| 摘要 |
PURPOSE:To eliminate DC fluctuation component and gain fluctuation component at the same time by sampling and holding a level of a part to be at a prescirbed level appearing at each horizontal synchronizing signal of a video format signal subject to FM detection at each period and controlling the FM detection sensitivity in response to the output. CONSTITUTION:A video format detected output by a multiplier 2 is inputted to a sample-and-hold circuit 3 and a level being a part of a pedestal level is sampled. This holding output is fed to an equalizer 5 via an inverter 4 and only its low frequency component is extracted. The low frequency component controls the current of a current source transistor Q2 of a multiplier 2 via an emitte follower circuit comprising a transistor Q1 and a resistor R2. The detecting sensitivity of an FM detector is controlled and a servo loop eliminating the pedestal level fluctuation at the detected output V is formed and the component of (1+dtE/ dt)<-1> at the detected output V is corrected automatically and both the DC fluctuation and gain fluctuation are corrected at the same time. |
