This paper proposes a new test data compression/decompression method for systems-on-a-chip. Themethod is based on analyzing the factors that influencetest parameters: compression ratio, area overhead and testapplication time. To improve compression ratio, the newmethod is based on a Variable-length Input Huffman Coding(VIHC), which fully exploits the type and length of the patterns,as well as a novel mapping and reordering algorithmproposed in a pre-processing step. The new VIHC algorithmis combined with a novel parallel on-chip decoder that simultaneouslyleads to low test application time and low areaoverhead. It is shown that, unlike three previous approaches[2, 3, 10] which reduce some test parameters at the expenseof the others, the proposed method is capable of improvingall the three parameters simultaneously. For example, theproposed method leads to similar or better compression ratiowhen compared to frequency directed run-length coding[2], however with lower area overhead and test applicationtime. Similarly, there is comparable or lower area overheadand test application time with respect to Golomb coding [3],with improvements in compression ratio. Finally, there issimilar or improved test application time when comparedto selective coding [10], with reductions in compression ratioand significantly lower area overhead. An experimentalcomparison on benchmark circuits validates the proposedmethod.
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