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SiGe firm gains traction in 802.11 RF design

Posted: 29 Jul 2004 ?? ?Print Version ?Bookmark and Share

Keywords:gaas? rf design? sige? cmos? power amplifier?

While GaAs, once an RF design forte, is slowly giving way to SiGe and CMOS technologies amid renewed industry efforts for lower costs and higher integration, one company that is striving to shatter myths about SiGe technology is its namesake: SiGe Semiconductor Inc.

Founded in 1997, SiGe Semiconductor was born out of a Canadian government's project to develop SiGe process technology. The Ottawa-based RF chipmaker has remained true to its roots since then. SiGe Semiconductor calls itself a noncompetition silicon firm for its focus on power amplifiers and on front-end modules as an extension.

An RF front-end module makes up the circuitry required between the antenna and the transceiver, including the power amplifier, power detector, antenna switch and associated filters.

SiGe Semiconductor has recently made a critical shift from a process technology-based strategy to a product-based strategy in which it establishes relationships with radio and baseband companies, while maintaining a fabless model in which it enjoys special terms with IBM and Cypress foundries.

SiGe Semiconductor claims to be the top power-amplifier supplier for 802.11b and .11g segments with 35 percent of market share. "Most WLAN silicon players, including Broadcom, don't have power amplifier capability," said Alistair Manley, senior marketing director. "So they acquire it from external resources like SiGe Semiconductor, which doesn't have the radio part." Only Atmel has the in-house power-amplifier capability among the leading WLAN chipmakers.

SiGe Semiconductor recently ported its front-end module to Broadcom's 54g WLAN chip. "SiGe Semiconductor's power amplifiers are included in several of our 54g reference designs," said Brian Bedrosian, senior product line manager for Broadcom's Home and Wireless Networking Business Unit.

Such relationships mark a clear trend in the RF design arena: transceiver part is moving to the CMOS space. Four years ago this was a predominantly GaAs territory. The trend is particularly evident in the Bluetooth and WLAN space where companies like Atheros have successfully built the CMOS radios. Venture-capital firms also favor RF CMOS approach because of better noise attributes.

"While baseband and MAC devices can be built on small CMOS geometry, doing power amplifier in the same process will become a technology mismatch as CMOS doesn't bring the required power and speed attributes," Manley added. An RF CMOS device consumes more power, while power-amplifier buffer needs 18dB of power transmission.

Cellular next front

Manley acknowledges that SiGe has still to make headway in cellular market. "Two years ago, the common perception was that SiGe can't meet the ruggedness requirements of cellphone design."

Now SiGe Semiconductor, while demonstrating it has the required ruggedness, is evangelizing SiGe's thermal and packaging benefits.

GaAs, being a specialized process for RF devices, is easier to design but doesn't allow integration. SiGe proponents say that GaAs is hard to integrate like SiGe because it can't combine RF HBTs and high-density FETs on the same die. GaAs uses only HBT transistors.

Doing radio in CMOS is a complex job, considered almost impossible from a high-yield standpoint. Today RF CMOS is more expensive than common digital CMOS and is considered slower than SiGe due to parasitics. Moreover, as SiGe designers reckon, CMOS die is larger than SiGe and it offers poor linear performance.

SiGe Semiconductor sees front-end module as key to cellular market because, as Manley puts it, "modularization is the next frontier for integration drive on the RF landscape." He said that SiGe is the best alternative to GaAs from a component-count standpoint. "SiGe has the advantage of integrating analog functions whereas GaAs has to rely on external circuits."

- Majeed Ahmad Kamran

Electronic Engineering Times - Asia

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