All About LCDs - Liquid Crystal Displays

A LCD is also known as a Liquid Crystal Display.  This is one of the fastest growing electronic component devices.

LCD Types

• TN (Twisted Nematic) - Least expensive LCD, limited display capabilities (90 degree viewing angle).  Passive, Monochrome.  Segment or Character.
• STN (Super Twisted Nematic) - Wider viewing angle.  Passive, Monochrome with gray, blue (negative only) and yellow-gree (least expensive) backgrounds.  Segment, Character or Graphic.
• FSTN (Film Compensated Super Twisted Nematic) - Better contrast.  Passive, Monochrome (black & white, but can have colored background with colored LED backlight).  Segment, Character or Graphic.
• Color STN - Passive, Color, Graphic.
• TFT (Thin Film Transistor) - Active (each pixel stores a charge), Color, Graphic.  Better colors and contract - highest cost.  Larger size must have a CCFL backlight.  Standard only - custom TFT is unlikely due to very high tooling costs.  Controller boards and touch screens are also available.

LCD Display Mode

• Segment - Most basic.  "Segments" that make up a digit or letter.
• Character - Alpha-numeric, Icons.  Measured by characters per rows (ie. 16x2, 20x4)
• Graphic - Alpha-numeric, Icons, Complex pictures.  Dot matrix - measured by pixels per row by pixels per column (ie. 128x64; 320x240=QVGA, 640x480=VGA)

IC Mounting/Bonding Techniques

• COG (chip on Glass) -Chip bonded directly onto LCD glass.  Lease expensive, slimmer.
• TAB (Tape automated bonding) - Chip bonded onto connecting tape.  Slimmer.
• COB (Chip on board) - Chip on PCB (under protective epoxy bubble).  PCB connected to LCD via rubber/pin/heat seal tape connectors.  Less expensive than SMT.
• SMT (Surface mount technology) - Chip on PCB (IC visible).  PCB connected to LCD via rubber/pin connectors.  Old technology - no longer popular.  Still used for larger sizes.

Display Mode

• Positive - Dark Letters/characters/images; light background.
• Negative - Light letters/characters/images; dark background.

Optic Mode

• Reflective - 100% of ambient light reflective reflected (no backlight needed).
• Transflective - 50% of light reflected; 50% passes through (uses ambient light or backlight).
• Transmissive - 100% of light passes through (backlight always needed).

Backlight

• LED (Light emitting diode) - Long life - 50,000 hours.  Yellow-green most popular and least expensive.  White is more expensive but brightest (most popular for character/graphic).  Other colors include blue, green, and amber.
• EL (Electro Luminescent) - Low power consumption; thin.
• CCFL (Cold cathode fluorescent lamp) - High brightness but bulkier.  TFT's greater than or equal to 4" in size must use CCFL.
• Bottom vs. Edge
• Bottom - Light directly under LCD
• Edge - Light on side; spread via light guide

Viewing Directions

• 12:00 - Best view comes from above LCD (most popular)
• 3:00 - Best view comes from the right
• 6:00 - Best view comes from below LCD (most popular)
• 9:00 - Best view comes from the left

The above guide is to help you plan the best LCD for your application and for better understanding of LCDs.  Competitive Components is a distributor of Beyondtek LCDs.  Beyondtek and CCI team-up to supply your LCD needs.