RF Amplifiers Based on DC SQUID for 3-4 GHz Band*

DC SQUID based RF Amplifiers (SRFAs) are known to dissipate very little power and can be integrated on-chip with existing micro-fabricated circuits for low-noise, low temperature measurements. The SRFA chip has 4 independent channels, which amplify at different signal frequencies and have integrated output filters, which prevent the leakage of high frequency resonances associated with the Josephson frequency. A compact two-layer input signal coil is integrated with the washer of the SQUID (L=20 pH) and planar capacitors for tuned frequency and impedance matching. The input reflected power is further reduced using proven balanced configuration on the SQUID. The shunt resistors are made from a multilayer film Ti(2 nm)/Pd(55 nm)/Ti(2 nm), which allow the SRFA~ to operate down to 0.4 K. Low-noise SRFAs have been tested with an operating frequency range of 3-4 GHz.