A high-speed four-bit full adder with a resistor coupled Josephson logic

A four-bit full adder circuit implemented in resistor coupled Josephson logic (RCJL) has been designed and successfully tested with 173-ps critical path delay. The full adder circuit uses dual rail logic with emphasis on high-speed operation. An experimental four-bit 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 173 ps/4 bits. This result demonstrates the RCJL potential for high-speed digital applications.