TMR voting in the presence of crosstalk faults at the voter inputs

In high reliability systems, the effectiveness of fault tolerant techniques, such as Triple-Modular-Redundancy (TMR), must be validated with respect to the faults that are likely in the current technology. In todays' Integrated Circuits (IC), this is the case of crosstalks, whose importance is growing because of device & interconnect scaling. This paper analyzes the problem of crosstalk faults at the inputs of voters in TMR systems. In particular, possible problems are illustrated, and it is shown that such crosstalk may invalidate the reliability of both voting, and diagnosing operations. The problem is analyzed from a probabilistic point of view. Its occurrence is estimated by using a set of TMR systems obtained with combinational benchmarks as functional modules. The possible problems of such operations are discussed in the presence of crosstalk faults. It is shown that crosstalk may invalidate the reliability of both voting, and diagnosis operations. A probabilistic model of the voting & diagnosis operations in the presence of crosstalk has been developed. Finally, such a model has been used to estimate the probability of voting & diagnosis failures in a set of TMR systems obtained by using combinational benchmarks as functional modules. We have shown that the presence of crosstalk faults at voter inputs may impair both the voting, and the diagnosis mechanisms. This problem has been quantified by applying a probabilistic model of crosstalk fault effects on voting and diagnosis to a set of benchmark circuits. Results show that crosstalk may create a reliability problem for TMR systems. Such a problem can be solved by using on-line testing or design for testability providing additional controllability & observability to the replicated functional units.