A fault tolerance technique for combinational circuits based on selective-transistor redundancy

With fabrication technology reaching nanolevels, systems are becoming more prone to manufacturing defects with higher susceptibility to soft errors. This paper is focused on designing combinational circuits for soft error tolerance with minimal area overhead. The idea is based on analyzing random pattern testability of faults in a circuit and protecting sensitive transistors, whose soft error detection probability is relatively high, until desired circuit reliability is achieved or a given area overhead constraint is met. Transistors are protected based on duplicating and sizing a subset of transistors necessary for providing the protection. In addition to that, a novel gate-level reliability evaluation technique is proposed that provides similar results to reliability evaluation at the transistor level (using SPICE) with the orders of magnitude reduction in CPU time. LGSynth'91 benchmark circuits are used to evaluate the proposed algorithm. Simulation results show that the proposed algorithm achieves better reliability than other transistor sizing-based techniques and the triple modular redundancy technique with significantly lower area overhead for 130-nm process technology at a ground level.