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Star Driver for Josephson Circuits

IP.com Disclosure Number: IPCOM000052656D
Original Publication Date: 1981-Jun-01
Included in the Prior Art Database: 2005-Feb-11
Document File: 2 page(s) / 34K

Publishing Venue

IBM

Related People

Kaplan, SB: AUTHOR [+2]

Abstract

Star drivers are often used in Josephson circuits to provide parallel fan-out to a plurality of logic circuits. Fig. 1 shows a Direct-Coupled Logic Star driver whose operation does not depend upon a LI(0) product and is therefore easier to scale to small linewidths. Stages D(1) and D(2) provide isolation and gain, and utilize Josephson tunneling devices J(1), J(2), J(3) and J(4). Stage D(3) is an amplifier which operates similarly to stage D(2). It includes Josephson tunnel devices J(5) and J(6). Gate currents I(G1), I(G2), and I(G3) are provided to D(1), D(2) and D(3), respectively. A parallel fan-out of four is provided to load resistors R(L1), R(L2), R(L3), and R(L4).

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Star Driver for Josephson Circuits

Star drivers are often used in Josephson circuits to provide parallel fan-out to a plurality of logic circuits. Fig. 1 shows a Direct-Coupled Logic Star driver whose operation does not depend upon a LI(0) product and is therefore easier to scale to small linewidths. Stages D(1) and D(2) provide isolation and gain, and utilize Josephson tunneling devices J(1), J(2), J(3) and J(4). Stage D(3) is an amplifier which operates similarly to stage D(2). It includes Josephson tunnel devices J(5) and J(6). Gate currents I(G1), I(G2), and I(G3) are provided to D(1), D(2) and D(3), respectively. A parallel fan-out of four is provided to load resistors R(L1), R(L2), R(L3), and R(L4).

In one design, the Josephson devices are biased at a nominal value of 0.7 times their respective critical currents. When input A is provided to D(1), that stage switches, thus diverting its gate current to stage D(2). This causes switching of D(2) which further delivers the combinatio of I(G1) and I(G2) to D(3). When D(3) switches, a large fraction of I(G1), I(G2), and I(G3) is delivered to the outputs R(L1)-R(L4).

A small leakage current can occur before switching and for this reason, an additional Josephson junction J(LK) is added as a shunt element, as shown in Fig. 2. The "Star" circuit box 10 represents the combination of D(1), D(2), and D(3) of Fig. 1.

An advantage in meeting circuit design tolerances is obtained by making junctions J(2) and J(6) as multip...