High-tolerance three-Josephson-junction curent-injection logic devices (HTCID)

A new 3-Josephson-junction interferometer is presented as a high-tolerance nonlinear current-injection 2-input AND gate. In Josephson LSI circuits, the tolerances are an important issue. Thus, in our new logic device emphasis has been placed on its static and dynamic tolerance properties. The new HTCID offers considerably better input-signal tolerances than known 2-junction current-injection devices (CID) for identical fabrication tolerance assumptions. The HTCID in this example has a Josephson current ratio of 1:3:1 and a characteristic phase λ = 0.72π. Including circuit parameter variations, this new 3-junction CID allows attractive, high input-signal tolerances of ± 33.3%. Therefore, an almost threefold tolerance improvement over the published 2-junction CID (λ = 0.66π) could be achieved. Trade-off between signal tolerances and device speed is discussed. Computer simulation indicates a worst-case delay of less than 47 ps.