JPH07113666B2 - Dummy-SQUID - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> This invention is a pseudo SQUID (Superconducting Quantum I).
ntreference Device, a superconducting quantum interference device) and a completely new dummy SQUID having the same signal input / output characteristics.

<Prior Art and Problem to be Solved by the Invention> SQUID has been applied in various fields, focusing on the characteristic that magnetic flux can be detected with extremely high sensitivity. In addition, Josephson junction (hereinafter J
There is an rf-SQUID that has only one (J) and a dc-SQUID that has two JJs. Conventionally, the rf-SQUID was generally used, but recently, semiconductor manufacturing technology has advanced. Since two JJs with uniform characteristics have been obtained, dc-SQUID with high magnetic flux detection sensitivity has come into wide use.

FIG. 6 is an electric circuit diagram for explaining the principle of the dc-SQUID magnetometer. Two JJ (7) are provided at predetermined locations in the superconducting loop (71).
2) is formed and a constant current source (70) sandwiches two JJs (72) to supply a bias current to the superconducting loop (71). An input coil (73) connected to the pickup coil (74) for detecting the magnetic flux to be measured is provided close to the superconducting loop (71). Further, the output voltage of the voltage transformer (75) that transforms the output voltage of the superconducting loop (71) by sandwiching the two JJs (72) is amplified by the amplifier (76) and output from the oscillator (77). The synchronous detector (78) demodulates based on the modulation signal, the integrator (79) integrates the demodulated signal, and outputs it as a voltage proportional to the external magnetic flux. Further, the output signal from the integrator (79) and the modulated signal from the oscillator (77) are added by the adder (80) and converted into a feedback current by the voltage-current converter (81) to obtain the modulation coil ( 82) to cancel the external magnetic flux detected by the pickup coil (74).

If the dc-SQUID is incorporated in the magnetic flux lock loop (hereinafter abbreviated as FLL) in this way, as shown in FIG.
It is possible to eliminate the inconvenience that the interlinkage magnetic flux of the superconducting loop cannot be measured as it is because the magnetic flux-voltage conversion coefficient changes periodically depending on the magnitude of the interlinkage magnetic flux. By continuing to hold it, it is possible to measure the interlinkage magnetic flux. Bundling, through the modulation coil (82), a magnetic flux having the same magnitude as the magnetic flux externally applied to the superconducting loop (71) through the pickup coil (74) and the input coil (73) but in the opposite direction. The external magnetic flux can be canceled by feedback, and the external magnetic flux can be measured by monitoring the feedback current supplied to the modulation coil (82).

Further, generally, in order to obtain a SQUID magnetometer having a FLL, it is necessary to design a FLL circuit.
When performing an operation test of the prototype FLL circuit, SQUID
Has to be actually connected, which causes various inconveniences. That is, SQ
In order to operate the UID, it is necessary to obtain an ultra-low temperature environment of about 4K, which makes it difficult to handle the SQUID including the connection of the SQUID, and the inconvenience that the SQUID itself has a short life and its secular change are relatively small. There is a disadvantage that the reproducibility of the magnetic flux-voltage conversion coefficient is large and the SQ
Since the UID is stored in the dewar, there is a disadvantage that it is extremely bulky as a whole. In addition, since SQUID has a remarkably high sensitivity, there is a disadvantage that both environmental noise and the measurement signal are detected. Further, it is necessary to give a known amount of magnetic flux as an input to the SQUID, but it is almost impossible to obtain a remarkably weak reference magnetic flux, and there is a disadvantage that a complete performance evaluation of the FLL circuit cannot be performed. Further, if any inconvenience occurs as a result of the operation including the signal detection circuit, it is not possible to identify whether the SQUID side is inconvenient or the signal detection circuit side is inconvenient. There is an inconvenience.

<Purpose of the Invention> The present invention has been made in view of the above problems,
It is an object of the present invention to provide a new dummy SQUID that is easy to handle, has a long life, can be downsized as a whole, and can eliminate the influence of environmental noise.

<Means for Solving the Problems> The dummy SQUID of the present invention for achieving the above object
Is a subtraction unit that receives the output signal from the external magnetic flux generator that outputs the modulation signal of the magnetic flux lock loop and the voltage signal that corresponds to the external magnetic flux as an input, and the subtraction unit that receives the output signal from the subtraction unit as a voltage. And a periodic signal generating means for obtaining a signal that changes continuously and periodically with respect to the change.

However, as the periodic signal generating means, an analog-digital converting means having a higher precision than the number of bits to be used for quantizing the output signal from the subtracting means, and a digital-analog converting operation in which higher-order bits of the analog-digital converting means are input. Means for subtracting the output signal of the digital-analog converting means from the output signal of the subtracting means, and subtracting the output signal of the subtracting means from the sum of the output signal of the digital-analog converting means and the predetermined signal And a selecting means for operating on the basis of the next higher bits of the analog-digital converting means and selecting an output signal of the left tilting subtracting means or the right tilting subtracting means. Is preferred.

<Operation> With the dummy SQUID having the above configuration, the difference signal is generated by the subtracting means using the modulation signal of the magnetic flux lock loop and the output signal from the external magnetic flux generator as inputs,
By using the output signal from the subtraction means as an input, the periodic signal generating means obtains a signal that continuously and periodically changes with respect to the voltage change. Therefore, by changing the output signal from the external magnetic flux generator, It is possible to make the state appear as if the external magnetic flux changed. Further, since no superconductor is used at all, it can be operated at room temperature, is easy to handle, has a significantly long life, and can be made compact as a whole. Also, because the dummy SQUID does not actually perform the magnetic flux detection operation,
The influence of environmental noise can be eliminated.

Then, the periodic signal generating means has an analog-digital converting means having a higher precision than the number of bits for quantizing the output signal from the subtracting means, and a digital-analog converting means for inputting a plurality of upper bits of the analog-digital converting means. And a left tilt subtraction means for subtracting the output signal of the digital-analog conversion means from the output signal of the subtraction means, and the output signal of the subtraction means from the sum of the output signal of the digital-analog conversion means and a predetermined signal. A right tilt subtraction means, and a selection means that operates based on the bits on the lower digit side next to the upper bits of the analog-digital conversion means and selects the output signal of the left tilt subtraction means or the right tilt subtraction means. , The output signal from the subtracting means is quantized into a predetermined bit (n bits from the upper digit) by both converting means. To obtain a signal that changes in a left-downward direction and a signal that changes in a rightward-downward direction, and the above-mentioned signal is selected by the selecting means based on the signal of the (n + 1) th bit from the upper digit from the analog-digital converting means. , It is possible to obtain a dummy SQUID characteristic that changes in a triangular waveform. And because the dummy SQUID characteristics are triangular wave,
Analysis, post-processing, etc. can be easily performed.

<Example> Hereinafter, detailed description will be given with reference to the accompanying drawings illustrating an example.

FIG. 1 is a block diagram showing an embodiment of the dummy SQUID of the present invention, in which the voltage-current converter (1
From the current-voltage converter (2) that converts the modulation current as the feedback current output from f) into the corresponding voltage signal as an input, and the external magnetic flux generator (3) that outputs the voltage signal corresponding to the external magnetic flux. Subtraction unit (4) for obtaining a voltage difference between the voltage signal of the above and the converted voltage signal
And a periodic signal generating section (5) for obtaining a signal (hereinafter, referred to as a continuous periodic signal) that continuously and periodically changes with respect to a voltage change by inputting the difference voltage, and a periodic signal generating section (5 ), To adjust the level of the periodic signal output from the) to the gain of the preamplifier (1a) of the FLL circuit (1),
It has a level converter (6) for converting.

FIG. 2 is a block diagram showing an example of the configuration of the FLL to be connected to the SQUID, which includes an oscillator (1b) for generating a modulated signal of a preamplifier (1a) for amplifying a voltage signal output from the SQUID, A demodulator (1 that performs demodulation using the voltage signal and the modulated signal output from the preamplifier (1a) as input
c), an integrator (1d) that integrates the output signal from the demodulator (1c) to generate a voltage signal proportional to the external magnetic flux, a voltage signal output from the integrator (1d), and an oscillator (1b) An adder (1e) that adds the modulated signal output from the adder (1e), and a voltage-current converter (1f) that converts the voltage signal output from the adder (1e) into a current signal and outputs the current signal as a modulation current, have.

In the case of connecting the dummy SQUID and FLL having the above-mentioned configuration and performing an operation test of the FLL, the external magnetic flux was changed by operating the external magnetic flux generator (3) to change the level of the voltage signal. A state equivalent to can appear.
Since the modulation current is not output from the FLL (1) at the beginning when the external magnetic flux generator (3) operates and outputs a predetermined voltage signal, the predetermined voltage signal is directly output as a difference voltage to the subtraction unit (4). ), And after being converted into a continuously changing periodic signal in the periodic signal generation unit (5), the FLL (1) is converted in the level conversion unit (6).
The signal is converted to a level that matches the gain of the preamplifier (1a).

Therefore, in the FLL (1), the converted signal is amplified by the preamplifier (1a), demodulated by the demodulation unit (1c) based on the modulated signal output from the oscillator (1b), and then the integrator (1d) is generated. ) Is integrated. Then, the voltage signal output from the integrator (1d) and the modulated signal are added by the adder (1e), converted into a current signal by the voltage-current converter (1f), and output as a modulation signal. .

Next, since the modulation signal is converted into a voltage signal by the current-voltage conversion unit (2) and supplied to the subtraction unit (4), the difference voltage output from the subtraction unit (4) becomes small. Then, since the FLL operates based on the reduced difference voltage, the modulation signal can be increased. Hereinafter, by repeating this operation, the voltage signal output from the external magnetic flux generator (3) becomes equal to the voltage signal output from the current-voltage converter (2), and the voltage signal output from the subtractor (4) is output. When the difference voltage is zero, the overall operation is stable. That is, SQ with a continuous periodic shape
The magnetic flux is locked in the valley of the UID characteristic (magnetic flux-voltage characteristic). Therefore, in this state, the integrator (1
The voltage signal output from d) is treated as an external magnetic flux detection signal. Further, when the signal output from the external magnetic flux generator (3) changes greatly at a high speed, the magnetic flux is greatly separated from the valley where the magnetic flux should be locked in the φ-V characteristic and crosses the peak following the valley, and the magnetic flux is locked. Will come off. Therefore, the behavior of the FLL (1) when the magnetic flux lock is released can be reproduced, and the limit state of the FLL (1) can be simulated.

However, when the dummy SQUID is connected, the external magnetic flux is not measured at all, so the voltage signal output from the integrator (1d) has no meaning in the stable state. That is, only a signal synchronized with the output signal of the external magnetic flux generator (3) is output. However, by performing the above series of operations, it is possible to determine whether or not the entire system operates normally. When it is determined that the dummy SQUID is not operating normally, the level conversion unit in this state is changed by changing the level of the voltage signal output from the external magnetic flux generator (3) to determine whether the dummy SQUID is operating normally. Since it can be determined by monitoring the output signal from (6), it can be easily determined whether or not the FLL (1) has an abnormality. On the contrary, if it is determined that it operates normally, the FLL noise level, frequency characteristic, linearity, maximum slew rate, dynamic range, etc. can be measured.
FLL (1) can be evaluated based on these measurement results, software for automatic adjustment of FLL (1), and self-diagnosis of FLL (1) can be performed.

It is also possible to incorporate the dummy SQUID with the above configuration into the SQUID magnetometer in advance. When evaluating the performance of a multi-channel SQUID magnetometer, each FLL (1) is based on the input / output characteristics of the dummy SQUID. Therefore, the characteristic of FLL (1) can be adjusted to absorb the characteristic variation of the SQUID by performing necessary correction based on the detected characteristic variation.

FIG. 4 is a block diagram showing a specific example of the configuration of the dummy SQUID so that a triangular wave-shaped SQUID characteristic is obtained.

In this dummy SQUID, the periodic signal generator (5)
Is an analog-to-digital converter (5a) that receives the difference voltage signal output from the subtraction unit (4), and a predetermined number of higher bits of the bits output from the analog-to-digital converter (5a) And a digital-analog converter (5b), a left slope output section (5c) that subtracts the output signal of the digital-analog converter (5b) from the difference signal, a resistance voltage divider circuit (5d), and a resistance voltage divider. The right slope output section (5e) for subtracting the difference signal from the sum of the voltage obtained by the circuit (5d) and the output signal of the digital-analog converter (5b), and the upper part of the analog-digital converter (5a) And a selection unit (5f) for selecting an output signal from any of the slope output units by using the lower-order digit side bit next to the predetermined number of bits as a control signal. The analog-to-digital converter (5a) uses n + 1 when a difference signal is quantized into n bits.
Any bit having an accuracy of more than a bit may be used, the most significant n bits are supplied to the digital-analog converter (5b), and the most significant n + 1th bit is supplied to the selection unit (5f) as a selection control signal. Since the other parts have the same configuration, detailed description thereof will be omitted.

The operation of the dummy SQUID having the above configuration is as follows.

The modulation signal fed back by the FLL (1) and the output signal from the external magnetic flux generator (3) are supplied to the subtraction section (4), so that a difference signal between them is output. Then, this difference signal is supplied to the analog-digital converter (5a) and converted into a digital signal of a predetermined accuracy. However, not all bits of this digital signal are used, but the above n bits (n is a predetermined integer)
Only the signal is supplied to the digital-analog converter (5b) and restored to an analog signal. Therefore, if the original difference signal and the restored analog signal are supplied to the left slope output unit (5c), the value corresponding to the upper n bits is canceled, the value corresponding to the residual is output, and the left down period A straight line (see FIG. 5 (A)) is obtained. Conversely, if the voltage obtained by the resistance voltage dividing circuit (5d), the original difference signal, and the restored analog signal are supplied to the right slope output section (5e), the value corresponding to the upper n bits is canceled. , A value corresponding to the residual is output, and a right downward periodic straight line (5th
(See FIG. 3B) is obtained. Then, since the selection unit (5f) is operated based on the value of the (n + 1) th bit output from the analog-digital converter (5a), for example,
It is possible to obtain a dummy SQUID characteristic having a triangular wave shape by combining the left half of each straight line in FIG. 5 (A) and the right half of each straight line in FIG. 5 (B).

This dummy SQUID characteristic does not match the actual SQUID characteristic, but the basic characteristics such as periodical changes are the same, and since there is a straight line between the peak and the valley, handling is remarkable. It will be easy.

The present invention is not limited to the above embodiment, and for example, a periodic signal generating section (5) that generates a trigonometric function can be used, and the gist of the present invention is changed. It is possible to make various design changes within the range that does not.

<Effects of the Invention> As described above, according to the first invention, it is possible to obtain a dummy SQUID having a periodic input / output signal characteristic similar to that of SQUID with a simple configuration, and using this dummy SQUID, development of FLL, By conducting a characteristic test, it has the unique effect that it is significantly easier to handle than the SQUID, has little change over time, and has a long service life, and that it can achieve highly accurate performance evaluation. .

FIG. 2 shows the invention as a dummy having a triangular wave input / output characteristic.
SQUID can be obtained, and the unique effect that signal processing can be easily performed due to high linearity is achieved.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a dummy SQUID of the present invention, FIG. 2 is a block diagram showing an example of a configuration of a FLL to be connected to the SQUID, and FIG. 3 is a magnetic flux-voltage conversion coefficient of the dummy SQUID. FIG. 4, FIG. 4 is an electric circuit diagram showing a specific configuration example of the dummy SQUID, FIG. 5 is a diagram for explaining the operation of the periodic signal generator, and FIG. 6 is for explaining the principle of the dc-SQUID magnetometer. Electric circuit diagram, FIG. 7 is a diagram showing a magnetic flux-voltage conversion coefficient of SQUID. (1) ... FLL, (3) ... external magnetic flux generator, (4) ... subtraction unit, (5) ... period signal generation unit, (5a) ... analog-digital converter, (5b) ... … Digital-analog converter, (5c) …… Left tilt output section, (5e) …… Right tilt output section, (5f) …… Selection section

Claims (2)

[Claims] 1. A subtraction means (4) for generating a difference signal with an output signal from an external magnetic flux generator (3) outputting a modulation signal of the magnetic flux lock loop (1) and a voltage signal corresponding to the external magnetic flux as an input. And a periodic signal generating means (5) that receives a signal output from the subtracting means (4) as an input and obtains a signal that continuously and periodically changes with respect to a voltage change. 2. A periodic signal generating means (5) includes an analog-digital converting means (5a) having a precision higher than the number of bits to quantize the output signal from the subtracting means (4), and an analog-digital converting means. Digital-to-analog conversion means (5b) that receives upper bits, and subtraction means (5c) for left tilt that subtracts the output signal of the digital-analog conversion means (5b) from the output signal of the subtraction means (4).
A right tilt subtraction means (5e) for subtracting the output signal of the subtraction means (4) from the sum of the output signal of the digital-analog conversion means (5b) and a predetermined signal, and the plurality of analog-digital conversion means. The above-mentioned patent which operates based on the bit on the lower digit side next to the bit and includes a selection means (5f) for selecting the output signal of the left tilt subtraction means (5c) or the right tilt subtraction means (5e). Dummy SQ according to claim 1
UID.