| 摘要 |
PURPOSE:To improve the tracking of the AGC voltage by controlling the charge/ discharge of a 2nd capacitor efficiently when the AGC voltage across a 1st smoothing capacitor is fluctuated while a changeover switch is thrown to the position of a longer time constant at the input of a television signal subjected to scrambling. CONSTITUTION:The 2nd capacitor C2 is connected in parallel with the 1st smoothing capacitor C1 smoothing an output voltage of an AGC (automatic gain control) circuit 4 provided to an amplifier detection circuit 3 of the video signal through the use of a changeover switch 6 so as to switch two long/short time constants to the AGC circuit 4 and a charge pump circuit is connected to the 2nd capacitor C2. At the input of a television signal with scrambling, the switch 6 is thrown to the position of longer time constant, if the ACC voltage across the 1st smoothing capacitor C1 is fluctuated, the charge/discharge is controlled efficiently to the 2nd capacitor C2. Thus, the AGC tracking to the scramble signal is improved. |
