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Single Flux Quantum Memory Cell for NDRO

IP.com Disclosure Number: IPCOM000081886D
Original Publication Date: 1974-Aug-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 2 page(s) / 43K

Publishing Venue

IBM

Related People

Jutzi, WW: AUTHOR

Abstract

A three Josephson junction interferometer type memory cell stores at most a single-flux quantum. The two lowest order states are used for storage, whereby one of these states is a degenerate state. Since switching between equivalent forms of a degenerate energy state does not change the binary information value, nondestructive readout (NDRO) operation is possible.

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Single Flux Quantum Memory Cell for NDRO

A three Josephson junction interferometer type memory cell stores at most a single-flux quantum. The two lowest order states are used for storage, whereby one of these states is a degenerate state. Since switching between equivalent forms of a degenerate energy state does not change the binary information value, nondestructive readout (NDRO) operation is possible.

Binary value "0" is assigned to a state (0,0) where no flux quantum is trapped in either loop. Binary "1" is assigned to a degenerate state where a single-flux quantum is trapped. Both equivalent forms are as follows: (1,0) with center junction current down, or (0,1) with center junction current up. A constant-bias digit current I-BB shifts the operating point into a region of the control characteristic I-W (I-B') where all three states are possible stable states.

Write-in is done by application of coincident word and bit currents I-W, I-B'. Thereby the bit current sign I-BO, I-BL defines if the (0,0) or the (1,0) state is taken by the cell. Readout is effected by application of an alternating word pulse pair (interrogate and reset). A stored 0 gives no output signal because the (0,0) state remains unchanged. A stored 1 causes a (1,0)-(0,1)-(1,0) transition, giving rise to flux changes inside the interferometer. These flux changes are picked up by an inductively coupled sense line. It is arranged on top in a manner as to compensate for disturbing voltage pulses r...