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Cellphone add-on raises power concerns

Posted: 16 Oct 2003 ?? ?Print Version ?Bookmark and Share

Keywords:portable power management? cellphone? regulator? gps? dsc?

Portable power management has drastically changed since we last explored it. The most influential players now talk about a package-level process, involving power management SoC, transferable cores and synthesizable IP.

We knew that adding miniaturized features and functions to the cellphone package - color screens, GPS, Internet browsers, MP3 players and now, digital still cameras (DSCs) and video - would tax battery life. The answer to this problem, as our contributors make clear, is not more hardware.

For instance, while the DSC's voltage and current requirements will be drastically different from everything else in the cellphone, powering it does not mean simply adding another voltage regulator, unless you are concentrating on magnifying the size, cost and battery power consumption associated with this feature. Rather, the answer involves rethinking power management for the entire phone. This year's cellphone may have a separate regulator. Next year, that regulator will be integrated with other voltage regulators on the same chip - maybe even with the cellphone CPU itself.

So while each contributor will focus on voltage and current requirements of cellphone components such as the CPU, color screen, audio, camera, RF power section and the USB (or Bluetooth) connection, they are also asking what can be integrated, and how.

National Semiconductor Corp.'s Ravi Ambatipudi, for example, reviews some of the goals set by his company's partnership with ARM cores. The ARM9 core serves as the CPU for many cellphones and handheld devices. The best answer to saving battery life, Ambatipudi writes, is more than a matter of using efficient regulators and/or putting the ARM to sleep when you do not need it. It is more a matter of voltage scaling, in which you assign priorities to the tasks the CPU must perform, and then scale the voltage and clock frequency supplied to the ARM according to those priorities. This requires a voltage regulation - a power delivery system - that is intimately tied, cycle by cycle, to the ARM CPU core. Ultimately, said Ambatipudi, this "system monitor" will not be a separate chip, but rather, specialized IP that will follow the ARM through its various instantiations.

Microchip Technology Inc.'s Bonnie Baker points out that power savings for MCUs in battery-powered applications can be obtained by paying attention to the kinds of clocking systems utilized. An internal R/C oscillator will burn less power than an external crystal, though the trade-off is in timing accuracy. Sleep modes and low-power CMOS peripherals also help cut power.

Of course, the CPU is not the only device that uses a sleep mode to conserve battery life. Motorola Inc.'s Bill Poole describes a "discontinuous-transmit" function that can be used to save RF transmitter power in GSM handsets. The discontinuous-transmit function turns the transmitter on/off during a voice call (that is, when the user is listening and not talking). Similar power savings can be applied to the audio amplifiers of the phone as well as the LCD backlight.

- Stephan Ohr

EE Times

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