LEDs an der Schwelle zum Einsatz in Projektionssystemen
Transcription
LEDs an der Schwelle zum Einsatz in Projektionssystemen
LEDs an der Schwelle zum Einsatz in Projektionssystemen: Herausforderungen, Grenzen und Anwendungen Dr. Anton Moffat Carl Zeiss Corporate Research Carl Zeiss AG, Jena, Germany [email protected] 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 Lifetime • Conventional Lamp: 50% preserve 50% brightness in x h, Æ 1/2 can fail Æ Guarantee for a few 100 h • Many More: • Cost • More suppliers • Simple electronics • Instant on/off • Low voltage • Low pressure • Colour Break-Up reduction • No Colour Wheel: noise reduction Moffat / CZ AG / LEDs an der Schwelle zum Einsatz in Projektionssystemen Semiconductor Lamp MTTF with confidence > 9x% Intensity degradation < 30% in 10.000 h Æ Guarantee is given for years -3- Introduction Timeline Starts Now for LED-Based Projection Systems Critical threshold is screen brightness D LE ap m ad o R Customer Threshold Highly optimized electro-optical system Standard Optical System with LEDs 2006 Moffat / CZ AG / LEDs an der Schwelle zum Einsatz in Projektionssystemen 2008 2010 -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 • 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 • Digital Micromirror Device (DMD) – Single panel requires sequential colour Moffat / CZ AG / LEDs an der Schwelle zum Einsatz in Projektionssystemen LCD LCOS DMD -5- 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 x LED – small area, large angle DMD – large area, small angle Geometrical match: etendue, aspect ratio, overfill Moffat / CZ AG / LEDs an der Schwelle zum Einsatz in Projektionssystemen -6- Geometrical Optical Requirements Useable System Etendue Æ Practical Limit on Light Source Area N max 30 Relative Intensity 25 20 Itotal( A) 15 Iuseable( A) 10 5 0 0 0 5 0 Moffat / CZ AG / LEDs an der Schwelle zum Einsatz in Projektionssystemen 10 15 20 A Emitting Area (mm²) 25 30 N max +/-60° xHD4 F/2.0 -7- Geometrical Optical Requirements Available DMDs Determine Useable System Etendue 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 DMD Larger DMD Æ 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) Moffat / CZ AG / LEDs an der Schwelle zum Einsatz in Projektionssystemen DMD F/2.0 (wider opening) Æ larger optics Æ ~30% more light throughput -9- System Design Methodology • Goals: – Maximum Screen Brightness – Good Image Quality – Competitive Cost Æ 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 Projection Lens F/2.4 Colour Wheel Optical Iris Relay Optics Mirror UHP Lamp Integrating Rod Field Lens UV, IR Filter DMD Colour Wheel Rotation Sensor Sync Moffat / CZ AG / LEDs an der Schwelle zum Einsatz in Projektionssystemen Video Electronics -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 Field Lens Microlens Array Heat Sink Green LED DMD Blue LED LED Driver Moffat / CZ AG / LEDs an der Schwelle zum Einsatz in Projektionssystemen Trigger, Dimming Video Electronics -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: Tiled Solution: Moffat / CZ AG / LEDs an der Schwelle zum Einsatz in Projektionssystemen Pro: Efficient – matched geometry Con: Costs for yield and custom size Spec. uniformity across chip area Thermal stress in pulsed operation Large drive currents Pro: Standard LED chips as building blocks Low Current, Voltage for LED-Strings Con: Less efficient – gaps, approx. geometry Spec. uniformity across chips on a module 2xN arrays (favoured due to bond wires) -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 • Here: Experimental results based on Osram Ostar – Method applies to other LED architectures PhlatLight 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 Current Temperature Duty Cycle LEDs Red Green Blue Moffat / CZ AG / LEDs an der Schwelle zum Einsatz in Projektionssystemen Optical System Dichroic mirrors Lens coatings DMD EOTs Integrating sphere Spectrometer -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! Æ Optimize driving conditions – current density – temperature Watts – duty cycle Moffat / CZ AG / LEDs an der Schwelle zum Einsatz in Projektionssystemen Lumens -17- Electro-Optic Transfer Function (EOT) Red LED Most Sensitive to Overdrive Current Red Green 25°C Blue 30°C 30°C 60°C 60°C 45°C Nominal 750mA Nominal 500mA Nominal 500mA Temperature Coefficients: -0.8% / K -0.25% / K -0.14% / K (thermal rollover) 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 Moffat / CZ AG / LEDs an der Schwelle zum Einsatz in Projektionssystemen Akai -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-