| 摘要 |
PURPOSE:To increase the scanning speed of a reader by providing a dividing circuit with an operational amplifier, fixed negative feedback resistance, plural bit- weighted input resistors, and switch element which is turned on and off under the control of the output of a ditital memory, and speeding up the response of the dividing circuit. CONSTITUTION:Switches S0-S3 are connected to resistance R, 2R, 4R, and 8R of the dividing circuit 32 in parallel. The switches S0-S3 are made of, for example, FETs. When a light source 11 scans on a white reflecting plate 12, a storage designating STROBE input turned to ''1'' and the switches S0-S3 are all turned off, so the gain G of the dividing circuit 35 is G=31R/(R+2R+4R+ 8R+16R)=1. Namely, when the light source 11 scans on the white reflecting plate 12, an image signal applied from a DC reproducing circuit 31 to the dividing circuit 32 is outputted as it is and applied to a texture detector 33 and an A/D converter 34. The texture detector 33 holds the maximum level of the input, i.e. maximum value of the white level of reflection by the white reflecting plate 12 as a reference level REF and applied to the A/D converter 34.
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