J. X. Przybysz, D. L. Miller, and E. H. Naviasky
Abstract - A two-loop modulator has been designed for a superconductive sigma-delta analog to digital converter. In contrast to semiconductor modulators, which use high-gain amplifiers in the signal feed forward path, the superconductive modulator used digital gain in the signal feedback path. The use of superconductive electronics to precisely feed back a single flux quantum into the second integrator loop and multiple flux quanta into the first integrator loop was key to this invention. At 40 GHz sampling rate, the modulator obtained a 98 dB signal to noise ratio on the dc - 60 MHz band. The modulator tolerated thermal noise well, obtaining a 98 dB SNR on the dc - 4 MHz band, while sampling at a rate of 4 GHz. The modulator tolerated clock timing jitter better than Nyquist-rate A/D converters, obtaining equivalent performance with 3 times as much rms jitter. Compared to single-loop sigma-delta and oversampled lobe-counting A/D converters, the two-loop modulator can achieve equivalent performance at a significantly reduced sampling and digital filter rate.
4 p. 11 refs. 7 illus.
Return to: Superconducting and Hybrid Digital Circuits | Cryoelectronics Publications | Cryoelectronics Home Page | Northrop Grumman STC Home Page
Copyright 1996 Northrop Grumman Corporation