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`Touchscreens 101: Understanding touch-
`screen technology and design
`
`JUNE 29, 2009
`BY PLANET ANALOG
`
`) COMMENT 1
`
`Emai
`A)
`Sl
`Aprint
`jPrint | PDF (~) Email
`
`
`
`(Editor's note : there is a list of related articles with links at the end, below the
`“About the authors”section.)
`
`.
`Touchscreens (sometimesspelled as touch screen) are everywhere: they are
`embeddedin phones, office equipment, speakers,digital photo frames, TV
`control buttons, remote controls, GPS systems, automotive keyless entry, and
`medical monitoring equipment. As a component, they have reached into every
`industry, every product type, every size, and every applicationat every price
`point.In fact, if a product has an LCD orbuttons, a designer somewhereis
`probably evaluating how that product, too, can implement touchscreen
`technology. As with any technology, there are manydifferent ways to
`implementation approaches, many promises of performance, and many
`different technical considerations whendesigning a touchscreen.
`
`Silent Switcher°2
`family reduces radiated
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`(Geetcrates
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`Recent Posts
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`Is Optical Computing in Our Future? / Just give mea
`Anatomyof a touchscreen
`decent data sheet, please / Five things to know
`about prediction and negative-delayfilters / Did the
`Knowing whatyou need is an importantfirst step in designing a touchscreen
`DopplerEffect even exist before railroads? / Diapers
`product. Vendors in the touchscreen supply chain frequently offerdifferent
`with RFID: Trivial Pursuit or Widely Useful?
`pieces of the puzzle, often times combining several to create a value chainfor
`the end customer. Figure 1 shows a blowupof the touchscreen ecosystem. This
`ecosystemis the same whether it is in the latest Notebook PC orthe latest
`touch-enabled mobile phone.
`
`Rackiit Coniiants
`
`“stop” in the Nameof Noise: Do I Shut Off That
`Switching Supply? — JWEasyTech on What Does
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`OurFuture?
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`please
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`Petitioner STMICROELECTRONICS, INC.,
`Ex. 1007, IPR2021-01160 Page 1 of 6
`
`

`

`Categories
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`Select Category
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`B C
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`Educating a Modern
`Engineer | "Round &
`*Round: Electronics
`and the Circular
`|
`| Economy
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`|
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`
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`
`immediate hands-on
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`Fully calibrated MEMS
`IMU offers significant
`height reduction for
`industrial applications
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`ifcular economy
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`© 27:43
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` Engineering students demand
`
`There are six key elements:
`1. Front panelor bezel : The front panel or bezel is the outermost skin of the end
`product. In someproducts, this bezel will encompassa protective clear overlay
`to keep weather and moisture out of the system, andto resist scratching and
`vandalism to the underlying sensor technology (see item 3 below). Othertimes,
`the outmost bezel simply covers the edges of the underlying touch sensor; in
`this case, it is purely decorative.
`
`2. Touch controller : The touch-controller is generally a small microcontroller-
`based IC that sits between the touch sensor and the embedded system
`controller. This IC caneither be located on a controller board inside the system
`or it can be located ona flexible printed circuit (FPC) affixed to the glass touch
`sensor. This touch controller takes information from the touch sensor and
`
`translates it into information that the PC or embedded systemcontroller can
`understand.
`
`3. Touch sensor : A touchscreen “sensor”is a clear glass panel with a touch-
`responsive surface. This sensoris placed over an LCD so that the toucharea of
`the panel covers the viewable area of the video screen. There are manydifferent
`touch-sensortechnologies on the markettoday, each using a different method
`to detect touch input. Fundamentally, these technologiesall use anelectrical
`current running through the panel that, whentouched, causes a voltage or
`signal change. This voltage changeis sensed by the touchcontrollerto
`determinethe location of the touch onthe screen.
`
`4. Liquid crystal display : Most touchscreen systems workovertraditional LCDs.
`LCDs for a touch-enabled product should be chosenfor the same reasons they
`would in a traditional system:resolution, clarity, refresh speed, and cost. One
`major consideration for a touchscreen, however,is the level of electrical
`emission. Because the technology in the touch sensoris based on small
`electrical changes whenthe panel is touched, an LCD that emitsa lot of
`electrical noise canbedifficult to design around. Touch sensor vendors should
`be consulted before choosing an LCDfor a touchscreen systein.
`
`5. System software : Touchscreendriver software canbe either shipped from the
`factory (within the embedded Osof a cell phone)or offered as add-on software
`(like adding a touchscreento a traditional PC). This software allows the
`touchscreen and system controller to work togetherandtells the product's
`operating system how to interpret the touch-event informationthatis sent
`from the controller. In a PC-style application, most touchscreen drivers work
`like a PC mouse. This makes touching the screen similarto clicking the mouse
`at the samelocation on the screen. In embedded systems, the embedded
`controller driver must compare the information presented onthe screen to the
`location of the received touch.
`
`The “big three” of touchscreen technology
`
`j
`
`ANALOG
`DEVICES
`LT Ree Tanckta
`
`- Resistive Louchscreens are the most commontouchscreen technology.
`They are used in high-traffic applications and are immuneto water or
`(BSee ADISI650x
`other debris on the screen. Resistive touchscreensare usually the
`lowest-cost touchscreen implementation. Because they react to
`pressure, they canbeactivated by a finger, gloved hand, stylus, or other
`object, such as a credit card.
`— Surface-capacitive touchscreens provide a muchclearerdisplay than the
`plastic cover typically used in a resistive touchscreen. In a surface-
`capacitive display, sensors in the four cornersof the display detect
`capacitance changesdue to touch. These touchscreens can only be
`activated by a finger or other conductive object.
`— Projected-capacitive touchscreens are the latest entry to the market. This
`technology also offers superioroptical clarity, but it has significant
`advantages over surface-capacitive screens. Projected capacitive sensors
`
`
`
`Search
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`SEARCH
`
`Petitioner STMICROELECTRONICS, INC.,
`Ex. 1007, IPR2021-01160 Page 2 of 6
`
`

`

`How touchscreens work
`
`Let's look inside the two most common touchscreentechnologies.
`
`The most widely used touchscreen technologyis resistive. Most people have
`used oneof these resistive touchscreens already, in the ATM at the bank, in the
`credit card checkout in moststores, or even for entering an order ina
`restaurant. Projective-capacitance touchscreens, on the other hand,are not as
`broadly available yet, but are gaining market momentum. Manycellphones and
`portable music players are beginning to cometo market withprojective-
`capacitance interfaces. Both resistive and capacitive technologies have a strong
`electrical component, both use ITO (Indium-Tin-Oxide, a clear conductor), and
`both will be aroundfor a long time to come.
`
`A resistive touchscreen(Figure 2 , left side) consists of a flexible top layer, then a
`layer of ITO (Indium-Tin-Oxide), an air gap and then another layerof ITO. The
`panel has4 wires attached to the ITO layers: one onthe left and rightsides of
`the 'X' layer, and one onthe top and bottom sides of the 'Y layer.
`
`Figure2. Stackup layers for “resistive”(left) and “capacitive” (right) screens
`
`(Click on imageto enlarge)
`
`A touchis detected when the flexible top layer is pressed downto contact the
`lower layer. The location of a touch is measured in twosteps: First, the 'X right’
`is driven to a knownvoltage, and the ‘x left’ is driven to ground andthe voltage
`is read from a Y sensor. This provides the X coordinate. This process is repeated
`for the other axis to determinethe exact finger position.
`
`Resistive touchscreens also come in 5-wire, and 8-wire versions. The 5-wire
`version replaces the top ITO layer with a low-resistance “conductive layer” that
`provides better durability. The 8-wire panel was developed to enable higher
`resolution by enabling better calibration of the panel's characteristics.
`
`There are several drawbacks toresistive technology. Theflexible top layer has
`only 75%-80% clarity and the resistive touchscreen measurementprocess has
`several error sources. If the ITO layers are not uniform,the resistancewill not
`vary linearly across the sensor. Measuring voltage to 10- or 12-bit precision is
`required, whichis difficult in many environments. Manyof the existing
`resistive touchscreensalso require periodic calibration to realign the touch
`points with the underlying LCD image.
`
`Petitioner STMICROELECTRONICS, INC.,
`Ex. 1007, IPR2021-01160 Page 3 of 6
`
`

`

`Conversely, projected-capacitive touchscreens have no moving parts. The only
`thing betweenthe LCD andtheuseris ITO andglass, which have near 100%
`optical clarity. The projected-capacitance sensing hardwareconsistsof a glass
`top layer(Figure 2, right side), followed by an array of X sensors, an insulating
`layer, then anarray of Y sensors onaglass substrate. The panel will have a wire
`for each X and Y sensor, so a 5 x G panel will have 11 connections (Figure3),
`while a 10 x 14 panel will have 24 sensor connections.
`
`Figure3. Signal intensity at rows and colunins denotelocation of touch
`
`(Click on imageto enlarge)
`
`As a finger or other conductive object approachesthe screen, it creates a
`capacitor betweenthe sensors andthe finger. This capacitor is small relative to
`the others in the system (about 0.5 pF outof 20 pF), but it is readily measured.
`One commonmeasuring technique knownas Capacitive Sensing using a Sigma-
`Delta Modulator (CSD) involves rapidly charging the capacitor and measuring
`the discharge time througha bleedresistor.
`
`A projected capacitive sensorarray is designed so that a finger will interact with
`more than one X sensor and more than oneY sensorat a time(See Figure 3).
`This enables software to accurately determinefingerpositionto a very fine
`degree throughinterpolation. For example, if sensors 1, 2 and 3 see signals of 3,
`10, and 7, the centerof the fingeris at:
`
`{(1 * 3) + (2 « 10) + (7 « 3)|/(3 + 10 + 7) = 2.2
`
`Since projected-capacitive panels have multiple sensors, they can detect
`multiple fingers simultaneously, whichis impossible with other technologies.
`In fact, projective capacitance has been shownto detect up to ten fingers at the
`sametime. This enables exciting new applications based on multiple finger
`presses, including multiplayer gaming on handheldelectronics or playing an
`touchscreenpiano.
`
`Without question, touchscreensare great looking. They have begunto define a
`new user interface and industrial design standard that is being adopted the
`world over. In everything from heart-rate monitors to the latest all-in-one
`printers, touchscreens are quickly becoming the standard of technology design.
`
`Beyondjust looks, however, touchscreens provide an unparalleled level of
`security from tampering, resistance from weather, durability from wear, and
`even enable entirely new markets with unique features such as multi-touch
`touchscreens. With touchscreens making their way into so many types of
`products,it's imperative that design engineers understand the technology
`ecosystem and technologyavailability.
`
`About the authors
`
`Steve Kolokowsky is a Memberof the Technical Staff in Cypress Semiconductor's
`Consumer and Computation Division (CCD). Steve's focus is high-speed USB
`peripheral products. He has participated in the design of manyof today's
`
`Petitioner STMICROELECTRONICS, INC.,
`Ex. 1007, IPR2021-01160 Page 4 of 6
`
`

`

`‘Trevor Davis 1s currently the Director of Marketing tor Cypress’s Consumer and
`Computation Division (CCD) focused on Universal Serial Bus (USB) in consumer
`products. Trevorreceived his undergraduate degree from the United States Air
`Force Academyand also holds his Masters in Business Administration. Trevor
`served as anAirForce Officer for five years before joining Cypress. Trevorlives in
`San Diego, CA and canbe reached at tmd@cypress.com
`
`Related articles of interest
`
`1. Using capacitive sensor userinterfaces in next generation mobile and embedded
`consumer devices, Mariel Van Tatenhove and Andrew Hsu, Synaptics, Inc.
`2. Designer's guide to rapidprototypingof capacitive
`sensors
`on any
`surface,
`Mark Lee, Cypress SemiconductorCorp.
`
`Palmer, Analog DevicesInc.
`
`Inc.
`
`4, Buildingareliablecapacitive-sensorinterface, Wayne Palmer, Analog Devices,
`
`3. Capacitivesensorscanreplace mechanicalswitches fortouchcontrol, Wayne
`
`5. The art ofcapacitive touch sensing, Mark Lee, Cypress SemiconductorCorp.
`6. Practical considerations forcapacitive touchscreen system design (Part 1 of2),.
`Yi Hang Wang, Cypress SemiconductorCorp.
`7. Basics and implementation ofcapacitive proximity sensing(Part 2 of2),Ganesh
`Raaja, Cypress SemiconductorCorp.
`
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`1 COMMENT ON “TOUCHSCREENS 101: UNDERSTANDING TOUCHSCREEN
`TECHNOLOGY AND DESIGN”
`
`oinoino
`April
`17, 2014
`
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`Petitioner STMICROELECTRONICS, INC.,
`Ex. 1007, IPR2021-01160 Page 5 of 6
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`Petitioner STMICROELECTRONICS, INC.,
`Ex. 1007, IPR2021-01160 Page 6 of 6
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