In the paper, we discuss piezoelectric-vibration energy-harvesting flipping active-diode rectifiers, including the full bridge rectifier (FBR), the active diode rectifier, the switch only rectifier (SOR), and the flipping-capacitor rectifier (FCR). The energy harvesting circuits were implemented in 0.35-μm CMOS process. Compared to the transferred-power ability of the conventional FBR, the simulation improved factors of an active diode rectifier, SOR and FCR can reach up to 2x, 3.2x and 4.6x at an excitation frequency of 100 Hz, respectively.