On using signature registers as pseudorandom pattern generators in built-in self-testing

Signature registers are commonly used to collect test responses in built-in self-testing (BIST). If the contents of signature registers can be used as test patterns, the overall testing time can be reduced due to improved testing parallelism. Moreover, the number of extra registers for implementing BIST could be reduced. Here, the characteristics of the patterns generated by signature registers are studied through analyses as well as experiments. It is shown that the patterns generated by signature registers are rarely repeated when the number of test patterns is relatively small compared to the number of possible patterns. It is also shown that the patterns generated are almost uniformly distributed. Therefore, signature registers can be used effectively as pseudorandom pattern generators. The practicality of using signature registers as pseudorandom pattern generators is investigated by fault simulation experiments using an example circuit