Josephson 4-bit digital counter circuit made by Nb/Al-oxide/Nb junctions

Abstract

A new Josephson 4-bit digital counter circuit has been demonstrated. Direct-coupled data-latch units which consists of a four-junction logic(4JL) gate family are utilized to make a flip-flop circuit for counting. The counter is designed to be driven by a two-phase mono-polar power supply. The counter circuit has been fabricated using 3μm-Nb/Al-oxide/Nb junction process. The counter has three operating modes of counting, data-loading and clearing which can be adapted to Josephson digital logic system. Experimental tests have been carried out successfully for these operating modes. Computer simulations indicate that the 4-bit counter operates in 315ps.