| 摘要 |
PURPOSE:To suppress the change in time and position of a reading temperature to a mininum by analog/digital converting according to the quantity of light detecting means of an original illuminating light source. CONSTITUTION:An optical fiber 17 or the like is disposed on a side opposite to the non-original surface of the light source and a detected light is guided to a photodiode 16 as an optical sensor. The output current of the photodiode 16 is proportional to the detected quantity of light, converted to a voltage by an operation amplifier 15, and then level converted to a proper value as a reference value for an A/D conversion in a buffer amplifier 10. In such a way, since the reference value Ref of an A/D converter 9 is determined as the voltage proportional to the detected light of a lamp 3, a fluctuation in an analog picture signal Vin according to the fluctuation in the quantity of light of the lamp 3 can be canceled to correctly make an A/D conversion output proportional to an original reflectance. Thereby, the change in time and position of a reading density can be suppressed to a minimum.
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