JPS62102175A - Superconductive circuit - Google Patents

Abstract

PURPOSE:To improve measuring accuracy by removing influence to be exerted upon the 1st DC magnetic flux parametron (DCFP) circuit by the operating current of a magnetic flux coupling element in a circuit consisting of the 2nd superconductive circuit including the magnetic flux coupling element connected to the 1st DCFP circuit and a signal line. CONSTITUTION:A transformer 10i and a control line 6 for a current detecting circuit 10 are connected to an output line 108 of a DCFP circuit having Josephson junctions 101, 102 and exciting windings 103, 104 as loads. A current IS is supplied from a pulse current source 200 to a magnetic flux coupling quantum interference element in a circuit 10 and monitored by a voltmeter 201 and a reference current Ir is supplied from a scanning current source 300. When an offset current Ig, is supplied in the reverse direction against the currents Ig, Ir through the wiring 110 of the transformer 109, magnetic flux based upon the currents Ig, Ir is prevented from being superposed to the control line 6 and the current IS to be measured can be found out from the reference current Ir on the basis of the thereshold characteristics of the circuit 10 by fizing the current Ig. Since the signal IS of the DCFP circuit can be extracted by removing the influence of the detecting circuit, the measuring accuracy can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention provides a magnetometer using a Josephson device, which is well known in the art, and is based on the SQ! JIL) magnetometer. Conventional S Q IJ I D magnetometers suffer from S Q due to thermal noise from the outside world and noise from the preamplifier used to amplify the signal.
The inherent sensitivity of U 11') could not be fully utilized. In order to compensate for the shortcomings of this 5QUID magnetometer and realize a magnetometer with even higher sensitivity, we developed a DC flux parametron (D
CF lux parameter, ron; hereinafter 1'
) A method using a circuit called CFP has been proposed.

A magnetic flux meter using this DCFP circuit was patented in 1986-1225.
26 is described in detail.

The DCFP circuit is sensitive to magnetic flux, has high circuit gain, and has excellent characteristics as a comparison circuit for a magnetometer. However, the operating energy of the D CF)' circuit is 1,0-2' J
Because it is extremely small, the current flowing through the detection circuit when detecting the current of the DCFP circuit is connected to the DCFP circuit through the transformer coupling.
It was found that this could affect the P circuit, causing a malfunction that would reverse the polarity of the signal maintained by the DCFP circuit, potentially destroying information.

[Purpose of the invention]

The purpose of the present invention is to reduce the output current of circuits such as DCFP circuits.
The object of the present invention is to provide a superconducting circuit suitable for detecting information in a circuit such as a CFP circuit without destroying it.
- [Summary of the Invention] In order to achieve this object, the present invention adds a new circuit to cancel the influence of the current detection circuit, or operates two current detection circuits differentially, and Adopt a method that eliminates the effect on other circuits.

[Embodiments of the invention]

Hereinafter, the present invention will be explained in detail using Examples.

FIG. 2(a) shows a magnetic flux coupling layer quantum interference device used in the current detection circuit used in the present invention. This element comprises two Josephson junctions 1, 2 and inductors 3, 4 forming a superconducting loop. A bias current is supplied to the superconducting loop by a bias line 5.

Further, two control lines 6 and 7 are installed near the superconducting loop, and the magnetic flux generated by the current flowing through the control lines 6 and 7 interlinks with the superconducting loop, and the current in the control line is magnetic flux coupled. Control the maximum superconducting current of a layered quantum interference device. Hereinafter, this magnetic flux coupling layer quantum interference device will be referred to as symbol 1 in Fig. 2(b).
Represented by 0. FIG. 3 is a diagram showing the operating principle of the current detection circuit.

In the magnetic flux coupling layer quantum interference device 10 of the current detection circuit, the first
The current to be measured Is is passed through the control line 6 of 0.degree., and the reference current Ir is passed through the second control line 7. FIG. 2 shows the threshold characteristics of the magnetic flux coupling layer quantum interference device. In this figure, if the bias current of the magnetic flux coupling layer quantum interference device is fixed at 1 g, the control current If required to switch the magnetic flux coupling layer quantum interference device from the superconducting state to the voltage state is uniquely determined. This current If is the first current If. Current Is flowing through the second control line.

It is clear that it is the sum of Ir. Therefore, when Ir is scanned, the flux-coupled quantum interference circuit switches to 1r.
If we sample , then we can know the value of s. From this, the current detection circuit can determine the value of the measured current Is from the reference current Ir. In the conventional technology, the magnetic flux generated by the bias current 1 pin and the reference current Ir of this current detection circuit is superimposed on the control line 6, and this is the DCF).
1 circuit was affected.

FIG. 1 shows a first embodiment of the invention. In this embodiment, Josephson junctions 101 and 102, an excitation inductor 10
3, 104, excitation line 105, input terminal 106, output line 1
A transformer 109 as a load inductor of a DCFP circuit consisting of 08 and a control line 6 of a current detection circuit 10 are connected. The flux-coupled quantum interference circuit 10 of the current detection circuit is supplied with 1 g of current from a pulse current source 200, and the voltage across it is monitored by a voltmeter 201. Reference current Ir is supplied from scan current source 300'. With this circuit configuration, if the canceling current Ig' is caused to flow through the transformer 109 through the wiring 110 in the opposite direction to the bias current Ig and the reference current 1r, the bias current Ig and the reference current 1r cause the control line 6
It can be canceled by a magnetic flux canceling current Ig/ superimposed on the magnetic flux canceling current Ig/.

The canceling current Ig' is the current Ig, Ir and the transformer 10.
A current value suitable for Q can be selected by the coupling coefficient of 9.

FIG. 4 shows a second embodiment of the present invention. In this embodiment, the current flowing through the transformer 109 in the first embodiment shown in FIG.
09 and the bias line 5 of the current detection circuit are connected in series. Further, the magnetic flux generated by the transformer 109 and the magnetic flux generated by the current detection circuit 10 are connected so that the directions of the currents are opposite so that they cancel each other out. In this configuration, the magnetic fluxes can be canceled by making the coupling coefficient of the transformer 109 the same as that of the current detection circuit. Furthermore, although this embodiment has a circuit configuration that can overcome the magnetic flux caused by the bias current, since most of the magnetic flux that causes interference is generated from this bias current, this circuit configuration can be sufficiently put to practical use. Furthermore, in order to cancel out the magnetic flux due to the reference current, it is obvious that the magnetic flux due to the reference current may be canceled by a transformer 109' as shown in FIG.

FIG. 6 shows a third embodiment of the present invention. In this embodiment, two current detection circuits 10a and 10b are connected to D CF'
The P circuit is used as a load, and the bias current Ig and reference current 1r of the two current detection circuits are differentially connected so that they flow in directions opposite to each other. With this configuration, the magnetic fluxes generated by the two current detection circuits cancel each other out, so there is no reaction given to the I) CF P circuit of the current detection circuit. In this case, only one of the two current detection circuits is effectively used for current detection, and the other is not used. FIG. 7 is a modification of the embodiment shown in FIG.
Two bias lines 5a and 5b are connected in series so that the same bias current flows through the two current detection circuits. In this embodiment, the two current detection circuits have bias currents directed in opposite directions so that the magnetic fluxes generated are in opposite directions.

Is the above explanation a two-junction magnetic flux coupled quantum transistor in the current detection circuit?
Although the explanation has been given using an example using a $ cable, based on the principle of the invention, the present invention can be implemented using a magnetic flux coupling type element with two or more junctions.
is clear.

〔Effect of the invention〕

According to the present invention, the D
CF'Pl! l! The circuit signal can be extracted without the influence of the detection circuit. This makes it possible to create an IJG that detects minute signals in a stable manner, and to greatly improve the measurement accuracy and measurement speed of the DCF P circuit, thereby providing a highly sensitive and highly accurate magnetometer. useful for.

[Brief explanation of drawings]

Fig. 1 shows the first embodiment of the present invention, Fig. 2 shows the magnetic flux coupling type element used in the current detection port of the present invention and its symbol, and Fig. 3
The figure is a diagram of the operating principle of the current detection circuit, and Figure 4 is the second embodiment of the present invention.
FIG. 5 is a modification of the fourth embodiment, No. 6 is a third embodiment of the present invention, and FIG. 7 is a modification of the embodiment of FIG. 1.2・° Josephson junction 3, 4... Inductor, 5... Bias line, 6, 7... Control line, 10...
・Symbol of magnetic flux coupling layer quantum interference device, 101.102...Josephson junction. 103.104...Excitation inductor, 105...Excitation line, 106...Input terminal, 108...Output line, 1
09...Transformer, 11O...Wiring, 200...
Pulse current source, 201... Voltmeter, 300... Scan current source. Agent A□Ya 41, 11 Kakarasu,] 'f, / Kunimi 2, Kuzu 3, Kuni, 4, No. t~≦

Claims (1)

[Claims] 1. A first superconducting circuit that outputs a current signal to a signal line;
In a superconducting circuit consisting of a second superconducting circuit including a magnetic flux coupling type element connected to the signal line and responsive to the signal current, a superconducting circuit is generated superimposed on the signal line by an operating current flowing through the magnetic flux coupling element. A superconducting circuit having means for superimposing magnetic flux that cancels magnetic flux on the signal line. 2. In the superconducting circuit according to claim 1, the magnetic flux superimposing means is a transformer coupling magnetically coupled to the signal line for flowing a current having a value corresponding to the operating current flowing through the magnetic flux coupling type element. A superconducting circuit characterized by consisting of elements. 3. In the superconducting circuit according to claim 1, the magnetic flux superimposing means is connected to the signal line, has the same structure as the magnetic flux coupling element, and has an operating current in the opposite direction to the operating current. A superconducting circuit characterized in that it consists of other flux-coupled elements. 4. A superconducting circuit according to any one of claims 1 to 3, wherein the first superconducting circuit is a DC magnetic flux parametron circuit. 5. In the superconducting circuit according to any one of claims 1 to 4, the second superconducting circuit has means for controlling the magnitude of the operating current depending on the magnitude of the signal current. superconducting circuit.