On Common-Mode Skewed-Load and Broadside Tests

Two-pattern tests for delay faults in standard scan circuits can be of one of two types: skewed-load or broadside. Each type of tests creates different conditions during test application due to the different way in which scan mode and functional mode are interleaved. Therefore, tests that are applicable both as skewed-load tests and as broadside tests are useful for comparing the two types of tests with respect to properties such as defect coverage or overtesting. In this work we investigate the possibility of generating tests that are applicable under both test application schemes. We refer to two-pattern tests that are applicable as both skewed-load and broadside tests as common-mode tests. We show that most benchmark circuits have sufficient numbers of common-mode tests to make them an interesting class of tests. Moreover, we show that the use of multiple scan chains increases the number of common-mode tests.