Bo Bai

1
Design of a Head Mounted Display for
Image-Guided Surgery

• Bo Bai
• Stephanie Dalquist
• Megan Galbraith
• 16 May 2002

2
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

3
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 1001
• Design for hospital environment, 100 Cdm-2
• Minimum brightness 60,000 Cdm-2

4
Display technology

• Active Matrix Organic LED
• Fast response time of 3 µs
• Pixel pitch down to around 12 µm
• Can reach brightness levels up to 106 Cdm-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)

5
Grey scale method

• Sub-framing
• Allows for 16 shades from black to white
• Minimizes flicker at high ? (1600 Hz)
• Other options
• Patterning Too much flicker, too few greys
• Voltage modulation
• Requires high sensitivity to ?V
• More complicated drivers

6
Pixel structure

• Stacked OLED
• True color
• High contrast
• Bright, emissive
• Flexible
• Makes pitch spec

7
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

8
Pixel circuit

• Diode equivalent for each color
• Single line addressing
• Voltage across rows
• Data down columns
• High frequency
• Simpler, cheaper drivers

9
OLED requirements

• 9V to reach 60,000 Cdm-2
• Current Density of 50 mA/cm2
• Area Apixel - Atransistors 570 µm2
• Current 2.87 x 10-4 mA

10
CMOS specification

• Choose n-doped CMOS Kn gt Kp
• Lowers power consumption
• VGS 0.6V
• ID 0.5Kn(VGS-VTn)2
• VG1 VGSVdiode 0.69 9.6V
• VG2 VG1VTn 9.60.5 10.1V
• Column voltage VG1 9.6V
• Row voltage VG2 10.1V

11
Driver specifications

• Generic driver circuit
• Can be used with OLED, ELD, LCD, etc.
• Row driver draws 10.1 V
• Column draws 9.6 V

12
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

13
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

14
Overall efficiency

• Display efficiency ?display 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 4p Cd/lm)
  0.9 W
• ?dipslay Pout/Pin
• Optical subsystem ?optics 15
• Overall ?display ?optics 4

15
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

16
questions?