Application of small-signal model to DC SQUID circuit design

As the performance of HTS DC SQUIDs continues to improve, their utilization in RF devices (e.g., amplifiers, nuclear magnetic resonance detectors) having complex circuitry becomes more attractive. To fully realize their potential in this application, accurate and efficient analysis techniques are required to assist the circuit designer. Beginning with measured V-phi and I-V data for the device, we have used the small-signal model to optimize the design of a two-stage low-noise amplifier (LNA) comprised of DC SQUIDs. Optimization criteria were maximum gain and minimum noise figure at the upper band edge. We have shown that the small signal model is an invaluable design tool which provides the analytical performance data needed to optimize the SQUID and its attendant RF circuitry.