An Adjacent Switching Activity Metric under Functional Broadside Tests

The local switching activity of scan-based tests is important due to the possibility that scan-based tests will result in excessive power dissipation in certain subcircuits even when the total power dissipation is acceptable. This paper focuses on the local switching activity during the fast functional capture cycles of functional broadside tests. This switching activity is guaranteed not to exceed the switching activity possible during functional operation. Therefore, with functional broadside tests it is possible to maximize the switching activity without causing excessive power dissipation. This is important for test quality since, in general, higher switching activity allows more delay defects to be detected. In addition, it allows smaller test sets to be obtained for delay faults. The paper defines a switching activity metric called the adjacent switching activity that captures the switching activity around the sites of detected transition faults, where additional switching activity is most likely to contribute to test quality. It compares the cases where the adjacent and the total switching activity of functional broadside tests for transition faults are maximized. The results demonstrate that the two objectives result in significantly different test sets. Moreover, better quality test sets are obtained by maximizing the adjacent switching activity.