LCD Display -- Principles

In everyday life
Displays (LCDs) are everywhere
The picture we show through the screen
Learn about the world
I love the rivers and mountains
Splendid China
Strange stories
Entertain and enrich your life

Mom: Look less at your phone This can affect your vision
*Open her phone*

These large and small screens
How did you present the picture to us?
What is the principle behind it?
Today, a small exhibition will unveil the back of the screen
(LCD) display principle and display timing

01

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Basic concepts

The common screen in life is called LCD (Liquid crystal display), which translates to

liquid crystal display, that is, liquid crystal display. LCD display has the advantages of low

 power consumption, small size, large amount of information and no eye damage, so it has

become the mainstream electronic display device in life.
The screen can display colors and pictures inseparable from a substance - liquid crystals.

Liquid crystal is a special substance between solid and liquid, it is an organic compound,

 which is in a liquid state under normal conditions. It is characterized by the same regularity

 of molecular arrangement as solid crystals. When an electric field is applied to the liquid crystal

 through the outside, it will change its molecular arrangement, which will change the propagation

 of light, and the polarized light sheet has the effect of controlling the light transmittance, and

then with a color filter, changing the voltage applied to the liquid crystal, it can change the amount

 of light transmittance of a certain color. Through this principle, a display structure with

controllable red (R), green (G) and blue (B) light output intensity can be made, and the

three display structures can be formed into a display unit. By controlling the intensity of red,

green, and blue, the unit can be mixed to output different colors, and by changing the ratio of

the three colors, various colors can be mixed, and such a display unit is called a pixel. After

having the LCD, the screen display is still black, because the LCD itself does not emit light,

and a backlight is needed to provide a light source for the visible picture color to appear.

The brightness of the screen, that is, the light goes through a series of processing processes

 to the output, so the intensity of the output light is much lower than the intensity of the light source,

 these processing processes will lead to a narrower display direction, which will affect the

observation range of the naked eye, that is, its viewing angle is smaller, and the screen will not

 be able to see its display content clearly from the side. It can be seen from this that behind

 a small screen is the integration of countless science and technology, which is interlocked,

 which has created the great development of film and television entertainment today.

02

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Basic parameters

Next, Xiaozhan will tell you what meaning is behind the "nouns" introduced behind the screen.

Pixels are the most basic unit elements that make up an image, and the pixels of the display refer to the smallest points it imaging,

which is composed of countless dots to form a pattern, and the more pixels there are, the more exquisite and beautiful the picture formed.

The resolution of the screen is usually indicated by "row pixel value X column pixel value". For example, a resolution of 1920x1080 means that

each row of the display has 1920 pixels, and each column has 1080 pixels, which can also be understood as having 1920 columns and 1080 rows.      

Color depth refers to how many colors each pixel of the display can represent, usually expressed in bits. 

Common display color depths are 16-bit and 24-bit.       

  The size of the monitor is generally expressed in inches, such as 5 inches, 21 inches, 24 inches, etc.,

 this length refers to the length of the diagonal of the screen. The smaller the size, the more science and technology it contains,

 and the more complex the form structure, Zhanhui Optoelectronics can support ultra-small LCD display modules with a

minimum size of 0.96 inches!     

 The distance between two adjacent pixels will affect the delicacy of the picture quality and the viewing distance,

and the screen of the same size, if the resolution is higher, the smaller the dot distance, the more delicate the picture quality.

03
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Signal control

Now that you know the basic parameters, how does the screen work?

RGB cables usually have 8 cables each, so the RGB888 format is supported, with a total of 24 bits of cables, 

each representing the red, green, and blue (RGB) color component of one pixel of the LCD screen.

The LCD screen uses synchronous communication with the outside world, usually using the CLK signal as the synchronization clock, 

and each clock transmits one pixel data under the drive of the synchronous clock.
 

    The horizontal synchronization signal is used to indicate the end of the transmission of a line of pixel data on the LCD screen,

 and every time the transmission of a line of pixel data on the LCD screen is completed, HSYNC will jump the level,

such as a display with a resolution of 1920*1080, the level of HSYNC will jump 1080 times to transmit a frame of image!       

 VSYNC signal is used to indicate the end of the transmission of one pixel data on the LCD screen, and VSYNC will undergo a level

jump every time the transmission of one frame of pixel data is completed. Among them, "frame" is the unit of image,

a pair of images becomes a frame, in liquid crystal, a frame refers to a full screen liquid crystal pixels. For example,

when the LCD screen runs at a rate of 60 per second, VSYNC level freezes 60 times per second and becomes 60 f0s,

and the frame rate displayed on a good screen is in line with the blink frequency of the naked eye.

  The data enabling signal DE is used to indicate the validity of the data, and when the DE signal line is high,

the RGB signal line indicates that the data is valid.              

  Every pixel in the display is data, and in practical applications, the data of each pixel needs to be cached and transmitted to the LCD screen.

Video memory can generally store at least one frame of display data of the LCD screen, such as an LCD screen with a resolution of 800x480,

using the ob888 format display, a data size is 300x480x3 = 1152000 bytes, 3 means that a pixel occupies 3 bytes of data (R:8bit, G:8bit, B:8bit);

If you use RGB565 format, the data size of a frame is: 2x800x480 = 768000 bytes, 2 means that a pixel occupies 2 bytes (R:5bt, G:6bt, B:5bit),

so it can be seen that the higher the number of bytes occupied by a pixel, the richer the colors that can be represented!

04

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LED and OLED

In life, we often hear about LED and OLED screens, do you know what the difference is between them? It's not just a difference in letters.

The LED screen does not need a backlight, and a single pixel of the LED dot matrix color display contains threeLED lights: red, green, and blue,

and by controlling the brightness of these three lights, the output of full color is realized, and multiple pixels constitute a whole screen.

Since every pixel is the light emitted by LED lights, it is also particularly clear outdoors during the day! This also brings a disadvantage,

due to the large size of LED lights, resulting in a very low screen pixel density, so it is generally only suitable for giant displays in squares.

When we encounter a huge display screen in life, we can get closer and find many small LED lights on the screen.

OLED (Organic Light Emiting Diode), on the other hand, uses an organic light-emitting diode with a pixel unit, so the pixel density is much

higher than that of ordinary LED lattices, so the image quality is also more delicate. 0LED displays also do not need backlight, high contrast,

thinness and lightness, viewing angle and response speed, etc., and the corresponding disadvantage is that their cost is rising.

Today's science popularization ends here, I believe that everyone's understanding of the screen has reached a higher level, we will see you in the next issue!