frontline technology
`
`Projected-Capacitive Touch Technology
`
`Projected-capacitive touch has grown extremely rapidly from obscurity in 2006 to the
`number-two touch technology in 2009. This article examines all aspects of projected-
`capacitive touch technology, delving into sensor, controller, and module details.
`
`by Gary Barrett and Ryomei Omote
`
`THE ADVENT of the iPhone has ushered
`
`in a seismic change in the touch-screen busi-
`ness. Projected capacitive (pro-cap), the
`touch technology used in the iPhone touch
`screen, has become the first choice for many
`small-to-medium (<10-in.) touch-equipped
`products now in development. The technol-
`ogy is not just Apple-trendy but incorporates
`some of the best characteristics of competing
`touch technologies.
`The three most important advantages of
`pro-cap technology are as follows:
`• High durability (long life)
`• Excellent optical performance (high
`transmissivity)
`• Unlimited multi-touch (controller-
`dependent)
`Pro-cap touch screens can be made entirely
`of plain glass, allowing them to be immune to
`most chemicals, operated in extreme tempera-
`tures, and sealed to meet the requirements for
`most wash-down and explosive environments.
`Pro-cap touch screens can also be made
`entirely of plastic, allowing them to be virtu-
`ally unbreakable and have the flexibility to be
`contoured or bent. The sensing range of
`pro-cap touch screens can be extended, allow-
`
`Gary Barrett is the Chief Technology Officer
`at Touch International. He can be reached
`at 512/832-8292 or gbarrett@touchintl.com.
`Ryomei Omote is the General Manager of the
`Sensor Module Engineering, Industrial Mate-
`rials and Input Device Business Unit at
`Nissha Printing. He can be contacted at
`+81-75-823-5271 or r-omote@nissha.co.jp.
`
`16 Information Display 3/10
`
`ing them to be used with cotton or surgical
`gloves. Pro-cap touch-screens have the capa-
`bility of sensing as many fingers as can fit on
`the screen.
`The three major disadvantages of pro-cap
`technology are as follows:
`• Difficulty of integration (noise sensitivity)
`• Finger-touch only (although this may be
`changing)
`• Relatively high cost (dropping rapidly)
`Because they must sense changes in capaci-
`tance as small as a few femtofarads (10–15 F),
`pro-cap touch screens are very sensitive to
`electromagnetic interference (EMI). This
`makes integration challenging, particularly
`when the touch screen is bonded to an LCD,
`and also makes screens larger than about
`22 in. (diagonal) very difficult to build. Pro-
`cap touch screens rely on human-body capaci-
`tance to cause a touch to be recognized, so
`they currently require a human as the touch
`object. Finally, a typical smartphone pro-cap
`touch screen (3.5 in.) is currently about three
`times more expensive than its analog-resistive
`equivalent – although that difference could
`drop by half in as little as 2 years.
`
`How Capacitive Sensing Works
`Capacitive sensing is a very old technology.
`Mature readers may remember novel room
`lamps that could be turned on by touching a
`growing plant, and every reader has probably
`used capacitive elevator buttons at least once
`in his or her life. These primitive capacitive-
`sensing applications typically used a solid-
`state timer (such as an NE555 integrated
`
`0362-0972/03/2010-016$1.00 + .00 © SID 2010
`
`circuit, first available in 1971) that “clicked”
`at a steady rate as determined by the time
`constant of an external resistor-capacitor (RC)
`network. A microcontroller was then pro-
`grammed to monitor the clicks from the timer
`and when the rate increased or decreased, it
`would react. A wire (or piece of ivy, in the
`case of the novel lamp) was routed to a touch
`point and when a human touched it, additional
`body capacitance was added to the RC
`network which, in turn, altered the click rate
`and caused a touch to be detected (see Fig. 1).
`Now, over 30 years later, the same function is
`typically accomplished by using a simple
`capacitive switch IC.
`
`Self-Capacitance
`The type of pro-cap described above is called
`“self-capacitance” because it is based on mea-
`suring the capacitance of a single electrode
`with respect to ground. When a finger is near
`the electrode, the human-body capacitance
`changes the self-capacitance of the electrode.
`In a self-capacitance touch screen, transpar-
`ent conductors are patterned into spatially
`separated electrodes in either a single layer or
`two layers. When the electrodes are in a sin-
`gle layer, each electrode represents a different
`touch coordinate pair and is connected indi-
`vidually to a controller. When the electrodes
`are in two layers, they are usually arranged in
`a layer of rows and a layer of columns; the
`intersections of each row and column repre-
`sent unique touch coordinate pairs. However,
`self-capacitance touch-screen controllers do
`not measure each intersection; they only
`measure each row and column; i.e., each indi-
`
`TPK 2001
`Wintek v. TPK Touch Solutions
`IPR2013-00567
`
`

`
`between human-body capacitance and either a
`single electrode or a pair of electrodes, this
`method of capacitive sensing is most com-
`monly called “charge transfer.” Table 1
`compares the key characteristics of self-
`capacitance and mutual-capacitance as applied
`in touch screens.
`
`Scanning
`Pro-cap touch screens are “scanned,” meaning
`that each individual electrode or electrode
`intersection is measured one-by-one in an
`endless cycle. Self-capacitance touch screens
`are scanned using a straightforward serial
`method because every electrode is connected
`individually to the controller. Mutual-capaci-
`tance touch screens, on the other hand, require
`a more-complex scanning mechanism that
`measures the capacitance at each row and
`column intersection. In this type of scan,
`often called “all points addressable,” the con-
`troller drives a single column (Y) and then
`scans every row (X) that intersects with that
`column, measuring the capacitance value at
`each X-Y intersection. This process is
`repeated for every column and then the entire
`cycle starts over. This makes a mutual-capac-
`
`Ghost Points
`
`Fig. 2: When a self-capacitance touch screen is touched with two fingers that are diagonally
`separated, a pair of “ghost points” are created because the controller only knows that two
`columns and two rows have been touched; it cannot tell which coordinate pairs belong together
`because it is only scanning individual electrodes, not electrode intersections. Source: Barrett
`and Omote.
`
`Information Display 3/10 17
`
`Ivy Network
`
`Finger Adding
`Capacitance to
`Ground
`
`RC Network
`
`NE555 Timer IC
`
`Micro Controller
`
`Fig. 1: Capacitive sensing is a very old technology. This schematic shows how a 1970s-era
`capacitive-sensing lamp could be turned on by touching a plant. It functioned by using body
`capacity to change the click rate of a timer. Source: Barrett and Omote.
`
`spatially separated electrodes in two layers,
`usually arranged as rows and columns.
`Because the intersections of each row and
`column produce unique touch-coordinate
`pairs, the controller in a mutual-capacitance
`touch screen measures each intersection indi-
`vidually (see Fig. 3). This produces one of
`the major advantages of mutual-capacitance
`touch screens – the ability to sense a touch at
`every electrode intersection on the screen.
`Because both self-capacitance and mutual-
`capacitance rely on the transfer of charge
`
`vidual electrode. This works well when only
`a single finger is touching the screen. For
`example, in Fig. 2, a single-finger touching
`location X2,Y0 can be sensed accurately by
`measuring all the X electrodes and then all the
`Y electrodes in sequence.
`Measuring individual electrodes rather than
`electrode intersections is the source of one of
`the major disadvantages of two-layer self-
`capacitance touch screens – the inability to
`unambiguously detect more than one touch.
`As shown in Fig. 2, two fingers touching in
`locations X2,Y0 and X1,Y3 produce four
`reported touch points. However, this dis-
`advantage does not eliminate the use of two-
`finger gestures with a self-capacitance touch
`screen. The secret is in software – rather than
`using the ambiguous locations of the reported
`points, software can use the direction of
`movement of the points. In this situation it
`does not matter that four points resulted from
`two touches; as long as pairs are moving away
`from or toward each other (for example), a
`zoom gesture can be recognized.
`
`Mutual Capacitance
`The other more common type of pro-cap
`today is “mutual capacitance,” which allows
`an unlimited number of unambiguous touches,
`produces higher resolution, is less sensitive to
`EMI, and can be more efficient in its use of
`sensor space. Mutual capacitance makes use
`of the fact that most conductive objects are
`able to hold a charge if they are very close
`together. If another conductive object, such
`as a finger, comes close to two conductive
`objects, the charge field (capacitance) between
`the two objects changes because the human-
`body capacitance “steals” some of the charge.
`In a mutual-capacitance touch screen, trans-
`parent conductors are always patterned into
`
`

`
`frontline technology
`
`Fig. 3: In a mutual-capacitance touch screen, every electrode intersection can be unambigu-
`ously identified as a touch point. Source: Barrett and Omote.
`
`itance controller relatively complex with a
`high processor load, but, in return, it supports
`unlimited multi-touch. Scanning rates in
`current pro-cap controllers range from
`approximately 20 to 200 Hz; a typical smart-
`phone touch screen may have nine columns
`and 16 rows, for a total of 25 electrodes and
`144 electrode intersections.
`In both types of pro-cap touch screens, to
`determine an exact touch location, the values
`from multiple adjacent electrodes or electrode
`intersections are used to interpolate the exact
`touch coordinates. The results are extremely
`precise and the resolution is usually at least
`1024 × 1024 (10 bits). Scanning also has the
`advantage of being free of coordinate drift. This
`is possible because the rows and columns are
`physically fixed and each measurement is made
`in a small area. Without the issue of coordinate
`drift, pro-cap touch screens do not have to be
`calibrated by the end-user as long as the touch
`screen is securely attached to the display.
`
`Touch-Screen Construction
`In the short time since the introduction of pro-
`cap touch screens in iPhones, a myriad of con-
`struction methods have been developed. All
`pro-cap touch-screen designs have two key
`features in common: (1) the sensing mecha-
`nism is underneath the touch surface and (2)
`there are no moving parts. The most common
`
`18 Information Display 3/10
`
`for each of the layers. Also common are
`touch screens that use one two-sided or two
`one-sided ITO-coated sheets of glass.
`
`Touch-Screen Conductors
`Patterning ITO on glass with line widths of
`20 µm and resistivity of 150 Ω/ᔤ is commonly
`accomplished using photolithographic methods;
`for example, using photoresist on an LCD fab.
`When the substrate is PET, line widths are
`typically 100–200 µm and patterning is
`accomplished using screen-printing, photolitho-
`graphy, or laser ablation. Research is in progress
`on fine-line patterning on PET with line widths
`of 30–50 µm. When used, the third unpat-
`terned LCD shield layer typically has a resis-
`tivity of 150–300 Ω/ᔤ. Standard-width (not
`narrow-border) signal lines at the edge of the
`sensor are typically constructed of a molybde-
`num/aluminum/molybdenum combination.
`
`Touch-Screen Conductor Patterns
`ITO layers in pro-cap touch screens can be
`etched in several different patterns, all of
`which cost the same to manufacture, and it is
`difficult to say that one pattern out-performs
`another since touch-screen sensors and con-
`troller electronics are highly interrelated.
`The pattern used in the original iPhone is
`one of the simplest, consisting of 10 columns
`of 1-mm-wide ITO spaced 5 mm apart on one
`side of a sheet of glass and 15 rows of 5-mm-
`high ITO with 37-µm deletions between them.
`The space between the 10 columns is filled
`with unconnected (floating) ITO in order to
`maintain uniform optical appearance. This
`design works well, but the geometry requires
`substantial processing power to generate accu-
`rate coordinates.
`
`design incorporates the simple concept shown
`in Fig. 4.
`Some of the newest products under devel-
`opment use a single-sided design, where all of
`the touch screen’s layers are on one side of a
`single substrate. In this design, currently the
`thinnest possible for pro-cap, all of the layers
`are deposited by sputtering. There are innu-
`merable variations on the basic design of the
`two-layer pro-cap shown in Fig. 4. For
`instance, micro-fine (10 µm) wires can be sub-
`stituted for the sputtered ITO. Many mobile
`phones and most current signature-capture
`terminals use ITO on separate sheets of PET
`
`Table 1: A comparison of the key characteristics of self-capacitance and
`mutual-capacitance as applied in touch screens.
`
`Characteristic
`
`Self-Capacitance
`
`Electrode types
`
`Sensing only
`
`Number of layers
`
`1 or 2
`
`Sensor design
`
`Multi-pad or row & column
`
`Mutual Capacitance
`
`Driving & sensing
`
`2
`
`Any design with unique electrode
`intersections; usually row & column
`
`Scanning method
`
`Each electrode individually
`
`Each electrode intersection
`
`Measurement
`
`Capacitance of electrode to ground
`
`Capacitance between electrodes
`
`Ghost points
`
`No in multi-pad; Yes in row &
`column
`
`No
`
`

`
`The most common pattern is an interlocking
`diamond that consists of squares on a 45º axis,
`connected at two corners via a small bridge.
`This pattern is typically applied in two layers –
`one layer of horizontal diamond rows and one
`layer of vertical diamond columns (see Fig. 5).
`Each layer adheres to one side of two pieces
`of glass or PET, which are then combined,
`interlocking the diamond rows and columns.
`The diamond size varies by manufacturer but
`is in the range of 4–8 mm; almost all pro-cap
`controllers work with the diamond pattern.
`
`Border Area
`One of the most important cost drivers in
`pro-cap touch-screen design is the border area.
`Unlike conventional analog-resistive touch
`screens, which have only four or five signal
`lines, pro-cap touch screens often have 40 or
`more connections because each row and
`column must be connected to the controller
`(or to an intermediate capacitive-to-digital
`signal-processing chip). This can require a
`significant border area around the touch-
`screen active area. Historically, connection
`traces have been silk-screen printed 1 mm
`wide with a 1-mm gap using silver inks.
`The latest mobile phones always require a
`narrow border. To achieve this, a technique
`similar to that utilized for TFT-LCDs is used.
`This technique requires the touch screen to be
`sputtered and etched to add multiple layers of
`thin films in the border area, which adds cost.
`Fine-line silver printing with 50–100-µm lines
`and gaps achieves a lower cost than the sputter-
`ing technique, but polyimide tails remain the
`most common method of attaching to the lines,
`which requires the material to protrude beyond
`the edge of the substrate and is also expensive.
`Cost can be reduced substantially if a device
`does not require flush mounting and can allow
`for a larger border area under the bezel.
`
`Cover Lens and Touch Surface
`Mobile-phone touch screens typically use a
`plastic or glass “cover lens” that is laminated
`to the touch screen. This allows product
`designers to make the touch screen flush with
`the top surface of the device housing (as in the
`iPhone). The cover lens can be screen-printed
`on the rear surface, in-mold decorated (IMD),
`or, more commonly, a decorated film can be
`laminated to the rear surface. The decoration
`hides the touch-panel circuitry, incorporates a
`logo, can have ruby coatings for a camera, and
`can act as a diffuser for backlights. A glass
`
`Transparent Thin-Film
`Conductor (ITO)
`
`Touch
`Surface
`
`Thin-Film Separator
`
`Fig. 4: The pro-cap design concept shows two transparent conductor layers separated by an
`insulator, all under the touch surface. (Note that the transparent conductors are shown as solid
`sheets when in fact they are actually patterned.) In some cases, an additional unpatterned ITO
`layer is added at the bottom of the stack as a shield for LCD noise. Source: Barrett and Omote.
`
`cover lens is typically 0.55, 0.75, or 1.1 mm
`thick for mobile devices and up to 3 mm thick
`for kiosk applications. The dielectric constant
`of the cover lens and its thickness have a
`direct bearing on the sensitivity of the pro-cap
`touch screen – a thinner cover lens and/or a
`higher dielectric constant results in better
`performance. Plastic (PMMA) can be used in
`place of glass; however, it has a lower dielec-
`tric constant and must be half the thickness of
`glass to achieve the same performance.
`When glass is used for the cover lens, some
`designers choose to chemically strengthen it
`to reduce the chance of breaking. Float glass
`(soda-lime) or aluminum silicate are the most
`commonly used types of glass. Chemically
`strengthened float glass is half as likely to break
`
`as plain float glass; chemically strengthened
`aluminum silicate is less than one-third as likely
`to break. Some cover-lens designs have become
`extremely complex with multiple holes and
`slots, rounded corners, and even bent edges.
`All of these processes must be performed
`before the glass is chemically strengthened.
`
`Curved Substrates
`As the industrial design of consumer products
`has become a bigger factor in the purchasing
`decision, curved substrates have become very
`important. Pro-cap is one of the few touch
`technologies that allows the sensor to be
`curved. Two-dimensional surfaces are
`straightforward to produce by sputtering ITO
`on polycarbonate or some other film and then
`
`Layer-1
`Diamond Rows
`
`Interlocking
`Diamonds
`
`Layer-2
`Diamond Columns
`
`Fig. 5: The diamond pro-cap sensor pattern is formed by two interlocking diamond-shaped
`layers. Source: Barrett and Omote.
`
`Information Display 3/10 19
`
`

`
`frontline technology
`
`putting the film into the cover-lens mold.
`Three-dimensional (3-D) surfaces are more
`challenging; one solution under development
`uses a molded or flexible substrate and elastic
`conductive material such as PEDOT.
`
`Controller Designs
`There are approximately 17 vendors selling
`pro-cap controllers today, several of whom
`offer both self-capacitance (one or two
`touches) and mutual-capacitance (unlimited
`multi-touch) types. Mutual capacitance is fast
`becoming the standard because of the strong
`market momentum toward multi-touch driven
`by the Apple iPhone and Windows 7. Avail-
`able pro-cap controllers range from dedicated
`controllers that are specific to a particular
`sensor size and row-column configuration, to
`fully programmable microcontrollers with
`advanced built-in gesture-recognition capabil-
`ities. Current controllers are limited to a
`maximum sensor size of around 10 in. at best;
`however, most controllers can be combined to
`support larger sensors. At least one controller
`supplier has announced that it is developing
`single-chip controllers that can support sen-
`sors up to 17 in. Figure 6 illustrates a typical
`controller implementation in a mobile phone.
`
`Historically, pro-cap has always been
`finger-touch only; it has supported only elec-
`trically tethered pens (which are highly desir-
`able on signature-capture terminals!). This
`has been a relatively significant shortcoming
`of the technology, particularly with mobile
`phones in Asia, where users often write Kanji
`characters on their resistive-touch-screen-
`equipped phones. In 2009, Atmel announced
`its pro-cap controller’s ability to respond to a
`conductive stylus; this resulted from the 3×
`increase in signal-to-noise (S/N) ratio it was
`able to achieve (from 25:1 to 80:1). The limi-
`tation is that the stylus tip diameter must be
`2–3 mm, which is considerably larger than the
`typical 0.8-mm PDA/smartphone stylus-tip
`diameter. The market acceptance of this
`stylus size is still to be determined.
`Another attribute of pro-cap technology is that
`the touch screen does not actually have to be
`touched to be activated. The touch screen’s
`level of sensitivity can be controlled by the
`electronics. In most cases, software is designed
`to require a physical touch to activate a function.
`However, the sensitivity can be increased so
`that the simple placement of a hand near the
`touch screen (in the Z-axis) can be detected.
`This is commonly called “proximity sensing.”
`
`Fig. 6: Most pro-cap controller implementations are on the touch-screen tail, located close to
`the sensor to minimize noise pickup. This photo shows an example of a touch-screen tail from a
`mobile phone. The controller is a PSoC chip from Cypress Semiconductor. The 25 pins along
`the lower edge of the tail connect to the sensor (nine columns plus two grounds in the middle;
`16 rows split into two groups of eight on the left and right). The connector in the upper-left
`corner of the tail connects to the phone’s main board. Source: Nissha Printing.
`
`20 Information Display 3/10
`
`The selection of a controller vendor typi-
`cally depends on two factors – performance
`specifications and the maturity and sophistica-
`tion of the customer. Some vendors are more
`oriented toward proposing a total solution for
`inexperienced customers (device OEMs),
`which naturally results in less flexibility.
`Some controller vendors work mainly with
`sensor manufacturers, who, in turn, work with
`the device OEMs. Other controller vendors
`work mainly directly with the device OEMs.
`The most important controller performance
`specifications include power consumption,
`scan speed, maximum number of touches,
`capacitance-measurement sensitivity, and chip
`size. The standard hardware interface for
`mobile-phone controllers is I2C; the standard
`interface for PC controllers is USB.
`
`Controller Firmware
`Controller firmware (especially algorithms) is
`evolving very rapidly in the pro-cap touch-
`screen industry, much faster than sensor or
`controller hardware.
`Conventionally, touch controllers have gen-
`erated only one X-Y coordinate pair. With
`pro-cap, controllers must now be capable of
`generating at least two pairs and often up to 10
`or more pairs. In small-to-medium (<10-in.)
`devices, the output format of the coordinate
`data varies depending on the controller sup-
`plier. In large-area (>10-in.) devices, Windows 7
`has now established a coordinate data-format
`standard to which most controllers capable of
`supporting large-area screens are expected to
`adhere. Microsoft has also established a stan-
`dard (part of the Windows 7 Touch Logo
`specification) on the minimum number of
`points per second per touch (50) that a multi-
`touch controller must deliver.
`
`Number of Touches
`How many touches are enough? On one
`hand, some industry participants believe that
`two touches on a mobile phone are enough;
`tablets and netbooks/notebooks used in
`gaming may require four touches and PCs
`with 15-in. or larger screens may require 10
`touches. Windows 7 supports up to 100
`touches. The reality is that today, other than
`multi-player games, there are very few appli-
`cations that make use of more than two
`touches. Other than observing that all humans
`have 10 fingers, nobody seems to have any
`clear concept of how real-world applications
`will use that many touches.
`
`

`
`On the other hand, it is clear that as the
`border width gets ever smaller on mobile devices,
`touch screens must reject the unwanted touches
`caused by fingers holding the device (i.e.,
`“grip suppression”). Apple’s patent applica-
`tion on the iPhone pro-cap touch screen1 says
`that the controller is designed to support up to
`15 touches for this purpose, consisting of “10
`fingers, 2 palms, and 3 others.” Related to
`this, many controllers are capable of sending
`a message indicating when a large number of
`locations are being activated at the same time.
`On mobile phones, this attribute is often used
`to determine that the phone is next to the face
`or the device has been put away in a pocket,
`signaling that all touches should be ignored.
`
`Business Model
`There are at least 36 suppliers in the pro-cap
`touch-screen industry today. Table 2 below
`lists some of the leading suppliers. Relatively
`few of them are currently capable of supply-
`ing modules (integrated sensor and controller
`assemblies); some examples include Cypress,
`ELAN, Melfas, N-trig, Nissha, Synaptics,
`Wacom, and Zytronic. The remainder of the
`36 is split more or less evenly between sensor
`and controller suppliers. Some of these have
`ambitions to become module suppliers
`because (theoretically) it is easier for module
`
`Table 2: Each of the leading
`suppliers in the pro-cap touch-screen
`industry listed below has shipped
`more than 1 million units.
`
`Controllers Modules
`
`Atmel
`
`N-trig
`
`Nissha
`Printing
`
`Synaptics
`
`Wacom
`
`Zytronic
`
`Sensors
`
`Cando
`
`DigiTech Systems
`
`Broadcom
`
`EELY
`
`Innolux
`
`JTouch
`
`Nanjing Wally
`
`Nissha Printing
`
`Cirque
`
`Cypress
`
`EETI
`
`ELAN
`
`Melfas
`
`Touch International Pixcir
`
`TPK Solutions
`
`Synaptics
`
`Wintek
`
`Young Fast
`Optoelectronics
`
`Fig. 7: Smartphone pro-cap touch-screen modules manufactured by Nissha Printing consist of
`a pro-cap sensor, a decorated cover lens laminated to the sensor and a controller mounted on
`the FPC (flexible printed circuit) that makes up the touch-screen connector tail. Source: Nissha
`Printing.
`
`makers to support their complete product, and
`the margin is higher. However, becoming a
`module supplier can be challenging. It
`requires a high level of expertise in EMI
`engineering, the ability to modify the
`firmware of any controller used in the module
`(in order to achieve uniformity of input across
`controllers), knowledge of and ability to sup-
`port any OS with which the module is used,
`and module manufacturing expertise. Figure
`7 shows some representative modules manu-
`factured by Nissha Printing.
`Device OEMs today want more module
`suppliers because that makes their job easier.
`But this may be the case only for a few years.
`If pro-cap touch becomes as popular as
`analog-resistive touch, then the device OEMs
`will probably want to buy the controller with
`software themselves and buy the sensor sepa-
`rately. In other words, the market may evolve
`into a more standardized commodity market.
`This is of course worrisome to potential mod-
`ule suppliers.
`
`Summary
`In the last 3 years, pro-cap has grown
`extremely rapidly to become the number-two
`touch technology. Pro-cap is used in two
`
`forms, self-capacitance and mutual-capaci-
`tance; only the latter supports unlimited multi-
`touch. Many different construction methods
`are used, the most common one today is mul-
`tiple sputtered layers on one side of a sub-
`strate. The most common pattern used for the
`sensor’s transparent conductors is an inter-
`locking diamond. Achieving narrow borders
`contributes substantially to the cost of a pro-
`cap touch screen. The design of a plastic or
`glass cover lens has become an important part
`of pro-cap touch screens used in mobile
`devices. Pro-cap controller hardware and
`firmware are evolving rapidly; the latest gen-
`eration supports the use of a conductive stylus
`with a 2–3-mm tip. While very few applica-
`tions today make use of more than two
`touches, mobile devices can make use of
`additional touches in providing “grip suppres-
`sion.” Some current pro-cap sensor and con-
`troller suppliers would like to become module
`suppliers, but doing so requires a significant
`investment in additional expertise.
`
`References
`1United State Patent Application
`2006/0097991. I
`
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