Reversible cascades with minimal garbage


Abstract:

The problem of minimizing the number of garbage outputs is an important issue in reversible logic design. We start with the analysis of the number of garbage outputs that must be added to a multiple output function to make it reversible. We give a precise formula for the theoretical minimum of the required number of garbage outputs. For some benchmark functions, we calculate the garbage required by some proposed reversible design methods and compare it to the theoretical minimum. Based on the information about minimal garbage, we suggest a new reversible design method that uses the minimum number of garbage outputs. We show that any Boolean function can be realized as a reversible network in terms of this new approach by giving the theoretical method of finding such a network. Using a heuristics synthesis approach, we create a program and run it to compare results of our synthesis to the previously reported synthesis results for the benchmark functions with up to ten variables. Finally, we show that the synthesis for the proposed model can be accomplished with lower cost than the synthesis of EXOR programmable logic arrays.
Page(s): 1497 - 1509
Date of Publication: 01 November 2004

ISSN Information:


I. Introduction

Energy loss is an important consideration in digital design. Part of the problem of energy dissipation is related to nonideality of switches and materials. Higher levels of integration and the use of new fabrication processes have dramatically reduced the heat loss over the last decades. The other part of the problem arises from Landauer's principle [9] for which there is no solution. Landauer's principle states that logic computations that are not reversible, necessarily generate heat for every bit of information that is lost, where is Boltzmann's constant and the temperature. For room temperature the amount of dissipating heat is small (i.e., ), but not negligible. The design that does not result in information loss is called reversible. It naturally takes care of heating generated due to the information loss. This will become an issue as the circuits become smaller.

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