Projection TV using DMD & GLV ChipsSeminar Report ‘03
INTRODUCTION
If you're thinking about assembling a home theatre system, you may be
looking at large screen televisions as the heart of your system. Projection TV
could give you the size that you want -- CRT screens generally top out at 40"
(101 cm) or so, and at that size, they are huge and heavy. Plasma screens can be
bigger than that and still manageable, but they can be extremely expensive.
Projection TV technology can create large screen sizes at a reasonable price. Or
maybe you need to equip a room, like a classroom or conference room, for
multimedia presentations with a large audience. A projection TV gives you a lot
of flexibility and is usually much better than the standard combination of a
35mm slide projector, overhead projector and TV/VCR.
Projection systems are mainly divided into Transmissive and Reflective
projection TVs. In transmissive the Picture is produced when the light source
shines through an image. While in reflective projection TVS, the light source
illuminates the image formed, and this is reflected onto the screen
Presentations have moved from still pictures to animated, thus relying on
the digital media. Projectors of more picture quality have been a requirement.
Also with the concepts of ‘Home theatres’ imply for more picture quality than
what CRT and LCD projection systems provide.
In the field of reflective projection TVs the recent innovations are Digital
Mirror device and Grating Valve technologies. They have been able to produce
lager pictures at much higher resolution than the existing CRT and LCD
projection systems. Under constant research and designing, these technologies
are sure to replace the CRT tube forever.
Dept. of ECE MESCE Kuttippuram-1-
Projection TV using DMD & GLV ChipsSeminar Report ‘03
DIGITAL MICROMIRROR DEVICE (DMD)
Digital Micromirror Device (DMD) developed by Texas Instruments (TI)
is a new MEMS-based Digital Light Processor (DLP). The DMD microchip is a
fast, reflective digital light switch. It uses standard 5-volt addressing and is
fabricated with a monolithic, CMOS-compatible process. It can be combined
with image processing, memory, a light source, and optics to form a DLP
system capable of projecting large, bright, seamless, high contrast colour images
with better colour fidelity and consistency than current displays. DLP systems
can also be configured to project images for the production of continuous tone,
near photographic quality printing.
DMD Architecture:
A DMD consists of numerous (10,000 to 2million) micromirrors. The
configuration of the array is flexible, depending on the application. Each
micromirror is 16 µm square. The array places each micromirror on a 17 µm
pitch, leaving a gap of less than 1µm between the micromirrors. This results in a
>90% fill factor and is one significant advantage of the DMD.
Dept. of ECE MESCE Kuttippuram-2-
Projection TV using DMD & GLV ChipsSeminar Report ‘03
A single micromirror (pixel unit) can be distinguished to be made of four
layers.
1) CMOS Layer
It is the bottom most layer of the DMD. It consists of SRAM cells, one
for each mirror. Thus each mirror can be individually addressed.
2) Metal-3 Layer
This layer is just above the CMOS layer. The layer consists of the Yoke
address electrode and the Bias reset bus.
3) Yoke and hinge layer
The Yoke and the Mirror address electrodes constitute this layer. The
mirror is connected to an underlying yoke which in turn is suspended by two
thin torsion hinges to support posts. It is allowed to swing through ±10o from the
normal flat position. It is limited with a spring tip, as a mechanical stop.
4) Mirror
The mirror is connected to the Yoke at the centre such that it covers the
whole structure. The mirror is made of aluminium, selected as
Dept. of ECE MESCE Kuttippuram-3-
Projection TV using DMD & GLV ChipsSeminar Report ‘03
The micromirror superstructure is fabricated through a series of
aluminium metal depositions, oxide masks, metal etches, and organic spacers.
The CMOS layer protected with a protective layer, excluding the contact sites.
Then the metal layer is deposited over protective layer. A sacrificial layer
covers this layer to a height for which the yoke and hinge layer can be
deposited. Later the organic spacers are subsequently ashed away to leave the
micromirror structure free to move.
Dept. of ECE MESCE Kuttippuram-4-
Projection TV using DMD & GLV ChipsSeminar Report ‘03
Digital Nature of DMD:
A micromirror is said to be ‘ON’ or ‘OFF’ depending to which direction
the light is reflected. The optical switching function is the rapid directing of
light into and out of the pupil of the projection lens.
Dept. of ECE MESCE Kuttippuram-5-
Projection TV using DMD & GLV ChipsSeminar Report ‘03
The yoke is electrostatically attracted to the underlying yoke address
electrodes. The mirror is electrostatically attracted to mirror address electrodes.
The direction of rotation is selected by a pair of address electrodes on either side
of the rotation axis. The torsion beam rotates until its “landing” tip touches a
landing electrode pad that is at the same potential as the beam. Complementary
voltage waveforms (Ф1 & Ф2 address) are applied to these electrodes by an
underlying memory cell. A bias voltage applied to the beam makes the beam
energetically bistable. The result is lower address voltages, permitting larger
deflection angles. The mirror and yoke are connected to a bias/reset bus. The
address electrodes are connected to the underlying CMOS memory through via
contacts. Movement of the mirror is accomplished by storing a 1 or a 0 in the
memory cell (one address electrode at ground and the other address electrode at
VDD) and applying a bias voltage to the mirror/yoke structure. When this occurs,
the mirror is attracted to the side with the largest electrostatic field differential,
as shown in figure. To release the mirror, a short reset pulse is applied to the
mirror that excites the resonant mode of the structure and the bias voltage is
Dept. of ECE MESCE Kuttippuram-6-
Projection TV using DMD & GLV ChipsSeminar Report ‘03
removed. The combination of these two occurrences results in the mirror
leaving the landing site. The mirror lands again when the bias voltage is
reapplied.
DMD in Projection TV:
DMD Optical switching principle:
In projection display technology DMD entered as “picture on chip”. In
this procedure a single chip projection was used. A bright light source was made
incident to the DMD chip, such that in the ‘ON’ position the light would be
reflected into the focusing lens. In ‘OFF” position of the mirror the light would
reflect outside, onto an absorbing field. Thus on ‘ON’ position the pixel
corresponding to the screen would be bright; and ‘OFF’ as dark.
Greyscale:
Dept. of ECE MESCE Kuttippuram-7-
Projection TV using DMD & GLV ChipsSeminar Report ‘03
Gray scale was achieved using a technique called binary-weighted pulse
width light modulation. Because the DMD is a digital light switch, its only
capability is to turn light on or off. But because of the high switching speed,
(order of µsec) it was possible (during each video frame time) to produce a burst
of digital light pulses of varying durations that led to the sensation of grey scale
as perceived by the viewer.
In the case of colour projection, the same unique feature of speed was
utilized, but with Red, Blue and Green colours and more chips. There came
three types of projectors, based on economic to high end clarity.
Dept. of ECE MESCE Kuttippuram-8-
Projection TV using DMD & GLV ChipsSeminar Report ‘03
Address Sequence:
The address sequence to be performed once each bit time can be
summarized as follows:
1. Reset all mirrors in the array.
A voltage pulse or reset pulse is applied to the mirror and yoke, causing
the mirror and yoke to flex. Because this is done at the resonant frequency of the
mirror/yoke structure and this frequency is well above the resonant frequency of
the hinges, the hinges flex very little during reset.
2. Turn off bias to allow mirrors to begin to rotate to flat state.
During this period the SRAM loads the yoke address electrode. But the
mirror doesn’t deflect as bias is absent.
3. Turn bias on to enable mirrors to rotate to addressed states (+10/-10
degrees).
4. Keep bias on to latch mirrors (they will not respond to new address
states).
The mirror is at a stable state, as long as the bias is present.
5. Address SRAM array under the mirrors, one line at a time.
6. Repeat sequence beginning at step 1.
Colour Fidelity:
Current DMD architectures have a mechanical switching time of ~15 µs
and an optical switching time of ~2 µs. Based on these times, 24-bit colour (8
bits or 256 grey levels per primary colour) is supported in a single-chip
projector while 30-bit colour (10 bits or 1024 grey levels per primary colour) is
supported in a three-chip projector. Twenty-four-bit colour depth yields 16.7
million colour combinations while 30-bit colour depth yields more than 1 billion
Dept. of ECE MESCE Kuttippuram-9-
Projection TV using DMD & GLV ChipsSeminar Report ‘03
colour combinations. Even higher bit depths can be achieved by multiplexing
techniques.
Projection Systems:
Single Chip Projector:
The single-chip projector has a colour disc that alternately passes R, G,
and B to the DMD chip. Although the singe-chip diagram in figure includes an
integrator rod and TIR prism, these may be omitted in lower cost designs.
Without a TIR prism, the projection and illuminating lens will mechanically
interfere unless the projection lens is offset from the centre of the DMD. The
single-chip projector is self-converged, lower in cost and permits the very
lightest portable designs.
Two-Chip Projector:
The two-chip projector has a spinning colour disc that alternately passes
yellow light (R+G) and magenta light (R+B). The dichroic colour-splitting
prisms direct R continuously to one chip and G and B alternately to the second
chip. The colour which goes exclusively to one chip is determined by the
spectral content of the lamp. Metal-halide lamps have a high colour temperature
that produces higher intensities for GB compared to R. Therefore, for that type
of lamp, the red is directed exclusively to one chip. This makes up for the
deficiency in R and provides the correct colour balance for the projected
images. The two-chip projector provides greater light efficiency and is well
suited in applications requiring the very longest lifetime lamps that may be
spectrally deficient in the red.
Dept. of ECE MESCE Kuttippuram-10-
Projection TV using DMD & GLV ChipsSeminar Report ‘03
Three-Chip Projector:
The three-chip projector has one chip for each of the primary colours, red
(R), green (G), and blue (B). Light from an arc lamp is focussed onto an
integrator rod, which acts to homogenize the light beam and change its cross-
sectional area to match the shape of the DMD. The white light (W) then passes
through a total internal reflection (TIR) prism. The prism adjusts the incidence
angle of the light beam onto the DMD so the beam can be properly switched
into and out of the pupil of the projection lens by the rotating action of the DMD
mirrors. A set of dichroic colour-splitting prisms splits the light by reflection
into the primary colours and directs them to the appropriate DMD. The
modulated light from each DMD traverses back through the prisms that now act
as a combiner for the primary colours. The combined light (R, G, B) passes
through the TIR prism and into the projection lens. It is not reflected at the TIR
prism because the angle of incidence has been reduced below the critical angle
for total internal reflection. The three-chip projector has the highest optical
efficiency and is required in the brightest large-venue applications such as trade
shows and public information displays.
The light source is usually metal halide because of its greater luminous
efficiency (lumens delivered per electrical watt dissipated). A condenser lens
collects the light, which is imaged onto the surface of a transmissive colour
wheel. A second lens collects the light that passes through the colour wheel and
evenly illuminates the surface of the DMD. Depending on the rotational state of
the mirror (+10 or -10 degrees), the light is directed either into the pupil of the
projection lens (on) or away from the pupil of the projection lens (off). The
projection lens has two functions: (1) to collect the light from each on-state
mirror, and (2) to project an enlarged image of the mirror surface to a projection
screen.
Dept. of ECE MESCE Kuttippuram-11-
Projection TV using DMD & GLV ChipsSeminar Report ‘03
Dept. of ECE MESCE Kuttippuram-12-
Projection TV using DMD & GLV ChipsSeminar Report ‘03
Dept. of ECE MESCE Kuttippuram-13-
Projection TV using DMD & GLV ChipsSeminar Report ‘03
Reliability Factors:
Many aspects of DMD reliability are predictable because of the similarity of
the DMD to other semiconductor products. The DMD superstructure is
fabricated using most of the same materials and processes as other
semiconductor CMOS chips.
To test hinge fatigue as a potential failure mechanism, sets of devices have
been tested to over 1 x1012 (1 trillion) cycles using accelerated cycling. This is
equivalent to over 20 years of normal operation. No broken hinges were
observed. Considering that each chip had approximately 1 x 106 hinges, hinge
fatigue was shown not to be a reliability concern for the life of an ordinary
DMD product.
The DMD superstructure has an intrinsically high resistance to shock and
vibration because its modes of vibration have frequencies at least two orders of
magnitude above the frequency of vibration generated during normal handling
and operation.
To reduce stiction levels, a thin, self-limiting, anti-stick layer is deposited to
lower the surface energy of the contacting parts. This so called passivation step
is followed by hermetic packaging to keep water vapour levels low and to
prevent capillary condensation.
Dept. of ECE MESCE Kuttippuram-14-
Projection TV using DMD & GLV ChipsSeminar Report ‘03
GRATING LIGHT VALVE (GLV)
The Grating Light Valve technology is a means for manufacturing high-
performance spatial light modulators on the surface of a silicon chip. The
technology is based on simple optical principles that leverage the wavelike
behavior of light by varying interference to control the intensity of light
diffracted from each GLV pixel. A GLV array is fabricated using conventional
CMOS materials and equipment, adopting techniques of Micro-
Electromechanical Systems (MEMS).
GLV Architecture:
The GLV chip consists of tiny reflective ribbons mounted over a silicon
chip. The ribbons are suspended parallel over the chip with a small air gap in
between it and the substrate. This constitutes the 1080 pixels arranged linearly.
The linear GLV array's 1,088 pixels are at a pitch of 25.5 µm, thus giving a total
active area of 25µm by 27.7mm. The linear GLV array is surrounded by four
custom driver chips (each with 272 output stages) and assembled into a multi-
chip module. The primary function of the driver chips is to provide the digital-
to-analog conversion needed for analog grayscale control. A linear GLV array
can be used to modulate a single column of image data, while a mechanical scan
mirror is used to sweep that column across the field of view
A GLV pixel is an addressable diffraction grating created from moving
parts on the surface of a silicon chip. A typical GLV pixel about 25 microns
square in area and include six (even numbered) ribbons, each about 3 µm wide,
100 µm long, but only about 125 nm thick. These ribbons are suspended above
a thin air gap (typically about 650 nm).
Dept. of ECE MESCE Kuttippuram-15-
Projection TV using DMD & GLV ChipsSeminar Report ‘03
The ribbons are made of flexible silicon nitride, a ceramic material
chosen for its high tensile strength and durability. The ribbons are over coated
with a thin layer of aluminum that functions as both an optical reflector and an
electrical conductor. Integrated-circuit-like package with a clear, optically flat,
hermetically sealed glass lid. .
Working of GLV:
These ribbons are suspended above a thin air gap allowing them to move
vertically relative to the plane of the surface. The ribbons are held in tension,
such that in their unaddressed state, the surfaces of the ribbons collectively
function as a mirror. When a GLV pixel is addressed by applying an
electrostatic potential between the top of the ribbons and the substrate, alternate
ribbons are deflected. Viewed in cross-section (as in figure), the up/down
pattern of reflective surfaces creates a square-well diffraction grating. By
varying the drive voltage applied—and thus the grating depth—at each pixel,
we can achieve analog control over the proportion of light that is reflected or
diffracted.
Dept. of ECE MESCE Kuttippuram-16-
Projection TV using DMD & GLV ChipsSeminar Report ‘03
Precise control of the vertical displacement of the ribbon can be achieved
by balancing this electrostatic attraction against the ribbon restoring force; more
drive voltage produces more ribbon deflection.
Because the electrostatic attraction is inversely proportional to the square
of the distance between the conductors, and also because the distances involved
are quite small, very strong attractive forces and accelerations can be achieved.
These are counter-balanced by a very strong tensile restoring force designed
into the ribbons. The net result is a robust, highly uniform and repeatable
mechanical system. The combination of low ribbon mass, small excursions
(about 1/800 of the ribbon length), and large attracting and restoring forces
produces extremely fast switching speeds. GLV pixel switching times have been
measured down to 20nsec—three orders of magnitude faster than any other
spatial light modulator we have seen reported.
GLV in Projection TV:
Dept. of ECE MESCE Kuttippuram-17-
Projection TV using DMD & GLV ChipsSeminar Report ‘03
In the Scanned GLV Architecture, a linear array of GLV pixels is used to
project a single column of image data. This column is optically scanned at a
high rate across a projection screen. As the scan moves horizontally, GLV
pixels change states to represent successive columns of video data, forming one
complete image per scan. The high inherent switching speed of GLV devices
makes a scanned linear architecture, and its many benefits, possible. For
example, to create a 1,920 x 1,080-HDTV image with a 100 Hz refresh rate,
each column of video data is displayed in stasis for about 4.2 µs (assuming a
20% flyback time); this requires a pixel switching time significantly less than
4.2 µs.
High speed operation facts:
The on/off switching speed (or the time required to switch between any
other two arbitrary intermediate values) of the GLV device can be several orders
of magnitude faster than competing technologies. Specific GLV devices capable
of switching speeds as fast as 20 nanoseconds have been fabricated.
Dept. of ECE MESCE Kuttippuram-18-
Projection TV using DMD & GLV ChipsSeminar Report ‘03
The fundamental switching time of the GLV element is related to the
resonant mechanical frequency of the ribbon design, determined by such factors
as ribbon length, ribbon width, ribbon tension, ribbon mass, composition of the
surrounding atmosphere, etc. Because the GLV ribbon is a mechanical element,
it can be subject to resonance effects that manifest themselves as a “ringing”
characteristic following a step excitation. These dynamic effects can be
mitigated through the proper design of electronic drive circuitry and by "tuning"
the GLV device and its ambient atmosphere so that it is critically damped at its
natural frequency.
Optical working: Analog and Digital
When a pixel is not addressed, the undeflected ribbon surfaces
collectively form a flat mirror that reflects incident light directly back to the
source, as shown to the left of figure below. When a GLV pixel is addressed,
alternate ribbons deflect downward creating a square-well diffraction grating, as
shown to the right in the same figure. Varying the applied drive voltage—and
thus the grating depth—at each pixel controls the proportion of light that is
either reflected back directly to the source or diffracted.
Dept. of ECE MESCE Kuttippuram-19-
Projection TV using DMD & GLV ChipsSeminar Report ‘03
A Schlieren optical system is used to discriminate between reflected and
diffracted light. By blocking reflected light and collecting diffracted light, very
high contrast ratios can be achieved. We have measured the contrast of our GLV
device at up to 1,000:1 (the sensitivity of our instruments). Thus the GLV pixel
can be said to be in an ‘ON’ state when diffraction occurs and ‘OFF’ when it is
reflected out of the system. For analog grayscale operation, the 1 µsec switching
times shown is more than sufficient to create a 1,920 x 1,080 HDTV display at a
96 Hz refresh rate.
Digital operation capitalizes on the GLV technology’s tremendous
switching speed to achieve shades of gray by alternately switching pixels fully
“ON” and fully “OFF” faster than the human eye can perceive. Very accurate
grayscale levels are obtained by controlling the proportion of time pixels are on
and off. In analog mode, video drivers precisely control the amount of GLV
ribbon deflection; pixels are fully “off” when not deflected, and fully “on” when
Dept. of ECE MESCE Kuttippuram-20-
Projection TV using DMD & GLV ChipsSeminar Report ‘03
deflected downward exactly one-quarter the wavelength of the incident light.
Deflecting GLV ribbons between these two positions creates variable grayscale
intensity.
Dependence of Grating:
This grating introduces phase offsets between the wavefronts of light
reflected off stationary and deflected ribbons. The functional dependence of the
1st order diffraction lobes is:
Where Imax is the maximum 1st order diffracted intensity (at d = l/4), d
is the grating depth, and l is the wavelength of the incident light. By varying the
drive voltage applied—and thus the grating depth—at each pixel, we can
achieve analog control over the proportion of light that is reflected or diffracted.
Optical efficiency:
The optical efficiency of the GLV device depends on three main factors:
1) the diffraction efficiency, 2) the aperture ratio (the ratio of ribbon width to
ribbon gap) and 3) the reflectivity of the top layer material chosen. In an ideal
square-well diffraction grating, 81% of the diffracted light energy is directed
into the +/- 1st orders. Aluminum alloys typically used in semiconductor
processes allow cost-effective manufacture and are greater than 90% reflective
over most of the wavelengths used for optical communications and imaging
applications. Device efficiency, then, is the product of diffraction efficiency
(81%); fill factor efficiency (typically >95%), and aluminum reflectivity
(typically >91%). Overall, the device efficiency is about 70%, corresponding to
an insertion loss of about 1.5dB.
Dept. of ECE MESCE Kuttippuram-21-
Projection TV using DMD & GLV ChipsSeminar Report ‘03
Optical precision:
When a voltage is applied to alternate ribbons, the GLV device is set to a
diffraction state. The source light is then diffracted at set angles. These
diffraction angles are fixed with photolithographic accuracy when the GLV
device is manufactured. Therefore, very precise light placement is achieved
without the need for complex control electronics. This feature of the GLV
device allows for significantly smaller and less expensive packaging and lower
power requirements for optical components and subsystems.
GLV Driver Chips:
The custom GLV driver chips are very similar in function to standard
LCD column driver chips – they receive and present data to the modulator at the
line rate. The GLV drivers are designed for line times as short as 4 µs
(corresponding to a pixel rate of 250 kHz per drive channel), which is adequate
to support a 1,920 x 1,080 HDTV display at a 96 Hz refresh rate. Each driver
output is programmable to 256 levels. The shape of the driver response curve is
programmable, such that the effective grayscale resolution of the drive circuitry
very closely matches the inherent electro-optic response of the GLV device,
thus preserving effective grayscale resolution and eliminating banding or
Dept. of ECE MESCE Kuttippuram-22-
Projection TV using DMD & GLV ChipsSeminar Report ‘03
contouring at low light levels. A module operating all 1,080 channels at 8 bits at
a line rate of 250 kHz is capable of processing video data at well over 2
Gbits/sec!
Laser and lens system:
A specific example of illumination optics for a high power laser bar is as
shown below. The red laser bar illustrated consists of 24 emitters (each 1 µm
high by 40 µm in length) spaced along their long axis at a pitch of ~400µm. A
single cylindrical lens is used along the length of the bar for the fast axis
collimation, while a perpendicularly oriented cylindrical lens array achieves
collimation along the width of the bar. In this system, each of the 24 emitters is
imaged to completely illuminate the entire array. Such an illumination design
gives good uniformity (essentially the average of all 24 emitters) and also offers
protection against potential failure of any given emitter (one emitter failure
would result in about a 4% power loss, distributed evenly across all pixels.)
Even with this relatively complex optical source, an illumination efficiency of
>70% is achievable.
Dept. of ECE MESCE Kuttippuram-23-
Projection TV using DMD & GLV ChipsSeminar Report ‘03
Although a mechanical scanning component is not common to other high-
resolution displays, the scanner requirements of the Scanned Linear GLV
Architecture do not pose a significant system challenge, as the system needs
only scan at the refresh rate, not at the line rate.
Projection Systems:
GLV elements can be operated in either a digital mode (with alternate
ribbons either not deflected or deflected to precisely λ/4) or a continuously
variable analog mode (with alternate ribbons deflecting to positions between
zero and λ/4). Results with actual projection display systems yield unparalleled
on-screen performance, having uniformity greater than 99% corner-to-corner,
high contrast, 10-bits of grayscale per color, and no visible pixel boundaries. A
linear GLV array can be used to modulate a single column of image data, while
a mechanical scan mirror is used to sweep that column across the field of view
Single chip refractive method:
One way of reproducing color images is by using different ribbon pitch
to create a red-green-blue pixel "triad" instead of the monochrome pixel
described earlier (see figure below). In such a system, white light is introduced
at an angle slightly out-off--axis of the GLV device. In essence, the red area,
having the widest pitch, refracts red light normal to the GLV plane while green
and blue light is refracted at other angles.
Dept. of ECE MESCE Kuttippuram-24-
Projection TV using DMD & GLV ChipsSeminar Report ‘03
The green and blue areas, having narrower pitch, do the same for green
and blue light, respectively. Color is produced by reducing the slit width to
allow only a limited bandwidth about each of the primary colors to be selected.
Single chip method:
In a frame-sequential projection system (figure below) a white light
source is filtered sequentially (by a spinning red-green-blue filter disk, for
instance). By synchronizing the image data stream’s red, green and blue pixel
data with the appropriate filtered source light, combinations of red, green and
blue diffracted light is directed to the projector lens. In this system, as shown, a
turning mirror is used both to direct light onto the GLV device, and as an optical
stop blocking reflected light.
Dept. of ECE MESCE Kuttippuram-25-
Projection TV using DMD & GLV ChipsSeminar Report ‘03
Single chip RBG method:
An even simpler, handheld, color display device uses three LED sources
(red, green and blue). A single GLV device diffracts the appropriate incident
primary -colour light to reproduce the color pixel information sent to the
controller board.
Three-Chip projection method:
A more elaborate and accurate color projection system can be build using
three GLV devices. By passing the source’s white light through dichroic filters,
Dept. of ECE MESCE Kuttippuram-26-
Projection TV using DMD & GLV ChipsSeminar Report ‘03
red, blue and green light are incident on three separate GLV devices. Diffracted
light is collected and directed through the optical system to a viewing screen.
This represents a much smaller and lower-cost solution, say, to the three-tube
projection systems now used for large screen projection of PC images and
videos.
RELIABILITY FACTORS:
The pixel was operated at 2 MHz – accelerated approximately 8 times
over its normal 250 kHz switching rate – and 20o C, for approximately 20 days.
The GLV pixel product design life of between 1013 and 1014 switching cycles.
For comparison, operating at a 100 Hz frame rate with 1,920 lines for 10,000
hours requires approximately 7 x 1012 cycles.
The ribbon natural frequencies decreased by ~ 2.5% as the temperature
changed from 18 to 100o C because the ribbon's positive temperature coefficient
resulted in less ribbon tension.
A higher incident power, orders of 30W, causes the GLV ribbon to heat
and linearly expand, thus reducing its tension and its natural frequency. The
same heating causes the device fill gas to become more viscous, thus increasing
Dept. of ECE MESCE Kuttippuram-27-
Projection TV using DMD & GLV ChipsSeminar Report ‘03
the damping time. But again, after an initial burn-in cycle and a ~0.5% change,
the resonant frequency and damping factor are stable over time at both low and
high operating powers.
Video Processing:
For GLV projectors, the system receives 1080p video data at 24 or 30
fps via a standard SMPTE 292M serial digital interface. The electronics
architecture supports the following system performance:
• 1920 x 1080 resolution
• Up to 120 Hz refresh, progressive scan
• 10 bits/channel R, G, B
The SMPTE 292M serial digital input contains luma (lightness) for all
pixels and chroma (red and blue color difference) for odd pixels. The even pixel
chroma values are generated by FIR filtering the red and blue chroma input. The
luma and chroma are decoded into red, green, and blue with gamma using
multipliers and adders. The use of 16-bit table entries results in maintaining a
human-perceived signal quality while RGB is expressed in linear intensity.
This step maps RGB intensity to the GLV intensity voltage characteristic.
Conventional spatial light modulators that create grayscale values through
digital pulse width modulation have an inherently linear optical response.
However, the inherent GLV electro optic response creates a natural, continuous
grayscale with wide dynamic range that is well matched to the human visual
system (Figure 5). Due to this mechanical simplicity, the GLV response is
highly predictable and can be mathematically calculated from relatively simple
models. If only a few data points near the peak intensity and maximum slope of
the I/V response curve are collected, the rest of the curve can be calculated with
a high degree of accuracy. Since the linear GLV array uses only a small number
Dept. of ECE MESCE Kuttippuram-28-
Projection TV using DMD & GLV ChipsSeminar Report ‘03
of physical pixels, each pixel can be exercised and the data necessary to fully
calibrate the complete image can be collected using a simple optical integrator
and single point detector. This simplicity enables a calibration technique that
can efficiently measure all sources of variation within a system (particularly
non-uniformities introduced by the system optics) and adjust the response of
each pixel to show the highest quality image at all times.
The SMPTE 292M input is row-centric, meaning the video data is
presented sequentially by row. Since the scanned linear GLV system as
currently implemented scans left to right by column, a frame buffer is used to
store data by rows and transpose it into column data for display. Since higher
refresh rates produce better image quality, the frame buffer accepts progressive
data at the source rate and sends it out at a faster rate for display. The frame
buffer in the current system typically reads data in at 24 or 30 fps and refreshes
the display up to four times the input rate.
By refreshing the display 3 or 4 times per frame, we can achieve 1.6 or 2
additional effective bits of grayscale through dithering. Through temporal
dithering, the system exploits the GLV device’s inherent speed and the novel
scanned line approach to achieve 10-bit grayscale using simpler and lower cost
8-bit drivers. For example, suppose the display needs to show the 10-bit
grayscale value of 201.75. Using 8-bit drivers and temporal dithering, the
system would display the refresh sequence below. Because we dither only the
least significant bit(s), no flicker is perceived.
Dept. of ECE MESCE Kuttippuram-29-
Projection TV using DMD & GLV ChipsSeminar Report ‘03
Benefits of horizontal scan:
First, it requires a smaller and less expensive linear GLV array (1080
pixels vs. 1920 pixels, a 44% pixel count reduction). Second, this smaller
modulator allows additional system cost savings, such as smaller recombination
and projection optics, smaller look-up tables, etc. Lastly, a horizontal scan also
enables electronic support for variable aspect ratios (Figure 5). For example, a
horizontal scan system can easily change from 4:3 to 16:9 for HDTV or from
flat (1.85) to cinemascope (2.35) for electronic cinema, without requiring
anamorphic lenses or complex scaling algorithms that tend to degrade image
quality
Dept. of ECE MESCE Kuttippuram-30-
Projection TV using DMD & GLV ChipsSeminar Report ‘03
COMPARISON OF DMD AND GLV TECHNOLOGY
Even if GLV technology involved column scanning to produce a
complete picture, its architecture over rules the possibility of DMD being better.
GLV had significant aadvantages over DMD as given below.
1. Significantly faster operating speeds.
At the order of 2µsec which is much higher than of DMD.
2. High optical efficiency (low insertion loss)
As GLV chip has high fill factor (of 95%) and continuous nature of the
pixels.
3. Continuously variable attenuation that is highly accurate and repeatable
GLV pixels can be varied dynamically, compared with DMD only
digitally.
4. Optical angular repeatability that is permanently set with photolithographic
precision
Any slight change in the DMD structure can result the light reflected at
some other angle.
5. No contact surfaces — high reliability and stability.
The DMD had to place springs and anti-stick layers (Teflon) so that the
mirrors didn’t stick to either sides of operation.
6. Scalability to very large numbers of separately addressed channels
7. Ease of manufacturing
The number of steps for manufacturing GLV chips is much lower than
that for DMD.
8. Ease of integration with CMOS logic.
Dept. of ECE MESCE Kuttippuram-31-
Projection TV using DMD & GLV ChipsSeminar Report ‘03
The GLV chip, having a linear structure, has its CMOS logic on either side.
But for DMD they are under the mirror and have to be fabricated before the mirror
level is.
Dept. of ECE MESCE Kuttippuram-32-
Projection TV using DMD & GLV ChipsSeminar Report ‘03
CONCLUSION
With these technologies projection TVs have become much more
meaningful. GLV and DMD Projection TVs have shown much higher quality
pictures and videos than any other. In the era where everything is getting
digitised, they will surely replace CRT technology.
For those who wished to bring essence of theatres into their homes have
now a dream come true.
Dept. of ECE MESCE Kuttippuram-33-
Projection TV using DMD & GLV ChipsSeminar Report ‘03
REFERENCES
1. Texas Instruments World Wide Web site http://www.ti.com/dlp
2. Silicon Light Machines Website www.slm.com
3. J.M. Younse, "Mirrors on a Chip," IEEE Spectrum, pp. 27-31
4. www.howstuffworks.com
Dept. of ECE MESCE Kuttippuram-34-
Projection TV using DMD & GLV ChipsSeminar Report ‘03
CONTENTS
INTRODUCTION
DIGITAL MICROMIRROR DEVICE (DMD) CHIP
DMD ARCHITECTURE
DIGITAL NATURE OF DMD
DMD IN PROJECTION TELEVISION
DMD OPTICAL SWITCHING PRINCIPLE
GREYSCALE
PROJECTION SYSTEMS
RELIABILITY FACTORS
GRATING LIGHT VALVE (GLV) CHIP
GLV ARCHITECTURE
WORKING OF GLV
GLV IN PROJECTION TV
OPTICAL WORKING: ANALOG AND DIGITAL
BENEFITS OF HORIZONTAL SCANNING
COMPARISON OF DMD & GLV TECHNOLOGIES
CONCLUSION
REFERENCES
Dept. of ECE MESCE Kuttippuram-35-
Projection TV using DMD & GLV ChipsSeminar Report ‘03
ACKNOWLEDGEMENT
I extend my sincere thanks to Prof. P.V.Abdul Hameed, Head of
the Department for providing me with the guidance and facilities for the
Seminar.
I express my sincere gratitude to Seminar coordinator
Mr. Manoj K, Staff in charge, for his cooperation and guidance for
preparing and presenting this seminar.
I also extend my sincere thanks to all other faculty members of
Electronics and Communication Department and my friends for their support
and encouragement.
Rajneesh C
Dept. of ECE MESCE Kuttippuram-36-