The output features of pixels in CMOS image sensors (CISs) are influenced by different exposure conditions. This article presents an analytical model to describe the output characteristics of the exposure process in pinned photodiode (PPD) CMOS image sensors with the accumulation of three charge sources: photogenerated charge, p-n junction-generated charge, and emission charge. In the proposed model, the difference between the time-based and light intensity-based photo response process is illustrated. The model also reveals the relationship between photodiode potential and light intensity at different exposure values. At the low exposure values, the PD potential increases with light intensity, and a contrary trend is observed at the high exposure values. This concludes that a larger linear output range can be obtained in high light intensity conditions. Furthermore, the improved model provides development analysis in terms of light intensity influence for long exposure time noise. The models were verified with technology computer-aided design simulation and the test devices were fabricated using a 0.18- ${\mu }\text{m}$ CIS process. The model demonstrates good consistency with simulation and measured results.

中文翻译：

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固定光电二极管 CMOS 图像传感器中曝光过程的分析建模

CMOS 图像传感器 (CIS) 中像素的输出特征受不同曝光条件的影响。本文提出了一个分析模型来描述钉扎光电二极管 (PPD) CMOS 图像传感器中曝光过程的输出特性，该传感器具有三个电荷源的积累：光生电荷、pn 结生成的电荷和发射电荷。在所提出的模型中，说明了基于时间和基于光强度的光响应过程之间的差异。该模型还揭示了不同曝光值下光电二极管电位与光强度之间的关系。在低曝光值下，PD 电位随着光强度的增加而增加，而在高曝光值下观察到相反的趋势。这得出结论，在高光强度条件下可以获得更大的线性输出范围。此外，改进的模型提供了长曝光时间噪声的光强度影响方面的发展分析。这些模型通过技术计算机辅助设计模拟进行了验证，并且使用 0.18-${\mu}\text{m}$ CIS 工艺制造了测试设备。该模型与仿真和实测结果具有良好的一致性。