Enhanced Test Compaction for Multicycle Broadside Tests by Using State Complementation

Multicycle tests support test compaction by allowing each test to detect more target faults. The ability of multicycle broadside tests to provide test compaction depends on the ability of primary input sequences to take the circuit between pairs of states that are useful for detecting target faults. This ability can be enhanced by adding design-for-testability (DFT) logic that allows states to be complemented. This article describes a test compaction procedure that uses such DFT logic to form a compact multicycle broadside test set for transition faults where the tests use constant primary input vectors. The use of complemented states also allows the procedure to increase the transition fault coverage beyond the transition fault coverage of a broadside test set. The procedure has the option of increasing the switching activity of the tests gradually in order to explore the tradeoff between the number of tests, the fault coverage, and the switching activity.