A DC current-voltage characteristic simulation circuit and method for series Josephson junctions

Abstract

The present invention discloses a DC current-voltage characteristic simulation circuit of a series-connected Josephson junction, through which an input external bias current is sampled and converted into a voltage, and the voltage is calculated by a control module to obtain the resistance value of the output resistor of the potentiometer module, so that the resistance value conforms to the current-voltage characteristics of the first-order Shapiro step and the transition process of the series-connected Josephson junction, and the zero-order Shapiro step output is realized by selecting a closed channel through the relay module to generate a reference voltage. Correspondingly, the present invention also discloses a method for simulating the DC current-voltage characteristics of a series-connected Josephson junction. The DC current-voltage characteristics of the Josephson junction are realized by using the simulation circuit of the present invention, and the circuit structure is simple and easy to realize, and the research and development cost is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of measuring and testing instruments, and in particular to a direct current voltage characteristic simulation circuit and method of a series-connected Josephson junction. Background Art

[0002] The Josephson effect is a quantum effect. The Josephson junction is a superconductor quantum device designed and manufactured based on the Josephson effect. Several to tens of thousands of Josephson junctions connected in series on a chip constitute a Josephson junction array. The Josephson junction array provides accurate voltage output under appropriate DC bias conditions. Since January 1, 1990, the Josephson effect principle has been used internationally to reproduce the voltage unit of the International System of Units to ensure consistent traceability internationally. This voltage reference is used in scientific research and engineering that requires precise measurement. At present, most of the programmable Josephson voltage reference systems use the Shapiro zero-order and first-order steps in the DC voltage characteristics of the Josephson effect to generate programmable reference voltages. Because the Josephson junction is difficult to prepare, and the Josephson junction array chip must be placed in a Dewar flask, it must be filled with liquid helium and cooled to an extremely low temperature every time it works, which has high operating costs and complex operations. Colleges and other teaching institutions generally do not have the conditions to purchase and operate a real Josephson voltage reference to carry out teaching and training. Summary of the invention

[0003] In view of this, the purpose of the present invention is to provide a DC current-voltage characteristic simulation circuit and method of a series Josephson junction, and realize the DC current-voltage characteristics of the Josephson junction through the simulation circuit. The circuit structure is simple and easy to implement, and the research and development cost is reduced.

[0004] To achieve the above object, the present invention provides a DC current-voltage characteristic simulation circuit of a series Josephson junction, the system comprising a bias current input terminal, a current sampling module, a control module, a relay module, a potentiometer module and a pair of voltage output terminals, wherein:

[0005] The bias current input terminal provides an external bias current;

[0006] The current sampling module samples the bias current and converts it into a voltage signal;

[0007] The control module calculates the current value of the bias current according to the voltage signal, and calculates the output resistance of the potentiometer module based on the direct current-voltage characteristic of the Josephson junction and the current value, and controls the channel to be closed by the relay module according to the resistance, and adjusts the position of the middle tap of the potentiometer module;

[0008] The bias current flows through a closed loop formed by the current sampling module, the relay module and the potentiometer module, and the voltage output terminal outputs a reference voltage.

[0009] Preferably, the channel control output end of the control module is connected to the channel control input end of the relay module, the sliding control output end of the control module is connected to the sliding control input end of the potentiometer module, the current output end of the current sampling module is connected to the common end of the relay module, the middle tap end and the low tap end of the potentiometer module are respectively connected to the first selection end and the second selection end of the relay switch module, the current input end of the current sampling module is connected to the high end of the voltage output terminal, and the current output end of the second selection end is connected to the low end of the voltage output terminal.

[0010] Preferably, the control module comprises a microcontroller, which is a mixed signal microcontroller having a unipolar analog-to-digital converter.

[0011] Preferably, the current sampling module includes a sampling resistor, a differential amplifier and an operational amplifier, wherein:

[0012] The sampling resistor is connected to the bias current input terminal, the high end of the voltage output terminal, and the common end of the relay module;

[0013] The input end of the differential amplifier is connected to the two ends of the sampling resistor, and the output end of the differential amplifier is connected to the input end of the operational amplifier;

[0014] The output terminal of the operational amplifier is connected to the control module;

[0015] The differential amplifier includes a gain resistor;

[0016] The operational amplifier, the first resistor, the second resistor and the third resistor form an in-phase proportional amplifier circuit.

[0017] Preferably, the current sampling module further includes a reference voltage device, an in-phase adder and a voltage follower, wherein:

[0018] The output end of the operational amplifier and the output end of the reference voltage device are both connected to the input end of the in-phase adder;

[0019] The output end of the in-phase adder is connected to the input end of the voltage follower;

[0020] The output end of the voltage follower is connected to the input end of the unipolar analog-to-digital converter in the microcontroller.

[0021] Preferably, the control module includes a first calculation unit, which is used to calculate the current value I of the bias current according to the acquired voltage V through equations (1), (2) and (3):

[0022]

[0023] Wherein, Rg is the resistance value of the gain resistor of the differential amplifier, and G1 is the voltage gain factor of the differential amplifier;

[0024]

[0025] Wherein, R2 and R3 are the resistance values ​​of the second resistor and the third resistor of the in-phase proportional amplifier circuit, and G2 is the gain factor of the in-phase proportional amplifier circuit;

[0026]

[0027] Among them, G1 is the voltage gain of the differential amplifier, G2 is the gain of the in-phase proportional amplifier circuit, Rs is the sampling resistor, V R The reference voltage output by the reference voltage device.

[0028] Preferably, the control module further comprises a second calculation unit, which is used to determine different calculation strategies according to the current value I of the bias current and the interval corresponding to the current value I, and calculate the reference voltage V to be output. o :

[0029] If the current value I is within 0≤I≤I 0+ Within the range, the reference voltage V is calculated by formula (4) o :

[0030] V o =0 (4);

[0031] If the current value I is 0+ <I<I 1- Within the range, the reference voltage V is calculated by formula (5) o :

[0032]

[0033] If the current value I is 1- ≤I≤I 1+ Within the range, the reference voltage V is calculated by formula (6) o :

[0034]

[0035] Among them, I 0+ is the Shapiro zero-step boundary current, I1- and I 1+ is the first-order boundary current of the Shapiro step, f is the bias microwave source frequency, n is the number of series Josephson junctions, and the Josephson constant K J =483597.9GHz / V.

[0036] Preferably, the control module further includes a third calculation unit for calculating the current value I and the reference voltage V o Calculate the output resistance R of the potentiometer module:

[0037] When the current value I is within 0≤I≤I 0+ Within the interval, the output resistance R is 0;

[0038] When the current value I>I 0+ When , the output resistance R is calculated by combining equations (5), (6) and (7):

[0039]

[0040] Preferably, the potentiometer module includes a digital potentiometer chip and a fixed-value resistor, the middle tap end and the low-end tap end of the digital potentiometer chip are connected in parallel with the fixed-value resistor, and the use strategy of the fixed-value resistor is determined based on the number of Josephson junctions.

[0041] To achieve the above object, the present invention provides a method for simulating the direct current-voltage characteristics of a series-connected Josephson junction, the method comprising:

[0042] Sampling an external bias current and converting it into a voltage signal, and calculating the current value of the bias current;

[0043] Determining different calculation strategies according to the current value of the bias current, the set simulation parameters and the interval corresponding to the current value, and calculating the reference voltage to be output;

[0044] The output resistance of the potentiometer module is calculated according to the current value and the reference voltage, and the channel to be closed by the relay module is controlled, and the position of the middle tap of the potentiometer module is adjusted so that the voltage output terminal outputs the corresponding reference voltage.

[0045] Compared with the prior art, the present invention provides a circuit and method for simulating the direct current voltage characteristics of a series-connected Josephson junction, and the beneficial effects brought about are as follows: the present invention utilizes an analog circuit to simulate the direct current voltage characteristics of a plurality of Josephson junctions connected in series, and in particular, the analog circuit simulates the zero-order and first-order Shapiro steps and the transition between the steps, and provides a stable voltage reference; the reference voltage value output by the analog circuit changes dynamically with the real-time current value of the input, and achieves the effect of simulating the voltage characteristics of the Josephson junction array; the technical solution has a simple structure, is easy to manufacture, does not require special operating conditions, and reduces costs, and can be widely used in laboratories, and can simply replace Josephson junctions that are difficult to prepare, complex in structure, and expensive, and is particularly suitable for teaching units such as universities to carry out relevant teaching and training work on Josephson voltage references; a plurality of analog circuits can be used in combination to generate a variety of different reference voltages. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 1 is a system schematic diagram of a DC current-voltage characteristic simulation circuit of a series Josephson junction according to an embodiment of the present invention.

[0047] Figure 2 Schematic diagram of a circuit of a current sampling module according to an embodiment of the present invention.

[0048] Figure 3 Schematic diagram of a circuit of a relay module and a potentiometer module according to an embodiment of the present invention.

[0049] Figure 4 It is a flow chart of a method for simulating direct current-voltage characteristics of a series Josephson junction according to an embodiment of the present invention. DETAILED DESCRIPTION

[0050] The present invention will be described in detail below in conjunction with the specific embodiments shown in the accompanying drawings, but these embodiments do not limit the present invention. Structural, methodological, or functional changes made by ordinary technicians in the field based on these embodiments are all included in the protection scope of the present invention.

[0051] like Figure 1 In one embodiment of the present invention shown, the present invention provides a DC current-voltage characteristic simulation circuit of a series Josephson junction, the system includes a bias current input terminal 10, a current sampling module 11, a control module 12, a relay module 13, a potentiometer module 14 and a pair of voltage output terminals 15, wherein:

[0052] The bias current input terminal 10 provides an external bias current;

[0053] The current sampling module 11 samples the bias current and converts it into a voltage signal;

[0054] The control module 12 calculates the current value of the bias current according to the voltage signal, and calculates the output resistance of the potentiometer module 14 based on the direct current-voltage characteristic of the Josephson junction and the current value, and controls the channel to be closed by the relay module 13 according to the resistance, and adjusts the position of the middle tap of the potentiometer module 14;

[0055] The bias current flows through a closed loop formed by the current sampling module 10 , the relay module and the potentiometer module 14 , and the voltage output terminal 15 outputs a reference voltage.

[0056] The present invention simulates the direct current voltage characteristics of the Josephson junction through an analog circuit to generate a Josephson junction voltage reference, samples an input external bias current through the analog circuit and converts it into a voltage, calculates the voltage through a control module, obtains the resistance value of the output resistor of the potentiometer module, so that the resistance value conforms to the current-voltage characteristics of the first-order Shapiro step and the transition process of the series Josephson junction, selects a closed channel through the relay module to realize the zero-order Shapiro step output, and achieves the effect of simulating the series Josephson junction characteristics within the range of the zero-order and first-order Shapiro steps.

[0057] Specifically, Figure 1As shown, the system includes a bias current input terminal 10, a current sampling module 11, a control module 12, a relay module 13, a potentiometer module 14 and a voltage output terminal 15, the channel control output end of the control module 12 is connected to the channel control input end of the relay module 13, the sliding control output end of the control module 12 is connected to the sliding control input end of the potentiometer module 14, the current output end of the current sampling module 11 is connected to the common end of the relay module 13, the middle tap end and the low tap end of the potentiometer module 13 are respectively connected to the first selection end and the second selection end of the relay switch module 12, the current input end of the current sampling module 11 is connected to the high end of the voltage output terminal 15, and the current output end of the second selection end is connected to the low end of the voltage output terminal 15. The bias current input terminal provides an external bias current. The current sampling module samples the bias current and converts it into a voltage signal, and then processes it into an input signal suitable for the control module through amplification, translation, buffering and other links. The control module calculates the current value of the bias current according to the voltage signal, and calculates the output resistance of the potentiometer module based on the direct current voltage characteristic of the Josephson junction and the current value, and outputs a channel control signal to the relay module according to the resistance value to control which channel of the relay module is closed. The control module also outputs a sliding control signal to the potentiometer module according to the resistance value to control the position of the middle tap of the potentiometer module to adjust the output resistance of the potentiometer module to the resistance value. The relay module closes the channel to be closed according to the channel control signal, that is, switches the common end of the relay module to the first selection end or the second selection end. The bias current flows through the closed loop formed by the current sampling module, the closed channel of the relay module and the potentiometer module, and outputs a reference voltage. The control module includes a microcontroller, which is a mixed signal microcontroller with a unipolar analog-to-digital converter. In a specific embodiment of the present invention, the microcontroller selects an S9KEAZ128 chip, which has a 12-bit unipolar analog-to-digital converter.

[0058] like Figure 2In a preferred embodiment of the present invention shown, the current sampling module 11 includes a sampling resistor Rs, a differential amplifier U1 and an operational amplifier U2, the sampling resistor Rs is connected to the high end of the bias current input terminal and the voltage output terminal, and the common end of the relay module, the input end of the differential amplifier U1 is connected to the two ends of the sampling resistor Rs, the output end of the differential amplifier U1 is connected to the input end of the operational amplifier U2, and the output end of the operational amplifier U2 is connected to the control module. The sampling resistor Rs is generally selected to have a small and stable resistance value, for example, the resistance value of the sampling resistor Rs is selected to be 100mΩ. The sampling resistor samples the input bias current. The differential amplifier U1 includes a gain resistor Rg. The differential amplifier U1 can use an instrumentation amplifier chip AD620. The differential amplifier U1 converts the differential voltage on the sampling resistor into a single-ended voltage to ground, and configures the voltage gain through the resistance value of the gain resistor Rg of the differential amplifier U1. The relationship between the voltage gain G1 and the gain resistor Rg is as follows:

[0059]

[0060] The operational amplifier U2 and the first resistor R1, the second resistor R2 and the third resistor R3 form a common-phase proportional amplifier circuit. The common-phase proportional amplifier circuit amplifies the voltage signal again to make up for the insufficient amplification factor. The amplification factor G2 of the common-phase proportional amplifier circuit is calculated by formula (2);

[0061]

[0062] Since the signal obtained after bias current sampling and amplification is bipolar, and the analog-to-digital converter inside the microcontroller is a unipolar input, a reference voltage circuit is required to generate a stable DC voltage to add to the amplified voltage, thereby raising the zero point of the signal to a position close to the midpoint of the voltage input range of the analog-to-digital converter. Figure 2As shown, the current sampling module 11 also includes a reference voltage device U3, an in-phase adder U4 and a voltage follower U5. The output end of the operational amplifier U2 and the output end of the reference voltage device U3 are both connected to the input end of the in-phase adder U4, the output end of the in-phase adder U4 is connected to the input end of the voltage follower U5, and the output end of the voltage follower U5 is connected to the input end of the unipolar analog-to-digital converter in the microcontroller. Specifically, the reference voltage device U3 can use the REF3020 chip to generate a stable DC reference voltage. The in-phase adder uses the operational amplifier chip OPA277, and the voltage signal output by the operational amplifier U2 is input into the in-phase adder U4 together with the reference voltage, thereby realizing the translation of the zero point of the voltage signal. The voltage signal output by the in-phase adder U4 is input to the voltage follower U5, and the voltage signal is buffered and then input to the input end of the analog-to-digital converter of the microcontroller.

[0063] The control module calculates the current value of the bias current according to the voltage signal, and calculates the resistance value of the potentiometer module based on the DC current-voltage characteristic of the Josephson junction and the current value. Specifically, the control module includes a first calculation unit, which calculates the current value I of the bias current according to the acquired voltage V through equations (1), (2), and (3).

[0064]

[0065] Among them, G1 is the voltage gain of the differential amplifier, G2 is the gain of the in-phase proportional amplifier circuit, Rs is the sampling resistor, V R The reference voltage output by the reference voltage device.

[0066] The control module further includes a second calculation unit, which determines different calculation strategies according to the current value I of the bias current and the interval corresponding to the current value I, and calculates the output reference voltage V o :

[0067] If the current value I is within 0≤I≤I 0+ Within the range, the reference voltage V is calculated by formula (4) o :

[0068] V o =0(4);

[0069] If the current value I is 0+ <I<I 1- Within the range, the reference voltage V is calculated by formula (5) o :

[0070]

[0071] If the current value I is 1- ≤I≤I 1+ Within the range, the reference voltage V is calculated by formula (6) o :

[0072]

[0073] Among them, I 0+ is the Shapiro zero-step boundary current, I 1- and I 1+ is the first-order boundary current of the Shapiro step, f is the bias microwave source frequency, n is the number of series Josephson junctions, and the Josephson constant K J =483597.9GHz / V.

[0074] The control module further includes a third calculation unit, based on the current value I and the reference voltage V o Calculate the output resistance R of the potentiometer module:

[0075] When the current value I is within 0≤I≤I 0+ Within the interval, the output resistance R is 0;

[0076] When the current value I>I 0+ When , the output resistance R is calculated by combining equations (5), (6) and (7):

[0077]

[0078] The control module obtains the output resistance of the potentiometer module according to calculation, controls the channel to be closed by the relay module according to the resistance, and adjusts the position of the middle tap of the potentiometer module.

[0079] like Figure 3 In a specific embodiment of the present invention shown in FIG. 1 , the relay module includes a single-pole double-throw magnetic latching relay U6. In this embodiment, the two control terminals of the relay chip U6 are respectively controlled by two MOS tubes, and the base of each MOS tube is connected to the control module. The opening and closing of each MOS tube is controlled by the channel control signal output by the control module, thereby realizing the channel opening of the relay chip U6. The potentiometer module includes a digital potentiometer chip U7, and the middle tap terminal RW and the low-end tap terminal RL of the digital potentiometer chip U7 are respectively connected to the first selection terminal 3 and the second selection terminal 5 of the relay chip U6. The potentiometer module also includes a constant value resistor R o , the middle tap terminal RW and the low-end tap terminal RL and the fixed value resistor R oSpecifically, when the output resistance R of the potentiometer module is 0, the channel control signal output by the control module controls the common end of the relay chip U6 to switch to the second selection end connected to the low-end tap end RL of the digital potentiometer chip U7, which is equivalent to short-circuiting the digital potentiometer chip U7, thereby achieving an output resistance R of 0. When the output resistance R is calculated according to formula (7), the fixed resistor R is determined according to the number of Josephson junctions. o When the number of Josephson junctions is small, according to the output resistance R, a fixed resistor R with a resistance slightly larger than the R value is used. o The digital potentiometer chip U7 is connected in parallel, and the resistance value of the digital potentiometer chip U7 is adjusted to meet the resistance value R of the output resistor; when the number of Josephson junctions is large, the fixed value resistor R o Open circuit, the resistance of the digital potentiometer chip U7 is the resistance R of the output resistor.

[0080] like Figure 4 In one embodiment of the present invention, a method for simulating the direct current voltage characteristics of a series Josephson junction is provided, the method comprising:

[0081] S401, sampling an external bias current and converting it into a voltage signal, and calculating the current value of the bias current;

[0082] S402, determining different calculation strategies according to the current value of the bias current, the set simulation parameters, and the interval corresponding to the current value, and calculating the reference voltage to be output;

[0083] S403, calculating the output resistance of the potentiometer module according to the current value and the reference voltage, controlling the channel to be closed by the relay module, and adjusting the position of the middle tap of the potentiometer module so that the voltage output terminal outputs the corresponding reference voltage.

[0084] The simulation parameters of the setup include the Shapiro zero-step boundary current I 0+ , the first-step boundary current I of the Shapiro step 1- and I 1+ , bias microwave source frequency f, number of series-connected Josephson junctions n, Josephson constant K J=483597.9GHz / V. Based on the DC current-voltage characteristic simulation circuit of the above-mentioned series Josephson junction, an external bias current is sampled and converted into a voltage signal, and the current value of the bias current is calculated according to the above-mentioned formulas (1), (2), and (3). According to the interval corresponding to the current value, different calculation formulas are determined to calculate the reference voltage to be output. The output resistance of the potentiometer module is calculated according to the current value and the reference voltage, and the channel to be closed by the relay module is controlled, and the position of the middle tap of the potentiometer module is adjusted so that the voltage output terminal outputs the corresponding reference voltage. The specific implementation method is consistent with the technical solution of the above-mentioned analog circuit and will not be described in detail here.

[0085] Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims

1. A DC current-voltage characteristic simulation circuit of a series-connected Josephson junction, characterized in that: The circuit includes a bias current input terminal, a current sampling module, a control module, a relay module, a potentiometer module and a pair of voltage output terminals, wherein: The bias current input terminal provides an external bias current; The current sampling module samples the bias current and converts it into a voltage signal; The control module calculates the current value of the bias current according to the voltage signal, and calculates the output resistance of the potentiometer module based on the direct current-voltage characteristic of the Josephson junction and the current value, and controls the channel to be closed by the relay module according to the resistance, and adjusts the position of the middle tap of the potentiometer module; The bias current flows through a closed loop formed by the current sampling module, the relay module and the potentiometer module, and the voltage output terminal outputs a reference voltage.

2. The DC current-voltage characteristic simulation circuit of the series-connected Josephson junction according to claim 1, characterized in that: The channel control output end of the control module is connected to the channel control input end of the relay module, the sliding control output end of the control module is connected to the sliding control input end of the potentiometer module, the current output end of the current sampling module is connected to the common end of the relay module, the middle tap end and the low tap end of the potentiometer module are respectively connected to the first selection end and the second selection end of the relay module, the current input end of the current sampling module is connected to the high end of the voltage output terminal, and the current output end of the second selection end is connected to the low end of the voltage output terminal.

3. The DC current-voltage characteristic simulation circuit of the series-connected Josephson junction according to claim 2, characterized in that: The control module includes a microcontroller, which is a mixed signal microcontroller with a unipolar analog-to-digital converter.

4. The DC current-voltage characteristic simulation circuit of the series-connected Josephson junction according to claim 3, characterized in that: The current sampling module includes a sampling resistor, a differential amplifier and an operational amplifier, wherein the sampling resistor is connected to the high end of the bias current input terminal and the voltage output terminal and the common end of the relay module; The input end of the differential amplifier is connected to the two ends of the sampling resistor, and the output end of the differential amplifier is connected to the input end of the operational amplifier; The output terminal of the operational amplifier is connected to the control module; The differential amplifier includes a gain resistor; The operational amplifier, the first resistor, the second resistor and the third resistor form an in-phase proportional amplifier circuit.

5. The DC current-voltage characteristic simulation circuit of the series-connected Josephson junction according to claim 4, characterized in that: The current sampling module also includes a reference voltage device, an in-phase adder and a voltage follower, wherein: The output end of the operational amplifier and the output end of the reference voltage device are both connected to the input end of the in-phase adder; The output end of the in-phase adder is connected to the input end of the voltage follower; The output terminal of the voltage follower is connected to the input terminal of a unipolar analog-to-digital converter in the microcontroller.

6. The DC current-voltage characteristic simulation circuit of the series-connected Josephson junction according to claim 4, characterized in that: The control module includes a first calculation unit, which is used to calculate the current value I of the bias current according to the acquired voltage V through equations (1), (2), and (3): Wherein, Rg is the resistance value of the gain resistor of the differential amplifier, and G1 is the voltage gain factor of the differential amplifier; R2 and R3 are the resistance values ​​of the second resistor and the third resistor of the in-phase proportional amplifier circuit, and G2 is the gain factor of the in-phase proportional amplifier circuit; Among them, G1 is the voltage gain of the differential amplifier, G2 is the gain of the in-phase proportional amplifier circuit, Rs is the sampling resistor, V R The reference voltage output by the reference voltage device.

7. The DC current-voltage characteristic simulation circuit of the series-connected Josephson junctions as claimed in claim 6, characterized in that: The control module further includes a second calculation unit, which is used to determine different calculation strategies according to the interval range corresponding to the current value I of the bias current, and calculate the reference voltage V to be output. o :If the current value I is between 0≤I≤I 0+ Within the range, the reference voltage V is calculated by formula (4) o :V o =0(4); If the current value I is 0+ <I<I 1- Within the range, the reference voltage V is calculated by formula (5) o : If the current value I is 1- ≤I≤I 1+ Within the range, the reference voltage V is calculated by formula (6) o : Among them, I 0+ is the Shapiro zero-step boundary current, I 1- and I 1+ is the first-order boundary current of the Shapiro step, f is the bias microwave source frequency, n is the number of series Josephson junctions, and the Josephson constant K J =483597.9GHz / V.

8. The DC current-voltage characteristic simulation circuit of the series-connected Josephson junctions as claimed in claim 7, characterized in that: The control module further includes a third calculation unit for calculating the current value I and the reference voltage V o Calculate the output resistance R of the potentiometer module: When the current value I is within 0≤I≤I 0+ Within the interval, the output resistance R is 0; When the current value I>I 0+ When , the output resistance R is calculated by combining equations (5), (6) and (7):

9. The DC current-voltage characteristic simulation circuit of the series-connected Josephson junctions as claimed in claim 8, characterized in that: The potentiometer module comprises a digital potentiometer chip and a fixed value resistor. The middle tap end and the low end tap end of the digital potentiometer chip are connected in parallel with the fixed value resistor, and the use strategy of the fixed value resistor is determined based on the number of Josephson junctions.

10. A method for simulating a DC current-voltage characteristic simulation circuit of a series Josephson junction as claimed in any one of claims 1 to 9, characterized in that: Sampling an external bias current and converting it into a voltage signal, and calculating the current value of the bias current; Determining different calculation strategies according to the current value of the bias current, the set simulation parameters and the interval corresponding to the current value, and calculating the reference voltage to be output; The output resistance of the potentiometer module is calculated according to the current value and the reference voltage, and the channel to be closed by the relay module is controlled, and the position of the middle tap of the potentiometer module is adjusted so that the voltage output terminal outputs the corresponding reference voltage.

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