Introduction to the working principles of TN, STN, and TFT liquid crystal display schemes in LCD screens

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. Without an electric field, the incident light passes through the polarizing plate and passes through the liquid crystal layer. The polarizing light is twisted and arranged by molecules, and the liquid crystal layer rotates 90 degrees. When it leaves the liquid crystal layer, its polarization direction is exactly the same as the direction of another 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 polarized light from the incident polarizer is perpendicular to the 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 glass plates attached to the optical axis perpendicular to the polarizing plate. The liquid crystal molecules will rotate and arrange in order according to the direction of the thin grooves of the film. If the electric field is not formed, the light will smoothly enter the polarizing plate, rotate its direction according to the liquid crystal molecules, and then shoot out from the other side. If two conductive glass sheets are electrified, an electric field will be created between them, which will affect the arrangement of liquid crystal molecules between them, causing their molecular rods to twist and prevent light from penetrating, thereby 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.