MULTILAYER HTS SFQ ANALOG-TO-DIGITAL CONVERTERS

We have fabricated and measured high T-c superconductor single flux qu antum 1-bit flux-counting analog-to-digital converters (ADCs). The ADC s were made with a multilayer all-epitaxial process which incorporates 10 edge SNS (superconductor-normal-superconductor) or step-edge grain boundary (SEGB) Josephson junctions with a YBa2Cu3O7-delta groundplan e. The ADC consists of a quantizer connected to a Toggle flip-flop thr ough a buffer-like stage. Direct readout of the flux state of the T fl ip-flop was made with a Read SQUID inductively coupled through a hole in the groundplane. The circuits were operated at 65 K and low speeds. The SNS circuits outperformed the SEGB circuits because of their high er readout voltage and tighter critical current spreads.