Challenges of Capacitive
Multi-touch for Large Displays
SOLOMON
SYSTECH
Solomon Systech Limited
Large
LED
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SOLOMON
SYSTECH
L-TFT
OLED
Mobile
Display Interface
Controller
2012 SID
Booth 111
Touch Panel IC
TFT / LTPS
STN
•
•
•
•
Mobile
Consumer
Wireless
Multimedia
• LED Backlight
• LED Lighting Solutions
(Indoor / Outdoor)
Display System Solution
Green Power
SID Display Week 2012
June 2012
P. 2
Different Sizes of Touch Panels
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Small Size (up to 5”)
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`
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SYSTECH
Smart phones and portable game
consoles
Medium Size (6” ~ 10”)
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Tablet PCs, Netbooks, GPS systems,
Ebook, etc.
Solomon Systech Limited
SID Display Week 2012
June 2012
P. 3
Different Sizes of Touch Panels (Cont’d)
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Medium Large Size (11” ~ 17”)
`
`
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SYSTECH
Notebook, Ultrabook etc.
Large Size (18” onwards)
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All-in-one desktop PC, industrial
applications, electronic billboards,
etc.
CHALLENGES: in particular with medium-large and
large size touch panels
Solomon Systech Limited
SID Display Week 2012
June 2012
P. 4
Challenge ONE: Mechanical Bending
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SYSTECH
Touch panel not solidly glued to the TFT Module Æ Capacitance
formed between touch panel ITO and the TFT module can vary with
touch pressure.
`
Mechanical bending
formed by touch pressure
Capacitive effect formed
between touch panel ITO
and the TFT module.
in to
Large and th
uch panel
TFT Module
Lightly coupled
region
Solomon Systech Limited
Heavily coupled
region
Lightly coupled
region
SID Display Week 2012
June 2012
P. 5
Challenge ONE: Mechanical Bending (Cont’d)
`
Even the variation in coupling
capacitance due to touch
pressure is only a few percents
of the total capacitance of an
ITO electrode Æ can be an
issue because:
250
200
150
100
50
The capacitance change due to
a finger touch is also a few
percents.
0
-50
-100
Signal Amplitude
Y
P ane l
Solomon Systech Limited
d
SOLOMON
SYSTECH
tio
c
ire
n
X direc
tion
A frame scan image of a single finger
touch with high touch pressure
SID Display Week 2012
June 2012
P. 6
Solution for Mechanical Bending
SOLOMON
SYSTECH
250
SOLUTION:
`
200
Apply appropriate filtering by
digital signal processing (DSP)
150
100
`
Bowl-shaped profile removed
while keeping the general
shape of the finger image
50
0
-50
-100
Signal Amplitude
Y
P ane l
Solomon Systech Limited
d
tio
c
ire
n
X direc
After applying appropriate filtering
by DSP
tion
SID Display Week 2012
June 2012
P. 7
Solution for Mechanical Bending (Cont’d)
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2-finger touch with extreme high
touch pressure
`
DSP engine inside the touch
controller reclaims the finger image
200
200
150
150
100
100
digital
filtering
50
0
50
0
-50
-50
-100
-100
Signal Amplitude
-150
Original sensed signal
Y
P ane l
Solomon Systech Limited
SOLOMON
SYSTECH
d
-150
io
ct
e
ir
n
X direc
Signal after digital filtering
tion
SID Display Week 2012
June 2012
P. 8
Challenge TWO: Many Sensing Nodes
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312 sensing nodes (or cross points): 5” smart phone
`
1856 sensing nodes: 11.6” Ultrabook
`
4400+ sensing nodes: 18” all-in-one desktop PC
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SYSTECH
11.6" panel size, 1856 crossover points
(Landscape orientation)
24 drive electrodes
32 drive electrodes
5" panel size,
312 crossover points
(Portrait orientation)
58 sense electrodes
Solomon Systech Limited
13 sense electrodes
SID Display Week 2012
June 2012
P. 9
Solution for Many Sensing Nodes
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SYSTECH
SOLUTIONS:
`
Option 1: Increase scanning speed and data conversion speed of the
touch controller.
`
Option 2: Use of partial or multiple-line scanning technique (Diagram)
Touch Panel
finger
location
scan region
non-scan region
Partial
Scan
Full
Scan
scan region
finger
location
Solomon Systech Limited
SID Display Week 2012
June 2012
P. 10
Challenge THREE: Higher Resistance &
Heavier Capacitance
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SYSTECH
`
As panel size becomes bigger, the capacitance per ITO electrode
becomes heavier.
`
The mutual capacitor and the capacitance of a finger keeps
constant.
Finger Model
Drive
Line
Drive
Line
ITO
ITO
Mutual
Capacitor
Sense
Line
Solomon Systech Limited
Sense
Line
SID Display Week 2012
June 2012
P. 11
Challenge THREE: Higher Resistance &
Heavier Capacitance (cont’d)
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SYSTECH
`
Resistance per ITO electrode is also higher
`
Higher resistance + heavier capacitance on larger touch panel Æ
transmission line effect more noticeable
`
Large panels have lower frequency response than small panels
`
Adverse effect: with more sensing nodes on a larger touch panel,
we want to scan faster rather than slower
Solomon Systech Limited
SID Display Week 2012
June 2012
P. 12
Solution for Higher Resistance & Heavier
Capacitance
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SYSTECH
SOLUTIONS:
`
Option 1: Drive the touch panel at both ends
`
Option 2: Increase the driving voltage so that over-drive pulses can be deployed
`
Option 3: Silver Nano Printing Technology
Large Touch Panel
Over-drive driving signal
Touch
Controller IC
Solomon Systech Limited
Drive at both ends
SID Display Week 2012
June 2012
P. 13
Challenge FOUR: Noise Coupling
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SYSTECH
`
As the panel becomes bigger, it becomes easier to pick up
coherence noise from the environment
`
A typical example is the coupling between TFT VCOM and the
touch panel when no ground shield is added.
`
Another example: switch mode power supply (SMPS) noise
Solomon Systech Limited
SID Display Week 2012
June 2012
P. 14
Solution for Noise Coupling
SOLOMON
SYSTECH
SOLUTION:
`
Counteract these noise sources by adding noise cancellation
circuitry to the analog front-end.
Sense Lines of Touch Panel
Coherence
noise
detection
Sense
front
end
Sense
front
end
Sense
front
end
Sense
front
end
Sense
front
end
Sense
front
end
Sense
front
end
Sense
front
end
Sense
front
end
Sense
front
end
Sense
front
end
Sense
front
end
ADC
Solomon Systech Limited
SID Display Week 2012
June 2012
P. 15
Solution for Noise Coupling (Cont’d)
SOLOMON
SYSTECH
350
350
300
300
250
250
200
200
150
150
100
100
50
50
0
0
-50
-50
-100
-100
350
Constructive interference by
applying a sinusoidal
coherence noise source.
Destructive interference by
applying a sinusoidal
coherence noise source.
300
250
200
Signal Amplitude
150
100
50
0
After noise cancellation the
finger signal is more stable.
Solomon Systech Limited
-50
-100
g
in ion
v
t
i
Dr irec
d
Sensin
SID Display Week 2012
g direc
tion
June 2012
P. 16
Solomon Systech Solution
uC
M
U
X
ROM
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SYSTECH
Working Memory
RAM
Program and Data
to Host MCU
IIC slave Controller
RAM
Sleep Control
1.8V Reg, band gap &
16MHz Osc.
EEPROM
IIC Master Controller
Prescaler
32KHz Osc
Watchdog & Timers
0
GPIO
0
1
1
2
3
4 Ch Osc Self Cap
2
3
USB Controller
Cal Delta + 2D filter
Cal finger C.G.
System Calibration
2X/3X
charge pumps
D
S
P
Scan Logic + M. Filter
* Develop partial scanning
scheme to increase
scanning speed for large
panels.
Scan RAM +
Delta RAM +
Reference RAM
3rd Generation Front End
3X drive channels
Solomon Systech Limited
to PC
Image Segmentation
2-step ADC
* DSP removes bowlshaped profile due to
mechanical bending.
* DSP engine divided into
various functions that can
be programmed by the uC.
Front
End
* For high voltage
driving.
* This over-sampling
ADC provide an
equivalent resolution
of more than 12-bit.
MUX
* Built-in noise
cancellation circuitry
4X sense channels
SID Display Week 2012
June 2012
P. 17
SOLOMON
SYSTECH
Thank You
http://www.solomon-systech.com
Email : sales@solomon-systech.com
Phone : 852-2207 1111
Fax : 852-2267 0800
Solomon Systech Solution
SOLOMON
SYSTECH
`
All-in-one touch controller
`
Support up to 13” panel
`
Can be interface through IIC or USB
`
10 fingers + 2 palms detection
`
4 independent GPIO pins and 4 independent self-cap sensing
pins
`
Automatic Power Down Mode to save power
`
DSP function to remove the bowl-shaped profile due to
mechanical bending.
`
Include smart partial scanning options
`
Include coherence noise cancellation for better S/N ratio
`
Built-in booster for programmable high voltage driving
Solomon Systech Limited
SID Display Week 2012
June 2012
P. 19