Seed Selection Procedure for LFSR-Based Random Pattern Generators

Kenichi ICHINO  Ko-ichi WATANABE  Masayuki ARAI  Satoshi FUKUMOTO  Kazuhiko IWASAKI  

IEICE TRANSACTIONS on Fundamentals of Electronics, Communications and Computer Sciences   Vol.E86-A   No.12   pp.3063-3071
Publication Date: 2003/12/01
Online ISSN: 
Print ISSN: 0916-8508
Type of Manuscript: Special Section PAPER (Special Section on VLSI Design and CAD Algorithms)
Category: Timing Verification and Test Generation
BIST,  LFSR,  test-per-clock,  test-per-scan,  seed,  polynomial,  

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We propose a technique of selecting seeds for the LFSR-based test pattern generators that are used in VLSI BISTs. By setting the computed seed as an initial value, target fault coverage, for example 100%, can be accomplished with minimum test length. We can also maximize fault coverage for a given test length. Our method can be used for both test-per-clock and test-per-scan BISTs. The procedure is based on vector representations over GF(2m), where m is the number of LFSR stages. The results indicate that test lengths derived through selected seeds are about sixty percent shorter than those derived by simple seeds, i.e. 0001, for a given fault coverage. We also show that seeds obtained through this technique accomplish higher fault coverage than the conventional selection procedure. In terms of the c7552 benchmark, taking a test-per-scan architecture with a 20-bit LFSR as an example, the number of undetected faults can be decreased from 304 to 227 for 10,000 LFSR patterns using our proposed technique.