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CMOS power amplifier rolls for GSM handsets

Posted: 12 Feb 2004 ?? ?Print Version ?Bookmark and Share

Keywords:silicon laboratories? si4300? cmos power amplifier? renesas technology? rf micro devices?

Silicon Laboratories Inc. will break new ground with the introduction of the first monolithic CMOS power amplifier for GSM cellular handsets. Four years in development, the chip integrates power control, filtering and matching circuitry, and could move Silicon Labs into the top tier of suppliers of front-end RF components and transceivers, analysts said.

The space and cost allotted for RF components by handset makers is shrinking rapidly, as manufacturers increasingly look for differentiation with the baseband, applications and interface portions of their designs. They therefore gravitate toward complete transceivers and front-ends from a single source, vs. mixing and matching parts from multiple vendors.

Silicon Labs' CMOS power amp strengthens its standing in a market ripe for consolidation, said Allen Leibovitch, manager of wireless and consumer semiconductors at research firm International Data Corp. "You'll see some consolidation in the radio players, and the ones that survive will have both the transceiver and the PA. Adding the PA was necessary for their [Silicon Labs'] survival."

Silicon Labs will pair its power amplifier with its successful Aero family of CMOS transceivers. Three suppliers owned three quarters of the market for RF front-end and transceiver devices in 2002, the last year for which figures are available, Leibovitch said. Renesas Technology, RF Micro Devices and SkyWorks probably will remain dominant, but Silicon Labs could be a leading supplier in 2005 based on its CMOS PA, he said. Vulnerable suppliers include Infineon Technologies, Philips' RF Division, Anadigics and TriQuint, he said.

Much of the time spent on the Si4300 CMOS power amp was devoted to overcoming the breakdown-voltage limitation of CMOS gate oxides. While CMOS PAs are widely available for Bluetooth devices, and to a lesser extent for wireless local-area networks, they operate at lower voltage and power levels. "GSM transmits at up to 33dBm, so that's why exotic materials such as gallium arsenide are used so widely" in GSM PAs, said Mendy Ouzillou, marketing manager for wireless products at Silicon Labs. A solution struck the design project's chief engineer "while she was mowing her lawn," Ouzillou said. "She realized that if the voltages could be dispersed among a bank of transistors, both high voltages and high output power could be achieved without straining any individual transistor." The solution veers away from the dogmatic physics of IC transistor design and focuses instead on circuit design. Outputs are combined before they are transferred to an antenna.

Citing pending patents, Silicon Labs would not detail the precise mechanism that disperses and combines the voltages, but said it will present that information at the International Solid-State Circuits Conference in 2005. The Si4300 outputs up to 34.7dBm and has a typical power-added efficiency (PAE) above 50 percent. Brian Daly, director of marketing with the RF solutions business group at SkyWorks Inc., said he was skeptical of CMOS' ability to meet the performance, reliability and rugggedness requirements of GSM cellphones. "We think it will be difficult," he said, especially when it comes to Edge [Enhanced Data Rates for GSM Evolution] handsets. He put the PAE of SkyWorks' PA line at 60 percent.

Mukund Ghangurde, marketing director at Silicon Labs' wireless-products center, said, "We meet all GSM specifications." The device also integrates an open-loop power controller, thermal and overvoltage protection, 50-ohm input and output matching networks and harmonic filtering.

The Si4300 is sampling now to 40 customers, packaged in an 18-pin land grid array. Volume production is expected in the third quarter. The part is priced at $2.82 each in quantities of 10,000.

- Patrick Mannion

EE Times

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