A New Design Method for Self-Checking Unidirectional Combinational Circuits

In this paper, a new method for the design of unidirectional combinational circuits is proposed. Carefully selected non-unidirectional gates of the original circuit are duplicated such that every single gate fault can only be propagated to the circuit outputs on paths with either an even or an odd number of inverters. Unlike previous methods, it is not necessary to localize all the inverters of the circuit at the primary inputs. The average area over head for the described method of circuit transformation is 16% of the original circuit, which is less than half of the area overhead of other known methods. The transformed circuits are monitored by Berger codes, or by the least significant two bits of a Berger code. All single stuck-at faults are detected by the method proposed.