“…The main issue for the battery-less energy harvesting system is the start-up period of the system, as the surrounding energy may not research over the past few years [2][3][4][5][6][7][8][9][10][11][12]. Several techniques have been reported to solve this issue, which can be divided into four categories: i.e., the mechanical method [2], the transformer-based method [3], the inductor-based method [4], and the fully integrated method [5][6][7][8][9][10][11][12]. Although the first three methods can realize an extremely low cold start voltage, usually below 50 mV, it is difficult to integrate the core devices with other circuits in one die.…”