A/D CONVERSION CIRCUIT FOR VIDEO SIGNAL

摘要

PURPOSE:To execute sampling at a sampling point having fixed relation with the phase of a color subcarrier by detecting a sampling phase error for an object phase and controlling the phase of a sampling clock in accordance with the detected error. CONSTITUTION:An input analog color video signal is digitized by an A/D converter 2. A sampling clock formed by a clock generating circuit 3 and phase- controlled by a phase shifting circuit 4 is supplied to the A/D converter 2. The digital color video signal digitized by the A/D converter 2 is supplied to a phase difference detecting/deciding circuit 7 to detect a phase error between an objective sampling phase and a practical sampling phase. The shift value of the circuit 4 is controlled in accordance with the phase error. When a sampling point to be controlled does not exist within a range controlled by the circuit 4, the sampling point is changed.