| 摘要 |
PURPOSE:To receive and detect a TV signal excellently without requiring any flyback pulse, by applying the output of a window comparator and that of a voltage-controlled oscillating circuit to a logical circuit for AND operation. CONSTITUTION:The TV signal received by an antenna 1 is passed through a tuner circuit 2 and a signal processing circuit 3 to apply a video IF signal to an automatic frequency tuning circuit AFT5, which outputs a voltage VAFT. A horizontal synchronizing signal VfH obtained by a synchronous separating circuit 4, on the other hand, is supplied to the AND circuit 11 of the logical circuit 10 and a phase comparator 7 and the result is supplied to the voltage-controlled oscillator 9 through an LPF8. When the period of its output voltage is within the lead-in range of the oscillator 8, the output of the oscillator is applied to the circuit 11. When not, the output of AND between the output of the window comparator 14 of the logical circuit 15 and that of the oscillator is not received and the circuit 2 is controlled through a control circuit 16 to intercept a noise appearing in an audio signal. |
