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: How does a TFT LCD Panel work?
A: On each column and row of the TFT LCD panel, a data source drive and a gate drive are attached,
respectively. The TFT drain of each cell is connected to the electrode. The molecular arrangement of
liquid crystal elements differ acceding to whether it is impressed with voltage or not. It varies the
direction of polarized light and the amount of light by letting 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 the spiral
structure of the liquid crystal molecules and goes 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 through 90 degrees. In this case, light that
comes through the top polarized panel may not go through the polarized panel at the bottom.
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 a 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
file:///D|/My%20documents/dfu/B2C_TV/ENGLISH/170T4/safety/saf_faq.htm (6 of 8) [3/2/2004 3:46:29 PM]
