Types of Digital Tv

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Types of Digital TVs Cathode-Ray Tube (CRT) Direct-View TVs Rear Projection CRT TVs (RPTV) Liquid-Crystal Display (LCD) TVs Plasma TVs Microdisplays Front Video Projectors

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Cathode-Ray Tube (CRT) Direct-View TVs

The time-tested CRT has been around for most of the past century and is still in use around the world in all kinds of TVs and test equipment.

CRTs are analog display devices. They consist of a cathode, a series of grids, and an anode, inside a sealed-vacuum glass housing. High voltage is applied to the outside of the tube when you switch on the TV to draw electrons from the cathode. The multiple grids and a yoke around the tube help to steer the electrodes in specific directions.

When this stream of electrons hits the face of the CRT, a phosphor coating is stimulated and glows. By the careful placement of rows of alternating red, green, and blue phosphors to the surface, along with a special grille to control three different electron guns within the CRT, bright, saturated full-color images are formed on the tube.

The rapid motion of the electrons across the screen creates lines of picture detail, and our persistence of vision sees them as complete pictures. In an analog TV system, 30 frames of video are traced each second, each containing 525 individual scan lines with about 480 of them visible. (Persistence of vision refers to the tendency to see a sequence of still images, if the images flash by quickly enough, as one smooth movement; see Module 3, Understanding TV Basics, for a more detailed explanation.)

The trick is to keep the three different electron beams from tripping over each other, and that’s where the grille comes into play. This grille, known as a shadow mask, is usually made out of a lightweight, heat-resistant metal alloy called INVAR. The INVAR mask makes sure only the phosphor area is contacted by the electron beam, not other areas of the tube’s surface.

When the three electron guns are perfectly registered atop each other, the result is full-color video. The guns are said to be in convergence at this point. The phosphors themselves are made from combinations of rare earths, combinations of naturally occurring chemical compounds that glow when struck by high-energy electron beams.

Although the process by which CRTs make pictures is an analog one, they can be driven by digital signal processing circuits to produce images of high quality. CRTs have been made as large as 43 inches, but size, weight, and power limitations pretty much limit them ot a maximum size of 36 inches.

However, CRTs are capable of resolving considerable image detail and are quite economical to manufacture, which keeps the prices of CRT direct-view TV sets much lower than any other display technology at present.

Direct-view TVs can be placed on stands and furniture

























Cathode-Ray Tube (CRT) Direct-View TVs

The time-tested CRT has been around for most of the past century and is still in use around the world in all kinds of TVs and test equipment.

CRTs are analog display devices. They consist of a cathode, a series of grids, and an anode, inside a sealed-vacuum glass housing. High voltage is applied to the outside of the tube when you switch on the TV to draw electrons from the cathode. The multiple grids and a yoke around the tube help to steer the electrodes in specific directions.

When this stream of electrons hits the face of the CRT, a phosphor coating is stimulated and glows. By the careful placement of rows of alternating red, green, and blue phosphors to the surface, along with a special grille to control three different electron guns within the CRT, bright, saturated full-color images are formed on the tube.

The rapid motion of the electrons across the screen creates lines of picture detail, and our persistence of vision sees them as complete pictures. In an analog TV system, 30 frames of video are traced each second, each containing 525 individual scan lines with about 480 of them visible. (Persistence of vision refers to the tendency to see a sequence of still images, if the images flash by quickly enough, as one smooth movement; see Module 3, Understanding TV Basics, for a more detailed explanation.)

The trick is to keep the three different electron beams from tripping over each other, and that’s where the grille comes into play. This grille, known as a shadow mask, is usually made out of a lightweight, heat-resistant metal alloy called INVAR. The INVAR mask makes sure only the phosphor area is contacted by the electron beam, not other areas of the tube’s surface.

When the three electron guns are perfectly registered atop each other, the result is full-color video. The guns are said to be in convergence at this point. The phosphors themselves are made from combinations of rare earths, combinations of naturally occurring chemical compounds that glow when struck by high-energy electron beams.

Although the process by which CRTs make pictures is an analog one, they can be driven by digital signal processing circuits to produce images of high quality. CRTs have been made as large as 43 inches, but size, weight, and power limitations pretty much limit them ot a maximum size of 36 inches.

However, CRTs are capable of resolving considerable image detail and are quite economical to manufacture, which keeps the prices of CRT direct-view TV sets much lower than any other display technology at present.

Direct-view TVs can be placed on stands and furniture


Direct-view TV profile

Direct-view TVs can be used for home theaters

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Lessons in this section (Types of Digital TVs):

Introduction – www.samsungusa.com/cgi-bin/nabc/campaign/dtvguide/module_4.jsp

Cathode-Ray Tube (CRT) Direct-View TVs – www.samsungusa.com/cgi-bin/nabc/campaign/dtvguide/module_4_1.jsp

Rear Projection CRT TVs (RPTV) – www.samsungusa.com/cgi-bin/nabc/campaign/dtvguide/module_4_2.jsp

Liquid-Crystal Display (LCD) TVs – www.samsungusa.com/cgi-bin/nabc/campaign/dtvguide/module_4_3.jsp

Plasma TVs – www.samsungusa.com/cgi-bin/nabc/campaign/dtvguide/module_4_4.jsp

Microdisplays – www.samsungusa.com/cgi-bin/nabc/campaign/dtvguide/module_4_5.jsp

Front Video Projectors – www.samsungusa.com/cgi-bin/nabc/campaign/dtvguide/module_4_6.jsp

Other sections:


Why Digital? – www.samsungusa.com/cgi-bin/nabc/campaign/dtvguide/module_2.jsp

Understanding TV Basics – www.samsungusa.com/cgi-bin/nabc/campaign/dtvguide/module_3.jsp

Types of Digital TVs – You are here. Selecting the Right TV –

www.samsungusa.com/cgi-bin/nabc/campaign/dtvguide/module_5.jsp The World of Connections –

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A flat CRT uses as much as 30% more glass than a curved CRT. This helps to explain why a flat tube TV is more expensive than a curved set.

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Types of Digital TVs Cathode-Ray Tube (CRT) Direct-View TVs Rear Projection CRT TVs (RPTV) Liquid-Crystal Display (LCD) TVs Plasma TVs Microdisplays


















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Front Video Projectors


Rear Projection CRT TVs (RPTV)

One way to get around the CRT size limitation is to project the images from a smaller CRT onto a much bigger screen. This technique requires a certain amount of space proportional to the size of the desired image, so mirrors are used to reduce that space by folding back the electron beams several times in a small area before they finally make it to the screen.

In a CRT rear-projection TV, three CRTs are used with color phosphors and sometimes color purity filters – one red, one green, and one blue. The images produced by each tube must be carefully aligned (converged) into one full-color image when it appears on the TV screen.

The screen itself is made of a translucent material. That is, light from the CRTs continues on to our eyes. Special lenses – thousands of them – make sure as much light as possible from the CRTs is gathered up and directed toward the viewer.

This is an easy way to make TVs with very large screens, including some models over 60 inches (diagonally measured). But the resolution of analog RPTVs with 5-inch and 7-inch tubes is only the same as an analog direct-view TV – about 450 to 500 lines. RPTVs using large tubes with much more resolving power can show HDTV programs with greater detail.

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CRT Rear Projection

Many RPTVs come with built in stands

RPTVs can be used for home theaters

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Research and development has always been the cornerstone of Samsung Electronics. In 2002, Samsung Electronics invested 2.4 billion dollars, approximately 7% of its revenue, in R&D. Annually, Samsung Electronics invests 6-8% of its revenue in technology and product development.

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Types of Digital TVs
















Cathode-Ray Tube (CRT) Direct-View TVs Rear Projection CRT TVs (RPTV) Liquid-Crystal Display (LCD) TVs Plasma TVs Microdisplays Front Video Projectors


Liquid-Crystal Display (LCD) TVs

What do the screens on notebook computers, PDAs, cell phones, and handheld electronic games have in common? They’re all LCD displays!

LCD technology isn’t new. The basic discovery dates back to the 1800’s but no one really knew what to use it for. Research and development into using LCDs as a display technology goes back to the 1950s, but it has come a long way since then. An LCD display consists of thousands of tiny elements, each of which has a liquid-crystal solution in it. Super-small transistors mounted on the surface of each element (or pixel) switches voltages on and off to make those tiny crystals twist into different positions.

Light from a backlight source is polarized before traveling to individual LCD pixels. The position of the liquid crystals determines how much of that light passes through each pixel. By twisting these liquid crystals quickly enough, black-and-white images are created. Add some miniature color filters, and presto – you have full-color video.

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For a simple real-world analogy, think of window blinds – changing the angle of the slats causes them to let in more or less light.

The backlight sources for LCD TVs are actually tiny fluorescent lamps, constructed in such a way as to ensure a uniform distribution of light across the screen. In an LCD TV, the backlight is always on and its brightness doesn’t change. The twisting LC motion is what changes images from dark to light.

LCD TVs are now available in sizes from as small as 2 inches all the way up to 46 inches, with screens as large as 60 inches in the works. For the purposes of this discussion, we will focus on screen sizes 10 inches and larger, as these are the screen sizes one would typically think of as a TV set for the home. Their screen resolutions can be quite high, with 1280:768 pixels being the standard for most models and 1920:1080 pixels coming in the near future.

In terms of weight, LCDs weigh about half as much as a comparable direct-view CRT television with the same size screen. LCD TVs are also very thin and can be hung on walls or placed on small counter tops. They’re popular in places where space is at a premium.

LCD panel

LCD TVs are perfect for small rooms like kitchens

LCD TVs can be mounted to walls

Large LCD TVs make for premium home theaters

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Liquid Crystal Displays can be optimized for motion (as is needed for TV), or static images (as would be important for computers). Not all LCD televisions are created equally. An LCD-TV requires very fast pixel switching speeds so that motion scenes do not blur. To cut cost some manufacturers will use lower quality LCD panels and market them as TVs. Before purchasing a new LCD-TV, view some programming on it to make sure it will really fit your needs.

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Plasma TVs

Plasma display panels (PDPs) offer what science fiction magazines dreamed about 60 years ago – a large television picture (32-inch to 63-inch diagonal) that can literally hang on the wall or stand on a tabletop. Plasma displays employ an imaging system that combines the RGB phosphors and brightness of a CRT picture tube with the simplicity, relatively low power consumption, and construction of an LCD panel.

Like LCD TVs, plasma panels have a fixed pixel structure whether they are “on” or “off.” Individual red, green, and blue pixels are formed inside a structure of intersecting ribs sealed between two glass plates, and an inert gas mixture is present in each pixel. When a charge is applied to any individual pixel, the inert gas is ionized, hence entering the state of producing ultraviolet light.

This UV energy then strikes a red, green, or blue phosphor at the rear of the pixel, causing it to glow. Remove the charge, and the gas deionizes. Extra electrodes are employed to charge and discharge the gas as fast as 85 times per second, making it possible to show full-motion video and still images with a technique similar to pulse-width modulation.

For a real-world analogy, look no further than a fluorescent light. A plasma panel is simply a collection of thousands of small fluorescent lamps fired on and off at a rapid rate. Because you are looking right at the source of colored light, you’ll find highly saturated colors on plasma TVs – similar to those you’d see on a direct-view CRT television.

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A plasma monitor or TV will be about 20% heavier than a LCD TV of the same screen size, although both types of flat panels are comparable in thickness (less than 4 inches). They are available in a wide range of display resolutions, most of which are derived from the world of the personal computer and not from digital television.

Currently, plasma monitors and TVs are being manufactured in several sizes with various pixel counts, for example – 32-inch designs with 852:1024 pixels and 16:9 screens, 37-inch 16:9 models with 852:480 pixels; 42-inch 16:9 panels with 852/853:480 or 1024:1024 pixels, 50-inch 16:9 panels with 1280:768 or 1365/1366:768 pixels, and 60-, 61-, and 63-inch 16:9 panels with 1365/1366:768 pixels.

Although plasma TVs offer an attractive combination of form factor and screen size, they cost quite a bit more than a direct-view TV that uses CRTs. Plasma TVs are also somewhat fragile and require a bit of care in handling and installation.

Plasma display panel

Plasma TVs can be mounted on walls

The narrow profile of a Plasma TV

Plasma TVs can also be mounted on various types of stands

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At the 2004 Consumer Electronics Show Samsung unveiled the worlds first prototype 80-inch plasma HDTV set. While there is no definitive launch plan at this time, Samsung has again taken a leadership roll in flat panel display technology development.

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Microdisplays


















Microdisplay TVs come in two forms. There are the transmissive type, like LCD rear projection (LCD RPTV) models, and the reflective type, which include digital light processing (DLP) and liquid crystal on silicon (LCoS) TVs. Let’s look at how they compare.

Digital Light Processing (DLP)

The semiconductor at the heart of DLP imaging is called a digital micromirror device, abbreviated DMD. If you look at a DMD under an electron microscope, you will see thousands of tiny mirrors, each mounted on a pedestal. All these mirrors do is to tilt back and forth about 10 to 12 degrees in response to “on” and “off” commands send to them by the DMD’s controller, making DLP a reflective-type system.

In the normal position, light is fully reflected to the imaging surface. In the “off” position, light is directed away from the surface (and in high-brightness projectors, into a heat-absorbing surface known as a “light dump”). This doesn’t seem like a very efficient way to make electronic images – that is, until you speed up the on/off cycle.

By using pulse-width modulation, defined as the ratio of “on” cycles to “off” cycles in a specified time interval, persistence of vision kicks in and we see a precise value of gray on the screen. Change the ratio to more “ons” than “offs,” and the image becomes brighter. With more “offs” than “ons,” the image will become darker.

DMD is the fastest-switching microdisplay, so the switching speed of these mirrors is correspondingly fast (it’s measured in microseconds). DMD is also the only microdisplay with binary (or true “on” and “off”) states. Since both the drivers and response of the mirrors are fully digital, DLP technology can produce amazingly good images. Because of this and its superior brightness, DLP technology is ideal for home theater use.

Because the DMD housing and polarized beam splitters take up a lot of room, a single-chip design for front and rear projection has been devised by Texas Instruments for addressing the compact data projector, the home theater projector and the recent popularity of the compact rear-projector design.

To obtain full RGB color, a special synchronized wheel is placed between the lamp and DMD. The desired color segments are timed to coincide with the motion of mirrors tied to the luminance value of each color, and once again persistence of vision integrates the process into a smooth blend of colors.

DMDs are popular choices for lightweight rear-projection TVs in sizes from 43 to 61 inches. HDTV-class DLP TV sets incorporate advanced 1280:720 resolution designed for home theater. Later this year, a new 1920:1080-pixel DMD will be introduced into this market.

Digital micro-display planel (DMD)

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In 1987 Texas Instruments scientist Dr. Larry Hornbeck developed the Digital Micromirror Device, or DMD

DLP™ Light Engine

Micrographic photo shows a single grain of salt on the surface of a DLP™ chip

LCD Rear Projection TVs

Another form of LCD display technology is found in camcorder viewfinders and portable video/data projectors, and it’s known as high-temperature polysilicon (HTPS) LCD.

The principles of light shuttering are essentially the same for HTPS LCD as they are for large LCD TVs. The difference is that HTPS LCD panels are much, much smaller. Current sizes range from just over one-half inch to just under 2 inches. They are too small for use in anything other than near-to-eye displays, but are ideal for a rear-projection TV set.

HTPS LCD panels are manufactured in a wide range of pixel resolutions, and there are widescreen panels with true high-definition pixel counts of 1280:768 and 1366:768. Like their larger brothers, polysilicon LCDs shutter light as pixels are turned on and off. Combined with small, high-pressure arc lamps, they deliver extremely bright images. These devices are transmissive, meaning light passes through them.

Unlike large LCD TVs, rear-projection LCD TVs must use three separate panels with special color filters (known as dichroics) to blend three black-and-white images into full color. The three images (red, green, and blue) are converged with a special prism into a single, precisely registered image, then magnified and projected onto the TV screen.

At present, a handful of companies are producing front projectors and rear-projection TVs with HTPS LCD panels specifically for the home.

Liquid Crystal on Silicon (LCoS)

LCoS and LCD panels have a lot in common. Both contain thousands of cells filled with liquid crystals that twist and align in response to control voltages. But that’s where the similarity ends.

LCoS devices shutter and bounce light off their reflective rear surface, so they fall under the “reflective” designation. This might seem like a neat trick, but it is accomplished by polarizing the light and keeping the reflection angle between 45 and 90 degrees. While this makes things a bit more complicated optically, it does improve the efficiency of the light shutter, and more light makes it to the screen when compared to the transmissive LCD panel.

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Here’s why: The controlling transistors are mounted on the back of the LCoS chip, not in the way of any beams of light. The spacing between each LC cell (known as the fill factor) is smaller, further improving illumination efficiency. Three LCoS panels are typically used with red, green, and blue filters to get full-color imaging, but recombining these color images with a device called a polarized beam splitter is a tricky process.

As a result, the pixel resolution of LCoS devices can be much higher than similarly sized HTPS LCDs. A .9-inch HTPS panel will have 1024:768 pixels on it, but a .9-inch LCOS panel will contain 1365:1024 pixels. LCoS panels with resolutions as high as 2048:1536 pixels are commercially available now.

LCoS panels can be used with any kind of short-arc projection lamp, although a few front-projection models have employed small xenon arc lamps. These lamps produce more accurate colors. However, xenon lamps are more expensive to operate and are found in costlier professional applications. What’s more, they don’t last nearly as long as the short-arc lamps found in consumer rear-projection TVs.

LCoS is a very difficult technology to manufacture. The panels are manufactured on wafers, and the yields from those wafers are quite low at present. It is hard to maintain the thin walls and high resolution that HD LCoS panels require, and still make enough of them to sustain high-volume sales of consumer rear-projection TV sets.

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Samsung is dedicated to research and development. In 2002, 17,000 researchers, 34% of Samsung’s total employees, were dedicated to developing the finest products. The effort continues today as Samsung pioneers new technologies in microdisplays, leading the new digital era.

Source: Samsung


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Front Video Projectors

Just as film is projected onto a large screen in a movie theater, so too can video be projected in your home, using a front video projector. The technology inside is very similar to that used in rear-projection TV sets.


















Front video projectors were sold exclusively with CRTs for over 20 years, but the trend today is away from tubes and toward using microdisplays to save on weight, size, and power consumption. There are two different ways to build a microdisplay engine – single-panel (or chip), and three-panel (or chip). The single-panel DMD designs are ideal for home theater in terms of cost and the screen sizes involved (6 to 12 feet). To achieve a bright image in larger screen sizes (20 feet or more), three-chip projectors should be considered. However, they are more costly.

Front projectors using single-chip DLP technology employ the same color wheel as rear-projection TVs. The DMD creates black-and-white images, and the precise synchronization of the color wheel results in the correct amounts of red, green, and blue being applied to the image. These full-color images then travel through a projection lens and on to the screen.

There is also a three-chip DLP design that makes use of separate red, green, and blue color filters, plus a polarized beam splitter to recombine the three images into one. This approach results in the best color, and it’s free of any possible flicker artifacts. But it is more complex and expensive, plus it requires more space inside a projector.

Front projectors are also available with HTPS LCD and LCoS technology. In both cases, three imaging panels are used with red, green, and blue color filters. A prism is also employed to recombine all three single-color images into a single image before projection and enlargement onto a screen.

In the case of HTPS LCD, light passes through the color filters and panels and continues on to the prism and lens. With LCoS panels, light is split into three channels by a polarized beam splitter and then passes back the other way to be recombined into a full-color image before traveling to the screen.

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A new Samsung front projection system is available with an adjustable projection screen size spanning from 40" to 250", this projector can be used anywhere from the average living room to an elaborate home theater.

Source: Samsung





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Types of Digital Tv