Implementation of Symmetric Functions Using Quantum Dot Cellular Automata

VLSI technology has made possible the integration of massive number of components into a single chip with the minimum power dissipation. But concerned by the wall that Moore’s law is expected to hit in the next decade, the integrated circuit community is turning to emerging nano-technologies for continued device improvements. Quantum dot cellular automata(QCA) is a technology which has the potential of faster speed, smaller size and minimum power consumption compared to transistor –based technology. In quantum dot cellular automata, the basic elements are simple cells. Each quantum cell contains two electrons which interact via Coulomb forces with neighboring cells. The charge distribution in each cell tends to align along one of two perpendicular axes, which allows the encoding of binary information using the state of the cell. These cells are used as building blocks to construct gates and wires. This paper utilizes these unique features of QCA to simulate symmetric functions. A general equation for the minimum number of gates required to an arbitrary number of input variables causing synthesis of symmetric function is achieved. Finally a general expression for the number of gates in benchmark circuits is also deduced. It provides significant reduction in hardware cost and switching delay compared to other existing techniques.