One of the emerging technologies at the nanoscale level is the Quantum-Dot Cellular Automata (QCA) technology, which is a potential alternative to conventional CMOS technology due to its high speed, low power consumption, low latency, and possible implementation at the atomic and molecular levels. Adders are one of the most basic digital computing circuits and one of the main building blocks of VLSI systems, such as various microprocessors and processors. Many research studies have been focusing on computable digital computing circuits. The design of a Full Adder/Subtractor (FA/S), a composite and computing circuit, performing both the addition and the subtraction processes, is of particular importance. This paper implements three new Full Adder/Subtractor circuits with the lowest number of cells, lowest area, lowest latency, and a coplanar (single-layer) circuit design, as was shown by comparing the results obtained with those of the best previous works on this topic.

Due to the development of integrated circuits and the lack of responsiveness to existing technology, researchers are looking for an alternative technology. Quantum-dot cellular automata (QCA) technology is one of the promising alternatives due to its higher switch speed, lower power dissipation, and higher device density. One of the most important and widely used circuits in digital logic calculations is the full adder (FA) circuit, which actually creates the problem of finding its optimal design and increasing performance. In this paper, we designed and implemented two new FA circuits in QCA technology and then implemented ripple carry adder (RCA) circuits. The proposed FAs and RCAs showed excellent performance in terms of QCA evaluation parameters, especially in cost and cost function, compared to the other reported designs. The proposed adders’ approach was 46.43% more efficient than the best-known design, and the reason for this superiority was due to the coplanar form, without crossovers and inverter gates in the designs.

The miniaturization of electronic devices and the inefficiency of CMOS technology due to the development of integrated circuits and its lack of responsiveness at the nanoscale have led to the acquisition of nanoscale technologies. Among these technologies, quantum-dot cellular automata (QCA) is considered one of the possible replacements for CMOS technology because of its extraordinary advantages, such as higher speed, smaller area, and ultra-low power consumption. In arithmetic and comparative circuits, XOR logic is widely used. The construction of arithmetic logic circuits using AND, OR, and NOT logic gates has a higher design complexity. However, XOR gate design has a lower design complexity. Hence, the efficient and optimized XOR logic gate is very important. In this article, we proposed a new XOR gate based on cell-level methodology, with the expected output achieved by the influence of the cells on each other; this design method caused less delay. However, this design was implemented without the use of inverter gates and crossovers, as well as rotating cells. Using the proposed XOR gate, two new full adder (FA) circuits were designed. The simulation results indicate the advantage of the proposed designs compared with previous structures.

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Reversible logic enables ultra-low power circuit design and quantum computation. Quantum-dot Cellular Automata (QCA) is the most promising technology considered to implement reversible circuits, mainly due to the correspondence between features of reversible and QCA circuits. This work aims to push forward the state-of-the-art of the QCA-based reversible circuits implementation by proposing a novel QCA design of a reversible full adder\full subtractor (FA\FS). At first, we consider an efficient XOR-gate, and based on this, new QCA circuit layouts of Feynman, Toffoli, Peres, PQR, TR, RUG, URG, RQCA, and RQG are proposed. The efficient XOR gate significantly reduces the required clock phases and circuit area. As a result, all the proposed reversible circuits are efficient regarding cell count, delay, and circuit area. Finally, based on the presented reversible gates, a novel QCA design of a reversible full adder\full subtractor (FA\FS) is proposed. Compared to the state-of-the-art circuits, the proposed QCA design of FA\FS reversible circuit achieved up to 57% area savings, with 46% and 29% reduction in cell number and delay, respectively.