FIGURE 3. A packaged DLP chip from
based TVs are currently not available
in quite as large screen sizes as PDP-based units. Continued progress in the
development of very high brightness
LED-based backlights and more controlled TFT process technologies will
lead to larger LCD panels in the future.
Digital Light Projection
Unlike plasma and liquid crystal
displays, Digital Light Projection (DLP)
technology forms images by projecting
a pattern of light and dark areas on a
translucent screen. The projector is a
specialized semiconductor chip that
carries an array of tiny movable mirrors
on its top surface. This Micro ElectroMechanical System (MEMS) device is
a true marvel of modern engineering
in that it can digitally switch an image
mosaic accurately and at very high
FIGURE 4. A commercial digital
cine projector from Barco.
speeds. The DLP device is capable of
steering light from a lamp source to a
viewing screen, creating images of
outstanding sharpness and vibrancy.
Invented by Larry Hornbeck of
Texas Instruments (TI) in 1987, the
DLP chip — which goes by the name
of Digital Micromirror Device (DMD),
combines both video processing and
light switching functions on a two
tier platform (see Figure 3 for what a
typical packaged chip looks like).
The MEMS mirror assembly is a
two-dimensional array of hinged mirror
flaps and piezoelectric actuators that sit
atop a CMOS under-layer that contains
processing and drive circuitry. The entire
chip is the same size as other commercial large size chips (about 1.5” x 1.5”).
A complete projection system is somewhat complicated as it has to include
such elements as a light source, filter
wheel, and various mirrors and lenses.
The projection assembly works by directing light from a powerful lamp, through a
red-green-blue filter wheel, on to a DLP
chip. The DMD mirror array then selectively projects a pixel pattern, through a
projection lens, on to a screen. Red,
green, and blue partial images are
thus projected in quick succession as the
filter wheel rotates. The three primary
color images get blended together and
one sees a composite full-color image.
The display screen itself could be
integrated with the rest of the system in
a short distance projection configuration
for producing domestic DLP televisions
or it could be a remote screen as in
movie theaters. In the latter case, of
course, especially powerful lamps have
to be used in order to provide sufficient
light for wide screen illumination.
A Rise in DLP Usage
Several consumer electronics companies are now offering DLP televisions
and these are rapidly replacing traditional CRT-based sets on account of their
much superior resolution and color
saturation properties. The high intensity
tungsten-halogen lamps in these sets
have a limited lifetime of 5,000 to
10,000 hours of continuous operation.
These are somewhat expensive but not
too difficult to replace. Needless to say,
all digital projection systems currently
rely on Texas Instruments’ DLP chips, as
no other company has developed any
alternative to this technology. The rest of
the projection system is built by major
manufacturers and purchased by smaller
companies. The much touted digital
projection cinema is also being enabled
by DLP technology. As digital cine-print
distribution and security issues are
resolved, we will see a steeper rise in
digital projection-equipped theaters
around the world. As opposed to
conventional film projection, digital
distribution and projection offers many
benefits such as low cost of print duplication, fast worldwide distribution, and
multiple screenings with the same digital
copy. In addition, 3D movies in the
IMAX format, projected with twin projectors, are particularly suited to digital
projection techniques and these might
make a big comeback with the advent
of mainstream digital projection cinemas. A digital cine projector from Barco
is shown in Figure 4. Such projectors are
commercially available now and are set
to claim a bigger share of the market as
digital projection gains further ground.
Yet another technology that is
under rapid development is the so-called electronic ink or E-ink that offers
extremely low power consumption
and is suitable for semi-static display
applications such as information
update panels, clocks, and books. Sony
Corporation has already introduced an
E-book called Libre that uses E-ink
technology developed by E-ink and
Toppan Corporations. Electronics manufacturers in Europe are also eyeing
this development for producing road-side signage and public information
display systems. Even more products
are expected in the next few years.
What is E-ink Made Of?
E-ink consists of millions of microcapsules, each filled with two types of
pigments, suspended in a clear fluid.
One pigment is white in color and
carries a permanent positive charge
while the other is black in color and
carries a permanent negative charge.
These ‘electrophoretic’ pigments make