A: A Liquid Crystal Display (LCD) is an optical device that is commonly used to
display ASCII characters and images on digital items such as watches, calculators,
portable game consoles, etc. LCD is the technology used for displays in notebooks
and other small computers. Like light-emitting diode and gas-plasma technologies,
LCD allows displays to be much thinner than cathode ray tube (CRT) technology.
LCD consumes much less power than LED and gas-displays because it works on the
principle of blocking light rather than emitting it.
Q:
What differentiates passive matrix LCDs from active matrix LCDs?
A: An 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
(your mouse pointer will appear to move more smoothly across the screen, for
example). The passive matrix LCD has a grid of conductors with pixels located at
each intersection in the grid.
Q: What are the advantages of TFT LCD compared with CRT?
A: In a CRT monitor, a gun shoots electrons and general light by colliding polarized
electrons on fluorescent glass. Therefore, CRT monitors basically operate with an
analog RGB signal. A TFT LCD monitor is a device that displays an input image by
operating a liquid crystal panel. The TFT has a fundamentally different structure than
a CRT: Each cell has an active matrix structure and independent active elements. A
TFT LCD has two glass panels and the space between them is filled with liquid
crystal. When each cell is connected with electrodes and impressed with voltage, the
molecular structure of the liquid crystal is altered and controls the amount of inlet
lighting to display images. A TFT LCD has several advantages over a CRT, since it
can be very thin and no flickering occurs because it does not use the scanning
method.
Q: Why is vertical frequency of 60Hz optimal for an LCD monitor?
A: Unlike a CDT monitor, the TFT LCD panel has a fixed resolution. For example, an
XGA monitor has 1024x3 (R, G, B) x 768 pixels and a higher resolution may not be
available without additional software processing. The panel is designed to optimize
the display for a 65MHz dot clock, one of the standards for XGA displays. Since the
vertical/horizontal frequency for this dot clock is 60Hz/48kHz, the optimum frequency
for this monitor is 60Hz.
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