Multipattern Scan-Based Test Sets With Small Numbers of Primary Input Sequences

When a multipattern scan-based test is applied at-speed to detect delay defects, it is necessary to change the primary input vectors at-speed. However, tester limitations can make this infeasible. The solution where the primary input vectors are held constant during the test reduces the fault coverage. An alternative solution is to store the primary input sequences of a multipattern test set on-chip and apply them at-speed from an on-chip memory. To support such a solution, this paper describes a procedure for computing a multipattern test set that requires a small number of different primary input sequences. Experimental results for single stuck-at faults and for transition faults show that a multipattern test set that detects all the detectable faults requires a number of primary input sequences that is significantly smaller than the number of tests.