Longer cell-phone chats

Oct. 9, 2003
Student engineers have developed a scheme to cut power consumption in 3G cell-phone transmitters, dramatically improving talk times. The project took second place in the premier international student chip-design contest organized by the Semiconductor Research Corp.

Students from the University of California, San Diego, Jacobs School of Engineering, designed an ultralow-power SiGe BiCMOS transmitter IC for 3G W-CDMA mobile-phone applications. A 3G cell phone can cut back its signal amplitude, depending on how far it is from the base station. But even putting out a weaker signal, the handset draws roughly the same amount of power from the battery. "Through a combination of architecture and circuit innovations, we've developed a technique to lower power consumption considerably, especially when the handset is very close to the base station," says graduate student Vincent Leung. "In a nutshell the basic innovation is 'current on demand,' thanks to a smart, adaptive bias scheme."

Leung, a third-year graduate student had just six months to design the chip from scratch, and his design was picked to be one of 15 entries fabricated in IBM 0.25 um BiCMOS SiGe 6 HP technology through MOSIS fabrication services. "Vincent's chip was highly integrated, but it came back working the very first time," says Leung's advisor and UCSD professor Lawrence Larson.

SiGe technology is key to developing high-performance digital, mixed-signal and wireless integrated-circuit products. "This technology is very sophisticated in a lot of areas," says Leung. "It handles digital capabilities really well, analog and RF capabilities, isolation, and so on. Our architecture makes use of those aspects, including high-speed digital logic, high-speed switching with low-current consumption, and high-quality inductors integrated on the chip."

Implementing the new technology would require a slight change of interface, says Larson, which is not yet a standard feature of today's 3G cell phones. But, the team expects to file patents on one or two of the key techniques in its research.

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