digital light projector

8/9/2019 Digital Light projector

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1. INTRODUCTION

Digital light processing or DLP, a TEXAS instrument technology, represents a

technology used in projectors and video projectors. One of its applications is the DLP

projector. This paper introduces a digital micro mirror device that receives a demanded

image to produce a video image that is projected onto a screen. DLP is one of the leading

technologies used in digital cinema projection. DLP projectors enjoy superior performance,

reduced volume and cheaper cost. DLP projectors utilize high luminance light streams

projected on display elements and reflect these light streams through a lens to reproduce

color images. A control method and a reflection principle are adopted in a DLP projector.

Thus DLP technology is an entirely digital design, the images produced are more stable and

precise than those generated by other technologies. So this paper shows the way to produce

a good quality image.



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2. DIGITAL MICRO MIRROR DEVICE

In DLP projectors, the image is created by microscopically small mirrors laid out in

a matrix on a semiconductor chip, known as a digital micro mirror device or DMD. This is

the key element of this technology. The figure shows a DMD. 800×600, 1024×768,

1280×720 and 1920×1080(HDTV) matrices are some common DMD sizes. This tiny

millions of mirrors make the picture amazing. DMD holds potential to provide a higher

luminous efficiency than other technologies. This is why DLP projectors are commonly

used in applications needing high resolution and high brightness.

Figure: 2-a

Digital Micro Mirror Device

2.1 DMD CONSTRUCTION

A DMD comprising a number of mirror elements with variable light reflection

angles adapted to change reflection angles of illumination light according to image signals so

as to reflect only the signal light required for forming an image toward a projection lens

system is used as image display. 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 (figure: 2-b).

The mirrors are made out of aluminum and are around 16µm in length. The mirrors

can be individually rotated at ±10° which correspond to an on or off state. This enables each

mirror to selectively reflect light to a photo detector or an absorbing surface. Each mirror



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represents one or more pixels in the projected image. The number of mirrors corresponds to

the resolution of the projected image.

Figure: 2-b

DMD

The DMD is a binary device and cannot represent analog grayscale levels. T o

generate grayscale images, the mirrors are pulse width modulated over the frame time. This

technique assigns a temporal weight to each bit in the grayscale intensity word.



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3. COLOR IN DLP PROJECTION

To create a color image in DLP projection systems, two primary methods are used.

One used by single chip projectors and other by three chip projectors. A third method,

sequentially illumination by three colored light emitting diodes, is being developed.

3.1 SINGLE CHIP PROJECTORS

In a projector with a single DMD chip, colors are either produced by wheel so that

placing a spinning color wheel between the lamp and the DMD or by using individual light

sources to produce the primary colors, LED s for example. The color wheel is usually

divided into four sectors: the primary colors: red, green and blue, and an additional clear

section to boost brightness(Figure: 3.1-a). 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 DMD chip is synchronized with the rotating motion of the color at the green

component is displayed on the DMD when the green section of the color wheel is in front

of the lamp. The same is true for the red and green sections. The red, green and blue images

are thus displayed sequentially at a sufficiently high rate that the observer sees a composite

´full color

image.

Figure: 3.1-a

A single chip projector design



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Thus, for portable applications, there is a field sequential color solution which

employs a color wheel and a single DLP chip. Light is delivered to the DLP which changes

from red to green to blue and the images delivered to the DLP chip are synchronized with

the changing colors. As a result, a color image is perceived by the viewer. A single chip

projector can produce at least 17 million colors. These projectors are used in TV·s, home

theatre systems and business projectors.

3.2 THREE CHIP PROJECTORS

A three chip 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(Figure: 3.2-a). 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. It·s more common to use a prism which makes it

necessary for only one topic, instead of three, and therefore removes the problem of color

separation.

Figure: 3.2-a

A three chip projector design The three-chip DLP projector used in movie theatres can produce 35 trillion colors,

which is more than the human eye can detect. The three chip projectors are used in cinema

and large venue displays to produce stunning images, whether moving or still. These

projectors have been in passive stereo systems. The images from the projectors are generally

orthogonally polarized.



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4. LIGHT SOURCE

The main light source used on DLP-based rear screen projection TVs is based on a

replaceable mercury vapor arc lamp unit, while in some newer DLP projectors high-power

LED·s are used as a source of illumination. The first commercially-available LED-based

DLP screen was the Samsung HL-S5679. Besides long lifetime eliminating the need for lamp

replacement and elimination of the color wheel, other advantages of LED illumination

include instant-on operation and improved color, with increased color saturation and

improved color gamut.

Ordinary LED technology does not produce the intensity and high lumen output

characteristics required to replace arc lamps. The special patented LED·s used in all of the

Samsung DLP TVs are Phlat Light LED·s, designed and manufactured by US based

Luminus Devices. PhlatLight LED·s long outstanding color quality, longevity and reliability

are well suited for high quality home theater, business and education projectors.

The PhlatLight LED·s are also used in a new class of ultra-compact DLP projector

commonly referred to as a ́ pocket projector¡

.

Home theater projectors will be the next category of DLP projectors

that will use PhlatLight LED technology. The other benefits of using PhlatLight technology

includes improved brightness, color, contrast, reliability, efficiency and environmental

friendliness.



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5. WORKING

The working of DLP projector can be explained on three steps:

5.1 THE SEMICONDUCTOR

At the heart of every DLP projection system is an optical semiconductor known as

the DLP chip (Figure: 5.1-a). The DLP chip is the world·s most sophisticated light switch. It

contains a rectangular array of millions of microscopic mirrors.

Figure: 5.1-a

DLP chip

When a DLP chip is coordinated with a digital video or graphic signal, a light source

and a projection lens, its mirrors can reflect a digital image onto a screen or other surface. A

DLP light engine directs white light from a lamp onto a color wheel producing red, green,

blue and white light. The DLP chip and the sophisticated electronics surrounding it are

called DLP technology.

5.2 THE GRAYSCALE IMAGE

A DLP chip·s micro mirrors are mounted on tiny hinges that enable them to tilt

either toward the light source in a DLP projection system (ON) or away from it (OFF)-

creating a light or dark pixel on the projection surface. The bit-streamed image code entering

the semiconductor directs each mirror switch on and off up to several thousand times per



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second. When a mirror is switched on more frequently than off, it reflects a light gray pixel: a

mirror that·s switched off more frequently reflects a darker gray scale (Figure: 5.2-a).

Figure: 5.2-a

Digital micro mirrors

To turn a pixel on, the respective mirror reflects the light into the engine·s optics. To

turn a pixel off, the mirror reflects the light away from the optics. When the DLP projection

system is under a light state, light beams projected onto the micro mirrors are reflected into

a projection lens by these micro mirrors and then focused on a screen. When the DLP

projection system is under a dark state, these micro mirrors are tilted to a specific angle, so

that light beams projected onto the mirrors are reflected to other directions.

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ADDING COLOR The white light generated by the lamp in a DLP projection system passes through a

color wheel as it travels to the surface of the DLP chip. The color wheel filters the light into

red, green and blue, from which a single-chip DLP projection system can create at least 17

million colors. And the three-chip system found in DLP cinema projection systems is

capable of producing no fewer than 35 trillion colors. The ON and OFF states of each

micro mirror are coordinated with these three basic building blocks of color.



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6. WHY DLP PROJECTORS?

The DLP projectors are more popular because of its good functional performance.

DLP projectors have many benefits than any other projection systems. so this chapter shows

the advantages of using a DLP projector.

6.1 PICTURE QUALITY

High native contrast ratio produces a vibrant image. Add to that the availability of

brilliant color technology, found in many DLP projectors, which employs multi-color

processing of up to six colors or more to produce the lifelike image. Figure: 6.1-a gives the

picture quality property.

Figure: 6.1-a Picture quality

6.2 FILTER-FREE DESIGN

Most DLP projectors feature a filter-free design. They also incorporate a completely

enclosed optical system to protect the critical imaging components. Dust, dirt and other

contaminants are less likely to degrade the projector·s picture overtime.

6.3

LOW MAINTENANCE

Low maintenance means lower cost. DLP technology enables a filter free design

and therefore does not require a filter. That saves time and money. DLP technology enables

filter-free design with sealed optics, to eliminate the need for periodic maintenance and filter

replacement.



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6.4 FASTER VIDEO PERFORMANCE

DLP projectors are ultra-fast, resulting in practically no blurring of video during

presentations, music videos, or other fast-motion video content.

6.5 SUPERIOR READABILITY

DLP projectors feature incredibly high native contrast ratios. Blacks are really black

whites are really white, making your projections extremely easy to read. Figure: 6.5-a shows

the readability of DLP projector. With DLP projectors high native contrast ratio, both song

lyrics and key sermon points are easier to read.

Figure: 6.5 -a

Superior readability

6.6 NO COLOR DECAY

DLP projectors are virtually immune to color decay, producing a sharp, clear image-

even after years of use. Because DLP projectors enjoy a technological advantage in

protecting against color decay (Figure: 6.6-a). Some LCD projectors may develop color

decay after extended use, making images and video look yellow or faded.

Figure: 6.6-a No color decay



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6.7 BRILLIANT COLORS

DLP projectors feature brilliant color technology, which processes up to six colors

or more resulting in stunning color performance. The color quality looks like real life. Figure:

6.7-a shows the brilliant color technology.

Figure: 6.7 -aBrilliant color technology

6.8 COMPACT AND LIGHTWEIGHT

DLP projectors use a single DLP chip, allowing an efficient design for lightweight,

portable projectors (Figure: 6.8-a). LCD systems require three imaging elements, which take

up space and add weight.

Figure: 6.8-a

Compact and light weight DLP



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7. DISADVANTAGES

The disadvantages of using DLP projectors are:

The ¶rainbow· effect, appearing as a momentary flash of rainbow- like striping

typically trailing the bright objects when looking from one side of the screen to the

other, or when looking away from the projected image to an off screen object.

Only some people see this effect.

The ¶halo· effect (or ¶light leakage·). It may bother some people using their

projector for home cinema. Basically it·s a grey band around the outside of the

image, caused by stray light being bounced off the edges of the tiny mirrors on

the DLP chip. It can be a distraction, but can be overcome by having a black border

a few inches wide around the screen, so the halo falls on to the border. However the

halo effect is less evident in the newer DLP chips.



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8. APPLICATIONS

They are used to Integrate inspirational videos, music and imagery to enhance the

message.

They can create a virtual hymnal by projecting lyrics.

They can be applied in projecting passages, prayers and responses.

They are used to celebrate events and anniversaries with a historical slideshow.

They are used as educational videos to engage students on a challenging topic.



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9. CONCLUSION

DLP is rapidly becoming a major player in every field. These new projectors will

improve the perceived image quality of many stereo systems since the projectors are very

bright, sharp and require less tuning and support. Progress continues to reach the best

quality stereo imagery through improved stereo glasses. DLP projectors do an excellent job

in its application field. This makes DLP an inevitable device.



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10.REFERENCE

LARRY J HORNBECK, ´DIGITAL LIGHT PROCESSINGµ.

WEBSITES:

a) www.dlp.com

b) www.wikipedia.org

c) www.aboutprojectors.com

d) www.ti.com

digital light projector

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