Wake-up timer promises picoWatt performance for IoT devices

Researchers have developed a low-cost ‘battery-less’ wake-up timer in the form of an on-chip circuit that is claimed to significantly reduce power consumption of silicon chips for IoT sensor nodes.

wake-up timer
Low-cost ‘battery-less’ wake-up timer that cuts power consumption of IoT sensor nodes by 1,000 times

The novel wake-up timer from researchers in the Green IC research group at the National University of Singapore (NUS) is said to demonstrate power consumption down to true picoWatt range for the first time.

“We have developed a novel wake-up timer that operates in the picoWatt range, and cuts power consumption of rarely-active IoT sensor nodes by 1,000 times,” said team leader Associate Professor Massimo Alioto from the Department of Electrical and Computer Engineering at the NUS Faculty of Engineering. “As an element of uniqueness, our wake-up timer does not need any additional circuitry, as opposed to conventional technologies, which require peripheral circuits consuming at least 1,000 times more power.

“This is a major step towards accelerating the development of IoT infrastructure and paves the way for the aggressive miniaturisation of IoT devices for long-lasting operations,” he added.

The research was conducted in collaboration with Associate Professor Paolo Crovetti from the Politecnico di Torino in Italy.

According to NUS, IoT technologies often require the extensive deployment of smart, miniaturised silicon-chip sensors with very low power consumption and decades of battery lifetime, and this remains a major challenge to date.

IoT sensor nodes are individual miniaturised systems containing one or more sensors, as well as circuits for data processing, wireless communication and power management. To keep power consumption low, they are kept in the sleep mode most of the time, and wake-up timers are used to trigger the sensors to carry out a task. As they are turned on most of the time, wake-up timers set the minimum power consumption of IoT sensor nodes. They also play a fundamental role in reducing the average power consumption of systems-on-chip.

“Under typical office lighting, our novel wake-up timer can be powered by a very small on-chip solar cell that has a diameter similar to that of a strand of human hair. It can also be sustained by a millimetre scale battery for decades,” said Assoc Prof Alioto.

NUS’ picoWatt range wake-up timer can operate without a voltage regulator due to its reduced sensitivity to supply voltage, thereby suppressing the additional power that is normally used by peripheral always-on circuits. The wake-up timer also works when battery is not available and under very scarce ambient power, which was demonstrated by a miniaturised on-chip solar cell exposed to moonlight.

In addition, the team’s wake-up timer can achieve slow and infrequent wake-up using a very small on-chip capacitor with half a picofarad capacitance. NUS said this helps to significantly reduce silicon manufacturing costs due to the small area – 40μm on each side – required.