DC SQUID series array amplifiers with 120 MHz bandwidth (corrected)

We report on the performance of dc SQUID (Superconducting Quantum Interference Device) series array amplifiers from dc to 500 MHz. The arrays consist of up to 100 dc SQUIDs, with varying degrees of intracoil damping; the flux focusing washer of each SQUID is electrically isolated from the SQUID loop (L_sq=18 pH). Using an rf network analyzer, we have observed high-frequency resonances in the response at bias points corresponding to distortions in the dc transfer functions. Increasing distance between SQUIDs in the array reduces the distortions. Distortions are also more pronounced, and bandwidth reduced, in devices incorporating the flux-focusing washer into the SQUID body. With intracoil damping of 0.25 Ω per turn on the input coil, the voltage-flux transfer characteristics of the isolated-washer design and 300 pm center-to-center SQUID spacing are free of significant distortions, and the bandwidth is not degraded compared to undamped devices. The 100-SQUID array has 150 nH input inductance, 500 V/A transimpedance, 2.5 pA/√Hz equivalent input current noise at 4 K, and 120 MHz bandwidth     

Optimization of input impedance and mechanism of noise suppressionin a DC SQUID RF amplifier

The optimal input impedance and noise of a DC SQUID RF amplifier at frequencies of the order of 1 GHz with a resonant input matching circuit have been studied analytically, numerically, and experimentally. A model for noise temperature and power gain has been developed for the practical resonant input tank circuit. A new effect of the output noise increasing or decreasing with changing the sign of voltage-to-flux transfer coefficient has been observed experimentally and explained analytically. The different values of noise temperature for the opposite dV/dΦ values have been interpreted using a model with partially correlated current and voltage noise sources. The equivalent layout for optimal input matching of a SQUID amplifier comprising series and parallel resonant circuits has been presented. Using such a matching circuit and SIS junction as a signal source the SQUID amplifier noise temperature about 1 K has been measured at 1.1 GHz     

Modelling of the coupling structure of a HTS DC SQUID amplifier

In order to estimate self- and mutual inductances of the input coil and the pick-up loop of a YBCO SQUID amplifier operating at 77 K, a simple method based on the determination of the current and flux distributions into the superconductors is presented. The cases of inductors (single loop and spiral) and induced circuits (closed and open loop) are considered. The authors stress the difference between a SQUID pick-up loop and a directly coupled magnetometer depending upon their action on the input inductance. Finally, the coupling efficiency and the ground plane effect are calculated and measured for various patterns     

A planar picoamperemeter based on a superconducting quantum interferometer

An optimized picoamperemeter based on a superconducting quantum interferometer device (SQUID) for a metal cold-electron bolometer is fabricated and experimentally studied. The intrinsic SQUID current noise caused by the input coil is estimated to be less than 1 pA/Hz^1/2. Owing to the application of modulation electronics, current sensitivity in the input coil reaches 5 pA/Hz^1/2 in the frequency band from 10 Hz to 10 kHz.     

DC SQUID-based position detector for gravitational experiments

Experiments like the test of the weak equivalence principle at the Bremen drop-tower, Germany, and STEP (Satellite Test of the Equivalence Principle) require a position detector with an extremely high resolution to measure tiny displacements of free falling test bodies.In order to develop a SQUID position detector numerous configurations of test bodies and pick-up coils with different geometries were tested experimentally. As a function of the position of the test body the inductance of the pick-up coil was measured with a commercial LCR meter as well as with a LTS DC SQUID system. This SQUID system, which is developed and manufactured at the Jena University, provides high sensitivity and extremely low intrinsic noise, especially at low frequencies.This contribution will also discuss some recent results in measuring the motion of one body during its free fall over 109 m at the Bremen drop-tower.     

A compact 220 GHz heterodyne receiver module with planar Schottky diodes

This letter presents the development of a compact 220 GHz heterodyne receiver module for radars application in which a novel low pass wide stop band intermediate frequency (IF) filter is integrated. The planar Schottky anti-parallel mixing diode based subharmonic mixer (SHM) is used as the receiver’s first stage. The diode is flip-chip mounted on a 50 μm thick quartz substrate. The accurate modeling of the self and mutual inductance of the diode’s air-bridges are discussed. The measured conversion loss (CL) of the SHM has a minimum value of 6.2 dB at 210.5 GHz, and is lower than 8.4 dB in the frequency range 209.4–219.6 GHz with a 10 mW input power from a local oscillator (LO). The LO chain consists of a 110 GHz passive tripler, two Ka-band amplifiers and a Ka-band active tripler. The tested minimum double side band (DSB) noise temperature of the integrated 220 GHz heterodyne receiver is 725 K at 205.2 GHz and lower than 1550 K in the frequency range 199–226 GHz.     

Performance of a flux locked series SQUID array

The operation of a SQUID array with 100 DC SQUIDs has been demonstrated using a single flux-locked loop. The SQUID array had a maximum dynamic range of ±1.3×10⁸/√(Hz) in the low frequency region, a high slewing rate over a wide frequency range, and an extrinsic white noise energy sensitivity of 6×10^-31J/Hz. These data were obtained with a very simple feedback circuit made from three inexpensive operational amplifiers that operated in the DC-feedback mode. The feedback loop did not have any impedance matching circuit between the SQUID array and the room temperature electronics. Our results show that a SQUID array can have a significant impact on those applications that demand good noise performance and a very high dynamic range     

A noise optimization technique for integrated low-noise amplifiers

Based on measured four-noise parameters and two-port noise theory, considerations for noise optimization of integrated low-noise amplifier (LNA) designs are presented. If arbitrary values of source impedance are allowed, optimal noise performance of the LNA is obtained by adjusting the source degeneration inductance. Even for a fixed source impedance, the integrated LNA can achieve near NF/sub min/ by choosing an appropriate device geometry along with an optimal bias condition. An 800 MHz LNA has been implemented in a standard 0.24 /spl mu/m CMOS technology. The amplifier possesses a 0.9 dB noise figure with a 7.1 dBm third-order input intercept point, while drawing 7.5 mW from a 2.0 V power supply, demonstrating that the proposed methodology can accurately predict noise performance of integrated LNA designs.     

High-current resolution broad-band SQUID amplifier suitable for TEScalorimeter

A superconducting quantum interference device (SQUID) amplifier has been developed as a current detector with both high-current resolution and broad bandwidth for a transition edge sensor calorimeter. The amplifier is a two stage SQUID (TSS) that consists of an input-SQUID with a 38-turn input coil and a 100-serial SQUID array (100-SSA) output, and has been integrated on a 3 × 3 mm Si chip using Nb thin film fabrication technology. It is designed to increase the amplifier gain and maintain matching with the parameters of the calorimeter. To avoid flux trapping in the SSA, the washer coil of the dc-SQUIDs in the SSA was made with a narrow line width of 17.5 μm. We experimentally confirmed that the designed output voltage was achieved using a one-layer p-metal magnetic shield tube in the earth's magnetic field. The performance of the shielded TSS amplifier was evaluated in liquid helium. The TSS amplifier had a gain of 10 kV/A and an impedance of 0.07 Ω at 100 kHz. When a flux locked loop circuit was used to drive the amplifier, a current resolution of 1 pA/√Hz and a rise time of 1 μs were achieved     

一种新颖的具有HEMT和GaAs MMIC的Ku波段低噪声放大器

本文介绍了一种具有高电子迁移率晶体管(HEMT)和砷化镓单片微波集成电路(GaAs MMIC)的Ku波段低噪声放大器。在11.7～12.2GHz频率范围内,该放大器的噪声系数小于1.9dB,相关增益大于27dB,输入和输出驻波比小于1.4。放大器第一级采用了HEMT和微波串联电感反馈技术,放大器未级采用了Ku波段GsAs MMIC。设计的关键是采用微波串联电感反馈方法同时获得最佳噪声和最小输入驻波匹配。放大器的输入端和输出端均为BJ-120波导。     

Study of the magnetic coupling between a SQUID and wires integratedon a chip

Magnetic coupling between a SQUID and wires in an integrated circuit has been studied. Using test integrated circuits, the coupling is measured by varying the distance from the SQUID to each wire. The coupling between the SQUID and the wires with and without a groundplane decreases with an increase in the distance. The coupling for the wires with the groundplane is smaller than that for the wires without the groundplane at distances less than 595 μm. However, the rate of the decrease in the coupling for the wires with the groundplane falls off for distances more than 595 μm and the coupling converges to around 2.9 pH. From two dimensional simulations for the magnetic flux coupling, the origin of the residual inductance is found to be the coupling between the SQUID, and shielding current in the groundplane. The value of the distance, 595 μm, does not depend on the size of the SQUID. To decrease the coupling, the use of wires with stripline structure or coplanar structure is desirable     

Principles and applications of SQUIDs

An overview of the current status of DC and RF SQUIDs (superconducting quantum interference devices) is presented. Using Nb-based thin-film technology, a number of groups can now routinely fabricate DC SQUIDS with input circuits integrated on the same chip. At 4.2 K, the DC SQUID, which operates with a constant bias current, can detect signals with an equivalent energy per unit bandwidth of a few hundred h2π. RF SQUIDs, which operate with an RF flux bias, are usually machined from bulk Nb, and have a typical energy sensitivity per unit bandwidth of 10⁵ to 10⁶h2π. Both types of SQUID can be used in a wide variety of applications, including magnetometers, gradiometers, susceptometers, voltmeters, RF amplifiers, gravity-wave antennas, and gravity gradiometers. Both DC and RF SQUIDs have been fabricated from high-temperature superconductors and operated at temperatures of up to 77 K. These devices exhibit high levels of 1/f noise, which generally arises from the motion of trapped magnetic flux     

集成运算放大器参数时漂的1/f噪声预测方法

寿命试验和噪声测试结果表明,如果集成运算放大器的主要失效模式是输入偏置电流或失调电流随时间的漂移,则这种漂移量与运放的1/f噪声电流具有强相关性,二者近似呈正比关系。理论分析表明,这种漂移可归因于作为1/f噪声直接起源的氧化层陷阱对硅中电子的慢俘获作用。据此,提出了通过1/f噪声测量对集成运放特定参数时漂进行快速无损评估的方法。     

感性负载方波电源功率放大器的分析计算

方波电源是采用数字技术的脉冲电源,具有相位严格、频率稳定度高,抗干扰能力强等独特的优点.该文以一个实例,对工作在方波信号输入下的功率放大器,带感性负载时的工作特点进行了分析,并且根据分析的结果,推导出了在方波信号输入下,功率放大器带感性负载时的各项性能指标的计算方法.并通过对实际电路的测试,验证了计算方法的可行性,同时还提出了减小感性负载对放大器影响的措施.     

Novel matched amplifiees with low noise positive feedback. Part 1: General features and resistive feedback

The prominent inventions of D.E. Norton as well as other similar schematics are widely used in different circuits of amplifiers and mixers. However, the use of these circuits in high-frequency integrated circuits (IC) is still hindered by the presence of the broadband feedback transformer. We propose new configuration schematics of transformer-less amplifiers with similar properties. Now we understand implicitly that this opportunity was already contained in our previous patents and papers. Here, the generalised circuit of an amplifier with a complex positive current feedback and with a common base (CB) transistor configuration is considered. Besides, the circuit of low noise amplifier (LNA) with a resistive positive feedback (RPF) is investigated in detail. RPF and CB amplifiers are compared. It is demonstrated that LNA RPF provides gain stability vs scattering of parameters, a good level of the input and output matching, a wider frequency band and the noise temperature more than twice as low as that in CB and, despite a positive feedback, it provides a high stability gain.     

Double relaxation oscillation SQUID with reference junction for biomagnetic multichannel applications

We have fabricated a four-channel SQUID gradiometer system based on double relaxation oscillation SQUIDs (DROSs) with a reference junction. For a biomagnetic multichannel system, we simplified the DROS design by using a single reference junction instead of the reference SQUID. The SQUIDs were fabricated from hysteretic Nb/AlO_x/Nb junctions using a simple four-level process. The DROSs provided very large flux-to-voltage transfers of typically 3 mV/Φ₀, enabling direct readout by a room-temperature dc preamplifier, and consequently simple flux-locked loop electronics were used. To realize a compact and reliable gradiometer, a first-order planar pickup coil was integrated on the same wafer with the SQUID. The flux noise of the gradiometer is about 5 μΦ₀/√Hz at 100 Hz, corresponding to a field noise of 8 fT/√Hz, measured inside a magnetically shielded room. A compact four-channel planar gradiometer system was implemented and operated to measure auditory evoked fields.     

Broadband nuclear magnetic resonance using DC SQUID amplifiers

We have constructed two pulsed NMR spectrometers in which the signal is coupled to the input coil of a low T_c DC SQUID using a superconducting flux transformer, yielding broadband response, with bandwidth determined by the SQUID electronics. A 50 kHz bandwidth commercial system has been used to observe free induction decay signals from platinum powder, bulk platinum, ³He gas and surface monolayers of ³He in the temperature range from 1.4 to 4.2 K and at frequencies from 5 to 40 kHz. The observed signal-to-noise ratio is as calculated with the noise dominated by flux noise in the SQUID in all samples but the bulk metal. A second system, which operates in flux-locked loop mode with bandwidth of 3.4 MHz using a SQUID with additional positive feedback, has been used to observe NMR signals from platinum powder at frequencies from 38 to 513 kHz and at a temperature of 4.2 K. The advantage of this technique in the study of systems with short T₂ at frequencies below 1 MHz is discussed. In addition we discuss the benefits of both broadband and tuned input circuits for NMR detection and we describe the performance of a spectrometer with a tuned input circuit which has been used to obtain signals at 1 MHz from platinum powder at 4.2 K and from ∼2 layers of ³He absorbed on a surface area of 0.11 m² at 1.7 K. The amplifier noise temperature is predicted to be 60 mK in the ³He experiment. This demonstrates the potential of the tuned set-up for measurements at low millikelvin temperatures on systems with low spin density and with T₂ greater than several hundred microseconds.     

Ultra-Low-Noise 1.2- to 1.7-GHz Cooled GaAsFET Amplifiers

A 3-stage GaAsFET amplifier operating at 13 K, utilizing source inductance feedback is described. The amplifier has a noise temperature of <10 K, input return loss >15 dB over the 1.2- to 1.7-GHz frequency range.     

32-GHz cryogenically cooled HEMT low-noise amplifiers

The cryogenic noise temperature performances of a two-stage and a three-stage 32-GHz HEMT (high-electron-mobility transistor) amplifier were evaluated. The amplifiers utilize quarter-micrometer conventional AlGaAs/GaAs HEMT devices, hybrid matching input and output microstrip circuits, and a cryogenically stable DC biasing network. The noise temperature measurements were performed in the frequency range of 31 to 33 GHz over a physical temperature range of 300 to 12 K. Across the measurement band, the amplifiers displayed a broadband response, and the noise temperature was observed to decrease by a factor of ten in cooling from 300 to 15 K. The lowest noise temperature measured for the two-stage amplifier at 32 GHz was 35 K with an associated gain of 16.5 dB, while for the three-stage amplifier it was 39 K with an associated gain of 26 dB. It was further observed that both amplifiers were insensitive to light     

First steps towards a high-Tc squid amplifier

A high-T_c DC SQUID amplifier has been prepared and tested. The principle of operation of the amplifier was first proved by using low-T_c Nb-Al₂O₃-Nb SQUIDs with integrated Nb input coils. A flux gain factor of about 20 was demonstrated at 4.2 K with the low-T_c SQUIDs. The operation of the high-T_c SQUID amplifier was demonstrated by using step edge and/or bicrystal DC SQUIDs. The input coils of the amplifier were wire wound copper coils. A flux gain of about 8 has been measured at 77 K. A flip chip arrangement with a thin film coil has also been tried. In this case, one input coil was a one turn high T_c superconducting strip. The second coil consisted of a 22-turn high-T_c superconducting stripline with a gold strip crossover. The measurements showed a high contact resistance between Au and YBa₂Cu₃O_7−δ which was detrimental for a proper operation of the amplifier.