Design for primitive delay fault testability

To guarantee the temporal correctness of a digital circuit a set of multiple path delay faults called primitive faults need to be tested. Primitive faults can contain one or more faulty paths. Existing techniques can identify and test primitive faults containing up to two or three paths. Identifying and testing primitive faults that consist of a larger number of paths is impractical for large designs. We propose a design for testability method that assures the temporal correctness of the circuit without the need to test all primitive faults in the circuit. In the test mode, only primitive faults that contain up to two paths can affect the circuit performance. Our methodology efficiently identifies a small set of potential locations for inserting control points to eliminate primitive faults with more than two paths. Addition of a single control point can lower the cardinality of several primitive faults. Our approach re-evaluates primitive delay fault testability of the circuit after insertion of every control point. After a few iterations only primitive faults with at most two paths can exist in the circuit in the test mode. Experimental results on several circuits are included to demonstrate our method.