Experimental Demonstration of Superconducting

Superconducting bandpass delta-sigma ( ) mod- ulators are being developed for direct analog-to-digital conversion of radio frequency signals in the GHz range. Recently we demon- strated operation of a superconducting bandpass modulator with the highest center frequency (2.23 GHz) and sampling rate (up to 45 GHz) reported to date. The test chip used in that experiment includes an integrated acquisition memory, which eliminates the need for very high speed interfacing. This paper describes key im- plementation details of this complex test chip, which contains 4065 Josephson junctions. The paper also explains how magnetic cou- pling from large power supply currents can be reduced through the use of optically-isolated current sources with independent grounds. The measured output spectra of the modulator at a 45 GHz sam- pling rate are presented.