Design of a Head Mounted Display for Image-Guided SurgeryIntroductionTechnology goalsDisplay technologyGrey scale methodPixel structureSlide 7Pixel circuitOLED requirementsCMOS specificationDriver specificationsI/O data rate for driversPower consumptionOverall efficiencyConclusionsquestions?Bo BaiStephanie DalquistMegan Galbraith16 May 2002Design of a Head Mounted Display for Image-Guided SurgeryIntroduction•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 sourceTechnology 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-2Display 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 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 driversPixel structure•Stacked OLED•True color•High contrast•Bright, emissive•Flexible•Makes pitch specPixel 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 dyesPixel circuit•Diode equivalent for each color•Single line addressing–Voltage across rows–Data down columns–High frequency–Simpler, cheaper driversOLED requirements•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 mACMOS specification•Choose n-doped CMOS: Kn > Kp–Lowers power consumption•VGS = 0.6V–ID = 0.5Kn(VGS-VTn)2 •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 = 10.1VDriver specifications•Generic driver circuit–Can be used with OLED, ELD, LCD, etc.•Row driver draws 10.1 V•Column draws 9.6 VI/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 neededPower 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 onOverall efficiency•Display efficiency ηdisplay = 27%–4 lumens/Watt power efficiency at 9 V –Input Power Pin = 4 W–Output PowerPout = 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
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