| 摘要 |
PURPOSE:To make a threshold value read from paper information constant regardless of the state of paper surface by controlling an input signal inputted from an image sensor to an amplifier circuit based on an output of an averaging circuit averaging the output of the amplifier circuit. CONSTITUTION:An output of an image sensor 1 is inputted to an amplifier 2 and an output of the amplifier 2 is inputted to a feedback section 3 and an A-D conversion section 4. The output of the amplifier 2 is averaged by the feedback section 2 and the amplifier 2 and the feedback section 3 constitute an automatic gain controller amplifier. Thus, the signal inputted to the A-D conversion section 4 is not a signal effected from the paper quality as the output of the image sensor 1 and converted into a signal having a prescribed peak value independently of the fetched information and the conversion level of the A-D conversion section 4 is made constant.
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