Efficient design of QCA optimal universal logic gate ULG.2 and its application

Quantum-dot cellular automata (QCA) is a promising nanotechnology which has potential applications in future computers. Its advantages such as faster speed, smaller size and lower power consumption than CMOS are very attractive. Universal logic gates have stronger function than traditional logic gates. This paper begins with a review of QCA,i.e. basic principles of QCA, QCA logic devices and modular design methodology. Then an efficient modular based QCA optimal universal logic gate ULG.2 is obtained using a new algorithm and modular design methodology. Finally three examples of 4-to-1 multiplexer, full adder/subtraction and full comparator are implemented with the ULG.2. Simulation results are obtained by using the QCADesigner tool for the proposed QCA circuits. The results confirm that all the proposed circuits hold correct logic function and achieve a considerable wire-crossing count reduction. Compared to the existing ULG and MI based design, proposed 4-to-1 multiplexer can respectively reduce 50%,62.5% number of wire-crossings apart from 26.7%,30.3% QCA cell reduction.