LONDON — ARM Holdings plc is working on a processor core optimized for operation close to the threshold voltage of CMOS transistors and at clock frequencies of the order of tens of kilohertz. The processor IP licensor has done multiple internal designs in research and is now developing a possible slow, very low-power microcontroller core for the Internet of Things (IoT) and other embedded applications.
Mike Muller, chief technology officer of ARM, told a group of UK journalists that strategies for processing small amounts of data and transmitting small payloads for the IoT might differ depending on whether a node was powered or relied on energy scavenging from the local environment. For the latter case, a processor optimized for exceedingly low-power consumption that could wake up whenever enough energy had been harvested could be useful.
"Normally, the best strategy is to do processing as fast as possible and then go to sleep for as long as possible -- get in and get out," Muller said. "But for energy scavenging, it can be different." In these cases, it may be best to power up and get the packet out at minimum energy as soon as enough energy has been harvested. "And it turns out the design tradeoffs are different."
Mike Muller, CTO of ARM.
His Cambridge, England, company already has a reputation for low-power processor designs in mobile phones, tablets, and embedded applications. But the IoT -- which may include larges numbers of wireless sensor nodes communicating with one another and host networks -- may require further improvements in the power-performance ratio.
One way to achieve that is to take the voltage down close to or even below the threshold where a transistor can be turned on and significant current flows -- in the region of 0.3-0.6V. Though transistors can be characterized at these near- and subthreshold voltages and consume much less energy there, switching times are longer, making performance slower.
Three years ago, when EE Times asked Muller about the possibility of subthreshold design, he expressed scepticism.
If you really want to save power, the laws of physics may say it is a good idea, but you are still trading off performance against voltage; you could only get a few hundred kilohertz of clock frequency. And because there is no major demand, it is not possible to get foundries to produce qualified silicon.