A clamping system for clamping a video signal, wherein the clamping system uses a charge-pump unit in company with a digital clamping controller to clamp the potential of the video signal, prior to the video signal being input to a programmable gain amplifier and an A/D converter, so as to reach a desired level. The charge-pump unit provides two charge-pump circuits, wherein one charge-pump circuit supplies a strong burst to boost the potential of the video signal while the video signal is below a threshold value. Otherwise, the other charge-pump circuit supplies a weak burst to fine tune the potential of the video signal when the video signal has reached the threshold value.