JOSEPHSON COUNTING ANALOG-TO-DIGITAL CONVERTER

A superconductive analog-to-digital converter which uses a dc SQUID as a quantizer and a flip-flop counter as a digitizer has been designed, fabricated, and tested. The circuit was fabricated using a ten-level niobium process. Tests at 4.2K demonstrated (1) counting to the full twelve-bit accuracy of the design, (2) monotonic A/D conversion with linearity to less than 1 LSB over the more than nine-bit range of conversion, (3) read-on-the-fly operation with counter overflow, and (4) counter operation with a gate current bus.