| 摘要 |
PURPOSE:To eliminate the necessity of a selective transformer, by adding a video IF output signal to an amplifier circuit having a large gain at the high frequency area and multiplying its output and a signal shifted by pi/2 in phase, and using the result as a controlling signal of local oscillator frequency. CONSTITUTION:A PLL loop is composed of an oscillator 10, a pi/2 phase shifter 11, a multiplier 4 for synchronously detection of an in-phase axial video, an orthogonal axis detector 12, and a low-pass filter 13. An AFC circuit is constituted in such a way that the output signal of a VIF amplifier circuit 3 is added to an amplifier circuit 14, whose high frequency area has larger gains than the low frequency area has, and signals which are obtained by making phase shifting by pi/2 on the output signal at a condenser 16 are multiplied by the output signal of the amplifier circuit 14 at a multiplier 17. The AFC controlling voltage output obtained at the multiplier is fed back to a tuner 2 and the local oscillation frequency is controlled. |
