LCD (Liquid Crystal Display)
A display technology that uses rod-shaped molecules (liquid crystals) that flow like liquid and bend light. Unenergized, the crystals direct light through two polarizing filters, allowing a natural background color to show. When energized, they redirect the light to be absorbed in one of the polarizers, causing the dark appearance of crossed polarizers to show. The more the molecules are twisted, the better the contrast and viewing angle.
Because it takes less power to move molecules than to energize a light-emitting device, LCDs replaced LEDs in digital watches years ago. The LCD was developed in 1963 at RCA's Sarnoff Research Center in Princeton, NJ.
TYPES OF LCDs
1. Passive Display (TN and STN)
Called "passive matrix" when used for computer screens and "passive display" when used for small readouts, all the active electronics (transistors) are outside of the display screen. Passive displays have improved immensely, but do not provide a wide viewing angle, and submarining is noticeable. The passive display types are:
TN - Twisted Nematic - 90º twist
Low-cost displays for consumer products and instruments. Black on gray/silver background.
STN - Supertwisted Nematic- 180-270º twist
Used extensively on laptops for mono and color displays. DSTN and FSTN provide improvements over straight STN. 180 º - green/blue on yellow background
270 º - blue on white/blue background
2. Dual Scan STN
Improves STN display by dividing the screen into two halves and scanning each half simultaneously, doubling the number of lines refreshed. Not as sharp as active matrix.
HPA (High Performance Addressing) (735-737) (Maximum resolution 800x600)
A type of active addressing technology that improves the quality of a passive matrix (LCD) screen (DSTN).
Active Display (TFT) (SONY 505)(Maximum resolution for the N505 : 800x600)
Typically used for laptop color screens and, increasingly, for flat desktop screens. Known as "active matrix" displays, transistors are built into each pixel within the screen. For example, 640x480 color VGA screen requires 921,600 transistors; one for each red, green and blue dot. Provides a sharp, clear image with good contrast and eliminates submarining, but fabrication costs are high. Uses a 90º (TN) twist. Also called TFT LCD (thin film transistor LCD).