Partial scan by use of empirical testability

The objective of the partial scan method proposed is to obtain maximum fault coverage for the number of scan elements selected. Empirical testability difference (ETD), a measure of the potential improvement in the overall testability of the circuit, is used to successively select storage elements for scan. ETD is calculated by using testability measures based on empirical evaluation of the circuit with the actual test sequence generator. In addition, ETD focuses on the hard-to-detect faults rather than all faults once such faults are known. The method has been extensively tested with ten of the sequential circuits given by F. Brglez et al. (1989) using the FASTEST provided by T. Kelsey and K. Saluja (1989). The results of these tests indicate that ETD yields on average either 27% of the number of uncovered faults for the same number of scan elements or 21% fewer scan elements for the same fault coverage compared to the other methods studied.<>