A digital lock-in amplifier with a large dynamic range

Abstract

This application belongs to the field of lock-in amplifier technology, specifically disclosing a large dynamic range digital lock-in amplifier, comprising: a signal generator for generating sine and cosine reference signals; a DAC for performing digital-to-analog conversion on the generated reference signal and providing the converted analog quantity to the device under test (DUT); an ADC for performing analog-to-digital conversion on the signal output by the DUT and providing the converted digital amplitude to a gain controller and a digital demodulator; a gain controller for comparing the difference between the desired voltage amplitude and the digital amplitude provided by the ADC, and adjusting the amplitude of the reference signal according to a negative feedback method; and a digital demodulator for approximating the amplitude-frequency and phase-frequency characteristics of the DUT based on the reference signal and the digital amplitude provided by the ADC through a fitting method, and outputting an estimated vector. This application adjusts the amplitude of the reference signal according to a negative feedback method to avoid the signal link entering the nonlinear region, thus achieving a large dynamic range.

Description

Technical Field

[0001] This application belongs to the field of lock-in amplifier technology, and more specifically, relates to a digital lock-in amplifier with a large dynamic range. Background Technology

[0002] Lock-in amplifiers (LIPs) are widely used instruments for weak signal detection. They utilize phase-sensitive detection technology to modulate signals to a specific frequency and suppress noise signals at other frequencies, enabling them to extract weak signals from noisy environments. However, current LIPs are generally bulky and consume a lot of power, making them unsuitable for miniaturization in precision instruments.

[0003] Furthermore, with the development of semiconductor technology, digital lock-in amplifiers have gradually replaced traditional analog demodulation circuits. Digital lock-in amplifiers overcome the temperature drift and low-frequency non-ideal characteristics of analog components, and achieve phase-sensitive detection of signals through high-performance digital signal processing algorithms. However, existing digital lock-in amplifiers have limited dynamic range. How to achieve a digital lock-in amplifier with a large dynamic range is a pressing technical problem to be solved in this field. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the purpose of this application is to realize a digital lock-in amplifier with a large dynamic range.

[0005] To achieve the above objectives, in a first aspect, this application provides a digital lock-in amplifier with a large dynamic range, comprising: a signal generator, a gain controller, a digital demodulator, a digital-to-analog converter (DAC), and an analog-to-digital converter (ADC);

[0006] The signal generator generates a sine reference signal and a cosine reference signal. One of the two reference signals is provided to the digital-to-analog converter (DAC), and the other two reference signals are provided to the digital demodulator. The two reference signals have the same amplitude. They have the same frequency and remain orthogonal;

[0007] A digital-to-analog converter (DAC) is used to convert one reference signal generated by a signal generator into a digital signal and convert the resulting analog signal into a digital signal. Provided to the device under test;

[0008] Analog-to-digital converters (ADCs) are used to convert the signals output by the device under test (DUT) into digital signals. Perform analog-to-digital conversion and convert the resulting digital amplitude. Provides a gain controller and a digital demodulator;

[0009] The gain controller is used to compare the desired voltage amplitude with the digital amplitude provided by the analog-to-digital converter (ADC). The difference between them is used to adjust the amplitude of the reference signal using a negative feedback method. ;

[0010] The digital demodulator is used to measure the digital amplitude based on two reference signals and the analog-to-digital converter (ADC). The amplitude-frequency and phase-frequency characteristics of the device under test (DUT) are approximated by fitting, and the estimated vector of the DUT is output. Estimated vector Estimated values ​​for the amplitude-frequency and phase-frequency characteristics of the device under test.

[0011] In one possible implementation, the gain controller includes: a rectification module, a difference calculation module, a low-pass filter, and a negative feedback adjustment module;

[0012] The rectifier module is used to rectify the digital amplitude provided by the analog-to-digital converter (ADC). Take absolute value ;

[0013] The difference calculation module is used to calculate the absolute value. With the expected voltage amplitude The difference between them;

[0014] The low-pass filter is used to perform low-pass filtering on the signal output by the difference calculation module, and the output signal... ;

[0015] The negative feedback adjustment module is used to adjust the signal. Take the reciprocal and based on Update the amplitude of the reference signal .

[0016] In one possible implementation, the digital demodulator includes: an error estimation module, an adaptive rate determination module, and an estimation vector update module;

[0017] The error estimation module is used to determine the estimation error using the following formula:

[0018] ;

[0019] in, Indicates the estimation error. , Indicates the frequency of the reference signal. Indicates time;

[0020] Indicates a sinusoidal reference signal. Indicates the cosine reference signal;

[0021] The adaptive rate determination module is used to determine the estimation vector using the following formula. Corresponding adaptive adjustment rate:

[0022] ;

[0023] in, Indicates the adaptive adjustment rate. It is a constant;

[0024] Represents the loss function. , This indicates the calculation of the descent gradient of the loss function;

[0025] The estimation vector update module is used to update the estimated vector. Corresponding adaptive adjustment rate Update the estimated vector .

[0026] In one possible implementation, the signal generator includes: an orthogonal numerically controlled oscillator and a multiplier;

[0027] Quadrature numerically controlled oscillators are used to generate initial sinusoidal signals. and initial cosine signal , Indicates the frequency of the reference signal. Indicates time;

[0028] The multiplier is used to adjust the amplitude of the initial sine signal and the initial cosine signal to generate a sine reference signal. Sum and cosine reference signal .

[0029] One possible implementation also includes: a sampling module and a serial communication module;

[0030] The sampling module is used to estimate the vector output of the digital demodulator. The signal is downsampled and then provided to the serial communication module.

[0031] Secondly, this application provides a digital phase-locked amplification method with a large dynamic range, including:

[0032] Generate a sine reference signal and a cosine reference signal, with the two reference signals having the same amplitude. They have the same frequency and remain orthogonal;

[0033] Perform digital-to-analog conversion on one reference signal and convert the resulting analog signal... Provided to the device under test;

[0034] The signal output by the device under test Perform analog-to-digital conversion to obtain the digital amplitude. ;

[0035] Compare the expected voltage amplitude with the digital amplitude The difference between them is used to adjust the amplitude of the reference signal using a negative feedback method. ;

[0036] Based on two reference signals and digital amplitude The amplitude-frequency and phase-frequency characteristics of the device under test (DUT) are approximated by fitting, and the estimated vector of the DUT is output. Estimated vector Estimated values ​​for the amplitude-frequency and phase-frequency characteristics of the device under test.

[0037] In one possible implementation, the desired voltage amplitude is compared with the digital amplitude. The difference between them is used to adjust the amplitude of the reference signal using a negative feedback method. ,include:

[0038] For digital amplitude Take absolute value ;

[0039] Calculate absolute value With the expected voltage amplitude The difference between them;

[0040] The difference signal is low-pass filtered to output the signal. ;

[0041] For signal Take the reciprocal and based on Update the amplitude of the reference signal .

[0042] In one possible implementation, it is based on two reference signals and digital amplitude. The amplitude-frequency and phase-frequency characteristics of the device under test (DUT) are approximated by fitting, and the estimated vector of the DUT is output. ,include:

[0043] The estimation error is determined using the following formula:

[0044] ;

[0045] in, Indicates the estimation error. , Indicates the frequency of the reference signal. Indicates time;

[0046] Indicates a sinusoidal reference signal. Indicates the cosine reference signal;

[0047] The estimated vector is determined using the following formula. Corresponding adaptive adjustment rate:

[0048] ;

[0049] in, Indicates the adaptive adjustment rate. It is a constant;

[0050] Represents the loss function. , This indicates the calculation of the descent gradient of the loss function;

[0051] Based on the estimated vector Corresponding adaptive adjustment rate Update the estimated vector .

[0052] In one possible implementation, generating the sine reference signal and the cosine reference signal includes:

[0053] Generate initial sine signal and initial cosine signal , Indicates the frequency of the reference signal. Indicates time;

[0054] Adjust the amplitudes of the initial sine and cosine signals to generate a sinusoidal reference signal. Sum and cosine reference signal .

[0055] One possible implementation also includes:

[0056] For the estimated vector The signal is downsampled, and the downsampled signal is used for serial communication.

[0057] Overall, the technical solutions conceived in this application have the following beneficial effects compared with the prior art:

[0058] (1) By using a gain controller, the desired voltage amplitude can be compared with the digital amplitude provided by the analog-to-digital converter (ADC). The difference between them is used to adjust the amplitude of the reference signal using a negative feedback method. This is to prevent the signal link from entering nonlinear regions such as saturation or full-scale bias, and to control the amplitude of the excitation signal. With the sensitivity of the circuit There is a linear relationship between them, achieving sensitivity without introducing additional devices. Adjustment, by adjusting sensitivity This allows for adjustment of the dynamic range of the lock-in amplifier to achieve a large dynamic range.

[0059] (2) Estimation vector of digital demodulator It will approximate the true vector, that is The closed-loop demodulation function approximates the state vector. Unaffected by gain control, the amplitude of the digital lock-in amplifier's output signal maintains a constant linear relationship with the amplitude of the device under test's output signal even under large dynamic range switching (when the excitation amplitude changes), ensuring the stability of the detection. Attached Figure Description

[0060] Figure 1 This is a schematic diagram illustrating the working principle of the digital lock-in amplifier provided in the embodiments of this application;

[0061] Figure 2 This is an orthogonal digital data conversion diagram of the orthogonal numerically controlled oscillator provided in the embodiments of this application;

[0062] Figure 3 This is a schematic diagram of the automatic gain control loop provided in the embodiments of this application;

[0063] Figure 4 This is a schematic diagram illustrating the working principle of the digital demodulator provided in the embodiments of this application;

[0064] Figure 5 This is a schematic diagram of the step response of the digital demodulator provided in the embodiments of this application;

[0065] Figure 6 This is a schematic diagram of the frequency response of the digital demodulator provided in the embodiments of this application;

[0066] Figure 7 This is a schematic diagram illustrating the application of large dynamic range capacitance detection provided in the embodiments of this application. Detailed Implementation

[0067] To facilitate a clearer understanding of the various embodiments of this application, some relevant background knowledge will be introduced as follows.

[0068] The dynamic range of a lock-in amplifier can be defined as follows:

[0069] ;

[0070] in, and These represent the maximum and minimum amplitude values ​​that the lock-in amplifier can recognize, respectively. The amplitude values ​​that the system can recognize are as follows:

[0071] ;

[0072] in, This represents the amplitude component of the output voltage at the demodulation frequency. This represents the sensitivity of the circuit. The presence of thermal noise and the circuit's maximum operating range limit its sensitivity. The range of sensitivity is typically 140dB. Therefore, to overcome the limitations of circuit non-ideality, the sensitivity can be adjusted. This allows for adjustment of the dynamic range of the lock-in amplifier to achieve a large dynamic range.

[0073] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0074] In the embodiments of this application, the terms "exemplary" or "for example" are used to indicate that something is an example, illustration, or description. Any embodiment or design that is described as "exemplary" or "for example" in the embodiments of this application should not be construed as being more preferred or advantageous than other embodiments or design. Specifically, the use of the terms "exemplary" or "for example" is intended to present the relevant concepts in a specific manner.

[0075] In the description of the embodiments of this application, unless otherwise stated, "multiple" means two or more, for example, multiple processing units means two or more processing units, multiple elements means two or more elements, etc.

[0076] The embodiments of this application are described below with reference to the accompanying drawings.

[0077] Figure 1 This is a schematic diagram illustrating the working principle of the digital lock-in amplifier provided in the embodiments of this application, as shown below. Figure 1 As shown, the digital lock-in amplifier includes: a signal generator, a gain controller, a digital demodulator, a digital-to-analog converter (DAC), and an analog-to-digital converter (ADC).

[0078] The signal generator, gain controller, and digital demodulator can be implemented using a field-programmable gate array (FPGA) or other control unit. Demodulation algorithms based on digital signal processing replace phase-sensitive demodulators with analog components, improving system reliability.

[0079] The signal generator generates a sine reference signal and a cosine reference signal. One of the two reference signals (sine and cosine) is provided to the digital-to-analog converter (DAC), and the other two are provided to the digital demodulator. The two reference signals have the same amplitude. They have the same frequency and remain orthogonal (there is a 90-degree phase difference between the two reference signals).

[0080] A digital-to-analog converter (DAC) is used to convert one reference signal generated by a signal generator into a digital signal and convert the resulting analog signal into a digital signal. Provided to the device under test.

[0081] Analog-to-digital converters (ADCs) are used to convert the signals output by the device under test (DUT) into digital signals. Perform analog-to-digital conversion and convert the resulting digital amplitude. Provided to the gain controller and digital demodulator.

[0082] The gain controller (or gain control loop) is used to compare the desired voltage amplitude with the digital amplitude provided by the analog-to-digital converter (ADC). The difference between them is used to adjust the amplitude of the reference signal using a negative feedback method. .

[0083] The digital demodulator is used to measure the digital amplitude based on two reference signals and the analog-to-digital converter (ADC). The amplitude-frequency and phase-frequency characteristics of the device under test (DUT) are approximated by fitting, and the estimated vector of the DUT is output. Estimated vector Estimated values ​​for the amplitude-frequency and phase-frequency characteristics of the device under test.

[0084] It is understandable that a DAC can perform digital-to-analog conversion on a reference signal and convert the resulting analog signal into an analog signal. Provided to the device under test, the digital amplitude can be determined by a digital demodulator based on two reference signals and the digital amplitude provided by the analog-to-digital converter (ADC). The phase of the reference signal is locked (signal components with the same phase as the reference signal are effectively extracted, while noise components with different phases are suppressed). The amplitude-frequency and phase-frequency characteristics of the device under test are approximated by fitting, and the estimated vector of the device under test is output. To realize the signal output by the device under test Perform phase-sensitive detection and extract the signal. The phase and amplitude information is obtained, thus enabling the amplitude-frequency and phase-frequency characteristics of the device under test at a specified modulation frequency (the frequency of the reference signal) to be obtained in a noisy environment.

[0085] Simultaneously, the desired voltage amplitude can be compared with the digital amplitude provided by the analog-to-digital converter (ADC) through the gain controller. The difference between them is used to adjust the amplitude of the reference signal using a negative feedback method. This is to prevent the signal link from entering nonlinear regions such as saturation or full-scale bias, and to control the amplitude of the excitation signal. With the sensitivity of the circuit There is a linear relationship between them, achieving sensitivity without introducing additional devices. Adjustment, by adjusting sensitivity This allows for adjustment of the dynamic range of the lock-in amplifier to achieve a large dynamic range.

[0086] It is also worth noting that traditional dynamic range adjustment methods often rely on front-end programmable amplifiers or variable gain amplifiers, and the introduction of additional devices increases the complexity and power consumption of the system.

[0087] Therefore, the amplitude of the reference signal is adjusted by the gain controller using a negative feedback method. Furthermore, by using a digital demodulator to approximate the amplitude-frequency and phase-frequency characteristics of the device under test in a fitting manner, a digital lock-in amplifier with a large dynamic range can be realized while taking into account noise and dynamic range.

[0088] In one possible implementation, the gain controller includes: a rectification module, a difference calculation module, a low-pass filter, and a negative feedback adjustment module;

[0089] The rectifier module is used to rectify the digital amplitude provided by the analog-to-digital converter (ADC). Take absolute value ;

[0090] The difference calculation module is used to calculate the absolute value. With the expected voltage amplitude The difference between them;

[0091] The low-pass filter is used to perform low-pass filtering on the signal output by the difference calculation module, and the output signal... ;

[0092] The negative feedback adjustment module is used to adjust the signal. Take the reciprocal and based on Update the amplitude of the reference signal .

[0093] In one possible implementation, the digital demodulator includes: an error estimation module, an adaptive rate determination module, and an estimation vector update module;

[0094] The error estimation module is used to determine the estimation error using the following formula:

[0095] ;

[0096] in, Indicates the estimation error. , Indicates the frequency of the reference signal. Indicates time;

[0097] Indicates a sinusoidal reference signal. Indicates the cosine reference signal;

[0098] The adaptive rate determination module is used to determine the estimation vector using the following formula. Corresponding adaptive adjustment rate:

[0099] ;

[0100] in, Indicates the adaptive rate, It is a constant (usually a positive number, used to control the speed of convergence). Represents the loss function. , This indicates the calculation of the descent gradient of the loss function;

[0101] The estimation vector update module is used to update the estimated vector. Corresponding adaptive adjustment rate Update the estimated vector .

[0102] For example, the estimated vector can be updated using the following formula. : .

[0103] Understandably, in the estimation error Close to 0 ( Under these conditions, the digital demodulator enters a stable state. , Since the automatic gain control factor G is not zero, and The modulus is always 1, indicating that the estimated vector of the digital demodulator is... It will approximate the true vector, that is The closed-loop demodulation function approximates the state vector. (Device under test at modulation frequency) Amplitude-phase frequency characteristics After decomposition in the complex plane, the state vector is used. Describe it. Indicates in-phase components, The quadrature components are not affected by gain control. Therefore, under the condition of large dynamic range switching (when the excitation amplitude changes), the amplitude of the output signal of the digital lock-in amplifier and the amplitude of the output signal of the device under test maintain a constant linear relationship, ensuring the stability of the detection.

[0104] In one possible implementation, the signal generator includes: an orthogonal numerically controlled oscillator and a multiplier;

[0105] Quadrature numerically controlled oscillators are used to generate initial sinusoidal signals. and initial cosine signal , Indicates the frequency of the reference signal. Indicates time;

[0106] The multiplier is used to adjust the amplitudes of the initial sine and cosine signals to generate a sinusoidal reference signal. Sum and cosine reference signal .

[0107] One possible implementation also includes: a sampling module and a serial communication module;

[0108] The sampling module is used to estimate the vector output of the digital demodulator. The signal is downsampled (to adapt to the serial communication rate) and the downsampled signal is provided to the serial communication module.

[0109] The following examples illustrate the large dynamic range digital lock-in amplifier provided in the application.

[0110] Figure 2 This is an orthogonal digital data conversion diagram of the orthogonal numerically controlled oscillator provided in the embodiments of this application, such as... Figure 2 As shown, the quadrature numerically controlled oscillator can employ Direct Digital Synthesis (DDS). DDS is a technique for generating waveform signals and is widely used in signal processing, communication, and electronic equipment.

[0111] Orthogonal Digital Data Conversion: In DDS, orthogonal digital data conversion mainly refers to the process of generating sine and cosine waves. Since there is a 90-degree phase difference between sine and cosine waves, orthogonal signal generation can be achieved through the following steps: phase generation, waveform lookup, and signal output. Phase Generation: The phase accumulator generates a linearly increasing phase value (e.g., ...) at a fixed frequency (which can be specified via the frequency control word M). Figure 2 The quantization phase (N) represents the phase at the current time point, usually represented by a binary number. Waveform lookup: Using the phase value as an index, the corresponding sine and cosine amplitude values ​​are retrieved from the waveform lookup table. Output signal: The retrieved sine and cosine amplitude values ​​are fed into the DAC to generate an analog signal.

[0112] Figure 3 This is a schematic diagram of the automatic gain control loop provided in the embodiments of this application, as shown below. Figure 3 As shown, a gain control loop is introduced, based on the output voltage of the device under test. Real-time adjustment of excitation signal amplitude and gain Its main operations include the following parts:

[0113] (1) Take the absolute value (Abs) of the ADC acquisition data to complete the signal processing. Rectification;

[0114] (2) and the set desired voltage amplitude The difference is calculated to obtain the power estimation error;

[0115] (3) Use the error signal as the input to the low-pass filter and output... As a signal, a low-pass filter is essentially an integrator, and its output... It is a positive number;

[0116] (4) To ensure negative feedback regulation, the amplitude gain should be equal to... Inversely correlated, for example ,because Since it is a positive number, A positive number ensures the existence of the excitation signal to meet the requirements of the phase-locked loop.

[0117] Figure 4 This is a schematic diagram illustrating the working principle of the digital demodulator provided in the embodiments of this application. Figure 5 This is a schematic diagram of the step response of the digital demodulator provided in the embodiments of this application. Figure 6 This is a schematic diagram of the frequency response of the digital demodulator provided in this application embodiment. The purpose of the digital demodulator is to complete the frequency response of the input signal. The amplitude and phase are identified to obtain the amplitude and phase of the device under test at the modulation frequency. The amplitude-frequency and phase-frequency characteristics are as follows, and their amplitude-frequency and phase-frequency characteristics are as follows. After decomposition in the complex plane, the state vector is used. Describe it. Indicates in-phase components, Let the orthogonal components be represented, then the following transformation equation holds:

[0118] ;

[0119] ;

[0120] Where a is the state vector Amplitude representation in polar coordinates express amplitude, express The phase.

[0121] To address this, a corresponding estimation vector is introduced. The estimation error is as follows:

[0122] ;

[0123] The signal acquired by the ADC in the complex plane can be written as follows: .

[0124] The loss function is defined as follows: .

[0125] The steepest gradient method can be used to find the descent gradient of the loss function, and then the adaptive regulation rate of the system's state vector can be obtained as follows:

[0126] ;

[0127] The calculation yields the following expression:

[0128] ;

[0129] ;

[0130] The definition expression of the loss function By substituting the values, we can calculate the state-space representation of the system:

[0131] ;

[0132] Will Substitute the expression and apply it to... Integrating over the period yields the discrete transfer function representation of the system:

[0133] ;

[0134] make Its equivalent transfer function can be calculated as follows:

[0135] .

[0136] Its principle is as follows Figure 4 As shown, note that the stability of the demodulator is based on In the case where the system enters a stable state, the following applies:

[0137] ;

[0138] Due to automatic gain control factor It will not be zero, and The modulus is always 1, therefore the demodulator's predicted vector will approximate the true vector, i.e. The closed-loop demodulation function approximates the state vector. Unaffected by gain control, the amplitude of the digital lock-in amplifier's output signal maintains a constant linear relationship with the amplitude of the device under test's output signal even under large dynamic range switching (when the excitation amplitude changes), ensuring the stability of the detection.

[0139] Figure 7 This is a schematic diagram illustrating the application of large dynamic range capacitance detection provided in the embodiments of this application, such as... Figure 7 As shown, to verify the feasibility of the proposed method, a large dynamic range capacitance detection was implemented using the proposed lock-in amplifier. By dynamically adjusting the DDS digital signal synthesis output and changing the amplitude of the reference signal, a digital demodulator based on the least squares method was designed at the demodulation end to realize variable-range capacitance measurement. The basic components include: a DAC module, a bandpass filter, an AC charge amplifier, a high-speed ADC module, and control and operation units (signal generator, digital demodulator, gain controller), etc. The implementation process includes the following parts.

[0140] (1) Connect the capacitor to be tested to the front part of the AC charge amplifier and connect it with the DAC module, the DAC module, the bandpass filter and other modules to form a lock-in amplifier circuit.

[0141] (2) The control and arithmetic unit internally generates two mutually orthogonal, same-frequency, and equal-amplitude sinusoidal signals based on the digital synthesis module. Its frequency is the same as the bandpass center frequency, and its amplitude depends on the carrier range control factor. One of the signals, S1, is used as the input to the DAC, and a bandpass filter is configured to generate a sinusoidal excitation carrier.

[0142] (3) Read the voltage signal obtained by ADC sampling Internally, it is fitted using the least squares method, through sampling signals. Generates a sinusoidal signal with DDS The capacitance signal is obtained after calculation. .

[0143] (4) To avoid range limitation due to circuit saturation, an adaptive range control loop is introduced internally to detect the voltage value sampled by the ADC. The absolute value is taken and passed through an internal filter to generate the carrier range control factor. , Determines the signal generated by the DDS The magnitude of the amplitude.

[0144] (5) In digital demodulation, a digital phase-sensitive demodulator based on the least squares method is selected, and the approximation error is defined as:

[0145] ;

[0146] After convergence and fitting, the sensitivity from capacitor to digital output is:

[0147] ;

[0148] The amplitude of the output signal of the digital lock-in amplifier remains constant, maintaining a constant linear relationship with the amplitude of the output signal of the device under test, unaffected by changes in the carrier amplitude.

[0149] The large dynamic range digital lock-in amplifier method provided in this application is described below. The large dynamic range digital lock-in amplifier method described below can be referred to in correspondence with the large dynamic range digital lock-in amplifier described above.

[0150] This application provides a digital phase-locked amplification method with a large dynamic range, including:

[0151] Generate a sine reference signal and a cosine reference signal, with the two reference signals having the same amplitude. They have the same frequency and remain orthogonal;

[0152] Perform digital-to-analog conversion on one reference signal and convert the resulting analog signal... Provided to the device under test;

[0153] The signal output by the device under test Perform analog-to-digital conversion to obtain the digital amplitude. ;

[0154] Compare the expected voltage amplitude with the digital amplitude The difference between them is used to adjust the amplitude of the reference signal using a negative feedback method. ;

[0155] Based on two reference signals and digital amplitude The amplitude-frequency and phase-frequency characteristics of the device under test (DUT) are approximated by fitting, and the estimated vector of the DUT is output. Estimated vector Estimated values ​​for the amplitude-frequency and phase-frequency characteristics of the device under test.

[0156] In one possible implementation, the desired voltage amplitude is compared with the digital amplitude. The difference between them is used to adjust the amplitude of the reference signal using a negative feedback method. ,include:

[0157] For digital amplitude Take absolute value ;

[0158] Calculate absolute value With the expected voltage amplitude The difference between them;

[0159] The difference signal is low-pass filtered to output the signal. ;

[0160] For signal Take the reciprocal and based on Update the amplitude of the reference signal .

[0161] In one possible implementation, it is based on two reference signals and digital amplitude. The amplitude-frequency and phase-frequency characteristics of the device under test (DUT) are approximated by fitting, and the estimated vector of the DUT is output. ,include:

[0162] The estimation error is determined using the following formula:

[0163] ;

[0164] in, Indicates the estimation error. , Indicates the frequency of the reference signal. Indicates time;

[0165] Indicates a sinusoidal reference signal. Indicates the cosine reference signal;

[0166] The estimated vector is determined using the following formula. Corresponding adaptive adjustment rate:

[0167] ;

[0168] in, Indicates the adaptive adjustment rate. It is a constant;

[0169] Represents the loss function. , This indicates the calculation of the descent gradient of the loss function;

[0170] Based on the estimated vector Corresponding adaptive adjustment rate Update the estimated vector .

[0171] In one possible implementation, generating the sine reference signal and the cosine reference signal includes:

[0172] Generate initial sine signal and initial cosine signal , Indicates the frequency of the reference signal. Indicates time;

[0173] Adjust the amplitudes of the initial sine and cosine signals to generate a sinusoidal reference signal. Sum and cosine reference signal .

[0174] One possible implementation also includes:

[0175] For the estimated vector The signal is downsampled, and the downsampled signal is used for serial communication.

[0176] It is understood that the various numerical designations used in the embodiments of this application are merely for the convenience of description and are not intended to limit the scope of the embodiments of this application.

[0177] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A digital lock-in amplifier with a large dynamic range, characterized in that, include: Signal generator, gain controller, digital demodulator, digital-to-analog converter (DAC), and analog-to-digital converter (ADC); The signal generator generates a sine reference signal and a cosine reference signal. One of the two reference signals is provided to the digital-to-analog converter (DAC), and the other two reference signals are provided to the digital demodulator. The two reference signals have the same amplitude. They have the same frequency and remain orthogonal; A digital-to-analog converter (DAC) is used to convert one reference signal generated by a signal generator into a digital signal and convert the resulting analog signal into a digital signal. Provided to the device under test; Analog-to-digital converters (ADCs) are used to convert the signals output by the device under test (DUT) into digital signals. Perform analog-to-digital conversion and convert the resulting digital amplitude. Provides a gain controller and a digital demodulator; The gain controller is used to compare the desired voltage amplitude with the digital amplitude provided by the analog-to-digital converter (ADC). The difference between them is used to adjust the amplitude of the reference signal using a negative feedback method. ; The digital demodulator is used to measure the digital amplitude based on two reference signals and the analog-to-digital converter (ADC). The amplitude-frequency and phase-frequency characteristics of the device under test (DUT) are approximated by fitting, and the estimated vector of the DUT is output. Estimated vector Estimated values ​​used to characterize the amplitude-frequency and phase-frequency characteristics of the device under test; The digital demodulator includes: an error estimation module, an adaptive rate determination module, and an estimation vector update module; The error estimation module is used to determine the estimation error using the following formula: ； in, Indicates the estimation error. , Indicates the frequency of the reference signal. Indicates time; Indicates a sinusoidal reference signal. Indicates the cosine reference signal; The adaptive rate determination module is used to determine the estimation vector using the following formula. Corresponding adaptive adjustment rate: ； in, Indicates the adaptive adjustment rate. It is a constant; Represents the loss function. , This indicates the calculation of the descent gradient of the loss function; The estimation vector update module is used to update the estimated vector. Corresponding adaptive adjustment rate Update the estimated vector .

2. The large dynamic range digital lock-in amplifier according to claim 1, characterized in that, The gain controller includes: a rectification module, a difference calculation module, a low-pass filter, and a negative feedback adjustment module; The rectifier module is used to rectify the digital amplitude provided by the analog-to-digital converter (ADC). Take absolute value ; The difference calculation module is used to calculate the absolute value. With the expected voltage amplitude The difference between them; The low-pass filter is used to perform low-pass filtering on the signal output by the difference calculation module, and the output signal... ; The negative feedback adjustment module is used to adjust the signal. Take the reciprocal and based on Update the amplitude of the reference signal .

3. The large dynamic range digital lock-in amplifier according to claim 1, characterized in that, The signal generator includes: an orthogonal numerically controlled oscillator and a multiplier; Quadrature numerically controlled oscillators are used to generate initial sinusoidal signals. and initial cosine signal , Indicates the frequency of the reference signal. Indicates time; The multiplier is used to adjust the amplitude of the initial sine signal and the initial cosine signal to generate a sine reference signal. Sum and cosine reference signal .

4. The large dynamic range digital lock-in amplifier according to any one of claims 1-3, characterized in that, Also includes: Sampling module and serial communication module; The sampling module is used to estimate the vector output of the digital demodulator. The signal is downsampled and then provided to the serial communication module.

5. A digital phase-locked amplification method with a large dynamic range, characterized in that, include: Generate a sine reference signal and a cosine reference signal, with the two reference signals having the same amplitude. They have the same frequency and remain orthogonal; Perform digital-to-analog conversion on one reference signal and convert the resulting analog signal... Provided to the device under test; The signal output by the device under test Perform analog-to-digital conversion to obtain the digital amplitude. ; Compare the expected voltage amplitude with the digital amplitude The difference between them is used to adjust the amplitude of the reference signal using a negative feedback method. ; Based on two reference signals and digital amplitude The amplitude-frequency and phase-frequency characteristics of the device under test (DUT) are approximated by fitting, and the estimated vector of the DUT is output. Estimated vector Estimated values ​​used to characterize the amplitude-frequency and phase-frequency characteristics of the device under test; The basis is two reference signals and digital amplitude. The amplitude-frequency and phase-frequency characteristics of the device under test (DUT) are approximated by fitting, and the estimated vector of the DUT is output. ,include: The estimation error is determined using the following formula: ； in, Indicates the estimation error. , Indicates the frequency of the reference signal. Indicates time; Indicates a sinusoidal reference signal. Indicates the cosine reference signal; The estimated vector is determined using the following formula. Corresponding adaptive adjustment rate: ； in, Indicates the adaptive adjustment rate. It is a constant; Represents the loss function. , This indicates the calculation of the descent gradient of the loss function; Based on the estimated vector Corresponding adaptive adjustment rate Update the estimated vector .

6. The large dynamic range digital phase-locked amplification method according to claim 5, characterized in that, The comparison of the expected voltage amplitude with the digital amplitude The difference between them is used to adjust the amplitude of the reference signal using a negative feedback method. ,include: For digital amplitude Take absolute value ; Calculate absolute value With the expected voltage amplitude The difference between them; The difference signal is low-pass filtered to output the signal. ; For signal Take the reciprocal and based on Update the amplitude of the reference signal .

7. The large dynamic range digital phase-locked amplification method according to claim 5, characterized in that, The generation of the sine reference signal and the cosine reference signal includes: Generate initial sine signal and initial cosine signal , Indicates the frequency of the reference signal. Indicates time; Adjust the amplitudes of the initial sine and cosine signals to generate a sinusoidal reference signal. Sum and cosine reference signal .

8. The large dynamic range digital phase-locked amplification method according to any one of claims 5-7, characterized in that, Also includes: For the estimated vector The signal is downsampled, and the downsampled signal is used for serial communication.

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