Automatic test pattern generation: Difference between revisions

Revision as of 17:45, 14 August 2016

Revision as of 17:59, 14 August 2016

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== Sequential ATPG ==

Sequential-circuit ATPG searches for a sequence of [[Test vector|test vectors]] to detect a particular fault through the [[State space|space of all possible test vector sequences]]. Various search strategies and heuristics have been devised to find a shorter sequence, and/or to find a sequence faster. However, according to reported results, no single strategy/ or heuristic out-performs others for all applications/ or circuits. This observation implies that a test generator should include a comprehensive set of heuristics.

Even a simple stuck-at fault requires a sequence of vectors for detection in a sequential circuit. Also, due to the presence of memory elements, the [[controllability]] and [[observability]] of the internal signals in a [[sequential circuit]] are in general much more difficult than those in a [[combinational logic]] circuit. These factors make the complexity of sequential ATPG much higher than that of combinational ATPG, where a scan-chain (i.e. switchable, for-test-only signal chain) is added to allow simple access to the individual nodes.

Due to the high complexity of the sequential ATPG, it remains a challenging task for large, highly sequential circuits that do not incorporate any [[Design For Test]]ability (DFT) scheme. However, these test generators, combined with low-overhead DFT techniques such as [[partial scan]], have shown a certain degree of success in testing large designs. For designs that are sensitive to area and/or performance overhead, the solution of using sequential-circuit ATPG and partial scan offers an attractive alternative to the popular full-scan solution, which is based on combinational-circuit ATPG.

== ATPG and nanometer technologies ==