Transcript 1. Introduction to LCD.

Introduction to display technologies
Jean-Michel Lechevallier
Summary


1. Introduction to LCD.

History.

How it works.

Optical modes.

CCFL, EL, Led.

Lightguides.

Optical films.

LED and their chromatic characteristics.
2. Bistable LCD.
Summary


3. LCD module architecture.

LCD - driver connection.

Complete architecture of a module.
4. Color LCD.


4.1. Passive matrix.

Color cell (Transmissive, Reflective, Transflective).

Optical modes comparison

Grey scale generation (FRC, PWM).
4.2. Active matrix.

Introduction to TFT.

LTPS

System on module.
Summary


5. Other technologies.
 5.1.
Field sequential
 5.2.
OLED
 5.3.
Others.
6. Display technical characteristics.
 6.1.
 6.2.

Main characteristics.
Measurement methods.
7. Comparison.
 CSTN,
TFT, OLED.
1. Introduction to LCD.
 History.
1888 : discovery of liquid crystal phase by an Austrian
botanist, Dr Rheinitzer
1968 : first liquid crystal display built by RCA
years 1970 : developement of first LCD for mass
production in Japan.
1. Introduction to LCD.
 How
it works (1/3).
1. Introduction to LCD.
How it works (2/3).
TN, STN, DSTN, FSTN technologies.
1. Introduction to LCD.
How it works (3/3).
Alignment layers.
1. Introduction to LCD.
 Optical
Backlight ON
modes.
Frontlight OFF
Transmissive
= LCD panel
Frontlight ON
Reflective
= backlight or frontlight
Backlight OFF
Backlight ON
Transflective
1. Introduction to LCD.
 sources
: CCFL, EL, Led.
 Lightguides

:
Frontlight
Backlight
1. Introduction to LCD.
 Optical
films

main supplier : 3M
2 technologies:
- microreplication :
adjustment of the light reflection
angles => ex. : BEF, xBEF
- multi layer :
light filtering => ex. : DBEF
LED and their chromatic characteristics.

1. Introduction to LCD.

LED and chromatic characteristics.
Cy
0,45
0,44
0,43
0,42
0,41
Coordonnées chromatiques
Rangs Nichia
0,4
0,39
0,38
0,37
0,36
c0
0,35
0,34
0,33
b1
0,32
0,31
b2
0,3
0,29
0,28
a0
0,27
0,26
0,25
0,24
0,23
0,22
0,21
0,2
0,19
0,24
0,25
0,26
0,27
0,28
0,29
0,3
0,31
0,32
0,33
0,34
0,35
0,36
0,37
0,38 Cx
2. Bistable LCD.
 Bistable
LCD - BiNem technology from Nemoptic
3. LCD module architecture.
 LCD
- driver connection.

COB : Chip On Board,

TAB : Tape Automated Bonding (TCP : Tab Carrier Package),

COF : Chip On Foil - Flex,

COG : Chip On Glass.
3. LCD module architecture.
 Complete
architecture of a module.
TAB
COG
Driver
Driver
4. Color LCD
4.1. Passive matrix
 Color cell
Transmissive display
4. Color LCD
4.1. Passive matrix
 Color cell
Reflective display
4. Color LCD
4.1. Passive matrix
 Color cell
Transflective display
solution 1 : with a transflective sheet
The display reflectivity is
adjusted by changing the
reflectivity (transmissivity) of
the transflector.
4. Color LCD
4.1. Passive matrix
 Color cell
Transflective display
solution 2 : reflective surface on color filters
Reflective area
Transmissive area
Open..Ratio 
transm issive..surface
totale..surface
4. Color LCD
4.1. Passive matrix
 Optical modes comparison
Transmissive
Reflective
Transflective
Indoor
readability
+++
+
++
Outdoor
readability
+
+++
++
contrast
+++
+
++
Color
gamut
(saturation)
+++
+
++
4. Color LCD
4.1. Passive matrix
 Grey scale generator
PWM = Pulse Width Modulation
FRC = Frame Rate Control
alternatively light on and off pixels
during several frames => the average
light creates the grey level.
ON OFF ON OFFONOFFOFF
Frames
1
2 3
4 5
6
7
Advantages:
lower power consumption
better contrast
less flickering
Disadvantage :
jittering
tH
Example
GL=3/7
Tframe
Duty cycle=tH/Tframe
Advantage:
No jittering
Disadvantage:
higher power consumption
4. Color LCD
4.2. Active matrix
 Introduction to TFT
4. Color LCD
4.2. Active matrix
 Introduction to TFT
 TFT cell structure
4. Color LCD
4.2. Active matrix
 Advantages of TFT
compared to CSTN
 Disadvantages of TFT
compared to CSTN
 contrast
 power consumption
 color saturation
 cost
 response time
 viewing angles
4. Color LCD
4.2. Active matrix
 TFT LTPS (Low temperature Poly Silicon)
LTPS : electron mobility increased
compared to amorphous TFT
technology :
electron mobility
p-SI TFT = 200cm²/V.S
a-Si TFT = 0.5cm²/V.S
=> enable to reduce transistor
size and embed more electronic
functions on the glass substrate.
4. Color LCD
4.2. Active matrix
 Advantages and disadvantages of LTPS
Advantages:
Disadvantages :
higher electron mobility
production yield
higher aperture ratio =>
enable to increase the
resolution
cost
4. Color LCD
4.2. Active matrix
 System On Module
Embedded functions :
Memories
Interface
Driver,DAC
Controller
Sensor
Display area
- driver / controller
- memories
- peripheral audio functions
- scanner
- finger print recognition
- etc.
5. Other technologies.
5.1. Field sequential
 Introduction
5. Other technologies.
5.1. Field sequential
 Advantages / Disadvantages
Advantages:
Disadvantages:
up to 85% of NTSC color
gamut
the display is black and
white in reflective mode
High resolution (1dot/pixel)
dedicated controller
specific LC cells (very fast
response time)
a sorting of tricolor LED is
necessary to reduce color
variations
Necessary to adjust the
color balance
5. Other technologies.
5.2. OLED.
Introduction
Current
Cathode (AL:Li)
Emission Layers
Hole Injection Layer
－－－－－－－－－－
Light
－
Electron
+
Hole
+++++++++++
Anode (ITO)
Light
Glass Substrate
5. Other technologies.
5.2. OLED.
Advantages / Disadvantages
Advantages
Disadvantages
contrast
lifetime (especially for
blue)
viewing angles
very thin module (no
backlight)
Brightness is a bit low
response time (1µs)
emissive technology
color saturation
power consumption
5. Other technologies.
5.3. Others.

6. Display technical characteristics
6.1. Characteristics

Contrast (transmissive and reflective)
Transmittance (%)
Reflectance (%)
Response time (ms)
Viewing angles (transmissive and reflective) (degrees)
Chromatic co-ordinates (transmissive and reflective) (defined in CIE 1931 diagram)
Color gamut (surface or % of NTSC triangle)
Open ratio (%)
Aperture ratio (%)
Brightness (cd/m²)
Backlight uniformity (%)
Power consumption (mW)
6. Display technical characteristics
6.2. Measurement methods
 2 methods for measurements in reflective mode (contrast, reflectivity, …)
Specular
Use a point light source.
diffuse
Use a sphere to diffuse the light in every
direction => this method is the most
representative of normal lighting condition.
7. Comparison

Thickness
Brightness
Response time
NTSC ratio
Contrast
Viewing angles
Power
consumption
(all on) based
on 96*64
display
Lifetime
(defined at half
brightness)
CSTN
2.7mm with backlight
TF : 70cd/m²
TM : 170cd/m²
150 à 300ms
TF : 15%
TM : 35%
TF : 20
TM : 30
60 à 90 degres
BL off : 2mW
BL on : 180mW
TFT
2.7mm with backlight
TF : 100cd/m²
TM : 250cd/m²
30ms
TF : 40%
TM : 60% (up to)
TF : 70
TM : 300
60 à 160 degres
BL off : 3~4mW
BL on : 180mW
>30K hrs
>30K hrs
AM OLED
1.7
150 to 200 cd/m²
1µs
65%
(50% for PM OLED)
500
180 degres
200mW
<5 to 10 K hrs (with
color deviation)
7. Comparison
Color gamut

FIN
