| 摘要 |
PURPOSE:To eliminate the necessity of a selective transformer, by adding a video IF output signal to a high-pass filter, multiplying its output by a signal shifted by pi/2 in phase and a filter output, and using the multiplied output as a controlling voltage of local oscillation 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 circuit 3 is added to a high-pass filter 15 after it is amplified at an amplifier circuit 14, 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 filter 15 at a multiplier 17. The AFC controlling voltage output obtained at the multiplier 17 is fed back to a tuner 2 and the local oscillation frequency is controlled. |
