How does the LCD work?
Author:Si Mingkang Time:2021-10-06 16:48 Browse(562)
The working principle of liquid crystal display is: under the action of electric field, the arrangement direction of liquid crystal molecules is changed to change the light transmittance of the external light source (modulation), so as to complete the electrical optical conversion. Then, the color re display in time domain and space domain is completed by using the different excitation of R, G and B primary color signals and through the red, green and blue primary color filter film.
The working principle of liquid crystal display is: under the action of electric field, the arrangement direction of liquid crystal molecules is changed to change the light transmittance of the external light source (modulation), so as to complete the electro-optic conversion. Then, the R, G and B primary color signals are used to excite the light through the red, green and blue primary color filter film, The LCD has the characteristics of thin body.
it saves space. Compared with the bulky CRT, the LCD only needs one third of the space; Power saving, no high temperature, it belongs to low power consumption products, compared with CRT display can do not burn; No radiation, conducive to health, LCD is completely radiation-free; The screen is soft and does not hurt the eyes.

How does the LCD work?






extended information:
safety and cleaning of LCD
if there is dust on the screen panel of the display.
the operation should be carried out with the advice of professional maintenance personnel. Do not use a rag or something rough to wipe it, because it is easy to damage the LCD due to improper personal operation, The correct wiping method should select a clean and soft cloth to wipe, so that it will not cause damage to the display panel.

during the wiping process.
do not spray water or detergent directly on the screen, you can dip a little special detergent on the soft cloth and gently wipe the screen, This avoids the short circuit caused by the detergent flowing into the screen.
when wiping the display screen panel, pay attention to use light force.
do not touch and scrape the panel with hard objects, Don't let any liquid enter into the gap of the boundary of the display.

source: Baidu Encyclopedia - liquid crystal display (1) physical properties of liquid crystalThe arrangement becomes orderly so that light can pass easily; When the power is off, the arrangement is disordered to prevent light from passing through.
let the liquid crystal block or let light pass through like a gate.
technically speaking, the liquid crystal panel contains two pieces of rather delicate sodium free glass material, called substrates, with a layer of liquid crystal in the middle.
when the light beam passes through this layer of liquid crystal.
the liquid crystal itself will stand or twist irregularly, Most liquid crystals are organic compounds.
they are made up of long rod-shaped molecules.
in the natural state, the long axes of these rod-shaped molecules are roughly parallel.
the liquid crystals are poured into a well-made slotted plane.
the liquid crystal molecules will be arranged along the grooves, so if those grooves are very parallel, the liquid crystal molecules will be aligned, (2) the principle of monochromatic liquid crystal display is that the liquid crystal is poured between two planes with thin grooves.
the grooves on the two planes are perpendicular to each other (intersecting 90 degrees).
that is to say,
if the molecules on one plane are arranged in the north-south direction, the molecules on the other plane are arranged in the east-west direction, The molecules between the two planes are forced into a state of 90 degree torsion.
because the light propagates along the alignment direction of the molecules,
the light is also twisted by 90 degrees when passing through the liquid crystal.
however, when a voltage is applied to the liquid crystal,
the molecules will rearrange vertically, making the light direct out, However, there is no twist.


LCD depends on the polarization filter (plate) and the light itself.
the natural light is randomly divergent in all directions.
the polarization filter is actually a series of thinner and thinner parallel linesThese lines form a net.
all the light that is not parallel to these lines are blocked.
the line of the polarization filter is just perpendicular to the first one.
so the polarized light can be completely blocked.
only the lines of two filters are completely parallel.
or the light itself has been twisted to match the second polarization filter, Light can be penetrated.

LCD is composed of such two mutually perpendicular polarization filters.
therefore, under normal circumstances, all the light trying to penetrate should be blocked.
however,
because the two filters are filled with twisted liquid crystals, the light will be twisted 90 degrees by liquid crystal molecules after passing through the first filter, On the other hand,
If a voltage is applied to the liquid crystal, the molecules will be rearranged and completely parallel, so that the light will not be twisted, so it is just blocked by the second filter.
in a word,
the light will be blocked by power on, but it will be emitted by no power on.

however,
the arrangement of liquid crystal in the LCD can be changed, so that the light will be emitted when power is applied, However, the computer screen is almost always on.
therefore, only the scheme of "power on to block the light" can achieve the goal of the most power saving.


from the perspective of the structure of LCD.
whether it is a laptop or a desktop system, The LCD screen used is a layered structure composed of different parts.
the LCD is composed of two glass plates.
the thickness is about 1 mm, between which there are 5 glass plates containing liquid crystal (LC) material μ Because the liquid crystal material itself does not emit light.
there are light tubes on both sides of the display screen as light sources,On the back of the LCD, there is a backlight plate (or uniform light plate) and a reflective film. The backlight plate is composed of fluorescent materials and can emit light, Its main function is to provide a uniform background light source.
the light emitted by the backlight enters the liquid crystal layer containing thousands of crystal droplets after passing through the first layer of polarization filter layer.
the crystal droplets in the liquid crystal layer are contained in a small cell structure.
one or more cells constitute a pixel on the screen.
there is a transparent electric field between the glass plate and the liquid crystal material The electrodes are divided into rows and columns. At the intersection of rows and columns, the optical rotation state of liquid crystal is changed by changing the voltage. The liquid crystal material acts like a small light valve.
around the liquid crystal material are the control circuit and the driving circuit.
when the electrode in the LCD generates an electric field.
the liquid crystal molecules will be distorted, The light passing through it is refracted regularly, (3) the working principle of color LCD displays.

for more complex color displays that need to be used in laptops or desktop LCD displays.
there should also be a color filter layer specially dealing with color displays.
generally.
in the color LCD panel, the color LCD displays should be equipped with a color filter layer, Each pixel is made up of three liquid crystal cells, and each cell has a red, green or blue filter in front of it.
in this way,
light from different cells can display different colors on the screen.


LCD overcomes the disadvantages of CRT, such as huge volume, power consumption and flicker.
however, it also brings high cost and low cost The visual angle is not wide and the color display is not idealCRT display can choose a series of resolutions.
and can be adjusted according to the requirements of the screen, but the LCD screen only contains a fixed number of liquid crystal cells, and can only use one resolution display (each cell is a pixel) in the full screen.


CRT usually has three electron guns.
the emitted electron flow must be accurately focused, However, LCD has no focus problem.
because each LCD unit is switched on and off separately.
this is why the same image is so clear on LCD screen.
LCD does not need to care about refresh rate and flicker.
LCD unit is either on or off, Therefore, the image displayed at a low refresh rate of 40-60hz will not flicker more than the image displayed at 75Hz.
however,
the LCD unit of the LCD screen will be prone to defects.
for 1024 × 768.
each pixel is composed of three units, which are respectively responsible for the display of red, green and blue, so a total of about 2.4 million units (1024 × seven hundred and sixty-eight × 3=2359296).
it is difficult to ensure that all these units are intact.
most likely, some of them have been short circuited (a "bright spot"), Or open circuit (black spot).
so.
not so expensive display products will not have defects.


LCD display contains some things that have not been used in CRT technology.
the fluorescent tube coiled behind the screen provides light source for the screen.
sometimes.
you will find abnormal bright lines in some part of the screen.
there may also be a light source Some indecent stripesA special light or dark color image will affect the adjacent display area.
in addition,
some fairly precise patterns (such as dithered images) may appear unsightly ripples or interference patterns on the LCD screen.


now.
almost all LCDs used in notebook or desktop systems use thin film transistors (TFTs) to activate the light in the LCD layer Cell.
TFT LCD technology can display more clear.
bright images.
due to its low speed, low efficiency and low contrast, the early LCD can display clear text, but it often produces shadow when it displays images quickly, which affects the display effect of video. Therefore, it is only used in palm computers that need black-and-white display, In pagers or mobile phones.


with the rapid development of technology,
LCD technology is also in continuous development and progress.
at present, the major LCD display manufacturers have increased the R & D cost of LCD.
strive to break through the technical bottleneck of LCD, further accelerate the industrialization process of LCD display and reduce production costs, (4) new technology for application and LCD display

(1) TFT active elements are used for driving

in order to create better picture structure.
the new technology uses unique TFT active elements for driving.
everyone knows.
the most important part of the extremely complex LCD screen is liquid crystal In addition, we need to calculate the backlight screen which is directly related to the brightness of the LCD and the color filter which is responsible for generating the color.
active pixels are added to each LCD pixel for point-to-point controlThe display screen is very different from the whole CRT display screen. The display precision of this control mode will be much higher than that of the previous control mode. Therefore, the poor image quality, color penetration and jitter will appear on the CRT display screen, However, when viewed on the LCD screen with new technology added, the picture quality is quite pleasing.

(2) the color filter manufacturing process is used to create a colorful picture

before the color filter body is made into shape.
the main material is dyed, This process requires a very high level of manufacturing.
however, compared with other ordinary LCD displays.
the LCD manufactured with this type of technology, no matter in terms of resolution, color characteristics or service life, (3) low reflection liquid crystal display technology is well known.

the external light has a great interference on the liquid crystal display screen. When the external light is strong, some LCD screens produce reflection because of the glass plate on their surface, However, it interferes with its normal display.
therefore, when it is used in some bright outdoor public places, its performance and observability will be greatly reduced.
at present, many LCD displays, even if the resolution is higher.
their reflection technology is not well handled, Therefore, it is not practical for practical applications.
relying on some pure data alone is actually a kind of biased behavior to guide users.
the "low reflection liquid crystal display screen" technology adopted by the new LCD display is to apply ar coat on the outermost layer of the LCD screen.
this paper introduces the AR coat technology used in the new LCD displayWith this coating, the glossiness of the LCD screen, the transmittance of the LCD screen itself, the resolution of the LCD screen (4) advanced "continuous crystal silicon" liquid crystal display mode

in some LCD products, This is due to the insufficient pixel response speed of the whole LCD screen.
in order to improve the pixel response speed.
the new technology LCD adopts the most advanced Si TFT LCD display mode, which has a pixel response speed 600 times faster than the old LCD screen, The effect is really different.
the advanced "continuous material boundary crystalline silicon" technology uses a special manufacturing method.
the original amorphous transparent silicon electrode is moved at a speed of 600 times the normal speed, which greatly speeds up the pixel reaction speed of the LCD screen and reduces the delay phenomenon of the screen.


now.
low temperature polysilicon technology The research of reflective liquid crystal materials has entered the application stage, which will also make the development of LCD enter a new era.
with the continuous development of liquid crystal displays.
other flat panel displays are also in progress, such as plasma display panel (PDP), liquid crystal display (LCD) and so on The technology of electroluminescent array display (FED) and light-emitting polymer display (LEP) will set off a new wave of flat panel display in the future.
among them,
the most noteworthy and promising is the field display, which has many better performance than the liquid crystal display... It can be concluded that the LCD display technology has entered a new era, as another new force of display products, They are likely to replace CRT displays.


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