I. Introduction
The growing demand for long-life autonomous portable equipment is driving the current trend toward low-power design. Wireless sensor networks (WSNs) with smart sensors are examples. Microsensor nodes in WSN generally have low-speed requirements. Nevertheless, the systems need to have very longtime battery lifetimes since, in most cases, it is not possible to recharge or replace batteries frequently. As a result, speed and/or dynamic range sometimes might have to be sacrificed in order to conserve energy [1].