High speed four-bit full adder with resistor coupled Josephson logic

A four-bit full adder circuit implemented in Resistor Coupled Josephson Logic (RCJL) has been designed and successfully tested with 173ps critical path delay, The full adder circuit uses dual rail logic with emphasis on high speed operation. Fast switching characteristics and large fan-out capabilities of the sum and carry generators have been verified by using computer-simulations. An experimental four-bit full adder circuit was fabricated using lead-alloy Josephson IC technology with a 5-µm minimum feature size and a 7-µm minimum junction diameter. The circuit consists of 80 devices with 264 junctions. The minimum critical path delay for the ripple carry adder was measured to be 173ps / 4 bits. This result demonstrates the RCJL potential for high speed digital applications.