Power Management for Mobile Devices

By Sabyasachi Dey

March 6, 2006

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Wireless mobile devices are approaching an impasse. With the convergence of new computing, communication and entertainment applications on wireless handsets, power demands are increasing rapidly, yet the capacity of batteries cannot keep up. At the same time, consumers want sleek, compact mobile devices they can slip into a pocket. Integration at the chip level--often combining multiple processing cores in the same device--and smaller, submicron fabrication processes help to reduce the size of wireless handsets while enabling added functionality. Unfortunately, smaller submicron processes exacerbate the problem of static leakage power. Manufacturers of wireless handsets and other mobile devices are challenged to reduce power consumption while enhancing system performance. In other words, do more for less.

Such rapid integration both in silicon and software space is posing a significant design problem for power management engineers. Power management no longer remains a hardware-only problem, rather it has become a system problem and being addressed by all engineers involved in system design process. Power management decisions are being taken at both hardware and software level. Techniques are invented and deployed in both hardware and software. Increasing focus towards system aspects of cellular phones forced designers to take a holistic and dynamic approach to power management to effectively decrease power consumption without degrading performance.

A good number of techniques are used by designers to reach the goal--efficient processors, variable-speed clocks, circuit shutdowns, low-voltage logic, software design aids, and advanced power-management software (see Figure 1). System-level power-management architecture typically starts with conservation at the source. For example, battery-management ICs and system-power regulators let engineers design power efficient products. Consider a typical wireless product with an RF receiver. Designers can employ a linear RF power controller to act as an on-off switch to conserve energy when the wireless feature is not in use.

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