A wide input voltage range start-up circuit for solar energy harvesting system

This paper presents design of an improved start-up circuit for a micro scale solar energy harvesting system. A wide input voltage range (270mV - 1.8V) start-up circuit that can work in strong as well as weak illumination levels without causing any stress and reliability issues to the CMOS devices has been proposed. The use of native device (zero-Vth) and ultra-low power Band-gap Reference (BGR) helps to operate the start-up circuit within 1.8V maximum voltage allowed by 40nm CMOS technology. The complete system works with minimum power of 2.841μW at 270mV in start-up mode and works with minimum voltage of 100mV once the system enters into main converter mode. The system uses fractional open circuit voltage method (FOCV) to extract maximum power from solar cell when operating in main converter mode.