LCD working principle

Liquid Crystal Display (LCD), liquid crystal is a substance between solid and liquid. When heated, it will appear as a transparent liquid, and when cooled, it will crystallize into a chaotic solid. Liquid crystal It is an organic compound with regular molecular arrangement. Liquid crystals are divided into three types according to their molecular structure arrangement: clay-like Smectic liquid crystals, Nematic liquid crystals similar to fine matchsticks, and Cholestic liquid crystals similar to cholesterol. The physical properties of these three liquid crystals are not the same. The second type of semitic liquid crystal is used for liquid crystal displays. The molecules are all long rod-shaped. In the natural state, the long axes of these long rod-shaped molecules are roughly parallel. With the deepening of research, people have begun to grasp many other properties of liquid crystals: when the liquid crystal is energized, the liquid crystal molecules are arranged in an orderly manner, allowing light to pass through; when not energized, the liquid crystal molecules are arranged chaotically, preventing light from passing through. With or without electricity, the liquid crystal can be blocked like a gate or light can pass through.

Liquid crystal light principle

The liquid crystal panel of the TN (twisted nematic) monochromatic liquid crystal display consists of two very delicate soda-free glass materials, called Substrates, with a layer of liquid crystal in between, and the structure is like a "sandwich". Let’s take a look at the middle layer, that is, the liquid crystal layer. The liquid crystal is not simply poured into it, but into two interlayers with grooves inside. These two interlayers with grooves mainly allow the liquid crystal molecules to be neatly arranged. Arrange well, because if the arrangement is not neat, the light cannot pass through the liquid crystal part smoothly. In order to achieve the effect of neat arrangement, these grooves are made very fine, the liquid crystal molecules will be arranged along the grooves, the grooves are very parallel, so the molecules are also completely parallel.

These two interlayers are usually called upper and lower interlayers. The upper and lower interlayers are all neatly arranged liquid crystal molecules, but the arrangement direction is different. The liquid crystal molecules of the upper interlayer are arranged in the direction of the upper groove, and the liquid crystal molecules of the lower interlayer are arranged according to the direction of the upper groove. The direction of the lower groove is aligned. During the production process, the upper and lower grooves are cross-staggered (90 degrees perpendicular), that is, the liquid crystal molecules in the upper layer are arranged horizontally, and the liquid crystal molecules in the lower layer are arranged vertically, which causes the liquid crystal molecules located between the upper and lower interlayers to approach The upper layer is arranged horizontally, and the one near the lower layer is arranged vertically.

TFT liquid crystal display principle

In fact, the working principle of the new TFT LCD is also based on the principle of TN LCD. The structure of the two is also basically the same. The design of filling liquid crystal molecules between the two interlayers is also adopted, except that the electrode of the upper interlayer of TN is changed to FET transistor, and the lower layer is changed to a common electrode. But there is still a certain difference in the working principle 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 TN liquid crystal, and the purpose of display is achieved by shielding and transmitting light. But the difference is that because the FET transistor has a capacitance effect and can maintain a potential state, the previously transparent liquid crystal molecules will remain in this state until the FET electrode is powered up next time to change its arrangement. Relatively speaking, TN does not have this characteristic. Once the liquid crystal molecules are not pressed, 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 advantage of TFT liquid crystal.