by Faiz Rahman
If a picture is worth a
thousand words, then
moving pictures are surely
worth many thousands of
words. It is this great
descriptive power of moving
imagery that has made
televisions so popular.
Televisions were introduced in the
late 1930s and rapidly replaced radio
sets as the prime entertainment
appliance for the home. In most of the
intervening years, the only notable
development had been the appearance of color TVs in the 1950s. For
the past few years, however, there
have been several new developments
in television technology. The most
visible of these are the emergence of
new displays which are spoiling us for
choice in the marketplace.
FIGURE 1. A PDP cell, showing
the placement of discharge
electrodes, phosphor, and cell rib.
In this article, we will look at a
number of the most prominent display
technologies that are available on the
market. These include Plasma Display
Panels (PDPs), Liquid Crystal Displays
(LCDs), Digital Light Projection (DLP),
and Electronic Ink Displays (EIDs). The
last one is still under development and
is targeted at semi-static applications
such as changeable signage.
Televisions, of course, are not the
only devices that incorporate displays.
A wide variety of handheld gadgets,
outdoor information signs, computers,
and even movie theaters require
means for displaying stationary and
moving images. Advances in display
technologies have far reaching consequences because they touch almost
every aspect of modern life. For this
reason, it is important that we understand the basic technical features
behind the new generation of display
technologies. If nothing else, this will
help us make informed choices as
consumers of display equipment.
Few display technologies have had
such an impact on consumer sentiments as flat panel plasma displays. In
recent years, their outstanding visual
appeal has rejuvenated a languishing
TV market. Plasma displays are actually
quite old, having been invented in the
1960s by Donald Bitzer and Gene
Slottow at the University of Illinois. They
developed a prototype monochrome
display for use as computer monitors.
This initial device was basically an
array of neon-filled cells that could be
selectively excited by an AC voltage.
Making large dot matrix displays from
the Nixie tubes of the 1950s and 1960s
was a revolutionary idea. A few years
later, a license was purchased by IBM
who developed it further into the 3290
Information Panel that came out in
1983. In the years that followed, several
Japanese companies also became interested in this display technology, and
with the backing of the Japanese national broadcaster NHK, began to aggressively develop it for TV applications.
As a result of subsequent efforts
in the United States and Japan, these
displays changed from monochrome
to color and thus gradually evolved
from high-tech neon signs to dense
arrays of fluorescent lights.
Structurally, plasma display panels
consist of an array of gas discharge cells
like the one shown in Figure 1. An entire
panel is made from a honeycomb-like
sheet of millions of such chambers.
These cells are filled with a mixture of
inert gases, such as krypton and xenon,
at low pressure. Applying a high voltage
across such a cell ionizes the gas mixture and causes it to emit ultraviolet radiation. While ultraviolet itself is invisible,
it can be efficiently converted to visible
light with the help of luminescent materials called phosphors. Actually, each
pixel is composed of three sub-pixels:
one each for red, green, and blue colors.
The phosphors used with these