Test response compaction method with improved detection and diagnostic abilities

This paper describes a test response compaction method that preserves diagnostic information and enables performing a test-per-clock offline test. The test response compaction system is based on a chain of T flip-flops. The T flip-flop signature chain can preserve the information about the positions of the erroneous test response occurrence and the information about the clock cycle when the erroneous test responses occurred. This information can be used for diagnostic purposes. An algorithm that localizes errors according to the T flip-flop chain output is presented. The paper discusses the possible benefits and limitations of the proposed test pattern compaction scheme. The influence of multiple errors on detection and localization capability of the compaction system and hardware overhead is discussed in the paper as well. The probability of error masking is analyzed, the proposed scheme provides substantially lower masking probability than a D flip-flop chain and a MISR. The scheme can spare the test time by the test-per-clock arrangement. The hardware overhead and reached test time are given for several benchmark circuits in the paper as well.