In this article, we present an overview of important market and technology trends behind the growth of low-power signal processing applications. We highlight developments in consumer electronics, medical devices, and military applications, and we take a close look at developments in the cell phone market.

Cell Phones Pile It On
The cell phone is the best-known low-power digital signal processing application. As shown in Table 1, about 500 million cell phones shipped last year. To put this figure in perspective, consider that worldwide shipments of DVD players—which are considered a highly successful product—reached only about 60 million units last year (source: iSuppli, September 2003). The extraordinarily large volumes associated with the cell phone market have made this market a dominant driver of developments in energy-efficient signal processing technology.

Like many other low-power products, cell phones spend most of the time in standby mode. In standby mode, a phone does little more than monitor for an incoming call. Hence, the power consumed during standby mode is much lower than the power consumed during phone calls or other activities. However, cell phones spend so much time in standby mode that the energy consumed during standby mode often determines the overall battery life of the phone. (Battery life depends primarily on energy consumption, as opposed to power consumption. However, it is sometimes important to minimize power consumption as well as energy consumption. For more on this topic, see "Power, Energy, and Battery Life.")

A cell phone's energy consumption in standby mode is typically dominated by the energy consumption of the baseband processor. (Baseband processors handle voice and communications processing in cell phones.) In practical terms, this means that the baseband processor's standby power plays a large role in determining the battery life of a phone. Unfortunately, standby power tends to increase as CMOS fabrication geometries shrink. This has made reducing baseband processor standby power a key challenge for cell phones. (See "Designing Low-Power Signal Processing Systems" for a discussion of standby power and ways designers can minimize it.)

Communications Loads Increase
Processor power consumption is a smaller percentage of total power consumption when the phone is in active use, but several factors are increasing the computational load—and hence creating a need for greater processor energy efficiency—when the phone is in use. First, the computational loads for wireless communications are increasing. For example, the computational loads for a "3G" transceiver are several times higher than those for a "2G" transceiver. In addition, phones are adding support for non-cellular communications such as wireless local area networks, which allow phones to communicate with computer networks, and Bluetooth, which allows phones to communicate wirelessly with headsets and other peripheral devices.