| 摘要 |
PURPOSE:To attain AFT independently of pattern and electric field strength, by controlling a local oscillating frequency of a local oscillating circuit based on a detection signal of a video intermediate frequency output in a vertical blanking period. CONSTITUTION:A detected output of a frequency discriminating circuit 21 is not smoothed and applied to a level discriminating circuit 23 and to a counter 17 controlling the local oscillating frequency via the 1st and 2nd gates. The 1st and 2nd gates 30, 31 apply the output of the circuit 23 during the vertical synchronizing pulse period with a vertical synchronizing pulse obtained a synchronizing separation circuit 33 and a filter 34 after the video detection to a counter. Thus, since the signals are not smoothed and a voltage applied to the level discriminating circuit is high, the AFT locking range is widened and no effect is given on the pattern since the processing is done in the synchronizing period. |
