Digital impedance measurement method and system

Abstract

The invention discloses a digital impedance measurement method and system, and the method comprises the steps: obtaining an excitation current and a reference current after a signal source is applied to a measured impedance and a reference impedance respectively, and enabling the excitation current and the reference current to be used for generating an unbalanced current; a data acquisition control system is used for carrying out real-variable sampling ratio mixed sampling on the unbalanced current, the measured impedance voltage and the reference impedance voltage and then carrying out digital conversion on the unbalanced current, the measured impedance voltage and the reference impedance voltage; respectively acquiring vector components of the deviation voltage, the measured impedance voltage and the reference impedance voltage by using a digital orthogonal coherent detection algorithm; adjusting the balance state of the bridge circuit according to the vector component of the deviation voltage; and after balance adjustment, vector components of the measured impedance voltage and the reference impedance voltage are transmitted to an impedance calculation unit, and a plurality of parameters of impedance are obtained. By adopting the methods of high-speed synchronous data acquisition, low-jitter sampling clock, variable-sampling-ratio mixed sampling and the like, the measurement range and the measurement efficiency of the system are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of impedance measurement, and in particular to a digital impedance measurement method and system. Background Art

[0002] Impedance is a concept widely used in the field of electronics and is a basic parameter for characterizing electronic materials, components and circuits. Impedance measurement is not only an important part of the field of electronic measurement, but many other physical quantities can also be indirectly obtained through the measurement of impedance parameters, such as temperature, humidity, pressure, displacement, speed, vibration, density, flow and other sensors commonly used in engineering, whose original signals are mostly impedance parameters such as resistance, capacitance or inductance. In addition, by measuring the AC impedance spectrum of the measured object, more kinetic information and electrode interface structure information can be obtained than other conventional electrochemical methods, which is the basis of AC impedance spectroscopy. AC impedance spectroscopy not only plays a very important role in the field of electrochemistry, but is also widely used in research on materials, devices, biomedicine and earth sciences.

[0003] The automatic balancing bridge is recognized as the impedance measurement method with the highest accuracy, the widest range and the most reliable performance. The traditional automatic balancing bridge based on the virtual ground characteristics of the inverting amplifier can achieve high measurement accuracy when the measurement frequency is less than 100kHz. However, when the measurement frequency is further increased, the open-loop gain of the amplifier decreases, and coupled with the influence of phase compensation, the output amplitude is attenuated, the phase is offset, and the measurement accuracy will become very poor. The automatic balancing bridge based on the principle of detection-modulation-amplification can achieve accurate measurement in a wide frequency range of more than 1MHz, and is widely used in various types of precision impedance analysis instruments and equipment. However, this solution also has disadvantages such as complex circuits, difficult debugging, high cost, and high prices, which greatly limits the application and promotion of broadband precision impedance measurement instruments.

[0004] In recent years, with the rapid development of high-speed sampling and digital signal processing technology, it has become possible to realize a digital automatic bridge balancing method characterized by direct high-speed sampling of unbalanced current signals and bridge balancing by algorithms. This method uses an analog front end to detect the deviation signal and executes a set of equations to provide output control based on each cycle, directly digitally synthesize the second signal source, and realize automatic control of bridge balance. The digital compensation feedback loop replaces the complex analog deviation feedback loop, eliminating a large number of analog discrete devices, improving the integration and cost performance, and the measurement accuracy is only limited by the word length error. The flexibility, consistency, stability and reliability of the system are also greatly enhanced. Domestic and foreign researchers have also proposed some digital automatic bridge balancing methods, such as adaptive bridge balancing algorithm based on LMS, fast balancing algorithm based on Gauss-Newton method, bridge balancing algorithm based on neural network, etc., but these methods usually require iterative operations, and their effectiveness depends on the selection of initial values. If the initial value is too different from the true solution, it may lead to failure to converge, and in a strong noise environment, it is easily interfered by noise, resulting in reduced measurement accuracy. In addition, due to the limitations of the acquisition system performance, the test frequencies of these systems are mostly less than 1MHz, and there is still a large gap in frequency range and test speed compared with analog bridge balance controllers. Summary of the invention

[0005] In order to solve the above technical problems, this application proposes the following technical solutions: In a first aspect, an embodiment of the present application provides a digital impedance measurement method, comprising: Respectively obtaining an excitation current and a reference current after a signal source is applied to the measured impedance and the reference impedance, wherein the excitation current and the reference current are used to generate an unbalanced current; The unbalanced current, the measured impedance voltage and the reference impedance voltage are respectively sampled with a real variable sampling ratio and mixed and then digitally converted by using a data acquisition control system; The digital orthogonal coherent detection algorithm is used to respectively obtain the vector components of the deviation voltage, the measured impedance voltage and the reference impedance voltage; The balance state of the bridge circuit is adjusted according to the vector component of the deviation voltage; After adjusting the balance, the vector components of the measured impedance voltage and the reference impedance voltage are transmitted to the impedance calculation unit to obtain multiple parameters of the impedance.

[0006] In a possible implementation, respectively obtaining the excitation current and the reference current after the measured impedance and the reference impedance are applied with a signal source, wherein the excitation current and the reference current are used to generate an unbalanced current, includes: Applying an excitation signal source to the impedance under test to generate a sinusoidal test voltage, and obtaining an excitation current generated by the sinusoidal test voltage in the impedance under test; Applying a reference signal source to a reference impedance to generate a sinusoidal reference voltage, and obtaining a reference current generated by the sinusoidal reference voltage in the reference impedance; The difference between the excitation current and the reference current is used as an unbalanced current.

[0007] In a possible implementation, the method of using a data acquisition control system to perform mixed sampling of the unbalanced current, the measured impedance voltage, and the reference impedance voltage at a variable sampling ratio and then performing digital conversion includes: When the signal frequency is high, the unbalanced current, the measured impedance voltage and the reference impedance voltage are sampled synchronously in real time by equivalent sampling; When the signal frequency is lower than a preset value, the unbalanced current, the measured impedance voltage and the reference impedance voltage are sampled synchronously in real time by oversampling; After sampling is completed, the unbalanced current is input into the cross-group amplifier and feedback resistor for IV conversion to obtain the deviation voltage; The deviation voltage, the measured impedance voltage and the reference impedance voltage are respectively sent to the analog-to-digital converter for digital conversion after passing through the corresponding analog front ends. In a possible implementation, the sampling rate formula for sampling by variable sampling ratio mixed sampling is: ; when hour, , ; when hour, , ; in, is the number of signal cycle samples, To increase the number of bits of resolution, is the sampling frequency, is the signal frequency.

[0008] In a possible implementation, the method of using a digital orthogonal coherent detection algorithm to respectively obtain vector components of a deviation voltage, a measured impedance voltage, and a reference impedance voltage includes: Multiply the digitized deviation voltage, measured impedance voltage and reference impedance voltage by the internal reference signal respectively; The corresponding in-phase component and orthogonal component are generated respectively through a digital low-pass filter. In a possible implementation, the generating corresponding in-phase components and orthogonal components respectively through a digital low-pass filter includes: After extracting data with a sampling ratio higher than a preset value, an in-phase reference sequence and an orthogonal reference sequence are obtained; The total length of the sampled data is processed in multiple batches, and the in-phase and quadrature components of each batch are accumulated; the accumulation formula is: ; in, The sum of the in-phase components of each batch is summed, Cumulative sum of orthogonal components for each batch, The length of data processed for each batch, , , To increase the number of bits of resolution, when When , the sampling mode is equivalent sampling; when When the sampling mode is oversampling, , is the sampling frequency, is the signal frequency; The accumulation formula is recursively extended until the length of the sampled data reaches the total length to obtain the in-phase component and the orthogonal component.

[0009] In a possible implementation, the calculation formulas for the in-phase component and the orthogonal component are: ; ; in, , are the in-phase component and the orthogonal component in the vector components respectively, The sum of the in-phase components of each batch is summed, Cumulative sum of orthogonal components for each batch, is the total number of batches, , is the total length of the data, The length of data processed for each batch, , , The number of bits of resolution increased.

[0010] In a possible implementation, adjusting the balance state of the bridge circuit according to the vector component of the deviation voltage includes: Initialize the parameter data; After obtaining the initial value of the iteration by extrapolation, the reference signal source is adjusted and the deviation voltage is calculated; judging a preset condition according to the deviation voltage; If the preset conditions are met, the actual impedance value is obtained according to the vector components of the measured impedance voltage and the reference impedance voltage; or; If the preset conditions are not met, the secant method is used to iterate and calculate the next input amount; The reference signal source is readjusted and the deviation voltage is recalculated and determined according to the next step input amount until the preset conditions are met.

[0011] In a possible implementation, obtaining the iteration initial value by using the extrapolation method includes: Obtaining a first unbalanced voltage and a second unbalanced voltage respectively by inputting two different balanced signals; The reference voltage when the bridge is balanced is calculated according to the first unbalanced voltage and the second unbalanced voltage, and the calculation formula is: ;in, ; , and The first input balanced signal and the second input balanced signal The amplitude of is the signal frequency, is the initial phase; and are the first unbalanced voltage and the second unbalanced voltage respectively; and Expressed in vector form, we get ; ;but ; The initial value is obtained by adjusting the unbalanced voltage.

[0012] In a possible implementation, the formula for calculating the next input amount by iterating using the secant method is: ; in, , and Respectively sequence Second and The input balanced signal, and Respectively Second and The unbalanced voltage.

[0013] In a second aspect, an embodiment of the present application provides a digital impedance measurement system, comprising: An acquisition module, used to respectively acquire an excitation current and a reference current after a signal source is applied to the measured impedance and the reference impedance, wherein the excitation current and the reference current are used to generate an unbalanced current; A digital conversion module is used to perform real variable sampling ratio mixed sampling on the unbalanced current, the measured impedance voltage and the reference impedance voltage according to the data acquisition control system, and then perform digital conversion; A vector component acquisition module, used for obtaining the vector components of the deviation voltage, the measured impedance voltage and the reference impedance voltage respectively by a digital orthogonal coherent detection algorithm; A regulating module, used for regulating the balance state of the bridge circuit according to the vector component of the deviation voltage; The parameter acquisition module transfers the vector components of the measured impedance voltage and the reference impedance voltage to the impedance calculation unit after adjusting the balance, and obtains multiple parameters of the impedance.

[0014] Compared with the prior art, the beneficial effects of this application are: In terms of impedance measurement, this application adopts high-speed synchronous data acquisition, low-jitter sampling clock, variable sampling ratio mixed sampling and other methods to solve the problems of limited maximum processing frequency and low measurement efficiency in the medium and low frequency bands of traditional fixed sampling ratio systems, thereby improving the measurement range and measurement efficiency of the system.

[0015] In terms of bridge balance control, the present application adopts a bridge balance control algorithm that combines the extrapolation method and the secant method, giving full play to the advantages of the convergence certainty of the extrapolation method and the fast convergence speed and good stability of the secant method, overcoming the shortcomings of the traditional iterative method that relies on initial values ​​and may diverge, and enhancing the stability and accuracy of the digital automatic balancing bridge.

[0016] In terms of noise resistance, the present application adopts methods such as power frequency notch filter and digital orthogonal coherent detection to effectively suppress power frequency interference and random noise, and improve the measurement accuracy and stability of the system in a strong noise environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 A schematic diagram of a flow chart of a digital impedance measurement method provided in an embodiment of the present application; Figure 2 A principle block diagram of a data acquisition and control system provided in an embodiment of the present application; Figure 3 A schematic diagram showing a performance comparison between a variable sampling ratio and a fixed sampling ratio of a digital impedance measurement system provided in an embodiment of the present application; Figure 4 A flow chart of a hybrid optimization algorithm for bridge balance control provided in an embodiment of the present application; Figure 5 A schematic diagram of bridge balance convergence provided in an embodiment of the present application; Figure 6 A schematic diagram of measurement time of a digital impedance measurement system provided in an embodiment of the present application; Figure 7A technical roadmap for a digital impedance measurement system provided in an embodiment of the present application. DETAILED DESCRIPTION

[0018] The present solution is described below in conjunction with the accompanying drawings and specific implementation methods.

[0019] Figure 1 A schematic diagram of a digital impedance measurement method provided in an embodiment of the present application, see Figure 1 , a digital impedance measurement method in this embodiment includes: S101, respectively obtaining an excitation current and a reference current after a signal source is applied to a measured impedance and a reference impedance, wherein the excitation current and the reference current are used to generate an unbalanced current.

[0020] In this embodiment, the excitation signal source is applied to the measured impedance to generate an excitation current according to the set test frequency, phase, amplitude and other parameters. The reference signal source with the same frequency as the excitation signal source is applied to the reference impedance to obtain the reference current generated by the sinusoidal reference voltage in the reference impedance, and the difference between the excitation current and the reference current is used as the unbalanced current.

[0021] The measured impedance includes various basic components such as capacitors, resistors, inductors, and complex devices such as ferroelectric crystals, piezoelectric ceramics, piezoelectric crystals, and ultrasonic transducers. The reference impedance is a standard resistor. In this embodiment, four 0.1% and 10ppm / ℃ precision thin film resistors are selected, with resistance values ​​of 100 Ω, 1 kΩ, 10 kΩ, and 100 kΩ, respectively. According to the measured impedance range, the four reference resistance positions can be automatically switched.

[0022] S102, using a data acquisition control system to perform mixed sampling of the unbalanced current, the measured impedance voltage and the reference impedance voltage with a real variable sampling ratio and then perform digital conversion.

[0023] See also Figure 2 , the principle block diagram of the data acquisition control system provided by the embodiment of the present application, in this embodiment, considering the single-frequency narrowband characteristics of the excitation signal, the unbalanced current, the measured impedance voltage and the reference impedance voltage are sampled synchronously in real time by equivalent sampling at high frequencies. This method converts the periodic high-frequency signal into a periodic low-frequency signal with a waveform similar to the periodic high-frequency signal. Its sampling frequency With signal frequency The relationship is: ; in, is the number of signal period samples, is the number of sampling points.

[0024] When the excitation signal frequency is low, a fixed sampling ratio will inevitably cause the measurement time to be too long. Oversampling technology can better solve this problem. For oversampling, when the sample value is extracted to obtain the result output data, each increase in resolution or decrease in resolution will increase the resolution. The noise needs to be oversampled at 4 times the sampling frequency, that is, ; in, is the number of bits of resolution added, is the sampling frequency, is the oversampling frequency.

[0025] Combining the oversampling formula with the equivalent sampling formula, we get the sampling rate formula: ; when hour, , ; when hour, , ; in, To increase the number of bits of resolution, is the number of sampling times of the signal period. When the frequency of the measured signal changes, by modifying the formula and , select the closest sampling rate as the actual sampling rate. Figure 3 As shown in the figure, when the upper limit sampling rate is 2MSPS, compared with the traditional fixed sampling ratio method, the upper limit frequency is extended from 500 kHz to 2MHz or above, and the average measurement efficiency of medium and low frequencies below 125kHz is also improved by nearly 10 times.

[0026] After sampling is completed, the unbalanced current is input into the cross-group amplifier and feedback resistor for IV conversion to obtain the deviation voltage. The deviation voltage, measured impedance voltage and reference impedance voltage are respectively sent to the analog-to-digital converter through analog front end 1, analog front end 2 and analog front end 3 for digital conversion, and the feedback resistor is adjusted respectively. Adjust the gain of analog front end 1 to optimize the range of the deviation voltage, adjust the gain of analog front end 2 to optimize the range of the measured impedance voltage; adjust the reference resistance and the gain of the analog front end 3 make the range of the reference impedance voltage optimal. In this embodiment, the analog front end is mainly composed of an instrument amplifier, an industrial frequency notch filter and a differential amplifier. The instrument amplifier uses the AD8253 chip, which has digital programmable gains of 1, 10, 100 and 1000, 10 MHz high bandwidth, GΩ input impedance, low output noise and low distortion, and is very suitable for interfacing with sensors. The industrial frequency notch filter uses a double-T active band-stop filter circuit, which is characterized by a gain of 1 outside the stop band, independently adjustable Q value, and stable characteristics. By optimizing the circuit parameter design, the center frequency of the notch filter is 50Hz and the Q value is 5. At this time, it can meet the requirements of narrowband filtering (3dB bandwidth is about 10Hz) and obtain a sufficiently large attenuation (greater than 40dB) at the notch point, thereby effectively suppressing industrial frequency interference, increasing the dynamic range of the measured signal, and improving the measurement sensitivity. The differential amplifier uses the THS4521 chip, which has the advantages of low power consumption, high precision, high input impedance, low noise and rail-to-rail output capability.

[0027] The analog-to-digital converter (ADC) uses the LTC2324-16 chip, which has a differential analog input 4-channel, 16-bit, 2MSPS synchronous sampling capability, and supports a high-speed SPI-compatible serial interface for CMOS or LVDS. The main control unit is designed based on the FPGA+ARM architecture. The FPGA uses the EP4CE10F17C8 chip, which has a maximum operating frequency of 200MHz, built-in 10320 logic units, and 414Kbits of embedded storage resources, suitable for applications that require high throughput and low latency. The ARM uses the STM32F429 chip, which is based on the Cortex-M4 core and has a maximum main frequency of up to 180MHz. It has a single-precision floating-point arithmetic unit and rich peripheral resources, suitable for processing complex digital signal algorithms and real-time control tasks. The peripheral circuits mainly include SDRAM, EEPROM, MicroSD, and an LCD interface that supports RGB565 format. The FPGA is responsible for the acquisition control of the ADC to ensure high precision and high speed of data acquisition, and the ARM is responsible for data processing, logic control, and communication with the host computer. ARM and FPGA use FMC bus to communicate and use DMA technology for data transmission to achieve efficient data acquisition and processing.

[0028] The transimpedance amplifier uses the AD8065 chip, which has a high input impedance of 1 TΩ || 2.1 pF, a low noise of 7 nV / √Hz, a low bias current of 2 pA, and a wide gain bandwidth of 145 MHz. Four 0.1%, 10ppm / ℃ precision thin film resistors are selected as feedback resistors, with resistance values ​​of 100 Ω, 1 kΩ, 10 kΩ, and 100 kΩ. They are used in conjunction with a programmable analog quad multiplexer ADG1609 to achieve wide-range automatic detection of unbalanced current, ensuring that the system obtains the highest signal-to-noise ratio and measurement accuracy.

[0029] The sampling clock is implemented based on a direct digital synthesizer (DDS). The DDS uses the AD9912 chip, which has a 1GSPS sampling rate, supports a 48-bit frequency tuning word, and can step less than 4μHz. Absolute frequency accuracy can be achieved by adjusting the DAC system clock. By increasing the output slew rate of the DDS to the maximum and then dividing it by an integer, a sampling clock signal with a low frequency and low jitter is obtained. Specifically, according to the test frequency and sampling rate selection algorithm, the DDS is adjusted to obtain the sampling clock SCLK, which is sent to the FPGA for ADC sampling. The FPGA generates a signal synchronized with the SCLK, starts sampling on the rising edge, starts conversion and transmission on the falling edge, and reads the ADC data in real time through the SPI interface. The FPGA uses FIFO ping-pong operation to transmit data to the ARM, which ensures the real-time transmission and processing of data.

[0030] S103, using a digital orthogonal coherent detection algorithm to respectively obtain vector components of the deviation voltage, the measured impedance voltage, and the reference impedance voltage.

[0031] The traditional digital orthogonal coherent detection algorithm consumes a lot of time to perform digital mixing and digital filtering. Usually, each sampling has to be paused and restarted, resulting in discontinuous final output and introducing large overshoot and noise. In this regard, in this embodiment, the digitized measured signal is multiplied by the internal reference signal, and then the in-phase component I and the orthogonal component Q are generated through a digital low-pass filter to realize vector analysis of the measured signal. The data with a sampling ratio higher than 4 is extracted and processed to generate 4 new data. The in-phase reference sequence is , the orthogonal reference sequence is In addition, to ensure the execution efficiency of the microprocessor, the total length is The sampling data is divided into batches are processed, and the length of data processed in each batch is ,Right now The cumulative sum of the in-phase and quadrature components of each batch is: ; in, The sum of the in-phase components of each batch is summed, Cumulative sum of orthogonal components for each batch, The length of data processed for each batch, , , To increase the number of bits of resolution, when When the sampling mode is equivalent sampling, When the sampling mode is oversampling, , is the sampling frequency, is the signal frequency, The accumulation formula is recursively extended until the length of the sampled data reaches the total length to obtain the in-phase component and the orthogonal component. ; go through batches, that is, the sampling length is When ; in, , are the in-phase component and the orthogonal component in the vector components respectively, The sum of the in-phase components of each batch is summed, Cumulative sum of orthogonal components for each batch, is the total number of batches, , is the total length of the data, The length of data processed for each batch, , , is the number of bits of resolution increased. It can be seen that the optimization algorithm of this embodiment only needs to perform a series of moving and negating operations, saving a lot of time. The processing can be performed during the sampling interval of each batch of data without pausing the sampling, thus solving the problem of unstable results caused by discontinuous output.

[0032] S104, adjusting the balance state of the bridge circuit according to the vector component of the deviation voltage.

[0033] See also Figure 4, a flow chart of a hybrid optimization algorithm for bridge balance control provided in an embodiment of the present application. In this embodiment, the bridge balance control adopts a hybrid optimization algorithm that combines the extrapolation method and the secant method. The extrapolation-secant method uses the extrapolation method to locate the boundary, providing a better initial solution for the secant method responsible for the iterative operation, improving the algorithm stability. Its model coefficients can change with changes in measurement conditions, so it has wide adaptability. In this embodiment, the parameter data is initialized, and the output parameters of the excitation source and the reference source are made the same by setting the test frequency, phase, amplitude and other parameters, and the frequency of the sampling clock is set according to the sampling rate formula to start data acquisition. After obtaining the initial value of the iteration by extrapolation, two different balanced signals are input. and , and the corresponding unbalanced voltages are obtained and , then the reference voltage when the bridge is balanced is: ; When solving, you can keep and The phases of do not change, only their amplitudes change. and They are and , and are obtained through the digital orthogonal coherent detection algorithm. and ,but ; By demodulating and , respectively get the initial value and .

[0034] After adjusting the reference signal source, the deviation voltage is calculated, and the preset conditions are judged according to the deviation voltage. If the preset conditions are met, the actual impedance value is obtained according to the vector components of the measured impedance voltage and the reference impedance voltage. If the preset conditions are not met, the secant method is used for iteration to calculate the next input quantity. The formula for iterating the next input quantity using the secant method is: in, , and Respectively sequence Second and The input balanced signal, and Respectively Second and The reference signal source is re-adjusted and the deviation voltage is recalculated and determined according to the next step input quantity until the preset conditions are met.

[0035] In this embodiment, the extrapolation method can be used to obtain a relatively accurate initial estimate, and the bridge function is approximately linear and belongs to local convergence, so the convergence time and the convergence order of the algorithm are And the final error About. The error is ,in is the error factor. Assume the initial error is , the error factor is , the convergence order of the secant method is , iteration end condition The bridge balance convergence process is as follows: Figure 5 After three iterations, the error is close to , satisfying the iteration end condition. Therefore, the bridge balance controller only needs 3 sampling cycles to achieve bridge balance.

[0036] S105, after adjusting the balance, the vector components of the measured impedance voltage and the reference impedance voltage are transmitted to an impedance calculation unit to obtain multiple impedance parameters.

[0037] In this embodiment, after multiple adjustments, tends to zero, the bridge reaches equilibrium, and the vector component and is passed to the impedance calculation program to obtain various impedance parameters, such as inductance (L), resistance (R), capacitance (C), phase angle (θ) and impedance modulus ( ), etc., and displayed on a graphical interface through a human-machine interface, or further advanced operations such as impedance analysis and data visualization can be performed. In this embodiment, the initial estimation of the bridge balance control requires 2 sampling cycles, and the iteration requires 3 sampling cycles. The impedance measurement and bridge balance control are performed synchronously. Therefore, it usually takes 5 sampling cycles to complete one impedance measurement. Impedance measurement is generally divided into long-term measurement, medium-term measurement, and short-term measurement, and the corresponding sampling points are 16384, 4096, and 1024, respectively. The test results are shown in Figure 1. Figure 6 It can be seen that in the three measurement modes of long time, medium time and short time, in the wide frequency range of 10Hz to 2MHz, the average time of system impedance measurement is approximately 95.3ms, 23.8ms and 5.9ms respectively.

[0038] In addition, see Figure 7In this embodiment, the digital impedance measurement system can be connected to the host computer via USB, Ethernet or other connection methods. The impedance data can be viewed, exported and analyzed through the user interface of the application software. The application software has impedance analysis functions, such as frequency response curve drawing, impedance spectrum display and impedance parameter calculation. The application software also has a data visualization function, which can display the analysis results in the form of icons or graphics, so that users can understand the impedance characteristics of the circuit.

[0039] Corresponding to the digital impedance measurement method provided in the above embodiment, the present application also provides an embodiment of a digital impedance measurement system.

[0040] A digital impedance measurement system in this embodiment includes: an acquisition module, which is used to respectively acquire an excitation current and a reference current after a signal source is applied to a measured impedance and a reference impedance, wherein the excitation current and the reference current are used to generate an unbalanced current.

[0041] The digital conversion module is used to perform digital conversion after real variable sampling ratio mixed sampling on the unbalanced current, the measured impedance voltage and the reference impedance voltage according to the data acquisition control system.

[0042] The vector component acquisition module is used for respectively acquiring the vector components of the deviation voltage, the measured impedance voltage and the reference impedance voltage by a digital orthogonal coherent detection algorithm.

[0043] The regulating module is used to regulate the balance state of the bridge circuit according to the vector component of the deviation voltage.

[0044] The parameter acquisition module transfers the vector components of the measured impedance voltage and the reference impedance voltage to the impedance calculation unit after adjusting the balance, and obtains multiple parameters of the impedance.

[0045] In the embodiments of the present application, "at least one" means one or more, and "more" means two or more. "And / or" describes the association relationship of the associated objects, indicating that three relationships may exist. For example, A and / or B can mean that A exists alone, A and B exist at the same time, and B exists alone. A and B can be singular or plural. The character " / " generally indicates that the associated objects before and after are in an "or" relationship.

[0046] It should be noted that, in this article, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0047] The above is only a specific implementation of the present application. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed in the present application, which should be included in the protection scope of the present application. The protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A digital impedance measurement method, characterized in that: include: Respectively obtaining an excitation current and a reference current after a signal source is applied to the measured impedance and the reference impedance, wherein the excitation current and the reference current are used to generate an unbalanced current; The unbalanced current, the measured impedance voltage and the reference impedance voltage are respectively sampled with a real variable sampling ratio and mixed and then digitally converted by using a data acquisition control system; The digital orthogonal coherent detection algorithm is used to respectively obtain the vector components of the deviation voltage, the measured impedance voltage and the reference impedance voltage; The balance state of the bridge circuit is adjusted according to the vector component of the deviation voltage; After adjusting the balance, the vector components of the measured impedance voltage and the reference impedance voltage are transmitted to the impedance calculation unit to obtain multiple parameters of the impedance.

2. The digital impedance measurement method according to claim 1, characterized in that: The step of respectively obtaining the excitation current and the reference current after the measured impedance and the reference impedance are applied with the signal source, wherein the excitation current and the reference current are used to generate the unbalanced current, comprises: Applying an excitation signal source to the impedance under test to generate a sinusoidal test voltage, and obtaining an excitation current generated by the sinusoidal test voltage in the impedance under test; Applying a reference signal source to a reference impedance to generate a sinusoidal reference voltage, and obtaining a reference current generated by the sinusoidal reference voltage in the reference impedance; The difference between the excitation current and the reference current is used as an unbalanced current.

3. The digital impedance measurement method according to claim 1, characterized in that: The method of using a data acquisition control system to perform mixed sampling with a variable sampling ratio on the unbalanced current, the measured impedance voltage and the reference impedance voltage and then performing digital conversion comprises: When the signal frequency is high, the unbalanced current, the measured impedance voltage and the reference impedance voltage are sampled synchronously in real time by equivalent sampling; When the signal frequency is lower than a preset value, the unbalanced current, the measured impedance voltage and the reference impedance voltage are sampled synchronously in real time by oversampling; After sampling is completed, the unbalanced current is input into the cross-group amplifier and feedback resistor for IV conversion to obtain the deviation voltage; The deviation voltage, the measured impedance voltage and the reference impedance voltage are respectively sent to the analog-to-digital converter for digital conversion after passing through the corresponding analog front ends.

4. The digital impedance measurement method according to claim 3, characterized in that: The sampling rate formula for sampling by variable sampling ratio mixed sampling is: ； when hour, , ; when hour, , ; in, is the number of signal cycle samples, To increase the number of bits of resolution, is the sampling frequency, is the signal frequency.

5. The digital impedance measurement method according to claim 1, characterized in that: The method of using a digital orthogonal coherent detection algorithm to respectively obtain vector components of a deviation voltage, a measured impedance voltage, and a reference impedance voltage includes: Multiply the digitized deviation voltage, measured impedance voltage and reference impedance voltage by the internal reference signal respectively; The corresponding in-phase component and orthogonal component are generated respectively through a digital low-pass filter.

6. The digital impedance measurement method according to claim 5, characterized in that: The digital low-pass filter generates corresponding in-phase components and orthogonal components respectively, including: After extracting data with a sampling ratio higher than a preset value, an in-phase reference sequence and an orthogonal reference sequence are obtained; The total length of the sampled data is processed in multiple batches, and the in-phase and quadrature components of each batch are accumulated; the accumulation formula is: ； in, The sum of the in-phase components of each batch is summed, Cumulative sum of orthogonal components for each batch, The length of data processed for each batch, , , To increase the number of bits of resolution, when When , the sampling mode is equivalent sampling; when When the sampling mode is oversampling, , is the sampling frequency, is the signal frequency; The accumulation formula is recursively extended until the length of the sampled data reaches the total length to obtain the in-phase component and the orthogonal component.

7. The digital impedance measurement method according to claim 6, characterized in that: The calculation formulas for the in-phase component and the orthogonal component are: ； ； in, , are the in-phase component and the orthogonal component in the vector components respectively, The sum of the in-phase components of each batch is summed, Cumulative sum of orthogonal components for each batch, is the total number of batches, , is the total length of the data, The length of data processed for each batch, , , The number of bits of resolution increased.

8. The digital impedance measurement method according to claim 1, characterized in that: The step of adjusting the balance state of the bridge circuit according to the vector component of the deviation voltage includes: Initialize the parameter data; After obtaining the initial value of the iteration by extrapolation, the reference signal source is adjusted and the deviation voltage is calculated; judging a preset condition according to the deviation voltage; If the preset conditions are met, the actual impedance value is obtained according to the vector components of the measured impedance voltage and the reference impedance voltage; or; If the preset conditions are not met, the secant method is used to iterate and calculate the next input amount; The reference signal source is readjusted and the deviation voltage is recalculated and determined according to the next step input amount until the preset conditions are met.

9. The digital impedance measurement method according to claim 8, characterized in that: The method of obtaining the iterative initial value by extrapolation includes: Obtaining a first unbalanced voltage and a second unbalanced voltage respectively by inputting two different balanced signals; The reference voltage when the bridge is balanced is calculated according to the first unbalanced voltage and the second unbalanced voltage, and the calculation formula is: ;in, ; , and The first input balanced signal and the second input balanced signal The amplitude of is the signal frequency, is the initial phase; and are the first unbalanced voltage and the second unbalanced voltage respectively; and Expressed in vector form, we get ; ;but ; The initial value is obtained by adjusting the unbalanced voltage.

10. The digital impedance measurement method according to claim 8, characterized in that: The formula for calculating the next step input quantity by iterating using the secant method is: ； in, , and Respectively sequence Second and The input balanced signal, and Respectively Second and The unbalanced voltage.

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