Avoiding Spurious Failure Indications in Testing Josephson Logic Chips
Original Publication Date: 1983-Oct-01
Included in the Prior Art Database: 2005-Feb-07
Designing Josephson logic chips for testability by directing all primary inputs to respective single input gates permits testing without the occurrence of the "double one problem" which might otherwise result in apparent failures in good chips. Testing of Josephson logic chips with DC inputs can potentially lead to the "double one problem" (Figs. 1 and 2). In this case a logic gate, such as a two-input OR receives two inputs directly from primary inputs (PIs). Since the controls are DC with respect to the AC power toggle frequency, there is a possible condition that with two ones presented to the PIs the operating point will fall below the 1,1 lobe and the gate will not switch. This leads to an error condition in testing -- the OR gate can behave like an exclusive OR.