A method for generating harmonic voltage of a pulse-driven type AC sub-voltage standard

Abstract

The application belongs to the technical field of electrical measurement, and particularly relates to a harmonic voltage debugging method of an alternating current sub-voltage standard based on a pulse-driven Josephson chip. The application provides a harmonic voltage debugging method of an alternating current sub-voltage standard based on a pulse-driven Josephson chip. By introducing a second-order Delta-Sigma modulation algorithm, a bias compensation signal source and a high-precision synchronous trigger mechanism, accurate synthesis and spectrum measurement of the output waveform of the alternating current sub-voltage are realized, the problems of waveform distortion, phase error and insufficient measurement accuracy in the prior art are overcome, and the application reliability of the alternating current sub-voltage standard in precise electrical measurement is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electrical metrology and the category of quantum precision measurement, and particularly relates to a harmonic voltage generation method of an AC voltage quantum standard based on a pulse-driven Josephson chip. BACKGROUND

[0002] The AC voltage quantum standard is a high-precision voltage reference technology based on the Josephson effect. By controlling the pulse driving of the superconducting Josephson junction array, a stable AC voltage signal can be accurately generated and applied to high-precision voltage measurement and calibration. In practical applications, the AC voltage quantum standard is not only used to generate a sinusoidal AC signal, but can also be extended to the output of complex waveforms, such as multi-frequency harmonics or custom waveforms, which is of great significance to the fields of power quality analysis, instrument calibration, and power system testing. However, traditional methods rely heavily on analog signal sources or software synthesis, which have problems such as insufficient amplitude accuracy, complex phase control, and system error accumulation, making it difficult to meet the requirements of high-precision quantum voltage standards. In the actual debugging and measurement process of the pulse-driven AC voltage quantum standard, key technical problems such as harmonic signal generation, amplitude control, phase matching, spectral purity, and measurement stability still need to be solved. Therefore, the present application proposes a harmonic voltage generation method of a pulse-driven AC voltage quantum standard, which is of great significance for realizing high-precision, multi-frequency voltage standardization output. SUMMARY

[0003] The purpose of the present application is to provide a harmonic voltage generation method of a pulse-driven AC voltage quantum standard, which introduces a second-order Delta-Sigma modulation algorithm, a bias compensation signal source, and a high-precision synchronous trigger mechanism to realize accurate synthesis and spectral measurement of the AC voltage quantum output waveform, overcoming the problems of waveform distortion, phase error, and insufficient measurement accuracy in the prior art, thereby improving the application reliability of the AC voltage quantum standard in precision electrical metrology.

[0004] The technical scheme of the harmonic voltage generation method of the pulse-driven AC voltage quantum standard of the present application is as follows:

[0005] Step one: code modulation and generation. According to the mathematical function of the target harmonic signal , the continuous-time harmonic signal is discretized using the Delta-Sigma modulation method to obtain the corresponding ternary code type, and the code type is transmitted to the code generator;

[0006] Step two: reference signal generation and storage. Based on the same mathematical function of the harmonic signal In the external signal source, a periodic waveform for compensation is generated, and the waveform is saved in the waveform generator through the self-defined output mode of the signal source as a bias compensation current source.

[0007] Step three: synchronous trigger and signal output. The same external trigger signal is used to trigger the code generator and the waveform generator. The trigger mode of the code generator is set to external trigger, the trigger mode of the waveform generator is set to external trigger and the burst mode is turned on, and the signal cycle mode is set to infinite cycle, so as to ensure that the two signals are output at the same time.

[0008] Step four: phase calibration and data acquisition. In the burst mode, the phase of the waveform generator is adjusted to make the phase difference of the two signals as close to zero as possible, so as to make the pulse-driven Josephson chip output the alternating current voltage; after the output signal is collected by the signal collection card, the amplitude and spectrum of the fundamental wave and each harmonic are obtained by using fast Fourier transform and spectrum analysis.

[0009] Further, the step one specifically includes: Delta-Sigma modulation is a modulation method based on oversampling and noise shaping. By mapping the analog signal to a high-speed ternary sequence, the quantization noise can be effectively shifted to the high-frequency region, so as to realize high-precision waveform reconstruction in the required low-frequency range.

[0010] The target function harmonic signal Mathematical modeling, the signal form is

[0011]

[0012] wherein, is the harmonic signal in continuous time, which represents the signal value at time , n is the harmonic index, from 1 to N, which represents the nth harmonic, and N is the total number of harmonics, that is, the number of harmonics contained in the signal, is the amplitude of the nth harmonic (amplitude), is the phase of the nth harmonic, is the fundamental frequency, that is, the basic frequency of the signal, and t represents continuous time.

[0013] Discretization processing is performed on the signal, and the sampling frequency is set to , and the discrete signal is obtained:

[0014]

[0015] wherein, represents the discrete time signal, that is, the continuous signal after sampling, the kth sampling value is obtained, k is a non-negative integer, which represents the sampling time point, The sampling frequency, i.e., the number of samples per second. This is equivalent to a discretized form of the continuous-time signal t. Inputting the discrete signal into a second-order Delta-Sigma modulator yields a ternary pulse output sequence. The core process is as follows:

[0016]

[0017] in, Indicates the current input signal Compared with the previous output The difference between them is used for feedback control. The state value of the first integrator represents the previous state. Difference from the current value The cumulative sum, The state value of the second integrator represents the previous state. With the output of the first integrator The cumulative sum, The output of the quantizer is a three-valued pulse sequence with values ​​{-1, 0, 1}. This is the quantization function used for the output of the second integrator. Quantization is performed. Typically, a quantizer maps continuous values ​​to discrete values ​​based on a comparator or threshold rule. A second-order Delta-Sigma modulator (DSM) uses a double-integration stage to shape noise, ensuring high fidelity of the signal within the low-frequency bandwidth.

[0018] Assuming the quantizer can be modeled as the input signal plus quantization noise In the Z-domain, the output of the second-order Delta-Sigma modulator is

[0019]

[0020] Where STF is the signal transfer function and NTF is the noise transfer function.

[0021] For a second-order Delta-Sigma modulator, we have:

[0022]

[0023] This means that the input signal can be transmitted to the output without distortion, while quantization noise is significantly suppressed within the low-frequency bandwidth and shifted to higher frequencies after second-order differential filtering. Input target harmonic function After passing through a second-order Delta-Sigma modulator, it is converted into a ternary pulse output sequence. The average of the output sequence is approximately equivalent to the original signal.

[0024]

[0025] Further, step two specifically comprises: using a Keysight 33500 series waveform generator as a compensation signal source, writing the generated harmonic signal periodic data into its storage module in the form of a self-defined waveform, so as to make it a bias compensation current source, compensate for the fundamental amplitude attenuation and nonlinear distortion caused by low-frequency distortion, and thus improve the fidelity of the final output quantum voltage waveform.

[0026] Further, step three specifically comprises: the external trigger signal can be provided by an experimental control platform or a synchronous clock module, and the trigger precision is better than 1 ns, so as to ensure that the code generator and the waveform generator are strictly aligned on the time axis; the Burst mode is used to limit the number of output signals and avoid waveform drift, and the signal loop mode is selected to be infinite loop, so as to ensure that the two signals maintain stable output in the whole measurement process.

[0027] Further, step four specifically comprises: the phase adjustment is realized by modifying the Burst start phase of the waveform generator, so that the compensation signal and the code driving signal are strictly in phase in the time domain, thereby eliminating the phase difference caused by clock jitter or line delay; the output signal collected is obtained through an NI PXI-5922 high-precision signal acquisition card; and the spectrum analysis is based on fast Fourier transform, so as to obtain the amplitudes of the fundamental wave and each harmonic wave, thereby realizing the quantitative measurement on the output characteristics of the alternating voltage.

[0028] To sum up, the present application has the following characteristics: improving the output waveform fidelity, effectively reducing the quantization noise and low-frequency distortion through the combination of the second-order Delta-Sigma modulation algorithm and the external compensation signal source, and ensuring the output accuracy of the alternating voltage; enhancing the system synchronization, reducing the phase difference between the code signal and the compensation signal through the unified external trigger signal and the phase calibration method, and improving the stability and consistency of the output voltage; improving the application value, and providing a reliable means for the application and promotion of the high-precision alternating voltage measurement, the precision power standard and the quantum metrology technology in the harmonic signal, and having important scientific and engineering application value. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 is a structure block diagram of a harmonic voltage generation method of a pulse-driven alternating voltage standard provided by the embodiment of the present application. DETAILED DESCRIPTION

[0030] The present application will be further described below with reference to the accompanying drawings. The harmonic voltage generation method of the present application adopts the following modules:

[0031] Code pattern modulation module: This is the digital core of the entire system, which receives the target waveform parameters (such as fundamental frequency , harmonic amplitude , and phase ), and calculates the corresponding discrete-time sequence code pattern according to these parameters.

[0032] Code pattern generator: This module is directly connected to the code pattern modulation module, responsible for converting the calculated three-value pulse output sequence into corresponding voltage signal output under clock control, at high speed and high accuracy. It can be regarded as a high-performance, programmable arbitrary waveform generator.

[0033] External trigger signal source: This module provides the synchronization clock or trigger signal for the entire system. It is connected to the code pattern generator and data acquisition card, ensuring that the waveform generation and data acquisition processes are strictly synchronized, avoiding timing chaos and ensuring the accuracy of measurement results.

[0034] Pulse-driven Josephson junction array: This is the key execution component of the system. It receives analog voltage pulse drive signals from the code pattern generator and generates highly accurate, step-like quantized voltages based on the Josephson effect. The target harmonic voltage signal is generated by this array.

[0035] Data acquisition card: This module is responsible for sampling and digitizing the actual voltage waveform generated by the Josephson junction array. It converts the analog voltage signal into discrete digital signals under the synchronization of the external trigger signal source for subsequent processing.

[0036] Data processing and spectrum analysis module: This is the backend processing and verification unit of the system. It receives the digital signals uploaded by the data acquisition card, performs Fourier transform and other spectrum analysis to extract the amplitude and phase of each harmonic in the generated signal, and compares it with the initial target value to verify the accuracy of the harmonic voltage generated by the entire system.

[0037] Based on the above system structure, the specific steps of the method are as follows:

[0038] 1. Code pattern calculation and generation: First, in the code pattern modulation module, according to the mathematical model of the target harmonic signal , combined with the pre-set sampling frequency , the corresponding discrete signal sequence is calculated. The three-value pulse output sequence is sent to the code pattern generator.

[0039] 2. Synchronous triggering and pulse driving: The external trigger signal source sends a synchronization signal to the code pattern generator and data acquisition card simultaneously. The code pattern generator is triggered by the synchronization signal to convert the digital code pattern The input signal is converted into a corresponding sequence of analog voltage pulses and output to a pulse-driven Josephson junction array.

[0040] 3. Quantum voltage synthesis: The input pulse sequence is synthesized into a highly accurate, AC voltage containing the required harmonic components, by the inherent quantum properties of the Josephson junction array under pulse driving.

[0041] 4. Data acquisition and processing: The generated quantum voltage signal is collected in real time by a data acquisition card under synchronous triggering and converted into digital data. The collected data is sent to a data processing and spectrum analysis module. The module processes the data (such as filtering, averaging) and performs spectrum analysis (such as FFT), accurately measuring the amplitude and phase of the fundamental wave and each harmonic in the actual generated signal.

[0042] 5. Process end: The accuracy of the harmonic voltage generation is verified by comparing the spectrum analysis results with the initial target values. At this point, a complete generation and verification process stops.

[0043] Through the coordinated work of the above modules and the strict implementation of the process, this method can generate traceable, high-precision complex harmonic voltage signals based on quantum reference.

[0044] Taking a multi-frequency signal as the target signal , the mathematical function of which is

[0045]

[0046] wherein, is the amplitude of the nth harmonic, is the phase, is the fundamental frequency. Discretize the signal, and set the sampling frequency to , to obtain the discrete signal:

[0047]

[0048] Input the discrete signal into a second-order Delta-Sigma modulator to obtain a three-value pulse output sequence. Delta-Sigma modulation is a modulation method based on oversampling and noise shaping. By mapping the analog signal to a high-speed ternary sequence, it can effectively quantize noise to the high-frequency region, thereby achieving high-precision waveform reconstruction in the required low-frequency range. Obtain the corresponding ternary code type and transmit the code type to the code generator.

[0049] Then, based on the same harmonic signal function as described above, digital waveform data for the complete cycle is generated. This waveform data is imported into the Keysight 33500 series arbitrary waveform generator and stored in its built-in memory using its custom waveform mode. The output channel of the waveform generator is set as a bias compensation current source to compensate for low-frequency distortion and fundamental amplitude deviation, thereby improving the quality of the system output waveform.

[0050] Next, a unified external trigger signal source is set up as the synchronization control signal for the pattern generator and the waveform generator. The trigger mode of the pattern generator is set to external trigger; the trigger mode of the waveform generator is also set to external trigger and Burst mode is enabled, with the signal loop mode set to infinite loop. When the external trigger signal is applied, the pattern generator and the waveform generator output signals simultaneously: the pattern generator outputs a pulse signal to drive the Josephson array, generating a quantized voltage step; the waveform generator outputs a compensation signal for superposition correction.

[0051] Finally, in Burst mode, the initial phase of the waveform generator is adjusted to ensure that its output signal is strictly in phase with the code drive signal, thereby reducing the phase difference between the two signals. The AC quantum voltage signal output is acquired by the signal acquisition card, and the acquired signal is subjected to fast Fourier transform and spectrum analysis to obtain the amplitude and spectrum of the fundamental wave and each harmonic.

[0052] It should be noted that the above refers to the form of discrete sinusoidal harmonic superposition. The target signal described is merely a typical example of the voltage waveform generated by this method. This method is based on the Delta-Sigma modulation principle and the quantum voltage synthesis capability of Josephson junctions, and its application is not limited to generating standard harmonic signals.

[0053] This method is also applicable to generating and synthesizing other periodic or aperiodic target signals of any other form, as long as they can be discretized and input as a code pattern to the modulator. These target signals include, but are not limited to:

[0054] 1. Standard waveforms: such as square waves, triangle waves, sawtooth waves, and other standard periodic waveforms with specific harmonic structures.

[0055] 2. Arbitrary Waveform: A voltage waveform of arbitrary shape defined by the user, whose discrete sequence... It can be defined directly through mathematical functions, table lookups, or measurement data.

[0056] 3. Modulated waveform: A complex signal containing amplitude modulation (AM), frequency modulation (FM), or phase modulation (PM) information.

[0057] 4. Pulse sequence: A specific pulse waveform used for testing or communication systems.

[0058] 5. Band-limited signal: Any band-limited signal satisfying the Nyquist sampling theorem, whose spectral components fall within .

[0059] The present application can convert the discrete representation of any target signal into an accurate sequence of pulses driving the array of Josephson junctions, thus enabling the synthesis of the target voltage waveform on a quantum reference.

Claims

1. A method for generating a harmonic voltage of a pulse-driven type AC voltage sub-voltage standard, characterized by, Comprising the following steps: Step one: code modulation and generation, according to the mathematical function of the target harmonic signal , using the Delta-Sigma modulation method (DSM) to discretize the continuous-time harmonic signal, obtaining the corresponding ternary code, and transmitting the code to the code generator; Step two: Reference signal generation and storage, based on mathematical functions of the same harmonic signal In the external signal source, a one-period waveform for compensation is generated, and the waveform is saved in the waveform generator through the custom output mode of the signal source, and used as a bias compensation current source; Step three: synchronous trigger and signal output, using the same external trigger signal to trigger the code generator and waveform generator, the trigger mode of the code generator is set to external trigger, the code generator converts the digital code into corresponding analog voltage pulse sequence under the trigger of the synchronization signal, and outputs to the pulse driven Josephson junction array, the trigger mode of the waveform generator is set to external trigger and burst mode is opened, and the signal cycle mode is set to infinite cycle, so as to ensure that the two signals are output at the same time; Step four: phase calibration and data acquisition, adjusting the phase of the waveform generator in burst mode to make the phase difference of the two signals zero, and then making the pulse driven Josephson chip output the alternating current voltage; After the output signal is collected by the signal acquisition card, the amplitude and spectrum of the fundamental wave and each harmonic are obtained by using fast Fourier transform and spectrum analysis; Step two includes: using Keysight 33500 series waveform generator as compensation signal source, writing the generated harmonic signal cycle data into its storage module as a bias compensation current source in the form of a custom waveform, to compensate for the amplitude attenuation and nonlinear distortion of the fundamental wave caused by low frequency distortion; Step three includes: the external trigger signal is provided by the experimental control platform or the synchronization clock module, and the trigger precision is better than 1 ns, so as to ensure that the code generator and the waveform generator are strictly aligned on the time axis; Burst mode is used to limit the number of output signals and avoid waveform drift; Step four includes: phase adjustment is realized by modifying the burst start phase of the waveform generator, so that the compensation signal and the code driving signal are strictly in phase in the time domain, thereby eliminating the phase difference caused by clock jitter or line delay; The collected output signal is obtained by a high-precision signal acquisition card.

2. The method of claim 1, wherein the method is a method of generating a harmonic voltage of a pulse-driven type AC voltage reference, characterized by, The step one specifically includes: Delta-Sigma modulation is a modulation method based on oversampling and noise shaping, which can effectively quantize noise shift to high frequency area by mapping analog signal to high-speed ternary sequence, so as to realize high-precision waveform reconstruction in the required low frequency range; The target function harmonic signal is mathematically modeled, and the signal form is wherein, is a harmonic signal in continuous time, representing the signal value at time , n is a harmonic index, from 1 to N, representing the nth harmonic, N is the total number of harmonics, i.e. the number of harmonics contained in the signal, is the amplitude of the nth harmonic, is the phase of the nth harmonic, is the fundamental frequency, i.e. the base frequency of the signal, t represents continuous time; The signal is discretized with a sampling frequency set to , resulting in a discrete signal: wherein, represents a discrete-time signal, i.e. a continuous signal the k-th sample value after sampling, k being a sampling index, is a non-negative integer, represents a sampling time point, is the sampling frequency, i.e. the number of samples per second, corresponds to a discretized form of the continuous time t, The discrete signal is input into the second-order Delta-Sigma modulator to obtain a ternary pulse output sequence, and the core process is: wherein, represents the current input signal the difference between the previous output and the current input signal, which is used for feedback control, is the state value of the first integrator, representing the previous state and the cumulative sum of the current difference , is the state value of the second integrator, representing the previous state and the cumulative sum of the first integrator output , is the output of the quantizer, which is a ternary pulse sequence taking values {-1, 0, 1}, is the quantization function used to quantize the output of the second integrator , the quantizer maps continuous values to discrete values based on comparator or threshold rules, and the second-order delta-sigma modulator realizes noise shaping through double integration links, ensuring high fidelity of the signal within the low frequency bandwidth; Assume that the quantizer can be modeled as the input signal plus quantization noise In the Z-domain, the output of a second order delta-sigma modulator is: Where STF is the signal transfer function, NTF is the noise transfer function, For the second-order Delta-Sigma modulator, we have: input target harmonic function is converted into a ternary pulse output sequence after passing through a second-order delta-sigma modulator ; the average value of the output sequence is equivalent to the original signal: 。

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