32英寸的IPS液晶电视的宽视角性能光学补偿方法解析

A 32-inch IPS-LCD with a significantly wide viewing angleperformance has been developed using a new opticalcompensation method. 一台32英寸的IPS液晶电视的宽视角性能明显已经开发，并使用了新的光学补偿方法。It provides a contrast ratio over 80: 1 atall viewing angles. According to our study, it is important toshorten the path for the optical compensation in the Poincaresphere. We have found an effective method using two retardationfilms, one with an Nz value larger than 0.5 and one with a valuesmaller than 0.5.  http://www.ukassignment.org/ygkczy/

IntroductionIn-Plane-Switching (IPS) -LCDs have good viewing angleperformance with bright images. With such images, they aresuitable for standard uses. However, it has been pointed out thatfurther improvement is needed with their dark image quality atoblique angles [1]. To solve this problem, some good opticalcompensation methods have been proposed earlier [2], [3].However, it is hard to achieve these methods because of theincrease in cost or the lack of the suitable retardation films.Our studies focused on the lowering costs and further improvingthe off-axis viewing performance by reducing light leakage andcolor shifts in the black representation. To deal with these issues,we developed a 32-inch IPS-LCD [4], applying two technologies:an optical compensation method using one biaxial film and thenew cell technology (IPS-Pro) with high transmittance andcontrast ratio (CR) [5]. Its viewing angle performance wasimproved, but not enough. We have continued to work to clarifythe issue.In this paper, the issue is discussed and a new design rule foroptical compensation of IPS-LCDs is introduced for the solution.Finally, the viewing angle performance of a newly developed 32-inch IPS-LCD which uses this design rule is shown.在本文中，针对这个问题进行了讨论，并介绍一个新的设计的规则，来解决IPS液晶显示器的显示的问题，新开发的32英寸IPS液晶中的表现出来的可视角度，其中就采用了这种设计规则。

Viewing Angle Characteristics of IPS-Pro with Conventional OpticalCompensation TechnologyFigure 1 shows respectively the measured CR viewing anglecharacteristic of 32-inch IPS-Pro with the conventional opticalcompensation using one biaxial film. It and the color shift in theblack representation have been improved, compared with theprevious typical IPS-LCDs with no compensation film .从它的和色偏黑来看，与以往典型的IPS-LCD的没有补偿的电影相比，色彩方面已经获得改善。

Typical color saturation at on-axis is 72 % in LCDs for TV. Thesatisfied color saturation can be obtained at oblique angles.However, the color saturation at low-middle gray scale is notsatisfied at oblique angles. For example, Fig. 3 shows a colorsaturation viewing angle characteristic measured at gray scale of159/255. For the further improvements of the viewing angleperformance, the further enhancement of CR at oblique angles isneeded [6].

Figure 4 shows the configuration of our conventional IPS-LCD,where typical polarizers are used. They have triacetylcellulose(TAC) films as protection films, which have small birefringence.Figure 5 shows the feature of polarization transformation for theconventional optical compensation using the Poincare sphere(projecting onto the S1-S3plane) when the black level isrepresented at an oblique angle. Tinis the polarization of theincident light through the polarizer and Aoutis the polarizationabsorbed by the analyzer at an oblique angle, respectively. TheTinis transformed to P1by the small retardation of the polarizer.The P1is transformed to the P2through the biaxial film. The P2istransformed to P3by the retardation of the liquid crystal. The P3istransformed near Aoutby the small retardation of the analyzer.Therefore, there is little light leakage at oblique angles in theblack representation.

However, one issue remains, namely the wavelength dependenceof the polarization. Although the polarization of the incident lightwith a certain wavelength becomes above-mentioned, one withanother wavelength is further from Aout. The factor is positivewavelength dispersion of each birefringent medium. However, itis difficult to make all of them negative wavelength dispersion.To reduce the influence of the wavelength dispersion as much aspossible, there are following two ideas.为了尽可能多的p减少的波长分散的影响，需要经过以下两个想法的验证。

. To shorten the path of the polarization transformation2. To use birefringent media with small wavelength dispersionFrom both points, the polarization transformation through theliquid crystal layer is the matter because the path from P2to P3isthe longest in Fig. 5 and the liquid crystal has large wavelengthdispersion. Fortunately, it is possible to make it invalid in IPS-LCDs because the optical axis of the liquid crystal layer is parallelto the absorption axis of the polarizer or the analyzer. To realizeit, the polarizer with no birefringence is needed. Recently, somefilms with significantly small birefringence are proposed as theprotection film for polarizers [7]. Either the polarizer or theanalyzer has to be non-birefringence at least.In such cases, it is necessary to achieve the optical compensationby retardation films or birefringent media except the liquid crystallayer. Additionally, the shortest path of the polarizationtransformation should be achieved in the optical compensation,considering above-mentioned 1. We have found the idealconfiguration and optical compensation to shorten the path of thepolarization transformation, shown in Fig. 6 and 7.在图6和图7中所示的偏振转换中，对于光学补偿缩短的路径，我们已经找到了理想的配置。