IEEE Computer Volume 12 Number 7 -- NEW APPLICATIONS & RECENT RESEARCH
Original Publication Date: 1979-Jul-01
Included in the Prior Art Database: 2005-Nov-11
Software Patent Institute
Prof. Demetrios Michalopoulos: AUTHOR [+3]
NEW APPLICATIONS & RECENT RESEARCH * Experimental Josephson circuits approach the speed of- light barrier
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NEW APPLICATIONS & RECENT RESEARCH
Prof. Demetrios Michalopoulos
California State University, Fullerton
Experimental Josephson circuits approach the speed of- light barrier
A new family of experimental computer circuits which operate so rapidly that they approach limits imposed by the speed of light has been developed by the Research Division of IBM.
The Josephson-technology circuits operate in as little as 13 picoseconds. Actual switching time is as little as 7 picoseconds, with 6 picoseconds required for the electrical signal to move from one circuit to the next. Electrical signals travel about .003 inch per picosecond in these circuits, corresponding to the speed of light in the materials used, a sandwich of metal alloys and insulators.
According to IBM, 13 picoseconds is the fastest measurement for an OR circuit; AND circuits switch in as little as 26 picoseconds. In both cases, the new circuits are
about three times faster than previous Josephson circuits (see Computer, May 1978, pp. 102- 103) and 10 or more times faster than the fastest transistor logic circuits. Equally important, IBM states, they generate thousands of times less heat than high-speed transistor circuits, so they can be fabricated in dense arrays to minimize the delay in sending signals from circuit to circuit.
The new circuits, called "current injection logic," differ from earlier Josephson circuits in that they use direct injection of current as well as magnetic fields to switch Josephson junctions. At the heart of the circuits is an "injection gate" consisting of two Josephson junctions connected by a superconducting inductance. The injection gate directly performs an AND operation on the two currents injected into it. (See drawing for equivalent circuit and operating characteristic.)
In addition to high speed, this design permits operation over a larger range of input currents than is characteristic of other Josephson circuits, and produces an output signal that is about twice as large. These features permit a larger number of input and output lines than is available in earlier circuits.
Tusher Gheewala, a scientist at IBM's T. J. Watson Research Center, has designed OR and AND circuits in which the number of inputs ranges from two to eight, and the numbe...