本研究將光二極體作為光感測元件,並操作於光伏模式,其感測訊號為光電壓訊號。光伏模式下,光電壓與照度的關係在低光強度時呈線性響應,在高光強度時則轉為對數響應。此特性使光伏模式在弱光條件下能精確量測微弱光訊號;而在強光條件下能擴展可偵測的範圍,適合高動態範圍成像的應用。
　　然而,此特性也導致在同樣的輸出電壓差下,高光強度時所對應到的照度範圍比起低光強度時更廣,更難分辨出準確的照度,使其於高光強度時解析度下降。為解決此問題,本研究採用雙倍率分段放大的設計,將低照度與高照度隔開,並分別以不同倍率放大。分段放大的方式能針對電壓變化較小的高照度範圍使用更大的增益而不會迅速飽和至VDD,進而提高倍率上限,增加解析度。
　　根據量測結果,光伏模式的對數響應特性能將動態範圍擴展,經放大電路處理後,能觀察到明顯的分段增益功能,提高輸出電壓的分辨率。未來若針對光二極體的光電壓響應進一步優化後續訊號處理電路,可期望實現兼具高動態範圍與高解析度的影像感測器。

This study employs photodiodes as optical sensing elements operating in photovoltaic mode, with the sensed signal represented as photovoltage. In photovoltaic mode, the relationship between photovoltage and illuminance exhibits a linear response under low light intensity and transitions to a logarithmic response under high light intensity. This characteristic enables precise measurement of weak light signals in low light conditions, while expanding the detectable range under high light conditions, making it suitable for high dynamic range imaging applications.
However, this characteristic also results in a broader illuminance range corresponding to the same output voltage difference under high light intensity compared to low light intensity, reducing resolution in high light conditions. To address this issue, this study proposes a dual-gain segmented amplification design, separating low and high illuminance regions and applying different gain values to each. The segmented amplification approach targets small voltage variations in high light conditions with higher gain avoiding rapid saturation to VDD, thereby increasing the maximum gain and enhancing resolution.
Measurement results demonstrate that the logarithmic response of photovoltaic mode effectively expands the dynamic range. After signal
processing through the amplification circuit, the segmented gain functionality is clearly observed, significantly enhancing the resolution of the output voltage. With further optimization of the subsequent signal processing circuit based on the photodiode’s photovoltage response, the development of an image sensor combining high dynamic range and high resolution can be anticipated.

[1] S. Guissi, “CMOS Image Sensors (CIS): Past, Present & Future,” Semiconductor Engineering, https://semiengineering.com/cmos-image-sensors-cis-past-present-future/, Jun. 2017 (Accessed Oct. 2024).
[2] 雷良煥, 黃吉成, 徐永珍, “後來居上的 CMOS 影像感測器,” 物理雙月刊, 32 卷 1 期, pp. 24-29, 2010
[3] Sony Semiconductor Solutions Group, “Introducing a new standard of security cameras, our security image sensor provides a wider dynamic range and captures images of moving objects without blur or color tints,” Sony Semiconductor Solutions Group, https://www.sony-semicon.com/en/feature/2022012801.html, Jan. 2022 (Accessed Dec. 2024).
[4] R. Tejas, P. Macherla, N. Shylashree, “Image sensor—CCD and CMOS,” in: V. Nath, J.K. Mandal (Eds.), “Microelectronics, communication systems, machine learning and internet of things: select proceedings of MCMI 2020,” Springer, Berlin, Germany, pp. 455-484, 2022.
[5] 葉奕良, “光伏模式 CMOS 影像感測器之動態範圍擴展”, 國立清華大學, 電子工程研究所, 碩士論文, 中華民國一百一十年十一月
[6] Yu-Yang Tsai, Chun-Yu Kuo, Bo-Chang Li, Po-Wen Chiu, Klaus Y. J. Hsu, “A Graphene/Polycrystalline Silicon Photodiode and Its Integration in a Photodiode–Oxide–Semiconductor Field Effect Transistor”, Micromachines 2020, 11(6), 596, Jun. 2020.
[7] M. Sasaki, M. Mase, S. Kawahito, Y. Tadokoro, “A Wide Dynamic Range CMOS Image Sensor with Multiple Short-Time Exposures”, IEEE Sensors, vol. 2, pp. 967-972, Oct. 2004.
[8] San Juan Capistrano, “IQinVision Announces Full Array Of Wide Dynamic Range Cameras,” Varinsights, https://www.varinsights.com/doc/iqinvision-
announces-full-array-of-wide-dynamic-range-cameras-0001, Apr. 2013 (Accessed Oct. 2024).
[9] J. G. Rocha, G. Minas, S. Lanceros‐Méndez, “Pixel Readout Circuit for X-Ray Imagers”, IEEE Sensors Journal, vol. 10, no. 11, pp. 1740-1745, Nov. 2010.
[10] Y. Ni, Y. Zhu, and B. Arion, “A 768×576 Logarithmic Image Sensor with Photodiode in Solar Cell mode,” International Image Sensor Workshop, Hokkaido, Japan, Jun. 2011.
[11] Yuanyuan Shang, Weigong Zhang, Yong Guan, Xiaohui Tan, “Research on a Method to Extend Dynamic Range of CMOS APS”, IEEE International
Workshop on Imaging Systems and Techniques, pp. 212-216, Sep. 2008.
[12] Ko-Chi Kuo, “A Novel Linear-Logarithmic Active Pixel CMOS Image Sensor with Wide Dynamic Range”, IEEE International Midwest Symposium on Circuits and Systems, vol. 59, pp. 1100-1103, Aug. 2021.
[13] Monika Gangwar, Atul Kumar Nishad, “Design and Simulation of Modified Ultra Low Power CMOS Comparator for Sigma Delta Modulator”, ICICCS, pp. 1425-1427, Jun. 2018.
[14] Cheng-Hsiao Lai, Ya-Chin King, Shi-Yu Huang, “A 1.2-V 0.25-μm Clock Output Pixel Architecture with Wide Dynamic Range and Self-Offset Cancellation”, IEEE Sensors Journal, vol. 6, no. 2, pp. 398-405, Apr. 2006.
[15] 李律, “0.18μm 標準 SiGe BiCMOS 製程之高動態範圍影像感測電路設計", 國立清華大學, 電子工程研究所, 碩士論文, 中華民國一百零八年一月
[16] 蔡葳品, “應用於 0.18μm 標準 SiGe BiCMOS 製程之 Full HD 影像感測器陣列電路設計", 國立清華大學, 電子工程研究所, 碩士論文, 中華民國一百零三年七月
[17] Satoshi Yoshihara et al., “A 1/1.8-inch 6.4 MPixel 60 frames/s CMOS Image Sensor with Seamless Mode Change”, IEEE JSSC, vol. 41, no. 12, pp. 2998-3006, Dec. 2006.
[18] X. Ge and A. Theuwissen, “A CMOS Image Sensor with Nearly Unity-Gain Source Follower and Optimized Column Amplifier”, IEEE Sensors, pp. 1-3, 2016.
[19] Hayato Wakabayashi et al., “A 1/2.3-inch 10.3Mpixel 50frame/s Back-Illuminated CMOS Image Sensor”, ISSCC, pp. 410-411, Feb. 2010.
[20] 林祐玄, “標準 CMOS 製程下實現高響應度橫向光感測電晶體之研究”, 國立清華大學, 電子工程研究所, 碩士論文, 中華民國一百零六年十月