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Superconductor Science and Technology

A single flux quantum logic gate with high functionality

W. Hioe, M. Hosoya, Reiji Suda, Eiichi Goto

Published Nov 1, 1991• 0 citations
Publisher

Abstract

The D-gate is a quantum flux parametron (QFP) logic gate which was proposed to reduce input interaction and improve input margin. It is basically a 2-input multiplexer with two select signals. By giving appropriate inputs, a single gate can also perform 2-input AND, 2-input OR, 2-input XOR, 3-input majority, 3-input parity or 1-bit equality. Since it is a QFP device, it has a self-latching effect which can be exploited for pipelined designs of many combinational logic functions. However, because QFP logic is a clocked logic expected to operate at 10 GHz or more, propagation delay becomes an important issue in circuit design.

DOI
10.1088/0953-2048/4/11/028

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The D-gate is a quantum flux parametron (QFP) logic gate which was proposed to reduce input interaction and improve input margin. It is basically a 2-input multiplexer with two select signals. By giving appropriate inputs, a single gate can also perform 2-input AND, 2-input OR, 2-input XOR, 3-input majority, 3-input parity or 1-bit equality. Since it is a QFP device, it has a self-latching effect which can be exploited for pipelined designs of many combinational logic functions. However, because QFP logic is a clocked logic expected to operate at 10 GHz or more, propagation delay becomes an important issue in circuit design.
The quantum flux parametron (QFP) is a flux-transfer, flux-activated Josephson logic device which realizes much lower power dissipation than other Josephson logic devices. Being a two-terminal device, its correct operation may be affected by coupling to other QFPs. The problems include backcoupling form active QFPs through inactive QFPs (relay noise), coupling between QFPs activated at different times because of clock skew (homophase noise), and interaction between active QFPs (reaction hazard). Previous QFP circuits worked by wired-majority, which is a linear input logic and has low input margin. A logic gate (D-gate) using a QFP to perform logic operations has been analyzed and tested by computer simulation. Relay noise, homophase noise, and reaction hazard are substantially reduced. Moreover, the inputs have little interaction, and hence input margin is greatly improved. Using only D-gates it is possible to realize any combinational logic function. Important logic functions can be realized using one gate, such as a two-input multiplexer, majority, and parity. Since the QFP has a latching effect, D-gates can realize fully pipelined circuits without additional registers.
The Quantum Flux Parametron (QFP) is a Josephson Junction device using the polarity of a quantum magnetic flux to represent a binary information. A quantum unit of magnetic flux in a QFP can be controlled to realize majority logic operation, consequently AND and OR logics can be realized. Together with negation, which can be realized by a flux-inverting transformer, various computing logic devices can be constructed. In addition, the QFP is also a latching device so that a flux can be confined in the device to realize memory function. Due to the homogenous nature of memory and logic circuits as well as the flux nature of the signal which can be transmitted inductively, an entirely new Josephson supercomputer with memory and CPU pipelining arranged in a 3D setting was conceived. The computer with 40 processors is expected to run at a maximum speed of 20 GFLOPS of scalar processing.
The quantum-flux parametron (QFP) is a single-flux quantum Josephson device with a high gain of over 20 dB and a low power dissipation of 1-nW order at 10 GHz. Logic and analog circuits using the device have been fabricated and tested. The device's margin may be reduced by a number of problems due to fabrication and design variations such as imbalance of Josephson-junction critical currents, flux loss in transformer self-inductances, and transformer coupling variations. The authors review these problems and describe three auxiliary circuits-booster, puller, and regulator-for alleviating them. A booster reduces the effect of critical current variations and doubles the output. A puller increases the activation current, thus allowing smaller clock signals. A regulator ensures full activation of the QFP over a wide range of activation levels. With these currents, the device has a much improved margin against variations originating from within itself.>
A quantum flux parametron (QFP), a single quantum flux superconductive device that has a potential of up to 100-GHz switching with nW-order power dissipation, is considered. The potential of the QFP and key technologies when QFPs are applied to a Josephson supercomputer are described. Switching speed, stability, and power dissipation of a QFP are discussed. QFP gates, circuits, and systems are next described. Then, ultra-fast clock distribution using a standing wave is explained. High-speed operation at more than 10 GHz and 10/sup 14/ error-free operations per QFP have been demonstrated. Finally described is a high-density packaging scheme by three-dimensional integration, which is very important for ultra-high speed circuits because the propagation delay becomes dominant in such circuits.>
The Quantum Flux Parametron (QFP) is a SFQ-type logic device which uses a single flux quantum (SFQ) to represent 1-bit of information. QFP circuits use a multi-phase external ac power which also acts as the clock for synchronization, hence QFP circuits are highly pipelined. The clock frequency must be increased to improve the throughputs of the circuits, so the control of a high frequency clock is a key technology for the QFP. This paper describes a clock distribution technique which utilizes the characteristics of a standing wave. Using this technique, the operation of a 1-bit QFP shift register by a 4-phase clock up to 36 GHz is shown. In the 4-phase clock operation of QFPs, the input is given in phase 1, the QFP switches in phase 2, the output is held during phase 3, and the QFP resets in phase 4. Therefore, the 4-phase 36-GHz operation means that each QFP switches or resets in less than 7 ps.>
Quantum Flux Parametron (QFP) logic gates were designed and fabricated from a single layer of YBa/sub 2/Cu/sub 3/O/sub 7/ thin film based on step-edge Josephson junctions. Self-inductance (L) of the QFP loop, an important circuit parameter, as is critical current (J/sub c/) of the Josephson junction, was determined by using directly coupled dc superconducting quantum interference devices (SQUIDs). Magnetically coupled dc SQUIDs were used to detect the output signal from the QFP. Simulated waveforms were used to identify the operation modes of the QFP as a function of the circuit parameters. From examination of the output waveforms of the QFP, operation in agreement with simulations was confirmed.