Simplification and modification of multiple controlled Toffoli circuits for testability

Testability dramatically enhances the operating cost in reversible logic circuits as it increases the cost metrics such as gate count, quantum cost, number of wires and garbage output. This increase also affects the utilization of resources, which further enhances overall cost of testing. This paper presents a new design for testability methodology for reversible circuits by exploring the properties of multiple controlled Toffoli and Fredkin gates, to produce online testable circuits at lower cost metrics. The method includes simplification and modification of Toffoli circuits to form parity-preserving Toffoli–Fredkin cascades. The testability in these cascades can be achieved by comparing the parity of inputs and outputs using controlled-NOT gates on an additional wire. Single-point failures in reversible logic circuits are targeted by means of detecting bit faults. In contrast to the existing work, the present model is robust, low cost and has lesser design complexity. Experiments are conducted on a set of benchmark circuits to prove the efficacy of the present work. The results show an average reduction by 15.9 % in gate cost and 11.0 % in total operating cost when compared to the most recent existing work formulated on the same platform.