At present, most of the liquid crystal display technologies are based on TFT technologies such as TN/HTN/STN/FSTN, so we will discuss their working principles from these technologies.
TN liquid crystal display technology can be said to be the most basic liquid crystal display, and other types of liquid crystal displays can also be said to be improved based on the TN type. Again, it works much simpler than other techniques, see diagram below. The figure shows the simple structure of TN LCD, including vertical and horizontal polarizers, alignment film with fine grooves, liquid crystal material and conductive glass substrate. The display principle is to place liquid crystal material between two pieces of transparent conductive glass, and a vertical polarizer is pasted on the optical axis. The liquid crystal molecules will be rotated and aligned in the direction of the thin film grooves. If no electric field is formed, the light will enter the polarizer smoothly, and the liquid crystal molecules will rotate in the direction of travel, and then emit from the other side. If two pieces of conductive glass are energized, an electric field will be generated between the two pieces of glass, which will affect the alignment of the liquid crystal molecules between them, causing their molecular rods to twist and prevent light from penetrating, thereby blocking the light source. The light-dark contrast phenomenon obtained in this way is called TNFE (Twisted Nematic Field Effect).
Almost all liquid crystal displays used in electronics are made using the twisted nematic field effect principle. The display principle of the STN type is similar, the difference is that the liquid crystal molecules of the 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. What I want to explain here is that the pure TN liquid crystal display itself only has two situations of light and dark (or black and white), and there is no way to change color. However, STN LCD involves the relationship between liquid crystal materials and the phenomenon of light interference, so the colors of the display are mainly light green and orange. However, if a color filter is added to the traditional monochrome STN LCD, any pixel of the monochrome display matrix is divided into three sub-pixels, and the three primary colors of red, green, and blue are displayed through the color filter, and then the three primary colors are reconciled. Proportion. It can also display colors in full color mode. In addition, if the TN-type liquid crystal display has a large display screen, the screen contrast will appear poor, but the improvement of STN technology can make up for the lack of contrast.
TFT liquid crystal displays are relatively complex, and the main components include fluorescent tubes, light guide plates, polarizers, filters, glass substrates, directional films, liquid crystal materials, and thin transistors. First, LCDs must use a backlight or fluorescent tubes to project light through polarizers and then through liquid crystals, where molecules are aligned at angles that change the way light passes through the liquid. The light then has to pass through a color filter and another polarizer in front of it. Therefore, we only need to change the voltage of the liquid crystal to control the intensity and color of the light, and then change the color combination of different shades on the liquid crystal panel.
