| 摘要 |
PURPOSE:To improve AFT operation, by giving priority to an AFT voltage among signals controlling a local oscillator circuit and controlling up and down of a local oscillator frequency through the presence of a synchronizing signal when no AFT voltage is used. CONSTITUTION:A signal from a tuner 1 is applied to a VIF circuit 2, detection circuit 3, synchronizing separation circuit 4 for normal TV reception. An AFT voltage is picked up from the circuit 2 through a frequency discrimination circuit 5 and applied to a discrimination circuit 6. A signal discriminating the presence of a synchronizing signal is picked up from the circuit 4 via a discriminating circuit 7 and applied to the circuit 6. Depending on the AFT voltage is above or below the specified value, the frequency is increased or decreased by the circuit 6, and if no AFT voltage is present, a signal increasing or decreasing the frequency through the presence of the synchronizing signal is formed. A signal from the circuit 6 is applied to a control circuit 8 for a PWM generating circuit. |
