Liquid crystals have been used for digital
calculators and watches for years, but the size
required had made them impractical for computer use.
Recent improvements in LCD technology reduced the
size of the LCD pixel to compare with the size of a
CRT pixel.
Liquid crystal displays operate on the principle of
scattering the light from an outside source to provide
the desired pattern. The display from a liquid crystal
is usually gray or black, but color can be achieved
through the use of filters or dyes. They require low
power and low voltage, making them ideal for laptop
and notebook computers.
In manufacturing LCDs, a clear, conductive
material is deposited on the inside surfaces of two
sheets of glass. This material acts as one electrode.
The liquid crystal material is then deposited on the
glass in the desired pattern. This pattern can be
segmented (watches and calculators), dot matrix
(graphic and computer screens), or a custom layout for
special purposes. A terminal conductor is connected
to an external terminal to control each liquid crystal.
The two sheets of glass are then hermetically sealed at
the edges.
Passive Matrix Liquid Crystal Displays
Passive matrix liquid crystal displays are used in
most monochrome and color laptop computers today.
The LCDs are arranged in a dot matrix pattern.
Resolution of 640 columns by 480 rows is not
uncommon.
Characters are formed by addressing
each row and column.
Color passive matrix LCDs use three layers of
crystals each separated by a color filter. Color is
achieved by energizing one, two, or all three LCDs for
each pixel.
Passive matrix LCDs have some distinct
disadvantages. They have low contrast. This lack of
contrast has required the addition of a backlight to aid
the user in viewing the screen. The response time to
turn the pixels on and off is too slow for full-motion
video and can produce a ghosting effect when
changing full-screen displays. Color passive matrix
LCDs are limited to displaying 16 colors
simultaneously, even though the VGA adapter can
have a palette of 262,144 colors.
Active Matrix Liquid Crystal Displays
Active matrix liquid crystal displays closely
emulate the capabilities of the full-color CRT. The
perfection of the thin film transistor (TFT) is largely
responsible for the development of the active matrix
LCD. Active matrix LCDs offer a brighter screen,
provide response times fast enough to accommodate
full-motion video, and can display 256 colors
simultaneously.
In manufacturing an active matrix display panel,
each pixel consists of three crystals, one each for red,
green, and blue. Three TFTs control each pixel, one
for each color. The TFT technology allows for entire
logic
circuits,
driver
circuits,
and
even
microprocessors to be deposited transparently on the
glass plates, increasing the brightness, speed, and
color quality of the display.
INPUT DEVICES
The displays discussed in this chapter are output
devices. They display information from the computer
for the user.
To allow the user to act on the
information being displayed, some type of input
device is required. The most common input device is
a keyboard.
Increasing in popularity are cursor
pointing devices such as the mouse or trackball.
KEYBOARD
The keyboard is the basic input device for
personal computers.
There are several styles of
keyboards available, but the most common one today
is the 101-key enhanced keyboard.
Keyboard Layout
The 101-key enhanced keyboard made several
improvements over the 84-key keyboard. Two new
function keys, F11 and F12, were added. The
function keys were moved from the left side of the
keyboard to the top of the keyboard. A group of
dedicated cursor and screen control keys were added
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