Dynamic characteristics of S-band DC SQUID amplifier

Abstract

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 1) dB, 3 dB bandwidth of 500 MHz and noise temperature (1 0 0 25) K. For the nonbalanced type SQA at 4.0 GHz gain was (15 1) dB, 3 dB bandwidth 200 MHz and noise temperature (0 5 0 25) K. The improved performance is obtained due to the increased characteristic voltage ( 420 V) of the small-area (down to 0.7-0.9 m 2 ) high-quality Nb-AlO -Nb SIS junctions. The saturation power (normalized to 1 GHz) referred to the input at 1 dB gain compression is estimated as 55 K*GHz at a bias voltage of 60 V. The reasons for saturation of the SQA are discussed.

High quality Nb-based tunnel junctions for high frequency and digital applications

“…As follows from [8] in the case of tunnel junctions, the in should be substituted by , the sub-gap resistance. Using external shunts made of sputtered Mo thin films we have fabricated nonhysteretic Nb-AlO -Nb tunnel junctions with m and characteristic voltage as much as 420 V. These junctions have been successfully employed for a high performance SQUID Amplifier [12].…”

Synthesis of high-linearity array structures

“…The developed array structures lead to the design of wide band, highly linear amplifiers for the gigahertz frequency range. The array-based amplifiers seem to be capable of providing essentially higher gain, linearity and dynamical range than the ones shown by the SQUID amplifier [5,6]. In fact, the transfer factor dV /dB is proportional to the number N of interferometer cells and the dynamic range increases as √ N for both parallel and series arrays.…”

Superconducting quantum interference device amplifiers at gigahertz frequencies

“…We then calculated the temperature T (s) at which a 50 ⍀ resistor produces Nyquist noise with the same power in the bandwidth of the amplifier. 15 Our estimated values of T (s) were in the range of 150-250 K.…”

“…By measuring the output noise from the system with the noise source on and off and subtracting the noise contribution of the HEMT amplifier we determined the values of T N listed in Table I. Although the errors are relatively large, the noise temperatures hover between 1 and 2 K. Prokopenko et al 15 have measured a comparable noise temperature at 3.9 GHz for a SQUID amplifier of a different design.…”