On-Chip Solar Energy Harvester and PMU With Cold Start-Up and Regulated Output Voltage for Biomedical Applications

This paper presents experimental results from a system that comprises a fully autonomous energy harvester with a solar cell of 1 mm<sup>2</sup> as energy transducer and a Power Management Unit (PMU) on the same silicon substrate, and an output voltage regulator. Both chips are implemented in standard <inline-formula> <tex-math notation="LaTeX">$0.18~\mu \text{m}$ </tex-math></inline-formula> CMOS technology with total layout areas of 1.575 mm<sup>2</sup> and 0.0126 mm<sup>2</sup>, respectively. The system also contains an off-the-shelf 3.2 mm <inline-formula> <tex-math notation="LaTeX">$\times2.5$ </tex-math></inline-formula> mm <inline-formula> <tex-math notation="LaTeX">$\times0.9$ </tex-math></inline-formula> mm supercapacitor working as an off-chip battery or energy reservoir between the PMU and the voltage regulator. Experimental results show that the fast energy recovery of the on-chip solar cell and PMU permits the system to replenish the supercapacitor with enough charge as to sustain Bluetooth Low Energy (BLE) communications even with input light powers of 510 nW. The whole system is able to self-start-up without external mechanisms at 340 nW. This work is the first step towards a self-supplied sensor node with processing and communication capabilities. The small form factor and ultra-low power consumption of the system components is in compliance with biomedical applications requirements.

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