一個應用於有機無機層感測元件上具有低雜訊之截波穩定型讀出電路

A Low Noise Readout IC with In-Pixel Chopper Stabilization for Organic Image Sensor

朱偉玓(Wei-Di Chu)

指導教授 ： 謝志成

國立清華大學/電機資訊學院/電機工程學系所/碩士(2018年)

摘要

本論文提出一個可應用於有機無機層感測元件(Organic Photoconductive Film)與需要穩定偏壓之感測元件的截波穩定型讀出電路，具有低雜訊(Low Noise)與高轉換增益(High Conversion Gain)的特性。
為了達到較好的雜訊表現，本論文所使用的電容反饋跨阻抗放大器(Capacitive Trans-Impedance Amplifier)配合像素內雙重關聯式取樣電路(In-Pixel Correlated Double Sampling)有效地消除了重置開關在重置完畢瞬間所取樣到的熱雜訊(Thermal Noise)以及電容反饋跨阻抗放大器的偏移電壓。而電路在長時間積分下所引進的閃爍雜訊(Flicker Noise)則是使用截波穩定技術(Chopper Stabilization Technique)，將低頻的閃爍雜訊移至選定的截波頻率(Chopper Frequency)，並且再配合後端的二階式雙斜率型類比數位轉換器(Two-Step Dual-Slope Analog to Digital Converter)對訊號做多重式取樣(Multiple Sampling)，取樣後的多筆資料最後再由一個截止頻率在截波頻率之下的數位低通濾波器(Digital Low-Pass Filter)做處理，進而壓抑被調變至高頻的閃爍雜訊。
此架構使用0.18微米1P6M互補式金氧半導體製程檔進行模擬，設計並擁有64×64像素陣列並搭載上述構想的讀出電路原型，操作在類比端及數位端3.3伏特之下。模擬結果為：在60張的每秒顯示幀數下，達到99.9%線性度，並且提高訊號雜訊比(SNR)從50.18dB至53.05dB。

關鍵字

低雜訊 ； 電容跨阻抗放大器 ； 截波穩定 ； 有機光導薄膜 ； 影像感測器

並列摘要

This thesis presents a low noise and high conversion gain readout IC with chopper stabilization technique for organic photoconductive film image sensor and a fixed biasing needed image sensor.
To achieve a nice noise performance, the proposed capacitive trans-impedance amplifier (CTIA) with in-pixel correlated double sampling (CDS) cancels the offset of CTIA and suppresses the reset phase thermal noise which is induced by reset switch and OP. On the other hand, chopper stabilization technique is also applied to modulate flicker noise to the chopping frequency for the purpose of separating low frequency noise with low frequency signal. After that, signals are readout with multiple sampling by column-wise two-step dual-slope analog to digital converters. Finally, digital low-pass filter (LPF), which cut-off frequency is designed to be much lower than chopping frequency, is used to process the collection of data of each pixel to filter out thermal noise and modulated flicker noise.
A prototype of 64×64 pixel imager employed these schemes has been designed and simulated in 0.18um 1P6M CMOS technology file with 3.3V supply voltage for both of analog and digital. The simulation results show that the proposed chopper stabilized CTIA ROIC achieves 99.9% linearity and improves SNR from 50.18dB to 53.05dB.

並列關鍵字

Low noise ； CTIA ； Chopper stabilization ； Organic photoconductive film ； Image sensor

參考文獻

[1] M. Mori et al., "Thin Organic Photoconductive Film Image Sensors with Extremely High Saturation of 8500 electrons um2," IEEE Symposium on VLSI Circuits, vol. IEEE Symposium on VLSI Circuits, pp. T22-T23, 2013.

[2] M. Ishii et al., "An Ultra-low Noise Photoconductive Film Image Sensor With a High-speed Column Feedback Amplifier Noise Canceller," IEEE Symposium on VLSI Circuits, pp. C8-C9, 2013.

[3] S. Shishido et al., "210ke-Saturation Signal 3μm-Pixel Variable-Sensitivity Global-Shutter Organic Photoconductive Image Sensor for Motion Capture," presented at the IEEE International Solid-State Circuits Conference (ISSCC), 2016.

[4] K. Nishimura et al., "An Over 120dB Simultaneous-Capture Wide-Dynamic-Range 1.6e- Ultra-Low-Reset-Noise Organic-Photoconductive-Film CMOS Image Sensor," presented at the IEEE International Solid-State Circuits Conference (ISSCC), 2016.

[5] K. Murari, R. Etienne-Cummings, N. V. Thakor, and G. Cauwenberghs, "A CMOS In-Pixel CTIA High-Sensitivity Fluorescence Imager," IEEE Transactions on Biomedical Circuits and Systems, vol. 5, no. 5, pp. 449-458, 2011.