JPS589381A - Josephson logical circuit - Google Patents

Abstract

PURPOSE:To obtain a DC driven circuit with large signal amplitude voltages by a method wherein two Josephson device free of hysteresis in their voltage/current characteristics are serially combined and a first controlling line is provided in their vicinity and a second in the vicinity of one of the two devices. CONSTITUTION:A first Josephson device 401 lacking a hysteresis featue in its voltage/current characteristics has a terminal connected to a power source terminal 311. The other terminal is connected to a circuit output terminal 310 and to one of the terminals of a second Josephson device 402 also lacking a hysteris feature. The other terminal of the device 402 is grounded. Next, a first load resistor 303 is provided across the terminals 311 and 310, and a second load resistor 304 is provided across the terminal 310 and the ground. A second controlling circuit 308 with a constant current source 309 is provided in the vicinity of the network just referred to. And a first controlling circuit 307 with terminals 305 and 307 is positioned in the vicinity of the two devices. The magnetic fluxes generated by the two devices are rendered to interlock, or to neutralize, each other.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a logic circuit using a Josephson element, and particularly to a circuit driven by a DC power supply.

For digital circuits using conventional Josephson elements, AC power drive systems were mainly considered, and DC power drive systems were overlooked. However, although the AC power drive type circuit has a simple structure, the mounting structure that houses the AC power drive circuit is complicated, so recently, the DC power drive type has been reconsidered and various types of circuits have been proposed. Problems with the conventional DC power supply drive circuit are listed below.

FIGS. 1a and 1b show the voltage-current characteristics of a Josephson element having a so-called sandwich structure in which an insulating layer is provided between superconducting materials, for example.

The maximum superconducting current that can flow through the Josephson device is controlled by the magnetic flux that interlinks with the Josephson device. For example, in Figure 1a, the Josephson element is not linked with magnetic flux, so the maximum superconducting current that can flow through the Josephson element is large, but in Figure 1b, the Josephson element is linked with magnetic flux, so the maximum superconducting current that can flow through the Josephson element is large. This indicates that the maximum superconducting current that can flow through the Sonn element is small. It is well known that when the DC voltage applied across a Josephson element in a voltage state is lowered below a certain value, the Josephson element returns to a superconducting state. The minimum voltage V that can remain in a voltage state
ms+a is approximately described by equation (1).

1.: Maximum superconducting current that can flow through the Josephson element CJ: Josephson junction capacitance f = Blank constant divided by two stomachs e: Electronic charge ■, 1. is clearly proportional to the square root of the maximum current that can flow through the Josephson element. Therefore, v in Figure 1a
, 1.11 is also larger than Vat□ in Fig. 1b.

FIG. 2 is an example of a known DC power supply drive circuit according to the prior art. One end of Josephson element 101 is grounded, and the other end is connected to terminal 104. One end of the load resistor 102 is grounded, and the other end is connected to the terminal 104. This terminal 1
04 is the output terminal of the circuit. One end of the DC current source 103 is grounded, and the other end is connected to the terminal 104. The control wiring 107 is placed near the Josephson element 101 and is connected to the control wiring 107 via terminals 105 and 106.
The magnetic flux generated by the current flowing through the controller 7 interlinks with the Josephson element 101. The region surrounded by dotted lines in FIG. 2 represents the magnetically coupled range. The Josephson element 101 has voltage-current characteristics shown in Figure 1 and Figure 1b. The operation of the circuit shown in FIG. 2 will be explained below. Figure 3 shows the load line of the resistor 102 in Figure 1a, and
The figure is a diagram obtained by adding the load line of the resistor 102 to Figure 1b. The operating point when no control current flows is the third
This is point A in the figure. That is, since no magnetic flux is linked to the Josephson element 101, the maximum superconducting current is large and Vwalm is also large. The resistance value of the load resistor 102 is
If the operating point of the voltage state is set to a smaller value than V, as shown in the figure, the only stable point of the circuit in this state is point A in FIG. 3. Therefore, Josephson element 10
1 is in a superconducting state, and the output terminal 104 is at ground potential, that is, Ov, so no current flows through the load resistor 102.

The operating point when the control current flows through the control line 107 is point B in FIG. That is, since the magnetic flux is interlinked with the Josephson element 101, the maximum superconducting current is small and Vaim is also small, so the only stable point of the circuit in this state is point B. Therefore, the Josephson element 101 is in a voltage state, and the output terminal 104 has a third
At a potential corresponding to point B in the figure, a portion of the gate current flowing from the DC current source 103 flows into the load resistor 102. Control current presence/absence of input signal @1m1°
If the presence or absence of current flowing through the load resistance is made to correspond to Om, or the level of the potential at the terminal 104 is made to correspond to the output signals @l#, @Q'', the circuit in Fig. 2 operates as a so-called converter circuit. However, the circuit shown in FIG. 2 has the disadvantage that the signal amplitude, especially the difference between the potentials of the "1" and '0' levels of the output terminal 104 is small. As already explained, the signal amplitude voltage Vm of the circuit shown in FIG. 2 is within the range shown by the expression (@).

V-1-*<Vmu<V,t□・・・・・・・・・
(2) Since it is about 0.3 mV or less, the signal amplitude voltage Vm becomes less than that.

FIG. 5 shows a conventional example in which the circuit shown in FIG. 2 is improved. A first Josephson element 301 with a first load resistor 303 connected in parallel and a second Josephson element 362 with a second load resistor 304 connected in parallel are connected in series,
One end thereof is grounded, the other end is connected to the power supply terminal 311, and at the same time, the middle point of the series connection is connected to the output terminal 310. An Ides wire 308 is placed near the first Josephson element 301, and the magnetic flux generated by the bias current flowing through the DC current source 309 and Is wire 308 is
interlinks with the Josephson element. control wiring 30
7 is placed near the first and second Josephson elements 301 and 302, and the magnetic flux generated by the control current flowing through the terminals 305 and 306 is connected to the melt 1 and the second Josephson elements 301 and 302. interlink. In this case, the directions of the control current and bias current are opposite to each other, and each current is generated, and the first Josephson element 301
Make sure that the magnetic fluxes interlinked with each other cancel each other out. The region surrounded by dotted lines in FIG. 5 represents the magnetically coupled range. Next, the operation of the circuit shown in FIG. 5 will be explained. The voltage-current characteristic of the first Josephson element 301 when no control current flows is shown in FIG. 1b, and the voltage-current characteristic of the second Josephson element 302 is shown in FIG. 1a. When a control current flows, the voltage-current characteristics of the first Josephson element 301 are shown in FIG. 1a, and the voltage-current characteristics of the second Josephson element 302 are shown in FIG. 1b. When the voltage applied to the power supply terminal 311 is set as shown in equation (3), the first and second Josephson ropes 301,
:102 is in a superconducting state, and the other is in a voltage state. If the control current does not flow, the first
Since the second Josephson element 301 is in a voltage state and the second Josephson element 302 is in a superconducting state, the output terminal 31O//'i is at the ground potential, that is, Ov. If control current flows, $1 Josephson Shigeko 301
is in a superconducting state, the Josephson element 302 is in a voltage state, and the output terminal 310 is at the same potential as the power supply terminal, that is, Vtt.
It's a bolt. The signal amplitude voltage Vm of the circuit shown in FIG. 5 is v8 volts. As is clear from the above description, the circuit shown in FIG. 5 can increase the signal amplitude voltage more than the circuit shown in FIG. 2. However, in the circuit shown in FIG. 5, an oscillation waveform appears in the circuit output during a switching transition, and the circuit may become unstable. This output oscillation phenomenon may continue for about 10 PS to 100 PS. This is because there are times when the condition of equation (3) is not satisfied during switching transients, so both the first and second Jo-Sefson elements 301 and 302 are not in a voltage state, and the voltage at the output terminal is This is because it becomes unstable.

An object of the present invention is to propose a DC drive circuit that has a large signal amplitude voltage and stable transient characteristics during switching.

The present invention will be explained below using examples. FIG. 6 shows the voltage-current characteristics of a Josephson cord without hysteresis characteristics. The maximum superconducting current that can flow through the Josephson cord is controlled by the magnetic flux that interlinks with the Josephson cord. For example, in FIG. 6, when the magnetic flux interlinking with the Josephson element is zero, the characteristics are shown by ., and when the magnetic flux is not zero, the characteristics are shown by . The magnetic flux is generated by a control current flowing in control wiring placed near the Josephson cord. When the superconducting current density is large for a bridge-type Josephson junction element, a Josephson junction element with a structure in which a semiconductor is sandwiched between superconducting materials, and a Josephson junction element in a structure in which an oxide is sandwiched between superconducting materials, the voltages shown in Figure 6 are shown. - Indicates current characteristics. For example, 2Xl
O@A/crr? pb-ox with a high current density of
It is known that the jde-Pb (In) Josephson element hardly exhibits hysteresis characteristics at a value of 4 or more (L, D, Jackel et ml: I
EEE'rrans, Mag.

Kite G-17, 295 (1981)).

FIG. 7 is a diagram showing an embodiment of the present invention. The circuit shown in FIG. 7 is obtained by replacing the Josephson element 101 shown in FIG. 2 with a Josephson element 201 having the voltage-current characteristics shown in FIG. The operation of the circuit shown in FIG. 7 will be explained below. The operating point of the circuit when no control current flows through the control wiring 107 is point A in FIG. In this case, the maximum superconducting current that can flow through the Josephson element 201 is large, so the Josephson probe is in a superconducting state. Therefore, the potential of the output terminal 104 of the circuit shown in FIG. 7 is OV. The operating point of the circuit when a control current flows through the control wiring 107 is point B in FIG.

In this case, since the maximum superconducting current that can flow through the Josephson element 201 is small, the Josephson element remains in a voltage state, and the potential of the output terminal 104 corresponds to point B. It is at a potential that is not v. Since the voltage-current characteristics of the Josephson element 201 do not have hysteresis characteristics, if the control current is then made zero, the operating point will move to point A in FIG. As explained above, the circuit shown in FIG. 7 operates as a so-called converter circuit.

Another embodiment of the invention is shown in FIG. One terminal of the first Josephson cable 401 is connected to the power supply terminal 311, and the other terminal is connected to the output terminal 31G of the circuit and simultaneously connected to one terminal of the second Josephson cable 402. be done. The other end of the second Josephson element 402 is grounded. One terminal of the first load resistor 303 is the power supply terminal 3
11, and the other terminal is connected to the output terminal 310 of the circuit and simultaneously connected to one terminal of the second load resistor 304. The other terminal of the second load resistor 304 is grounded. The first control wiring ao7 is the 1s second Josephson element 401.

The magnetic flux generated by the control current flowing to the first control wiring 307 through the terminals 305 and 306 is placed near the 11th and 2nd Josephson element 402.
Interlinks with 01,402. Second control wiring 30
8 is placed near the first Josephson element 401, the bias current supplied from the constant current power supply 309 flows through the second control wiring, and the magnetic flux generated by the bias current is passed through the first Josephson element. Make it interlink with 401. In this case, the flow directions of the control current flowing through the first control wiring flA 307 and the bias current flowing through the second control wiring 308 are set to be opposite to each other, and the first Josephson element 40 where each current is generated
The magnetic fluxes interlinked with 1 are made to cancel each other out.

The region surrounded by dotted lines in FIG. 10 indicates a magnetically coupled region. The eleventh second Josephson element has voltage-current characteristics shown in FIG. A DC voltage Vm volts is applied to the power supply terminal 311. The operation of the circuit shown in FIG. 10 will be explained below. When the control current does not flow, the first Josephson element 401 is linked with the magnetic flux generated by the bias current, but the second Josephson element 402 is not linked with the magnetic flux. Therefore, the maximum superconducting current that can flow through the first Josephson element 401 is large,
The maximum superconducting current that can flow through the second Josephson element 402 is small. Therefore, when no control current flows, the operating point is point A in Figure 11, the first Josephson element is in a voltage state, the second Josephson element is in a superconducting state, and the output terminal 310 is at ground potential. In other words, it becomes 0 volts. When the control current flows, the magnetic fluxes generated by both the control current and the bias current intersect with the first Josephson element 401, but as explained earlier, the magnetic fluxes cancel each other out, so the first Josephson element 401 The magnetic flux is not linked to the element 401 under equal constraints, and the magnetic flux generated by the control current is linked to the second Josephson element 402. Therefore, the maximum superconducting current that can flow through the first Josephson element 401 is large, and the maximum superconducting current that can flow through the ts2 Josephson element 402 is small. Therefore, the operating point when the control current flows is point B in FIG.
01 is in a superconducting state, the second Josephson element 402 is not in a voltage state, and the output terminal 310 is at the same potential as the power supply voltage.
That is, it becomes V1 volt. From the above explanation, it is clear that the circuit shown in FIG. 10 operates as a so-called converter circuit. It is also clear that if the second (7) conductor wiring 11308 is placed near the second Josephson element 402, the circuit operates as a so-called inverter circuit. The circuit shown in FIG. 10 includes first and second Josephson elements 40.
1°402 are connected in series, the signal amplitude voltage is large, and the first and second Josephson elements 401.40
Since the voltage-current characteristics of No. 2 do not have hysteresis characteristics, there are no factors that make the transient characteristics during switching unstable, and the characteristics are stable.

FIG. 13 is a diagram showing a configuration when another circuit is driven by the circuit shown in FIG. 1O (the figure shows a case where the circuit shown in FIG. 10 is connected in two stages). Load resistance 3 shown in Figure 10
The circuit can be driven by allowing the current flowing in the control wiring 307 to flow through the transmission line 501 and the terminals 305 and 306 of the circuit to be driven.

With the above explanation, the Josephson element 201, 401° 402
Although not specified in any way, it is clear that these Josephson elements may be either Josephson junctions or Josephson interferometers.

As described above, according to the present invention, it is possible to easily configure a DC power supply drive circuit that performs stable switching operation and has a large signal amplitude voltage, and it is possible to increase the design and operation margin of a digital system.

[Brief explanation of drawings]

Figures 1a and 1b are voltage-current characteristics of the Josephson element, Figures 2 to 5 are diagrams for explaining conventional examples, and Figure 6 is the voltage and current characteristics of the Josephson element used in the present invention. FIGS. 7, 10, and 13 are examples of the present invention, and FIGS. 8, 9, 11, and 12 are for explaining the operation of the embodiments of the present invention. This is a diagram. 101.301,302...Josephson element with hysteresis characteristics, 201,401,402...Josephson element without hysteresis characteristics, 102.3
03,304...Load resistance, 107,307th 1α
To 'O Y 2 Figure 7/θ4 ノ'fi13 Agony ■ 4 Figure 'fJ 5 Figure 'f) tθ Figure 11 Figure 13 Figure jOφ -

Claims (1)

[Claims] Eleventh and second Josephson elements having no hysteresis characteristic in voltage-current characteristics are connected in series, and the eleventh
A Josephson logic circuit characterized in that a first control wiring is provided in the vicinity of the second Josephson element, and a second control wiring is provided in the vicinity of either the first or second Josephson element. .