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IEEE Transactions on Applied Superconductivity

Multi-gigahertz operation of 3-junction-interferometer-based Josephson latching logic circuits

W. Hioe, M. Hosoya, S. Kominami, Hideyuki Nagaishi, T. Nishino

Published Jun 1, 1997• 2 citations
Publisher

Abstract

Josephson latching logic gates require an ac power supply for correct operation. Owing to the difficulty in fabricating Josephson regulators for large power currents, multi-phase sinusoidal power supply is the preferred method for multi-gigahertz operation. However, the inherently variable ac power reduces device margin for covering process variations. As a result, there exists a strong relationship between circuit size, maximum operating frequency and circuit throughput for a given available margin. The trade-offs between these performance criteria are analyzed for 3-junction-interferometer-based logic gates. Experimental evaluation of the multi-gigahertz operation of small circuits showed that careful design of power supply networks that reduce power supply fluctuations will be needed to maximize performance. Simulation and experimental results are discussed.

DOI
10.1109/77.621743

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Josephson latching logic gates require an ac power supply for correct operation. Owing to the difficulty in fabricating Josephson regulators for large power currents, multi-phase sinusoidal power supply is the preferred method for multi-gigahertz operation. However, the inherently variable ac power reduces device margin for covering process variations. As a result, there exists a strong relationship between circuit size, maximum operating frequency and circuit throughput for a given available margin. The trade-offs between these performance criteria are analyzed for 3-junction-interferometer-based logic gates. Experimental evaluation of the multi-gigahertz operation of small circuits showed that careful design of power supply networks that reduce power supply fluctuations will be needed to maximize performance. Simulation and experimental results are discussed.
Josephson latching logic gates require an ac power supply for correct operation. Owing to difficulty in fabricating Josephson regulators for large power currents, multi-phase sinusoidal power supply is the preferred method for multi-gigahertz operation. However, the inherently variable ac power reduces device margin for covering process variations. As a result, there exists a strong relationship between circuit size, maximum operating frequency and circuit throughput for a given available margin. The trade-offs between these performance criteria are analyzed for 3-junction-interferometer- based logic gates. Experimental evaluation of the multi- gigahertz operation of small circuits showed that careful design of power supply networks that reduce power supply fluctuations will be needed to maximize performance. Simulation and experimental results will be discussed.
We have developed an ac power distribution scheme which provides switched regulated power of alternating polarity (no rectification necessary) for Josephson interferometer latching logic circuits. Distribution from the power source relies on a tree system of thin film transformers having single primaries and multiple secondaries to maintain low current levels and small phase skews throughout the system. Power signals are clipped on chip to the desired voltage supply level by series connected large area Josephson junctions ("regulator" junctions) and distributed across the chip by voltage busses. Supply resistors between the regulated voltage bus and the logic circuits define the operating current level. A detailed design is presented for a specific interferometer latching circuit family. We report experimental data on the two major components of the power system design - the regulators and the transformers. A series string of four regulator junctions provides a trapezoidal waveform of 11 mV amplitude at > 66% logic duty cycle (that portion of the machine cycle in which logic operations can be performed). Thin film transformers have their designed inductance (350 pH) and coupling coefficient ( > .90).
High-speed operation of Josephson processors is demonstrated. They are a 4-b microprocessor, a 4-b processor, and an 8-b digital signal processor. Key technologies to realize these circuits are described from the viewpoint of circuit design. The technologies are a high-speed logic gate, named MVTL (modified variable threshold logic), and a three-phase sinusoidal power supply system. The MVTL gate has a large operating margin and high sensitivity. The MVTL gate family consists of OR, AND, 2/3 majority (MJ), and timed inverter (TI). Using these gates a variety of processors have been designed. These processors operate with three-phase power. The waveform is sinusoidal with DC-offset. This power supply system needs no latch and regulator circuit. This makes the processor very simple, and thus results in high-speed operation. To fabricate these processors, niobium junctions are very important, because they are reliable, uniform, controllable, and reproducible. High-speed gates, three-phase power supplies, and niobium junctions are indispensable for high-speed Josephson processors.
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.