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27 September 2007


VT raises $3.3m to develop SiGe chips for WiMAX

VT Silicon, a startup based at the Advanced Technology Development Center (ATDC) of the Georgia Institute of Technology in Atlanta, GA, has received a $3.3m Series A round of financing from Silicon Valley-based Menlo Ventures. The funding will help the firm to design and produce prototypes of its new ‘intelligent power amplifier’ silicon-germanium chips for mobile WiMAX-enabled devices.

WiMAX is intended to provide significantly higher bandwidth and broader coverage for next-generation mobile devices supporting applications such as streaming video. US telecom network operator Sprint Nextel Corp plans to roll out WiMAX service in large metropolitan areas during 2008, spurring supply of the corresponding chipsets. However, this demands engineering innovation, as the new WiMAX mobile devices will require more power, while being less forgiving of the distortion caused by nonlinear effects that occur at higher power levels, notes VT’s CEO Mike Hooper. “They [the new devices] are going up on the complexity curve because they are trying to get more and more information into the same bandwidth.”

Meeting the technical demands in potentially high-volume devices will require new levels of optimization - in addition to new techniques for controlling distortion. “What you want to do is build a power amplifier that is more linear for higher power levels,” Hooper says. “That can give you more range, better battery life and compensate for other issues that you associate with higher performance,” he adds. “Since power amplifiers require a balance of power, linearization, efficiency and other factors, you have to optimize each of these for the specific application where they will be used.” 

For its chips, VT has developed proprietary, patent-pending linear enhancement technology (LET) which should permit the higher power levels used by WiMAX devices. The technology is designed to boost the range of power amplifiers, decreasing the distortion in signals while improving battery life.  

“This funding will allow us to take the linearization techniques we have already proven in a test chip and apply them to commercial chips within the next 9 to 12 months,” says Hooper. “Our plan is to be shipping samples to customers early next year and to begin ramping to production by the middle of next year.”

The firm says that, to justify high-volume consumer applications, it is fabricating its amplifiers on low-cost SiGe instead of gallium arsenide (used in most existing WiMAX power amplifiers). Because SiGe can support both conventional bipolar transistors as well as CMOS, LET can be implemented on the same chip as the power amplifier, providing cost and design simplicity advantages, the firm reckons.

Hardware costs will be a significant issue for WiMAX, which is just one of the technologies vying for dominance for next-generation mobile devices.  “If the chipsets can be produced inexpensively compared to current WiFi devices, WiMAX can supplant WiFi and become the leading technology for mobile broadband applications,” Hooper says.

“SiGe affords us the ability to put very sophisticated control and intelligence within the power amplifier because SiGe can combine both CMOS – which is low power control circuitry – and bipolar transistors in one fabrication process,” Hooper notes.  “It gives us the ability to get fairly complex, allowing us to make intelligent power amplifiers.”

However, the designers will have to compensate for the relatively low RF power levels currently produced by most SiGe power ICs.  “We have some proprietary technologies to get the power we need,” said Hooper.  “We can be competitive with gallium arsenide on power levels.”

VT initially plans to launch two power amplifiers operating at 2.5GHz or 3.5GHz for the WiMAX market, manufactured by the foundry Jazz Semiconductor Inc in Newport Beach, CA, USA. As a step toward volume manufacturing, it will work with customers to create a reference design for each prototype chip.

“The combination of silicon germanium and unique linearization techniques makes the company's technology attractive to the key players in this new market,” reckons Menlo Ventures’ managing director Hal Calhoun.

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