1. INTRODUCTION
With the evolution of microelectronics, more and more high-complexity digital systems have been designed. A common characteristic of these systems is the fact that they are battery-fed, and are conceived for different applications such as wireless communication, portable computers, aerospace (satellites, missiles, etc), aviation, automobile, medical applications, etc. Since they are battery-fed, it is desirable that the batteries have a long life span, and, therefore, power dissipation is a very important parameter in the design of such systems [1]. These systems may be implemented in VLSI technology and/or FPGAs (Field Programmable Gate Array). The FPGAs have become a popular means to implement digital circuits. FPGA technology has grown considerably in the past few years, generating FPGAs with up to 50 million gates, thus allowing complex digital systems to be programmed in such devices [2]. Traditionally, digital circuits are implemented with components built using CMOS technology.