From the archive, originally posted by: [ spectre ]

New Super-Efficient Chip Could Run on Body Heat
BY Alexis Madrigal  /  02.04.08

A new chip uses so little power, it could enable sensors,
communication devices and other gadgets that run on body heat and
movement alone.

The chip uses 70 percent less voltage than current chip technologies.
It could lead to an order-of-magnitude increase in energy efficiency
for electronics in the next five years, said the MIT researchers who
developed the new technology.

“It will extend the battery lifetime of portable devices in areas like
medical electronics,” said Anantha Chandrakasan, a professor of
electrical engineering at MIT. “When you look at the digital
processor, the fact is that we may be able to reduce the energy needed
by 10 times.”

Better circuit design and batteries have already led to smaller, more-
mobile electronics. But changing a battery is not an option for many
medical and military devices. Military researchers at Darpa, which
helped fund the MIT work, are keen to increase the lifespan of these
technologies or even eliminate the need to charge them. Military
strategists imagine these types of low-power chips could be used in
the battlefield, particularly in body and environmental sensors. Among
more mundane uses, Nokia is looking at low-voltage chips for use in
cellphones and computers. Intel also has a low-power-chip research

Designing a low-voltage chip is complicated, because transistors —
the bases of chips — use voltage changes to switch on and off.
Increase the voltage to the system, and the transistor eventually hits
its threshold and switches on. Decrease it, and the transistor
switches off. That ability is what allows it to store the binary
information — the 1’s and 0’s — that forms the basis of computing.

But at low voltages, variations introduced during transistor
production can cause errors.

“When you scale voltages, the first thing to break is memory on a
chip,” Chandrakasan said. “You have to redesign the memory and logic
so you can handle the variation.”

Working with scalable energy voltages, he said, required a whole suite
of design techniques, including a fundamental change in the memory
cell from six transistors to eight.

The researchers think medical devices like pacemakers and various
military applications could use the new chip within five years.

Decreasing power consumption is the key to unleashing medical
technologies on the battlefield, said Barry Perlman, associate
director for technology at the Army’s Communications Electronics
Research and Development Center at Fort Monmouth, New Jersey.

“Sensors that are involved in monitoring the soldier’s health,
managing blood flow or heart rate, or measuring the thermal profile of
the soldier — there’s no question all of this is very, very
important,” Perlman said. “But it’s not realistic unless the power
requirement associated with them is really low.”

The power requirements for sensors attached to the body could be
reduced to near zero, Chandrakasan said. The body’s heat and movement
could generate the microwattage necessary to power the devices.

MIT graduate student Joyce Kwong will discuss the new chip at the
International Solid-State Circuits Conference in San Francisco on
Tuesday. The researchers designed their proof-of-concept chip with
researchers at Texas Instruments, using a standard semiconductor-
fabrication process.

The major trade-off for the lower power usage is raw speed, said
Connie Brown, spokeswoman for Intel’s mobile platforms. Intel’s newest
mobile platform, SilverThorne, cuts power consumption to less than 2
watts. That’s less than one-fifth of any previous offerings and one-
eighth the power draw of ballyhooed products like the MacBook Air’s
new chip, which draws 17 watts. The MIT team’s chip uses between 1 and
100 microwatts.

While a couple of watts in energy savings might not be a big deal to
consumers with access to the power grid, Perlman said soldiers often
have to carry all the power for their battlefield communications
devices — which are about 10 times bigger than typical cellphones.

“You can start to imagine how power becomes a very, very important
parameter to the soldier,” he said.


Prof. Anantha Chandrakasan
phone: (617) 258-7619
e-mail: anantha [at] mtl [dot] mit [dot] edu


Nokia’s Low-Voltage Chips May Slash Mobile Devices’ Power Use

Researchers’ work may result in devices that better handle the taxing
power demands placed on them by ever-expanding functionality.

BY Darrell Dunn  /  September 4, 2006

Researchers at Nokia (NYSE: NOK) and MIT’s Microsystems Technology
Laboratories are developing techniques to cut semiconductors’ energy
consumption by reducing their operating voltage levels. Their work may
result in mobile electronic devices that better handle the taxing
power demands placed on them by ever-expanding functionality.

Jamey Hicks, director of the Nokia Research Center, says the company
has made leaps in developing chips that can operate at voltage levels
below the normal thresholds required to switch individual transistor
pairs on and off for regular operation.

Transistors inside semiconductors usually act like switches.
Individual transistors move to an open or closed position depending on
the charge applied to them. By reducing that voltage, the size of the
openings of individual transistor gates is reduced, thereby cutting
the volume of current flowing through the gates.

“It’s like turning a water tap on only half way,” Hicks says.

Those “subthreshold” transistors could reduce the energy consumption
of chips to between a fifth and a tenth of typical levels. For
semiconductors that use a lot of power, such as video-compression
chips in cell phones, that reduction will boost devices’ battery life,
perhaps as much as three to 10 times normal, Hicks says.

Nokia research teams are analyzing areas for using subthreshold
semiconductors, but commercialization of the chips is probably four to
five years away.

MIT’s ultra-low power CMOS design explained
BY Steve Bush  /  2/16/2007

Researchers at the Massachusetts Institute of Technology (MIT) have
developed a feedback-control scheme that interactively tunes CMOS
operating voltage to minimize dissipation.

Energy consumption in CMOS drops quadratically as its supply voltage
is bought below its threshold voltage. However, according to MIT,
leakage increases exponentially at the same time.

This means that for any given circuit workload and temperature, there
is a particular supply voltage that trades capacitive losses with
leakage in a way that minimizes power consumption.

The example CMOS “load” in the 65-nm MIT circuit, fabricated by TI, is
a hardware 7-tap FIR filter, whose power supply comes from an on-chip
DC-DC converter capable of delivering 250 to 700mV at 1-100µW at over
80 percent efficiency.

The loop consists of an energy sensor and a controller that moves the
supply voltage slightly — via the DC-DC converter — to see what
effect it has on energy consumption. In this way the controller can
push the supply voltage in the improving-energy direction until it
settles at the bottom of the power dip.

Changing the 7-tap filter (at optimal voltage) to a 1-tap version
drops power by 25 percent at constant voltage, whereas feedback
control achieves a cut of over 40 percent.

In the presence of leakage — added as a 1µA constant load to the
circuit — power would almost triple, but the loop pulls this down to
an increase of only 30 percent.

With temperature increasing from 0°C to 85°C, the loop saves around 50
percent of power compared with constant voltage operation, claimed

The technique places no burden on the controlled load and consumes a
tiny fraction of the power it saves.




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