This document summarizes a research paper that proposes new algorithms for field sequential color LCD displays without color filters. It describes a Multi-Area Control (MAC) algorithm that divides the display and backlight into three areas to increase LED flash time. A Color Local Dimming Sequential (CLDS) algorithm further divides the backlight into multi-areas and sets dimming values. Prototypes including a 32-inch LCD TV and 15.4-inch notebook demonstrate the approaches, showing improved brightness, color accuracy and efficiency over basic field sequential methods. The algorithms aim to address challenges of fast scanning, response times and light switching for color-filterless displays.

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SID2008 71.1:
Field Sequential Color LCD-TV Using
Multi-Area Control Algorithm
Wen-Chih Tai, Chi-Chung Tsai, Shian-Jun
Chiou, Chih-Ping Su, Huang-Min Chen,
Chia-Lin Liu and Chi-Neng Mo
TFT-LCD R&D Center, Chunghwa Picture Tubes, Ltd.
1127, Heping Rd., Bade City, Taoyuan, Taiwan, 334, R.O.C
e-mail. taiwc@cptt.com.tw
Fax. + 886-3-3773159

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Outline
1. Introduction
– Color-filter vs. Color-filter-less
– Color Sequential concept
2. New Algorithm
– Multi-Area Control algorithm
(MAC)
– Color Local Dimming
Sequential algorithm (CLDS)
3. Prototype
– 32-inch OCB LCD TV
– 15.4-inch TN Notebook
4. Conclusion

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Introduction
Color-filter vs. Color-filter-less
LCD Standard Structure Color FilterLCD Standard Structure Color Filter
Remove Color Filter
• Color Filter
– R G B sub-pixel to display color
– Spatial additive color mixing
– obstruct most of light (according
to their different wave lengths)
• Advantage of no color filter
– Higher optical efficiency
– Low Power Consumption
– Raise the manufacture yield rate
– Reduce the cost of the panel
– Sunlight readable
• display a color image
– The theorem of visual residue
– display a color image by turning
on light sources Red, Green and
Blue sequentially within a frame
periods

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Introduction
color sequential concept
• LCD color-filter-less panel
must combine with a
backlight that has 3
separate alternating light
sources
• the visual residue of
human’s eyes is about 1/60
(one sixtieth) second
• Increase the field frequency
above 180 Hz to display the
full color image
• Waited the LC transfer to
position, then light on
60Hz 180Hz
Temporal color mixing

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Basic Algorithm
• one field time is 1/3(one third) frame time 5.57 ms,
• the response of LC and the flash of the backlight must be completed.
• LCD scanning data must be shorter than 4.28 ms,
• the LED flashing time is about 1.28 ms.
• In this case, due to the short flash time the LED number must be
increase, If the brightness of the module want to achieve market
specification with the slower LC response time
RGB LED
Backlight
TFT
scanning
tTFT
tLC
tBL
1/3 f
R G B
1.28ms 1.28ms 0.5ms
Timing chart in the color sequential LCD with TFT addressing

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MAC Algorithm
(Multi-Area Control)
• if 3 gate IC were
applied to the panel.
• Panel and backlight is
divided into three
areas
• Control the timing of
the LCD with 180 Hz
field rate
• the backlight show 9
flashing pattern in one
frame time
• LCD address time is
reduced to one third of
the whole panel
Fig. 1 MAC algorithm of LED light on time
sequential

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MAC Algorithm – time chart
• the panel and
backlight were
divided into three
area I, II, III
• the LCD address
time can be
reduced to 1/3(one
third) from 4.28 ms
to 1.18 ms
• the LED flash time
was increased from
1.28 ms to 3.5 ms
• 2nd area was the
same with 1st but
delay 1.85 ms
• 3rd area was the
same with 1st but
delay 3.7 ms
RGB
LED BL
Area I
TFT LCD
Area I
1/3f(5.56ms)
tL
C
R G B
tL
C
tL
C
tL
C
R G B
tL
C
tL
C
tL
C
R G B
tL
C
tL
C
RGB
LED BL
Area II
TFT LCD
Area II
RGB
LED BL
Area III
TFT LCD
Area III
f(16.67ms)
tTFT tTFT tTFT
tTFT tTFT tTFT
tTFTtTFTtTFT
tLED tLED tLED
tLED tLED tLED tLED
tLED tLED tLED tLED
R
tTFT
R
G
B
B
B
B
B
R
R
G
G
3.5ms 3.5ms3.5ms
1.18ms
Timing chart in the MAC LCD with TFT addressing

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CLDS Algorithm
(Color Local Dimming Sequential)
• Determinate the amount of
dimming areas
• for example 4 x 6 area
• LCD is portioned into several
areas according to the Backlight
unit
• Raster scan is used to scan the
picture pixel by pixel from the left-
top to the right-bottom.
• After the maximum or average
value is computed then
• A critical value can be found from
a signal area, or several area and
set the intensity of backlight
Fig. 2 MAC algorithm
combined with CLDS method

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X8
X8
X8
X8
X8
X8
Prototype
32-inch OCB LCD TV – Panel Driver Circuit
• Use the
mass
product
standard IC
• FSC does
not need
sub-pixel
• Connect R G
B Sub-pixel
of standard
panel into
the same I/O
line
•FSC increase 3
times I/O speed
but connect R G
B into one I/O
decrease 3
times I/O speed
•Maintain the
same I/O speed
and use the
standard panel
MASK

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Prototype
32-inch OCB LCD TV - Optical Mechanism Layout
• The basic optical films
structure of the module is
the same with the
standard display.
• Under the LCD panel
– diffuse film,
– brightness enhance film
(BEF),
– diffuse film,
– diffuse plate,
– LEDs and reflective layer
Fig. 4 32”TV backlight structure

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Prototype
32-inch OCB LCD TV - Backlight Mechanism Layout
• the advantage of LEDs
– Low power consumption
– Smaller form factor
– Wide color gamut
• 24 x 48 LEDs layout backlight
source
• low power RGB chips set of tri-
color in one LEDs
• reduce the flash duty and
overdrive the power supplied
current,
• high-speed flashing
• the LED chip can be emitted
more light flashing energy and
more light efficient of low power
LED chip can be achieve. Fig. 5 Backlight module with the low power
RGB chips set of tri-color in one LED

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Prototype
32-inch OCB LCD TV - The Liquid Crystal Mode
• The FSC method requires
– fast scanning driver,
– fast response of the display
device and
– fast switching of the RGB
light sources.
• the OCB mode was adopted
for its fast response time and
uniform alignment in FSC
display
• The average gray to gray
response time of OCB mode
is 1.4 ms and on/off 3 to 4 ms.
• All state transition below 3.5
ms
255
223
191
159
127
95
63
31
0
255
223
191
159
127
95
63
31
0
0
2
4
6
8
10
12
14
16
Time(ms)
Rising Time
Falling Time
Fig. 9 OCB LCD-TV response time

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Prototype
32-inch OCB LCD TV - Basic FSC Algorithm
• display image by
basic field
sequential method
• bottom Image of
the display with
wrong mixed color
• There is not
enough time to
wait the LC to
transfer to the
required position
• Brightness : 350
nits
Wrong Mixed ColorWrong Mixed Color
The color filterless 32-inch TFT TV by
using basic sequential principle

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Prototype
32-inch OCB LCD TV - MAC Algorithm
• The 32-inch color filter
less liquid crystal
module with the MAC
Algorithm
• Brightness : 500 nits
– (max 900 nits)
• the color gamut 114.6 %
as compare to the NTSC
Right Mixed ColorRight Mixed Color
The color filterless 32-inch TV by
using multi-area sequential algorithm

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Prototype
32-inch OCB LCD TV - MAC +CLDS Algorithm
• Maximum Power consumption 65 Watt
• Brightness : 500 nits
Fig. 6 CLDS backlight and power
consumption
Fig. 7 CCFL image and power
consumption
Fig. 8 CLDS image and power
consumption
CLDS illustration

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Prototype
15.4-inch TN Note Book - The Liquid Crystal Mode
• the TN Notebook response time
gray to gray is about 3.8 ms
• on/off about 5 ms
• the standard field sequential
method will not work in this type of
liquid crystal
• The notebook backlight structure is
the same as light guide standard
• 72 low power RGB LEDs were used
on left and right side
• the backlight driver was also divided
into 3 control areas according the
gate IC position of the LCD panel

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Prototype
15.4-inch TN Note Book - The Liquid Crystal Mode
• Turn On backlight
– Quality like TV
– The color image displays
correctly, and
– the brightness of about 400
nits can be achieved
• Turn Off backlight
– High optical efficient
– good enough to see the
gray image on the panel
without turning on the
backlight source.

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Conclusion
• Two major FSC alogrithm were propose
– MAC algorithm implements the backlight with 9 flash patterns
– CLDS algorithm divides backlight into multi-areas and set the
critical backlight dimming value
• The MAC+CLDS field sequential color display was
proposed for
– high brightness
– high color reproduction
– high light efficiency
– no heat sink
– low power consumption
• In the future, the advanced method will be proposed to
reduce the color break-up artifacts
• for example RGBW, YBGRC, and YBWGRC technique

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•Thank for your attention