In the last month, FPGA vendors launched a wave of architectures targeting signal processing. These new architectures—the Xilinx Virtex-4, the Lattice Semiconductor LatticeECP, and the Altera Cyclone II—differ in many important respects, but all three feature hard-wired multipliers sprinkled among their reconfigurable logic elements.

Energy consumption is a chief concern for many digital signal processing applications, especially for portable applications where battery life is paramount. In these applications, an accurate understanding of energy consumption is critical to processor selection and to system design. Unfortunately, many obstacles hinder comparisons of processors' energy consumption.

In recent years, ARM has come to dominate the market for licensable general-purpose processor (GPP) cores. Its main competitor, MIPS, has fallen into a distant second place and most other GPP core licensors are niche players. ARM has become so dominant that its competitors are unlikely to threaten its number-one position in the near future.

Power, Energy, and Battery Life

The terms "power" and "energy" are often used interchangeably. Although these terms are related, they describe different concepts. Power consumption is the rate at which a device consumes energy. In other words, if a device consumes a fixed amount of power P over time t, then energy = P x t. An obvious (but important) point is that energy consumption can be reduced by minimizing P, t, or both.

Many embedded signal-processing systems require good energy efficiency. Some devices, such as medical implants and wireless sensors, must operate for years on just one battery charge. To do so, these devices must consume only microwatts of power—a significant design challenge to say the least! Larger devices such as cellular phones and multimedia-oriented PDAs can afford larger batteries and higher energy consumption, but they also must support heavy processing loads.

Processor power consumption is a hot topic today (no pun intended). Consumers' appetites for sophisticated portable electronic devices are strong. But consumers want it all: they want feature-packed devices in small, slim hand-held form factors with good battery life. To meet these expectations, system designers must give high priority to minimizing power consumption.

In many low-power applications, the processor is a major contributor to the overall system energy consumption. Hence, the processor typically plays a key role in determining a product's battery life. The choice of processor also affects many other critical aspects of the system, such as price and performance. In this article we explore processor options for low-power signal processing applications. We begin with a discussion of the criteria to consider when selecting a processor for a low-power signal processing application. Next, we highlight energy-efficient architectural approaches.

Low-power Signal Processing Trends