A DETERMINISTIC BIST SCHEME BASED ON RESEEDING OF FOLDING COUNTERS

A new scheme for deterministic and mixed mode scan based BIST is presented in this paper. It relies on a new type of test pattern generator which resembles a programmable Johnson counter and is called folding counter. Firstly, this new technique uses a small LFSR to generate pseudo random patterns to eliminate the easy to detect faults and obtain a set T of hard fault test cubes. Secondly, the test cube width of the set T may be compressed with classical technique—input reduction. Finally, both the theoretical background and practical algorithms are presented to characterize the set T of deterministic test cubes by a reasonably small number of seeds for a folding counter. Experimental results show that the proposed scheme outperforms previously published approaches based on the reseeding of LFSRs or Johnson counters. It therefore provides an efficient and flexible solution for scan based BIST.