Calculation of LFSR Seed and Polynomial Pair for BIST Applications

Polynomial selection for LFSR-based BIST schemes has been typically left out of the scope of active research in the recent works due to lack of analytical methods that address this issue. Usage of primitive polynomial with a small number of feedbacks is considered a classical rule of thumb that is usually implemented. Although being beneficial for very long test sequences, primitive polynomial cannot guarantee fast fault coverage growth, which is a critical issue in pseudo-random-pattern-generator-based embedded test approaches. Hence, selecting a good initial state would be the main instrument for getting the fast coverage gain. In this work, we propose a formal analytical method to calculate a customized polynomial and seed pair for each separate design/test case. This novel technique allows shortening BIST runtimes and increasing fault coverage by embedding given efficient test patterns into the LFSR sequence. Being used in mixed-mode BIST techniques, the method shows decreasing trend in test application time and/or necessary test pattern storage resources. Our comparison against primitive polynomial based sequences support these observations.