SOLOMONSYSTECH Solomon Systech Limited

Challenges of Capacitive Multi-touch for Large Displays

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E-paper

LED

Green Power

Touch Panel IC

TFT / LTPS

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dvan

ced

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(Indoor / Outdoor)

Display System Solution

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L-TFT

Display Interface Controller 2012 SID

Booth 111

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Different Sizes of Touch Panels

Solomon Systech Limited

Small Size (up to 5”)Smart phones and portable game consoles

Medium Size (6” ~ 10”)Tablet PCs, Netbooks, GPS systems, Ebook, etc.

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Different Sizes of Touch Panels (Cont’d)

Solomon Systech Limited

Medium Large Size (11” ~ 17”)Notebook, Ultrabook etc.

Large Size (18” onwards)All-in-one desktop PC, industrial applications, electronic billboards, etc.

CHALLENGES: in particular with medium-large and large size touch panels

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Challenge ONE: Mechanical Bending

Solomon Systech Limited

Touch panel not solidly glued to the TFT Module Capacitance formed between touch panel ITO and the TFT module can vary with touch pressure.

TFT Module

Large and thin touch panel

Capacitive effect formedbetween touch panel ITOand the TFT module.

Heavily coupledregion

Lightly coupledregion

Lightly coupledregion

Mechanical bendingformed by touch pressure

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SOLOMONSYSTECHChallenge ONE: Mechanical Bending (Cont’d)

Solomon Systech Limited

Even the variation in coupling capacitance due to touch pressure is only a few percents of the total capacitance of an ITO electrode can be an issue because:

The capacitance change due to a finger touch is also a few percents.

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Signal Amplitude

Panel X direction

Y directi

on

A frame scan image of a single finger touch with high touch pressure

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Solution for Mechanical Bending

Solomon Systech Limited

SOLUTION:

Apply appropriate filtering by digital signal processing (DSP)

Bowl-shaped profile removed while keeping the general shape of the finger image

Signal Amplitude

Panel X direction

Y directi

on

After applying appropriate filtering by DSP

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Solution for Mechanical Bending (Cont’d)

Solomon Systech Limited

2-finger touch with extreme high touch pressure

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digital filtering

Signal Amplitude

Panel X direction

Y directi

on

Original sensed signal Signal after digital filtering

DSP engine inside the touch controller reclaims the finger image

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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

58 sense electrodes

11.6" panel size, 1856 crossover points(Landscape orientation)

5" panel size,312 crossover points(Portrait orientation)

13 sense electrodes

32 d

rive

elec

trode

s

24 d

rive

elec

trode

s

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Solution for Many Sensing Nodes

Solomon Systech Limited

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)

non-scan region

scan region

scan region

fingerlocation

fingerlocation

Touch Panel

PartialScan

FullScan

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Challenge THREE: Higher Resistance & Heavier Capacitance

Solomon Systech Limited

As panel size becomes bigger, the capacitance per ITO electrode becomes heavier.

The mutual capacitor and the capacitance of a finger keeps constant.

DriveLine

SenseLine

DriveLine

SenseLine

ITO

ITO

Finger Model

MutualCapacitor

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Challenge THREE: Higher Resistance & Heavier Capacitance (cont’d)

Solomon Systech Limited

Resistance per ITO electrode is also higher

Higher resistance + heavier capacitance on larger touch panel 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

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Solution for Higher Resistance & Heavier Capacitance

Solomon Systech Limited

SOLUTIONS:Option 1: Drive the touch panel at both endsOption 2: Increase the driving voltage so that over-drive pulses can be deployedOption 3: Silver Nano Printing Technology

Over-drive driving signal

Large Touch Panel

Drive at both endsTouchController IC

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Challenge FOUR: Noise Coupling

Solomon Systech Limited

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

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Solution for Noise Coupling

Solomon Systech Limited

SOLUTION:

Counteract these noise sources by adding noise cancellation circuitry to the analog front-end.

Sense Lines of Touch Panel

Sensefrontend

Sensefrontend

Sensefrontend

Sensefrontend

Sensefrontend

Sensefrontend

Sensefrontend

Sensefrontend

Sensefrontend

Sensefrontend

Sensefrontend

Sensefrontend

Coherencenoise

detection

ADC

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Solution for Noise Coupling (Cont’d)

Solomon Systech Limited

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Constructive interference by applying a sinusoidal coherence noise source.

Destructive interference by applying a sinusoidal

coherence noise source.

After noise cancellation the finger signal is more stable.

Signal Amplitude

Sensing direction

Driving

directi

on

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Solomon Systech Solution

Solomon Systech Limited

Watchdog & Timers

uC

IIC slave Controller

ROM

Program and Data

Working Memory

to Host MCU

RAM

1.8V Reg, band gap &16MHz Osc.

GPIO

4 Ch Osc Self Cap

RAM

MUX

IIC Master ControllerEEPROM

0 1 2 3

32KHz OscPrescaler

23

1

0

Sleep Control

3rd Generation Front End

System Calibration

Scan Logic + M. Filter

Scan RAM +Delta RAM +

Reference RAM

Image Segmentation

4X sense channels3X drive channels

Cal Delta + 2D filter

MUX

2X/3Xcharge pumps

Cal finger C.G.

* DSP removes bowl-shaped profile due tomechanical bending.* DSP engine divided intovarious functions that canbe programmed by the uC.

* Develop partial scanningscheme to increasescanning speed for largepanels.

USB Controller FrontEnd to PC

DSP

2-st

ep A

DC

* This over-samplingADC provide anequivalent resolutionof more than 12-bit.

* Built-in noisecancellation circuitry

* For high voltagedriving.

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Thank Youhttp://www.solomon-systech.com

Email : sales@solomon-systech.comPhone : 852-2207 1111 Fax : 852-2267 0800

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Solomon Systech Solution

Solomon Systech Limited

All-in-one touch controllerSupport up to 13” panelCan be interface through IIC or USB10 fingers + 2 palms detection4 independent GPIO pins and 4 independent self-cap sensing pinsAutomatic Power Down Mode to save powerDSP function to remove the bowl-shaped profile due to mechanical bending.Include smart partial scanning optionsInclude coherence noise cancellation for better S/N ratioBuilt-in booster for programmable high voltage driving