LCD monitor information share ...
February 13, 2007 8:51pm CST
A Liquid Crystal Display (LCD) is an optical device that is commonly used to display simple ASCII characters, and images on digital items such as watches, calculators, and portable game consoles. LCD is also the technology used for displays in notebooks and other small computers. Like light-emitting diode and gas-plasma technologies, LCD allows display devices to be much thinner than those employing cathode ray tube (CRT) technology. LCD devices consume much less power than LED and gas-display displays because they work on the principle of blocking rather than emitting light. How are LCDs made? LCDs are created from two glass plates separated from each other at a distance of a few microns. Plates are filled with liquid crystal, then sealed together. The top plate is colored with an RGB pattern to create a color filter. Then polarizers are glued to both plates. This combination is sometimes called a 'glass' or 'cell'. The LCD cell is assembled into a 'module' by adding the backlight, driver electronics and frame. LCD TFT components include: 1. Polarizing filter: Regulates in and out 2. Glass substrate: With electrodes 3. Transparent electrodes: These electrodes with high transparency ratios are used to operate the LCD materials. 4. Alignment layer: Films used to align liquid crystal elements in a fixed direction 5. Liquid crystal 6. Spacer: Maintains a consistent gap between two glass plates 7. Color filter: Displays all color with RGB filter 8. Backlighting: Sends light to the screen In the active matrix LCD, a switching transistor (TFT) and a diode are attached to each color element to switch each element on and off. X and Y electrodes are attached to the same circuit board as the TFT. A switching signal is impressed on X electrodes; video signals go to the Y electrode. What is polarization? Light is an electromagnetic wave. Electric and magnetic fields oscillate in a direction perpendicular to the propagation of the light beam. The direction of these fields is called 'polarization direction'. Normal or non-polarized light has fields in multiple directions; polarized light has fields in only one direction. What is a polarizer? A polarizer is a sheet of special plastic that transmits light with a given polarization direction and absorbs all light with different polarization directions. What differentiates passive matrix LCDs from active matrix LCDs? A LCD is made with either a passive matrix or an active matrix display grid. An active matrix has a transistor located at each pixel intersection, requiring less current to control the luminance of a pixel. For this reason, the current in an active matrix display can be switched on and off more frequently, improving the screen refresh time. For example, with an active matrix LCD, your mouse will appear to move more smoothly across the screen. On the other hand, a passive matrix LCD has a grid of conductors with pixels located at each intersection in the grid. How does a TFT LCD panel work? On the TFT LCD panel, a data source drive is attached to each column while a gate drive is attached to each row. Each cell's TFT drain is connected to the electrode. The molecular arrangement of liquid crystal elements differs depending on whether or not it is impressed with voltage. The voltage varies the direction of polarized light and the amount of light by passing it through different arrays of liquid crystal elements. When two polarized filters are arranged vertically on a polarized light pole, the light that passes through the upper polarized panel is turned 90 degrees along with spiral structure of the liquid crystal molecules and passes through the polarized filter at the bottom. When impressed with voltage, liquid crystal molecules are arranged vertically from the original spiral structure and the direction of the light is not turned 90 degrees. In this case, light that comes through the top polarized panel may not go through the polarized panel at the bottom. What are the advantages of TFT LCD compared to CRT? In a CRT monitor, a gun shoots electrons and general light by colliding polarized electrons on fluorescent glass. Therefore, CRT monitor basically operate with analog RGB signals. A TFT LCD monitor displays an input image by operating a liquid crystal panel. The TFT's structure is fundamentally different than that of a CRT: Each cell has an active matrix structure and independent active elements. A TFT LCD is comprised of two glass panels. The space between them is filled with liquid crystal. When each cell is connected with electrodes and impressed with voltage, the molecular structure of liquid crystal is altered. This controls the amount of inlet lighting used to display images. A TFT LCD has several advantages over a CRT: It can be very thin and does not flicker because it does not use the scanning method. Why is a vertical frequency of 60 Hz optimal for an LCD monitor? Unlike a CRT monitor, the TFT LCD panel has fixed resolution. For example, an XGA monitor has 1024 x 3(R,G,B) x 768 pixels and higher resolution may not be available without additional software processing. The panel is designed to optimize display for a 65 MHz dot clock, one of the standards for XGA displays. Since the vertical/horizontal frequency for this dot clock is 60/48 Hz, the optimum frequency for this monitor is 60 Hz. What kind of wide angle technology is available. How does it work? The TFT LCD panel controls/displays input of a backlight using the dual refraction of liquid crystal. Employing the property that makes the projection of input light refract toward the major axis of the liquid element, it controls the direction of input light and displays it. Since the refraction ratio of input light on liquid crystal varies with the inlet angle of the light, the viewing angle of a TFT is much narrower than that of a CRT. Usually, viewing angle refers to the point where the contrast ratio is 10. Many methods to widen the viewing angle are currently being developed. The most common approach is to use wide viewing angle film, which increases the viewing angle by varying refraction ratio. Also IPS (In Plane Switching) or MVA (multi Vertical Aligned) is used to widen the viewing angle. The new range of LCD monitors employs advanced IPS Technology. Why is there no flicker on an LCD monitor? Technically speaking, LCDs do flicker; however, the cause of the phenomena is different than that of a CRT monitor -- and has no impact on ease of viewing. In an LCD monitor, 'flicker' refers to usually undetectable luminance caused by the difference between positive and negative voltage. On the other hand, CRT flicker - the kind that can irritate the human eye -- occurs when the on/off action on the fluorescent object becomes visible. Since the reaction speed of liquid crystal in an LCD panel is much slower, this troublesome form of flicker is not present in LCD display. Why is an LCD monitor virtually free of Electro Magnetic Interface? Unlike a CRT, the LCD monitor does not have key points that generate Electro Magnetic Interfaces, especially magnetic fields. Also, since LCD display utilizes relatively little power, its power supply is extremely quiet. At what percentage is the brightness level preset? At the factory, Contrast Level is preset at 100% and Brightness Level is set to the maximum level. Liquid Chrystal Displays Liquid chrystal display is the type of display used in laptop computers, in desk computers LCDs have not yet become as common. For their advatages LCDs will possibly replace the traditional CRT monitors, but the development has not been as fast as first was believed. It has been estimated that LCDs have 50% of the market before the year 2004. The advatages of LCDs compared to CRTs are * LCDs consume less power * do not produce electromagnetic radiation as CRTs do * flicker less than CRTs * are light and small in size The drawbacks are * poorer viewing angle * higher price * problems with contrast ratio and response time * less accurate colour performance Other differences: 1. resolutions: CRTs are able to display more resolutions than LCDs which have only one resolution at full screen size. Lower resolutions are possible by using only a part of the sreeen. If a panel with 1024 x 768 resolution needs to display a resolution of 640 x 480 it uses only 66% of the screen. 2. diagonal measurement: LCD's viewable area is the same as its diagonal measurement. CRTs lose about an inch behind the faceplate or bezel. 3. convergence: In LCDs each cell is switched on or off individually so there is no convergence problems as in CRTs in which use electron guns and need faultless convergence if a sharp picture is wanted. 4. signals: CRTs require analogue and LCDs digital signals. Current graphic cards have analogue outputs, hence analogue signals must be converted into digital: 1) graphics signal generated digitally in PC, 2) converted to analogue signal by the graphics card, and 3) fed into LCD where converted back into digital. How LCD works Liquid chrystal displays are based on technique in which current is lead through liquid chrystals. Liquid chrystals are substances that are almost transparent and have properties of both solid and liquid matter. There are two kinds of LCDs: DSTN (dual-scan twisted nematic) and TFT (thin film transistor), which are also known as passive and active matrix displays. LCD is made of several layers that are arranged according to the following order: E) polarising filter D) sheet of glass C) electrode B) alignment layer A) liquid chrystals B) alignment layer C) electrode D) sheet of glass E) polarising filter CRT's look better because they are, this is mostly becuase of the resolution. The resolution on a LCD monitor for the size is MUCH smaller then an CRT, My 20inch monitor goes too 1920x1440, an LCD of equivalent size would g