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Electronics and Communications in Japan (Part I Communications)

An interferometer direct‐coupled Josephson logic gate

K. Hohkawa, Akira Ishida

Published Jan 1, 1983• 0 citations
Publisher

Abstract

Abstract New interferometer direct‐coupled Josephson logic gates are proposed which have good input‐output signal separation and stable, high‐gain, wide‐margin operation. Formulas for evaluating the threshold characteristics and conditions for high gain and high sensitivity are derived. Dynamic properties such as switching times and waveforms are obtained by computer simulation. These gates were tested‐fabricated with a lead alloy whose properties agreed with the results of computer simulation: sensitivity was 2.5 over a bias range of more than 50%. Thus, they can be used as basic logic elements in buffers and OR gates.

DOI
10.1002/ecja.4400661014

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Abstract New interferometer direct‐coupled Josephson logic gates are proposed which have good input‐output signal separation and stable, high‐gain, wide‐margin operation. Formulas for evaluating the threshold characteristics and conditions for high gain and high sensitivity are derived. Dynamic properties such as switching times and waveforms are obtained by computer simulation. These gates were tested‐fabricated with a lead alloy whose properties agreed with the results of computer simulation: sensitivity was 2.5 over a bias range of more than 50%. Thus, they can be used as basic logic elements in buffers and OR gates.
Abstract This paper proposes a Josephson threshold logic circuit, which is best suited to high‐speed operations. Using the proposed circuit, the adder can be constructed by four Josephson elements. The scale of the circuit can be reduced both in the number of circuits and the number of logic stages, compared with the conventional Josephson logic circuits. The circuit is shown to be useful in the realization of the high‐speed and highly integrated adders and multipliers. Then it is demonstrated that the Josephson threshold logic circuit can be constructed by the magnetically coupled interferometer element, the current‐injection interferometer element and the direct‐coupled element. A typical circuit construction is shown with the adder as an example. To verify the correct operation of the Josephson threshold logic circuit, a 1‐bit adder by magnetically coupled interferometer elements was constructed by Nb‐Pb alloy process, and the operation of the circuit was verified.
This paper describes the dynamic threshold characteristics of Josephson switching gates. When high speed input signals are applied to the Josephson logic gate, the threshold characteristics of the gate are not always in accord with the well-known static threshold curves. This is because the static threshold curves are affected by quantum flux change in Josephson junctions under the high speed operation. The dynamic threshold characteristics of two typical logic gates, one is the CIL gate and the other the interferometer, are described in detail.
We describe a one-bit full adder circuit constructed from direct-coupled Josephson logic elements. The basic gate, which can perform various logic functions, consists of two Josephson junctions and two resistors connected in a loop. Switching the junctions into the finite-voltage state diverts the bias current into a parallel output line, which is directly coupled through the junctions of successive logic elements. The adder is constructed with a 100 μm basic linewidth and 25 μm square tin tunnel junctions. It operates under all input data conditions with an add time of about 1 nS and a power dissipation of 1 μW per gate.