Study On How To Avoid Wire-crossing Structure In QCA Circuit

The integrated circuit technology based on CMOS technology follows Moore's Law and develops rapidly.Because of the improvement of manufacturing process,device size is getting smaller and approaching its physical limit gradually.It will generate non-ideal phenomena such as high power consumption,high density,complex wiring and crosstalk.So lots of researchers are applying themselves to exploring novel devices which could replace CMOS device.Quantum-dot cellular automata(QCA)is to be discussed a lot due to its characteristic of low power,high speed and high density.And it is considered to be one of the new alternatives to replace CMOS device.Due to the unique working method,the position of the cross structure is equivalent to the basic device in QCA.However,wire crossing is the redundant part of QCA circuits functionally.Hence,it is necessary to study the optimization of QCA structure.This article is devoted to the research of how to avoid cross structure in QCA circuit.The study is divided into two sides: One is the optimization method of reducing cross structure in QCA circuit and the other is the redesign of QCA basic unit without crossings.In terms of the optimization method of reducing cross structure in QCA circuit,this paper first analyzes the applicability of the virtual node method and the heuristic up-down median algorithm to the QCA circuit design of reducing wire crossing because of the characteristic that the QCA circuit diagram is a natural directed graph.Then,based on the Karnaugh map method,an optimization method based on pseudo IP cores is proposed.The application analysis is carried out on the 3-input,4-input,and n-input combinational logic circuits with minimum term's forms.Experimental results show that this method could effectively reduce crossings in the circuit and the optimized circuits perform better original circuits in area,cell number and delay.Finally,the cross-edge method is analyzed briefly which is the optimization of reducing wire crossings in routing.In the aspect of redesign of QCA basic unit without crossings,based on inter-cellular response device,the sequential circuit basic unit,flip-flop,is redesigned.Firstly,the advantages and disadvantages of existing five-input majority gate and XOR gate based on inter-cellular response theory is summarized and analyzed.Using some of these structures,SR,D,JK and T flip-flop are proposed without cross structure.Than the2-bit,4-bit and n-bit binary counters and 4-bit twisted ring counters with no cross structure are designed.The various parameters of the redesigned circuits are compared with the existing design's.The results show that the performance of redesigned circuits is better in all aspects which are compared.