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Analog to Digital Converter in Josephson Tunneling Technology Utilizing Flux Quantization

IP.com Disclosure Number: IPCOM000083802D
Original Publication Date: 1975-Jul-01
Included in the Prior Art Database: 2005-Mar-01
Document File: 3 page(s) / 38K

Publishing Venue

IBM

Related People

Anacker, W: AUTHOR

Abstract

An analog-to-digital converter comprising a Josephson tunneling gate G and a superconducting loop L, and utilizing the fact that magnetic flux is admitted and released from loop L only in amounts of flux quanta Phi(o) = 2 . 10/-15/ Vsec, is described.

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Analog to Digital Converter in Josephson Tunneling Technology Utilizing Flux Quantization

An analog-to-digital converter comprising a Josephson tunneling gate G and a superconducting loop L, and utilizing the fact that magnetic flux is admitted and released from loop L only in amounts of flux quanta Phi(o) = 2 . 10/-15/ Vsec, is described.

A schematic of the circuit is shown in Fig. 1. On the left is the Josephson tunneling gate G with a bias control line C. A superconducting branch B is connected across the gate G. The inductance of the branch is designated by L(B); the inductance of the gate branch by L(g).

The analog (current) signal I(A) is fed into the input node IN.

The Josephson threshold current I(max) of the gate G is set by design and bias control C to equal I(max) = I(N)/N, where I(N) denotes the total analog signal magnitude and N indicates the desired resolution of the converter. An inductance ratio L(g)/L(B) approx.
0.02 is desirable. A total ring inductance (L(g)+ L(B)) approx. Phi(o)/I(max) is required.

Operation of the circuit is as indicated in Fig. 2 for a triangular analog signal. Clearly, when the analog signal rises, most of the current (98%) will flow through gate G until the current threshold I(max) is reached. Then the gate G will switch to the voltage state, forcing the total actual analog current to flow through branch
B. The gate will automatically switch back at near zero gate current and a single- flux quantum is trapped in the loop.

Upon further rise of the analog signal, current through the gate will again increase until the gate switches when I(g) = I(max) for a second time, causing a second flux quantum to be admitted to the loop and a current of about 2I(max) to flow through branch B. The procedure repeats itself as long as the analog signal is rising (in general, at unequal time intervals).

When the analog signal starts to fall, the trapped flux forces a current to flow through gate G in the opposite direction un...