USOO8462135B1
`
`(12) United States Patent
`Xiao et al.
`
`(10) Patent No.:
`(45) Date of Patent:
`
`US 8.462,135 B1
`Jun. 11, 2013
`
`(54)
`(75)
`
`(73)
`
`(*)
`
`(21)
`(22)
`
`(60)
`
`(51)
`
`(52)
`
`(58)
`
`MULTI-TOUCH DISAMBIGUATION
`
`(56)
`
`References Cited
`
`Inventors: Browley Xiao, Shanghai (CN); Nelson
`Chow, Shanghai (CN); Victor Drake,
`San Jose, CA (US); Igor Polishchuk,
`Fremont, CA (US)
`Assignee: Cypress Semiconductor Corporation,
`San Jose, CA (US)
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 313 days.
`Appl. No.: 12/684,791
`
`Notice:
`
`Filed:
`
`Jan. 8, 2010
`Related U.S. Application Data
`Provisional application No. 61/143,199, filed on Jan.
`8, 2009, provisional application No. 61/145,457, filed
`on Jan. 16, 2009.
`
`(2006.01)
`
`Int. C.
`G06F 3/045
`U.S. C.
`USPC ............................ 345/174; 34.5/156; 34.5/173
`Field of Classification Search
`USPC .......................................... 345/156, 173–174
`See application file for complete search history.
`
`U.S. PATENT DOCUMENTS
`5,495,077 A * 2/1996 Miller et al. ............... 178/1806
`5,872,561 A * 2/1999 Figie et al. .....
`... 345,168
`7,428,191 B1* 9/2008 Klein .............................. 368,82
`7,982,723 B2 *
`7/2011 Ningrat ...
`... 345,174
`2008. O150906 A1* 6, 2008 Grivna ...........
`... 345,173
`2009/0096757 A1* 4/2009 Hotelling et al. .
`... 345,173
`2009.0128516 A1* 5/2009 Rimon et al. ..........
`... 345,174
`2009.0160787 A1* 6, 2009 Westerman et al.
`... 345,173
`2010/0007631 A1* 1/2010 Chang ................
`... 345,174
`2010.003.9405 A1
`2/2010 Chen et al. .........
`... 345,174
`2010/0073301 A1* 3/2010 Yousefpor et al. .
`... 345,173
`2010/0097.328 A1* 4/2010 Simmons et al. ............. 345,173
`* cited by examiner
`
`Primary Examiner — Christopher E Leiby
`
`(57)
`ABSTRACT
`Identification of at least one of a plurality of possible touch
`locations as an actual touch location may include detecting a
`plurality of possible touch locations at a touch sensing Sur
`face, wherein detecting the plurality of possible touch loca
`tions comprises performing a resolve scan of at least a first
`sensor element at the touch sensing Surface, where the first
`sensor element corresponds to at least a first coordinate of the
`plurality of coordinates.
`
`18 Claims, 16 Drawing Sheets
`
`sensor ai'ay
`( 3.
`
`X axis iristogram
`
`... peak
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`- peak
`33
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`351 Ne 3. O GOOOO
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`
`320, 32O2) 3203 320 - 3205) 3206) 3207) 3208) 320.9)
`
`
`
`Yaxis
`histegras:
`3.
`
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`DELL EXHIBIT 1026 PAGE 1
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`

`

`U.S. Patent
`
`Jun. 11, 2013
`
`Sheet 1 of 16
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`US 8.462,135 B1
`
`
`
`
`
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`
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`
`
`
`
`
`DELL EXHIBIT 1026 PAGE 2
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`DELL EXHIBIT 1026 PAGE 2
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`

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`US. Patent
`
`Jun. 11,2013
`
`Sheet 2 of 16
`
`US 8,462,135 B1
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`DELL EXHIBIT 1026 PAGE 3
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`DELL EXHIBIT 1026 PAGE 3
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`DELL EXHIBIT 1026 PAGE 3
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`

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`U.S. Patent
`
`Jun. 11, 2013
`
`Sheet 3 of 16
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`US 8.462,135 B1
`
`self capacitance
`circuit
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`al
`
`switch
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`node
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`2
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`FIGURE 2B
`
`DELL EXHIBIT 1026 PAGE 4
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`

`

`U.S. Patent
`
`Jun. 11, 2013
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`Sheet 4 of 16
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`US 8.462,135 B1
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`Seaso; 38 ray
`
`X axis iristogra:
`33
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`Y axis
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`
`FIGURE 3
`
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`DELL EXHIBIT 1026 PAGE 5
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`

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`U.S. Patent
`
`Jun. 11, 2013
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`Sheet 5 of 16
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`US 8.462,135 B1
`
`seases eitesment
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`FGRE 4A
`
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`DELL EXHIBIT 1026 PAGE 6
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`

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`U.S. Patent
`
`Jun. 11, 2013
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`Sheet 6 of 16
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`US 8.462,135 B1
`
`sensor eierneat
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`FGURE 43
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`

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`U.S. Patent
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`Jun. 11, 2013
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`Sheet 7 of 16
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`US 8.462,135 B1
`
`Seiso seeitman
`3 {}{S}
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`FIGURE 5
`
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`U.S. Patent
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`Jun. 11, 2013
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`Sheet 8 of 16
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`US 8.462,135 B1
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`equivalent circuit
`{{f}
`
`FIG RE 6A
`
`
`
`silipified
`equivalent circuit
`6S
`
`FIGURE 6B
`
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`

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`U.S. Patent
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`Jun. 11, 2013
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`Sheet 9 of 16
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`US 8.462,135 B1
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`differettia
`easil rement ciscuit
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`
`FIGURE 7A
`
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`

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`U.S. Patent
`
`Jun. 11, 2013
`
`Sheet 10 of 16
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`US 8.462,135 B1
`
`differenitia (east: etent
`&quivalent circuit
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`32(7)
`
`FIGURE 73
`
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`

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`U.S. Patent
`
`Jun. 11, 2013
`
`Sheet 11 of 16
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`US 8.462,135 B1
`
`se:sor arsay
`800-
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`DELL EXHIBIT 1026 PAGE 12
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`

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`U.S. Patent
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`Jun. 11, 2013
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`Sheet 12 of 16
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`US 8.462,135 B1
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`? \
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`
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`DELL EXHIBIT 1026 PAGE 13
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`

`

`U.S. Patent
`
`Jun. 11, 2013
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`Sheet 13 of 16
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`US 8.462,135 B1
`
`nautiple touch
`detection process
`
`i
`1.
`
`perform standard scan to detect a plurality of
`-- possible touch locations (including row and collama
`coodinates)
`0.
`
`rail contacts aligned?
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`(34
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`
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`identify at least a first sensor element corresponding
`to one of the row or ctitia coordinates
`{{s
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`:
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`it response to detecting the putatity of coordinates,
`performing a resolve scan of at east the first sensor
`element at the toach sensing surface
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`
`based on the standard scan and resolve seat (if any),
`identifying at east one of the possible contact
`it cations as at actuai ix38&ct location.
`
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`
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`
`FGRE ()
`
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`DELL EXHIBIT 1026 PAGE 14
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`

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`U.S. Patent
`
`Jun. 11, 2013
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`Sheet 14 of 16
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`US 8.462,135 B1
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`Beseive scan process
`{}
`
`perform a first measurement of a
`first sessor eiement in conjunction
`with a second sensor element.
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`perform a second measurement of:
`the first seiso eleven is:
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`
`FCGRE
`
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`DELL EXHIBIT 1026 PAGE 15
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`

`

`U.S. Patent
`
`Jun. 11, 2013
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`Sheet 15 of 16
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`US 8.462,135 B1
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`resolve seat process
`i{
`
`
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`
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`perform a first scar of the at east ore seasir elevent
`while oating a second sessor element corresponding to a
`secord coordinate of the plurality of coordinates
`32
`
`perform a seconciscan of the at least one sense: element
`while floating a third sensor element corresponding to a
`third coordinate of the ptuality &f coordinates
`(i.
`
`
`
`determine a difference betwee: a neas repres: obtaired
`from the first scan and a measurement obtained from the
`Secois Scast.
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`
`
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`a a a a X axia a a -- s
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`
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`
`FIGURE 2
`
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`

`U.S. Patent
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`Jun. 11, 2013
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`Sheet 16 of 16
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`US 8.462,135 B1
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`resolve scan process
`
`,
`
`detect 8 first tire constant at the first &nd of the first seaso: eier8nt
`whiie the second end of the first sensor element is connected to a high
`impedance,
`
`"-
`
`detect a seconditine erstait at the secondi end of the first sensor
`eierent while the first ent of the first seaso; eieinent is connected to 3.
`high impedance,
`
`
`
`y
`determine a first distance between the actual contact ocation and a first
`ead of the first sensor eierkeat and a second distance between the actual
`contact iocation and a second end of the irst seaser elenaea.
`
`x
`
`compare the first distance with the second distance.
`38
`
`to block 100
`
`FIGURE 3
`
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`

`

`1.
`MULTI-TOUCH DISAMBIGUATION
`
`US 8,462,135 B1
`
`RELATED APPLICATIONS
`
`This application claims the benefit of U.S. Provisional
`Application No. 61/143,199, filed on Jan. 8, 2009 and U.S.
`Provisional Application No. 61/145.457, filed on Jan. 16,
`2009.
`
`TECHNICAL FIELD
`
`This disclosure relates to the field of user interface devices
`and, in particular, to disambiguation of multiple touches at a
`touch sensing Surface.
`
`BACKGROUND
`
`10
`
`15
`
`25
`
`30
`
`35
`
`Computing devices, such as notebook computers, personal
`data assistants (PDAs), kiosks, and mobile handsets, have
`user interface devices, which are also known as human inter
`face devices (HID). One user interface device that has
`become more common is a touch-sensorpad (also commonly
`referred to as a touchpad). A basic notebook computer touch
`sensorpad emulates the function of a personal computer (PC)
`mouse. A touch-sensor pad is typically embedded into a PC
`notebook for built-in portability. A touch-sensor pad repli
`cates mouse X/Y movement by using two defined axes which
`containa collection of sensorelements that detect the position
`of an object, Such as a finger. Mouse right/left button clicks
`can be replicated by two mechanical buttons, located in the
`vicinity of the touchpad, or by tapping commands on the
`touch-sensorpad itself. The touch-sensorpad provides a user
`interface device for performing Such functions as positioning
`a pointer, or selecting an item on a display. These touch
`sensor pads may include, for example, sensor arrays having
`two dimensions for detecting movement in a plane. The sen
`sor array may include a one-dimensional sensor array, detect
`ing movement in one axis. The sensor array may also be two
`dimensional, detecting movements in two axes.
`Another user interface device that has become more com
`40
`mon is a touch screen. Touch screens, also known as touch
`screens, touch panels, or touchscreen panels, are transparent
`display overlays which are typically either pressure-sensitive
`(resistive or piezoelectric), electrically-sensitive (capacitive),
`acoustically-sensitive (surface acoustic wave (SAW)), or
`photo-sensitive (infra-red). The effect of such overlays allows
`a display to be used as an input device, removing the keyboard
`and/or the mouse as the primary input device for interacting
`with the displays content. Such displays can be attached to
`computers or, as terminals, to networks. There are a number
`of types of touch screen technologies, such as optical imag
`ing, resistive, Surface acoustical wave, capacitive, infrared,
`dispersive signal, piezoelectric, and strain gauge technolo
`gies. Touch screens have become familiar in retail settings, on
`point-of-sale systems, on ATMs, on mobile handsets, on
`kiosks, on game consoles, and on PDAS where a stylus is
`Sometimes used to manipulate the graphical user interface
`(GUI) and to enter data. A user can touch a touch screen or a
`touch-sensor pad to manipulate data. For example, a user can
`apply a single touch, by using a finger to press the Surface of
`a touch screen, to select an item from a menu.
`
`45
`
`50
`
`55
`
`60
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`The present disclosure is illustrated by way of example,
`and not by way of limitation, in the figures of the accompa
`nying drawings.
`
`65
`
`2
`FIG. 1 illustrates a block diagram of one embodiment of an
`electronic system that processes touch sensor data.
`FIG. 2A illustrates a block diagram of an embodiment of an
`electronic system that processes touch sensor data.
`FIG. 2B illustrates a circuit for measuring a self capaci
`tance, according to an embodiment.
`FIG. 3 illustrates one embodiment of a sensor array.
`FIG. 4A illustrates an equivalent circuit representing a
`sensor array, according to one embodiment.
`FIG. 4B illustrates an equivalent circuit representing a
`sensor array with contacts applied, according to one embodi
`ment.
`FIG.5 illustrates an equivalent circuit representing a sensor
`array, according to one embodiment.
`FIG. 6A illustrates an equivalent circuit of a sensor array,
`according to one embodiment.
`FIG. 6B illustrates an equivalent circuit of a sensor array,
`according to one embodiment.
`FIG. 7A illustrates an equivalent circuit of a sensor array,
`according to one embodiment.
`FIG. 7B illustrates an equivalent circuit of a sensor array,
`according to one embodiment.
`FIG. 8A illustrates one embodiment of a sensor array.
`FIG. 8B illustrates an equivalent circuit of a sensor array,
`according to one embodiment.
`FIG. 9 illustrates one embodiment of a sensor array having
`a manufacturing defect.
`FIG. 10 is a flow diagram illustrating a multiple touch
`detection process, according to one embodiment.
`FIG. 11 is a flow diagram illustrating a resolve scan pro
`cess, according to one embodiment.
`FIG. 12 is a flow diagram illustrating a resolve scan pro
`cess, according to one embodiment.
`FIG. 13 is a flow diagram illustrating a resolve scan pro
`cess, according to one embodiment.
`
`DETAILED DESCRIPTION
`
`The following description sets forth numerous specific
`details such as examples of specific systems, components,
`methods, and so forth, in order to provide a good understand
`ing of several embodiments of the present invention. It will be
`apparent to one skilled in the art, however, that at least some
`embodiments of the present invention may be practiced with
`out these specific details. In other instances, well-known
`components or methods are not described in detail or are
`presented in a simple block diagram format in order to avoid
`unnecessarily obscuring the present invention. Thus, the spe
`cific details set forth are merely exemplary. Particular imple
`mentations may vary from these exemplary details and still be
`contemplated to be within the spirit and scope of the present
`invention.
`One embodiment of a multi-touch gesture trackpad or
`other device including a touch sensing Surface operates by
`performing self-capacitance measurements on each of the
`rows and columns in an array of touch sensing elements,
`including row elements and column elements, at the touch
`sensing Surface. These measurements can be represented as a
`histogram of measured values for the row elements and a
`histogram of measured values for the column elements. For
`detecting a single contact at the touch sensing Surface, the
`peak of each histogram indicates the row and column location
`of the contact.
`In one embodiment, when multiple touches are applied to
`Such a touch sensing Surface, the row and column histograms
`may have two or more peaks such that the system cannot
`distinguish the actual locations of the contacts at the touch
`
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`US 8,462,135 B1
`
`3
`sensing Surface based on the histograms alone. For example,
`two touches at a touch sensing Surface that are not aligned in
`either the X or Y directions may result in two peaks for each
`of the row and column histograms, indicating four possible
`contact locations. To determine which of the possible touch
`locations is a location of an actual contact, the system may
`perform a disambiguation process.
`The touch sensing system may perform a resolve scan as
`part of a disambiguation process. In one embodiment, the
`resolve scan may include measurements of sensor elements
`corresponding to the histogram peaks. For example, two
`touches at the touch sensing Surface may result in four histo
`gram peaks (two row peaks and two column peaks) and four
`possible touch locations. These four possible contact loca
`tions can be disambiguated to determine the locations of the
`original two actual contacts by performing a measurement of
`the sensor elements intersecting at least one of the possible
`contact locations to determine whether an actual contact is
`present at the measured possible contact location.
`In cases where more than two actual contacts are applied to
`the touch sensing Surface, the number of possible contact
`locations also increases. For example, three actual contacts
`may result in up to three peaks for each of the row and column
`histograms, which correspond to nine possible contact loca
`tions. A resolve scan may be performed to determine whether
`an actual contact is present at each of these possible contact
`locations. In one embodiment, deducing the locations of all
`the actual contacts does not require scanning all of the pos
`sible contact locations and may be accomplished with a
`resolve scan that includes only some of the possible contact
`locations.
`In an alternative embodiment, the resolve scan may include
`two or more measurements of a sensor element correspond
`ing to one of the histogram peaks. The two measurements
`may be compared to determine whether the location of an
`actual contact is closer to a first end of the sensor element or
`a second end of the sensor element. For example, where two
`possible contact locations are presentata sensor element, the
`resolve scan may identify which of the two possible contacts
`is an actual contact by determining that the actual contact is
`closer to one end of the sensor element or another.
`FIG. 1 illustrates a block diagram of one embodiment of an
`electronic system 100 including processing logic 102 that
`may be configured to perform a disambiguation process for
`determining locations of multiple touches at a touch sensing
`surface. The electronic device 100 includes a touch-sensing
`Surface 116 (e.g., a touchscreen, or a touch pad) coupled to a
`processing device 110 and a host 150. In one embodiment, the
`touch-sensing Surface 116 is a two-dimensional user interface
`that uses a sensor array 121 to detect touches on the Surface
`116.
`In one embodiment, the sensor array 121 includes sensor
`elements 121(1)-121(N) (where N is a positive integer) that
`are disposed as a two-dimensional matrix (also referred to as
`an XY matrix). The sensor array 121 is coupled to pins 113
`(1)-113(N) of the processing device 110 via an analog bus 115
`transporting multiple signals. In this embodiment, each sen
`sor element 121(1)-121(N) is represented as a capacitor. The
`capacitance of each sensor in the sensor array 121 is measured
`by a capacitance sensor 101 in the processing device 110.
`In one embodiment, the capacitance sensor 101 may
`include a relaxation oscillator or other means to convert a
`capacitance into a measured value. The capacitance sensor
`101 may also include a counter or timer to measure the oscil
`lator output. The capacitance sensor 101 may further include
`Software components to convert the count value (e.g., capaci
`tance value) into a sensor element detection decision (also
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`referred to as Switch detection decision) or relative magni
`tude. It should be noted that there are various known methods
`for measuring capacitance, such as current versus Voltage
`phase shift measurement, resistor-capacitor charge timing,
`capacitive bridge divider, charge transfer, Successive approxi
`mation, Sigma-delta modulators, charge-accumulation cir
`cuits, field effect, mutual capacitance, frequency shift, or
`other capacitance measurement algorithms. It should be
`noted however, instead of evaluating the raw counts relative to
`a threshold, the capacitance sensor 101 may be evaluating
`other measurements to determine the user interaction. For
`example, in the capacitance sensor 101 having a sigma-delta
`modulator, the capacitance sensor 101 is evaluating the ratio
`of pulse widths of the output, instead of the raw counts being
`over a certain threshold.
`In one embodiment, the processing device 110 further
`includes processing logic 102. Operations of the processing
`logic 102 may be implemented in firmware; alternatively, it
`may be implemented inhardware or Software. The processing
`logic 102 may receive signals from the capacitance sensor
`101, and determine the state of the sensor array 121, such as
`whetheran object (e.g., a finger) is detected on or in proximity
`to the sensor array 121 (e.g., determining the presence of the
`object), where the object is detected on the sensor array,
`tracking the motion of the object, or other information related
`to an object detected at the touch sensor.
`In another embodiment, instead of performing the opera
`tions of the processing logic 102 in the processing device 110.
`the processing device 110 may send the raw data or partially
`processed data to the host 150. The host 150, as illustrated in
`FIG.1, may include decision logic 151 that performs some or
`all of the operations of the processing logic 102. Operations
`of the decision logic 151 may be implemented in firmware,
`hardware, software, or a combination thereof. The host 150
`may include a high-level Application Programming Interface
`(API) in applications 152 that perform routines on the
`received data, Such as compensating for sensitivity differ
`ences, other compensation algorithms, baseline update rou
`tines, start-up and/or initialization routines, interpolation
`operations, or scaling operations. The operations described
`with respect to the processing logic 102 may be implemented
`in the decision logic 151, the applications 152, or in other
`hardware, Software, and/or firmware external to the process
`ing device 110. In some other embodiments, the processing
`device 110 is the host 150.
`In another embodiment, the processing device 110 may
`also include a non-sensing actions block 103. This block 103
`may be used to process and/or receive/transmit data to and
`from the host 150. For example, additional components may
`be implemented to operate with the processing device 110
`along with the sensor array 121 (e.g., keyboard, keypad,
`mouse, trackball, LEDs, displays, or other peripheral
`devices).
`The processing device 110 may reside on a common carrier
`Substrate Such as, for example, an integrated circuit (IC) die
`substrate, or a multi-chip module substrate. Alternatively, the
`components of the processing device 110 may be one or more
`separate integrated circuits and/or discrete components. In
`one embodiment, the processing device 110 may be the Pro
`grammable System on a Chip (PSOCTM) processing device,
`developed by Cypress Semiconductor Corporation, San Jose,
`Calif. Alternatively, the processing device 110 may be one or
`more other processing devices known by those of ordinary
`skill in the art, such as a microprocessor or central processing
`unit, a controller, special-purpose processor, digital signal
`processor (DSP), an application specific integrated circuit
`(ASIC), a field programmable gate array (FPGA), or other
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`programmable device. In an alternative embodiment, for
`example, the processing device 110 may be a network pro
`cessor having multiple processors including a core unit and
`multiple micro-engines. Additionally, the processing device
`110 may include any combination of general-purpose pro
`cessing device(s) and special-purpose processing device(s).
`In one embodiment, the electronic system 100 is imple
`mented in a device that includes the touch-sensing Surface
`116 as the user interface. Such as handheld electronics, por
`table telephones, cellular telephones, notebook computers,
`personal computers, personal data assistants (PDAs), kiosks,
`keyboards, televisions, remote controls, monitors, handheld
`multi-media devices, handheld video players, gaming
`devices, control panels of a household or industrial appli
`ances, or other computer peripheral or input devices. Alter
`natively, the electronic system 100 may be used in other types
`of devices. It should be noted that the components of elec
`tronic system 100 may include all the components described
`above. Alternatively, electronic system 100 may include only
`Some of the components described above, or include addi
`tional components not listed herein.
`FIG. 2A is a block diagram illustrating one embodiment of
`a capacitive touch sensor array 121 and a capacitance sensor
`101 that converts measured capacitances to coordinates. The
`coordinates are calculated based on measured capacitances.
`In one embodiment, sensor array 121 and capacitance sensor
`101 are implemented in a system Such as electronic system
`100. Sensor array 220 includes a matrix 225 of NXM elec
`trodes (N receive electrodes and M transmit electrodes),
`which further includes transmit (TX) electrode 222 and
`receive (RX) electrode 223. Each of the electrodes in matrix
`225 is connected with capacitance sensing circuit 201
`through multiplexers 212 and 213.
`Capacitance sensor 101 includes multiplexer control 211,
`multiplexers 212 and 213, clock generator 214, signal gen
`erator 215, demodulation circuit 216, and analog to digital
`converter (ADC) 217. ADC 217 is further coupled with touch
`coordinate converter 218. Touch coordinate converter 218
`outputs a signal to the processing logic 102.
`The transmit and receive electrodes in the electrode matrix
`225 may be arranged so that each of the transmit electrodes
`overlap and cross each of the receive electrodes Such as to
`form an intersection, while maintaining galvanic isolation
`from each other. Thus, each transmit electrode may be capaci
`tively coupled with each of the receive electrodes. For
`example, transmit electrode 222 is capacitively coupled with
`receive electrode 223 at the point where transmit electrode
`222 and receive electrode 223 intersect.
`Clock generator 214 Supplies a clock signal to signal gen
`erator 215, which produces a TX signal 224 to be supplied to
`the transmit electrodes of touch sensor 220. In one embodi
`ment, the signal generator 215 includes a set of Switches that
`operate according to the clock signal from clock generator
`214. The switches may generate a TX signal 224 by periodi
`cally connecting the output of signal generator 215 to a first
`Voltage and then to a second Voltage, wherein said first and
`second Voltages are different.
`The output of signal generator 215 is connected with mul
`tiplexer 212, which allows the TX signal 224 to be applied to
`any of the M transmit electrodes of touch sensor 220. In one
`embodiment, multiplexer control 211 controls multiplexer
`212 so that the TX signal 224 is applied to each transmit
`electrode in a controlled sequence. Multiplexer 212 may also
`be used to ground, float, or connect an alternate signal to the
`other transmit electrodes to which the TX signal 224 is not
`currently being applied.
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`Because of the capacitive coupling between the transmit
`and receive electrodes, the TX signal 224 applied to each
`transmit electrode induces a current within each of the receive
`electrodes. For instance, when the TX signal 224 is applied to
`transmit electrode 222 through multiplexer 212, the TX sig
`nal 224 induces an RX signal 227 on the receive electrodes in
`matrix 225. The RX signal 227 on each of the receive elec
`trodes can then be measured in sequence by using multiplexer
`213 to connect each of the N receive electrodes to demodu
`lation circuit 216 in sequence.
`The capacitance associated with each intersection between
`a TX electrode and an RX electrode can be sensed by select
`ing every available combination of TX electrode and an RX
`electrode using multiplexers 212 and 213. To improve perfor
`mance, multiplexer 213 may also be segmented to allow more
`than one of the receive electrodes in matrix 225 to be routed
`to additional demodulation circuits 216. In an optimized con
`figuration, wherein there is a 1-to-1 correspondence of
`instances of demodulation circuit 216 with receive elec
`trodes, multiplexer 213 may not be present in the system.
`When an object, Such as a finger, approaches the electrode
`matrix 225, the object causes a decrease in the mutual capaci
`tance between only some of the electrodes. For example, if a
`finger is placed near the intersection of transmit electrode 222
`and receive electrode 223, the presence of the finger will
`decrease the mutual capacitance between the two electrodes
`222 and 223. Thus, the location of the finger on the touchpad
`can be determined by identifying the one or more receive
`electrodes having a decreased mutual capacitance in addition
`to identifying the transmit electrode to which the TX signal
`224 was applied at the time the decreased mutual capacitance
`was measured on the one or more receive electrodes.
`By determining the mutual capacitances associated with
`each intersection of electrodes in the matrix 225 the locations
`of one or more contacts may be determined. The determina
`tion may be sequential, in parallel, or may occur more fre
`quently at commonly used electrodes.
`In alternative embodiments, other methods for detecting
`the presence of a finger or conductive object may be used
`where the finger or conductive object causes an increase in
`capacitance at one or more electrodes, which may be arranged
`in a grid or other pattern. For example, a finger placed near an
`electrode of a capacitive sensor may introduce an additional
`capacitance to ground that increases the total capacitance
`between the electrode and ground. The location of the finger
`can be determined from the locations of one or more elec
`trodes at which an increased capacitance is detected.
`The induced current waveform 227 is rectified by demodu
`lation circuit 216. The rectified current output by demodula
`tion circuit 216 can then be filtered and converted to a digital
`code by ADC 217.
`The digital code is converted to touch coordinates indicat
`ing a position of an input on touch sensor array 121 by touch
`coordinate converter 218. The touch coordinates are transmit
`ted as an input signal to the processing logic 102. In one
`embodiment, the input signal is received at an input to the
`processing logic 102. In one embodiment, the input may be
`configured to receive capacitance measurements indicating a
`plurality of row coordinates and a plurality of column coor
`dinates. Alternatively, the input may be configured to receive
`row coordinates and column coordinates.
`In one embodiment, the sensor array 121 can be configured
`to detect multiple touches. One technique for multi-touch
`detection uses a two-axis implementation: one axis to Support
`rows and another axis to Support columns. Additional axes,
`Such as a diagonal axis, implemented on the Surface using
`additional layers, can allow resolution of additional touches.
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`US 8,462,135 B1
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`While FIG. 2A illustrates a capacitance sensing circuit that
`measures mutual capacitance between sensor elements, Vari
`ous circuit implementations for performing capacitance mea
`Surement may measure self capacitances of each electrode.
`FIG. 2B illustrates a self-capacitance circuit 200 that uses a
`charge accumulation technique to measure the capacitance
`C 204. In an embodiment, the capacitance C 204 may
`represent the self capacitance of a sensor element similar to
`the sensor elements in the electrode matrix 225 of sensor
`array 121.
`A charge accumulation technique operates in the following
`manner: initially the integration capacitor is reset