Increasing processor efficiency: match power with demand
For decades, chipmakers strove to develop the fastest and most powerful chips possible and damn the amount of electricity needed to power them, but these days raw grunt isn't the only consideration. As more and more devices go mobile and these devices become more and more powerful, chipmakers must also take the energy efficiency into account. Harvard graduate student Wonyoung Kim has developed and demonstrated an on-chip, multi-core voltage regulator (MCVR) that he says could allow the creation of "smarter" smartphones, slimmer laptops and more energy efficient data centers by more closely matching the power supply to the demand of the chip.
Kim's MCVR is essentially a DC-DC converter that addresses the mismatch between power supply and demand through its ability to take a 2.4-volt input and scale it down to voltages ranging from 0.4 to 1.4 V. It is able to increase or decrease the output by 1 V in under 20 nanoseconds. In a process that Kim likens to "shutting off the lights when you leave the room," the MCVR also uses an algorithm to save power by cutting power to parts of the processor that are not in use. Kim says this results in longer battery life for mobile devices and lower energy bills for stationary data centers, without a reduction in performance.
Because the MCVR is located on the chip it is able to manage the power supply of not only each processor chip, but also each individual core on the chip. Thanks to the short distance the signals have to travel between the voltage regulator and the cores, the power scaling happens in a matter of nanoseconds.
"Wonyoung Kim's research takes an important step towards a higher level of integration for future chips," says Gu-Yeon Wei, Gordon McKay Professor of Electrical Engineering at Harvard's School of Engineering and Applied Sciences (SEAS). "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," added Wei.
Kim believes mobile phones are where the greatest demand for the MCVR lies but says the technology could also cut the cost of powering servers and reduce the heat output of laptop processors, which is one of the barriers to slimmer models.
"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 percent to the manufacturing cost, but with the potential for 20 percent or more in power savings."
In 2008, Kim's research at SEAS showed that fine-grain voltage control was a theoretical possibility and earlier this month 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. Kim has obtained a provisional patent for the MCVR with his Ph.D. co-advisers at Harvard, Gu-Yeon Wei, and David Brooks, Gordon McKay Professor of Computer Science, who are coauthors on the paper.