On the front side of the screen and with address electrodes running along its back side. The gas discharge produces ultraviolet radiation, which in turn initiates the visible glow of the phosphor. In color plasma panels, each pixel of the screen consists of three identical microscopic cavities containing an inert gas (xenon) and having two electrodes, front and back. Once a strong voltage is applied to the electrodes, the plasma will begin to move. At the same time, it emits ultraviolet light, which hits the phosphors in the lower part of each cavity. Phosphors emit one of the primary colors: red, green or blue. The colored light then passes through the glass and enters the viewer's eye. Thus, in plasma technology, pixels work like fluorescent tubes, but creating panels from them is quite problematic. The first difficulty is the pixel size. A plasma panel's sub-pixel has a volume of 200 µm x 200 µm x 100 µm, and several million pixels need to be stacked on the panel, one to one. Secondly, the front electrode should be as transparent as possible. Indium tin oxide is used for this purpose because it is conductive and transparent. Unfortunately, plasma panels can be so large and the oxide layer so thin that when large currents flow across the resistance of the conductors there will be a voltage drop that will greatly reduce and distort the signals. Therefore, it is necessary to add intermediate connecting conductors made of chromium - it conducts current much better, but, unfortunately, is opaque.
Finally, you need to choose the right phosphors. They depend on the required color:
- Green: Zn 2 SiO 4:Mn 2+ / BaAl 12 O 19:Mn 2+
- Red: Y 2 O 3:Eu 3+ / Y0.65Gd 0.35 BO 3:Eu 3
- Blue: BaMgAl 10 O 17:Eu 2+
These three phosphors produce light with wavelengths between 510 and 525 nm for green, 610 nm for red and 450 nm for blue. The last problem remains the addressing of pixels, since, as we have already seen, in order to obtain the required shade, you need to change the color intensity independently for each of the three sub-pixels. On a 1280x768 pixel plasma panel there are approximately three million sub-pixels, resulting in six million electrodes. As you can imagine, laying out six million tracks to control the sub-pixels independently is not possible, so the tracks must be multiplexed. The front tracks are usually lined up in solid lines, and the back tracks in columns. The electronics built into the plasma panel, using a matrix of tracks, selects the pixel that needs to be lit on the panel. The operation occurs very quickly, so the user does not notice anything - similar to beam scanning on CRT monitors.
A little history.
The first plasma display prototype appeared in 1964. It was designed by University of Illinois scientists Bitzer and Slottow as an alternative to the CRT screen for computer system Plato. This display was monochrome and did not require additional memory or complex electronic circuits and was highly reliable. Its purpose was mainly to display letters and numbers. However, it never had time to be realized as a computer monitor, since thanks to semiconductor memory, which appeared in the late 70s, CRT monitors turned out to be cheaper to produce. But plasma panels, due to their shallow body depth and large screen, have become widespread as information boards at airports, train stations and stock exchanges. IBM was heavily involved in information panels, and in 1987, Bitzer's former student, Dr. Larry Weber, founded the company Plasmaco, which began producing monochrome plasma displays. The first 21" color plasma display was introduced by Fujitsu in 1992. It was developed jointly with the design bureau of the University of Illinois and NHK. And in 1996, Fujitsu bought the Plasmaco company with all its technologies and plant, and launched the first commercially successful plasma panel on the market – Plasmavision with a 42" diagonal 852 x 480 resolution screen with progressive scan. The sale of licenses to other manufacturers began, the first of which was Pioneer. Subsequently, actively developing plasma technology, Pioneer, perhaps more than anyone else, succeeded in the plasma field, creating a number of excellent plasma models.
With all the stunning commercial success of plasma panels, the image quality at first was, to put it mildly, depressing. They cost incredible amounts of money, but quickly won an audience due to the fact that they differed favorably from CRT monsters with a flat body, which made it possible to hang the TV on the wall, and screen sizes: 42 inches diagonally versus 32 (maximum for CRT TVs). What was the main defect of the first plasma monitors? The fact is that, despite all the colorfulness of the picture, they were completely unable to cope with smooth color and brightness transitions: the latter disintegrated into steps with torn edges, which looked doubly terrible in a moving image. One could only guess why this effect arose, about which, as if by agreement, not a word was written by the media, which praised the new flat displays. However, after five years, when several generations of plasma had changed, steps began to appear less and less often, and in other indicators the image quality began to increase rapidly. In addition, in addition to 42-inch panels, 50" and 61" panels appeared. The resolution gradually increased, and somewhere during the transition to 1024 x 720, plasma displays were, as they say, in their prime. More recently, plasma has successfully crossed a new threshold of quality, entering the privileged circle of Full HD devices. Currently, the most popular screen sizes are 42 and 50 inches diagonally. In addition to the standard 61", a size of 65" has appeared, as well as a record 103". However, the real record is only to come: Matsushita (Panasonic) recently announced a 150" panel! But this, like the 103" models (by the way, the famous American company Runco produces plasma based on Panasonic panels of the same size), is an unbearable thing, both in the literal and even more literal sense (weight, price).
Plasma panel technologies.
Just something complicated.
Weight was mentioned for a reason: plasma panels weigh a lot, especially large models. This is due to the fact that the plasma panel is mainly made of glass, apart from the metal chassis and plastic case. Glass is necessary and irreplaceable here: it stops harmful ultraviolet radiation. For the same reason, no one produces fluorescent lamps made of plastic, only glass.
The entire design of a plasma screen is two sheets of glass, between which there is a cellular structure of pixels consisting of triads of subpixels - red, green and blue. The cells are filled with inert, so-called. “noble” gases - a mixture of neon, xenon, argon. Passing through gas electricity makes it glow. Essentially, a plasma panel is a matrix of tiny fluorescent lamps controlled by the panel's built-in computer. Each pixel cell is a kind of capacitor with electrodes. An electrical discharge ionizes gases, turning them into plasma - that is, an electrically neutral, highly ionized substance consisting of electrons, ions and neutral particles. In fact, each pixel is divided into three subpixels containing red (R), green (G) or blue (B) phosphor: Green: Zn2SiO4:Mn2+ / BaAl12O19:Mn2+ Red: Y2O3:Eu3+ / Y0.65Gd0.35BO3:Eu3 Blue : BaMgAl10O17:Eu2+ These three phosphors produce light with wavelengths between 510 and 525 nm for green, 610 nm for red and 450 nm for blue. In fact, the vertical rows R, G and B are simply divided into separate cells by horizontal constrictions, which makes the screen structure very similar to the mask kinescope of a regular TV. The similarity with the latter is that it uses the same colored phosphorus that coats the subpixel cells from the inside. Only the phosphorus phosphor is ignited not by an electron beam, as in a kinescope, but by ultraviolet radiation. To create a variety of color shades, the light intensity of each subpixel is controlled independently. In CRT TVs this is done by changing the intensity of the electron flow, in 'plasma' - using 8-bit pulse code modulation. The total number of color combinations in this case reaches 16,777,216 shades.
How light is made. The basis of each plasma panel is plasma itself, i.e. a gas consisting of ions (electrically charged atoms) and electrons (negatively charged particles). Under normal conditions, the gas consists of electrically neutral, i.e., particles without a charge.
If you introduce a large number of free electrons into a gas by passing an electric current through it, the situation changes radically. Free electrons collide with atoms, “knocking out” more and more electrons. Without an electron, the balance changes, the atom acquires a positive charge and turns into an ion.
When an electric current passes through the resulting plasma, the negatively and positively charged particles move towards each other.
Amid all this chaos, particles are constantly colliding. The collisions 'excite' the gas atoms in the plasma, causing them to release energy in the form of photons in the ultraviolet spectrum.
When photons hit the phosphor, the particles of the latter become excited and emit their own photons, but they will already be visible and take the form of light rays.
Between the glass walls are hundreds of thousands of cells coated with a phosphor that glows in red, green and blue. Beneath the visible glass surface - all along the screen - are long, transparent display electrodes, insulated on top with a sheet of dielectric and below with a layer of magnesium oxide (MgO).
For the process to be stable and controllable, it is necessary to provide a sufficient number of free electrons in the gas column plus a sufficiently high voltage (about 200 V), which will force the ion and electron flows to move towards each other.
And for ionization to occur instantly, in addition to control pulses, there is a residual charge on the electrodes. Control signals are supplied to the electrodes via horizontal and vertical conductors, forming an address grid. Moreover, the vertical (display) conductors are conductive paths on the inner surface of the protective glass from the front side. They are transparent (a layer of tin oxide mixed with indium). Horizontal (address) metal conductors are located on the back side of the cells.
Current flows from the display electrodes (cathodes) to the anode plates, which are rotated at 90 degrees relative to the display electrodes. The protective layer serves to prevent direct contact with the anode.
Under the display electrodes are the already mentioned RGB pixel cells, made in the form of tiny boxes, coated on the inside with a colored phosphor (each “color” box - red, green or blue - is called a subpixel). Below the cells is a structure of address electrodes positioned at 90 degrees to the display electrodes and passing through the corresponding color subpixels. Next is a protective level for the address electrodes, covered by the rear glass.
Before the plasma display is sealed, a mixture of two inert gases - xenon and neon - is injected into the space between the cells under low pressure. To ionize a specific cell, a voltage difference is created between the display and address electrodes located opposite each other above and below the cell.
A little reality.
In fact, the structure of real plasma screens is much more complex, and the physics of the process is not at all so simple. In addition to the matrix grid described above, there is another type - co-parallel, which provides an additional horizontal conductor. In addition, the thinnest metal tracks are duplicated to equalize the potential of the latter along the entire length, which is quite significant (1 m or more). The surface of the electrodes is covered with a layer of magnesium oxide, which performs an insulating function and at the same time provides secondary emission when bombarded with positive gas ions. There are also Various types geometry of pixel rows: simple and “waffle” (cells are separated by double vertical walls and horizontal bridges). Transparent electrodes can be made in the form of a double T or a meander, when they seem to be intertwined with the address electrodes, although they are in different planes. There are many other technological tricks aimed at increasing the efficiency of plasma screens, which was initially quite low. For the same purpose, manufacturers vary the gas composition of the cells, in particular, they increase the percentage of xenon from 2 to 10%. By the way, the gas mixture in the ionized state glows slightly on its own, therefore, in order to eliminate contamination of the spectrum of the phosphors by this glow, miniature light filters are installed in each cell.
Signal control.
The last problem remains the addressing of pixels, since, as we have already seen, in order to obtain the required shade, you need to change the color intensity independently for each of the three subpixels. On a 1280x768 pixel plasma panel there are approximately three million subpixels, resulting in six million electrodes. As you can imagine, laying out six million tracks to control the subpixels independently is not possible, so the tracks must be multiplexed. The front tracks are usually lined up in solid lines, and the back tracks in columns. The electronics built into the plasma panel, using a matrix of tracks, selects the pixel that needs to be lit on the panel. The operation occurs very quickly, so the user does not notice anything - similar to beam scanning on CRT monitors. Pixels are controlled using three types of pulses: starting, supporting and damping. The frequency is about 100 kHz, although there are ideas for additional modulation of control pulses with radio frequencies (40 MHz), which will ensure a more uniform discharge density in the gas column.
In fact, the control of pixel lighting is in the nature of discrete pulse-width modulation: the pixels glow exactly as long as the supporting pulse lasts. Its duration with 8-bit encoding can take 128 discrete values, respectively, the same number of gradations of brightness is obtained. Could this be the reason for the torn gradients breaking up into steps? Plasma of later generations gradually increased the resolution: 10, 12, 14 bits. The latest Runco Full HD models use 16-bit signal processing (probably encoding as well). One way or another, the steps have disappeared and, hopefully, will not appear again.
In addition to the panel itself.
Not only the panel itself was gradually improved, but also signal processing algorithms: scaling, progressive conversion, motion compensation, noise suppression, color synthesis optimization, etc. Each plasma manufacturer has its own set of technologies, partially duplicating others under other names, but partially their own. Thus, almost everyone used Faroudja's DCDi scaling and adaptive progressive conversion algorithms, while some ordered original developments (for example, Vivix from Runco, Advanced Video Movement from Fujitsu, Dynamic HD Converter from Pioneer, etc.). In order to increase contrast, adjustments were made to the structure of control pulses and voltages. To increase brightness, additional jumpers were introduced into the shape of the cells to increase the surface covered with phosphor and reduce the illumination of neighboring pixels (Pioneer). The role of “intelligent” processing algorithms gradually grew: frame-by-frame optimization of brightness, a dynamic contrast system, and advanced color synthesis technologies were introduced. Adjustments to the original signal were made not only based on the characteristics of the signal itself (how dark or light the current scene was or how fast objects were moving), but also on the level of ambient light, which was monitored using a built-in photosensor. With the help of advanced processing algorithms, fantastic success has been achieved. Thus, Fujitsu, through an interpolation algorithm and corresponding modifications to the modulation process, has achieved an increase in the number of color gradations in dark fragments to 1019, which far exceeds the screen’s own capabilities with the traditional approach and corresponds to the sensitivity of the human visual system (Low Brightness Multi Gradation Processing technology). The same company developed a method of separate modulation of even and odd control horizontal electrodes (ALIS), which was then used in models from Hitachi, Loewe, etc. The method gave increased clarity and reduced jaggedness of inclined contours even without additional processing, and therefore, in the specifications of those using his plasma models appeared with an unusual resolution of 1024 × 1024. This resolution, of course, was virtual, but the effect turned out to be very impressive.
Advantages and disadvantages.
Plasma is a display that, like a CRT TV, does not use light valves, but emits already modulated light directly by phosphorus triads. This, to a certain extent, makes plasma similar to cathode ray tubes, which are so familiar and have proven their worth over several decades.
Plasma has a noticeably wider coverage of the color space, which is also explained by the specifics of color synthesis, which is formed by “active” phosphorus elements, and not by passing the light flux of the lamp through light filters and light valves.
In addition, the plasma resource is about 60,000 hours.
So, plasma TVs are:
Large screen size + compactness + no flickering element; - High definition image; - Flat screen with no geometric distortions; - Viewing angle 160 degrees in all directions; - The mechanism is not affected by magnetic fields; - High resolution and image brightness; - Availability of computer inputs; - 16:9 frame format and progressive scan mode.
Depending on the rhythm of the pulsating current that is passed through the cells, the intensity of the glow of each subpixel, which was controlled independently, will be different. By increasing or decreasing the intensity of the glow, you can create a variety of color shades. Thanks to this principle of operation of the plasma panel, it is possible to obtain high image quality without color and geometric distortions. Weak side is a relatively low contrast. This is due to the fact that current must be constantly supplied to the cells low voltage. Otherwise, the response time of the pixels (their lighting and fading) will be increased, which is unacceptable.
Now about the disadvantages.
The front electrode should be as transparent as possible. Indium tin oxide is used for this purpose because it is conductive and transparent. Unfortunately, plasma panels can be so large and the oxide layer so thin that when large currents flow across the resistance of the conductors there will be a voltage drop that will greatly reduce and distort the signals. Therefore, it is necessary to add intermediate connecting conductors made of chromium - it conducts current much better, but, unfortunately, is opaque. Plasma is afraid of not very delicate transportation. Electricity consumption is quite significant, although in recent generations it has been possible to significantly reduce it, at the same time eliminating noisy cooling fans.
The commercial cycle of any invention does not last forever, and manufacturers who have launched mass production of LCD monitors are preparing the next generation of information display technologies. The devices that will replace liquid crystal devices are at different stages of development. Some, such as LEP (Light Emitting Polymer), are just coming out of scientific laboratories, while others, for example based on plasma technology, are already complete commercial products.
Size has always been the main obstacle when creating widescreen monitors. Monitors larger than 24 inches, created using CRT technology, are too heavy and bulky. LCD monitors are flat and lightweight, but screens larger than 20 inches are too expensive. New generation plasma technology is ideal for creating large screens. It allows the production of flat and lightweight monitors with a depth of only 9 centimeters. Therefore, despite big screen, they can be installed anywhere - on the wall, under the ceiling, on the table.
Thanks to the wide viewing angle, the image is visible from any point. And most importantly, plasma monitors are capable of delivering color and sharpness that were previously unattainable at this screen size.
The idea of using a gas discharge in display media is not new. Similar devices were produced many years ago in the USSR in Ryazan at NPO Plazma. However, the size of the image element was large enough that to get a decent image it was necessary to create huge panels. The image quality was poor, few colors were reproduced, and the devices were extremely unreliable.
Abroad, research and development in the field of this technology began in the early 60s. Fifty years ago, one interesting phenomenon was discovered. As it turns out, if the cathode is sharpened like a sewing needle, then the electromagnetic field is able to independently “pull” free electrons out of it. You just need to apply voltage. Fluorescent lamps work on this principle. The emitted electrons ionize the inert gas, causing it to glow. The only difficulty was in developing the technology for producing such needle-shaped matrices. It was solved at the University of Illinois in 1966. In the early seventies, the Owens-Illinois company brought the project to commercial status. In the eighties, Burroughs and IBM tried to translate this idea into a real commercial product, but then it was still unsuccessful.
It must be said that the idea of a plasma panel did not come from purely scientific interest. None of the existing technologies could cope with two simple tasks: to achieve high-quality color reproduction without inevitable loss of brightness and to create a TV with wide screen so that it does not occupy the entire area of the room. And plasma panels (PDP), then only theoretically, could solve a similar problem. At first, experimental plasma screens were monochrome (orange) and could satisfy the demand only of specific consumers who required, first of all, a large image area. Therefore, the first batch of PDP (about a thousand pieces) was bought by the New York Stock Exchange.
The direction of plasma monitors was revived after it became finally clear that neither LCD monitors nor CRTs are able to inexpensively provide screens with large diagonals (more than twenty-one inches). Therefore, leading manufacturers of household TVs and computer monitors, such as Hitachi, NEC and others, have returned to PDP. Korean companies of the “second world line” have also turned their attention to the field of plasma technology, including, for example, Fujitsu, which produces cheaper electronics, which immediately increased the intensity of competition. Now Fujitsu, Hitachi, Matsushita, Mitsubishi, NEC, Pioneer and others produce plasma monitors with a diagonal of 40 inches or more.
The principle of operation of a plasma panel is a controlled cold discharge of rarefied gas (xenon or neon) in an ionized state (cold plasma). The working element (pixel), which forms a separate point in the image, is a group of three subpixels responsible for the three primary colors, respectively. Each subpixel is a separate microchamber, on the walls of which there is a fluorescent substance of one of the primary colors (see Appendix L, Fig. 12). The pixels are located at the intersection points of transparent control chromium-copper-chromium electrodes, forming a rectangular grid.
In order to “light up” a pixel, approximately the following happens. A high rectangular control alternating voltage is supplied to the supply and control electrodes, orthogonal to each other, at the intersection point of which the desired pixel is located. The gas in the cell gives up most of its valence electrons and turns into a plasma state. Ions and electrons are alternately collected at the electrodes on opposite sides of the chamber, depending on the phase of the control voltage. To “ignite” a pulse is applied to the scanning electrode, the potentials of the same name are added, and the electrostatic field vector doubles its value. A discharge occurs - some of the charged ions give off energy in the form of radiation of light quanta in the ultraviolet range (depending on the gas). In turn, the fluorescent coating, being in the discharge zone, begins to emit light in the visible range, which is perceived by the observer. 97% of the ultraviolet component of radiation, harmful to the eyes, is absorbed by the outer glass. The brightness of the phosphor is determined by the value of the control voltage.
High brightness up to 650 cd/m2 and contrast ratio up to 3000:1, along with the absence of jitter, are the big advantages of such monitors (for comparison: a professional CRT monitor has a brightness of approximately 350 cd/m2, and a TV - from 200 to 270 cd/m2 m2 with a contrast from 150:1 to 200:1). High image clarity is maintained across the entire working surface of the screen. In addition, the angle relative to the normal at which a normal image can be seen on plasma monitors is significantly greater than that of LCD monitors. In addition, plasma panels do not create magnetic fields (which guarantees their harmlessness to health), do not suffer from vibration like CRT monitors, and their short regeneration time allows them to be used for displaying video and television signals. The absence of distortion and problems of electron beam convergence and focusing is inherent in all flat panel displays. It should also be noted that PDP monitors are resistant to electromagnetic fields, which allows them to be used in industrial environments - even a powerful magnet placed next to such a display will not affect the image quality in any way. At home, you can put any speakers on the monitor without fear of color spots appearing on the screen.
The main disadvantages of this type of monitor are the rather high power consumption, which increases with increasing monitor diagonal, and low resolution due to the large size of the image element. In addition, the properties of the phosphor elements quickly deteriorate, and the screen becomes less bright. Therefore, the service life of plasma monitors is limited to 10,000 hours (this is about 5 years at office use). Due to these limitations, such monitors are currently used only for conferences, presentations, information boards, that is, where large screen sizes are required to display information. However, there is every reason to assume that the existing technological limitations will soon be overcome, and with a reduction in cost, this type of device can be successfully used as television screens or computer monitors.
PDP's good prospects are associated with relatively low requirements for production conditions; Unlike TFT matrices, PDP screens can be produced at low temperatures using direct printing.
Almost every plasma panel manufacturer adds some of its own know-how to the classic technology to improve color reproduction, contrast and controllability. In particular, NEC offers capsulated color filter (CCF) technology, which cuts out unwanted colors, and a technique for increasing contrast by separating pixels from each other with black stripes (the same technology used by Pioneer). Pioneer monitors also use Enhanced Cell Structure technology, the essence of which is to increase the area of the phosphor spot, and a new chemical formula of blue phosphor, which gives a brighter glow and, accordingly, increases contrast. Samsung has developed a monitor design for increased controllability - the panel is divided into 44 sections, each of which has its own electronic control unit.
Sony, Sharp and Philips are jointly developing PALC (Plasma Addressed Liquid Crystal) technology, which should combine the advantages of plasma and LCD screens with an active matrix. Displays created on the basis of this technology combine the advantages of liquid crystals (brightness and richness of colors, contrast) with a large viewing angle and high speed upgrades of plasma panels. 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. The first samples based on PALC technology appeared in 1998.
There are several successful examples of using plasma monitors. A shopping center in Oslo has 70 displays on which small shops buy advertising time. There, PDP monitors paid for themselves in 2.5 months. They are also used at airports. In particular, in Washington they are installed in the arrivals hall. Due to its dynamism, this method of presenting information attracts much more attention than traditional displays. There is experience in using plasma monitors in McDonalds restaurants. Various television companies, such as CBS, NBC, BBS, MTV and Russian NTV, use PDP monitors in the design of their studios. This is because the high refresh rate allows the PDP display to be captured with a regular camera without any flickering or stroboscopic effects.
If you want to buy a modern TV model, then you need to choose the model especially carefully, since today there are many types. Mostly, buyers are interested in which TV is better: LCD or plasma? Before making a choice, you should not only compare all the advantages and disadvantages of these types of TV, but also find out how LCD differs from plasma. This is exactly what we will talk about today.
Once cathode ray tubes became a thing of the past, and TVs themselves became thinner and lighter, each manufacturing and display technology began to try to prove that it was the best. This competition, in turn, led to higher quality televisions and an attempt to lower prices. However, it is worth saying that the latter does not always work out, since what more modern device, the more there is in it various functions, interfaces, etc., and this automatically increases its cost, whatever one may say.
Plasma TV
Today there are not many companies involved in the production of plasma TVs. Fujitsu from Japan was the first to use this technology. Modern models of monitors, panels and displays are produced based on their technology. To date this technology is in great demand among buyers.
Before purchasing equipment, you should understand the difference between a plasma TV and a plasma panel. The plasma panel is a monitor to which you can connect DVD player or a flash drive for watching videos. At the same time, such equipment is not provided with a TV tuner, so if you want to buy a full-fledged TV, it is better to choose a model that does have it.
When buying a plasma TV, choose models from well-known companies that provide a one-year warranty on their equipment. The greater the guarantee, the better device. It is also important to consider whether there is service center of this manufacturer in your city.
LCD TV
LCD displays appeared 20 years ago and quickly became popular among users. Today there are many models with a large diagonal, low weight and screen thickness. These parameters of the TV allow you, if desired, to install it using a bracket on the wall, on a special hanging shelf, or to build it into furniture and walls.
Such TVs are cheaper than plasma TVs with the same dimensions. In addition, such displays often have noticeably better color rendering and brightness than plasma models. This is due to the fact that such TVs have fairly good resolution.
Technological features of LCD TVs
Such a display consists of two plates and liquid crystals placed between them. Transparent polished plates have the same transparent electrodes through which voltage is transmitted to the matrix cells.
Liquid crystals between such plates are arranged in a special way. A beam of light passes through a polarizer installed near the plates, which turns at a right angle. This design is complemented by backlighting and a light filter with RGB colors.
To increase the speed of operation in these devices, special thin-film transistors, better known as TFT, are produced. Thanks to them, each cell is controlled separately. Because of this, the response speed can reach 8 milliseconds.
Technological features of plasma
Plasma also consists of the same plates with electrodes as LCD monitors. The difference is that instead of liquid crystals, the space between them is filled with inert gases such as argon, neon, xenon or their compounds. Each cell is colored with a specific phosphor, which determines the future color of the pixel. One cell is separated from another by a partition that does not allow ultraviolet radiation or light from the other cell to pass through. This ensures the maximum level of contrast is achieved, regardless of the intensity of external lighting.
When applying for specific cell voltage, it begins to glow with the color in which its phosphor is painted. The difference between such TVs and LCDs is that each of the cells itself emits light, so the backlight of such a display is not required.
Comparative characteristics of plasma and liquid crystal panels
|
Characteristic |
Winner |
Details |
| Screen size | Not so long ago, large-diagonal LCD TVs practically did not exist, and plasma TVs were the undisputed winner, so the question of choosing plasma or LCD did not arise. But time passes and today LCD models have almost caught up with plasma. Therefore, the difference according to this criterion has disappeared and it is very difficult to determine the winner. | |
| Contrast | This happens due to the fact that plasma TVs themselves emit light, which makes the image better and more saturated. | |
| Glare in bright light | The brightness of the lamp backlight allows you to see the image on the screen even in bright lighting or direct sunlight. Plasma panels will produce glare. | |
| Black depth | The reason for the loss of an LCD TV in this parameter is the same. Due to the additional illumination, the black is less deep than that of plasma, where its depth is achieved due to the fact that this cell There's just no electricity coming through. | |
| Fast response | Electricity is transmitted almost instantly through inert gas, so there are no problems. But with older models of LCD displays, shadows could appear when the picture was moving quickly. But today, thanks to TFT technology, the response speed in such TVs has decreased to 8 milliseconds. Therefore, if you choose new model TV, you won’t notice any artifacts. | |
| Viewing angle | Plasma TVs started with a viewing angle of 160 degrees, but an older LCD TV model can have a viewing angle of only 45 degrees. But if you choose one of the modern models, then you don’t need to worry, since today the viewing angle on LCD and plasma TVs is the same. | |
| Illumination Uniformity | In plasma TVs, uniformity of illumination is ensured by the fact that each of the pixels is itself a light source and glows in the same way as the others. On LCD TVs, lighting uniformity depends on the lamp, but uniformity is still difficult to achieve. | |
| Screen burn-in | Screen burn-in mainly affects plasma displays when viewing a static image. Over time, all objects may develop non-existent shadows, which is actually fixable. This a common problem for devices containing phosphorus. LCD monitors do not have it, and, therefore, they do not face such a problem. | |
| Energy efficiency | LCD TVs consume almost 2 times less electricity than plasma TVs. This is due to the fact that the main amount of energy in plasma TVs is spent on cooling and powerful fans, but in LCD panels, practically nothing is used except the lighting lamp. | |
| Durability | For LCD TV, the service life can reach up to 100,000 hours, while plasma has no more than 60,000 hours. In addition, for LCD screens this figure means the resource of the backlight lamp, and for plasma it means the resource of the matrix. If you choose plasma, by the time those 60,000 hours have passed, the screen brightness will be half as bright. | |
| Compatibility | In principle, both plasma and LCD modern TVs have a variety of functions and interfaces. This may also be the ability to connect various game consoles, audio systems, Smart TV and 3D functions. However, LCD displays win due to the fact that they are best suited for use with a computer. They make it easier to see various diagrams and graphics, since more pixels are used per inch than in plasma monitors. | |
| Price | Plasma TVs currently cost significantly more than LCD models with the same diagonal. |
As a result, we can say that plasma panels have better color reproduction and response speed, while liquid crystal models are more energy efficient, durable and not subject to screen burnout. Therefore, before choosing what you need: LCD or plasma, decide what is most important for you in such a device.
In monitor based cathode ray tube The image points are displayed using a beam (a stream of electrons) that causes the phosphor-coated surface of the screen to glow. The beam runs around the screen line by line, from left to right and from top to bottom. The complete cycle of displaying a picture is called a “frame”. The faster the monitor displays and redraws frames, the more stable the picture appears, the less flickering is noticeable and the less tired our eyes are.
CRT monitor device. 1 - Electron guns. 2 - Electron rays. 3 - Focusing coil. 4 - Deflection coils. 5 - Anode. 6 - A mask, thanks to which the red beam hits the red phosphor, etc. 7 - Red, green and blue phosphor grains. 8 - Mask and phosphor grains (enlarged).
LCD
Liquid crystal displays were developed in 1963 at RCA's David Sarnoff Research Center in Princeton, New Jersey.
Device
Structurally, the display consists of an LCD matrix (a glass plate, between the layers of which liquid crystals are located), light sources for illumination, a contact harness and a frame (case), often plastic, with a metal rigid frame. Each pixel of the LCD matrix consists of a layer of molecules between two transparent electrodes, and two polarizing filters, the planes of polarization of which are (usually) perpendicular. If there were no liquid crystals, then the light transmitted by the first filter would be almost completely blocked by the second filter. 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 electric 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, use alternating current or changing the polarity of the field each time the cell is addressed (since the change in transparency occurs when the current is turned on, regardless of its polarity). 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 backlight). But more often an artificial light source is used; in addition to independence from external lighting, this also stabilizes the properties of the resulting image. Thus, a full-fledged monitor with an LCD display consists of high-precision electronics that processes the input video signal, an LCD matrix, a backlight module, a power supply and a housing with controls. 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.
Backlight
Liquid crystals themselves do not glow. For the image on a liquid crystal display to be visible, a light source is needed. The source can be external (for example, the Sun) or built-in (backlight). Typically, built-in backlight lamps are located behind the layer of liquid crystals and shine through it (although side lighting is also found, for example, in watches).
- External lighting
- Incandescent lighting In the past in some wristwatch with a monochrome LCD display, a subminiature incandescent lamp was used. But due to high energy consumption, incandescent lamps are unprofitable. In addition, they are not suitable for use, for example, in televisions, as they generate a lot of heat (overheating is harmful to liquid crystals) and often burn out.
- Illumination with gas-discharge (“plasma”) lamps During the first decade of the 21st century, the vast majority of LCD displays were backlit by one or more gas discharge lamps (most often cold cathode lamps - CCFL). In these lamps, the light source is plasma produced by an electrical discharge through a gas. Such displays should not be confused with plasma displays, in which each pixel itself glows and is a miniature discharge lamp.
- Light-emitting diode (LED) backlight At the border of the first and second decades of the 21st century, LCD displays backlit by one or a small number of light-emitting diodes (LEDs) became widespread. These LCD displays (often called LED displays in the trade) should not be confused with true LED displays, in which each pixel itself lights up and is a miniature LED.
Monochrome displays of wristwatches and mobile phones use external lighting most of the time (from the Sun, room lighting lamps, etc.). Typically behind the liquid crystal pixel layer is a mirror or matte reflective layer. For use in the dark, such displays are equipped with side lighting. There are also transflective displays, in which the reflective (mirror) layer is translucent and the backlight is located behind it.
Advantages and disadvantages
Currently, LCD monitors are the main, rapidly developing direction in monitor technology. Their advantages include: small size and weight compared to CRTs. LCD monitors, unlike CRTs, have no visible flicker, beam focusing defects, interference from magnetic fields, or problems with image geometry and clarity. The energy consumption of LCD monitors, depending on the model, settings and displayed image, can either coincide with the consumption of CRT and plasma screens of comparable sizes, or be significantly - up to five times - lower. 95% of the energy consumption of LCD monitors is determined by the power of the backlight or LED matrix backlight (English backlight - back light) of the LCD matrix. Many monitors in 2007 use pulse-width modulation of the backlight lamps with a frequency of 150 to 400 or more hertz to adjust the screen brightness by the user. 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 320*200) cannot be displayed on many monitors at all.
- 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 the strict requirements for the constant thickness of the matrices, there is a problem of unevenness of uniform color (backlight unevenness) - on some monitors there is an irreparable unevenness in brightness transmission (strips in gradients) associated with the use of blocks of linear mercury lamps.
- 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 poorly protected from damage. The matrix unprotected by glass is especially sensitive. If pressed hard, irreversible degradation may occur. There is also the problem of defective pixels. The maximum permissible number of defective pixels, depending on the screen size, is determined in international ISO standard 13406-2 (in Russia - GOST R 52324-2005). The standard defines 4 quality classes for LCD monitors. The highest class - 1, does not allow the presence of defective pixels at all. The lowest is 4, which allows for up to 262 defective pixels per 1 million working ones.
- LCD monitor pixels degrade, although the rate of degradation is the slowest of all display technologies, with the exception of laser displays, which are not subject to it.
A plasma panel is a matrix of gas-filled cells enclosed between two parallel glass plates, inside of which there are transparent electrodes that form scanning, illumination and addressing buses. The gas discharge flows between the discharge electrodes (scanning and backlight) on the front side of the screen and the addressing electrode on the back side.
To create organic light-emitting diodes (OLEDs), thin-film multilayer structures consisting of layers of several polymers are used. When a voltage positive relative to the cathode is applied to the anode, a flow of electrons flows through the device from the cathode to the anode. Thus, the cathode gives electrons to the emissive layer, and the anode takes electrons from the conducting layer, or in other words, the anode gives holes to the conducting layer. The emissive layer receives a negative charge, and the conductive layer receives a positive charge. Under the influence of electrostatic forces, electrons and holes move towards each other and recombine when they meet. This occurs closer to the emissive layer because in organic semiconductors holes have greater mobility than electrons. During recombination, a decrease in the energy of the electron occurs, which is accompanied by the emission (emission) of electromagnetic radiation in the visible light region. That is why the layer is called emissive. The device does not work when a voltage negative relative to the cathode is applied to the anode. In this case, holes move towards the anode and electrons move in the opposite direction towards the cathode, and no recombination occurs. The anode material is usually tin-doped indium oxide. It is transparent to visible light and has a high work function, which promotes hole injection into the polymer layer. Metals such as aluminum and calcium are often used to make the cathode because they have a low work function that facilitates the injection of electrons into the polymer layer.
A projector is a lighting device that redistributes lamp light with a concentration of luminous flux on a small surface or in a small volume. Projectors are mainly optical-mechanical or optical-digital devices that allow, using a light source, to project images of objects onto a surface located outside the device - a screen.
A multimedia projector is used in conjunction with a computer (the term “Digital Projector” is also used). A real-time video signal (analog or digital) is supplied to the device input. The device projects an image onto the screen. It is possible that there is an audio channel.
Speaking of projectors, it is worth mentioning the so-called pico projector. This is a small, pocket-sized projector. Often made in the form factor of a cell phone and has a similar size. The term pico projector can also refer to a miniature projector built into a camera, cell phone, PDA, or other mobile device.
Anaglyph method(anaglyph means “relief” in Greek). In the early stages of 3D cinema, only black and white 3D films were released. In each appropriately equipped cinema, two film projectors were used to show them. One projected the film through a red filter, the other displayed slightly horizontally shifted film frames on the screen, passing them through a green filter. Visitors wore light cardboard glasses, in which pieces of red and green transparent film were installed instead of glasses, thanks to which each eye saw only the desired part of the image, and viewers perceived a “three-dimensional” picture. However, both film projectors must be directed strictly at the screen and work absolutely synchronously. Otherwise, a split image is inevitable and, as a result, headaches instead of viewing pleasure for viewers.
Shutter method. Optimal for watching color films. Unlike anaglyph, this method involves the projector alternately displaying images intended for the left and right eyes. Due to the fact that the alternation of images is carried out at a high frequency - from 30 to 100 times per second - the brain builds a complete spatial picture and the viewer sees a solid three-dimensional image on the screen. Previously, this method was called NuVision, now it is more often called XpanD.
Polarization method. In the film industry, this solution is called RealD. Its essence is that the projector alternately displays film frames in which light waves have different directions of polarization of the light flux. The special glasses required for viewing have filters that transmit only light waves that are polarized in a certain way. So both eyes receive images with different information, on the basis of which the brain forms a three-dimensional picture.
But several manufacturers announced the release of 3D TVs working in tandem with glasses at the international exhibition IFA 2009. For example, Panasonic intends to release TV models with 3D support by mid-2010, just like Sony and Loewe, relying on the shutter method. JVC, Philips and Toshiba are also trying to get on the 3D podium, but they prefer the polarization method. LG and Samsung develop their devices based on both technologies.
However, these devices had a number of shortcomings that scared off most buyers. The Forte cyber helmet, which appeared in the mid-90s, was bulky, ineffective and reminiscent of a medieval torture device. A modest resolution of 640x480 pixels was clearly not enough for computer programs and games. And although more advanced glasses were later released, for example the LDI-D 100 model from Sony, even they were quite heavy and caused severe discomfort.Plasma screen
The plasma panel is a bit like an ordinary picture tube - it is also coated with a composition that can glow. At the same time, like LCDs, they use a grid of electrodes coated with a protective coating of magnesium oxide to transmit a signal to each pixel cell. The cells are filled with intervening gases - a mixture of neon, xenon, and argon. An electric current passing through the gas causes it to glow.
Essentially, a plasma panel is a matrix of tiny fluorescent lamps controlled by the panel's built-in computer. Each pixel cell is a kind of capacitor with electrodes. An electrical discharge ionizes gases, turning them into plasma - that is, an electrically neutral, highly ionized substance consisting of electrons, ions and neutral particles.
Under normal conditions, individual atoms of a gas contain an equal number of protons (particles with a positive charge in the nucleus of an atom) and electrons, and thus the gas is electrically neutral. But if you introduce a large number of free electrons into the gas by passing an electric current through it, the situation changes radically: free electrons collide with atoms, “knocking out” more and more electrons. Without an electron, the balance changes, the atom acquires a positive charge and turns into an ion. When an electric current passes through the resulting plasma, the negatively and positively charged particles move towards each other. Amid all this chaos, particles are constantly colliding.
The collisions “excite” the gas atoms in the plasma, causing them to release energy in the form of photons.
In plasma panels Mostly inert gases are used - neon and xenon. When "excited" they emit light in the ultraviolet range, invisible to the human eye. However, ultraviolet light can also be used to release photons in the visible spectrum.
After the discharge, ultraviolet radiation causes the phosphor coating of the pixel cells to glow. Red, green or blue component of the coating. In fact, each pixel is divided into three subpixels containing red, green or blue phosphorus. To create a variety of color shades, the light intensity of each subpixel is controlled independently. In CRT TVs this is done using a mask (and the spotlights are different for each color), and in “plasma” - using 8-bit pulse code modulation. The total number of color combinations in this case reaches 16,777,216 shades.
The fact that plasma panels themselves are the light source provides excellent vertical and horizontal viewing angles and excellent color reproduction (unlike, for example, LCDs, which require backlighting). However, conventional plasma displays normally suffer from low contrast. This is due to the need to constantly supply low-voltage current to all cells. Without this, the pixels will “turn on” and “off” like regular fluorescent lamps, that is, for a very long time, prohibitively increasing the response time. Thus, the pixels must remain on, emitting low-intensity light, which, of course, will affect the display's contrast.
At the end of the 90s. last century, Fujitsu managed to somewhat mitigate the problem by improving the contrast of its panels from 70:1 to 400:1.
By 2000, some manufacturers stated in panel specifications a contrast ratio of up to 3000:1, now it is already 10000:1+.
The manufacturing process for plasma displays is somewhat simpler than the LCD manufacturing process. Compared to the production of TFT LCD displays, which requires the use of photolithography and high-temperature technologies in sterile clean rooms, “plasma” can be produced in dirtier workshops, at low temperatures, using direct printing.
However, the age of plasma panels is short-lived - just recently the average panel life was 25,000 hours, now it has almost doubled, but this does not solve the problem. In terms of operating hours, a plasma display is more expensive than an LCD. For a large presentation screen, the difference is not very significant, however, if you equip numerous plasma monitors office computers, the benefit of LCD becomes obvious to the purchasing company.
Another important disadvantage of “plasma” is the large pixel size. Most manufacturers are unable to create cells smaller than 0.3 mm - this is larger than the grain of a standard LCD matrix. It doesn't look like the situation will change for the better in the near future. In the medium term, such plasma displays will be suitable as home TVs and presentation screens up to 70+ inches in size. If “plasma” is not destroyed by LCD and new display technologies appearing every day, in some ten years it will be available to any buyer.
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