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IEEE Transactions on Applied Superconductivity

DC SQUID RF amplifiers

Michael A. Tarasov, Victor Y. Belitsky, G.V. Prokopenko

Published Jun 1, 1992• 15 citations
Publisher

Abstract

The noise and signal parameters of several types of RF amplifiers based on different SQUIDs with integrated and hybrid input coils were studied. A new type of multiloop DC SQUID with an integrated input coil and extremely low stray capacitances was designed. The inductance of a four-loop SQUID was 100 pH, the input coil inductance 1.3 nH, and mutual inductance 300 pH. The tuned integrated four-loop amplifier at 420 MHz had a noise temperature lower 0.5 K and a power gain of nearly 20 dB in a 60-MHz bandwidth. For the noise calibration of such amplifiers, SIS junctions were used as a shot noise source, or a cooled attenuator and a room temperature semiconductor noise source were used.>

DOI
10.1109/77.139223

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The authors report a SQUID (superconducting quantum interference device) amplifier with a novel tuning circuit that can be easily coupled to a finite-impedance source. The SQUID amplifier is designed for a source impedance of 50 Omega and a signal frequency of nearly 150 MHz. The performance of the SQUID amplifier has been measured at 4.2 K. The measured gain and noise temperature of the SQUID amplifier are 20 dB and 0.7 K, respectively. A saturation temperature as high as 200 K at the input of the SQUID amplifier is achieved. It is concluded that this type of tuned SQUID amplifier is applicable to the IF (intermediate frequency) amplifier of the SIS (superconductor-insulator-semiconductor) receiver.>

IEEE Transactions on Magnetics•Mar 1, 1989•15 citations
The noise and signal parameters of several types of RF amplifiers based on different SQUIDs with integrated and hybrid input coils were studied. A new type of multiloop DC SQUID with an integrated input coil and extremely low stray capacitances was designed. The inductance of a four-loop SQUID was 100 pH, the input coil inductance 1.3 nH, and mutual inductance 300 pH. The tuned integrated four-loop amplifier at 420 MHz had a noise temperature lower 0.5 K and a power gain of nearly 20 dB in a 60-MHz bandwidth. For the noise calibration of such amplifiers, SIS junctions were used as a shot noise source, or a cooled attenuator and a room temperature semiconductor noise source were used.>
The power gain and the noise temperature of a DC SQUID RF amplifier at a signal frequency 400 MHz were measured in the presence of external microwave radiation at 2 cm, 8 mm and 4 mm wavelengths. The authors used a four-loop planar DC SQUID with an integrated input coil and very low values of inductances and stray capacitances. In the noise measurements they used an SIS junction as a precise source of input noise at high DC bias voltage V b >V 2 Delta . In such a configuration the studied system is the same as an SIS mm-wave mixer with a SQUID IF amplifier.
Integrated radio-frequency amplifiers comprising a 4-loop dc SQUID, seriesly connected input coil turns, a resonant capacitor parallel to the input coil, series capacitors at the input and output ports and bias resistors have been designed, fabricated and experimentally studied. A multiloop dc SQUID with parallel loops and seriesly connected single-turn input coils placed inside each loop and integration with the input resonant matching circuit elements and with elements of dc bias circuit allows one to increase signal frequency and reduce the influence of external noise. The amplifiers with three different capacitors have resonant frequencies 560, 656, 758 MHz and bandwidth about 50 MHz. The noise temperature of such amplifiers below 1.5 K has been measured using cold attenuator and room-temperature noise sources. The layout comprising three pairs of such amplifiers placed on the same 15/spl times/24 mm substrate was designed to increase the bandwidth over the bandwidth of the individual amplifiers.>
A low-noise RF amplifier based on a dc SQUID (SQA) has been tested in the frequency range 3.0-4.6 GHz in the open-loop configuration. The following parameters have been measured for the single-stage balanced type SQA at 4.0 GHz: gain (12/spl plusmn/1) dB, 3 dB bandwidth of 500 MHz and noise temperature (1.0/spl plusmn/0.25) K. For the nonbalanced type SQA at 4.0 GHz gain was (15/spl plusmn/1) dB, 3 dB bandwidth 200 MHz and noise temperature (0.5/spl plusmn/0.25) K. The improved performance is obtained due to the increased characteristic voltage (/spl ap/420 /spl mu/V) of the small-area (down to 0.7-0.9 /spl mu/m/sup 2/) high-quality Nb-AlO/sub x/-Nb SIS junctions. The saturation power (normalized to 1 GHz) referred to the input at 1 dB gain compression is estimated as /spl ap/55 K*GHz at a bias voltage of 60 /spl mu/V. The reasons for saturation of the SQA are discussed.
The dc SQUID based RF amplifier (SQA) looks very attractive as an IF amplifier for integration with a SIS mixer and a flux-flow oscillator (FFO) in a fully superconducting submillimeter wave receiver suitable for space applications. Important advantages of the SQA are its low noise, extremely low power consumption, and complete compatibility with the fabrication process currently used for SIS mixers. Single stage amplifiers with a novel signal coupling circuit have been developed and tested in the frequency range 3.6-4.1 GHz. The 1 /spl mu/m/sup 2/ area Nb-AlO/sub x/-Nb junctions shunted by Ti resistors are grouped in a double washer dc SQUID. Two samples with slightly different designs showed the following gain, noise temperature and 3 dB bandwidth: 10.0/spl plusmn/1 dB, 5.0/spl plusmn/1.5 K, 3.86-3.90 GHz, and 6.8/spl plusmn/1 dB, 22/spl plusmn/7 K, 3.89-4.05 GHz, respectively.
Radio-frequency (RF) amplifiers based on direct current (DC) superconducting quantum interference device (SQUID) have low-noise performance for precision physics experiments. Gain curves of SQUID RF amplifiers depend on several parameters of the SQUID and operation conditions. We are developing SQUID RF amplifiers for application to measure very weak RF signals from ultra-low-temperature high-magnetic-field microwave cavity in axion search experiments. In this study, we designed, fabricated and characterized SQUID RF amplifiers with different SQUID parameters, such as number of input coil turn, shunt resistance value of the junction and coupling capacitance in the input coil, and compared the results.
The authors report a SQUID (superconducting quantum interference device) amplifier with a novel tuning circuit that can be easily coupled to a finite-impedance source. The SQUID amplifier is designed for a source impedance of 50 Omega and a signal frequency of nearly 150 MHz. The performance of the SQUID amplifier has been measured at 4.2 K. The measured gain and noise temperature of the SQUID amplifier are 20 dB and 0.7 K, respectively. A saturation temperature as high as 200 K at the input of the SQUID amplifier is achieved. It is concluded that this type of tuned SQUID amplifier is applicable to the IF (intermediate frequency) amplifier of the SIS (superconductor-insulator-semiconductor) receiver.>