A/D CONVERTER WITH CLAMP

PURPOSE:To prevent coloring in a part having no color and to eliminate fine adjustment of the clamp potential by deriving a difference of the reference clamp potential and the actual clamp potential by digital data at every one horizontal scanning period, and adding the digital data of the difference to output digital data of an A/D converter. CONSTITUTION:When a pulse (f) from a timing pulse generating circuit 8 is high, output digital data (e) from an A/D converter 9 is switched by a switching circuit 10 and outputted to a subtracter 13, and digital data from a reference clamp voltage data generating circuit 11 is outputted to an adder 12. The subtracter 13 subtracts the digital data and the digital data from the reference clamp voltage data generating circuit 11 in accordance with a pulse (h) and a clock (d) from the timing pulse generating circuit 8. The subtracted difference is averaged by an averaging circuit 14, and outputted to the adder 12. The adder 12 corrects an error and outputs it by adding a difference between the digital data obtained by bringing an input video signal to A/D conversion and the reference digital data.