Accelerated test pattern generators for mixed-mode BIST environments

Linear feedback shift registers (LFSRs) are used to generate both pseudorandom and deterministic patterns in the scan-based built-in self-test environment to raise the fault coverage and reduce the test cost. However, like other scan-based methods, the LFSR based pattern generation schemes take a long test application time on feeding deterministic patterns from the LFSR into a scan chain. In this paper we derive a generalized relationship between the bits in the original scan chain and the states of the LFSR such that the bits generated by an LFSR in any future clock cycle can be pre-generated by the proposed test pattern generator. With this relationship, we can divide a scan chain into multiple sub-chains and use an LFSR-based multiple sequence generator to simultaneously generate all the subsequences required by the sub-chains, hence can greatly reduce the test application time.