电容屏原理及技术介绍

1、 Touch TechnologyTouch Technology Touch Technology An OverviewAn Overview Touch TechnologyTable of ContentTable of Contentn Atmels Touch Technology Divisionn Market presencen Technology Overviewn Changing product designn Competing Technologiesn Software Libraryn Touch screen solutionsn Summary Touch

2、 TechnologyAtmels Touch Technology DivisionAtmels Touch Technology DivisionFounded as Quantum Research Group in 1996Located in Southampton, UKPart of Atmel corp since March 2008Solutions in production for 12 yearsLeaders in capacitive sensing technologyTechnology: charge-transferSubstantial patent b

3、aseFlexible Business Models Touch TechnologyMarket success to dateMarket success to datenMobile handsetsShipped in over 50M handsetsOver 200M buttons rotors and sliders in handsetsOver 5m touchscreensCustomers include Nokia, Motorola, Samsung, Bird, Sagem and Toshiba.nNote booksShipped over 2 millio

4、n buttons and slidersButtons and sliders for function keysOn/Off buttonsShipping in models for HP, Dell and Lenovo Touch TechnologyMarket SuccessMarket SuccessnKitchen AppliancesShipping in appliances for over 8 years successfullyMore that 20 design wins in various global manufacturersApplications i

5、n cooker hobs, cooker hoods (extractors) microwave controls, refrigerator controls and dishwasher controls.Customers include LG Appliances, GE, Whirlpool, Electrolux, Gorenje, Samsung, HaiernConsumer ElectronicsMultiple wins in desktop monitorsMultiple wins in MP3 appsCustomers include Apple, Philip

6、s, Samsung, LG, Bose, Logitech, Neovo, Asus, Acer Touch TechnologyTechnology OverviewTechnology Overview For 1 to 10 buttons Simple key shapes Easy to wire QTouchQSlideQWheel Linear touch Rotary touch 3 channels High resolutionQMatrix Up to 48 keys Water resistant High temperatureQFieldQTwo Single-t

7、ouch screens Multi-touch screensFunctionality also implemented through Atmel Touch Software Library part of AVR studio Touch TechnologyQTouchQTouchn QTouch simple solution 1-10 keysn 1.8V operationn Low power operationsn UART, SPI and I2Cn Always stays calibratedn Patented Adjacent Key Suppression(A

8、KS)Supports small keypadsn Small footprint ideal for mobile devicesn Supports clear discrete button touch screensn Most popular in the consumer marketQTouch Popular in consumer market Touch Technology8QTouch Basics: GoalsQTouch Basics: Goalsn Detect finger presence near electroden Electrode behind a

9、 dielectric panel so no direct galvanic connection to measuring circuitElectrodeMeasuring Circuit Touch Technology9QTouch Basics: Charge Transfer BasicsQTouch Basics: Charge Transfer Basicsn Cs Cxn example (1000:1 ratio)Cs = 10nFCx = 10pFn S1,S2 and S3 are CMOS IO pinsswitching between GND, Z and Vd

10、dCsGNDGNDVDDS1S2S3Sampling capacitorMCUCxEARTH Touch TechnologyQTouch: Charge Transfer BasicsQTouch: Charge Transfer Basicsn Uses a switched capacitor methodemploying a “sampling” capacitor CsUsually 1000+ times bigger than the sense electrode capacitance Cx (normally around 1pF to 10pF)n The sense

11、electrode is just an “open circuit” padWe measure the “self capacitance” of this pad Touch TechnologyQTouch: Charge Transfer BasicsQTouch: Charge Transfer Basicsn Cs is switched using “bit banging”n A series of voltage pulses cause current to flow in Cs and CxCharge on Cs builds up by each pulseCx i

12、s discharged after each pulsen The voltage over the Capacitor (U = Q/C) builds up as welln We measure the voltage by checking a digital inputLike a comparator, comparing vs VIHn We measure the number of pulses to reach VIHn When we touch the sensor, the number of pulses will be decreased Touch Techn

13、ology12QTouch Basics: Charge Transfer BasicsQTouch Basics: Charge Transfer BasicsCsSampling capacitorMCUCxEARTHGNDVDDS2S3GNDS1 Touch Technology13Step 1: Discharge Cx and CsStep 1: Discharge Cx and CsCsSampling capacitorMCUCxEARTHGNDVDDS2S3GNDS1Create Initial condition: Takes time Touch Technology14S

14、tep 2: Float CsStep 2: Float CsCsSampling capacitorMCUCxEARTHGNDVDDS2S3GNDS1Prevents cross-conduction between P and N-channel transistors in *some* MCU IO cellsWell designed I/O blocks does this automatically Touch Technology15Step 3: Charge TransferStep 3: Charge TransferCsSampling capacitorMCUCxEA

15、RTHGNDVDDS2S3GNDS1Rising edge on SNS pin drives charge through Cs into Cx Touch Technology16Step 4: Float Cs and settling timeStep 4: Float Cs and settling timeCsSampling capacitorMCUCxEARTHGNDVDDS2S3GNDS1 Touch Technology17Step 5: Measure Vcs and discharge CxStep 5: Measure Vcs and discharge CxCsSa

16、mpling capacitorMCUCxEARTHGNDVDDS2S3GNDS1SNS = Vcs SNSK = Gnd Touch Technology18Step 5: Measure Vcs and discharge CxStep 5: Measure Vcs and discharge CxCsSampling capacitorMCUCxEARTHGNDVDDS2S3GNDS1SNS = Vcs = VDD * (Cx / (Cs + Cx)Cs = 1000 * CxVcs = VDD / 1000Qs = Cs * VcsQx = Cx * VxVx = 0 = Qx = 0

17、 SNSK = Gnd Touch Technology19Repeat 1 - 5:Repeat 1 - 5:CsSampling capacitorMCUCxEARTHGNDVDDS2S3GNDS1Vcs = VDD / 1000 initiallyAdd approximately 0,999 * VDD * (Cx / (Cs + Cx)GndQs = Cs * Vcs Touch TechnologyContinuously add charge to CsContinuously add charge to CsVIHWhen Vcs reached VIH, the I/O po

18、rt will read as ”1”. Touch TechnologyReal WaveformReal WaveformVcsTimeVdd Touch TechnologyCharging WaveformCharging WaveformVsnsTimeVihVddVsnskTimeVdd Touch TechnologyNormal modeNormal modenTypically uses 200 pulses to reach VIHnTypical burst length = 500 us . 5 ms Long burst lengths mainly for prox

19、imity detectionnRun several bursts before declaring detection ”Detect integration - DI” Similar to debouncingnDI count normally from 3 upwards, 10 = commonnHysteresis: detection level changes on detect Touch Technology24Add a finger = Ct increaseAdd a finger = Ct increaseCsSampling capacitorMCUCxEAR

20、THGNDVDDS2S3GNDS1Vcs = VDD / 1000 initiallyAdd approximately 0,999 * VDD * (Cx/Ct / (Cs + Cx/Ct)GndQs = Cs * VcsCtEARTH Touch TechnologyEffect of increasing CtEffect of increasing CtnThe charge added each pulse will increase.nCs will charge faster, than if no finger is presentnVIH is reached fastern

21、Fewer pulses are needednBurst time gets shorternBurst change (delta) is proportional to Ct Touch TechnologyContinuously add charge to CsContinuously add charge to CsVIHWhen Vcs reached VIH, the I/O port will read as ”1”.No fingerFinger present Touch TechnologyQTouch: SensitivityQTouch: Sensitivityn

22、Larger key surface area = more sensitivity n Sampling Capacitor, Cs controls sensitivity Increasing Cs = Increased differential sensitivity makes the burst length longer Improves resolutionn Simple tuning procedure Changing a single capacitor value per key Can be done without softwaren One time tuni

23、ng for a design Touch TechnologyTechnology OverviewTechnology Overview For 1 to 10 buttons Simple key shapes Easy to wire QTouchQSlideQWheel Linear touch Rotary touch 3 channels High resolutionQMatrix Up to 48 keys Water resistant High temperatureQFieldQTwo Single-touch screens Multi-touch screensFu

24、nctionality also implemented through Atmel Touch Software Library part of AVR studio Touch TechnologyQMatrixQMatrix UART, SPI and I2C Efficient X-Y interleaved electrodes Support up to 48keys Low power operations 1.8V operation Always stays calibrated Available in small packages (up to 24 Keys) Pate

25、nted Adjacent Key Suppression(AKS) for small keypads Low power and small footprint ideal for mobile devices Supports clear discrete button touch screens Most popular in the consumer marketQMatrix - Popular in appliance market and mobile market Touch TechnologySelf CapacitanceSelf Capacitance Touch T

26、echnologySelf CapacitanceSelf Capacitance Touch TechnologySelf CapacitanceSelf Capacitance Touch TechnologySelf CapacitanceSelf Capacitance Touch TechnologySelf CapacitanceSelf Capacitance Touch TechnologySelf CapacitanceSelf Capacitance Touch TechnologySelf CapacitanceSelf Capacitance Touch Technol

27、ogySelf CapacitanceSelf Capacitance Touch TechnologySelf CapacitanceSelf Capacitance Touch TechnologySelf CapacitanceSelf Capacitance Touch TechnologySelf CapacitanceSelf Capacitance Touch TechnologySelf CapacitanceSelf Capacitance Touch TechnologySelf CapacitanceSelf Capacitance Touch TechnologySel

28、f CapacitanceSelf Capacitance Touch TechnologySelf CapacitanceSelf Capacitance Touch TechnologyMutual CapacitanceMutual Capacitance Touch TechnologyMutual CapacitanceMutual Capacitance Touch TechnologyMutual CapacitanceMutual Capacitance Touch TechnologyMutual CapacitanceMutual Capacitance Touch Tec

29、hnologyMutual CapacitanceMutual Capacitance Touch TechnologyMutual CapacitanceMutual Capacitance Touch TechnologyMutual CapacitanceMutual Capacitance Touch TechnologyMutual CapacitanceMutual Capacitance Touch TechnologyMutual CapacitanceMutual Capacitance Touch TechnologyMutual CapacitanceMutual Cap

30、acitance Touch TechnologyMutual CapacitanceMutual Capacitance Touch TechnologyMutual CapacitanceMutual Capacitance Touch TechnologyMutual CapacitanceMutual Capacitance Touch TechnologyMutual CapacitanceMutual Capacitance Touch TechnologyMutual CapacitanceMutual Capacitance Touch TechnologyMutual Cap

31、acitanceMutual Capacitance Touch TechnologyQMatrix: Charge Transfer BasicsQMatrix: Charge Transfer Basicsn Also uses a switched capacitor method employing a “sampling” capacitor Cs that is usually 1000+ times bigger than the sensor capacitance Cx (normally around 1pF to 5pF)n The sensor in this case

32、 is formed at the “intersection” of two electrodes, X (transmitter) and Y (receiver). n In other words QMatrix measures the *mutual* transverse (usually) coupling capacitance between X and Yn X and YFixed number of voltage pulsesEach pulse cause current to flow in Cx and Cs (in series with each othe

33、r)Current only flows in selected pairs or Cx and Cs. This is how a sequential matrix scan is achievedn The voltage on Cs builds up pulse-by-pulse and after the fixed number of pulses is done, the voltage on Cs is measured to give us our reading Touch TechnologyQMatrix: Charge Transfer BasicsQMatrix:

34、 Charge Transfer BasicsCsGNDGNDVDDS1S2S3Sampling capacitorMCUCxGNDS4XYkYVyk|Vcs|TimeApproximately linear0.25VApproximately linearVsnsTime-0.25VtTerminal voltageY0Y1X0X1X2X3 Touch TechnologyQMatrix : Measuring TechniqueQMatrix : Measuring TechniqueWe can use Atmel AVRs e.g. Tiny44/84/88, Mega48/88/16

35、8 (including PicoPower), Mega164P/324P for QMatrix because they have the required internal comparator + counter/capture registersCsGNDGNDVDDS1S2S3MCUCxGNDS4XYkYRsmpSMPCAPTURECTRCLK+-VDDS5GNDS6VcsTime Touch TechnologyQMatrix Basics: What Happens During QMatrix Basics: What Happens During Touch ?:Touc

36、h ?:n Now we bring a finger close to electroden This diverts charge from Cx, and so away from Csn So each charge pulse now charges Cs by a smaller amountn This means charge builds up in Cs less quicklyn So if each pulse deposits less charge, then Vcs rises slower, soreaches a smaller terminal voltag

37、eneeds less time to discharge to GNDso counter value gets lesscount change (delta) is proportional to CtE-fieldXYEARTHCtVcsTimeNo touchDeltaTimeTouchVcs Touch TechnologyQMatrix: SensitivityQMatrix: SensitivitynOptimise key designs for improved sensitivity and SNRnIncreasing Burst Length (number of c

38、harge pulses), increases sensitivity Software based tuning Does not require component changesnIncreasing Rsmp, increases signal resolutionnOne time tuning for a design Touch TechnologyBest in class solutions:n Excellent signal-to-noise ration Excellent field penetrationn Spread spectrum modulationn

39、Failure mode detectionn Best in class EMC characteristic Ease of design:n Highly integrated solutionsn Reference designsFlexible:n Standard or custom productsn User developed solutionsCost effectiveAtmels Charge Transfer TechnologyAtmels Charge Transfer TechnologyQMatrix charge transfer principle To

40、uch TechnologyTechnology OverviewTechnology Overview For 1 to 10 buttons Simple key shapes Easy to wire QTouchQSlideQWheel Linear touch Rotary touch 3 channels High resolutionQMatrix Up to 48 keys Water resistant High temperatureQFieldQTwo Single-touch screens Multi-touch screensFunctionality also i

41、mplemented through Atmel Touch Software Library part of AVR studio Touch Technologyn Usable over LCD displayn iPod-type functionality n Low voltage, low powern Slider/Wheel available in QTouch devices: QT1106n Slider available in QMatrix device: AT42QT2160n Only three channels used to make a 256 pos

42、ition absolute scrollerQSlide & QWheel - Easy scrollingQSlide & QWheel - Easy scrollingQSlide/QMatrix - Popular in personal media devices Touch TechnologyQSlide & QWheel: QTouchQSlide & QWheel: QTouchi) Small 10-12mm diaii) Medium 12-16mm diaiii) Large 16-40mm diai) Small 20-25mm lon

43、gii) Medium/Large 25-60mm long Touch TechnologyQSlide & QWheel: QMatrixQSlide & QWheel: QMatrixX0X1X2X3YYX0X1X2X3X4X5X6X7nOne Layer Designs Touch TechnologyQSlide & QWheel: QMatrixQSlide & QWheel: QMatrixn2 Layer Designs - Flooded XnIncreases design possibilitiesnImproved directional

44、 noise immunityYX0X1X2X3X4X5YX0X1X2X3 Touch TechnologyQSlide & QWheel : Touch PositionQSlide & QWheel : Touch PositionABS SX XL EF TRI G HTRI G HTABCn Uses geometric calculations in between 2 points (channels) to determine absolute touch position Touch TechnologyCapacitive sensing - changing

45、 product designCapacitive sensing - changing product designn Flexible No longer restricted to using buttons Increasing focus on industrial design UI innovation with multi-touchn Innovative Slimmer products - no mechanical parts required Easy to clean Hidden until lit Touch TechnologyOther MarketsOth

46、er MarketsnCapsensing is not only for Mobile and appliances.Atmel have many design wins in .nMedicalnAutomotivenIndustrial nVendingnSecuritynToys Touch TechnologyAtmel Industry Presence : recent design winsAtmel Industry Presence : recent design winsConsumerMobile and PNDMobile phonesSmart phonesHea

47、dsetsPNDsLaptopsDigital photo framesTVs and Home cinemasStereos and speakersMP3 playersApplianceOvensRefrigeratorsWashing machines Touch TechnologyAtmel advantagesAtmel advantagesnEarly market entry long experiencenAddresses many diverse marketsnRobust solution Very few competitors are even closenCo

48、mpetitor analysis data available on request Touch TechnologyDifferentiation: Atmel Touch SensorsDifferentiation: Atmel Touch Sensorsn Very high signal to noise ratioMakes designs easier from the outsetSupports small sensorsOK in noisy environmentsn Broad range of key sizes & shapes due to size o

49、f integration capacitorsInherent flexibility of technologyn Key patent for close pitched key arraysAdjacent Key Suppression (AKS) Touch TechnologyQMatrixQMatrixn Strong suppression of moisture effectsDue to X and Y electrode design and touch aquisitionn Remote placement of chipSensitive to X/Y cross

50、ingNot sensitive to X linesNot sensitive to Y lines Touch TechnologyQTouch/QMatrix on AVRQTouch/QMatrix on AVRn AVR has plenty of processing power.Can complete sensing fasterCan spend more time in sleepn Minimal amount of H/W neededChip resource available for other applicationsnLower power consumpti

51、onnBroad range of applications with a lower cost chip Touch TechnologyQ-Touch/Q-Matrix librariesQ-Touch/Q-Matrix librariesEmpowering Atmel AVR users with Touch Sensor Technology Touch TechnologyAims of librariesAims of librariesn Flexible, high performance capacitive sensing firmware n Well proven c

52、apacitive sensing solutionn Support for buttons, sliders and wheelsn Easy to implementn No license feen Can coexist with user application Touch TechnologyAdvantages of the Atmel Code ModuleAdvantages of the Atmel Code Modulen Recognised industry leading Charge Transfer techniquen n Best signal to no

53、ise rationMakes designs fundamentally easier to implementn Flexible implementationarbitrary key sizes & shapesno need to balance channelsn All digital techniqueNone of the disadvantages of analogue sensing techniquesn Easy implementation using Quantum reference designsn Access to key Atmel/Quant

54、um patents Adjacent Key Suppression Touch TechnologyAdvantages of the Atmel Code ModuleAdvantages of the Atmel Code Modulen Uses AVR as the hardware platform AVR32, Cortex-M3 to follown Industry leading microcontroller price / performancen Lowest power consumptionn Broad product range can be develop

55、ed & implementedn Fully flexible user implementation Touch TechnologyAdvantages of the Atmel Code ModuleAdvantages of the Atmel Code Modulen Simple, easy to implement code library Robust front end capacitive acquisitionn Highly experienced Quantum Atmel teamApplications / implementation supportn

56、 Low cost solutionn No license costn Support provided by the Atmel FAEs Touch TechnologyCode Module AvailabilityCode Module Availabilityn Code modules will be available in two basic versions QTouch module recommended as first approach- High sensitivity- High system noise tolerant- Easy design QMatri

57、x module- Less pins needed for 3+ channels- More tolerant of moisture and ground loading- Electrode design needs caren Support packages available in both cases Library module and API GUI front end Evaluation module & PC Application Software Reference implementation & application note Touch T

58、echnologyAtmel Touch Software Library - FlexibleAtmel Touch Software Library - FlexiblenAvailable on standard Atmel parts using libraries in AVR studionEnvironmental changes tracked and compensatednError conditions detected and correctednWorks seamlessly with main device applicationnFor volume progr

59、ams, application and code development availableAtmel TouchSoftwareLibraryHost AppHost AppAtmel TouchSoftwareLibrary Touch TechnologyAtmel Capacitive Touchscreen Atmel Capacitive Touchscreen SolutionsSolutionsTwo Touch and Single Touch TouchscreensRoadmap for TouchcreensJanuary 2009 Touch TechnologyP

60、rojected Capacitive Touch ScreensProjected Capacitive Touch Screensn Sensors realised with patterned conductorsUsually realised using ITO/PET or ITO/GlassMostly 2+ layers, Atmels solution supports single layer sensorsn Multiple sensing elementsn Sequential sensingAtmels QField technologyn AdvantagesExcellent signal to noise ratio Accuracy across the wh