Single and Variable-State-Skip LFSRs: Bridging the Gap Between Test Data Compression and Test Set Embedding for IP Cores

Abstract

Even though test set embedding (TSE) methods offer very high compression efficiency, their excessively long test application times prohibit their use for testing systems-on-chip (SoC). To alleviate this problem we present two new types of linear feedback shift registers (LFSRs), the Single-State-Skip and the Variable-State-Skip LFSRs. Both are normal LFSRs with the addition of the State-Skip circuit, which is used instead of the characteristic-polynomial feedback structure for performing successive jumps of constant and variable length in their state sequence. By using Single-State-Skip LFSRs for testing single or multiple identical cores and Variable-State-Skip LFSRs for testing multiple non-identical cores we get the well-known high compression efficiency of TSE with substantially reduced test sequences, thus bridging the gap between test data compression and TSE methods.