3M
Multimedia Projector MP8670/8745/8755/8770
Theory and Diagrams
Copyright
2000, 3M IPC. All Rights Reserved.
4-4
4-3.
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
MP8670/8745 are a 1.3” square, poly-silicon
design. Each LCD panel is composed of a layer
of liquid crystal cells, electrodes, and glass.
4-3-1.
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.
4-3-2.
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.
4-3-3.
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.
