Process scaling and aggressive performance improvements have resulted in power consumption becoming a first-order design criterion. For example, the latest Intel Pentium 4 processor (Prescott, 2004) has a power consumption of 103 Watts, almost four times larger than that of the Pentium III (1999). In addition to its clear impact on battery lifetime in portable embedded systems, processor power consumption has also become a primary constraint on workstation performance. Therefore, reducing power dissipation is a top priority in modern VLSI design.