A New Pixel Circuit Compensating for Brightness Variation in Large Size and High Resolution AMOLED Displays

A new pixel design and driving method for active-matrix organic light-emitting diode (AMOLED) display using low-temperature polycrystalline silicon thin-film transistor (LTPS-TFT) is proposed. The new circuit consists of five TFTs and one capacitor to eliminate the variation in the threshold voltage of the TFTs, and the drop in the supply voltage in a single frame operation. The proposed pixel circuit has been verified to realize uniform output current by the simulation work using HSPICE software. The simulated error rate of the output current is also discussed in this paper. The novel pixel design has great potential for use in large size and high resolution AMOLED displays.     

Functional Pixel Circuits for Elastic AMOLED Displays

While fabrication of active matrix organic LED (AMOLED) displays on plastic substrates continues to face technological challenges, stable electrical operation of thin-film transistor (TFT) pixel circuits under mechanical stress induced by substrate bending remains a critical issue. This paper investigates strain-induced shifts in hydrogenated amorphous silicon TFT characteristics and the compound impact on TFT circuit behavior. Measurements show that the magnitude of the shifts is determined by the direction of current flow in the TFT with respect to the bending stress orientation as well as bias conditions. Physically based compact models are developed that relate device characteristics to material behavior for design and optimization of AMOLED pixel circuits that can maintain immunity to bending stress. In particular, current mirror-based pixel circuits are presented that compensate for the long term threshold voltage shift and instantaneous strain-induced shifts in device characteristics.     

A Novel Voltage-Feedback Pixel Circuit for AMOLED Displays

This study presents a novel voltage-modulated pixel circuit for active-matrix organic light-emitting diode (AMOLED) consisting of five n-type thin-film transistors (TFTs), one additional control signal, and one storage capacitor. The proposed circuit, which can be implemented in all-n-type and all-p-type low temperature poly-silicon (LTPS) TFT technologies, successfully compensates for threshold voltage deviation of TFTs and facilitates correction of OLED degradation using a voltage feedback method. Simulation and experimental results for all-n-type TFTs indicate that the proposed pixel circuit reduced the nonuniformity brightness problem effectively by compensating for threshold voltage variation in TFTs and reduced the degradation of emission efficiency in OLEDs.     

A Stable Voltage-Programmed Pixel Circuit for a-Si:H AMOLED Displays

Hydrogenated amorphous silicon (a-Si:H) active matrix organic light-emitting diode (AMOLED) displays are attractive given the potentially low manufacturing cost and ultimately low-temperature fabrication enabling using flexible substrates. Although the conventional two thin-film transistor (2-TFT) AMOLED voltage-programmed pixel circuit (VPPC) can provide high resolution and high yield, the 2-TFT VPPC is prone to image retention over time due to shift in the threshold voltage (V_T-shift) of a-Si:H TFTs. This paper presents a new driving scheme that not only preserves the simplicity of the 2-TFT VPPC, but also demonstrates high uniformity. Experimental results indicate that the current drop in the new driving scheme is less than 11% after 15 days of operation whereas it is over 50% for the conventional driving scheme. Moreover, the new driving scheme is less sensitive to temperature variations due to an internal feedback mechanism. After a 70% change in the temperature, the current in the conventional driving scheme increases by as much as 300%. However, the current in the driving scheme presented here is approximately constant     

Transparent Electronics for See-Through AMOLED Displays

Transparent thin-film-transistors (TFTs) with a channel semiconductor based on the zinc–tin–oxide (ZTO) system are presented. Specifically, the technological and material aspects of the plasma-assisted pulsed laser deposition of these materials are discussed. The supply of additional radical oxygen species will be evidenced to significantly reduce defects in the material and as a consequence allows for well-behaved n-channel TFTs with mobilities higher than 10 ${hbox{cm}}^{2} {hbox{V}} ^{-1} {hbox{s}} ^{-1}$ and a threshold voltage in the range of 0 V. In addition the devices are extremely stable versus bias/current stress, which is especially important for active matrix OLED applications. Based on a detailed understanding of the interaction of the TFT channels with oxygen a strategy for the thin-film encapsulation of the TFTs will be presented, which leaves their device characteristics unaffected.      

中小尺寸AMOLED面临的挑战

有源矩阵有机发光二极管显示器（AMOLED）在实现大规模生产的过程中仍然需要解决屏幕显示（front-of-screen，FOS）效果、基础设施的成本和良品率控制等问题。本文就上述问题提出了解决方案，包括实现更卓越的显示效果，降低制造成本以及增加良品率。     

Design Considerations Between Color Gamut and Brightness for Multi-Primary Color Displays

Color displays show a vivid colorful image by combination of three or above primary colors on every individual pixel. Brightness of color displays, however, strongly restricts the color gamut of displays. From the color mixing theory, the area of color gamut on the color coordination would shrink smaller when brightness grows up. At the maximal brightness, displays can show one system white point only. The difficulties how to obtain the maximal brightness under an assigned color point or color gamut have been a key issue for display manufacturers. The paper proposes a theory to analyze the relation between brightness and color gamut based on the multi-primary color display. Simulations estimate the boundary of color gamut of multi-primary color displays under required brightness which had been proved by experimental results of tri-primary color display. The theory can be applied on the color temperature (CT) design which experimental results show the fact that a display apparatus with higher color temperature could sacrifice brightness less compared to one with lower color temperature when color temperature of the display image needs to change. The theory provides a design guideline for optimization between color gamut, color temperature and brightness on multi-primary color displays     

彩色显示器亮度和对比度的最优化设置

实验研究了彩色显示器亮度和对比度设置对显示器颜色特性的影响.将Neso彩色显示器的亮度和对比度分别设置为最大值的20、50、80和100 %共16种组合,详细地测试和比较了每种设置下显示器的黑点亮度、白点亮度、阶调再现曲线(TRC)、通道可加性、色域和色品恒定性等颜色特性,实验结果表明,亮度设置对黑点亮度影响明显,对比度设置主要影响的白点亮度,黑点对通道可加性、色域和色品恒定性影响很大.通过亮度、对比度设置使黑点亮度尽可能小,白场亮度达到使用要求,同时TRC不出现"横剪切"和"纵剪切"现象,则显示器达到了最优化设置.     

AMOLED Pixel Circuit With Electronic Compensation of Luminance Degradation

A new voltage-programmed pixel circuit using hydrogenated amorphous silicon (a-Si:H) thin-film transistors (TFTs) for active-matrix organic light-emitting diodes (AMOLEDs) is presented. In addition to compensating for the shift in threshold voltage of TFTs, the circuit is capable of compensating for OLED luminance degradation by employing the shift in OLED voltage as a feedback of OLED degradation     

A Current-Mode Comparator for Digital Calibration of Amorphous Silicon AMOLED Displays

We present a digital calibration driving scheme for stabilizing the uniformity of large area amorphous silicon active-matrix organic light emitting diode displays. A current-mode analog-to-digital converter (ADC) is used to extract the differential aging of the individual pixels. For the ADC, a configurable current comparator is designed that employs the output buffer of the source driver to reduce the die area. The comparator and pixel circuit were fabricated in 0.8-$mu$m high-voltage CMOS and amorphous silicon technologies, respectively. Analysis and measurement results show a calibration refresh time of 2 s for a high-definition display (1920$,times,$RGB$,times,$1080). Moreover, the pixel current is highly stable despite a 5-V shift in the threshold voltage of the thin-film transistor driver.      

基于改善AMOLED TFT均匀性和稳定性像素补偿电路

有机发光二极管显示器(OLED)正越来越多地用于中小尺寸的显示,但在大尺寸方面进展缓慢,因为在有源大尺寸方面对OLED的稳定性和均匀性要求较高,需要设计像素补偿电路。各研究机构提出了像素补偿电路用于改善OLED的均匀性和稳定性等问题,文中对目前采用有源OLED的α-Si TFT和p-Si TFT的各种像素补偿电路进行了分析。分析结果表明,文中设计方案取得了一定的效果,但尚存不足。     

A New Thin-Film Transistor Pixel Structure Suppressing the Leakage Current Effects on AMOLED

We propose a new pixel structure employing solid-phase crystallized silicon thin-film transistors which suppresses the leakage current effects on active-matrix organic light-emitting diode (AMOLED) displays. The pixel structure has been fabricated on a glass substrate employing the field-enhanced rapid thermal annealing technology. In the proposed pixel, the charge holding capability is considerably enhanced due to the capacitor located between two series-connected switch transistors. Our experimental results shows that the average variation range of the OLED current is suppressed less than 0.5% while the conventional one exceeded 4%.      

一种改善LED背光亮度均匀性的新型反射膜研究

在LCD的LED背光腔体的底面设计了新型曲面形状及性能的反光膜,将扩散膜反射回灯腔底部的光重新反射回出光口以改善亮度均匀性能;在侧面设计了镜面反射膜,将位于LED矩阵边缘区域由LED射向灯腔侧壁的光反射重新射向出光口,增加了LED背光边缘区域的亮度,从而改善了背光边缘区域较暗的亮度不均匀状况.根据此类反射膜的设计完成了反射膜的制备,并应用于38 cm LED背光源样品.测试结果显示,设置反射膜的LED背光的亮度均匀性值为10.2%,明显优于未设置反射膜的值16.8%,亮度提高了29%左右,表明该种新型反射膜可以提高亮度并改善亮度均匀性.     

LED背光源亮度均匀性的研究

讨论LED的偏置电阻和发光亮度对LED背光源亮度均匀性的影响。     

无源OLED显示屏亮度均匀性研究

利用无源矩阵驱动原理,计算了有机发光二极管(OLED)器件中阴极和阳极电阻上的电压降.结果表明,恒压驱动条件下,电阻上的压降将产生严重的亮度不均匀性.分析表明辅助电极可以改善亮度非均匀性.采用恒流驱动及高效率的OLED可以进一步提高亮度均匀性,降低功耗.计算及分析结果与实验现象一致.     

A Novel Voltage Driving Method Using 3-TFT Pixel Circuit for AMOLED

A novel voltage driving method using three thin-film transistors (TFTs) for active-matrix organic light-emitting diodes (OLEDs) is presented and verified by automatic integrated circuit modeling SPICE simulation. The proposed novel 3-TFT pixel circuit, which successfully compensates for the threshold voltage variations, uses few TFTs with simplified control signals, and the current nonuniformity of the proposed circuit is 0.19% to 1.99% throughout the entire data range. To compensate for variations in OLED current, the proposed circuit utilizes a novel driving scheme that uses a diode connection current source with a biased voltage.     

高清显示中的伽马校正、亮度和明视度探索

高画质显示器中的伽马校正增强了显示界面效果,并且是基于推定的明视度和亮度之间的数学关系。随着新型高清技术在市场上的扩展,有必要对高分辨率显示器亮度一明视度的关系式进行矫正．DICOM标准代表了一种可能的实现方法。     

Data Supply Voltage Reduction Scheme for Low‐Power AMOLED Displays

This paper demonstrates a new driving scheme that allows reducing the supply voltage of data drivers for low‐power active matrix organic light‐emitting diode (AMOLED) displays. The proposed technique drives down the data voltage range by 50%, which subsequently diminishes in the peak power consumption of data drivers at the full white pattern by 75%. Because the gate voltage of a driving thin film transistor covers the same range as a conventional driving scheme by means of a level‐shifting scheme, the low‐data supply scheme achieves the equivalent dynamic range of OLED currents. The average power consumption of data drivers is reduced by 60% over 24 test images, and power consumption is kept below 25%.     

基于不同TFT技术的AMOLED像素电路仿真分析

非晶硅、非晶氧化铟镓锌、多晶硅薄膜晶体管是可用于设计AMOLED像素驱动电路的3种典型的薄膜晶体管(TFT)技术。文中基于3种TFT的模型,针对大尺寸、高分辨率的AMOLED,分别在典型的电压式驱动和电流式驱动像素电路进行了建模仿真,并对仿真结果做了分析和比较。该研究方法为像素电路的设计提供了一定理论依据。     

A Novel LTPS-TFT Pixel Circuit Compensating for TFT Threshold-Voltage Shift and OLED Degradation for AMOLED

This letter presents a novel pixel circuit that uses low-temperature polycrystalline-silicon thin-film transistors (LTPS-TFTs) composed of one driving and four switching TFTs for active-matrix organic light-emitting diodes (AMOLEDs) with a voltage-source method. The proposed circuit effectively enables threshold-voltage-shift correction of the drive TFT and compensates for degradation of the OLED using a feedback structure