Automatic phase shifting circuit and method for a current transformer bridge

Abstract

This invention relates to an automatic phase-shifting circuit and method for an AC quantum resistance transfer bridge. The circuit includes: a waveform memory; a controller connected to the waveform memory; a digital-to-analog converter connected to the controller; a power amplifier connected to the input terminals of the digital-to-analog converter and the AC quantum resistance transfer bridge; a switching circuit connected to the output terminal of the AC quantum resistance transfer bridge; a low-noise amplifier connected to the switching circuit; a phase-sensitive detector connected to the low-noise amplifier; a trigger connected to the controller and the phase-sensitive detector; an amplifier circuit connected to the phase-sensitive detector; and an analog-to-digital converter connected to the amplifier circuit and the controller. The method automatically shifts the phase of the AC quantum resistance transfer bridge based on the circuit, effectively solving the problem of a non-zero phase difference between the reference signal and the measured resistor voltage signal, and improving the zero-pointing accuracy of the AC quantum resistance transfer bridge.

Description

Technical Field

[0001] This invention relates to the field of circuit technology, specifically to an automatic phase-shifting circuit and method for an AC quantum resistance transfer bridge. Background Technology

[0002] In AC quantum resistance transfer bridges, zero balance is a key factor affecting accuracy during bridge measurements. AC quantum resistance transfer bridges typically use turns ratio technology to achieve the transfer ratio, forming a bridge circuit with a standard resistor and the resistor being measured, such as... Figure 1 As shown, Figure 1 A schematic diagram of an AC quantum resistance transfer bridge is shown. The balance of the bridge is determined by a null pointer; the accuracy and resolution of the null pointer measurement determine the uncertainty of the measurement result. The measurement uncertainty of the AC quantum resistance transfer bridge needs to reach 10. -8 The order of magnitude, therefore, indicates that the resolution of the null measurement needs to reach 10. -9 The order of magnitude is typically when the voltage drop across the resistor being measured is 1V, 10 -9 The required resolution is down to 1 nV for zero-point measurement. Due to various noise effects, the measurement is very difficult, necessitating the use of phase-locked loop (PLL) technology to suppress noise interference. Therefore, PLL technology is a key component of the AC quantum resistance transfer bridge for zero-point measurement. Through its phase-sensitive detector, the weak signal being measured is correlated with a reference signal of the same frequency and phase, thereby extracting the weak signal from the background noise and converting it into an easily measurable DC signal.

[0003] In traditional lock-in amplifier-based AC resistance transfer bridge null pointer measurement systems, an excitation signal is applied to the power supply port of the AC quantum resistance transfer bridge to generate the signal to be tested at the null pointer port. A square wave with the same frequency as the excitation signal is applied as a reference signal to the lock-in amplifier. During measurement, the phase difference between the reference signal and the signal to be tested significantly affects the measurement results. Two problems exist: first, the phase of the internal coordinate system of the lock-in amplifier differs from that of the reference signal; commercial lock-in amplifiers can use automatic phase synchronization to achieve this. Second, the AC resistance transfer bridge system has a phase-shifting effect on the excitation signal, causing the voltage phase on the measured resistor to be inconsistent with the phase at the power supply port. This requires manual adjustment of the lock-in amplifier's phase adjustment knob to achieve a zero phase difference, but this often fails to achieve the ideal state, thus affecting the accuracy of the AC resistance transfer bridge null pointer measurement. Therefore, automatic phase adjustment between the reference signal and the excitation signal is needed to achieve a zero phase difference between the reference signal and the voltage signal on the measured resistor, ensuring the high accuracy of the AC quantum resistance transfer bridge null pointer system. Summary of the Invention

[0004] In view of this, the present invention aims to provide an automatic phase-shifting circuit and method for an AC quantum resistance transfer bridge, which solves the problem that the phase difference between the reference signal and the voltage signal on the measured resistor of the AC quantum resistance transfer bridge is not zero, thereby improving the zero-pointing accuracy of the AC quantum resistance transfer bridge.

[0005] In a first aspect, a first embodiment of the present invention provides an automatic phase-shifting circuit for an AC quantum resistance transfer bridge, the circuit comprising:

[0006] Waveform memory;

[0007] The controller is connected to the waveform memory;

[0008] A digital-to-analog converter, connected to the controller;

[0009] A power amplifier is connected to the input terminals of the digital-to-analog converter and the AC quantum resistance transfer bridge.

[0010] A switching circuit is connected to the output terminal of the AC quantum resistance transfer bridge;

[0011] A low-noise amplifier is connected to the switching circuit.

[0012] A phase-sensitive detector is connected to the low-noise amplifier;

[0013] A trigger, connected to the controller and the phase-sensitive detector;

[0014] An amplifier circuit is connected to the phase-sensitive detector;

[0015] An analog-to-digital converter is connected to the amplifier circuit and the controller.

[0016] In a preferred embodiment of the present invention, the output terminal of the waveform memory is connected to the input terminal of the controller, and the waveform memory is configured to output sine wave signal data to the controller;

[0017] The output terminal of the controller is connected to the input terminal of the digital-to-analog converter. The controller is configured to output the sine wave signal data to the digital-to-analog converter, and the digital-to-analog converter is configured to convert the sine wave signal data into a sine wave signal.

[0018] The output terminal of the digital-to-analog converter is connected to the input terminal of the power amplifier. The digital-to-analog converter is configured to output the sine wave signal to the power amplifier. The power amplifier is configured to process the sine wave signal and output the processed signal to the AC quantum resistance transfer bridge as the excitation signal of the AC quantum resistance transfer bridge.

[0019] The AC quantum resistance transfer bridge generates a signal of the same frequency at the measured resistor terminal and the null pointer port according to the excitation signal;

[0020] The input terminal of the switching circuit is connected to the output terminal of the AC quantum resistance transfer bridge, and is used to select the voltage signal or zero-pointing signal on the resistor under test as the signal to be tested.

[0021] The input terminal of the low-noise amplifier is connected to the output terminal of the switching circuit;

[0022] The input terminal of the phase-sensitive detector is connected to the output terminal of the low-noise amplifier;

[0023] The input terminal of the trigger is connected to the output terminal of the controller, and the controller is configured to send reference signal parameters to the trigger;

[0024] The output of the trigger is connected to the input of the phase-sensitive detector, and the trigger is configured to output the reference signal to the phase-sensitive detector.

[0025] The input terminal of the amplifier circuit is connected to the output terminal of the phase-sensitive detector, and the phase-sensitive detector is configured to output a corresponding DC signal to the amplifier circuit according to the signal to be measured and the reference signal.

[0026] The input terminal of the analog-to-digital converter is connected to the output terminal of the amplifier circuit, and the amplifier circuit is configured to amplify the DC signal and output it to the analog-to-digital converter.

[0027] The output terminal of the analog-to-digital converter is connected to the input terminal of the controller, and the analog-to-digital converter is configured to digitize the output signal of the amplifier circuit and send it to the controller.

[0028] In a preferred embodiment of the present invention, the circuit further includes:

[0029] A synchronous clock source is connected to the controller.

[0030] The controller is configured to send the sine wave signal data to the digital-to-analog converter before each trigger edge of the synchronous clock source.

[0031] In a preferred embodiment of the present invention, the circuit further includes:

[0032] The first isolator is connected at both ends to the controller and the digital-to-analog converter, respectively.

[0033] The second isolator is connected at both ends to the controller and the trigger, respectively.

[0034] The third isolator is connected at both ends to the controller and the analog-to-digital converter, respectively.

[0035] The fourth isolator is connected at one end to the synchronous clock source and at the other end to the CLK input of the flip-flop and the update trigger port of the digital-to-analog converter. The fourth isolator is configured to synchronously update the reference signal and the excitation signal at the trigger edge of the synchronous clock source.

[0036] In a preferred embodiment of the present invention, the phase-sensitive detector includes a preamplifier module, a bandpass module, a correlator module, and a low-pass filter module.

[0037] In a preferred embodiment of the present invention, the trigger is a D-type trigger.

[0038] In a preferred embodiment of the present invention, the reference signal is a square wave signal.

[0039] In a second aspect, a second embodiment of the present invention provides an automatic phase-shifting method for an AC quantum resistance transfer bridge, employing the automatic phase-shifting circuit of the AC quantum resistance transfer bridge as described in any one of the first aspects, the method comprising:

[0040] S010, Set the convergence threshold V th The phase-sensitive detector outputs a DC voltage signal based on the signal to be measured and the reference signal;

[0041] S020, the phase of the reference signal is shifted forward by 90 degrees, and the controller receives the DC voltage data V fed back by the analog-to-digital converter. FB1 ;

[0042] S030, Determine |V FB1 Is it less than the convergence threshold V? th If V FB1 Greater than the convergence threshold V th If the phase shifts, proceed to S040; otherwise, shift the phase of the reference signal backward by 90 degrees and then end.

[0043] S040, the phase of the reference signal is shifted forward by 90 degrees, and the controller receives the DC voltage data V fed back by the analog-to-digital converter. FB2 ;

[0044] S050, the controller, based on the DC voltage data V fed back twice... FB1 and V FB2 The phase shift θ1 is calculated.

[0045] S060, the phase of the reference signal is shifted backward by 90 degrees, and the controller receives the DC voltage data V fed back by the analog-to-digital converter. FB3 ;

[0046] S070, the controller, based on the DC voltage data V fed back twice...FB1 and V FB3 The phase shift θ2 is calculated.

[0047] S080, the controller obtains the phase shift phase θ of the reference signal by averaging the phases θ1 and θ2 obtained from the two phase shifts;

[0048] S090, if θ is greater than 0, shift the reference signal forward by θ; if θ is less than 0, shift the reference signal backward by |θ|.

[0049] S100, return to S020.

[0050] In a preferred embodiment of the present invention, the output terminal of the AC quantum resistance transfer bridge is also connected to a switching circuit;

[0051] Before S010, the method further includes: switching the output of the switching circuit to the measured resistance signal;

[0052] Following S100, the following step is also included: switching the output of the switching circuit to the zero-point signal.

[0053] The automatic phase-shifting circuit and method of the AC quantum resistance transfer bridge in this invention can effectively solve the problem that the phase difference between the reference signal and the voltage signal on the measured resistor of the AC quantum resistance transfer bridge is not zero, and can improve the zero-pointing accuracy of the AC quantum resistance transfer bridge. Attached Figure Description

[0054] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0055] Figure 1 This is a schematic diagram of the principle of an AC quantum resistance transfer bridge in the prior art;

[0056] Figure 2 This is a schematic diagram of the automatic phase-shifting circuit of the AC quantum resistance transfer bridge according to an embodiment of the present invention;

[0057] Figure 3 This is a schematic diagram of the automatic phase-shifting circuit of the AC quantum resistance transfer bridge according to an embodiment of the present invention.

[0058] Figure 4 This is a flowchart illustrating the automatic phase-shifting method of the AC quantum resistance transfer bridge according to an embodiment of the present invention. Detailed Implementation

[0059] The description of the embodiments in this specification should be taken in conjunction with the accompanying drawings, which should form part of the complete specification. In the drawings, the shape or thickness of the embodiments may be exaggerated and may be indicated in a simplified or convenient manner. Furthermore, parts of the various structures in the drawings will be described separately; it is worth noting that elements not shown in the figures or not described in words are in a form known to those skilled in the art.

[0060] The descriptions of the embodiments herein, including any references to directions and orientations, are for ease of description only and should not be construed as limiting the scope of the invention. The following description of preferred embodiments involves combinations of features, which may exist independently or in combination; the invention is not particularly limited to the preferred embodiments. The scope of the invention is defined by the claims.

[0061] like Figures 2-3 As shown, the automatic phase-shifting circuit of the AC quantum resistance transfer bridge in this embodiment of the invention includes a waveform memory, a controller, a digital-to-analog converter (DAC), a power amplifier, a switching circuit, a low-noise amplifier, a phase-sensitive detector, a trigger, an amplifier circuit, and an analog-to-digital converter (ADC). The output of the waveform memory is connected to the input of the controller, and the waveform memory is configured to output sinusoidal signal data to the controller. The output of the controller is connected to the input of the ADC, and the controller is configured to output sinusoidal signal data to the ADC. The ADC is configured to convert the sinusoidal signal data into a sinusoidal signal. The output of the ADC is connected to the input of the power amplifier, and the ADC is configured to output a sinusoidal signal to the power amplifier. The power amplifier is configured to process the sinusoidal signal and output the processed sinusoidal signal to the AC quantum resistance transfer bridge as the excitation signal for the AC quantum resistance transfer bridge. The AC quantum resistance transfer bridge generates a test signal of the same frequency at the measured resistor terminal and the null pointer port according to the excitation signal. The input of the switching circuit is connected to the measured resistor terminal and the null pointer port, and outputs the test signal according to the configuration state. A low-noise amplifier, connected to the output of the switching circuit, is configured to amplify the signal under test to a phase-sensitive detector. The phase-sensitive detector is connected to the output of the low-noise amplifier. The input of a trigger is connected to the output of the controller, which is configured to send a reference signal to the trigger. The output of the trigger is connected to the input of the phase-sensitive detector, which is configured to output a reference signal to the phase-sensitive detector. The input of an amplifier circuit is connected to the output of the phase-sensitive detector, which is configured to output a corresponding DC signal to the amplifier circuit based on the signal under test and the reference signal. The input of an analog-to-digital converter (ADC) is connected to the output of the amplifier circuit, which is configured to amplify the DC signal and output it to the ADC. The output of the ADC is connected to the input of the controller, which is configured to send the output signal of the digital amplifier circuit to the controller.

[0062] like Figures 2-3 As shown, in this embodiment, the automatic phase-shifting circuit of the AC quantum resistance transfer bridge further includes a synchronous clock source connected to a controller. The controller is configured to send sinusoidal signal data to the digital-to-analog converter before each trigger edge of the synchronous clock source. The synchronous clock source may be an active crystal oscillator.

[0063] like Figures 2-3 As shown, in this embodiment, the automatic phase-shifting circuit of the AC quantum resistance transfer bridge further includes a first isolator, a second isolator, a third isolator, and a fourth isolator. The two ends of the first isolator are connected to the controller and the digital-to-analog converter (DAC), respectively. The two ends of the second isolator are connected to the controller and the flip-flop, respectively. The two ends of the third isolator are connected to the controller and the DAC, respectively. One end of the fourth isolator is connected to a synchronous clock source, and the other end is connected to the CLK input of the flip-flop and the update trigger port of the DAC. The fourth isolator is configured to synchronously update the reference signal and the excitation signal at the trigger edge of the synchronous clock source.

[0064] like Figures 2-3 As shown, in this embodiment, the output of the phase-sensitive detector is also connected to a switching circuit. The phase-sensitive detector includes a preamplifier module, a bandpass module, a correlator module, and a low-pass filter module. Inside the phase-sensitive detector, the reference signal, after further triggering and shaping, is correlated with the measured signal, which has been preamplified and bandpass filtered. The correlator can be either an analog multiplier or a switched multiplier; this embodiment uses a switched multiplier as an example. The correlated signal is then low-pass filtered to become a DC signal before being output. The DC signal output from the phase-sensitive detector is amplified by the amplifier circuit to a value matching the range of the analog-to-digital converter.

[0065] like Figures 2-3 As shown, in this embodiment, the reference signal is a square wave signal. The controller is a microcontroller, such as an ARM-based single-chip microcontroller. The waveform memory is a non-volatile memory, such as a FLASH memory, which can store quarter, half, or a single cycle of sine wave data. The digital-to-analog converter (DAC) is a high-speed DAC capable of outputting bipolar voltages and equipped with necessary peripheral circuitry such as a reference voltage. The DAC can reduce output impedance to allow for a larger output current. The flip-flop is a D-type flip-flop, which has a data input terminal and a clock input terminal. Its output is refreshed to the data level of the data input terminal at the trigger edge of the clock input terminal.

[0066] like Figures 2-3As shown, in this embodiment, an AC quantum resistance transfer bridge is used as the circuit under test. The sinusoidal signal output by the digital-to-analog converter is amplified and then applied as an excitation signal to both ends of the AC quantum resistance transfer bridge. Under the action of the excitation signal, signals of the same frequency are generated at the measured resistance end and the null pointer end of the AC quantum resistance transfer bridge. After differential amplification and conditioning, these signals become the signal under test.

[0067] The automatic phase-shifting circuit of the AC quantum resistance transfer bridge in this embodiment of the invention can effectively solve the problem that the phase difference between the reference signal and the voltage signal of the measured resistor in the AC quantum resistance transfer bridge is not zero, and can improve the zero-pointing accuracy of the AC quantum resistance transfer bridge.

[0068] like Figure 4 The diagram shown is a schematic of an automatic phase-shifting method for an AC quantum resistance transfer bridge according to an embodiment of the present invention. The method of this embodiment can be applied to the circuit described in the above embodiment to automatically shift the phase of the AC quantum resistance transfer bridge. The method includes:

[0069] S010, Set the convergence threshold V th The phase-sensitive detector outputs a DC voltage signal based on the signal to be measured and the reference signal;

[0070] S020, the phase of the reference signal is shifted forward by 90 degrees, and the controller receives the DC voltage data V fed back by the analog-to-digital converter. FB1 ;

[0071] S030, Determine |V FB1 Is it less than the convergence threshold V? th If V FB1 Greater than the convergence threshold V th Perform S040; otherwise, shift the phase of the reference signal backward by 90 degrees and end.

[0072] S040, the phase of the reference signal is shifted forward by 90 degrees, and the controller receives the DC voltage data V fed back by the analog-to-digital converter. FB2 ;

[0073] S050, the controller, based on the DC voltage data V fed back twice... FB1 and V FB2 The phase shift θ1 is calculated.

[0074] S060, the phase of the reference signal is shifted backward by 90 degrees, and the controller receives the DC voltage data V fed back by the analog-to-digital converter. FB3 ;

[0075] S070, the controller, based on the DC voltage data V fed back twice... FB1 and V FB3The phase shift θ2 is calculated.

[0076] S080, the controller obtains the phase shift phase θ of the reference signal by averaging the phases θ1 and θ2 obtained from the two phase shifts.

[0077] S090, if θ is greater than 0, shift the reference signal forward by θ; if θ is less than 0, shift the reference signal backward by |θ|.

[0078] S100, return to S020.

[0079] In this embodiment, V FB1 V FB2 and V FB3 It can be the average value after multiple readings and digital filtering. The output terminal of the AC quantum resistance transfer bridge is also connected to a switching circuit; before step S010, the method further includes: switching the output of the switching circuit to the measured resistance signal;

[0080] The following uses the convergence threshold V as an example. th The initial phase of the sine wave output by the digital-to-analog converter is 0 degrees, with a value of 0.001. The initial phase of the reference square wave signal output by the given trigger is also 0 degrees. The output signal to be measured, V, is then used. s (t) = sin(2πt + θ), and the method of the present invention will be specifically described based on the circuit of the present invention:

[0081] The phase of the reference signal is shifted forward by 90°, and after demodulation by the phase-sensitive detector, a DC signal V0(t) = 0.5cos(θ-90°) is obtained; the controller reads and records the digitized DC voltage data V fed back from the analog-to-digital converter. FB1 =0.04962;

[0082] The controller determines |V FB1 |Greater than the convergence threshold V th Perform the S040 cycle;

[0083] The phase of the reference signal is shifted forward by 90°, and after demodulation by the phase-sensitive detector, a DC signal V0(t) = 0.5cos(θ-180°) is obtained; the controller reads and records the digitized DC voltage data V fed back by the analog-to-digital converter. FB2 = -0.49752;

[0084] The controller is based on the DC voltage data V fed back twice. FB1 and V FB2 The phase shift θ1 is calculated to be arctan(-V FB1 / V FB2 ) = 5.69556°;

[0085] The phase of the reference signal is shifted backward by 180°, and after demodulation by the phase-sensitive detector, a DC signal V0(t) = 0.5cos(θ) is obtained; the controller reads and records the digitized DC voltage data V fed back by the analog-to-digital converter. FB2 =0.49541;

[0086] The controller is based on the DC voltage data V fed back twice. FB1 and V FB3 The phase shift θ2 is calculated to be arctan(V). FB1 / V FB3 ) = 5.71961°;

[0087] The controller takes the average of the phases θ1 and θ2 obtained from the two phase shifts to obtain the phase shift phase of the excitation signal θ = (θ1 + θ2) / 2 = 5.707585°;

[0088] If θ is greater than 0, shift the reference signal forward by θ and return to S020;

[0089] After demodulation by the phase-sensitive detector, a DC signal V0(t) = 0.5cos(θ - 95.707585°) is obtained; the controller reads and records the digitized DC voltage data V fed back by the analog-to-digital converter. FB1 = -0,000066;

[0090] The controller determines |V FB1 | Less than the convergence threshold V th The loop ends, and the reference signal is finally shifted forward by 5.707585°.

[0091] The automatic phase-shifting method of the AC quantum resistance transfer bridge in this invention can effectively solve the problem that the phase difference between the reference signal and the voltage signal of the measured resistor in the AC quantum resistance transfer bridge is not zero, and can improve the zero-pointing accuracy of the AC quantum resistance transfer bridge.

[0092] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An automatic phase-shifting method for an AC quantum resistance transfer bridge, comprising an automatic phase-shifting circuit for an AC quantum resistance transfer bridge, characterized in that, The circuit includes: Waveform memory; The controller is connected to the waveform memory; A digital-to-analog converter, connected to the controller; A power amplifier is connected to the input terminals of the digital-to-analog converter and the AC quantum resistance transfer bridge. A switching circuit is connected to the output terminal of the AC quantum resistance transfer bridge; A low-noise amplifier is connected to the switching circuit. A phase-sensitive detector is connected to the low-noise amplifier; A trigger, connected to the controller and the phase-sensitive detector; An amplifier circuit is connected to the phase-sensitive detector; An analog-to-digital converter, connected to the amplifier circuit and the controller; The automatic phase-shifting method of the AC quantum resistance transfer bridge includes: S010, setting a convergence threshold V th The phase-sensitive detector outputs a direct current voltage signal according to the signal to be measured and the reference signal. S020, the phase of the reference signal is moved forward by 90 degrees, and the controller receives the direct current voltage data V FB1 ; S030, judgment Is it less than the convergence threshold V? th If V FB1 Greater than the convergence threshold V th If the phase shifts, proceed to S040; otherwise, shift the phase of the reference signal backward by 90 degrees and then end. S040, the phase of the reference signal is shifted forward by 90 degrees, and the controller receives the DC voltage data V fed back by the analog-to-digital converter. FB2 ; S050, the controller, based on the DC voltage data V fed back twice... FB1 and V FB2 The phase shift θ1 is calculated. S060, the phase of the reference signal is shifted backward by 180 degrees, and the controller receives the DC voltage data V fed back by the analog-to-digital converter. FB3 ; S070, the controller, based on the DC voltage data V fed back twice... FB1 and V FB3 The phase shift θ2 is calculated. S080, the controller obtains the phase shift phase θ of the reference signal by averaging the phases θ1 and θ2 obtained from the two phase shifts; S090, if θ is greater than 0, shift the reference signal forward by θ; if θ is less than 0, shift the reference signal backward by θ. ; S100, return to S020.

2. The automatic phase-shifting method of the AC quantum resistance transfer bridge according to claim 1, characterized in that, The output of the AC quantum resistance transfer bridge is also connected to a switching circuit. Before step S010, the method further includes: switching the output of the switching circuit to the measured resistance signal; The process after step S100 further includes: switching the output of the switching circuit to the zero signal.

3. The automatic phase-shifting method for the AC quantum resistance transfer bridge according to claim 1, characterized in that, The output terminal of the waveform memory is connected to the input terminal of the controller, and the waveform memory is configured to output sine wave signal data to the controller; The output terminal of the controller is connected to the input terminal of the digital-to-analog converter. The controller is configured to output the sine wave signal data to the digital-to-analog converter, and the digital-to-analog converter is configured to convert the sine wave signal data into a sine wave signal. The output terminal of the digital-to-analog converter is connected to the input terminal of the power amplifier. The digital-to-analog converter is configured to output the sine wave signal to the power amplifier. The power amplifier is configured to process the sine wave signal and output the processed signal to the AC quantum resistance transfer bridge as the excitation signal of the AC quantum resistance transfer bridge. The AC quantum resistance transfer bridge generates a signal of the same frequency at the measured resistor terminal and the null pointer port according to the excitation signal; The input terminal of the switching circuit is connected to the output terminal of the AC quantum resistance transfer bridge, and is used to select the voltage signal or zero-pointing signal on the resistor under test as the signal to be tested. The input terminal of the low-noise amplifier is connected to the output terminal of the switching circuit; The input terminal of the phase-sensitive detector is connected to the output terminal of the low-noise amplifier; The input terminal of the trigger is connected to the output terminal of the controller, and the controller is configured to send reference signal parameters to the trigger; The output of the trigger is connected to the input of the phase-sensitive detector, and the trigger is configured to output the reference signal to the phase-sensitive detector. The input terminal of the amplifier circuit is connected to the output terminal of the phase-sensitive detector, and the phase-sensitive detector is configured to output a corresponding DC signal to the amplifier circuit according to the signal to be measured and the reference signal. The input terminal of the analog-to-digital converter is connected to the output terminal of the amplifier circuit, and the amplifier circuit is configured to amplify the DC signal and output it to the analog-to-digital converter. The output terminal of the analog-to-digital converter is connected to the input terminal of the controller, and the analog-to-digital converter is configured to digitize the output signal of the amplifier circuit and send it to the controller.

4. The automatic phase-shifting method of the AC quantum resistance transfer bridge according to claim 3, characterized in that, The automatic phase-shifting circuit also includes: A synchronous clock source is connected to the controller. The controller is configured to send the sine wave signal data to the digital-to-analog converter before each trigger edge of the synchronous clock source.

5. The automatic phase-shifting method of the AC quantum resistance transfer bridge according to claim 4, characterized in that, The automatic phase-shifting circuit also includes: The first isolator is connected at both ends to the controller and the digital-to-analog converter, respectively. The second isolator is connected at both ends to the controller and the trigger, respectively. The third isolator is connected at both ends to the controller and the analog-to-digital converter, respectively. The fourth isolator is connected at one end to the synchronous clock source and at the other end to the CLK input of the flip-flop and the update trigger port of the digital-to-analog converter. The fourth isolator is configured to synchronously update the reference signal and the excitation signal at the trigger edge of the synchronous clock source.

6. The automatic phase-shifting method for an AC quantum resistance transfer bridge according to any one of claims 1-5, characterized in that, The phase-sensitive detector includes a preamplifier module, a bandpass module, a correlator module, and a low-pass filter module.

7. The automatic phase-shifting method for an AC quantum resistance transfer bridge according to any one of claims 1-5, characterized in that, The trigger is a D-type trigger.

8. The automatic phase-shifting method for an AC quantum resistance transfer bridge according to any one of claims 3-5, characterized in that, The reference signal is a square wave signal.

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