一個具有臨界電壓消除技術及可調變轉換曲線之高動態範圍線性對數互補式金氧半導體影像感測器

A High Dynamic Range Linear-Logarithmic CMOS Image Sensor with Threshold Voltage Cancellation Scheme and Tunable Response Curve

周韋帆(Wei-Fan Chou)

指導教授 ： 謝志成

國立清華大學/電機資訊學院/電機工程學系/碩士(2012年)

摘要

本論文描述了一個應用臨界電壓消除技術以降低固定圖像雜訊及可調變轉換曲線之高動態範圍線性對數互補式金氧半導體影像感測器。此論文貢獻了許多創新之處，首先是提出了一個不需要任何的外部影像處理的五電晶體畫素線性對數互補式金氧半導體影像感測器，其感測器可藉由調整不同線性對數轉換點來改變線性範圍，因此在不同的影像環境皆能獲得最佳的影像對比度。第二為提出一個具有三個操作時序並內嵌於畫素的臨界電壓消除技術，用來消除在強光源環境的對數模式下因電晶體臨界電壓漂移所造成的固定圖像雜訊，藉此改善影像的均勻度。第三為提出一個具有可程式化的增益之欄共用式運算放大器，用於解決在傳統主動式畫素感測器中因源級跟隨器所造成的增益耗損。
此操作電壓為3.3伏特之高動態範圍線性對數互補式金氧半導體影像感測器晶片使用n+/p-sub 感光二極體的100 x 100畫素陣列，每畫素包含五個電晶體，其畫素大小為6 x 6 um2，填充因子為32.54%，並以TSMC 0.18μm CMOS 1P6M 標準製程製作。本影像感測器晶片的量測結果於50幀率下其動態範圍為143.89dB，在對數模式下的固定圖像雜訊相較於對數感光度下為1.96% (rms/log-sensitivity)，相較於線性感光度下為0.45% (rms/Vlog-swing)，線性感光度為651mV/lux-s，對數感光度為55mV/decade，時間雜訊及功率消耗分別為0.7462mV及1.88mW。

關鍵字

互補式金氧半導體影像感測器 ； 線性對數反應 ； 高動態範圍 ； 固定圖像雜訊

並列摘要

This thesis presents a high dynamic range linear-logarithmic CMOS image sensor pixel with threshold voltage cancellation scheme for reducing fix pattern noise (FPN) and tunable response curve for different environment. There are three innovations in this thesis. First, a novel five transistors pixel linear-logarithmic CMOS image sensor with adjustable linear region provides a tunable switching point between linear and logarithmic response without any post-processing to obtain the best image contrast in different environment. Second, A novel in-pixel threshold voltage cancellation scheme in three phases operation can eliminate the offset FPN from MOSFET’s threshold variation due to logarithmic mode operation at high illumination environment and improve the non-uniformity of the image efficiently. Third, a column shared-OPAMP with column amplifier is used in column circuit for solving the gain loss problem caused by source follower in convention active pixel sensor and providing a programmable gain to magnify pixel signal.
The prototype high dynamic linear-logarithmic CMOS image sensor chip consisting of 100 x 100 5-T pixel array with n+/p-sub photodiode and pixel pitch as 6 x 6 μm2 with 32.54% fill factor and 3.3V operation has been designed and fabricated in TSMC 0.18μm CMOS 1P6M standard process. The measured results achieve a dynamic range of 143.89dB, a FPN related to sensitivity in logarithmic response (rms/log-sensitivity) of 1.96%, and a FPN related to full-swing in logarithmic response (rms/Vlog-swing) of 0.45%, respectively. Linear and logarithmic sensitivity are 651mV/lux-s and 55mV per decade of illuminance 50 frames/s. The temporal noise and power consumption are 0.7462mV and 1.88mW.

並列關鍵字

CMOS image sensor ； linear-logarithmic response ； high dynamic range ； fixed pattern noise

參考文獻

[1] W. F. Chou, S. F. Yeh, and C. C. Hsieh, “A 143dB 1.96% FPN Linear-Logarithmic CMOS Image Sensor with Threshold-Voltage Cancellation and Tunable Linear Range,” in Proc. ICSENS, Oct. 2012.

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