LCD projector is the product of the combination of LCD display technology and projection technology. It uses the electro-optic effect of liquid crystal to control the transmittance and reflectivity of liquid crystal box through the circuit, thus producing beautiful images with different gray levels and up to 654.38+06.7 million colors. The main imaging device of LCD projector is LCD panel. The size of the LCD projector depends on the size of the LCD panel. The smaller the LCD panel, the smaller the projector.
According to electro-optic effect, liquid crystal materials can be divided into active liquid crystal and inactive liquid crystal, in which active liquid crystal has high transparency and controllability. The LCD panel adopts active liquid crystal, and people can control the brightness and color of the LCD panel through related control systems. Like LCD, LCD projectors use twisted nematic liquid crystals. The light source of LCD projector is a special high-power bulb, and its luminous energy is much higher than that of CRT projector using fluorescence, so the brightness and color saturation of LCD projector are higher than that of CRT projector. Pixels of a liquid crystal projector are liquid crystal cells on a liquid crystal panel. Once the LCD panel is selected, the resolution is basically determined, so the function of adjusting the resolution of LCD projector is worse than that of CRT projector.
LCD projectors can be divided into single LCD panel and three LCD panels according to the number of internal LCD panels. Modern LCD projectors mostly use three-piece LCD panels (Figure 1). The three-piece LCD projector uses three LCD panels of red, green and blue as the control layers of red, green and blue respectively. The white light emitted by the light source is converged to the dichroic mirror group after passing through the lens group, and the red light is first separated and projected on the red liquid crystal panel, and the image information expressed transparently under the "recording" of the liquid crystal panel is projected to generate the red light information in the image. Green light is projected onto the green LCD panel, forming green information in the image. Similarly, blue light passes through a blue liquid crystal panel to generate blue light information in an image. The three colors of light converge in the prism and are projected onto the projection screen by the projection lens to form a full-color image. The three-piece LCD projector has higher image quality and brightness than the single-piece LCD projector. The LCD projector is small in size, light in weight, simple in manufacturing process, high in brightness and contrast, and moderate in resolution. At present, the market share of LCD projectors accounts for more than 70% of the total market share, and it is the most widely used projector in the market.
Main technical parameters of liquid crystal display
1 contrast
The control IC, filter, orientation film and other accessories used in LCD manufacturing are all related to the contrast of the panel. For ordinary users, the contrast ratio of 350: 1 is enough, but this contrast level can not meet the needs of users in professional fields. Compared with CRT display, it can easily achieve a contrast ratio of 500: 1 or even higher. Only high-end liquid crystal displays can reach this level. Because the contrast is difficult to measure accurately with instruments, you should look at it yourself when choosing.
Tip: Contrast is very important. It can be said that the choice of LCD is more important than the bright spot. When you know that customers buy LCDs for entertainment and watching DVDs, you can emphasize that contrast is more important than no bad spots. When we watch streaming media, the brightness of the source is generally not large, but to see the contrast of the character scene and the texture change from gray to black, it depends on the contrast. Excellent VG and VX always emphasize the index of contrast. VG9 10S is the contrast ratio of 1000: 1 At that time, we compared this with one of Samsung and a dual-head graphics card. Samsung LCD is obviously inferior. You can try it if you are interested. In the 256-level gray scale test in the test software, you can see more small gray squares when you look up, which shows that the contrast is very good!
2 brightness
Liquid crystal is a kind of substance between solid and liquid, which cannot emit light by itself. It needs an extra light source. Therefore, the number of lamps is related to the brightness of LCD. The earliest LCD only had two lights. Up to now, the lowest-end Volkswagen LCD is four lights, and the high-end LCD is six lights. The design of the four lamps can be divided into three arrangements: one is that there is one lamp on each side, but there is a shadow in the middle. The solution is that four lights are arranged horizontally up and down, and the last one is in the form of "U", which is actually two lights in disguise. In fact, the six-lamp design is to use Three Lamps District. The manufacturer bends Three Lamps District into a "U" shape, and then places it in parallel to achieve the effect of six lamps.
Tip: Brightness is also an important indicator. The brighter the liquid crystal, the brighter it will stand out from a row of liquid crystal walls. The highlight technologies we often see in CRT (Youpai is called highlight, Philips is called bright, and BenQ is called sharp color) are all produced by increasing the current of cathode tube and bombarding phosphor. This technology is generally adopted at the expense of image quality and display life. Press one to watch DVD with 5X brightness, and it's all burnt at a glance. If you want to read the text, you have to honestly return to the ordinary text mode. This design is actually to make people not highlight frequently. The principle of. The display brightness of LCD is different from CRT, which is realized by the brightness of backlight behind the panel. Therefore, more lamps should be designed so that the light will be uniform. When I sold LCDs in the early days, I told others that it was awesome to have three LCDs, but at that time Chi Mei CRV began to do it. This six-lamp design, coupled with the strong light of the lamp itself, makes the panel bright. This masterpiece is represented by VA7 12 in Youpai. But all highlighted panels will be fatal and the screen will leak light. This term is rarely mentioned by ordinary people. The editor personally thinks it is very important. Light leakage indicates that the LCD is not black, but gray. So a good LCD should not emphasize brightness blindly, but should emphasize contrast more. Excellent VP and VG series are products that don't talk about brightness but only contrast!
3 signal response time
Response time refers to the response speed of liquid crystal display to input signals, that is, the response time of liquid crystal from dark to bright or from bright to dark, usually in milliseconds (ms). To make this clear, we should also talk about the human eye's perception of dynamic images. There is a phenomenon of "visual residue" in the human eye, and the high-speed moving picture will form a short impression in the human brain. Cartoons, movies, etc. So far, the latest game only applies the principle of visual residual, so that a series of gradual images are displayed in front of people quickly and continuously, and then dynamic images are formed. Generally speaking, the acceptable display speed of pictures is 24 frames per second, which is also the origin of the 24-frame playback speed of movies. If the display speed is lower than this standard, people will obviously feel the pause and discomfort of the picture. According to this index, the display time of each picture needs to be less than 40ms, in this case, the response time of 40ms becomes a hurdle for LCD, and the display below 40 ms will have obvious picture flicker, which makes people feel dizzy. If you want the image not to flicker, you'd better reach the speed of 60 frames per second.
I use a very simple formula to calculate the number of frames per second under the corresponding reaction time as follows:
Response time 30ms= 1/0.030= approximately 33 frames per second are displayed.
The response time is 25ms= 1/0.025= about 40 frames are displayed every second.
Response time16 ms =1/0.016 = approximately 63 frames are displayed every second.
Response time12 ms =1/0.012 = about 83 frames are displayed per second.
Response time 8ms= 1/0.008= approximately 125 frames are displayed every second.
Response time 4ms= 1/0.004= about 250 frames per second are displayed.
Response time 3ms= 1/0.003= about 333 frames per second are displayed.
Response time 2ms= 1/0.002= about 500 frames per second are displayed.
Response time 1 ms = 1/0.00 1= approximately 1000 frames are displayed every second.
Tip: From the above, we know the relationship between response time and frame number. It seems the shorter the response time, the better. At that time, the LCD market had just started, and the minimum acceptable range of response time was 35ms, mainly products represented by EIZO. Later, BenQ's FP series introduced 25 ms, which was almost imperceptible from 33 frames to 40 frames. The real qualitative change is 16MS, which displays 63 frames per second, meeting the requirements of movies and general games, so up to now, 16MS is not out of date. With the improvement of panel technology, BenQ and Youpai started a speed struggle. Youpai was released to 1MS from 8MS, 4ms and 4ms, so it can be said that 1MS is the final argument of liquid crystal speed. For game enthusiasts, the speed of 1MS means that CS can shoot more accurately, at least psychologically, so customers will recommend VX series monitors. But when selling, people should pay attention to the text difference between gray-scale response and full-color response. Sometimes grayscale 8MS and full-color 5MS mean the same thing, just like when we used to sell CRT, we said that the dot pitch was .28,28, and LG had to say .2655. The horizontal point distance is ignored. In fact, both sides said the same thing. Now recently LG has come up with the sharpness of 1600: 1, which is also a concept hype. Basically, most users have very few screens. Only LG can do 1600: 1, and everyone stays at 450. When it comes to consumers, it clearly means sharpness and contrast, just like AMD's PR value, which is meaningless.
4 visual angle
The viewing angle of LCD is a headache. When the backlight passes through the polarizer, the liquid crystal and the alignment layer, the output light will be directional. In other words, most of the light is emitted vertically from the screen, so when you look at the LCD from a larger angle, you can't see the original color, or even see all white or all black. In order to solve this problem, manufacturers also began to develop wide-angle technology. So far, there are three popular technologies: TN+ thin film, IPS (in-plane exchange) and MVA (multi-domain vertical arrangement).
TN+ membrane technology is to add a wide viewing angle compensation film on the original basis. This compensation film can increase the viewing angle to about 150 degrees, which is a simple and easy method and widely used in liquid crystal displays. But this technology can't improve the performance such as contrast and response time. Perhaps TN+ film is not the best solution for manufacturers, but it is the cheapest solution, so most manufacturers in Taiwan Province Province use this method to build 15 inch LCD.
IPS(IN-PLANE -SWITCHING) technology claims that it can make the visual angle of up, down, left and right reach 170 degrees. Although IPS technology increases the viewing angle, using two electrodes to drive liquid crystal molecules requires more power consumption, which will increase the power consumption of liquid crystal displays. In addition, it is fatal that the response time of driving liquid 32 LCD molecules will be slower.
MVA (multi-domain vertical alignment) technology, the principle is to add protrusions to form multiple visual areas. Liquid crystal molecules are not completely vertically aligned at rest, but horizontally aligned after voltage is applied, so that light can pass through each layer. MVA technology improves the viewing angle to more than 160 degrees, and provides shorter response time than IPS and TN+ films. This technology was developed by Fujitsu. At present, Chi Mei in Taiwan Province Province (Chi Li is a subsidiary of Chi Mei in Chinese mainland) and AUO in Taiwan Province Province are authorized to use this technology. VX2025WM is the representative work of this kind of panel. Horizontal vertical viewing angle 175 degrees, basically no visual dead angle, no bright spot promised. The visual angle is divided into parallel visual angle and vertical visual angle. The horizontal angle is centered on the vertical central axis of the liquid crystal, and the angular range of the image can be clearly seen by moving left and right. The vertical angle is centered on the parallel central axis of the display screen, and the angle range of the image can be clearly seen by moving up and down. The viewing angle is in degrees. At present, the commonly used labeling form is to directly label the total horizontal and vertical range, such as 150/ 120 degrees. At present, the lowest viewing angle is 120/ 100 degrees (horizontal/vertical). Below this value is unacceptable, and it is better to reach 100 degrees.
There is fierce competition among various brands of flat panel displays in the domestic computer market, and all businesses want to get the largest share in the flat panel display cake. When people buy flat-screen TVs to go home like 15 inch monitors. We should not only ask: What is the hot spot of the next generation display? Point your finger at the LCD screen. Liquid crystal display has the advantages of clear and accurate image, flat display, thin thickness, light weight, no radiation, low energy consumption and low working voltage.
Classification of liquid crystal displays
According to different control methods, LCD can be divided into passive matrix LCD and active matrix LCD.
1. Passive matrix LCD is greatly limited in brightness and viewing angle, and its response speed is also slow. Due to the problem of image quality, this kind of display equipment is not conducive to the development of desktop display, but due to the low cost, some displays in the market still use passive matrix LCD. Passive matrix liquid crystal displays can be divided into TN-TN-LCD (twisted nematic liquid crystal display), STN-LCD (super TN-LCD) and DSTN-LCD (double layer STN-LCD).
2. At present, the widely used active matrix liquid crystal display is also called TFT-LCD. TFT liquid crystal display is a transistor built into each pixel in the picture, which can make the brightness brighter, the colors richer and the visual area wider. Compared with CRT display, the flat panel display technology of LCD display is characterized by less parts, less desktop occupation and low power consumption, but CRT technology is more stable and mature.
Working principle of liquid crystal display
We have long known that there are three forms of matter: solid, liquid and gas. Although there is no regularity in the centroid arrangement of liquid molecules, if these molecules are long (or flat), their molecular orientation may be regular. So we can subdivide liquids into many types. Liquid with irregular molecular orientation is directly called liquid, and liquid with directional molecules is simply called "crystalline liquid" or "liquid crystal". In fact, liquid crystal products are no strangers to us. The mobile phones and calculators we often see belong to LCD products. Liquid crystal was discovered by Austrian botanist Reinitzer in 1888. It is an organic compound with regular molecular arrangement between solid and liquid. The most commonly used type of liquid crystal is nematic liquid crystal, and its molecular shape is slender rod, and its length and width are about 1 nm ~ 10 nm. Under the action of different current and electric field, liquid crystal molecules will rotate 90 degrees regularly, resulting in the difference of light transmittance, thus resulting in the difference of light and dark when the power supply is on/off. According to this principle, each pixel can be controlled to form a desired image.
1. Working principle of passive matrix liquid crystal display
The display principles among TN-LCD, STN-LCD and DSTN-LCD are basically the same, but the twist angles of liquid crystal molecules are somewhat different. Taking a typical TN-LCD as an example, its structure and working principle are introduced.
In a TN-LCD panel with a thickness less than 1 cm, it usually consists of two large glass substrates with a color filter and an alignment film sandwiched between them. Two polarizers are wrapped outside, which can determine the maximum luminous flux and color generation. Color filters are filters composed of red, green and blue, which are regularly made on large glass substrates. Each pixel consists of cells (or sub-pixels) of three colors. If the resolution of a panel is 1280× 1024, then it actually has 3840× 1024 transistors and sub-pixels. The upper left corner (gray rectangle) of each sub-pixel is an opaque thin film transistor, and the color filter can produce three primary colors of RGB. Each interlayer contains electrodes and grooves formed on the alignment film, and the upper and lower interlayers are filled with multiple layers of liquid crystal molecules (the liquid crystal spacing is less than 5× 10-6m). In the same layer, although the position of liquid crystal molecules is irregular, the long axis orientation is parallel to the polarizer. On the other hand, between different layers, the long axis of liquid crystal molecules is continuously twisted by 90 degrees along the parallel plane of the polarizer. Wherein, the long axis orientation of the two layers of liquid crystal molecules adjacent to the polarizer is consistent with the polarized light direction of the adjacent polarizer. The liquid crystal molecules near the upper interlayer are arranged along the direction of the upper trench, while the liquid crystal molecules in the lower interlayer are arranged along the direction of the lower trench. Finally, it is packaged into a liquid crystal box and connected with a driving IC, a control IC and a printed circuit board.
In general, when the light is irradiated from top to bottom, usually only one angle of light can penetrate downward, and it is introduced into the groove of the upper interlayer through the upper polarizer, and then it passes through the lower polarizer through the twisted arrangement of liquid crystal molecules, forming a complete light penetration path. Two polarizers are attached to the interlayer of the LCD, and the arrangement and light transmission angle of the two polarizers are the same as those of the grooves in the upper and lower interlayers. When a certain voltage is applied to the liquid crystal layer, due to the influence of external voltage, the liquid crystal will change its initial state, no longer arranged in a normal way, but become an upright state. Therefore, the light passing through the liquid crystal will be absorbed by the second polarizer, and the whole structure will be opaque, resulting in black on the display screen. When no voltage is applied to the liquid crystal layer, the liquid crystal is in its initial state, which will distort the direction of the incident light by 90 degrees, thus allowing the incident light of the backlight to pass through the whole structure, resulting in the appearance of white on the display screen. In order to realize that each independent pixel on the panel can produce the color you want, multiple cold cathode tubes must be used as the backlight of the display.
2. The working principle of active matrix liquid crystal display.
The structure of TFT-LCD liquid crystal display is basically the same as TN-LCD liquid crystal display, except that the upper interlayer electrode of TN-LCD is changed to FET transistor and the lower interlayer electrode is changed to * * * on electrode.
There are many differences in the working principles between TFT-LCD and TN-LCD. The imaging principle of TFT-LCD liquid crystal display is "back-transparent" illumination. When the light source illuminates, it first passes through the lower polarizer and transmits light with the help of liquid crystal molecules. Because the electrodes of the upper and lower interlayers are changed to FET electrodes and * * * through electrodes, when the FET electrodes are turned on, the arrangement state of liquid crystal molecules will also change, and the purpose of display can be achieved through shading and light transmission. But the difference is that the FET transistor can keep the potential state because of the capacitance effect, and the liquid crystal molecules that have been transparent before will keep this state until the FET electrode is electrified again to change its arrangement.
Technical parameters of liquid crystal display
1. Visible area
The size of LCD display is the same as the screen range that can actually be used. For example, an LCD of 15. 1 inch is approximately equal to the visual range of a CRT screen of 17 inch.
2. Perspective
The viewing angle of LCD is symmetrical left and right, but not necessarily symmetrical up and down. For example, when the incident light from the backlight passes through the polarizer, the liquid crystal and the alignment film, the output light has a specific directional characteristic, that is, most of the light emitted from the screen has a vertical direction. If we look at an all-white picture from a very oblique angle, we may see black or color distortion. Generally speaking, the upper and lower angles are less than or equal to the left and right angles. If the viewing angle is 80 degrees left and right, it means that the screen image can be clearly seen from the position 80 degrees perpendicular to the screen. However, due to the different visual range of people, if you don't stand in perfect angle, you will see errors in color and brightness. Now some manufacturers have developed various wide viewing angle technologies, trying to improve the viewing angle characteristics of liquid crystal displays, such as IPS (in-plane switching), MVA (multi-domain vertical alignment), TN+ film and so on. These technologies can improve the viewing angle of LCD to 160 degrees or even more.
3. Point distance
We often ask about the dot distance of LCD, but most people don't know how to get this value. Now let's see how it was obtained. For example, the visual area of a general 14 inch LCD is 285.7mm×2 14.3mm, and its maximum resolution is 1024×768, so the dot distance is equal to: visual width/horizontal pixel (or visual height/vertical pixel), that is, 285.7 mm//kloc.
4. Sexuality
Of course, the importance of LCD lies in color representation. We know that any color in nature is composed of three basic colors: red, green and blue. The LCD panel consists of 1024×768 pixels, and the color of each independent pixel is controlled by three basic colors: red, green and blue (R, G and B). The LCD produced by most manufacturers has six basic colors (R, G, B), that is, 64 expressions, so each independent pixel has 64×64×64=262 144 colors. There are also many manufacturers who use the so-called FRC (Frame Rate Control) technology to simulate full-color pictures, that is, each basic color (R, G, B) can reach 8 bits, that is, 256 expressive forces, so each independent pixel has as many as 256× 256× 256 =1677 7216 colors.
Step 5 compare values
The comparison value defines the ratio of the maximum brightness value (all white) divided by the minimum brightness value (all black). The comparative value of CRT display is usually as high as 500: 1, so it is easy to present a real black picture on CRT display. But it is not easy for LCD. The backlight composed of cold cathode ray tubes is difficult to switch quickly, so the backlight is always on. In order to get a completely black picture, the liquid crystal module must completely block the light from the backlight, but from the physical characteristics, these components can not fully meet this requirement, and there will always be some light leakage. Generally speaking, the comparison value acceptable to human eyes is about 250: 1.
6. Brightness value
The maximum brightness of LCD is usually determined by cold cathode ray tube (backlight), and the brightness value is generally between 200-250 CD/m2. The brightness of LCD is slightly lower, which will darken the screen. Although it is technically possible to achieve higher brightness, it does not mean that the higher the brightness value, the better, because a display with too high brightness may harm the eyes of the viewer.
7. Response time
Response time refers to the response speed of each pixel of LCD to input signal, and the smaller this value, the better. If the response time is too long, it may make the LCD display have the feeling of trailing shadow dragging when displaying dynamic images. The response time of ordinary LCD is between 20 and 30 milliseconds.
Reference website: -lanyuan.com
[Edit this paragraph] Features of ]LCD
Low voltage micropower consumption
Flat plate structure
Passive display type (no glare, no irritation to human eyes, no eye fatigue)
Display a lot of information (because pixels can be smaller)
Easy to color (can be reproduced very accurately in chromatography)
No electromagnetic radiation (safe for human body and beneficial to information confidentiality)
Long life (this device has almost no deterioration problem, so its life is extremely long, but the LCD backlight life is limited, but the backlight part can be replaced)
Working principle of liquid crystal display
From the structure of LCD, whether it is a notebook computer or a desktop system, the LCD screen used is a layered structure composed of different parts. LCD consists of two glass plates with a thickness of about 1 mm, which are evenly spaced by 5 microns and contain liquid crystal materials. Because the liquid crystal material itself does not emit light, there are lights on both sides of the display screen as light sources, and there are backlight plates (even light guide plates) and reflective films on the back of the liquid crystal display screen. The backlight board is made of fluorescent substances, which can emit light, and its main function is to provide a uniform background light source.
The light emitted by the backlight plate enters the liquid crystal layer containing thousands of liquid crystal droplets after passing through the first polarizing filter layer. The droplets in the liquid crystal layer are all contained in a fine cell structure, and one or more cells constitute a pixel on the screen. Between the glass plate and the liquid crystal material are transparent electrodes, which 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, and the liquid crystal material acts like a small light valve. Around the liquid crystal material are a control circuit part and a drive circuit part. When the electrodes in the liquid crystal display generate an electric field, the liquid crystal molecules will be distorted, so that the light passing through them will be refracted regularly, and then displayed on the screen after being filtered by the second filter layer.
There are also weaknesses and technical bottlenecks in LCD technology. Compared with CRT display, there are obvious gaps in brightness, picture uniformity, viewing angle and reaction time. The reaction time and viewing angle depend on the quality of the LCD panel, and the picture uniformity has a great relationship with the auxiliary optical module.
For LCD, brightness is usually related to its backlight. The brighter the backlight, the higher the brightness of the whole LCD. Early liquid crystal displays, because only two cold light source tubes were used, often had uneven brightness and unsatisfactory brightness. It was not until the introduction of four cold light source lamp products that it was greatly improved.
The signal reaction time is also the response delay of the liquid crystal cell of the liquid crystal display. In fact, it refers to the time required for the liquid crystal cell to change from one molecular arrangement state to another. The shorter the response time, the better. It reflects the response speed of each pixel of the LCD to the input signal, that is, the speed at which the screen changes from dark to bright or from bright to dark. The shorter the response time, the user will not feel dragged to the tail shadow when watching the moving picture. Some manufacturers will reduce the concentration of conductive ions in liquid crystals to achieve fast signal response, but their color saturation, brightness and contrast will be reduced accordingly, and even color cast will occur. In this way, the signal reaction time goes up, but the display effect of LCD is sacrificed. Some manufacturers adopt the method of adding IC image output control chip to the display circuit to process the display signal. IC chip can adjust the signal response time according to the frequency of VGA output graphics card signal. Because the physical properties of liquid crystal are not changed, its brightness, contrast and color saturation are not affected, and the manufacturing cost of this method is relatively high.
As can be seen from the above, the quality of LCD panel does not fully represent the quality of LCD. Without excellent display circuit, even the best panel can't make an LCD with excellent performance. With the increase of LCD output and the reduction of cost, LCD will be widely used.
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