Classification and Test Generation for Path-Delay FaultsUsing Single Struck-at Fault Tests

We classify all path-delay faults of a combinational circuit into three categories: {\it singly-testable} (ST), {\it multiply-testable} (MT), and {\it singly-testable\ dependent} (ST-dependent). The classification uses any unaltered single stuck-at fault test generation tool. Only two runs of this tool on a model network derived from the original network are performed. As a by-product of this process, we generate single and multiple input change delay tests for all testable faults. With these tests, we expect that most defective circuits are identified. All ST faults are guaranteed detection in the case of a single fault, and some may be guaranteed detection through robust and validatable non-robust tests even in the case of multiple faults. An ST-dependent fault can affect the circuit speed only if certain ST faults are present. Thus, if all ST faults are tested, the ST-dependent faults need not be tested. MT faults cannot be guaranteed detection, but affect the speed only if delay faults simultaneously exist on a set of paths, none of which is ST. Examples and results on several ISCAS ‘89 benchmarks are presented. The method of classification through test generation using a model network is complex and can be applied to circuits of moderate size. For larger circuits, alternative methods will have to be explored in the future.