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The principles of various LCD display technologies such as TN, STN, and TFT

2022-09-05 16:25:09 Announcer：Shenzhen Rogin Electronics Co., Ltd 305

1. TN type LCD display principle
The TN type LCD display technology can be said to be the most basic among LCD displays, and other types of LCD displays can also be said to be improved based on the TN type. Similarly, its operating principle is simpler than other technologies. The structure of TN type liquid crystal displays includes polarizing plates in both vertical and horizontal directions, directional films with fine grooves, liquid crystal materials, and conductive glass substrates. In the absence of an electric field, the incident light passes through the polarizing plate and passes through the liquid crystal layer. The polarizing light is rotated 90 degrees by the molecular twisted arrangement of the liquid crystal layer. When it leaves the liquid crystal layer, its polarization direction is exactly the same as the direction of the other polarizing plate, so the light can pass smoothly and the entire electrode surface is bright. When an electric field is applied, the optical axis of each liquid crystal molecule turns in the same direction as the electric field, causing the liquid crystal layer to lose its ability to rotate light. As a result, the polarization direction from the incident polarizer is perpendicular to the polarization direction of the other polarizer and cannot pass through, resulting in a dark state on the electrode surface. The imaging principle is to place the liquid crystal material between two transparent conductive glasses attached to a polarizing plate perpendicular to the optical axis. The liquid crystal molecules will rotate and arrange in order according to the direction of the grooves in the film. If the electric field is not formed, the light will smoothly enter from the polarizing plate, rotate in the direction of the liquid crystal molecules, and then exit from the other side. If two conductive glasses are electrified, an electric field will be generated between them, which will affect the arrangement of liquid crystal molecules between them, causing their molecular rods to twist, making it impossible for light to penetrate and thus blocking the light source. The phenomenon of light dark contrast obtained in this way is called the twisted nematic field effect, abbreviated as TNFE (twisted nematic field effect). Almost all liquid crystal displays used in electronic products are made using the principle of twisted nematic field effect.
2. STN LCD display principle
The display principle of STN type is similar to TN, except that the liquid crystal molecules in TN twisted nematic field effect rotate the incident light by 90 degrees, while the STN super twisted nematic field effect rotates the incident light by 180-270 degrees. It should be noted here that a simple TN LCD display only has two scenarios (black and white), and cannot achieve color changes. STN liquid crystal displays involve the relationship between liquid crystal materials and the interference phenomenon of light, so the displayed color tones are mainly light green and orange. But if a color filter is added to a traditional monochrome STN LCD display, and any pixel in the monochrome display matrix is divided into three sub pixels, the red, green, and blue primary colors are displayed through the color filter, and then the color in full color mode can be displayed by adjusting the proportion of the three primary colors. In addition, the larger the display screen of TN type LCD displays, the poorer the screen contrast will appear. However, with the improvement technology of STN, the insufficient contrast can be compensated for.

3. TFT LCD display principle
TFT type liquid crystal displays are relatively complex, mainly composed of fluorescent tubes, light guide plates, polarizers, filters, glass substrates, directional films, liquid crystal materials, thin mode transistors, and so on. Firstly, the LCD display must first use a backlight, which is a fluorescent tube to project a light source. These light sources will first pass through a polarizing plate and then through the LCD. At this time, the arrangement of the LCD molecules will change the angle of light passing through the LCD. Then these light rays must pass through the colored filter film and another polarizing plate in front. Therefore, by changing the voltage value that stimulates the LCD, we can control the intensity and color of the light that ultimately appears, and thus create color combinations with different shades on the LCD panel.

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