Selecting Path Delay Faults Through the Largest Subcircuits of Uncovered Lines

Abstract

Tests for path delay faults are important for covering small delay defects whose cumulative effect causes a circuit to fail. The number of path delay faults, and the number of tests for them, may be large even when a path selection criterion requires the detection of a path delay fault through every line in the circuit. This article suggests a refinement of this criterion that targets a uniform coverage of the circuit using path delay faults. To address this target, the test generation procedure finds contiguous subcircuits whose lines are uncovered by path delay faults, and targets path delay faults through the largest such subcircuits. When a path delay fault is detected, the subcircuit it goes through is partitioned into smaller subcircuits. The sizes of the resulting subcircuits are evaluated in advance to select the path delay faults with the largest impact on coverage. Experimental results for benchmark circuits use a transition fault test set as a baseline, and demonstrate that a limited number of additional tests can improve the coverage of the circuit significantly based on this criterion.