A robust algorithm for pessimistic analysis of logic masking effects in combinational circuits

Analyzing logic masking effects is an important key to evaluate soft error tolerance of circuits. The computing complexity of analyzing logic masking effects exactly is proportional to the square of circuit size, which is unacceptable to achieve a scalable analyzer. This paper shows a robust algorithm to analyze logic masking effects pessimistically with multiple CODCs (Compatible combinations of Observability Don't Cares). It is guaranteed that an upper bound of the susceptibility of each gate is estimated using the proposed algorithm. The computing complexity of the proposed algorithm is proportional to circuit size. Experimental results show that the proposed algorithm runs about 91 times faster than an algorithm which analyzes logic masking effects exactly with fault simulation. The proposed algorithm estimates average susceptibility 11.5% larger than that of the exact algorithm for circuits in ITC'99 benchmark set. The state-of-the-art heuristic AnS ER estimates average susceptibility with 96% underestimation for circuits protected with partial TMR (Triple Modular Redundancy) on average, which can be fatal error for soft error tolerance evaluation. On the other hand, the proposed algorithm estimates average susceptibility with 37.9% overestimation for such circuits on average. The proposed algorithm is useful to estimate an upper bound of the susceptibility of each gate quickly.