Design and fabrication of an adder circuit in the extended phase-mode logic

We present the design and the fabrication of an adder circuit in the extended phase-mode logic family. The phase-mode logic is a single flux quantum (SFQ) logic which utilizes an SFQ as an information bit carrier. The single-bit adder circuit is made up of an INHIBIT gate which is the basic device of the phase-mode logic. The circuit has been designed and fabricated using Nb/AlO/sub x//Nb Josephson junctions with Josephson critical current density of 1.0 kA/cm/sup 2/. In order to confirm the circuit operation, the fabricated adder circuit has been tested at low speed. For investigating the possibility of a high-frequency operation, dc voltages generated by fluxon pulse trains have been measured. From the Josephson voltage-frequency relation, the result shows that the circuit has potential to complete the carry operation within 20 psec.