Functional fault models for non-scan sequential circuits

The paper presents two functional fault models that are applied for functional delay test generation for non-scan synchronous sequential circuits: the pin pair state (PPS) fault model and the pin pair full state (PPFS) fault model. The PPS fault model deals with the pairs of stuck-at faults on the primary inputs and the primary outputs, as well as, with the pairs of stuck-at faults on the previous state bits and the primary outputs. The PPFS fault model encompasses the PPS model, and additionally deals with the pairs of stuck-at faults on the primary inputs and the next state bits, as well as, with the pairs of stuck-at faults on the previous state bits and the next state bits. The main factor in assessing the quality of obtained test sequences was the transition fault coverage at the gate level of the selected according to the appropriate fault model test sequences from the generated randomly ones. The experimental results demonstrate that the implementation using presented functional fault models allow selecting the test sequences from the initial test set without the loss of transition fault coverage in many cases, and the number of the selected test sequences is much lesser than that of the initial test set. This result demonstrates that the functional delay test can be generated using the presented functional delay fault models before structural synthesis of the circuit.