Impact of Hazards on Pattern Selection for Small Delay Defects

Hazards ubiquitously exist in combinational circuits, and then should be taken into account for delay testing. This paper analyzes the impact of hazards on small-delay defect (SDD) detection, and presents a new test pattern selection method considering hazards. The concept of arrival time window is introduced and the concept of output deviation is redefined to accurately reflect the pattern capability on SDD detection. A new signal transition probability calculation method is presented to calculate output deviation more practical than that without considering hazards. Patterns from an N-detect test set for transition faults are then selected according to their output deviations. Experimental results show that, for the same pattern count, the patterns selected by the proposed method excite more long paths, and are capable of detecting more small delay defects at the early stage of delay testing compared to the method without considering hazards.