LOCST: A Built-In Self-Test Technique

A built-in self-test technique utilizing on-chip pseudorandom-pattern generation, on-chip signature analysis, a ``boundary scan'' feature, and an on-chip monitor test controller has been implemented on three VLSI chips by the IBM Federal Systems Division. This method (designated LSSD on-chip self-test, or LOCST) uses existing level-sensitive scan design strings to serially scan random test patterns to the chip's combinational logic and to collect test results. On-chip pseudorandom-pattern generation and signature analysis compression are provided via existing latches, which are configured into linear-feedback shift registers during the self-test operation. The LOCST technique is controlled through the on-chip monitor, IBM FSD's standard VLSI test interface/controller. Boundary scan latches are provided on all primary inputs and primary outputs to maximize self-test effectiveness and to facilitate chip I/O testing. Stuck-fault simulation using statistical fault analysis was used to evaluate test coverage effectiveness. Total test coverage values of 81.5, 85.3, and 88.6 percent were achieved for the three chips with less than 5000 random-pattern sequences. Outstanding test coverage (≫97%) was achieved for the interior logic of the chips. The advantages of this technique, namely very low hardware overhead cost (≪2%), design-independent implementation, and effective static testing, make LOCST an attractive and powerful technique.