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Application Report
DLPA022–July 2010
DLP™ System Optics
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ABSTRACT
This application note describes typical architectures for optical systems employing a single DMD device
for projection applications, primarily for small portable projectors. Pros and cons of architectures are
discussed in general terms. Front- and rear screen applications are discussed briefly. Techniques and
trades for maximizing critical system performance parameters, defined by the application, are discussed.
Unique considerations for DMD devices in optical systems are addressed. A general discussion of image
quality and specific design metrics for acceptable performance is included.
Note the majority of this document describes the use of the DMD in a projection optical system, and the
DMD is designed with this application in mind. However, there are many other ways to use the DMD to
manage and steer light energy. This document addresses some of the non-projection applications briefly,
but cannot anticipate all uses.
Contents
1 Overview of DMD Use in Projection Optical Systems .................................................................. 2
2 Projection Optical System Architectures ................................................................................. 2
2.1 Telecentric Architectures .......................................................................................... 3
2.2 Nontelecentric Architectures ...................................................................................... 5
3 Projection Optical System Design Considerations ..................................................................... 8
3.1 Illumination-System Components and Design Parameters ................................................... 8
3.2 Projection-System Components and Design Parameters ................................................... 13
4 System Performance Tuning Tips and Techniques ................................................................... 15
4.1 Contrast Ratio ..................................................................................................... 15
4.2 Lumens ............................................................................................................ 19
4.3 Optimizing Optical Costs ........................................................................................ 19
5 Alternate Light Sources and Systems .................................................................................. 21
5.1 LED Sources ...................................................................................................... 21
5.2 Laser Sources ..................................................................................................... 24
5.3 Non-Imaging or Non-Projection Applications ................................................................. 25
List of Figures
1 Simplified Optical Function of a 12-Degree-Mirror-Tilt Device........................................................ 2
2 Generic Telecentric Optical System Components Using a TIR Prism............................................... 3
3 Telecentric TIR Prism Design Layout for Minimum Package Height Due to Projection-Lens Offset ........... 4
4 Nontelecentric Optical-System Components............................................................................ 6
5 Effect of Projection Offset on Illumination Angle, Nontelecentric Design, Side View.............................. 7
6 Nontelecentric Optical Layout for Flat Projector Using Reflective and Refractive Illumination Elements
(Isometric View) ............................................................................................................. 7
7 Spatial Irradiance Distribution of a Small-Arc Lamp at Focus of Elliptical Reflector Before Integration (left,
at rod input) and After Integration (right, at rod output) .............................................................. 12
8 Frustrated TIR in TIR Prism Air Gap Should be Biased Toward Illumination Path............................... 13
9 Scattering Incident-Beam Geometry.................................................................................... 16
10 Scattered Light Into Projection Pupil for Off-State Mirror, 10-Degree Device ..................................... 16
11 Contrast and Lumens as a Function of Illumination Angle for F/3 Telecentric System ......................... 17
12 Keystone Distortion for 0.9 XGA by Throw Ratio and Offset ........................................................ 20
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DLPA022–July 2010 DLP™ System Optics
Copyright © 2010, Texas Instruments Incorporated
