JP2807519B2 - Superconducting device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Overview] Regarding a superconducting device, an appropriate slew rate can be selected according to the application, and the measurement sensitivity and the response speed can be set to desired values without incurring a complicated configuration and an increase in cost. A pickup coil composed of a superconducting loop that extracts magnetic flux interlinking in the loop, and a superconducting quantum that is magnetically coupled to the pickup coil and pulsates the extracted magnetic flux with an alternating current bias to provide a superconducting device. An interference element, and superconducting feedback means for measuring a pulse output from the superconducting quantum interference element, and feeding back a flux quantum according to the measurement result to the input side of the superconducting quantum interference element through magnetic field coupling, In a superconducting device that measures magnetic flux linked to a pickup coil based on pulses output from a superconducting quantum interference device Switching command means for commanding switching of the magnetic flux quantum fed back to the superconducting quantum interference element, wherein the superconducting feedback means feeds back to the superconducting quantum interference element based on a command from the switching command means. The magnetic flux quantum is configured to be electrically switched.

[Industrial applications]

The present invention relates to a superconducting device used as a high-sensitivity magnetic field sensor, and more specifically, to a SQUID (Super
The present invention relates to a superconducting device using a conducting Quantum Interfernce Device (superconducting quantum interference device) sensor.

In fields such as biomagnetic measurement, SQUIDs (hereinafter referred to as squids) are used as indispensable devices. In this field, many squids are arranged to measure the magnetic field distribution of organs such as the brain and heart in a short time. A multi-channel squid system is desired and is being developed.

[Conventional technology]

When a conventional superconducting device is used as a high-sensitivity magnetic field sensor, a multi-channel squid system is superior as described above, and in order to realize such a multi-channel squid, a digital squid is useful. (For example, see D. Drung, Cryogenics
vol.26 pp.623-627.1986 and Fujimaki et al. IEEE Tra
ns. Electron Devices vol.35, No.12 (1988) pp.2412
−2418). This is because while many conventional squids are so-called dc-SQUIDs, which operate in analog, digital squids output pulses and output.
There is an advantage that S / N can be increased and digital processing can be performed as it is.

Also, the feedback circuit was realized by a superconducting circuit,
The present applicant has previously proposed a so-called one-chip squid (see Japanese Patent Application No. 62-177515), in which a feedback circuit is integrated on the same chip as a squid sensor. And has the advantage of reducing crosstalk between channels.

[Problems to be solved by the invention]

However, in such a conventional superconducting device, since the feedback magnetic flux amount of the superconducting feedback circuit is constant, the so-called feedback slew rate cannot be changed, and the measurement sensitivity (resolution) and response speed are reduced. There was a problem that the desired value could not be freely switched.

In other words, in the case of a digital squid, the operation of counting pulses output from the digital squid as a function of a feedback circuit and the number of pulses counted
A D / A conversion operation is required, and this circuit increases a fixed amount of feedback magnetic flux ΔΦ for each pulse. The larger the value of ΔΦ, the higher the slew rate of the feedback circuit and the higher the response speed. However, if the value of ΔΦ is too large, the quantization error increases and the measurement sensitivity deteriorates (resolution decreases). Therefore, for example, if the feedback magnetic flux ΔΦ is set to a small value in order to increase the measurement sensitivity, the slew rate is limited, and the response speed is deteriorated. On the other hand, in practical use, it may be required to increase the measurement response speed even if the sensitivity is sacrificed. That is, in reality, it is necessary to select an appropriate slew rate according to the application and set the measurement sensitivity and the response speed to desired values.

In order to cope with such conflicting demands with a conventional superconducting device, for example, feedback flux ΔΦ
In other words, another digital squid having a different configuration is prepared, which is inconvenient and troublesome, and undesirably complicates the configuration and increases the cost.

Therefore, an object of the present invention is to provide a superconducting device that can select an appropriate slew rate according to an application and can set a measurement sensitivity and a response speed to desired values without causing a complicated configuration and an increase in cost. I have.

[Means for solving the problem]

In order to achieve the above object, a superconducting device according to the present invention has a pickup coil composed of a superconducting loop for extracting magnetic flux interlinked in a loop, and a superconducting device magnetically coupled to the pickup coil for pulsing the extracted magnetic flux with an AC bias. A conduction quantum interference device and superconducting feedback means for measuring a pulse output from the superconducting quantum interference device and feeding back a flux quantum corresponding to the measurement result to the input side of the superconducting quantum interference device through magnetic field coupling. Prepared,
In a superconducting device that measures a magnetic flux linked to a pickup coil based on a pulse output from a superconducting quantum interference device, a switching instruction unit that instructs switching of the magnetic flux quantum fed back to the superconducting quantum interference device. The superconducting feedback means is configured to electrically switch the magnetic flux quantum fed back to the superconducting quantum interference device based on a command from the switching command means.

Further, the superconducting feedback means includes a plurality of feedback circuits, an AND gate is provided between the superconducting quantum interference device and the feedback circuit, and the superconducting quantum interference device is controlled based on a command from the switching command device. Switching the output pulse to be transmitted to which feedback circuit, wherein the superconducting feedback means comprises a superconducting loop, including a superconducting inductor and a gate for writing magnetic flux quanta, The superconducting feedback means includes a plurality of write gates in the superconducting loop, and provides an AND gate between the pulse output from the superconducting quantum interference device and the write gate,
Switching the pulse output from the superconducting quantum interference device to be transmitted to which write gate based on a command from the switching command means, wherein the superconducting feedback means includes a superconducting inductor in the superconducting loop. A plurality of superconducting inductors are connected in parallel, and at least a part of these superconducting inductors is a channel part of a field effect type superconducting three-terminal element, and the superconducting feedback means compares a part of the superconducting loop. The shunt is performed by a superconducting inductor having a very small size, and at least a part of the small superconducting inductor is a channel portion of a field effect type superconducting three-terminal device.

[Action]

In the present invention, when switching of the feedback magnetic flux amount is instructed by the switching instruction means, the superconducting feedback means electrically switches the magnitude of the feedback magnetic flux amount to change the slew rate.

Therefore, an appropriate slew rate can be selected according to the application with one digital squid, and the measurement sensitivity and the response speed can be set to desired values.

〔Example〕

 Hereinafter, the present invention will be described with reference to the drawings.

1 to 6 are views showing a first embodiment of a superconducting device according to the present invention. FIG. 1 is a block diagram of a superconducting device. In this figure, reference numeral 1 denotes a pickup coil which is composed of a superconducting loop and takes out a magnetic flux interlinked in the loop to pick up a magnetic flux to be measured. This is a squid sensor (superconducting quantum interference device) that receives the difference between the measured signal magnetic flux Φ _S and the feedback magnetic flux Φ _{FB that} are magnetically coupled and that is pulsed by an AC bias. The squid sensor 2 has an input magnetic flux (Φ
A pulse corresponding to _S− Φ _FB ) is output. As the squid sensor 2, a sensor for alternating current biasing a two-junction quantum interference device or a sensor for obtaining a pulse by inputting an analog output of a conventional dc-SQUID sensor to a superconducting comparator is used.

Reference numeral 3 denotes a superconducting feedback unit. The superconducting feedback unit 3 measures a pulse output from the squid sensor 2, feeds back a magnetic flux quantum corresponding to the measurement result to the input side of the squid sensor 2 through magnetic field coupling, and outputs a switching command. The magnetic flux quantum to be fed back is electrically switched based on a switching signal from a circuit (corresponding to switching command means) 4. The switching instruction circuit 4 is for instructing switching of the magnetic flux quantum fed back to the squid sensor 2 by an operation from an external operator. For example, by operating a knob, the switching signal such that a slew rate of feedback can be appropriately selected. Is generated and output to the superconducting feedback means 3. Alternatively, with reference to the pulse output, in accordance with the change of the signal magnetic flux [Phi _S, it may be provided to automatically provide the control circuit 4a of the switching signal to the switching command circuit 4.

Here, the detailed circuit configuration of the superconducting feedback means 3 is shown in FIG. 2, and the superconducting feedback means 3 is composed of superconducting feedback circuits 5, 6, superconducting OR gates 7 to 10 and superconducting OR gates 7 to 10. The AND gates 11 and 12 are provided. Since feedback to the squid sensor 2 is performed by magnetic field coupling, the feedback line 3a is simply connected to the squid sensor 2 in FIG. In the superconducting feedback circuits 5 and 6, the amount of magnetic flux ΔΦ to be fed back per pulse is changed for each circuit. For example, the superconducting feedback circuit 6 has 10 times the amount of feedback magnetic flux ΔΦ with respect to the superconducting feedback circuit 5. It is set as follows. For example, as shown in FIG. 3, the superconducting feedback circuits 5 and 6 include Josephson junctions J ₁ and J ₂ in the superconducting loop 15 and include the squid sensor 2.
A write gate 16 for converting pulses from
A superconducting storage loop consisting of a superconducting inductor 17 that converts a pulse passed through the write gate 16 into a magnetic flux quantum and stores it.
An up / down counter 21 composed of a Josephson circuit for counting pulses from the squid sensor 2 and a D / A converter 22 for performing D / A conversion of the pulse count number may be used as shown in FIG. May be used. The feedback to the input side of the squid sensor 2 is magnetically coupled to the superconducting inductor 17 in FIG.
M _f ), and in FIG. 4 through a feedback coil 24 which is magnetically coupled to the coil 23 connected to the output of the D / A converter 22 (the mutual inductance is also M _f ).

Returning to FIG. 2 again, the output pulse of the squid sensor 2 passes through the OR gates 8 and 10 and the AND gates 11 and 1 respectively.
The signals a and b (corresponding to the switching signal) from the switching command circuit 4 are supplied to the AND gates 11 and 12 through the OR gates 7 and 9, respectively. The AND gates 11 and 12 supply output pulses from the squid sensor 2 to the superconducting feedback circuits 5 and 6, respectively, when the signals a and b are "1". Therefore, by changing the levels of the signals a and b, one of the superconducting feedback circuits 5 and 6 is operated to change the feedback slew rate.

In the above configuration, the squid sensor 2 receives the difference between the measured signal magnetic flux Φ _S transmitted from the pickup coil 1 and the feedback magnetic flux Φ _FB , and pulsates this with an AC bias to respond to the difference (Φ _S −Φ _FB ). Output pulse. On the other hand, the superconducting feedback means 3 operates to increase the feedback magnetic flux for each pulse, and the total flux linkage applied to the squid sensor 2 is maintained at zero by this feedback. Is measured from the feedback amount that cancels out.

Here, when performing normal measurement, that is, when maintaining the sensitivity at a predetermined resolution from the measurement response speed, the knob of the switching command circuit 4 is set to the normal position and the signal a is set to “1”. Thereby, the output pulse of the squid sensor 2 is supplied from the OR gate 8 to the superconducting feedback circuit 5 through the AND gate 11, and the superconducting feedback circuit 5
As a result, the signal is fed back with a magnetic flux amount ΔΦ per pulse, and a normal slew rate is obtained. On the other hand, when the slew rate is to be changed, for example, when the response speed of the measurement is desired to be higher than the sensitivity (resolution), the knob of the switching signal circuit 4 is operated to set the signal b to "1". As a result, the output pulse of the squid sensor 2 is supplied from the logic gate 10 to the superconducting feedback circuit 6 through the AND gate 12, and the superconducting feedback circuit 6 provides a feedback magnetic flux amount 10 times per pulse (10 × ΔΦ). Is fed back and becomes a 10 times slew rate, and the response speed is improved. In other words, even if sensitivity is sacrificed, it is possible to meet the demand for increasing the response speed of measurement. Therefore, in this embodiment, 1
An appropriate slew rate can be selected in accordance with the use of the digital squid 2 so that the measurement sensitivity and the response speed can be set to desired values without complicating the configuration and increasing the cost.

The signals a and b may both be set to “1” so that the sum of the feedback magnetic fluxes in the superconducting feedback circuits 5 and 6 is fed back to the squid sensor 2.

In addition to providing two superconducting feedback circuits, more than two superconducting feedback circuits may be provided, and at the same time, some switching signals may be set to "1" to change the slew rate widely. Further, the switching of the slew rate may be automatically selected by the control circuit 4a depending on the nature of the signal as well as externally by a knob. By doing so, for example, when the time change of the signal is sharp, the slew rate can be increased, and when the signal is gentle, the slew rate can be reduced and the sensitivity can be increased. FIG. 5 shows a detailed example of the control circuit 4a and the switching command circuit 4 shown in FIG. 1. The slew rate can be automatically changed depending on the nature of the signal. That is, in FIG. 5, 101 to 107 are Josephson OR gates, 108 to 111 are Josephson AND gates, 112 and 113 are timed inverters, 114 is a superconducting up / down counter, and 115 is a switching circuit. Φ _{1 to} Φ ₃ are three-phase power supplies for driving these gates and circuits, and have waveforms as shown in FIG. In the case of FIG. 6, the sensor output pulse includes (Φ
_A positive pulse or a negative pulse is generated according to the sign of ( _S− Φ _FB ). Since these output pulses are generated in synchronization with the sensor bias, the sensor output can be transmitted to the Josephson gate by adjusting the phases of the three-phase power supply waveform as described above.

Therefore, the circuit shown in FIG. 5 works to gradually increase the feedback amount per pulse when the positive or negative feedback amount continues, and to reduce the feedback amount when it does not continue, that is, when the feedback is excessive. For this reason, when the signal changes sharply, the response can be made faster, and when the signal is warm, the response can be made slower to increase the sensitivity. Note that the method of changing the response by a signal is not limited to the above circuit side, and various control circuits can be used.

Next, FIG. 7 is a view showing a second embodiment of the present invention.
This embodiment is an example in which a superconducting inductor 17 and a storage loop 28 including a plurality of write gates 16a, 16b... Are used as a superconducting feedback circuit. Then, one write gate is configured to add one flux quantum to the storage loop 28 for each pulse received. Therefore, the number of write gates to be operated can be determined by the signals a, b,..., And the number of magnetic flux quanta added per pulse can be switched by the signals a, b,.

FIG. 8 is a view showing a third embodiment of the present invention. In this embodiment, a superconducting inductor is used as a superconducting feedback circuit.
In this example, two 17a and 17b are connected in parallel, channel portions 30a and 30b of the field-effect superconducting transistor are provided in a part of each, and a storage loop 29 including one write gate 16 is used. The feedback to the input side of the squid sensor 2 is
Magnetic coupling to the superconducting inductors 17a and 17b (coupling degrees are M _f1 and M
_f2 ) This is performed through the feedback coils 19a and 19b, respectively. When any of the signals a and b is applied, the superconductivity of any of the channel portions 30a and 30b of the field-effect superconducting transistor is lost, and the magnetic flux is accumulated only in the superconducting inductor where the superconductivity is alive. . Therefore, by changing the degree of coupling of the superconductivity to the storage loop 29 as M _f1 and M _f2 , the feedback magnetic flux amount per pulse can be switched by the switching signal.

FIG. 9 is a view showing a fourth embodiment of the present invention. In this embodiment, a superconducting inductor is used as a superconducting feedback circuit.
Shunting a part of 31 with a superconducting small inductor 32,
A channel portion 33 of a field effect type superconducting transistor is provided in a part of the inductor 32, and one write gate is provided.
This is an example in which an accumulation loop including 16 is used. The magnetic field coupling for feedback is the same as in FIG. Also in the case of the present embodiment, when the signal a is given, the superconductivity of the channel portion 33 of the field effect type superconducting transistor is lost, the shunt is no longer effective, and the inductor of the superconducting inductor 31 becomes large. The inductor of the conduction inductor 31 becomes smaller. Therefore, the amount of feedback magnetic flux per pulse can be switched by switching the inductor of the superconducting inductor 31 according to the signal a.

〔The invention's effect〕

According to the present invention, an appropriate slew rate can be selected according to the application with one digital squid, and the measurement sensitivity and the response speed can be set to desired values without complicating the configuration and increasing the cost. can do.

[Brief description of the drawings]

1 to 6 are diagrams showing a first embodiment of a superconducting device according to the present invention, FIG. 1 is a block diagram thereof, FIG. 2 is a circuit diagram of the superconducting feedback means, and FIG. FIG. 4 is a diagram showing another configuration of the superconducting feedback circuit, FIG. 5 is a detailed circuit diagram of the control circuit, etc., and FIG. 6 is a diagram of the control circuit, etc. FIG. 7 is a diagram showing a configuration of a superconducting feedback circuit of a second embodiment of the superconducting device according to the present invention. FIG. 8 is a diagram showing a third embodiment of the superconducting device according to the present invention. FIG. 9 is a diagram showing a configuration of a superconducting feedback circuit of the fourth embodiment of the superconducting device according to the present invention. 1. Pickup coil 2. Squid sensor (superconducting quantum interference device) 3. Superconducting feedback means 4. Switching command circuit (switching command means) 5, 6.
Superconducting feedback circuit (superconducting feedback means), 7 to 10: OR gate, 11, 12: AND gate, 15: Superconducting loop, 16, 16a, 16b ... Write gate, 17, 17a, 17b, 31 ... Superconducting inductor, 18, 28,
29, 34… accumulation loop, 19, 19a, 19b, 24… feedback coil, 21… up-down counter, 22… D /
A converter, 30a, 30b, 33 ... channel part of field effect type superconducting transistor, 32 ... inductor.

Claims (6)

(57) [Claims] A pickup coil comprising a superconducting loop for taking out a magnetic flux interlinked in the loop; a superconducting quantum interference device magnetically coupled to the pickup coil for pulsing the taken out magnetic flux with an AC bias; Superconducting feedback means for measuring a pulse output from the quantum interference element and feeding back a flux quantum corresponding to the measurement result to the input side of the superconducting quantum interference element through magnetic field coupling, In a superconducting device that measures a magnetic flux linked to a pickup coil based on an output pulse, a switching command unit that commands switching of the magnetic flux quantum fed back to the superconducting quantum interference element is provided, and the superconducting feedback is provided. Means for feeding the superconducting quantum interference device based on the command from the switching command means. Superconducting apparatus characterized by being configured to switch said magnetic flux quanta to back electrically. 2. The superconducting feedback means includes a plurality of feedback circuits, a logical product gate is provided between the superconducting quantum interference device and the feedback circuit, and the superconducting quantum is controlled based on a command from the switching command means. 2. The superconducting device according to claim 1, wherein a pulse output from the interference element is transmitted to which feedback circuit. 3. The superconducting feedback means includes a superconducting inductor and a gate for writing flux quanta.
The superconducting device according to claim 1, comprising a superconducting loop. 4. The superconducting feedback means includes a plurality of write gates in a superconducting loop thereof, and a logical product gate is provided between a pulse output from the superconducting quantum interference device and the write gate. 4. The superconducting device according to claim 3, wherein a pulse output from the superconducting quantum interference device is switched to which write gate based on the instruction. 5. The superconducting feedback means includes a plurality of superconducting inductors connected in parallel to the superconducting loop, and at least a part of these superconducting inductors is a channel portion of a field effect type superconducting three-terminal element. 4. The superconducting device according to claim 3, wherein: 6. The superconducting feedback means shunts a part of the superconducting loop with a relatively small superconducting inductor, and at least a part of the small superconducting inductor includes a field effect type superconducting three-terminal element. 4. The superconducting device according to claim 3, wherein the superconducting device is a channel portion.