Epson PX-8 Technical Manual page 98

REV.-A
2.8.1 Liquid Crystal Display Panel Structure
The Liquid Crystal Display (LCD) display panel is a 480 x 64 dot matrix display panel which uses a
twisted nematic (TNM) effect type liquid crystal - one of the voltage effect types. It is struc-
tured as shown in Fig. 2-75.
Upper polarizer plate...........
I
~======~~/ ~~(====~
~ uppe.r glass pia. te
!
L
t
:=:',,'
~~~:~~~::~."=!:t:==~=--::::=::seallng
material
r
~
Liquid crystal
6fz2ZZZl~ZZI/~ZZ/l~Z2ZZI/~ZZI/~Z2ZZ/l~I/Z2Z2ZZIZZ2ZZZZzJ~==~~.Lower
glass plate
-_i~;;;;;;;;;;;;;;;;~~
~ower
polarizer plate
=---l~mmmmm:Z;::Zmii:i:iiilV
Reflector plate
Note: The polarization angles of the upper and lower polalrizer plates differ by
90
degrees.
Oscillation directions
of light
~--
Polarizer plate
Upper polarizer plate
~1r-l'to.I-----"!~ Light
Polarized by 90°.
(areas where no electric field is applied)
Polarization direction
Dark
(areas where an electric field is applied)
Liquid crystal molecule
Lower glass plate
Upper glass plate
Lower polarizer plate
Fig. 2-75
2.8.2 Theory of Operation
The liquid crystal is confined between the upper and lower glass plates. The upper glass plate has
many of electrodes regularly arranged on it. The liquid crystal characteristically shows a twisted
motion, when a voltage is applied across it, depending on the magnitude of the voltage any the
direction it takes determined by the direction of the applied electric field. Using of this character-
istic for the display screen, light and dark contrast are produced on the panel by applying a vol-
tage across the liquid crystal. To maintain this contrast, however, a refresh operation (a repeated
application of voltage) is required simalar to the refresh system used for the dynamic RAM.
2-74