A charge pump includes a first transistor, a second transistor, a first, a second and a third selectors. The first transistor includes a gate electrode, a first electrode, and a second electrode which serves as an output port of the charge pump. The second transistor includes a gate electrode, a first electrode and a second electrode, where the gate electrode of the first transistor is coupled to the gate electrode of the second transistor, and the gate electrode of the second transistor is coupled to the second electrode of the second transistor. The first selector is utilized for selectively connecting the first transistor to a first supply voltage. The second selector is utilized for selectively connecting the first transistor to a second supply voltage. The third selector is utilized for selectively connecting the second transistor to the second supply voltage.