Josephson look-back analog to digital converter

A Josephson analog-to-digital (A/D) converter which uses a look-back algorithm to increase accuracy was designed and experimentally verified. The look-back A/D algorithm and its implementation in a Josephson 6-b A/D converter are described. High-speed measurements verified that the 3-b look-back A/D converter functions at 534 Msamples/s. The look-back algorithm increases the margins of an A/D converter that uses the lobes of a superconducting quantum interference device´s (SQUID´s) threshold curve. The self-gating AND circuits (SGAs) give the A/D converter a short aperture time. The SGAs sample the analog signal in parallel and then the look-back logic decodes the two´s complement outputs in series with only one stage of logic per bit. With a stable process the look-back A/D converter can be generated on chip.<>