Tuesday, May 16, 2006

Ultra-Low-Power Cell Phones

Programmable analog circuits could drastically reduce the power needs and cost of electronics in portable devices.

By Kevin Bullis

A schematic of a new type of chip that replaces digital with analog computation, which could be the basis of ultra-low-power cell phones. (Courtesy of Benjamin Vigoda, Mitsubishi Electric Research Laboratories.)

A radical approach to making the electronics in cell phones could cut the power consumption of cell phones anywhere from 10 to 100 times, while also dramatically reducing the size and cost.

The mobile phone of tomorrow faces competing demands: the need for more and more sophisticated ways of using available bandwidth and the need to accommodate ever-more power-hungry procesasing. Benjamin Vigoda, research scientist at Mitsubishi Electric Research Laboratories in Cambridge, MA, and research associate at MIT, says the solution may come from an unexpected approach: replacing the combination of analog and digital circuitry used today with what he calls "analog logic."

Vigoda has already built a prototype chip using his approach, which is now being tested for accuracy, power consumption, and noise, among other things. He says a cell phone using the technology could be completed in five years.

Today's cell phones already use specialized analog components for sending and receiving high frequencies, for example, which are too fast for digital processing to handle. Meanwhile, digital components handle computational functions, such as error correction, with programmable, general purpose logic gates.

Vigoda's programmable analog devices can replace both the traditional analog and digital components. This saves power in two ways. First, converting between analog and digital is wasteful in both space and power. Going all-analog cuts out the analog-to-digital middleman, thereby reducing the power required. The analog circuits are also more efficient -- Vigoda says one can do the work of 1,000 digital logic gates.

At the same time, Vigoda is keeping the advantages of digital processors by using modular components that permit, for example, an automated design process. Also, because he uses standard CMOS transistors, his new circuits can be built using a standard semiconductor manufacturing process.

While the new components can replace power-hungry digital chips, they can also replace old analog components, such as oscillators, with analog components that can be programmed. The result would be radios which can produce more complex signals that can be changed "on the fly," Vigoda says, making it possible for many more callers to use the same bandwidth without the signals interfering with each other, as well as making it possible to optimize power savings for different environments. "For 80 years we've been relying on these special-purpose analog circuits that are designed and set in stone," says Vigoda. "What we can do now is make the radio programmable all the way to the antenna. You can imagine much better system-wide optimization given this flexibility at the physical layer."