digital light processing

DIGITAL LIGHT PROCESSING Digital Micromirror Device 1

DIGITAL LIGHT

PROCESSING

JESSIE JAYE R. BALBIN, ECE, MEP-ECE


DLP

Digital Light Processing (DLP) is a trademark owned by Texas Instruments, representing a technology used in projectors and video projectors.

It was originally developed in 1987 by Dr.

Larry Hornbeck of Texas Instruments. In March 2008, TI announced the initial

production of the DPP1500 Chipset, which are micro projectors to be used in mobile devices.

Availability for final products would show up in

the market early 2009.


DLP chip


Digital Micromirror Device

A Digital Micromirror Device, or DMD is an optical semiconductor that is the core of DLP projection technology, and was invented by Dr. Larry Hornbeck and Dr. William E. Nelson of Texas Instruments (TI) in 1987.



A DMD chip has on its surface several hundred thousand microscopic mirrors arranged in a rectangular array which correspond to the pixels in the image to be displayed.

The mirrors can be individually rotated 10-

12, to an on or off state. In the on state, light from the projector bulb

is reflected into the lens making the pixel appear bright on the screen.

In the off state, the light is directed elsewhere (usually onto a heatsink), making the pixel appear dark.



To produce greyscales, the mirror is toggled on and off very quickly, and the ratio of on time to off time determines the shade produced (binary pulse-width modulation).

Contemporary DMD chips can produce up to 1024 shades of gray.

The mirrors themselves are made out of aluminium and are around 16 micrometres across



Applications

Televisions and HDTVs Holographic Versatile Discs Head-mounted displays DLP projector, Digital Light Processing (DLP)


Schematic Diagram of DMD


Color in DLP projection

There are two primary methods by which DLP projection systems create a color image, those utilized by single-chip DLP projectors, and those used by three-chip projectors.

A third method, sequential illumination by three colored light emitting diodes, is being developed, and is currently used in televisions manufactured by Samsung.


Single-chip projectors

In a projector with a single DMD chip, colors are either produced by placing a spinning color wheel between the lamp and the DMD or by using individual light sources to produce the primary colors, LEDs for example.


Single-chip projectors

The color wheel is usually divided into four sectors: the primary colors: red, green, and blue, and an

additional clear section to boost brightness.

Since the clear sector reduces color saturation, in some models it may be effectively disabled, and in others it is omitted altogether.

Some projectors may use additional colors (for example, yellow).

The color wheel technique was used in the early 1950s by the original CBS color television system before the standardization of NTSC color.


A single-chip projector alternates between

colors and produces separate red, green,

and blue images when displaying a moving

image, or in this case, illuminating a

moving hand.


The DLP "rainbow effect" in single-chip systems

This visual artifact is best described as brief flashes of perceived red, blue, and green "shadows" observed most often when the projected content features bright/white objects on a mostly dark/black background (the scrolling end credits of many movies are a common example).

Some people perceive these rainbow artifacts all of the time, while others say they only see them when they let their eyes pan across the image. The effect is likely rooted in the concept of the flicker fusion threshold


The DLP "rainbow effect" in single-chip systems

In some viewers the effect can lead to eye strain, headaches, or migraines after as little as a few minutes of viewing.

New LED based DLPs can produce the alternating images fast enough so that most people will not be affected by the rainbow effect.


Flicker fusion threshold

The flicker fusion threshold (or flicker fusion rate) is a concept in the psychophysics of vision.

It is defined as the frequency at which an intermittent light stimulus appears to be completely steady to the observer (centers around human observers).

Flicker fusion threshold is related to persistence of vision.



When fusion is attained, all that is needed to change the intensity is change the relative periods of light and darkness.

One can prolong the dark periods and thus darken, therefore the effective and average brightness are equal; this is the Talbot-Plateau law.



Another way to reduce the rainbow effect is to replace a segmented wheel with a wheel whose colors are in an Archimedean spiral.

This forms bands of color that move down (or up) the screen. With segmented wheels, the DMD must "go black" while the wheel transitions from one color to another.


Archimedean spiral

The Archimedean spiral (also known as the arithmetic spiral) is a spiral named after the 3rd century BC Greek mathematician Archimedes.

It is the locus of points corresponding to the locations over time of a point moving away from a fixed point with a constant speed along a line which rotates with constant angular velocity. Equivalently, in polar coordinates (r, ) it can be described by the equation

with real numbers a and b. Changing the parameter a

will turn the spiral, while b controls the distance between successive turnings.


Three 360 turnings of one arm of

an Archimedean spiral


Mechanism of a scroll pump


Three-chip projectors

A three-chip DLP projector uses a prism to split light from the lamp, and each primary color of light is then routed to its own DMD chip, then recombined and routed out through the lens.

Three-chip DLP projectors can resolve finer gradations of shade and color than one-chip projectors, because each color has a longer time available to be modulated within each video frame; furthermore, there won't be any flicker or rainbow effect like with the single chip solution.


Three-chip projectors

The three-chip projectors used in movie theaters can produce 35 trillion colors, which many suggest is more than the human eye can detect.

The human eye is suggested to be able to detect around 16 million colors


Light source

The main light source used on DLP-based rear screen projection TVs is based on a replaceable mercury vapor arc lamp unit (containing a quartz arc tube, reflector, electrical connections, and sometimes a quartz/glass shield),

In some newer DLP projectors high-power LEDs are used as a source of illumination.


Light source

The first commercially-available LED-based DLP screen was the Samsung HL-S5679W in 2006, which also eliminated the use of color wheel.

For spring 2008, the third generation of Samsung LED DLP products are available in 61" (HL61A750) and 67" (HL67A750)screen sizes.


Light source

At InfoComm, June 2008 Luminus and TI announced their collaboration on using their technology on home theater and business projectors and demonstrated a prototype PhlatLight LED based DLP home theater front projector.

They also announced products will be available in the marketplace later in 2008 from Optoma and other companies to be named later in the year.


Digital Cinema

DLP is the current market-share leader in professional digital movie projection, largely because of its high contrast ratio and available resolution as compared to other digital front-projection technologies.

As of December 2007, there are 5,827 DLP-based Digital Cinema Systems installed, of which 79% are in North America.

DLP projectors are also used in Real D Cinema for 3-D films.


Persistence of vision

Persistence of vision is the phenomenon of the eye by which even nanoseconds of exposure to an image result in milliseconds of reaction (sight) from the retina to the optic nerves.

This is because persistence of vision depends on chemical transmission of nerve responses, and this biochemical hysteresis is much slower than the light transmission.

Persistance of vision was discovered by a Roman poet by the name of Lucretius


Texas Instruments remains the primary manufacturer of DLP technology, which is used by many licensees who market products based on T.I.'s chipsets.

The Fraunhofer Institute of Dresden, Germany, also manufactures Digital Light Processors, termed Spatial Light Modulators, for use in specialized applications.

For example, Micronic Laser Systems of Sweden utilizes Fraunhofer's SLMs to generate deep-ultraviolet imaging in its Sigma line of silicon mask lithography writers.


Pros

Smooth (at 1080p resolution), jitter-free images.

Perfect geometry and excellent grayscale linearity achievable.

Usually great ANSI contrast.

No possibility of phosphor burn-in.

Less "screen door effect" than with LCD projectors.


DLP rear projection TVs are smaller, thinner, and lighter than CRT projectors.

DLP rear projection TVs are considerably

cheaper than LCD or plasma flat-panel displays and can still offer 1080p resolution.

The use of a replaceable light source means a

potentially longer life than CRTs and plasma displays (this may also be a con).

The light source is more-easily replaceable than

the backlights used with LCDs, and on DLPs is often user-replaceable.


New LED DLP TVs and projectors eliminate the need for lamp replacement.

Using two projectors, one can project full color stereoscopic images using polarized process (because beams can be polarized).

Lighter weight than LCD and Plasma televisions.

Unlike their LCD and Plasma counterparts, DLP screens do not rely on fluids as their projection medium and are therefore not limited in size by their inherent mirror mechanisms, making them ideal for increasingly larger high-definition theater and venue screens.


Cons

In single-chip designs, some viewers are bothered by the "rainbow effect," explained above.

Some viewers experience eye strain, headaches, and migraines when viewing DLP screens.

Not as thin as LCD or plasma flat-panel displays (although approximately comparable in weight), they are not able to be wall-mounted.


Replacement of the lamp / light bulb. The average life span of a TV light source averages 1-3 years (based upon how often the television is powered on and off and the duration of viewing) and the replacement cost for these range from $99 - $350, depending on the brand and model. After replacing the bulb a few times the cost can easily exceed the original purchase price of the television itself. Newer generations units use LED which effectively eliminates this issue, although a replacement bulb may be required over the extended lifespan of the television.

Some devices may have fan noise.

Silk screen effect


"Screen door effect" (SDE) may be visible at close distance and/or with lower resolution models (720p resolution and lower). SDE can also be perceived as artificially sharp looking (due to dark gaps between mirrors/pixels which are high frequency content, not part of the image displayed) and not film-like.

Dithering noise may be noticeable, especially in dark image areas. Newer chip generations have less noise than older ones

Error-diffusion artifacts caused by averaging a shade over different pixels, since one pixel cannot render the shade exactly.


Mediocre on-off contrast compared to CRT reference.

Response time in video games may be affected

by upscaling lag. While all HDTVs have some lag when upscaling lower resolution input to their native resolution, DLPs are commonly reported to have noticeably longer delays. Newer consoles such as the Xbox 360 and PlayStation 3 do not have this problem as long as they are connected with HD-capable cables.

Color rendition can be off, especially the bright

reds and yellows when at maximum brightness.


Lower viewing angle than direct-view technologies such as CRT, Plasma, and LCD.

Noise level is elevated due to two factors: The first

being due to the heat of the halogen light bulb (this lighting option is in the majority of DLP sets currently on the market) a fan is necessary to dissipate the heat built up. Many consumers may hear this fan during viewing and it will run for a few minutes even after powering off the set. The second issue is with the light engine itself (also called the color wheel), which may create a loud, high pitched whine as it spins to create the picture on screen. Many consumers have commented that this whine is not apparent in new sets but sets in as the TV ages. This is caused by the part beginning to fail, however this part is also replaceable and this noise goes away once the part has been replaced.


The DMD Widget (Chip) Tipped Mirrors & Missing Mirrors

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How the DMD Works

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How DLP Technology Works

The DMD Switches Light ...very quickly, to create the sensation of grayscale ...using a PWM algorithm.

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digital light processing

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