Browse Prior Art Database

Serial, Flux Redistribution D/A and A/D Converters

IP.com Disclosure Number: IPCOM000089403D
Original Publication Date: 1977-Oct-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 3 page(s) / 55K

Publishing Venue

IBM

Related People

Gheewala, TR: AUTHOR

Abstract

A high speed digital-to-analog (D/A) converter, which uses only two inductors and three switches, is described. This D/A also forms an important part of a compact analog-to-digital (A/D) converter.

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Serial, Flux Redistribution D/A and A/D Converters

A high speed digital-to-analog (D/A) converter, which uses only two inductors and three switches, is described. This D/A also forms an important part of a compact analog-to-digital (A/D) converter.

Fig. 1 is a schematic diagram of a serial D/A converter (DAC) circuit which uses Josephson logic devices. The DAC is based upon the flux redistribution principle which states that for series connected inductors (L(1),L(2),...L(n)), final flux = initial flux or I(final) = L(1)I(1)(0) + L(2)I(2)(0) + ...L(n)I(n)(0) over L(1) + L(2) + ...L(n) = total flux over total inductance

Referring to Fig. 1, the current through both inductors L1,L2 is initially set to zero by turning off Josephson devices S(2) and S(2). Next, when C1 = 1, switch S(1) is turned off if the digital input data (b(1)) is `1', and switch S(2) is turned off if b(1) = 0.

Thus the current through inductor L(1) is given by IL(1) = b(1) . I(REF). Next, when C1 = 0, S(3) is turned OFF. From the principle of flux redistribution, the output current IL(2) is given by
IL(2)(1) = b(1) . I(REF). The same sequence is repeated for the second clock cycle with input data b(2). This time the output current is given by
IL(2)(2) = 1 over 2 (b(2).I(REF) + b(1).I(REF) over 2) = (b(1) over 4 + b(2) over 2) I(REF). Thus, after n bits of data, the output current is
IL(2)(n) = (b(n) over 2 + b(n - 1) over 4 + ... b(1) 2/n/) . I(REF)

(Image Omitted)

which is the analog equivalent of the digital input {b(n), b(n - 1) ... b(1)}, where b(n) is the most significant bit.

Fig. 2 shows an example of a 3-bit serial D/A conversion using the above...