Photovoltaic energy harvesting is an attractive method of developing battery-free systems for wireless sensors, biomedicai electronics, and the internet of things (IoT). To obtain an energy-efficient system, low-power digital circuits operating in the near/sub-threshold region are widely used in such applications. Therefore, the design of a low-voltage buck converter, which converts the harvested energy to the regulated output is critical. Sub-1V buck converters have been implemented using a large inductor  to operate in a continuous conduction mode (CCM). Both CCM and discontinuous conduction mode (DCM) operation has been demonstrated in , using an analog zero current detection (ZCD) technique to extend the available output power range. However, the analog circuit limits the minimum output power to 50μW, and reduces the conversion efficiency under light load conditions.