This paper proposes a method to take advantage of the configurable capacitor array to cope with the input voltage instability caused by changes in ambient energy input variation. The proposed energy harvesting circuit can extend its input voltage to a much wider range in theory. Moreover, with our proposed adaptive conversion ratio technique, the input voltage range is not limited by the boundary of set-up or step-down conversion when implemented only one style, but not both. According to the measurement results, this design achieves about 70% in overall end-to-peak efficiency while start-up voltage is around 750mV. With adaptive conversion ratio control, the proposed circuit can maintain its conversion efficiency over 40% for the input voltage range from 300mV to 1.2V.