JPH0429408A - Superconductive threshold value logical circuit - Google Patents

Abstract

PURPOSE:To realize a computer which performs fast and multifunctional learning and with superior recognizing and judging function by using a current switching tape logical circuit, and changing the current value of a bias current to be supplied to a Josephson device as a means to change weight. CONSTITUTION:The bias current is supplied from a variable current source 2 to a superconductive loop 6 forming the close circuit of a magnetic flux coupling type Josephson device 1 and an inductance 3. In the magnetic flux coupling type Josephson device, the maximum superconductive current of the Josephson device is controlled by digital input signals supplied from terminals 5, 5'. The parameter of a circuit is changed by the change of the outside status, and circuit structure and configuration can be changed on the whole. Such process itself is equivalent to the learning. To attain the above purpose, the variable power source 2 is used to change the bias current Ib, and the variable power source 2 is formed in structure controlled by an applied bias control signal via a terminal 4.

Description

Detailed Description of the Invention (Field of Application of the Invention) The present invention relates to a superconducting circuit, particularly a so-called current switching type superconducting logic circuit that supplies a bias current to a superconducting loop and switches the current within the superconducting loop. It is concerned with the circuit configuration of threshold logic circuits using .

(Background of the Invention) Conventional computers are configured with a logic circuit system combining AND or OR circuits. It is a well-known fact that these computers operate at extremely high speeds, exhibit performance that far exceeds human computing ability, and contribute to society. However, it has become increasingly clear that conventional computers are unsuitable for the recognition and judgment operations that humans perform on a daily basis. For this reason, for the purpose of constructing a computer suitable for recognition and judgment, threshold logic circuits modeled after human brain cells (neurons) and computer system technology using them have been developed, for example, by Toshi Seri. "Mathematics of Circuit Networks" Sangyo Tosho, 1978, L, D, Jacklel + R.

E., Howard, H.P., Graf, B.
Straughn+ and J.

D, Denker+ “Artificial n
ural networks for compute
ing Journal of Vacur+a+ S
ocietyTechnogV 84(1), J
an/Feb, 1986.1) 9.61-63.

The operation of the threshold logic circuit will be explained below to clarify the positioning of the present invention. FIG. 22 is a diagram showing the operation of the threshold logic circuit. The threshold logic circuit 650 is a circuit that has a plurality of input terminals 600, an input line 610, and one output line 620. Alternatively, if a digital signal Xi of "1" is applied and the weighted addition fee ΣW i X i of the digital signal Xi exceeds the threshold T, the output is "1".
”, otherwise it performs a logical operation that becomes “0”.

Here, Wi represents weight. A feature of threshold logic circuits is their learning function. That is, the weight Wi is changed through learning, and a circuit system adapted to the purpose is finally constructed. Therefore, in order to configure a threshold logic circuit, it is necessary to have not only a function of performing weighted addition of input signals and switching elements, but also a function of changing the weight Wi. Normally, this weight is controlled by a weight control signal input from a control terminal 630.

In the conventional technology, for this purpose, a threshold logic circuit model is configured in software on a computer, and multiplication and addition operations are performed by software as part of the computer's operations, or by using a dedicated multiplier as hardware. It adopted a complex circuit format. These conventional threshold logic circuits have the following drawbacks. That is, circuit representation using software has a slow calculation speed, and a circuit using multipliers has a large number of circuits, resulting in a large scale circuit system. As is clear from the example of brain cells, when a computer is constructed from threshold logic circuits, the more circuits there are, the more functions can be achieved, and the higher the accuracy.

Furthermore, the calculation accuracy of each circuit does not necessarily need to be high. Therefore, the threshold logic circuit must be of simple construction and capable of increasing the degree of integration. Furthermore, in order to perform learning, recognition, and judgment at high speed, the threshold logic circuit itself must be constructed from a high-speed switching circuit.

Josephson elements operate at high speed with low power consumption, so
Excellent as a computer element. Therefore, if a threshold logic circuit using Josephson elements is employed, computer performance will be dramatically improved. Conventionally, threshold logic circuit technology using this Josephson element has been developed by, for example, Harada, Hatano, Sanno,
Kawabe, “Josephson Threshold Logic Circuits and Applications,” Journal of the Institute of Electronics and Communication Engineers, vol. J70-C, no. 6.
pp, 912-919 and Y, latano,
Y, t(arada, Y, Yamashita,
Y, Tarutaniand U, Kawabe
”A 4-bitx4-bit Multiplier
and3-bit Counter in Jos
ephson Threshold Logic'.

IEEE Journal of 5olid-3ta
te C1rcuits, vol.

5C-22, no-4, August 1987. However, in the threshold logic circuit according to the prior art, the weight Wi shown in FIG. 22 is fixed and no learning function is provided.

(Objective of the Invention) The object of the present invention is to provide a threshold logic circuit in which weights can be arbitrarily changed using a switching circuit using a high-speed Josephson element, and to provide a high-speed and multifunctional switching circuit using a threshold logic circuit. The objective is to realize a computer with excellent recognition and judgment functions that can perform learning.

(Summary of the Invention) For this purpose, the present invention uses a current-switching carved logic circuit with excellent high-speed performance and low power consumption performance as a switching circuit using a Josephson element, and uses the Josephson element as a means for changing weights. A method is adopted in which the current value of the bias current supplied to the SON element is changed.

(Example of the invention) The present invention will be explained below using Examples.

FIG. 2 shows an example of the input weight addition circuit 50 used in the first embodiment of the present invention. In the example shown in FIG. 2, a bias current Ib is supplied from a variable current source 2 to a superconducting loop 6 in which a flux-coupled Josephson element 1 and an inductance 3 form a closed circuit. In the flux-coupled Josephson element, terminal 5.5
The maximum superconducting current of the Josephson element is controlled by a digital input signal supplied from '. Further, in the variable current source 2, the bias current value supplied to the superconducting loop 6 is controlled by a bias control signal (corresponding to a weight control signal) applied via a terminal 4.

In this circuit, the value of inductance 3 is generally set larger than the equivalent inductance of the Josephson element. 1.
flows through the magnetic flux-coupled Josephson element 1. In this state, when a digital input signal current is passed through the terminal 5.5', the maximum superconducting current of the flux-coupled Josephson element becomes small, and the flux-coupled Josephson element temporarily enters a voltage state. Switch the bias current ■.

flows into inductance 3. This operation corresponds to a current switching operation that switches the bias current Ib supplied from the variable current source 2 from the flux-coupled Josephson element 1 to the inductance 3.

The switching operation of the Josephson element described above is a technique that has already been disclosed, and for example, T, R, Ghe
ewala, “Josephson-Logic
DevicesandC1rcuit'', IEEE
Trans, Electron Devices+
vol1. HD-27, no, 10. pP, 18
It is described in detail in 574869. In the prior art disclosed in these publications, the bias current supplied to the Josephson element is 1. is a fixed value, and the circuit structure and configuration do not change. On the other hand, in the present invention, the bias current
, is variable and is characterized by being controlled from the outside.

That is, depending on changes in external conditions, circuit parameters can be changed, and from a broader perspective, the circuit structure and configuration can be changed. This process itself corresponds to the learning described above. For this purpose, in the circuit shown in FIG. It is a structure controlled by With this structure, if the digital input signal Xi is "0", the output current I flows through the inductance 3. at is zero, and if the digital input signal Xi is "1", a bias current I flows through the inductance 3 as an output current Iout. Therefore, the output current 1 out flowing through the inductance 3 is (
1) It is expressed by the formula.

I out−1bχi, Xi= (1, O)
(1) Here, changing the bias current 5 corresponds to changing the weight Wi of the threshold logic circuit (
1) It is clear from equation. Therefore, in the circuit shown in FIG. 2, the circuit itself can have a new function called learning. FIG. 3 is an improved example of the circuit of FIG. 2. In this circuit, a superconducting loop 6 includes the flux-coupled Josephson element 1, an inductance 3, a superconducting wire 7, and its feedback current wire 7'.
It consists of In the configuration shown in FIG. 3, the superconducting wiring 7
can be used to transmit the output signal of a circuit over a long distance. It is clear that in the circuit of FIG. 3, the function of the feedback current line 7' can be realized using a ground plane.

In this case, the feedback current wiring 7' does not necessarily need to have the shape of a wiring. Furthermore, since the superconducting wiring 7 itself has a function as an inductance, it is clear that the inductance 3 does not necessarily need to be shaped as a coil in order to realize the circuit function shown in FIG.

FIG. 4 shows a first method of configuring the variable current source 2. In FIG.

In the circuit configuration of FIG. 4, the variable current source 2 is replaced by the variable voltage source 20.
1 and a fixed resistor 202. With this circuit configuration,
By changing the voltage of the variable current source 201, the bias current can be changed. FIG. 5 shows a second method of configuring the variable current source 2. In FIG. In the configuration example shown in FIG. 5, the variable current source 2 includes a voltage source 211 and a variable resistor 212. With this circuit configuration, the bias current I can be changed by changing the resistance value of the variable resistor 212. FIG. 6 shows a third method of configuring the variable current source 2. In FIG. In the configuration example shown in FIG. 6, the variable current source 2 is the voltage source 22.
1. Resistor 222.223. Consists of one or more magnetic flux coupling Josephson elements 225 and a resistor 226 connected in series. A control signal (current) is applied to the Josephson element 225 through terminals 227 and 227' according to the learning conditions, causing the Josephson element 225 to transition from the superconducting state to the voltage state. In this circuit configuration, the voltage source 221
A current flowing from a current source composed of a resistor 222 and a resistor 222 is shunted to a series connection of a resistor 223, a Josephson element 225, and a resistor 226. It is clear that the current flowing through the resistor 223 becomes the bias current (2) of the superconducting loop 6. here,
If Josephson element 225 is placed in a voltage state to prevent current from flowing through a certain branch of Josephson element 225, that current will flow into resistor 223. Therefore, terminal 2
The bias current 1 can be changed by a control signal applied through 27 and 227'. In the circuit example of FIG. 6, a magnetic flux coupling type Josephson element is used as the Josephson element 225, but a so-called current injection type Josephson element is also used, which directly injects current into the Josephson element to transition the element to a voltage state. It is clear that the same functionality can be achieved using . FIG. 7 shows a fourth method of configuring the variable current source 2. In FIG. In the configuration example shown in FIG. 7, the variable current source 2 is composed of a superconducting transformer 231. The first winding of the superconducting transformer 231 is connected to the terminals 232, 232' and the second winding is connected to the superconducting loop 6. In this circuit configuration, if the mutual self-inductance of the superconducting transformer 231 is Mb, the self-inductance of the second winding is Lb, and the bias control current flowing to the second winding via the terminals 232 and 232' is 11. , the bias current supplied to the superconducting loop {circle over (2)} is expressed by equation (2).

1,=Mb-1,/Lb (2) From equation (2), the bias control current 1. The bias current ■ is controlled by

The circuit shown in Figure 2 has a bias current in the superconducting loop 6,
The circuit configuration is such that the bias current can be supplied as a superconducting circulating current. FIG. 8 shows this embodiment. In the circuit configuration shown in FIG. 8, the bias current source circuit includes a variable current source 2, a Josephson element 242, and an inductance 241. Variable current source 2 is controlled by a bias control signal supplied from terminal 4.

Furthermore, the Josephson element 242 has terminals 243 and 243'.
is controlled by a write signal applied via the . In this circuit configuration, the value of the inductance 241 is larger than the equivalent inductance of the Josephson element 242, so the bias current 1b supplied from the variable current source 2 flows to the Josephson element 242 in the initial operating state of the circuit.

Next, when a write signal is applied via terminals 243 and 243', the Josephson element 242 transitions to a voltage state, and the bias current I, supplied by the variable current source 2, passes through the inductance 241 to It is fed into a conducting loop 6 and returns to the variable current source 2. Next, when the current supplied from the variable current source 2 is cut off, the bias current (5) flowing through the superconducting loop 6 flows through the Josephson element 242 and the inductance 241. Therefore, in this state, the bias current Ib circulates as a superconducting current through a closed loop composed of the inductance 241, the superconducting loop 6, and the Josephson element 242. Here, the bias current ■
Since ゎ is the current initially supplied from the variable current source 2, the bias current I supplied to the superconducting loop 6 can be changed by changing the flow supplied from the variable current source. Furthermore, with the circuit configuration shown in FIG. 8, a plurality of signal weight addition circuits 50 can be driven by one variable current source 2, and the overall circuit scale can be reduced.

FIG. 1 is a first embodiment 500 of a superconducting threshold logic circuit according to the present invention. In the embodiment shown in FIG. 1, a plurality of input weight addition circuits 50 shown in FIG. The configuration is such that the signal is input to a type Josephson element 8. A bias current 11+r is supplied to the flux-coupled Josephson element 8 from a current source 9. Furthermore, a threshold current signal is input to the flux-coupled Josephson element 8 via a terminal 13. This threshold signal determines the signal level at which the flux-coupled Josephson element becomes in a voltage state. That is, the magnetic flux generated by the signal current transmitted via the plurality of superconducting wires 7 and the threshold current input via the terminal 13 interlinks with the flux-coupled Josephson element 8. When the magnetic flux exceeds a certain value, the flux-coupled Josephson element transitions from a superconducting state to a voltage state. The signal of the flux-coupled Josephson element is detected via the terminal 10. From the circuit operation explained above, the magnetic flux interlinking with the flux-coupled Josephson element 8 is determined by the addition of the output signal of each input weight addition circuit and the threshold signal.
It is clear that the magnetic flux coupling type Josephson element 8 performs an operation of discriminating it into a "1" or "0" signal at a constant signal level. It is therefore clear that the embodiment shown in FIG. 1 implements the circuit operation of FIG. 22.

FIG. 9 shows an embodiment 500' that is an improved version of the embodiment shown in FIG.
It is. In the embodiment shown in FIG. 1, the plurality of superconducting wires 7 are input in parallel to the flux-coupled type Josephson element 8, but in the embodiment shown in FIG. This structure is grounded via the input line 12 of the Josephson element.

With this method, the number of input lines of the flux-coupled Josephson element can be reduced, and the circuit structure can be simplified.

FIG. 10 shows an embodiment of a multi-output threshold logic network constructed using a plurality of superconducting threshold circuits 500' shown in FIG. 9. In this network, a digital input signal is commonly applied to each superconducting threshold logic circuit, and multiple output patterns can be created depending on the input signal conditions.

In the first embodiment of the present invention shown in FIG. 1, the superconducting loop 6 was composed of one flux-coupled Josephson element 1 and an inductance 3. Therefore, in order to return the bias current flowing through the inductance 3 to the flux-coupled Josephson element after completing the logic operation, the variable current source 2 must be temporarily shut off and the bias current set again. It requires operations and is complicated. However, if functions are added to the circuit shown in FIG. 2, a circuit that does not require this complicated operation can be realized. FIG. 11 shows an example of 100 input weight adding circuits used in the second embodiment of the present invention.

In the circuit shown in FIG. 11, a bias current 1 is supplied from a variable current source 2 to a superconducting loop 60 in which first and second flux-coupled Josephson elements 21, 22 and inductances 23, 24 are arranged in a closed loop. It is. A digital input signal is applied to the first flux-coupled Josephson element 21 via terminals 25, 25'. This digital input signal controls the maximum superconducting current of the flux-coupled Josephson element, which is similar to the circuit operation shown in FIG. 2. Also the second
The flux-coupled Josephson element 22 has terminals 26 and 26.
A reset current is applied through .

The reset current similarly controls the maximum superconducting current of the flux-coupled Josephson element 2. In this circuit, inductance 23 serves as a circuit load and corresponds to inductance 3 in FIG. Inductance 24 is a general term for parasitic inductance, etc., and its capacitance is generally small and is not necessarily required for circuit operation. The circuit operation will be explained below. At the initial stage of operation, the digital input signal and reset signal are suppressed, and the bias current 1. is applied to the superconducting loop 60. At this time, the sum of the equivalent inductances of the inductance 23 and the second flux-coupled Josephson element 22 is the sum of the equivalent inductance of the inductance 24 and the first flux-coupled Josephson element 2.
Since the bias current I is greater than the sum of the equivalent inductances of 1.

flows through the first flux-coupled Josephson element 21.

Next, when a digital input signal is applied via the terminals 25, 25', the flux-coupled Josephson element 21 transitions to a voltage state, and the bias current 1b is transferred to the second flux-coupled Josephson element 22, the inductance 23 flows through. The operation up to this point is similar to the operation of the input weight addition circuit 50 shown in FIG. Next, when the logic operation is completed and the digital human input signal is removed, the path through which the bias current Ib flows remains unchanged and flows through the second flux-coupled Josephson element 22. Therefore, in order to enable the next logical operation, a reset signal current is applied from the terminals 26 and 26', and the second
flux-coupled Josephson element 22 to a voltage state and returns the bias current I to the first flux-coupled Josephson element. It is clear that this state allows the following logical operation. From the above circuit operation, it is sufficient that the variable current source 2 always supplies current to the superconducting loop as quasi-direct current,
Unlike the input weight adding circuit 50 shown in FIG. 2, there is no need to cut off the variable current source 2 every time a logic operation is completed. 1st
In the embodiment shown in FIG. 1, by changing the bias current Ib supplied from the variable current source 2, the current output to the inductance 23 can be changed. This corresponds to changing the weight Wi in equation (1). FIG. 12 is an improved example of FIG. 11, and is an example of a circuit using superconducting wiring 7, 7' to transmit signals over long distances. FIG. 13 is an example of a circuit that automatically performs a reset operation. In the embodiment shown in FIG. 13, the first and second flux-coupled Josephson elements 21
．． 22 through terminals 25, 25', and the second flux-coupled Josephson element 22.
is an offset current I supplied from a constant current source 31. f
This is a configuration in which f is applied. Here, the offset current applied to the flux-coupled Josephson element 22 is set so that the flow direction is opposite to the current in the case of the digital input signal "1" and the current value is the same, so the offset current is The magnetic flux generated by the current and the digital input signal current cancel each other out. In the embodiment of FIG. 13, when no input signal is applied, an offset current I flows through the second flux-coupled Josephson element 22. Since the magnetic fluxes generated by f are interlinked, the bias current I flows through the first flux-coupled Josephson element. Logical operations are now possible. Next, when the digital input signal "1" is applied, the magnetic flux interlinks with the first flux-coupled Josephson element, and the magnetic flux interlinks with the second flux-coupled Josephson element 22 becomes zero. Therefore, the bias current flows through the inductance 23 via the second magnetic flux coupling type Josephson element 22. Then, when the digital input signal is removed, the bias current I,
flows into the first flux-coupled Josephson element 21, and the next logical operation becomes possible. From the above, it is clear that the embodiment shown in FIG. 13 automatically performs the reset operation.

Variable current source 2 of input weight addition circuit 100 shown in FIG.
can adopt a configuration similar to that of the variable current source shown in the input weight adding circuit 50 of FIG. Figure 14, Figure 15, Figure 16
17 and 18 show a method of configuring the variable current source 2 of the input weight addition circuit 100. Each corresponds to the configuration method of the variable current source shown in FIG. 4, FIG. 5, FIG. 6, FIG. 7, and FIG. 8.

FIG. 19 shows the second superconducting threshold logic circuit according to the present invention.
This is Example 510. The embodiment shown in FIG. 19 uses a plurality of input weight addition circuits 100 shown in FIG. Coupled Josephson element 8
A superconducting threshold logic circuit 510 inputs to the superconducting threshold logic circuit 510. This circuit configuration is similar to that of the embodiment shown in FIG.

FIG. 20 shows the superconducting threshold logic circuit 51 shown in FIG. 19.
This is an example of a multi-output threshold logic circuit network configured using a plurality of 0's. In this network, a digital input signal is commonly applied to each superconducting threshold logic circuit, and multiple output patterns can be created depending on the input signal conditions.

In the input weight addition circuits shown in Figs. 2 and 11, the case where there is one digital input signal was taken up, but it is possible to input multiple input lines of the flux-coupled Josephson element to which each digital input signal is applied. It is clear that it can be used as a signal circuit. Furthermore, as shown in FIG. 21, a plurality of flux-coupled Josephson elements 31, 32 are arranged in the superconducting loop as input elements, and terminals 33, 33' 34 are connected to the plurality of flux-coupled Josephson elements. It is clear that a multi-input weighted addition circuit can be constructed by applying a plurality of digital input signals via .34'.

(Effects of the Present Invention) As described above, by using the present invention, a threshold logic circuit having a learning function can be constructed using a high-speed Josephson switching circuit. Therefore, according to the present invention, it is possible to realize a high-speed computer suitable for executing recognition judgment using a threshold logic circuit. Therefore, the present invention is indispensable for realizing a high-speed computer that performs this sophisticated recognition judgment.

[Brief explanation of the drawing]

FIG. 1 shows a first embodiment of a superconducting threshold logic circuit according to the present invention, and FIG. 2 shows the basic structure of a weight addition circuit used in the first embodiment of the superconducting threshold logic circuit. Figure 3 shows an improved example of Figure 2, Figures 4, 5, and 6.
7 and 8 are diagrams each showing a configuration example of the variable current source of the input weight addition circuit, and FIG. 9 is a diagram showing a modification of the first embodiment of the superconducting threshold logic circuit. Figure 10 is the first
Figure 11 shows the basics of the weight addition circuit used in the second embodiment of the superconducting threshold logic circuit. Figures 12 and 13 are diagrams showing the structure of Figure 11, respectively, and Figures 14, 15, 16, 17, and 18 are diagrams of the input weight addition circuit. FIG. 19 is a diagram showing a configuration example of a variable current source, FIG. 19 is a diagram showing a second embodiment of the superconducting threshold logic circuit according to the present invention, and FIG. 20 is a diagram showing a second embodiment of the superconducting threshold logic circuit according to the present invention. FIG. 21 is a diagram showing a configuration example of a multi-output threshold logic circuit network, FIG. 21 is a diagram showing a configuration example of a multi-manual weight addition circuit, and FIG. 22 is a diagram showing the principle operation of the threshold logic circuit. 1...Flux-coupled Josephson element, 2...Variable current source, 3...Inductance, 4,5°5'...
Terminal, 6... Superconducting loop, 7... Superconducting wiring, 7
'...Feedback current wiring, 8...Flux-coupled Josephson element, 9...constant current source, 10...terminal, 12...
...Input line, 13...Terminal, 21.22...Flux-coupled Josephson element, 23.24...Inductance, 25.25', 26.26'...Terminal, 31
...Constant current source, 60...Superconducting loop, 50°10
0... Input weight addition circuit, 201... Variable current source,
202...Resistor, 211... Constant voltage source, 212...
・Variable resistance, 221...constant voltage source, 222, 223・
...Resistance, 225...Flux-coupled Josephson element,
226...Resistance, 227, 227'...Terminal,
230...Closed loop, 231...Superconducting transformer,
232゜232'...terminal, 241...inductance, 242...Josephson element, 243゜24
3'...terminal, 500,500' 510...
Superconducting threshold logic circuit, 600...input terminal, 61
0...Input line, 620...Output line, 630...Control terminal, 650...Threshold logic circuit. Figure 1 Figure 2 Figure 4 Figure 3 Figure 9 Figure 5 f Figure 6 Figure 7 Figure 11 Figure 12 Figure 13 Figure 14 Figure 15 Figure 16 Figure 17 Figure 19 Figure 21 Figure 22

Claims (1)

[Claims] 1. A structure in which a bias current is supplied from a current source to a superconducting closed circuit consisting of at least one Josephson element and an inductance, and means for applying an input signal to the Josephson element. and has a function of switching the flow of the bias current in the Josephson element according to the input signal, and the current source includes at least one superconducting current switching circuit having a function of changing the bias current, The superconducting current switching circuit is composed of another Josephson circuit that receives the current of the superconducting closed circuit as an input,
A superconducting threshold logic circuit characterized in that the Josephson circuit is switched by the current of the superconducting closed circuit. 2. The superconducting threshold logic circuit according to claim 1, characterized in that the superconducting closed circuit of the superconducting current switching circuit includes superconducting wiring. . 3. The superconducting threshold logic circuit according to claim 2, wherein the superconducting closed circuit of the superconducting current switching circuit includes a branch including at least one Josephson element and a Josephson element. 1. A superconducting threshold logic circuit comprising two branches connected in parallel, the bias current being supplied to a connection point between the two branches. 4. The superconducting threshold logic circuit according to claim 2, wherein the superconducting closed circuit of the superconducting current switching circuit includes a first branch including at least one Josephson element and at least one 1. A superconducting threshold logic circuit comprising a second branch connected in parallel including at least one Josephson element, the bias current being supplied to a connection point between the two branches. 5. The superconducting threshold logic circuit according to claim 4, wherein an input signal is applied to the Josephson element in the first branch, and a reset signal is applied to the Josephson element in the second branch. A superconducting threshold logic circuit characterized by: 6. The superconducting threshold logic circuit according to claim 4, wherein an input signal is applied to the Josephson elements of the first branch and the second branch, and further includes a Josephson element of the second branch. A superconducting threshold logic circuit characterized in that a constant current is applied to the element, and the magnetic flux generated by the constant current cancels the magnetic flux generated by the input signal current. 7. The superconducting threshold logic circuit according to claim 2, wherein the current source is comprised of a variable voltage source and a resistor. 8. The superconducting threshold logic circuit according to claim 2, wherein the current source of the superconducting current switching circuit is comprised of a variable resistor and a voltage source. 9. The superconducting threshold logic circuit according to claim 2, characterized in that the current source of the superconducting current switching circuit has a current shunting circuit made of a Josephson element connected in parallel to the current source. superconducting threshold logic circuit. 10. The superconducting threshold logic circuit according to claim 2, wherein the current source of the superconducting current switching circuit is composed of a superconducting transformer and superconducting wiring, and one winding of the superconducting transformer A superconducting threshold logic circuit characterized in that the bias current is induced by a current flowing through a line. 11. The superconducting threshold logic circuit according to claim 2, in which the current source of the superconducting wiring comprises one or more Josephson elements and the superconducting closed circuit forming a second superconducting closed circuit. , the second superconducting closed circuit is supplied with current from a variable current source, and the circulating current flowing through the second superconducting closed circuit is a bias current of the superconducting current switching circuit. A superconducting threshold logic circuit characterized by: 12. The superconducting threshold logic circuit according to claim 2, wherein the other Josephson circuit is provided with means for applying a signal current in addition to the signal current from the superconducting switching circuit. A superconducting threshold logic circuit characterized by: 13. The superconducting threshold logic circuit according to claim 2, characterized in that superconducting wires of a plurality of superconducting current switching circuits are connected to fewer input lines of other Josephson circuits. superconducting threshold logic circuit. 14. A plurality of superconducting threshold logic circuits according to claim 2 are arranged, an input signal is used as a common input of the plurality of superconducting threshold logic circuits, and a plurality of output signals are outputted. superconducting threshold logic circuit.