Multiscan-based test compression and hardware decompression using LZ77

Abstract

In this paper we present a new test data compression technique and an associated decompression scheme for testing VLSI chips. Our method is based on our novel use of the much utilized, in software, LZW, particularly LZ77 algorithm. We adapt LZ77 to accommodate bit strings rather than character sets. Moreover, we exploit the large presence of don't cares in the uncompressed test sets that we generated using commercial ATPG tools. Our decompression scheme makes effective use of the on chip boundary scan during decompression and then feeding the internal multiple scan chains for testing. The hardware overhead cost for this scheme is minimal. Experimental results are provided.