Projection TVs
The desire to get a large picture appeared simultaneously with the creation kineskopnogo TV. The most simple solution can be seen in old movies - a lens in front of a small screen. The decision poslozhnee - projection TV - was realized almost simultaneously. Even domestic producers noted in this regard: in 60 - years of our country produced black and
Until recently, in the market segment bolsheekrannyh televisions (from 40 "diagonally or more) dominated the three models using cathode ray tubes (tubes) as a light source. Despite its popularity, such CRT televisions, analog in fact, provide inadequate brightness and limited angle.
The latest models of projection TVs are increasing the use of other devices to create images. Using the matrix devices, especially in models with screens ranging from 40 "to 60", helps to improve image quality, making them even more popular. These matrix displays include such devices as prosvetnye matrix TFT LCD, LCOS-reflecting panels and mikrozerkalnye DMD-chips. TFT-LCD matrix most often used in trehmatrichnyh structures, and DMD-chips in systems odnochipovyh DLP-projectors.
Such projection televisions actively traded in the U.S., China and Europe. Japan with its traditionally small rooms, among which there are no large living room, more inclined to TV with flat LCD or LCDs, to be selected with a large screen minimum living space. The new generation of projection TV with pixel matrix provides significant improvement in the image (especially in parts of brightness and clarity), compared with traditional projection televisions based on kineskopnyh projectors. For comparison: the brightness of the projection TV with a projector while reviewing kineskopnym strictly in front of about 200 cd/m2. In so doing, often peripheral area of the screen look darker. In similar circumstances on the basis of projection TV mnogopikselnyh matrices provide about 500 cd/m2 brightness, which is already equivalent to the brightness of modern plasma and LCD panels. That is for the viewer, sitting right in front projection televisions, image quality is comparable to the picture quality of plasma and LCD TVs. Moreover, through the use of advanced optical systems, new models PTV significantly thinner than its predecessors. The best image quality and lower thickness - additional incentive to purchase the reasons for such televisions.
Matrix PTV regardless of the type panels provide greater resolution. For this reason they are able to reproduce HDTV-image as a progressive (720p), and interlaced (1080i). Note that the projection TV based on CRT HDTV-quality images worse - because of the large diameter of the electron beam spots.
Among the weaknesses of projection TV - the depth of their relatively large in comparison with television on flat panels (LCD and plasma). However, developers are taking steps to improve these TV, and now you can buy PTV screen with 61 ", a depth of less than 20 cm and a wide viewing angle. Market analysts predict that in the event of such a significant improvement in problem parameters projection TV and closer to their values ploskopanelnyh TV DTH market will threaten the LCD and plasma TV not only in North America and China, but throughout the world.
projection TV Thomson
Presented this year by Thomson HDTV-projection TV based on DLP-technology, 61DSZ644, with 61 inch screen has a total depth of 17.4 cm
Projectors depending on the method of obtaining images can be divided into two categories: forward and backward. Direct or front - is the classic stand-alone video, which we have repeatedly told. Backward or rear, as a rule, are part of the projection TV. In addition to the projector, in a single shell that housed the TV reflecting mirror, prosvetny screen, TV tuner and acoustics with amplifiers (Fig. 1). The image projected on the screen at the rear prosvetny (hence the name) are reflected from a mirror mounted on the rear of the hull. Prosvetny screen has high optical transmission, that is transparent to external lighting and because practically does not reflect it. Thus, rear projection screen provides greater brightness than front projectors, and the loss of contrast due to ambient light from them insignificant.
Prosvetny screen design contains two layers of lenses. On the inside of a Fresnel lens is circular, which the major task to send light from the projector at the viewer). Outside the layer is vertical lenticular lenses, which provide a wide viewing angle in the horizontal plane.
In seeking to improve the quality of the image projection TV manufacturers reduce step lenticular lenses. This solution eliminates a number of problems. First, get rid of Flashing. Flashing is often the reason for presence in the screen material dispersion additive which increases the scattering and thus increases the vertical angle. In doing so, the display looks granulated. Another problem - moire, which arises because of interference between the discrete structure of the image projected on the screen and projector matrix linear structure lenticular lenses. As the step vertical lenses and flicker, and less noticeable moire. Naturally, in the projection TV uses the same matrix projectors with a fixed structure, as in front projectors. This may be reflecting prosvetnye or LCD panels, or DLP-projectors that use chips mikrozerkalnye DMD.
However, the projection TV picture quality depends not only on the matrix, but also from the other components. So light source (lamp) is making a major contribution to the brightness of images and colors. At last, and strongly influences the optical system. For permission and the transfer of gray scale is responsible pixel matrix. And finally, depend on screen brightness with ambient light and viewing angle. Electronics can be trimmed gray scale transfer and color reproduction. That is, producers can improve their projection TVs in many ways. The two main shortcomings PTV - a large compared with plasma and LCD television with the same depth and small vertical diagonal angle. So far the main way of increasing the vertical angle of view - this is improving the optical system. For a classical design with PTV screen 60 "diagonally corps depth ranges from 40 to 60 cm To reduce the depth of the hull, the projector does not possess under the screen, but at the bottom of the hull, while maintaining sufficient distance projection required to obtain images of large size. Pravda In this case, a mirror image projected by the acute angle, and at the top and bottom of the screen it may be distorted. However, Mitsubishi Electric and Thomson Multimedia has already sold a screen projection TVs 60 "and a depth of less than 20 cm Packaging To increase the vertical angle review in PTV often used to supplement the material dispersion screen. This way there is a negative side: the more additives, the biggest falls brightness. The modern way to solve this problem - the use of LCOS-reflecting panels.
Projection TV with LCD matrices are high resolution and relatively cheap. But they have little contrast and inadequate channel grayscale scale. Major manufacturers LCD HDTV-matrices with permission - Seiko Epson (panel 1.3 "and 1.6" with a resolution of 1920 pixels h1080) and Sony (panel 1.35 ", 1365 õ768 pixels). Seiko Epson said to PTV with its LCD prosvetnymi - panels sold in the U.S., and the contrast of 1000:1 Announces appearance in next year's models contrast to 1500:1.
Much more effectively used in the flux reflecting LCD panels - LCOS. The benefits of such TVs, in addition, include high resolution, great contrast and good gray scale reproduction. However, their construction is very complex and requires the use of specific components. This greatly increases the price of PTV with LCOS-panels, compared with models using other technologies. To reduce the price of JVC, which calls its prosvetnye LCD panel D-ILA, has developed a design using mirrors and prisms dihroichnyh (Fig. 2). Matrix JVC has size 0.8 "and ensures full compliance with the requirements of HDTV - 1920 h1080 pixels. In addition, PTV this company through the use of LCOS-panel provides a relatively large vertical angle of view. The American Intel produces LCOS-panel with a resolution of 1280 h720 and 1920 h1080 pixels. O PTV develop these panels have already reported InFocus (USA), TCL and SkyWorth (both - China) and Trimax PDC (Taiwan). Also produce LCOS-matrix matching HDTV, Philips (matrix with a resolution of 1280 pixels h720 already used in models sold televisions, but with a resolution of 1920 pixels h1080 will be used in the next model). Company Sony in the early 2003, reported the development of its LCOS-panel, which developers called SXRD. This high-resolution panels, a large contrast and response time of 5 ms. The company intends to ispolzoval this panel in the projection TV and video. While Sony showed at the spring 2004 InfoComm exhibition of professional quality video with a resolution of 8.8 million pixels. Proizvodit LCOS-matrix with a resolution of HDTV and even Hitachi.
Finally, technology DLP, the sole producer DMD-chips for which today is at Texas Instruments. In all commercial PTV models used odnochipovy option with tsvetodelitelnym range. This type of projection TVs have high contrast, excellent reproduces images with great momentum, passes well and has a gray scale of long service life. However, permission and the transfer of black (gradations of gray with a minimum brightness) require improvement. These televisions have defined a specific color mode of transmission interference. Often it is called color noise, which occurs when switching colors because of the range of filters.
