アクティブ・パッシブ方式画素読出しの併用によるCMOSイメージセンサのダイナミックレンジ拡大手法の提案と原理実証

概要

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We propose a dynamic range extension method for CMOS imagers with an in-pixel lateral overflow structure, in which one of active and passive readout schemes is selected at each pixel on the basis of the illumination. For a high illumination, the charges stored in both photodiode and area-effective MOS capacitor as an overflow capacitor in a pixel are read with high linearity by a charge amplifier at each column to extend the range of the readable voltage. The column circuit area is suppressed and row-wise pixels are accessed by sharing the pixel control signals and the column amplifier between two readout modes. We also describe an image reproduction scheme that makes use of electric calibration from a pixel-wise mixed-mode image. The signal-to-noise ratio of the scheme is discussed. Preliminary experiments with a 128 x96-pixel prototype imager fabricated in 0.35μm CMOS technology showed an extension of the dynamic range of 18.5 dB (72.8 dB in total) and offline wide-dynamic-range image reproduction. Optimizing of the capacitances in the pixels and the column amplifier and reducing the amount of noise in the column amplifiers will provide a total dynamic range of around 120dB.
社団法人映像情報メディア学会の論文
2009-04-01