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IEEE Transactions on Applied Superconductivity

Josephson compensating junction logic

C.J. Anderson

Published Mar 1, 1993• 0 citations
Publisher

Abstract

A Josephson superconducting quantum interference device (SQUID) digital logic family was developed that uses the R/sub nn/ region of a Josephson junction (JJ) to compensate for variations in where R/sub nn/ is the effective resistance of a JJ in the linear I-V region beyond the gap. The basic compensating junction logic (CJL) circuit is two 2-input-OR 1-2-1 interferometer isolators that, when switched, inject current into a 2-input-AND 1-2-1 interferometer. The R/sub nn/ region of several JJs is used in series with a resistor to set the current from the power supply to the 2-input-OR interferometers. The 2-input-AND interferometer is implemented with both current injection and magnetic coupling. The latch circuit uses both current injection and magnetic coupling design techniques to increase the range of I/sub O/, inductance, and resistance variation over which the latch will function correctly. Experimental measurements of CJL circuits are described.>

DOI
10.1109/77.233512

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A Josephson superconducting quantum interference device (SQUID) digital logic family was developed that uses the R/sub nn/ region of a Josephson junction (JJ) to compensate for variations in where R/sub nn/ is the effective resistance of a JJ in the linear I-V region beyond the gap. The basic compensating junction logic (CJL) circuit is two 2-input-OR 1-2-1 interferometer isolators that, when switched, inject current into a 2-input-AND 1-2-1 interferometer. The R/sub nn/ region of several JJs is used in series with a resistor to set the current from the power supply to the 2-input-OR interferometers. The 2-input-AND interferometer is implemented with both current injection and magnetic coupling. The latch circuit uses both current injection and magnetic coupling design techniques to increase the range of I/sub O/, inductance, and resistance variation over which the latch will function correctly. Experimental measurements of CJL circuits are described.>
A new current-injection Josephson latch employing a single-flux quantum is proposed. It has a master-slave circuit configuration and operates under ac power supply. In the circuit, data are stored as a circulating current in a superconducting loop consisting of a single junction and inductances. A two-junction interferometer gate directly coupled to the loop reads out the stored data. Dual-rail signals are generated from the read-out data by Josephson junctions and resister-coupled Josephson logic gates. The isolation between a master circuit and a slave circuit is realized using high-impedance states in the Josephson junctions. The circuit design and computer-simulation results on the circuit operation are described in this paper.
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A method of accurately estimating the I/sub 0/ (critical current) of a Josephson junction (JJ) with thermal noise was developed by measuring the effective thermal noise temperature of a JJ. The effective thermal noise temperature of various JJ devices was measured and calculated. The JJ devices evaluated included inductively and resistively coupled logic devices and JJ devices in the presence of various noise sources. The noise sources included room-temperature resistors, switched JJ devices, and JJ devices in the linear I-V region beyond the gap. The R/sub NN/ compensator is shown to result in a noise temperature of about 6 K at an interferometer. The addition of a shunt junction lessens the noise penalty introduced by the compensator. A switched isolation interferometer in a two-input AND gate contributes negligible noise at the injection device. It is also shown that bandwidth connections to room-temperature equipment result in very large excess noise and require special input and output circuits on the chip.>
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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. © 2005 Wiley Periodicals, Inc. Syst Comp Jpn, 36(2): 42–50, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/scj.20136