CN211603984U - Direct current voltage characteristic analog circuit of series connection Josephson junction - Google Patents
Direct current voltage characteristic analog circuit of series connection Josephson junction Download PDFInfo
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- CN211603984U CN211603984U CN202020508051.6U CN202020508051U CN211603984U CN 211603984 U CN211603984 U CN 211603984U CN 202020508051 U CN202020508051 U CN 202020508051U CN 211603984 U CN211603984 U CN 211603984U
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Abstract
The utility model discloses a direct current voltage characteristic analog circuit of series connection Josephson knot samples and converts the external bias current of input into voltage through this analog circuit, calculates this voltage through control module, obtains the resistance of the output resistance of potentiometre module for this resistance accords with the current voltage characteristic of series connection Josephson knot first-order summer pirome step and transition, through the relay module selects closed channel to realize zero order summer pirome step output, generates reference voltage. Utilize the utility model discloses an analog circuit realizes the direct current voltage characteristic of Josephson junction, and this circuit structure is simple easily realizes to research and development cost has been reduced.
Description
Technical Field
The utility model relates to a measurement test instrument technical field especially relates to a direct current voltage characteristic analog circuit of series connection Josephson knot.
Background
The josephson effect is a quantum effect. The josephson junctions are superconductor quantum devices designed and manufactured according to the josephson effect, and a plurality of josephson junctions to several tens of thousands of josephson junctions connected in series are manufactured on one chip, namely, a josephson junction array is formed. Josephson junction arrays provide accurate voltage outputs under appropriate dc bias conditions. Since 1990, 1/1, the Josephson effect principle has been used internationally to reproduce voltage units manufactured by International units to ensure consistent traceability within the international range, and the voltage reference is applied to scientific research and engineering which need to be accurately measured. At present, most programmable Josephson voltage reference systems utilize the zero order and the first order steps of the Charcot-Perot in the direct current 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, liquid helium needs to be filled for refrigeration to extremely low temperature during each work, the operation cost is high, and the operation is complex. Teaching units such as colleges and universities generally do not have the condition to purchase and operate the real josephson voltage reference so as to carry out teaching and training work.
Disclosure of Invention
In view of this, the present invention provides a dc current-voltage characteristic analog circuit of serial josephson junction, which realizes dc current-voltage characteristic of josephson junction through analog circuit, and the circuit structure is simple and easy to realize, and the research and development cost is reduced.
In order to achieve the above object, the present invention provides a DC current-voltage characteristic simulation circuit for series connection of Josephson junctions, the circuit comprises 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 inputs an externally connected bias current to the current sampling module, the current sampling module samples the bias current and converts the bias current into a voltage signal, and inputs the voltage signal to the control module, the control module receives the voltage signal and outputs a channel control signal to the relay module, and outputting a sliding control signal to the potentiometer module, wherein 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 reference voltage.
Preferably, the channel control output end of the control module is connected with the channel control input end of the relay module, the sliding control output end of the control module is connected with the sliding control input end of the potentiometer module, the current output end of the current sampling module is connected with the common end of the relay module, the middle tap end and the low tap end of the potentiometer module are respectively connected with 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 with the high end of the voltage output terminal, and the current output end of the second selection end is connected with the low end of the voltage output terminal.
Preferably, the control module comprises a microcontroller which is a mixed signal microcontroller having a single polarity analog to digital converter.
Preferably, the current sampling module comprises a sampling resistor, a differential amplifier and an operational amplifier, wherein,
the sampling resistor is connected with the high ends 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 end 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 amplifying circuit.
Preferably, the current sampling module further comprises a reference voltage, a non-inverting 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 with 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 end of the voltage follower is connected with the input end of a unipolar analog-to-digital converter in the microcontroller.
Preferably, the potentiometer module comprises a digital potentiometer chip and a fixed value resistor, and the middle tap end and the low tap end of the digital potentiometer chip are connected with the fixed value resistor in parallel.
Compared with the prior art, the utility model provides a direct current voltage characteristic analog circuit of series connection Josephson knot, the beneficial effect who brings is: the utility model discloses utilize analog circuit simulation direct current voltage characteristic after a plurality of josephson knot establish ties, especially through the transition between zero order, first order sharp-edged compass step and the step among the analog circuit simulation wherein, provide stable voltage reference, the reference voltage value of this analog circuit output is along with the real-time current value dynamic change of input, has reached the effect of simulation josephson knot array voltage characteristic; the technical scheme has the advantages of simple structure, easy manufacture, no need of special operating conditions, cost reduction, wide application in a common laboratory, simple replacement of Josephson junctions which are difficult to prepare, complex in structure and high in price, and particular suitability for teaching units such as colleges and universities to carry out relevant teaching and training work of Josephson voltage references; multiple analog circuits can be used in combination to generate a variety of different reference voltages.
Drawings
Fig. 1 is a system diagram of a dc current-voltage characteristic simulation circuit of a series josephson junction in an embodiment in accordance with the present invention.
Fig. 2 is a circuit schematic diagram of a current sampling module in an embodiment in accordance with the present invention.
Fig. 3 is a schematic circuit diagram of a relay module and a potentiometer module in one embodiment according to the present invention.
Fig. 4 is a schematic flow chart illustrating a method for simulating dc current-voltage characteristics of a series josephson junction according to an embodiment of the present invention.
Detailed Description
The present invention will be described in detail with reference to the specific embodiments shown in the drawings, but the embodiments are not limited to the present invention, and structural, methodological, or functional changes made by those skilled in the art according to the embodiments are included in the scope of the present invention.
In one embodiment of the present invention as shown in fig. 1, the present invention provides a dc current-voltage characteristic simulation circuit of a serial josephson junction, the circuit 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 the bias current input terminal 10 inputs an external bias current to the current sampling module 11, the current sampling module 11 samples the bias current to convert it into a voltage signal and inputs the voltage signal to the control module 12, the control module 12 receives the voltage signal and outputs a channel control signal to the relay module 13 and outputs a sliding control signal to the potentiometer module 14, the bias current flows through a closed loop formed by the current sampling module 11, the relay module 13 and the potentiometer module 14, the voltage output terminal 15 outputs a reference voltage.
The bias current input terminal provides an external bias current. The current sampling module samples the bias current and converts the bias current into a voltage signal. The control module calculates a current value of the bias current according to the voltage signal, calculates an output resistance value of the potentiometer module based on a direct current voltage characteristic of a Josephson junction and the current value, controls a channel to be closed by the relay module according to a channel control signal, and adjusts a position of a middle tap of the potentiometer module according to a sliding control signal. 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 reference voltage.
The utility model discloses a direct current voltage characteristic of analog circuit simulation Josephson knot generates Josephson knot voltage benchmark, samples the external bias current of input and converts into voltage through this analog circuit, calculates this voltage through control module, obtains the resistance of the output resistance of potentiometre module for this resistance accords with the current-voltage characteristic of series connection Josephson knot first-order summer pirome step and transition process, through relay module selects closed channel to realize zero order summer pirome step output, reaches the effect of simulating series connection Josephson knot characteristic in zero order and first-order summer pirome step within range.
Specifically, as shown in fig. 1, the circuit 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 with the channel control input end of the relay module 13, the slide control output of the control module 12 is connected to the slide control input of the potentiometer module 14, the current output terminal of the current sampling module 11 is connected with the common terminal of the relay module 13, the middle tap end and the low tap end of the potentiometer module 13 are respectively connected with the first selection end and the second selection end of the relay switch module 12, the current input terminal of the current sampling module 11 is connected to the high terminal of the voltage output terminal 15, the current output terminal of the second selection terminal is connected to the low side 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 the bias current into a voltage signal, and the voltage signal is processed into an input signal suitable for the control module through links such as amplification, translation and buffering. The control module calculates a current value of the bias current according to the voltage signal, calculates an output resistance value of the potentiometer module based on direct current voltage characteristics of the Josephson junction and the current value, and outputs a channel control signal to the relay module according to the resistance value so as 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 so as to control the position of a middle tap of the potentiometer module and adjust the output resistance value of the potentiometer module to be the resistance value. And the relay module closes the channel to be closed according to the channel control signal, namely, the common end of the relay module is switched to the first selection end or the second selection end. The bias current flows through a closed loop formed by the current sampling module, a closed channel of the relay module and the potentiometer module, and a reference voltage is output. The control module includes a microcontroller that is a mixed signal microcontroller having a unipolar analog-to-digital converter. In one embodiment of the present invention, the microcontroller selects the S9KEAZ128 chip, which has a 12-bit unipolar analog-to-digital converter.
In a preferred embodiment of the present invention as shown in fig. 2, the current sampling module 11 includes a sampling resistor Rs, a differential amplifier U1 and an operational amplifier U2, the sampling resistor Rs connects the high terminals of the bias current input terminal and the voltage output terminal, the common terminal of the relay module, the input terminal of the differential amplifier U1 is connected to the two terminals of the sampling resistor Rs, the output terminal of the differential amplifier U1 is connected to the input terminal of the operational amplifier U2, and the output terminal 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, for example, the resistance of the sampling resistor Rs is selected to be 100m Ω. The sampling resistor samples an input bias current. The differential amplifier U1 includes a gain resistor Rg. The differential amplifier U1 can be selected by an instrumentation amplifier chip AD 620. The differential amplifier U1 converts the differential voltage on the sampling resistor into single-ended voltage to ground, and configures voltage amplification factor through the resistance value of the gain resistor Rg of the differential amplifier U1, and the relationship between the voltage amplification factor G1 and the gain resistor Rg is formula (1);
the operational amplifier U2, the first resistor R1, the second resistor R2 and the third resistor R3 form an in-phase proportional amplifying circuit. The voltage signal is amplified again through the in-phase proportional amplifying circuit to make up for insufficient amplification factor. The amplification factor G2 of the in-phase proportional amplification circuit is calculated by a formula (2);
because the signal obtained by sampling and amplifying the bias current is bipolar, and the analog-to-digital converter in the microcontroller is unipolar input, a reference voltage circuit is needed to generate a stable direct current voltage to be added with the amplified voltage, so that the zero point of the signal is raised to a position close to the midpoint of the voltage input range of the analog-to-digital converter. As shown in fig. 2, the current sampling module 11 further includes a reference voltage device U3, a non-inverting adder U4, and a voltage follower U5, an output terminal of the operational amplifier U2 and an output terminal of the reference voltage device U3 are both connected to an input terminal of the non-inverting adder U4, an output terminal of the non-inverting adder U4 is connected to an input terminal of the voltage follower U5, and an output terminal of the voltage follower U5 is connected to an input terminal of a single-polarity analog-to-digital converter in the microcontroller. Specifically, the reference voltage U3 may employ a REF3020 chip to generate a regulated dc reference voltage. The in-phase adder adopts an operational amplifier chip OPA277, and the voltage signal output by the operational amplifier U2 and the reference voltage are input into the in-phase adder U4 together, so that the translation of the zero point of the voltage signal is realized. The voltage signal output by the in-phase adder U4 is input to the voltage follower U5, and after buffering the voltage signal, the voltage signal is input to the input terminal of the analog-to-digital converter of the microcontroller.
The control module calculates a current value of the bias current according to the voltage signal, and calculates a resistance value of the potentiometer module based on a direct current voltage characteristic of a Josephson junction and the current value. Specifically, the control module comprises a first calculating unit which calculates a current value I of the bias current according to the acquired voltage V through equations (1), (2) and (3),
wherein G1 is the voltage amplification factor of the differential amplifier, G2 is the amplification factor of the in-phase proportional amplifier circuit, Rs is the sampling resistor, VRIs the reference voltage output by the reference voltage device.
The control module further comprises a second calculation unit, the second calculation unit 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 Vo：
If the current value I is more than or equal to 0 and less than or equal to I0+Within the interval, the reference voltage V is calculated by the formula (4)o:
Vo＝0(4)；
If the current value I is at I0+＜I＜I1-Within the interval, the reference voltage V is calculated by the formula (5)o：
If the current value I is at I1-≤I≤I1+Within the interval, the reference voltage V is calculated by the formula (6)o：
Wherein, I0+Is the Charperot zero order step boundary current, I1-And I1+Is boundary current of a first step of a Charcot step, f is offset microwave source frequency, n is the number of series Josephson junctions, and the Josephson constant KJ＝ 483597.9GHz/V。
The control module also comprises a third calculation unit which is used for calculating the reference voltage V according to the current value IoCalculating the output resistance R of the potentiometer module:
when the current value I is more than or equal to 0 and less than or equal to I0+Within the interval range, the output resistance R is 0;
when the current value I > I0+Then, the output resistance R is calculated by combining equations (5), (6), and (7):
the control module obtains the output resistance value of the potentiometer module according to calculation, controls a channel to be closed of the relay module according to the resistance value, and adjusts the position of a middle tap of the potentiometer module.
In an embodiment of the present invention as shown in fig. 3, the relay module comprises a single pole double throw magnetic latching relay U6. In this embodiment, two control ends of the relay chip U6 are respectively controlled by two MOS transistors, a base of each MOS transistor is connected to the control module, and the on/off of each MOS transistor is controlled by a channel control signal output by the control module, so that the channel of the relay chip U6 is turned on. The potentiometer module comprises a digital potentiometer chip U7, and a middle tap RW and a low tap RL of the digital potentiometer chip U7 are respectively connected with a first selection end 3 and a second selection end 5 of the relay chip U6. The potentiometer module further comprises a constant value resistor RoThe middle tap end RW and the low tap end RL and the fixed value resistor RoAnd (4) connecting in parallel. In particular, when the output resistance of the potentiometer moduleWhen the value R is about 0, the channel control signal output by the control module controls the common terminal of the relay chip U6 to switch to the second selection terminal connected to the low-end tap terminal RL of the digital potentiometer chip U7, which is equivalent to short-circuiting the digital potentiometer chip U7, thereby achieving the resistance value R of the output resistor being 0. Determining a constant value resistor R according to the number of Josephson junctions when calculating an output resistance value R according to equation (7)oThe usage policy of (1). When the number of the Josephson junctions is small, according to the output resistance value R, the constant value resistor R with the resistance value slightly larger than the R value is usedoThe resistance value R of the output resistor is met by adjusting the resistance value of the digital potentiometer chip U7 in parallel with the digital potentiometer chip U7; when the number of the Josephson junctions is large, the constant value resistor R is connectedoAnd when the circuit is opened, the resistance value of the digital potentiometer chip U7 is the resistance value R of the output resistor.
In one embodiment of the present invention, as shown in fig. 4, a method for simulating dc current-voltage characteristics of a serial josephson junction is provided, the method comprising:
s401, sampling an external bias current, converting the external bias current into a voltage signal, and calculating the current value of the bias current;
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;
and S403, calculating the output resistance value of the potentiometer module according to the current value and the reference voltage, controlling a channel to be closed by the relay module, and adjusting the position of a middle tap of the potentiometer module to enable a voltage output terminal to output the corresponding reference voltage.
The set simulation parameters comprise Charpy zero-order step boundary current I0+Boundary current I of Xiapiro step1-And I1+Offset microwave source frequency f, number of series Josephson junctions n, Josephson constant KJ483597.9 GHz/V. Based on the DC current-voltage characteristic analog circuit of the serial Josephson junction, an external bias current is sampled and converted into a voltage signalThe current value of the bias current is calculated according to the above equations (1), (2), and (3). And determining different calculation formulas according to the interval corresponding to the current value, and calculating the reference voltage to be output. And calculating the output resistance value of the potentiometer module according to the current value and the reference voltage, controlling a channel to be closed by the relay module, and adjusting the position of a middle tap of the potentiometer module to enable the voltage output terminal to output the corresponding reference voltage. The specific implementation is consistent with the technical solution of the analog circuit, and will not be described herein.
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 (6)
1. A DC current-voltage characteristic simulation circuit of series Josephson junction is characterized in that, the circuit comprises 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 inputs an externally connected bias current to the current sampling module, the current sampling module samples the bias current and converts the bias current into a voltage signal, and inputs the voltage signal to the control module, the control module receives the voltage signal and outputs a channel control signal to the relay module, and outputting a sliding control signal to the potentiometer module, wherein 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 reference voltage.
2. The series josephson junction dc current-voltage characteristic simulation circuit of claim 1, wherein the channel control output of the control module is connected to the channel control input of the relay module, the slide control output of the control module is connected to the slide control input of the potentiometer module, the current output of the current sampling module is connected to the common terminal of the relay module, the middle tap terminal and the low tap terminal of the potentiometer module are connected to the first selection terminal and the second selection terminal of the relay switch module, respectively, the current input of the current sampling module is connected to the high terminal of the voltage output terminal, and the current output of the second selection terminal is connected to the low terminal of the voltage output terminal.
3. The series josephson junction dc current-voltage characteristic analog circuit of claim 2, wherein the control module comprises a microcontroller that is a mixed signal microcontroller having a single polarity analog-to-digital converter.
4. The series josephson junction dc current-voltage characteristic simulation circuit of claim 3, wherein the current sampling module comprises a sampling resistor, a differential amplifier and an operational amplifier, wherein the sampling resistor connects the high ends of the bias current input terminal and voltage output terminal, 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 end 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 amplifying circuit.
5. The series Josephson junction DC current-voltage characteristic simulation circuit of claim 4, wherein the current sampling module further comprises a reference voltage, a non-inverting summer, and a voltage follower, wherein,
the output end of the operational amplifier and the output end of the reference voltage device are both connected with 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 end of the voltage follower is connected with the input end of a unipolar analog-to-digital converter in the microcontroller.
6. The analog circuit of direct current to voltage characteristics of a series josephson junction of claim 5, wherein the potentiometer module comprises a digital potentiometer chip and a fixed resistor, the middle and low tap ends of the digital potentiometer chip being connected in parallel with the fixed resistor.
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