Principle of LCD

Principle of LCD

Because the liquid crystal material itself does not emit light, there are lamp tubes as the light source on both sides of the display. At the same time, there is a backlight plate and reflective film on the back of the liquid crystal display. The backlight plate is composed of fluorescent materials and can emit light. The main function is to provide a uniform background light source. Here, the light emitted from the backlight plate enters the liquid crystal layer containing thousands of crystal droplets after passing through the polarizing filter layer. The crystal droplets in the liquid crystal layer are all contained in a small cell structure, one or more A cell constitutes a pixel on the screen, and these pixels can be bright or not bright. A large number of neatly arranged pixels are bright or not bright to form a monochromatic image. The lighting or non-lighting of a large number of pixels is mainly controlled by the control circuit. There are transparent electrodes between the soda-free glass plate and the liquid crystal material. The electrodes are divided into rows and columns, at the intersection of rows and columns. , By changing the voltage to change whether the liquid crystal is in the light state, at this time, the role of the liquid crystal material is similar to a small light valve, controlling the passage of light or not. There are also control circuit parts and drive circuit parts around the liquid crystal material, so that signals can be used to control the generation of monochrome images.

In fact, the working principle of the new TFT liquid crystal display is also based on the principle of TN liquid crystal display. The structure of the two is also basically the same. The same design of filling liquid crystal molecules between the two interlayers is adopted, except that the electrode of the upper interlayer of TN is changed to a FET transistor, and the lower layer is changed to a common electrode. But there are still some differences in the working principles of the two. In terms of light source design, the TFT display adopts the "back-through" illumination method, that is, the imaginary light source path is not from top to bottom like TN liquid crystal, but from bottom to top. This approach is to install a fluorescent lamp on the back of the liquid crystal. Light pipe. When the light source is irradiated, it first penetrates upward through the lower polarizer. It also uses the principle of liquid crystal to transmit light. Because the upper and lower interlayer electrodes are changed to FET electrodes and common electrodes. When the FET electrode is turned on, the behavior of the liquid crystal molecules will change like the arrangement state of the TN liquid crystal, and the purpose of display is also achieved by shading and transmitting light. But the difference is that because the FET transistor has a capacitance effect and can maintain a potential state, the liquid crystal molecules that have previously transmitted light will remain in this state until the FET electrode is re-energized next time to change its arrangement. Relatively speaking, TN does not have this characteristic. Once the liquid crystal molecules are absent, they immediately return to the original state. This is the biggest difference between TFT liquid crystal and TN liquid crystal display, and it is also the superiority of TFT liquid crystal. In summary, the liquid crystal display receives digital signals from the computer display card through the DVI interface. These signals are transmitted to the control circuit through the data line. The control circuit adjusts the thin film transistors and transparent display panels of the liquid crystal display to realize the light and No light characteristics. In this way, the background light source passes through the polarizer and the light filter layer to finally achieve the display effect.