An Indoor Solar Energy Harvester with Ultra-Low-Power Reconfigurable Power-On-Reset-Styled Voltage Detector

An ultra-lower-power reconfigurable voltage detector for indoor solar energy harvester is presented. The voltage detector monitors the solar cell voltage and sends out a flag signal if the solar cell voltage surpasses the triggering threshold of the detector. Instead of using a traditional dynamic comparator, this design is based on a power-on-reset (POR) circuit. A POR circuit has ultra-low quiescent loss and a fixed triggering threshold, which is determined by its topology and process. Our improvement is to use a feedback loop that allows the triggering threshold to be reconfigurable. The average quiescent loss of this POR voltage detector circuit is 2.774nW. Process and temperature variations can also be compensated by the feedback loop. The energy harvesting system is designed with a 0.18 p,m CMOS process. Equipped with the proposed voltage detector, the whole system achieves a 93.21% peak efficiency at 200μW input power.