GSM/GPRS monolithic radio integrates complete phone on one chip

The GSM/GPRS market is growing, but so are all of the rest of the wireless markets. So, how do manufacturers keep up with the necessary R&D and inventory management to support all of the current and emerging 3G and now 4G technologies? The team at Silicon Laboratories has an answer: reduce component count by 75 percent without sacrificing performance.

They believe they have achieved this with their AeroFONE Si4905, which integrates a power management unit (PMU), battery interface and charging circuitry, digital baseband, analog baseband and a quad-band RF transceiver in a 12-by-12mm package. The complete phone modem including memory and power amplifier fit in 6.1 cm². Now, we have all heard about the latest "complete" system on chip or radio on chip before, but the team at Silicon Laboratories seems to have really done it this time. Typical entry level GSM/GPRS handsets use approximately 245 components to implement the radio; Silicon Labs gets it down to about 58.

"Integration and ease of use drastically reduce the R&D load on our customers," said Dan Rabinovitsj, VP at Silicon Laboratories. In the handset market, being able to respond quickly to operator demands for the most popular phones is crucial. Predicting which phones will be the best sellers has been traditionally challenging, so OEMs have been forced into nail-biting inventory decisions in order to be able to support the market without adversely affecting their bottom lines. "The Si4905 can really help them to be more profitable," added Rabinovitsj, "The integration of all of these different functions in one monolithic CMOS chip is unprecedented; it is an extraordinary benchmark."

The team at Silicon Laboratories knew that their design would only have real value, though, if it had stellar RF performance. With the company known for its RF sensitivity performance, the design team was very sensitive to maintaining the reputation. As a result, the new chip demonstrates typical sensitivity of -111dBm in the 900MHz GSM band and -110dBm in the DCS (1,800MHz) band.

So, how did they shrink the radio and maintain the performance? "The biggest challenge was how to integrate a very sensitive RF circuit with an extremely noisy digital subsystem," admits Rabinovitsj. Typically, radios and basebands have been in separate packages, separate cavities, and were shielded. The team credits a few things with its success. First, they had no legacy baseband solution, so they were more open to consider all of the design possibilities. "We started with a great radio that is realized in deep submicron CMOS," says Rabinovitsj. "So, we built the rest of the subsystem around that RF and crafted the system architecture to preserve the existing RF performance." The team admits it was a very tough project that was conceived in 2002 and finally taped out in June 2005. They credit key enablers as CMOS technology, an existing digitally intensive architecture in their transceiver, and rigorous verification methodologies.

The device is sampling now, along with evaluation boards. The company reports that early customers are already making calls with the chips/evaluation boards and that things are looking good. If you are in the market for GSM/GPRS radio components, this chip should really get your attention.

The Si4905 is available in a standard 12-by-12 mm, Pb-free, RoHS-compliant plastic ball grid array (PBGA) package. Pricing is dependant on volume. The Si4905 is sampling now, with mass production scheduled for Q2 2006. An evaluation platform is available for $5,000.

- Janine Love
eeProductCenter