LCD Screen

11.Whats an LCD

LCD (liquid crystal display), is the flat and ultra-thin display device, get through the liquid crystal molecules are stimulated by current to generate dots, lines, and surfaces, and the backlights of the mirrors and the back lamps are combined to form a picture, however the liquid crystal itself does not emit light.

Note: Liquid crystal is a kind of special substance between solid and liquid. It is an organic compound, normally in the liquid state, but its molecular arrangement is very regular like that of solid crystal, so it is named liquid crystal. In addition, LCD is a general term.

2.Types of LCD screen

Currently, LCD display screens are usually referred to as tft-lcd, mainly because TN-LCD, VA-LCD, and IPS-LCD all adopt TFT driver technology, which requires backlight support. TN, VA and IPS are liquid crystal display technologies, the difference is that liquid crystal molecules are arranged in different forms. In terms of the arrangement of liquid crystal molecules in the dimension of panel materials, LCD screen mainly includes the following types:

 

  • TN Screens (Soft panel)

TN Panels namely Twisted Nematic Panel. Due to its low production cost, TN has become the most widely used entry-level liquid crystal Panel and is widely used in the mainstream medium and low-end liquid crystal displays in the market. The disadvantages of TN panels are small visual Angle and limited color restoration ability. The advantage of TN panels is that the number of gray output is small, the liquid crystal molecule deflection speed is fast, the response time is easy to improve.

 

  1. In terms of visual Angle, the TN panel we see on the market is mostly improved TN+film, film namely the compensation film, and the visual Angle can reach 160°. Of course, this is only the limit value measured by the contrast in the case of 10:1. In fact, when the contrast drops to 100:1, the image will be distorted or even biased.
  2. In terms of color reproduction, as 6 bit panel, TN panels can only display the red/green/blue color, 64 largest actual color is only 262.144, through "jitter" technology can make it get more than 16 million kinds of color performance ability, can only show 0 to 252 gray-scale of the three primary colors, so the resulting color display number is 16.2 M, not we usually say the TrueColor of 16.7 M; In addition, TN panel is difficult to improve the contrast, which directly exposed the problem of thin color, poor ability to restore, transition is not natural.
  3. As for response speed, the current market under 8ms LCD products is basically used TN panel. In addition, Samsung also developed a B-TN (Best-TN) panel, which is actually an improved type of TN panel. In order to balance the high-speed response of the TN panel, the contradiction of picture quality must be sacrificed. At the same time, the contrast ratio can reach 700:1, which is close to MVA or early PVA panels.

 

Taiwan a lot of panel manufacturers produce TN panel, TN panel belongs to soft screen, with the hand gently will appear similar water pattern.

  • VA Screens (Soft panel)

VA Panels namely Vertical Alignment Panel. VA Panels are Panel that is widely used in high-end liquid crystal and belongs to the Panel of wide Angle. Compared with TN panel, the advantage of the 8bit VA panel is that it can provide 16.7m color, large visual Angle and better color restoration ability, but the disadvantage is also obvious that the price is more expensive than TN panel. There are two types of VA panels: the MVA panel led by Fujitsu and the PVA panel developed by Samsung, among which the latter is the inheritance and improvement of the former.

In addition, the front (Face) contrast of VA panels is the highest, but the uniformity of the screen is not good enough, and color drift often occurs. Sharp text is its killer, with high contrast between black and white.

 

  1. Fujitsu's MVA (multi-domain Vertical Alignment) is the earliest wide-angle LCD panel technology. Such panels can provide a larger viewing Angle, usually up to 170°. Through technology authorization, CHIMEI electronics, AU optoelectronics, and other panel enterprises have adopted this panel technology. The improved P-MVA panel can reach a visual Angle of nearly 178°, and the gray-scale response time can reach less than 8ms.
  2. Samsung's PVA (Patterned Vertical Alignment) technology also belongs to the category of VA technology, which is the successor and developer of MVA technology. Its comprehensive quality has surpassed the latter, while the improved S-PVA has been able to keep pace with P-MVA, obtaining extremely wide visual Angle and faster and faster response time. PVA adopts a transparent ITO electrode to replace the liquid crystal layer bulge in MVA. The transparent electrode can obtain a better opening rate and minimize the waste of backlight. This mode greatly reduces the possibility of "bright spot" of LCD panel. At present, PVA technology is widely used in high-end LCD or LCD TV.

 

The VA panel is also a soft screen. A similar water pattern will appear when you carefully look at the screen and gently stroke it.

  • IPS Screens (Hard panel)

IPS Panels namely Vertical Alignment Panel. It is the LCD panel technology launched by Hitachi company in 2001, commonly known as "Super TFT".

The advantages of IPS panel are large visual Angle, fast response, accurate color restore, cheap. However, the disadvantage is that the problem of light leakage is serious and black purity is not enough, which is slightly worse than PVA. Therefore, it needs to rely on the compensation of optical film to achieve a better black.

The biggest feature of the IPS panel is that its poles are all on the same surface, unlike the electrodes of other liquid crystal modes, which are arranged in a three-dimensional arrangement on the top and bottom. Since the electrodes are in the same plane, the liquid crystal molecules are always parallel to the screen in whatever state, which will reduce the opening rate and light transmittance, so IPS will need more backlight lamps in LCD TV.

3.Advantages of LCD screen

In general, the advantages of the LCD screen are compared to CRT displays, while those for OLED self-illumination types have their own advantages.

LCD VS CRT, Take up much less space and be lighter.

LCD VS CRT, Energy saving, low power consumption.

LCD VS CRT, The display is much brighter, with better resolution and contrast, and the output is sharper.

LCD VS CRT, The screen is visible with little flicker and the eyes are more comfortable.

LCD VS CRT, Extended service life of 1.3-1.5 million hours.

4.Working of LCD display

The LCD display is mainly composed of backlight module and LCD screen module.

 

Note: The above picture shows how the transmissive LCD Screen works. For the transflective modes etc., the same is true, except in slightly different ways.

Backlight module: provides light source

Top and bottom polarized plates, TFT Glass Substrate, liquid crystal: form polarized light and control the passage of light

Color filter: the source of TFT LCD R/G/B(three primary colors)

ITO transparent conductive layer: provides a transparent conductive path

Photo Spacer: provides a fixed height to color filters and TFT Glass Substrate, as a space to inject liquid crystals, and as a support for the upper and lower layers of Glass

 

Having said that, I believe readers should have a general understanding of the LCD screen.It is very common in life, used in many fields such as laptop computer screen, TVs, cell phones, tablets, and portable video games.