No abstract

We have extended our previous study of SFQ balanced comparatom which use two overdamped Josephsoa junctions to (a) finite sampling rate and @) junctions with higher critical current density. The effective width AI, of the gray Zone of the comparators fabricated using the niobium-triiayer technology of HYPRES, Inc. &-l kA/cmz) and Stony Brook's domestic planarized process ( i p s kA/cmf) has been measured as a function of the SFQ pulse rate (from 2.5 to 55 GHz) and temperature (from 1.6 to 4.2 K), for various drivers which determine the SFQ pulse shape and external impedance. The data have been compared with available theories of Josephson junction dynamics in the presence of thermal and quantum fluctuations. We have found that Nx can be substantially reduced by using relatively broad ("soft") SFQ pulses. For high-j, comparators fed by short (-2-ps) SFQ pulses the temperature dependence is practically negligible, indicating the dominance of quantum fluctuations.

Digital superconductor electronics has been experiencing rapid maturation with the emergence of smaller-scale, lower-cost communications applications which became the major technology drivers. These applications are primarily in the area of wireless communications, radar, and surveillance as well as in imaging and sensor systems. In these areas, the fundamental advantages of superconductivity translate into system benefits through novel Digital-RF architectures with direct digitization of wide band, high frequency radio frequency (RF) signals. At the same time the availability of relatively small 4 K cryocoolers has lowered the foremost market barrier for cryogenically-cooled digital electronic systems. Recently, we have achieved a major breakthrough in the development, demonstration, and successful delivery of the cryocooled superconductor digital-RF receivers directly digitizing signals in a broad range from kilohertz to gigahertz. These essentially hybrid-technology systems combine a variety of superconductor and semiconductor technologies packaged with two-stage commercial cryocoolers: cryogenic Nb mixed-signal and digital circuits based on Rapid Single Flux Quantum (RSFQ) technology, room-temperature amplifiers, FPGA processing and control circuitry. The demonstrated cryocooled digital-RF systems are the world's first and fastest directly digitizing receivers operating with live satellite signals in X-band and performing signal acquisition in HF to L-band at ∼30 GHz clock frequencies.