|
Arabic
Bengali
Chinese
English
French
German
Hebrew
Hindi
Italian
Japanese
Korean
Malay
Polish
Portuguese
Spanish
Turkish
Ukrainian
Vietnamese|
BOOKS AND ARTICLES And instead of a lamp, a plasma motor
Once upon a time, TVs were completely lamp-based and the entire "box" was densely packed with a chassis with boards and numerous surface-mounted elements. At the same time, the main lamp of the TV - the kinescope was lost in the web of bundles with connecting conductors. It seemed that it was impossible to understand such an economy, and the television masters, who, having poked back and forth with the probes of the tester, quickly found the "burnt victim", looked like magicians, for which they took a decent tip. Then transistors replaced the lamps, printed circuit boards replaced the hinged mounting, "air" appeared inside the TV, and finally, the last TV lamp - the kinescope appeared in all its mastodon grandeur - especially since by this time the kinescope had noticeably increased in volume and mass. The transistor "had a short life", it was very quickly replaced by corporate elements - integrated circuits, on the standard chip area of \uXNUMXb\uXNUMXbwhich hundreds, then thousands, and now millions of transistors were found. In a decent volume and size case of a modern TV, only a few microcircuits and a couple of power blocks are missing, which have also been thoroughly shrunken since the time of the tube riot of flesh. Everything else is filled with the hollow immensity of the kinescope. Therefore, one should not be surprised that from the moment the first “air” appeared inside the TV and to this day there has been a persistent search for ideas and designs for a new type of reproducing screens. And from the first steps of this work, it became clear that flat screens should become a promising replacement for the kinescope. And the best evidence of the difficulty of the task is the fact that the kinescope still dominates in television construction. I happened to re-read a huge number of survey "projects" on a variety of ideas for the implementation of television scanning outside the kinescope framework. A variety of proposals and ideas from funny to global - they numbered in the thousands - and sunk into oblivion. To our time, only three approaches to flat screens have found practical implementation. Liquid crystal displays are one of the proven and promising areas, the other is a flat matrix of light-emitting elements. For huge video walls, any light source that can be turned on / off quickly enough is suitable here. For flat screen consumer TVs, the choice is not great, and semiconductor LEDs are one of the real contenders. This is all the more interesting because the technology for manufacturing flat LED screens can be based on proven technologies for the production of integrated circuits. The whole business in this direction is stopped only by the supercost of the LED screen. Of the actively emitting screens, the most advanced in the direction of practical implementation, or rather, already implemented and mass-produced, although so far in relatively small runs, are flat plasma screens. According to domestic terminology, they are called screens with gas-discharge elements. Modern civilization quite often encounters the use of gas-discharge light sources. These are, for example, "neon" lamps in the form of straight and curved tubes, widely used in billboards. The epithet "neon" has been attached to such lamps for a long time - since the appearance of the first gas-discharge elements with neon filling and pink gas glow. Now a variety of gas fillings are used, and the epithet itself - a slang definition of a lamp - keeps the memory of the first "date". There are also lamps of "daylight" lighting, the gas content of which is mercury vapor, which emit in the ultraviolet part of the spectrum. But the composition of the radiation of the lamps themselves is determined by the phosphor, which converts dangerous ultraviolet into safe light in the visible range. According to the scheme of operation, it is these lamps that are closest to those gas-discharge elements and flat screens based on them, which will be discussed below. gas discharge Flat-panel TVs based on gas-discharge elements use the natural property of plasma to emit electromagnetic waves in the visible range and ultraviolet. Plasma is a partially or fully ionized gas. In an equilibrium state, the number of positively and negatively charged plasma elements (ions, electrons) is mutually balanced, therefore, for an outside observer, plasma appears to be a body that does not have an electric charge. Since plasma is a gas, the spirit of wandering is natural to all of its elements. Plasma can be kept in a limited space with the help of fields. In the universe, the main role of the jailer of plasma packed in stars and nebulae is played by gravitational fields, and in some cases magnetic fields. Thus, the Earth's magnetic field keeps in its traps streams of high-energy cosmic particles, especially numerous at the moments of explosions on the Sun and capable of "burning" everything that exists on our planet. In its man-made terrestrial specializations, and there are a lot of them, the plasma is kept exclusively by electromagnetic fields and the walls of cells, vessels and other gas-impervious cylinders. Under normal conditions that exist near the surface of the Earth, gas molecules are electrically neutral. Therefore, to turn these gases into plasma, you need to work hard. There are quite a lot of physical processes leading to the ionization of gases and turning them into plasma. The most natural and replicated ionization process in numerous stars is heating to temperatures when the average kinetic energy of molecules exceeds the potential energy of the outer electrons of atomic shells. Further heating of the gas leads to the removal of electrons from ever deeper layers. In stars, this process can continue to the limit, when only nuclei remain from atoms, and in neutron stars and during gravitational collapse, even nuclei are destroyed. Another effective process of gas ionization is the bombardment of its molecules by sufficiently energetic charged particles. It is this process that leads to the formation of ionized layers in the Earth's atmosphere that reflect electromagnetic waves in the SW and HF radio bands. Photoionization, as a possible process of plasma formation, is worth mentioning for the reason that the reverse process of deionization provides the glow of plasma, so widely used by people. However, based on the objectives of this article, we are especially interested in the ionization process, which is called a gas discharge. From the point of view of physics, a gas discharge arises as a result of the already mentioned bombardment of gas molecules by electrons dispersed by an applied electric field. Therefore, the physical features of the gas discharge essentially depend on the applied potential. It must be said that the possible realizations of an electric discharge in gases, or, in other words, the passage of an electric current through a gaseous medium, are numerous and significantly depend on the composition and pressure of the gas, on the material, shape and placement of the electrodes, and the configuration of the electric field in the gas. The physics of the passage of currents through gases is complex and, in general, does not obey Ohm's law. Distinguish between independent and non-independent categories. In the case of a non-self-sustained or so-called quiet discharge, gas ionization is maintained by external processes, and the electric field controls only the discharge current. We are interested in an independent discharge, which is created and maintained by a sufficiently high electric potential. The potential from which an independent discharge occurs is called the breakdown potential, and the electrical voltage that provides this potential is called the ignition voltage. Quiet discharges can be observed at night, especially in the pre-storm hours, around the tip of metal objects. Lightning is a spectacular natural manifestation of an independent gas discharge. The ignition voltage depends, of course, on the composition of the gas and, in uniform electric fields, on the product of the distance between the electrodes and the pressure of the gas. In inhomogeneous fields, this dependence is somewhat more complicated, but the main character is retained. At a relatively low gas pressure (a few millimeters of mercury), a glow discharge occurs - it is this discharge that is used in gas-discharge light sources. In a certain range of currents, the glow intensity of a glow discharge depends on the discharge current more or less linearly. It is necessary to emphasize one property of a glow discharge, the importance of which for the topic discussed here will become clear below: the potential capable of supporting a glow discharge is noticeably smaller than the breakdown potential. That is why the designs of gas-discharge lamps provide for special discharge ignition devices, which, at the moment of switching on, generate a pulse with an amplitude greater than the ignition voltage. At sufficiently high pressures, for example, atmospheric pressure, one or several channels (streamers) filled with plasma are formed during the breakdown. Lightning is a typical example of such a discharge through streamers. The interaction of electrically charged plasma elements is mainly determined by long-range electromagnetic fields, and not by short-range forces of molecular attraction. Therefore, the physical processes in plasma are fundamentally collective in nature. Although the mean free paths of electrons and ions in plasma are long, collisions of electrons with gas molecules occur quite often. An electron accelerated by an electric field knocks out a colleague from the outer shell of an atom, creating an oppositely charged ion, which, under the influence of an electric field, accelerates in the direction opposite to the movement of electrons. A certain energy is expended on this action, which cannot be lower than the potential of an electron in an atom. Hence, the threshold character of the dependence of the glow discharge current on voltage arises. The mutual attraction of negatively charged electrons and positively charged ions leads to their frequent "meetings", which end in recombination. A neutral molecule is formed - a target for the next bombardment - and a photon, which carries away the excess energy that arises when an electron is placed in a free place in the atom. Usually, in gas discharge devices, a gaseous medium of a certain composition is used. In this case, the energy of the electrons bombarding the gas molecules is sufficient only to strip off the electrons that are most weakly bound in the atoms of the gas molecules. The potential of this thinnest "thread" determines the energy of the emitted photon, and, hence, its "color". That is why gas-discharge lamps, as a rule, emit in a rather narrow region of the spectrum. gas discharge cells
The screen of a flat TV or display on gas discharge elements is composed of a large number of cells, each of which is an independent radiating element. There are two basic designs of such cells. The one that is easier to manufacture uses a volumetric discharge. The electrodes in this design, which received the abbreviation DC as an international marking, are placed on opposite substrates. This design is illustrated in Fig. A. DC cells will find - this is now clear - a relatively narrow field of application due to the short service life. The fact is that in such a design, the phosphor layer is inevitably subjected to ion bombardment, which, because of this, burns out rather quickly. For this reason, surface discharge designs, abbreviated AC, are preferred in display/television applications. This design is illustrated in Fig. b. The principal feature of this variant lies in the placement of display (discharge maintaining) electrodes on one substrate. The ion flows connecting the electrodes do not reach the opposite substrate with the phosphor coating and therefore do not destroy it. The construction of the cells is quite simple. Its main bearing elements are glass plates - substrates. Through one of them, light radiation is output. In the variant with a volumetric discharge, a transparent electrode is placed on the output plate, covered with a layer of a dielectric - magnesium oxide. And, finally, a layer of phosphor is deposited on the surface of the dielectric. In the surface discharge design, the phosphor is applied directly to the glass plate. The lower glass plates are coated on the inside with a layer of conductor and dielectric (volumetric discharge) or two layers of conductor and dielectric (surface discharge). The purpose of the elements of the described structures is quite obvious and only the presence of a phosphor layer requires comments. The gas discharge cell emits electromagnetic waves in the ultraviolet range. The phosphor actively absorbs this radiation, for which it is an opaque medium. The last remark is important in the sense that ultraviolet is quite harmful to humans. Therefore, one of the additional functions of the phosphor is to cut off dangerous radiation. In the atoms of a phosphor that has absorbed ultraviolet photons, levels corresponding in transition energy (metastable, i.e., relatively long-lived) are excited and part of the excitation energy due to a transition in which no photon emission occurs. The excess part of the energy is removed by a thermal quantum, transferred to unstable (short-lived) levels of lower potential, which quickly return to their original state, emitting photons in the visible range. This is how ultraviolet light is converted to visible light. In flat gas discharge screens that reproduce a color image, three types of phosphors are used that emit red, green and blue light. The screen of a standard TV contains more than 300000 independent elements - in each RGB emitting cells. The composition of the flat screen TV is the same. So, a flat screen TV with gas discharge elements should contain about a million small neon bulbs, assembled in RGB triads. Using sputtering or electrolytic technologies, electrodes, layers of dielectric (MgO) and phosphors are applied to glass plates in appropriate places, partitions are created that separate one gas-discharge cell from another, the space between the plates is filled with working gas, everything is filled with a gas-tight substance around the perimeter - and the screen is ready . The electrodes are formed in the form of two mutually intersecting grids. The first such screen with a surface gas discharge was released by Fujitsu back in 1979. It must be said that for two decades this company has been and remains the main enthusiast and source of ideas for improving the designs of flat-screen plasma TVs. It took a decade to improve the design of the gas discharge screen. The first problem was the operating time. The transition to a surface discharge significantly extended the lifetime of the phosphor, but did not completely eliminate the problem, since the bombardment of the phosphor by ions weakened, but did not completely disappear. It was necessary to make the surface discharge flatter, for which it was necessary to place the discharge electrodes on the same surface. But how then to create a crossed structure of video signal switching electrodes? The final solution was found in a three-electrode structure, which was first created in 1986. It is shown in fig. V. The third electrode is addressable. It is the address electrodes that create the dashed electrode system orthogonal to the strokes of the discharge electrodes. The discharge electrodes are constantly supplied with a voltage sufficient to maintain the discharge, but less than the ignition voltage. Pulses are applied to the address electrodes, the amplitude of which is large enough to ignite the discharge. The switching system of the TV with an element-by-element clock frequency switches the potentials supplied to the address electrodes, and from the line - to the discharge electrodes. In this case, the potential difference between a pair of discharge electrodes is maintained constant. This decision removed many problems and practically opened the way for the implementation of mass production. But the problem of more efficient use of phosphor radiation remains. The fact is that the atoms of the phosphor are completely indifferent in which direction to shoot the photon. But from a flat screen, it is required that it send photons mainly towards the viewer. For this reason, it was decided to "flip" the cell, as shown in Fig. G. So, the phosphor and the address electrode migrated to the bottom plate, and the discharge electrodes, which had to become transparent, moved to the top one. The address electrode, along with the main function of the conductor, also performs the second - a mirror that reflects half of the light emitted by the phosphor towards the viewer. At the same time, the discharge electrodes acquired protrusions that localize the discharge more compactly. This cell structure of the gas discharge screen was implemented in 1989 by the same company Fujitsu. From that moment, in principle, the practical use of gas discharge screens in televisions, displays and video walls became possible. Plasma TV In 1993 at NAB, Fujitsu showed a flat-panel television receiver with an 86 cm diagonal screen containing 640 x 480 triads of gas discharge cells. The TV provided reproduction of 260000 color shades, which corresponds to six-bit level quantization - the quality of color reproduction is somewhat lower than that provided by the standard. This is explained by the insufficiently wide linear interval of gas-discharge cells. However, there is still room for further improvement in playback quality. The thickness of the gas-discharge TV is only 3,5 cm. It is hard to believe that such a flat, almost devoid of thickness, design can replace a box of more than half a meter in length, height and width! The mass of the flat TV is also indecently small - less than 5 kg! But the service life in comparison with the first versions has grown to 30000 hours. Viewing angle 140 degrees. not inferior to this parameter of TVs on kinescopes. Televisions are not the only area of application for gas discharge panels. It is assumed that they will find the most widespread use, at least in the first place, in computer technology as graphic displays. This circumstance is reflected, in particular, in the placement of RGB cells. In the mask kinescopes of TVs, they are round in shape and are placed at the vertices of an equilateral triangle - a delta design. In computer displays, the square shape of triads and their linear (horizontally or vertically) placement are adopted. The same is done in a flat plasma panel. Each triad of the 86 cm panel is a square with a side of 0,66 mm and consists of three rectangular elements with dimensions of 0,66 vertically and 0,22 horizontally. In total, there are 3 x 640 = 1920 cells in the row. The brightness of the panel glow is quite high - 180 candela per square meter. Contrast 60:1. A significant disadvantage of gas-discharge panels, unfortunately fundamental, is a fairly high switching voltage of tens and hundreds of volts. It is determined by the breakdown potential and, unfortunately, cannot be lowered. This leads to high power consumption of the device. High-frequency systems with such a large signal span are quite complex and capricious devices. Less fundamental, but significant is another drawback - too high a price - $ 10000. It excludes, for now, the mass use of flat panels. Such a high price is a consequence of technological difficulties, including those just mentioned. With the expansion of mass production, it is quite possible to count on a reduction in the cost of gas discharge panels. However, it is unlikely that it will become comparable to the cost of reproducing devices on kinescopes. However, such predictions are fraught with errors. They have no number More precisely, the total number of firms that have taken up Fujitsu's challenge and are developing their own versions of reproducing devices, in which a plasma panel will replace a vacuum tube - a kinescope, has already exceeded three dozen. Thus, Mitsubishi Electric, only a year behind Fujitsu, presented its version of the panel with an 81 cm screen and is already starting mass production of panels with a meter screen. Perhaps the most authoritative among "display" companies, NEC, made a similar application for the production of AC-type meter screens. But it was NHK who took the risk of investing in the development of systems of the DC type, that is, with the use of a volumetric gas discharge. The firm was attracted by the main advantage of the system with a volume discharge - the simplicity of design, followed by a shadow of a relatively low cost. The developers of NHK, of course, were aware of the main drawbacks - low reliability due to the rapid burnout of the phosphor. The result of the work was a panel with a meter screen. Its thickness is only 6 mm, weight 8 kg. The panel is still not up to the best in terms of clarity, but impressed everyone with unexpectedly high reliability - 15000 hours of guaranteed operation. Surprised, Hitachi, Sharp, Toshiba, Pioneer, and two dozen other firms quickly formed a consortium to fine-tune and produce NHK-designed, meter-long DC-type plasma screens in the form of televisions, displays, and other suitable video playback devices. NHK itself does not remain aloof from the passions caused by its initiative, and plans to install meter-long plasma screens containing more than two million elements at the Olympic Games venues at the Nogano Winter Olympics in 1988. In 1999, it is planned to release screens with a diagonal of 1,2 ... 1,3 m. Russia also did not stand aside. Back in 1975, the first domestic developments with gas discharge screens appeared. They were intended for large screens of collective use. Now the greatest success has been achieved, in our opinion, by the company NII GRP Plasma, which operates on the basis of Moscow State University. The company is ready to offer panels of a "television" size of one or so meters or large video walls with a diagonal of 2 ... 5 m. These are not the ideas of scientists, but the proposals of developers looking for a market. I don't know what the flat-panel TV of the future will be like. I know - it will be, I'm sure - soon! The current contenders are good, but not very good! However, "we will not stand behind the price"! Author: Leonid Chirkov
▪ Elementary rules for filming
The existence of an entropy rule for quantum entanglement has been proven
09.05.2024 Mini air conditioner Sony Reon Pocket 5
09.05.2024 Energy from space for Starship
08.05.2024
▪ SEAGATE hard drives in TOSHIBA video recorders
▪ Telephony site section. Article selection ▪ article by Major Pronin. Popular expression ▪ article How many planets are there in the solar system? Detailed answer ▪ Eloh article. Legends, cultivation, methods of application ▪ article Grease for hair. Simple recipes and tips
Home page | Library | Articles | Website map | Site Reviews
www.diagram.com.ua |
We recommend interesting articles Section 
See other articles Section 
Latest news of science and technology, new electronics:
All languages of this page