3M
Multimedia Projector MP8620
Theory and Diagrams
3M 1999
4-4
4-4.
LCD Structure Theory
An understanding of LCD Structure theory provides a background for making the convergence adjustments
discussed in section 6.
LCD is the acronym for Liquid Crystal Display. The three LCD panels (Red, Green, Blue) in the MP8610 are a
1.3” square, poly-silicon design. Each LCD panel is composed of a layer of liquid crystal cells, electrodes, and
glass.
4-4-1.
LCD Cells
Each cell is composed of long, rod shaped molecules that react to an electrical charge. In their normal state, the
molecules form a spiral. When an electrical charge is applied, the molecules align themselves allowing the light
to pass through the pixels. Shades of gray are obtained by inputting voltages that fall between full off (no
voltage) and full on (full voltage). The cells are refreshed at the speed of 1/60
th
of a second and are sensitive to
high temperatures.
4-4-2.
How Light Passes Through An LCD
Polarized light entering the cells from the rear is aligned so that it will pass the light through the polarizer on the
other side. Patterned transparent electrodes on the inner surfaces of the glass form an addressing system that
creates a distinct electric field for each pixel. The light that was not aligned as it passed through the liquid
crystal cell is blocked.
4-4-3.
Example Projection
If 100% of the red light is emitted through the red LCD panel and 50% of the green light makes it through the
green LCD panel and the blue light is blocked entirely, a light brown screen is projected.
