DESIGN AND OPERATION OF JOSEPHSON CIRCUITS USING HUFFLE GATES WITH A STACKED STRUCTURE

DC-powered Josephson logic gates have the advantage of being free from operation error due to crosstalk from power current in contrast to or dinary ac-powered Josephson logic gates. One of these, the HUFFLE (hyb rid unlatching flip-flop logic element) gate using stacked Josephson i nterferometers (JI) can execute complicated logic functions by itself. Therefore, high-speed operation of logic circuits using HUFFLE gates may be expected because the number of logic stages in the circuits is reduced. To investigate the improvement in circuit performance by usin g HUFFLE gates with the stacked structure, the authors have fabricated a 6-bit arithmetic logic unit (ALU) and tested its operation. Two new logic gates, exclusive OR and majority, newly developed using the sta cked structure have been developed. The ALU which performs the four fu nctions, AND, OR, exclusive OR, and ADD, is realized with seven logic stages. Accordingly, reduction in the number of logic stages and execu tion time of the ALU by use of the stacked HUFFLE gate family is confi rmed.