Electronic Design

Candidates For Head-Mounted Displays

Liquid crystal on silicon (LCoS) is a microdisplay technology that builds upon the two mature, existing silicon and display technologies. LCoS is a low-power, low-voltage (3.3 V) reflective technology. It's likely that LCoS will be successful in HMDs because there's no cost penalty attendant to adding pixels. The liquid crystal can be made in successively higher resolutions—SVGA, XGA, and SXGA—without a cost penalty because the cost is in the silicon backplane, not in the liquid crystal material. Significant cost advantages also arise by shrinking the size of the silicon due to the fact that more display backbones can be fabricated on a single wafer.

A variation on LCoS, Ferroelectric LCoS is championed by Displaytech Inc., Longmont, Colo. It's very fast, has excellent color and brightness, and operates in a near-eye mode. Ferroelectric LCoS uses light-emitting diodes (LEDs) and enables real-time video performance. Plus, it's said to be a lower-power, reflective technology.

Organic light-emitting diodes (OLEDs) are emissive microdisplays, rather than transmissive or reflective. The light output of the OLED is lambertian, which means equal light intensity in all directions. The lambertian characteristic is crucial for near-eye applications because it lets the image be fully visible from a wide range of pupil positions. OLEDs also are energy efficient because the only emitted light is from pixels, and there aren't any light-scattering background issues. The construction of OLEDs is simple. They don't require light to be brought in through the back, and there's no need to assemble a separate light source.

TAGS: Components
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