LFSR Reseeding Based Test Compression Respecting Different Controllability of Decompressor Outputs

The paper discusses possibilities of rearranging test decompress or internal structure and linking its outputs with the parallel scan chain inputs in order to obtain better compression efficiency while the hardware overhead is not increased. We have experimentally verified that the controllability of decompress or outputs can be used as a simple and easily computable measure of the decompress or efficiency. Based on this observation we have developed a procedure that chooses a sub optimal LFSR outputs and parallel scan chain inputs interconnection. The procedure proposes a permutation of the scan chain inputs so that the scan chains that are fed with patterns with higher number of care bits are linked with the highly controllable decompress or outputs. We have experimentally verified on the benchmark circuits that adopting the proposed strategy improves the compression efficiency.