Cathode ray tube (CRT)
Cathode ray tube (CRT) is a hollow tube containing an electron gun (electron source) and a fluorescent screen, with internal or external means to accelerate and deflect the electron beam, which is used to create images in the form of light emitted from the fluorescent screen. Pictures may represent electrical waveforms (oscilloscope), pictures (television, computer monitor), radar and other targets. Color CRT has three separate electron gun (shadow mask-type) or electron guns that share some of the electrodes for all three pillars (Sony Trinitron, and the licensed version)
CRT uses evacuated glass envelopes are large, deep, heavy, and relatively fragile. Display technologies without these shortcomings, such as flat plasma screens, liquid crystal displays, DLP, OLED displays have replaced CRTs in many applications and is becoming increasingly common as costs decline. Exceptions to the typical bowl-shaped CRT would be a flat CRT that is used by Sony in the series Watchman (FD-210 was introduced in 1982). The last one is a flat CRT model FD-120A. The CRT in these units is flat with an electron gun located roughly at the bottom right corner of the screen surface thus requiring sophisticated electronics to create an undistorted picture free from effects such as keystoning.
History
The earliest version of the CRT was created by the German physicist Ferdinand Braun in 1897 and also known as the "Braun tube". [3] This is a cold-cathode diode, a modification of the Crookes tube with a phosphor-coated screen. The first version uses the hot cathode was developed by John B. Johnson (who gave his name the term Johnson noise) and Harry Weiner Weinhart Western Electric, and became a commercial product in 1922.
Cathode rays are now known as electron beam emitted from a heated cathode inside the vacuum tube and accelerated by the potential difference between cathode and anode. The screen is covered with a layer of crystalline phosphorus (anesthetized with transition metals or rare earth elements), which emit light when excited by high energy electrons. File (or blocks, in a color CRT) is deflected either by magnetic or electric field to move a bright spot (s) to the required position on the screen. External electromagnet magnetically deflect rays, while the internal plate is placed near and in addition electrostatically deflect light. (Electrostatic deflection is used for single-beam tube only.)
General Descriptions
Aplications
On television and computer monitor tubes entire front area is scanned repeatedly and systematically in a fixed pattern called a raster. A raster is a rectangular array of closely-spaced parallel lines, scan one by one, from left to right (and, with very little, "down", because the beam to move on down while drawing a picture frame). An image generated by modulating the intensity of each of the three electron beams, one for each primary color (red, green, and blue) by receiving a video signal (or other signals derived from it). In all models except CRT TV antenna very beginning, the beam is deflected by magnetic deflection, varying magnetic field generated by the coil (deflection yoke), driven by electronic circuits, around the neck tube. Some of the small screen used a commercial TV antenna electrostatic deflection to the end of the 1940s, usually employing 7 "CRT type 7JP4.
Constructions
Electron beam source is an electron gun, which produces a flow of electrons through thermionic emission, and focused into a thin beam. Previously, black and white CRT TV used a magnetic focus, but focus electrostatic focus entirely replaced the coil. The gun is located in a narrow, cylindrical neck at the extreme rear of a CRT and has electrical connecting pins, usually arranged in a circular configuration, extending from the tip. This pin provides an external connection to the cathode, the grid elements in the weapons used to focus and modulate the beam, and, in the electrostatic deflection CRT, the deflection plate. Because CRT is a hot-cathode device, these pins also provide connections to one or more filament heaters within the electron gun. When a CRT operation, the heater is often seen glowing orange through the glass wall of the CRT neck. The need for this heater to 'warm up' cause the delay between the time of the first CRT monitor is turned on, and when the view becomes visible. In older tubes, this could take fifteen seconds or more; modern CRT displays have fast-start circuit that produces an image in about two seconds, either use the heater while the current increases or increased cathode voltage. Once the CRT has been heated, the heater remains constant. Electrodes are often covered with a black coating, a patented process used by all major CRT manufacturers to increase the density of electrons.
Electron gun is not only accelerate the electrons but also ions present in the vacuum is not perfect (some of which result from outgassing of internal tube components). Ion, which is much heavier than electrons, is much less deflected by magnetic or electrostatic field is used to position the electron beam. Ions striking damage to the screen; to prevent the electron gun can be positioned slightly from the tube axis so that the ions strike the inside of the neck of the CRT is not the screen. Permanent magnet (ion trap) deflect the lighter electrons, so they attack the screen. Some very old TV without ion trap showing brown from the center of the screen, known as ions on fire. Layer of aluminum that is used in the CRT eliminates the need for ion trap: they are no longer used.
When electrons strike a bad-conductive layer of phosphor on the CRT glass, it becomes electrically charged, and tends to repel electrons, reducing the brightness (this effect is known as "sticky"). To prevent this side of the interior of the phosphor layer can be covered with a layer of aluminum is connected to a conductive layer in the tube, which dispose of this cost. It has the added advantage of increased brightness by reflecting, toward the viewer, the light emitted toward the back of the tube. Aluminum layer also protects the phosphors of the shooting ions.
Color CRT's (Full Color)
Color tubes use three different phosphors that emit red, green, and blue respectively. They are packed together in lines (as in the design of the grille aperture) or a group called "triads" (as in the shadow mask CRT). Color CRT has three electron guns, one for each primary color, arranged either in a straight line or in a triangular configuration (usually weapons are built as one unit). Each gun's beam reaches the points exactly one color.A grating or mask, which absorbs electrons that would otherwise hit the wrong phosphor. A shadow mask tube using a metal plate with small holes, placed so that the electron beam illuminates only the correct phosphors on the face of the tube. Another type of color CRT using an aperture grille to achieve the same results. Since each file starts on a slightly different location in the tube, and the three affected files in the same way, the cost of certain deflection will cause the beam to hit a slightly different location on the screen (called 'sub-pixels'). Color CRT with arms arranged in a triangular configuration is known as delta-gun CRT, because the triangle triangular formation resembles the Greek letter shapes? (Delta). Despite having a deep color reproduction, CRT can often exaggerate red.
CRT Resolution
Dot pitch defines "native resolution" of the screen, assuming delta-gun CRT (although this is not really a native resolution as the flat panel display, because these points are not real subpixels). In this case, as an approach to scan resolution dot pitch resolution, moiré (a kind of soft-edged appeal) appears, due to mask interference pattern between the structure and pattern as drawn pixel grid. Defines the term track pitch aperture grille monitor resolution. This monitor does not suffer from vertical moiré, however, because it has no vertical phosphor stripes detail. Aperture grille is something like a wooden fence, in the sense that it has a vertical slot between the metals. CRT smaller, strip it maintains its own position, but a larger aperture-grille CRT require one or two transverse (horizontal) support strip. However, this strip is almost not visible on the screen. Sony Trinitron aperture grille CRT use, and they are faceplates toroid, although very different from the radius of curvature make Trinitron CRT's faceplate looks cylinder.
Future Technology CRT
Demise
Demand for CRT screens have been falling fast, [5] and manufacturers are responding to this trend. For example, in 2005 Sony announced that they would stop production of CRT computer displays. It has been common to replace CRT-based televisions and monitors as the only 5-6 years, although they are generally able to satisfy the performance that much longer.
End of the most high-end CRT production in the mid-2000s (including high-end Sony, and Mitsubishi product line) erosion means the ability of CRT. [6] [7] Samsung did not introduce any CRT models for model 2008 years in 2008 Consumer Electronics Show, and on February 4, 2008 Samsung released their 30 "widescreen CRT from their web sites in North America and has not been replaced with newer models. [8]
In the United Kingdom, DSG (Dixons), the largest retailer of electronic equipment in the country, reported that the CRT model consists of 80-90% of the volume of televisions sold in the Christmas 2004 and 15-20% a year later, and that they expected less than 5% at the end of 2006. Dixons to stop selling CRT televisions in 2007.
Causes
CRT, despite recent progress, still relatively heavy and bulky compared to other display technologies, and this becomes a significant weakness as the consumer is considered thin and wall-mountable flat-panel sales point. CRT screens have much deeper than the cabinets with flat panel displays and rear projection to a particular screen size, and so would be impractical to have CRTs larger than 40 inches (102 cm). In general, rear projection displays and LCDs require less power per area of the screen, although plasma displays consume as much or more than CRT
CYRSTAL LIQUID DISPLAY (LCD)
A liquid crystal display (LCD) is a thin, flat panels used to display electronic information such as text, images and moving images. Its use includes monitors for computers, televisions, instrument panels, and other devices ranging from aircraft cockpit displays, for every-day consumer devices such as video players, gaming devices, clocks, watches, calculators, and telephone. Among the main features is its lightweight construction, with the portability, and ability to be produced in sizes much larger screen than practical for the construction of cathode ray tube (CRT) display technologies. Its low power consumption allows for use in battery-powered electronic equipment. This is a modulated electronic-optical device consisting of a number of pixels filled with liquid crystal and are arranged in front of a light source (backlight) or reflector to produce images in color or monochrome. The discovery of the earliest towards the development of LCD technology, the discovery of liquid crystals, dates from 1888. [1] In 2008, worldwide sales of television with LCD screen has surpassed sales of CRT units.
Each pixel of an LCD typically consists of layers of molecules aligned between two transparent electrodes, and two polarizing filters, the axes of transmission (in most cases) perpendicular to each other. Without the actual liquid crystal between the polarizing filters, light passing through the first filter would be blocked by the second (crossed) polarizer.
Nematic-optic effect device is hooked-on voltage is much less dependent on variations in the thickness of the device that is turned-off voltage. Therefore, these devices are usually operated between crossed polarizers such that they appear bright with no voltage (the eye is much more sensitive to variations in the dark from the bright state). This device can also be operated between parallel polarizers, in this case light and dark behind the state. The voltage-off dark state in this configuration appears acne, however, because small variations in device thickness.
Both the liquid crystal materials and alignment layer material contain ionic compounds. If the electric field of one particular polarity is applied for a long time, this ionic material attracted to the surface and degradation of device performance. This is avoided either by applying an alternating current or by reversing the polarity of the electric field as the device is addressed (the response of the liquid crystal layer is identical, regardless of the polarity of the applied field).
Surface electrodes associated with liquid crystal material are treated so as to align the liquid crystal molecules in a certain direction. This treatment usually consists of a thin polymer layer is unidirectionally rubbed using, for example, cloth. The direction of liquid crystal alignment was determined by the direction of rubbing. Electrodes made of a transparent conductor called Indium Tin Oxide (ITO).
Before applying an electric field, the orientation of liquid crystal molecules is determined by the alignment at the electrode surface. In the Twisted Nematic (still the most common liquid crystal device), the alignment direction at the two electrode surfaces perpendicular to each other, so the molecules arrange themselves in a helical structure, or twist. This will reduce the rotation of the incident light polarization, and the device appears gray. If the applied voltage is large, then the liquid crystal molecules in the middle layer is almost completely untwisted and the polarization of incident light is not rotated as it passes through the liquid crystal layer. This light will then be mainly polarized perpendicular to the second filter, and thus will be blocked and will appear black pixels. By controlling the voltage applied across the liquid crystal layer in each pixel, light can be allowed to pass varying amounts thus represents different levels of gray.
When a large number of pixels required in a screen, it is technically not possible to drive each directly since then each pixel would require independent electrodes. Instead, the display multiplexing. In a multiplexed display, electrodes on one side of the display are grouped and linked together (usually in columns), and each group getting its own voltage source. On the other hand, the electrodes are also grouped (typically in rows), with each group get a voltage sink. The groups are designed so that each pixel has a unique, unshared combination of source and sink. Electronic, or electronic software to drive then the lights in the sink in the order, and the resources to drive pixels of each sink.
Color Display
At each pixel color LCD is divided into three cells, or subpixels, red, green, and blue, respectively, with additional filters (pigment filters, dye filters and metal oxide filters). Each subpixel can be controlled independently to yield thousands or millions of possible colors for each pixel. CRT monitors use a similar 'subpixel' structures via phosphors, although the electron beam working at a CRT do not hit exact 'subpixels'. Color components may be arranged in various pixel geometries, depending on the use of monitors. If the software knows which type of geometry being used in an LCD, it can be used to improve the resolution of the monitor through subpixel rendering clear. This technique is especially useful for text anti-aliasing. To reduce smudging in a moving picture when pixels are not fast enough to respond to changes in color, called pixel overdrive may be used.
Energy efficiency
Among the new TV models, the LCD displays need less energy on average than their plasma counterparts. A 42-inch LCD screen consumes 203 watts compared with an average of 271 watts consumed by 42-inch plasma screen. Energy use per inch the better [citation needed] How to compare different technologies. CRT technology is more efficient to use 0.23 watts / square inch, while LCDs require 0.27 watts / square inch. Plasma displays are at the high end at 0.36 watts / square inch and DLP / rear projection TVs represent the low end at 0.14 watts / square inch. Bistable displays do not consume any power when displaying still images, but requires a significant amount of power [citation needed] To change the displayed image.
Deficiency
LCD technology still has some shortcomings compared to other display technologies:
* While CRTs capable of displaying various video resolutions without introducing artifacts, LCDs produce sharp images only in their native resolution and, sometimes, fragments of the original resolution. Attempting to run LCD panels at non-native resolutions usually results in an image scale of the panel, which introduces blurriness or "blockiness" and is generally susceptible to various kinds of HDTV blur. Many LCDs are not capable of displaying a very low resolution screen modes (such as 320 × 200) because of the limitations of this scaling.
* Several types of color LCD has a resolution of more limited than advertised, [citation needed] And must use spatial and / or temporal dithering to increase the color depth is clear. This can cause the shimmering effect by displaying some kind that can be distracting for some users.
* Although LCDs typically have more vibrant images and better "real world" contrast ratios (the ability to maintain contrast and color variations in the light of the environment) than CRTs, they have lower contrast ratios than CRTs in terms of how deep they are black people . A contrast ratio is the difference between fully on (white) and off (black) pixel, and LCDs can have "backlight bleed" where light (usually seen around the corners of the screen) leaks out and turns into a black or even gray bluish / purple color with TN-film-based display. However, in 2009, the best LCD TV that does not use LED backlighting to achieve a dynamic contrast ratio of 150,000:1.
* LCDs typically have longer response times than their plasma and CRT counterparts, especially older displays, creating visible ghosting when images rapidly change. For example, when the mouse is moving quickly on the LCD, multiple cursors can sometimes be seen. ** See also: CRT phosphor persistence
* LCD appears to show motion blur as the human eye to follow moving objects, where some CRT screens are not. This is because an individual pixel LCD always looks for the entire duration of the frame (typically 16.7ms), while the CRT pixel lights up only a fraction of a microsecond once per frame as a scanned electron beam to pass through. Which means that even in the hypothetical LCD panels with zero response time, a panning image will appear to have motion blur while panning images on CRT monitors will not. This is due to eye movement during the time frame seen [citation needed]. Blur can be reduced by increasing the refresh rate to a multiple frame rates (eg 120 or 240 Hz) and employs a variety of image processing techniques. Blur or ghosting to some "correction" software using techniques that show the negative image blur to compensate with a cancel-out the estimated blur. For example, if the ghost image caused by remaining where it is 5% brighter than usual, the software will draw a negative ghost of the image that minus-5 percent, and the results will increase the expected value (n + 5-5 = n). However, these techniques require processing delays, which can be Problematic for fast-action video game usage. Some monitors even come with "game mode" to turn off the anti-ghosting when necessary.
* Using the TN LCD panels tend to have limited viewing angle compared to CRT and plasma displays. This will reduce the number of people who can easily see the same image - laptop screen is a prime example. Usually when looking down the screen, it will be much darker; visible from above makes it look lighter. This distorts the color and make a cheap LCD monitor is not suitable for work where color is important, as in the graphic design work, as color changes when the eyes move slightly up or down, or when looking both at the top of the screen or at the bottom of the position that remain. Many displays are based on thin film transistor variants such as the IPS, MVA, or PVA, has many good points of view, usually only the color becomes a little brighter when viewing at extreme angles, although a lot from the standpoint of improvements have been made [citation needed] on lateral corner, not on the vertical.
* Consumer LCD monitors tend to be more fragile than their CRT counterparts. The screen may be particularly vulnerable because of the lack of a thick glass shield as in CRT monitors, ie, piercing of an LCD will cause the color circle (popular with young children) that can damage the screen. CRT has a thick glass to protect them from scratches or 'poke' the damage.
* Dead pixels can occur when the screen is damaged or pressure put on the screen; few manufacturers replace screens with dead pixels under warranty.
* Horizontal and / or vertical banding is a problem in some LCD screens. This defect occurs as part of the manufacturing process, and can not be repaired (short of total replacement of the screen). Appeals can vary substantially even among LCD screens and the same model. The level is determined by the manufacturer of quality control procedures.
* Cold Cathode Fluorescent lights are usually used to back-light LCD screen contains mercury, toxic substances, although the LED-backlit LCD display is mercury-free.
* Pattern-based flicker, caused by imperfect voltage balance. [29]] - one or more of the accepted tests will usually show the flickering, which also can indicate if a problem occurs as a pattern hatch pattern in the region is significant.
PLASMA DISPLAY
A plasma display panel (PDP) is a common type of flat panel screens to display a large TV (32 "inches or larger). Many small cells between two panes of glass that holds a mixture of noble gases. Gas in an electric cell which is then turned in the plasma excites phosphors to emit light. Plasma displays should not be confused with LCDs, another lightweight flatscreen display uses a different technology.
General characteristics
Plasma displays are bright (1000 lux or higher for the module), having a wide color gamut, and can be produced in large enough sizes - up to 381 cm (150 inches) diagonally. They have a very low lighting "dark room" black level compared with the more gray light from the parts of an unilluminated LCD screen. Display panel is only about 6 cm (2.5 inches) thick, while the total thickness, including electronics, is less than 10 cm (4 inches). Plasma displays use as much power per square meter as a CRT or a AMLCD television. [Edit] Power consumption varies greatly with picture content, with clear views of significantly more power than the darker, as it also applies to CRT. Nominal power rating 400 watts usually for 50-inch (127 cm) screen. Post-2006 models consume 220-310 watts for 50-inch (127 cm) display when set to cinema mode. Most of the display set to 'shop' mode by default, which attracts at least twice the power (around 500-700 watts) of a 'home' setting of less extreme brightness. [3] Panasonic has greatly reduced power consumption by using Neo-PDP screens in their 2009 series of VIERA Plasma HDTV. Panasonic claims that PDPs will consume only half the strength of the previous series plasma sets to achieve the same overall brightness for a particular screen size. The lifetime of the latest generation of plasma displays is estimated at 100,000 hours of actual display time, or 27 years on 10 hours per day. This is the approximate time at which maximum picture brightness degrades half the original value.
Plasma displays have a deficiency in addition to power consumption. They are often criticized for being more reflective environment than LCD displays. Front screen made of glass, which reflects more light than the material used to make LCD screens, which produce light from objects is reflected in the display area. Companies such as Panasonic coat newer plasma screen them with anti-glare filter material. Currently, plasma panels can not be produced economically in smaller screen sizes from 32 ". Although some companies have been able to make small plasma EDTVs this, even fewer have made a 32 "plasma HDTV. With trends showing greater and greater, a 32 "screen sizes are rapidly disappearing. Although considered to be big and bulky compared to LCD counterparts, some sets such as Z1 and the Panasonic Samsung B860 series is as thin as one inch thick to make them comparable with LCD in this regard.
Competing displays include the CRT, OLED, AMLCD, DLP, SED-tv, LEDs, and field emission flat panel display. The advantage of a large plasma screen technology, very thin screen that can be produced, and that picture is very bright and has a wide viewing angle. The angle of view characteristics of plasma and flat face CRT displays are basically the same, topping all LCD displays, which have a reduced angle of view in at least one direction. Plasma TV also showed no blurred images common in many LCD TVs.
How Plasma Works
The xenon, neon, and helium gas in a plasma television is contained in hundreds of thousands of tiny cells positioned between two glass plates. Long electrodes are also included together between glass plates, in front of and behind the cell. The address electrodes sit behind the cells, along the rear glass plate. A transparent display electrodes, which are surrounded by insulating dielectric material and covered by a protective layer of magnesium oxide, which is installed in front of the cell, along the front glass plate. Cost control electrode circuit that crosses the road in a cell, creating a voltage difference between front and rear and causing the gas to ionize and form a plasma. As gas ions rush to the electrodes and collide, photons are emitted.
In a monochrome plasma panel, the ionizing state can be maintained by applying low-level voltage between all horizontal and vertical electrodes - even after the ionizing voltage is removed. To remove the cell voltage is removed from a pair of electrodes. Type of panel has inherent memory and does not use phosphors. A small amount of nitrogen added to the neon to increase hysteresis.
Color panel, the back of each cell is coated with phosphor. Ultraviolet photons emitted by the plasma to arouse this phosphors give off light in color. The operation of each cell thus can be compared with a neon lamp.
Each pixel consists of three separate subpixel cells, each with different colored phosphors. One subpixel has a red light phosphor, one subpixel has a green light phosphor and one subpixel has a blue light phosphor. These colors blend together to create the overall color pixels, the same as the "triad" of shadow mask color CRT or LCD. Plasma panel using pulse-width modulation to control brightness: by varying the pulses of current flowing through the different cells thousands of times per second, the control system can increase or decrease the intensity of each subpixel color to create billions of different combinations of red, green and blue. In this way, the control system can produce most of the visible colors. Plasma displays use the same phosphors as CRTs, which accounts for a very accurate color reproduction when viewing television or computer video image (which uses the RGB color system is designed for CRT display technology).
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