Experimental implementation of SFQ NDRO cells and 8-bit ADC

Two single-flux quantum (SFQ) logic elements have been designed, fabricated, and successfully tested: an 8 b analog-to-digital converter (ADC) and nondestructive readout (NDRO) cells. The converter consists of an input coil, a comparator, and a reversible ripple counter. The ADC shows a good linearity (+or-12 mA) and a quite high calculated frequency range (up to 2.5 GHz). Two types of input coils differing in inductance and two types of NDRO units also have been investigated: with direct and magnetic coupling between interferometers. The integrated circuits are fabricated using 4 mu m Nb-AlO/sub x/-Nb trilayer technology with a critical current density of about 1000 A/cm. This techniques makes it possible to produce NDRO cells operating up to 10 GHz frequency.<
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