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IEEE Transactions on Magnetics

A Josephson associative memory circuit

Michitada Morisue, H. Shimizu, H. Fukuzawa

Published Mar 1, 1987• 0 citations
Publisher

Abstract

This paper proposes a novel associative memory circuit using Josephson interferometers. This associative memory circuit is mainly constructed with the nondestructive memory cell in which a self-rewriting operation can be achieved by setting a coil between the terminals of the interferometer. The principle of the associative memory circuit is described and the results of simulation for the operation are illustrated. The results show that the cycle time of operation is less than 75ps and the design tolerance of input signals for the memory circuit is about 8%.

DOI
10.1109/tmag.1987.1064920

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This paper proposes a novel associative memory circuit using Josephson interferometers. This associative memory circuit is mainly constructed with the nondestructive memory cell in which a self-rewriting operation can be achieved by setting a coil between the terminals of the interferometer. The principle of the associative memory circuit is described and the results of simulation for the operation are illustrated. The results show that the cycle time of operation is less than 75ps and the design tolerance of input signals for the memory circuit is about 8%.
This paper presents a novel nondestructive memory cell using a two-junction interferometer. Most of single-flux-quantum memory cells have been the destructive ones, which must rewrite the information for logic "1" after a reading operation. This makes the circuitry of the cell complex. To avoid this disadvantage, a novel self-rewriting technique is introduced by setting a coil between the terminals of the interferometer. The principle of the operation of the cell is described and the simulation for the behaviours of the cell are illustrated in detail. The results of the simulation show that the reliable operation of the cell can be achieved with high operating speed.
An improved single flux-quantum Josephson interferometer memory cell which brought stable nondestructive read-out (NDRO) operation was proposed. The cell was constructed with an end-fed asymmetric two-junction interferometer, in which the bit operating current level could be set far above the critical point for stable NDRO operation. Damping condition for proper memory operation was studied by computer simulation. The NDRO operation was experimentally obtained for the McCumber damping parameter βc of 300–400.
Abstract In this paper, experimental verification for a cryogenic memory cell consisting of three inductively coupled Josephson junctions is presented. Design and operational logic of this type of cell was recently introduced. The basic memory cell operations (read, write, reset) can be implemented on the same simple circuit and this type of memory cell is fundamentally different from the existing single flux quantum-based memory cells. Here, we present design principles and experimental validation for write operations and readout operation for four versions of the design, each with different parameters. Our experimental results show excellent resemblance with the previously presented memory cell operational logic and also show an excellent fit with simulations of the entire memory cell circuit that includes the memory cell and all the peripheral circuitry.
Josephson-junction interferometers have previously been proposed as memory devices in which information is stored as a single flux quantum, (SFQ). To investigate the feasibility of making large arrays of SFQ cells suitable for the memory of a cryogenic computer, arrays containing 80 interferometers have been made and measured. The prime objective was to determine the distribution of the dc Josephson current i1 within the arays and to compare it with the design value required for successful operation of all cells in high density arrays. The results show that a substantial fraction of the arrays has standard deviations in i1 less than the maximum allowable, thus demonstrating for the first time that such a memory can be made with present technology. The fabrication, measurement technique and a detailed analysis of the current distributions on the arrays are presented.
A proposal vortex transitional nondestructive read-out Josephson memory cell is successfully fabricated and tested. The memory cell consists of two superconducting loops in which a single flux quantum is stored and a two-junction interferometer gate as a sense gate. The memory cell employs vortex transitions in the superconducting loops for writing and reading data. The vortex transitional memory operation of the cell contributes to improving its sense discrimination and operating margin. The memory cell is activated by two control signals without timing control signals. Memory cell chips have been fabricated using a niobium planarization process. A±21% address signal current margin and a ±33% sense gate current margin have been obtained experimentally. Successful memory operations of a cell driven by two-junction interferometer gates has been demonstrated. The single flux quantum operations of this memory cell makes it an attractive basic element for a high-speed cache memory.