Principles and specifications LCD

 Principles and specifications of LCD (popular posts)
What is LCD
LCD (Liquid Crystal Display) is what we commonly known as LCD monitors, LCD displays the main raw material is the was found, but the real application in life is a thing since 1970. LCD display is widely used in general electronic products, such as electronic watches, cell phone screen, apparatus or digital cameras and other products, but what is LCD What image do?
physical and chemical properties of liquid crystal I feel a bit like ice, it has the fluid flow of liquid and solid-state optical properties of crystals, simply, when the voltage of the LCD by the LCD will change its the physical nature of the deformation, so the angle of reflection will be different, and thus produce changes in color. The concept of liquid crystal displays, from a technical side, the LCD panel contains two non-soda glass material (Substrates), sandwiched a layer of liquid crystal, when the beam passing through this layer of the LCD, the LCD experience side by side, or reverse the shape of irregular, so the LCD is more like a one gate, choose whether the light penetration, we can see the shades on the screen, the patchwork of image.
imaging basic principles of the LCD screen is only black and white color
LCD itself and no changes in color (we used mobile phones, digital watches and so is its color screen), the color of the generation principle is similar to traditional CRT cathode-ray phosphor screen point of the mechanism, there must be a backlit LCD screen, the light will hit the first polarizer layer, and then come to light to the LCD, and when the light through the LCD, it will produce light color change, shot through the LCD to light, but also must go through a color filter, and a second polarizer, the first piece of the polarizer and the second polarizer blocks at the front and rear LCD, two Polarizer difference of 90 degrees, coupled with the physical properties according to the LCD, we can know the voltage of liquid crystal can be used to change the crystal shape, which at the same time through the power, we can see from the screen color changed.
It is because of the LCD display screen and the CRT's electron gun is completely different, so most of the LCD screen when the angle is too large will not know or do not see the present situation, although the installation of some equipment can be improved, but the viewing angle is still smaller than the traditional cathode ray tube, which is the future of LCD display technology to actively solve the problem.
active and passive LCD contact LCD
people, how many should have heard of DSTN, TFT and other specifications, What the two displayed different? Strictly speaking, LCD is divided into active matrix (also known as TFT Active Matrix), that is, the TFT LCD, the other is passive matrix (also known as super-torque display Passive Matrix). active screen is generally TFT, while the passive civilians there are TN, STN, DSTN, respectively (during which there have been such as ESTN other specifications, but did not become mainstream), first let's look at relatively early passive screen .
principle of passive imaging screen is more complex, simply, is the original LCD back version of the order for the smooth passage of light, but a but a voltage change will produce distortion of liquid crystal will the light back to do a considerable degree of change, we now see on the screen will have changed color. passive common in small-screen electronic products like digital watches or cell phone screen, most of the use of passive screen The TN display, that is pure black and white color display, but later position on the demand, but also developed a STN (super TN) and DSTN (Double layer Super TN). DSTN is TN, STN LCD body larger twist angle of deformation, so that the LCD screen can display more colors to express the delicacy, so a laptop about two years ago, was also divided into two kinds of DSTN and TFT, the TFT price was high, so DSTN product was high status. The active screen TFT (Thin Film Transistor TFT) of the imaging methods and DSTH to be different, but generally the imaging principle is the same, but in design of backlight and polarizer, etc. location and direction of change, and the use of field effect transistor FET and the common electrode, the TFT LCD screen can remain potential until the next time the voltage changes, this design is different so will not produce as TFT screen DSTN ghosting or picture delayed afterimage. arrangement and the design and selected materials as different, so color TFT screen, or to good viewing angle than DSTN.
LCD viewing angle
Speaking of visual angle, is important for liquid crystal displays, and if a viewing angle of LCD is only 60 degrees, so users have to constantly change the position of the eyes, that have turned around and stop to look at to the normal color performance. viewing angle of the algorithm is when the liquid crystal display on the desktop, point to what you can clearly see the screen imaging, specifically, you were standing on the LCD Zuoyouliangfang 50 degrees, clear picture can be seen that the level of the LCD viewing angle is 100 degrees (visual angle is about adding the sum and the upper and lower), vertical viewing angle is also true.
LCD's
resolution and dot pitch CRT monitor dot pitch in the interpretation of two adjacent pixels is the shortest distance between the current pitch CRT monitors are mostly around 0.28-0.25, but the current design of LCD monitors and technology, and CRT is different to most of the 0.32-0.297mm dot pitch around (a close look at the surface of LCD monitors, one can see a tiny point of light).
As for the LCD display resolution up to considerable interpretation Interestingly, the main image display pixels (Pixels) consisting of points and lines generated, so the number of pixels is an important factor in the impact of the resolution. the general CRT display is the use of cathode ray tube, a support to the 1024t768 the CTR monitor, or 800t600 640t480 it in terms of the resolution, can show relatively superior color screen (using the flexible adjustment of the electron beam to do), but the LCD can not be so, because the LCD liquid crystal display only supports the so-called resolution effect. Once the resolution is lower than the true resolution, the image can be displayed though, but only ineffective, LCD resolution settings for realistic, there are two kinds of display, in accordance with the LCD's designs, one is centered , that is, the image displayed on the screen, the other has not been shown with the grid pattern of pixels to maintain the dark background, so the whole picture looks like a middle narrow, but there are shadows around the image periphery.
another kinds of display mode for the extended display, this display method is extended to the image of each pixel on the screen, they will not cast a shadow around the edge, but once the resolution is set lower than the actual resolution, then the LCD presents the image will be affected, not only pixels tend to distort the picture of exquisite clarity will be destroyed, which is LCD technology is inherently weaker than the CRT place.
LCD monitor refresh rate problems
different due to the design principle , LCD monitor refresh rate will not be as the level of CRT because of the situation arising from flicker, for CRT monitors, the refresh rate related to the stability of the screen display, the higher the screen refreshes are less likely to blink more than normal CRT refresh rate is 75Hz , users will not feel the image was flickering, CRT monitors is so because the quality is the fluorescence on the CRT electron beam scan through the production of light and dark and continuous light response, and this change if the low frequency , the user will be aware of it. For LCD monitors, the refresh rate at 60Hz, the screen will get better results, why do you say? because each pixel LCD in continuous light, until the non-luminous voltage change and was sent to the controller, so LCD will not have There is a main display backlight light source, the brightness of the light source to dominate entire LCD screen brightness and color saturation, in theory, the brightness of the LCD display is as high as possible, the brightness is measured in cd/m2 ( candle per square meter) was also called the NIT lumens. Most of the current brightness TFT screen is from 150Nits off, usually 200Nits to show better picture, but not the same on the CRT, the same as 150Nits brightness, CRT display will be better than LCD; but 200Nits the brightness, LCD's picture quality is more beautiful than the CRT.
If the LCD screen on the manufacturing or design flaws, then the performance will be a large brightness discount, the general poor performance of the LCD will be darker around the edges of the case, so when you want to buy LCD screen showing the status of anti-white, so most can see the difference of brightness. contrast that is both black and white Comparison of color measurement of the degree of different levels, good 120:1 contrast ratio to display vivid, rich color (because the human eye can distinguish contrast to about 100:1 or so), when the ratio up to 300:1 can support the Ranks color, so in our eyes since the screen which will be even more rich and vibrant! we can use CPU Mark to test the CPU, you can use 3D Mark to test the graphics card, but no one has a fair value to measure the brightness of the standard contrast contrast values (there are many reasons, such as East and West physiological color contrast of different decisions to adapt to the different colors cool Asians, Westerners, warm tone, coupled with the situation of each person's vision different and can not find a balance point, so in almost all have a color temperature adjustment on the monitor and adjust the brightness and contrast a large degree of item), so the purchase of LCD thanks to a pair of sharp eyes.
dead pixels, phase and ripple problem
LCD display fear most is the dead pixels, the so-called dead pixels, that is, no matter how the screen displays the image, LCD display is always a point on the same color (usually green and blue for the dead pixel more But have seen the splash of color and gray), check the dead pixels very simple way, as long as the LCD display brightness and contrast adjustment to the maximum (so that the screen was anti-white screen), and transferred into a minimum (so that the screen was all black screen), you can easily find out the dead pixels can not display color.
LCD production capacity to one of the largest test case of Taiwan LCD (LCD production in Taiwan in the world and second in 2000), a LCD display There are three dead pixels are considered within the qualified products; and Japan should be much stricter, only one less than the dead pixel exists, both price and quality LCD products have a certain reputation or gaps.
In addition, LCD display manufacturing costly, most of the costs are on the LCD panel. the greater the size of the LCD panel more expensive, the price gap to CRT displays is much higher than the ratio of size difference on the price, you know why? LCD screen manufactured by the factory have a certain size, and if you want to create a large 40-inch LCD, can be divided into four 18,19-inch LCD panel, but such a large piece of the LCD screen There will always be the generation of dead pixels, if the dead pixels are too many manufacturers will choose to cut a smaller size, so as to avoid the loss of substantial cost, so there has been no dead pixels or less dead pixels on the large LCD screen seemed more precious, the extraordinarily high prices is natural.
LCD dead pixels in addition to the basic test items, there are the so-called The OSD function to adjust, the most easy to see the bad timing of the phase is observed off the screen, choose Windows, then the screen should have been a shadow mask, if the phase poor, then the display will be like TV ratings the adverse effect of the screen, as if this situation can not be adjusted through the OSD menu, then advise you not to buy this LCD is good, but the phase difference between good and bad, under normal circumstances is not apparent. Water ripple (Moire), also and phase as in ordinary cases, is not apparent, and it demonstrated the symptoms displayed on the screen as the waves ripple effect of Qi in general, and sometimes you can just stand back and observe, but of course not the water ripple a good thing and should be avoided, through the OSD menu can eliminate this situation.
LCD display card special connector
DFP interfaces for liquid crystal displays more realistic effects, and have a special connection standards, such standard called Italian neighbor is always a slight ghosting and color saturation phenomenon, and the current video card support DFP few joints, so the future development and direction DFP I could not say.
LCD's future direction
compared to CRT for LCD technology, while a certain degree of maturity, but away from the developed to the full extent of popularity will take a long time, the main problem of course is the price. Having said that, LCD replaced CRT in some applications the pace is getting faster and faster. LCD display size and power advantages are mainly small, the radiation is zero. but not high resolution LCD is a problem, with large easy to produce graphics pitch from the teeth, so for some workers for the games and graphic design is not appropriate.
LCD LCD Additional features are an important part of future development, in addition to USB HUB, built-in speaker, microphone, but also new entrants to the swivel, wall, etc. function (December Acer's latest LCD with these characteristics to), LCD screen rotation advantage of all users will see a vertical screen display, can display completely A4 picture of a very wide field of vision.
LCD and Comparison of the total CRT
let us look at each of CRT and LCD works now:
LCD (Liquid Crystal Display) is what we commonly known as liquid crystal displays, LCD monitors not only in terms of applications, like electronic watches, PDA, handheld game consoles and LCD products could be seen in the shadow. LCD can be divided into twisted nematic (TN-LCD), super twisted nematic (STN-LCD), thin film transistor (TFT-LCD), such as several species, is now a laptop and LCD are the vast majority of desktop TFT-LCD, it has become the main development direction of liquid crystal displays. like a CRT as the main component is the CRT, LCD is the main components of its LCD panels, LCD panel contains two sodium-free glass material (Substrates), sandwiched between a layer of liquid crystal, when the beam passing through this layer of the LCD, the LCD experience side by side, or reverse the shape of irregular, so the LCD is more like a one gate, choose to wear light Through it, we can see the shades on the screen, the patchwork of images.
the CRT is completely different, CRT works by the filament, cathode, control grid composed of the electron gun, after the filament heating power, the cathode is excited , emitted electron flow, electron flow by a high voltage to accelerate the internal metal layer, after the formation of very fine lens focusing the electron beam hit the screen, so that the light-emitting phosphors. the electron beam deflection coil magnetic field generated by You can control the shooting at the screen at the specified position, the electron beam hit the screen after the formation of a luminous point, a number of light-emitting points can form the image. RGB three-color dots of different intensities of the electron beam is hit, it will produce a variety of colors, by controlling the intensity and the electron beam off, you can form a variety of colorful images. generally the internal shadow mask CRT with a layer similar to the sieve mesh cover, the electron beam through a triangular mesh in order to play fluorescent point, three electron guns corresponding to the three RGB colors, so called Grille is a fixed number of vertical grating formed in the box.
Now we compare the various aspects of LCD and CRT:
one dot pitch.
the so-called pixel pitch means the same in the two a color similar to the distance between phosphor. screen is composed of many pixels, each pixel in turn, composed of red, green and blue phosphors, because the pixels and the pixels are next, so the pixels in the adjacent same color phosphor dot pitch is the distance between. current CRT monitors mostly 0.22-0.26 mm dot pitch, while the LCD and CRT because of their technical differences, mostly 0.297-0.32 mm dot pitch.
Second, the resolution rate.
resolution is a very important performance indicators. It refers to the horizontal and vertical directions on the screen can be displayed by the points (the screen line and the surface is formed by a point) how much resolution higher within the same screen can accommodate, the more information. For a CRT can support 1280x1024 resolution, whether it is 320x240 or 1280x1024 resolution, are able to compare the performance of out perfectly (for flexible adjustment of the electron beam can be done .) maximum resolution, but it may not be the most appropriate resolution, because if the 17-inch monitor to 1280x1024 resolution, then, WINDOWS fonts will be very small, eyes fatigue over time, so the best 17-inch display resolution should be 1024x768.
but it is not true LCD. LCD's maximum resolution is that it's true resolution, which is the best resolution. Once the resolution is less than the real set resolution (such as the 15-inch LCD, the true resolution of 1024x768, and set the resolution WINDOWS 800x600), then there will be two kinds of display. The first center, only the middle of the 800x600 LCD displays the image points, the other does not point will not be used in light, keep the dark background, it seems the screen is centered reduced. Another is to extend the show will be used in this way each pixel on the screen, but pixels are prone to distortion, so will display some impact. Third, the refresh rate.
terms of the CRT, graphic image on the screen is a result of a light beam striking the fluorescent dots, by the CRT electron beam hitting the phosphor short time after the light, so the electron beam hitting phosphor must continue to make steady glow. electron gun from the top left corner of the screen the first line (line number according to the resolution of the display is determined at that time, such as 800X600 resolution, the electron gun will scan 600 lines), the progressive scan from left to right, and then scanned the first line of the extreme left from the second row start to the second line of the far right, has been to scan the full screen of the left and then from the screen Point start, then to complete a refresh on the screen, again and again. so we can understand why the higher the resolution of the monitor, the maximum value can reach the lower the refresh rate. Generally speaking, the screen refresh rate must be more than 75HZ, was not easy to feel the human eye blinking screen, CRT monitor refresh rate is determined by its line frequency and the resolution was the decision, the higher line frequency, the same resolution the higher the refresh rate; The line frequency in certain circumstances, the higher the resolution it can achieve the lower the refresh rate.
refresh rate for LCD is the problem does not exist, it does not refresh. because each LCD pixels are continuous light, no light until the voltage change and was sent to the controller, so the LCD does not have Most flat viewing angle can reach 180 degrees, that is, from any direction in front of the screen can clearly see the displayed content. The LCD is different, it's viewing angle based on advanced technology and not vary, some new products have been able to achieve the 160 viewing angle of about 180 degrees with the CRT has been very close. Although there are some LCD viewing angle of 160 degrees nominal, but actually able to meet this standard. Users Once in the course of the actual visual angle beyond its scope, it will diminish the color screen, darken, or even just as negative as the situation becomes.
V, visual area.
means the viewing area is that in practice, can be used to display images of that part of the screen area. because of the size of CRT monitor is actually the size of the tube, the part can be used to display images failed to reach this size, because the border CRT accounted for part of the space. Generally speaking, 17-inch CRT monitor in the viewing area of about 15.8-16 inches, while the 15-inch display viewing area is only 13.8 inches. but for LCD, the nominal size viewing area is basically the size of the space occupied by a very small frame, 15-inch LCD viewing area of about 14.9 inches, which is why the LCD appears larger than the same size as the reasons for CRT.
Sixth, the brightness and contrast.
main LCD display is a backlit light source, the brightness of the light decision entire LCD screen brightness and color saturation. In theory, the higher the brightness of the LCD display better brightness measured in cd/m2 (candle per square meter), also known as NIT lumens. Most of the current brightness TFT screen is from 150Nits started, usually 200Nits to show better picture. that is, the contrast of two colors black and white contrast levels measured in different degrees. 120:1 contrast ratio to display when the vivid, rich color (because the human eye can distinguish about the contrast of about 100:1), contrast ratio of up to 300: 1 will be able to support the order degree of color. Most LCD monitors are in the 100:1 contrast ratio ~ 300:1 or so. Currently the standard does not have a fair value to measure the contrast of brightness and contrast values, so the purchase of LCD thanks to a pair of sharp eyes.
VII, the reaction rate.
speed of response time measured in milliseconds (ms), refers to the pixel dark by the light turned dark by the time required to switch the two. The lower, the better, with smaller values, indicating that the faster speed of response. the current mainstream LCD 25ms response speed are more than in the general commercial use (such as word processing or text processing) does not have much matter, because such purposes need not be too concerned about the response time LCD. And if it is to play games, watch VCD / DVD and other high-speed dynamic full-screen image, the reaction time is particularly important, and if a longer reaction time, then the screen will appear tailing , blur and so on. cite a simple example, most LCD monitors on the market today while playing QUAKE3 will have different degrees of tailing, high-speed screen updates in particular. The CRT is not the problem, because CRT response time of only 1ms, is tailing phenomenon will not occur.
eight colors.
comes to color, LCD is also smaller than CRT, in theory, CRT TV can display colors with machine as for the infinite. The LCD can display only about 26 million colors, most products are claimed capable of displaying 16.77 million colors (16,777,216 colors, 32-bit), but in fact through dithering algorithm (dithering) to achieve, and true 32-bit color still a big gap compared, so the expression in color and tradition of the transition are still not CRT. By the same token, LCD's ability in the performance of gray is not as CRT. all conditions, then you can compare his own it: looking for a 17-inch Trinitron CRT monitor, and then put a 15-inch LCD, also showed a 16.77 million-color image. CRT display screen is very bright, but LCD is a bit ;, although it can not to anything wrong, but at that station is not comfortable Longguan the CRT.
IX display.
start with CRT, CRT is currently most of the household level there are different degrees of focus , aggregation, respiratory effects and other issues, which manufacturers the technology process are inseparable. If the manufacturer designs the control circuits were not advanced enough, it is prone to those problems previously mentioned. that is why the same is Trinitron picture tube, SONY original production of displays and other display manufacturers performance produced by different reasons. The LCD is totally out of focus and so on, because it does not need to focus. But online form and non-linear distortion problem, LCD may also occur, but more likely nothing more CRT.
ten, other issues.
CRT all claim they passed the small, but the radiation no matter how small, is certain there will be. The LCD works determines that it does not exist any radiation, so the LCD often marked their approximately equal to its diagonal, ie, CRT display area is larger, the greater its volume, often a large number of users occupying the desktop space. The 15-inch LCD, or whether it is 19 inches, its thickness are only a few centimeters or more than ten centimeters, or even hung on the wall, which is impossible in any case CRT. Price, the current use of the 17-inch flat Trinitron CRT monitor prices around 2,500-3,000 yuan so, while its LCD viewing area roughly equal to at least close to 4,000 yuan, slightly more upscale some of the LCD is easily six or seven thousand dollars, not the average family can accept this.
In summary, LCD in the text environmental performance and much better than CRT, but the color, the reaction rate is much less so on CRT's. In the long run, with the continuous improvement of production technology, LCD prices will continue to decline, it will gradually become the general users. but by no means can it replace the CRT, the focus on the commercial use of text effects, it is the best choice. The average family can choose CRT can also choose LCD, because the main focus of the different users, play games, CRT is certainly the best looking DVD. The main purpose is to word processing, play the stock market and the Internet, then the best selection of LCD. In any case, the performance is far cheaper than LCD CRT, but the price is expensive, so we still be better use of CRT, such as LCD technology is mature, and the price lower and back too late.