Motorola's Bluetooth headset: Headlong into hands-free

Developed under an OEM alliance with Danish technology group GN Netcom, and weighing under 30 grams, the 5-cm-diameter headset uses a single 4 x 4.5-mm elliptical circuit board within. This simplicity is enabled by Cambridge Silicon Radio's BC01B-URT BlueCore one-chip Bluetooth device. The BlueCore provides the 2.45-GHz radio, including transmit-and- receive filtering, on-chip synthesizer, baseband DSP and microcontroller. An interesting feature of the board design is the built-in antenna formed by a gold-plated trace along the edges and sides of the board. Also noteworthy is the apparent addition of an external RF low-noise amplifier implemented with discrete components-a stated option in the BlueCore data sheets. Whether receive sensitivity issues lie with the single-chip radio, integral antenna or a combination of the two remains unclear, but the additional LNA circuitry is modest in scope.

Of course "single-chip Bluetooth solution" does not mean "single-chip end product." Since the BlueCore device is only a data radio, Motorola's linear PCM codec (MC145483) is required for analog/digital transformations and bit stream coding/decoding to create a voice radio. A separate 512-kbyte SST flash memory holds system software. Rounding out system components, a National Semiconductor flip-chip audio amplifier provides the necessary drive for the headset earpiece while Linear Technology's LTC1731 controller manages charging of the built-in 150-mA-hr. lithium polymer battery.

Control switches for the microphone-activated power switch and left-right polarity configuration consist of board contacts shorted by carbon buttons tied to headset mechanics. Swing the microphone out and the unit wakes up, an intuitive choice. Change the position of the ear clip for left or right-sided use and the volume button polarity is reconfigured so "up is up" and "down is down"-a clever touch.

Cost-of-goods-sold for the headset was judged to be around $30, well under the $199 retail price. Advances in integration demonstrated with the design (and resulting low cost) imply that inexpensive Bluetooth accessories are at hand, particularly once early premium margins erode. Key Bluetooth connectivity components were around $10 by our estimates, demonstrating that the $5 "promised land" for embedded Bluetooth solutions is within striking distance.

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DAVID CAREY IS CEO OF PORTELLIGENT (AUSTIN, TEXAS; WWW.PORTELLIGENT. COM), WHICH DOES TEARDOWN REPORTS ON PORTABLE ELECTRONIC SYSTEMS.