In Cell觸摸屏原理

1、In-Cell觸摸屏原理2010.3.15Introduction of touch panel 1. Resistive touch panel 1.1 traditional resistive touch panel (directly glue on LCD module) a. 4/5/6/8-wire resistive touch panel b. digital resistive touch panel (touch switches, matrix) 1.2 integrate resistive touch panel into LCD cell (between top

2、 and bottom glasses) 2. Capacitive touch panel 2.1 capacitance changed by deformation of top glass 2.2 capacitance changed by induced current from finger 2.2.1 surface capacitive touch panel 2.2.2 projective capacitive touch panel detect self capacitance detect mutual capacitance 3. Ot

3、her touch panel (Infrared, SAW, Electromagnetic, Optical) Resistive touch panel基本原理：觸摸時(shí)，兩層ITO互相接觸，從而在兩層ITO之間形成電阻通路根據(jù)上下基板材料，可分為film on glass, glass on glass, film on film等結(jié)構(gòu)。1.1 4-wire resistive touch panel在兩電極上加5V直流電在ITO均勻電阻平面上形成均勻穩(wěn)恒電流場(chǎng)在另一面的ITO電極上測(cè)量電壓根據(jù)測(cè)得電壓值（0-5V）確定觸摸點(diǎn)的位置用同樣方法測(cè)量Y坐標(biāo)1.1 4-wire resisti

4、ve touch panelLow life time (around 1 million times)Low transmissivity (75%-85%)Not resist scratchLowest costEasy detect circuitWorks with any stylus1.2 Incell resistive touch panelsamsung(1)Basic principle:When pressed, the sensor switch is on (conductive column spacer contact sensor electrode)From

5、 plan view, at touch point, common electrode contact two sensing lines perpendicular with each other respectively 2. Capacitive touch panel 2.1 capacitance changed by deformation of top glass 2.2 capacitance changed by induced current from finger 2.2.1 surface capacitive touch panel 2.2.2 projective

6、 capacitive touch panel detect self capacitance detect mutual capacitance2.1 Capacitive touch panel (壓力式壓力式)This integrate type has some different structures, includes:Cell gap change typeSamsung filed a patent (US20080048994). AUO has made a demo.LC alignment change typeSamsung filed

7、patent (US20050094038) very early, but Samsungs demo applied another detect circuit (SID07 24.3), and Epson made a demo (SID08 55.2) based on Samsungs structure by using LTPS, IPS and active matrix sensor so that improved the performance.Cell gap change type(1)Samsungs patent (US20080048994) only po

8、sed a basic principle, its layer structure and detailed detect method is not shown in the patent.Though AUO has made a demo, there are very few open materials of its detect principle.They use the same principle: detect the capacitance change between common electrode and sense electrode by cell gap d

9、eformation.There are many ways to detect capacitance change, which way Samsung and AUO used is unknown.AUOSamsungCell gap change type(2)AUO和和LG的壓力式內(nèi)嵌觸摸屏樣品的壓力式內(nèi)嵌觸摸屏樣品LC alignment change typeSamsung(1) Samsungs patent (US20050094038) first proposed this method: Because different LC alignment has diffe

10、rent dielectric constant, and when pressed, the LC alignment is changed, so that the LC capacitance changed.LC alignment change typeSamsung(2)Samsung和Epson的in-cell LC alignment change type TPSamsungEpson2.2.1 Surface capacitive touch panel Have 2 conductive coatings. Upper conductive coating is the

11、working plane. Lower coating is shielding plane.Surface capacitive touch panelSurface capacitive touch panel principle: Touch point is treated as connecting to ground by a capacitor. The resistor from touch point to 4 corners R1-4 is related to the distance from touch point to 4 corners. The more th

12、e distance is, the more the resistor is.When add sine signal on 4 corners, the current at 4 corners I1-4 is inverse proportion to related R1-4. By measuring I1-4, the touch point can be detected.Surface capacitive touch panelLong life time (around 100 million times)Higher transmissivity (Can reach 9

13、0%)Only work with fingersHigher costPatent issueComplex detect circuitFast response speed2.2.2投射電容觸摸屏投射電容觸摸屏(PCT)投射電容觸摸屏（projective capacitive touch panel）可分為兩種不同的結(jié)構(gòu)：自電容(self capacitive)與互電容(mutual capacitive)自電容為較早的技術(shù)，來(lái)源于touch key, touchpad互電容技術(shù)由iphone發(fā)揚(yáng)光大，發(fā)展迅猛，將逐漸取代自電容類型Self capacitance自電容原理為當(dāng)手接觸時(shí)

14、，等效為parasitic capacitance增加，而且自電容檢測(cè)都是在前端（提供電源端）。檢測(cè)原理有很多，可檢測(cè)電壓、電流、電荷，下圖為charge transfer檢測(cè)原理。通過(guò)開關(guān)依次開合不斷對(duì)parasitic capacitance進(jìn)行充電放電，檢測(cè)放電時(shí)通過(guò)的電荷，當(dāng)有手指接觸時(shí)，流出電荷增加。Detect self capacitancePanel layout: generally using diamond pattern, so the capacitor from finger to both ITO layers will be big enough. The de

15、tect sequence is, first detect self capacitance at one layer (red), one line by one line, to get X position, then detect another layer (blue), to get Y position. So this is fake multi-touch.Projective capacitive touch panel自電容的多點(diǎn)觸摸定位問(wèn)題：自電容的多點(diǎn)觸摸定位問(wèn)題：Mutual capacitance互電容原理為：當(dāng)手指接觸時(shí)，等效為互電容改變，互電容檢測(cè)一般是在后

16、端（sense端）?？梢詸z測(cè)電壓或者電荷。下圖為電荷檢測(cè)等效電路。手指接觸后等效為互電容減小，此時(shí)讀出電荷減小。模型一Mutual capacitancePanel 圖案圖案Mutual capacitanceDriving method: At drive layer (red), add pulse signal one line by one line, and other lines connect to ground. At sense layer (blue), detect charge one by one. When all intersection is detected,

17、 the most charge decreased intersection is the touch point.This method is true multi-touch. So apple claimed that iphone is the first image sensing touch panel in the world.上表面和下表面diamond是錯(cuò)開的模型仿真結(jié)果No touchTouch互電容的優(yōu)點(diǎn)互電容的優(yōu)點(diǎn)互電容相對(duì)自電容的顯著優(yōu)點(diǎn)：1.對(duì)地寄生電容對(duì)觸控檢測(cè)影響很小，更適合在集成觸摸屏結(jié)構(gòu)2.具有更強(qiáng)的抵抗LCD噪聲能力3.可以實(shí)現(xiàn)真正的多點(diǎn)觸摸（不會(huì)有鬼點(diǎn)）但互電容是一個(gè)更加新的技術(shù)，目前幾乎所有觸控IC廠商采用的感應(yīng)技術(shù)都不一樣，各自研發(fā)自己的觸控技術(shù)。Other touch technology紅外：透光度好，價(jià)格低，適應(yīng)惡劣環(huán)境缺點(diǎn)：分辨率較低，易損壞在屏幕四邊排布紅外發(fā)射管和紅外接收管，一一對(duì)應(yīng)形成橫豎交叉的紅外線矩陣。用戶在觸摸屏幕時(shí)，手指就會(huì)擋住經(jīng)過(guò)該位置的橫豎兩條紅外線，因而可以判斷出觸摸點(diǎn)在屏幕的位置。 Other touch technology聲表面波：透光好，壽命長(zhǎng)缺點(diǎn)：易被油污，灰塵等影響，需經(jīng)常維護(hù)X 軸發(fā)射器X 軸接收器反射陣列可觸摸區(qū)域吸收殘波膠帶Y 軸接收器Y 軸發(fā)射器當(dāng)手