On validating data hold times for flip-flops in sequential circuits

We consider the problem of validating flip-flop data hold time requirements in sequential circuits. The data hold time violations considered are related to the presence of short paths that allow changes in next-state values to occur fast enough so as to cause latching of erroneous next-states. Three fault models are proposed that are related to the presence of short paths in the circuit. Propagation conditions for robust and non-robust tests for short paths are given. A test generation procedure is described for one of the proposed models, and experimental results are provided for benchmark circuits.