Graduate student Wonyoung Kim says multi-core voltage regulation is “like shutting off the lights when you leave the room.” His energy-saving device cuts power to parts of a microprocessor that are not in use. Credit: Flickr user tamakisono. |
There was a time when a laptop could weigh
10 pounds and still sell—a time when a cell phone was larger than a pocket—and
a time when an iPod only played music.
Today’s consumers expect mobile devices
that are increasingly small, yet ever-more powerful. All the bells and
whistles, however, suck up energy, and a phone that lasts only 4 hours because
it’s also a GPS device is only so much use.
To promote energy-efficient multitasking,
Harvard graduate student Wonyoung Kim has developed and demonstrated a new
device with the potential to reduce the power usage of modern processing chips.
The advance could allow the creation of
“smarter” smartphones, slimmer laptops, and more energy-friendly data
centers.
Kim’s on-chip, multi-core voltage
regulator (MCVR) addresses what amounts to a mismatch between power supply and
demand.
“If you’re listening to music on your
MP3 player, you don’t need to send power to the image and graphics processors
at the same time,” Kim says. “If you’re just looking at photos, you
don’t need to power the audio processor or the HD video processor.”
“It’s like shutting off the lights
when you leave the room.”
Kim’s research at Harvard’s School of Engineering and Applied Sciences (SEAS)
showed in 2008 that fine-grain voltage control was a theoretical possibility. He
presented a paper at the Institute
of Electrical and
Electronics Engineers’ (IEEE) International Solid-State Circuits Conference
(ISSCC) showing that the MCVR could actually be implemented in hardware.
Die micrograph of the fully integrated DC-DC converter chip. Credit: Wonyoung Kim. |
Essentially a DC-DC converter, the MCVR
can take a 2.4-volt input and scale it down to voltages ranging from 0.4 to 1.4
V. Built for speed, it can increase or decrease the output by 1 V in under 20
nanoseconds.
The MCVR also uses an algorithm to
recognize parts of the processor that are not in use and cuts power to them,
saving energy. Kim says it results in a longer battery life (or, in the case of
stationary data centers, lower energy bills), while providing the same
performance.
The on-chip design means that the power
supply can be managed not just for each processor chip, but for each individual
core on the chip. The short distance that signals then have to travel between
the voltage regulator and the cores allows power scaling to happen quickly—in a
matter of nanoseconds rather than microseconds—further improving efficiency.
Kim has obtained a provisional patent for
the MCVR with his Ph.D. co-advisers at SEAS, Gu-Yeon Wei, Gordon McKay
Professor of Electrical Engineering, and David Brooks, Gordon McKay Professor
of Computer Science, who are coauthors on the paper.
“Wonyoung Kim’s research takes an
important step towards a higher level of integration for future chips,”
says Wei. “Systems today rely on off-chip, board-level voltage regulators
that are bulky and slow. Integrating the voltage regulator along with the IC
chip to which it supplies power not only reduces broad-level size and cost, but
also opens up exciting opportunities to improve energy efficiency.”
“Kim’s three-level design overcomes
issues that hamper traditional buck and switch-capacitor converters by merging
good attributes of both into a single structure,” adds Brooks. “We
believe research on integrated voltage regulators like Kim’s will be an
essential component of future computing devices where energy-efficient
performance and low cost are in demand.”
The multi-core voltage regulator responds almost instantaneously to changes in power demand from each core of the processor. As a result, the power supply matches the demand more closely, conserving energy. Credit: Wonyoung Kim. |
Although Kim estimates that the greatest
demand for the MCVR right now could be in the market for mobile phones, the
device would also have applications in other computing scenarios. Used in
laptops, the MCVR might reduce the heat output of the processor, which is
currently one barrier to making slimmer notebooks. In stationary scenarios, the
rising cost of powering servers of ever-increasing speed and capacity could be
reduced.
“This is a plug-and-play device in the
sense that it can be easily incorporated into the design of processor
chips,” says Kim. “Including the MCVR on a chip would add about 10%
to the manufacturing cost, but with the potential for 20% or more in power
savings.”
The research was supported by the National
Science Foundation’s Division of Computer and Network Systems and Division of
Computing and Communication Foundations.
