C-4. Basic Construction Of Lcd; Construction Of Lcd Panel - Tandy 102 Service Manual

C-4. Basic Construction of LCD
Liquid crystal is a substance midway between a liquid and a solid, although its appearance is much
like a liquid. From an electrical and optical stand point, it possesses the properties of a crystal.
Items which use this substance are called liquid-crystal display elements. The LCD used in the
Tandy 102 is a TN (Twisted Nematic) type of liquid crystal. Its basic construction is shown in Figure
C-16.
Liquid Crystal
Front Glass
Electrode
Front Polarizer
Filler
Reflector
Rear Polarizer
Rear Glass Electrode
Figure C- 16. Construction of LCD Panel
The LCD operates as an "electric shutter " that controls the passage of light.
If voltage is applied, the transmission of light is blocked , otherwise , light is allowed to pass so that
letters and numbers can be displayed.
Figure C-17 demonstrates how the LCD operates:
• The liquid-crystal display element is sandwiched between the two polarization plates. The
polarized axes of the upper and lower plates are placed at right angles to each other to use the
optical "twisting" of light.
• As shown in Figure C-17 (a), if voltage is not applied, the liquid-crystal molecules between the
upper and lower plates twist 90° to distribute light. This results in a 90° optical movement and the
transmission of light.
• In Figure C-17 (b), however, voltage is applied and the liquid appears frosted in current-carrying
areas , thus blocking light transmission.