Method for identifying untestable faults in logic circuits

摘要

A method of identifying untestable faults in a logic circuit. A lead in the circuit is selected and the circuit is analyzed to determine which faults would be untestable if the selected circuit lead were unable to assume a logic 0 and which faults would be untestable if the selected circuit lead were unable to assume a logic 1. Faults that would be untestable in both (hypothetical) cases are identified as untestable faults. Faults which would be untestable if the selected lead were unable to assume a given value may be determined based on an implication procedure. Untestable faults may be identified in a sequential circuit by generating an equivalent combinational iterative array circuit model for a fixed number of time frames. Faults that would be untestable in both (hypothetical) cases and which are located in the last (i.e., latest-in-time) time frame are identified as untestable faults. <IMAGE>