A capacitive fingerprint sensor which includes capacitive sensing units is disclosed. Each of the capacitive sensing unit includes a sensing electrode; a first switch; a voltage follower; and a reference capacitor. The voltage follower includes an adjustable current source, for providing at least two distinct current levels; and a MOS transistor. The MOS transistor includes a source node, connected to ground via the adjustable current source and serves as an output node of the voltage follower; a gate node, connected to the sensing electrode and serves as an input node of the voltage follower; a drain node, connected to a power source, for providing power to the voltage follower; and a bulk node, connected to the source node.