output terminal; A switching circuit, connected to the negative input terminal and the output terminal of the first isolation buffer; The impedance under test and the reference impedance, connected to the switching circuit; An operational amplifier, whose positive input terminal is connected to a reference voltage, and whose negative input terminal is connected to the impedance under test and the reference impedance; A sampling impedance, connected between the negative input terminal and the output terminal of the operational amplifier; A first selection switch and a second selection switch, one input terminal of the first selection switch is connected to the negative input terminal of the first isolation buffer, the other input terminal of the first selection switch and one input terminal of the second selection switch are connected to the negative input terminal of the operational amplifier, and the other input terminal of the second selection switch is connected to the output terminal of the operational amplifier; A second isolation buffer and a third isolation buffer, whose positive input terminals are respectively connected to the output terminals of the first selection switch and the second selection switch, and whose negative input terminals are respectively connected to their corresponding output terminals; A fully differential I / Q modulation rectifier, a low-pass filter, an analog-to-digital converter and an MCU / DSP module; Among them, the switching circuit includes a plurality of switches. By controlling the plurality of switches, the impedance under test or the reference impedance is connected between the first isolation buffer and the operational amplifier; The switching circuit includes a first switch, a second switch, a third switch and a fourth switch. Among them, the first switch is connected between the output terminal of the first isolation buffer and the reference impedance; the second switch is connected between the output terminal of the first isolation buffer and the impedance under test; the third switch is connected between the negative input terminal of the first isolation buffer and the reference impedance; the fourth switch is connected between the negative input terminal of the first isolation buffer and the impedance under test; The switching circuit is controlled by a first control signal. When the first control signal is at a high level, the first switch and the third switch are turned on, so that the reference impedance is connected between the first isolation buffer and the operational amplifier, and the reference impedance is connected between the output terminal of the first isolation buffer and the negative input terminal of the operational amplifier; when the first control signal is at a low level, the second switch and the fourth switch are turned on, so that the impedance under test is connected between the first isolation buffer and the operational amplifier, and the impedance under test is connected between the output terminal of the first isolation buffer and the negative input terminal of the operational amplifier.

2. The high-precision and low-power AC impedance measurement circuit according to claim 1, wherein The sine wave signal output terminal of the waveform generator is used to output a sine wave signal, which is used as an AC excitation signal; The square wave signal output terminal of the waveform generator is used to output a periodic square wave signal, which has two mode signals, namely the I demodulation mode signal for in-phase demodulation and the Q demodulation mode signal for quadrature demodulation, so as to extract the real part and the imaginary part components of the AC excitation voltage signal input to the fully differential I / Q modulation rectifier.

3. The high-precision and low-power AC impedance measurement circuit according to claim 1, characterized in that, The first selection switch and the second selection switch are controlled by a second control signal. When the second control signal is at a high level, the negative input terminal of the first isolation buffer and the positive input terminal of the second isolation buffer are turned on, and at the same time, the negative input terminal of the operational amplifier and the positive input terminal of the third isolation buffer are turned on. When the second control signal is at a low level, the negative input terminal of the operational amplifier and the positive input terminal of the second isolation buffer are turned on, and at the same time, the output terminal of the operational amplifier and the positive input terminal of the third isolation buffer are turned on.

4. The high-precision and low-power AC impedance measurement circuit according to claim 1, wherein The fully differential I / Q modulation rectifier includes two first input terminals and two second input terminals for receiving the output signals of the second isolation buffer and the third isolation buffer, a third input terminal for receiving the square wave signal generated by the waveform generator, and two first output terminals and two second output terminals for outputting the rectified signals. The fully differential I / Q modulation rectifier is controlled in an I demodulation mode of in-phase demodulation or a Q demodulation mode of quadrature demodulation by the received square wave signal generated by the waveform generator. When the square wave signal is at a high level, the first input terminal and the first output terminal of the fully differential I / Q modulation rectifier are turned on, and the second input terminal and the second output terminal of the fully differential I / Q modulation rectifier are turned on. When the square wave signal is at a low level, the first input terminal and the second output terminal of the fully differential I / Q modulation rectifier are turned on, and the second input terminal and the first output terminal of the fully differential I / Q modulation rectifier are turned on.

5. The high-precision and low-power AC impedance measurement circuit according to claim 1, wherein The low-pass filter is used to filter the rectified signal. The analog-to-digital converter is used to quantize the filtered signal into a DC signal. The MCU / DSP module is used to calculate the modulus and phase angle of the impedance to be measured based on the quantized signal data.

6. An AC impedance measurement method, implemented based on the high-precision and low-power AC impedance measurement circuit described in any one of claims 1-5, characterized in that, The method includes the following steps: (1) Set the modulus of the reference impedance, and the type, amplitude, and frequency of the sine wave signal generated by the waveform generator. (2) Control the voltage signal fed into the fully differential I / Q modulation rectifier by controlling the first control signal of the switch circuit and the second control signal of the first selection switch and the second selection switch. Control the conversion result output by the analog-to-digital converter by controlling the demodulation mode of the square wave signal to obtain the conversion results D1I and D1Q, the conversion results D2I and D2Q, the conversion results D3I and D3Q, and the conversion results D4I and D4Q. Among them, the square wave signal is output from the square wave signal output terminal of the waveform generator and received by the third input terminal of the fully differential I / Q modulation rectifier. (3) The MCU / DSP module calculates and caches the modulus |Vr(s)| and phase angle ∠Vr(s) of the voltage signal across the reference impedance according to the conversion results D1I and D1Q, calculates and caches the modulus |Vb1(s)| and phase angle ∠Vb1(s) of the voltage signal across the sampling impedance according to the conversion results D2I and D2Q, calculates and caches the modulus |Vt(s)| and phase angle ∠Vt(s) of the voltage signal across the impedance to be measured according to the conversion results D3I and D3Q, and calculates and caches the modulus |Vb2(s)| and phase angle ∠Vb2(s) of the voltage signal across the sampling impedance according to the conversion results D4I and D4Q. (4) The MCU / DSP module calculates the modulus and phase angle of the impedance to be measured based on the modulus |Vr(s)| and phase angle ∠Vr(s) of the voltage signal across the reference impedance cached therein, the modulus |Vb1(s)| and phase angle ∠Vb1(s) of the voltage signal across the sampling impedance, the modulus |Vt(s)| and phase angle ∠Vt(s) of the voltage signal across the impedance to be measured, and the modulus |Vb2(s)| and phase angle ∠Vb2(s) of the voltage signal across the sampling impedance.

7. The AC impedance measurement method according to claim 6, wherein The specific steps of step (2) include the following sub-steps: (2.1) Set the first control signal of the switch circuit to high level, and set the second control signals of the first selector switch and the second selector switch to high level to send the voltage signal across the reference impedance into the fully differential I / Q modulation rectifier; set the square wave signal to I demodulation mode and Q demodulation mode respectively to obtain the conversion results D1I and D1Q output by the analog-to-digital converter; (2.2) Set the first control signal of the switch circuit to high level, and set the second control signals of the first selector switch and the second selector switch to low level to send the voltage signal across the sampling impedance into the fully differential I / Q modulation rectifier; set the square wave signal to I demodulation mode and Q demodulation mode respectively to obtain the conversion results D2I and D2Q output by the analog-to-digital converter; (2.3) Set the first control signal of the switch circuit to low level, and set the second control signals of the first selector switch and the second selector switch to high level to send the voltage signal across the impedance to be measured into the fully differential I / Q modulation rectifier; set the square wave signal to I demodulation mode and Q demodulation mode respectively to obtain the conversion results D3I and D3Q output by the analog-to-digital converter; (2.4) Set the first control signal of the switch circuit to low level, and set the second control signals of the first selector switch and the second selector switch to low level to send the voltage signal across the sampling impedance into the fully differential I / Q modulation rectifier; set the square wave signal to I demodulation mode and Q demodulation mode respectively to obtain the conversion results D4I and D4Q output by the analog-to-digital converter.

8. The AC impedance measurement method according to claim 6, wherein The calculation formulas for the modulus |Vr(s)| and phase angle ∠Vr(s) of the voltage signal across the reference impedance are respectively: ∠Vr(s) = atan(D1Q / D1I) The calculation formulas for the modulus |Vb1(s)| and phase angle ∠Vb1(s) of the voltage signal across the sampling impedance are respectively: ∠Vb1(s) = atan(D2Q / D2I) The calculation formulas for the modulus |Vt(s)| and phase angle ∠Vt(s) of the voltage signal across the impedance to be measured are respectively: ∠Vt(s) = atan(D3Q / D3I) The calculation formulas for the modulus |Vb2(s)| and phase angle ∠Vb2(s) of the voltage signal across the sampling impedance are respectively: ∠Vb2(s) = atan(D4Q / D4I) In the formula, atan() represents the arctangent value; The calculation formulas for the modulus and phase angle of the impedance to be measured are respectively: |Zt| = |Zr|·|Vb1(s)|·|Vt(s)| / [|Vr(s)|·|Vb2(s)|] ∠Zt = ∠Vb1(s) + ∠Vt(s) - ∠Vr(s) - ∠Vb2(s) Where, |Zt| represents the modulus value of the impedance Zt to be measured, and ∠Zt represents the phase angle of the impedance Zt to be measured.

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