To put it simply, the LCD module is the screen + backlight assembly. The display component of the LCD TV is the liquid crystal module, which is equivalent to the picture tube in the CRT. Other parts include power supply circuits, signal processing circuits, etc., and of course the housing. Modules are mainly divided into screen and backlight components. The two parts are assembled together, but are independent of each other when working (that is, the circuits are not related).

The principle of liquid crystal display is that the backlight assembly emits uniform surface light, and the light is transmitted to our eyes through the LCD screen. The function of the screen is to process these lights in pixels to display images. Both parts contain a lot of parts, so I won't go into details here. Currently the best technology is Sharp, followed by Samsung Sony.

The main parameters

Contrast

The control ICs, filters and oriented films used in the manufacture of LCD panels are related to the contrast of the panel. For general users, a contrast ratio of 350:1 is sufficient, but such a contrast ratio in the professional field is not enough. Meet the needs of users. Relative to CRT monitors easily reach a contrast ratio of 500:1 or even higher. Only high-end liquid crystal displays can achieve this level. Since the contrast is difficult to accurately measure with the instrument, it is better to see it yourself when you choose.

Little ant tip: Contrast is very important. It can be said that selecting an indicator of LCD is more important than bright spots. When you understand that your customers buy LCDs for entertainment and watching DVDs, you can emphasize that contrast is more important than no pixels. When we are watching streaming media, the source brightness is generally not large, but to see the contrast of light and dark in the character scene, and the texture change from gray to black hair, we must rely on the level of contrast to show. ViewSonic’s VG and VX have always emphasized the contrast index. The VG910S has a contrast ratio of 1000:1. We tested this with a dual-head graphics card from Samsung at the time, and Samsung’s LCD was clearly inferior. If you are interested, you can try it. In the 256-level grayscale test in the test software, more small gray grids can be seen clearly when looking up, which is a good contrast!

brightness

Liquid crystal is a substance between solid and liquid. It cannot emit light by itself and requires additional light sources. Therefore, the number of lamps is related to the brightness of the liquid crystal display. The earliest liquid crystal displays had only two upper and lower lamps. Up to now, the lowest of the popular type is four lamps, and the high-end one is six lamps. The four-lamp design is divided into three types of placement: one is that there is one lamp on each of the four sides, but the disadvantage is that dark shadows appear in the middle. The solution is to arrange the four lamps from top to bottom. The last one is the "U"-shaped placement, which is actually two tubes produced by two lamps in disguise. The six-lamp design actually uses three lamps, and the manufacturer bends all three lamps into a "U" shape, and then places them in parallel to achieve the effect of six lamps.

Little Ant Tip: Brightness is also a relatively important indicator. The brighter the LCD is far away, it will stand out from a row of LCD walls. The highlight technology we often see in CRT (ViewSonic is called Gaoliang, Philips It is called Xianliang, and BenQ is called Ruicai) are all through increasing the current of the shadow mask tube to bombard the phosphor to produce a brighter effect. This kind of technology is generally traded at the expense of image quality and the life of the display. The products using this kind of technology are all bright by default, and you have to press a button to do it. Press 3X bright to play games; press again to turn to 5X bright to watch the DVD, and he gets confused after a closer look. , Depending on the text, you have to return to the normal text mode. This design actually prevents you from frequently highlighting. The principle of LCD display brightness is different from CRT. They are realized by the brightness of the backlight tube behind the panel. Therefore, the lamp has to be designed more so that the light will be uniform. In the early days when we sold LCDs, we told others that there were three LCDs, so it was pretty awesome, but at that time, Chi Mei CRV came up with a six-lamp technology. In fact, the three tubes were bent into a "U" shape. The so-called six; such a six-tube design, plus the strong luminescence of the lamp itself, the panel is very bright, such a masterpiece is represented by VA712 in ViewSonic; but all bright panels will have a fatal The screen will leak light. This term is rarely mentioned by ordinary people. I personally think it is very important. Light leakage means that under a completely black screen, the LCD is not black, but whitish and gray. Therefore, a good LCD should not emphasize brightness blindly, but more emphasis on contrast. ViewSonic's VP and VG series are products that do not emphasize brightness but contrast!

Signal response time

Response time refers to the response speed of the liquid crystal display to the input signal, that is, the response time of the liquid crystal from dark to bright or from bright to dark, usually in milliseconds (ms). To make this clear, we have to start with the human eye's perception of dynamic images. There is a phenomenon of "visual residue" in the human eye, and high-speed moving pictures will form a short-term impression in the human brain. Animations, movies, and other up-to-date games have applied the principle of visual residue, allowing a series of gradual images to be displayed in rapid succession in front of people, forming dynamic images. The acceptable picture display speed is generally 24 frames per second, which is the origin of the movie playback speed of 24 frames per second. If the display speed is lower than this standard, people will obviously feel the picture pause and discomfort. According to this index calculation, the time required for each picture to be displayed is less than 40ms. In this way, for the liquid crystal display, the response time of 40ms becomes a hurdle, and the display below 40ms will have obvious "tailing" or "after-image" phenomenon, which makes people feel chaotic. If you want the image to be smooth, you need to reach 60 frames per second.

I used a very simple formula to calculate the number of frames per second under the corresponding response time as follows:

Response time 30ms=1/0.030=approximately 33 frames per second

Response time 25ms=1/0.025=approximately 40 frames per second

Response time 16ms=1/0.016=approximately 63 frames per second

Response time 12ms=1/0.012=approximately 83 frames per second

Response time 8ms=1/0.008=approximately 125 frames per second

Response time 4ms=1/0.004=approximately 250 frames per second

Response time 3ms=1/0.003=approximately display 333 frames per second

Response time 2ms=1/0.002=approximately 500 frames per second

Response time 1ms=1/0.001=approximately 1000 frames per second

Little Ant Tip: Through the above content, we understand the relationship between response time and the number of frames. From this, the response time is as short as possible. At that time, when the LCD market first started, the lowest acceptable range of response time was 35ms. It was mainly products represented by EIZO. Later, BenQ's FP series was launched to 25ms. From 33 to 40 frames, it was basically undetectable. It was really quality. The change is 16MS, 63 frames per second, in order to meet the requirements of movies, general games, so until now 16MS is not obsolete, with the improvement of panel technology, BenQ and ViewSonic started a speed battle, ViewSonic started from 8MS, 4 milliseconds have been released to 1MS, it can be said that 1MS is the final controversy of LCD speed. For game enthusiasts, 1MS faster means that CS's marksmanship will be more accurate, at least psychologically, such customers should recommend VX series monitors. But when you sell, you should pay attention to the difference between grayscale response and full-color response text. Sometimes grayscale 8MS and full-color 5MS mean the same thing, just like when we sold CRTs before, we said that the dot pitch is .28, LG just I have to say that it is .21, but the horizontal dot pitch is ignored. In fact, the two sides are talking about the same thing. Recently, LG has come up with a sharpness of 1600:1. This is also a conceptual hype, and everyone uses it. Which ones are basically the screens? How can only LG do 1600:1, and everyone stays at the 450:1 level? When it comes to consumers, the meaning of sharpness and contrast is clear. It is like AMD's PR value, which has no real meaning.

 

Viewing angle

The viewing angle of the liquid crystal is a headache. When the backlight passes through the polarizer, the liquid crystal and the orientation layer, the output light becomes directional. In other words, most of the light is emitted vertically from the screen, so when viewing the LCD from a larger angle, you cannot see the original color, or even see the entire white or all black. In order to solve this problem, manufacturers have also started to develop wide-angle technology. There are three popular technologies: TN+FILM, IPS (IN-PLANE-SWITCHING) and MVA (MULTI-DOMAIN VERTICAL alignMENT).

The TN+FILM technology is to add a layer of wide viewing angle compensation film on the original basis. This layer of compensation film can increase the viewing angle to about 150 degrees, which is a simple and easy method and is widely used in liquid crystal displays. However, this technology cannot improve performance such as contrast and response time. Perhaps for manufacturers, TN+FILM is not the best solution, but it is indeed the cheapest solution, so most Taiwanese manufacturers use this Method to build a 15-inch LCD monitor.

IPS (IN-PLANE-SWITCHING) technology claims to allow up, down, left, and right viewing angles to reach a greater 170 degrees. Although the IPS technology increases the viewing angle, the use of two electrodes to drive the liquid crystal molecules requires more power consumption, which will increase the power consumption of the liquid crystal display. In addition, the fatal thing is that the response time of driving liquid crystal molecules in this way will be relatively slow.

The principle of MVA (MULTI-DOMAIN VERTICAL alignMENT) technology is to increase protrusions to form multiple visible areas. The liquid crystal molecules are not completely arranged vertically in a static state. After a voltage is applied, the liquid crystal molecules are arranged horizontally so that light can pass through the layers. MVA technology increases the viewing angle to more than 160 degrees and provides a shorter response time than IPS and TN+FILM. This technology was developed by Fujitsu, and Taiwan's Chi Mei (Chi Mei is a subsidiary of Chi Mei in the mainland) and Taiwan AUO are authorized to use this technology. ViewSonic’s VX2025WM is a representative of this type of panel. The horizontal and vertical viewing angles are both 175 degrees, basically no blind spots, and promises no bright spots; the viewing angle is divided into parallel and vertical viewing angles, and the horizontal angle is based on LCD The vertical axis is the center, moving left and right, you can clearly see the angle range of the image. The vertical angle is centered on the parallel central axis of the display screen, moving up and down, the angle range of the image can be clearly seen. The viewing angle is in "degrees". The more commonly used marking form is to directly mark the total horizontal and vertical ranges, such as 150/120 degrees, and the lowest viewing angle is 120/100 degrees (horizontal/vertical), which is lower than This value is unacceptable, and it is best to reach 150/120 degrees or more.

classification

There are two main types of liquid crystal modules, one is color liquid crystal; the other is monochromatic liquid crystal. Monochrome LCD is divided into monochrome graphic dot matrix LCD screen, monochrome character dot matrix LCD screen, and monochrome customized pen segment LCD screen.

application

Application of LCD module: power measurement and control terminal, injection molding machine computer, numerical control system, human-machine interface, medical instrument, biochemical analysis, textile machinery control, tax control machine, lottery machine, food inspection, chromatography analysis, electronic measurement, environmental laboratory equipment , Fire safety, automotive electronics and data acquisition.

LCD module