| 摘要 |
PURPOSE:To prevent the deterioration of the picture quality, by controlling the reference voltage of an A-D converting circuit in accordance with the amplitude fluctuation of the horizontal synchronous signal of the video signal and avoiding an effect of fluctuation of the video signal to the data after a conversion. CONSTITUTION:The analog video signal is amplified up to the prescribed level by the video amplifying circuit 1 and then applied to the sample holding circuit 2 as an input. The circuit 2 receives a synchronous sampling pulse that is integer- fold of the horizontal synchronous signal in the video signal from the control circuit 3 and then samples the input video signal. This sampling signal is applied to the A-D converting circuit 5 as an input. The reference voltage of the circuit 5 is controlled so that it has a fluctuation following the fluctuation of the amplitude of the video signal, e.g., the fluctuation of the amplitude of the horizontal synchronous signal. The reference voltage of the circut 5 is made to follow the ampitude fluctuation of the input video signal, and accordingly the quantizing level obtained by dividing equally the reference voltage also has a fluctuation. Thus the digital value after an conversion receives no effect of the amplitude fluctuation of the video signal. |
