| 摘要 |
PURPOSE:To obtain the circuit mainly comprising a horizontal AFC and a horizontal oscillator used for a television receiver, by comparing both phases of an oscillation pulse and a horizontal synchronizing signal, detecting the difference and forming a prescribed output signal at the input of a non-video signal. CONSTITUTION:When a normal video signal exists, the phase of the horizontal oscilation pulse and the horizontal synthconizing signal is coincident, the horizontal AFC circuit section 2 is operated normally and the horizontal oscillation frequency is adjusted in the horizontal locking range, then a zoero voltage is outputted to an output terminal 17 of a phase detection circuit 16. Thus, a suitable capacitor circuit is provided, the peak value of the output pulse is held, then since no video signal exists, that is, when the horizontal synchronizing signal does not exist, a pulse in synchronizing with the horizontal oscillation pulse is outputted. When the horizontal synchronizing signal does not exist and only noise is inputted, since a pulse having noise is outputted to a itme axis of the horizontal oscillation pulse, a DC voltage is obtained, it is discriminated from the case at zero voltage and the presence of the video signal is discriminated. |
