Structure design and optimization of 2-D LFSR-based multisequence test generator in built-in self-test

This paper addresses the optimization of very large scale integration testing systems, specifically the structure design and optimization of a built-in self-test (BIST) design based on two-dimensional (2-D) linear feedback shift registers (LFSRs). The 2-D LFSRs can generate both precomputed test patterns (for detecting random-pattern-resistant faults) and random patterns (for detecting random-pattern-detectable faults) and have the advantages of high fault coverage and at-speed testing. To guarantee solutions, it is necessary and desirable to generate subsequences of the precomputed test patterns through the 2-D LFSRs, where these subsequences retain the order of the test patterns, particularly for testing sequential circuits. For the design and optimization of the 2-D LFSRs, the following two problems need to be solved: 1) the good partitioning of the precomputed test patterns into disjoint subsequences in order to achieve a minimal hardware and 2) the structure design and optimization of the 2-D LFSRs to generate the test patterns in each partitioned subsequence. The optimization of the 2-D LFSRs is modeled as an integer program (a logic optimization model) that determines the coefficients of the recursive Boolean equations that govern the generation of the test patterns. For a sequence of the test patterns, this model finds the minimal-hardware implementation of the 2-D LFSRs. This logic optimization model can be applied to both test-per-scan (serial BIST) and test-per-clock (parallel BIST). This paper presents how this model is embedded in a heuristic framework to partition the test patterns into subsequences from the configurable 2-D LFSRs. The testing hardware is small as the configurable architecture allows the tester to incrementally generate the precomputed test patterns by modification to the feedback of the 2-D LFSRs. Results of benchmark circuits show that significant hardware reduction and higher fault coverage are achieved. The resulting multisequence test generator is a regular structure and is easy to implement. The logic optimization model is applicable to both completely and partially specified test patterns and can be adopted for other LFSR-based structure design and optimization.