projection tv using dmd & glv chips full report

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-


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.



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



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.



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.



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



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:



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.



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



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.



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.



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.



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).



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.



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:



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.



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.



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



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.



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



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.



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.



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.



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,



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



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



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.



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



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.



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.



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.



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



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



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


projection tv using dmd & glv chips full report

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