JPH05264697A - Bias regulating circuit for squid comparator - Google Patents

Abstract

PURPOSE:To automatically conform the amplitude of AC bias current to the threshold of a squid comparator and reduce the number of bias cables. CONSTITUTION:This device has a counter circuit 13 for adding positive and negative plus numbers of output pulse trains of a squid comparator 1 and operating the difference between the addition value and the pulse number of a reference signal; and a control circuit 14 for conforming the amplitude of AC bias current to the threshold (including its neighborhood value) of the squid comparator 1. A reference signal generator 11 is connected to a counter circuit 13, and an AC bias generator 10 is connected to the control circuit 14. The counter circuit 13 and the control circuit 14 are formed from a superconductive circuit together with the squid comparator 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bias adjusting circuit for a SQUID comparator. For more details,
The present invention relates to a bias adjusting circuit formed of a superconducting circuit that automatically adjusts the bias of a comparator.

This SQUID comparator is a SQUID magnetometer that detects minute magnetism such as biomagnetism.
perconducting Quantum Interference Device). The SQUID magnetometer is a high-sensitivity magnetic detector capable of detecting a magnetic field up to several tens fT (femto-Tesla), and is classified into an AC type (RF-SQUID) and a DC type (DC-SQUID) depending on the operation method. Both AC type and DC type SQUID magnetometers have
It is a ring made of a superconductor and has a Josephson junction in a part of the ring. The number of Josephson junctions is one AC type and two DC types. The DC type SQUID magnetometer has a one-digit detection sensitivity better than that of the AC type.

Further, the SQUID magnetometer including two junctions is classified into an analog operation type and a digital operation type. Digitally operated SQUID magnetometers output positive or negative pulses. Among them, SQUID comparator (“SQUID sensor” or “SQUID body”)
(Also called) and its superconducting feedback circuit in a single chip is a one-chip SQUID magnetometer, which is a superconducting element advantageous for multichannelization required for biomagnetic measurement. The present invention also relates to a bias control circuit that can be preferably implemented in a one-chip SQUID magnetometer.

[0004]

2. Description of the Related Art Circuits and operating characteristics of a conventional SQUID comparator are shown in FIGS. As shown in FIG. 25, the SQUID comparator 1 has an AC bias current I
As shown in FIG. 26, a superconducting quantum interference device (superconducting ring) 1a having a part of Josephson junctions JJ1 and JJ2 is a main part of the device that operates by adding g. An input current Ic corresponding to the measured magnetic flux is supplied to the interference element 1a by magnetic field coupling. The superconducting quantum interference device 1a typically has two Josephson couplings, but may be a multi-junction quantum interference device generally having three or more Josephson couplings.

As shown in FIG. 27, the Squid comparator 1 has a current-voltage (I-V) characteristic in which the output voltage V is zero while the applied bias current Ig is smaller than the thresholds Ih, -Ih. When the threshold values Ih and -Ih are exceeded, a voltage V of several millivolts is generated. This current-voltage characteristic has a hysteresis characteristic, and when the bias current Ig is made sufficiently small, the output current V can be reset to zero.

The threshold in this current-voltage characteristic is
It depends on the input current Ic. Therefore, the threshold characteristics are set asymmetrical as shown in FIG. 28 by making the bias current injection points asymmetrical or making the critical currents of the two Josephson junctions JJ1 and JJ2 different values. .. The amplitude of the AC bias current Ig is adjusted to a threshold value of zero input. This adjustment value is determined by thermal noise, but is about 1
%, And the occurrence probabilities of positive and negative pulses are usually adjusted to about 0.5, respectively. For this reason,
When a positive input is applied to the SQUID comparator 1, more positive pulses are output than negative pulses. On the other hand, when a negative input is applied, more negative pulses are output than positive pulses. That is, the SQUID comparator 1 can convert the positive / negative of the input current into the positive / negative occurrence probability of the output pulse. The waveform of the AC bias current Ig is typically a sine wave, but it may be a triangular wave, a rectangular wave, or a waveform in which impulses are superimposed.

As described above, adjusting the amplitude of the AC bias current Ig to within about 1% requires a small number of one-chip chips.
Operating the SQUID is relatively easy. However, in the case of a multi-channel system in which a large number of one-chip SQUIDs such as 100 or more are used side by side, the adjustment is very troublesome.

In response to this bias adjustment, conventionally, a manual AC bias current adjusting device is provided, or it is disclosed in Japanese Patent Laid-Open No. 2-2.
There is a method of providing a room temperature operation bias current adjusting circuit like the circuit described in Japanese Patent No. 57076 (the name of the invention is "digital SQUID control system").
When the main part of the adjusting circuit described in No. 76 is shown as a block,
It becomes like FIG. The adjustment circuit shown in FIG. 29 includes a pulse counter 2 for addition, a subtraction circuit 3 and a control circuit 4 with respect to the SQUID comparator 1, and outputs positive and negative output pulses of the SQUID comparator 1 with the pulse counter 2. The subtraction circuit 3 subtracts the reference pulse number from the added value, and the control circuit 4 adjusts the AC bias current in accordance with the subtraction result.
In the circuit configuration shown in FIG. 29, the SQUID comparator 1 is formed by a superconducting circuit (dotted line portion in the figure), and the other pulse counter 2, subtraction circuit 3 and control circuit 4 are formed by room temperature electronic circuits. ing.

[0009]

However, among the above-mentioned prior arts, the method of providing a manual AC bias current adjusting device is not effective for a system in which a large number of one-chip SQUIDs are arranged in parallel. Is also unsuitable. On the other hand, since the adjusting circuit described in Japanese Patent Laid-Open No. 2-257076 is electrically automatically adjusted, it can be adjusted even when a large number of one-chip SQUIDs are arranged in parallel, but it is an electronic circuit operating at room temperature. Moreover, since it is necessary to provide an adjusting circuit for each one-chip SQUID, the cable for supplying the bias current from the room temperature side to the SQUID comparator 1 in the low temperature environment, that is, the cable for supplying the bias current is the same as the number of chips. Only needed. As a result, the number of cables connecting the room temperature side to the low temperature environment side has increased, leading to an increase in the size of the device and an increase in cost.

Regarding the adjusting circuit described in JP-A-2-257076, the adjusting circuit can be formed by a superconducting circuit as it is, but the operation of the superconducting element is significantly different from that of the room temperature semiconductor element. , Such a mere replacement is impossible.

The present invention has been made in view of the above-mentioned conventional problems, and makes it possible to automatically adjust the amplitude of the supplied AC bias current and the threshold value of the comparator in a low temperature environment. The aim is to reduce the cable between the comparator and its bias adjustment circuit.

[0012]

In order to achieve the above object, a bias adjusting circuit for a SQUID comparator according to the present invention has a superconducting quantum interference device (1a). AC bias generator (1
0), a SQUID comparator (1) that outputs a pulse train consisting of positive and negative pulses according to the input with a bias current applied, and the number of positive and negative pulses in the pulse train are added, and this addition is performed. A counter circuit (13) that calculates the difference between the value and the number of pulses of the reference signal supplied from the reference signal generator (11), and the amplitude of the AC bias current based on the calculated value of this counter circuit (13). A control circuit (14) for making the threshold value of the SQUID comparator at least substantially coincide with each other, and the counter circuit (13) and the control circuit (14) are formed of a superconducting circuit together with the SQUID comparator (1). The configuration.

According to one aspect, the counter circuit (13) comprises a superconducting inductor (20) and two write gates (WG1, WG2) connected to both ends of the superconducting inductor (20). , The two write gates (WG1, WG2) have a superconducting quantum interference device (22 or 24) and one write gate (WG1)
The output pulse train of the SQUID comparator is added to
The reference signal is applied to the other write gate (WG2).

According to another aspect, said control circuit (14)
Is a circuit configuration for matching the amplitude of the AC bias current with the threshold value. One of preferable modes of the control circuit (14) is a superconducting inductor (L1) magnetically coupled to the superconducting quantum interference device (1a) of the SQUID comparator (1) and a superconducting device having a Josephson junction. A counter circuit (13) is provided in the superconducting nonlinear inductor (L2), which includes a parallel circuit with the conducting nonlinear inductor (L2).
The output of is magnetically coupled. This control circuit (1
Another preferred embodiment of 4) has a SQUID amplifier (30), and the output of the counter circuit (13) is magnetically coupled to the input terminal of the SQUID amplifier (30) and the SQUID amplifier (30) is The output terminal is connected to the AC bias current supply path. This control circuit (1
Yet another preferred aspect of 4) has an impulse generator (35) including a SQUID circuit (36), and the output of the counter circuit (13) is magnetically coupled to the input terminal of the impulse generator (35). In addition, the output terminal of the impulse generator (35) is connected to the AC bias current supply path.

According to still another aspect, the control circuit (14) has a circuit configuration for adjusting the threshold value to the amplitude of the AC bias current. Where the SQUID
The superconducting quantum interference device (1a) of the comparator (1) is
Three or more Josephson junctions (JJ1 to JJ4) and a magnetic field coupling (4) that supplies the output of the counter circuit (13).
2, 42) and the above Josephson junction (JJ1 to
It is also one of the preferable modes that the JJ4) and the magnetic field coupling (42, 42) also serve as the control circuit (14).

[0016]

The output pulse train of the SQUID comparator consists of positive and negative pulses. This pulse generation is a stochastic event due to the thermal noise of the SQUID comparator (1). The positive pulse occurrence probability p ⁺ and the negative pulse occurrence probability are The difference from p ⁻ changes according to the input current. The amplitude of the AC bias current is
The sum q of p ⁺ and p ⁻ is adjusted to be, for example, about “1”. The desired value of this pulse generation probability is obtained by setting the frequency of the reference signal applied to the counter circuit (13). In order to achieve this set pulse generation probability,
The bias of the Squid comparator (1) is automatically adjusted by the counter circuit (13) and the control circuit (14). Particularly, in the bias adjusting circuit according to any one of claims 1 to 6, the amplitude of the AC bias current supplied from the AC bias generator (10) is automatically adjusted so as to at least substantially match the threshold of the SQUID comparator (1). The bias adjusting circuit according to claims 1, 2, 7 and 8 is automatically adjusted so that the threshold value of the SQUID comparator (1) at least approximately matches the amplitude of the AC bias current.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. Note that the same reference numerals as those in FIGS. 25 and 26 described above are used for the SQUID comparator.

(First Embodiment) FIGS. 1 to 11 of the first embodiment.
It will be explained based on. In FIG. 1, reference numeral 1 indicates a SQUID comparator, and reference numeral 8 indicates a bias adjusting circuit. The SQUID comparator 1 and the bias adjusting circuit 8, that is, the portion A shown by the dotted line in FIG. 1, is integrally formed by a superconducting circuit.

The SQUID comparator 1 has the superconducting quantum interference device (superconducting ring) 1a including the Josephson junction as described above, and the input current Ic supplied to the input terminal via the pickup coil 9 is positive or negative. It is a digital type that outputs positive and negative pulses corresponding to. Further, the output terminal of the SQUID comparator 1 directly reaches the processing circuit under the room temperature environment and also reaches the bias adjusting circuit 8 as a feedback path for bias adjustment. Further, the bias input terminal of the SQUID comparator 1 receives the AC bias current Ig from the bias adjusting circuit 8.
Is being supplied.

The bias adjusting circuit 8 includes, as shown in the drawing,
Output signals of the AC bias generator 10 and the reference signal generator 11 provided in a room temperature environment are supplied. The bias adjustment circuit 8 includes a counter circuit 13 that receives the output pulse of the SQUID comparator 1 and the output signal of the reference signal generator 11, and a control circuit 14 that receives the count output of the counter circuit 13 and controls the bias state. I have it. Both counter circuit 13 and control circuit 14
Is formed of a superconducting circuit as described above.

The counter circuit 13 is constructed and operates as shown in FIGS. The counter circuit 13 has a superconducting inductor 20 as shown in FIG. 2, and the write gates WG1 and WG1 are provided at both ends of the superconducting inductor 20.
Each WG2 is connected. One write gate WG1
The output pulse of the SQUID comparator 1 is input to
The reference signal output from the reference signal generator 11 is input to the other write gate WG2. This superconducting inductor 20 has a magnetic field coupling 21 to control circuit 13
It is connected to the.

The structure of one write gate WG1 is shown in FIG. 3 and its threshold characteristic is shown in FIG. Write gate W
G1 is also formed of a superconducting quantum interference device 22 having two Josephson junctions 22, and the superconducting quantum interference device 22 receives the input current Ic by the magnetic field coupling 23 and also injects the direct current I _DC. It has become so. Whether the input pulse is positive or negative, the operating point is twice the threshold value of the mode transition shown by the dotted line (points A and B for positive pulse, points C and D for negative pulse). ), A flux quantum is added to the superconducting inductor 20. In other words, the write gate WG1 performs positive pulse quantum writing in the superconducting inductor 20 each time an input pulse is supplied, whether positive or negative, and performs an additive pulse count.

The other write gate WG2 is also formed by a superconducting quantum interference device 24 having two Josephson junctions as shown in FIG. 5, and is referred to this superconducting quantum interference device 24 via a magnetic field coupling 25. The signal Ir is input and the direct current I _DC is also injected. As the reference signal Ir, as shown in FIG. 5, the rate of qf _B (the probability of outputting a positive pulse is p ⁺ , the probability of outputting a negative pulse is p ⁻ , the sum of both probabilities is q, and the alternating current is The frequency of the bias current Ig is f _B )
Or a bipolar waveform with a rate of qf _B / 2. The waveform itself may be a pulse or a sine wave, but in general, a monotonous waveform having one positive and one negative peak value per cycle is suitable. The operating characteristics of the write gate WG2 are as shown in FIG. 4, and the flux quantum is written by the mode transition as well.
Is connected to the end of the superconducting inductor 20 on the side opposite to the write gate WG1, so a negative flux quantum is written.

Therefore, both write gates WG1 and W
Due to the writing of G2, the magnetic flux quantum stored in the superconducting inductor 20 is an amount obtained by time integration of (p ⁺ + p ⁻ −q) f _B. This magnetic flux “∫ ^t (p ⁺ + p ⁻ −q) f _B dt”
Are supplied to the superconducting control circuit 14 by magnetic field coupling 21. Here, as described below, - since "p ⁺ + p ^-q" is to operate so as to zero, want to adjust the "q" ^- may be set to the target value of "p ⁺ + p". q is typically "1".

By connecting the write gate WG2 as shown in FIG. 7, the direct current I _DC can be eliminated, and in this case, the reference signal Ir is unipolar.
This operating characteristic is shown in FIG.

Further, the control circuit 14 has a parallel circuit of a superconducting inductor L1 and a superconducting inductor L2 as shown in FIG. 8, and the bias current Ig is shunted to this parallel circuit and the SQUID comparator 1. Is becoming
The superconducting inductor L1 is magnetically coupled to the SQUID comparator 1. The superconducting inductor L2 has a Josephson junction and an inductor, and is formed as shown in FIG. This superconducting inductor L2 has a counter circuit 13
Output current Ip and DC offset current I _DC of coupling degree α
It is connected by 1, α2. Therefore, in the circuit of the superconducting inductor L2, the phase difference φ changes nonlinearly as shown in FIG. 10 due to the injection current or the magnetic field coupling current. That is, by selecting the DC offset current _IDC to a proper negative value, the differential inductance DL2 changes as shown in FIG. 10, and the current _{Ib2x of the} superconducting inductor L1 changes. The current I _b2x is I _b2x = I _b2 × (L2 / (L1 + L
2)).

FIG. 11 shows the threshold characteristic of the SQUID comparator 1. When the bias current I _b1 is applied, the injection current and the magnetic field coupling current are simultaneously applied, so that the locus of the operating point becomes oblique. Now, operating point B1 in FIG. 11 (see FIG.
In the case (corresponding to point B2), it is assumed that the bias amplitude exactly matches the vicinity of the threshold value.

From this state, if the magnetic field coupling current I _b2x becomes small and the operating point becomes like the operating point A1, the bias current I _b1 does not exceed the threshold value, so the SQUID comparator 1 does not output a pulse. That is, the pulse generation probability “p ⁺ + p ⁻ ” becomes zero, and only the negative magnetic flux quantum is written in the counter circuit 13, so that the counter output current Ip increases in the negative direction. As a result, since the differential inductance DL2 shown in FIG. 10 increases up to the point A2, the magnetic field coupling current I _b2x increases, and the operating point _returns to FIG.
It is returned to B1 point.

On the contrary, the operating point is the point C1 in FIG.
If SQUID Comparator 1 outputs a pulse every time
Pulse generation probability “p⁺+ P^-Becomes 2
It Therefore, in the counter circuit 13, the positive flux quantum is
It will be written more than negative flux quanta.
The counter output current Ip increases in the positive direction. As a result,
The inductance DL2 is reduced to point C2 as shown in Fig. 10.
A little, magnetic field coupling current I _b2xAlso decreases, so in Fig. 11
The operating point is finally returned to B1.

As described above, in the case where the operating point is deviated from the desired position B1, and the starting point is either the operating point A1 or C1, the counter circuit 13 formed by the superconducting circuit is formed.
And the control circuit 14 set the operating point B1 (p ⁺ + p
^- = Q) is automatically returned to. That is, the bias amplitude is automatically adjusted.

Therefore, compared with the conventional manual bias adjustment, the bias can be adjusted with high accuracy and speed, and a system in which a large number of SQUID comparators are arranged in parallel can be easily dealt with, reducing the operator's burden. it can.
Also, when adjusting the bias of a system in which multiple SQUID comparators are installed side by side, multiple SQUID comparators can be commonly biased, so the number of bias cables connecting the room temperature side and the low temperature environment is reduced, and the entire system is reduced. Wiring can be prevented from becoming complicated and large-sized.

(Second Embodiment) Second Embodiment FIGS. 12 to 1
6 will be described. The same or equivalent components as those in the first embodiment are designated by the same reference numerals (the same applies to the following embodiments).

In the second embodiment, the control circuit 14 in the first embodiment is constructed as shown in FIG. 12, and the other elements are the same as those in the first embodiment. The control circuit 14 shown in FIG. 12 has a SQUID amplifier 30 and is formed of a superconducting circuit. As shown in FIG. 13, the SQUID amplifier 30 is formed of a two-junction type superconducting quantum interference device 32 shunted by resistors 31 and 31, and outputs an output current Ip of the counter circuit 13 by magnetic field coupling to generate an AC bias. The bias current Ig from the device 10 is input. The output current of the SQUID amplifier 30 is supplied to the bias circuit of the SQUID comparator 1.

The current-voltage characteristic of the SQUID amplifier 30 has no hysteresis characteristic as shown in FIG. 14, and the threshold characteristic with respect to the input current Ip is as shown in FIG. Then, as the threshold changes, the current-voltage characteristic characteristic is shown in FIG.
4, the output voltage V changes along the load line as shown in FIG. This changing output is superimposed on the bias of the SQUID comparator 1.

Therefore, H in FIG._ThreeThe case of
Assume that the ear amplitude is close to the threshold value. this
When the bias amplitude decreases from the state, the bias current I
Since g does not exceed the threshold, SQUID comparator
1 does not output a pulse, and "p ⁺+ P^-= 0 ”. This
As a result, in the counter circuit 13, only the negative magnetic flux quantum
Is written, and its output current Ip increases in the negative direction.
For example, I in Figure 15_TwoMove to a point. As a result, SQUID increases
The output of the width device 30 is I_ThreeBias current Ig
Are returned to or near the threshold.

[0036] On the contrary, when the amplitude of the bias current Ig is greater than the value of the threshold vicinity, the SQUID comparator 1 outputs a pulse each time, - a "p ^{+ +} p ⁼ 2". Therefore, more positive flux quanta are written in the counter circuit 13 than negative flux quanta, and the output current Ip of the counter circuit 13 increases in the positive direction.
Move to G _{2 in} 5. As a result, the output of the SQUID amplifier 30 is reduced to point G ₃ , and the bias amplitude is finally returned to near the threshold value.

As described above, when the amplitude of the bias current Ig is higher or lower than the value in the vicinity of the threshold value, the control circuit 14 including the counter circuit 13 and the SQUID amplifier 30 controls the same as in the first embodiment. The bias amplitude is automatically adjusted so that “p ⁺ + p ⁻ = q”.

(Third Embodiment) Third Embodiment FIGS. 17 to 2
A description will be given based on 0. In the third embodiment, the control circuit 14 in the first embodiment is constructed as shown in FIG. 17, and the other elements are the same as those in the first embodiment.

The control circuit 14 shown in FIG. 17 has an impulse generator 35 formed of a superconducting circuit, and the impulse generated by this impulse generator 35 is converted into a sinusoidal bias current Ig from the AC bias generator 10. _{3 is} to be superimposed.

The impulse generator 35 is a SQUID circuit 36 (FIG. 18) composed of a two-junction type superconducting quantum interference device 37.
Reference) and a Josephson junction JJ3 formed in series at the output end of the SQUID circuit 36. The superconducting quantum interference device 37 of the SQUID circuit 36 includes a counter circuit 13
Output current Ip and the DC offset current _IDC are magnetically coupled to each other, and the bias current Ig ₁ is supplied from another AC bias generator 38. This impulse generator 3
The threshold value characteristics of No. 5 are set symmetrically as shown in FIG. Bias current I applied to SQUID circuit 36
An impulse occurs when g ₁ exceeds the threshold value, and an impulse current Ig ₂ resulting from this impulse is superimposed on the sine wave bias current Ig ₃ (see FIG. 20) and supplied to the SQUID comparator 1.

In such a configuration, it is assumed that the peak value of the combined bias current "Ig ₂ + Ig ₃ " is near the threshold when the operating point is the K ₁ point in FIG. 19 due to the offset. From this state, if the combined bias current falls below the threshold value or in the vicinity thereof, the combined bias current does not exceed the threshold value, so the SQUID comparator 1 does not output a pulse, so “p ⁺ + p ⁻ = 0”. Becomes Therefore, in the counter circuit 13, only the negative magnetic flux quantum is written, and the output current Ip of the counter circuit 13 increases in the negative direction and moves to point J1 in FIG. This allows
Since the impulse generation time is delayed like J ₂ and the peak value of the combined bias current “Ig ₂ + Ig ₃ ” is increased, the peak value of the combined bias current finally matches the threshold value or its vicinity.

[0042] Conversely, if the amplitude of the combined bias current is too high, since the SQUID comparator 1 outputs a pulse each time, in the same manner as the embodiment described above, "p ⁺ + p ^-
= 2 ”. Therefore, the counter circuit 13 still writes more positive flux quanta than negative ones.
The counter output current Ip increases in the positive direction and, for example, as shown in FIG.
At 9, the operating point moves to point L ₁ . As a result, the impulse generation time is advanced as shown by L _{2 in} FIG. 20, and the peak value of the combined bias current “Ig ₂ + Ig ₃ ” is reduced,
The bias amplitude is also eventually returned to or near the threshold.

Thus, the combined bias current "Ig ₂ + I
When “g ₃ ” is deviated from the threshold value or a predetermined vicinity thereof, the bias amplitude is automatically adjusted by the counter circuit 13 and the impulse generating control circuit 14 to be “p ⁺ + p ⁻ = q”. ..

(Fourth Embodiment) A fourth embodiment will be described with reference to FIGS.
It will be described based on 3. In the fourth embodiment, the control circuit is integrally formed with the SQUID comparator as shown in FIG. 21, and unlike the first to third embodiments, the characteristics of the SQUID comparator itself are controlled to make the bias state. Is a configuration for adjusting. The other elements are the same as in the first embodiment.

The SQUID comparator 40 shown in FIG.
Is formed of a 4-junction superconducting quantum interference device 41. Here, two left and right Josephson junctions JJ1,
JJ2 and JJ3 and JJ4 have one joint Q1 and Q2, respectively.
Considering that, it becomes a two-joint type. This Josephson junction Q
An output current Ip of the counter circuit 13 is supplied to 1 and Q2 via magnetic field couplings 42 and 42. Since the threshold values of the Josephson junctions Q1 and Q2 change according to the counter output current Ip as shown in FIG. 22, the threshold characteristic of the SQUID comparator 40 with respect to the input current Ic also changes as shown in FIG. To do.

In the circuit configuration of FIG. 21, the Josephson junctions Q1 and Q2 and the magnetic field couplings 42 and 42 correspond to the control circuit of the present invention. Now, when the bias current is in the state of E ₃ in FIG. 23, it is assumed that the amplitude thereof is exactly equal to or near the threshold value. In this state, if the bias current amplitude becomes small and the state becomes F _{3 in} FIG. 23, the bias current does not exceed the threshold value, so the SQUID comparator 40 does not output a pulse. For this reason, "p ^{+ +} p ^- = 0"
Therefore, only the negative magnetic flux quantum is written in the counter circuit 13, and the counter output current Ip increases in the negative direction. That is, in FIG. 22, the operating point of the counter output current Ip moves to F ₁ , and the threshold characteristic becomes low as indicated by F ₂ in FIG. In this way, the threshold value of the SQUID comparator 40 is adjusted so that the threshold value of the input current Ic = 0 finally matches the amplitude value of the bias current or its vicinity.

On the contrary, the bias current amplitude is shown in FIG.
When D _{3 in 3} is large, the SQUID comparator 40 outputs a pulse every time, so “p ⁺ + p ⁻ = 2”.
Becomes Therefore, in the counter circuit 13, the positive flux quantum is written more than the negative flux quantum, and the counter output current Ip moves in the positive direction (for example, the operating point of D ₁ in FIG. 22). As a result, the threshold characteristic becomes high as indicated by D2 in FIG. 23, and finally the threshold value of the input current Ic = 0 comes to coincide with the amplitude value of the bias current or its vicinity.

In this way, the bias amplitude is larger than the threshold value.
If it is too large or too small, the counter circuit 13 and
Control circuit built into the SQUID comparator 40
Depending on the route, the threshold of the SQUID comparator 40
Body is near bias (p⁺+ P ^-Automatically moves to = q)
Then, the bias is adjusted.

The control circuit in each of the above-described embodiments has a method of bringing the amplitude of the AC bias current closer to the threshold value of the SQUID comparator, or conversely, bringing the threshold value closer to the bias current amplitude. Although the control circuit according to the present invention is provided with only the circuit configuration according to the above, the control circuit according to the present invention may have a configuration including the circuit configurations according to both methods at the same time.

Also, the bias current amplitude and the threshold value are
The adjustment value for matching is “p⁺+ P ^-= Q ”condition
The probability p at the input zero is⁺= P^-To
When adjusting to 0.5, set the reference signal so that q = 1.
Frequency (qf_B), And only in this case,
The output signal of the AC bias generator 10 is also used as a reference signal
The reference signal generator 11 can be omitted, and
It can be simplified.

(Application Example) FIG. 24 shows an application example of the present invention. This application example is applied to the one-chip SQUID magnetometer 50. One-chip SQUID magnetometer 50
It includes a Josephson logic circuit 52 and a superconducting feedback circuit 53 connected to the output side of the SQUID comparator 51. Superconducting feedback circuit 53
Measures the magnitude of the magnetic flux input through the pickup coil 54 by counting the pulse generation probability “p ⁺ −p ⁻ ” and feeding back the magnetic flux quantum so that this subtraction value becomes zero. To do.

The bias adjusting circuit according to the present invention, that is, the AC bias generator 10, the reference signal generator 11, the counter circuit 13, and the control circuit 14 are added to the SQUID comparator 51. Among them, the one-chip SQUID magnetometer 50 including the pickup coil 54, the counter circuit 13, and the control circuit 14 (the portion shown by the dotted line in the drawing) are integrally formed by a superconducting circuit. The counter circuit 13 and the control circuit 14 use the pulse generation probability “p ⁺ + p
^- "Is kept constant so that the bias is automatically adjusted as in the previous embodiments. Further, when the one-chip SQUID magnetometer 50 is provided with multiple channels, the number of bias cables connecting the room temperature side and the low temperature environment can be reduced.

[0053]

As described above, the bias adjusting circuit for a SQUID comparator according to the present invention adds positive and negative pulses of a pulse train output from the SQUID comparator, and adds the added value and the number of pulses of the reference signal. And a control circuit that substantially matches the amplitude of the AC bias current and the threshold value of the SQUID comparator on the basis of the calculated value of the counter circuit. -Formed with a superconducting circuit together with a comparator. Therefore, even if the amplitude of the AC bias current applied from the outside does not match the threshold of the SQUID comparator or its vicinity, the counter circuit and control circuit automatically adjust the two so that they are at least approximately the same. To be done.

[0054] adjustment value at this time is the sum of the pulse generation probability ^- is represented by "p ^{+ +} p = q" The condition, for example the probability p ⁺ = ^p in the input zero - When adjusting the = 0.5, q = 1
The frequency (qf _B ) of the reference signal is set so that Only in this case, an alternating bias current can be used as the reference signal. If the probability p ⁺ = p ⁻ is adjusted to 0.4, q = 0.8, and if the probability p ⁺ = p ⁻ is adjusted to 0.6, q = 1.2 may be set. The bias is automatically adjusted so as to obtain a desired pulse generation probability determined by the frequency of the reference signal.

As a result, the bias can be adjusted more quickly and more accurately than in the conventional case where the bias is manually adjusted, and even when a large number of SQUID comparators such as a multi-channel SQUID are used, they can be adjusted at room temperature. Since it is not necessary to adjust the bias amplitude one by one, it is possible to easily cope with such multi-channelization, the operator's burden can be reduced due to its good operability, and the number of bias cables can be reduced. It is possible to reduce the size and complexity of the entire circuit by reducing the number.

[Brief description of drawings]

FIG. 1 is an overall block diagram of a bias adjusting circuit of a SQUID comparator according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram of a counter circuit of the bias adjustment circuit shown in FIG.

FIG. 3 is a circuit diagram of one write gate of the counter circuit in FIG.

FIG. 4 is a threshold characteristic diagram of one write gate.

5 is a circuit diagram showing an example of the other write gate of the counter circuit in FIG.

FIG. 6 is a threshold characteristic diagram of the other write gate shown in FIG.

FIG. 7 is a circuit diagram showing another example of the other write gate of the counter circuit in FIG.

8 is a configuration diagram showing an example of a control circuit of the bias adjustment circuit shown in FIG.

9 is a circuit diagram of the nonlinear inductor in FIG.

FIG. 10 is a characteristic diagram of a phase difference and a differential inductance of a nonlinear inductor.

FIG. 11 is a threshold characteristic diagram of the SQUID comparator in FIG.

FIG. 12 is a configuration diagram showing a control circuit according to a second embodiment.

13 is an equivalent circuit diagram of the SQUID amplifier in FIG.

FIG. 14 is a current-voltage characteristic diagram of the SQUID amplifier.

FIG. 15 is a threshold characteristic diagram of a SQUID amplifier.

FIG. 16 is an output characteristic diagram of the SQUID amplifier.

FIG. 17 is a configuration diagram showing a control circuit according to a third embodiment.

FIG. 18 is a detailed circuit diagram of the SQUID circuit in FIG. 17.

FIG. 19 is a threshold characteristic diagram of the SQUID circuit.

FIG. 20 is a waveform diagram of a combined bias current according to the third embodiment.

FIG. 21 is a configuration diagram of a control circuit and a SQUID comparator according to the fourth embodiment.

22 is a threshold characteristic diagram of the Josephson junction of the four-junction SQUID comparator shown in FIG. 21.

23 is a threshold characteristic diagram of the 4-junction SQUID comparator shown in FIG. 21. FIG.

FIG. 24 is a block diagram of a one-chip SQUID magnetometer according to an application example of the invention.

FIG. 25 is a block diagram of a Squid comparator.

FIG. 26 is a circuit diagram of a two-junction SQUID comparator.

FIG. 27 is a current-voltage characteristic diagram of the SQUID comparator of FIG. 26.

FIG. 28 is a threshold characteristic diagram of the SQUID comparator of FIG. 26.

FIG. 29 is a block diagram according to a conventional example of bias adjustment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... SQUID comparator 8 ... Bias adjusting circuit 1a ... Superconducting quantum interference device 10 ... AC bias generator 11 ... Reference signal generator 13 ... Counter circuit 14 ... Control circuit 20 ... Superconducting inductors WG1, WG2 ... Write gate 22, 24 ... Superconducting quantum interference device L1 ... Superconducting inductor L2 ... Superconducting nonlinear inductor 30 ... Squid amplifier 31 ... Superconducting quantum interference device 35 ... Impulse generation 36 ... Squid circuit JJ3 ... Josephson junction 40 ... Squid comparators JJ1 to JJ4 … Josephson junction 42… Magnetic field coupling

Claims (8)

[Claims] 1. A superconducting quantum interference device (1a), wherein a positive pulse according to an input is applied to the superconducting quantum interference device (1a) with a bias current applied from an AC bias generator (10). The SQUID comparator (1) that outputs a pulse train composed of negative pulses and the number of positive and negative pulses of the pulse train are added, and the added value and the number of pulses of the reference signal supplied from the reference signal generator (11). And a control circuit (14) for making the amplitude of the AC bias current and the threshold value of the SQUID comparator at least substantially coincide with each other based on the calculated value of the counter circuit (13). ), And the counter circuit (13) and the control circuit (14) are formed by the superconducting circuit together with the SQUID comparator (1). Bias adjusting circuit for comparator. 2. The counter circuit (13) comprises a superconducting inductor (20) and two write gates (WG1, WG2) connected to both ends of the superconducting inductor (20).
And two write gates (WG1, WG2)
Has a superconducting quantum interference device (22 or 24), adds the output pulse train of the SQUID comparator to one write gate (WG1), and adds the reference signal to the other write gate (WG2). Item 1
A bias adjusting circuit for the described SQUID comparator. 3. The bias adjusting circuit for a SQUID comparator according to claim 1, wherein the control circuit (14) has a circuit configuration for adjusting the amplitude of the AC bias current to the threshold value. 4. The control circuit (14) comprises a superconducting inductor (L1) magnetically coupled to the superconducting quantum interference device (1a) of the SQUID comparator (1), and a superconducting nonlinear circuit having a Josephson junction. The superconducting non-linear inductor (L2) is provided with a parallel circuit with the inductor (L2).
4. The bias adjusting circuit for a SQUID comparator according to claim 3, wherein the output of the counter circuit (13) is magnetically coupled to the. 5. The control circuit (14) has a SQUID amplifier (30), the output of the counter circuit (13) is magnetically coupled to the input terminal of the SQUID amplifier (30), and the SQUID amplifier (30) is also provided. The bias adjusting circuit for a SQUID comparator according to claim 3, wherein the output terminal of 30) is connected to the supply path of the AC bias current. 6. The control circuit (14) has an impulse generator (35) including a SQUID circuit (36), and an output of the counter circuit (13) is provided at an input terminal of the impulse generator (35). The bias adjusting circuit for a SQUID comparator according to claim 3, wherein the impulse generator (35) is magnetically coupled, and the output end of the impulse generator (35) is connected to the AC bias current supply path. 7. The bias adjusting circuit for a SQUID comparator according to claim 1, wherein the control circuit (14) has a circuit configuration for adjusting the threshold value to the amplitude of the AC bias current. 8. The superconducting quantum interference device (1a) of the SQUID comparator (1) includes three or more Josephson junctions (JJ1 to JJ4) and the counter circuit (13).
8. The magnetic field coupling (42, 42) for supplying the output of the above, wherein the Josephson junctions (JJ1 to JJ4) and the magnetic field coupling (42, 42) also serve as the control circuit (14). A bias adjusting circuit for the described SQUID comparator.