Implication-based concurrent error detection (CED) has been shown to have promising performance for on-line testing. However, many error indication signals may be required for this CED method, and thus incur much additional interconnection. This would result in not only complicated error checking circuits, but also a large compactor design to process the error indication signals. Both would incur high area overhead. In this paper, we present a collapsing technique that can significantly reduce the total number of required error indication signals for implications. This issue has never been addressed in the literature. We find that equivalence and dominance relationships exist between error indication signals, which are quite helpful for signal reduction. Therefore we develop an efficient algorithm to first identify these relationships, and then make good use of them to merge error indication signals without sacrificing the probability of detecting errors. We also employ 19 ISCAS'85 and ITC'99 benchmark circuits to evaluate the effectiveness of the proposed technique. The results show that 48.48% of error indication signals are reduced by our technique on average. This also leads to 39.23% and 34.52% averaged area overhead reduction to the error checking circuit and the compactor design, respectively.
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