LEDs an der Schwelle zum Einsatz in Projektionssystemen

Transcription

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
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
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
LCD
LCOS
DMD
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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
-6-
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
10
15
20
A
Emitting Area (mm²)
25
30
N max
+/-60°
xHD4
F/2.0
-7-
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%
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Low F-number for Higher Light Throughput
Projection Lens
Projection Lens
Illumination
DMD
F/2.4 (standard)
DMD
F/2.0 (wider opening)
Æ larger optics
Æ ~30% more light throughput
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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)
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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
Video Electronics
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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
Trigger, Dimming
Video Electronics
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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:
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)
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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
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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)
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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
Optical
System
Dichroic mirrors
Lens coatings
DMD
EOTs
Integrating sphere
Spectrometer
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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
Lumens
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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)
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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?
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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
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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
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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
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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
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Mobile Application
Pocket Projector
Prototype
Product
Samsung
-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
-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
-26-

LEDs an der Schwelle zum Einsatz in Projektionssystemen

Transcription

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