LEDs an der Schwelle zum Einsatz in Projektionssystemen: Herausforderungen, Grenzen und Anwendungen Dr. Anton Moffat Carl Zeiss Corporate Research Carl Zeiss AG, Jena, Germany moffat@zeiss.de
Contents Introduction System Design Methodology Applications Conclusions Moffat / CZ AG / LEDs an der Schwelle zum Einsatz in Projektionssystemen -2-
Introduction Motivation for using LEDs: Colours, Lifetime, Colour Saturation > 100% NTSC achievable for saturated colours Colour space can be made to match video standards exactly Selectable white point Many More: Cost More suppliers Simple electronics Instant on/off Low voltage Low pressure Colour Break-Up reduction No Colour Wheel: noise reduction Lifetime Conventional Lamp: 50% preserve 50% brightness in x h, 1/2 can fail Guarantee for a few 100 h Semiconductor Lamp MTTF with confidence > 9x% Intensity degradation < 30% in 10.000 h Guarantee is given for years Moffat / CZ AG / LEDs an der Schwelle zum Einsatz in Projektionssystemen -3-
Introduction Timeline Starts Now for LED-Based Projection Systems Critical threshold is screen brightness LED Roadmap Highly optimized electro-optical system Customer Threshold Standard Optical System with LEDs 2006 2008 2010 Moffat / CZ AG / LEDs an der Schwelle zum Einsatz in Projektionssystemen -4-
Introduction DMD Microdisplays for High Light Throughput at High Contrast 120 W Lamp : 6000-7000 Lumens 4000 5000 in Aperture 500-1000 out of projector ~10% light throughput standard Goal: reach same screen brightness (Nits) with only ~1000 Lumens from LEDs LCD High light throughput Large area microdisplays: 0.7", 0.85", 0.9" diagonal Wide opening angle optics (Low F/#) Liquid Crystal Imagers (LCD, LCOS) Three panels with colour combiner for polarized light Required low F/# limits constrast ratio LCOS Digital Micromirror Device (DMD) Single panel requires sequential colour Moffat / CZ AG / LEDs an der Schwelle zum Einsatz in Projektionssystemen -5- DMD
Geometrical Optical Requirements DMD is the key component Etendue is the geometric extent of the optical system E = π n² A sin²θ Component with the smallest etendue limits the brightness of the system (usually the DMD) x LED small area, large angle DMD large area, small angle x Geometrical match: etendue, aspect ratio, overfill Moffat / CZ AG / LEDs an der Schwelle zum Einsatz in Projektionssystemen -6-
Geometrical Optical Requirements Useable System Etendue Practical Limit on Light Source Area N max 30 25 Relative Intensity Itotal( A) Iuseable( A) 20 15 10 5 0 0 0 5 10 15 20 25 30 0 A Emitting Area (mm²) N max +/-60 xhd4 F/2.0 Moffat / CZ AG / LEDs an der Schwelle zum Einsatz in Projektionssystemen -7-
Geometrical Optical Requirements Available DMDs Determine Useable System Etendue DMD Diagonal Resolution DMD Size Area F/2.0 Etendue Max Area (mm²) (pixels) (mm²) (mm²) (mm² sr) (Surface Emitter) xhd5 0.67" 1920 x 1080 14.74 x 8.29 122.2 24.1 7.7 HD2+ 0.78" 1280 x 720 17.51 x 9.85 172.5 34.0 10.8 xhd4 0.85" 1920 x 1080 18.67 x 10.51 196.2 38.6 12.3 sxhd5 0.88" 2560 x 1440 19.58 x 11.02 215.8 42.5 13.5 Larger DMD More Light ~ DMD area But: System is larger and more expensive: Larger optics ~ DMD diagonal Larger LED area ~ DMD area + Overfill 10..20% Moffat / CZ AG / LEDs an der Schwelle zum Einsatz in Projektionssystemen -8-
Geometrical Optical Requirements Low F-number for Higher Light Throughput Projection Lens Projection Lens Illumination DMD F/2.4 (standard) DMD F/2.0 (wider opening) larger optics ~30% more light throughput Moffat / CZ AG / LEDs an der Schwelle zum Einsatz in Projektionssystemen -9-
System Design Methodology Goals: Maximum Screen Brightness Good Image Quality Competitive Cost Optimize combination of parameters: Optical (light throughput, image quality) Electrical (driving conditions, power consumption) Thermal (heat dissipation, operating temperature) Upstream design: from the screen through the lens to the LED (surface emitter) instead of to the lamp (volume emitter) Moffat / CZ AG / LEDs an der Schwelle zum Einsatz in Projektionssystemen -10-
Basic Projection System Design DMD Lamp-based System White light source with rotating colour wheel DMD Digital Micromirror Device F/2.4 Standard opening optics Screen Colour Wheel Projection Lens F/2.4 Optical Iris Relay Optics Mirror UHP Lamp UV, IR Filter Integrating Rod Field Lens DMD Colour Wheel Rotation Sensor Sync Video Electronics Moffat / CZ AG / LEDs an der Schwelle zum Einsatz in Projektionssystemen -11-
Basic Projection System Design DMD LED-based System 3 coloured light sources, electronically controlled DMD Digital Micromirror Device F/2.0 Wider opening optics Screen Projection Lens F/2.0 Collection Optics Dichroic Mirrors Relay Optics Red LED Mirror Heat Sink Green LED Blue LED Microlens Array DMD Field Lens LED Driver Trigger, Dimming Video Electronics Moffat / CZ AG / LEDs an der Schwelle zum Einsatz in Projektionssystemen -12-
LED Module Configuration Since LEDs are brightness-limited, make full use of available etendue NB. Additional constraints imposed by power consumption, heat dissipation, manufacturing tolerances, cost,... Monolithic Solution: Pro: Con: Efficient matched geometry Costs for yield and custom size Spec. uniformity across chip area Thermal stress in pulsed operation Large drive currents Tiled Solution: Pro: Con: Standard LED chips as building blocks Low Current, Voltage for LED-Strings Less efficient gaps, approx. geometry Spec. uniformity across chips on a module 2xN arrays (favoured due to bond wires) Moffat / CZ AG / LEDs an der Schwelle zum Einsatz in Projektionssystemen -13-
Available LED Light Sources Osram Ostar: 12 chips (two 2x3 arrays) with primary optics Luminus PhlatLight : PT85 (1-chip), PT180 (4-chips) Input power 10 60 Watts Peak output power approx.: 200mW/mm² Green 400mW/mm² Red, Blue PhlatLight Here: Experimental results based on Osram Ostar Method applies to other LED architectures Ostar Moffat / CZ AG / LEDs an der Schwelle zum Einsatz in Projektionssystemen -14-
Physical Optical Requirements Colour primaries and white point Potential to display oversaturated colours Can dynamically adjust illumination source to video standards Need an initial setup, specific to each set of LED subassembly Green Red Blue (4000K..15000K) Moffat / CZ AG / LEDs an der Schwelle zum Einsatz in Projektionssystemen -15-
Electro-Optic Transfer Function (EOT) Basic System Performance Data to Optimize Driving Conditions Vary driving conditions one at a time Measure system output EOT data to optimize driving conditions and establish correlation with testing conditions Driving Conditions LEDs Optical System EOTs Current Temperature Duty Cycle Red Green Blue Dichroic mirrors Lens coatings DMD Integrating sphere Spectrometer Moffat / CZ AG / LEDs an der Schwelle zum Einsatz in Projektionssystemen -16-
Driving Conditions Approximately Equal Radiant Power for RGB at the White Point Green determines the Luminous Output Red and Blue need ~ equal Radiant Flux! Optimize driving conditions current density temperature duty cycle Watts Lumens Moffat / CZ AG / LEDs an der Schwelle zum Einsatz in Projektionssystemen -17-
Electro-Optic Transfer Function (EOT) Red LED Most Sensitive to Overdrive Current Red Green Blue 25 C 30 C 30 C 45 C 60 C 60 C Nominal 750mA Nominal 500mA Nominal 500mA Temperature Coefficients: -0.8% / K (thermal rollover) -0.25% / K -0.14% / K Moffat / CZ AG / LEDs an der Schwelle zum Einsatz in Projektionssystemen -18-
LED Light Output Variations Adjust Duty Cycles to Maintain White Point LEDs manufactured in brightness bins Bin width of +/-20% typical for high-brightness LEDs Full distribution typically 2:1 in luminous flux (4-5 bins)! ~20% Minimum to ensure image bit depth What happens to projector s output? Moffat / CZ AG / LEDs an der Schwelle zum Einsatz in Projektionssystemen -19-
LED Light Output Variations Projector Manufacturability with Matched Sets of Three LEDs Projector output shows less variability than LEDs But: total projector output variability should be +/-10% over all components! Avoid arbitrary combinations of LEDs Specify and obtain matched sets of three LEDs Applications Moffat / CZ AG / LEDs an der Schwelle zum Einsatz in Projektionssystemen -20-
Mainstream Application Rear Projection Television Recent results from CES in Las Vegas Samsung (xhd4 DMD) 56 Akai (xhd4 DMD) 46, 52 HP (xhd4 DMD) 52 Sanyo (3-Chip LCD) 55 JVC (3-Chip D-ILA LCOS) 46 (All 1080p HDTV resolution) Samsung PDP LED Sanyo Akai Moffat / CZ AG / LEDs an der Schwelle zum Einsatz in Projektionssystemen -21-
Mainstream Application Front Projection Today s front projectors 500-1000 Lumens Noisy, heavy and bulky Brightness versus colour saturation High lamp replacement cost New approach: Mobile Pocket Projector for controlled ambient lighting conditions Moffat / CZ AG / LEDs an der Schwelle zum Einsatz in Projektionssystemen -22-
Mobile Application Pocket Projector Small size paramount: 100x70x40 mm³ Robust and mobile, battery operated 25 Lumen from 8 W (LEDs) Illumination path length 30% shorter field lens shared in illumination path use of two LED Modules: RB, G Core optical module assembled with two LED modules, heat sink, and DMD on interface board Moffat / CZ AG / LEDs an der Schwelle zum Einsatz in Projektionssystemen -23-
Mobile Application Pocket Projector Prototype Product Samsung Moffat / CZ AG / LEDs an der Schwelle zum Einsatz in Projektionssystemen -24-
Conclusions LEDs provide significant advantages over lamps System EOTs crucial data for optimizing brightness Matched set of three colours needed LEDs have crossed the threshold for use in projection systems A highly optimized system is required LED-based RPTV and the Pocket Projector are ready for the market now Moffat / CZ AG / LEDs an der Schwelle zum Einsatz in Projektionssystemen -25-
Vielen Dank für Ihre Aufmerksamkeit. Acknowledgements: Osram Opto Semiconductors in Regensburg, Germany Fraunhofer IOF in Jena, Germany Bundesministerium fuer Bildung und Forschung (BMBF): Grants 01BD150 and 13N8270 Moffat / CZ AG / LEDs an der Schwelle zum Einsatz in Projektionssystemen -26-