JPH0381240B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention generally relates to a method of driving a Josephson storage circuit that stores at least one piece of information in the form of a circulating current. More specifically, the present invention relates to a storage circuit capable of non-destructively reading out stored binary information (hereinafter referred to as NDRO). More specifically, the present invention provides a superconducting closed loop in one of the pairs of branches forming a superconducting closed loop in the storage circuit.
Josefson with two write gates
This relates to the NDRO storage circuit. More specifically, the present invention relates to a method for driving a Josephson NDRO memory circuit in which a second gate is connected to the control line of the first gate in the memory circuit.

The Josephson NDRO memory circuit is described in, for example, the literature Journal of Applied Physics Vol. 50 No.
12 December 1979 PP, 8143-8169, are well known to those skilled in the art.

FIG. 1 is a diagram for explaining one of the conventional examples of Josephson NDRO storage circuit. In this example, Josephson stores binary information depending on whether or not the circulating current Icirc is held in superconducting loop 2.
A 2x2 array of NDRO storage circuits is shown.

In order to maintain the circulating current Icirc in the superconducting loop 2 of A, a bias current Iy is applied to the column line 5 related to A, and control currents Iy' and Iy are applied to the control lines 6 and 7 related to A, respectively. simultaneously from the power supplies 10, 11, and 12 related to the. As a result, the memory cell 1 of A is designated, and since the control currents Iy and Ix flowing through the control lines 6 and 7, respectively, are configured to apply a control magnetic field to the switch element 8 of A, the control current Iy ' and Ix at the same time, the switch element 8 included in the memory cell 1 of A
becomes a temporary voltage state. As a result, of the current Iy injected into the superconducting closed loop 2 of A, the A switch element 8
After subtracting the lowest drive current Imin flowing through branch 3 that includes switch element 8, the remainder flows to branch 4 that does not include switch element 8 of A. After that, if Iy, Iy' and Ix are set to 0, then A
A clockwise circulating current in the superconducting closed loop 2 of
Hold Icirc.

In order to realize a state in which the circulating current Icirc is not held in the superconducting loop 2 of A, the control current Iy is applied to the control lines 6 and 7 related to A without flowing the bias current Iy to the column line 5 related to A. ' and Iy are made to flow simultaneously from the power supplies 11 and 12 related to A, respectively, and then the control currents Iy' and Ix are set to zero. As a result, no circulating current Icirc remains in the superconducting closed loop 2 of A.

The state in which the circulating current Icirc is maintained in the superconducting closed loop 2 of A is the current in the column line 5 related to A.
If current Is is simultaneously applied to the readout line 15 related to A, and memory cell 1 of A is designated, the current (1-K) flowing through branch 4 of A is the sum of Iy and the above circulating current Icirc. (1-K) The magnetic field created by Iy + Icirc sets the switch element 9 of A, which is electromagnetically coupled to the branch 4 of A, into a voltage state, and this state is detected and read by the detector 14 related to A. . However, K≡(self-inductance of branch 4)/(sum of self-inductance of branch 3 and branch 4).

In a state where the circulating current Icirc is not held, if the current Iy is applied to the column line 5 related to A, and the current Is is applied to the readout line 15 related to A at the same time, and the memory cell 7 of A is specified, the branch 4 of A is The switch element 9 of A, which is electromagnetically coupled to the branch 4 of A, maintains a zero voltage state due to the magnetic field created only by the current (1-K) Iy flowing through it, and this state causes the detector 14 related to A to maintain a zero voltage state. detected and read by

In the above memory circuit configuration, two lines are required for each cell: a control line 7 for flowing a control current Ix as a row line, and a read line 15 for flowing a read current Is, and each line is connected to a power source. Since this requires a complicated circuit configuration, a simplified Josephson NDRO memory circuit as shown in FIG. 2 can be considered.

That is, a superconducting closed loop consisting of a first branch 3 and a second branch 4, a first switch element 8 arranged in the first branch 3 and capable of passing Josephson current, and the first switch a control line 7 arranged to be electromagnetically coupled to the element 8; and the second branch 4.
and a second switch element 9 through which Josephson current can flow, which is arranged so as to be electromagnetically coupled to the superconducting closed loop 2. The first switch element 8 is used as a write gate to store information in the superconducting closed loop 2. In a Josephson memory device using a second switch element 9 as a read gate, a simplified Josephson memory device in which the second switch element 9 is connected to the control line of the first switch element 8 is arranged.
An NDRO storage circuit is considered.

The object of the present invention is to simplify the
The purpose is to provide an unknown driving method for the NDRO memory circuit.

According to the present invention, a superconducting closed loop consisting of a first branch and a second branch, a first switch element arranged in the first branch and capable of flowing Josephson current, and a superconducting closed loop comprising a first branch and a second branch; A plurality of control lines arranged to be electromagnetically coupled to the element, coupled to at least one control line among the control lines, and arranged so as to be electromagnetically coupled to the second branch. and a second switch element through which Josephson current can flow, and the first switch element is used as a write gate to transfer binary information into the superconducting closed loop as circulating currents flowing in different directions or as circulating currents. In driving a Josephson memory circuit that uses the second switch element as a read gate, the current flowing through the control line of the first switch element connected to the second switch element is different during writing and reading. A method for driving a Josephson memory circuit featuring the same characteristics is obtained.

The present invention will be described in detail below with reference to the drawings.
The principle of the present invention is based on the control characteristics shown in Figure 3a and b, respectively. Characteristics in which there is a gate current Ix in a voltage state for
It is in a zero voltage state when , and Iy' is the second control current, and for this control current, it is in a zero voltage state both when the gate current is KIy and when KIy + Icirc, and the first control For the control current Ix + Iy' when the current and the second control current flow simultaneously, even when the gate current is KIy, KIy + Icirc
(Although Ix and Iy' are shown as having the same magnitude in Figure 3a, this is not a necessary condition), two switch elements with the characteristic of being in a voltage state also in the case of (Figure 3a) are shown in Figure 2. As shown in FIG.
A switch element 9 is used as a switch element 9 which is electromagnetically coupled to the control lines 6 and 7 in the first branch 3 in the superconducting closed loop 2 using the switch element having the characteristic (b) as a write gate. It is used for 8. However, Iy is the cell current flowing through the column line 5 and flowing into the superconducting closed loop 2, and K is the circuit constant determined from (self-inductance of branch 4)/(sum of self-inductance of branches 3 and 4). be. Icirc is a clockwise circulating current maintained in the superconducting closed loop 2, and if the lowest drive current of the switch element 8 is Imin, its magnitude is |KIy−
Equal to Imin｜. Ix is the current flowing through row line 7 and Iy' is the control current flowing through column line 6.

Next, an example will be given and explained. FIG. 4 is a diagram for explaining the present invention and shows a 2×2 array of Josephson NDRO storage circuits.

Switch elements 8 and 9 are shown in FIG. 3a and b, respectively.
It is designed to have the control characteristics of

A method of writing circulating current Icirc into cell A is shown.
First, the case where no circulating current flows through cell A before writing (Icirc=0) will be described. A cell current Iy and control currents Iy' and Ix are applied to column lines 5 and 6 and row line 7 related to cell A, respectively, from power supplies 10, 11 and 12, respectively. Here, the Iy is the Iy′,
When injected into superconducting loop 2 of cell A earlier than Ix, currents temporarily flow into branches 3 and 4 of cell A, respectively.
When KIy, (1-K)Iy flows, and then Iy', Iy flows, the switch element 8 of cell A switches to the voltage state due to its control characteristics, so that branches 3 and 4 of cell A are supplied with respective voltages. Currents Imin and Iy−Imin flow. Conversely, if Iy' and Ix act on cell A earlier than Iy, the switch element 8 of cell A operates in a voltage state, and as a result, branches 3 and 4 of cell A receive currents Imin and Iy, respectively. -Imin flows. In either case, when the current flowing through the branch 4 exceeds a certain value (Fig. 3b, point P), the switch element 9 of cell A enters a voltage state, and Ix related to cell A is cut off.
Since the switch element 8 of cell A is already in a voltage state, the above-mentioned currents will eventually flow in the branches 3 and 4 of cell A, respectively. Then in both cases, Iy′,
When Ix is set to 0 and Iy is set to 0, a clockwise circulating current KIy-Imin flows through the superconducting loop 2 of cell A.

Next, Icirc=KIy− is already in cell A before writing.
Let's talk about the case where Imin is flowing. Cell A
A cell current Iy and a control current Iy', Ix are applied to column lines 5, 6 and row line 7, respectively, from power supplies 10, 11, 12, respectively. Here, the Iy is
When injected into the superconducting loop 2 of cell A earlier than Iy′, Ix, currents Imin and Iy−Imin flow in branches 3 and 4 of cell A, respectively, and even if Iy′ and Ix are subsequently applied, The currents flowing in branches 3 and 4 of cell A remain at Imin and Iy-Imin, respectively. On the other hand, if Iy' and Ix are applied to cell A before Iy,
The switch element 8 of cell A switches to a voltage state due to its control characteristics, and Icirc of cell A becomes 0,
When Iy is then injected, the currents flowing through branches 3 and 4 of cell A become Imin and Iy-Imin, respectively.
In these cases, the switch element 9 of cell A becomes a voltage state when the current flowing through branch 4 exceeds a certain value (point P in Figure 3b), and Ix related to cell A is cut off. Since the switch element 8 of cell A is already in a voltage state, the above-mentioned currents will eventually flow in the branches 3 and 4 of cell A, respectively. In either case, if Iy' and Ix are then set to 0 and Iy is set to 0, a clockwise circulating current will be created in superconducting loop 2 of cell A.
KIy−Imin remains.

In this way, to write the circulating current Icirc to cell A, the cell A
After flowing the cell current Iy acting on the cell current Iy and the control currents Iy′ and Ix in any order, Iy′ and Ix are set to 0, and then Iy is set to 0.
Make it.

At this time, Iy and Iy' act on unselected cells C, but the switch element 8 of cell C maintains a zero voltage state due to its control characteristics, and even if Iy is injected into cell C,
After setting Iy=Iy′=0, the initial state is maintained.
Similarly, Ix acts on unselected cell B, but the switch element 8 of cell B maintains a zero voltage state due to its control characteristics, and the state of cell B remains unchanged.

A method of writing circulating current Icirc=0 to cell A will be shown.

Control currents Iy' and Ix are supplied to the column line 6 and row line 7 related to cell A by power supplies 11 and 11, respectively.
It starts from 12. As a result, switch element 8 of cell A
is in a voltage state due to its control characteristics, and the circulating current Icirc is 0 whether or not a circulating current is flowing through the cell A before writing.
After that, if Iy' and Ix are set to 0, a circulating current flows through cell A.
Icirc=0 is written.

At this time, unselected cells B and C are each
Only Ix or Iy' acts, and the switch element 8 of each cell maintains a zero voltage state due to its control characteristics, and the states of cells B and C remain unchanged.

A method for reading the state of cell A will be shown.

A cell current Iy and read current Ix are applied to the column line 5 and row line 7 associated with cell A, respectively, from power supplies 10 and 12, respectively. In this case, the read current is the same as the current applied to the row line 7 during writing. If Icirc flows in cell A, the currents flowing in branches 3 and 4 of cell A are Imin and Iy−, respectively.
Imin=(1-K)Iy+Icirc, and if Icirc does not flow in cell A, the currents flowing in branches 3 and 4 of cell A will be KIy and (1-K)Iy, respectively. As a result, when Icirc is flowing through cell A, the switch element 9 of cell A is switched to the voltage state due to its control characteristics, and when Icirc is not flowing through cell A, the switch element 9 of cell A is switched to the zero voltage state. , and these two states are related to cell A.
4. After that, if Iy and Ix are set to 0, even if Icirc is flowing before reading,
Even when Icirc is not flowing, in either case, the state of cell A reproduces the state before reading, and non-destructive reading becomes possible.

At this time, Iy acts on the unselected cell C, but Iy=
After 0, the initial state is maintained, and the same cell B has Ix
However, the switch element 28 of cell B maintains a zero voltage state due to its control characteristics, and the state of cell B remains unchanged.

Although the embodiments have been explained above, the main part of the present invention is that the current flowing through the control line of the write gate connected to the read gate is the same during writing and reading, and the result is that the current flowing through the control line of the write gate connected to the read gate is the same during writing and reading. Josephson with readout gate
Its ability to drive the NDRO memory circuit.

[Brief explanation of drawings]

Figure 1 shows Josephson's diagram for explaining the conventional technology.
FIG. 2 shows a 2×2 array of NDRO storage circuits.
FIG. 2 is a diagram illustrating one cell of a simplified Josephson NDRO storage circuit for explaining the present invention. 3a and 3b are diagrams each showing the control characteristics of the switch element used in the cell of FIG. 2 to realize the driving method of the present invention. FIG. 4 shows Josephson's diagram for explaining one embodiment of the present invention.
FIG. 2 shows a 2×2 array of NDRO storage circuits. In FIGS. 1, 2, and 4, 1 is a storage cell, 2 is a superconducting closed loop, 3 and 4 are branch paths, 5 is a column line, 6 is a control column line, 7 is a row line,
8, 9 are switch elements, 10, 11, 12, 13
is a power supply, 14 is a detector, and 15 is a readout line.

Claims (1)

[Claims] 1. A superconducting closed loop consisting of a first branch and a second branch, a first switch element arranged in the first branch and capable of flowing Josephson current, and a Josephson current connected to at least one control line among the plurality of control lines arranged to be coupled to each other, and arranged to be electromagnetically coupled to the second branch; The first switch element is used as a write gate to store binary information in the superconducting closed loop as circulating currents having different flow directions or the presence or absence of the circulating current. In driving a Josephson memory circuit using a second switch element as a read gate, the first switch element connected to the second switch element is
A method for driving a Josephson memory circuit characterized in that the current flowing through the control line is the same during writing and during reading.