| 摘要 |
PURPOSE:To obtain gradation with a suitable display in response to a level of a video signal by combining a video detection circuit, a level detecting circuit, a gain control circuit, a clamp circuit and an A/D converting circuit. CONSTITUTION:An output of the video detection circuit 1 is inputted to the gain control circuit 6 and the level detection circuit 7, which detects the head value of the video signal in one field and inputs a control signal in response to the value to the gain control circuit 6. The gain control circuit 6 compresses or expands the video signal by using the control signal inputted from the level detection circuit 7 so as to process the video signal as a suitable signal for the A/D conversion in one field. When the peak value of the input signal level is smaller than 100%, for example, the input/output characteristic of the gain control circuit 6 is set as shown in Fig. (a) and when the peak of the input signal level is close to 100%, the input/output characteristic of the gain control circuit 6 is set as shown in Fig. (b), and when the peak is an intermediate value as above, the input/output characteristic of the gain control circuit 6 is set to the linear (1:1) input/output characteristic.
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