Direct coupled nonlinear injection josephson logic circuits

Abstract

Direct coupled, nonlinear injection logic circuits having high gain, good isolation between input and output, the capability of parallel fan-in and fan-out, and which do not require a large area. These circuits are comprised of a first stage that isolates the input from the output and other stages which can be used for additional gain, or for building logic circits, such as AND, and DOT-OR. The first stage isolation is a parallel network comprised of two circuits, each circuit of which includes a series connection of resistor-Josephson tunnelling device. A gate current I.sub.g flows through each Josephson device when the devices are in their zero voltage states. An input current I.sub.c is injected into one of the parallel circuits while an output is taken from the other parallel circuit. When an input current is injected, one of the Josephson devices is switched to the nonzero voltage state, which then causes a greater amount of gate current I.sub.g to be switched to the other Josephson device, thereby also switching it to the nonzero voltage state. The gate current is then delivered to a load, or used as an input to other stages of a logic circuit. Complete isolation between input and output is achieved by the two Josephson devices in their nonzero voltage states.