JP3148479B2 - High sensitivity magnetic field detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-sensitivity magnetic field detecting apparatus using a DC-SQUID (DC driven superconducting quantum interference device).

2. Description of the Related Art Conventionally, a bias current supply circuit constituting a part of a DC-SQUID drive circuit device has been constituted by a constant current circuit. FIG. 8 is a diagram showing a configuration of a conventional high-sensitivity magnetic field detection device. 1 is a DC-SQUID, 2 is a constant current circuit, 5 is a voltage amplifying circuit, 6 is an integrating circuit, 7 is a voltage-current converting circuit, and a portion surrounded by a dotted line of 8 is a feedback circuit. DC-SQUID 1 is supplied with a bias current from constant current circuit 2. The signal voltage of the DC-SQUID 1 is amplified by the voltage amplifying circuit 5 and transmitted to the feedback circuit 8, and the feedback current is converted by the feedback coil 9 as a feedback magnetic flux into the DC-SQUID 1.
It is returned to D1. FIG. 9 shows a conventional DC-SQUI.
FIG. 9 is a diagram showing a relationship between a current-voltage characteristic of D and a bias current. In the current-voltage characteristics of the DC-SQUID, the superconducting critical current changes by ΔI according to the magnitude of the magnetic flux input to the DC-SQUID. When a bias current having the same magnitude as the maximum superconducting critical current value is supplied by using a constant current circuit, a voltage change of ΔV1 at maximum is obtained according to the magnitude of the input magnetic flux as shown in FIG.

In the above-described conventional high-sensitivity magnetic field detecting apparatus, the value of ΔV1 is a value unique to DC-SQUID and cannot be further increased. When the voltage change ΔV1 of the connected DC-SQUID is small, the magnetic flux-voltage conversion efficiency dV / dφ deteriorates, and there is a problem that the noise characteristics and the frequency characteristics of the high-sensitivity magnetic field detection device deteriorate.

According to the present invention, in order to solve the above-mentioned problems, a bias current supply circuit constituting a part of a DC-SQUID drive circuit device includes a constant current circuit and a signal voltage. And a voltage / current conversion means for adding to the bias current. Alternatively, the bias current supply circuit includes a constant voltage circuit, a voltage addition circuit that adds the output voltage of the constant voltage circuit and the signal voltage, and a voltage-current conversion unit that converts the output voltage of the voltage addition circuit into a current.

In the above-described high-sensitivity magnetic field detecting device, the voltage change ΔV is determined on the current-voltage characteristic of the connected DC-SQUID.
Even when 1 is small, a larger voltage change can be realized with respect to the magnetic flux change, that is, the magnetic flux voltage conversion efficiency dV / dφ can be improved.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram illustrating a configuration of a high-sensitivity magnetic field detection device according to a first embodiment of the present invention. 1 is DC-SQUA
ID and 5 are voltage amplifier circuits, 6 is an integration circuit, 7 is a voltage-current conversion circuit, and a portion surrounded by a dotted line of 8 is a feedback circuit.
A portion 4 is a bias current supply circuit comprising a voltage / current conversion means 3 and a constant current circuit 2 installed according to the present invention. DC
The signal voltage of -SQUID1 is amplified by the voltage amplifier circuit 5 and transmitted to the feedback circuit 8, and the feedback current is fed back to the DC-SQUID1 by the feedback coil 9 as feedback magnetic flux. On the other hand, the output of the voltage amplifier 5 is converted into a current by the voltage-current conversion means 3 and added to the constant current from the constant current circuit 2 so that the DC-S
Supplied to QUID1. According to the configuration of the high-sensitivity magnetic field detection device as described above, the bias current supplied to DC-SQUID1 increases as the voltage of DC-SQUID1 increases. FIG. 6 shows a DC-DC according to the first embodiment of the present invention.
FIG. 4 is a diagram illustrating a relationship between a current-voltage characteristic of a SQUID and a bias current. The superconducting critical current changes by ΔI according to the change of the input magnetic flux to the DC-SQUID. When the current value of the constant current circuit 2 is set to the same value as the maximum superconducting critical current value, the bias current supplied to the DC-SQUID 1 increases as the voltage increases, as shown in FIG. Therefore, the maximum value of the output voltage becomes the magnitude indicated by ΔV2 in the figure, and a voltage change larger than the output voltage ΔV1 shown in the conventional example of FIG. 9 can be realized. In the high-sensitivity magnetic field detection device as described above, when the voltage change at the time of the constant current bias of the DC-SQUID is small, the voltage-current conversion unit that converts the signal voltage into the current and adds the current to the bias current is provided.
It is possible to realize a larger voltage change with respect to the magnetic flux change, improve the magnetic flux-voltage conversion efficiency dV / dφ, and improve the noise characteristics and frequency characteristics of the high-sensitivity magnetic field detection device. FIG. 2 is a diagram illustrating a configuration of a high-sensitivity magnetic field detection device according to a second embodiment of the present invention. The voltage detection position of the voltage / current converter 3 is different from that of the embodiment shown in FIG. The embodiment shown in FIG. 1 has a configuration in which the output voltage of the voltage amplifying circuit 5 is detected and converted into a current by the voltage-to-current converter 3, but in this embodiment, the voltage-to-current converter 3 is a DC-SQUID.
1 is directly detected, converted into a current, and added to the current of the constant current circuit 3. Other configurations are the same as those of the embodiment shown in FIG. The operation and effect of the configuration of the high-sensitivity magnetic field detection device described above are the same as those of the previous embodiment except that the voltage before amplification is converted into a current. FIG. 3 is a diagram showing a configuration of a bias current supply portion of a high sensitivity magnetic field detection device according to a third embodiment of the present invention. 1
2 is a voltage adding circuit, and 13 is a constant voltage circuit. The difference from the previous embodiment is that the output voltage of the constant voltage circuit 13 and the signal voltage output from the voltage amplifying circuit 5 are added in advance by the voltage adding circuit 12 and then converted into a bias current by the voltage / current means 3. The operation and effect of the configuration of the high-sensitivity magnetic field detection device described above are the same as those of the previous embodiment except that the voltage is added in advance and then converted to the bias current. FIG. 4 is a diagram showing a configuration of a bias current supply portion of a high sensitivity magnetic field detection device according to a fourth embodiment of the present invention. The bias current is set to DC-SQ
The difference is that the power is supplied via the damping resistor 10 of UID1. By supplying the bias current through the damping resistor 10, high frequency noise included in the bias current can be reduced. Further, in the current-voltage characteristics, the voltage represented by the product of the resistance value and the current value of a quarter of the damping resistance value Rd increases. FIG. 7 is a diagram showing a relationship between a current-voltage characteristic and a bias current of a DC-SQUID according to a fourth embodiment of the present invention. In the current-voltage characteristics, the slope of the characteristic increases to the right (to the voltage side) by the voltage increase represented by the product of the resistance value and one-fourth of the damping resistance value Rd. With the conventional constant current bias, the maximum voltage change obtained according to the magnitude of the input magnetic flux is the same as ΔV1 shown in the conventional example of FIG. According to the configuration of the bias current supply circuit 4 according to the present invention, the maximum value of the output voltage is ΔV3 in FIG.
, And a voltage change larger than the output voltage ΔV2 shown in FIG. 6 can be realized. According to the configuration of the high-sensitivity magnetic field detection device as described above, a larger voltage change can be realized with respect to a change in magnetic flux, and the operation and effect are the same as those in the previous embodiment. FIG. 5 is a diagram showing a configuration of a bias current supply portion of a high sensitivity magnetic field detection device according to a fifth embodiment of the present invention. The difference from the previous embodiment is that the bias current is supplied to the DC-SQUID 1 via the resistor 11. By supplying the bias current through the resistor 11, high frequency noise included in the bias current can be reduced. Further, in the current-voltage characteristic, the resistance 11
The voltage represented by the product of the resistance value twice the resistance value R and the current value increases. The operation and effect of the configuration of the high-sensitivity magnetic field detection device described above are the same as those of the previous embodiment. Although FIG. 5 shows an example in which two resistors 11 are arranged, the bias supply circuit 4 according to the present invention can be used even if one resistor 11 is used.
The operation and effect of the configuration of the high-sensitivity magnetic field detection device using the same are not different from the previous embodiment. In the above embodiment, the non-modulation type high-sensitivity magnetic field detecting device is shown. However, in the high-sensitivity magnetic field detecting device in which the feedback circuit 8 is a modulation type, the bias supply circuit 4 is connected to the voltage-current converting means 3 and the constant current Even if the circuit 2 is used, the operation and effect are the same as those of the previous embodiment. Further, in the high-sensitivity magnetic field detecting device in which the feedback circuit 8 is a modulation type, the bias supply circuit 4 has a constant voltage circuit 13 and an output of the constant voltage circuit 13 as in the third embodiment of the present invention shown in FIG. Even if it is composed of the voltage adding circuit 12 for adding the voltage and the signal voltage and the voltage-current converting means 3 for converting the output voltage of the voltage adding circuit into a current, the operation and the effect are the same as those of the previous embodiment. DC-
As the SQUID 1, besides a conventional DC-SQUID having one superconducting ring, a series-coupled DC-SQUID as disclosed in Japanese Patent Laid-Open No.
DC-SQUI of parallel connection type as shown in 2980
D is also used.

As described above, according to the present invention, in the high-sensitivity magnetic field detecting apparatus, the voltage-current converting means for converting the signal voltage into the current and adding the signal voltage to the bias current is provided, whereby the connected DC-DC converter is provided. Even when the voltage change during the constant current bias of the SQUID is small, a larger voltage change can be realized with respect to the magnetic flux change, the magnetic flux voltage conversion efficiency dV / dφ is improved, and the noise of the high-sensitivity magnetic field detection device is improved. It is possible to improve characteristics and frequency characteristics.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a high-sensitivity magnetic field detection device showing a first embodiment of the present invention.

FIG. 2 is a configuration diagram of a high-sensitivity magnetic field detection device according to a second embodiment of the present invention.

FIG. 3 is a configuration diagram of a bias current supply part of a high sensitivity magnetic field detection device according to a third embodiment of the present invention.

FIG. 4 is a configuration diagram of a bias current supply portion of a high sensitivity magnetic field detection device according to a fourth embodiment of the present invention.

FIG. 5 is a configuration diagram of a bias current supply portion of a high sensitivity magnetic field detection device according to a fifth embodiment of the present invention.

FIG. 6 is a diagram illustrating a relationship between a current-voltage characteristic and a bias current of the DC-SQUID according to the embodiment of the present invention.

FIG. 7 is a diagram illustrating a relationship between a current-voltage characteristic and a bias current of a DC-SQUID according to a fourth embodiment of the present invention.

FIG. 8 is a diagram illustrating a configuration of a conventional high-sensitivity magnetic field detection device.

FIG. 9 is a diagram showing a relationship between a current-voltage characteristic and a bias current of a DC-SQUID according to a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 DC-SQUID 2 Constant current circuit 3 Voltage-current conversion means 4 Bias current supply circuit 5 Voltage amplifier circuit 6 Integration circuit 7 Voltage-current conversion circuit 8 Feedback circuit 9 Feedback coil 10 Damping resistor 11 Resistance 12 Voltage addition circuit 13 Constant voltage circuit

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-4-340488 (JP, A) JP-A-4-204279 (JP, A) JP-A-4-269680 (JP, A) (58) Field (Int. Cl. ⁷ , DB name) G01R 33/00-33/18

Claims (4)

(57) [Claims] 1. A DC-SQUID (DC driven superconducting quantum interference device), a bias current supply circuit for supplying a bias current to the DC-SQUID, and the DC-SQUI
The bias current supply circuit is fixed in a high-sensitivity magnetic field detection device including a voltage amplification circuit for amplifying the signal voltage of D and a feedback circuit for integrating the signal voltage and converting the voltage to a current to feed back the DC-SQUID. A high-sensitivity magnetic field detection device comprising a current circuit and voltage-current conversion means for converting a signal voltage into a current and adding it to a bias current, thereby improving magnetic flux-voltage conversion efficiency . 2. DC-SQUID (DC-driven superconducting amount)
And a bias current to the DC-SQUID.
A bias current supply circuit for supplying the DC-SQUI;
The product of the signal voltage and the voltage amplifier circuit that amplifies the signal voltage of D
Divide the voltage and current and feed back to the DC-SQUID
High sensitivity magnetic field detector consisting of feedback circuit for
The bias current supply circuit includes a constant voltage circuit, a voltage addition circuit that adds an output voltage of the constant voltage circuit and a signal voltage, and a voltage / current conversion unit that converts an output voltage of the voltage addition circuit into a current. Configure to improve magnetic flux voltage conversion efficiency
Sensitive magnetic field detecting device, characterized in that cause. 3. The high-sensitivity magnetic field detecting device according to claim 1, wherein the bias current supply line of the DC-SQUID is connected to a damping resistor of the DC-SQUID. 4. The high-sensitivity magnetic field detection device according to claim 1, wherein the bias current supply line of the DC-SQUID is connected to the DC-SQUID via a resistor.