COMPARATIVE ANALYSIS OF 4-BIT AND 8-BIT REVERSIBLE BARREL SHIFTER DESIGNS USING REVKIT

ABSTRACT In the recent years, reversible logic has emerged as a viable approach in power optimization and also has found its importance in low power CMOS, quantum computing, nanotechnology, and optical computing. The main challenge in reversible circuits is to optimize the quantum cost, time delay and the garbage outputs associated with the reversible circuit. 'RevKit' in recent years has become a popular and powerful tool for design visualization, implementation and analysis in reversible computing. In this work, we have implemented the design of reversible 4-bit and 8-bit barrel shifter circuits in RevKit and results are analyzed in terms of quantum cost, delay, garbage outputs, gate count, line count and transistor cost. Further, the simulation results have been documented and tabulated to facilitate a comparative study with conventional designs. Keywords: reversible circuits, barrel shifters, quantum cost, time delay, garbage output, RevKit. INTRODUCTION In irreversible logic computations [1], each bit of information lost generates kTln2 joules of heat energy, where k is Boltzmann's constant and T is the absolute temperature at which the computation is performed. Thus, the amount of energy dissipated in a system bears a direct relationship to the number of bits erased during the computation. The kTln2 energy dissipation can be avoided [2] if a computation is carried out in a reversible manner Rotating and shifting data in a single cycle are required in several applications like efficient computations and arithmetic operations. Barrel shifters, more suitable for this kind of operations, since, it is capable of shifting or rotating the inputs in a single cycle and find great importance in the digital signal processing computation. In reversible system information is not erased. The number of inputs and outputs are equal in reversible gates, which means that the input stage can always be retained from the output stage. Thus, such an implementation of reversible barrel shifter will be highly efficient when compared to any conventional design in terms of time delay, garbage output or the quantum cost associated with such a structure. The majority of the work that currently exists in literature focuses on optimizing the reversible sequential designs in terms of number of reversible gates and garbage outputs using functional verification. A few prior works have used design tools such as RevKi

A Novel Approach to Design 2-bit Binary Arithmetic Logic Unit (ALU) Circuit Using Optimized 8:1 Multiplexer with Reversible logic

Reversible circuit designing is the area where researchers are focussing more and more for the generation of low loss digital system designs. Researchers are using the concept of Reversible Logic in many areas such as Nanotechnology, low loss computing, optical computing, low power CMOS design etc. Here we have proposed a novel design approach for a 2-bit binary Arithmetic Logic Unit (ALU) using optimized 8:1 multiplexer circuit with reversible logic concept [1]. This ALU circuit can perform complement, transfer, addition, subtraction, multiplication, OR, XOR, NAND functions on given values. The ALU circuit has been simulated on Modelsim tool and synthesised for Xilinx Spartan 3E with Device XC3S500E with 200 MHz frequency. This 2-bit ALU using reversible logic is useful for the designs of low power loss systems

Synthesis, testing and tolerance in reversible logic

In recent years, reversible computing has established itself as a promising research area and emerging technology. This thesis focuses on three important areas of reversible logic, which is an area of reversible computing. Firstly, this thesis proposes a transformation based synthesis approach for realizing conservative reversible functions using SWAP and Fredkin gates. This thesis also proposes ten templates for optimizing SWAP and Fredkin gates-based reversible circuits. Secondly, this thesis proposes an approach for the design of online testable reversible circuits. A reversible circuit composed of NOT, CNOT and Toffoli gates can be made online testable by adding two sets of CNOT gates and a single parity line. Finally, we have proposed an approach to achieve fault tolerance in reversible circuits. A design of a 3-bit reversible majority voter circuit is presented. This voter circuit can be used to design fault tolerant reversible circuits