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Nonlatching Josephson Junction Logic Device

IP.com Disclosure Number: IPCOM000082057D
Original Publication Date: 1974-Sep-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 3 page(s) / 39K

Publishing Venue

IBM

Related People

Schlig, EE: AUTHOR [+2]

Abstract

The inherent hysteresis of the voltage state of Josephson junctions requires that a Josephson junction logic circuit must be reset into the zero-voltage state, after each function of a logic block. To perform this necessary operation, it has been proposed to reduce the current in the power supply lines or to connect elements in parallel with each gate, so that the system self-resets after a pulse is sent into the logic lines.

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Nonlatching Josephson Junction Logic Device

The inherent hysteresis of the voltage state of Josephson junctions requires that a Josephson junction logic circuit must be reset into the zero-voltage state, after each function of a logic block. To perform this necessary operation, it has been proposed to reduce the current in the power supply lines or to connect elements in parallel with each gate, so that the system self-resets after a pulse is sent into the logic lines.

All known solutions have serious drawbacks. The power clocking scheme is slow, unless only a few gates are connected in series with each power line. In reducing the number of gates per power line, however, the amount of current required for a large-scale circuit becomes prohibitively large. Self-resetting schemes have the disadvantage that the resetting time is fixed, thereby imposing timing restrictions on the control pulses, or if more than one junction is used per gate, that one junction is continuously dissipating energy.

Ideally, it would be desirable to use a circuit which develops a voltage (sending current into the logic line) as long as the control field, which results from a linear superposition of the control currents exceeds a given threshold. As soon as the control field decreases below this threshold the voltage would vanish. There is an important additional requirement, which is that the output voltage be well defined and essentially unaffected by variations of the circuit parameters.

Shown is how such a circuit can be built with Josephson junctions. It is known that if a Josephson junction has a sufficiently low-parallel resistance R, the voltage hysteresis vanishes when CR/2/I(m) </- phi(0)/2 pi. (1) Here C is the junction capacitance, I(m) the maximum Josephson current and phi(0) the magnetic flux quant...