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Motorola cellphone has lights, camera, action

Posted: 26 Sep 2006 ?? ?Print Version ?Bookmark and Share

Keywords:Motorola? ROKR? iTunes? Apple? backlight?

Announced at the time that Apple's iPod was moving forward to a fifth-generation platform in the form of the Nano, Motorola's ROKR was the first cellular handset to support Apple's iTunes for music playback. The bar-form phone changed little from its non-iTunes predecessor other than getting new software, an iconic white plastic case and a few buttons.

This article does not focus on communications and media processing, however; it is system lighting that is worth a closer look.

Motorola's ROKR handset

Motorola's ROKR
(Click image to view teardown diagram)

An ATI Imageon 2250 processor handles multimedia tasks, including MP3 decode and display interface. Core communications functions come from a Freescale platform comprised of baseband processor and single-chip GSM transceiver. Skyworks supplies the RF Power amplifier and a two-chip package from Intel is used for system memory. The ever-important power-management needs of battery charging and system voltage regulation are left to a TI-manufactured analog ASIC, also likely tasked with the cellular audio subsystem. All quite integrated in most respects, though architecturally still separating digital processing functions, analog and RF content.

The design features several lighting dimensions that are both common to many other handsets and unique to the ROKR. In the former category are keyboard illumination, white-LED backlighting for the LCD andat least for many phones with camerasa white-LED flash lamp.

In the "unique" category, the ROKR's music-synchronized blinking "sidelights" add a new twist. Along with ringtones, your chosen iTunes music can drive a miniature light show of sorts and even the vibrator can be made to dance to the beat. To roll up support for multifaceted illumination, the ROKR uses National Semiconductor's LP3933, a chip designed to pack all of the essential lighting-management elements for a handheld into one device.

Since LEDs require voltages above the typical 3.7V Li-ion supply, the LP3933 integrates a 300mA boost converter (note the sizable SMT inductor) with programmable voltage output ranging from 4.1V to 5.3V. It then provides constant-current sinks of 0 to 25mA for up to six backlight LEDs. To drive the high-intensity flash lamp for the built-in camera, an additional bank of LED drivers in the LP3933 serves up brief but high-current spikes to a multi-LED cluster, using pulse-width modulation of drive currents to affect the flash intensity control.

While the ROKR has been criticized for its Apple-mandated 100-song limitation (the newer non-iTunes ROKR E2 supports up to 500 songs), the design points to selective islands of integration to support an increasing range of lighting-management needs. The ROKR's musical light show illustrates the triumph of "bling" over maximum battery life.

- David Carey, President, Portelligent
Planet Analog




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