Tuesday, June 17, 2008

Microchip Goes Low-Power with Sleep Mode

source: http://media.cleantech.com/2990/microchip-goes-low-power-with-sleep-mode

By David Ehrlich, Cleantech Group

Even though they're small, some microchips can be big consumers of power, but a new chip that uses an extreme sleep mode could help bring efficiency to the processor.

Researchers at the University of Michigan have developed a microchip for use in sensors that they say uses 30,000 times less power in sleep mode and 10 times less in active mode than comparable chips now on the market.

"What people usually think is they say, 'Okay, well I need to design my chip for a certain performance point, or for a certain active mode power consumption.' We completely changed that mindset," Dennis Sylvester, an associate professor in the university's Department of Electrical Engineering and Computer Science, told the Cleantech Group.

"We said from the ground up, sleep mode power dominates."

Called the Phoenix Processor, the university said the chip sets a low-power record, consuming just 30 picowatts during sleep mode.

A picowatt is one-trillionth of a watt.

It's intended for use in sensor-based devices such as medical implants, environment monitors or surveillance equipment.

With such low power consumption, the university said energy stored in a watch battery would theoretically be enough to run the chip for 263 years.

Doctoral students Scott Hanson and Mingoo Seok, who jointly lead the project, will be presenting the chip's design to the Institute of Electrical and Electronics Engineers' Symposium on VLSI Circuits in Honolulu later this week.

"The most significant design component that we did was to rethink the concept of power gating," said Sylvester.

Power gates block the electric current from parts of a chip not essential for memory during sleep. But those gates are usually wide with low resistance to let through as much electric current as possible when the device is turned on.

These state of the art chips wake up quickly and run fast, but a significant amount of electric current leaks through in sleep mode, according to the university.

The Phoenix engineers used much narrower power gates that restrict the flow of electric current.

"One of things we did was go to back in time a little bit in terms of the technology we use," said Sylvester.

"If you keep going back the transistors tend to be, of course they're larger, they're less leaky, and so there's a sweet spot there where you kind of balance out the size of the chip and the size of the battery at about one square millimeter."

The university said that in most cases, batteries are much larger than the processors they power. For example, the battery in a laptop is about 5,000 times larger than the processor and it provides only a few hours of power.

Sensors spend more than 99 percent of their lives in sleep mode, according to the university researchers, waking up only briefly to compute at regular intervals.

The Phoenix system defaults to sleep, with a low-power timer acting as an alarm clock, waking the chip every ten minutes for one-tenth of a second to run a set of 2,000 instructions.

The instructions include checking the sensor for new data, processing it, compressing it, and storing it before going back to sleep.

The first test for the new chip will be in a biomedical sensor to monitor eye pressure in glaucoma patients.

"For diagnosis and for optimizing treatment they'd like to be able to have sort of a more in-situ type of monitoring system," said Sylvester. "And the form factor requirements in the eye, as you can imagine, are very, very small."

Sylvester said animal testing of the monitoring system could happen within the next year.

The university engineers also see the possibility of chips like this being spread around to make a nearly invisible sensor network to monitor air or water or detect movement.

"Sprinkling these things in concrete for structural integrity monitoring of new buildings or bridges, these are the kinds of things we're looking toward," said Sylvester.

Although it's still in the research stage, if it does go commercial, Sylvester said there would no issues with manufacturing.

"The costs of manufacturing are very low. There's no special device technologies. We don't use a lot of different, special transistor technologies or anything."

"It's all in the design — the architecture."

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