The promise of smart cities and other aspects of “smart living” is dependent upon the growth of the internet of things (IoT) — but that vision relies upon extensive deployment of miniaturized silicon-chip sensors with low power consumption and decades of battery lifetime. That’s a major challenge faced by the builders of IoT devices, which is why an innovation from the GREEN IC research group at the National University of Singapore (NUS) could provide a significant leg up.

IoT sensor nodes — miniature systems containing one or more sensors plus circuits for data processing, wireless communication and power management — keep power consumption low by staying in “sleep mode” most of the time. Wake-up timers, which stay on most of the time, trigger the sensors to carry out a task as needed. While this is an effective short-term strategy, these timers rely upon energy-hungry peripheral circuits such as voltage regulators.

The NUS approach, by contrast, uses an on-chip circuit as a wake-up timer. Its reduced sensitivity to supply voltage reduces power consumption by a factor of at least 1,000 and into the range of picowatts — units on the scale of one billion times lower than the power used by a smartwatch. Even when the battery is unavailable, the timer can function from very scarce ambient power — such as moonlight.

“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 human hair,” said Massimo Alioto, research team leader and associate professor in the electrical and computer engineering department at NUS. “It can also be sustained by a millimeter-scale battery for decades.”

The NUS timer can also reduce silicon manufacturing costs due to the pico-range size of its on-chip capacitor, on which it depends for slow and infrequent wake-ups.

The technology was introduced at the 2018 Symposia on VLSI Technology and Circuits in Honolulu, Hawaii, a global forum known for presentations on solid-state circuit and system-on-chip advances. The team is currently working on various silicon systems with power consumption ranging from picowatts to sub-nanowatts. These critical subsystems are aimed ultimately toward the goal of building a completely battery-less system-on-chip.

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