When it comes to LCD screens, most people must be familiar with them, but there are still many places where LCD screens are used in reality. Such as home TV display, electronic scale display, mobile phone display and so on.
Most people know the term LCD screen, but not many people really understand its working principle. Recently, Xiaobai has used LCD screens when working on mobile phone projects, and has a basic understanding of the working principles of LCD screens. I would like to take this opportunity to share my insights with you.
When explaining the working principle of the LCD display, first understand two basic knowledge points.
(1) The three primary colors of light. In the study of physics in middle school, we have the most basic understanding of light. Understand that the three primary colors of light are mainly divided into red, green and blue. As long as the three colors of light are mixed in different proportions, a variety of colors can be produced.
(2) Pixels, people in the machine circle should have a little idea of this, that is, the smallest image unit, this smallest graphic unit can be displayed on the screen, usually a single dye point, which is composed of the aforementioned light The three primary colors are combined, and the display of LCD is composed of thousands of pixels, which finally constitute the colorful picture displayed by LCD.
For a better understanding, do a simple experiment.
Make a simple color card, the color card is divided into nine colors
Open the color card picture on the mobile phone and adjust the brightness to the highest display. Use a microscope to keep zooming in, and you can see that there are different color block areas on the screen.
White
It can be seen that in the white state, it is composed of three RGB colors: red, green and blue.
Black
In the black state, the red elements and green elements of RGB pixels are off, and only the blue elements are slightly bright.
• Purple
When purple is displayed, the blue and red elements of RGB pixels are highlighted, and the green elements are off.
• Blue
In the blue area, the blue elements of RGB pixels are always on, the green elements are slightly bright, and the red elements are off.
• Red
It can be seen that when red is displayed, the blue elements and green elements of RGB pixels are off, and the red elements are highlighted.
After understanding the three primary colors of light and pixels, let's talk about the working principle of LCD display.
First, briefly describe the working principle of LCD and LCM: LCD liquid crystal display is a display component based on liquid crystal. It controls the rotation direction of liquid crystal molecules by controlling the voltage at both ends of the liquid crystal molecules, and then controls the polarization of each pixel. Light projection to achieve the purpose of display . At present, what we often call LCM (LCD Module) is the LCD module. It includes a liquid crystal display (LCD), control driver chip, PCB board, backlight, structural parts, connectors and many other components assembled together . So strictly speaking, LCD is only a part of LCM, and LCM includes LCD.
Maybe you don't understand it very well, don't worry, read the following content, and then carefully figure out the working principle above, you will have a better understanding.
First of all, let's look at the components of the LCD:
it is mainly divided into: backlight layer, vertical polarizer, positive circuit, liquid crystal layer (including liquid crystal molecules), negative circuit, horizontal polarizer, and color filter. It seems that there are a lot of materials, and more materials means that the LCD screen is relatively thicker. For mobile phone design, the influence of thickness is still very important. Saving a little thickness may play a big role in improving battery capacity. In addition, as both the backlight layer and the liquid crystal layer are made of hard materials, LCD screens are not suitable for folding screens. Therefore, the folding screens of mobile phones seen on the interface do not use LCD screens.
The liquid crystal molecules mentioned above are located in the liquid crystal layer, and the orientation of the liquid crystal molecules has certain regularity.
When its two sides are energized, they will be arranged in an orderly manner, making it easy for optical fibers to pass through; when they are not energized, they will be arranged chaotically, preventing light from passing through . When the power is turned on and off, it will affect the light transmittance or reflectance of the liquid crystal unit, thereby controlling the light source transmission or shielding function, thereby controlling each pixel, and producing images with different gray levels and colors .
Hahaha, what I said earlier is not very empty, so for a better understanding, here we first compare the liquid crystal layer to blinds. The different arrangements of liquid crystal molecules are like the blinds, which can be freely flipped and changed .
The bottom of the picture is the backlight layer, which has only one function to emit white light. In the state of the picture above, the louvers are perpendicular to the backlight layer. After white light passes through the filter layer, red, green and blue are mixed in the same proportion, resulting in a white pixel.
Take the area of the red filter on the far left as an example. When we apply voltage to the positive and negative poles, the blinds will flip over. At this time, the liquid crystal molecules in the liquid crystal layer will reflect part of the light like blinds, causing the light to reach the filter. Everbright discounted. In this way, when red, green and blue are mixed, red light will generate a theoretical color in a weaker proportion, instead of white. To control the folding of the blinds (the arrangement of liquid crystal molecules), we only need to control the magnitude of the voltage, and then we can control the color of the pixels.
If the LCD screen wants to display black, the blinds need to be fully extended and parallel to the polarizer to completely block the emitted backlight. However, LCD liquid crystal molecules have certain defects, that is, liquid crystal molecules cannot be completely closed. That is to say, when the liquid crystal molecules are closed to the greatest extent, there will still be some light. Therefore, when displaying black, it is impossible to achieve true black, and a slight light will be emitted.
Secondly, since the LCD has a backlight layer, and the screen will eventually be installed in the mobile phone, the gap between the screen and the frame will cause a part of the light source to be exposed. When the display is black, a halo phenomenon can be observed at the edge, that is, light leakage.
When using an LCD screen, our screen does not always display images statically. If you want to display a dynamic picture, it means that each pixel needs to switch colors quickly. However, it takes time for a pixel to switch from one color to another, which we call screen response time. If the corresponding time is too long, the pixels are too late to switch, and the previous picture has not disappeared, and the next picture has already started, that is, afterimages will appear. The switching of LCD colors, as we said before, is done through the deflection of liquid crystal molecules. Therefore, the deflection speed of the liquid crystal molecules also determines the gray scale response time of the LCD. However, its deflection speed is related to temperature, the lower the temperature, the slower the deflection speed. Therefore, when using the LCD screen in winter, it is easy to find afterimages when switching screens quickly.
However, LCD screens are not without advantages. From the perspective of materials, LCD screens are made of inorganic materials, which age slowly and have a long life. At the same time, in terms of cost, the price is relatively affordable. At the same time, LCD has a long history of development and the technology is more mature. Therefore, some models of mobile phones still use LCD screens.
Even though OLED screens are dominant today, LCD screens are still the mainstream display in some fields, so don’t just say that LCD screens are outdated. Remember, classics never go out of date!