首页 > 基础知识, 最新技术研究, 液晶电视维修技术 > 现代液晶电视的基本原理及维修——TFT液晶显示屏原理(2)

现代液晶电视的基本原理及维修——TFT液晶显示屏原理(2)

2009年10月10日 郝铭 发表评论 阅读评论

郝铭

三、液晶的成像原理

1、光、自然光、偏振光

显像管、液晶屏、等离子屏都是是一种把图像电信号转换为明亮图像的电光器件,特别是液晶屏,液晶的本身是不发光的,但是液晶的分子可以在电信号的作用下控制光线的通过,也就是控制了一个像素的亮度,液晶的分子是怎么控制光线的通过?首先要对“光”有所了解:

光是什么?光是一种物质,是能量,是电磁波。是波长在380毫微米(nm 纳米)到780毫微米之间的一段电磁波,如图1-3-1这一段电磁波刺激人的眼睛,人眼就会有感觉,这种感觉就是“亮”也就是光感,人眼就是一个电磁波接收器。380毫微米到780毫微米这一段波长的电磁波同时射入人眼,就会有白光的感觉,当某一单一波长的电磁波射入人眼,人眼就有色光的感觉,例如770毫微米波长的电磁波射入人眼;人眼就感觉是红光,比红光波长再长的电磁波人眼就看不见了,这就是红外线;550毫微米电磁波射入人眼就有绿光的感觉;385毫微米的电磁波射入人眼就有紫光的感觉,比紫光波长再短的电磁波人眼就看不见了,这就是紫外线。从780毫微米到380毫微米这一段内部不同波长的电磁波分别射入人眼,人眼就会有:红、橙、黄、绿、青、蓝、紫光的感觉,同时射入人眼就是白光的感觉。

既然光是电磁波那么它就是一个正弦振动的无线电波,它的振动面不只限于一个固定方向而是在各个方向上均匀分布的,振动的方向就有垂直的水平的,45度角的135度角的等等,总之是多方位的集合,如图1-3-2所示。这种光叫做自然光;太阳、电灯、日光灯,液晶屏的背光灯等普通光源发出的光,都是自然光。

光的振动面只限于某一固定方向的;垂直的或水平的或其它方向振动的;叫做偏振光或线偏振光,如图1-3-3所示;

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                        图1-3-1                                                              图 1-3-2

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            垂直方向振动偏振波                                              水平方向振动偏振波

                                                          图1-3-3

自然光和偏振光对人眼的刺激效果是相同的;人的眼睛是无法鉴别射入眼睛的光是自然光还是偏振光。

2、液晶屏的组成结构及原理

液晶屏的基本构造及组成

液晶屏是一块薄薄地图像显示屏,组成结构比较复杂,是由多层不同作用的薄片组成,有偏振片、配向膜、滤色片、液晶层、背光板等,要弄明白液晶的成像原理必要把最主要的;偏振片、配向膜及液晶层的构造和原理搞清楚,图1-3-4所示就是液晶屏的最主要组成的断面示意图

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                     图1-3-4                                                              图1-3-5

从图中可以看出最前面是偏振片(由上至下),偏振片的下面是配向膜、液晶层、配向膜、偏振片,最下面是提供光源的背光灯。在这其中,偏振片有两片、配向膜有两片(两片偏振片构造不同、两片偏振模构想也不同)。液晶层在配向膜的中间,光线由下部背光灯射入,穿后过偏振片、配向膜在液晶层受到电信号控制的液晶分子的控制再穿过配向膜及前偏振片,我们看到的就是图像。图1-3-5所示是前后偏振片纹理结构和上下配向膜沟槽结构的不同及液晶分子扭曲的关系。

3、偏振片

能透过偏振光的透光片就叫偏振片;

偏振片是特制的透光(玻璃或薄膜)片,上面特制密集的垂线,如图1-3-6;和密集的水平线,如图1-3-7。作为液晶屏用的偏振片是聚乙烯醇高分子化合物薄膜作为片基制作。

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                 图1-3-6                                            图1-3-7

偏振片具有这样的特性:只允许和偏振片上线条平行的光振动波通过,,如图1-3-8所示,其它振动方向的光波全部被阻止通过,如图1-3-9所示。偏振片上能透光的方向称为偏振片的透光轴,也就是说;和透光轴平行的偏振光可以通过偏振片。

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                  图1-3-8                                                           图1-3-9

当自然光要通过偏振片时,偏振片只允许自然光中振动面和偏振片透光轴平行的通过,如图1-3-10所示,偏振片实际上是一个滤波器;偏振光滤波器,也称为:极化滤波器。

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                                                              图1-3-10

我们可以用眼睛透过一块偏振片(不管上面的线条是什么方向)去看室外的景物。只会看感到亮度略有下降外,其它没有任何异样的变化,就像带了一副很浅的有色眼镜。把两块透光轴相同的偏振片重叠在一起,观看景物和上面用一块观看景物是一样的现象,如图1-3-11所示。透过第一块偏振片的偏振波也可以顺利透过第二块偏振片达到人眼睛。但是如果要用两块透光轴相互垂直的偏振片重叠在一起,再观看景物,或者光源,这就什么也看不见了,如图1-3-12所示。为什么看不见了?

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              图1-3-11                                                        图1-3-12

这个道理大家已经很清楚了;在图1-3-12中,用用两块透光轴相互垂直的偏振片重叠在一起,观看景物,这时景物的自然光中的和第一块偏振片透光轴平行的水平偏振光,透过第一块偏振片后;是无法透过第二块偏振轴垂直的偏振片的,就好象没有光线穿透过来,所以看到的只能是黑屏。这个道理搞清楚了,液晶屏的成像原理也就非常容易了。

4、液晶屏的控制作用

根据上述的道理;两块透光轴相互垂直的偏振片重叠在一起光线是不能通过的,此时保持两块透光轴相互垂直的偏振片的位置不变,只要把通过第一块偏振片的水平偏振光扭曲90度,变成垂直的偏振光就可以穿过过第二块偏振片,如图1-3-13所示。

液晶屏的作用就是控制由A偏振片透过的偏振光;扭曲还是不扭曲;从而决定是否能穿过B偏振片。液晶的分子在周边施加电场和不加电场就可以控制分子扭转90度,同时带动通过的光振动波扭转90度,使水平的偏振波变成垂直的偏振波,或者使垂直的偏振波变成水平的偏振波。就达到了用电信号控制光线“亮”与“暗”的目的,如图1-3-14所示。

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                                                                   图1-3-13

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                                                                     图1-3-14

我们如果把这一个偏振波看成形成一个像素点的光源,那么在一个平面上,众多的偏振波由图像电信号在液晶屏中进行控制,就在B偏振片这一面看到一幅图像。(待续)

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