2-LOOP MODULATOR FOR SIGMA-DELTA ANALOG-TO-DIGITAL CONVERTER

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 circuit In simulations of a 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 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.