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Electronic Design

IC Delivers GSM/GPS/Bluetooth Performance Without Interference

Most future-generation cell phones will incorporate not only multiband operation, but also Global Positioning System (GPS) capability for enhanced 911 compliance, as well as Bluetooth (BT) for peripheral connectivity. Designers are now struggling to create an RF chip that will accommodate these three technologies, which typically interfere with each other.

Startup company Ashvattaha Semiconductor Inc., Jacksonville, Fla., believes it has the answer. It's proposing a single-chip design that resolves the co-existence issue. This new chip incorporates a two-band (900- and 1800-MHz) GSM transceiver, a Bluetooth transceiver, and a GPS receiver that can operate simultaneously without compromising each other's performance.

The greatest challenge for designers of 2.5G and 3G cell-phone handsets is finding the pc-board space for the chips needed to implement the added GPS location services and Bluetooth capability while also minimizing power consumption. Ashvattaha plans to integrate all of the RF on one chip to save space.

Also, the design minimizes the need for external IF filters and discrete components (see the figure). Power consumption should be no more than that of a single-band GSM transceiver. Today, a typical single-chip GSM transceiver draws less than 200 mW. Yet Ashvattaha believes that its multifunction chip will draw much less than that.

Interference is the main hurdle in integrating two or more RF systems on one chip. Noise and crosstalk from one system can cause a nearby system to be completely unusable or significantly compromised. Ashvattaha won't reveal the details of how it solved this multimode problem because it is going through the patent process now. But the company does say that it involves advanced top-to-bottom systems architecture, clever chip layout with unique isolation and shielding structures, and circuitry that is less sensitive to noise.

Another key part of the solution is Ashvattaha's trade-secret multimode frequency plan. Carefully selecting voltage-controlled oscillator (VCO) frequencies in the on-chip synthesizers and IFs substantially reduces interference between systems. Ashvattaha had to meet the individual standards set forth by the GSM, GPS, and Bluetooth standards. Each section of the chip, then, has to function and meet standards while all other sections are operating. Interference and noise reduction is down more than 100-fold, or 40 dB, from one section to another.

The chip will be implemented in a 0.2-µm biCMOS process in IBM's silicon-germanium fab facility. The technology is generic enough to apply to any applications requiring the use of multiple RF protocols and systems-on-a-chip.

Beta samples of the chip are expected in the fall. Production quantities will come in late 2001 or early 2002. Future chips are planned for CDMA/GPS/BT and W-CDMA/GPS/BT operation. Ashvattaha, which means banyan tree in Hindu, is funded by Comstellar Technologies of Florham Park, N.J., and Redwood Ventures of Los Altos, Calif.

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