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IEEE Transactions on Applied Superconductivity

A dc SQUID based low-noise 4 GHz amplifier

G.V. Prokopenko, S. V. Shitov, V. P. Koshelets, Dmitry B. Balashov, J. Mygind

Published Jun 1, 1997• 18 citations
Publisher

Abstract

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.

DOI
10.1109/77.622147

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IEEE Transactions on Applied Superconductivity•Jun 1, 2003•3 citations
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.
The dc SQUID based RF amplifier (SQA) looks very attractive as an IF amplifier for integration with a §I§ mixer and a flux-flow oscillator (FFO) in a fully superconducting submiltimeter 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 has been developed and tested in the frequency range 3.6-4.1 GHz. The 1 pm2 area Nb-AlO,-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+1 dB, 5.0k1.5 K, 3.86- 3.90 GHz, and 6.M dB, 22+7 K, 3.89-4.05 GHz, respectively.
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.
A low-noise rf amplifier based on a dc SQUID (SQA) is tested in the frequency range 3.3-4.1 GHz. A new signal launching system for the SQA rf coupling has been developed and successfully implemented. The following parameters have been measured at 3.65 GHz using a band-pass filter at the input of a single-stage SQA: gain (11.0/spl plusmn/1.0) dB, 3 dB bandwidth of 300 MHz and noise temperature (4.0/spl plusmn/1.0)K. This figure corresponds to a flux noise S/sub /spl Phi///sup 1/2 /=0.6 /spl mu//spl Phi//sub 0//Hz/sup 1/2 / and an energy sensitivity /spl epsi//sub i//spl ap/75 h. The input saturation power, P/sub s/, (1 dB gain compression) is measured for different bandwidths of the input band-pass filter, A corresponding input signal saturation temperature (normalized for a 1 GHz bandwidth) T/sub SAT//sup 1GHZ/=P/sub SAT//k/sub B/ is estimated to be 11.5 K GHz at an SQA bias voltage 27 /spl mu/V (condition for minimum noise temperature). The dependencies of the SQA gain, noise temperature and saturation level on the operation point are studied. The reason for the SQA saturation is discussed.
A 6 mm/spl times/6 mm chip comprising two identical DC SQUID based amplifiers (SQAs) has been designed, fabricated and tested as a two-stage RF amplifier in a frequency range 3.5-4.0 GHz. Each SQA consists of a double washer type DC SQUID with novel integrated input resonant circuit. The reflection coefficient of both input and output of the SQA has been measured in the two stage configuration. To avoid SQA saturation at the wide band noise tests a tunable 40 MHz bandpass YIG-filter has been used. The following parameters of the two-stage SQA have been measured at the 3.65 GHz: gain of (17.5/spl plusmn/1) dB, 3 dB bandwidth of about 250 MHz, and noise temperature (4.0/spl plusmn/0.5)K what corresponds to intrinsic flux noise S/spl phi//sup 1/2//spl ap/0.6 /spl mu//spl Phi//sub 0/Hz/sup -1/2/ and energy sensitivity /spl epsiv//sub i//spl ap/75 /spl planck/ (7.8/spl middot/10/sup -33/ J/Hz). If the measured RF mismatch between the input/output of SQA and source signal/post-amplifier is taken into account a gain of (20.5/spl plusmn/1.5) dB and noise temperature as low as (2.5/spl plusmn/1.0) K (intrinsic flux noise S/spl phi//sup 1/2//spl ap/0.4 /spl mu//spl Phi//sub 0/Hz/sup -1/2/, energy sensitivity /spl epsiv//sub i//spl ap/47 /spl planck/) can be estimated.
A low-noise rf amplifier based on a dc SQUID (SQA) is developed and tested within frequency range 3.0-4.5 GHz. The 4-channel chips are designed using proven balanced output configuration; they employ special damping filters. Each channel is tested separately demonstrating the following parameters at 3.95 GHz central frequency: gain (9.5 /spl plusmn/ 1.0) dB, 3-dB bandwidth 300 MHz and noise temperature (1.0 /spl plusmn/ 0.5) K. The 1-dB gain compression estimate is 50 K*GHz for bias voltage 80 /spl mu/V and characteristic voltage 285 /spl mu/V.
We present an X-band amplifier concept based on a HTS grain boundary dc SQUID, which allow for extended dynamic range for use with SIS mixers, e.g., as a buffer amplifier in front of an RSFQ ADC, or possibly for satellite and cellular phone communications. The proposed RF design is based on a combination of single-layer slot and coplanar lines forming novel input and output circuits. The following parameters (per stage) are obtained via simulation for central frequency 11 GHz: bandwidth 0.5-1 GHz, power gain 11-12 dB, noise temperature 5-10 K. A saturation product as high as 500-1000 K/spl middot/GHz is estimated for a characteristic voltage of 1-2 mV. The realization of these parameters makes HTS SQA competitive with existing coolable HEMT-amplifiers for radio astronomy and satellite communication.