So it's a TFT screen. What is TFT

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Answers:

Yuri Alexandrovich Peysakhovich:
The doctor, in my opinion, is a monster. Best quality Images are still provided by CRT monitors, but not all of them and only if they are configured correctly. And with liquid crystal ones there will be, firstly, a hassle with the screen resolution, since they normally display only at a resolution of 1152x1024 pixels, in other modes the quality drops noticeably, then a significantly smaller viewing angle, which consists in the fact that when the position in front of the screen changes, its color changes , and also the fact that they have square pixels, unlike the round ones on a CRT, which leads to rapid fatigue of the eyes, which are forced to constantly approximate the broken curves that make up all the lines. In addition, LCD monitors, unlike CRT monitors, have insufficient contrast gradation, which leads to the loss of image elements (for example, buttons in windows do not have separate visible elements). Therefore, all those who are professionally involved in graphics do not mess with LCD monitors. Doctors' arguments that CRT monitors emit, unlike LCDs, were heard back in the mid-90s, and now TCO 03 and 05 standards do not allow any noticeable frontal radiation at all. Of course, even among the same manufacturer of monitors there are completely different quality ones. For example, LG - from the completely unusable LG775FT to the very decent LG F720P. Therefore, in my opinion, there is currently no alternative to a good CRT monitor, with a resolution that is comfortable for the eyes and the maximum possible frequency updates.

TU-154:
TFT and LCD monitor are the same thing. But there is no point in switching to them for this reason alone - modern CRT monitors affect vision no more than TFT ones, and in terms of image quality and characteristics they are noticeably ahead of TFT ones (for now). Although if your monitor is 10 years old, then, of course, it makes sense...

Shurovik:
Roughly speaking, TFT and LCD are the same thing. But LCD is a type of monitor (Liquid Crystal Display), and TFT is a type of matrix that forms an image (Thin Film Transistor). Monitors with a TFT matrix type are called "active matrix monitors". Its peculiarity is that the image does not lose color at a large viewing angle. But a "flat monitor" is not necessarily an LCD. There are already conventional (CRT, Cathode Ray Tube - CRT) flat screen monitors.

Forward:
TFT is the most common type, or more precisely, technology of LCD monitors.

Alexeyslav:
The doctor is lying about the TFT monitor being better for vision. After all, vision is impaired not by the radiation of the monitor, but by the way it is used, in particular the constancy of looking at almost the same point from the same position. TFT monitors may be better if it can be placed further from the eyes, because A bulky CRT cannot always be placed far enough from the eyes, so it turns out that you sit almost point-blank towards it and damage your vision. Remember, the optimal distance to the screen surface from an ergonomic point of view is at arm's length, but unfortunately this is not always convenient (almost always inconvenient). And try to use large fonts as much as possible so that it is easy to read without straining your eyes.

Pumba:
TFT and LCD are synonyms with this approach. But image clarity and lack of distortion are a huge advantage of LCD monitors and are unattainable for CRTs. So the doctor may be right about something.

Sash:
All this is nonsense, TFT and LCD technologies are still very weak and do not provide the characteristics that CRT monitors can. The advantage of TFT and LCD is that they are energy efficient, take up little space and are harmless to the eyes. Otherwise, they are inferior to CRT monitors.

Antonio:
Guys, if you don’t understand monitors, then there’s no need to at least talk about it in front of everyone, LSD differs from TFT in viewing angle, i.e. (for the gifted) if you look at an LSD monitor at an angle, YOU WILL NOT SEE the image, which is not observed with TFT monitors, the image is viewed from ANY ANGLE.

SpectreLX:
I have an LCD, I can say that in complete darkness it can be darkened so that it does not hurt the eyes and does not particularly lose the image display.

Nick:
I installed TFT - the colors are excellent, the distance to the monitor has increased, I think it's better for the eyes.

Sasha.:
It's a pity there are no dates here... A lot of information becomes outdated over time. LCD monitors Now they definitely rule.

Itfm:
The most objective explanation was given by Shurovik, and I would like to ask: so what is better - TFT or LSD?

Yaroslav:
I think vision gets worse when reading or typing. Your eyes get tired at this very moment! I worked with TFT and CRT displays - my eyes get tired equally. Eyes get tired in TFT due to the contrast of monitors. The doctor doesn't seem to be very right!

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TFT technology is used to create displays for all kinds of electrical devices, including TVs, tablets, computer monitors, mobile phones, navigators, etc. Undoubtedly, the screen in such devices plays an important role, so before purchasing equipment and gadgets, it is worth understanding the intricacies of their manufacture. The design of the display determines the quality and clarity of the image, viewing angle, and color reproduction. In some cases, these parameters are of great importance.

Concept of TFT display

TFT LCD is a type of active matrix liquid crystal display. Each pixel of such displays is controlled by 1-4 thin film transistors (in English - Thin Film Transistor, abbreviated as TFT), which help to easily turn on / off the LEDs, creating a clearer, higher-quality image.

The TFT display has two glass substrates, inside of which there is a layer of liquid crystals. The front glass backing contains a color filter. The back substrate contains thin transistors arranged in columns and rows. Behind everything is a backlight.

Interesting to know: Each pixel is a small capacitor with a layer of liquid crystal sandwiched between transparent conductive layers of indium tin oxide. When the display turns on, the molecules in the liquid crystal layer bend at a certain angle and allow light to pass through. This creates the pixel we see. Depending on the angle of bending of liquid crystal molecules, one color or another appears. All pixels together form a picture.

A standard TFT monitor has 1.3 million pixels, each of which controls its own transistor. They consist of thin films of amorphous silicon deposited on glass using PECVD technology (this method is usually used to create microprocessors). Each element operates on a small charge, so the image is redrawn very quickly, the image is updated many times per second.

Is it worth buying equipment with TFT displays?

Displaying moving images on a large LCD display is challenging because it requires changing the state of a large number of liquid crystals in a fraction of a second. In passive matrix LCDs, transistors are located only at the top and left of the screen. They control entire rows and columns of pixels. In such devices, crosstalk can occur due to the fact that the signal sent to one pixel affects its “neighbors”. Because of this, we see slowdown or blurring of the picture.

TFT displays do not have this problem. Installing a control device in the form of a thin film transistor directly on the pixel prevents the blurring effect during video playback. The unidirectional current flow characteristic prevents the charges of multiple LEDs from merging. Therefore, today Thin Film Transistor technology has become the standard for LCD screen production. What other advantages does it have?

TFT allows you to get a stable, fairly high-quality image with a good viewing angle. In this case, it is possible to produce a screen of different sizes with different resolutions(from a calculator or smart watch to a TV on the entire wall).
Such screens have bright backlighting, which is important for mobile phones and computers. Bright LED backlights provide greater adaptability and can be adjusted based on the user's visual preferences. Some devices have a function to automatically adjust the brightness level depending on the lighting.
The advantages of TFT over older CRT monitors are obvious. CRTs are bulky, dim and small. CRTs generate a large amount of heat, as well as electromagnetic radiation, which negatively affects vision. TFT matrices are safe in this regard.
TFT screens have a fairly competitive price, although this method is used to produce not only budget devices, but also professional, expensive equipment.

At first glance it looks tempting. However, before you buy, you need to know: there are several types of TFT displays and they have different characteristics.

Types of TFT displays, their advantages and disadvantages

Names such as TN, IPS and MVA are all TFT displays. It's easy to get confused by these names. Let's try to figure out how they differ, and what is better.

Tweeted Nematic (TN) + Film

It is simpler, cheaper and quick option. The response time of the TFT TN screen matrix is only 2-4 ms. They can display more frames per second, which is especially important when watching videos and playing video games.

However, TN-based devices have many disadvantages in terms of image quality:

The viewing angle of a TN display is only 50-90°. This means that you can only get the full effect of graphics on a screen made using TFT TN technology by looking at it directly. If you look from the side, above or below, the picture will change its color;
low contrast ratios (maximum 500:1) and a small range of colors. Such a device will not convey all colors;
The blacks in TN screens are too bright and lack depth, and the whites are not bright enough, meaning that nothing will be visible in sunlight.

If you use your device for regular web browsing, office work, or other everyday tasks, then a display with TFT technology TN will meet your needs. It is also suitable for gamers, since the image transmission speed is still more important during gaming. But for doing business or fulfilling graphic work, which requires the highest level of color and graphic accuracy, it is best to choose a display with IPS technology.

Super TFT (or IPS)

IPS TFT technology solves all the problems of TN screen. The main difference from TN panels is the direction of movement of the crystals. In IPS displays, they move parallel to the panel plane, rather than perpendicular to it. This change reduces light scattering in the matrix and allows for wider viewing angles (from 170°), a large color spectrum (up to 1 billion), and high contrast (1:1000). Blacks will be deeper and more refined.

However, IPS also has a drawback: the response time of such matrices is 10-20 ms, which is not enough for modern video games, although acceptable. AMOLED screens have even longer response times.

It is impossible to say which is better: IPS or TN TFT technology. Each of them has pros and cons, so you need to proceed from the purpose for which you are buying the device. IPS is widely used in high-end monitors aimed at professional graphic artists.

MVA

This technology is the most advanced - it combines the advantages of the two previous options. MVA displays have a wide viewing angle, excellent color and contrast, deep black color and at the same time optimal time response.

If you compare displays with TFT IPS and SVA technology (a type of MVA), it will be difficult to choose the best option. Everyone has merits. SVA has only a slight difference in structure - in such a display the crystals are aligned vertically rather than horizontally. This affects their ability to transmit or block light, which determines the display's brightness level and black output. In SVA displays, these parameters are at their best, although this does not mean that IPS shows a bad picture. Compared to IPS, SVA has a smaller viewing angle.

Flaws

Thin film transistors are very sensitive to voltage fluctuations and mechanical stress. They can be easily damaged, resulting in the formation of “dead” pixels – dots without an image. However, AMOLED screens, which are now gaining popularity, are even more fragile. From reboot or mechanical damage they stop working completely.

Another small minus is the thickness of the TFT display. Due to the additional layer, it will be slightly thicker than the thickness of a plasma panel, regular LCD or AMOLED. However, the TFT screen is quite compact.

Another relative disadvantage of the technology is its higher energy consumption when compared to other types of screens. But again, TFT displays are economical enough for everyday use.

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 tension, 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, for different types matrices and different manufacturers are 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 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.

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 the contrast and response time for TN panels has not yet been found, and the response time of this type of matrix is 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 IPS was able to increase the viewing angle to 170°, as well as high contrast and color reproduction, the response time remained at a low level.

At the moment, matrices made using IPS technology are the only LCD monitors that always transmit the 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 matrix, 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 a voltage is applied, the 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 has approached conventional CRT monitors, the 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 greater viewing angles 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 light 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.

Advantages MVA technologies are 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 lamps or LED backlight matrix. 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 backlighting is primarily used in small displays, although in recent years it has been 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, resolutions that are too low (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. Increasing the actual contrast is often associated with simply increasing the brightness of the backlight, up to uncomfortable levels. The widely used glossy coating of the matrix only affects subjective contrast in ambient lighting conditions.
Due to strict requirements for constant matrix thickness, there is a problem of uneven color (backlight unevenness).
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.

For many, liquid crystal displays (LCDs) are associated primarily with flat-panel monitors, “cool” TVs, laptops, video cameras and cell phones. Some will add PDAs, electronic games, and ATM machines here. But there are many other areas where displays with high brightness, rugged construction, and operating over a wide temperature range are needed.

Flat displays have found application where minimum power consumption, weight and dimensions are critical parameters. Mechanical engineering, automobile industry, railway transport, offshore drilling rigs, mining equipment, outdoor retail outlets, avionics, marine, special vehicles, security systems, medical equipment, weapons - this is not a complete list of applications of liquid crystal displays.

The constant development of technology in this area has made it possible to reduce the cost of LCD production to a level at which a qualitative transition has occurred: expensive exotics have become commonplace. An important factor rapid spread LCD displays have become popular in the industry and are easy to use.

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

The entire 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 LCD production (Fig. 1): passive matrix (PMLCD-STN) and active matrix (AMLCD).

MIM-LCD and Diode-LCD technologies are not widely used 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 higher contrast, saturation, and shorter switching times (there are no “tails” for moving objects).

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

The operating principle and “sandwich” structure of all TFT LCDs are approximately the same (Fig. 2). Light from a backlight (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. Having passed 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 absorption will be partial (spectrum colors). The color of the image is determined by color filters (similarly cathode ray tubes, each pixel of the matrix consists of three subpixels - red, green and blue).

Rice. 2. TFT LCD structure

Pixel TFT

Color filters for red, green and blue are integrated into the glass base and placed close to each other. It could be vertical stripe, mosaic structure or 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 sub-pixels) for a 15.1" TFT LCD (1024 x 768 pixels) is approximately 0.30 mm, and for 18.1" (1280 x 1024 pixels) it is 0.28 mm. TFT LCDs have a physical limitation, which is determined by the maximum screen area. Don't expect 1280 x 1024 resolution with a 15" diagonal and 0.297mm dot pitch.

Rice. 3. Color filter structure

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

Types of LCD Displays

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

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

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

UA-IPS (Ultra Advanced IPS), UA-SFT (Ultra Advanced SFT) (NEC). The reaction time is sufficient to ensure minimal distortion colors 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 least time reactions and high contrast. The main disadvantage is the high cost.

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

Design

The design of the liquid crystal display is determined by the arrangement of layers in the “sandwich” (including the light-conducting layer) and has the greatest impact on 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 currently in use:

transmissive, intended mainly for equipment operating indoors;
reflective is used in calculators and watches;
projection (projection) is used in LCD projectors.

A compromise type of transmissive display type for operation both indoors and with external lighting is a translucent type of design.

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

Rice. 4. Transmission type liquid crystal display design

To work in daylight in the shade, a backlight lamp is required that provides 500 cd/m2, in direct sunlight - 1000 cd/m2. A brightness of 300 cd/m2 can be achieved by maximizing the brightness of one CCFL (Cold Cathode Fluorescent Lamp) lamp or by adding a second lamp located opposite. Models of liquid crystal displays with increased brightness use from 8 to 16 lamps. However, increasing the brightness of the backlight increases battery power consumption (one backlight lamp consumes about 30% of the energy used by the device). Therefore, high-brightness screens can only be used if there is external source nutrition.

Reducing the amount of reflected light is achieved by applying an anti-reflective coating to one or more layers of the display, replacing the standard polarizing layer with a minimally reflective one, and adding films that increase brightness and thus increase the efficiency of the light source. In Fujitsu LCD displays, 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 impacts the cost).

Translucent display type (transflective) similar to transmitting, but it has a so-called between the layer of liquid crystals and the backlight. partially reflective layer (Fig. 5). It can be either partially silver or completely mirrored with many small holes. When such a screen is used indoors, it works similarly to a transmissive LCD, in which part of the light is absorbed by a reflective layer. In daylight sunlight is reflected from the mirror layer and illuminates the LCD layer, while the light passes through the liquid crystals twice (inside and then out). As a result, image quality under daylight is lower than under artificial lighting indoors, when light passes through the LCD once.

Rice. 5. Translucent type liquid crystal display design

The balance between image quality indoors and in daylight is achieved by selecting the characteristics of the transmitting and reflective layers.

Reflective display type(reflective) has a completely reflective mirror layer. All illumination (sunlight or front light) (Fig. 6) passes through the LCD, is reflected from 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 both cases use similar technologies). Indoors, front lighting is not as effective as back lighting, and, accordingly, image quality is lower.

Rice. 6. Reflective type liquid crystal display design

Basic parameters of liquid crystal panels

Permission. A digital panel, the number of pixels in which strictly corresponds to the nominal resolution, must scale the image correctly and quickly. A simple way to check the quality of scaling is to change the resolution (text written on the screen small print). It is easy to notice the quality of interpolation by the contours of the letters. A high-quality algorithm produces smooth, but slightly blurry letters, while fast integer interpolation necessarily introduces distortions. Performance is the second resolution parameter (scaling one frame requires interpolation time).

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

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

Table 1

Type 1 - constantly glowing pixels (white); Type 2 - "dead" pixels (black); Type 3 - defective red, blue and green subpixels.

Viewing angle. The maximum viewing angle is defined as the angle from which the image contrast decreases by 10 times. But first of all, when the viewing angle changes 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 liquid crystal molecules (the less, the better). To ensure that fast-moving objects do not 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). Response time (more precisely, turn-off time as the longest time during which an individual pixel changes its brightness to its maximum) determines the refresh rate of the image on the screen

FPS = 1 sec/response time.

Brightness- the advantage of an LCD display, which is on average two times higher than 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 obtaining a black point, because The backlight is constantly on and the polarization effect is used to obtain dark tones. Black color depends on the quality of the overlap luminous flux backlight.

LCD displays as sensors. The reduction in cost and the emergence of LCD models operating in harsh operating conditions made it possible to combine the output means in one person (in the form of a liquid crystal display) visual information and an information input means (keyboard). The task of building such a system is simplified by using a controller serial interface, which connects, on the one hand, to the LCD display, and on the other, directly to the serial port (COM1 - COM4) (Fig. 7). To control, decode signals and suppress “bounce” (if touch detection can be called that), a PIC controller is used (for example, IF190 from Data Display), which provides high speed and accuracy of touch point detection.

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

Let’s complete the theoretical research here and move on to the realities of today, or more precisely, to what is now available on the liquid crystal display market. Among all TFT LCD manufacturers, consider products from NEC, Sharp, Siemens and Samsung. The choice of these companies is due to

leadership in the market of LCD displays and TFT LCD production technologies;
availability of products on the market of the CIS countries.

NEC Corporation has been producing liquid crystal displays (20% of the market) almost since their introduction and offers not only wide choose, but also various versions: standard (Standard), special (Special) and special (Specific). Standard option - computers, office equipment, home electronics, communication systems, etc. The special design 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, nuclear reactor control systems, life support systems and other similar ones, a special version is designed (it is clear that this is not cheap).

The list of manufactured LCD panels for industrial use (the inverter for the backlight is supplied separately) is given in Table 2, and the block diagram (using the example of a 10-inch display NL6448BC26-01) is shown in Fig. 8.

Rice. 8. Appearance display

Table 2. Models of NEC LCD panels

Model	Diagonal size, inch	Number of pixels	Number of colors	Description
NL8060BC31-17	12,1	800x600	262144	High brightness(350cd/m2)
NL8060BC31-20	12,1	800x600	262144	Wide viewing angle
NL10276BC20-04	10,4	1024x768	262144	-
NL8060BC26-17	10,4	800x600	262144	-
NL6448AC33-18A	10,4	640x480	262144	Built-in inverter
NL6448AC33-29	10,4	640x480	262144	High brightness, wide viewing angle, built-in inverter
NL6448BC33-46	10,4	640x480	262144	High brightness, wide viewing angle
NL6448CC33-30W	10,4	640x480	262144	Without backlight
NL6448BC26-01	8,4	640x480	262144	High brightness (450 cd/m2)
NL6448BC20-08	6,5	640x480	262144	-
NL10276BC12-02	6,3	1024x768	16, 19M	-
NL3224AC35-01	5,5	320x240	Full color
NL3224AC35-06	5,5	320x240	Full color	Separate NTSC/PAL RGB input, built-in inverter, slim
NL3224AC35-10	5,5	320x240	Full color	Separate NTSC/PAL RGB input, built-in inverter
NL3224AC35-13	5,5	320x240	Full color	Separate NTSC/PAL RGB input, built-in inverter
NL3224AC35-20	5,5	320x240	262, 144	High brightness (400 cd/m2)

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. In the second half of the 70s, the transition began from eight-segment liquid crystal displays to the production of matrices with addressing of each point. In 1976, Sharp released a black-and-white TV with a 5.5-inch screen diagonal, based on an LCD matrix with a resolution of 160x120 pixels. A short list of products is in Table 3.

Table 3. Sharp LCD panel models

Produces active matrix liquid crystal displays based on low-temperature polysilicon thin-film transistors. The main characteristics of 10.5" and 15" displays are shown in Table 4. Pay attention to the operating temperature range and shock resistance.

Table 4. Main characteristics of Siemens LCD displays

Notes:

I - built-in inverter l - in accordance with the requirements of the MIL-STD810 standard

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

Table 5. Main characteristics of Samsung LCD displays of small and medium sizes

Notes:

LED - light-emitting diode; CCFL - cold cathode fluorescent lamp;

The displays use PVA technology.

Conclusions.

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

With the development of display technology, users are increasingly faced with questions when choosing a suitable monitor. In addition to its physical dimensions, in particular the diagonal of the visible zone, it is necessary to select the type of matrix and related parameters - contrast, color rendering, response time, etc. Choosing a monitor, understanding all these subtleties, will not be difficult if you first study the principles of its operation and the main characteristics of its main component - the matrix, which will be discussed below.

Comparison of matrix types at different viewing angles

Understanding displays and their components

A computer monitor, for all its apparent simplicity, is a very technically complex component, which, like other hardware, has many different parameters, manufacturing technologies, and characteristics. Almost all PC displays consist of the following parts:

a housing that contains all the electronic components. The case also has mounts for mounting the display on vertical or horizontal surfaces;
matrix or screen is the main component of the monitor on which the output of graphic information depends. IN modern devices Various monitor matrices are used, differing in many parameters, among which resolution, response time, brightness, color rendition and contrast are of paramount importance;
power supply - part of the electronic circuit responsible for converting current and powering all other electronics;
electronic components on special boards responsible for converting signals received by the monitor and their subsequent output to the display for display;
other components, which may include low-power acoustic system, USB hubs and more.

The set of basic parameters of the display, on the basis of which it is made, determines the scope of its use. Inexpensive consumer monitors may be equipped with screens with not the most impressive characteristics, since such devices are most often inexpensive and are not required for professional work. graphics applications. Displays for professional gamers must first and foremost have minimal display latency, as this is critical in modern games. Displays for graphic editors, used by designers, are distinguished by the highest brightness levels, color rendering and contrast levels, because accurate image reproduction plays the most important role here.
Currently, displays found on the market typically use several types of matrices. IN technical descriptions You can find a large number of monitors, but this variety may be based on the same basic technologies, improved or slightly modified to improve their performance. These main types of screens include the following.

"Twisted Nematic" or TN matrix. Previously, the prefix “Film” was added to the name of this technology, meaning an additional film on its surface, increasing the viewing angle. But this designation is becoming less and less common in descriptions, since most matrices produced today are already equipped with it.
“In-Plane Switching” or IPS matrix type, as the more common abbreviated name.
"Multidomain Vertical Alignment" or MVA matrix. A more modern incarnation of this technology is referred to as the VA matrix. This technology also differs in its advantages and disadvantages and is something in between those presented above.
"Patterned Vertical Alignment". A type of MVA technology that was developed as a competitive response to its creators, Fujitsu.
"Plane-to-Line Switching". This is one of the newest types of display matrices, which was developed relatively recently - in 2010. The only drawback of this type of matrix, with other characteristics superior to competing technologies, is the relatively long time response. Also, the PLS matrix is very expensive.

Matrix TN, TN+film

The TN matrix type is one of the most common and at the same time it is a very outdated manufacturing technology by modern standards. It was with this type of matrix that the victorious march of liquid crystal replacement to cathode ray tubes began. It is worth noting that their only indisputable advantage is their extremely short response time, and in this parameter they are superior to even more modern analogues. The remaining parameters that are critical for a monitor - image contrast, brightness and acceptable viewing angles, alas, this type matrices are no different. In addition, the cost of monitors based on this development is low and we can say that this is another advantage of the “Twisted Nematic” technology.
The reason for the main disadvantages of Twisted Nematic lies in the technology of their production and the structure of the optical elements. In TN matrices, the crystals between the electrodes (each of which is a separate pixel in the visible zone) are arranged in a spiral when voltage is applied to them. The amount of light passing through it depends on the degree of its rounding, and the picture on the screen is formed from many such elements. But due to the uneven formation of the spiral in each element of the matrix, the level of contrast of the image displayed on it drops greatly (Fig. 1). And given that the refraction of light when passing through the formed spiral is very different from the direction of view, the viewing angle of such a matrix is very small.

Rice. 1. Comparison of IPS and TN matrices

Displays VA/MVA/PVA

The VA matrix was developed as an alternative to TN technologies, which were popular at that time and had already gained the loyalty of users, although not yet so widespread in the IPS market. The developers positioned its main competitive advantage as the response time, which was about 25 ms at the time of introduction to the market. Another important advantage new technology was a high level of contrast, which was ahead of similar indicators in TN and IPS matrix manufacturing technologies.
This technology, which was originally called “Vertical Alignment,” also had a very significant drawback in the form of relatively small viewing angles. The problem was hidden in the structure of the optical elements of the matrix. The crystals of each matrix element were oriented along the voltage lines or parallel to them. This led to the fact that the viewing angle of the matrix was not only small, but also the image could differ depending on which side the user was looking at the screen from. In practice, this led to the fact that the slightest deviation in the viewing angle led to a strong gradient filling of the picture on the screen (Fig. 2).

Rice. 2. Monitor viewing angles with MVA technology

It was possible to get rid of this drawback with the development of technology in “Multidomain Vertical Alignment”, when groups of crystals inside the electrodes were organized into a kind of “domain”, as reflected in the name. Now they began to be placed differently within each domain that makes up a whole pixel, so the user could look at the monitor from different angles and the image would remain virtually unchanged.
Today, displays with MVA screens are used for working with text and are practically unsuitable for dynamic images, which are typical for any modern game or movie. High contrast, as well as viewing angles, allow those who work, for example, with drawings, or do a lot of printing and reading, to work confidently with them.

Do not confuse the contrast of the matrix and such a thing as dynamic contrast of the monitor. The latter is a technology for adaptively changing screen brightness depending on the displayed image and uses the built-in backlight for this. Latest models monitors from LED backlight have excellent dynamic contrast since the LED on time is very short.

IPS screen

The TFT IPS matrix was developed taking into account the elimination of the main disadvantages of the previous technology - “Twisted Nematic”, namely small viewing angles and poor color reproduction. Due to the peculiar arrangement of crystals in the TN matrix, the color of each pixel varied depending on the direction of view, so the user could observe a “shimmering” picture on the monitor. The TFT IPS matrix consists of crystals that are located in a parallel plane to its surface, and when voltage is applied to the electrodes of each element, they rotate at a right angle.
Subsequent development of technology led to the emergence of such types of matrices as Super IPS, Dual Domain IPS and Advanced Coplanar Electrode IPS. All of them, one way or another, are based on the same principle with the only difference being the location of the liquid crystals. At the dawn of its appearance, the technology was distinguished by a significant disadvantage - a long response time of up to 65 ms. Its main advantage is amazing color rendition and wide viewing angles (Fig. 1), at which the image on the screen was not distorted, inverted, or an unwanted gradient did not appear.
Monitors with IPS matrix Today they are in great demand and are used not only in PC displays, but also in portable devices - tablets and smartphones. They are also used mainly where the color of the picture and its most accurate rendering are important - when working with graphics software, in design, photography, etc.

Often many users confuse the abbreviations IPS or TFT, although in fact, this is fundamentally different concepts. "Thin Film Transistor" is a general technology for creating liquid crystal matrices, which can have various incarnations. “In-Plane Switching” is a specific implementation of this technology, based on the unique construction of individual matrix elements and the arrangement of liquid crystals in it. TFT matrix can be made on the basis of TN, VA, IPS or others technology.

Matrix PLS

The PLS matrix type is the cutting edge in the development of technologies for their creation. Samsung Company, which is the developer of this unique technology, set itself the goal of producing matrices that significantly exceed the parameters of the competing technology - IPS, and in many ways it succeeded. The undoubted advantages of this technology include:

one of the lowest current consumption rates;
high level of color rendering, fully covering the sRGB range;
wide viewing angles;
high density of individual elements - pixels.

Among the disadvantages, it is worth highlighting the response time, which does not exceed similar indicators in the “Twisted Nematic” technology (Fig. 3).

Rice. 3. Comparison of PLS (right) and TN (left)

Important! When choosing which type of monitor matrix is better, you should first of all decide on the tasks, since in many cases the purchase of the modern display may turn out to be economically unjustified. The latest developments, characterized by high response times, are useful for professional games or watching dynamic scenes in videos.

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Monitors with a high level of color rendering are suitable for designers and artists. And if you need an inexpensive monitor for surfing the Internet and working with text, then options based on old, but time-tested technologies are suitable.