Indoor energy harvesting using photovoltaic cell for battery recharging

The recent development in modern electronic indoor microsystems such as monitoring and remote sensing equipment, tiny volume radio transceivers and ultra-low power devices requires a reliable uninterruptible regulated power supply. Due to the limited energy capacity and performance inefficiency of common ultra-capacitors, demand for rechargeable batteries has grown increasingly. This paper presents an indoor energy harvesting system which employs a self-V_th-cancellation differential rectifier instead of dc to dc converter to minimize area and power consumption. The regulated output voltage recharges the battery and supplies voltage to the load. A 500 mV photovoltaic cell provides energy for the system while operating under a room lighting illumination of at least 2338 lux. The circuit occupies a chip area of 0.962×0.935 mm² and fabricated using 0.18μm 1P6M process with a power dissipation of 1.25 mW when delivering a load current of 395 μA at 1.3 V.