Advanced display technologies. Monitors What technology are used to make flat-panel monitors?

02.04.2022

The first working liquid crystal display was created by Fergason in 1970. Previously, LCD devices consumed too much power, had a limited service life, and had poor image contrast. The new LCD display was introduced to the public in 1971 and then it received warm approval. Liquid crystals are organic substances that can change the amount of light transmitted under voltage. A liquid crystal monitor consists of two glass or plastic plates with a suspension between them. The crystals in this suspension are arranged parallel to each other, thereby allowing light to penetrate the panel. When an electric current is applied, the arrangement of the crystals changes and they begin to block the passage of light. LCD technology has received wide use in computers and projection equipment.

Note that the first liquid crystals were characterized by their instability and were not very suitable for mass production. The real development of LCD technology began with the invention by English scientists of a stable liquid crystal - biphenyl. The first generation of liquid crystal displays can be seen in calculators, electronic games and watches.

Let's enjoy the flat screen

Modern LCD monitors are also called flat panels, active matrix dual scanning, thin film transistors. The idea of LCD monitors has been in the air for more than 30 years, but the research conducted did not lead to an acceptable result, so LCD monitors did not gain a reputation for providing good quality Images. Now they are becoming popular - everyone likes their elegant appearance, slim figure, compactness, efficiency (15-30 watts), in addition, it is believed that only wealthy and serious people can afford such luxury.

Time passes, prices fall, and LCD monitors get better and better. Now they provide high-quality contrast, bright, clear images. It is for this reason that users are switching from traditional CRT monitors to LCD monitors. In the past, LCD technology was slower, it wasn't as efficient, and its contrast levels were low. The first matrix technologies, the so-called passive matrices, worked quite well with text information, but when the picture suddenly changed, so-called “ghosts” remained on the screen. Therefore, this type of device was not suitable for watching videos and playing games. Today, most black-and-white laptop computers, pagers and mobile phones operate on passive matrices. Since LCD technology addresses each pixel individually, the resulting text is clearer than a CRT monitor. Note that on CRT monitors, if the beam convergence is poor, the pixels that make up the image are blurred.

There are two types of LCD monitors: DSTN (dual-scan twisted nematic) and TFT (thin film transistor), 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.

The first computers used eight-inch (diagonally) passive black-and-white matrices. With the transition to active matrix technology, the screen size has increased. Almost all modern LCD monitors use thin-film transistor panels, which provide bright, clear images of a much larger size.

How does an LCD monitor work?

The cross-section of a thin-film transistor 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 electrical 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 using electrical charges - thereby changing the orientation of the crystals.

As in traditional cathode ray tubes, a pixel is formed from three regions - red, green and blue. And different colors are obtained as a result of changing the value of the corresponding electric charge (which leads to 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 operation of each color section of each pixel is controlled by a separate transistor. This is where we need to talk about permission. 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-ray monitors, the forming factor was the kinescope. Its size and shape could not be changed. LCD monitors do not have a kinescope, so monitors of any shape can be produced.

Compare a 15-inch CRT monitor weighing 15 kg with an LCD panel with a depth (including stand) of less than 15 cm and weighing 5-6 kg. The advantages of such monitors are clear. They are not as bulky, have no focusing problems, and their clarity makes it easier to work on high screen resolutions, even if the screen size is not that large. 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. In addition, unlike CRT monitors, most LCDs are digital. This means that a graphics card with a digital output will not have to perform the digital-to-analog conversions that it does with a CRT monitor. In theory, this allows for more accurate color and pixel location information to be conveyed. 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). This may result in various unwanted artifacts. Now that the appropriate standards have been adopted and an increasing number of cards are provided digital outputs, the situation will become much simpler.

Advantages of LCD monitors

LCD monitors are more economical;
They have no electromagnetic radiation compared to CRT monitors;
They don't flicker like CRT monitors;
They are light and not so bulky;
They have a large visible screen area.

Other differences include:

Permission: CRT monitors can operate at multiple resolutions in full screen mode, whereas an LCD monitor can only operate at one resolution. Lower resolutions are only possible 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 diagonal size of the visible area of the LCD monitor corresponds to the size of its real diagonal. In CRT monitors, the actual diagonal loses more than an inch outside the monitor frame.

Beam convergence: In LCD monitors, each pixel is turned on or off separately, so there are no problems with beam convergence, unlike CRT monitors, where the flawless operation of electron guns is required.

Signals: CRT monitors operate on analog signals, while LCD monitors use digital signals.

No flicker: The image quality on LCD monitors is higher, and during work there is less strain on the eyes - the flatness of the screen and the absence of flicker are reflected.

How to choose an LCD monitor?

“Appearances can be deceiving” - this saying applies to everything, including LCD monitors. Most inexperienced buyers make their choice influenced by the appearance of the monitor. When purchasing a monitor, the first thing to consider is the following.

"Dead pixels" - several 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 purchasing a specific monitor.

Viewing Angle - If you've ever used a laptop before, you most likely know that it's best to work at an LCD monitor at a certain angle. On 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 to not see what's happening on your monitor screen. So, an angle of 120 degrees is considered good.

Contrast - the pixels themselves do not produce light, they only transmit light from the backlight. AND dark screen Doesn't mean the backlight doesn't work - 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 create. Typically, a contrast ratio of 250:1 is considered good.

Brightness - How bright can an LCD monitor be? In truth, the brightness of an LCD 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, the size of LCD monitors is determined by the diagonal. However, note that LCD monitors do not have the black frame that CRT monitors have. Therefore, 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 operate at a resolution of 1280x1024.

How to choose an LCD monitor?

There are many different manufacturers of LCD monitors. The most famous monitors are Viewsonic, Sony, Silicon Graphics, Samsung, Nec, Eizo Nano and Apple. Usually, cool guys sit behind such monitors. Please note, not a single modern film can do without LCD monitors - they are so attractive. Remember, for example, the latest action films: Lara Croft from Tomb Raider was surrounded by Sony N50s, and in Swordfish the Silicon Graphics 1600SW were used in the computer room. Don't they look attractive?

look good, light, very thin (only 1.2 cm) - 15"

Only 1.2 cm thick, beautiful, expensive, high-quality picture, and in general, the thing is a sight for sore 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 in fact they look a little different, not like in this picture - 18"

SGI 1600SW - distinguished by design, excellent characteristics, expensive - 17";
Sony L181 - very thin, very expensive, but use Trinitron technology - 18";
Eizo Nano - look elegant, expensive - 18"

When preparing to test 19-inch LCD monitors, we encountered unusually high interest in this topic. The problem of choice, which has never been easy, in this case is aggravated by a wide variety of models, the price of which lies in a wide range - from $300 to $800 with comparable (at first glance) characteristics. In order to understand how they differ from each other and which product to prefer, we have to look at the structure of a modern LCD display.

We will not dwell in detail on the basic principles of the functioning of LCD matrices, believing that most of our readers are already sufficiently familiar with them. only that they use the phenomenon of rotation of the plane of polarization of the light flux by liquid crystals. But the technologies and approaches used by different manufacturers to solve problems that arise when creating monitors sometimes differ significantly.

We inherited from the era of CRT monitors analog interface RGB VGA D-sub. The video adapter converts the frame buffer data from digital to analog, and the electronics of the LCD monitor, for its part, is forced to perform the reverse, analog-to-digital conversion. It is easy to understand that such redundant operations, at a minimum, do not improve image quality; moreover, they require additional costs for their implementation. Therefore, with the widespread use of LCD displays, the VGA D-sub interface has no future and will soon be replaced by digital DVI.

Do not think that manufacturers deliberately do not support the DVI interface in cheap monitors, limiting themselves to only VGA D-sub. It just requires the use of a special TMDS receiver on the monitor side, and the cost of a device that supports both analog and digital interfaces compared to the option with a single analog input will be higher.

Electronics

If you disassemble the case of a modern LCD monitor and look at the control electronics board, at first you may be slightly perplexed. In fact, even the power supply board located next to it looks much more impressive!

The functional diagram of the image processing unit in an LCD display cannot be called simple, and the brevity of its board can be explained differently: thanks to the System-on-a-Chip approach, most functions (from analog-to-digital conversion of the RGB signal, its scaling, processing and even to the generation of output LVDS signals) is performed by a single highly integrated IC called the Display Engine. Among monitor manufacturers today, ICs from ST Microelectronics (ADE3xxx family), operating under the control of 8-bit microcontrollers, are very popular.

The LCD matrix block also appears to be quite simple, and its board usually contains a single control circuit, the so-called matrix driver, which integrates the LVDS receiver and the source and gate drivers that convert the video signal to address specific pixels in columns and rows. In general, the share of electronic components in the cost of a monitor, according to IDC experts, is only 11% - it’s easy to guess that most of the costs fall on the TFT LCD panel itself.

The LCD matrix block also includes its backlight system, which, with rare exceptions, is made using gas-discharge lamps with a cold cathode (Cold Cathode Fluorescent Lamp, CCFL). The high voltage for them is provided by an inverter located in the monitor's power supply. The lamps are usually located at the top and bottom, their radiation is directed to the end of a translucent panel located behind the matrix and acting as a light guide. The quality of matting and the uniformity of the material of this panel determines the important characteristic, as the uniformity of the matrix illumination.

Modern TFT LCD technology

For LCD monitors, the main element that determines image quality is the TFT LCD matrix. Today, there are three competing basic LCD panel technologies on the market and a number of their varieties. These are Twisted Nematics (TN, previously they also added +Film, but now there are simply no others), In-Plane Shutter (IPS, S-IPS) and Vertical Alignment (VA, MVA, PVA). Without touching on the technical features of these technologies, which are widely discussed on the relevant technical sites on the Internet, we will focus only on their practical and market aspects.

Highly integrated IC (Display engine) of the ADE3xxx family from ST Microelectronics (a) controlled by an eight-bit microcontroller (b) and output signal conditioners (c) - that’s all the devices on the LCD control board

TN. The oldest and cheapest type of matrix to produce, it is also characterized by minimal response time, which is why it is widely used. Most 17-inch displays and up to 50% of 19-inch displays contain TN matrices. This is where the advantages end, and a long list of disadvantages begins.

Specific, “hard” color rendition, very far from the reference (and with the advent of “ultra-fast” panels it has worsened even more); clipping in light areas of the image; small viewing angles, especially vertical; low contrast. In addition, “dead pixels” on such matrices transmit light, so they will be visible on the screen as a bright blue, red or green dot.

But still, if you need a monitor with minimal blurring of a moving image, for now TN remains best choice. However, do not forget that it is not at all suitable for working with graphics.

It is quite easy to recognize such matrices by the darkening of the picture when viewed from below and fading, up to the inversion of light areas when viewed from above.

IPS/S-IPS. The characteristics of matrices made using this technology (developed by Hitachi) are the direct opposite of those for TN. IPS has an impressive list of benefits. This includes excellent color rendition, wide viewing angles, and good contrast (deep black color). But the success of IPS in the market is hampered by its shortcomings: complexity in production (as a result, high cost) and long matrix response time.

IPS can be an ideal choice for static image processing tasks. But, unfortunately, you won’t be able to play computer games comfortably. In addition, there are still no IPS matrices with overdrive technology on the market (more about it below), so monitors with such matrices are chosen mainly by graphics professionals.

It is also easy to recognize IPS matrices: if you look at an angle at a switched-on monitor with a black fill on the screen, the black color will have a purple tint.

MVA/PVA. MVA (Multi-domain Vertical Alignment) technology was developed by Fujitsu as a compromise between IPS and TN. The advantages of such matrices: excellent viewing angles, good color rendition, high contrast; however, the response time still cannot match that of the TN.

Samsung produces PVA (Pattern Vertical Alignment) and S-PVA matrices, which, roughly speaking, are improved versions of MVA. The Korean company managed to significantly improve the contrast, up to a record 1000:1, and also, using overdrive technology, seriously reduce the response time - now on the top models of 19-inch monitors from this manufacturer it is quite possible to comfortably play dynamic computer games.

If we summarize all the experience of testing LCD monitors in our Test Laboratory, then today it is PVA matrices that we see as the optimal compromise between the short response time of TN and high-quality color rendition of IPS. Therefore, displays equipped with such matrices can best claim to be universal.

How is quality determined?

After considering the advantages and disadvantages of matrix manufacturing technologies used in LCD displays, you may have a completely logical question: if image quality is 80% dependent on the matrix, why do prices for similar monitors from different brands sometimes differ several times?

Even if we leave aside the build quality and case material, as well as the design of the stand and the ability to customize image parameters, such a burning question remains as the manufacturer’s policy regarding “dead” pixels. The latter are cells whose control thin-film transistors have failed. This is usually caused by a manufacturing defect, since it is not at all easy to make an ideal large-diagonal panel with three million cells, but new defects rarely appear during the operation of the monitor.

The ISO 13406-2 standard defines four classes of LCD panels, each of which is allowed to have a certain number of dead cells per million pixels. For mass distribution to this moment Only matrices of the first (“no broken” subpixels) and second class (the number of failed subpixels is no more than five) are certified. However, due to the continuous fall in prices, it is becoming increasingly difficult for manufacturers to maintain such a quality level: too many panels are wasted, and it will not be possible to work at a loss under dumping conditions for long. Therefore, if the trend towards cheaper LCD displays continues in the future, then it is not at all impossible for panels of the third class to appear on the market (from 6 to 50 failed subpixels).

Someone may ask: what about those manufacturers who guarantee that there are no “dead” pixels in their monitors? Have they learned how to make LCD panels with virtually no defects? No, everything is much simpler here. The guarantee for the complete absence of failed subpixels is usually given only for certain monitor models (top of product lines) and indicates the use of first-class panels. The second class is simply installed in cheaper models of the line. In addition, such a guarantee for their displays can be fearlessly given primarily by those brands that make LCD panels for themselves, since at the same time they have the opportunity to select for own devices the highest quality ones are: Samsung, LG and Philips.

Thus, to answer the notorious question “why should we pay more?” When it comes to LCD monitors, there is a very clear answer. As M. Zhvanetsky said, you don’t have to do this if you are not interested in the result - in our case, the quality of the purchased device.

Not all specs are created equal

If you look at any manufacturer's LCD specifications page, it lists technical characteristics usually looks quite impressive. For potential buyers, specifications are often the only source of information about a product, and therefore it is quite popular among people to compare the characteristics of devices from different brands. Nevertheless, this approach to LCD monitors, unfortunately, is completely inapplicable - drawing conclusions about quality by comparing specifications is correct only for products from one company (and even then not always).

This situation with seemingly completely objective indicators, initially intended to bring clarity, requires additional consideration. To begin with, we note that although the VESA standard for measuring the parameters of flat-panel displays clearly defines their methodology, not all manufacturers adhere to it. Moreover, when it comes to the most critical specification items from a marketing point of view, the methods and conditions for measuring them often become a real mess.

Let's try to figure out which of the characteristics of the LCD display are the most important and are worth paying attention to when choosing.

The backlight unit (a) consists of gas-discharge lamps with a cold cathode CCFL (b), a polymer light guide (c), diffusers and a polarizer (d)

Diagonal size and resolution. If the first parameter is obvious and does not require any special comments, then the second is worth dwelling on in more detail. CRT displays can perform equally well at a wide range of resolutions because the cell size of their shadow mask or aperture grille is much smaller than the image pixel. However, the picture on the LCD panel looks optimal if the video adapter operates in the “native” resolution of the LCD monitor. The cells of the LCD panel are quite large compared to the cells of the shadow mask, and there is only one RGB matrix cell per pixel of the image. Therefore, for 15-inch displays the main working resolution is 1024x768, for 17- and 19-inch displays - 1280x1024. All other modes will only be compromises: when a lower resolution is installed on the PC video adapter, the image is scaled to the required size by the display electronics and, as a result, is “blurred”. If the resolution of the video mode exceeds the optimal one, then most monitors refuse to work with it, or again the picture deteriorates due to recalculation.

Please note that despite the two-inch difference in diagonal size, 17- and 19-inch monitors (for the most part) have the same “native” resolution. That is, the amount of information that can be placed on them is the same, the gain is only larger size dots for 19-inch display. In practice, it most often turns out that it is much more pleasant to work with the latter - due to the increased size of the matrix cells (and, accordingly, the reduced distance between them), the image formed by a 19-inch device seems better.

Screen refresh rate. In the era of CRT monitors, this parameter was critical to achieving a comfortable, flicker-free image on the display. But in order for the human eye to perceive rapidly changing frames as a moving picture, 30 frames per second is enough (60 with interlaced formation). The need to raise the “refresh” frequency to 85, 100 and even 120 Hz was caused by the fact that on CRT displays the image is formed by line-by-line scanning, and while the electron beam “illuminates” the line at the bottom of the screen, the phosphor at the top has a short luminosity time its part already manages to give up a significant percentage of its energy, and the picture darkens - until the next pass of the beam.

Since in LCD displays the entire frame is formed, and each matrix cell is a transistor with a storage capacitor that stores charge for a long time, no flickering (alternating light and dark frames) occurs, and the necessary and sufficient refresh rate is value at 60 Hz. It is for this that the LCD matrix electronics are designed, and therefore, even if more than high frequency, the display DSP will skip extra frames, which can lead to jerky images moving on the screen.

Brightness and Contrast. The maximum brightness of an LCD panel depends on the power of its backlight and the transmittance of the matrix and filters. Contrast is determined by the ratio of the intensity of white to the luminosity of black. Manufacturers often indicate in the passport data of monitors the values that are stated for the panels installed in them, which, strictly speaking, is not entirely true, since the electronics and build quality of the display can have a significant impact on these values.

The rated maximum brightness value of 250 cd/m2 is considered quite sufficient, and for working in artificial lighting a real level of 100–120 cd/m2 is sufficient, and higher brightness may be needed only in bright conditions. sunlight.

With contrast, not everything is so simple: ideally, the higher it is declared (at equal brightness), the purer the black color on the monitor. In practice, it sometimes happens that with a lower declared contrast on one monitor, the black color looks noticeably cleaner and deeper than on another, the passport of which indicates a higher value: here the type, effectiveness of the anti-reflective coating of the screen and other factors come into force.

Number of colors displayed. This, at first glance, not very informative specification item can sometimes say a lot about the LCD matrix installed in the monitor. The point here is this: the bit depth of most “ultra-fast” TN matrices, which have appeared in abundance on the market over the past few years, is less than 8 bits per color channel (24 bit RGB), usually only 6 (18 bit RGB), which is not used special means are completely insufficient to form the entire spectrum of the True Color mode: 28∙28∙28 gives 16,777,216 colors, and 26∙26∙26 – only 262,144. To emulate the missing shades, dithering algorithms are incorporated into the control electronics - either traditional spatial ones (when the colors of neighboring points vary), or temporary, when the color displayed by the pixel switches every frame; and sometimes various combinations of them. As a result, the eye can be deceived, but the image quality on such a matrix still cannot be compared with that of a full-fledged 24-bit matrix.

Therefore, quite recently, when installing a matrix with a reduced bit depth in a monitor, manufacturers indicated 16.2 million shades in the “number of colors” column, and for a full 24-bit one – 16.7 million. Today, unfortunately, some companies even for 18-bit panels record 16.7 million shades, and therefore it is not possible to determine using the specifications what matrix is in the monitor.

Viewing Angles. This parameter is very important for comfortable work with the monitor. However, alas, it has lost its information content - since manufacturers began to indicate values of 140–160° in the specifications of even fast LCD matrices. No, this does not mean that viewing angles have become better; rather, on the contrary, the method of measuring them has changed slightly.

Historically, the limiting viewing angle entered into the specifications was considered to be one at which the contrast dropped to 10:1. As you can see, even then, the resulting color rendering distortions, which for TN matrices are sometimes expressed in color inversion, were not taken into account at all. For “fast” matrices, the actual viewing angles are even narrower than for conventional ones. Therefore, recently, some manufacturers, out of the blue, began to consider the viewing angles of a matrix to be limiting with a contrast of not 10:1, but only 5:1, which gives them grounds to specify values above 140° even for “fast” TN matrices.

In practice, the difference between viewing angles for different types matrices, as they say, are heaven and earth. If for “fast” TN noticeable distortions are observed even with a slight deviation of the view from the normal angle (sometimes with a normal viewing angle in the center of the monitor they are already noticeable in its corners), then modern monitors equipped with PVA and IPS matrices can be viewed almost from any angle. Therefore, the viewing angles of monitors on TN and MVA/PVA/IPS matrices are incomparable, although the specification numbers are sometimes quite similar.

Response time. This is one of the most controversial and controversial parameters of modern LCD displays. The race of milliseconds, which has been going on for several years now, has led to the fact that many users, especially amateurs computer games, choose a monitor for themselves based solely on this characteristic. However, as we have repeatedly emphasized in testing, in practice, the declared low response time of the matrix does not yet guarantee the absence of blurring of the moving image - moreover, there are often cases when, say, a monitor with a rated response time of 16 ms turns out to be faster than a 12-ms model.

The point, as usual, is in the chosen measurement technique. Until recently, reaction time was considered to be the total time for a pixel to switch from black to white (trise) and back (tfall), or more precisely to reach brightness values of 90% and 10%, respectively. But this figure did not give an idea of how the monitor would behave in real conditions, and here's why. When moving from the minimum level to the maximum, the voltage applied to the electrodes of the matrix is also maximum; therefore, the effect on liquid crystals is quite strong, which ensures their rapid reorientation in the desired direction. It is much more difficult to carry out an equally rapid rotation through a small angle (we are still talking about crystals, albeit “liquid” ones - their viscosity is high), which corresponds to transitions from one intermediate state to another (between shades of gray). The applied voltage will no longer be so high, and the response time may exceed the stated one several times - it all depends on the type and design of the matrix. As a result, for one 16-ms model, blurring is clearly visible on the screen, but for another it practically does not appear, and it can only be assessed by eye or by measuring and then averaging the duration of all transitions between different states of the LC cell (the number of which is for 8- bit RGB matrix will be 256).

Let's overclock... the monitor!

Is it possible to somehow adjust the leisurely crystals in order to speed up the time of their rotation during the transition between intermediate states? It turns out that it is possible. To do this you need to know them initial position(remember the previous frame) and accurately calculate the so-called accelerating voltage pulse for the new pixel value in the next frame. It significantly exceeds the nominal voltage applied after it for the desired state, and will therefore quickly turn the crystals into the desired position. This technology called overdrive, and its correct implementation can reduce the response time of an LCD cell to a minimum over almost the entire range of its states.

The problem here is maintaining the required precision: even in conventional panels, the voltage values for generating 256 states are in such a narrow range that controlling them is a real balancing act on a knife's edge. For normal operation of the forced panel, the accuracy needs to be increased by an order of magnitude, which is not yet possible for everyone.

At this stage, correctly setting up an overdrive circuit for a panel is still a technically difficult task, and not all manufacturers can do it. As a result, when the state of the cell changes, artifacts may become noticeable - for example, if the optimal value of the accelerating pulse is exceeded and the crystals rotate at a larger angle than necessary, more light will pass through the cell for some time. Visually, for a black object moving against a gray background, this will be expressed in a light border instead of the usual blurred fronts, although, we repeat, with correctly implemented technology such artifacts should not appear.

To highlight the benefits of monitors equipped with panels with overdrive technology, manufacturers have chosen a different technique for measuring response time. If previously this was the sum of the time spent switching a cell from black to white and back, now the average time of switching from one shade of gray to another (Gray-to-Gray, GTG) is often indicated. However, it is easy to notice that in the latter version of the measurement there is one less switching, so the result, even without the use of overdrive, is a more beautiful figure. Well, this was quickly taken advantage of by the marketing departments of those companies that had not yet even implemented overdrive support in their matrices...

In a word, the response time stated in the specification, unfortunately, has little to do with the degree of blurring of a moving image in real tasks. For an objective assessment this parameter must be carried out a large number of measurements, and also taking into account that custom settings monitors, which will be discussed below, can make significant adjustments to them.

Setting up the LCD Monitor

Of all the parameters of the LCD display that the user can adjust, we highlight brightness, contrast, gamma and color temperature as the most important. The following statement may seem ridiculous at first glance, but this is the bitter truth: when you set them to values other than the factory settings (more precisely, optimal for a given LCD matrix), there is a high probability of a noticeable deterioration in color rendition. The only exception here will be adjusting the brightness of the backlights, although this is not found on all models.

If you remember the design and operating principle of an LCD monitor, it will not be difficult to understand why this happens. Without changing the brightness and emission spectrum of the backlight lamps (the first is possible, but the second is not), the only way to implement all such settings is by mixing some constant component to the video signal supplied to the matrix. And this will lead to a narrowing of the working range of matrix cell values and, as a consequence, to a reduction in the number of displayed colors (which, even for the best panels, is already relatively small).

It’s even easier to verify this in practice: just download the popular program TFTtest.exe and display a monochrome gradient fill on the screen (or draw it in any raster graphic editor), and then change the values of the mentioned settings and observe the emerging distortions, which are expressed in the form of steps and/or colored streaks on the gradient.

Execute full reset installations.
Display a smooth monochrome gradient fill on the screen.
Adjust brightness, contrast, gamma and color temperature so that there are no stripes, steps or color anomalies in the gradient.
In the future, of all the monitor settings, adjust only the brightness of the backlight, if possible, since it does not affect the quality of color rendering.
All other parameters can be configured using video adapter drivers or a hardware calibrator.

LCD monitors: a bright future?

The market prospects of these devices are not in doubt, since the observed high demand for them clearly indicates: users have made their choice and are eager to quickly replace the bulky CRT devices on their desks with compact and elegant LCD monitors, while forgetting about the shortcomings of LCD technology. Unfortunately, price and marketing wars unleashed by manufacturers lead to a deterioration in a number of parameters that are important for image quality, while only two improve – response time and cost. This trend is especially noticeable for mainstream displays – 17- and 19-inch devices with panels based on TN technology.

Thus, the predictions of the imminent death of TN-type matrices turned out to be, to put it mildly, somewhat exaggerated: since the majority of users are quite satisfied with this image quality, then there is simply no need to improve it today. For demanding buyers who are willing to pay for quality, there are displays on PVA and IPS matrices with large diagonals (19 inches or more). And until their response time and price are equal to those of TN matrices (which is unlikely), the dominance of the latter in the market is unquestionable.

Currently, there are a large number of types or types of monitors, which have differences in screen manufacturing technology, and as a result, the quality of image reproduction and application in various fields of activity. Let's list the main types of monitors and we'll give brief description:

Cathode ray monitors. Historically the very first. Consist of vacuum vacuum tube, in which beams of electrons, using a magnetic deflection system, are formed and controlled. These beams of electrons bombard the phosphor layer on which the image is projected, a glow occurs and, as a result, an image appears. Since these monitors have been practically replaced everywhere, we will not consider them in more detail.

The main disadvantages of these monitors:

⁃Large dimensions associated with the fundamental design of the cathode ray tube.

⁃Large mass associated with the first characteristic.

⁃Image distortion on the periphery of the monitor associated with the physical structure of the cathode ray tube and the fundamental impossibility of producing flat-panel monitors using this technology.

⁃The design necessity of using high voltage, up to 50 kV, which does not have the best effect on energy-saving characteristics, as well as safety.

Liquid crystal monitors or LCD in English. The effect of changing the position of a liquid crystal molecule under the influence of voltage has been known for a long time. The practical effect was obtained back in the early 60s of the last century. Then miniature displays first appeared in wristwatch, calculators, various indicators. Over time, technology has improved, helped by the advent of laptops and other portable computers.

The use of this technology in the production of monitors made it possible to completely solve the problems that their predecessors, cathode-ray monitors, had. The dimensions have decreased significantly, tenfold. Now there is no need to specifically highlight great place under the monitor. In this regard, the weight of the monitor itself has been significantly reduced. Now in weight it is comparable to a laptop. Naturally, this applies to not very large monitors. The distortion typical of cathode ray monitors has disappeared because the LCD screen is truly flat.

However, LCD monitors have their own disadvantages, which manufacturers are trying to overcome by introducing new technologies. These disadvantages include lower contrast and color saturation of the image. Matrix response time (appeared new feature for LCD) was large at first, which led to dynamic scenes being shown with image artifacts. This is due to the inertia of switching the state of liquid crystals. Small viewing angles, when the same picture, if viewed from the side, from above or from below, begins to distort or invert colors.

To overcome these shortcomings, manufacturing companies began to improve the technology of liquid crystal matrices, which led to the creation of the following types of monitors, differing in matrix manufacturing technology:

⁃TN+film (Twisted Nematic or twisted nematically), historically the first liquid crystal matrices in which the crystals are lined up one behind the other, but located relative to the display plane or view in a spiral. When voltage is applied, this spiral “twists” by an amount that depends on the voltage. The pixel is painted in one color or another.

⁃S-IPS, developed by Hitachi, the crystals are not twisted into a spiral, but lined up one after another in parallel. This produces better colors, but the response time increases as it takes more time to rotate the entire array of crystals.

⁃MVA/PVA, Fujitsu has developed another technology that eliminates the color rendering disadvantages of TN technology and reduces response time compared to S-IPS technology. To do this, it was necessary to significantly complicate the structure of both the matrix and the polarizer filters. Samsung has developed its own PVA technology to avoid paying licensing fees. These technologies are similar, but the difference is greater image contrast.

⁃PLS, a technology developed by Samsung, is positioned to provide more contrast image compared to S-IPS technology, and is 10% cheaper than it. The manufacturing technology and design of the matrix is unknown. Until recently, this type of matrix was used in mobile devices.

Plasma monitors or PDP in English. The effect of glow of inert gases under high voltage is used. This technology is free from the disadvantages inherent in liquid crystal matrices. The brightness and contrast of the picture are high, and since the matrix elements are quite large, which does not affect the resolution in the best way, it is practically invisible. Images of dynamic scenes are also transmitted without distortion. The viewing angles are large, the picture can be seen without loss of color from any direction. The thickness of the screen has become even smaller compared to LCD monitors.

OLED monitors or monitors with a matrix of organic light-emitting diodes. They are receivers for LCD monitors. The advantages include extremely low power consumption as these LEDs light up on their own. No need for a backlight. Extremely high contrast, high performance, response time measured in microseconds, as opposed to milliseconds in LCD monitors. The depth of an OLED monitor is even thinner than that of plasma monitors. And the viewing angles are 180 degrees, since we are looking at the LEDs themselves, and not at filters, like LCD monitors.

Despite such outstanding characteristics, there are also disadvantages. This fragility of the OLED matrix, coupled with the high cost of such monitors, is a decisive factor in the low demand for them. And this affects the speed of implementation of developments, because firms incur losses. Why spend large resources on an unprofitable business?

But despite this, developers do not give up trying to solve these problems, since OLED technology allows you to do fantastic things: roll the screen into a tube, create transparent displays, use it in a wide temperature range, etc. For fans of such things, OLED monitors are sold, costing about $8,000, with a screen diagonal of about 60 cm.

Today these are the most common types of monitors, with the exception of the very first and last on our list. The times of the former have already passed, but the latter still has everything ahead. Let's take a closer look at the technologies for manufacturing monitor matrices.

Cathode ray monitors. Historically the very first. They consist of a vacuum electron tube in which beams of electrons are formed and controlled using a magnetic deflection system. These beams of electrons bombard the phosphor layer on which the image is projected, a glow occurs and, as a result, an image appears. Since these monitors have been practically replaced everywhere, we will not consider them in more detail.

The main disadvantages of these monitors:

Large dimensions associated with the fundamental design of the cathode ray tube.

Large mass associated with the first characteristic.

Image distortions on the periphery of the monitor associated with the physical structure of the cathode ray tube and the fundamental impossibility of producing flat-panel monitors using this technology.

The design requires the use of high voltage, up to 50 kV, which does not have the best effect on energy-saving characteristics, as well as safety.

Liquid crystal monitors or LCD in English. The effect of changing the position of a liquid crystal molecule under the influence of voltage has been known for a long time. The practical effect was obtained back in the early 60s of the last century. Then, for the first time, miniature displays appeared in wristwatches, calculators, and various indicators. Over time, technology has improved, helped by the advent of laptops and other portable computers.

The use of this technology in the production of monitors made it possible to completely solve the problems that their predecessors, cathode-ray monitors, had. The dimensions have decreased significantly, tenfold. Now there is no need to specially allocate a large space for the monitor. In this regard, the weight of the monitor itself has been significantly reduced. Now in weight it is comparable to a laptop. Naturally, this applies to not very large monitors. The distortion typical of cathode ray monitors has disappeared because the LCD screen is truly flat.

However, LCD monitors have their own disadvantages, which manufacturers are trying to overcome by introducing new technologies. These disadvantages include lower contrast and color saturation of the image. The response time of the matrix (a new characteristic for LCD has appeared) was high at first, which led to dynamic scenes being shown with image artifacts. This is due to the inertia of switching the state of liquid crystals. Small viewing angles, when the same picture, if viewed from the side, from above or from below, begins to distort or invert colors.

Historically, the first liquid crystal matrices in which the crystals are lined up one after another, but arranged relative to the display plane or view in a spiral. When voltage is applied, this spiral “twists” by an amount that depends on the voltage. The pixel is painted in one color or another.

Developed by Hitachi, the crystals are not twisted into a spiral, but lined up one after another in parallel. This produces better colors, but the response time increases as it takes more time to rotate the entire array of crystals.

Fujitsu has developed another technology that eliminates the color rendering disadvantages of TN technology and reduces response time compared to S-IPS technology. To do this, it was necessary to significantly complicate the structure of both the matrix and the polarizer filters. Samsung has developed its own PVA technology to avoid paying licensing fees. These technologies are similar, but the difference is greater image contrast.

The technology developed by Samsung is positioned to provide a higher contrast image compared to S-IPS technology, and is 10% cheaper than it. The manufacturing technology and design of the matrix is unknown. Until recently, this type of matrix was used in mobile devices.

in English. The effect of glow of inert gases under high voltage. This technology is free from the disadvantages inherent in liquid crystal matrices. The brightness and contrast of the picture are high, and since the matrix elements are quite large, which does not affect the resolution in the best way, it is practically invisible. Images of dynamic scenes are also transmitted without distortion. The viewing angles are large, the picture can be seen without loss of color from any direction. The thickness of the screen has become even smaller compared to LCD monitors.

or monitors with a matrix of organic light-emitting diodes. They are receivers for LCD monitors. The advantages include extremely low power consumption as these LEDs light up on their own. No need for a backlight. Extremely high contrast, high performance, response time measured in microseconds, as opposed to milliseconds in LCD monitors. The depth of an OLED monitor is even thinner than that of plasma monitors. And the viewing angles are 180 degrees, since we are looking at the LEDs themselves, and not at filters, like LCD monitors.

Today, these are the most common types of monitors, with the exception of the very first and last on our list. The times of the former have already passed, but the latter still has everything ahead. Let's take a closer look at the technologies for manufacturing monitor matrices.

Matrix manufacturing technologies.

The TN+film liquid crystal matrix consists of the following elements:

A pixel in a liquid crystal matrix is formed from 3 cells or dots of blue, red and green. By turning these points on and off, combining these states, one color or another is obtained. The matrix is controlled pixel by pixel. Here lies the big drawback of these passive matrices: while the signal reaches the last pixels, the brightness of the first ones will decrease due to loss of charge. And it is also impractical to build matrices with a large diagonal using such technology. It will be necessary to increase the voltage, which will lead to increased interference.

To overcome these obstacles, TFT (Thin Film Transistor) technology was developed. Since the transistor is an active element, the matrices have accordingly become active. The use of such transistors made it possible to control each pixel separately, which made it possible to significantly increase response time and produce large-sized liquid crystal matrices.

Each cell of one color or another that makes up a pixel contains liquid crystal molecules. In TN+film technology, they are lined up one after another, but rotated relative to each other in a spiral in such a way that the outer molecules are rotated 90 degrees relative to each other. These molecules are located in special grooves, which create such an arrangement on the glass substrate.

Electrodes are connected to the ends of this spiral, to which a voltage is applied that controls the pixel. In response to this, depending on the voltage, the spiral begins to compress. Thus, in the absence of voltage, the light passes through the first polarizing filter, then the liquid crystal molecules rotate the light 90 degrees so that it is in the same plane as the 2nd filter and passes through it. This way we get a white pixel.

If submitted maximum voltage, the crystal molecules will take a position in which the light will be completely absorbed by the second polarizer filter. Accordingly, the pixel will turn black. When the applied voltage varies, the light will be partially absorbed by the polarizer due to the arrangement of the crystals. The pixel will be colored in shades of gray, which means the light will be partially transmitted and partially absorbed.

Since the matrix made using this technology has small viewing angles, a special film was used, applied on top and expanding the view. The result is TN+film technology, in which the color intensity does not change so sharply when changing the viewing angle. This technology is still used today because it is the cheapest. But it is not suitable for working with graphics.

high performance of the matrix;

low cost;

Disadvantages of technology:

small viewing angles;

low contrast;

color rendering quality;

The S-IPS technology is based on the same principles, the difference is that the molecules are lined up one after another in parallel, and not twisted into a spiral, as in the TN+film technology. The electrodes are located on the bottom substrate. In the absence of voltage, light does not pass through a 2 polarizing filter, the polarization plane of which is located at an angle of 90 degrees. This produces a rich black color. The viewing angles of matrices made using this technology are up to 170 degrees horizontally and vertically, which distinguishes these monitors very favorably from previous ones.

large viewing angles horizontally and vertically;

high contrast;

Disadvantages of technology;

long response time, since the molecules need to be rotated to a larger angle;

more powerful lamps for panel illumination;

more powerful voltages are needed to rotate the molecules, since the electrodes are in the same plane;

high price;

Based on the characteristics of matrices made using this technology, they are best used in design tasks where high performance of dynamic scenes is not required, but high-quality color rendition is required.

A compromise between the high color rendering of S-PS technology and the performance of TN+film is MVA technology. The essence of this technology is that the molecules are located parallel to each other, and in relation to the 2nd filter at an angle of 90 degrees. The second filter has a complex structure; it consists of triangles, to the sides of which the crystal molecules are deployed in this way. Getting to the second filter through the molecules, the light is polarized by 90 degrees (the work of the crystal molecules) and is absorbed by the 2nd filter, which does not transmit such light. The result is black light.

By applying voltage, the molecules begin to rotate and thereby direct light to filter 2 at an angle other than 90 degrees. As a result, light begins to pass through filter 2 with an intensity proportional to the applied voltage. This technology, voluntarily or involuntarily, divides the screen into 2 parts, according to the direction of the molecules to the 2nd filter, it turns out that being from the side of the screen, the crystal molecules of the other side do not act for us. We see only the zone that is closer to us and which does not distort the color. The use of such technology significantly complicates the structure of polarizer filters and the matrices themselves, since each point of the screen is duplicated from 2 zones.

Samsung did not want to pay for the license and developed its own PVA technology, which is very similar to MVA and has even greater contrast. Therefore, MVA/PVA is often indicated in the characteristics of monitors.

large viewing angles;

good color rendering and contrast;

Disadvantages of technology:

the complexity of making the matrix;

response time is longer than TN+film technology matrices

This concludes the review of liquid crystal matrix technologies. As for the relatively recently introduced PLS (Plane-to-Line Switching) technology by Samsung, it is most likely a development of S-IPS technology. In this case, third-party experts examined the PLS and S-IPS matrices under a microscope and found no differences. Moreover, Samsung filed a lawsuit against LG, in which it claimed that the AH-IPS technology used by LG is a modification of PLS, which indirectly confirms the above.

Plasma monitors are now widespread due to the fact that production technology has become cheaper. Monitors with a large diagonal are produced, since it is technologically difficult to produce with a small diagonal. Therefore, their prices may be higher than widescreen ones.

The matrix of a plasma monitor consists of cells, the walls of which are coated with phosphorus, and the cells themselves are filled with an inert gas: neon or xenon. When voltage is applied to the cell, a discharge occurs, the inert gas begins to emit photons, which in turn bombard the phosphorus coating of the cell. Phosphorus, in turn, begins to emit photons of light. Everyone knows how phosphorus luminesces even in daylight.

The cells of the plasma matrix have 3 colors: red, green, blue, and in this composition they form a pixel. Accordingly, by applying voltages of different intensities and combining colors, the color that is needed is obtained at the moment. The principle is the same as that of liquid crystal matrices, but instead of crystals, cells with inert gas are used. Moreover, each pixel cell is controlled separately, which has the best effect on color rendition and contrast.

In general, the plasma matrix screen consists of 2 glasses, outer and inner, between which there are 2 layers of dielectric with electrodes. One layer of dielectric is adjacent to the outer glass. The supply electrodes or screen electrodes are built into this dielectric. After the dielectric layer there is a thin layer of magnesium oxide or a protective layer. And then the layer itself with cells of inert gas.

On the side of the inner glass there is also a dielectric layer in which electrodes are built in, which are called address or control. Thus, when voltage is applied between the supply and address electrodes, a gas-discharge current arises, which leads to the emission of photons in a separate cell and the entire plasma panel as a whole, according to the required plot.

As can be seen from this description, the matrix technology of plasma monitors is somewhat simpler than that of liquid crystal monitors. Let us now consider the pros and cons of this technology.

large viewing angles;

unparalleled quality of color rendering and contrast, color saturation;

absolutely flat screen and its small thickness;

short image regeneration time;

Every technology has some limit, so its

increased energy consumption due to the gas-discharge effect;

big size pixel, which affects the resolution of a picture with small details;

The service life of plasma panels is lower than that of liquid crystal panels;

panels with a small diagonal are more expensive than similar liquid crystal panels;

The OLED matrix consists of organic light-emitting diodes. The LED consists of a cathode and anode, between which there is an organic substance. When an electric current passes, the cathode emits electrons, and the anode emits positive ions. The electric field directs these particles towards each other and, recombining with each other, they emit light. An anode made of indium isoxide with tin additives transmits light in the visible range.

To create color OLED displays, substances were selected that can emit light of different wavelengths and, accordingly, colors. Blue, red and green LEDs form a matrix cell. This cell controlled by applying voltage to it. The matrix controller sequentially supplies control voltage at high speed, as in line scan cathode ray tube. Due to this, the human eye does not have time to perceive the difference in color when the cell received an impulse and when it stopped influencing the cell. This OLED matrix is passive.

There are also active OLED matrices, where each cell is controlled by its own transistor, and all diodes light up almost simultaneously. Such a matrix is more expensive than a passive one due to the complexity of production.

The possibilities of OLED technology are amazing. For example, not only the anode, but also the cathode can be made transparent. In this case, the display will be completely transparent, and this will not affect the perception of the picture due to the brightness of the LEDs. Or, instead of a glass substrate, use a flexible material. In this case, the screen can be rolled into a tube.

Mass production of OLED monitors has not yet been observed due to the high price. And it’s more difficult to produce displays with large diagonals. However, firms do not stop in their research. Not so long ago, Samsung announced a monitor with a diagonal of 55 inches, so the problems arising in the manufacturing technology of OLED matrices are being overcome.

viewing angles are the largest compared to other technologies;

the highest contrast among existing technologies;

response time is measured in microseconds, and for liquid crystal matrices in milliseconds;

the absence of a backlight means lower energy consumption;

The thickness of the screen is even smaller;

can be used in a wide temperature range;

lifetime of organic LEDs;

the need to carefully seal the matrix from moisture;

high cost;

Prospects for the development of various technologies for creating displays.

At this stage, an interesting picture is observed: there are several technologies for manufacturing display matrices and all of them are actively developing and eliminating their shortcomings. With all this, there is no tough confrontation between products made according to different technologies.

If you need a large screen, then choose a plasma matrix; if smaller, choose a liquid crystal matrix. Need to solve design problems? Choose a liquid crystal display made using S-IPS technology. Need a picture with more or less high definition and short response time? We choose MVA/PVA technology. Don't want to pay big money? Then select TN+film. Do you want something like this? OLED monitors are already being produced, albeit for a lot of money.

Since each technology has essentially found its niche, there is accordingly a demand for it and it will develop further, getting rid of its shortcomings. But as soon as any of them turns out to be similar or superior to the other in terms of technological and consumer characteristics, it will accordingly displace the competitor.

The latest OLED technology is very promising; it can displace plasma displays and liquid crystal displays, but not before the issue of increasing the lifetime of organic LEDs and reducing the cost of technology is resolved.

LCD monitors are now the cheapest and they also get rid of their shortcomings, but by definition they cannot surpass plasma monitors in terms of color quality, viewing angles, screen thickness, response time and diagonal size.

Accordingly, plasma monitors cannot replace others in the class of medium and small monitors, and, accordingly, in the degree of image detail. Small details, and even on a small monitor, will look poor quality.

Therefore, work to improve the characteristics of matrices manufactured using different technologies is ongoing, but there is no need to talk about the decisive superiority of any technology. While superior in some characteristics, each of them is inferior to its rivals in others. Therefore, there is only one conclusion: all these technologies will develop, and therefore they are all promising.

We looked at what exist types of monitors at present and the structure of their matrices. In the following articles we will continue our review of the technical characteristics of monitors.

There are only two mass technologies for manufacturing displays for phones: screens based on LCD, that is, liquid crystals, and based on OLED- organic luminescent technologies. Liquid crystal displays are still the most common, but the development and implementation of more modern OLED technology is proceeding at an incredibly fast pace! There is still technology E-ink— such displays can theoretically be used in mobile phones and other “small” equipment, but the costs of their production are still quite high, and there are disadvantages.

Liquid Crystal LCD

Devices with LCD screens - LCD(liquid crystal display) - can be seen everywhere today: computer displays (flat panels), televisions, pocket computers. And, of course, mobile phones. Almost all phones sold today are equipped with LCD screens: monochrome (amber, gray-green) or color.

What kind of crystals are these? They, like solid crystalline substances, for example, 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, and become opaque. The dark elements on the screen are areas of the LCD coating to which current is applied. 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 back in 1888. It was only in 1963 that scientists discovered that in their normal state such crystals transmit light, but can change their structure and reflect or absorb light under the influence of electric current. This discovery 10 years later made it possible to create 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. Let us only note that almost all of 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've probably come across the abbreviation STN (super twisted nematic - structure with ultra-high distortion); in such displays, the crystals are able to “twist” especially strongly, which provides increased contrast to the black-and-white or color picture on the screen. 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 the coordinates, as in the game “Battleship,” then where these strips intersect, the crystals will change the structure, and a dot can be seen in the corresponding place on the screen. Depending on the strength of the current, the crystals rotate (distort) to a greater or lesser extent, allowing more or less light to pass through, respectively. In color displays, they also polarize light. When polarized from white light An electroluminescent backlight lamp “cuts out” certain color components 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 rainbow stains can be observed on the surface of a compact disc. Note that one of the main disadvantages of such screens is their low performance - for static pictures this does not matter, 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 designated by the abbreviation TFT(Thin Film Transistors) or AM (Active Matrix). Under the surface of the screen, based on them, there is a layer of tiny transistors, semiconductors, each of which controls one point of the screen. In a color phone display, their number can reach several tens (or even hundreds) of thousands. This control method allows you to speed up the operation of the display several times, although this method is not very effective for playing a video; the image may be slightly “blurry”, since the crystals themselves will not have time to rotate with the required speed.

It happens that the transistor fails. Such a defect is easy to notice with the naked eye - a point on the screen constantly glows as a bright “star” against the background of others or does not glow at all. Therefore, when buying a mobile phone, do not be lazy to turn it on and take a close 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 UFB(Ultra Fine and Bright). Behind this abbreviation lies a screen with increased brightness and contrast, while power consumption is reduced compared to traditional LCDs. In addition, the production of the new display, according to the developers, is cheaper. It’s interesting that we managed to break through the barrier of 65 thousand colors; since 2003, screens with 260 thousand colors have been produced.

Organic OLED displays

The dominance of LCD displays has broken through new technology OLED(Organic Light Emitting Diodes) - electroluminescent displays based on organic light-emitting semiconductors. The main difference is that backlight lamps 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, a wide viewing angle (up to 180 degrees), and can have a wide color gamut. Among the shortcomings, we note the relatively low “lifetime” (about 5–8 thousand hours), however, for a phone it is more than enough.

The thickness of organic displays is comparable to ordinary window glass, however, there are even flexible samples that are predicted to have a great future as, for example, large format screens. They can be pulled out of the phone if necessary, and after use, such a screen will again be rolled up inside the body of the device.

“Organics” are mainly used to equip expensive high-end devices, the mass production of which is not yet on such a large scale. However, leading display manufacturers (Sanyo, Sony, Samsung, Philips and others) are so actively promoting OLED technology on the market that very soon this kind of display will begin to displace the STN we are used to.

How do organic OLED screens work?

There is no need to explain to readers what ordinary LEDs (inorganic) are - they can be seen in various electronic equipment, from televisions and tape recorders to telephones and computers. Humanists usually call green or red LEDs (for example, those that blink to indicate whether you are in the coverage area of a cellular network) “light bulbs”: in fact, these are semiconductor devices capable of emitting light of one color or another when exposed to current.
Organic luminescent semiconductors (diodes) were first created in 1987 by the Japanese company Kodak. In nature, a glow similar in origin (but not in the method of production) is observed in fireflies and deep-sea fish. Scientists studied the processes of their glow and synthesized the necessary substances. Over the past years, organic display production technologies have been actively developed and improved, and in 2003, OLED displays splashed onto the mass market.

The inventors of fluorescent diodes discovered that if two layers of certain organic materials were combined and passed through them at any point electricity, then a glow will appear in this 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 OLEDs with passive, and there are also with 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 OLED is the fastest and provides simply amazing pictures. Such a screen will not help even when 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 influence of current, particles of the lower layer can pass into the upper one (and return back), creating the desired picture. As usual, current can be supplied to the layers using either a passive matrix or an active TFT. According to the developer company, electronic ink displays can theoretically have very low power consumption (exact data are not reported) and retain the image even when the power is turned off. It sounds tempting, but we have to see how it will look 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 how liquid crystals work determines the low frame rate on the screen and high power consumption, since some phones, in addition to the backlight of the screen, also have a front one. Color LCD screens are almost always difficult to see in sunlight and are quite fragile. Active matrix displays (LCD TFT) are brighter and more contrasty 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 is devoid of almost all the disadvantages characteristic of LCD displays and provides much best characteristics Images. To begin with, you can forget about the need to backlight the screen from the front or back - the screen elements glow themselves!

For fans of technical details:

Displays UFB, capable of displaying 65 thousand colors, have a contrast ratio of 100:1, and 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 performance, then organic differs from a conventional LCD display in that it can respond 100–1000 times faster - this will be appreciated by owners of 3G video phones and phones with video players.

Categories:/ from 04/24/2017