Comput Syst Sci & Eng (2014) 3: 197–204 © 2014 CRL Publishing Ltd International Journal of Computer Systems Science & Engineering A novel reversible design for double edge triggered flip-flops and new designs of reversible sequential circuits Mariam Zomorodi Moghadam, Keivan Navi and Mahmood Kalemati Faculty of Electrical and Computer Engineering, Shahid Beheshti University, G. C., Iran E-mail: m_zomorodi@sbu.ac.ir, m.kalemati@mail.sbu.ac.ir, k-navi@sbu.ac.ir In recent years, reversible computing and reversible logic has rapidly emerged as one of the promising technologies for designing low-power circuits. It has applications in nanotechnology, quantum computing, quantum dot cellular automata (QCA), DNA computing, optical computing and even in CMOS low-power designs. In this work, we propose basic circuits of reversible sequential logic which are the building blocks of a sequential CPU. First, a novel design of a reversible D-flip flop is proposed which is two times faster than the conventional D flip- flop as well as its reversible counterparts. Further new designs of a sequential shift register, reversible adder and multiplier is proposed. These circuits can be used for constructing a reversible CPU which has sequential elements. Practical implementation of the proposed designs can be achieved with the existing technologies in CMOS and nanotechnology. Keywords: Reversible logic, Sequential circuits, Reversible double edge triggered flip-flop, Sequential reversible circuits 1. INTRODUCTION In nanoscale design of current circuits, the power consumption which leads to heat dissipation in computer machinery has be- come one of the major challenges and attracted the attention of many researchers in various fields of computing such as [1, 2, 3] just to name a few. This challenge represents the strongest mo- tivation to study the field of reversible computing. According to [4, 5, 6], any computation can be performed reversible both logi- cally and thermodynamically which approaches zero energy dis- sipation. Quantum physics is also reversible by its nature. This is due to the existence of the reverse-time evolution specified by the unitary operator U -1 = U † and also the recognition that re- versible computation is executed within a quantum-mechanical system. First, R. Landauer in 1961 [4] demonstrated that irre- versibility in the computing process which leads to loss of in- formation, requires minimum heat generation in the order of KT for each irreversible function, where K is Boltzmann’s constant and T is the absolute temperature at which the computation is performed. He argued that this feature is unavoidable, since the computer performs irreversible operations. Consequently C.H. Bennett in 1973 [5] showed that an irreversible computer can al- ways be made reversible. Since then many reversible circuits for implementing conventional systems have been suggested. In se- quential networks, Fredkin and Toffoli [7] have proved that any computation that can be carried out by a conventional irreversible sequential network can also be carried out by a conservative net- work which is by nature reversible and also they proved that it is ideally possible to build sequential circuits with zero internal power dissipation. When we try to build classical irreversible computers on the atomic scale, the dissipated heat is one of the encountered problems which can be avoided by using reversible computation. vol 29 no 3 May 2014 197