A 640×512 CMOS Image Sensor with Ultra Wide Dynamic Range Floating-Point Pixel-Level ADC
A 640×512 CMOS Image Sensor with Ultra Wide Dynamic Range Floating-Point Pixel-Level ADC
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DOI：
10.1109/isscc.1999.759263
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发表时间：
1999-02
期刊：
影响因子：
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通讯作者：
David X. D. Yang;A. Gamal;B. Fowler;H. Tian
中科院分区：
文献类型：
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作者：
David X. D. Yang;A. Gamal;B. Fowler;H. Tian
分析结果表明，与使用其他图像传感器动态范围增强方案（例如井容量调整）相比，多次采样可以在相同或更高的动态范围下始终获得更高的信噪比。然而，实现多重采样需要比使用典型 CMOS 有源像素传感器 (APS) 更高的读出速度。本文证明，使用每 4 个像素具有 8 位串行奈奎斯特速率模数转换器 (ADC) 的 640 512 CMOS 图像传感器，像素级 ADC 能够高度灵活且高效地实施多重采样，以增强动态范围。由于像素值始终可供 ADC 使用，因此可以自由选择样本的数量和时序以及从每个样本获得的位数，并以快速 SRAM 速度读出。通过以指数增加的曝光时间进行采样，可以获得具有二进制浮点分辨率的像素值。 640 512 传感器采用 0.35 m CMOS 技术实现，在 29% 填充因子下实现 10.5 × 10.5 m 像素尺寸。介绍了表征技术和测量的量子效率、灵敏度、ADC 传输曲线和固定模式噪声。对测量的动态范围超过 10 000 : 1 的场景进行九次采样，以获得动态范围为 65 536 : 1 的图像。提出了使用多次采样可实现的动态范围的限制。
Analysis results demonstrate that multiple sampling can achieve consistently higher signal-to-noise ratio at equal or higher dynamic range than using other image sensor dynamic range enhancement schemes such as well capacity adjusting. Implementing multiple sampling, however, requires much higher readout speeds than can be achieved using typical CMOS active pixel sensor (APS). This paper demonstrates, using a 640 512 CMOS image sensor with 8-b bit-serial Nyquist rate analog-to- digital converter (ADC) per 4 pixels, that pixel-level ADC enables a highly flexible and efficient implementation of multiple sam- pling to enhance dynamic range. Since pixel values are available to the ADC's at all times, the number and timing of the samples as well as the number of bits obtained from each sample can be freely selected and read out at fast SRAM speeds. By sampling at exponentially increasing exposure times, pixel values with binary floating-point resolution can be obtained. The 640 512 sensor is implemented in 0.35- m CMOS technology and achieves 10.5 10.5 m pixel size at 29% fill factor. Characterization techniques and measured quantum efficiency, sensitivity, ADC transfer curve, and fixed-pattern noise are presented. A scene with measured dynamic range exceeding 10 000 : 1 is sampled nine times to obtain an image with dynamic range of 65 536 : 1. Limits on achievable dynamic range using multiple sampling are presented.