JPH07280903A - Superconducting magnetometer - Google Patents

Abstract

PURPOSE:To obtain a superconducting magnetometer which eliminates a phase change and an amplitude change in the output of a preamplifier and which reduces a measuring error by installing a phase comparator, a variable phase shifter, an AGC circuit, a level comparator, a variable bias circuit and an AGC/defect discrimination circuit. CONSTITUTION:A SQUID 1 is immersed in liquid helium, it is cooled, and it is changed into a superconducting state. The interlinkage magnetic flux of the SQUID 1 at the time when an integrator switch 13 has been opened in a magnetic field to be measured, is used as the origin of an output zero, and the change amount of the magnetic flux from there is output as a voltage VH corresponding to the change amount of the magnetic field. The operating point of the SQUID 1 is situated in the position of a point A, and a full-wave-rectification- shaped signal is output. However, when the magnetic field to be measured is increased or decreased and the position is moved to a position B and a position C, a modulation signal OS and sine-wave-shaped signals in a positive phase and an opposite phase are output. Then, the voltage VH corresponding to the change amount of the magnetic field by an FLL circuit which is constituted of a bias circuit 6, of a preamplifier 7, a multiplier 8, a phase shifter 9, an oscillator 10, an integrator 11, a feedback resistor 12 and an AGC circuit 16 is output, it is fed back to a superconducting ring 2 via the resistor 12 and a modulation feedback coil 4, and it is returned to the point A.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a superconducting quantum interference device (Superconducting Quantum).
(Interference Device: hereinafter referred to as SQUID for short) relating to improvement of a highly sensitive magnetometer.

[0002]

2. Description of the Related Art FIG. 13 is a block diagram showing an embodiment of a conventional superconducting magnetometer. In the figure, 2 is a superconducting ring, 3A and 3B are Josephson junctions provided in the superconducting ring 2, 4 is a modulation feedback coil magnetically coupled to the superconducting ring 2, 1 is the superconducting ring 2, SQUID composed of Josephson junctions 3A and 3B and modulation feedback coil 4, 6 bias circuit, 7 preamplifier, 8 multiplier, 9 phaser, 10 oscillator, 12 feedback resistor, 13 integrator Switch, 14 is an integrating capacitor, 1
5A is an amplifier, 11 is an integrator composed of the integrator switch 13, the integrating capacitor 14 and the amplifier 15A,
Reference numeral 5 is a drive circuit composed of the bias circuit 6, the preamplifier 7, the multiplier 8, the phase shifter 9, the oscillator 10, the integrator 11 and the feedback resistor 12, and has a role of driving the SQUID 1 to take out a desired output. To do. V _P is SQUID amplification signal outputted from the preamplifier 7, O _S modulation signal outputted from the oscillator 10, V _H is the voltage output as a magnetic field measurement signal from the integrator 11.
A cable is connected between the SQUID 1 and the preamplifier 7.

The drive circuit 5 is generally a FLL (Flux).
This is a known circuit called a Locked Loop circuit, and its operation is, for example, Review of S.
scientific Instrument, 1984
, 55, 952-957.

Next, the operation will be described. Figure 14 is SQ
9 shows a Φ-V characteristic of a UID. In the figure, a is the output waveform of SQUID1 with respect to an external magnetic field, and b, c, and d are operating points when a sinusoidal modulation magnetic flux is applied,
It is an output waveform of SQUID1 for B and C. However, Φ
₀ is magnetic flux quantum, and its value is 2.07 × 10 ⁻¹⁵ Wb
Is. When SQIUD1 is cooled by immersing it in liquid helium and transitions to a superconducting state, the output of SQUID changes in voltage with respect to the magnetic flux linking itself with Φ ₀ as the cycle. Now, assuming that the operating point of SQUID1 is set as the point A in the figure, the modulation feedback coil 4 is generated based on the modulation signal O _S of several 100 KHz output from the oscillator 10.
For example, when a sinusoidal modulation magnetic flux of several 100 KHz is applied, the output of SQUID1 has a full-wave rectified waveform having a frequency twice that of the modulation signal O _s .

Here, when the external magnetic field increases and the operating point shifts to point B in the figure, the modulation signal O _S from SQUID1.
An output phase signal of the operating point external magnetic field is reduced on the contrary in the case of displaced point C is the output signal of the modulating signal O _S opposite phase. The preamplifier 7 amplifies a signal that changes in response to an increase or decrease in the external magnetic field to a desired magnitude, then phase-detects it with the multiplier 8, the phaser 9, and the oscillator 10, and further integrates it with the integrator 11. The magnetic field change amount by D
When converted into C voltage and the amount of change is fed back to the superconducting ring 2 by the modulation feedback coil 4 via the feedback resistor 12, the voltage generated by the feedback current flowing through the feedback resistor 12 is the external magnetic field. The amount of change in the electric field can be measured by extracting this voltage.

That is, when the integrator switch 13 which is initially closed is opened, the integrating capacitor 14 and the amplifier 15 operate as an integrator, and when the integrator switch 13 is opened, the closest points, such as points A and D, are generated. When the operating point is locked at the minimum and maximum positions and the magnetic flux Φ in the superconducting ring 2 is attempted to increase or decrease in this state in response to the increase or decrease of the external magnetic field, the multiplier 8 is output based on the output signal of the SQUID 1. , The phase shifter 9, the oscillator 10, and the integrator 11 generate a DC voltage corresponding to the increase or decrease of the external magnetic field, and this DC voltage cancels the magnetic flux of the superconducting ring 2 via the feedback resistor 12 and the modulation feedback coil 4. Control so that it is always fixed in the same position.

A circuit system for performing such control / measurement is generally called a FLL (Flux Locked Loop) circuit, and the change amount of the external magnetic field from the state where the magnetic flux is locked is a voltage generated by the feedback current flowing through the feedback resistor 12. V _H can be taken out as a magnetic field measurement value.

[0008]

In the conventional superconducting magnetometer, since the output of the SQUID is sent to the multiplier through the cable and the preamplifier, the temperature changes, the shape of the cable changes due to the vibration of the body, or the temperature and the power supply change. When phase fluctuations and amplitude fluctuations of the preamplifier output occur due to fluctuations, etc.,
The output of the phase detection fluctuates in proportion to these fluctuations, and finally the output of the integrator fluctuates, resulting in a magnetic field measurement error.

The present invention has been made in order to solve the above-mentioned problems, and compares the phase variation and amplitude variation of the preamplifier output due to temperature variation, cable shape variation due to machine vibration, temperature variation and power source variation. And variable phase shifter,
AGC circuit, level comparator and variable bias circuit, AGC
/ The purpose is to obtain a superconducting magnetometer with less measurement error by providing a defect determination circuit.

[0010]

In the superconducting magnetometer of the present invention, an AGC circuit for controlling the amplitude of a signal output from the preamplifier to a constant value is provided at the output stage of the preamplifier. It is a thing.

Further, according to the present invention, a phase comparator for inputting the output of the preamplifier and the modulation signal to detect a phase shift between them, and adjusting the phase of the modulation signal based on the output of the phase comparator. And a variable phase shifter that matches the phase with the output signal of the preamplifier.

According to the present invention, a level comparator for detecting a change in bias current based on the output of the preamplifier to generate a current control signal and the SQU by inputting the current control signal.
A variable bias circuit for supplying an appropriate bias current to the ID is provided.

According to the present invention, the phase of the modulation signal is adjusted based on the output of the phase comparator for detecting the phase shift between the output of the preamplifier and the modulation signal and the phase difference between the two. In addition to the variable phase shifter that matches the phase with the output signal of the preamplifier, input the level comparator that detects the fluctuation of the bias current based on the output of the preamplifier and generate the current control signal and the current control signal. A variable bias circuit for supplying an appropriate bias current to the SQUID is provided.

The present invention controls the amplitude of this signal to a constant value based on the signal output from the preamplifier, and
The output stage of the preamplifier is provided with an AGC / pass / fail judgment circuit that generates an abnormal signal that indicates an abnormality when the output of the preamplifier exceeds a certain range.

[0015]

According to the present invention, the AGC circuit controls the amplitude of the output signal of the preamplifier to a constant value based on the signal output from the preamplifier to prevent measurement errors.

According to the present invention, the phase comparator detects the phase difference between the output of the preamplifier and the modulation signal output from the oscillator, and based on the output of the phase comparator, the phase of the modulation signal is changed by the variable phase shifter. Is adjusted to make the phase difference between them zero, thereby preventing a measurement error.

According to the present invention, the level comparator detects the variation of the bias current based on the output of the preamplifier and outputs it as a current control signal, and based on this current control signal, the variable bias circuit appropriately controls the SQUID. The measurement error is prevented by supplying the bias current.

Further, according to the present invention, the phase difference between the output of the preamplifier and the modulation signal output from the oscillator is detected by the phase comparator, and the phase of the modulation signal is changed by the variable phase shifter based on the output of the phase comparator. Is adjusted to make the phase difference between the two zero, and the level comparator detects variation in the bias current based on the output of the preamplifier and outputs it as a current control signal. Based on this current control signal, the variable bias circuit Therefore, a measurement error is prevented by supplying an appropriate bias current to the SQUID.

According to the present invention, the AGC / defective judgment circuit controls the amplitude of the output signal of the preamplifier to a constant value on the basis of the signal output from the preamplifier to prevent a measurement error, and the amplitude of the output signal of the preamplifier. When a certain range is exceeded, an abnormal signal is output to notify that there is an abnormality.

[0020]

【Example】

Example 1. FIG. 1 is a block diagram showing an embodiment of the present invention. In the figure, 1 to 4 and 6 to 15A are the same as the conventional one, 1
6 is an AGC for controlling the output of the preamplifier 7 to a constant value
Circuit, V _P is a SQUID amplified signal, O _S is a modulated signal, V
_H is a voltage output from the integrator 11 as a magnetic field measurement signal.

FIG. 2 is a block diagram showing an example of the configuration of the AGC circuit 16. In the figure, 15B is the same amplifier as 15A, 17 is a voltage dividing resistor, and 18A is FET (F
field effect transistor), D,
S and G are the drain, source, and gate of the FET 18A, and 19A is a bridge rectifier circuit for full-wave rectification.
Reference numeral 20 is a smoothing resistor, 21A and 21B are smoothing capacitors, 22A is a differential amplifier, and V _P is a SQUID amplified signal.

Next, the operation of the superconducting magnetometer according to the first embodiment of the present invention will be described. First, SQUID 1 is cooled by immersing it in liquid helium to be transformed into a superconducting state, and the SQUID interlinkage magnetic flux at the time when the integrator switch 13 is opened in the magnetic field to be measured is set as the origin of output zero, and from that point. The change amount of the interlinkage magnetic flux is output as a voltage V _H corresponding to the change amount of the magnetic field.

That is, the operating point of SQUID1 is normally shown in FIG.
There is a full-wave rectified signal at the position of point A of 4, but
B of the measured magnetic field is increased or decreased for example FIG. 14, when moving to the position and C, the modulation signal O _S and positive phase, and outputs a sinusoidal signal of opposite phase, then the bias circuit 6, a preamplifier 7, a multiplier 8, phaser 9, oscillator 10, integrator 11, feedback resistor 1
The FLL circuit composed of 2 and the AGC circuit 16 outputs a voltage V _H corresponding to the amount of change in the magnetic field, and this voltage V _H is fed back to the superconducting ring 2 via the feedback resistor 12 and the modulation feedback coil 4 for an instant. Return to the position of point A.

At this time, since the output of the SQUID passes through the cable and the preamplifier, the SQUID amplified signal V output from the preamplifier 7 due to changes in temperature, power supply, etc.
_Although the amplitude of _P fluctuates and tends to cause a measurement error, the AGC circuit 16 keeps the amplitude of the SQUID amplified signal V _{P at} a constant value to prevent the measurement error.

Specifically, the SQUID amplified signal V _P output from the preamplifier 7 is amplified and full-wave rectified by the amplifier 15B and the bridge rectifier circuit 19A, and further, the smoothing resistor 20 and the smoothing capacitors 21A and 21B. Smooth by.

After being amplified by the differential amplifier 22A, it is fed back to the gate G of the FET 18A to change the operating resistance R _DS between the drain D and the source S of the FET 18A in inverse proportion to this voltage. And the resistance value R _{B of the} voltage dividing resistor 17 and the operating resistance R _DS.
Is divided into the partial pressure ratio K shown in the following equation by
The increase / decrease of the amplified signal V _P is canceled and the amplitude of the SQUID amplified signal V _P is maintained at a constant value.

R _DS ∝ 1 / V _P ··· (1) K = R _DS / (R _DS + R _B ) ··· (2)

In the above embodiment, the SQUID 1 may be an RF-SQUID which includes one Josephson junction in the superconducting ring and is driven by an AC bias current.

Example 2. FIG. 3 is a block diagram showing a second embodiment of the present invention. In the figure, 1-4, 6-8, 10-1
5A is the same as the conventional one, 23 is a phase comparator, 24 is a variable phase shifter, V _P is a SQUID amplified signal, O _S is a modulation signal, and V _PS , V _PO and V _D are from the phase comparator 23, respectively. The phase lead signal, the phase delay signal, the phase discrimination signal, and V _H output are the voltages output from the integrator 11 as the magnetic field measurement signal.

FIG. 4 is a block diagram showing an example of the configuration of the phase comparator 23. In the figure, 25 is a frequency divider, 26A,
26B is a comparator, 27 is a phase detector, 28A, 2
8B is an integrating capacitor, 15C and 15D are amplifiers 15A
29A is an integrating circuit composed of the integrating capacitor 28A and the amplifier 15C, 29B is an integrating circuit composed of the integrating capacitor 28B and the amplifier 15D, 30 is a phase advance control signal generating circuit, and 31 is a phase delay. control signal generating circuit, 32 is a phase discriminating circuit, phase advance output terminal of the S, Q each said phase detector 27, phase delay output terminal, V _P is SQUID amplified signal, O _S modulation signal, DV _P is the comparator 26A is a digital divided signal, DV _O is a digital modulation signal output from the comparator 26B, V _S is a phase advance pulse signal output from the phase advance output terminal S of the phase detector 27, and V _O is phase delay pulse signal outputted from the phase delay output terminal Q of the phase detector 27, V _SA is output from the integrating circuit 29A Analog phase advance signal, V
_OA is an analog phase delay signal output from the integration circuit 29B, V _PS is a phase advance control signal output from the phase advance control signal generation circuit 30, and V _PO is output from the phase delay control signal generation circuit 31. Phase delay control signal, V
_D is a phase discrimination signal output from the phase discrimination circuit 32.

FIG. 5 is a block diagram showing an example of the configuration of the variable phase shifter 24. In the figure, 33A and 33B are selector switches for switching signals, and 18B and 18C are FETs.
The same FET as 18A, 34 is a phase advance capacitor,
35 phase lag capacitor, a, b, c are the changeover switch 33A, 33B of the contact, O _S modulation signal, V _PS
Is a phase lead control signal, V _PO is a phase delay control signal, and V _D is a phase determination signal.

Next, the operation of the superconducting magnetometer according to the second embodiment of the present invention will be described. First, SQUID 1 is cooled by immersing it in liquid helium to be transformed into a superconducting state, and the SQUID interlinkage magnetic flux at the time when the integrator switch 13 is opened in the magnetic field to be measured is set as the origin of output zero, and from that point. The change amount of the interlinkage magnetic flux is output as a voltage V _H corresponding to the change amount of the magnetic field.

That is, the operating point of SQUID1 is normally shown in FIG.
There is a full-wave rectified signal at the position of point A of 4, but
B of the measured magnetic field is increased or decreased for example FIG. 14, when moving to the position and C, the modulation signal O _S and positive phase, and outputs a sinusoidal signal of opposite phase, then the bias circuit 6, a preamplifier 7, a multiplier 8, an oscillator 10, integrator 11, a feedback of the voltage V _H and outputs a voltage V _H corresponding to the magnetic field variation by composed FLL circuit feedback resistor 12, a phase comparator 23 and the variable phase shifter 24, It is fed back to the superconducting ring 2 via the resistor 12 and the modulation feedback coil 4 and instantly returned to the position of point A.

On the other hand the divider 25 is normally observed are full-wave rectified like waveform i.e. the modulated signal O SQUID amplification signal V _P 1/2 frequency-divided to the modulation signal having a frequency twice that of the _S It converted to O _S same frequency sinusoidal signals with further, H zero or the signal at the comparator 26A
The i level and below are converted into a low-level square wave digital frequency division signal DV _P. Similarly the comparator 26B is converted into a digital modulation signal DV _O of the same period and which the modulated signal O _S.

Next, the phase detector 27 inputs the digital frequency-divided signal DV _P and the digital modulation signal DV _O and compares the phases of these signals, depending on whether the former leads or lags the latter. , A phase lead output signal S from the phase lead output terminal S and a phase lead output terminal Q of the phase detector 27, respectively, with a pulse width corresponding to the phase difference.
_S or outputs a phase delay pulse signal V _O , and further,
An analog phase lead signal V _SA or an analog phase delay signal V _{OA of} a DC voltage which is smoothed by the integrating circuits 29A and 29B and corresponds to the phase difference is generated.

That is, when the phase of the SQUID amplified signal V _P is ahead of the modulation signal O _S , that is, when the digital divided signal DV _P is ahead of the digital modulation signal DV _{O in} phase, the digital component is divided. Circular signal DV
_P , digital modulation signal DV _O , phase advance pulse signal V _S
, The relationship with the analog phase lead signal V _SA is shown in FIG.
~ Is as (d), the case where SQUID amplified signal V _P is phase delayed from the modulation signal O _S, i.e., when the digital division signal DV _P is a digital modulation signal DV _O than the phase is delayed Is the digital divided signal DV
_P , digital modulation signal DV _O , phase delay pulse signal V
The relationship between _O and the analog phase delay signal V _OA is shown in FIG.
~ (H).

Further, the analog phase lead signal V _SA ,
Based on the analog phase delay signal V _OA , the phase advance control signal generation circuit 30 and the phase delay control signal generation circuit 31 generate a phase advance control signal V _PS and a phase delay control signal V _PO corresponding to the phase difference, respectively. At the same time, the phase discriminating circuit 32 generates a phase discriminating signal V _D which becomes Hi level and Low level, respectively, in accordance with the phase advance and the phase delay, and sends it to the variable phase shifter 24.

Next, when the changeover switches 33A and 33B of the variable phase shifter 24 input the phase discrimination signal V _D and this is at the Hi level, that is, the SQUID amplified signal V _P is out of phase with the modulation signal O _S. Contact points a and c when moving forward
Are connected to connect the phase lead capacitor 34 and the FFT1.
At the same time as switching to the phase advance circuit composed of 8B, the above FET 18B causes FET1 to operate based on the phase advance control signal V _PS.
The operating resistance R _{DS of} 8B is changed to change the phase of the modulation signal O _{S by} a phase shift amount, and the SQUID amplified signal V
_P and in phase with the modulation signal O _S, to prevent measurement errors due to phase fluctuation.

When the phase discrimination signal V _D is at low level, that is, the SQUID amplified signal V _P is the modulation signal O _S.
When the phase is more delayed, the contacts a and b are connected to switch to the phase delay circuit composed of the phase delay capacitor 35 and the FET 18C, and at the same time, the FET 18 is switched.
C changes the operating resistance R _{DS of the} FET 18C on the basis of the phase delay control signal V _PO to change the phase of the modulation signal O _S by a deviated amount, thereby changing the phases of the SQUID amplified signal V _P and the modulation signal O _S. In addition, measurement error due to phase fluctuation is prevented.

Example 3. FIG. 7 is a block diagram showing a third embodiment of the present invention. In the figure, 1～4,7～15A is the same as the prior art, 36 the level comparator 37 is variable bias circuit, V _P is SQUID amplified signal, O _S modulation signal,
V _H is a voltage output from the integrator 11 as a magnetic field measurement signal.

FIG. 8 is a block diagram showing an example of the configuration of the level comparator 36. In the figure, 15E is an amplifier 15A
The same amplifier, 19B is the same bridge rectifier circuit as the bridge rectifier circuit 19A, and 22B and 22C are the differential amplifier 2
2A same differential amplifier, 38 smoothing resistor, 39
A and 39B are smoothing capacitors, 40 is a peak hold circuit, and V _P is a SQUID amplified signal.

Next, the operation of the superconducting magnetometer according to the third embodiment of the present invention will be described. First, SQUID 1 is cooled by immersing it in liquid helium to be transformed into a superconducting state, and the SQUID interlinkage magnetic flux at the time when the integrator switch 13 is opened in the magnetic field to be measured is set as the origin of output zero, and from that point. The change amount of the interlinkage magnetic flux is output as a voltage V _H corresponding to the change amount of the magnetic field.

That is, the operating point of SQUID1 is normally shown in FIG.
There is a full-wave rectified signal at the position of point A of 4, but
B of the measured magnetic field is increased or decreased for example FIG. 14, when moving to the position and C, the modulation signal O _S and positive phase, and outputs a sinusoidal signal of opposite phase, then the preamplifier 7, the multiplier 8, the phaser 9. The FLL circuit including the oscillator 10, the integrator 11, the feedback resistor 12, the level comparator 36, and the variable bias circuit 37 outputs a voltage V _H corresponding to the amount of change in the magnetic field and feeds back the voltage V _H. Resistor 12, modulation feedback coil 4
It returns to the superconducting ring 2 via and is instantly returned to the position of point A.

At this time, when the bias current of SQUID1 is large, proper, and small, the voltage changes in the cycle of Φ _O with respect to the magnetic flux that links SQUID1 with itself. ) Is represented. When the bias current deviates from the proper value as shown in (a) and (c) of FIG. 9, the amplitude of the periodic voltage having a cycle of Φ _o decreases,
Number 100 applied by oscillator 10 and modulation coil 4
SQUI output corresponding to KHz sinusoidal modulation magnetic flux
Although the amplitude of the D amplified signal V _P decreases, the output of the phase detection and the output of the integrator decrease accordingly, and finally a measurement error occurs, but the level comparator 36 causes the fluctuation of the bias current to the SQUID. Detected as the amplitude fluctuation of the amplified signal V _P ,
Further, the variable bias circuit 37 keeps the bias current at an appropriate value based on the amplitude fluctuation.

Specifically, it is as follows. First, the amplifier 15E and the bridge rectifier circuit 19B perform amplification and full-wave rectification, and further smoothing is performed by the smoothing resistor 38 and the smoothing capacitors 39A and 39B, and then the differential amplifier 22.
It is amplified by B and output as an amplitude fluctuation signal. That is, S
When the bias current of QUID1 is the optimum value, the above SQUI
The amplitude of the ID amplified signal V _P also becomes maximum, and therefore the rectification /
The smoothed voltage also becomes the maximum, which is stored in the peak hold circuit 40, and when it deviates from the optimum value, the SQ
The amplitude of the UID amplified signal V _P also decreases, and the rectified and smoothed voltage decreases accordingly. However, the differential amplifier 2
2C compares the rectified and smoothed voltage output from the differential phase amplifier 22B with the output voltage of the peak hold circuit 40, and outputs the difference as an amplitude fluctuation signal. Before measuring the magnetic field, the bias current of the variable bias circuit 37 is increased or decreased and the maximum value is stored in the peak hold circuit 40 in advance.

Next, the variable bias circuit 37 inputs the amplitude fluctuation signal and increases or decreases the bias current until the voltage becomes zero to keep the bias current at an optimum value. Prevent measurement error.

Example 4. FIG. 10 is a block diagram showing a fourth embodiment of the present invention. In the figure, 1-4, 7-8, 10
15A is the same as the conventional one, 23 and 24 are the same as those in the second embodiment, 36 and 37 are the same as those in the third embodiment, V _P is a SQUID amplified signal, O _S is a modulation signal, and V _PS and V _PO. , V
_D is a phase lead signal, a phase delay signal, a phase discrimination signal output from the phase comparator 23, and V _H is a voltage output from the integrator 11 as a magnetic field measurement signal.

Next, the operation of the superconducting magnetometer according to the fourth embodiment of the present invention will be described. First, SQUID 1 is cooled by immersing it in liquid helium to be transformed into a superconducting state, and the SQUID interlinkage magnetic flux at the time when the integrator switch 13 is opened in the magnetic field to be measured is set as the origin of output zero, and from that point. The change amount of the interlinkage magnetic flux is output as a voltage V _H corresponding to the change amount of the magnetic field.

That is, the operating point of SQUID1 is normally shown in FIG.
There is a full-wave rectified signal at the position of point A of 4, but
Of the measured magnetic field is increased or decreased for example, FIG. 3 B, when moving to the position and C, and outputs a modulation signal O _S positive phase, the sinusoidal signals of opposite phase, then the preamplifier 7, the multiplier 8, the oscillator 10 , Integrator 11, feedback resistor 12, phase comparator 23, variable phase detector 24, level comparator 36, and variable bias circuit 37.
The voltage V _H feedback resistor and outputs a voltage V _H corresponding to the magnetic field variation by configured FLL circuit in 1
2. Return to the superconducting ring 2 via the modulation feedback coil 4 and instantly return to the position of point A.

At this time, the SQUID amplified signal V _P tends to cause phase fluctuation and amplitude fluctuation due to cable shape fluctuations, bias fluctuations caused by temperature / power supply fluctuations, etc. First, the phase comparator 23 and the variable phase shifter 24 are used. By the same operation as shown in the second embodiment, the above-mentioned SQUID amplified signal V _P ,
The combined phases of the modulated signal O _S, further, increase the amplitude of the SQUID amplification signal V _P is the same operation as the level comparator 36 and the variable bias circuit 37 is shown in Example 3, i.e., SQUID 1 of the bias current By keeping the cable in the optimum state, SQUID due to the shape variation of the above cable, bias variation due to temperature / power supply variation, etc.
A measurement error is prevented by preventing a phase variation and an amplitude variation of the amplified signal V _P.

Example 5. FIG. 11 is a block diagram showing a fifth embodiment of the present invention. In the figure, 1～4,6～15A is the same as the prior art, the AGC / quality decision circuit 41, V _P S
A QUID amplified signal, O _S is a modulation signal, V _H is a voltage output as a magnetic field measurement signal from the integrator 11, and V _F is a pass / fail determination signal output from the AGC / pass / fail determination circuit 41. Outputs Hi level, and when abnormal, outputs Low level.

FIG. 12 is a block diagram showing an example of the configuration of the AGC / good / bad determination circuit 41. In the figure, 15B, 1
7 to 22A are the same as those in the first embodiment, and 42 is a SQUID
Is a pass / fail determination circuit for determining pass / fail of the FLL circuit, and V _F is a pass / fail determination signal output from the pass / fail determination circuit 42.

Next, the operation of the superconducting magnetometer according to the fifth embodiment of the present invention will be described. First, SQUID 1 is cooled by immersing it in liquid helium to be transformed into a superconducting state, and the SQUID interlinkage magnetic flux at the time when the integrator switch 13 is opened in the magnetic field to be measured is set as the origin of output zero, and from that point. The change amount of the interlinkage magnetic flux is output as a voltage V _H corresponding to the change amount of the magnetic field.

That is, the operating point of SQUID1 is normally shown in FIG.
There is a full-wave rectified signal at the position of point A of 4, but
B of the measured magnetic field is increased or decreased for example FIG. 14, when moving to the position and C, the modulation signal O _S and positive phase, and outputs a sinusoidal signal of opposite phase, then the bias circuit 6, a preamplifier 7, a multiplier 8, phaser 9, oscillator 10, integrator 11, feedback resistor 1
The FLL circuit composed of 2 and the AGC / goodness judgment circuit 41 outputs a voltage V _H corresponding to the amount of change in the magnetic field, and this voltage V _H is fed back to the feedback resistor 12 and the modulation feedback coil 4.
It returns to the superconducting ring 2 via and is instantly returned to the position of point A.

At this time, the amplitude of the SQUID amplified signal V _P output from the preamplifier fluctuates due to temperature / power supply fluctuations and the like, which tends to cause a measurement error. However, the amplifier 15B of the AGC / pass / fail judgment circuit 41, the bridge Rectifier circuit 19A
Is the SQUID amplified signal V _P output from the preamplifier 7.
Is amplified and full-wave rectified, further smoothed by the smoothing resistor 20 and the smoothing capacitors 21A and 21B, and then amplified by the differential amplifier 22A, which is fed back to the gate G of the FET 18A. The FET 18 is proportional to this voltage.
Controlled to operate resistance R _DS between the drain D- source S of A is increased, the resistance value of the operating resistance R _DS and the voltage voltage-dividing resistors 17 wherein the R _B (1), (2) The SQUID amplified signal V _P is divided into the voltage division ratios shown to cancel the increase / decrease of the SQUID amplified signal V _P , and the amplitude of the SQUID amplified signal V _P is maintained at a constant value to prevent a measurement error and the pass / fail judgment circuit 4
2 determines whether or not the output voltage of the differential amplifier 22A is within a certain range, and when it is out of the range, the quality determination signal V _{F is set} to the Low level to generate the SQUID amplified signal V _P SQUID, driving Informs that there is an abnormality in the circuit.

[0056]

As described above, according to the present invention, the following effects can be obtained.

The present invention adds an AGC circuit for controlling the amplitude of this signal to a constant value on the basis of the signal output from the preamplifier to the output stage of the preamplifier, so that the output fluctuation of the preamplifier due to temperature, power supply fluctuation, etc. Since it does not occur, a superconducting magnetometer with less measurement error can be obtained.

Further, according to the present invention, the modulation signal is input based on the output of the phase comparator instead of the phase comparator for detecting the phase shift between the output of the preamplifier and the modulation signal and detecting the phase difference between them. By providing a variable phase shifter that adjusts the phase of the output signal of the preamplifier to match the phase of the output signal of the preamplifier, it is possible to prevent a phase shift between the output signal of the preamplifier and the modulation signal due to a change in the shape of the cable. A superconducting magnetometer with less measurement error can be obtained.

According to the present invention, based on the output of the preamplifier, a level comparator for detecting a change in bias current and generating a current control signal, and the current control signal are input to the SQU.
By providing a variable bias circuit for supplying a proper bias current to the ID, the output fluctuation of the preamplifier due to the fluctuation of the SQUID bias current does not occur, so that the superconducting magnetometer with less measurement error can be obtained.

Further, according to the present invention, the phase of the modulation signal is adjusted based on the output of the phase comparator which receives the output of the preamplifier and the modulation signal and detects the phase shift between the two. In addition to the variable phase shifter that matches the phase of the output signal of the preamplifier, the level comparator that detects the fluctuation of the bias current based on the output of the preamplifier and generates the current control signal and the current control signal are input. By providing a variable bias circuit for supplying an appropriate bias current to the SQUID, it is possible to prevent a phase shift between the output signal of the preamplifier and the modulation signal due to a change in the shape of the cable and the SQUID bias current. The output of the preamplifier is prevented from fluctuating due to fluctuations in the above, so that a superconducting magnetometer with less measurement error can be obtained.

The present invention controls the amplitude of this signal to a constant value based on the signal output from the preamplifier, and
By adding an AGC / discrimination circuit to the output stage of the preamplifier, which generates an abnormal signal that indicates an abnormality when the output of the preamplifier exceeds a certain range,
The output of the preamplifier does not fluctuate due to power supply fluctuations, etc., and an abnormality is reported when the output of the preamplifier exceeds a certain range, so that a superconducting magnetometer with few calculation errors can be obtained and an electronic circuit can be obtained. The quality can be automatically determined.

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention.

FIG. 2 is a block diagram showing an example of a configuration of an AGC circuit 16.

FIG. 3 is a block diagram showing a second embodiment of the present invention.

FIG. 4 is a block diagram showing an example of a configuration of a phase comparator 23.

5 is a block diagram showing an example of a configuration of a variable phase shifter 24. FIG.

FIG. 6 is a diagram showing a relationship with a digital frequency division signal, a digital modulation signal, a phase advance pulse signal, an analog phase advance signal, a phase delay pulse signal, and an analog phase delay signal.

FIG. 7 is a block diagram showing a third embodiment of the present invention.

8 is a block diagram showing an example of a configuration of a level comparator 36. FIG.

FIG. 9 is a diagram showing a relationship between a bias current of SQUID and a voltage that changes in a cycle of Φ _O.

FIG. 10 is a block diagram showing a fourth embodiment of the present invention.

FIG. 11 is a block diagram showing a fifth embodiment of the present invention.

FIG. 12 is a block diagram showing an example of a configuration of an AGC / good / bad determination circuit 41.

FIG. 13 is a block diagram showing an example of a conventional superconducting magnetometer.

FIG. 14 is a diagram showing the principle by which a DC-SQUID measures an external magnetic field.

[Explanation of symbols]

 1 SQUID 2 Superconducting ring 3A, 3B Josephson junction 4 Modulation feedback coil 5 Drive circuit 6 Bias circuit 7 Preamplifier 8 Multiplier 9 Phaser 10 Oscillator 11 Integrator 12 Feedback resistor 13 Integrator switch 14 Integrating capacitor 15A, 15B, 15C, 15D, 15E amplifier 16 AGC circuit 17 voltage dividing resistor 18A, 18B, 18C FET 19A, 19B bridge rectifier circuit 20 smoothing resistor 21A, 21B smoothing capacitor 22A, 22B, 22C differential amplifier 23 phase comparator 24 variable phase shifter 25 frequency divider 26A, 26B comparator 27 phase detector 28A, 28B integrating capacitor 29A, 29B integrating circuit 30 phase lead control signal generating circuit 31 phase delay control signal generating circuit 32 phase discriminating circuit 33A, 33B switching Switch 34 phase lead capacitor 35 a phase delay capacitor 36 level comparator 37 variable bias circuit 38 smoothing resistors 39A, 39B smoothing capacitor 40 peak hold circuit 41 AGC / quality decision circuit 42 quality decision circuit

Claims (5)

[Claims] 1. A superconducting quantum interference device, a bias circuit for supplying a bias current to the superconducting quantum interference device, and a preamplifier for amplifying the output of the superconducting quantum interference device.
An AGC circuit that controls the output of the preamplifier to a constant value, an oscillator that generates a sine wave, a phase shifter that adjusts the phase of the sine wave output from the oscillator, an output of the phase shifter, and an output of the AGC circuit. A superconducting magnetic force, comprising: a multiplier for multiplying, an integrator for integrating the output of the multiplier, and a feedback resistor for returning the voltage output from the integrator to the superconducting quantum interference device. Total. 2. A superconducting quantum interference device, a bias circuit for supplying a bias current to the superconducting quantum interference device, and a preamplifier for amplifying the output of the superconducting quantum interference device.
An oscillator that generates a sine wave, a phase comparator that detects the phase shift between the output of this preamplifier and the output of the oscillator, and a sine wave output from the oscillator based on the output of the phase comparator. , A multiplier for multiplying the output of the preamplifier and the output of the variable phaser, an integrator for integrating the output of the multiplier, and a superconducting voltage output from the integrator. A superconducting magnetometer, comprising: a feedback resistor that returns to a quantum interference device. 3. A superconducting quantum interference device, a preamplifier for amplifying the output of the superconducting quantum interference device, and a level comparator for detecting a change in bias current based on the output of the preamplifier and generating a current control signal. And a variable bias circuit that inputs the current control signal to supply an appropriate bias current to the superconducting quantum interference device, an oscillator that generates a sine wave, and a phase of the sine wave that is output from the oscillator. A phaser, a multiplier that multiplies the output of the preamplifier and the output of the phaser, and an integrator that integrates the output of the multiplier,
A superconducting magnetometer, comprising: a feedback resistor for returning the voltage output from the integrator to the superconducting quantum interference device. 4. A superconducting quantum interference device, a preamplifier for amplifying the output of the superconducting quantum interference device, and a level comparator for detecting a change in bias current based on the output of the preamplifier to generate a current control signal. A variable bias circuit for inputting the current control signal to supply an appropriate bias current to the superconducting quantum interference device, an oscillator for generating a sine wave, and an output of the preamplifier and an output of the oscillator. A phase comparator that detects the phase shift between the two, a variable phaser that adjusts the phase of the sine wave output from the oscillator based on the output of the phase comparator, and an output of the preamplifier and an output of the variable phaser. A superconducting device comprising: a multiplier for multiplying, an integrator for integrating the output of the multiplier, and a feedback resistor for returning the voltage output from the integrator to the superconducting quantum interference device. Magnetometer. 5. A superconducting quantum interference device, a bias circuit for supplying a bias current to the superconducting quantum interference device, and a preamplifier for amplifying the output of the superconducting quantum interference device.
An AGC / good / bad determination circuit for controlling the output of the preamplifier to a constant value and for generating an abnormal signal notifying an abnormality when the output of the preamplifier exceeds a certain range.
An oscillator that generates a sine wave, a phaser that adjusts the phase of the sine wave that is output from the oscillator, a multiplier that multiplies the output of the phaser and the output of the AGC / good / bad determination circuit, and the output of the multiplier. A superconducting magnetometer, comprising: an integrator for integrating and a feedback resistor for returning the voltage output from the integrator to the superconducting quantum interference device.