1. What is LCD?

As the name suggests, a liquid crystal display (LCD for short) is a display that uses "liquid crystal" as its material. So what is liquid crystal?

In fact, 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 state. Liquid crystal is an organic compound with a regular molecular arrangement. . Liquid crystals are divided into three types according to the different molecular structure arrangements: clay-like Smectic liquid crystals, Nematic liquid crystals similar to thin matchsticks, and Cholestic liquid crystals similar to cholesterol. The physical properties of these three liquid crystals are different. The second type of Semitic liquid crystals are used in 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 easily; 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. The two states that can control the light are the prerequisites for the formation of images by the liquid crystal display. Of course, a certain structure is needed to realize the conversion of light to an image. 

2. How does the LCD monitor work?

(1) The working principle of ordinary LCD

Where does light come from? Because the liquid crystal material itself does not emit light, there are lamp tubes as the light source on both sides of the display screen. At the same time, there is a backlight plate and reflective film on the back of the liquid crystal display screen. 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 by the backlight plate enters the liquid crystal layer containing thousands of crystal droplets after passing through the polarization filter layer (that is, the interlayer mentioned above). The crystal droplets in the liquid crystal layer are all contained in small In the cell structure of, one or more cells constitute a pixel on the screen, and these pixels can be bright or not bright. A large number of neatly arranged pixels are bright and not bright to form a single color image.

So how can we control whether the dots in this large number of pixels are bright or not bright? This 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 the rows and columns, the connection of the liquid crystal is changed by changing the voltage. The light state, at this time, the role of the liquid crystal material is similar to a small light valve, controlling the passage or non-passing of light. There are a control circuit part and a drive circuit part around the liquid crystal material, so that signals can be used to control the generation of monochromatic images.

(2) TFT liquid crystal display principle

What we mentioned earlier is the principle of the most basic liquid crystal display. At present, liquid crystal display technology has undergone rapid development. TFT (Thin Film Transistor) liquid crystal display has become the mainstream. It is necessary for us to understand the working principle of this kind of liquid crystal display.

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, and 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 a 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 polarizing plate. 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 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 next time the FET electrode is energized to change its arrangement. Relatively speaking, TN does not have this characteristic. Once the liquid crystal molecules are not pressed, they immediately return to their 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 the 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 transistor and the transparent display board of the liquid crystal display to realize the light and the liquid crystal. 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.

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