| 摘要 |
PURPOSE:To prevent an oscillation output of a video carrier from feedback to the input side of a VIF amplifier, by decreasing the gain of a video carrier oscillator for a synchronizing detection circuit when an RF input signal is small and the gain of the VIF amplifier circuit is large. CONSTITUTION:An RF input from an antenna is inputted to a multiplication circuit 5 via a tuner 1 and a VIF amplifier 2 and after it is multiplied and detected, the result is inputted to a video amplifier 6. An oscillator AGC voltage is formed at an oscilator AGC circuit 11 based on a VIF-AGC voltage generated depending on the amplitude of a video detection output at the video amplifier 6 and this is fed back to the oscillator 8, allowing to control the oscillation output of the oscillator 8 automatically, when the RF input is small. |
