DIGITAL DECODER SYSTEM FOR COMPOSITE VIDEO SIGNAL

摘要

PURPOSE:To unnecessitate the conversion of sampling conversion and to prevent the deterioration of picture quality by holding the interchangeability of a horizontal effective picture element number while turning the frequency to 910 times that of the horizontal synchronizing frequency fH at the time of an NTSC and turning to 916 times that of the horizontal effective picture element number at the time of a PAL as a sampling clock. CONSTITUTION:A horizontal synchronization signal made by frequency-dividing the output of a voltage control oscillation circuit 5 by frequency dividers 6 and 7 and a signal with the identical frequency are inputted to a phase comparator 4. The sampling clock of 910fH or 916H can be obtained by the 1/2 frequency divider 6 when turning the oscillation frequency of the voltage control oscillation circuit 5 to 1820fH when the input is NTSC, and to 1832fH when the PAL. Thus, the conversion of the sampling frequency conventionally necessary is unnecessitated since the sampling frequency is common in both systems and turned to be the integral multiple of the horizontal synchronization frequency. Therefore, the deterioration of picture quality accompanied by the conversion of the sampling frequency can be eliminated.