AMOLED 패널 측정 시스템을 위한 소면적 고해상도 범용 데이터 드라이버 IC : A Small-Area and High-Resolution Universal Data Driver IC for AMOLED Panel Test Systems

다국어 초록 (Multilingual Abstract)

Active-matrix organic light emitting diode (AMOLED) displays have been highlighted as alternatives to liquid crystal displays (LCDs) due to their outstanding performance including high contrast ratio, fast response time, wide viewing angle, and high color reproducibility. Moreover, since AMOLED displays do not require a backlight unit, they can be manufactured in a light and thin form factor, thereby being widely employed in multimedia products. However, the non-uniform electrical characteristics of thin-film transistors (TFTs) and OLED degradation, which deteriorate image quality, prevent AMOLED displays from dominating the display market.
To solve these issues, various external compensation systems have been studied. To implement an accurate external compensation system, its driving and sensing ranges should be properly determined according to the initial variations in the electrical characteristics of the TFTs and OLEDs of the target panel. Therefore, a panel test system that can accurately measure the initial variations in electrical characteristics is necessary for testing prior to assembling the external compensation system with the panel. However, since conventional panel test systems have been developed only for panels with specific backplane structures, they cannot be used for panels with various backplane structures and should be redeveloped whenever a new AMOLED panel with a different backplane structure is made. This leads to an increase in the research-and-development cost and the turn-around time for developing AMOLED displays. Therefore, this dissertation proposes a panel test system including small-area and high-resolution data driver ICs, a general purpose architecture for various backplane structures, and a fast and accurate measurement method to achieve high-image quality and low-development cost of AMOLED displays.
First, an area-efficient and high-resolution resistor-string digital-to-analog converter (R-DAC) with a reverse ordering scheme is proposed. The proposed R-DAC is designed in a two-stage DAC along with a DAC-embedded amplifier. The proposed reverse ordering scheme decreases the area of the proposed R-DAC, which occupies most of the area of the data driver IC. To verify the proposed reverse ordering scheme, a 640-channel data driver IC with a 12-bit two-stage DAC was fabricated using a 0.18-μm CMOS process with 1.8 V and 18 V devices. The fabricated 12-bit two-stage DAC consists of a 10-bit R-DAC with the reverse ordering scheme and a 2-bit DAC-embedded amplifier. The proposed 10-bit R-DAC occupies only 50.1% of the area of the conventional 10-bit R-DAC. Measurement results show that the differential nonlinearity and integral nonlinearity are +0.25/-0.26 LSB and +0.54/-0.42 LSB, respectively. The measured inter-channel and inter-chip deviation of voltage outputs are 2.40 mV and 7.42 mV, respectively.
Second, a small-area and low-power data driver IC using a two-stage DAC with a capacitor array is proposed. The proposed data driver IC employs a capacitor array in the two-stage DAC so as to both decrease the DAC area and eliminate the need for the resistor-string, which has high power consumption. To verify the proposed two-stage DAC, a 20-channel data driver IC with the proposed 10-bit two-stage DAC was fabricated using a 0.18-μm CMOS process with 1.8 V and 6 V CMOS devices. The proposed 10-bit two-stage DAC occupies only 43.8% of the area of a conventional 10-bit two-stage DAC. Measurement results show that the differential nonlinearity and integral nonlinearity are +0.58/-0.52 LSB and +0.62/-0.59 LSB, respectively. The measured inter-channel deviation of the voltage outputs is 8.8 mV, and the measured power consumption of the 20-channel data driver IC decreases to 7.1 mW, which is less than half of the power consumed by the conventional one.
Finally, a test system for AMOLED panels with various backplane structures with external compensation method is proposed. The proposed AMOLED panel test system employs universal data drive ICs to measure the current of a driving TFT and the anode voltage of the OLED in various backplanes by only programming the field-programmable gate array in the proposed test system. The universal data driver IC is fabricated and implemented in the proposed AMOLED panel test system whose test board is assembled with a 55-inch full high-definition AMOLED panel. A fabricated universal data driver IC includes 640 data channels with a 12-bit linear gamma DAC and 12-bit variable current sources. To evaluate the repeatability error of the proposed panel test system, the driving TFT current is repeatedly measured and the measured maximum repeatability error is 9.8 nA. Moreover, to evaluate the measurement accuracy of the proposed panel test system, the variation in the currents of the driving TFTs are measured and compensated for, and its maximum value after compensation is measured to be 26 nA.

목차 (Table of Contents)

• 국문요지 i
• Abstract iii
• Acknowledgements vi
• Table of Contents viii
• List of Figures x
• List of Tables xiii
• Chapter 1 Introduction 1
• 1.1 OVERVIEW OF AMOLED DISPLAYS 1
• 1.2 BACKGROUND 3
• 1.2.1 Technical Issues of TFT and OLED 3
• 1.2.2 Internal Compensation Methods 6
• 1.2.3 External Compensation Methods 11
• 1.3 REQUIREMENTS FOR AMOLED PANEL TEST SYSTEM 12
• 1.3.1 High-Resolution and Small-Area Data Driver IC 13
• 1.3.2 General Purpose Architecture for Various Backplane Structures 15
• 1.3.3 Fast and Accurate Measurement Method 15
• 1.4 RESEARCH OBJECTIVES 16
• 1.5 ORGANIZATION 17
• Chapter 2 High-Resolution and Small-Area Data Driver IC with Resistor-String Two-Stage DAC Using Reverse Ordering Scheme 18
• 2.1 INTRODUCTION 18
• 2.2 ARCHITECTURE AND OPERATING PRINCIPLE OF TWO-STAGE DAC WITH REVERSE ORDERING SCHEME 20
• 2.2.1 R-DAC with Reverse Ordering Scheme 20
• 2.2.2 Optimized Design for Area-Efficient Decoders 23
• 2.2.3 Level Shifter with Inverter Stage 25
• 2.3 DAC-EMBEDDED AMPLIFIER WITH CHOPPING SCHEME 27
• 2.4 EXPERIMENTAL RESULTS 29
• 2.5 SUMMARY 34
• Chapter 3 Small-Area and Low-Power Data Driver IC with Two-Stage DAC Using Capacitor Array 35
• 3.1 INTRODUCTION 35
• 3.2 ARCHITECTURE OF TWO-STAGE DAC WITH CAPACITOR ARRAY 37
• 3.3 CAPACITOR ARRAY 39
• 3.3.1 Operation Principle and Conversion Error 39
• 3.3.2 Power Consumption Analysis between Conventional and Proposed Two-Stage DACs 41
• 3.4 IMPLEMENTATION OF DATA DRIVER IC 44
• 3.5 EXPERIMENTAL RESULTS 47
• 3.6 SUMMARY 51
• Chapter 4 AMOLED Panel Test System for Various Backplane Structures 52
• 4.1 INTRODUCTION 52
• 4.2 UNIVERSAL DATA DRIVER IC 54
• 4.2.1 Mini-LVDS Interface 56
• 4.2.2 Two-Stage DAC and Variable Current Source 57
• 4.2.3 Output Switch Array and Sensing Buffers 58
• 4.3 EXTERNAL SENSING BLOCK 60
• 4.3.1 Architecture of Transimpedance Amplifiers and ADC 60
• 4.3.2 Measurement Procedure 61
• 4.4 IMPLEMENTATIONS OF PANEL TEST SYSTEM WITH UNIVERSAL DATA DRIVER IC 63
• 4.5 EXPERIMENTAL RESULTS 65
• 4.5.1 Extraction of Electrical Characteristics of Driving TFT 65
• 4.5.2 Modulation of Image Data Using Compensation Scheme 67
• 4.5.3 Verification of Proposed Panel Test System 69
• 4.6 SUMMARY 76
• Chapter 5 Conclusions and Future Works 77
• Reference 80
• Curriculum Vitae 91