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Stacked package trims Motorola's Bluetooth radio

Posted: 07 Jun 2002 ?? ?Print Version ?Bookmark and Share

Keywords:bluetooth radio packaging? bluetooth radio transceiver? ic packaging?

While others tout the benefits of single-chip Bluetooth radio transceivers, Motorola Inc.'s Semiconductor Products Sector has turned to advanced packaging as an alternative to CMOS integration. According to Motorola, the performance of the RF portion of the Bluetooth circuitry takes a hit when it is integrated with a CMOS digital baseband.

To retain the advantages of a dual-die approach but still reduce the overall footprint of the Bluetooth radio, the company is set to introduce two new package types. A 7-by-7-by-1.3mm transceiver module encapsulates the 2.4GHz RF functions for a Bluetooth 1.1 solution (Class 2).

And a 7-by-7-by-1.6mm BGA package includes both the RF and baseband chips in a stacked-die format.

The LTCC module was designed so that multiple layers can be stacked in a thin ceramic substrate, which allows component matching. Many of the passives that would normally be mounted to a board are already embedded in the substrates, and their number is halved compared with the discrete approach, the company said.

The remaining passives mount atop the LTCC substrate along with the transceiver IC.

The stacked solution is based on the same type of technology used for stacking Flash memory and SRAM chips in a single package, a technique often used in cellular phones. An undisclosed company will assemble the packages, which include a 0.355m BiCMOS RF device and 0.185m CMOS baseband processor.

The stacked-die package is designed to use existing power and crystal components in a cell phone. The transceiver module does not include the baseband but is otherwise more self-contained because it includes matching components that the stacked-die package lacks.

Single-chip solutions that integrate both the baseband and the RF receiver portions of a Bluetooth radio have existed for some time. But having separate devices for each function is still the most common approach, Motorola said.

Motorola is using a BiCMOS process for its RF device, which the company says gives it better biasing, higher gain, more throughput and improved sensitivity.

"CMOS can do a lot, but to really get optimized performance people are going to use BiCMOS or [gallium arsenide]," said John Breeden, a Motorola product manager. "There are single-chip guys out there today, and they're adequate for the Bluetooth specs. We believe we can provide something with a little bit better RF performance than some of our competitors."

Interference rejected

One advantage of higher sensitivity is that it improves the module's capacity to reject interference. That may not be a problem now because Bluetooth is still so young, but it could be an issue in the future.

"Just meeting the Bluetooth specs today are OK for some customers," Breeden said, but as Bluetooth gains more users, "not being interfered with is going to be more important. You can't ignore it as the band gets full."

Motorola's transmitter includes a direct-modulation FM transmitter controlled by a dual-port, fractional-N synthesizer and a VCO. Also on board are an LPA and a transmit/receive control function. The module dissipates 27mA during transmit and 33mA during receive, and there are several power-down modes to reduce power consumption.

Motorola said it will provide the LTCC Bluetooth transceiver module in sample quantities starting in the third quarter. It expects production to begin by year's end. Samples of the stacked-die BGA will be available in June, the company said.

Anthony Cataldo

EE Times

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