How The LCD LCD Works

- Jul 16, 2018 -



At present, most of the liquid crystal display technologies use TN, STN, and TFT as the main axes, so we will discuss their operation principles from these three technologies. The TN type liquid crystal display technology can be said to be the most basic in the liquid crystal display, and then other types of liquid crystal displays can be said to be improved by using the TN type as the origin. Similarly, its operation principle is simpler than other technologies, please refer to the picture below. Shown in the figure is a simple configuration diagram of a TN type liquid crystal display, which includes a polarizing plate in a vertical direction and a horizontal direction, an alignment film having fine grooves, a liquid crystal material, and a conductive glass substrate. The imaging principle is that the liquid crystal material is placed between two transparent conductive glasses attached to the optical axis vertical polarizing plate, and the liquid crystal molecules are sequentially arranged according to the direction of the fine grooves of the alignment film. If the electric field is not formed, the light will be smooth. The light is incident from the polarizing plate, and the liquid crystal molecules are rotated in the traveling direction, and then emitted from the other side. If two sheets of conductive glass are energized, an electric field is generated between the two sheets of glass, which affects the alignment of the liquid crystal molecules therebetween, so that the molecular rods are twisted, and the light cannot penetrate, thereby blocking the light source. The phenomenon of the light-dark contrast obtained in this way is called the twisted nematic field effect, which is referred to as the twisted nematic field effect (TNFE). Liquid crystal displays used in electronic products are almost always made using the principle of torsional nematic field effect. The display principle of the STN type is similar, as shown in the following figure. The difference is that the TN twisted nematic field effect liquid crystal molecules rotate the incident light by 90 degrees, and the STN super twisted nematic field effect rotates the incident light by 180~270. degree. To be explained here, the simple TN liquid crystal display itself has only two cases of light and dark (or black and white), and there is no way to change the color. The STN liquid crystal display involves the relationship of liquid crystal materials and the interference of light, so the color tone of the display is mainly light green and orange. However, if a color filter is added to a conventional monochrome STN liquid crystal display, and any pixel (pixel) of the 

monochrome display matrix is divided into three sub-pixels, respectively, the color filter is transmitted through the color filter. The film displays the three primary colors of red, green and blue, and can also display the color of the full color mode through the harmony of the three primary colors. In addition, if the TN-type liquid crystal display is made larger, the screen contrast will be poor, but with the improved technology of STN, the contrast can be compensated for.

The TFT type liquid crystal display is relatively complicated, and the main components include a fluorescent tube, a light guide plate, a polarizing plate, a filter plate, a glass substrate, an alignment film, a liquid crystal material, a thin mode transistor, and the like. First of all, the liquid crystal display must first use a backlight, that is, a fluorescent tube to project a light source. These light sources pass through a polarizing plate and then pass through the liquid crystal. At this time, the arrangement of the liquid crystal molecules changes the angle of light passing through the liquid crystal. These rays must then pass through the front colored filter and the other polarizer. Therefore, we only need to change the voltage value of the stimulating liquid crystal to control the intensity and color of the last appearing light, and then change the color combination of different shades on the liquid crystal panel.


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