Liquid Crystal Display (LCD) technology. Flat screen technology What determines quality
There are only two mass technologies for manufacturing displays for phones: screens based on LCD, i.e. liquid crystals, and based on OLED- organic luminescent technologies. Liquid crystal displays are by far the most common, but the development and adoption of more modern OLED technology is incredibly fast! There is still technology e-ink- such displays can theoretically be used in mobile phones and other "small" equipment, but the cost of their production is still quite high, and there are drawbacks.
Liquid Crystal LCD
Devices with LCD screens - LCD(liquid cristal display) - today you can see everywhere: computer displays (flat panels), TVs, PDAs. And, of course, cell phones. Almost all phones sold today are equipped with LCD screens: monochrome (amber, gray-green) or color.
What are these crystals? They, like solid crystalline substances, such as salt, have a strictly defined structure - a crystal lattice - and are transparent to light. But, unlike ordinary crystals, liquid crystals can change their structure under external influence (electric current or temperature), twist, becoming opaque. Dark elements on the screen are areas of the LCD coating that are energized. By controlling the current, you can create inscriptions or pictures on the screen and just as easily make them disappear.
Liquid crystals were discovered by the Austrian botanist Reinitzer in 1888. And only in 1963, scientists discovered that in the normal state, such crystals transmit light, but can change their structure and reflect or absorb light under the influence of an electric current. This discovery, 10 years later, led to the creation of the first LCD screen, which appeared on the market in 1973 in Sharp calculators.
Since then, scientists have created several more information display technologies based on the use of liquid crystals. We only note that almost all today's LCD displays can be divided into those where the crystals reflect / absorb external light, and those where the crystals convert (polarize) the light that comes from the source built into the phone. The latter are now used everywhere, because they are able to provide generally acceptable image quality, and the range of displayed color shades is not so small.
You must have come across the abbreviation STN (super twisted nematic - a structure with super high distortion), in such displays the crystals are able to “twist” especially strongly, which provides a black and white or color picture on the screen with increased contrast. In STN, the degree of "twisting" is very high - up to 140 percent! Such screens are found in many modern phones.
LCD displays can use an active or passive matrix for control. The passive matrix is formed by superimposing layers of horizontal and vertical contact strips. If you apply current to a vertical and horizontal strip, setting coordinates, as in the Sea Battle game, then where these strips intersect, the crystals will change their structure, and you can see a dot in the corresponding place on the screen. Depending on the strength of the current, the crystals rotate (distort) to a greater or lesser extent, letting in more or less light, respectively. In color displays, they also polarize light. When polarized from the white light of an electroluminescent backlight lamp, certain color components are “cut out” in the required proportions, which ultimately determines the color of the screen dot. By the way, it is the effect of light polarization that leads to the fact that iridescent stains can be observed on the surface of the CD. Note that one of the main disadvantages of such screens is their low performance - this does not matter for static pictures, but dynamic pictures, for example, animated screensavers or toys, look unsightly on such displays. An example of a passive matrix is the screen installed in Nokia 7210/6610 devices.
Active matrices
Active matrices are another way to control liquid crystals. Active matrices are abbreviated TFT(Thin Film Transistors) or AM (Active Matrix). Under the surface of the screen based on them - a layer of tiny transistors, semiconductors, each of which controls one point of the screen. In the color display of the phone, their number can reach several tens (or even hundreds) of thousands. This control method allows you to speed up the display several times, although this method is not very effective for playing a video, the image may be slightly “blurred”, since the crystals themselves will not have time to turn around with the required speed.
It happens that the transistor fails. Such a defect is easy to notice with the naked eye - the dot of the screen constantly glows with a bright "star" against the background of others or does not glow at all. Therefore, when buying a mobile phone, do not be too lazy to turn it on and carefully look at the display and, if you notice “broken” elements, change the device in time.
Samsung developers are going their own way - last year the company introduced LCD displays made using its own technology. UVB(Ultra Fine and Bright). Behind this acronym is a screen that has increased brightness and contrast, while power consumption is reduced compared to traditional LCDs. In addition, the production of a new display, according to the developers, is cheaper. It is interesting that it was possible to break through the barrier of 65 thousand colors, since 2003 screens for 260 thousand have already been in the series.
Organic OLED displays
Breach in the dominance of LCDs broke a new technology OLED(Organic Light Emitting Diodes) - electroluminescent displays based on organic light-emitting semiconductors. The main difference is that backlights are not needed; in the new displays, surface elements glow directly. And they glow brightly, ten times brighter than LCD screens! At the same time, they consume much less electricity, provide good color reproduction, high contrast, large viewing angle (up to 180 degrees), and can have a wide color gamut. Of the shortcomings, we note a relatively low "lifetime" (about 5-8 thousand hours), however, for a phone - more than enough.
In terms of thickness, organic displays are commensurate with ordinary window glass, however, there are even flexible samples that are predicted to have a great future as, for example, large-format screens. If necessary, they can be pulled out of the phone, and after use, such a screen will again roll into a roll inside the body of the device.
"Organics" equip mainly expensive devices of the highest class, the mass production of which is not yet so large-scale. However, leading display manufacturers (Sanyo, Sony, Samsung, Philips and others) are so actively promoting OLED technology to the market that very soon such displays will begin to replace the usual STN.
How are organic OLED screens arranged?
Readers do not need to explain what ordinary LEDs (inorganic) are - they can be seen in various electronic equipment, from televisions and tape recorders to telephones and computers. Humanitarians usually call green or red LEDs (for example, those that, by blinking, tell you if you are in a cellular network coverage area) “bulbs”: in fact, these are semiconductor devices capable of emitting light of one color or another under the influence of current.
For the first time, organic luminescent semiconductors (diodes) were created in 1987 by the Japanese company Kodak. In nature, a glow similar in origin (but not in the method of obtaining) is observed in fireflies and deep-sea fish. Scientists investigated the processes of their glow and synthesized the necessary substances. Over the past years, organic display technologies have been actively developed and improved, and in 2003 OLED displays spilled onto the mass market.
The inventors of luminescent diodes have discovered that if two layers of certain organic materials are combined and an electric current is passed through them at any point, then a glow will appear at that place. Using different materials and light filters, you can get different colors.
Existing models, as in the case of LCDs, are divided according to the type of control matrix. There are OLED with passive, and there are active matrices (TFT). The principle of operation of the matrix is the same, but instead of a layer of liquid crystals, a layer of organic semiconductors is used. TFT OLEDs are the fastest and provide a stunning picture. Such a screen does not save even in sunlight, and the video on it will look no worse than on a TV screen.
e-ink displays
Rumor has it that this is another promising technology. Working black-and-white samples have already been created, but there are problems with the implementation of color. The simplest e-ink display consists of two layers: white (top) and black (special ink) underneath the white. Under the action of the current, the particles of the lower layer can pass into the upper one (and return back), creating the required picture. As usual, current can be applied to the layers either with the help of a passive matrix or with the help of an active TFT. According to the assurances of the developer company, electronic ink displays can theoretically have very low power consumption (exact data are not reported) and keep the picture even when the power is off. Sounds tempting, but we'll have to see what it looks like in the end.
OLED vs LCD
Let's pay attention to the advantages and disadvantages of displays. LCD displays are already at their limit. The very essence of the operation of liquid crystals determines the low frame rate on the screen and high power consumption, since in some phones, in addition to the backlight of the screen, there is also a front one. Color LCDs are almost always hard to see in sunlight and are very fragile. Active matrix displays (LCD TFT) are brighter and more contrast than similar passive matrix displays, but active displays are more difficult to manufacture and therefore more expensive. The only exception is UFB screens.
Organic display technology eliminates almost all of the disadvantages of LCDs and provides much better picture performance. To begin with, you can forget about the need to highlight the screen in front or behind - the screen elements glow by themselves!
For lovers of technical details:
Displays UVB, capable of displaying 65 thousand colors, have a contrast ratio of 100: 1, a brightness of 150 cd / sq. m, while consuming no more than 3 mW.
Display OLED, introduced by Sony back in 2002, had a brightness of 300 cd/sq. m, and the contrast ratio for OELD can reach 300:1. If we compare the speed, then organic differs from a conventional LCD display in that it is able to respond 100-1000 times faster - owners of 3G video phones and phones with video players will appreciate this.
Not so long ago, cathode ray tube monitors occupied a large place on the desktops of users. , and even more so smartphones, have just begun to appear on store shelves. Not much time passed, and bulky CRT monitors began to replace the first liquid crystal displays, and all sorts of gadgets filled the pockets, in which the screen was a necessary attribute.
Over time, screens began not only to increase in diagonal, but the display technology also changed, and in the characteristics of devices, we increasingly began to notice such incomprehensible abbreviations as TN, TN-Film, IPS, Amoled, etc.
This article was written for the average consumer who wants to choose their monitor, smartphone or tablet. Therefore, there will not be a lot of terms and deep introduction to this or that technology, but the operation of the screens will be described in an accessible language that is understandable to the average user. I hope this article will shed some light on new technologies in the field of display information, as well as help people in the future in choosing a device that they will enjoy using.
LCD (Liquid crystal display), aka LCD (liquid crystal display), is built on the basis of liquid crystals, which change their location when voltage is applied to them. If you look closely at the monitor, you will notice that it consists of small dots - pixels. This is liquid crystals. In turn, each pixel consists of red, blue and green subpixels. When a voltage is applied, the sub-pixels line up in a certain order and allow light to pass through them, thus forming a pixel of a certain color.
From a large number of such pixels, an image is formed on the screen of a monitor or other device.
TN and TN+Film matrices
The first mass monitors were equipped with TN matrices. This is the simplest, but at the same time not the highest quality type of matrix. This technology is based on the fact that in the absence of voltage, subpixels let light pass through themselves, forming a white dot on the screen. When voltage is applied to subpixels, they line up in a certain order, forming a pixel of a given color.
Due to the fact that the standard pixel color, in the absence of voltage, is white, this type of matrix does not have the best color rendering. Colors appear dimmer and faded, while blacks appear more of a dark grey.
Another main disadvantage of TN matrix is the small viewing angles. Partially, they tried to cope with this problem by improving the TN technology to TN + Film, using an additional layer applied to the screen. Viewing angles have become larger, but still remained far from ideal. At the moment, TN + Film matrices have completely replaced TN.
But, in addition to disadvantages, such matrices also have their advantages. These include a short response time and a relatively inexpensive cost.
Considering all the advantages and disadvantages, we can say that if you need an inexpensive monitor for occasional use in working with documents or for surfing the Internet, then monitors with TN + Film matrices are perfect for these needs.
IPS matrices
The main difference from TN's IPS technology is the arrangement of subpixels in the absence of voltage. They are perpendicular to each other, forming a black dot. Thus, in a state of calm, the screen remains black. This gives an advantage in color reproduction over screens with TN matrices. The colors on the screen look bright, juicy, and the black color remains really black. When voltage is applied, the pixels change color. Taking this feature into account, owners of smartphones and tablets with IPS screens can be advised to use dark color schemes and wallpapers on the desktop, then the smartphone battery will last a little longer.
Also a nice feature of IPS matrices are large viewing angles. In most screens they are 178°. For monitors, and especially for smartphones and tablets, this feature is important when a user chooses a device.
But, of course, there are also disadvantages. The main disadvantage is the longer screen response time. This affects the display in dynamic pictures such as games and movies. In modern IPS panels, the response time has been improved, so now this drawback is not so critical.
Another feature of IPS screens is their high cost compared to TN. But recently, the price of IPS panels has decreased and has become affordable for most users.
Thus, it is better to choose phones and tablets with IPS matrices, and then the user will receive great aesthetic pleasure from using the device. The matrix for the monitor is not so critical, but if possible, it is recommended to pay attention to modern IPS monitors.
AMOLED screens
In the past few years, smartphones have begun to equip AMOLED displays and at the same time advertise such phones to buyers a lot. So let's figure out what PR managers of companies are trying to convey to us, and what is in their words a common publicity stunt.
The technology for creating AMOLED matrices is based on active LEDs, which begin to glow and display color when voltage is applied to them. What does this give us? And it gives us rather contradictory features.
Let's start with color reproduction. The saturation and contrast of such screens go off scale. Colors are displayed so vividly that some users may experience eye fatigue when using their smartphone for extended periods of time. But the black color is displayed even more black than even in IPS-matrices.
Such bright colors greatly affect the power consumption of the display. As with IPS, displaying black requires less power than displaying a particular color, much less white. But the difference in power consumption between displaying black and white in AMOLED screens is much larger. Displaying white requires several times more power than displaying black.
Another negative feature is "picture memory". When a static image is displayed for a long time, traces may remain on the screen, and this in turn affects the quality of the display of information.
Also, due to its rather high cost, AMOLED screens are still used only in smartphones. Monitors built on this technology are unreasonably expensive.
Conclusion
At the end of the article, I would like to say that the perception of the image is quite subjective for each user. For some, a TN matrix will be enough, and someone will change dozens of monitors until they find their ideal. Thus, despite all the technologies for creating displays, the choice always remains with the user and depends on his individual perception of the picture on the screen. And how screens work in touch input mode, you can read.
The first working liquid crystal display was created by Fergason in 1970. Prior to this, liquid crystal devices consumed too much power, their life was limited, and the image contrast was deplorable. The new LCD was presented to the public in 1971 and then it received enthusiastic approval. Liquid crystals (Liquid Crystal) are organic substances that can change the amount of transmitted light under voltage. The liquid crystal monitor consists of two glass or plastic plates, between which there is a suspension. The crystals in this suspension are arranged parallel to each other, thereby allowing light to pass through the panel. When an electric current is applied, the arrangement of the crystals changes, and they begin to interfere with the passage of light. LCD technology has become widespread in computers and projection equipment.
Note that the first liquid crystals were notable for their instability and were of little use for mass production. The real development of LCD technology began with the invention by English scientists of a stable liquid crystal - biphenyl (Biphenyl). First generation liquid crystal displays can be seen in calculators, electronic games and watches.
Enjoy the flat screen
Modern LCD monitors are also called flat panels, dual scan active matrix, thin film transistors. The idea of LCD monitors has been in the air for more than 30 years, but the research has not led to an acceptable result, so LCD monitors have not gained a reputation for good image quality. Now they are becoming popular - everyone likes their elegant appearance, thin body, compactness, economy (15-30 watts), in addition, it is believed that only wealthy and serious people can afford such a luxury.
As time goes by, prices drop, and LCD monitors get better and better. Now they provide a high-quality contrast, bright, distinct image. It is for this reason that users are switching from traditional CRT monitors to LCDs. In the past, LCD technologies were slower, they were not as efficient, and their contrast levels were low. The first matrix technologies, the so-called passive matrices, worked quite well with textual information, but with a sharp change in the picture, so-called "ghosts" remained on the screen. Therefore, this kind of device was not suitable for watching videos and playing games. Today, most black-and-white portable computers, pagers and mobile phones operate on passive matrices. Because LCD technology addresses each pixel individually, the resulting text is crisper than a CRT monitor. Note that on CRT monitors, with poor beam convergence, the pixels that make up the image are blurred.
There are two types of LCD monitors: DSTN (dual-scan twisted nematic - crystal screens with double scanning) and TFT (thin film transistor - on thin film transistors), they are also called passive and active matrices, respectively. Such monitors consist of the following layers: a polarizing filter, a glass layer, an electrode, a control layer, liquid crystals, another control layer, an electrode, a glass layer, and a polarizing filter.
Early computers used eight-inch (diagonal) passive black and white matrices. With the transition to active matrix technology, the screen size has grown. Virtually all modern LCD monitors use thin-film-transistor panels, which provide a bright, clear image of a much larger size.
How the LCD monitor works
The cross section of the TFT panel is a multilayer sandwich. The outer layer of either side is made of glass. Between these layers is a thin film transistor, a color filter panel that provides the desired color - red, blue or green, and a layer of liquid crystals. On top of that, there is a fluorescent backlight that illuminates the screen from the inside.
Under normal conditions, when there is no electric charge, liquid crystals are in an amorphous state. In this state, liquid crystals transmit light. The amount of light passing through liquid crystals can be controlled by electrical charges - this changes the orientation of the crystals.
As in traditional cathode ray tubes, a pixel is formed from three sections - red, green and blue. And different colors are obtained as a result of a change in the magnitude of the corresponding electric charge (which leads to the rotation of the crystal and a change in the brightness of the passing light flux).
A TFT screen consists of a whole grid of such pixels, where the work of each color area of each pixel is controlled by a separate transistor. This is where it is worth talking about resolution. To properly provide a screen resolution of 1024x768 (SVGA mode), the monitor must have exactly this number of pixels.
Why LCD?
LCD monitors have a completely different style. In traditional cathode-beam monitors, the kinescope was the shaping factor. Its size and shape could not be changed. There is no kinescope in LCD monitors, so monitors of any shape can be produced.
Compare a 15-inch CRT monitor weighing 15 kg with an LCD panel less than 15 cm deep (including stand) and weighing 5-6 kg. The advantages of such monitors are clear. They're not as bulky, don't have trouble focusing, and their clarity makes it easy to work at high screen resolutions, even if the screen size isn't that big. For example, even a 17-inch LCD monitor perfectly displays at a resolution of 1280x1024, while even for 18-inch CRT monitors this is the limit. Also, unlike CRT monitors, most LCDs are digital. This means that a digital-out graphics card does not have to do the digital-to-analog conversion that it does with a CRT monitor. Theoretically, this allows more accurate transmission of color and pixel location information. At the same time, if you connect an LCD monitor to a standard analog VGA output, you will have to carry out analog-to-digital conversions (after all, LCD panels are digital devices). In this case, various unwanted artifacts may occur. Now that standards have been adopted and more and more cards are provided with digital outputs, the situation will be much simpler.
Benefits of LCD monitors
- LCD monitors are more economical;
- They have no electromagnetic radiation compared to CRT monitors;
- They do not flicker like CRT monitors;
- They are light and not as bulky;
- They have a large visible screen area.
Permission: CRT monitors can run at multiple resolutions in full screen mode, while an LCD monitor can only run at one resolution. Smaller resolutions are possible only when using part of the screen. So, for example, on a monitor with a resolution of 1024x768, when working at a resolution of 640x480, only 66% of the screen will be used.
Diagonal measurement: the size of the diagonal of the visible area of the LCD monitor corresponds to the size of its real diagonal. In CRT monitors, the real diagonal loses more than an inch outside the monitor frame.
Ray convergence: in liquid crystal monitors, each pixel is turned on or off separately, so there are no problems with beam convergence, unlike CRT monitors, where flawless operation of electron guns is required.
Signals: CRT monitors use analog signals while LCD monitors use digital signals.
No flicker: the image quality on LCD monitors is higher, and during operation, the load on the eyes is less - the flat plane of the screen and the absence of flickering affect.
How to choose an LCD monitor?
"Appearances are deceptive" - this statement applies to everything, including LCD monitors. Most inexperienced buyers make their choice based on the appearance of the monitor. When buying a monitor, first of all, you should consider the following.
"Dead Pixels" - A few pixels may not work on a flat panel. It is not difficult to recognize them - they are always the same color. They arise during the production process and cannot be restored. It is considered acceptable when the monitor has no more than three such pixels. In some cases, these pixels can be annoying - especially when watching movies. Therefore, if the absence of dead pixels is critical for you, check it before buying a specific monitor.
Viewing Angle - If you've ever used a laptop before, you probably know that working with an LCD monitor is best done at a certain angle. With some monitors, this angle is quite large, so you can see the image on the monitor even when the monitor is not directly in front of you. Note that some laptop owners find small angle values useful in cases where you want your neighbor not to see what is happening on the screen of your monitor. So, an angle of 120 degrees is considered quite good.
Contrast - The pixels themselves do not produce light, they only transmit light from the backlight. And a dark screen doesn't mean the backlight isn't working - it's just that the pixels block that light and don't let it through the screen. The contrast of an LCD monitor refers to how many levels of brightness its pixels can produce. Generally, a contrast ratio of 250:1 is considered good.
Brightness - how bright can an LCD monitor be? In truth, the brightness of a liquid crystal display can be higher than that of a cathode ray tube. But, as a rule, the brightness of an LCD monitor does not exceed 225 candelas per square meter - this is comparable to the brightness of a TV.
Screen size - Like CRT monitors, LCD monitors are sized by the diagonal. Note, however, that LCD monitors do not have the black frame that CRT monitors have. So a 15.1-inch screen actually shows 15.1 inches (usually this corresponds to a resolution of 1024x768). A 17.1-inch LCD monitor will work at a resolution of 1280x1024.
How to choose an LCD monitor?
There are many different manufacturers of LCD monitors. The best known monitors are Viewsonic, Sony, Silicon Graphics, Samsung, Nec, Eizo Nano and Apple. Usually cool guys sit behind such monitors. Please note that no modern film is complete without LCD monitors - they are so attractive. Recall, for example, recent action films: Lara Croft from Tomb Raider was surrounded by Sony N50s, and Swordfish used Silicon Graphics 1600SW in the computer room. Don't they look attractive?
looks good, light, very thin (only 1.2 cm) - 15"
Only 1.2 cm thick, beautiful, expensive, high-quality picture, and in general, a feast for the eyes - 18"
Viewsonic VP181 - expensive, has inputs and outputs for TV, VCD, DBD, in addition, built-in speakers - 18 ";
Apple Cinema Display - high resolution, large screen, different design - 22";
Sony M81 - thin, but actually look a little different than in this picture - 18"
SGI 1600SW - distinguished by design, excellent performance, expensive - 17";
Sony L181 - very thin, very expensive, but uses Trinitron technology - 18";
Eizo Nano - look elegant, expensive - 18"
Currently, there are quite a lot of models on the LCD monitor market based on various technologies for manufacturing LCD matrices. In addition, these technologies are constantly being developed and supplemented. Let us consider only the main ones, which are basic for modern developments.
The very first technology used to make active LCD monitors. It has been worked out to the subtleties, so the cost of matrices is the lowest. The abbreviation TN+Film stands for Twisted Nematic + Film. In the normal state, in the absence of a control voltage, the liquid crystals in TN+Film are in a twisted phase and the sub-pixel glows brightly. The greater the voltage applied to the cell, the more the liquid crystal molecules straighten. At the maximum control voltage, the subpixel will be darkened to the limit. This technology has several disadvantages. Firstly, each pixel will never be completely dark, and the black color will turn out to be imperfect. Secondly, if the control of at least one subpixel fails, an unpleasant luminous dot forms on the screen, and thirdly, the viewing angle, despite the special coating film, rarely exceeds 140-150 degrees.
Rice. 6.10. TN technology.
In-Plane Switching is a technology developed by Hitachi and NEC in 1989. A distinctive feature is that both control semi-transparent electrodes are located in the same plane - only on the lower side of the LCD cell. Liquid crystals are arranged differently than in the case of TN + Film: in a relaxed state, they do not transmit light. The higher the control voltage, the more the crystals twist the polarization of the light beam. In addition, IPS-matrices have a larger viewing angle than TN + Film. But this technology also has a significant drawback - a long subpixel response time - up to 50 ms.
Rice. 6.11. IPS technology.
Fujitsu's patented technology is called Multi-Domain Vertical Alignment. Liquid crystal molecules are oriented in the vertical direction (Vertical Alignment) and in the absence of a control voltage do not change the polarization of the light flux. Due to the design features (long, vertically oriented chains of crystals), when the viewing angle changes, the light output of the subpixel (and, consequently, the color of the resulting pixel) can change dramatically. Therefore, each subpixel is divided into several zones (Multi-Domain), each of which is optimized for the best light output in its field of view. In this original way, the problem of severely limited viewing angles in the original VA technology was solved.
MVA matrices have all the advantages of IPS technology (deep black background color, dark color of broken pixels, wide viewing angles), but at the same time they have a better response speed. But there are also disadvantages - such a panel changes sharp color transitions faster, and much slower - smooth ones. There is a special kind of this technology - PVA (Patterned Vertical Alignment) from Samsung.
The predecessor of MVA technology was single domain VA technology, also developed at Fujitsu in 1996. Its main disadvantage was a small viewing angle. Look at the diagram below - it specifically shows an incompletely open pixel on the right. If you look at it from above, everything will be as it should be, the crystals will be located at an angle of 45 degrees relative to the eye, and therefore the pixel will have a gray color; however, if you look to the right, you will see the same crystals at a right angle, which corresponds to white, and if you look to the left, you will look along the crystals, which corresponds to the color already black.. Thus, VA-matrices did not just have small angles view - the specific effects of increasing the viewing angle also depended on which way the user deviates from the center of the screen.
Rice. 6.12. VA technology.
The solution to this problem was found in the division of each pixel into domains that fire synchronously. The crystals in the domains are oriented differently, and therefore, no matter from which side the user looks at the screen, if the crystals of one domain are turned so that they transmit light, then the crystals of the neighboring domain will be at an angle to them and the light will be delayed (of course, except when it is necessary to display a white color - then all the crystals are located almost parallel to the plane of the matrix). As with IPS matrices, when the pixel is off, it does not transmit light, and therefore dead pixels on MVA matrices look like black dots.
Rice. 6.13. MVA technology.
TFT monitors
The concept of TFT is not related to the technology of manufacturing a matrix of liquid crystals, but to the method of selecting the elements of this matrix when forming an image. It is obvious that the choice of the matrix element is carried out due to control signals along the lines of rows and columns (a more detailed description in this case is unnecessary). If the control elements (keys) are at the beginning of the lines that form the rows and columns, they speak of a passive matrix. The large sizes of the matrices cause different triggering conditions for the nodes, depending on their distance from the control device. In passive matrix monitors, this causes deterioration in image quality (brightness, contrast, etc.) and an increase in response time.
TFT, or Thin-film transistor, is a technology used in the creation of another type of liquid crystal matrix, LCD screens. Thin-film transistor translated from English is a thin-film transistor. Such thin-film transistors control a TFT-matrix, which is also called active. Compared to the passive matrix LCD, the active matrix has a much faster display, a higher level of image clarity and contrast, and a wider viewing angle. The control element for each pixel is a transistor, or a diode structure (in this case sometimes referred to as TFD technology), which acts as a control key (see Figure 6.14).
Rice. 6.14. TFT technology.
This increases the contrast of the image, its clarity, increases the performance of the monitor. TFT displays first appeared in 1972. Today, TFT technology is used by almost all manufacturers of flat-panel monitors and television screens. The disadvantages of such displays include that, due to the sophisticated technology, they cost more and consume more power. Due to the large number of pixels, broken, that is, non-working pixels, are more common among them.
Telling about the differences between IPS and TN matrices as part of advice when buying a monitor or laptop. It's time to talk about all modern display technologies, which we may encounter and have an idea about types of matrices in devices of our generation. Do not confuse with LED, EDGE LED, Direct LED - these are types of screen backlights and display technologies are indirectly related.
Probably, everyone can remember their monitor with a cathode ray tube, which they used earlier. True, there are still users and fans of CRT technology. Currently, screens have increased in diagonal, display manufacturing technologies have changed, there are more and more varieties in the characteristics of matrices, denoted by the abbreviations TN, TN-Film, IPS, Amoled, etc.
The information in this article will help you choose a monitor, smartphone, tablet and other various kinds of equipment. In addition, it will highlight the technologies for creating displays, as well as the types and features of their matrices.
A few words about liquid crystal displays
LCD (Liquid Crystal Display)- This is a display made on the basis of liquid crystals, which change their location when voltage is applied to them. If you come close to such a display and look closely at it, you will notice that it consists of small dots - pixels (liquid crystals). In turn, each pixel consists of red, blue and green subpixels. When a voltage is applied, the sub-pixels line up in a certain order and allow light to pass through them, thus forming a pixel of a certain color. Many of these pixels form an image on the screen of a monitor or other device.
The first mass-produced monitors were equipped with matrices TN- having the simplest design, but which cannot be called the highest quality type of matrix. Although among this type of matrices there are very high-quality specimens. This technology is based on the fact that in the absence of voltage, subpixels let light pass through themselves, forming a white dot on the screen. When voltage is applied to subpixels, they line up in a certain order, forming a pixel of a given color.
Disadvantages of TN matrix
- Due to the fact that the standard pixel color, in the absence of voltage, is white, this type of matrix does not have the best color reproduction. Colors appear dimmer and faded, while blacks appear more of a dark grey.
- Another main disadvantage of TN matrix is the small viewing angles. Partially, they tried to cope with this problem by improving the TN technology to TN + Film, using an additional layer applied to the screen. Viewing angles have become larger, but still remained far from ideal.
At present, TN+Film matrices have completely replaced TN.
Advantages of TN matrix
- short response time
- relatively low cost.
Drawing conclusions, it can be argued that if you need an inexpensive monitor for office work or surfing the Internet, monitors with TN + Film matrices are the best fit.
The main difference between IPS matrix technology and TN- perpendicular arrangement of subpixels in the absence of voltage, which form a black dot. That is, in a state of calm, the screen remains black.
Advantages of IPS matrices
- better color reproduction compared to TN screens: you have bright and rich colors on the screen, and the black color remains really black. Accordingly, when voltage is applied, the pixels change their color. Given this feature, owners of smartphones and tablets with IPS screens can be advised to use dark color schemes and wallpapers on the desktop, then the smartphone battery will last a little longer.
- large viewing angles. In most screens they are 178°. For monitors, and especially for mobile devices (smartphones and tablets), this feature is important when a user chooses a gadget.
Disadvantages of IPS matrices
- great screen response time. This affects the display in dynamic pictures such as games and movies. In modern IPS panels, things are better with response time.
- high cost compared to TN.
Summing up, it is better to choose phones and tablets with IPS matrices, and then the user will get great aesthetic pleasure from using the device. The matrix for the monitor is not so critical, modern.
AMOLED screens
The latest smartphone models are equipped with AMOLED displays. This technology for creating matrices is based on active LEDs, which begin to glow and display color when voltage is applied to them.
let's consider features of Amoled matrix:
- Color reproduction. The saturation and contrast of such screens is higher than required. Colors are displayed so vividly that some users may experience eye fatigue when using their smartphone for extended periods of time. But the black color is displayed even more black than even in IPS-matrices.
- Display power consumption. As with IPS, displaying black requires less power than displaying a particular color, much less white. But the difference in power consumption between displaying black and white in AMOLED screens is much larger. Displaying white requires several times more power than displaying black.
- "Memory pictures". When a static image is displayed for a long time, traces may remain on the screen, and this in turn affects the quality of the display of information.
Also, due to its rather high cost, AMOLED screens are still used only in smartphones. Monitors built on this technology are unreasonably expensive.
VA (Vertical Alignment)- This technology, developed by Fujitsu, can be considered as a compromise between TN and IPS matrices. In VA matrices, the crystals in the off state are located perpendicular to the plane of the screen. Accordingly, the black color is provided as pure and deep as possible, but when the matrix is rotated relative to the direction of view, the crystals will not be visible in the same way. To solve the problem, a multi-domain structure is used. Technology Multi-Domain Vertical Alignment (MVA) provides protrusions on the plates, which determine the direction of rotation of the crystals. If two subdomains are rotated in opposite directions, then when viewed from the side, one of them will be darker and the other lighter, thus for the human eye the deviations cancel each other out. PVA matrices developed by Samsung do not have protrusions, and in the off state, the crystals are strictly vertical. In order for the crystals of neighboring subdomains to rotate in opposite directions, the lower electrodes are shifted relative to the upper ones.
To reduce response time, Premium MVA and S-PVA matrices use a dynamic voltage boost system for certain sections of the matrix, which is commonly referred to as Overdrive. The color reproduction of PMVA and SPVA matrices is almost as good as that of IPS, the response time is slightly inferior to TN, viewing angles are as wide as possible, blacks are the best, brightness and contrast are the highest possible among all existing technologies. However, even with a slight deviation of the direction of view from the perpendicular, even by 5–10 degrees, distortions in semitones can be noticed. For most, this will go unnoticed, but professional photographers continue to dislike VA technology for this.
MVA and PVA matrices have excellent contrast and viewing angles, but things are worse with the response time - it grows as the difference between the final and initial pixel states decreases. Early models of such monitors were almost unsuitable for dynamic games, and now they show results close to TN matrices. The color reproduction of *VA matrices is, of course, inferior to IPS matrices, but remains at a high level. However, due to their high contrast ratio, these monitors are an excellent choice for text and photo work, drawing graphics, and as home monitors.
In conclusion, I can say that the choice is always yours ...