The first plasma screen. Plasma panel vs LCD TV: which is better? (“Plasma vs. LCD: Which is Better?” - Phil Conner). Advantage: plasma panel, with a large margin

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 the Plato computer system. This display was monochrome and did not require additional memory and complex electronic circuits and was different high reliability. 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 the shallow depth of the case and big 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 color plasma display 21" 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 resolution screen 852 x 480 42" diagonal 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 whole line magnificent 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 it arose this effect, about which, as if by agreement, not a word was written by the media, which extolled the new flat-panel 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 Full devices HD. 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 models large sizes. 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 from plastic, only from 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 not ignited electron beam, as in a kinescope, but with 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 produced. 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 protective glass from the front. 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. Protective layer serves to avoid 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. Latest models Runcos that fall into the Full HD category 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, we introduced into the shape of the cells additional jumpers 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 CRT TV, does not use light valves, but emits already modulated light directly by phosphorus triads. This is in to a certain extent Plasma is similar to cathode ray tubes, which are so familiar and have proven their worth over several decades.

Plasma has a noticeably wider coverage 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 without geometric distortion; - Viewing angle 160 degrees in all directions; - The mechanism is not affected by magnetic fields; - High resolution and brightness of the image; - 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 quality images without color and geometric distortions. Weak side is a relatively low contrast. This is due to the fact that the cells must be constantly supplied with low voltage current. 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 recent generations It was possible to significantly reduce it, at the same time eliminating noisy cooling fans.

The main problem in the development of LCD technologies for the sector desktop computers It seems to be the size of the monitor that affects its cost. However, despite this LCD monitors Today they have become the undisputed leaders in the display market. However, there are other technologies that create and develop different manufacturers, and some of these technologies are called PDP (Plasma Display Panels), or simply "plasma", and FED (Field Emission Display).

Plasma monitors

The development of plasma displays, which began back in 1968, was based on the use of the plasma effect, discovered at the University of Illinois in 1966. Now the operating principle of the monitor is based on plasma technology: the effect of the glow of an inert gas under the influence of electricity is used. Neon lamps work using approximately the same technology. Note that the powerful magnets that are part of the dynamic sound emitters located next to the screen do not affect the image in any way, since in plasma devices, as in LCDs, there is no such thing as an electron beam, and at the same time all the elements of a CRT, on which are affected by vibration.

The formation of an image in a plasma display occurs in a space approximately 0.1 mm wide between two glass plates, filled with a mixture of noble gases - xenon and neon. The thinnest transparent conductors, or electrodes, are applied to the front, transparent plate, and mating conductors are applied to the back plate. By applying electrical voltage to the electrodes, it is possible to cause a gas breakdown in the desired cell, accompanied by the emission of light, which forms the required image. The first panels, filled mainly with neon, were monochrome and had a characteristic Orange color. The problem of creating a color image was solved by applying phosphors of primary colors - red, green and blue - in triads of adjacent cells and selecting a gas mixture that, when discharged, emitted ultraviolet radiation invisible to the eye, which excited the phosphors and created a visible color image.

However, traditional plasma screens on panels with discharge direct current There are also a number of disadvantages caused by the physics of the processes occurring in this type of discharge cell. The fact is that despite the relative simplicity and manufacturability of the DC panel, the weak point is the discharge gap electrodes, which are subject to intense erosion. This significantly limits the service life of the device and does not allow achieving high image brightness, limiting the discharge current. As a result, it is not possible to obtain a sufficient number of shades of color, typically limited to sixteen gradations, and speed suitable for displaying a full-fledged television or computer image. For this reason, plasma screens were commonly used as signboards to display alphanumeric and graphical information. The problem is fundamentally solved by physical level by applying a dielectric protective coating to the discharge electrodes.

Modern plasma displays used as computer monitors use the so-called technology - plasmavision - this is a set of cells, in other words, pixels, which consist of three subpixels that transmit colors - red, green and blue. The gas in plasma state is used to react with phosphorus in each subpixel to produce a color (red, green or blue). Each subpixel is individually controlled electronically and produces more than 16 million various colors. IN modern models Each individual dot of red, blue or green can glow at one of 256 brightness levels, which when multiplied gives about 16.7 million shades of a combined color pixel. On computer jargon This color depth is called “True Color” and is considered quite sufficient to convey a photographic quality image.

Speaking about the functionality of a plasma monitor, we can say that the screen has the following functional advantages:

• Wide viewing angle both horizontally and vertically (160° degrees or more).

• Very fast response time (4 µs per line).

• High color purity, equivalent to the purity of the three primary colors of a CRT.

• Ease of production of large-format panels, unattainable with the thin-film process.

• Low thickness (the gas discharge panel is about one centimeter or less thick, and the control electronics add a few more centimeters).

• Compact (depth does not exceed 10 - 15 cm) and light with fairly large screen sizes (40 - 50 inches).

• High refresh rate (about five times better than an LCD panel).

• No flickering or blurring of moving objects that occurs during digital processing.

• High brightness, contrast and clarity without geometric image distortion.

• Wide temperature range.

• The absence of problems of electron beam convergence and focusing is inherent in all flat panel displays.

• No uneven brightness across the screen field.

• 100% use of screen area for images.

• Absence of X-rays and other radiation harmful to health, since high voltages are not used.

• Immunity to magnetic fields.

• No need for image adjustment.

• Mechanical strength.

• Wide temperature range.

• The short response time allows them to be used for displaying video and television signals.

• Higher reliability.

All this makes plasma displays very attractive for use. However, the disadvantages include the limited resolution of most existing plasma monitors, which does not exceed 640x480 pixels. The exception is the Pioneer PDP-V501MX and 502MX models. Providing real resolution 1280x768 pixels, this display has the current maximum screen size of 50 inches diagonally (110x62 cm) and a good brightness indicator (350 Nit), due to new technology cell formation, and improved contrast. The disadvantages of plasma displays also include the impossibility of “stitching” several displays into a “video wall” with an acceptable gap due to the presence of a wide frame around the perimeter of the screen.

The fact that commercial plasma panel sizes typically start at forty inches suggests that the display industry is smaller size It's not economically feasible, which is why we don't see plasma panels in, say, laptop computers. This assumption is supported by another fact: the level of energy consumption of such monitors implies connecting them to the network and does not leave any possibility of operating on batteries. Another unpleasant effect known to specialists is interference, the “overlapping” of microdischarges in adjacent screen elements. As a result of such “mixing,” the image quality naturally deteriorates.

Also, the disadvantages of plasma displays include the fact that, for example, the average white brightness of plasma displays is currently about 300 cd/m2 for all major manufacturers.

Plasma Displays (PDP)

Plasma panels, along with LCD TVs, currently reign in the flat-panel display market, almost completely replacing CRT and projection TVs. No wonder: with a body thickness of several centimeters, these “living pictures” are much more convenient and easily fit into the interior. And while LCD TVs are still just picking up the pace of development, plasma, having come a long way in 15 years, seems to have reached its peak. Another competing flat-panel display technology is on the horizon - OLED (organic light-emitting diode displays), which, logically, will sooner or later mercilessly bury both plasma and LCD. Sometimes information appears about another advanced technology, promising an unimaginable breakthrough in image quality - surface cathodes. This direction originates in the field of nanotechnology and uses the tunnel transition effect. It is possible that this is the future, although with LEDs everything would be much simpler: an understandable, ridiculously simple design of the matrices, a colossal resource. Surely, sooner or later plasma will leave the scene, but no one knows how soon this will happen. Therefore, plasma still remains relevant as the most high-quality display, suitable not only for the role of a “duty” TV for briefly watching news and sports broadcasts, but also for a home theater of a relatively modest scale.

History of Plasma Displays

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 the Plato computer system. This display was monochrome, 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 properly implemented 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.

It must be said that if the first monochrome prototypes were no more similar to modern plasma than chimpanzees are to modern man, then the color plasma panels of the first generations did not rise above the level of Pithecanthropus. 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 technology

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 body. Glass is necessary and irreplaceable here: it stops harmful ultraviolet radiation. For the same reason, no one produces fluorescent lamps from plastic, only from glass. And a plasma panel is, in fact, a large fluorescent lamp, only rolled out into a rectangular pancake and chopped into many cells.

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. 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 ignition of the phosphor phosphor is carried out not by an electron beam, as in a kinescope, but by ultraviolet radiation (which is precisely destined for “life behind glass” in order to avoid harmful effects on the human body).

Where does ultraviolet light come from? The cells are filled with an inert gas - a mixture of neon and xenon (the latter makes up only a few percent of the mixture); some plasma manufacturers also add helium. A gas tends to relatively easily transform into a plasma state when its atoms, losing an electron, turn into positive ions. In this case, the substance moves to a higher energy level. Free electrons periodically collide with neutral atoms, knock out an electron from them and turn them into positive ions. And the other part, encountering ions, reduces them to neutral atoms, which at the same time emit energy in the form of ultraviolet photons. The latter affects the phosphorus phosphor, which begins to glow in visible spectrum. 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. How is it done in fluorescent lamp which works on the same principle? At the moment of start-up, the tungsten spirals at the ends of the tube heat up and begin to emit electrons (thermionic emission). And at the same time, a high voltage is applied between these spirals, an ion-electron current begins to flow, causing the gas to transition to the plasma state, ultraviolet radiation and the glow of a phosphor deposited on the inner surface of the glass tube. Only the phosphor has a white glow. In a plasma screen there are no spirals, but the electrodes are located much closer to each other, and an electrical impulse is enough to ionize the gas high voltage. 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.

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 and run parallel to transparent ones 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 different types of pixel row geometry: 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.

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.

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 who used it plasma models, an unusual resolution of 1024 × 1024 appeared. This resolution, of course, was virtual, but the effect turned out to be very impressive.

Advantages and disadvantages of plasma

The paradox is that when prices for plasma were truly frightening with very, very mediocre image quality, it had no competitors (projection TVs due to their bulkiness worthy alternative did not imagine). It was then, logically, that there was an urgent need to develop LCD technology. But either it was luck, or, on the contrary, everything was thought out, this competitor appeared when plasma was already firmly on its feet. Moreover, it appeared in the same crude and unconvincing form as plasma once did. The first pancake, as you know, is lumpy, and the display, obviously, too. Today we can already talk about competition more or less on equal terms, although plasma, having started earlier, has still managed to do much more than LCD displays, which still have room to develop in order to achieve a status similar to plasma.

What are the advantages and disadvantages of plasma compared to LCD? Undoubtedly, and no one dares to deny this, the image quality of plasma displays is much better. Deeper blacks, higher resolution in dark scenes, while on the LCD screen everything quickly slides into pitch black (more precisely, a dark gray mass, since the residual light is quite significant here). The situation is no better with white: the brightest fragments of the image are often whitened out to a uniform spot. For plasma, all these are annoying details of the distant past.

Viewing angle

One of weaknesses Liquid crystals have traditionally been known to have limited viewing angles. Polarized light is emitted primarily at right angles to the screen surface, excluding scattering in the screen coating. True, in Lately this disadvantage has been largely overcome, but in comparison with plasma it is still noticeable. 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.

Color rendition

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. Color purity and shade resolution are unconditionally leading among plasma displays: LCD screens continually “smooth out”, or even smear, delicate color gradations to the point of a single-color spot, which is especially noticeable on the faces of movie characters and in the background, which are often blurred literally into some kind of amorphous mass, while plasma demonstrates excellent depth of field and three-dimensionality of the picture.

Plasma matrices, undoubtedly, are distinguished by a certain inertia, if only because of the afterglow of the phosphor phosphor, but this inertness cannot be compared with the slowness of liquid crystals. The image on a plasma screen is always more energetic, vibrant, with clear contours.

Plasma resource

The long service life of a plasma display (60,000 hours) is also unlikely to be surpassed or even duplicated by liquid crystals. Moreover, the “horror stories” about dead pixels (at first Fujitsu even introduced a standard - it seems that 16 dead pixels on a 42-inch screen were considered acceptable) turned out to be false alarm: there has not yet been a tendency to increase their number during operation. And the improvement of production technologies has made it possible to completely get rid of this congenital defect.

Screen sizes

Finally, plasma is still the leader in screen size compared to LCD, and if we take the maximum size for LCD at 50??, then such plasma is cheaper. Of course, everything here may change in the next year or two, but for now this is how things stand.

Now about the disadvantages. Unfortunately, the largest plasma displays weigh so much that it is not always possible to hang them on a wall, unless it is made of solid concrete. Plasma is also afraid of not very delicate transportation: glass, after all. 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.

Pixel burn-in

An important disadvantage of plasma is the uneven burnout of pixels during long-term playback of a static image, the contours of which then appear when the scene changes. To prevent degradation of displays from burnout, we use various methods: screen savers (as in computer monitors), automatic shutdown after some time with a static signal or its absence, as well as smooth movements images on the screen.

Glare

But perhaps still the most main drawback Plasma screens are glare. Glass is glass. Yes, plasma is practically insensitive to external light, the colors on the screen remain bright and the image does not lose clarity, but this image is superimposed on the reflection of everything that is behind the viewer, including himself. And if a reflection from a window or a burning floor lamp gets there, then this is pure hell. These items become the main characters of any video! In principle, standing in front of the plasma, which shows the brightest scenes, you can even shave. And all this despite the declaration by manufacturers of new and increasingly improved anti-reflective coatings. Here, involuntarily, the surface of the LCD TV screen comes to mind: velvety-matte, practically does not reflect anything... But where is such clarity and clarity as on plasma, even with the reflection of an open window? If you place two displays next to each other, plasma and LCD, the picture on the second one will appear as if in a slight haze.

In a word, there is no good without bad. The consolation is that this phrase is true in reverse order words

I decided to look into such a cool topic as a plasma display.

Many people are tormented by the question: “What is a plasma display and how cool is it, or better yet, how convenient is it?” We will look at this topic piece by piece and find out the whole point!

Name

Why did we start with the title? That's right, there are at least 3 different and frequently used options this device(Display, panel, screen) that need to be dealt with first.
Panel - the most sonorous and commonly used name of this type screen. The expression “I have a plasma panel at home” has become something attractive and powerful, because in our subconscious we imagine something big, high-tech with a rich picture. The irony is that the word panel is incorrect to use in relation to, monitor, etc. Stylistically correct word, grammatically incorrect.
Display is the second most used, correct and grammatical. Because the patent registered by the three men who were the first to bring this technology to life contained precisely the word Display.
The screen is fine, why not. Synonym for the word display.

Let's compare

We will present the data in comparison with, this is obvious. Yes, they have their own benefits, but they are not used in the segment where plasma and LCD are.

Advantages

• Show off.
• Realism of the image (debatable).
• Initially, deep color reproduction, but this pales against the background of new LED backlights and OLED, which already convey better colors.

Flaws

• The price of devices with such screens and the presence of functions is higher than their counterparts with LCD.
• Higher power consumption.
• Due to their structure, pixels quickly burn out when a static picture is turned on for a long time. As a result, it can only be used for viewing dynamic scenes.
• Large pixels, resulting in relatively small screens with poor resolution.
• The smallest width of the displays is greater than the smallest width of the LCD.

Design

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.

Design Features

• The plasma panel sub-pixel has the following dimensions: 200 µm x 200 µm x 100 µm;
• The front electrode is made of indium tin oxide because it conducts current and is as transparent as possible.
• when large currents flow through a fairly large plasma screen, due to the resistance of the conductors, a significant voltage drop occurs, leading to signal distortion, and therefore intermediate conductors made of chromium are added, despite its opacity;
• To create plasma, cells are usually filled with gases - neon or xenon (less commonly, helium and/or argon, or, more often, mixtures thereof) are used with the addition of mercury.

Principle of operation

1. initialization, during which the position of the charges of the medium is ordered and prepared for the next stage (addressing). In this case, there is no voltage at the addressing electrode, and an initialization pulse, which has a stepped form, is applied to the scanning electrode relative to the backlight electrode. At the first stage of this pulse, the arrangement of the ionic gas medium is ordered, at the second stage there is a discharge in the gas, and at the third the ordering is completed.
2. addressing, during which the pixel is prepared for highlighting. A positive pulse (+75 V) is supplied to the addressing bus, and a negative pulse (-75 V) is supplied to the scanning bus. On the backlight bus, the voltage is set to +150 V.
3. illumination, during which a positive pulse equal to 190 V is applied to the scanning bus, and a negative pulse equal to 190 V is applied to the backlight bus. The sum of the ion potentials on each bus and additional pulses leads to exceeding the threshold potential and discharge in a gaseous environment. After the discharge, the ions are redistributed at the scanning and illumination buses. Changing the polarity of the pulses leads to a repeated discharge in the plasma. Thus, by changing the polarity of the pulses, multiple discharges of the cell are ensured.

Thus, when high-frequency voltage is applied to the electrodes, gas ionization or plasma formation occurs. A capacitive high-frequency discharge occurs in the plasma, which leads to ultraviolet radiation, which causes the phosphor to glow: red, green or blue. This glow passes through the front glass plate and enters the viewer's eye.

Conclusion: If you are a terrible major and are not even going to look at this TV. Buy the most big size display available in the store and feel free to bang your home cinema, then say that you have all this at home and invite a bunch of friends who won’t look there either. True, my dear reader, because of your wallet, you should stick to the voice of reason and buy a TV or monitor only with an LCD screen.