Cascade Of Reversible Gates Research Articles

Design‐for‐testability for reversible logic circuits based on bit‐swapping

AbstractThe emerging technology of reversible circuits offers a potential solution to the synthesis of ultra low‐power quantum computing systems. A reversible circuit can be envisaged as a cascade of reversible gates only, such as Toffoli gate, which has two components: k control bits and a target bit (k‐CNOT), k ≥ 1. While analysing testability issues in a reversible circuit, the missing‐gate fault model is often used for modelling physical defects in k‐CNOT gates. A new design‐for‐testability (DFT) technique is proposed for reversible circuits that deploys bit‐swapping using Fredkin reversible gates. It is shown that in an (n × n) circuit implemented with k‐CNOT gates, addition of only two extra inputs along with a few Fredkin gates yields easy testability in the circuit. The modified design admits a universal test set of maximum size 2n + 1 that detects all detectable missing gate faults in the original circuit, where n is the number of input/output lines in the circuit. The DFT overhead in terms of quantum cost is much less compared to that of previous approaches. The method is more advantageous for large circuits.

A new online testing technique for reversible circuits

Any technology offering zero power dissipation must be reversible. A reversible circuit can be envisaged as a cascade of reversible gates only, such as Toffoli gate, which has two components: k control bits and a target bit (k-CNOT), k ≥ 1. Analysing testability issues in a reversible circuit is an important phenomenon. A new online design-for-testability (DFT) technique for reversible circuits is proposed. The authors’ method yields less overhead in terms of quantum cost as compared to the previous online approaches.

Reversible Circuit Synthesis Time Reduction Based on Subtree-Circuit Mapping

Several works have been conducted regarding the reduction of the energy consumption in electrical circuits. Reversible circuit synthesis is considered to be one of the major efforts at reducing the amount of power consumption. The field of reversible circuit synthesis uses a large number of proposed algorithms to minimize the overall cost of circuits synthesis (represented in the line number and quantum cost), with minimal concern paid for synthesis time. However, because of the iterative nature of the synthesis optimization algorithms, synthesis time cannot be neglected as a parameter which needs to be tackled, especially for large-scale circuits which need to be realized by cascades of reversible gates. Reducing the synthesis cost can be achieved by Binary Decision Diagrams (BDDs), which are considered to be a step forward in this field. Nevertheless, the mapping of each BDD node into a cascade of reversible gates during the synthesis process is time-consuming. In this work, we implement the idea of the subtree-based mapping of BDD nodes to reversible gates instead of the classical nodal-based algorithm to effectively reduce the entire reversible circuit synthesis time. Considering Depth-First Search (DFS), we convert an entire BDD subtree in one step into a cascade of reversible gates. A look-up table for all possible combinations of subtrees and their corresponding reversible gates has been constructed, in which a hash key is used to directly access subtrees during the mapping process. This table is constructed as a result of a comprehensive study of all possible BDD subtrees and considered as a reference during the conversion process. The conducted experimental tests show a significant synthesis time reduction (around 95% on average), preserving the correctness of the algorithm in generating a circuit realizing the required Boolean function.