How is the LCD display. What is the difference between IPS and TFT screen types

Telling about the differences between IPS and TN matrices as part of advice when buying a monitor or laptop. It's time to talk about all modern display technologies, which we may encounter and have an idea about types of matrices in devices of our generation. Do not confuse with LED, EDGE LED, Direct LED - these are types of screen backlights and display technologies are indirectly related.

Probably, everyone can remember their monitor with a cathode ray tube, which they used earlier. True, there are still users and fans of CRT technology. Currently, screens have increased in diagonal, display manufacturing technologies have changed, there are more and more varieties in the characteristics of matrices, denoted by the abbreviations TN, TN-Film, IPS, Amoled, etc.

The information in this article will help you choose a monitor, smartphone, tablet and other various kinds of equipment. In addition, it will highlight the technologies for creating displays, as well as the types and features of their matrices.

A few words about liquid crystal displays

LCD (Liquid Crystal Display)- This is a display made on the basis of liquid crystals, which change their location when voltage is applied to them. If you get close to such a display and look closely at it, you will notice that it consists of small dots - pixels (liquid crystals). In turn, each pixel consists of red, blue and green subpixels. When a voltage is applied, the sub-pixels line up in a certain order and allow light to pass through them, thus forming a pixel of a certain color. Many of these pixels form an image on the screen of a monitor or other device.

The first mass-produced monitors were equipped with matrices TN- having the simplest design, but which cannot be called the highest quality type of matrix. Although among this type of matrices there are very high-quality specimens. This technology is based on the fact that in the absence of voltage, subpixels let light pass through themselves, forming a white dot on the screen. When voltage is applied to subpixels, they line up in a certain order, forming a pixel of a given color.

Disadvantages of TN matrix

Due to the fact that the standard pixel color, in the absence of voltage, is white, this type of matrix does not have the best color reproduction. Colors appear dimmer and faded, while blacks appear more of a dark grey.
Another main disadvantage of TN matrix is the small viewing angles. Partially, they tried to cope with this problem by improving the TN technology to TN + Film, using an additional layer applied to the screen. Viewing angles have become larger, but still remained far from ideal.

At present, TN+Film matrices have completely replaced TN.

Advantages of TN matrix

short response time
relatively low cost.

Drawing conclusions, it can be argued that if you need an inexpensive monitor for office work or surfing the Internet, monitors with TN + Film matrices are the best fit.

The main difference between IPS matrix technology and TN- perpendicular arrangement of subpixels in the absence of voltage, which form a black dot. That is, in a state of calm, the screen remains black.

Advantages of IPS matrices

better color reproduction compared to TN screens: you have bright and rich colors on the screen, and the black color remains really black. Accordingly, when voltage is applied, the pixels change their color. Given this feature, owners of smartphones and tablets with IPS screens can be advised to use dark color schemes and wallpapers on the desktop, then the smartphone battery will last a little longer.
large viewing angles. In most screens they are 178°. For monitors, and especially for mobile devices (smartphones and tablets), this feature is important when a user chooses a gadget.

Disadvantages of IPS matrices

great screen response time. This affects the display in dynamic pictures such as games and movies. In modern IPS panels, things are better with response time.
high cost compared to TN.

Summing up, it is better to choose phones and tablets with IPS matrices, and then the user will get great aesthetic pleasure from using the device. The matrix for the monitor is not so critical, modern.

AMOLED screens

The latest smartphone models are equipped with AMOLED displays. This technology for creating matrices is based on active LEDs, which begin to glow and display color when voltage is applied to them.

let's consider features of Amoled matrix:

Color rendering. The saturation and contrast of such screens is higher than required. Colors are displayed so vividly that some users may experience eye fatigue when using their smartphone for extended periods of time. But the black color is displayed even more black than even in IPS-matrices.
Display power consumption. As with IPS, displaying black requires less power than displaying a particular color, much less white. But the difference in power consumption between displaying black and white in AMOLED screens is much larger. Displaying white requires several times more power than displaying black.
"Memory pictures". When a static image is displayed for a long time, traces may remain on the screen, and this in turn affects the quality of the display of information.

Also, due to its rather high cost, AMOLED screens are still used only in smartphones. Monitors built on this technology are unreasonably expensive.

VA (Vertical Alignment)- This technology, developed by Fujitsu, can be considered as a compromise between TN and IPS matrices. In VA matrices, the crystals in the off state are located perpendicular to the plane of the screen. Accordingly, the black color is provided as pure and deep as possible, but when the matrix is rotated relative to the direction of view, the crystals will not be visible in the same way. To solve the problem, a multi-domain structure is used. Technology Multi-Domain Vertical Alignment (MVA) provides protrusions on the plates, which determine the direction of rotation of the crystals. If two subdomains are rotated in opposite directions, then when viewed from the side, one of them will be darker and the other lighter, thus for the human eye the deviations cancel each other out. PVA matrices developed by Samsung do not have protrusions, and in the off state, the crystals are strictly vertical. In order for the crystals of neighboring subdomains to rotate in opposite directions, the lower electrodes are shifted relative to the upper ones.

To reduce response time, Premium MVA and S-PVA matrices use a dynamic voltage boost system for certain sections of the matrix, which is commonly referred to as Overdrive. The color reproduction of PMVA and SPVA matrices is almost as good as that of IPS, the response time is slightly inferior to TN, viewing angles are as wide as possible, blacks are the best, brightness and contrast are the highest possible among all existing technologies. However, even with a slight deviation of the direction of view from the perpendicular, even by 5–10 degrees, distortions in semitones can be noticed. For most, this will go unnoticed, but professional photographers continue to dislike VA technology for this.

MVA and PVA matrices have excellent contrast and viewing angles, but things are worse with the response time - it grows as the difference between the final and initial pixel states decreases. Early models of such monitors were almost unsuitable for dynamic games, and now they show results close to TN matrices. The color reproduction of *VA matrices is, of course, inferior to IPS matrices, but remains at a high level. However, thanks to their high contrast ratio, these monitors will be an excellent choice for text and photo work, drawing graphics, and as home monitors.

In conclusion, I can say that the choice is always yours ...

What is LCD? In short and clear, this is a liquid crystal screen. Simple devices that have such equipment can work either with a black and white image, or with 2-5 colors. Currently, the described screens are used to display graphical or textual information. They are installed in computers, laptops, TVs, phones, cameras, tablets. Most electronic devices currently work with just such a screen. One of the popular varieties of such technology is the active matrix liquid crystal display.

Story

Liquid crystals were first discovered in 1888. This was done by the Austrian Reinitzer. In 1927, the Russian physicist Frederiks discovered the crossing, which was named after him. At the moment, it is widely used in the creation of liquid crystal displays. In 1970, RCA introduced the first screen of this type. It immediately began to be used in watches, calculators and other devices.

A little later, a matrix display was created that worked with a black and white image. The color LCD screen appeared in 1987. Its creator is Sharp. The diagonal of this device was 3 inches. Reviews for this type of LCD screen have been positive.

Device

When considering LCD screens, it is necessary to mention the design of the technology.

This device consists of an LCD matrix, light sources that directly provide the backlight itself. There is a plastic case framed by a metal frame. It is necessary to give rigidity. Contact harnesses, which are wires, are also used.

LCD pixels consist of two transparent type electrodes. A layer of molecules is placed between them, and there are also two polarizing filters. Their planes are perpendicular. One nuance should be noted. It lies in the fact that if there were no liquid crystals between the above filters, then the light passing through one of them would be immediately blocked by the second one.

The surface of the electrodes, which is in contact with liquid crystals, is covered with a special sheath. Due to this, the molecules move in the same direction. As mentioned above, they are mostly perpendicular. In the absence of tension, all molecules have a helical structure. Due to this, the light is refracted and passes through the second filter without loss. Now any person should understand that this is an LCD from the point of view of physics.

Advantages

When compared with cathode ray devices, it wins here. It is small in size and weight. LCD devices do not flicker, they have no problems with focusing, as well as with the convergence of rays, there are no interference that arise from magnetic fields, there are no problems with the picture geometry and its clarity. You can attach the LCD display on the brackets to the wall. It is very easy to do this. In this case, the picture will not lose its qualities.

How much an LCD monitor consumes depends entirely on the image settings, the model of the device itself, and also on the characteristics of the signal supply. Therefore, this figure can either coincide with the consumption of the same beam devices and plasma screens, or be much lower. At the moment, it is known that the energy consumption of LCD monitors will be determined by the power of the installed lamps that provide illumination.

It is also necessary to say about small-sized LCD displays. What is it, how do they differ? Most of these devices do not have a backlight. These screens are used in calculators, watches. Such devices have a completely low power consumption, so they can work autonomously for up to several years.

Flaws

However, these devices also have disadvantages. Unfortunately, many shortcomings are difficult to eliminate.

When compared with electron-beam technology, a clear image on the LCD display can only be obtained at standard resolution. To achieve a good characterization of other pictures, you will have to use interpolation.

LCD monitors have average contrast as well as poor black depth. If you want to increase the first indicator, then you need to increase the brightness, which does not always provide comfortable viewing. This problem is noticeable in LCD devices from Sony.

The frame rate of LCD displays is much slower when compared to plasma or cathode ray displays. At the moment, Overdrive technology has been developed, but it does not solve the speed problem.

With viewing angles, there are also some nuances. They are completely dependent on contrast. Electron-beam technology has no such trouble. LCD monitors are not protected from mechanical damage, the matrix is not covered with glass, so if you press hard, you can deform the crystals.

Backlight

Explaining what it is - LCD, it should be said about this characteristic. The crystals themselves do not glow. Therefore, in order for the image to become visible, it is necessary to have a light source. It can be external or internal.

The first is to use the sun's rays. In the second option, an artificial source is used.

As a rule, lamps with built-in illumination are installed behind all layers of liquid crystals, due to which they shine through. There is also a side illumination, which is used in watches. In LCD TVs (which is the answer above), this type of design is not used.

As for ambient lighting, as a rule, black-and-white displays of watches and mobile phones work in the presence of such a source. Behind the layer with pixels is a special matte reflective surface. It allows you to beat off sunlight or radiation from lamps. Thanks to this, you can use such devices in the dark, as manufacturers build in side lights.

Additional information

There are displays that combine an external source and additionally built-in lamps. Previously, some watches that had a monochrome type LCD screen used a special small incandescent lamp. However, due to the fact that it consumes too much energy, this solution is not profitable. Such devices are no longer used in televisions, as they generate a large amount of heat. Because of this, liquid crystals are destroyed and burn out.

At the beginning of 2010, LCD TVs became widespread (what is it, we examined above), which had such displays should not be confused with truly real LED screens, where each pixel glows on its own, being an LED.

The search module is not installed.

Liquid crystal displays (TN, TN+Film and TFT technologies)

Sergei Yaroshenko

An ever-increasing number of users are changing their CRT monitors to LCDs. If for 19-inch CRT monitors a large case size that did not fit comfortably on an office desk led to fatal consequences, then the price reduction and minimal size of 19-inch LCD monitors today increase their attractiveness.

The principle of operation of LCD monitors (Liquid Crystal Display - liquid crystal display) is based on the use of a substance that is in a liquid state, but at the same time has some properties inherent in crystalline bodies. These amorphous substances are called "liquid crystals" because of their similarity to crystalline substances in electro-optical properties, as well as the ability to take the shape of a vessel.

Origin of LCD Monitors

Liquid crystal materials were discovered 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. Things did not go further than a patent, because at that time the technological base was still too weak to create reliable and functional devices. The first breakthrough was made by scientists Fergeson and Williams from RCA (Radio Corporation of America). One of them created a temperature sensor based on liquid crystals, using their selective reflective effect, the other studied the effect of an electric field on nematic crystals. As a result, at the end of 1966, the RCA Corporation demonstrated a digital clock with an LCD prototype.

Sharp Corporation played a significant role in the development of LCD technology. It is this corporation:

In 1964, the world's first CS10A calculator was produced;
- in 1975, the first compact digital watch was made using TN LCD technology;
- in 1976, a black-and-white TV with a screen diagonal of 5.5 inches based on an LCD matrix with a resolution of 160x120 pixels was released.

How LCDs work

Liquid crystal molecules under the influence of electricity can change their orientation, and as a result, change the properties of the light beam passing through them.

The screen of an LCD monitor is an array of segments (pixels) that can be manipulated to display information. The display has several layers, where the key role is played by two panels made of a sodium-free and very pure glass material called a substrate or substrate. Between the panels is a thin layer of liquid crystals. The panels have grooves that guide the crystals, giving them the desired orientation. On each panel, the grooves are parallel, and between the panels are perpendicular. Longitudinal grooves are formed as a result of placing thin films of transparent plastic on the glass surface, which is then processed in a special way. In contact with the grooves, the molecules of liquid crystals take the same orientation. The glass panels are very close to each other. They are illuminated by a light source (depending on where it is located, LCD displays work by reflection or transmission of light). When passing through the panel, the plane of polarization of the light beam rotates by 90°. The appearance of an electric current causes the molecules of liquid crystals to line up along the electric field, and the angle of rotation of the plane of polarization of light becomes different from 90°.

The rotation of the plane of polarization of the light beam is imperceptible to the eye, so it becomes necessary to add two more layers to the glass panels, which are polarizing filters. These filters pass only that component of the light beam, in which the polarization axis corresponds to the given direction of polarization. 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, because the first polarizer transmits only light with the corresponding polarization vector. Thanks to liquid crystals, the light polarization vector rotates, and by the time the beam passes to the second polarizer, it has already been rotated so that it passes through the second polarizer without problems.

In the presence of an electric field, the rotation of the polarization vector occurs through a smaller angle, thereby the second polarizer becomes only partially transparent to light. If the potential difference is such that the rotation of the plane of polarization in liquid crystals does not occur, then the light beam will be completely absorbed by the second polarizer, and the display will appear black.

By placing a large number of electrodes that create electric fields in local areas of the display (cell), we will be able (with proper control of the potentials of these electrodes) to display letters and other image elements on the screen. Technological innovations made it possible to limit the size of the electrodes to a point, respectively, it became possible to place a larger number of electrodes on the same panel area, which increased the resolution of the LCD monitor and made it possible to display complex images in color.

To form a color image, the LCD was backlit. The color was obtained by using three filters that separated three main components from white light. By combining these components for each point (pixel) of the display, it became possible to reproduce any color.

Passive (passive matrix) and active matrix (active matrix)

The functionality of active matrix LCD monitors is almost the same as that of passive matrix displays. The difference lies in the electrode array that drives the display's liquid crystal cells.

In the case of a passive matrix, the electrodes are electrically charged in a cyclic manner as the display updates progressively. As a result of the cell capacitance discharge, the image disappears as the crystals return to their original configuration. Due to the large electrical capacitance of the cells, the voltage on them is not able to change quickly, so the picture is updated slowly.

In the case of the active matrix, a storage transistor is added to each electrode, which can store digital information (0 or 1), and as a result, the image is stored only until another signal is received.

Dull and "brake" liquid crystal monitors with a passive matrix are long gone, in stores you can only find models based on an active matrix that provides a bright, clear image.

When using active matrices, it became possible to reduce the number of liquid crystal layers. Memory transistors are made from transparent materials, which allows the light beam to pass through them, which means that the transistors can be placed on the back of the display, on a glass panel that contains liquid crystals. For these purposes, plastic films are used - Thin Film Transistor (TFT).

TN manufacturing technology

Historically, the first technology for manufacturing LCD displays was the so-called. Twisted Nematic (TN) technology. The name comes from the fact that in the off state, the crystals in the cells form a spiral. The effect was due to the placement of the crystals between the leveling panels with grooves directed perpendicular to each other. When an electric field was applied, all crystals lined up in the same way, i.e. the spiral straightened out, and upon removal, the crystals again tended to orient themselves along the grooves.

TN displays had several significant drawbacks:

Firstly, the natural state of the display, when the crystals form a spiral, was transparent, i.e. she missed the light. Due to this, when one of the thin-film transistors failed, the light went out unhindered, forming a very noticeable constantly burning point;
- secondly, it turned out to be almost impossible to turn all liquid crystals perpendicular to the filter, so the contrast of such displays left much to be desired, and the black level could exceed 2 cd/m2. This color looked like dark gray, but by no means like black;
- thirdly, low reaction speed, the first displays had a response time of about 50 ms. However, the second and third shortcomings were overcome with the introduction of Super Twisted Nematic (STN) technology, which reduced the response time to 30 ms.
- fourthly, small viewing angles, only about 90 °. However, the application of a polymer film with a high refractive index to the screen surface made it possible to expand viewing angles up to 120-160° without a significant change in technology. Such displays are called TN+Film.

STN manufacturing technology

STN technology made it possible to increase the torsional angle (torsion angle) of the orientation of the crystals inside the LCD from 90° to 270°, which provided better image contrast as the panel size increased.

DSTN mode. Often, STN cells were used in pairs. This design was called Double Super Twisted Nematic (DSTN). In it, one two-layer DSTN cell consisted of 2 STN cells, molecules that turned in opposite directions during operation. Light, passing through such a construction in a "locked" state, lost most of its energy. The contrast and resolution of DSTN displays has increased, so it became possible to produce a color display with three LCD cells and three primary color optical filters per pixel. Color displays were not able to work from reflected light, so the backlight lamp is their mandatory attribute.

The technology of LCD TFT matrices provides for the use of special thin-film transistors in the production of liquid crystal displays. The name TFT itself is an abbreviation for Thin-film transistor, which in translation means thin-film transistor. This type of matrix is used in a wide variety of devices, from calculators to smartphone displays.

Probably, everyone has heard the concepts of TFT and LCD, but few people have thought about what it is, which is why unenlightened people have a question, how does TFT differ from LCD? The answer to this question is that they are two different things that should not be compared. To understand the difference between these technologies, it is worth understanding what is LCD and what is TFT.

1. What is LCD

LCD is a technology for manufacturing TV screens, monitors and other devices based on the use of special molecules called liquid crystals. These molecules have unique properties, they are constantly in a liquid state and are able to change their position when exposed to an electromagnetic field. In addition, these molecules have optical properties similar to those of crystals, which is why these molecules got their name.

In turn, LCD screens can have different types of matrices, which, depending on the manufacturing technology, have different properties and indicators.

2. What is TFT

As already mentioned, TFT is a technology for manufacturing LCD displays, which involves the use of thin film transistors. Thus, we can say that TFT is a subspecies of LCD monitors. It should be noted that all modern LCD TVs, monitors and phone screens are of the TFT type. Therefore, the question of what is better than TFT or LCD is not entirely correct. After all, the difference between FTF and LCD is that LCD is a technology for manufacturing liquid crystal screens, and TFT is a subspecies of LCD displays, which includes all types of active matrices.

Among TFT users, matrices have a name - active. Such matrices have a significantly higher performance, in contrast to passive LCD matrices. In addition, the LCD TFT screen type is distinguished by an increased level of clarity, image contrast and large viewing angles. Another important point is that there is no flicker in active matrices, which means that it is more pleasant to work with such monitors, while the eyes are less tired.

Each pixel of the TFT matrix is equipped with three separate driving transistors, which achieves a significantly higher screen refresh rate compared to passive matrices. Thus, each pixel contains three colored cells, which are controlled by the corresponding transistor. For example, if the screen resolution is 1920x1080 pixels, then the number of transistors in such a monitor will be 5760x3240. The use of such a number of transistors became possible due to the ultra-thin and transparent structure - 0.1-0.01 microns.

3. Types of TFT screens

Today, due to a number of advantages, TFT displays are used in a wide variety of devices.

All well-known LCD TVs available on the Russian market are equipped with TFT displays. They may differ in their parameters depending on the matrix used.

At the moment, the most common matrices of TFT displays are:

Each of the presented types of matrices has its own advantages and disadvantages.

3.1. LCD matrix type TFT TN

TN is the most common type of LCD TFT screen. This type of matrix has gained such popularity due to its unique features. With their low cost, they have quite high performance, and in some moments, such TN screens even have advantages over other types of matrices.

The main feature is the fast response. This is a parameter that indicates the time during which a pixel is able to respond to a change in the electric field. That is, the time it takes for a complete color change (from white to black). This is a very important indicator for any TV and monitor, especially for fans of games and movies, full of all sorts of special effects.

The disadvantage of this technology is limited viewing angles. However, modern technology has made it possible to correct this shortcoming. Now TN+Film matrices have large viewing angles, thanks to which such screens are able to compete with new IPS matrices.

3.2. IPS matrices

This type of matrix has the greatest prospects. The peculiarity of this technology is that such matrices have the largest viewing angles, as well as the most natural and saturated color reproduction. However, the disadvantage of this technology until now has been a long response time. But thanks to modern technology, this parameter has been reduced to acceptable readings. Moreover, current monitors with IPS matrices have a response time of 5 ms, which is not inferior even to TN + Film matrices.

According to most manufacturers of monitors and TVs, the future lies precisely with IPS matrices, due to which they are gradually replacing TN + Film.

In addition, manufacturers of mobile phones, smartphones, tablet PCs and laptops are increasingly choosing IPS TFT LCD modules, paying attention to excellent color reproduction, good viewing angles, as well as economical power consumption, which is extremely important for mobile devices.

3.3. MVA/PVA

This type of matrices is a kind of compromise between TN and IPS matrices. Its peculiarity lies in the fact that in a calm state, the molecules of liquid crystals are located perpendicular to the plane of the screen. Thanks to this, manufacturers were able to achieve the deepest and purest blacks. In addition, this technology allows you to achieve large viewing angles, in comparison with TN matrices. This is achieved with the help of special protrusions on the plates. These protrusions determine the direction of liquid crystal molecules. It should be noted that such matrices have a shorter response time than IPS displays, and more than TN matrices.

Oddly enough, but this technology has not found wide application in the mass production of monitors and televisions.

4. Which is better Super LCD or TFT

To begin with, it is worth disassembling what a Super LCD is.

Super LCD is a screen technology that is widely used by manufacturers of modern smartphones and tablet PCs. In fact, Super LCDs are the same IPS matrices that have received a new marketing name and some improvements.

The main difference between such matrices is that they do not have an air gap between the outer glass and the picture (image). Thanks to this, it was possible to achieve a reduction in glare. In addition, visually, the image on such displays seems closer to the viewer. When it comes to touch screens on smartphones and tablet PCs, Super LCD screens are more sensitive to touch and more responsive to movements.

5. TFT/LCD Monitor: Video

Another advantage of this type of matrix is the reduced power consumption, which again is extremely important in the case of a stand-alone device such as a laptop, smartphone and tablet. This efficiency is achieved due to the fact that in a resting state, liquid crystals are positioned so as to transmit light, which reduces energy consumption when displaying bright pictures. At the same time, it is worth noting that the vast majority of background images on all Internet sites, splash screens in applications, and so on, are just the same light.

The main field of application of SL CD displays is mobile technology, due to low energy consumption, high image quality, even in direct sunlight, and lower cost, unlike, for example, AMOLED screens.

In turn, LCD TFT displays include the SLCD matrix type. Thus, Super LCD is a type of active matrix TFT display. At the very beginning of this publication, we already said that TFT and LCD have no difference, they are basically the same thing.

6. Display selection

As mentioned above, each type of matrix has its own advantages and disadvantages. All of them have already been discussed. First of all, when choosing a display, it is worth considering your requirements. It is worth asking yourself the question - What exactly is needed from the display, how will it be used and in what conditions?

Based on the requirements, and it is worth choosing a display. Unfortunately, at the moment there is no universal screen to which one could say that it is really better than all the others. Because of this, if color reproduction is important to you, and you are going to work with photographs, then IPS matrices are definitely your choice. But if you are an avid fan of action-packed and vibrant games, then it is still better to give preference to TN + Film.

All modern matrices have fairly high performance, so ordinary users may not even notice the difference, because IPS matrices are practically not inferior to TN in response time, and TN, in turn, have rather large viewing angles. In addition, as a rule, the user is located opposite the screen, and not on the side or on top, which is why large angles are not required in principle. But the choice is still yours.

The image is formed with the help of individual elements, as a rule, through a scanning system. Simple devices (electronic watches, telephones, players, thermometers, etc.) may have a monochrome or 2-5 color display. Multi-color image is generated using 2008) most desktop monitors based on TN- (and some *VA) matrices, as well as all laptop displays, use matrices with 18-bit color (6 bits per channel), 24-bit emulation is flickering with dithering .

LCD monitor device

Sub-pixel color LCD

Each pixel of an LCD display consists of a layer of molecules between two transparent electrodes, and two polarizing filters whose planes of polarization are (usually) perpendicular. In the absence of liquid crystals, the light transmitted by the first filter is almost completely blocked by the second.

The surface of the electrodes in contact with liquid crystals is specially treated for the initial orientation of the molecules in one direction. In a TN matrix, these directions are mutually perpendicular, so the molecules line up in a helical structure in the absence of stress. This structure refracts light in such a way that before the second filter its plane of polarization rotates, and light passes through it without loss. Except for the absorption of half of the unpolarized light by the first filter, the cell can be considered transparent. If a voltage is applied to the electrodes, the molecules tend to line up in the direction of the field, which distorts the helical structure. In this case, the elastic forces counteract this, and when the voltage is turned off, the molecules return to their original position. At a sufficient field strength, almost all molecules become parallel, which leads to the opacity of the structure. By varying the voltage, you can control the degree of transparency. If a constant voltage is applied for a long time, the liquid crystal structure may degrade due to ion migration. To solve this problem, an alternating current is applied, or a change in the polarity of the field with each addressing of the cell (the opacity of the structure does not depend on the polarity of the field). In the entire matrix, it is possible to control each of the cells individually, but as their number increases, this becomes difficult, as the number of required electrodes increases. Therefore, addressing by rows and columns is used almost everywhere. The light passing through the cells can be natural - reflected from the substrate (in LCD displays without backlight). But more often used, in addition to independence from external lighting, this also stabilizes the properties of the resulting image. Thus, a full-fledged LCD monitor consists of electronics that processes the input video signal, an LCD matrix, a backlight module, a power supply, and a housing. It is the combination of these components that determines the properties of the monitor as a whole, although some characteristics are more important than others.

LCD Monitor Specifications

The most important characteristics of LCD monitors:

Resolution : Horizontal and vertical dimensions expressed in pixels. Unlike CRT monitors, LCDs have one, "native", physical resolution, the rest are achieved by interpolation.

Fragment of LCD monitor matrix (0.78x0.78 mm), enlarged 46 times.

Dot Size: The distance between the centers of neighboring pixels. Directly related to physical resolution.

Screen aspect ratio (format): The ratio of width to height, for example: 5:4, 4:3, 5:3, 8:5, 16:9, 16:10.

Visible Diagonal: The size of the panel itself, measured diagonally. The display area also depends on the format: a 4:3 monitor has a larger area than a 16:9 monitor with the same diagonal.

Contrast: The ratio of the brightness of the lightest to the darkest point. Some monitors use an adaptive backlight level using additional lamps, and the contrast figure given for them (called dynamic) does not apply to a static image.

Brightness: The amount of light a display emits, usually measured in candela per square meter.

Response Time: The minimum time it takes for a pixel to change its brightness. Measurement methods are ambiguous.

Viewing angle: the angle at which the drop in contrast reaches the specified value is calculated differently for different types of matrices and by different manufacturers, and is often not comparable.

Matrix Type: The technology by which the LCD is made.

Inputs: (eg DVI, HDMI, etc.).

Technologies

Clock with LCD display

LCD monitors were developed in 1963 at RCA's David Sarnoff Research Center in Princeton, New Jersey.

The main technologies in the manufacture of LCD displays: TN + film, IPS and MVA. These technologies differ in the geometry of surfaces, polymer, control plate and front electrode. Of great importance are the purity and type of polymer with liquid crystal properties used in specific developments.

The response time of LCD monitors designed using SXRD technology (eng. Silicon X-tal Reflective Display - silicon reflective liquid crystal matrix), reduced to 5 ms. Sony, Sharp and Philips have jointly developed PALC technology. Plasma Addressed Liquid Crystal - plasma control of liquid crystals), which combines the advantages of LCD (brightness and richness of colors, contrast) and plasma panels (large viewing angles horizontally, H, and vertically, V, high refresh rate). These displays use gas-discharge plasma cells as a brightness control, and an LCD matrix is used for color filtering. PALC technology allows you to address each display pixel individually, which means unsurpassed controllability and image quality.

TN+film (Twisted Nematic + film)

The part "film" in the name of the technology means an additional layer used to increase the viewing angle (approximately from 90° to 150°). Currently, the prefix "film" is often omitted, calling such matrices simply TN. Unfortunately, a way to improve the contrast and response time for TN panels has not yet been found, and the response time for this type of matrix is \u200b\u200bcurrently one of the best, but the contrast level is not.

TN + film is the simplest technology.

The TN + film matrix works as follows: if no voltage is applied to the sub-pixels, the liquid crystals (and the polarized light they transmit) rotate relative to each other by 90° in a horizontal plane in the space between the two plates. And since the direction of polarization of the filter on the second plate makes an angle of 90° with the direction of polarization of the filter on the first plate, light passes through it. If the red, green, and blue sub-pixels are fully illuminated, a white dot will form on the screen.

The advantages of the technology include the shortest response time among modern matrices, as well as low cost.

IPS (In-Plane Switching)

In-Plane Switching technology was developed by Hitachi and NEC and was intended to overcome the shortcomings of TN + film. However, while IPS was able to achieve a 170° viewing angle, as well as high contrast and color reproduction, the response time remained low.

Currently, IPS technology matrices are the only LCD monitors that always transmit full RGB color depth - 24 bits, 8 bits per channel. TN matrices are almost always 6-bit, as is the MVA part.

If no voltage is applied to the IPS, the liquid crystal molecules do not rotate. The second filter is always rotated perpendicular to the first, and no light passes through it. Therefore, the display of black color is close to ideal. If the transistor fails, the “broken” pixel for the IPS panel will not be white, as for the TN matrix, but black.

When a voltage is applied, liquid crystal molecules rotate perpendicular to their initial position and transmit light.

IPS has now been supplanted by technology S-IPS(Super-IPS, Hitachi year), which inherits all the advantages of IPS technology while reducing response time. But, despite the fact that the color of S-IPS panels has come close to conventional CRT monitors, contrast still remains a weak point. S-IPS is actively used in panels from 20", LG. Philips, NEC remain the only manufacturers of panels using this technology.

AS-IPS- Advanced Super IPS technology (Advanced Super-IPS), was also developed by Hitachi Corporation in the year. The main improvements were in the contrast level of conventional S-IPS panels, bringing it closer to that of S-PVA panels. AS-IPS is also used as the name for LG.Philips Corporation monitors.

A-TW-IPS- Advanced True White IPS (Advanced IPS with real white), developed by LG.Philips for the corporation. The increased power of the electric field made it possible to achieve even greater viewing angles and brightness, as well as to reduce the interpixel distance. AFFS-based displays are mainly used in tablet PCs, on matrices manufactured by Hitachi Displays.

*VA (Vertical Alignment)

MVA- Multi-domain Vertical Alignment. This technology was developed by Fujitsu as a compromise between TN and IPS technologies. Horizontal and vertical viewing angles for MVA matrices are 160° (up to 176-178 degrees on modern monitor models), while thanks to the use of acceleration technologies (RTC), these matrices are not far behind TN + Film in terms of response time, but significantly exceed the characteristics of the latter color depth and fidelity.

MVA is the successor to VA technology introduced in 1996 by Fujitsu. The liquid crystals of the VA matrix, when the voltage is off, are aligned perpendicular to the second filter, that is, they do not transmit light. When voltage is applied, the crystals rotate 90° and a bright dot appears on the screen. As in IPS-matrices, pixels do not transmit light in the absence of voltage, therefore, when they fail, they are visible as black dots.

The advantages of MVA technology are the deep black color and the absence of both a helical crystal structure and a double magnetic field.

Disadvantages of MVA in comparison with S-IPS: loss of detail in the shadows with a perpendicular view, dependence of the color balance of the image on the angle of view, longer response time.

The analogues of MVA are technologies:

PVA (Patterned Vertical Alignment) from Samsung.
Super PVA from Samsung.
Super MVA from CMO.

Matrices MVA / PVA are considered a compromise between TN and IPS, both in terms of cost and consumer qualities.

Advantages and disadvantages

Image distortion on the LCD monitor at a wide viewing angle

Closeup of a typical LCD matrix. In the center, you can see two defective subpixels (green and blue).

Currently, LCD monitors are the main, rapidly developing direction in monitor technology. Their advantages include: small size and weight in comparison with CRT. LCD monitors, unlike CRTs, do not have visible flicker, focusing and convergence defects, interference from magnetic fields, problems with image geometry and clarity. The power consumption of LCD monitors is 2-4 times less than that of CRT and plasma screens of comparable sizes. The power consumption of LCD monitors is 95% determined by the power of the backlight lamps or the LED backlight matrix (eng. backlight- rear light) LCD matrix. In many modern (2007) monitors, to adjust the brightness of the screen glow by the user, pulse-width modulation of the backlight lamps with a frequency of 150 to 400 or more Hertz is used. LED backlighting is mainly used in small displays, although in recent years it has been increasingly adopted in laptops and even desktop monitors. Despite the technical difficulties of its implementation, it also has obvious advantages over fluorescent lamps, such as a wider emission spectrum, and hence the color gamut.

On the other hand, LCD monitors also have some drawbacks, often fundamentally difficult to eliminate, for example:

Unlike CRTs, they can display a clear image in only one (“standard”) resolution. The rest are achieved by interpolation with loss of clarity. Moreover, too low resolutions (for example, 320x200) cannot be displayed at all on many monitors.
Color gamut and color accuracy are lower than those of plasma panels and CRTs, respectively. On many monitors there is an unrecoverable unevenness in the transmission of brightness (bands in gradients).
Many LCD monitors have relatively low contrast and black depth. Increasing the actual contrast is often associated with simply increasing the brightness of the backlight, up to uncomfortable values. The widely used glossy coating of the matrix affects only the subjective contrast in ambient light conditions.
Due to the strict requirements for a constant thickness of the matrices, there is a problem of uniform color unevenness (backlight unevenness).
The actual image change rate also remains lower than that of CRT and plasma displays. Overdrive technology solves the problem of speed only partially.
The dependence of the contrast on the viewing angle is still a significant disadvantage of the technology.
Mass-produced LCD monitors are more vulnerable than CRTs. The matrix unprotected by glass is especially sensitive. With strong pressure, irreversible degradation is possible. There is also the problem of defective pixels.
Contrary to popular belief, LCD monitor pixels degrade, although the rate of degradation is the slowest of all display technologies.

A promising technology that can replace LCD monitors is often considered OLED displays. On the other hand, this technology has met with difficulties in mass production, especially for matrices with a large diagonal.

Literature

Artamonov O. Parameters of modern LCD monitors
Mukhin I. A. How to choose an LCD monitor? . "Computer-Business Market", No. 4 (292), January 2005, pp. 284-291.
Mukhin I. A. Development of liquid crystal monitors. "BROADCASTING Television and radio broadcasting": part 1 - No. 2 (46) March 2005, p.55-56; Part 2 - No. 4(48) June-July 2005, p.71-73.
Mukhin I. A. Modern flat panel display devices "BROADCASTING Television and radio broadcasting": No. 1(37), January-February 2004, p.
Mukhin I. A., Ukrainskiy O. V. Methods for improving the quality of a television image reproduced by liquid crystal panels. Materials of the report at the scientific and technical conference "Modern Television", Moscow, March 2006.