Accumulator-based output selection for test response compaction

Output selection is a recently proposed test response compaction method, where only a subset of output response bits is selected for observation. It can achieve zero aliasing, full X-tolerance, and high diagnosability. We propose an output selection scheme for multiple scan designs, which employs only accumulators and multiplexers, and thus involves small area overhead and simple test control. An efficient selection procedure is presented to determine a minimal test set and the corresponding output bits to select for complete fault coverage. Experimental results show that when only one accumulator and one multiplexer are employed, 100% single stuck-at fault coverage for ISCAS'89 (ITC'99) circuits can be achieved by observing only 9.84% (8.19%) of the test response bits with only 1.86% (1.18%) area overhead.