An efficient technique for obtaining unate implementation of functions through input encoding

Abstract

Unate circuits have the desirable property that a single stuck-at fault manifests as multiple unidirectional error at the output. If the valid outputs belong to a unidirectional error detecting code, we can add circuitry to determine if the outputs have suffered any error and implement a self-checking system. The key contribution here is that we can start with an arbitrary circuit with arbitrary number of inputs and outputs and convert that to a unate circuit with coded input outputs. Earlier techniques were based on enumeration of truth space and therefore suffered from a combinatorial explosion for large number of inputs. The technique presented here proceeds with local transformations, producing a sub-optimal solution as a consequence, as opposed to no solution. The results are shown to be within acceptable bounds. © 1994.