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Use of Superconducting Loops for Josephson Device Fan In

IP.com Disclosure Number: IPCOM000081882D
Original Publication Date: 1974-Aug-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 2 page(s) / 38K

Publishing Venue

IBM

Related People

Terlep, KD: AUTHOR

Abstract

Fan-in for Josephson gates is kept low, partially because of the physical problem of providing the control lines above the gate to be controlled. As an example, an in-line gate with a fan-in of three requires a device of width about 6X, where X is the minimum allowed line dimension. Furthermore, device Im(0) threshold current level is directly proportional to device width and thus to device fan-in.

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Use of Superconducting Loops for Josephson Device Fan In

Fan-in for Josephson gates is kept low, partially because of the physical problem of providing the control lines above the gate to be controlled. As an example, an in-line gate with a fan-in of three requires a device of width about 6X, where X is the minimum allowed line dimension. Furthermore, device Im(0) threshold current level is directly proportional to device width and thus to device fan-in.

The figure demonstrates the use of a superconducting loop 10 uhich may be physically isolated from all other circuits. The control lines are designated as A, B, and C. Summing of control currents Io is due to DC transformer characteristics (to ensure zero net flux change) for coupling from control lines A, B, and C to the intermediate, summing loop 10. A portion of the loop 10 routes the total, induced control current I1 to the Josephson device 12 to be controlled. Use of a single control line 10 permits control of a device, with width and current threshold about four times less than the initial example requiring a 6X wide device.

The current coupled from each control line A, B, and C (containing current I) is related to the ratio of inductances of the control line segment passing across the summing loop 10 and the total inductance, L(S), of the summing loop 10:

(Image Omitted)

The above equation shows the desirability of maximizing the inductance ratio, Y, to develop efficient coupling. DC or clocked currents ma...