A high-precision programmable electronic load circuit based on feedforward and feedback

Abstract

The application discloses a high-precision programmable electronic load circuit based on feedforward and feedback. The current sampling module in the application is used for sampling the input bias current, and the amplified voltage value is transmitted to the main controller. The high-speed voltage output module is used for rapidly outputting the voltage of the main controller, and the module constitutes the feedforward part of the programmable electronic load circuit. The high-precision voltage compensation module is used for obtaining a compensation voltage value, and the compensation voltage value is superposed with the output voltage of the high-speed voltage output module through the same-direction adder; the module constitutes the feedback part of the programmable electronic load circuit. The application adds the feedforward and feedback control, the rough voltage is established through the feedforward control of the high-speed digital-to-analog converter, so that the circuit has a faster response speed; the voltage compensation is realized through the feedback control of the high-precision digital-to-analog converter and the PI module, so that the whole circuit guarantees high precision and has a faster response speed.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of circuit design, and relates to a high-precision programmable electronic load circuit based on feedforward and feedback. BACKGROUND

[0002] In the development process of a programmable Josephson voltage standard system (PJVS), in order to reduce the risk of quantum chip damage and save liquid helium refrigeration cost, a research and development target based on a programmable series I-V characteristic simulator is proposed. A numerical calculation method of Josephson junction I-V characteristics and a prototype verification of a single I-V characteristic simulation unit have been realized.

[0003] In the past programmable electronic load circuit, due to the performance limitation of digital-to-analog converters and analog-to-digital converters, the circuit is difficult to ensure high precision while ensuring high response speed, and in actual application, it is hoped that it can establish accurate and stable voltage value in a short time. For example, in order to restore the characteristics of Josephson junction as much as possible, the Josephson junction array unit simulator should improve the performance of the existing simulation unit as much as possible.

[0004] In recent years, according to the I-V numerical characteristics of Josephson, research and development of simulation units have been carried out, and it is found in the research process that the previous design scheme uses one DAC and one ADC to cooperate, but if a high-precision DAC converter is selected, the response speed of the unit simulator will be reduced, and if a DAC converter with fast response speed is selected, the accuracy of the unit simulator will be limited. When the accuracy is improved, the transient response speed will be lost, and the voltage establishment time will be prolonged. When the response speed is improved, the accuracy cannot be guaranteed. SUMMARY

[0005] The application provides a high-precision programmable electronic load circuit based on feedforward and feedback to solve the problems of the prior art.

[0006] The technical scheme adopted by the application to solve the technical problems is:

[0007] The application is used for simulating nonlinear current-voltage characteristics, and includes a simulation unit and a main controller. The simulation unit includes a current sampling module, a high-speed voltage output module, a high-precision voltage compensation module and a same-direction adder.

[0008] The current sampling module is used for sampling the input bias current and transmitting the amplified voltage value to the main controller.

[0009] The high-speed voltage output module is used for rapidly outputting the voltage of the main controller, and this module constitutes the feedforward part of the programmable electronic load circuit.

[0010] The high-precision voltage compensation module is used to obtain a compensation voltage value, which is superimposed on the output voltage of the high-speed voltage output module through the same-direction adder; this module constitutes the feedback part of the programmable electronic load circuit.

[0011] The beneficial effects of this invention are as follows: The high-precision programmable electronic load circuit incorporates feedforward and feedback control. The circuit establishes a coarsely measured voltage through feedforward control using a high-speed digital-to-analog converter, enabling the circuit to have a faster response speed. Voltage compensation is achieved through feedback control using a high-precision digital-to-analog converter in conjunction with a PI module. This circuit design ensures high precision while maintaining a fast response speed. Attached Figure Description

[0012] Figure 1 This is a structural block diagram of the present invention;

[0013] Figure 2 This is a circuit structure diagram of an embodiment of the present invention;

[0014] Figure 3 This is a schematic diagram. Detailed Implementation

[0015] like Figure 1 As shown, the programmable electronic load circuit includes an analog unit, a main controller 2, and an optocoupler 3. The main controller and the external controller are connected through the optocoupler. The 6N137 high-speed optocoupler is used, which provides complete isolation between the input and output in the circuit, improves the anti-interference capability of the signal, and has the characteristics of high speed, high precision, and high isolation voltage.

[0016] The simulation unit includes a current sampling module 1, a high-speed voltage output module 4, a high-precision voltage compensation module 5, and a co-current adder 6.

[0017] The current sampling module includes a sampling resistor 10, a differential operational amplifier 11, and an analog-to-digital converter 12. It mainly samples the input bias current and transmits the amplified voltage value V0 to the main controller.

[0018] In one embodiment, such as Figure 2 As shown, the sampling resistor Rs is a 0.1Ω low-temperature-drift resistor, whose function is to convert the bias current IO1 into a differential voltage; the differential operational amplifier is an AD8221, configured with a gain of 1000 times through the gain resistor Rg, amplifying the input differential voltage signal V0, i.e., the voltage across Rs, by 1000 times before inputting it to the analog-to-digital converter. The gain calculation formula is as follows:

[0019]

[0020] Analog-to-digital converter selects 8 channels bipolar, 16-bit digital-to-analog converter AD7606, which has relatively high precision and high sampling rate in digital-to-analog converter, ensures the voltage value reading accuracy is higher, while also provides a guarantee for the high precision of the entire circuit.

[0021] As shown in Figure 1 , Figure 2 and Figure 3 , the main controller reads the voltage value converted by the analog-to-digital converter, the external controller inputs the I-V characteristic model to be simulated, and the light coupling isolator is transmitted to the main controller for storage, the main controller simulates according to the bias current value IO1 and the amplified differential voltage value V0, and outputs the calculated value to the high-speed digital-to-analog converter AD5545 and the high-precision digital-to-analog converter AD5623 at the same time. The main controller selects the FPGA chip, which has a high transmission rate and can provide high conversion speed and precision for digital-to-analog conversion and analog-to-digital conversion.

[0022] The high-speed voltage output module includes a voltage follower 40 and a high-speed digital-to-analog converter 41, which is the feedforward part of the programmable electronic load circuit. The main requirement of this part is to quickly output the voltage of the main controller to establish a rough voltage value for the entire circuit, which ensures that the entire high-precision electronic load circuit has a fast response speed. Therefore, the high-speed digital-to-analog converter is required to have a short voltage build-up time, i.e. a small simulation step.

[0023] In an embodiment, as shown in Figure 2 , the high-speed digital-to-analog converter selects a 12-bit digital-to-analog converter AD5445, which has a voltage build-up time of 80ns and a fast voltage build-up time.

[0024] In an embodiment, as shown in Figure 2 , the voltage follower U3 is built by OP37 operational amplifier, which buffers the voltage value Vs output by the high-speed digital-to-analog converter and inputs it to the same-direction adder U4. At this time, the circuit establishes a rough voltage at a fast speed, outputs the initial voltage value through the same-direction adder, and waits for the high-precision voltage compensation module to perform voltage compensation adjustment and finally output.

[0025] The high-precision voltage compensation module includes a proportional-integral operation circuit (i.e., PI module 50), an analog switch 51, a subtractor 52, and a high-precision digital-to-analog converter 53. The high-precision voltage compensation module realizes a feedback function in the entire circuit. Since the high-speed voltage output module discards a certain degree of accuracy to achieve a faster voltage build-up, the circuit compares the voltage VOUT output by the summing amplifier and the voltage VREF output by the high-precision digital-to-analog converter through the subtractor, and the difference is V1. The difference V1 is then fed back to the proportional-integral operation circuit to obtain the voltage value that needs to be compensated. The voltage value is then superimposed with the voltage output by the high-speed voltage output module through the summing amplifier and output again to realize a high-precision programmable electronic load circuit with a faster response speed.

[0026] In an embodiment, as shown in FIG. 2, the high-precision digital-to-analog converter is a dual-channel 16-bit AD5623 chip. The chip itself has an internal reference voltage source, which provides a guarantee for higher accuracy. The relative accuracy of the chip can reach ±1 LSB, which is relatively high in digital-to-analog converters. Figure 2

[0027] The voltage VREF output by the high-precision digital-to-analog converter and the voltage value VOUT output by the summing amplifier U4 through the buffer U5 are input into the analog switch S1 through the subtractor U1 built by the OP07C operational amplifier. The voltage value is:

[0028]

[0029] R1 and R2 are selected to be resistors with the same resistance value, i.e., 1kΩ. Thus, we have:

[0030] V1 = VOUT - VREF

[0031] The analog switch is controlled by the output VOUT of the summing amplifier. When it is determined that the fast voltage has been built and the circuit needs voltage compensation, the voltage value V1 output by the subtractor is input into the PI module through the analog switch. The analog switch S1 is a single-pole double-throw high-speed analog switch ADG1419. The PI module in this example mainly includes the OP07C operational amplifier U2, resistors R4 and R5, and a capacitor C1. The resistance values of the resistors R4 and R5 are 1kΩ. The hardware implementation can achieve a faster adjustment and operation speed than the software implementation.

[0032] ​Considering that the circuit needs high response speed while ensuring high precision, a PI module is adopted, which uses the same-direction adder U4 and the resistor R6 to form feedback to compensate the voltage back to the total output voltage VOUT. The performance of the PI module is mainly limited by the size of the capacitor, so the circuit simulation software LTspice is used to simulate different capacitance conditions, and finally the capacitor C1 is selected as a 3nF capacitor, so that the voltage value output through the PI module is:

[0033]

[0034] The same-direction adder is built by the OP37 operational amplifier U4 and resistors R7, R6, R8, and R9 (R6=R7=R8=R9=R10=1kΩ), and the rough measurement voltage Vs quickly established by the high-speed voltage output module is superimposed with the compensation voltage value V PI Superposition, that is:

[0035]

[0036] Select R6, R7, and R9 as resistors with the same resistance value, then:

[0037] VOUT=V s +V PI

[0038] Get the final voltage value VOUT as output.

[0039] The same-direction adder in this example is also connected with a voltage follower for buffering, forming the buffer U5, which is built by the OP37 operational amplifier.

[0040] As Figure 1 shown, the programmable electronic load circuit also includes a first power supply system 7 and a second power supply system 8. The first power supply system is a ±12V dual-track power supply, mainly providing power for each operational amplifier in the circuit to ensure normal operation. The second power supply system is a 3.3V single power supply, providing power for the main controller.

[0041] In summary, the application provides a high-precision programmable electronic load circuit based on feedforward and feedback, which can simulate nonlinear current-voltage characteristics, output voltage according to the input bias current, and provide a high-precision programmable electronic load circuit built by two digital-to-analog converters for feedforward control circuit and a PI module for feedback circuit, so as to ensure high precision of output voltage and reduce the voltage establishment time. The Josephson junction array unit simulator is actually a voltage source controlled by the input bias current, and the voltage output conforms to the I-V characteristic curve under the condition of microwave radiation, that is, it can be used to realize the programmable Josephson voltage reference. In the prior art, the programmable Josephson system voltage simulation step of NIST can reach 2 μs, and the circuit can be used to improve the performance of the existing simulation unit, shorten the simulation step to less than 1 μs, and at the same time, the unit simulator accuracy can be improved from the mV level to the 10-100 μV level.

Claims

1. A high-precision programmable electronic load circuit based on feedforward and feedback for simulating nonlinear current-voltage characteristics, characterized by: It comprises an analog unit and a main controller; the analog unit comprises a current sampling module, a high-speed voltage output module, a high-precision voltage compensation module and a same-direction adder; The current sampling module is used for sampling the input bias current and transmitting the amplified differential voltage to the main controller; The high-speed voltage output module is used for rapidly outputting the voltage of the main controller, and the module constitutes a feedforward part of a programmable electronic load circuit; The high-precision voltage compensation module is used for obtaining a compensation voltage value, and the compensation voltage value is superimposed with the output voltage of the high-speed voltage output module through the same-direction adder; the module constitutes a feedback part of the programmable electronic load circuit; The high-speed voltage output module comprises a voltage follower and a high-speed digital-analog converter; The voltage follower buffers the voltage output by the high-speed digital-analog converter and inputs the voltage into the same-direction adder, at this time, the circuit establishes a rough voltage at a faster speed, outputs an initial voltage value through the same-direction adder, and waits for the high-precision voltage compensation module to perform voltage compensation adjustment and finally output; The high-precision voltage compensation module comprises a proportional-integral operation circuit, an analog switch, a subtracter and a high-precision digital-analog converter; The high-precision digital-analog converter outputs a voltage and the voltage output by the same-direction adder through a buffer is input into the subtracter, and then the voltage is input into the analog switch through the subtracter; the analog switch is controlled by the same-direction adder, when it is judged that the fast voltage has been established and the circuit needs voltage compensation, the voltage value output by the subtracter is input into the proportional-integral operation circuit through the analog switch.

2. The high precision programmable electronic load circuit based on feed forward and feedback according to claim 1, characterized in that: The current sampling module comprises a sampling resistor, a differential operational amplifier and an analog-digital converter; The sampling resistor is used for converting the input bias current into a differential voltage, and the differential voltage is amplified through the differential operational amplifier and then input into the analog-digital converter.

3. A high precision programmable electronic load circuit based on feed forward and feedback according to claim 2, characterized in that: The sampling resistor is selected as a 0.1Ω low-temperature-drift resistor, and the analog-digital converter is selected as an 8-channel bipolar 16-bit digital-analog converter.

4. The high precision programmable electronic load circuit based on feed forward and feedback of claim 1, wherein: The high-speed digital-analog converter is selected as a 12-bit digital-analog converter.

5. The high precision programmable electronic load circuit based on feed forward and feedback according to claim 1, characterized in that: The high-precision digital-analog converter is selected as a double-channel 16-bit high-precision digital-analog converter.

6. The high precision programmable electronic load circuit based on feed forward and feedback of claim 1, wherein: The main controller reads the voltage value output by the current sampling module, an I-V characteristic model to be simulated is input by an external controller and is stored in the main controller; the main controller simulates according to the bias current and the amplified differential voltage, and outputs the calculated value to the high-speed voltage output module and the high-precision voltage compensation module.

7. A high precision programmable electronic load circuit based on feed forward and feedback according to any one of claims 1 to 6, characterized in that: It further comprises an optocoupler isolator, and the main controller is connected with the external controller through the optocoupler isolator.

8. The high precision programmable electronic load circuit based on feed forward and feedback of claim 1, wherein: It further comprises a first power supply system and a second power supply system; the first power supply system is a ±12V double-track power supply, mainly used for supplying power to various operational amplifiers in the circuit; and the second power supply system is a 3.3V single power supply, used for supplying power to the main controller.

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