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SiGe power amp seeks socket in CDMA handsets

Posted: 19 Mar 2004 ?? ?Print Version ?Bookmark and Share

Keywords:sige semiconductor? cdma? cellular handset? amplifier?

SiGe Semiconductor Inc. has introduced a line of silicon germanium power amplifiers that it believes will break gallium arsenide devices' lock on CDMA cellphones.

Fabricated in IBM's 5DM SiGe BiCMOS process, the amplifiers deliver comparable performance to GaAs but at a lower cost, and with higher integration that allows on-board power detectors, bias control, matching circuits and regulators, SiGe Semiconductor said.

Entrenched in a market that has seen much consolidation over the past year as manufacturers seek to provide one-stop shopping for all things wireless, the Ottawa company believes its focused approach to power-amp design will keep it competitive as a standalone entity. "Our strategy is to focus only on the front end and take nonthreatening steps to work with reference design houses to get our PA [into] the reference design," said Jose Harrison, director of the cellular-power-amp line.

With the announcement of the SE5103, SE5106, and SE5107, the company is flexing its muscle as a power-amp player with parts built in IBM's SiGe process, which delivers the high efficiency of bipolar technology along with a high-power capability that's comparable with parts made in GaAs processes. "We combine that with the CMOS devices, and we can now integrate more sophisticated controls such as the power detectors and 2.8V regulators," Harrison said.

The 5DM process' thick metals allow SiGe to place the output match on the amplifier die. The device "gets assembled onto a lead frame instead of a laminate substrate," Harrison said. "The die sits on top of a copper slug, so the thermal attributes-lower junction temperature leads to greater reliability-are better than for multilayer laminate." And lead frames cost less than laminates, he said.

The end result is a two-stage code-division multiple-access amp for the 824- to 849MHz band that has an output power of 28dBm at a 50dB adjacent channel power ratio and 41 percent power-added efficiency. The SE5103 includes digital bias control and is packaged in a QFN measuring 4 x 4 x 0.9mm; it sells for 80 cents each in order volumes of 100,000. The SE5106 and SE5107 provide digital and analog bias control, respectively; each comes in a 3 x 3 x 0.9mm QFN and costs 85 cents each per 100,000.

All three have separate power-supply pins to the control circuits and power-amplifier cells, so designers can regulate Vcc down to 0.8 volt to improve efficiency at low power levels, said Harrison. Each device also features a sleep mode with a standby current of 2?A.

"We're in the same size as a GaAs die for the same performance, but with lower cost and more integration," Harrison said.

GaAs comparison for comparison's sake, the RF3163 CDMA power amplifier module announced last week by RF Micro Devices Inc., a GaAs HBT device now in production, outputs 28dBm with an efficiency of 41 percent and a linearity of -51dBc. Like the SiGe Semiconductor part, the RF Micro module comes in a 3 x 3 x 0.9mm lead frame. High-volume production shipments have begun to two leading CDMA handset makers in South Korea, RF Micro Devices said.

SiGe plans to capitalize on the integration capabilities of its technology after determining whether customers want to integrate the radio and baseband portions of the module into one IC. "This has proven difficult, as the driver amplifiers that pump the signal into the PA operate at 0 to 10dBm, so you get voltage swings that limit how far into submicron technology you can go," Harrison said.

SiGe's solution, he said, is to integrate the driver onto the PA module. Then handset makers "can take the radio and go to submicron technology and integrate it [the radio] with the baseband. That seems to be what some consider to be the next step."

- Patrick Mannion

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