FAQs (Frequently Asked Questions)
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.
Q:
What kind of wide-angle technology is available? How does it work?
A:
The TFT LCD panel is an element that controls/displays the inlet of a backlight using
the dual-refraction of a liquid crystal. Using the property that the projection of inlet light
refracts toward the major axis of the liquid element, it controls the direction of inlet light
and displays it. Since the refraction ratio of inlet 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 CDT.
Usually, the viewing angle refers to the point where the contrast ration is 10. Many ways
to widen the viewing angle are currently being developed and the most common
approach is to use a wide viewing angle film, which widens the viewing angle by varying
the refraction ratio. IPS (In Plane Switching) or MVA (Multi Vertical Aligned) is also used
file:///H|/OEM MODELS/Philips 2008/CD MANUAL/190SW9 EDFU/190SW9 EDFU/lcd/manual/ENGLISH/190S9/safety/saf_faq.htm 第 6 頁 / 共 8 [2008/5/29 上午 11:35:14]
