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