Home > ANSYS Q3D 教學 > One-Layer and True Multi-touch for TSP

 

The article is intended to introduce some design and simulation tips for the one-layer ITO, which is true multi-touch (not two touch gesture) TSP.

1. Introduction

   1.1 What is the cause of "Ghost"

   1.2 One-layer and multi-touch -- Low Cost and No Ghost

   1.3 The nature limitation of one-layer multi-touch

   1.4 The last 1T-2R for one-layer multi-touch

2. Design Challenge

   2.1 Performance Criteria

   2.2 Linearity and Accuracy

3. ITO Pattern Optimization

   3.1 Pattern gap sweep

   3.2 Pattern branch width sweep with gap=100um

   3.3 Number of pattern branch

   3.4 Scan the shape of sensing cell

4. Linearity Optimization

   4.1 Sweep width of guard trace for isolating

   4.2 Sweep width of Rx channel

5. Q&A

6. Reference

1. Introduction

1.1 What is the cause of "Ghost" 

The two pictures above show different sensing methods using self-capacitor technology, and both of them will cause "ghost" points.

1.2 One-layer and multi-touch  Low Cost and No Ghost. 

1.3 The nature limitation of one-layer multi-touch 

Some non-sensing area in VA region is necessary for traces routing.

It works as translating the complexity of one-layer ITO with bridge to the one with more trace routing in VA and FPC region. What we want is to design ITO patterns fully covering the panel as possible as it can and minimize the non-sensing region.

單層多點技術就像是把原本單層跨橋製程的複雜性，轉嫁到在可視區(VA region)增加走線與外圍的軟板上增加走線連接. 而這在可視區聚集走線的區域, 是無法得到有效互感變化的, 這也是單層多點技術先天上的限制, 會影響線性度. 故才會有後面1T2R技術的發明, 即盡可能的減少總通道數, 進而減少可視區的走線佔用區域.

1.4 The last 1T2R for one-layer multi-touch, to minimize the number of total channels and non-sensing region. [1] 

2. Design Challenges

2.1 Performance Criteria 

High SNR
  High delta_Cm/base_Cm , and delta_Cm>160fF for 5 phi touch (suggest)
Good Linearity and Accuracy (less than 1mm with 5phi touch)
  Symmetrical shape of sensing cell
  Larger region of fringe affect
  Smaller non-sensing region
  Multi-touch can't affect accuracy
Low Cost and No Ghost
  Support true multi-touch
  One-layer ITO without bridge and shielding layer
Support large panel size with minimized number of total channels
  Minimize the RC time constant
Water Rejection

2.2 Linearity and Accuracy 

3. ITO Pattern Optimization

   3.1 Pattern gap sweep 

Increasing ITO gap will decrease base-Cm very much and delta-Cm a bit. To embed some dummy patterns will be better.

3.2 Pattern branch width sweep with gap=100um 

delta-Cm does not keep increasing with the width of sensing branch increasing

3.3 Number of pattern branch 

(number of branch, width of branch)=(4, 0.7mm) is the best design for max. delta-Cm.

Tx, Rx的分界線(gap), 在單位區域裡, 長一些是可以導致較高的delta-Cm, 這就是為何會有毛毛蟲圖案的原因. 但Tx, Rx分界線在單位面積的密度並非越大越好, 這Tx, Rx的分界線彼此若靠太近/太密可能會導致反效果(delta-Cm/base-Cm反而變小). 因為上方的手指反而不易拉走電力線以降低電容.

3.4 Scan the shape of sensing cell 

3.4.1 scanning the performance of sensing cell 1(brantch width=0.8mm), cell 2(brantch width=0.6mm) pattern horizontally

                

3.4.2 Scanning the performance of sensing cell 1(brantch width=0.8mm), and cell 2(brantch width=0.6mm) pattern vertically

Cell 1 pattern is more uniform and sensitive over all the sensing region. It will get better linearity performance of TSP for smaller touch size.

     別只把模擬軟體當model extraction tool, 要把她當analysis tool用, 才能真正發揮她的強大功能.

4. Linearity Optimization

可視區走線的區域，因為無法產生有效的互容變化，是造成單層多點結構線性度不佳的主要原因。故盡量縮小在可視區的走線區域面積，是改善線性度的關鍵。

4.1 Sweep width of guard trace for isolating 

Tx與Rx的走線間一定要穿插接地線以降低走線所引入的多餘電容感應量，但這地線其實有 加就有效果了，增加地線寬度雖然可以得到更好的隔離效果，但增加寬度20倍，才降低感應電容30%，犧牲這樣的VA區面積來放隔離地線(guard trace)，不太划算

4.2 Sweep width of Rx channel 

縮減Rx寬度(尤其是離Tx最近的那條)可以較有效的降低走線所引入的多餘電容感應量，降低寬度20倍，降低感應電容60%。但降低Rx寬度會導致R大幅增加，必須trade-off

5. Q&A

6. Reference

[1] Synaptics Inc. patent, US2013\0181943 A1