METHODS FOR ANALYZING SCAN CHAINS, AND FOR DETERMINING NUMBERS OR LOCATIONS OF HOLD TIME FAULTS IN SCAN CHAINS

摘要

An environmental variable of a scan chain is set to a value believed to cause a hold timefault, and a pattern is shifted through the scan chain. The pattern has a background patternof at least n contiguous bits of a first logic state, followed by at least one bitof a second logic state, where n is the scan chain's length. The number ofpossible hold time faults in the scan chain is determined as a difference between i)a clock cycle when the at least one bit is expected to cause a transition at the scanchain's output, and ii) a clock cycle when the at least one bit actually causesa transition at the scan chain's output. If there is a value of the environmentalvariable at which the scan chain operates correctly, the location(s) of holdtime faults can be determined.