Transcript 2.87x10

Design of a Head Mounted Display
for Image-Guided Surgery
Bo Bai
Stephanie Dalquist
Megan Galbraith
16 May 2002
Introduction
• Develop HMD for surgeons
• Projects diagnostic images on patient
– Compare digital X-Rays, NMR
– Overlay text plans
– High resolution and accuracy
• Design micro-display for image source
Technology goals
• Full color, 4 bits/color grey scale
• Minimum frame rate of 100 Hz
• High resolution – 1280 x 1024
– Pixel pitch at most 24 μm
• High contrast ratio, at least 100:1
– Design for hospital environment, 100 Cd•m-2
– Minimum brightness 60,000 Cd•m-2
Display technology
• Active Matrix Organic LED
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Fast response time of 3 μs
Pixel pitch down to around 12 μm
Can reach brightness levels up to 106 Cd•m-2
Reliable to 106 hours
• Preferred over other technologies
– AMEPD: color difficulties
– AMLCD: less bright
– AMELD: not very bright (23 Cd/m2 at 60 V)
Grey scale method
• Sub-framing
– Allows for 16 shades from black to white
– Minimizes flicker at high ν (1600 Hz)
• Other options
– Patterning: Too much flicker, too few greys
– Voltage modulation:
• Requires high sensitivity to ΔV
• More complicated drivers
Pixel structure
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Stacked OLED
True color
High contrast
Bright, emissive
Flexible
Makes pitch spec
Pixel structure
• Stacked OLED preferred
• Other options:
– Side-by-side monochrome
• Large pitch or lower resolution
• Many have decreased viewing angles
– Color filters
• Absorption loss
• Need efficient blue dyes
Pixel circuit
• Diode equivalent for each
color
• Single line addressing
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Voltage across rows
Data down columns
High frequency
Simpler, cheaper drivers
OLED requirements
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9V to reach 60,000 Cd•m-2
Current Density of 50 mA/cm2
Area = Apixel - Atransistors = 570 μm2
Current = 2.87 x 10-4 mA
CMOS specification
• Choose n-doped CMOS: Kn > Kp
– Lowers power consumption
• VGS = 0.6V
– ID = 0.5Kn(VGS-VTn)2
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VG1 = VGS+Vdiode = 0.6+9 = 9.6V
VG2 = VG1+VTn = 9.6+0.5 = 10.1V
Column voltage = VG1 = 9.6V
Row voltage = VG2 = 10.1V
Driver specifications
• Generic driver circuit
– Can be used with OLED,
ELD, LCD, etc.
• Row driver draws 10.1 V
• Column draws 9.6 V
I/O data rate for drivers
• Row data rate
– Selects a row to update
– Consider 16 sub-frames for grey scaling
– 1.6 MHz or 205 Kbps
• Column data rate
– Sends color information
– 6.29 GHz or 786 Mbps
– Much more data, much faster data rate needed
Power consumption
• Total power consumption of 4 W
– 2 x 10-6 W per pixel
• Ppixel = VI = 9V x 2.87x10-4 mA
– Display requires 4 W
• Ptotal = PpixelNrowsNcolumns
– Conservative estimate assuming all pixels on
Overall efficiency
• Display efficiency ηdisplay = 27%
– 4 lumens/Watt power efficiency at 9 V
– Input Power Pin = 4 W
– Output Power
Pout = 60,000 Cd/m2 • Area/(4 lm/W • 4π Cd/lm) = 0.9 W
– ηdipslay = Pout/Pin
• Optical subsystem
ηoptics = 15%
• Overall
ηdisplay • ηoptics = 4%
Conclusions
• Meet target specifications at low cost with
current technology
– Not power hungry
– Safe (low voltage, amperage, etc.)
• Take it to the lab for prototyping
• Revolutionize health-care by 2010
questions?