On-Chip Inductor-Less Indoor Light Energy Harvester with Improved Efficiency for WSN/IoT Device Design

An on-chip inductor-less indoor light energy harvester circuit block for internet-of-things wireless sensor node device design is implemented in 65nm CMOS process technology. The design of the indoor light energy harvester comprises a bootstrapped ring oscillator, a two-phase non-overlapping clock generator, a tapered buffer, a multi-stage differential-drive CMOS rectifier, a charge controlling circuit and a voltage regulator. The system boosts an input of 500 mV from a photovoltaic cell without using a typical boost converter circuit that employs an inductor element. Hence, a simplified on-chip design charges an external 1.3-V rechargeable battery. The use of a multi-stage differential-drive rectifier eliminates the need for expensive on-chip inductors. A charge control circuit is implemented to maintain the battery voltage and avoid overcharging, thus improving battery life. A low-dropout voltage regulator further regulates the battery voltage to produce a stable dc voltage. The chip core design has a total area of 1342µm×1011µm. The output of the harvesting system is a regulated 0.9 V supply with 1.05 mA current at full load.