WO2016008352A1 - 采用单个运算放大器的超导量子干涉器磁传感器 - Google Patents

采用单个运算放大器的超导量子干涉器磁传感器 Download PDF

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WO2016008352A1
WO2016008352A1 PCT/CN2015/082289 CN2015082289W WO2016008352A1 WO 2016008352 A1 WO2016008352 A1 WO 2016008352A1 CN 2015082289 W CN2015082289 W CN 2015082289W WO 2016008352 A1 WO2016008352 A1 WO 2016008352A1
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operational amplifier
squid
feedback
voltage
terminal
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王永良
张懿
常凯
克劳斯⋅汉斯-约阿希姆
徐小峰
邱阳
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Shanghai Institute of Microsystem and Information Technology of CAS
Forschungszentrum Juelich GmbH
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Shanghai Institute of Microsystem and Information Technology of CAS
Forschungszentrum Juelich GmbH
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Priority to JP2016576033A priority patent/JP6577496B2/ja
Priority to EP15822841.1A priority patent/EP3171188B1/de
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/02—Measuring direction or magnitude of magnetic fields or magnetic flux
    • G01R33/035—Measuring direction or magnitude of magnetic fields or magnetic flux using superconductive devices
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/02—Measuring direction or magnitude of magnetic fields or magnetic flux
    • G01R33/035—Measuring direction or magnitude of magnetic fields or magnetic flux using superconductive devices
    • G01R33/0354—SQUIDS

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  • the invention relates to a superconducting quantum interference device magnetic sensor using a single operational amplifier, and more particularly to a superconducting quantum interference device readout circuit, belonging to the technical field of circuits.
  • a magnetic sensor constructed using a Superconducting Quantum Interference Device is currently the most sensitive magnetic sensor. It is widely used in the field of weak magnetic field detection such as biological magnetic field, earth magnetic field anomaly, and extremely low field nuclear magnetic resonance. Its magnetic field detection sensitivity has reached the level of Feite (10 -15 Tesla). It is an important magnetic sensor for the detection and research of extremely weak magnetic fields.
  • SQUID Superconducting Quantum Interference Device
  • the DC superconducting quantum interference device (referred to as dc SQUID) is a superconducting ring formed by two superconducting Josephson junctions connected in parallel. The wires are led out at both ends of the Josephson junction to form a two-terminal component.
  • dc SQUID The DC superconducting quantum interference device
  • the voltage generated across the SQUID will vary with the magnitude of the external flux induced by the superconducting ring. Since the SQUID output voltage is nonlinearly related to its sensed flux, the magnitude of the detected flux cannot be obtained directly by measuring the voltage across the SQUID. Therefore, the practical SQUID magnetic sensor is realized by a Flux-Locked Loop (FLL) formed by a SQUID device and an amplifying circuit. This flux lock loop is called a SQUID readout circuit.
  • FLL Flux-Locked Loop
  • the current state of the bias current I b , the bias voltage V b , and the loaded magnetic flux ⁇ a of the SQUID is referred to as an operating point.
  • the preamplifier output is integrated into the integrator for integration.
  • the output of the integrator drives the feedback resistor to inject a feedback current into the feedback coil, which is coupled to the SQUID by the feedback coil and the mutual inductance of the SQUID.
  • the working principle of the flux lock loop is: when the flux lock loop keeps the SQUID operating point stable, when the measured magnetic flux changes by ⁇ , the SQUID end generates a voltage change ⁇ v from the operating point, and the preamplifier After amplification, send it to the integrator for integration and adjust the output voltage of the integrator.
  • the feedback resistance and the feedback coil adjust the feedback magnetic flux to cancel the magnetic flux variation of the external input, so that the voltage input to the integrator of the SQUID at the working point is zero, the integrator stops integrating, and the loop returns to stability.
  • the steady state of the operating point is called the readout circuit lock.
  • the traditional SQUID flux lock loop usually uses a preamplifier to perform low noise amplification on the SQUID weak voltage signal, and then the amplified signal is connected to the integrator for integral feedback. Therefore, the conventional SQUID flux lock loop is constructed by using at least one preamplifier circuit and an integrator cascade circuit to connect the feedback resistor and the feedback coil. In practical applications, the SQUID flux lock loop using the integrator has the following problems:
  • the slew rate is limited: the output of the integration circuit is the result of integrating the input signal with time. When the detection signal is abrupt, the integrator cannot respond quickly, so the slew rate of the sensor voltage output is limited. It is difficult to meet the requirements of high slew rate magnetic field detection.
  • At least two or more operational amplifiers and peripheral circuits are used, and the circuit is complicated and consumes a large amount of power.
  • the signal response of SQUID devices can range from DC to GHz with high speed and high bandwidth.
  • the above described readout circuit using an integrator limits the performance of the SQUID magnetic sensor in response bandwidth and slew rate characteristics.
  • the SQUID chip is fabricated using microelectronic technology and has the advantages of small size and integration. It is widely used in multi-channel, high-resolution detection systems such as SQUID's 64-channel magnetocardiograph and 200-channel magnetoencephalograph. application. Multi-channel systems place higher demands on the miniaturization of SQUID magnetic sensors. Therefore, simplifying the SQUID readout circuit design is of great significance and practical value for SQUID multi-channel applications.
  • the present invention seeks to create technological work in solving this problem.
  • the present invention is directed to a multi-channel highly integrated SQUID system, and a more simplified readout circuit is constructed to construct a SQUID magnetic sensor.
  • SQUID has a higher response speed than a semiconductor amplifier, and it can achieve a stable negative feedback loop with the amplifier. It is therefore contemplated that only a low noise operational amplifier is used to amplify the SQUID voltage signal in an open loop manner and the feedback resistor and feedback coil are directly driven by a single operational amplifier open loop output. This replaces the preamplifier and integrator in the traditional flux lock loop, enabling the construction of a simpler SQUID flux lock loop.
  • SQUID flux lock loops with a single op amp are available in two ways:
  • the positive input wiring method has one of three modes of implementations 1, 3, and 5 (ie, A, B, and C) (see the detailed description for details).
  • Negative input wiring method as shown in Figure 3.
  • the bias current I b provided by the bias current source is loaded into the SQUID, the SQUID voltage signal is connected to the negative input of the operational amplifier, and the offset voltage V b is connected to the positive input of the operational amplifier.
  • One end of the output end of the operational amplifier feedback resistor of R f, and the other end is connected to a feedback resistor feedback coil, and feedback coil SQUID via mutual inductance coupling, driving the operational amplifier output voltage generating a current feedback resistor R f, and the feedback coil by mutual inductance M f SQUID
  • a feedback flux is generated to form a flux lock loop.
  • the negative input wiring method has any one of the implementation modes 2, 4 and 6 (ie D, E and F) (see the detailed description for details).
  • the present invention uses only one operational amplifier to implement a SQUID flux lock loop, and the circuit is simple.
  • the use of the integrator circuit in the conventional loop is avoided, the loop delay is reduced, and the flux lock loop achieves a higher bandwidth.
  • the op amp directly outputs the feedback feedback resistor and feedback coil to avoid the effects of the integrated capacitor.
  • the flux lock loop allows for higher slew rates.
  • the above circuit is composed of a single operational amplifier and a small number of peripheral circuits. The circuit is small in size and low in power consumption, which greatly reduces the overall volume and power consumption of the multi-channel SQUID sensor integration, and is of great significance in SQUID multi-channel applications.
  • Figure 2 Schematic diagram of a single op amp flux-lock loop for the SQUID positive input.
  • Figure 3 Schematic of a single op amp flux-lock loop for the SQUID negative input.
  • Embodiment 1; B1, B2 are bias current or bias voltage regulation circuits, respectively.
  • Power supply +Vs and -Vs The whole circuit is powered by a bipolar power supply, that is, the positive power supply terminal +Vs is connected to the positive voltage power supply and the negative power supply terminal -Vs is connected to the negative voltage power supply.
  • the positive power supply +Vs supply range is from +5V to +15V, and the corresponding negative power supply -Vs supply range is between -5V and -15V.
  • SQUID Bias Current Regulation Circuit B1 Its function is to load the SQUID with a bias current flowing to the two Josephson junctions of the SQUID. The current can be adjusted. By adjusting the magnitude of the bias current applied to the SQUID, the SQUID achieves the best flux voltage conversion characteristics.
  • the specific example of the adjustable bias current circuit is shown in the B1 module of FIG. 3: the adjustable potentiometer R A1 is a three-terminal adjustable resistor, wherein the ends of the potentiometers 1 and 2 are a fixed resistance resistor. Its resistance value is optimal between 10k ohms and 100k ohms. The 3 end of the potentiometer is an adjustable resistance tap.
  • Both ends 1 and 2 of the potentiometer R A1 are connected to the positive power supply +Vs and the negative power supply -Vs, respectively.
  • the 3-terminal output potentiometer resistor of the potentiometer R A1 is divided, and an adjustable voltage is generated by adjusting the position of the potentiometer tap.
  • the voltage output is connected to the resistor R 1 , and the other end of the resistor R 1 is used as a bias current source in series with the SQUID.
  • the value of the resistor R 1 is between 50 k ohms and 200 k ohms.
  • a dc bias current in the range of ⁇ 100uA can be produced by adjusting the adjustable potentiometer R A1 .
  • SQUID Bias Voltage Regulation Circuit B2 Its function is to generate an adjustable DC voltage that is connected to the negative input of the op amp. The operating point is zeroed by adjusting the voltage to the same DC voltage at the SQUID operating point.
  • the specific example of the adjustable bias voltage circuit is shown in the B2 module in Fig. 3: the adjustable potentiometer R A2 is a three-terminal adjustable resistor, wherein the ends of the potentiometers 1 and 2 are a fixed resistance resistor. Its resistance value is optimal between 10k ohms and 100k ohms.
  • the two ends of the potentiometer R A1 are connected to the positive power supply +Vs and the negative power supply -Vs respectively, and the variable resistor leads to the output end of the 3-terminal output resistor of the tap terminal.
  • the voltage is connected to one end of the resistor R 3 and the other end of the R 3 and the R 2 in series, the other end of R 2 is grounded.
  • the resulting resistor divider is taken at the junction of R 2 and R 3 as a bias voltage signal V b .
  • the bias voltage is adjustable within ⁇ 100uV.
  • the resistance value R 3 is typically between 1 ohm to 10 ohms, which is incorporated to reduce thermal noise in the input of the operational amplifier.
  • the resistance R 2 ranges from 10 k ohms to 100 k ohms.
  • SQ1 uses a low temperature DC superconducting quantum interference device (operating at a liquid helium temperature of 4.2K) or a high temperature DC superconducting quantum interference device (laid at a liquid nitrogen temperature of 77K), which is a two Terminal device. One end of the SQ1 is connected to the positive input terminal of the operational amplifier, and is connected to the current output terminal of the bias current circuit B1. The other end of SQ1 is grounded.
  • Feedback coil L1 It is a coil with mutual inductance coupling with SQUID, and the mutual inductance is M f .
  • the feedback coil converts the current generated by the feedback loop into a feedback flux coupled into the SQUID to form a cancellation flux.
  • One end of the feedback coil L1 is connected to the feedback resistor R f and the other end is grounded.
  • Operational amplifier U1 A low-noise operational amplifier with bipolar supply, with two voltage signal inputs at the positive input and the negative input, and a voltage signal amplification output.
  • the positive input of the operational amplifier is connected to the SQUID voltage output
  • the negative input is connected to the bias voltage output
  • the output of the amplifier acts as the output of the flux lock loop as the output of the entire sensor.
  • the feedback resistor R f is connected.
  • the operational amplifier of the present invention preferably has low input voltage noise and high bandwidth, high open loop gain characteristics: the amplifier voltage noise is around 1 nV/ ⁇ Hz, The open loop gain is greater than 120 dB and the bandwidth gain product is greater than 10 MHz.
  • Commonly used low-noise operational amplifiers are the AD797 from Analog Devices, Inc. and the LT1028 from Linear Technology.
  • Feedback resistor R f The feedback resistor R f is connected to the output of the operational amplifier U1 at one end and the feedback coil L1 at the other end.
  • the feedback resistor R f converts the amplifier output voltage into a feedback current input feedback coil that produces a feedback flux.
  • R f is between 100 ohms and 10 k ohms.
  • the SQUID voltage signal in Embodiment 1 is connected to the negative input terminal of the operational amplifier U1, and the bias voltage signal is connected to the positive input terminal of the operational amplifier, and the remaining wiring is the same as Embodiment 1.
  • Embodiment 3 as shown in Figure 6, that is, the positive input wiring mode B;
  • a reset switch K1 is added to realize a reset function.
  • One end of K1 is connected to the negative input terminal of operational amplifier U1, and the other end of K1 is connected to the output end of operational amplifier U1.
  • the reset switch is closed, the output of operational amplifier U1 is equipotential to the negative input.
  • the op amp is amplified from open-loop high gain amplification to unity gain, the output is rapidly reduced, and the circuit is reset.
  • the reset switch K1 is turned off, the circuit is relocked.
  • Embodiment 4 as shown in Figure 7, that is, the positive input wiring mode E;
  • the SQUID voltage signal in Embodiment 3 is connected to the negative input terminal of the operational amplifier U1, and the bias voltage signal is connected to the positive input terminal of the operational amplifier, and the remaining wiring is the same as Embodiment 3.
  • a feedback resistor R g and a single-pole double-throw switch SW1 are added to enable the magnetic flux lock loop to have a working point debugging function.
  • the single pole double throw switch has three terminals, wherein terminal 3 is defined as a single pole fixed terminal, terminal 1 is defined as a first contact terminal, and terminal 2 is defined as a second contact terminal.
  • the single-pole fixed terminal of SW1 is connected to the output of operational amplifier U1.
  • the terminal 1 terminal of SW1 is connected to one end of the resistor Rg, and the other end of R g is connected to the negative input terminal of the operational amplifier U1.
  • the terminal 2 terminal of SW1 is connected to one end of the feedback resistor R f , and the other end of the feedback resistor Rf is connected to the feedback coil L1.
  • the resistor R g is connected to the output terminal of the operational amplifier U1.
  • the flux lock loop is opened in an open loop, and the operational amplifier U1 operates in a proportional amplification mode to achieve proportional amplification of the SQUID voltage signal.
  • the SQUID voltage signal in Embodiment 5 is connected to the negative input terminal of the operational amplifier U1, and the bias voltage signal is connected to the positive input terminal of the operational amplifier, and the remaining wiring is the same as Embodiment 5.

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  • Condensed Matter Physics & Semiconductors (AREA)
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Abstract

一种采用单个运算放大器的超导量子干涉器磁传感器，其使用一个低噪声的运算放大器，以开环的方式对SQUID电压信号进行放大，并由单个运算放大器开环输出直接驱动反馈电阻及反馈线圈，取代了传统磁通锁定环路中的前置放大器和积分器。该采用单个运算放大器的SQUID磁通锁定环路有正、负端输入接线方式，且正、负端输入接线方式各有三种形式可选。该传感器只使用一个运算放大器实现SQUID磁通锁定环路，电路简单；避免了传统电路中积分器的使用，减小环路延时，使磁通锁定环路实现更高的带宽；在SQUID多通道应用中具有重要的意义。

Description

采用单个运算放大器的超导量子干涉器磁传感器 技术领域
本发明涉及一种采用单个运算放大器的超导量子干涉器磁传感器，更确切地说涉及一种超导量子干涉器件读出电路，属于电路技术领域。
背景技术
采用超导量子干涉器件(Superconducting Quantum Interference Device,以下简称SQUID)构建的磁传感器是目前已知最灵敏的磁传感器。广泛应用于生物磁场、地球磁场异常、极低场核磁共振等微弱磁场探测应用领域，其磁场探测灵敏度已经达到飞特(10-15特斯拉)量级。是极微弱磁场探测和研究中重要的磁传感器。
直流超导量子干涉器(简称dc SQUID)是由两个超导约瑟夫森结并联形成一个超导环。在约瑟夫森结两端引出接线，形成了一个两端子元件。当SQUID两端加载一定的偏置电流时，基于超导量子化效应和约瑟夫森效应，SQUID两端产生的电压将随超导环感应外磁通大小而变化。由于SQUID输出电压与其探测磁通成非线性关系，无法直接通过测量SQUID两端电压来获得探测的磁通大小。因此，实际应用的SQUID磁传感器是由SQUID器件与放大电路构成的磁通锁定环路(Flux-Locked Loop，以下简称FLL)来实现的。该磁通锁定环路称为SQUID读出电路。
文献【D.Drung and M.Mück,The SQUID Handbook,vol.I,J.Clarke and A.I.Braginski,Ed.Weinheim:Wiley-VCH,pp.128–155,2006.】中典型的SQUID磁通锁定环路如图1所示。首先给SQUID加载一定偏置电流Ib使其具有最大的磁通电压传输率。将SQUID电压信号接入一个前置放大器进行放大。同时调节偏置电压Vb,使得SQUID在具有最大磁通电压传输率时输出电压的直流量为零。此时SQUID当前的偏置电流Ib、偏置电压Vb及所加载磁通Φa取值状态称为工作点。前置放大器输出接入积分器进行积分，积分器的输出驱动反馈电阻向反馈线圈注入反馈电流，由反馈线圈与SQUID的互感产生反馈磁通耦合到SQUID中。
磁通锁定环路的工作原理是：在磁通锁定环路保持SQUID工作点稳定时，当被测磁通发生一个变化量ΔΦ，SQUID端产生一个偏离工作点的电压变化Δv,经前置放大器放大后，送入积分器进行积分，调整积分器的输出电压。经反馈电阻、反馈线圈调整反馈磁通抵消上述外部输入的磁通变化量，使SQUID在工作点输入积分器的电压为零，积分器停止积分，环路恢复稳定。工作点稳定状态称为读出电路锁定。在锁定状态下，磁通锁定环路输出电压Vf就与SQUID感应的外磁通变化量成正比【D.Drung“High-Tc and low-Tc dc SQUID electronics”Supercond.Sci.Technol.161320–1336(2003).】，即Vf＝ΔΦ·Rf/Mf，其中ΔΦ为SQUID检测的磁通变化量，Rf为反馈电阻，Mf为反馈线圈与SQUID的互感。,
在电路实现上，传统SQUID磁通锁定环路通常使用前置放大器对SQUID微弱电压信号进行低噪声放大，再将放大后的信号接入积分器进行积分反馈。因此传统的SQUID磁通锁定环路采用至少一个前置放大电路与一个积分器级联电路再连接反馈电阻、反馈线圈构成。在实际应用中，采用积分器的SQUID磁通锁定环路存在以下几个问题：
1)带宽受限：采用积分器的读出电路，使用至少两级以上的放大电路，增大了环路信号的延时，使高频信号传输产生相移，造成环路振荡【D.Drung and M.Mück,The SQUID Handbook,vol.I,J.Clarke and A.I.Braginski,Ed.Weinheim:Wiley-VCH,pp.128–155,2006.】，因此必须增大积分电容，消除振荡，实现磁通锁定环路稳定工作，积分电容的增大，降低了磁通锁定回路的带宽。
2)摆率受限：积分电路的输出是其输入信号随时间积分的结果，当检测信号发生突变，积分器无法快速响应，因此传感器电压输出的摆率受限。难以满足高摆率磁场探测的要求。
3)至少使用两个以上的运算放大器及外围电路，电路复杂，功耗大。
SQUID器件的信号响应可以从直流到GHz，具有高速高带宽特性。上述采用积分器的读出电路在响应带宽、摆率特性上限制了SQUID磁传感器性能。此外，SQUID芯片采用微电子技术制备，具有体积小，集成化的独特优势，在多通道，高分辨率探测系统如采用SQUID的64通道心磁图仪、200多通道的脑磁图仪中广泛应用。多通道系统对SQUID磁传感器小型化提出更高要求。因此，简化SQUID读出电路设计对SQUID多通道应用具有重要意义和实用价值。本发明试图在解决这方面问题作开创性工作。
发明内容
本发明的目的在于提供一种采用单个运算放大器的超导量子干涉器磁传感器，本发明是针对多通道高度集成的SQUID系统，设计更简化的读出电路构建SQUID磁传感器。
SQUID比半导体放大器具有更高的响应速度，它可与放大器实现稳定的负反馈回路。因此本发明构思是只使用一个低噪声的运算放大器，以开环的方式对SQUID电压信号进行放大，并由单个运算放大器开环输出直接驱动反馈电阻及反馈线圈。从而取代了传统磁通锁定环路中的前置放大器和积分器，实现了更简单的SQUID磁通锁定环路的构建。采用单个运算放大器的SQUID磁通锁定环路有以下两种接线方式：
1)正端输入接线方式，如图2所示。偏置电流源提供的偏置电流Ib加载到SQUID中，SQUID电压信号接入运算放大器的正输入端。偏移电压Vb接入运算放大器的负输入端。运算放大器的输出端接反馈电阻Rf的一端，反馈电阻的另一端接反馈线圈，反馈线圈与SQUID通过互感耦合，运算放大器输出电压驱动反馈电阻Rf产生电流，通过反馈线圈与SQUID互感Mf产生反馈磁通，构成磁通锁定环路。
所述的正端输入接线方式有实施方式1、3和5(即A、B和C)三种中的一种(详见具体实施方式)。
2)负端输入接线方式，如图3所示。偏置电流源提供的偏置电流Ib加载到SQUID中，SQUID电压信号接运算放大器的负输入端，偏移电压Vb接运算放大器的正输入端。运算放大器的输出端接反馈电阻Rf的一端，反馈电阻的另一端连接反馈线圈，反馈线圈与SQUID通过互感耦合，运算放大器输出电压驱动反馈电阻Rf产生电流，通过反馈线圈与SQUID互感Mf产生反馈磁通，构成磁通锁定环路。
所述的负端输入接线方式有实施方式2、4和6(即D、E和F)三种中的任一种(详见具体实施方式)。
本发明只使用一个运算放大器实现SQUID磁通锁定环路，电路简单。避免了传统环路中积分器电路的使用，减小环路延时，使磁通锁定环路实现更高的带宽。运算放大器直接输出驱动反馈电阻和反馈线圈，避免了积分电容的影响，磁通锁定环路可实现更高的摆率。此外，上述电路采用单个运算放大器和少量外围电路构成，电路体积小，功耗低，大大减少多通道SQUID传感器集成的整体体积和功耗，在SQUID多通道应用中具有重要的意义。
附图说明
图1.典型直读式读出电路原理。
图2.SQUID正端输入的单个运算放大器磁通锁定环路原理图。
图3.SQUID负端输入的单个运算放大器磁通锁定环路原理图。
图4.单个运算放大器SQUID磁通锁定环路具体实施方式1；图中B1、B2分别为偏置电流或偏置电压调节电路。
图5.单个运算放大器SQUID磁通锁定环路具体实施方式2。
图6.单个运算放大器SQUID磁通锁定环路具体实施方式3。
图7.单个运算放大器SQUID磁通锁定环路具体实施方式4。
图8.单个运算放大器SQUID磁通锁定环路具体实施方式5。
图9.单个运算放大器SQUID磁通锁定环路具体实施方式6。
具体实施方式
本发明有以下六种具体实施方式：
1)具体实施方式1，如图4所示，即正端输入接线方式A；
1.供电电源+Vs和-Vs：整个电路采用双极性电源供电，即正电源端+Vs接入正电压电源和负电源端-Vs接入负电压电源。正电源+Vs供电范围从+5V到+15V，相应的负电源-Vs供电范围在-5V到-15V之间。
2.SQUID偏置电流调节电路B1：其功能是给SQUID加载一个流向SQUID两个约瑟夫森结的偏置电流，电流大小可调节。通过调节加载到SQUID的偏置电流的大小，使得SQUID获得最佳的磁通电压转换特性。可调偏置电流电路具体实例如图3中B1模块所示：可调电位器RA1是一个三端子的可调电阻，其中电位器的1和2的两端为一个固定阻值的电阻，其电阻值在10k欧姆到100k欧姆之间取值为最优。电位器的3端为可调电阻抽头。电位器RA1的1和2两端分别接到正电源+Vs和负电源-Vs。电位器RA1的3端输出电位器电阻分压，通过调节电位器抽头位置产生可调电压。该电压输出接电阻R1,电阻R1的另一端作为偏置电流源的输出端与SQUID串联。电阻R1的取值在50k欧姆～200k欧姆之间。通过调节可调电位器RA1可产生±100uA范围的直流偏置电流。
3.SQUID偏置电压调节电路B2：其功能是产生一个可调节的直流电压，接入运算放大器的负输入端。通过调节使该电压与SQUID工作点处的直流电 压相同，实现工作点调零。可调偏置电压电路具体实例如图3中B2模块所示：可调电位器RA2是一个三端子的可调电阻器，其中电位器的1和2两端为一个固定阻值的电阻，其电阻值在10k欧姆到100k欧姆之间取值为最优。电位器RA1的1和2两端分别接正电源+Vs和负电源-Vs，可变电阻引出抽头端3端输出电阻分压，该电压接电阻R3的一端，R3另一端与R2串联，R2另一端接地。在R2与R3连接端将产生的电阻分压引出作为偏置电压信号Vb。该偏置电压的调节范围为±100uV。电阻R3取值通常在1欧姆到10欧姆之间，以降低其在运算放大器输入端引入的热噪声。电阻R2的取值范围在10k欧姆到100k欧姆之间。
4.SQUID器件SQ1：SQ1使用低温直流超导量子干涉器件(放置在4.2K的液氦温度下工作)或高温直流超导量子干涉器件(放置在77K的液氮温度下工作)，是一个两端子器件。SQ1的一端接入运算放大器正输入端，同时与偏置电流电路B1的电流输出端相连。SQ1的另一端接地。
5.反馈线圈L1：是一个与SQUID具有互感耦合的线圈，互感值为Mf。反馈线圈将反馈回路产生的电流转变成反馈磁通耦合到SQUID中，形成抵消磁通。反馈线圈L1一端接反馈电阻Rf,另一端接地。
6.运算放大器U1：采用双极性供电的低噪声运算放大器，具有正输入端和负输入端两个电压信号输入端，一个电压信号放大输出端。图中运算放大器正输入端接SQUID电压输出，负输入端接偏置电压输出，放大器输出作为磁通锁定环路的输出，作为整个传感器的输出。同时接反馈电阻Rf。为了实现SQUID电压信号的低噪声放大和磁通锁定环路高线性度输出，本发明的运算放大器优选低输入电压噪声和高带宽、高开环增益特性的器件：放大器电压噪声在1nV/√Hz左右，开环增益大于120dB，带宽增益积大于10MHz。常用的低噪声运算放大器有美国ADI公司的AD797和凌特(Linear Technology)公司的LT1028。
7.反馈电阻Rf：反馈电阻Rf一端接运算放大器U1的输出，另一端接反馈线圈L1。反馈电阻Rf将放大器输出电压转换为反馈电流输入反馈线圈，产生反馈磁通。Rf取值在100欧姆到10k欧姆之间。
2)具体实施方式2，如图5所示，即正端输入接线方式D；
将实施方式1中的SQUID电压信号接入运算放大器U1的负输入端，偏置电压信号接入运算放大器的正输入端，其余接线同具体实施方式1。
3)具体实施方式3，如图6所示，即正端输入接线方式B；
磁通锁定环路受外部干扰会发生失锁，造成输出溢出。通过复位开关可以使磁通锁定环路恢复锁定。本实施方式3是在实施方式1的基础上，增加一个复位开关K1，实现复位功能。K1的一端接运算放大器U1的负输入端，K1的另一端接运算放大器U1的输出端。当复位开关闭合时，运算放大器U1的输出端与负输入端等电位。运算放大器由开环高增益放大变为单位增益的放大，输出迅速减小，电路实现复位。当复位开关K1断开时，电路重新锁定。
4)具体实施方式4，如图7所示，即正端输入接线方式E；
将实施方式3中的SQUID电压信号接入运算放大器U1的负输入端，偏置电压信号接入运算放大器的正输入端，其余接线同具体实施方式3。
5)具体实施方式5，如图8所示，即正端输入接线方式C；
SQUID磁传感器在上电使用时，需要重新调节偏置电流和偏置电压，使SQUID获得最佳工作点。本实施方式5是在实施方式3的基础上，增加一个反馈电阻Rg和一个单刀双掷开关SW1，使得磁通锁定环路具备工作点调试功能。单刀双掷开关具有三个接线端子，其中端子3定义为为单刀固定接线端，端子1定义为第一触点接线端，端子2定义为第二触点接线端。SW1的单刀固定接线端与运算放大器U1的输出端相连。SW1的端子1接线端与电阻Rg一端连接，Rg的另一端接运算放大器U1的负输入端。SW1的端子2接线端与接反馈电阻Rf一端相连，反馈电阻Rf另一端接反馈线圈L1。当SW1单刀开关与第二触点断开，与第一触点接通，电阻Rg与运算放大器U1输出端连接。此时，磁通锁定环路开环运行，运算放器U1工作在比例放大模式，实现SQUID电压信号的比例放大。监测运算放大器的输出电压Vf，可观测磁通电压传输特性曲线，辅助SQUID工作点，偏置电流和偏置电压的调节。在完成最佳的偏置电压、偏置电压调节后，将SW1单刀开关与第一触点断开，与第二触点接通，运算放大器U1输出端与反馈电阻Rf连接，此时磁通锁定环路闭环实现锁定输出。
6)具体实施方式6，如图9所示，即正端输入接线方式F；
将实施方式5中的SQUID电压信号接入运算放大器U1的负输入端，偏置电压信号接入运算放大器的正输入端，其余接线同具体实施方式5。

Claims (5)

  1. 一种采用单个运算放大器的超导量子干涉器磁传感器，其特征在于只使用一个低噪声的运算放大器，以开环的方式对SQUID电压信号进行放大，并由单个运算放大器开环输出直接驱动反馈电阻及反馈线圈，从而取代了传统磁通锁定环路中的前置放大器和积分器。
  2. 按权利要求1所述的传感器，其特征在于采用单个运算放大器的SQUID磁通锁定环路有以下两种接线方式：
    1)正端输入接线方式：偏置电流源提供的偏置电流Ib加载到SQUID中，SQUID电压信号接入运算放大器的正输入端；偏移电压Vb接入运算放大器的负输入端，运算放大器的输出端接反馈电阻Rf的一端，反馈电阻的另一端接反馈线圈，反馈线圈与SQUID通过互感耦合，运算放大器输出电压驱动反馈电阻Rf产生电流，通过反馈线圈与SQUID互感Mf产生反馈磁通，构成磁通锁定环路；
    2)负端输入接线方式：偏置电流源提供的偏置电流Ib加载到SQUID中，SQUID电压信号接运算放大器的负输入端，偏移电压Vb接运算放大器的正输入端，运算放大器的输出端接反馈电阻Rf的一端，反馈电阻的另一端连接反馈线圈，反馈线圈与SQUID通过互感耦合，运算放大器输出电压驱动反馈电阻Rf产生电流，通过反馈线圈与SQUID互感Mf产生反馈磁通，构成磁通锁定环路。
  3. 按权利要求2所述的传感器，其特征在于：
    (一)正端输入接线方式有以下A、B和C三种中的任一种：
    A：
    ①供电电源+Vs和-Vs：整个电路采用双极性电源供电，即正电源端+Vs接入正电压电源和负电源端-Vs接入负电压电源；
    ②SQUID偏置电流调节电路B1：其功能是给SQUID加载一个流向SQUID的两个约瑟夫森结的偏置电流，通过调节加载到SQUID偏置电流的大小，使得SQUID获得最佳的磁通电压转换特性；可调偏置电流电路中可调电位器RA1是一个三端子的可调电阻，其中电位器的1和2的两端为一个固定阻 值的电阻，电位器的3端为可调电阻抽头，电位器RA1的1和2两端分别接到正电源+Vs和负电源-Vs；电位器RA1的3端输出电位器电阻分压，通过调节电位器抽头位置产生可调电压；该电压输出接电阻R1,电阻R1的另一端与SQUID串联；
    ③SQUID偏置电压调节电路B2：其功能是产生一个可调节的直流电压，接入运算放大器的负输入端；通过调节使该电压与SQUID工作点处的直流电压相同，实现工作点调零，可调偏置电压电路中的可调电位器RA2是一个三端子的可调电阻器，其中电位器的1和2两端为一个固定端，其电阻值在10k欧姆到100k欧姆之间，电位器RA1的1和2两端分别接正电源+Vs和负电源-Vs，可变电阻引出抽头端3端输出电阻分压，该电压接电阻R3的一端，R3另一端与R2串联，R2另一端接地；R2与R3的连接端将产生的电阻分压引出作为偏置电压信号Vb；
    ④SQUID器件SQ1：SQ1使用放置在4.2K的液氦温度下工作的低温直流超导量子干涉器件或放置在77K的液氮温度下工作的高温直流超导量子干涉器件，是一个两端子器件，SQ1的一端接入运算放大器正输入端，同时与偏置电流电路B1的电流输出端相连，SQ1的另一端接地；
    ⑤反馈线圈L1：是一个与SQUID具有互感耦合的线圈，反馈线圈将反馈回路产生的电流转变成反馈磁通耦合到SQUID中，形成抵消磁通；反馈线圈L1一端接反馈电阻Rf,另一端接地；
    ⑥运算放大器U1：采用双极性供电的低噪声运算放大器，具有正输入端和负输入端两个电压信号输入端，一个电压信号放大输出端；运算放大器正输入端接SQUID电压输出，负输入端接偏置电压输出，放大器输出作为整个传感器的输出，同时接反馈电阻Rf；
    ⑦反馈电阻Rf：反馈电阻Rf一端接运算放大器U1的输出，另一端接反馈线圈L1。反馈电阻Rf将放大器输出电压转换为反馈电流输入反馈线圈，产生反馈磁通；
    B：
    在A的基础上，增加一个复位开关K1实现复位；K1的一端接运算放大器U1的负输入端，K1的另一端接运算放大器U1的输出端，当复位开关闭合时，运算放大器U1的输出端与负输入端等电位，运算放大器由开环高增益放大变为单位增益的放大，输出迅速减小，电路实现复位；当复位开关K1断 开时，电路重新锁定。
    C：
    在B的基础上，再增加一个反馈电阻Rg和一个单刀双掷开关SW1，使得磁通锁定环路具备工作点调试功能，其中，单刀双掷开关具有三个接线端子，其中端子3定义为为单刀固定接线端，端子1定义为第一触点接线端，端子2定义为第二触点接线端；单刀双掷开关的SW1的单刀固定接线端与运算放大器U1的输出端相连，SW1的端子1与电阻Rg一端连接，Rg的另一端接运算放大器U1的负输入端；SW1的端子2与反馈电阻Rf的一端相连，反馈电阻Rf的另一端接反馈线圈L1；当SW1单刀开关与第二触点断开，与第一触点接通，电阻Rg与运算放大器U1输出端连接；此时，磁通锁定环路开环运行，运算放器U1工作在比例放大模式，实现SQUID电压信号的比例放大，监测运算放大器的输出电压Vf，观测磁通电压传输特性曲线，辅助SQUID工作点，偏置电流和偏置电压的调节；在完成最佳的偏置电压、偏置电压调节后，将SW1单刀开关与第一触点断开，与第二触点接通，运算放大器U1输出端与反馈电阻Rf连接，此时磁通锁定环路闭环实现锁定输出。
    (二)负端输入接线方式有以下D、E和F中的任一种：
    ①D为(一)中A方式的SQUID电压信号接入运算放大器U1的负输入端，偏置电压信号接入运算放大器的正输入端，其余特征同A；
    ②E为(一)中B方式的SQUID电压信号接入运算放大器U1的负输入端，偏置电压信号接入运算放大器的正输入端，其余特征同B；
    ③F为(一)中C方式的SQUID电压信号接入运算放大器U1的负输入端，偏置电压信号接入运算放大器的正输入端，其余特征同C。
  4. 按权利要求3所述的传感器，其特征在于：
    (1)正端或负端输入接线方式中，正电源+Vs供电范围从+5V到+15V，相应的负电源-Vs供电范围在-5V到-15V之间；
    (2)SQUID偏置电流调节电路B1中电位器1和2的电阻值在10k欧姆到100k欧姆之间；电阻R1的取值在50k欧姆到200k欧姆之间；通过可调电位器RA1可产生160μA范围的直流偏置电流；
    (3)SQUID偏置电压的调节电路B2中偏置电压Vb的调节范围为±100μV，电阻R3取值在1-10Ω之间，R2的取值范围在10k-100k之间；
    (4)运算放大器电压噪声为1nV/√Hz，开环增益>120dB，带宽增益积大于10MHz；
    (5)反馈电阻Rf取值在100Ω-10kΩ之间。
  5. 按权利要求4所述的传感器，其特征在于运算放大器的型号为美国ADI公司的AD797或凌特公司的LT1028。
PCT/CN2015/082289 2014-07-18 2015-06-25 采用单个运算放大器的超导量子干涉器磁传感器 Ceased WO2016008352A1 (zh)

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EP3171188B1 (de) 2019-04-10
CN104198961B (zh) 2017-06-13
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