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Changing the Position of Critical Points for Improving the Margins of the SFQ Cell

IP.com Disclosure Number: IPCOM000088967D
Original Publication Date: 1977-Aug-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 2 page(s) / 30K

Publishing Venue

IBM

Related People

Gueret, P: AUTHOR

Abstract

In a Josephson junction memory cell of the interferometer type, the position of the critical points is essential for the margins of the single flux quantum cell. In the conventional underdamped cell the critical point regions for a given value of Lambda are largely independent of the cell parameters if the cell is symmetrical. The position of the critical points can be changed by making the junctions of different sizes. However, this is undesirable for it influences the static characteristic and is, therefore, of no use for widening margins. In the arrangement depicted schematically in Fig. 1, critical points can be moved in a direction favorable for the margins without affecting the characteristic of the cell. One of the junctions in the known SFQ cell is shunted by resistor R(A).

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Changing the Position of Critical Points for Improving the Margins of the SFQ Cell

In a Josephson junction memory cell of the interferometer type, the position of the critical points is essential for the margins of the single flux quantum cell. In the conventional underdamped cell the critical point regions for a given value of Lambda are largely independent of the cell parameters if the cell is symmetrical. The position of the critical points can be changed by making the junctions of different sizes. However, this is undesirable for it influences the static characteristic and is, therefore, of no use for widening margins. In the arrangement depicted schematically in Fig. 1, critical points can be moved in a direction favorable for the margins without affecting the characteristic of the cell. One of the junctions in the known SFQ cell is shunted by resistor R(A). Obviously, this resistor does not affect the static characteristic.

Without R(A) the critical points A, B, C on the mode boundaries are all about at the same level I(g) crit/I(0) = 0.5 for Lambda Approximately = Pi. Fig. 2 indicates the critical points together with the drive scheme.

With R(A) applied, however, both B and C are higher than A. B and C move up rapidly with decreasing R(A), whereas A moves up only slowly' With a drive scheme as indicated in Fig. 3, the asymmetric dynamic properties of the cell are employed optimally. The available regions for writing are now larger than those indicated in F...