JPS58130624A - Josephson circuit - Google Patents

Abstract

PURPOSE:To ensure a normal operation with a simple constitution attained at a supply part of a power supply current, by generating an AC current at a temperature of liquid helium like a circuit to be driven. CONSTITUTION:A figure 25 shows an external constant current source, and 21-24 are Josephson circuits for generation of AC currents. A series circuit of Josephson junction is shown by 21 and is switched to a constant voltage state with the signal of an input line 22. The currents of a power supply 25 flow all to the junction 21 at first. When a logical gate operation is carried out, an input signal is first applied to the line 22 and the junction 21 is switched to a voltage state. The current branched by resistances 11- 19 flow to logical gates 1-9. The currents of circuits 23 and 24 are set substantially at 0 in about 200ps after the switching of the junction 21 owing to a large inductance 23. The logical gate works in a time band when the current division quantity is small. The supply currents are concentrated to the circuit 23 and 24 after an operation is over. In this case, the current of the junction 21 is substantially set at 0 to be reset to a zero voltage state of a junction 21 which is in a switch state. As a result, all currents given from the power supply 25 flow to the junction 21 to regenerate an initial state. That is, a current can be supplied stably to an AC current driving type Josephson circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a Josephson circuit characterized by a current supply portion, and particularly to a circuit system suitable for operation of an alternating current driven Josephson logic circuit.

The Josephson circuit, which operates stably even in current quantities, is of the alternating current drive type. In this Josephson circuit, the circuit goes from a zero voltage state to a voltage state.

Logic operations are performed by being checked. Next, it is necessary to prepare for the next logic operation by lowering the supply current to near zero to return to the original zero voltage state and release the latch. Therefore, normal operation is impossible if a constant DC current is supplied, and an AC power source whose current value periodically becomes zero is used.

Traditionally, this alternating current was generated at room temperature and fed into a Josephson circuit in liquid helium (J, Matiaoo: IBM J.).

RgS DEVELOP, 24, March 19
80).

However, in this method, +1) 200-500M
High-precision transmission wiring is required to efficiently supply Hz high-frequency alternating current to the Jisefson circuit. (2)
(It is difficult to supply phase-aligned current to the Josephson circuit of the faith) Which drawback was it?

Therefore, the present invention is characterized in that it provides a power supply current supplying circuit which has a simple structure and which can operate normally.

In the present invention, while externally supplying the smudge current with a DC current, the Josephnon logic circuit, which is driven by an alternating current and requires release of the latch due to interruption of the smear flow, is operated normally. For this purpose, a circuit (hereinafter referred to as an AC power generation circuit) that periodically makes the current flowing through the logic circuit zero is provided on the driven circuit side. That is, the present invention eliminates the above-mentioned drawbacks by generating alternating current at the liquid helium temperature like the driven circuit. The Josephson circuit for generating alternating current may be provided on the same chip as the driven circuit, or may be provided on a separate chip.

An embodiment of the present invention will be described below with reference to the drawings. Numbers 1 to 9 in the figure are nine Josephson logic gates. Each logic gate consists of two 5μm junctions.
It is a QUID gate. The gate load is 7Ω.

The 5QUID gate used in this example is a gate that switches between zero ohm and 70 ohm states, and it is necessary to realize two states of supply current: 0.35 mA and 0 mA. 11 to 19 in the figure are resistors that shunt current from the power supply. All are 50Ω. 25 is an external constant current source. 21. provided between the external power supply and the logic gate.
22.23°24 is a Josephson circuit for generating alternating current.

All circuit components except 25 are placed in liquid helium. Reference numeral 21 denotes a circuit in which ten Josephson junctions of 30 μm are connected in series, and these ten Josephson junctions change into and out of voltage states at the same time by a signal input to the input line 22. Inductance 23. The resistor 24 constitutes a current path reset circuit. Each resistance value is 0.01Ω
, the inductance amount is 6n)1.

The actual circuit operation is performed as follows.

Current source 25 provides a current of 3.87 mA. This current initially flows entirely through the Josephson junction 21.

At this time, no current flows through the logic gate. When performing a logic gate operation, an input signal is first applied to the input line 22 prior to the gate operation. This results in junction 21 switching to a voltage state. The resistance value of 21 in the voltage state is approximately 2.4Ω×10=24Ω. On the other hand, resistance 11.1
The total of 113.14°15.16.17.18.19 is about 5.60 (that is, about 0.35 mA x 9) flowing to the logic gate. In this circuit, the inductance 23
is as large as 6nH, so 200pi after 21 switches
After about a period of time, the current flowing through 23 and 24 becomes almost zero. The logic gate operates during a time period when the amount of shunt current to 23° and 24 is small. After the logical operation is completed, the supply current begins to flow concentrated at 23.24. Since the resistor 24 is as small as 0.01Ω, all supply currents are 2
It can be said that it flows through 3-24. At this time, the current flowing through the Josephson junction 21 becomes almost zero. As a result, a phenomenon occurs in which the junction 21 in the switched state returns to the zero voltage state. That is, the current flowing through 23 and 24 is again connected to junction 21.
Return to the current path. Therefore, all the current from current source 25 is made to flow through 21.

The logic gate is cleared. The initial state will be recreated. In this example, all Josephson circuits are fabricated using lead-based alloys. The maximum Josephson current density is lkA/cm''.

According to the present invention, current can be stably supplied to the alternating current driven logic circuit, so a stable high-speed logic circuit can be easily realized.

[Brief explanation of drawings]

The drawing is a circuit diagram showing an embodiment of the present invention. Explanation of symbols 1 to 9...5QUID logic gates, 11 to 19...
Shunt resistor, 21... Josephson junction, 22...
Input line, 23...inductance, 24...resistance,
25...External constant current source

Claims (1)

[Claims] 1. An alternating current generating circuit that is in a voltage state only during a predetermined period of time after startup and then returns to a zero voltage state is connected in parallel with the plurality of logic gates, and a constant direct current is connected to both ends of the parallel circuit. A diagonal Sefson circuit characterized by connecting a current source.