| 摘要 |
PURPOSE:To relax the restriction of a dynamic range due to an active filter by inserting the active filter giving a frequency characteristic to an input signal after a gain control amplifier in a loop of a gain control system. CONSTITUTION:After the gain of an input chrominance signal of a television receiver is adjusted by a gain control amplifier 2, the result is led to the post- stage through the active filter 1 providing the frequency characteristic. An output of the filter 1 is given also to a detection circuit 3 and the level detecting output of the circuit 3 is given to the amplifier 2 as a gain control signal through an LPF4. Since a signal passing through the filter 1 is limited to a prescribed amplitude by the amplifier 2, the dynamic range of the filter 1 is small enough to allow the filter 1 to be formed with a building block of an RC element and an active element. The change in the filter characteristic due to variation in constants of the components of the filter 1 is corrected by negative feedback.
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