# US 4,400,631 A · High current gain Josephson junction circuit

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- Number: US 4,400,631 A
- Document ID: US4400631A
- Status: Granted
- Kind: A
- Application number: 06/233,949
- Filed: 1981-02-12
- Granted: 1983-08-23
- Earliest claimed: 1981-02-12
- Assignees: Bell Telephone Laboratories, Incorporated
- Inventors: Theodore A. Fulton
- Web page: https://patentgrep.com/patent/US4400631A

## CPC

- H03K 17/92: by the use, as active elements, of superconductive devices
- H03K 19/1952: {with electro-magnetic coupling of the control current}
- Y10S 505/861: with josephson junction
- H03K: PULSE TECHNIQUE (measuring pulse characteristics G01R; modulating sinusoidal oscillations with pulses H03C; transmission of digital information H04L; discriminator circuits detecting phase difference between two signals by counting or integrating cycles of oscillation H03D3/04; automatic control, starting, synchronisation or stabilisation of generators of electronic oscillations or pulses where the type of generator is irrelevant or unspecified H03L; coding, decoding or code conversion, in general H03M)
- Y10S: TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS

## Abstract

A superconductive circuit is described for diverting bias current to an output line in response to magnetic field control means. A first plurality of branches containing magnetically switchable Josephson junction gates are connected in parallel, and a second plurality of the same gates, less than or equal in number to the first plurality, are actuated essentially simultaneously by the control means. As a consequence, high-gain, high-speed operation is made possible.

## Claims

### Claim 1

A high current gain superconductive circuit for diverting bias current from a shunt branch to an output branch comprising:
a plurality n of Josephson junction gates connected in said shunt branch in parallel with each other, each of said gates capable of being switched from a low impedance state to a high impedance state by the application thereto of a magnetic field which depresses the critical current of said gates below the bias current flowing therethrough, each of said gates also being individually capable of diverting said bias current to said output branch when switched to said high impedance state,
electrode means for causing bias current to flow through said gates at a level below said critical currents, and
control means comprising a single control signal source coupled to a single control line for applying said magnetic field essentially simultaneously and directly to a second plurality k of said gates, where 2.ltoreq.k.ltoreq.n, thereby diverting said bias current to said output branch.

### Claim 2 (depends on 1)

The circuit of claim 1 wherein said control means applies said magnetic field essentially simultaneously to all of said gates (k=n).

### Claim 3 (depends on 1)

The circuit of claim 1 for controlling a second circuit by means of the current flowing in said output branch wherein each of said gates itself has insufficient current gain to control said second circuit.

### Claim 4

A high current gain superconductive circuit for diverting bias current from a shunt branch to an output branch comprising:
a plurality n of Josephson junction gates connected in said shunt branch in parallel with each other, each of said gates capable of being switched from a low impedance state to a high impedance state by the application thereto of a magnetic field which depresses the critical current of said gates below the bias current flowing therethrough, each of said gates also being individually capable of diverting said bias current to said output branch when switched to said high impedance state,
electrode means for causing bias current to flow through said gates at a level below said critical currents,
each of said gates being essentially identical to one another and further including a resistor connected in series with each of said gates so that each of said gates carries essentially the same amount of bias current, and
control means comprising a single control signal source coupled to a single control line for applying said magnetic field essentially simultaneously and directly to a second plurality k of said gates, where 2.ltoreq.k.ltoreq.n, thereby diverting said bias current to said output branch.