Design and implementation of cryogenic semiconductor amplifiers as interface between RSFQ circuits

Rapid single flux quantum (RSFQ) circuits create high interest in cryogenic amplifiers as interface to commercial room temperature electronics. The requirements for the amplifiers are an extremely high bandwidth (SFQ pulses with trise ¼ tfall ¼ 10 ps), high voltage gain of about 104 (common RSFQ output voltage level of about 200 lV), low power consumption (cryogenic environment at 4 K) and low noise. Hybrid amplifiers, based on commercial available p-HEMT transistors, can solve the problematic highspeed interface. In this paper, we present measurement results of a hybrid four stage coplanar amplifier in combination with a RSFQ Toggle Flip-Flop (RSFQ T-FF) and a Josephson array quantizer (JA-Q).