嚴重的眼疾每年奪走許多人的視力。在台灣，視網膜相關疾病的比率更是高居東亞之冠。以人工視網膜治療黃斑病變(AMD)以及視網膜退化病變(RP)的技術在近年來大有斬獲。人工視網膜以取代視網膜中受損細胞功能的方式治療黃斑病變以及視網膜退化病變，希望能藉此恢復受損視網膜病人的視力。
　　由於雙相波的特性使其適於使用於電荷平衡刺激，雙相波經常被使用在神經義體裝置中。電荷平衡刺激是刺激神經時的一大挑戰，不平衡的刺激可能會造成刺激電極水解，更甚者可能造成神經的二度傷害。本篇論文提出了一個使用電極接地、自我校準電路、脈波寬度調整的方式來達成電荷平衡刺激之雙相神經刺激器。本篇論文提出的雙相神經刺激器可以依照照射光強度以及控制訊號輸出穩定的、陽極優先或陰極優先的0~50微安培刺激電。流在每個刺激週期結束後，與總輸出電荷相比，若以最大照射光強度照射，剩餘電荷將小於1.20%；而以一般照射光強度照射，剩餘電荷將小於0.31%。整體功耗為5.17毫瓦特，屬於安全範圍內的每平方公釐1毫瓦特。
　　每個雙相神經刺激器會與周圍的八個像素共用。共用像素的數量、陽極優先刺激或陰極優先刺激、陽極相、陰極相以及相間間隔的時間長度皆為可以調整。

Severe eye diseases take away many subjects’ vision every year. Taiwan has the highest percentage of people with related disease in Eastern Asia. Treatments by retina prosthesis for Age-related macular degeneration (AMD) and retinitis pigmentosa (RP) have achieved great progress in recent years. Retinal prosthesis is used to replace the function of the damaged cells as treatment for AMD and RP in effort to restore the vision of the subjects.
Biphasic electrical signal is widely used in neural prosthetic devices. The characteristic of biphasic wave is ideal to achieve charge neutral stimulation, which is a major challenge in neural stimulation. In neural stimulation, unbalanced stimulation can cause electrolysis on electrode and cause harm to the neurons. In this thesis, we present a biphasic stimulation driver using shorting to ground, self-calibration technique, and pulse width control to achieve charge neutral stimulation. It is also capable of delivering stable stimulation current in the range of 0~50uA in either anodic-first or cathodic-first biphasic case. The peak stimulation current is proportional to illumination intensity. Residual charge under maximum illumination intensity is less than 1.20% of the net output charge. In typical cases, residual charge is less than 0.31% of the net output charge. Total power under maximum illumination is 5.17mW, which is less than the safety limit of 1mW/mm2.
One biphasic stimulation driver is shared by eight neighboring pixels to save area. In addition, the number of shared pixels, the pulse width of the anodic phase, cathodic phase, and the inter-phase delay can all be easily modified, together with the selection of anodic- or cathodic-first stimulation.

摘要 ii
Abstract iii
誌謝 v
Table of Contents vii
List of Figures x
List of Tables xiv
Chapter 1 Introduction 1
1.1 Background 1
1.2 Motivation 3
1.3 Organization 4
Chapter 2 Retina stimulation system 5
2.1 Related works 5
2.1.1 Pulse-frequency modulator 6
2.1.2 Frequency-voltage converter 6
2.1.3 Biphasic stimulation driver 7
2.2 Proposed retina stimulation system and biphasic stimulation driver 7
2.3 Design targets 8
2.3.1 High resolution 8
2.3.2 Charge neutral stimulation 9
2.3.3 Signal fidelity 12
2.3.4 Low power consumption 13
2.3.5 Anodic-first and Cathodic-first switching 13
Chapter 3 Biphasic stimulation driver 15
3.1 Simulation environment 15
3.2 Circuit operation 15
3.3 Current generator 27
3.3.1 High linearity voltage controlled current source 27
3.3.2 High output impedance current mirror 35
3.4 Self-calibration circuit 42
3.5 Comparator 51
3.6 MUX/DEMUX 57
3.7 Variation on simulation sites 63
3.8 Power consumption 67
Chapter 4 Layout and pixel arrangement 68
4.1 Layout 68
4.1.1 One pixel without biphasic stimulation driver 68
4.1.2 Eight pixels 69
4.1.3 Biphasic stimulation driver 70
4.1.3.1 8-to-1 MUX 70
4.1.3.2 High linearity voltage controlled current source 70
4.1.3.3 Self-calibration circuit 71
4.1.3.4 High output impedance current mirror 72
4.1.3.5 1-to-8 DEMUX 73
4.2 Pixel arrangement 75
4.3 Stimulation order 76
Chapter 5 Conclusion and future works 77
5.1 Conclusion 77
5.2 Future works 80
References 81

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