Sensors with long lifetimes are ideal for infrastructure monitoring. Miniaturized sensor systems are only capable of
storing small amounts of energy. Prior work has increased sensor lifetime through the reduction of supply voltage ,
necessitating voltage conversion from storage elements such as batteries. Sensor lifetime can be further extended by
harvesting from solar, vibrational, or thermal energy. Since harvested energy is sporadic, it must be detected and stored.
Harvesting sources do not provide voltage levels suitable for secondary power sources, necessitating DC-DC upconversion.
We demonstrate a 8.75mm<sup>3</sup> sensor system with a near-threshold ARM microcontroller, custom 3.3fW/bit
SRAM, two 1mm<sup>2</sup> solar cells, a thin-film Li-ion battery, and integrated power management unit. The 7.7μW system
enters a 550pW data-retentive sleep state between measurements and harvests solar energy to enable energy autonomy.
Our receiver and transmitter architectures benefit from a design strategy that employs mixed signal and digital circuit
schemes that perform well in advanced CMOS integrated circuit technologies. A prototype transmitter implemented in
0.13μm CMOS satisfies the requirements for Zigbee, but consumes far less power consumption than state-of-the-art