SFQ BALANCED COMPARATORS AT A FINITE SAMPLING RATE

We have extended our previous study of SFQ balanced comparators which use two overdamped Josephson junctions to (a) finite sampling rate and (b) junctions with higher critical current density, The effective wid th Delta I-x of the gray zone of the comparators fabricated using the niobium-trilayer technology of HYPRES, Inc. (j(c) approximate to 1 kA/ cm(2)) and Stony Brook's domestic planarized process (j(c) approximate to 5 kA/cm(2)) has been measured as a function of the SFQ pulse rate (hem 2.5 to 55 GHz) and temperature (from 1.6 to 4.2 K), for various d rivers 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 Delta I-x can be substantially reduced by using relatively broad (''soft'') SFQ pulses, For high-j(c) comparators fed by short ( similar to 2-ps) SFQ pulses the temperature dependence is practically negligible, indicating the dominance of quantum fluctuations.