This paper presents a batteryless system-on-chip (SoC) that operates off energy harvested from indoor solar cells and/or thermoelectric generators (TEGs) on the body. Fabricated in a commercial 0.13 μW process, this SoC sensing platform consists of an integrated energy harvesting and power management unit (EH-PMU) with maximum power point tracking, multiple sensing modalities, programmable core and a low power microcontroller with several hardware accelerators to enable energy-efficient digital signal processing, ultra-low-power (ULP) asymmetric radios for wireless transmission, and a 100 nW wake-up radio. The EH-PMU achieves a peak end-to-end efficiency of 75% delivering power to a 100 μA load. In an example motion detection application, the SoC reads data from an accelerometer through SPI, processes it, and sends it over the radio. The SPI and digital processing consume only 2.27 μW, while the integrated radio consumes 4.18 μW when transmitting at 187.5 kbps for a total of 6.45 μW.
This paper presents a top-down methodology for designing battery-less systems for the Internet-of-Things (IoT). We start by extracting features from a target IoT application and the environment in which it will be deployed. We then present strategies to translate these features into design choices that optimize the system and improve its reliability. We look into how to use these features to build the digital subsystem by determining the blocks to implement, the digital architecture, the clock rate of the system, the memory capacity, and the low power states. We also review how these features impact the choice of energy harvesting power management units.
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