| 摘要 |
PURPOSE:To obtain accurate color temperature information by providing a reference voltage generator to which one terminal of the 1st photodiode is connected and a reverse logarithmic compressing circuit composed of a differential amplifier to which the output of an amplifier and the voltage of the reference voltage generator are connected. CONSTITUTION:The cathode of the 1st PD(photodiode) 1G is connected to the cathodes of the 2nd PD 1R and the 3rd PD 1B, and corresponding filters of green, blue, and blue are arranged in front of the respective PDs 1G, 1R, and 1B. The anodes of the PD 1R and 1B are connected to the input terminals of the 1st and the 2nd amplifiers 9 and 11. Further, the anode of the PD 1G is connected to a reference voltage generating circuit 8 and this connection point is connected to one input terminal sides of reverse logarithmic compressing circuits 10 and 12. When two photodiodes are arranged one over another in the opposite directions, their difference voltage corresponds to a quantity by converting logarithmically light incident on the two PDs. A reference voltage Vref with a small temperature coefficient is generated by a band gap reference circuit and compressed logarithmically with temperature compensation to obtain accurate color temperature information.
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