Patent ID: 8063688

Claim:
A clamp circuit for a video input comprising: a coupling capacitor having a first terminal receiving a video input an a second terminal; a differential amplifier having a first input terminal connected to said second terminal of said coupling capacitor, a second input terminal receiving a predetermined reference voltage and an output terminal generating a voltage signal proportional to a difference between a voltage on said first input terminal and a voltage on said second input terminal; a clamp transistor having a gate connected to said output terminal of said differential amplifier and a source-drain path having a first terminal connected to a power supply voltage and a second terminal; a resistive element having a first terminal connected to said second terminal of said source-drain path of said clamp transistor and a second terminal connected to said second terminal of said coupling capacitor; a first current sink having a first terminal connected to said second terminal of said coupling capacitor and a second terminal connected to ground, said current sink carrying a first predetermined current from said second terminal of said coupling capacitor to ground; a second current sink having a first terminal jointly connected to said second terminal of said source-drain path of said clamp transistor and to said first terminal of said resistive element, and a second terminal connected to ground, said second current sink carrying a second predetermined current from said second terminal of said source-drain path of said clamp transistor to ground; and a output terminal connected to said second terminal of said coupling capacitor.