Superconductive logic circuits constructed by the use of two thresholds of SQUID

This paper proposes a method for constructing superconductive logic circuits by actively using two thresholds in a superconducting quantum interference device (SQUID). First, it is demonstrated that the input-output characteristics of a SQUID with multiple inputs can be represented as a two-threshold logic function. Next, a SQUID structure is shown in which all of the input currents have the same significance and the threshold current can be varied without varying the characteristics of the Josephson junction. Each input is weighted by adjusting the internal impedance rather than the input current, and the SQUID thresholds are varied using the value of the steady current applied to an additional input. Finally, it is explained that when logic functions of two to four variables are realized using such SQUIDs, the number of logic functions that can be realized with a single SQUID is much greater than when an existing method is used, and the operating regions are reduced only slightly.