Epson PX-8 Technical Manual page 99

REV.-A
Optical contrast of the liquid crystal is produced in the mechanism as follows:. First, only the
light elements which oscillate in a specific direction are transmitted through the upper polarizer
plate onto the liquid crystal. The light, arriving on the liquid crystal, is affected, depending on
whether an electric field is applied or not:
<
When no electric field is applied>
The penetrating light is polarized by 90
0
•
This causes the oscillation direction of the light to coin-
cide with the polarization direction of the polalrilzer plate and the light is transmitted through it.
Then, the light strikes the bottom reflector plate and is reflected, so that the panel looks light
(white).
<
When an electric field is applied>
The twisted orientation of the liquid crystal is corrected by the electric field and the optical activity
is removed. The oscillation direction of the light penetrating the liquid crystal layer does not
coincide with the polarization direction of the lower polarizer plate and is shut off by it. suits in no
reflection from the bottom reflector plate so that the panel looks dark (black).
The reaction to the electric field varies depending on temperature. To compensate this, a variable
resistor, called VIEW ANGLE is provided in the voltage source circuit.
• Display dot (segment)
Each display dot has an area of 0.45 (high) x
0.41 (wide) mm
2 •
These dots are laid out at a
vertical pitch of 0.5 mm and at a horizontal
pitch of 0.46 mm as shown in Fig. 2-76.
Notes:
046
0.41
D
9
~
()1
o
()1
(Unit: mm)
Fig. 2-76 Display Dot Dimensions And
Layout
As described above, variation of liquid crystal reaction can be compensated for by adjusting the
X-V drive line signal voltage with the sliding type variable resistor VIEW ANGLE over a certain
temperature range. If the range is exceeded, however, this compensation is no longer possible,
and the LCD panel may exhibit one of the following problems:
<
Lower temperature>
• Liquid crystal reaction is slow and a long time is required until selected dots become visible (up
to several seconds may be required)
• When the temperature further falls, no selected dots are visible over the entire panel.
<
Higher temperature>
• The entire area of the panel looks dark (black) and selected dots are not easily recognizable.
2-75