| 摘要 |
PROBLEM TO BE SOLVED: To provide a photocurrent/voltage conversion circuit improved in the light input range of a light detection element. SOLUTION: The photocurrent generated by the input of light to a photodiode 3 is converted to voltage by the feedback resistor 5 connected across the input and output of an amplifier 304 formed by the DC connection of a plurality of amplifying stages comprising Nch type MOS transistors 11, 13 and 15 of source earthing and constant current sources 12, 14 and 16, and the converted voltage is compared with reference potential Vref by a comparator 6 to output a binary signal. In this light detection IC, the amplifier 304 has a constant current source 41 provided to the input thereof and an Nch type MOS transistor 41 short-circuited between a gate and a drain is provided between the gate and source of the MOS transistor 11. When the light input of the photodiode 3 becomes excessive, a part of the photocurrent Ipd is supplied by the current from a constant current source 42 to prevent the cutting-off of the MOS transistors 11 and 15.
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