Researchers at MIT and Texas Instruments (TI) (NYSE: TXN) today unveiled a new chip design for portable electronics that can be up to ten times more energy-efficient than present technology. The design could lead to cell phones, implantable medical devices and sensors that last far longer when running from a battery in about five years (2013+).
The key to the improvement in energy efficiency was to find ways of making the circuits on the chip work at a voltage level much lower than usual, Anantha Chandrakasan, lead MIT researcher on this project explains. While most current chips operate at around 1 volt, the new design works at just 0.3 volts.
Reducing the operating voltage, however, is not as simple as it might sound, because existing microchips have been optimized for many years to operate at the higher standard voltage level. “Memory and logic circuits have to be redesigned to operate at very low power supply voltages,” Chandrakasan says.
One key to the new design, he says, was to build a DC-to-DC converter – which reduces the voltage to the lower level – right onto the same chip, which is more efficient than having the converter as a separate component. The redesigned memory and logic, along with the DC-to-DC converter, are all integrated to realize a complete system-on-a-chip solution.
One of the biggest problems the team had to overcome was the variability that occurs in typical chip manufacturing. At lower voltage levels, variations and imperfections in the silicon chip become more problematic. “Designing the chip to minimize its vulnerability to such variations is a big part of our strategy,” Chandrakasan says.
So far the new chip is a proof of concept. Commercial applications could become available “in five years in a number of exciting areas,” Chandrakasan says. For example, portable and implantable medical devices, portable communications devices and networking devices could be based on such chips, and thus have greatly increased operating times. There may also be a variety of military applications in the production of tiny, self-contained sensor networks that could be dispersed in a battlefield.
In some applications, such as implantable medical devices, the goal is to make the power requirements so low that they could be powered by “ambient energy,” Chandrakasan says – using the body’s own heat or movement to provide all the needed power. In addition, the technology could be suitable for body area networks or wirelessly-enabled body sensor networks.
Researchers at the Massachusetts Institute of Technology (MIT) have developed a feedback-control scheme that interactively tunes CMOS operating voltage to minimise 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 minimises power consumption.
Changing the 7-tap filter (at optimal voltage) to a 1-tap version drops power by 25 per cent at constant voltage, whereas feedback control achieves a cut of over 40 per cent. 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 per cent. With temperature increasing from 0 to 85°C, the loop saves around 50 per cent of power compared with constant voltage operation, claimed MIT. The technique places no burden on the controlled ‘load’ and consumes a tiny fraction of the power it saves.