5 May 2015 Modeling of CMOS image sensors for time-of-flight applications
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This contribution describes the modeling of CMOS image sensors employed in time-of-flight (ToF) sensor systems for 3D ranging applications. Our model relies on the theoretical description of photo-generation, charge transfer including diffusion, fringing field, and self-induced drift (SID). This method makes it possible to calculate the time-dependent charge carrier generation, transfer, and distribution. The employed approach allows elimination not only of irradiance-dependent charge transfer, but also of undesired reflectance effects, and the influence of ambient light through an in-pixel background measurement. Since the sensor is operated with very short integration times it is crucial to accomplish a fast transfer of the generated charge from the photodetector to the sense node, and speedy conversion into an electrical signal at its output. In our case, we employed a lateral drift field photodetector (LDPD), which is basically a pinned photodiode with a built-in drift field formed by a doping gradient. A novel pixel structure is presented which is optimized for a fast charge transfer by the appliance of the shown model. Numerical calculations predict a two times faster charge collection.
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Adrian Driewer, Bedrich J. Hosticka, Andreas Spickermann, Holger Vogt, "Modeling of CMOS image sensors for time-of-flight applications", Proc. SPIE 9506, Optical Sensors 2015, 950603 (5 May 2015); doi: 10.1117/12.2178390; https://doi.org/10.1117/12.2178390

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