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GaAs still dominant in cellphone RF

Posted: 14 Mar 2003 ?? ?Print Version ?Bookmark and Share

Keywords:sige? cmos? wireless transceiver ic? gaas? cellphone?

Despite the promotion for silicon germanium (SiGe) and CMOS for wireless transceiver ICs, gallium arsenide (GaAs) still dominates among cellphone power amplifiers (PAs) according to a new study released by Strategy Analytics.

The market research firm said four players - RFMD, Skyworks, Hitachi, and Motorola - dominated the $1.2-billion market for cell phone power amplifiers last year.

GaAs HBT's (hetero-junction bipolar transistors) dominated the 2002 market for PA components. This is not likely to change with a recovery in the cellphone market, the rollout of 2.5- and 3G products, or the ascendancy of SiGe, said Chris Taylor, Strategy Analytics' director of RF component strategies.

Only Hitachi's LDMOS power transistors, a technology adopted from basestation transmitters, made any inroads against GaAs in handsets, Taylor said. But this technology still takes a back seat to GaAs HBTs as GSM PA modules needed to support GPRS and other 2.5G technologies.

GaAs HBTs are more power efficient at 2-GHz frequencies than LDMOS devices, Taylor noted. Thus, GSM handset makers favor GaAs for new GPRS and W-CMDA designs. Consequently, LDMOS module vendors like Hitachi lost some share in the market for cellphone PAs.

GaAs HBT amplifiers are not only preferred over older GaAs MESFET products, Taylor said, but also over newer GaAs pHEMTs (Pseudomorphic High Electron Mobility Transistors). The enhancement-mode devices are being promoted by companies like Agilent Technologies for their single-supply operation. One reason is that they eliminate the charge pump required to generate the negative supply rail used to power depletion-mode GaAs FETs. But so far pHEMTs occupy a less than 10 percent of the GaAs PA market, Taylor added.

Strategy Analytics said 418 million cellular handsets were shipped in 2002, and that as many as 450 million units would be shipped this year. Cost pressures favor module packaging for PAs, using separate drivers and GaAs power transistors, Taylor said.

PA modules using several chips in a 4-by-4mm package cost about $1.50. This is a less costly means of extending cellphone transmission frequencies into the 1,800-, 1,900-, and 2,100MHz range, he explained. Earlier PAs used more integrated driver-transistor devices, but a $3.50 to $4 cost.

- Stephan Ohr

EE Times

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