Efficient Test Set Modification for Capture Power Reduction

The occurrence of high switching activity when the response to a test vector is captured by flip-flops in scan testing may cause excessive IR drop, resulting in significant test-induced yield loss. This paper addresses the problem using a novel method based on test set modification, featuring (1) a new constrained X-identification technique that changes a properly selected set of bits in a fully-specified test set into X-bits without fault coverage loss, and (2) a new LCP (low capture power) X-filling technique that optimally assigns 0's and 1's to the X-bits for the purpose of reducing the switching activity of the test set in capture mode. This method can be readily applied in any test generation flow for capture power reduction without any impact on area, timing, test set size, and fault coverage.