LCDs (Liquid Crystal Displays) are passive or active-matrix displays that can demonstrate information as text or in a dot matrix pattern. This type of technology is generally less expensive than VFD or OLED display technology. We have many different LCD products which can be classified under the following display types: TFT displays (full color RGB), COG displays (Chip-on-Glass) and standard character or graphic module displays (Chip-on-Board).
In order to understand how LCDs work, it is important to know how they are made. To start, LCDs are composed of two pieces of polarized glass. On the non-polarized side of the glass, a special polymer is added to create grooves that run in the same direction as the polarizing film. Once this is done, a liquid crystal material is added to the grooved side of one of the polarized glasses. These grooves align the liquid crystal with the glass. The second piece of glass is placed on top with the grooved side in, aligned perpendicular to the first pieces of glass creating a row and column arrangement.
Image from www.howstuffworks.com
Where the grooves of the two pieces of polarized glass intersect is a pixel. By blocking the light from passing through the top
piece of glass, it creates an area that is darker than its surrounding. This gives the appearance of pixels being turned on or off.
In order to block the light from passing though, the orientation of the liquid crystal has to be changed. To do this, an electric charge is needed. Without an electric charge, the liquid crystal is twisted which changes the angle of the light to match the angle of the top polarized glass. This allows light to pass through.
When an electric charge is applied, the liquid crystal untwists leaving the angle of the light unchanged. This causes the light to be blocked by the top perpendicular piece of polarized glass. The controllers on the display will determine which pixels turn on and off. These controllers are programmed to translate user data into predefined fonts or turn on the appropriately addressed pixels.
TN (Twisted Nematic)This technology consists of nematic liquid crystal sandwiched between two plates of glass. When power is applied to the electrodes, the liquid crystals twist 90°.
STN (Super Twisted Nematic)This technology has rapidly become a standard for most monochrome passive-matrix LCDs. It uses the same principle as TN displays but uses less power and is typically less expensive. The liquid crystals in STN technology have a 210° - 270° twist which allows for a broader transition region for gray scaling. STN displays can also be made purely reflective for viewing under direct sunlight.
FSTN (Film Compensated Super Twisted Nematic)This technology uses a film compensating layer between the STN display and rear polarizer. This additional film increases the overall sharpness and contrast of the display.
Positive type displaysPositive displays provide an image with dark pixels on a light background. Ambient light or a backlight can be used for this type of display and is capable of multiple background colors.
Negative type displaysNegative displays provide an image with light pixels on a dark background. The backlight must be used for this type of display and is capable of multiple pixel colors.
|Transmissive LCDs always require
a backlight and provide the highest brightness display. They are best suited for applications where direct sunlight viewing is not involved.
|Reflective polarizers are used in
high ambient light environments
or whenever sufficient power is not available to drive the backlight.
|Transflective polarizers have both reflecting and transmitting properties and offer the most versatile viewing characteristics. They can be viewed in direct sunlight and when combined with a backlight in low light conditions.|