The principle of operation of the lcd monitor. Types of lcd matrices. Rules for the operation and maintenance of the LCD panel

LCD or liquid crystal display is based on the polarization of the light flux. Liquid crystals "sift" the light, passing only certain waves of the light beam with the corresponding polarization axis, and remaining opaque to all other waves. The change in the polarization vector is carried out by liquid crystals depending on the electric field applied to them. In other words, with the help of electricity, you can change the orientation of the crystal molecules and thereby ensure the creation of an image.

Almost any LCD display has an active matrix of transistors that form an image, a layer of liquid crystals with light filters that selectively transmit light, and a backlight system (usually LEDs). The latter is necessary for displaying color images. An LCD display has several layers, the main of which are two glass panels, which contain a thin layer of liquid crystals between them. The panels have grooves that guide the crystals to give them orientation. The grooves are parallel on each panel, but perpendicular between the two panels. In contact with the grooves, molecules in liquid crystals are oriented in the same way in all cells.


The LCD screen itself is an array of small segments - pixels. For each pixel there are three transistors, each of which is responsible for one of three colors, and a capacitor that maintains the required voltage. By combining the three primary colors for each pixel on the screen, you can get any color.

The most common currently are TFT liquid crystal displays, in which thin-film transparent transistors are used in the active matrix. The number of transistors in such displays can reach several hundred thousand.


Among the advantages of LCD displays are relatively low cost, excellent focusing, very high image clarity and brightness. And also the absence of color registration errors and screen flickering. The fact is that such displays do not use an electron beam to draw every line on the screen. Among the disadvantages of LCD - the appearance of dead pixels due to the combustion of transistors, a small number of color shades, uneven brightness of the picture (often the illumination at the edge of the display is stronger) and a relatively small viewing angle.

A few years ago, the choice of a monitor for a personal computer was carried out according to the price category, where it was clear that a more expensive device has a high-quality matrix, and a cheap monitor does not shine with characteristics. At the moment, in the monitor market, the division is by screen size, each manufacturer produces devices with different matrix technologies. Because of this, the choice when buying has become more complicated. This article will help users choose the right type of monitor matrix. Which screen is better to buy on the market, for what purposes and how it differs from competitors, will be presented in an accessible form.

To make it clearer

Before choosing the type of monitor matrix, you need to understand the principle of its operation, as well as identify all the advantages and disadvantages. Having compiled a list of needs (for what purposes this device is purchased), it will be very easy to compare the reality with the desired. Without affecting the screen size, the use of the monitor is divided according to needs into several groups:

1. Office monitor. A high level of contrast is the only requirement.
2. Designer computer (photo, prepress). Accurate color rendition is important.
3. Multimedia. Watching movies requires wide viewing angles and real blacks on the screen.
4. Game computer. An important indicator is the response time of the matrix.

The production technology and the movement of electrons between matrices are hardly interesting to anyone, so this article will consider the advantages and disadvantages, as well as use data from the media - reviews of owners and recommendations of sellers. Having found out what technologies exist, it remains only to combine them with the stated requirements and the finances allocated for the purchase of a monitor.

The state employee does not give up positions

The type of monitor matrix TN (Twisted Nematic) is considered a long-liver in the market among competitors. Due to the low price and availability, monitors with this matrix are installed in all government and educational institutions, offices of many companies in the world and in large enterprises. According to statistics, 90% of all monitors in the world have a TN matrix. Along with the price, another advantage of such a monitor is the low response time of the matrix. This parameter is very important in dynamic games, where the speed of drawing is of paramount importance.

But with the color rendition and viewing angle, these monitors did not work out. Even the modernization of the TN-matrix by adding an additional layer to increase the viewing angles did not give the desired results, only added "+ film" to the name of the screen type. We must not forget about energy consumption, which significantly exceeds all competitors in the operating mode.

But still

Apart from office use, TN + film is the best type of monitor matrix for gaming. After all, most gamers prefer to overpay for high-performance components, such as a processor or video card, and you can save money on the screen. However, do not forget about the color rendition, in modern games, developers try to make the plot as realistic as possible, and without a real transfer of all colors and shades, this will be very difficult to achieve.

As a result, besides the low price and short response time, the TN-matrix will not be able to surprise a potential buyer with anything. After all, it is very difficult not to pay attention to the shortcomings:

1. Low color rendering with inability to display perfect blacks. The defect is visible while watching dynamic films, where all the action takes place in the dark - "Van Helsing", "Harry Potter and the Deathly Hallows", "Dracula" and the like.
2. The low cost of production leads to a high probability of acquiring a defective matrix, the broken pixel of which is immediately visible, because it turns white.
3. Very low viewing angles do not allow contemplating the picture on the screen with a large family.

A step in the right direction

The VA (Vertical Alignment) monitor matrix type uses technology with vertical alignment of molecules, and is better known in the post-Soviet space as MVA or PVA. And quite recently, the suffix "S", which has the decoding "Super", was added to the existing modifications, however, the monitors did not acquire any special characteristics compared to competitors, except that the price went up a little.

VA technology was designed to eliminate defects in TN + film matrices, and manufacturers have achieved some results, however, when comparing the two screens, the user will find that they have opposite characteristics. That is, the disadvantages of VA matrices are the advantages of TN, and the advantages of VA are the disadvantages of cheap matrices. It is not known what the manufacturers were thinking, but the market situation has not changed for these dies so far, even with the introduction of the Super marking.

Pros and cons of VA technology

If VA technology is compared with the cheapest TN + film matrix on the market, then the advantages are obvious: excellent viewing angles, very high-quality reproduction of shades with deep blacks. In fact, this type of photo monitor matrix is ​​the best in its price range. The only thing that confuses is the response time. Compared to a cheap TN screen, it is several times higher. Naturally, a device with such a matrix is ​​not suitable for game lovers, since the dynamic picture will be constantly blurred.

Designers, layout designers, amateur photographers and all professionals who need to work with real color and its shades will love monitors with VA technology. In addition, the wide viewing angle does not distort the image on the screen, even with a strong tilt. Such monitors are suitable for multimedia - watching any movies with your family will be interesting, because the screen provides an opportunity to see real black, and not its resemblance in the form of fifty shades of gray.

No flaws?

IPS matrices and their various modifications have been on the market for a long time. However, their cost is not as attractive to buyers as the impeccable characteristics of screens that use an expensive type of monitor matrix. Which is the best screen for a businessman and designer, company president or traveler, only Apple knows, because all its devices, without exception, have IPS (In-Plane Switching) matrix technology.

From year to year, various technologies appear, specialists are trying to improve the quality of an already expensive and high-quality matrix, as a result of which there are a number of modifications on the market: AH-IPS, P-IPS, H-IPS, S-IPS, e-IPS. The difference between them is insignificant, but there is. For example, e-IPS (Enhanced) has technology to increase the contrast and brightness of the screen, and also has a reduced response time. The professional P-IPS series can display 30-bit color, it's a pity, the user will not notice this clearly.

Reach for a dream

Without going into deciphering the modifications of the IPS-matrix, you can see that this technology is a kind of symbiosis of VA- and TN + film-productions. Naturally, only the merits were selected, which were embodied in one device. For example, the AH-IPS (Advanced High performance) monitor matrix type is a direct competitor to plasma panels, which have no analogues in the world in terms of high-definition picture reproduction quality. Such a serious statement was made back in 2011, but apart from the inflated price for a device with an AH-IPS matrix, it has not yet been possible to prove superiority.

And yet, if a game lover has a question about which type of monitor matrix to choose - IPS or TN, then the right decision would be to purchase a more expensive and high-quality screen. Let the price of the device be several times higher than the cheap competitor, but the time spent with your favorite toy will be more interesting. After all, the realistic picture quality will always come first.

Funny games producers

First of all, we will talk about the Korean giant Samsung, which is constantly striving to invent new technology, but it does not always work out for him, because along with the quality, the buyer is also interested in the cost of the device, which for some reason seeks to increase disproportionately.

By introducing single pixel separation technology, Samsung has achieved better image clarity. First of all, this is noticeable on the screen when typing multi-colored text in small print. The technology was approved by many layout designers, and PVA-labeled monitors quickly found fans.

The WVA monitor matrix type was an improved version of Samsung's technology and, judging by the low cost of the devices, competed freely in the market. The lack of response speed of the matrix in all devices created with VA technology has not been eliminated.

A radical solution

AH-IPS monitor matrix type interested only buyers in developed countries of the world. After all, for the best quality you have to pay a very large sum, which is beyond the means of the residents of the post-Soviet space. And there is no point in purchasing a monitor that is slightly more expensive than a modern personal computer assembly. Therefore, manufacturers of an expensive device had to reduce the cost of technology by reducing the quality in the production of components. This is how a new type of monitor matrix PLS (plane-to-line switching) appeared on the market.

After analyzing the characteristics and studying the principle of the new matrix, you might think that this is just an improved modification of Samsung's PVA matrix. This is true. As it turned out, the manufacturer developed this technology a long time ago, but the introduction took place quite recently, when there was a huge difference in price between the devices of the middle class and the expensive ones, and it was urgently required to occupy an empty price niche.

Who won?

Apparently, this is the only case when a buyer wins in a war between manufacturers for a sales market, who gets a decent device according to its characteristics for a price that is quite acceptable for him. The disadvantage can be attributed to a small selection of manufacturers, because Samsung has not released the technology outside of its concerns, so the Korean brand has few competitors - Philips and AOC.

But, being faced with the choice of which type of monitor matrix is ​​better - IPS or PLS, a potential buyer who decides to save money will definitely give preference to the latter. After all, in fact, there is not much difference between the devices. And if you pay attention to the fact that most mobile devices, including tablets, have a PLS matrix, which is very often presented by the seller as a more expensive IPS, then there is only one conclusion.

In pursuit of perfection

Not so long ago, Sharp introduced a type of monitor matrix made using IGZO technology (indium, gallium and zinc oxides). According to the manufacturer, the material has a very high conductivity and less power consumption, due to which it was possible to achieve a higher pixel density per square inch. In fact, IGZO technology is suitable for the production of 4K monitors and all mobile devices produced in the Ultra HD format.

The technology is far from cheap, and prices for IGZO monitors and TVs are breaking world records. However, the well-known company Apple found its way very quickly, concluding contracts with the matrix manufacturer. This means that the future belongs to this technology, it remains only to wait for the price decrease in the world market.

The best choice for the gamer

Having studied the existing production technologies, you can without hesitation determine which type of monitor matrix is ​​better. For games, response time and color rendition are a priority, so there is not much choice here. For those who want to save money, a device with a PLS-matrix is ​​quite suitable. Although the choice among manufacturers is small, but there is an opportunity to decide among the modifications. In addition to the standard type of matrix, the manufacturer offers an improved Super-PLS model, which has higher brightness, contrast, and the screen allows displaying a resolution exceeding FullHD.

But if the price of the issue is not critical for the buyer, then the IPS screen will allow you to enjoy the most realistic picture. It will not be possible to get confused in the markings, because they all boil down to improving the viewing angle and dynamic contrast. The only difference is in price - the better, the more expensive. Having given preference to a device with an IPS monitor matrix type, the gamer does not lose.

Photo processing and graphics are a priority

It is clear that the IPS device is suitable for designers and layout designers. But does it make sense to overpay? After all, photo processing and layout involve working with colors and their shades. The response time of the matrix is ​​not considered at all. Professionals recommend not to waste your money and choose VA-type monitor matrix. Yes, this is an old technology, yes, this is the last century, but in terms of price-quality criterion, matrices of this type have no competitors. And if there is a desire to purchase something from the new products, then the choice can be stopped on the PLS-matrix.

If there is a need to work behind a monitor with a high resolution, for example 4K, then professionals recommend giving preference to IGZO devices. Their price has not gone that far from the popular IPS screens, but in terms of quality they are undeniably better.

Multimedia lovers can save money

Oddly enough, but for those who like to watch movies on the monitor screen and surf the Internet, it is quite enough to purchase a device with a TN + film-matrix. An inexpensive gadget with an improved screen can easily replace a small TV. The problem may appear only in dark dynamic scenes, where instead of a black background, the viewer will have to observe a gray cloud. If this is critical, you need to look towards VA matrices. Yes, the price is higher, but the color issue will be resolved. In addition, the buyer will receive very high contrast and wide viewing angles. Do not forget about the physical resolution of the matrix - the higher it is, the better the picture is.

Office option

It would seem that the universal type of monitor matrix TN + film is very suitable for working with text. But, as practice shows, working with small print behind such a screen is extremely inconvenient. And if the monitor is purchased directly for working with large amounts of text, then you should worry about your vision. The closest technology to TN at an affordable price is VA. Regardless of the manufacturer and screen size, such a device will allow you to sit at the computer for more than one hour without any problems.

When choosing a monitor for office work, attention should be paid to both the size and the physical resolution of the matrix. The diagonal of the screen for working with text should not exceed the distance from the user's eyes to the matrix. It is also recommended to select office monitors with an aspect ratio of 4: 3, because in this ratio more readable information is placed on the screen.

New trend: for yourself

Having studied all the existing technologies of liquid crystal screens, before choosing the type of monitor matrix, a potential buyer should get acquainted with the information obtained through user surveys in the media.

1. The monitor is a durable purchase. That is, the next acquisition, with a high probability, will not be earlier than in 10 years.
2. In 99% of cases, the stated requirements for equipment do not coincide with the operating conditions. That is, gaming battles are taking place on the office monitor, and only news feeds are viewed on elite devices.
3. Multi-connection. For the convenience of work, 25% of users in the world connect several monitors to one computer (2, 3, 4), and the number of such owners is constantly growing. Convenience is that for each connected device a specific role is assigned - games, movies, office, etc.

The above information allows us to rethink our earlier knowledge. It is recommended to make a purchase, relying not on needs, but on desire and capabilities. In fact, it is worth focusing on the most expensive and high-quality device that a user can afford. You cannot save here.

Finally

Having found out which type of monitor matrix is ​​best for the user, what the letter marking on the device display means and how it affects the price and quality, you can proceed to the choice of the diagonal. However, many IT professionals recommend paying attention to screen resolution - how many dots per square inch it can display. Very often, the correct choice of the required resolution leads to the purchase of a monitor with a smaller diagonal, and, accordingly, to significant savings in money. An important role is played by the manufacturer of monitors - a matrix of its own production, the presence of a service center at the place of residence and a long warranty period hint to the future owner that he is acquiring a worthy device that will never fail.

How a CRT Monitor Works

How the LCD works

How a touchscreen works

There are three types of sensor technologies:

Resistive: resistive touch panels are covered with a metal plate that conducts electricity and a resistive layer that causes a change in electrical flow that is recognized as being touched and sent to the dispatcher for processing. Resistive touchpads are usually the most affordable, but only give 85% clarity and can be damaged by any sharp object. Dust or water ingress will not affect the operation of resistive touch panels.

Surface acoustic wave (SAW): SAW technology uses ultrasonic waves to pass through the surface of a touch panel. When the panel is touched, some of the waves are absorbed. This change in ultrasonic waves is detected as a touch and sends the information to the controller for processing. Surfactant panels are the most progressive.

Capacitive: capacitive touch panels are coated with a material that contains an electrical charge. When the panel is touched, the contact point receives a small charge. The circuit is located at all corners of the panel, measures the charge and sends the information to the dispatcher for processing. Capacitive touch panels should be used with the touch of your fingers, as opposed to resistive and SAW panels, which can be used with your finger or stylus. Dust or water ingress will not affect the operation of the capacitive touch panels.

More detailed information about touch screens can be obtained at: http://digitaldevice.ua/project/tehnologii-sensornih-ekranov

How the 3D monitor works

Monitor specifications:

Permission There is one LCD monitor, and it is also called native, it corresponds to the maximum physical resolution of CRT monitors. It is in native resolution that the LCD monitor reproduces the image best. This resolution is determined by the pixel size, which is fixed on the LCD monitor. For example, if the LCD monitor has a native resolution of 1024x768, this means that there are 1024 electrodes on each of the 768 lines, read: pixels. At the same time, it is possible to use a resolution lower than native. There are two ways to do this. The first is called "Centering"; the essence of the method is that only the number of pixels is used to display the image, which is necessary to form an image with a lower resolution. As a result, the image is not full screen, but only in the middle. All unused pixels remain black, i.e. a wide black border appears around the image. The second method is called "Expansion". Its essence is that when reproducing an image with a lower than native resolution, all pixels are used, i.e. the image fills the entire screen. However, because the image is stretched to fill the entire screen, slight distortion occurs and sharpness deteriorates. Therefore, when choosing an LCD monitor, it is important to be clear about the exact resolution you need.

Monitor screen resolution:

Brightness and contrast LCD monitors are not standardized. At the same time, in the center, the brightness of an LCD monitor can be 25% higher than at the edges of the screen. The contrast of an LCD monitor is determined by the ratio of brightness between the brightest white and the darkest black, and is one of the main parameters of the display.

In relation to light, the matrix of an LCD display is not an active, but a passive element; it is not capable of emitting light, but is only capable of modulating the light passing through it. Therefore, a backlight module is always located behind the LCD matrix, and the matrix only controls its transparency. Transparency is adjusted by rotating the plane of polarization - liquid crystals are located between two co-directional polarizers: co-directionality means that if the light between them has not changed its plane of polarization, then it passes through the second polarizer without loss.

Comparison of LCD monitors and CRT monitors:

Safety standards:

On all modern monitors, you can find stickers with the abbreviation TCO or MPRII. On very old models there are also the inscriptions "Low Radiation", which in fact do not say anything. It’s just that once, solely for marketing purposes, manufacturers from Southeast Asia attracted attention to their products. Such an inscription does not guarantee any protection.

Most of the measurements during TCO compliance testing are taken at a distance of 30 cm in front of the screen and at a distance of 50 cm around the monitor. For comparison, when testing monitors against another MPRII standard, all measurements are taken at a distance of 50 cm in front of the screen and around the monitor. This explains why TCO standards are more stringent than MPRII.

TCO'99 is more demanding than all other standards in the following areas: ergonomics (physical, visual and usability), energy, radiation (electric and magnetic fields), environment and ecology, and fire and electrical safety. The TCO'99 standard applies to traditional CRT monitors, Flat Panel Displays, Laptop and Notebook computers, system units and keyboards. The TCO'99 specifications contain requirements taken from the TCO'95, ISO, IEC and EN standards, as well as from EC Directive 90/270 / EEC and the Swedish national standard MPR 1990: 8 (MPRII) and from earlier TCO recommendations. The TCO'99 standard was developed by TCO, Naturskyddsforeningen and and Statens Energimyndighet (The Swedish National Energy Administration).

Environmental requirements include restrictions on the presence of heavy metals, brominates and chlorinates, freons (CFCs) and chlorinated substances within materials.

Any product must be prepared for recycling, and the manufacturer must have a developed disposal policy that must be followed in each country in which the company operates.

Power saving requirements include the need for the computer and / or monitor to reduce power consumption by one or more steps after a certain period of inactivity. In this case, the period of time for recovery to the operating mode of energy consumption should suit the user

Now the technology of flat panel monitors, including liquid crystal ones, is the most promising. Although LCD monitors currently account for only about 10% of worldwide sales, this market sector is the fastest growing (65% per year).

Principle of operation

LCD screens (Liquid Crystal Display, liquid crystal monitors) are made from a substance (cyanophenyl), which is in a liquid state, but at the same time has some of the properties inherent in crystalline bodies. In fact, these are liquids with anisotropy of properties (in particular, optical) associated with ordering in the orientation of molecules.
Oddly enough, but liquid crystals are almost ten years older than CRT, the first description of these substances was made back in 1888.However, for a long time, no one knew how to apply them in practice: there are such substances and everything, and no one except physicists and chemists, they were not interesting. So, liquid crystal materials were discovered back in 1888 by the Austrian scientist F. Renitzer, but only in 1930 researchers from the British corporation Marconi received a patent for their industrial application. However, things did not go further than this, since the technological base at that time was still too weak. The first real breakthrough was made by scientists Fergason and Williams of RCA (Radio Corporation of America). One of them created a thermal sensor based on liquid crystals, using their selective reflective effect, the other studied the effect of an electric field on nematic crystals. And at the end of 1966, RCA Corporation demonstrated a prototype LCD monitor - a digital clock. Sharp Corporation has played a significant role in the development of LCD technology. She is still among the technological leaders. The world's first calculator CS10A was produced in 1964 by this corporation. In October 1975, the first compact digital clock was manufactured using TN LCD technology. In the second half of the 70s, the transition from eight-segment liquid crystal displays to the production of matrices with addressing of each point began. So, in 1976 Sharp released a black and white TV with a screen diagonal of 5.5 inches, made on the basis of an LCD matrix with a resolution of 160x120 pixels.
LCD operation is based on the phenomenon of luminous flux polarization. It is known that the so-called polaroid crystals are capable of transmitting only that component of light, the electromagnetic induction vector of which lies in a plane parallel to the optical plane of the polaroid. For the rest of the luminous flux, the polaroid will be opaque. Thus, the polaroid "sifts" the light, this effect is called the polarization of light. When liquid substances were studied, whose long molecules are sensitive to electrostatic and electromagnetic fields and are able to polarize light, it became possible to control polarization. These amorphous substances for their similarity to crystalline substances in electro-optical properties, as well as for their ability to take the shape of a vessel, were called liquid crystals.
Based on this discovery and as a result of further research, it became possible to find a relationship between an increase in electrical voltage and a change in the orientation of the crystal molecules to provide imaging. Liquid crystals were first used in displays for calculators and electronic clocks, and then they began to be used in monitors for laptop computers. Today, as a result of progress in this area, LCD displays for desktop computers are becoming more common.

An LCD monitor screen is an array of small segments (called pixels) that can be manipulated to display information. An LCD monitor has several layers, where the key role is played by two panels made of sodium-free and very pure glass material called a substrate or substrate, which actually contain a thin layer of liquid crystals between them [see. rice. 2.1]. The panels have grooves that guide the crystals to give them a special orientation. The grooves are located in such a way that they are parallel on each panel, but perpendicular between the two panels. Longitudinal grooves are obtained by placing thin films of transparent plastic on the glass surface, which are then processed in a special way. In contact with the grooves, molecules in liquid crystals are oriented in the same way in all cells. Molecules of one of the types of liquid crystals (nematics), in the absence of voltage, rotate the vector of the electric (and magnetic) field in the light wave by a certain angle in the plane perpendicular to the beam propagation axis. The application of grooves on the glass surface makes it possible to ensure the same angle of rotation of the plane of polarization for all cells. The two panels are very close to each other. The liquid crystal panel is illuminated by a light source (depending on where it is located, liquid crystal panels work for reflection or for transmission of light).

The plane of polarization of the light beam is rotated 90 ° when passing through one panel [see. rice. 2.2].
When an electric field appears, the molecules of liquid crystals are partially aligned vertically along the field, the angle of rotation of the plane of polarization of light becomes different from 90 degrees and the light freely passes through the liquid crystals [see. rice. 2.3].
The rotation of the plane of polarization of the light beam is imperceptible to the eye, so it became necessary to add two more layers to the glass panels, which are polarizing filters. These filters transmit only that component of the light beam, for which the polarization axis corresponds to the given one. Therefore, when passing through the polarizer, the light beam will be attenuated depending on the angle between its plane of polarization and the axis of the polarizer. In the absence of voltage, the cell is transparent, since the first polarizer only transmits light with the corresponding polarization vector. Thanks to liquid crystals, the polarization vector of light is rotated, and by the time the beam passes to the second polarizer, it is already rotated so that it passes through the second polarizer without problems [see. Figure 2.4a].

In the presence of an electric field, the rotation of the polarization vector occurs at a smaller angle, thereby the second polarizer becomes only partially transparent for radiation. If the potential difference is such that the rotation of the plane of polarization in liquid crystals does not occur at all, then the light beam will be completely absorbed by the second polarizer, and the screen will appear black when illuminated from behind from the front (the backlight beams are completely absorbed in the screen) [see. Figure 2.4b]. If you place a large number of electrodes that create different electric fields in separate places of the screen (cell), then it will be possible, with the correct control of the potentials of these electrodes, to display letters and other image elements on the screen. The electrodes are placed in transparent plastic and can be of any shape. Technological innovations have made it possible to limit their size to the size of a small dot, respectively, on the same screen area, more electrodes can be placed, which increases the resolution of the LCD monitor, and allows us to display even complex images in color. To display a color image, the backlight of the monitor is required so that the light comes from the back of the LCD. This is necessary in order to be able to observe the image with good quality, even if the environment is not bright. Color is obtained by using three filters that separate three main components from the emission of a white light source. By combining the three primary colors for each point or pixel of the screen, it becomes possible to reproduce any color.
In fact, in the case of color, there are several possibilities: you can make several filters one after another (leads to a small fraction of transmitted radiation), you can use the property of a liquid crystal cell - when the electric field strength changes, the angle of rotation of the plane of polarization of the radiation changes differently for the light components with different wavelengths. This feature can be used to reflect (or absorb) radiation of a given wavelength (the problem is the need to accurately and quickly change the voltage). Which mechanism is used depends on the specific manufacturer. The first method is simpler, the second more effective.
The first LCD displays were very small, about 8 inches, while today they have reached 15 "sizes for use in laptops, and 20" or more LCD monitors are produced for desktop computers. The increase in size is followed by an increase in resolution, which results in the appearance of new problems that have been solved with the help of the emerging special technologies, we will describe all this below. One of the first challenges was the need for a standard to define display quality at high resolutions. The first step towards the goal was to increase the angle of rotation of the plane of polarization of light in crystals from 90 ° to 270 ° using STN technology.

Advantages and Disadvantages of LCD Monitors

Among the advantages of TFT are excellent focusing, no geometric distortion and color registration errors. In addition, their screen never flickers. Why? The answer is simple - these displays do not use an electron beam that draws from left to right every line on the screen. When in a CRT this beam is transferred from the lower right to the upper left corner, the image is momentarily extinguished (reverse path of the beam). In contrast, the pixels of a TFT display never go out, they just continuously change their intensity.
Table 1.1 shows all the main differences in performance for different types of displays:

Table 1.1. Comparative characteristics of CRT and LCD monitors.

Legend: ( + ) dignity, ( ~ ) is admissible, ( - ) flaw

From table 1.1 it follows that the further development of LCD monitors will be associated with an increase in the clarity and brightness of the image, an increase in the viewing angle and a decrease in the thickness of the screen. So, for example, there are already promising developments of LCD monitors, made by technology using polycrystalline silicon. This makes it possible, in particular, to create very thin devices, since the control chips are then placed directly on the glass substrate of the display. In addition, the new technology provides high resolution on a relatively small screen (1024x768 pixels on a 10.4-inch screen).

STN, DSTN, TFT, S-TFT

STN is an abbreviation for Super Twisted Nematic. STN technology increases the torsion angle (angle of twisting) of the crystal orientation inside the LCD from 90 ° to 270 °, which provides better image contrast when increasing the size of the monitor.
Often STN cells are used in pairs. This design is called DSTN (Double Super Twisted Nematic), in which one double-layer DSTN cell consists of 2 STN cells, the molecules of which turn in opposite directions during operation. Light passing through such a structure in a "locked" state loses most of its energy. The contrast and resolution of DSTN are high enough, so it became possible to make a color display, in which there are three LCD cells and three optical filters of primary colors for each pixel. Color displays cannot operate on reflected light, so a backlight is a must. To reduce the size of the lamp is on the side, and opposite it is a mirror [see. rice. 2.5], so most LCDs in the center have a brighter brightness than the edges (this does not apply to desktop LCD monitors).

STN cells are also used in TSTN (Triple Super Twisted Nematic) mode, when two thin layers of polymer film are added to improve the color rendering of color displays or to provide good quality monochrome monitors.
The term passive matrix appeared as a result of dividing the monitor into points, each of which, thanks to the electrodes, can set the orientation of the plane of polarization of the beam, independently of the others, so that as a result, each such element can be individually illuminated to create an image. The matrix is ​​called passive, because the technology for creating LCD displays, which was described above, cannot provide a quick change of information on the screen. The image is formed line by line by sequentially applying a control voltage to individual cells, making them transparent. Due to the rather large electrical capacity of the cells, the voltage across them cannot change quickly enough, so the image is updated slowly. Such a display has many disadvantages in terms of quality, because the image is not displayed smoothly and shakes on the screen. The low rate of change in the transparency of the crystals does not allow the moving images to be displayed correctly.
To solve some of the problems described above, special technologies are used. To improve the quality of the dynamic image, it was proposed to increase the number of control electrodes. That is, the entire matrix is ​​divided into several independent sub-matrices (Dual Scan DSTN - two independent image scan fields), each of which contains a smaller number of pixels, therefore, one-by-one control of them takes less time. As a result, the inertia time of the LCD can be shortened.
Also, the best results in terms of stability, quality, resolution, smoothness and brightness of the image can be achieved using screens with an active matrix, which, however, are more expensive.
The active matrix uses separate amplifying elements for each screen cell to compensate for the effect of cell capacitance and significantly reduce the time of changing their transparency. The active matrix has many advantages over the passive matrix. For example, the best brightness and the ability to look at the screen even with a deviation of up to 45 ° or more (i.e., at a viewing angle of 120 ° -140 °) without compromising image quality, which is impossible in the case of a passive matrix, which allows you to see a high-quality image only from the front position in relation to the screen. Note that expensive models of LCD monitors with an active matrix provide a viewing angle of 160 ° [see fig. 2.6], and there is every reason to believe that the technology will be improved in the future. The active matrix can display moving images without visible jitter, since the response time of an active matrix display is about 50ms versus 300ms for a passive matrix, in addition, the contrast of active matrix monitors is higher than that of CRT monitors. It should be noted that the brightness of an individual screen element remains unchanged over the entire time interval between image updates, and does not represent a short pulse of light emitted by a phosphor element of a CRT monitor immediately after an electron beam has passed this element. That is why, for LCD monitors, a vertical scan frequency of 60 Hz is sufficient.

The functionality of an active matrix LCD is almost the same as a passive matrix display. The difference lies in the electrode array that drives the display's liquid crystal cells. In the case of a passive matrix, different electrodes receive an electric charge in a cyclic method when the display is updated line-by-line, and as a result of the discharge of the capacities of the elements, the image disappears, since the crystals return to their original configuration. In the case of an active matrix, a storage transistor is added to each electrode that can store digital information (binary values ​​0 or 1) and as a result the image is stored until another signal arrives. The problem of delaying image fading in passive matrices is partially solved by using a larger number of liquid crystal layers to increase passivity and reduce displacements, but now, when using active matrices, it became possible to reduce the number of liquid crystal layers. Storage transistors must be made of transparent materials, which will allow the light beam to pass through them, which means that the transistors can be located on the back of the display, on a glass panel that contains liquid crystals. For these purposes, plastic films are used, called "Thin Film Transistor" (or simply TFT).
Thin Film Transistor (TFT) i.e. TFT are the controls that control every pixel on the screen. Thin film transistor is really very thin, its thickness is 0.1 - 0.01 microns.
The first TFT displays, which appeared in 1972, used cadmium selenide, which has high electron mobility and maintains a high current density, but over time, a transition was made to amorphous silicon (a-Si), and high-resolution matrices used polycrystalline silicon ( p-Si).
The technology for creating TFTs is very complex, and there are difficulties in achieving an acceptable percentage of good products due to the fact that the number of transistors used is very large. Note that a monitor that can display an image with a resolution of 800x600 pixels in SVGA mode and with only three colors has 1,440,000 individual transistors. Manufacturers set standards for the maximum number of transistors that can be inoperative in an LCD display. True, each manufacturer has its own opinion about how many transistors may not work.
The TFT pixel is arranged as follows: in a glass plate, three color filters (red, green and blue) are integrated one after the other. Each pixel is a combination of three colored cells or subpixel elements [see. rice. 2.7]. This means, for example, that a display with a resolution of 1280x1024 has exactly 3840x1024 transistors and subpixel elements. The pixel size for a 15.1 "TFT display (1024x768) is approximately 0.0188" (or 0.30 mm), and for an 18.1 "TFT display it is about 0.011 inches (or 0.28 mm).

TFTs have a number of advantages over CRT monitors, including lower power consumption and heat dissipation, a flat screen and no traces of moving objects. Recent developments allow for higher quality images than conventional TFTs.

More recently, Hitachi has developed a new Super TFT Multi-Layer LCD Panel technology that significantly increases the confident viewing angle of the LCD panel. Super TFT technology uses simple metal electrodes mounted on a bottom glass plate and causes the molecules to rotate while constantly being in a plane parallel to the plane of the screen [cf. rice. 2.8]. Since the crystals of a conventional LCD panel are rotated to the surface of the screen with their ends, such LCDs are more dependent on the angle of view than Hitachi LCD panels with Super TFT technology.As a result, the image on the display remains bright and clear even at large viewing angles, achieving quality, comparable to the image on a CRT screen.

Japan's NEC recently announced that its LCD displays will soon reach the level of laser printers in image quality, surpassing the 200 ppi threshold, which is 31 dots per mm 2 or 0.18 mm dot pitch. According to NEC, TN (twisted nematic) liquid crystals used today by many manufacturers allow you to build displays with a resolution of up to 400 dpi. However, the main limiting factor in increasing the resolution is the need to create appropriate light filters. In the new technology "color filter on TFT", the light filters covering the thin film transistors are formed by photolithography on the lower glass substrate. In conventional displays, filters are applied to a second, top substrate, which requires very precise alignment of the two plates.

At the conference "Society for information Display" held in 1999 in the USA, several reports were made, testifying to the success in the creation of liquid crystal displays on a plastic substrate. Samsung has presented a prototype of a monochrome display on a polymer substrate with a diagonal of 5.9 inches and a thickness of 0.5 mm. The thickness of the substrate itself is about 0.12 mm. The display has a resolution of 480x320 pixels and a contrast ratio of 4: 1. Weight - only 10 grams.

The engineers from the Film Technology Laboratory of the University of Stuttgart did not use thin-film transistors (TFT), but MIM (metal-insulator-metal) diodes. The latest achievement of this team is a two-inch color display with a resolution of 96x128 pixels and a contrast ratio of 10: 1.

An IBM team has developed a technology for producing thin film transistors using organic materials to make flexible screens for e-books and other devices. Elements of IBM-designed transistors are sprayed onto a plastic substrate at room temperature (traditional LCD displays are manufactured at high temperatures, which eliminates the use of organic materials). Barium Zirconate Titonate (BZT) is used to make the seal instead of conventional silica. An organic substance called pentacene is used as a semiconductor, which is a compound of phenylethylammonium with tin iodide.

To increase the resolution of LCD-screens, Displaytech proposed not to create an image on the surface of a large LCD-screen, but to display the image on a small high-resolution display, and then use an optical projection system to enlarge it to the required size. In doing so, Displaytech used the original Ferroelectric LCD (FLCD) technology. It is based on the so-called chiral smectic liquid crystals, which were proposed for use back in 1980. A layer of a material with ferroelectric properties and capable of reflecting polarized light with rotation of the plane of polarization is deposited on a CMOS substrate that supplies control signals. When the reflected light flux passes through the second polarizer, a picture of dark and light pixels appears. A color image is obtained due to the rapid alternation of illumination of the matrix with red, green and blue light. On the basis of FLCD-matrices, it is possible to produce screens of large size with high contrast and color quality, with wide viewing angles and fast response time. In 1999, an alliance of Hewlett-Packard corporations and DisplayTech announced a full color micro display based on FLCD technology. The matrix resolution is 320x240 pixels. Distinctive features of the device are low power consumption and the ability to play full-color "live" video. The new display is designed for use in digital cameras, camcorders, handheld communicators and wearable computer monitors.

Toshiba is developing low-temperature technology using LTPS polysilicon. According to representatives of this corporation, they are positioning new devices so far only as intended for the market of mobile devices, not including laptops, where the a-Si TFT technology dominates. 4 "VGA displays are already in production, with 5.8" matrices on the way. Experts believe that 2 million pixels on the screen is far from the limit. One of the distinguishing features of this technology is its high resolution.

According to experts from DisplaySearch Corporation, which researches the flat panel display market, at present, in the manufacture of almost any liquid crystal matrix, technologies are being replaced: TN LCD (Twisted Nematic Liquid Crystal Display) to STN (Super TN LCD) and especially to a-Si TFT LCD ( amorphous-Silicon Thin Film Transistor LCD). In the next 5-7 years, in many areas of application, conventional LCD screens will be replaced or supplemented by the following devices:

• microdisplays;
• light emitting displays based on organic LEP materials;
• displays based on field emission FED (Field Emisson Display);
• displays using low-temperature polycrystalline silicon LTPS (Low Temperature PolySilicon);
• plasma displays PDP (Plasma Display Panel).

Taken from http://monitors.narod.ru

For many, liquid crystal displays (LCDs) are associated primarily with flat panel monitors, cool TVs, laptops, camcorders and cell phones. Some will add here PDA, electronic games, ATMs. But there are many more areas where displays with high brightness, rugged construction, and a wide temperature range are needed.

Flat panel displays are used where minimum power consumption, weight and dimensions are critical parameters. Mechanical engineering, automotive, rail transport, offshore drilling rigs, mining equipment, outdoor retail outlets, aviation electronics, marine, special vehicles, security systems, medical equipment, weapons - this is not a complete list of applications for LCD displays.

The constant development of technologies in this area has made it possible to reduce the cost of LCD production to such a level at which a qualitative transition has taken place: expensive exotic has become commonplace. Ease of use has also become an important factor in the rapid adoption of LCDs in industry.

This article discusses the basic parameters of various types of liquid crystal displays, which will allow you to make an informed and correct choice of LCD for each specific application (the "bigger and cheaper" method is almost always too expensive).

All the variety of LCD displays can be divided into several types depending on production technology, design, optical and electrical characteristics.

Technology

Currently, two technologies are used in the production of LCDs (Fig. 1): passive matrix (PMLCD-STN) and active matrix (AMLCD).

MIM-LCD and Diode-LCD technologies are not widespread and therefore we will not waste time on them.

Rice. 1. Types of liquid crystal display technologies

STN (Super Twisted Nematic) is a matrix consisting of LCD elements with variable transparency.

TFT (Thin Film Transistor) is an active matrix in which each pixel is controlled by a separate transistor.

Compared to a passive matrix, TFT LCD has a higher contrast, saturation, shorter switching time (no "tails" in moving objects).

The brightness control in the liquid crystal display is based on the polarization of light (general physics course): light is polarized by passing through a polarizing filter (with a specific polarization angle). In this case, the observer sees only a decrease in the brightness of the light (almost 2 times). If you put another such filter behind this filter, then the light will be completely absorbed (the polarization angle of the second filter is perpendicular to the polarization angle of the first one) or completely pass (the polarization angles coincide). With a smooth change in the polarization angle of the second filter, the intensity of the transmitted light will also change smoothly.

The principle of operation and the "sandwich" structure of all TFT LCDs is approximately the same (Fig. 2). Light from a backlight lamp (neon or LED) passes through the first polarizer and enters a layer of liquid crystals controlled by a thin film transistor (TFT). The transistor creates an electric field that shapes the orientation of the liquid crystals. After passing through such a structure, the light changes its polarization and will either be completely absorbed by the second polarizing filter (black screen), or will not be absorbed (white), or the absorption will be partial (spectrum colors). The color of the image is determined by color filters (similar to cathode-ray tubes, each pixel of the matrix consists of three subpixels - red, green and cyan).

Rice. 2. Structure of TFT LCD

Pixel TFT

Color filters for red, green and blue are integrated into the glass base and are located close to each other. This can be a vertical stripe, a mosaic structure, or a delta structure (Fig. 3). Each pixel (point) consists of three cells of the specified colors (subpixels). This means that at m x n resolution the active matrix contains 3m x n transistors and subpixels. The pixel pitch (with three subpixels) for a 15.1 "TFT LCD (1024 x 768 dots) is approximately 0.30 mm, and for an 18.1" (1280 x 1024 dots) it is 0.28 mm. TFT LCDs are physically limited by the maximum screen area. Don't expect 1280 x 1024 resolution at 15 "diagonal and 0.297 mm dot pitch.

Rice. 3. Color filter structure

At a close distance, the points are clearly distinguishable, but this is not a problem: when forming a color, the property of the human eye is used to mix colors at an angle of view of less than 0.03 °. At a distance of 40 cm from the LCD with a subpixel pitch of 0.1 mm, the angle of view will be 0.014 ° (the color of each subpixel can only be distinguished by a person with eagle vision).

LCD types

TN (Twist Nematic) TFT or TN + Film TFT is the first technology to appear on the LCD market, the main advantage of which is its low cost. Disadvantages: black is more like dark gray, which leads to low image contrast, "dead" pixels (if the transistor fails) are very bright and noticeable.

IPS (In-Pane Switching) (Hitachi) or Super Fine TFT (NEC, 1995). It is characterized by the largest viewing angle and high color accuracy. The viewing angle is expanded to 170 °, other functions are the same as in TN + Film (response time is about 25ms), almost perfect black color. Advantages: good contrast, dead pixel - black.

Super IPS (Hitachi), Advansed SFT (manufacturer - NEC). Advantages: bright contrast image, color distortion is almost invisible, viewing angles are increased (up to 170 ° vertically and horizontally) and exceptional clarity is provided.

UA-IPS (Ultra Advanced IPS), UA-SFT (Ultra Advanced SFT) (NEC). The response time is sufficient to ensure minimal color distortion when viewing the screen from different angles, increased panel transparency and expanded color gamut at a sufficiently high brightness level.

MVA (Multi-Domain Vertical Alignment) (Fujitsu) The main advantage is the shortest response time and high contrast. The main disadvantage is the high cost.

PVA (Patterned Vertical Alignment) (Samsung). Microstructural vertical placement of LCDs.

Design

The design of the liquid crystal display is determined by the arrangement of the layers in the "sandwich" (including the light-conducting layer) and is of the greatest importance for the quality of the image on the screen (in any conditions: from a dark room to working in sunlight). There are three main types of color LCDs in use today:

• transmissive, designed primarily for indoor equipment;
• reflective is used in calculators and watches;
• projection is used in LCD projectors.

A compromise type of transmissive display type for both indoor and outdoor use is the transflective design.

Transmissive display type... In this type of design, light enters through the LCD panel from the back (backlight) (Figure 4). This technology is used in most LCDs used in laptops and PDAs. Transmissive LCD has high image quality indoors and low (black screen) in sunlight. the sun's rays reflected from the surface of the screen completely suppress the light emitted by the backlight. This problem is (currently) solved in two ways: increasing the brightness of the backlight and decreasing the amount of reflected sunlight.

Rice. 4. Construction of transmissive type liquid crystal display

To work in daylight in the shade, a backlight is required that provides 500 cd / m2, in direct sunlight - 1000 cd / m2. A brightness of 300 cd / m2 can be achieved by increasing the brightness of one CCFL (Cold Cathode Fluorescent Lamp) lamp to the maximum or by adding a second lamp opposite. High brightness LCD models use 8 to 16 lamps. However, increasing the brightness of the backlight increases the drain on the battery (a single backlight consumes about 30% of the power used by the device). Therefore, screens with increased brightness can only be used with an external power supply.

Reducing the amount of reflected light is achieved by applying an antireflection coating to one or more layers of the display, replacing the standard polarizing layer with a minimally reflective layer, adding films that increase brightness and, thus, increase the efficiency of the light source. In Fujitsu LCDs, the transducer is filled with a liquid with a refractive index equal to that of the touch panel, which significantly reduces the amount of reflected light (but greatly affects the cost).

Translucent display type (transflective) similar to transmissive, but it has a so-called. partially reflective layer (fig. 5). It can be either partially silver or completely mirrored with many small holes. When used indoors, it works in a similar way to a transmissive LCD, in which some of the light is absorbed by the reflective layer. In daylight, sunlight reflects off the mirror layer and illuminates the LC layer, with the light passing through the liquid crystals twice (inward and then outward). As a consequence, the picture quality in daylight is lower than in artificial lighting indoors, when the light passes through the LCD once.

Rice. 5. Construction of semi-transparent type liquid crystal display

The balance between indoor and daylight image quality is achieved by matching the characteristics of the transmissive and reflective layers.

Reflective display type(reflective) has a fully reflective specular layer. All lighting (sunlight or front light) (Figure 6) passes through the LCD, reflects off the mirror layer, and passes through the LCD again. In this case, the image quality of reflective type displays is lower than that of semi-transmissive ones (since in both cases similar technologies are used). Indoors, front lighting is not as effective as back lighting, and therefore the picture quality is lower.

Rice. 6. Design of reflective type liquid crystal display

Basic parameters of liquid crystal panels

Permission. A digital panel, the number of pixels in which strictly corresponds to the nominal resolution, must correctly and quickly scale the image. An easy way to check the quality of scaling is to change the resolution (small print on screen). It is easy to see the quality of the interpolation from the contours of the letters. A high-quality algorithm produces even, but slightly blurry letters, while fast integer interpolation is bound to introduce distortion. Speed ​​is the second resolution parameter (it takes time to interpolate to scale one frame).

Dead pixels. Several pixels may not work on a flat panel (they are always the same color), which appear during the production process and cannot be restored.

The ISO 13406-2 standard defines the limit values ​​for the number of defective pixels per million. According to the table, LCD panels are divided into 4 classes.

Table 1

Viewing angle. The maximum viewing angle is defined as the angle at which the image contrast is reduced by 10 times. But first of all, when changing the viewing angle from 90 (color distortions are visible. Therefore, the larger the viewing angle, the better. There are horizontal and vertical viewing angles, the recommended minimum values ​​are 140 and 120 degrees, respectively (the best viewing angles are provided by MVA technology).

Response time(inertia) - the time during which the transistor manages to change the spatial orientation of the liquid crystal molecules (the less, the better). For fast moving objects not to appear blurry, a response time of 25 ms is sufficient. This parameter consists of two values: the time to turn on the pixel (come-up time) and the time to turn off (come-down time). The response time (more precisely, the shutdown time as the longest time during which a single pixel changes its brightness to the maximum) determines the refresh rate of the image on the screen

FPS = 1 s / response time.

Brightness- the advantage of the LCD display, which is, on average, twice as high as that of a CRT: with an increase in the intensity of the backlight, the brightness immediately increases, and in a CRT it is necessary to increase the flow of electrons, which will lead to a significant complication of its design and increase electromagnetic radiation. The recommended brightness value is at least 200 cd / m2.

Contrast is defined as the ratio between maximum and minimum brightness. The main problem is the difficulty of getting a black point, because the backlight is always on and the polarization effect is used to produce dark tones. The black color depends on the quality of the blocking of the luminous flux of the backlight.

LCDs as sensors. The decrease in cost and the appearance of LCD models operating in harsh operating conditions made it possible to combine in one person (in the face of a liquid crystal display) a means of displaying visual information and a means of entering information (keyboard). The task of building such a system is simplified by using a serial interface controller, which is connected, on the one hand, to the LCD display, and on the other, directly to the serial port (COM1 - COM4) (Fig. 7). For control, decoding of signals and suppression of "bounce" (if you can call the definition of touch), a PIC controller (for example, IF190 from Data Display) is used, which provides high speed and accuracy in determining the touch point.

Rice. 7. Block diagram of TFT LCD on the example of NL6448BC-26-01 display from NEC

We will complete the theoretical research on this and move on to the realities of today, or rather, to what is now available on the market of liquid crystal displays. Among all TFT LCD manufacturers, consider products from NEC, Sharp, Siemens and Samsung. The choice of these firms is due to

1. market leadership of LCD displays and TFT LCD manufacturing technologies;
2. availability of products on the market of the CIS countries.

NEC Corporation has been producing liquid crystal displays (20% of the market) since their inception and offers not only a wide selection, but also various options: Standard, Special and Specific. The standard option is computers, office equipment, home electronics, communications systems, etc. A special version is used in transport (any: land and sea), traffic control systems, security systems, medical equipment (not related to life support systems). For weapons systems, aviation, space equipment, control systems for nuclear reactors, life support systems and others similar, a special version is intended (it is clear that it is not cheap).

The list of manufactured LCD panels for industrial use (inverter for the backlight lamp is supplied separately) is shown in Table 2, and the block diagram (using the example of a 10-inch display NL6448BC26-01) is shown in Fig. eight.

Rice. 8. Display appearance

Table 2. NEC LCD Panel Models

Played a significant role in the development of LCD technologies. Sharp is still one of the technology leaders. The world's first calculator CS10A was produced in 1964 by this corporation. In October 1975, the first compact digital clock was manufactured using TN LCD technology. In the second half of the 70s, the transition from eight-segment liquid crystal displays to the production of matrices with addressing of each point began. In 1976, Sharp released a 5.5-inch black-and-white TV based on a 160x120 pixel LCD matrix. A short list of products is in table 3.

Table 3. Sharp LCD Panel Models

Produces liquid crystal displays with an active matrix on low-temperature polysilicon thin-film transistors. Key specifications for 10.5 "and 15" displays are shown in Table 4. Pay attention to operating temperature range and shock resistance.

Table 4. Main characteristics of Siemens LCD displays

Notes:

I - built-in inverter l - according to MIL-STD810 standard

The firm produces liquid crystal displays under the brand name "Wiseview ™". Starting with a 2-inch TFT panel to support the Internet and animation in mobile phones, Samsung now produces a range of displays from 1.8 "to 10.4" in the small to medium-sized TFT LCD segment, with some models designed to work in natural light ( table 5).

Table 5. Key Features of Samsung LCDs Small and Medium Sizes

Notes:

LED - LED; CCFL - cold cathode fluorescent lamp;

The displays use PVA technology.

Conclusions.

Currently, the choice of a liquid crystal display model is determined by the requirements of a particular application and, to a much lesser extent, by the cost of the LCD.