LFSR-Based Test Generation for Path Delay Faults

Abstract

Two challenges are combined when compressed tests are computed for path delay faults: 1) path delay faults that are important to detect are associated with long paths, and many of these faults are undetectable and 2) it may not be possible to compress a given test for a path delay fault. This paper addresses these challenges in the context of test data compression methods that are based on a linear-feedback shift-register (LFSR). The basic approach that this paper uses modifies initially random seeds for the LFSR into seeds that produce tests for detecting target faults. This approach can find seeds even if the available tests cannot be compressed into seeds. In addition, the procedure described in this paper also selects detectable path delay faults to address the presence of undetectable path delay faults in the set of target faults. For this purpose it uses a metric that measures the similarity between target and detected path delay faults, and attempts to compute seeds that increase the values of this metric. Experimental results are presented to demonstrate the ability of the procedure to detect path delay faults in benchmark circuits.