20-11-2012, 05:37 PM
Liquid Crystal Display Technology
[attachment=40422]
Introduction
Liquid Crystal Display (LCD) technology is a
critical facet of the electronics industry
Readily available, relatively inexpensive way to
provide detailed feedback
Technology Overview
Liquid crystal sandwiched between electrodes,
alignment layers, glass, and polarizers
Most common liquid crystal structure used is
‘twisted nemantic’ (TN)
Light enters first polarizer into helical liquid crystal
Rotated light exits the second, offset polarizer
Apply bias across electrodes - result: dark area
Crystal molecules no longer have helical structure
Light not rotated - blocked by second polarizer
Tech Overview - Color & Contrast
Types of LCD contrast - reflective and transmissive
Grayscale achieved by varying bias across cell
Color typically achieved through color filters
Must be capable of passing white light for full color
Other methods are currently being explored
Color via filters decreases already inefficient light
transmission
Passive vs Active Matrix Displays
Two different methods for producing multi-bit
images
Both rely on ‘slow’ electrical response of crystal to
retain a bit for duration of scan time
Directly related to addressing schemes
Passive Matrix
Row & Column approach
Apply small bias to perpendicular lines of
electrodes
Bias strong enough to darken bit at line
intersection
Multiplexed addressing scheme
Advantage: Simple to implement
Disadvantage: Can cause distortion
(‘ghosting’ or ‘crosstalk’)
Active Matrix
Each cell has its own thin-film transistor (TFT)
Addressed independently from behind LCD
Direct addressing scheme
Advantages: Sharp display, better viewing angle,
40:1 contrast
Disadvantages: Need better
backlight, complex hardware
PET: Sub-Pixel Addressing
Old algorithm applied to new technology
Uses optical illusion to increase perceived
resolution
Complimentary color pixels eliminate need for full
pixel to be used
PET: Material Experimentation
Goals:
Improve response
Expand operational environment
Heaters employed for low-temp conditions
“Barrier coatings” protect from
contamination by conductive particles
Liquid crystal material must be carefully
chosen for correct viscosity at desired
operating temp.
[attachment=40422]
Introduction
Liquid Crystal Display (LCD) technology is a
critical facet of the electronics industry
Readily available, relatively inexpensive way to
provide detailed feedback
Technology Overview
Liquid crystal sandwiched between electrodes,
alignment layers, glass, and polarizers
Most common liquid crystal structure used is
‘twisted nemantic’ (TN)
Light enters first polarizer into helical liquid crystal
Rotated light exits the second, offset polarizer
Apply bias across electrodes - result: dark area
Crystal molecules no longer have helical structure
Light not rotated - blocked by second polarizer
Tech Overview - Color & Contrast
Types of LCD contrast - reflective and transmissive
Grayscale achieved by varying bias across cell
Color typically achieved through color filters
Must be capable of passing white light for full color
Other methods are currently being explored
Color via filters decreases already inefficient light
transmission
Passive vs Active Matrix Displays
Two different methods for producing multi-bit
images
Both rely on ‘slow’ electrical response of crystal to
retain a bit for duration of scan time
Directly related to addressing schemes
Passive Matrix
Row & Column approach
Apply small bias to perpendicular lines of
electrodes
Bias strong enough to darken bit at line
intersection
Multiplexed addressing scheme
Advantage: Simple to implement
Disadvantage: Can cause distortion
(‘ghosting’ or ‘crosstalk’)
Active Matrix
Each cell has its own thin-film transistor (TFT)
Addressed independently from behind LCD
Direct addressing scheme
Advantages: Sharp display, better viewing angle,
40:1 contrast
Disadvantages: Need better
backlight, complex hardware
PET: Sub-Pixel Addressing
Old algorithm applied to new technology
Uses optical illusion to increase perceived
resolution
Complimentary color pixels eliminate need for full
pixel to be used
PET: Material Experimentation
Goals:
Improve response
Expand operational environment
Heaters employed for low-temp conditions
“Barrier coatings” protect from
contamination by conductive particles
Liquid crystal material must be carefully
chosen for correct viscosity at desired
operating temp.