JP3522104B2 - 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 DC-driven superconducting quantum interference device (DC-SQUID: DC Superconducti).
DC-S using ng Quantum Interference device)
For details of the QUID magnetometer, refer to F. L. L. The present invention relates to the configuration of a phase detection circuit that constitutes a part of a circuit device.

2. Description of the Related Art A high-sensitivity magnetic field detecting device has been conventionally used for detecting a minute magnetic field emitted from a living body. FIG. 2 is a block diagram showing an example of the configuration of a conventional high sensitivity magnetic field detection device. The part surrounded by the dotted line is the phase detection circuit 10. The modulated signal from the DC-SQUID 20 amplified by the amplifier 30 is detected by the phase detection circuit 10. The phase detection circuit 10 uses the rectangular wave of the oscillator 40 as a reference signal.
The phase detector 11 and the second phase detector 12 using the signal obtained by changing the phase of the rectangular wave of the oscillator 40 by the first phase shifter 13 as a reference signal. The outputs of the first phase detector 11 and the second phase detector 12 are added by the adder 50. With this configuration, for example, when the phase shift amount of the first phase shifter 13 is θ = −90 °, the DC-SQUID 20
When the phase of the modulation signal transmitted from the to the phase detection circuit is within the range of θ = 90 ° to θ = 180 ° and θ = 270 ° to θ = 360 ° with respect to the phase of the oscillator 40, special phase adjustment is performed. Even without the circuit, the detection signal after the adder 50 becomes constant, and the DC-SQUID 20 operates stably.

In the conventional high-sensitivity magnetic field detection device described above, the phase of the modulation signal transmitted from the DC-SQUID 20 to the phase detection circuit 10 is θ = 90 ° with respect to the phase of the oscillator 40. θ = 180 ° and θ = 27
Out of the range of 0 ° to θ = 360 ° θ = 0 ° to θ =
When 90 ° and θ = 180 ° to θ = 270 °, the adder 50 makes a difference between the output of the first phase detector and the output of the second phase detector, so that the detection output decreases and DC-
There are problems that the operation of the SQUID is unstable and the magnetic field detection performance is deteriorated.

(First Means) In order to solve the above-mentioned problems, the present invention provides a reference signal inverting circuit between a first phase shifter 13 and a second phase detector 12. Further, the reference signal inversion switch is provided so that the phase of the reference signal of the second phase detector 12 can be easily changed by 180 °. (Second Means) In addition to the first means, a monitor terminal is installed at the outputs of the first phase detector and the second phase detector. According to the structure of the high-sensitivity magnetic field detection device according to the first means, the reference signal of the phase detector 12 is phase-shifted by 180 ° according to the phase difference between the modulation signal and the oscillator, so that the position of the modulation signal and the oscillator is changed. The detection output of the adder 50 can be made substantially constant in the entire range of the phase difference θ = 0 ° to 360 °, and stable DC-SQUID driving and the best magnetic field detection performance can be obtained. Since the output of the first phase detector and the output of the second phase detector can be monitored by the second means, it is possible to easily detect the phase difference between the modulated signal and the oscillator, which is usually difficult. Thus, it becomes possible to easily determine the phase shift switching of the reference signal of the phase detector 12.

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. (Embodiment 1) FIG. 1 is a diagram showing the structure of a high-sensitivity magnetic field detection apparatus showing Embodiment 1 of the present invention. In addition to the configuration of the conventional high-sensitivity magnetic field detection device, the reference signal inversion circuit 15 and the reference signal inversion switch 16 are provided between the first phase shifter 13 and the second phase detector 12. The rectangular wave from the oscillator 40 is phase-shifted to θ = −90 ° by the first phase shifter 13 and becomes the reference signal of the second phase detector 12. The reference signal of the phase detector 12 is O
In the N state, the signal passes through the reference signal inverting circuit 15, and when the reference signal inverting switch 16 is in the OFF state, the signal does not pass through the reference signal inverting circuit 15. The phase difference between the modulated signal from the DC-SQUID 20 amplified by the amplifier 30 and the output signal of the oscillator 40 is from θ = 0 ° to θ =
In the case of 90 ° and θ = 180 ° to θ = 270 °, the reference signal reversing switch 16 is turned on, and in the case of θ = 90 ° to θ = 180 ° and θ = 270 ° to θ = 360 °, the reference signal is turned on. The reversing switch 16 is turned off. Although the amount of phase shift by the first phase shifter 13 is set to θ = −90 °, the phase may be shifted to θ = 90 °. In this case, the phase difference between the modulated signal and the output signal of the oscillator 40 is from θ = 0 ° to θ =
When 90 ° and θ = 180 ° to θ = 270 °, the reference signal inversion switch 16 is turned off, and θ = 90.
From θ to θ = 180 ° and θ = 270 ° to θ = 360
In the case of °, the reference signal inversion switch 16 is turned on. (Embodiment 2) FIG. 3 is a diagram showing the configuration of a phase detection circuit 10 of a high-sensitivity magnetic field detection apparatus showing Embodiment 2 of the present invention.
The configuration other than the phase detection circuit 10 is the same as that of the first embodiment. A first phase shifter 13 and a second phase shifter 14 are provided in parallel between the oscillator 40 and the second phase detector 12, and the reference signal inversion switch 1 is provided at the output of the two phase shifters.
6 is connected. The output of the oscillator 40 is phase-shifted to θ = −90 ° in the first phase shifter 13 and + 90 ° in the second phase shifter 14. The phase difference between the modulated signal from the DC-SQUID 20 amplified by the amplifier 30 and the output signal of the oscillator 40 is from θ = 0 ° to θ = 90 ° and θ.
= 180 ° to θ = 270 °, the reference signal inversion switch 16 is switched to the second phase shifter side, and θ = 90.
From θ to θ = 180 ° and θ = 270 ° to θ = 360
In the case of °, the reference signal inversion switch 16 is switched to the first phase shifter side. (Embodiment 3) FIG. 4 is a diagram showing the configuration of a phase detection circuit 10 of a high-sensitivity magnetic field detection apparatus showing Embodiment 3 of the present invention.
Embodiment 1 except that the first detection monitor terminal 17 for monitoring the output of the first phase detector 11 and the second detection monitor terminal 18 for monitoring the output of the second phase detector 12 are provided. There is no difference from 1. First
Waveform of the detection monitor terminal 17 and the second detection monitor terminal 1
When the waveform of 8 is monitored, there is a case where the phase of the signal at the two detection monitor terminals is the same as that of the signal at the two detection monitor terminals and a case where the two are shifted by 180 ° due to the phase relationship between the modulation signal from the DC-SQUID 20 and the reference signal of the two phase detectors. is there. By switching the reference signal inversion switch 16, the phases of the signals at the two detection monitor terminals are always the same.

According to the present invention, the second phase detector 12
Since it is possible to easily change the phase of the reference signal of 180 °, the detection output of the adder 50 must be constant over the entire range of the phase difference between the modulated signal and the oscillator from θ = 0 ° to 360 °. It is possible to obtain stable integrator output for the phase drift of the modulation signal transmitted from the DC-SQUID and for driving a plurality of DC-SQUIDs with different characteristics, and improve the measurement accuracy. can do.

[Brief description of drawings]

FIG. 1 is a diagram showing a structure of a high-sensitivity magnetic field detection apparatus showing Example 1 of the present invention.

FIG. 2 is a block diagram showing an example of a configuration of a conventional high sensitivity magnetic field detection device.

FIG. 3 is a diagram showing a configuration of a phase detection circuit 10 of a high sensitivity magnetic field detection device showing a second embodiment of the present invention.

FIG. 4 is a diagram showing a configuration of a phase detection circuit 10 of a high sensitivity magnetic field detection device showing a third embodiment of the present invention.

[Explanation of symbols]

10 Phase detection circuit 11 First phase detector 12 Second phase detector 13 First phase shifter 14 Second phase shifter 15 Reference signal inversion circuit 16 Reference signal inversion switch 17 First detection monitor terminal 18 Second detection monitor terminal 20 DC-SQUID 30 amplifier 40 oscillator 50 adder 60 low pass filter 70 integrator

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-4-43978 (JP, A) JP-A-6-94815 (JP, A) JP-A-7-280903 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) G01R 33/035 ZAA

Claims (2)

(57) [Claims] 1. A DC-S in which a voltage is changed by detecting a magnetic field.
QUID (DC drive type superconducting quantum interference device) and DC-S
F. for driving the QUID. L. L (FluxLocked Loo
p) In a high-sensitivity magnetic field detection device consisting of a circuit device,
The F. L. L. A high-sensitivity magnetic field characterized in that a phase detection circuit forming a part of a circuit device is composed of two or more phase detectors, and the phase of a reference signal of at least one of the phase detection circuits can be switched. Detection device. 2. The high-sensitivity magnetic field detection device according to claim 1, wherein a monitor terminal is provided at an output of the two phase detectors.