| 摘要 |
PURPOSE:To discriminate on whether a vertical synchronizing signal appears at the large or small timing of a decision limit and to discriminate automatically the NTSC and PAL systems by setting the decision limit of a horizontal scanning line to points which is distant from any scanning period position in equal proportion. CONSTITUTION:The output side of a clock signal generating circuit 1 is connected to a counter 2, and an output side of the counter 2 and the output side of a vertical synchronizing signal generating circuit 3 are connected to a gate circuit 4. The output of an OR gate 10 which inputs another output of the circuit 3 and the output of the counter 2 is connected to the reset terminal of the counter 2, and a memory 7 is connected to the output side of the circuit 4. When a decision on the composite video signal of the NTSC or PAL system which differ in the number of horizontal scanning lines is made, the decision limit of the number of horizontal scanning lines is set distantly from any horizontal scanning period in equal proportion. Then, whether a vertical synchronizing signal appears at the large or small timing of the decision limit is discriminated to discriminate automatically between the NTSC and PAL system. |
