本論文提出了一個使用截波穩定技術(Chopper Stabilization Technique)的互補式金氧半導體飛時測距型深度影像感測器，具有偏移誤差(Offset)消除及閃爍雜訊(Flicker Noise)壓抑的能力。
為了解決飛時測距型深度影像感測器的像素(Pixel)內背景光飽和的問題，我們在考慮了像素內背景光消除的能力以及像素面積之後，選擇了一個使用感光二極體(photodiode)做極性轉換積分的架構。然而，此架構會有偏移誤差累加的問題，偏移誤差累加的量甚至比背景光的積分還要更嚴重，除此之外，還有閃爍雜訊累加的問題，會使距離量測的準確度大幅下降。因此，我們採用了截波穩定技術，考慮了P+/N-well接面的感光二極體與N-well/P-sub接面的寄生感光二極體之後，我們將截波穩定的頻率設定在調變頻率(Modulation Frequency)的二分之一，如此一來，不論是感光二極體或是寄生感光二極體所造成的偏移誤差的累加以及閃爍雜訊的累加都可以被消除。此外，為了達到更好的距離準確度，我們也提升了調變頻率。
此架構使用TSMC 0.18微米1P6M互補式金氧半導體標準製程檔進行模擬，設計並模擬驗證一個擁有64×64像素陣列的飛時測距型深度影像感測器原型，類比端的操作電壓為3.3伏特，數位端為1.8伏特。影像感測器的像素間距(Pixel Pitch)為22微米，填充因子(Fill Factor)為26%。模擬結果顯示，在距離範圍為0.45到2.1公尺達到99%線性度，並且可將1公尺下的準確度提升10倍。

This thesis presents a CMOS time-of-flight (TOF) depth image sensor with in-pixel offset cancellation and flicker noise suppression by adopting chopper stabilization technique.
To deal with in-pixel background light saturation issue in TOF depth image sensors, a TOF pixel with photodiode polarity switching integration technique is chosen for its great performance in in-pixel background light cancellation and relatively small pixel area by using only one integration capacitor. However, this TOF pixel structure suffers from offset accumulation even more critical than the original background light issue, and the low frequency flicker noise accumulation degrades the accuracy. Therefore, chopper stabilization technique is implemented. After taking both P+/N-well photodiode and N-well/P-sub parasitic photodiode into consideration, with chopper stabilization performed at half of the modulation frequency, both offset accumulation and low frequency flicker noise accumulation induced by photodiode and parasitic photodiode are eliminated. Moreover, for better accuracy performance, the modulation frequency is increased.
A prototype of 64×64 pixel array TOF depth image sensor has been designed and simulated in TSMC standard 0.18μm 1P6M CMOS technology with 3.3V supply voltage for analog and 1.8V for digital. The pixel pitch is 22μm with a fill-factor of 26%. The simulation results show that the proposed chopper stabilized TOF depth sensor achieves 99% linearity within a range of 0.45 to 2.1 meters, and the accuracy at 1 meter achieved a 10 times improvement.

ABSTRACT II
CONTENTS III
LIST OF FIGURES VII
LIST OF TABLES X
CHAPTER 1 INTRODUCTION 1
1.1 MOTIVATION 1
1.2 THESIS CONTRIBUTION 2
1.3 THESIS ORGANIZATION 3
CHAPTER 2 BACKGROUND INFORMATION 4
2.1 FUNDAMENTALS OF CMOS IMAGE SENSOR 4
2.1.1 Basic Terms of Image Sensor 4
2.1.1.1 Frame Rate 4
2.1.1.2 Array Size 5
2.1.1.3 Pixel Pitch 5
2.1.1.4 Fill Factor 5
2.1.1.5 Integration Time 5
2.1.2 Active Pixel Sensor (APS) 6
2.1.2.1 3T-APS 7
2.1.2.2 4T-APS 9
2.1.2.3 Readout Integrated Circuit (ROIC) 11
2.2 DEPTH IMAGING TECHNIQUES 13
2.2.1 Passive Triangulation 13
2.2.2 Active Triangulation 14
2.2.3 Time-of-Flight (TOF) 15
2.2.3.1 Direct Time-of-Flight 16
2.2.3.2 Indirect Time-of-Flight 17
2.2.4 Summary 20
2.3 DESIGN CONSIDERATION OF TOF SENSOR 21
2.3.1 Depth Accuracy 21
2.3.2 Background Light Interference 23
2.4 SUMMARY 24
CHAPTER 3 TOF DEPTH SENSOR WITH BACKGROUND LIGHT SUPPRESSION ……………………………………………………………………..25
3.1 BACKGROUND LIGHT SUPPRESSION TECHNIQUE IN INDIRECT TOF 25
3.1.1 Minimum-Charge Transfer (MCT) 26
3.1.2 Voltage-Mode Subtraction 27
3.1.3 Current-Domain Subtraction 28
3.1.4 Charge-Domain Subtraction 29
3.1.5 Summary 34
3.2 IN-PIXEL BACKGROUND LIGHT SUPPRESSION WITH OFFSET CANCELLATION AND FLICKER NOISE SUPPRESSION 35
3.2.1 Offset Accumulation Problem 36
3.2.2 Flicker Noise Accumulation Problem 37
3.2.3 Finite Gain Error Accumulation 37
3.2.4 Chopper Stabilization (CHS) 38
3.2.5 Summary 39
CHAPTER 4 PROTOTYPE IMPLEMENTATION OF TOF DEPTH IMAGE SENSOR……… 41
4.1 SYSTEM ARCHITECTURE OF TOF SENSOR 41
4.2 TOF PIXEL CIRCUIT 43
4.2.1 CTIA with Chopper 43
4.2.1.1 Chopping Frequency 45
4.3 MODULATION FREQUENCY 47
4.4 COLUMN READOUT CIRCUITS 48
4.5 CHIP OPERATION 49
4.6 SUMMARY 50
CHAPTER 5 SIMULATION RESULTS 51
5.1 CTIA OP-AMP 51
5.2 TOF PIXEL WITH CHOPPER 52
5.2.1 Accumulation cycle 52
5.2.2 Finite Gain Error Accumulation 54
5.2.3 Noise Simulation 57
5.2.4 Depth Simulation 59
5.3 POST-LAYOUT SIMULATION 60
5.3.1 Coupling Effect 61
5.3.2 Accuracy 64
5.4 SUMMARY 64
CHAPTER 6 CONCLUSION 66
6.1 SUMMARY 66
6.2 FUTURE WORK 67
BIBLIOGRAPHY 68

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