US0087.49512B2
`
`(12) United States Patent
`Westerman et al.
`
`(10) Patent No.:
`(45) Date of Patent:
`
`US 8,749,512 B2
`Jun. 10, 2014
`
`(54) NEGATIVE PIXEL COMPENSATION
`
`sco,
`(75) Inventors: Ways St. San
`(US): Sean Eri
`onnor, Falo
`Alto, CA (US)
`
`(73) Assignee: Apple Inc., Cupertino, CA (US)
`
`(*) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 1164 days.
`
`(21) Appl. No.: 12/571,061
`
`(22) Filed:
`
`Sep. 30, 2009
`
`(65)
`
`O
`O
`Prior Publication Data
`US 2011 FOOT4725A1
`Mar. 31, 2011
`
`(2006.01)
`
`(51) Int. Cl.
`G06F 3/045
`(52) U.S. Cl.
`USPC ........................................... 345/174; 34.5/173
`(58) Field of Classification Search
`USPC ................................ 345/173, 174; 178/18.02
`See application file for complete search history.
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`1/1996 Yasutake
`5,483.261 A
`1/1996 Mead et al.
`5.488.204 A
`5,825,352 A 10, 1998 Bisset et al.
`5,835,079 A 11, 1998 Shieh
`5,880,411 A
`3/1999 Gillespie et al.
`6,188,391 B1
`2/2001 Seely et al.
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`10/2001 Beaton et al.
`6,323,846 B1
`1 1/2001 Westerman et al.
`6,690,387 B2
`2, 2004 Zimmerman et al.
`7,015,894 B2
`3, 2006 Morohoshi
`7,184,064 B2
`2/2007 Zimmerman et al.
`7,663,607 B2
`2/2010 Hotelling et al.
`8,479,122 B2
`7/2013 Hotelling et al.
`
`2/2006 Hotelling et al.
`2006/0026521 A1
`5/2006 Hotelling et al.
`2006/0097991 A1
`9/2006 Hotelling
`2006/O197753 A1
`7/2008 Westerman
`2008. O158145 A1
`7/2008 Westerman et al.
`2008. O158147 A1
`7, 2008 Westerman
`2008. O1581.85 A1
`2009.0160787 A1* 6/2009 Westerman et al. .......... 345,173
`2009, O174676 A1
`7, 2009 Westerman
`2009/017.4688 A1
`7/2009 Westerman
`2010/0073301 A1
`3/2010 Yousefpor et al.
`FOREIGN PATENT DOCUMENTS
`1335 318 A2
`8, 2003
`EP
`1335 318 A3
`8, 2003
`EP
`1335 318 B1
`8, 2003
`EP
`2O77487 A2
`7, 2009
`EP
`2000-163031 A
`6, 2000
`JP
`2002-342033. A 11, 2002
`JP
`WO WO-2011/041192 A1
`4, 2011
`OTHER PUBLICATIONS
`
`GB Combined Search and Examination Re port for GB Application
`No. 1016359.0, filed Sep. 29, 2010, five pages.
`
`(Continued)
`
`Primary Examiner — Latanya Bibbins
`(74) Attorney, Agent, or Firm — Morrison & Foerster LLP
`
`ABSTRACT
`(57)
`Negative pixel compensation in a touch sensor panel is dis
`closed. The panel can compensate for a negative pixel effect
`in touch signal outputs due to poor grounding of an object
`touching the panel. To do so, the panel can reconstruct a
`captured touch image to remove negative pixel values indica
`tive of the negative pixel effect and compute a composite
`image from the captured image and the reconstructed image
`to replace the captured image. In addition or alternatively, the
`panel can reconstruct a captured touch image to remove nega
`tive pixel values indicative of the negative pixel effect and
`replace the captured image with the reconstructed image.
`
`10 Claims, 8 Drawing Sheets
`
`USER319
`FINGER
`
`TOUCH
`CAPACTIVE PATH ses PANE
`--808-a
`
`''
`
`DRIVE
`LINE
`
`
`
`-308.
`CAPACTIVE
`
`DELL EXHIBIT 1032 PAGE 1
`
`DELL EXHIBIT 1032 PAGE 1
`
`

`

`US 8,749,512 B2
`Page 2
`
`(56)
`
`References Cited
`
`OTHER PUBLICATIONS
`
`International Search Report mailed Jan. 18, 2011, for PCT Applica
`tion No. PCT/US2010/049882, filed Sep. 22, 2010, three pages.
`Lee, S.K. et al. (Apr. 1985). "A Multi-Touch Three Dimensional
`Touch-Sensitive Tablet.” Proceedings of CHI: ACM Conference on
`Human Factors in Computing Systems, pp. 21-25.
`Rubine, D.H. (Dec. 1991). “The Automatic Recognition of Ges
`tures. CMU-CS-91-202, Submitted in Partial Fulfillment of the
`
`Requirements for the Degree of Doctor of Philosophy in Computer
`Science at Carnegie Mellon University, 285 pages.
`Rubine, D.H. (May 1992). “Combining Gestures and DirectManipu
`lation.” CHI '92, pp. 659-660.
`Westerman, W. (Spring 1999). “Hand Tracking, Finger Identifica
`tion, and Chordic Manipulation on a Multi-Touch Surface.” A Dis
`sertation Submitted to the Faculty of the University of Delaware in
`Partial Fulfillment of the Requirements for the Degree of Doctor of
`Philosophy in Electrical Engineering, 364 pages.
`U.S. Appl. No. 12/500,870, filed Jul. 10, 2009, by Land et al.
`* cited by examiner
`
`DELL EXHIBIT 1032 PAGE 2
`
`DELL EXHIBIT 1032 PAGE 2
`
`

`

`U.S. Patent
`
`Jun. 10, 2014
`
`Sheet 1 of 8
`
`US 8,749,512 B2
`
`
`
`TOUCH
`SENSORPANEL
`124
`/
`
`SO
`
`S1
`
`S2
`
`S3
`
`TOUCH
`
`DO
`
`D
`
`D2
`
`D3
`
`126
`PXEL
`FIG.2
`
`DELL EXHIBIT 1032 PAGE 3
`
`DELL EXHIBIT 1032 PAGE 3
`
`

`

`U.S. Patent
`
`Jun. 10, 2014
`
`Sheet 2 of 8
`
`US 8,749,512 B2
`
`USER319-
`
`TOUCH
`CAPACTIVE PATH SEsple.
`y
`
`L
`VBODy
`
`FINGER
`-308-b
`CAPACTIVE
`
`W
`St.
`
`
`
`DRIVE
`LINE
`30
`DO
`
`D
`
`
`
`D2
`
`D3
`
`SO 302 S
`SENSE
`LINE
`
`FIG. 3
`
`i.
`DOS
`
`NEGATIVE
`EXE
`DO, S2
`
`TRUE
`TOUCH
`DS2
`
`NEGATIVE
`PXEL
`D1, S1
`
`TOUCH
`
`D3
`
`DELL EXHIBIT 1032 PAGE 4
`
`DELL EXHIBIT 1032 PAGE 4
`
`

`

`U.S. Patent
`
`Jun. 10, 2014
`
`Sheet 3 of 8
`
`US 8,749,512 B2
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`501
`
`
`
`MORE THAN
`ONE FINGER)
`
`Y
`CALCULATE
`RECONSTRUCTED IMAGE
`
`CALCULATE
`OVERCOMPENSATIONRATIO
`
`
`
`
`
`RATIOX
`THRESHOLD?
`
`
`
`N
`CALCULATE NEGATIVE
`PXELRATIO
`
`RATIO K
`THRESHOLD?
`
`N
`USERECONSTRUCTED
`IMAGE
`
`
`
`USE ORIGINAL
`IMAGE
`
`FIG. 5
`
`DELL EXHIBIT 1032 PAGE 5
`
`DELL EXHIBIT 1032 PAGE 5
`
`

`

`U.S. Patent
`
`Jun. 10, 2014
`
`Sheet 4 of 8
`
`US 8,749,512 B2
`
`--UNGROUNDED----GROUNDED->
`GROUNDING CONDITION
`FIG. 6
`
`
`
`Nmax
`
`--UNGROUNDED --GROUNDED
`GROUNDING CONDITION
`FIG. 7
`
`DELL EXHIBIT 1032 PAGE 6
`
`DELL EXHIBIT 1032 PAGE 6
`
`

`

`U.S. Patent
`
`Jun. 10, 2014
`
`Sheet 5 of 8
`
`US 8,749,512 B2
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`y
`
`80
`
`
`
`MORE THAN
`ONE FINGER
`
`Y
`CALCULATE
`RECONSTRUCTED IMAGE
`
`CALCULATE
`OVERCOMPENSATIONRATIO
`
`CALCULATE NEGATIVE
`PXELRATIO
`
`DETERMINE CONFIDENCE
`WALUES
`
`CALCULATE WEIGHTED
`RATIOCOMBINATION
`
`
`
`
`
`
`
`
`
`DETERMINE
`MXINGFACTOR
`
`CALCULATE
`COMPOSITE IMAGE
`
`
`
`USE COMPOSITE
`IMAGE
`
`FIG. 8
`
`USEORIGINAL
`IMAGE
`
`
`
`817
`
`DELL EXHIBIT 1032 PAGE 7
`
`DELL EXHIBIT 1032 PAGE 7
`
`

`

`U.S. Patent
`
`Jun. 10, 2014
`
`Sheet 6 of 8
`
`US 8,749,512 B2
`
`
`
`
`
`--ONE FINGER->
`T
`
`--MULTIPLEFINGERS--
`T2
`TOUCH MAGNITUDE
`FIG. 9
`
`--GROUNDED->
`-UNGROUNDED-
`Ng
`Nu
`NEGATIVEPXELRATIO
`FIG. 10
`
`
`
`--GROUNDED
`-UNGROUNDED-
`Wg
`Wu
`WEIGHTEDRATIOCOMBINATION
`FIG 11
`
`DELL EXHIBIT 1032 PAGE 8
`
`DELL EXHIBIT 1032 PAGE 8
`
`

`

`U.S. Patent
`
`Jun. 10, 2014
`
`Sheet 7 of 8
`
`US 8,749,512 B2
`
`COMPUTING SYSTEM
`1200
`
`1230
`
`1228
`
`1232
`
`DISPLAY
`DEVICE
`
`HOST
`PROCESSOR
`
`
`
`PROGRAM
`STORAGE
`
`
`
`
`
`PROCESSOR 11202
`SUBSYSTEM
`1212
`
`1206
`TOUCH
`CONTROLLER
`
`1215
`
`CHARGE
`PUMP
`
`1210
`
`1214
`
`PANELSCAN
`LOGIC
`
`TRANSMIT
`SECTION
`
`STIMULATION
`SIGNALS
`1216
`
`
`
`
`
`1209
`
`DEMOD.
`SECTION
`
`RECEIVE
`SECTION
`ls,
`
`1208
`CONTROLSIGNALS
`
`TOUCHSENSOR
`PANEL C
`1224 VSIG
`TOUCHSIGNALS
`1203
`
`
`
`
`
`SENSOR
`
`121
`
`
`
`1226 PXEL
`
`FIG. 12
`
`DELL EXHIBIT 1032 PAGE 9
`
`DELL EXHIBIT 1032 PAGE 9
`
`

`

`U.S. Patent
`
`Jun. 10, 2014
`
`Sheet 8 of 8
`
`US 8,749,512 B2
`
`MOBILE
`TELEPHONE
`1300
`
`DISPLAYDEVICE
`1336
`
`TOUCH
`SENSOR
`PANEL
`
`
`
`FIG. 13
`
`TOUCH
`SENSORPANEL
`
`DISPLAYDEVICE
`1436
`
`
`
`MEDIA
`PLAYER
`1400
`
`
`
`PERSONAL
`COMPUTER
`1500
`
`DISPLAY
`1536
`
`
`
`
`
`TRACKPAD
`1524
`
`DELL EXHIBIT 1032 PAGE 10
`
`DELL EXHIBIT 1032 PAGE 10
`
`

`

`1.
`NEGATIVE PXEL COMPENSATION
`
`US 8,749,512 B2
`
`FIELD
`
`This relates generally to touch sensor panels and, more
`particularly, to compensating for negative pixel effects in
`touch sensor panels.
`
`BACKGROUND
`
`Many types of input devices are presently available for
`performing operations in a computing system, Such as buttons
`or keys, mice, trackballs, joysticks, touch sensor panels,
`touch screens and the like. Touch sensitive devices, such as
`touch screens, in particular, are becoming increasingly popu
`lar because of their ease and versatility of operation as well as
`their declining price. A touch sensitive device can include a
`touch sensor panel, which can be a clear panel with a touch
`sensitive Surface, and a display device Such as a liquid crystal
`display (LCD) that can be positioned partially or fully behind
`the panel so that the touch-sensitive surface can cover at least
`a portion of the viewable area of the display device. The touch
`sensitive device can allow a user to perform various functions
`by touching the touch sensor panel using a finger, stylus or
`other object at a location often dictated by a user interface
`(UI) being displayed by the display device. In general, the
`touch sensitive device can recognize a touch event and the
`position of the touch event on the touch sensor panel, and the
`computing system can then interpret the touch event in accor
`dance with the display appearing at the time of the touch
`event, and thereafter can perform one or more actions based
`on the touch event.
`When the object touching the touch sensor panel is poorly
`grounded, touch output values indicative of a touch event can
`be erroneous or otherwise distorted. The possibility of such
`erroneous or distorted values can further increase when two
`or more simultaneous touch events occur at the touch sensor
`panel.
`
`SUMMARY
`
`This relates to compensating touch signals indicative of a
`touch at a touch sensor panel for errors that can be caused by
`poor grounding of a user or other objects touching the panel.
`One Such error can be a negative pixel effect, in which an
`apparent negative amount of touch can be sensed by the panel
`during multiple simultaneous touches. In some embodi
`ments, to compensate for this effect, the panel can reconstruct
`a captured touch image to eliminate negative pixel values and
`then compute a composite of the captured touch image and
`the reconstructed touch image to replace the captured image.
`In other embodiments, to compensate for this effect, the panel
`can reconstruct a captured touch image to eliminate negative
`pixel values and then replace the captured image with the
`reconstructed image. The ability to compensate for a negative
`pixel effect in a touch sensor panel can advantageously pro
`vide faster and more accurate touch detection, as well as
`power savings, by not having to repeat measurements subject
`to poor grounding conditions. Additionally, the panel can
`more robustly adapt to various grounding conditions of a user
`or other object.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 illustrates an exemplary touch sensor panel in a
`no-touch condition according to various embodiments.
`
`10
`
`15
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
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`
`60
`
`65
`
`2
`FIG. 2 illustrates an exemplary touch map of a touch sensor
`panel in a no-touch condition according to various embodi
`mentS.
`FIG. 3 illustrates an exemplary touch sensor panel having
`multiple touches from an ungrounded object which can create
`negative pixel effect according to various embodiments.
`FIG. 4 illustrates an exemplary touch map of a touch sensor
`panel having multiple touches from an ungrounded object
`which can create negative pixel effect according to various
`embodiments.
`FIG. 5 illustrates an exemplary method for compensating
`for negative pixel effect according to various embodiments.
`FIG. 6 illustrates an exemplary plot of a grounding condi
`tion of an object versus an overcompensation ratio which can
`be utilized to compensate for negative pixel effect according
`to various embodiments.
`FIG. 7 illustrates an exemplary plot of a grounding condi
`tion of an object versus a negative pixel ratio which can be
`utilized to compensate for negative pixel effect according to
`various embodiments.
`FIG. 8 illustrates another exemplary method for compen
`sating for negative pixel effect according to various embodi
`mentS.
`FIG. 9 illustrates an exemplary plot of touch magnitude
`Versus one finger touch confidence which can be utilized to
`compensate for negative pixel effect according to various
`embodiments.
`FIG. 10 illustrates an exemplary plot of negative pixel ratio
`Versus negative pixel grounding confidence which can be
`utilized to compensate for negative pixel effect according to
`various embodiments.
`FIG. 11 illustrates an exemplary plot of weighted ratio
`combination versus image mixing factor which can be uti
`lized to compensate for negative pixel effect according to
`various embodiments.
`FIG. 12 illustrates an exemplary computing system that
`can compensate for negative pixel effect according to various
`embodiments.
`FIG. 13 illustrates an exemplary mobile telephone that can
`compensate for negative pixel effect according to various
`embodiments.
`FIG. 14 illustrates an exemplary digital media player that
`can compensate for negative pixel effect according to various
`embodiments.
`FIG. 15 illustrates an exemplary personal computer that
`can compensate for negative pixel effect according to various
`embodiments.
`
`DETAILED DESCRIPTION
`
`In the following description of various embodiments, ref
`erence is made to the accompanying drawings which form a
`part hereof, and in which it is shown by way of illustration
`specific embodiments which can be practiced. It is to be
`understood that other embodiments can be used and structural
`changes can be made without departing from the scope of the
`various embodiments.
`This relates to compensating for a negative pixel effect in a
`touch sensor panel due to poor grounding of a user or other
`objects touching the panel. In some embodiments, the panel
`can reconstruct a captured touch image to remove negative
`pixel values indicative of the negative pixel effect and then
`compute a composite image of the captured image and the
`reconstructed image to replace the captured image, thereby
`compensating for the negative pixel effect. In some embodi
`ments, the panel can reconstruct a captured touch image to
`remove negative pixel values indicative of the negative pixel
`
`DELL EXHIBIT 1032 PAGE 11
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`DELL EXHIBIT 1032 PAGE 11
`
`

`

`US 8,749,512 B2
`
`3
`effect and then replace the captured image with the recon
`structed image, thereby compensating for the negative pixel
`effect.
`The ability to compensate for a negative pixel effect in a
`touch sensor panel can advantageously provide faster and
`more accurate touch detection, as well as power savings, by
`not having to repeat measurements subject to poor grounding
`conditions. Additionally, the panel can more robustly adapt to
`various grounding conditions of a user or other object.
`The terms “poorly grounded,” “ungrounded,” “not
`grounded,” “partially grounded.” “not well grounded.”
`“improperly grounded, “isolated,” and “floating can be
`used interchangeably to refer to poor grounding conditions
`that can exist when an object is not making a low impedance
`electrical coupling to the ground of the touch sensor panel.
`The terms “grounded,” “properly grounded,” and “well
`grounded can be used interchangeably to refer to good
`grounding conditions that can exist when an object is making
`a low impedance electrical coupling to the ground of the
`touch sensor panel.
`Although various embodiments can be described and illus
`trated herein in terms of mutual capacitance multi-touchsen
`sor panels, it should be understood that the various embodi
`ments are not so limited, but can be additionally applicable to
`other sensors in which single stimulation signals can be used
`to generate a touch signal and in which multiple simultaneous
`stimulation signals can be used to generate a composite touch
`signal. Moreover, although various embodiments described
`and illustrated herein can be implemented using double-sided
`ITO (DITO) touch sensor panels, it should be understood that
`the various embodiments can be also applicable to other touch
`sensor panels configurations, including opaque touch sensor
`panels, such as configurations in which the drive and sense
`lines can beformed on different substrates or on the back of a
`cover glass, and configurations in which the drive and sense
`lines can be formed on the same side of a single Substrate.
`Furthermore, although various embodiments can be
`described and illustrated herein in terms of rows and columns
`of conductive lines orthogonal to each other, it should be
`understood that the various embodiments are not so limited,
`but additionally encompass other geometric configurations,
`Such as concentric and radial lines of a polar-coordinate con
`figuration, diagonal lines of an oblique configuration, non
`orthogonal lines, and so on.
`FIG. 1 illustrates an exemplary touch sensor panel in a
`no-touch condition, i.e., where there are presently no touches
`at the panel, according to various embodiments. In the
`example of FIG. 1, touch sensor panel 124 can include an
`array of pixels 126 that can beformed at the crossings of rows
`of drive lines 101 (D0-D3) and columns of sense lines 102
`(S0-S3). Each pixel 126 can have an associated mutual
`capacitance Csig 114 when the drive line 101 forming the
`pixel is stimulated with a stimulation signal Vistm 116. Each
`pixel 126 can also have an associated Stray capacitance Cstray
`when the drive line 101 forming the pixel is not stimulated
`with a stimulation signal Vistm 116 but is connected to DC. In
`this example, drive line D0 can be stimulated with stimulation
`signal 116 (Vstm), forming mutual capacitance Csig 114 at
`the pixels 126 formed between the drive line D0 and the
`crossing sense lines S0-S3. One or more drive lines 101 can
`be stimulated at a time.
`FIG. 2 illustrates an exemplary touch map of a touch sensor
`panel in a no-touch condition according to various embodi
`ments. In the example of FIG. 2, drive lines D0-D3 of a touch
`sensor panel can be individually and/or simultaneously
`stimulated with stimulation signal(s) Vistm. Since there are no
`fingers (or other objects) touching the pixels 126 formed by
`
`40
`
`45
`
`4
`the drive lines D0-D3 and the crossing sense lines S0-S3, the
`fingers cannot block some of the electric field lines formed
`when the drive lines are stimulated so as to reduce the mutual
`capacitance Csig by an amount ACsig. As such, the touch map
`can remain substantially flat at the pixels 126 to indicate no
`touch.
`Referring again to FIG. 1, when a grounded user's finger
`(or other object) touches the panel 124, the finger can cause
`the capacitance Csig 114 to reduce by an amount ACsig at the
`touch location as previously mentioned. This capacitance
`change ACsig can be caused by current or charge from the
`electric field lines being shunted through the touching finger
`to ground. Touch signals representative of the capacitance
`change ACsig can be transmitted by the sense lines 102 to the
`sense circuitry for processing. The touch signals can indicate
`the pixel 126 where the touch occurred and the amount of
`touch that occurred at that pixel location.
`Conversely, when an ungrounded user's finger (or other
`object) touches the panel 124, the current or charge from the
`electric field lines can be transmitted by the touching finger
`back into the crossing sense line 102 rather than being
`shunted to ground. As a result, instead of the capacitance Csig
`114 of the pixel at the touch location being reduced by ACsig,
`Csig may only be reduced by (ACsig-Cneg), where Cneg can
`represent a so-called “negative capacitance' resulting from
`the charge coupled into the crossing sense line due to the
`finger's poor grounding. The touch signals can still generally
`indicate the pixel 126 where the touch occurred but with an
`indication of a lesser amount of touch than actually occurred.
`When multiple ungrounded user's fingers (or other
`objects) touch the panel 124, the lesser amount of touch can
`be exacerbated to create a so-called “negative pixel effect.”
`FIG. 3 illustrates an exemplary touch sensor panel having
`multiple touches from an ungrounded user (or other objects)
`which can create a negative pixel effect according to various
`embodiments. In the example of FIG.3, one of drive lines 301
`(D0) of touch sensor panel 124 can be stimulated with a
`stimulation signal 116 (Vstm) to form a mutual capacitance
`Csig 114 between the stimulated drive line D0 and the cross
`ing sense lines 302 (S0-S3). In this example, user 319 can
`touch with finger 319-a at pixel 126-a formed by drive line D0
`and sense line S1 (“pixel D0.S1) and with finger 319-bat
`pixel 126-b formed by drive line D1 and sense line S2 (“pixel
`D1.S2). Because the user319 is ungrounded, the user's body
`capacitance Cbody to ground can vary significantly, e.g.,
`between 10-100 pF in some embodiments. The user's finger
`319-a can also form a capacitance Cfd from the stimulated
`drive line D0 to that finger. When the finger 319-a touches at
`the touch sensor panel 124, the finger can block some of the
`electric field lines formed when the drive line D0 is stimu
`lated. But instead of those electric field lines being shunted to
`ground, a capacitance Cfs from the finger 319-a to the sense
`line S1 can form, sending some of the electric field charge
`through capacitive path 308-a from the finger to the sense line
`S1. As a result, instead of the mutual capacitance Csig at pixel
`D0.S1 being reduced by ACsig, Csig can only be reduced by
`(ACsig-Cneg), resulting from the charge sent into sense line
`S1 due to the poor grounding of the user, as described previ
`ously.
`Similarly, a capacitance Cfs from the finger 319-b to the
`sense line S2 can also form, sending some of the electric field
`charge through capacitive path 308-b from the finger to the
`sense line S2. As a result, though drive line D1 is not being
`stimulated with Vistm while drive line D0 is being stimulated,
`the finger 319-b at pixel D1.S2 can increase that pixels
`capacitance by Cneg (a negative capacitance at the pixel
`resulting from the charge sent into sense line S2 due to the
`
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`DELL EXHIBIT 1032 PAGE 12
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`DELL EXHIBIT 1032 PAGE 12
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`US 8,749,512 B2
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`poor grounding of the user) to a capacitance above that of a
`no-touch condition to give the appearance of a so-called
`“negative pixel’ or a theoretical negative amount of touch at
`pixel D1, S2.
`Adjacent pixels can also experience this negative pixel
`effect. The pixel 126-c formed by the drive line D0 and the
`crossing sense line S2 (“pixel D0.S2) can increase that pix
`els capacitance Csig by Cneg, due to the capacitance Cfs
`introduced by the finger 319-b into the sense line S2. Simi
`larly, the pixel 126-d formed by the drive line D1 and the
`crossing sense line S1 (“pixel D1.S1) can increase that pix
`els capacitance by Cneg to a capacitance above that of no
`touch, due to the capacitance Cfs introduced by the finger
`319-a into the sense line S1.
`Similar to the finger 319-a, when drive line D1 is stimu
`lated with Vistm, the finger 319-b can reduce the mutual
`capacitance Csig by (ACsig-Cneg) at pixel D1.S2, where
`Cneg can be a negative capacitance at the pixel resulting from
`the electric field charge sent into sense line S2 when drive line
`D1 is stimulated. In this example, since drive line D0 is not
`stimulated while drive line D1 is stimulated, the finger 319-a
`at pixel D0.S1 can increase that pixel’s capacitance by Cneg
`to give the appearance of a negative pixel. Adjacent pixels
`D1.S2 and D0. S1 can similarly experience the negative pixel
`effect.
`FIG. 4 illustrates an exemplary touch map of a touch sensor
`panel having multiple touches from an ungrounded user (or
`other objects) which can create a negative pixel effect accord
`ing to various embodiments. In the example of FIG. 4, drive
`lines D0-D3 of a touch sensor panel can be individually
`and/or simultaneously stimulated with stimulation signal(s)
`Vstm. User 319 can touch with finger 319-a at pixel D0,S1
`and with finger 319-bat pixel D1, S2, as in FIG.3. When drive
`line D0 is stimulated, the finger 319-a at pixel D0.S1 can
`shunt some of the blocked electric field lines into the sense
`line S1 instead of into ground, such that the touch map can
`indicate an attenuated true touch (or positive pixel) at that
`pixel (symbolically illustrated by a slight peak in FIG. 4).
`Similarly, when drive line D1 is stimulated, the finger 319-b
`at pixel D1.S2 can shunt some of the blocked electric field
`lines into the sense line S2 instead of into ground. Such that
`the touch map can indicate an attenuated true touch (or posi
`tive pixel) at that pixel (symbolically illustrated by a slight
`peak in FIG. 4). Adjacent pixels D1.S1 and D0.S2 can expe
`rience a negative pixel effect, as described previously, Such
`that the touch map can indicate a negative touch (or negative
`pixel) at these pixels (symbolically illustrated by hollows in
`FIG. 4). The net result of the user being poorly grounded can
`be that the touch signal of the pixel being touched can be
`attenuated and the adjacent pixels can have negative touch
`signals.
`The touch map in this example indicates the touches when
`both drive lines D0 and D1 are stimulated. However, in the
`case where only drive line D0 is stimulated, the touch map can
`indicate an attenuated touch of the finger 319-a at pixel D0.S1
`and negative touches of various magnitudes of the finger
`319-bat pixel D1.S2 and at adjacent no-touch pixels D1, S1
`and D0.S2. Conversely, in the case where only drive line D1
`is stimulated, the touch map can indicate an attenuated touch
`of the finger 319-bat pixel D1.S2 and negative touches of
`various magnitudes of the finger 319-a at pixel D0.S1 and at
`adjacent no-touch pixels D1, S1 and D0.S2.
`Accordingly, detecting the negative pixel effect and com
`pensating the touch signals for the effect can improve touch
`65
`sensing of the touch sensor panel in poor grounding condi
`tions.
`
`6
`FIG. 5 illustrates an exemplary method for compensating
`for negative pixel effect according to various embodiments.
`In the example of FIG. 5, a touch can be detected at a touch
`sensor panel and captured in a touch image. A determination
`can be made whether more than one finger (or other objects)
`is touching the panel based on the captured touch image
`(501). Various metrics can be used to make this determina
`tion. For example, a touch magnitude can be measured from
`the touch image, where the magnitude can be indicative of the
`number of fingers making the touch at the panel. That is, a
`certain magnitude range can indicate one finger touching and
`another magnitude range can indicate more than one finger
`touching. The touch magnitude can be calculated as the Sum
`of touch image pixel values above a particular threshold. Such
`as a background noise threshold, for example. If more than
`one finger is touching, the touch sensor panel may be more
`likely to experience a negative pixel effect for which the touch
`image can be compensated. Conversely, if one finger is touch
`ing, the touch sensor panel may be less likely to experience a
`negative pixel effect such that touch image compensation can
`be omitted. Accordingly, if only one finger is touching, the
`captured touch image can be used for further processing
`without negative pixel compensation (515). It should be noted
`that, in some embodiments, one flattened finger touching the
`touch sensor panel can create a negative pixel effect similar to
`multiple touching fingers, such that the touch image can be
`compensated. Therefore, a one-flat-finger touch can be
`treated as a multi-finger touch.
`If more than one finger is touching the touch sensor panel,
`the captured touch image can be reconstructed without nega
`tive pixel values, i.e., as if the negative pixel effect had not
`occurred (503). Various methods can be used to produce the
`reconstructed image. For example, in one method, an actual
`touch signal value ACsig.a at a pixel can be reconstructed
`from a measured touch signal value ACsigm at that pixel as
`follows,
`
`.
`.
`ACsiga (i, j) = AC sign (i, j) + RX X. ACsign (i, j) XX ACsign (i, j),
`alli
`alli
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`(1)
`
`where R a negative pixel compensation factor, which can be
`a function of Cfd, Cfs, and Cbody, thereby representative of a
`user's grounding condition;
`
`XACsign (i, j) =
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`alli
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`the sum off all measured touch signal outputs along drive line i:
`
`and
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`XACsign (i, j) =
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`all i
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`the sum of all measured touch signal outputs along sense line i.
`
`The negative pixel compensation factor R can be approxi
`mated as follows,
`
`1
`R = to (
`= b X
`-,
`X at all ACsign (i, j) + Cbody
`
`(2)
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`DELL EXHIBIT 1032 PAGE 13
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`DELL EXHIBIT 1032 PAGE 13
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`where b-a touch sensor panel design constant, which can be
`obtained through simulation and/or empirical measurements
`for a given panel sensing pattern design; and Cbody a user's
`nominal body ground capacitance in an ungrounded condi
`tion.
`In the reconstructed touch image, the negative pixel values
`from the captured touch image can be attenuated and the true
`(or positive) touch pixel values from the captured touch image
`accentuated.
`An overcompensation ratio can be calculated for a particu
`lar nominal value of Cbody (505). The overcompensation
`ratio can be an indication of the grounding condition of the
`user and hence whether the negative pixel effect is likely. For
`example, a grounded user is less likely to cause the negative
`pixel effect. The overcompensation ratio can be calculated as
`the ratio of the sum of the positive touch values in the recon
`structed image to the Sum of the positive touch values in the
`original captured touch image. Alternatively, the overcom
`pensation ratio can be calculated as the ratio of the Sum of all
`touch values in the reconstructed image to the Sum of all touch
`values in the original captured touch image. Alternatively, the
`overcompensation ratio can be calculated as the ratio of a
`peak touch value in the reconstructed image to a maximum
`possible touch value in the original captured touch image. A
`higher overcompensation ratio can indicate little or no nega
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`tive pixel effect. The higher ratio can be a result of the recon
`structed image including unnecessarily compensated pixels
`such that the intensity and number of positive pixel values
`increases significantly over the number in the captured image
`due to the fact that the reconstruction can be performed for a
`finite value of Cbody rather than an actual value of Cbody at
`infinity for the grounded condition. Conversely, a lower over
`compensation ratio can indicate more negative pixel effect.
`The lower ratio can be a result of the reconstructed image
`including properly compensated pixels such that the number
`of positive pixel values more closely matches the number in
`the captured image.
`FIG. 6 illustrates an exemplary plot of a grounding condi
`tion of an object, e.g., a user, Versus an overcompensation
`ratio. In the example of FIG. 6, an overcompensation ratio
`above threshold Ot can indicate a grounded user touching the
`touch sensor panel and, hence, little or no negative pixel
`effect. In contrast, an overcompensation ratio below thresh
`old Ot can indicate an ungrounded user touching the panel
`and, hence, more negative pixel effect. In some embodiments,
`the overcompensation ratio threshold Otcan be determined to
`be 1.8. In some embodiments, the minimum overcompensa
`tion ratio Omin can be determined to be 1.3, indicating an
`ungrounded user.
`Referring again to FIG. 5, a determination can be made
`whether the calculated overcompensation ratio is above a
`threshold Ot indicating that the touching user is grounded
`(507). If so, the captured touch image can be used for further
`processing without negative pixel compensation (515).
`If the calculated overcompensation ratio is below the
`threshold Ot indicating that the touching user is ungrounded,
`additional analysis can be performed to confirm the ground
`ing condition. Here, a negative pixel ratio can be calculated
`(509). The negative pixel ratio can be an indication of the
`grounding condition of the user and hence whether the nega
`tive pixel effect is likely. For example, a grounded user is less
`likely to cause the negative pixel effect. The negative pixel
`ratio can be calculated as the ratio of the Sum of negative
`touch values to the Sum of positive touch values in the original
`captured touch image. A higher negative pixel ratio can indi
`cate the negative pixel effect because the number of negative
`pixels (indicative of the negative pixel effect) can be larger
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`and closer to the number of positive pixels. Conversely, a
`lower negative pixel ratio can indicate little or no negative
`pixel effect because the number of negative pixels can be
`much lower than the number of positive pixels.
`FIG. 7 illustrates an