LCD TV, flat screen TV

Friday, 19 January 2007

LCD TV is flat screen television that uses liquid crystal display (LCD) technology for its visual output. There are many different types of video display technology being commercialized for a number of different applications. Cathode ray tube (CRT) monitors have been commonly used for displaying information on television displays. The CRT has been used for image display in a television over the longest period of time. The CRT has enjoyed the highest market share because of high image quality and brightness. However, it also has much disadvantage such as heavy weight, large volume and high power consumption. Since the volume of traditional cathode ray tube television (CRT TV) is large in addition to its problem of loosing originality of color and proportion, CRT TV is eliminated gradually. Due to rapid development of semiconductor technologies, various kinds of electronic devices are driven at lower voltage and consuming less power, rendering the electronic equipments much slimmer and lighter. Efforts have been made to develop various flat panel display devices, such as liquid crystal display (LCD) devices, plasma display panel (PDP) devices, electroluminescent display (ELD) devices, and vacuum fluorescent display (VFD) devices. Currently, some type of the flat display devices have been incorporated into various display equipment such as televisions and home theatre systems. Such flat panel monitor devices can be manufactured owing to the rapidly improved semiconductor technology. Among the various types of flat display devices, the LCD devices have been commonly used in portable devices due to their advantageous characteristics, such as thin profile, light weight, and low power consumption. Thus, with liquid crystal display's advantage on size, weight, style, power consumption and/or modulation transfer function in comparison to many other display technologies, the LCD TV is commonly substituted for cathode ray tube (CRT) TV to receive and display broadcast signals.

A liquid crystal display (LCD) is a flat screen display with property of low power consumption, and decreased significantly in either occupied space or weight in comparison with a conventional cathode ray tube (CRT) and without curve surface as a CRT display has. A liquid crystal display device is a display device that comprises a liquid crystal sealed between two opposing substrates and that uses electrical stimulus for optical switching by exploiting the electro-optical anisotropy of a liquid crystal. An LCD displays an image containing information by adjusting the arrangement of the liquid crystal. The liquid crystal changes a transmissivity of light passing through the liquid crystal according to an electric field applied to the liquid crystal. The liquid crystal display changes the optical properties of liquid crystal layers that pass light according to the molecular arrangement, and uses the modulation of the light of the liquid crystal cells. The liquid crystal layer is applied with electric field, and the transmittance of light passing through the liquid crystal layer is adjusted by controlling the electric field, thereby obtaining desired images. Utilizing the refractive index anisotropy that the liquid crystal possesses, the brightness of the light transmitted by the liquid crystal panel is controlled by applying a voltage to the liquid crystal and thereby reorienting the axis of the refractive index anisotropy. In the LCD devices, liquid crystal materials are injected between two thin glass substrates that have specially treated surfaces. The arrangement of the liquid crystal molecules is varied by an induced electric field generated by electrodes that are disposed on facing surfaces of the two thin glass substrates in order to display images. The LCD device is classified into a twisted nematic (TN) type LCD device and a super-twisted nematic (STN) type LCD device. The LCD device also may be classified into an active matrix type LCD device and a passive matrix type LCD device according to a method of driving the LCD device. The active matrix type LCD device uses the thin film transistors as a switching element so as to drive the LCD device. A typical active-matrix liquid crystal display has a plurality of switching elements and pixel electrodes, which are arranged in an array matrix on the lower substrate. Therefore, the lower substrate of the active-matrix liquid crystal display is alternatively referred to as an array substrate. The passive matrix type LCD device does not use transistors so as to drive the LCD device, so that the passive matrix type LCD device does not require complicated circuits for driving the LCD device. Active-type thin film transistor liquid crystal displays (TFT-LCDs) are the most popular LCD monitors due to the fact that the viewing angle and the contrast performance are much better than those of a super-twisted nematic liquid crystal display (STN-LCD) of passive matrix type and the TFT-LCD shows more rapid response than the STN-LCD does. The primary elements of a TFT-LCD device include a fluorescent light tube, a light-guiding plate, a polarized film, a color filter, two glass substrates, a rubbing film, liquid crystal materials, and thin film transistors. Liquid crystal between the picture element electrode and the counter electrode is driven by applying a desired voltage between the picture element electrode and the counter electrode through a TFT. In this way, an image is displayed on a liquid crystal display panel. The TFT LCD device is classified into amorphous-Si TFT LCD (or a-Si TFT LCD) device and a poly-Si TFT LCD device. The poly-silicon TFT LCD (or poly-Si TFT LCD) device has lower power consumption and a low price, but is manufactured through complex processes compared with the a-Si TFT LCD device. Accordingly, the poly-Si TFT LCD is used in a display device having a small display screen such as a mobile phone. The a-Si TFT LCD device may provide a large display screen and a high yield (or high productivity), and is used in a display device having a large display screen such as a laptop computer, an LCD monitor or a high definition television (HDTV).

Most of the LCD televisions require a backlight module as the light source; the so-called backlight stands for the position of the light source coming from the backside of the liquid crystal panel. The LCD device does not emit light in itself. That is, the LCD device displays a picture image by controlling light transmittance from an external source. Thus, the LCD device requires an additional light source such as a backlight. The basic structure of a backlight module mainly includes 3 main sections: light source, light guide plate, and optical film. LCD device uses a light source such as an electro luminescence (EL), a light emitting diode (LED), a cold cathode fluorescent lamp (CCFL) or a hot cathode fluorescent lamp (HCFL). The CCFL has a long lifetime, low power consumption and thin profile and is used as the light source for large-sized color TFT LCD devices. Backlights for liquid crystal displays based on cold cathode fluorescent lamps (CCFL) are known that have a high lumen efficacy of 50 60 lm/W. This high lumen efficacy is due to the unique properties of mercury vapor. However, due to environmental constraints the display industry is forced to develop alternative backlights without using mercury. The number of lamps can be changed according to the size of LCD television. In order to meet the requirement of high brightness, the quantity of lamps used in a direct-light type backlight module can be up to sixteen or more. In order to reduce motion artifacts in LCD-TV displays, a beam is continually scrolled over the panel. Scrolling backlight systems used in the reduction of motion artifacts for LCD TV use either direct backlit cold cathode fluorescent lamps (CCFLs) or edge-backlit white RGB (red, green, blue) LEDs. According to the location of light sources, the backlight module of the liquid crystal display device is classified as a side-light or edge-light type and a direct-light (bottom light) type. Generally, the liquid crystal television uses the direct-light type backlight module. Liquid crystal displays have found extensive uses in a variety of electronic devices such as television receivers, laptop computers, personal digital assistances (PDAs), mobile phones, digital cameras, and camcorders.

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