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Superconducting digital circuits are capable of producing high dynamic range analog-to-digital converters (ADCs). We present sigma-delta architectures using large (>100) oversampling ratios to give signal-to-noise ratios of greater than 100 dB in simulation. Three distinct designs, using two distinct mechanisms for feedback, are presented. All of the designs use only shunted junctions, and are therefore compatible with HTS SNS junctions. Simulations are presented for a modulator which creates feedback pulses by SQUID lobe-crossings, a modulator which uses the transresistance of a SQUID for feedback, and a modulator which uses threshold crossings in both the first and second loops for feedback.
Date of Publication: June 1999