Appendix B - Lcd; Lcd Concept; Lcd Operation - Sony XM-1502SX Training Manual

LCD Concept

A Liquid Crystal Display (LCD) is a panel consisting of pixels (picture elements) that pass light when a voltage is
applied to its crystal. The higher the voltage, the more light is passed.
Unfortunately, after a short time, the LCD element no longer responds and the crystal element remains dark. To
keep the LCD picture element active, the next series of voltages (the RGB signal) to the element is reversed.
This keeps the crystal from polarizing and operation continues unaffected. Operation continues because even if
the applied voltage is reversed, if the potential across the element remains the same (although the polarity has
changed), the picture element will still pass the same amount of light.

LCD Operation

To work, the Liquid Crystal Display (LCD) needs:
1) + Voltages (power supply)
2) RGB information
Figure B-2 shows a typical LCD block.
2) RGB Information
LCD assemblies consist of internal transistor matrixes that operated at high speed to place the video, picture
element (pixel) by picture element, on the screen. The LCD assembly's input signal is usually RGB while the
vertical and horizontal sync signals lock the high-speed timing pulses used to pinpoint each pixel target to insert
the RGB information.
COMPOSITE
VIDEO

Appendix B - LCD

+ / --
LCD
Back
element
Light
-- / +
Figure B-1 - Picture Element
3) Timing signals
4) Backlight (not shown).
SYNC
HIGH SPEED
VIDEO
DECODER
R G B
H+V SYNC
RGB
OSD
3.58MHz
(TEXT)
FIGURE B-2 - TYPICAL LCD CIRCUIT
R, G or B Filter
COLOR
BRIGHT
CONTRAST
VIDEO
SWITCH
INTERFACE
RGB
SYSCON
H+V
GENERATOR)
SYNC
iii
User
B1A125 11/11/02
+ - VOLTAGES
LCD
R G B
ASSEMBLY
(PIX ELEMENT)
COM
FRPT
FRPU
LCD DRIVER
(TIMING
H VCO
23A125 1543 11/11/02
Appendix B - LCD
TIMING
PULSES