Nanotechnology-based full-adder design with three-input majority and XOR gates using quantum-dots technology

Abstract

Quantum-dot cellular automata (QCA) is an emerging nanocomputing paradigm in which binary information is represented and propagated through cell polarization and Coulombic interactions. QCA technology provides a potential alternative to conventional complementary metal–oxide–semiconductor circuits for implementing compact digital logic structures. This paper presents a multilayer QCA architecture for implementing a one-bit full adder using a three-input XOR gate and a three-input majority gate. The three-input XOR gate generates the SUM output, whereas the majority gate directly produces the CARRY output. The proposed full-adder cell is subsequently employed as the basic building block of a four-bit ripple-carry adder, in which the carry output of each stage is connected to the carry input of the following stage. The proposed layouts are implemented using a three-layer arrangement and provide direct accessibility to the input and output cells. The functional behavior of the proposed circuits was evaluated using QCADesigner, whereas their energy-dissipation characteristics were analyzed using QCADesigner-E, which supports the evaluation of the adopted multilayer structures. Simulation results demonstrate that the proposed one-bit full adder consists of 21 QCA cells, occupies an area of 0.02 μm², and produces the SUM and CARRY outputs with a latency of 0.5 clock cycle. The proposed four-bit ripple-carry adder consists of 141 cells, occupies an area of 0.25 μm², and generates the final carry output after two clock cycles. The simulated output waveforms verify the functional correctness of both circuits for the applied input combinations. The results indicate that the proposed multilayer structures provide compact implementations of a one-bit full adder and a four-bit ripple-carry adder while maintaining direct access to their input and output cells.