A voltage generator includes a first transistor, a second transistor, an operational amplifier, a capacitor, a third transistor, a fourth transistor and a first resistor. The operational amplifier includes a first terminal coupled to a second terminal of the first transistor, and a second terminal coupled to a second terminal of the second transistor. The capacitor is coupled between an output terminal of the operational amplifier and a ground terminal. The third transistor is coupled to the first transistor and the output terminal of the operational amplifier. The fourth transistor is coupled to the second transistor, the output terminal of the operational amplifier and the ground terminal. The first resistor is utilized for generating a complementary to absolute temperature voltage according to a voltage difference between a gate-source voltage of the third transistor and a gate-source voltage of the fourth transistor.