具動態範圍延展及雜訊抑制之超低電壓0.5伏特脈衝寬度調變互補式金氧半導體影像感測器

An Ultra-Low Voltage 0.5V PWM CMOS Imager with Dynamic Range Extension and Noise Suppression

鍾孟廷(Meng-Ting Chung)

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飄移消除(TVC)技術及可程式化電流控制閥值電壓(PCCT)技術之超低電壓0.5伏特脈衝寬度調變互補式金氧半導體影像感測器，使影像感測晶片可達到雜訊抑制和動態範圍延展的效果。一個64×40的影像感測器應用這些技術後，其量測結果顯示出擁有82dB動態範圍、0.055%rms固定模式雜訊(FPN)和0.65 LSBrms隨機雜訊，同時僅消耗147.3 pW/frame∙pixel於78.5幀率，使其成為了一個相當具高功率效率的高動態範圍影像感測器。此影像感測器實現了像素陣列及其周邊十位元以每條欄共用的斜波式類比數位轉換器，並使得像素間距為10μm達到25.4%填充因子，使用0.18μm互補式金氧半導體製程。
此論文貢獻了許多創新之處，此帶來的功效已概述如上。首先是提出一個創新具TVC技術的三電晶體畫素比較器在其兩次操作上給予不同的電流值。將畫素重置到曝光的電位差轉換為一個不與電晶體臨界電壓相關的脈衝寬度，並消除了由電晶體臨界電壓造成的變異和於低電壓操作下影像感測器的均勻性。第二為提出一個創新可調整的單端反相器架構比較器的閥值電壓方式，稱為PCCT技術。此技術簡單地實現低供應電壓下動態範圍延展技術於脈衝寬度調變應用。第三為一個用於像素上自動控制像素比較器運行之省電技術，避免了不必要的功率消耗當比較器完成了脈衝寬度轉換。總結，這些創新完成了具高功耗效率和高動態範圍的互補式金氧半導體影像感測器，適用於生醫環境如可攜式、值入式或者甚至拋棄式的醫療產品。

關鍵字

低電壓 ； 低功耗 ； 高動態範圍 ； 低雜訊 ； 影像感測器

並列摘要

This thesis describes an ultra-low voltage 0.5V PWM CMOS imager with threshold-variation-canceling (TVC) scheme and programmable current-controlled threshold (PCCT) scheme to achieve noise suppression and dynamic range extension. A prototype 64×40 pixel imager employed these schemes experimentally achieve 82dB dynamic range, 0.055%rms fixed-pattern-noise (FPN), and random noise of 0.65 LSBrms, while consuming 147.3 pW/frame∙pixel at 78.5 fps, making it one of the most power-efficient wide-dynamic-range imagers. The imager implements pixels and their associated 10b column parallel ramp ADCs, enabling a pixel pitch of 10μm with 25.4% fill factor in a 0.18μm CMOS process.
The innovations are contributed by this thesis, leading to the performance outlined above. First, a novel 3T in-pixel comparator with TVC scheme in two phase operations is biased in different current value. The difference of voltage from pixel reset and exposure transforms to a transistor threshold independent pulse width, eliminating the offset FPN from MOSFET threshold variation and improves the uniformity of imager at low voltage operation. Second, a novel adjusting method for giving the threshold of single-ended inverter-based comparator is proposed as PCCT scheme, which easily implements the dynamic-range-extension method of PWM with functional threshold of comparator with low supply voltage. Third, a power saving scheme used in pixel circuit for auto controlling the function of in-pixel comparator, avoiding the consumption of unnecessary power from completed comparator as pulse width occurred. Together, these innovations result in power-efficient wide-dynamic-range CMOS imager, which is suitable for using in biomedical environment as portable, implantable, or even disposable applications.

參考文獻

[1] J.N. Burghartz, T. Engelhardt, H.-G. Graf, C. Harendt, H. Richter, C. Scherjon, K. Warkentin, “CMOS Imager Technologies for Biomedical Applications,” in Proc. IEEE ISSCC Dig. Tech. Papers, pp.142-602, Feb. 2008

[2] H.-G. Graf, C. Harendt, T. Engelhardt, C. Scherjon, K. Warkentin, H. Richter, J.N. Burghartz, “High Dynamic Range CMOS Imager Technologies for Biomedical Applications,” IEEE J. Solid-State Circuits, vol.44, no.1, pp.281-289, Jan. 2009

[3] S.U. Ay, “A 1.32pW/frame•pixel 1.2V CMOS energy-harvesting and imaging (EHI) APS imager,” in Proc. IEEE ISSCC Dig. Tech. Papers, pp.116-118, Feb. 2011

[4] S.U. Ay, “A CMOS Energy Harvesting and Imaging (EHI) Active Pixel Sensor (APS) Imager for Retinal Prosthesis,” IEEE Trans. Biomedical Circuits and Systems, vol. 5, no. 6, pp. 535-545, Dec. 2011

[6] S. Hanson, F. ZhiYoong, D. Blaauw, D. Sylvester, “A 0.5 V Sub-Microwatt CMOS Image Sensor With Pulse-Width Modulation Read-Out,” IEEE J. Solid-State Circuits, vol.45, no.4, pp.759-767, Apr. 2010