The smaller a silicon transistor becomes, the more electrons it leaks. That can mean unreliable, battery-draining chips. Researchers at Intel have come up with a way of dealing with the problem that subverts the industry’s strong preference for precision. The company’s prototype chip operates in a low-power but error-prone mode, but it detects and corrects its errors. This approach, researchers have found, saves 37 percent on power compared with running in conventional mode with no loss of performance.
One way to ensure better performance, even as transistors get smaller and leakier, is to operate them at a relatively high voltage all the time. Most microprocessors today are designed to run at a level that represents a kind of worst-case scenario, says Wen-Hann Wang, director of circuits and systems research at Intel and vice president of Intel Labs in Hillsboro, OR. But it’s rare that a user is doing so many things at once–say, playing a graphics-rich game, uploading video to Facebook, and surfing the Web–that the microprocessor needs to be running in its highest range.
And the high-voltage, high-performance design strategy is becoming a problem for mobile devices, where battery life is important. One way to prolong battery life is to run the chip at a lower voltage, but this leads to errors.
“When a circuit operates at a low voltage, the system gets noisy,” says Wang. Circuits running at low voltages are particularly vulnerable to variations in temperature, and to a phenomenon called “voltage droop”: running a low level of electrical current through billions of transistors at the same time is like taking a shower while the washing machine and dishwasher are running. Just as this heavy water usage can cause a drop in water pressure, running many operations at low voltage can cause sudden drops in current through an individual transistor, and this can lead to errors. Another source of errors that becomes more of a problem at low voltages are inconsistencies that emerge as a chip ages.
These errors are rare, but significant. For example, they might lead an image to freeze as it’s being rendered, forcing the user to restart the process. To cope with the errors that occur when running at low voltage, Intel is developing a strategy the company calls “resilient” circuits. “You don’t know how things will vary, and in which circuits errors will happen,” says Wang. “But if you don’t worry about it, it will be okay most of the time.”