Patent ID: 7825990

Claim:
A video signal conversion device constructed to receive an analog signal of a video image formed as a sequence of frames of video lines of pixels, and to produce a digital signal representative of the video image, comprising: a clock with a selectable phase and a controllable frequency for controlling the sampling points of the analog signal; an analog-to-digital converter, coupled to the clock, for receiving the analog signal and converting it at sampling points controlled by the clock into the digital signal: a correction circuit that corrects the clock frequency using a period of a measure of the difference between successive frames taken in a columnar region of the video image, wherein the measure is a function that is dependent on columnar region location; a computation circuit to compute, for each phase in a sequence of selected phases for the clock, a second measure of the difference between successive frames of the video image, using the digital signal; and a verification circuit to verify the frequency of the clock using a characteristic of the second measure of the difference between successive frames, wherein the characteristic is the ratio of the maximum of the second measure over the sequence of selected phases to the minimum of the second measure over the sequence of selected phases.