Abstract: A coding scheme of relative length of runs was presented. It reduces the length of runs needing to be encoded by not increasing the number of runs in encoded test data. So the compression effect is enhanced by shortening the length of codeword. Experimental results on some ISCAS 89 benchmark circuits show that the proposed scheme obvi- ously outperforms the traditional coding methods in the compression ratio and the implementation of decompression, such as Uolomb, FDR, EFDR coding.

Key words: Test data compression, Encoding, Built in self-test, Built off self-test, Codeword