What is lcd. Technologies for creating displays: types of matrices and their features

The image is formed using individual elements, usually through a scanning system. Simple devices (electronic watches, phones, players, thermometers, etc.) can have a monochrome or 2-5 color display. The multicolor image is generated using 2008) in most desktop monitors based on TN- (and some *VA) matrices, as well as in all laptop displays, matrices with 18-bit color (6 bits per channel) are used, 24-bit is emulated with flickering and dithering .

LCD monitor device

Subpixel of color LCD display

Each pixel of an LCD display consists of a layer of molecules between two transparent electrodes, and two polarizing filters, the planes of polarization of which 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 the liquid crystals is specially treated to initially orient the molecules in one direction. In a TN matrix, these directions are mutually perpendicular, so the molecules, in the absence of voltage, line up in a helical structure. This structure refracts light in such a way that the plane of its polarization rotates before the second filter, and light passes through it without loss. Apart from the absorption of half of the unpolarized light by the first filter, the cell can be considered transparent. If voltage is applied to the electrodes, the molecules tend to line up in the direction of the field, which distorts the screw structure. In this case, elastic forces counteract this, and when the voltage is turned off, the molecules return to initial position. With a sufficient field strength, almost all molecules become parallel, which leads to an opaque structure. By varying the voltage, you can control the degree of transparency. If constant pressure applied for a long time - the liquid crystal structure may degrade due to ion migration. To solve this problem, alternating current is used, or changing the polarity of the field each time the cell is addressed (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 to achieve, as the number of required electrodes increases. Therefore, row and column addressing is used almost everywhere. The light passing through the cells can be natural - reflected from the substrate (in LCD displays without backlighting). But it is more often used; in addition to being independent of external lighting, it 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 the LCD monitor matrix (0.78x0.78 mm), enlarged 46 times.

Point size: the distance between the centers of adjacent 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.

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

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

Brightness: The amount of light emitted by a display, usually measured in candelas per square meter.

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

Viewing angle: the angle at which the drop in contrast reaches a given value, for different types matrices and by different manufacturers calculated differently and often cannot be compared.

Matrix type: the technology used to make the LCD display.

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

Technologies

Clock with LCD display

LCD monitors were developed in 1963 at the David Sarnoff Research Center of RCA, 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. Great importance have the purity and type of polymer with liquid crystal properties used in specific designs.

Response time of LCD monitors designed using SXRD technology. Silicon X-tal Reflective Display - silicon reflective liquid crystal matrix), reduced to 5 ms. Sony companies, Sharp and Philips jointly developed PALC technology. Plasma Addressed Liquid Crystal - plasma control of liquid crystals), which combines advantages of LCD(brightness and richness of colors, contrast) and plasma panels(large viewing angles horizontally, H, and vertically, V, high speed updates). These displays use gas-discharge plasma cells as brightness control, and an LCD matrix is used for color filtering. PALC technology allows each display pixel to be addressed individually, meaning unrivaled controllability and image quality.

TN+film (Twisted Nematic + film)

The “film” part in the technology name 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 contrast and response time for TN panels has not yet been found, and the response time is of this type matrices is on currently one of the best, but the contrast level is not.

TN + film is the simplest technology.

The TN+ film matrix works like this: When no voltage is applied to the subpixels, the liquid crystals (and the polarized light they transmit) rotate 90° relative to each other in the horizontal plane in the space between the two plates. And since the polarization direction of the filter on the second plate makes an angle of 90° with the polarization direction 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 appear 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 disadvantages of TN+ film. However, although using IPS it was possible to increase the viewing angle to 170°, as well as high contrast and color rendering, response time remained at a low level.

At the moment, matrices made using IPS technology are the only LCD monitors that always convey full depth RGB colors- 24 bits, 8 bits per channel. TN matrices are almost always 6-bit, as is the MVA part.

If to IPS matrix no voltage is applied, the liquid crystal molecules do not rotate. The second filter is always turned 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 an IPS panel will not be white, as for a TN matrix, but black.

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

IPS is now being 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 is close to regular monitors CRT, contrast still remains weak point. S-IPS is actively used in panels ranging in size from 20", LG.Philips, NEC remain the only manufacturers of panels using this technology.

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

A-TW-IPS- Advanced True White IPS (Advanced IPS with true white), developed by LG.Philips for the corporation. The increased power of the electric field made it possible to achieve even more large angles visibility and brightness, as well as 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°(at modern models monitors up to 176-178 degrees), and thanks to the use of acceleration technologies (RTC), these matrices are not far behind TN+Film in response time, but significantly exceed the characteristics of the latter in terms of color depth and accuracy of their reproduction.

MVA is the successor to VA technology introduced in 1996 by Fujitsu. When the voltage is turned off, the liquid crystals of the VA matrix 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 when there is no voltage, so 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 compared to S-IPS: loss of details in shadows when viewed perpendicularly, dependence of the image color balance on the viewing angle, longer response time.

Analogues of MVA are technologies:

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

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

Advantages and disadvantages

Image distortion on the LCD monitor at a wide viewing angle

Macro photograph 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 compared to CRT. LCD monitors, unlike CRTs, do not have visible flicker, focusing and convergence defects, interference from magnetic fields, or problems with image geometry and clarity. The energy consumption of LCD monitors is 2-4 times less than that of CRT and plasma screens of comparable sizes. The energy consumption of LCD monitors is 95% determined by the power of the backlight or LED matrix backlight (English) backlight- back light) LCD matrix. In many modern (2007) monitors, to adjust the screen brightness by the user, pulse-width modulation of the backlight lamps with a frequency of 150 to 400 or more Hertz is used. LED lights mainly used in small displays, although in last years it is increasingly used in laptops and even desktop monitors. Despite the technical difficulties of its implementation, it has obvious advantages compared to fluorescent lamps, for example, a wider spectrum of radiation, and therefore a wider color gamut.

On the other hand, LCD monitors also have some disadvantages, which are 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 on many monitors at all.
Color gamut and color accuracy are lower than those of plasma panels and CRTs, respectively. Many monitors have irreparable unevenness in brightness transmission (stripes in gradients).
Many LCD monitors have relatively low contrast and black depth. An increase in actual contrast is often associated with simple amplification backlight brightness, up to uncomfortable values. Widely used glossy finish matrix affects only subjective contrast in ambient lighting conditions.
Due to the strict requirements for the constant thickness of the matrices, there is a problem of unevenness of uniform color (unevenness of illumination).
The actual image change speed also remains lower than that of CRT and plasma displays. Overdrive technology solves the speed problem only partially.
The dependence of contrast on viewing angle still remains a significant disadvantage of the technology.
Mass produced LCD monitors are more vulnerable than CRTs. The matrix unprotected by glass is especially sensitive. If pressed hard, irreversible degradation may occur. 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 any display technology.

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

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, pp. 71-73.
Mukhin I. A. Modern flat-panel display devices."BROADCASTING Television and Radio Broadcasting": No. 1(37), January-February 2004, p.43-47.
Mukhin I. A., Ukrainsky O. V. Methods for improving the quality of television images reproduced by liquid crystal panels. Materials of the report at the scientific and technical conference " Modern television", Moscow, March 2006.

LCD TVs appeared on the market quite a long time ago and everyone has already gotten used to them. However, every year more and more new models appear, differing appearance, screen diagonal, interface and more. In addition, there are also models of liquid crystal displays that differ in their special update speed, types of LEDs and backlighting. However, let's talk about everything one by one. To begin with, I propose to understand what it is – LCD monitors.

Probably many of you have heard the concept of LCD panels. LCD is an abbreviation that stands for: Liquid Crystal Display. Translated into Russian, this means liquid crystal display, which means LCD and LCD panels are one and the same.

The technology for displaying pictures is based on the use of crystals in liquid form and their amazing properties. Such panels have a huge amount positive qualities thanks to the use of this technology. So let's figure out how it works.

How does an LCD monitor work?

The crystals used to create these monitors are called cyanophenyls. When they are in a liquid state, they develop unique optical and other properties, including the ability to position themselves correctly in space.

Such a screen consists of a pair of transparent polished plates, onto which transparent electrodes are applied. Between these two plates the cyanophenyls are located in a certain order. Voltage is supplied through the electrodes on the plates, which is supplied to sections of the screen matrix. There are also two filters located parallel to each other near the plates.

The resulting matrix can be manipulated, causing the crystals to transmit a beam of light or not. In order to obtain different colors, filters of three basic colors are installed in front of the crystals: green, blue and red. Light from the crystal passes through one of these filters and produces the corresponding pixel color. A certain combination of colors allows you to create other shades that will match the moving picture.

Types of matrices

LCD monitors can use several types of matrices, which differ from each other in their technology.

TN+film. This is one of the simplest standard technologies, which is distinguished by its popularity and low cost. This type of module has low power consumption and a relatively low update frequency. You can especially often find a similar module in older panel models. The “+film” in the name means that another layer of film was used, which should make the viewing angle larger. However, since today it is used everywhere, the name of the matrix can be shortened to TN.

A similar LCD monitor has a large number of shortcomings. Firstly, they have poor color rendering due to the use for each color channel only 6 bits. Most shades are obtained by mixing primary colors. Secondly, the contrast of LCD monitors and viewing angle also leaves much to be desired. And if some subpixels or pixels stop working for you, then most likely they will constantly glow, which will make few people happy.

IPS. Such matrices differ from other types in that they have best transmission colors and wide viewing angle. The contrast in such matrices is also not the best, and the refresh rate is lower than even that of a TN matrix. This means that if you move quickly, a noticeable trail may appear behind the picture, which will interfere with watching TV. However, if a pixel burns out on such a matrix, it will not glow, but, on the contrary, will remain black forever.

Based on this technology, there are other types of matrix, which are also often used in monitors, displays, TV screens, etc.

S-IPS. Such a module appeared in 1998 and differed only in its lower response update frequency.
AS-IPS. The next type of matrix, in which, in addition to the update speed, the contrast has also been improved.
A-TW-IPS. This is essentially the same S-IPS matrix, to which a color filter called True White was added. Most often, such a module was used in monitors intended for publishing houses or photo laboratories, since it did White color more realistic and increased the range of its shades. The disadvantage of such a matrix was that the black color had a purple tint.
H-IPS. This module appeared in 2006 and was distinguished by screen uniformity and improved contrast. It does not have such an unpleasant black light, although the viewing angle has become smaller.
E-IPS. Appeared in 2009. This technology has helped improve the viewing angle, brightness and contrast of LCD monitors. In addition, the screen refresh time has been reduced to 5 milliseconds and the amount of energy consumed has been reduced.
P-IPS. This type of module appeared relatively recently, in 2010. This is the most advanced matrix. It has 1024 gradations for each subpixel, resulting in 30-bit color, which no other matrix could achieve.

V.A.. This is the very first type of matrix for LCD displays, which is a compromise solution between the previous two types of modules. Such matrices best convey image contrast and color, but at a certain viewing angle some details may disappear and the white color balance may change.

This module also has several derivative versions that differ from each other in their characteristics.

MVA is one of the first and most popular matrices.
PVA this module was released by Samsung and features improved video contrast.
S-PVA was also manufactured by Samsung for LCD panels.
S-MVA
P-MVA, A-MVA - manufactured by AU Optronics. All further matrices differ only in the manufacturing companies. All improvements are based only on the reduction in response speed, which is achieved by feeding more high voltage at the very beginning of changing the position of subpixels and using a full 8-bit system that encodes color on each channel.

There are also several other types of LCD matrices, which are also used in some panel models.

IPS Pro - they are used in Panasonic TVs.
AFFS – matrices from Samsung. Used only in some specialized devices.
ASV - matrices from Sharp Corporation for LCD TVs.

Types of backlight

Liquid crystal displays also differ in the types of backlighting.

Plasma or gas discharge lamps. Initially, all LSD monitors were backlit by one or more lamps. Basically, such lamps had a cold cathode and were called CCFL. Later, EEFL lamps began to be used. The light source in such lamps is plasma, which appears as a result of an electrical discharge passing through a gas. At the same time, you should not confuse LCD TV with plasma TV, in which each of the pixels is an independent light source.
LED backlight or LED. Such TVs appeared relatively recently. Such displays have one or more LEDs. However, it is worth noting that this is only the type of backlight, and not the display itself, which consists of these miniature diodes.

Fast response and the required value for watching 3D video

Response speed is how many frames per second the TV can display. This setting affects the image quality and smoothness. In order for this quality to be achieved, the refresh rate must be 120 Hz. In order to achieve this frequency, TVs use a video card. In addition, this frame rate does not create screen flickering, which in turn is better for the eyes.

To watch movies in 3D format, this refresh rate will be quite enough. At the same time, many TVs have a backlight that has a refresh rate of 480 Hz. This is achieved by using special TFT transistors.

Other characteristics of LCD TVs

Brightness, black depth and contrast	The brightness of such TVs is quite high level, but the contrast leaves much to be desired. This is due to the fact that with the polarization effect, the depth of black color will be as much as the backlight allows. Due to insufficient black depth and contrast, dark shades may merge into one color.
Screen diagonal	Today you can easily find LCD panels with both large diagonals, which can be used as a home theater, and models with rather small diagonals.
Viewing angle	Modern TV models have a fairly good viewing angle, which can reach 180 degrees. But older models don't have enough angle, which can cause the screen to look quite dark or the colors to be distorted when looking at the screen from certain angles.
Color rendition	The color rendition of such displays is not always quite good. good quality. This again applies mainly to older screen models. But modern models are often inferior to other types of TV.
Energy efficiency	LCD displays consume 40% less electricity than other types.
Dimensions and weight	Such TVs are quite light in weight and thickness, but today there are panels with less thickness and weight.

TFT (Thin film transistor) is translated from English as thin film transistor. So TFT is a type of liquid crystal display that uses an active matrix controlled by these transistors themselves. Such elements are made of thin film, the thickness of which is approximately 0.1 microns.

In addition to their small size, TFT displays are fast. They have high contrast and image clarity, as well as a good viewing angle. These displays do not have screen flickering, so your eyes don't get tired as much. TFT displays also do not have beam focusing defects, interference from magnetic fields, or problems with image quality and clarity. The energy consumption of such displays is 90% determined by the power of the LED backlight matrix or backlight lamps. Compared to the same CRTs, the energy consumption of TFT displays is approximately five times lower.

All these advantages exist due to the fact that this technology updates the image to more high frequency. This is because the display dots are controlled by individual thin film transistors. The number of such elements in TFT displays is three times greater than the number of pixels. That is, there are three color transistors per point, which correspond to the primary RGB colors - red, green and blue. For example, in a display with a resolution of 1280 by 1024 pixels, the number of transistors will be three times larger, namely 3840x1024. This is precisely the basic operating principle of TFT technology.

Disadvantages of TFT matrices

TFT displays, unlike CRTs, can show a clear image in only one “native” resolution. Other resolutions are achieved by interpolation. Another significant disadvantage is the strong dependence of contrast on the viewing angle. In fact, if you look at such displays from the side, top or bottom, the image will be greatly distorted. This problem never existed in CRT displays.

In addition, transistors on any pixel can fail, resulting in dead pixels. Such points, as a rule, cannot be repaired. And it turns out that somewhere in the middle of the screen (or in the corner) there may be a small but noticeable dot, which is very annoying while working at the computer. Also, for TFT displays, the matrix is not protected by glass, and irreversible degradation is possible if the display is pressed hard.

LCD monitor device

Subpixel of color LCD display

The surface of the electrodes in contact with the liquid crystals is specially treated to initially orient the molecules in one direction. In a TN matrix, these directions are mutually perpendicular, so the molecules, in the absence of voltage, line up in a helical structure. This structure refracts light in such a way that the plane of its polarization rotates before the second filter, and light passes through it without loss. Apart from the absorption of half of the unpolarized light by the first filter, the cell can be considered transparent. If voltage is applied to the electrodes, the molecules tend to line up in the direction of the field, which distorts the screw structure. In this case, elastic forces counteract this, and when the voltage is turned off, the molecules return to their original position. With a sufficient field strength, almost all molecules become parallel, which leads to an opaque 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, alternating current is used, or changing the polarity of the field each time the cell is addressed (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 to achieve, as the number of required electrodes increases. Therefore, row and column addressing is used almost everywhere. The light passing through the cells can be natural - reflected from the substrate (in LCD displays without backlighting). But it is more often used; in addition to being independent of external lighting, it 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 the LCD monitor matrix (0.78x0.78 mm), enlarged 46 times.

Point size: the distance between the centers of adjacent 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.

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

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

Brightness: The amount of light emitted by a display, usually measured in candelas per square meter.

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

Viewing angle: the angle at which the drop in contrast reaches a given value is calculated differently for different types of matrices and by different manufacturers, and often cannot be compared.

Matrix type: the technology used to make the LCD display.

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

Technologies

Clock with LCD display

LCD monitors were developed in 1963 at the David Sarnoff Research Center of RCA, 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. The purity and type of polymer with liquid crystal properties used in specific designs are of great importance.

Response time of LCD monitors designed using SXRD technology. Silicon X-tal Reflective Display - silicon reflective liquid crystal matrix), reduced to 5 ms. Sony, Sharp and Philips 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 update speed). These displays use gas-discharge plasma cells as brightness control, and an LCD matrix is used for color filtering. PALC technology allows each display pixel to be addressed individually, meaning unrivaled controllability and image quality.