Indoor light energy harvesting system for battery recharging and wireless sensor networks implemented in 90nm CMOS technology

This paper presents an indoor photovoltaic energy harvesting system which utilizes a 500mV single unit solar cell operating under room lighting illumination. This voltage supplies the input stage of the whole system including the bootstrapped ring oscillator and self-Vth-cancellation differential rectifier, whose output frequency is 27MHz, which in turn generates the supply for the low-dropout regulator (LDO) and the charging circuit of the rechargeable NiMH battery of the output stage. The regulated output voltage from the LDO is equal to 1V with load current ranging from 50μA to 300μA which is suitable for wireless sensor networks application. The whole system is implemented using 90nm CMOS technology to minimize power consumption and extend battery life by utilizing low-threshold voltage transistors which results to a more efficient design architecture.