First CMOS 3G power amp heads for Mobile World Congress

HASBROUCK HEIGHTS, N.J. — The founding engineers of Javelin Semiconductor have developed the first working CMOS implementation of a 3G power amplifier (PA), pulling ahead in a small field of competitors that have spent several years chasing what Javelin's CEO called "the holy grail of the handset IC design."

Javelin representatives will demonstrate the JAV5001 operating in a cell phone at the Mobile World Congress in Barcelona, Spain, Feb. 15-18. The part is sampling now and is expected to be in production by June.

Power amps are a key piece of the signal path in a cell phone, the piece that connects to the antenna. The PA has also been the last key IC in the cell phone that has not gone to a CMOS implementation. The lion's share of PAs available today are gallium arsenide (GaAs) devices; a small percentage use silicon germanium (SiGe).

"This topic of finally doing a PA in CMOS has been struggled with and attempted for the better part of 10 years," said Brad Fluke, president and CEO of Javelin (Austin, Texas). "It's kind of the holy grail of the handset IC design." Many of the founders and early hires of Javelin came from Silicon Laboratories, which made its name developing high-performance CMOS ICs.

Several arguments had been posed against the feasibility of designing power amps in CMOS. The first, which was disproved in 2005 by Silicon Laboratories' 2G PA, was that the transistors weren't fast enough to support high-frequency, low-noise operation. The second had to do with the breakdown voltage limitations of CMOS. Axiom cleared that hurdle in 2007, showing that those voltages could be effectively managed using a clever CMOS architecture. Axiom's PA couldn't reach handset OEMs' required efficiency levels, however, so the part never achieved market success.

One of the motivating factors for designing in CMOS is that it provides for enormous economies of scale, meaning that you can build wafers at established foundries, such as Javelin partner Taiwan Semiconductor Manufacturing Co. Ltd. (TSMC). Javelin would not reveal the line widths to be used for its device, other than to say that the PA doesn't require bleeding-edge technology; a relatively older process works just fine.

But in several respects, Javelin's design breaks new ground. The company has filed for 15 patents related to the architecture and implementation.

One key spec of the JAV5001 PA—the one with which handset vendors are chiefly concerned—is the amp's current draw from the battery. Power amplifiers generally offer high-, mid- and low-power modes of operation. The Javelin part shines brightest in the low- and medium-power modes, where cell phones spend most of their time. (Note that a 3G phone, unlike earlier models, is full duplex, meaning that the PA is always on.)

Handset OEMs tend to use the GSMA DG.09 usage model to specify average current because it captures the true battery drain while the phone is being used in a real-life application. In the case of the Javelin part, the average current is less than 30 mA, generally closer to 27 or 28 mA. Average current draw for GaAs PAs usually exceeds 30 mA, approaching or exceeding 40 mA in some cases.

"The numbers they've shown look pretty promising," said Brian Modoff, managing director and senior telecommunications technology analyst at Deutsche Bank Securities. "In particular, I'm referring to the 28-mA average current. If they can deliver that commercially, they could have an interesting product."

Forward Concepts analyst Will Strauss echoed the sentiment, noting that Javelin has "something no one else has got. They're claiming better performance than the GaAs parts, which are the 3G market leaders."