Research Article
First Steps in Creating Reversible Sequential Circuits
Research Article
First Steps in Creating Reversible Sequential Circuits
Kushal Jain
B. Tech. Student at Vellore Institute of Technology, Vellore
Synthesis of reversible sequential circuits is a very new research area. It has been shown that such circuits can be implemented using quantum dot cellular automata. Other work has used traditional designs for sequential circuits and replaced the flip-flops and the gates with their reversible counterparts. Our earlier work uses a direct feedback method without any flip-flops, improving upon the replacement technique in both quantum cost and ancilla inputs. We present here a further improved version of the direct feedback method. Design examples show that the proposed method produces better results than our earlier method in terms of both quantum cost and ancilla inputs. We also propose the first technique for online testing of single line faults in sequential reversible circuits.
1. Introduction
Moore’ s law [ 1 ] predicted a continuous rise in the number of transistors per chip due to the continuous reduction in feature size. The popular thought is that Moore’ s law will
no longer hold true in about a decade when the feature size will approach the atomic level. DeBenedictis [ 2 ] showed that
in CMOS technology feature size is no longer the primary challenge; rather energy dissipation is the new limiting factor. Current CMOS circuits implement Boolean logic networks, where the main contributor to heat generation is the energy in the 0 and 1 signals stored on wires. Each time a signal
changes from one state to another and back again, CV joules
of energy are turned into heat, where C is the capacitance
between the wire and the ground and V is the power
2 supply voltage. The most common number cited is CV ≥
2
Therefore reversible logic may be the next promise for CMOS technology.
In a theoretical study, Landauer [ of 3 ] stated heat energy that irreversible when a logic operations dissipate kTln2 k constant and is the operating temperature in kelvin. In bit of information is lost, where again is Boltzmann’ s
T
another theoretical study, Bennett [ 4 ] showed that, from a thermodynamic point of view, if a circuit is both logidissipated cally and physically. Experiments reversible have, shown then kTln2 that dissipation heat will not of no be
demonstrated that reversible logic dissipates less heat than the thermodynamic limit of kTln2
heat is not achievable; however, it has been experimentally in physically irreversible lowpower CMOS logic [ 5 ] and physically reversible superconductor flux logic( SFL) [ 6 ]. Thus, reversible logic is a favorable
100kT, where k is Boltzmann’ s constant and T is the a mbient choice for low-power emerging computing technologies. adiabatic and reversible logic essentially recycle CV joules
temperature in kelvin [ 2 ]. DeBenedictis [ 2 ] also stated that of signal energy many times before dissipating as heat. Consequently, the energy drawn from the power supply could be reduced by as much as 100 times. However, signal energy recycling cannot take place in traditional Boolean networks.
2
computing technologies such as superconductor flux logic
Reversible logic has become realizable in many emerging( SFL) technology [ 6, 7 ], optical technology [ 8, 9 ], quantum dot cellular automata technology [ 10, 11 ], and nanotechnology [ 12 ]. In addition, quantum circuits are inherently reversible [ 13 ]. This is another reason why reversible logic has become