| 摘要 |
PURPOSE:To exactly discriminate the frequency of nonmodulation carrier of a back porch part, by using a frequency discriminating circuit which has adopted a digital technique. CONSTITUTION:A horizontal synchronizing signal seprated from a composite color video signal triggers a monostable multivibrator 2 and 3 from an input terminal 1. A toggle flip-flop 7 is triggered at rise if an output the monostable multivibrator 2. An output of the toggle flip-flop 7 is obtained by an output terminla 11 as a line discriminating signal. An output of the monostable multivibrator 3 is provided to a preset terminal of a counter 5. An FM-changed color signal is applied to an input terminal 4 together with a nonmodulation carrier, and is supplied to a clock terminal of the counter 5. An output of the counter 5 is provided to a decoder 6, and its output is provided to an enable terminal of a counter 8. An output of the counter 8 resets the toggle flip-flop 7 through a decoder 9. |
