(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2010/0060608 A1
`YOUSEFPOR
`(43) Pub. Date:
`Mar. 11, 2010
`
`US 2010.0060608A1
`
`(54) CORRECTION OF PARASITIC
`CAPACITANCE EFFECT N TOUCH SENSOR
`PANELS
`
`(75) Inventor:
`
`Medits YOUSEFPOR, San Jose,
`
`Publication Classification
`
`(51) Int. Cl.
`G06F 3/045
`(2006.01)
`H04B I/38
`(2006.01)
`(52) U.S.C. . 345/174; 455/566
`(57)
`ABSTRACT
`Compensation of pixels included in a touch sensor panel that
`Correspondence Address:
`APPLE C/O MORRISON AND FOERSTERLLP generate erroneous readings (so called “negative pixels') due
`LOS ANGELES
`to a poor grounding condition of the object touching the touch
`555 WEST FIFTH STREETSUITE 3500
`sensor panel is disclosed herein. To compensate for the erro
`LOS ANGELES, CA 90013-1024 (US)
`neous readings, sense lines of the touch sensor panel can
`include reverse driving circuits to facilitate calculation of an
`object-to-ground capacitance. If the calculated object-to
`ground capacitance indicates the presence of a poor ground
`ing condition, then the object-to-ground capacitance and
`detected pixel touch output values are used to estimate new
`pixel touch output values that are used instead of the detected
`pixel touch output values to determine touch event(s).
`
`(73) Assignee:
`
`Apple Inc., Cupertino, CA (US)
`
`(21) Appl. No.:
`
`12/208,324
`
`(22) Filed:
`
`Sep. 10, 2008
`
`COVER
`204
`f
`7
`
`FINGER
`200
`
`ELECTRIC
`FIELD
`LINES
`202
`
`-
`
`
`
`DRIVE
`
`102
`
`SENSE
`LINE
`104
`
`DELL EXHIBIT 1005 PAGE 1
`
`DELL EXHIBIT 1005 PAGE 1
`
`

`

`Patent Application Publication
`
`Mar. 11, 2010 Sheet 1 of 12
`
`US 2010/0060608 A1
`
`PXEL
`DRIVE (SENSOR)
`LINES
`106
`102
`
`SENSE
`LINES
`104
`
`D \ }{}{}(– :
`
`M
`V
`M
`M
`S/ NCN/ NCN/ NCN/
`1N 71N, 1TN, 1N
`MS / \S / MS / \S /
`
`ENSOR
`PANEL
`100
`-/
`
`DRIVE
`CIRCUITS
`108
`
`NS/ NS/ NS/ NS/
`
`Y
`
`NS/ NS/ NS/
`
`N.
`
`V
`n
`
`MUTUAL
`CAENGIANCE C- C - X- X
`114
`GO GO GO GO
`
`V7
`
`N7
`
`N7
`
`N7
`
`(SENSE)
`EARSE
`AMPLIFIERS
`110
`
`REVERSE VOLTAGE
`SOURCES
`112
`FIG. 1
`
`DELL EXHIBIT 1005 PAGE 2
`
`DELL EXHIBIT 1005 PAGE 2
`
`

`

`Patent Application Publication
`
`Mar. 11, 2010 Sheet 2 of 12
`
`US 2010/0060608 A1
`
`FINGER
`200
`
`ELECTRIC
`FIELD
`LINES
`
`
`
`-
`
`COVER
`204
`f
`7
`
`SENSE
`LINE
`104
`
`DELL EXHIBIT 1005 PAGE 3
`
`DELL EXHIBIT 1005 PAGE 3
`
`

`

`Patent Application Publication
`
`Mar. 11, 2010 Sheet 3 of 12
`
`US 2010/0060608 A1
`
`TOUCH
`SENSOR
`PANEL
`300
`
`SENSE
`LINES
`304
`
`
`
`/, C r
`
`SENSE
`AMPLIFIERS
`
`310
`
`PRY
`
`302
`
`GO
`
`SFSR
`DRIVE
`CIRCUITS
`308
`
`FIG. 3
`
`DRIVE
`W1
`
`MUTUAL CAPACITANCE
`114
`
`CSIG
`
`DRIVE
`CIRCUIT
`108
`
`FEEDBACK
`CAPACITANCE
`400 (NO TOUCH)
`PXEL TOUCH
`CFB OUTP:ALUE
`S
`WO
`
`SENSE
`
`
`
`SENSE
`AMER
`
`FIG. 4A
`
`DELL EXHIBIT 1005 PAGE 4
`
`DELL EXHIBIT 1005 PAGE 4
`
`

`

`Patent Application Publication
`
`Mar. 11, 2010 Sheet 4 of 12
`
`US 2010/0060608 A1
`
`TOUCH CAPACITANCE
`404
`
`CSIG – CSIG SENSE
`
`TOUCH
`FEEDBACK
`Pixatch
`CAPACITANCE
`CFB OUTALUE
`
`
`
`SENSE
`
`Vo-VS-Vn
`
`DRIVE
`
`
`
`Er
`108
`
`
`
`CFS
`CFD
`CGND
`TOUCH
`ANEEve
`CAPACITANCE ? CAPACITANCE
`AND SENSE
`406
`408
`
`
`
`GROUND
`CAPACITANCE
`410
`
`DRIVE
`W1
`
`TOUCH CAPACITANCE
`404
`CSIG - CSIG SENSE
`
`
`
`SENSE
`
`CNEG
`NEGATIVE
`CAPACITANCE
`414
`
`TOUCH CAPACITANCE
`404
`
`CSIG - CSIG SENSE
`
`SENSE
`
`DRIVE
`V1
`
`SENSE
`AMPLIFIER
`110
`
`FIG. 4B
`
`(TOUCH)
`PXEL TOUCH
`CFB Out: ALUE
`
`Vo-WSWn
`
`FIG. 4C
`
`(GOOD GROUND)
`PIXEL TOUCH
`CFB Outy ALUE
`
`WoWs
`
`FIG. 4D
`
`DELL EXHIBIT 1005 PAGE 5
`
`DELL EXHIBIT 1005 PAGE 5
`
`

`

`Patent Application Publication
`
`Mar. 11, 2010 Sheet 5 of 12
`
`US 2010/0060608 A1
`
`DRIVE
`LINES
`
`
`
`TOUCH
`SENSOR
`
`SENSE
`LINES
`104
`
`NEGATIVE
`guch
`D0, S2
`
`NEGATIVE
`TOUCH
`D2, S1
`
`
`
`DRIVE
`LINES
`102
`
`FIG. 5A
`
`TRUE
`Iguch
`DO, S1
`
`SENSE
`AMPLIFIERS
`110
`
`SENSE
`LINES
`104
`
`NEGATIVE
`TOUCH
`D0, S2
`
`
`
`NEGATIVE
`TOUCH
`D0, S1
`
`DELL EXHIBIT 1005 PAGE 6
`
`DELL EXHIBIT 1005 PAGE 6
`
`

`

`Patent Application Publication
`
`Mar. 11, 2010 Sheet 6 of 12
`
`US 2010/0060608 A1
`
`FEEDBACK
`CAPACITANCE
`400
`
`MUTUAL CAPACITANCE
`114
`CSIG, CO
`
`
`
`
`
`DRIVE C)
`CIRCUIT
`108
`
`
`
`
`
`
`
`ROW PANELY
`LUMPED
`PARASITIC
`CAPACITANCE
`600
`
`COLUMN PANEL
`LUMPED
`PARASITIC
`CAPACITANCE
`602
`
`(NO TOUCH)
`PXEL TOUCH
`OUTPUT
`WALUE
`S.
`
`CFB
`
`WO
`SENSE
`AMPLIFER
`110
`REVERSE
`WOLTAGE
`SOURCE
`112
`
`
`
`DRIVE
`CIRCUIT
`108
`
`
`
`CFS, C3
`CFD, C2
`TOUCH AND I TOUCH AND
`DRIVE
`SENSE
`CAPACITANCE
`CAPACITANCE
`406
`408
`
`CPD, C5
`ROW PANEL
`LUMPED
`PARASITIC
`CAPACITANCE
`600
`
`CGND, Cg
`GROUND
`CAPACITANCE
`410
`
`CPS, C4
`COLUMN
`PANEL
`LUMPED
`PARASITIC
`AACTANCE
`
`REVERSE
`VOLTAGE
`SOURCE
`112
`
`W2
`
`FIG. 6B
`
`DELL EXHIBIT 1005 PAGE 7
`
`DELL EXHIBIT 1005 PAGE 7
`
`

`

`Patent Application Publication
`
`Mar. 11, 2010 Sheet 7 of 12
`
`US 2010/0060608 A1
`
`700
`
`702
`
`704
`
`706
`
`708
`
`710
`
`712
`
`
`
`SIMULTANEOUSLY
`STIMULATE ALL
`DRIVE LINES
`
`OBTAIN MEASURED
`TOUCH OUTPUT
`WALUES
`
`CALCULATE
`AVERAGE CSIG
`
`SIMULTANEOUSLY
`(REVERSE) STIMULATE
`ALL SENSE LINES
`
`OBTAIN MEASURED
`TOUCH OUTPUT
`WALUES
`
`CALCULATE
`AVERAGE
`CSIGCFS
`
`CALCULATE
`AVERAGE
`CPS
`
`FIG. 7
`
`DELL EXHIBIT 1005 PAGE 8
`
`DELL EXHIBIT 1005 PAGE 8
`
`

`

`Patent Application Publication
`
`Mar. 11, 2010 Sheet 8 of 12
`
`US 2010/0060608 A1
`
`814
`
`800
`
`802
`
`804
`
`806
`
`808
`
`810
`
`812
`
`SIMULTANEOUSLY
`STIMULATE ALL
`DRIVE LINES
`
`OBTAIN MEASURED
`TOUCH OUTPUT
`WALUES
`
`CALCULATE
`AVERAGE
`U
`
`SIMULTANEOUSLY
`(REVERSE) STIMULATE
`ALL SENSE LINES
`
`OBTAIN MEASURED
`TOUCH OUTPUT
`WALUES
`
`CALCULATE
`AVERAGE
`W
`
`CALCULATE
`AVERAGE
`CGND
`
`FIG. 8
`
`DELL EXHIBIT 1005 PAGE 9
`
`DELL EXHIBIT 1005 PAGE 9
`
`

`

`Patent Application Publication
`
`Mar. 11, 2010 Sheet 9 of 12
`
`US 2010/0060608 A1
`
`930
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`SEQUENTIALLY
`STIMULATE
`DRIVE LINES
`
`OBTAIN MEASURED
`TOUCH OUTPUT
`WALUES
`
`
`
`
`
`NO ACTUAL TOUCH OUTPUT
`WALUES=MEASURED
`TOUCH OUTPUT WALUES
`
`
`
`
`
`IS
`CGND <=
`THRESHOLD
`VALUE
`
`ESTIMATE (k+1)TH
`ACTUAL TOUCH
`OUTPUT WALUES
`
`HAS
`STOP
`CRITERIA BEEN
`REACH ED
`
`ACTUAL TOUCH OUTPUT
`VALUES=ESTIMATED
`(k+1)TH ACTUAL TOUCH
`OUTPUT WALUES
`
`FIG. 9
`
`DELL EXHIBIT 1005 PAGE 10
`
`DELL EXHIBIT 1005 PAGE 10
`
`

`

`Patent Application Publication
`
`Mar. 11, 2010 Sheet 10 of 12
`
`US 2010/0060608 A1
`
`1000
`
`2.
`
`1.
`
`0. 5
`
`O
`O
`
`1004
`
`8
`
`9
`
`10
`
`1.
`
`2
`
`7
`6
`5
`4.
`3
`NUMBER OF TERATIONS
`
`No.
`
`FIG. 10
`
`DELL EXHIBIT 1005 PAGE 11
`
`DELL EXHIBIT 1005 PAGE 11
`
`

`

`Patent Application Publication
`
`Mar. 11, 2010 Sheet 11 of 12
`
`US 2010/0060608 A1
`
`COMPUTING
`SYSTEM
`1100
`
`N
`
`
`
`PERIPHERALS
`(E.G. MEMORY)
`1104
`
`
`
`
`
`
`
`PROCESSOR
`1102
`
`PANEL SUBSYSTEM
`1106
`
`
`
`
`
`CHANNEL
`SENSE
`CHANNELS-SCAN LOGIC
`1108 t 1110
`
`DRIVER
`LOGIC
`1114
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`DISPLAY
`DEVICE
`1130
`
`HOST
`PROCESSOR
`1128
`
`PROGRAM
`STORAGE
`
`STIMULATION
`SIGNALS
`1116
`
`E.VR
`
`TOUCH SENSOR
`PANEL 1124
`
`1126
`
`FIG 11
`
`DELL EXHIBIT 1005 PAGE 12
`
`DELL EXHIBIT 1005 PAGE 12
`
`

`

`Patent Application Publication
`
`Mar. 11, 2010 Sheet 12 of 12
`
`US 2010/0060608 A1
`
`TOUCH
`SENSOR
`PANEL
`
`MOBILE
`TELEPHONE
`1236
`N
`
`s
`
`s
`COMPUTING
`SSS" FIG. 12A
`
`
`
`AUDIO/WIDEO
`PLAYER
`1240
`FIG. 12B N
`
`O
`
`TOUCH
`SENSOR
`PANEL
`1224
`
`W
`
`COMPUTING
`SYSTEM
`1238
`
`COMPUTING
`SYSTEM
`1238
`
`PERSONAL
`COMPUTER
`1244.
`
`
`
`
`
`
`
`
`
`TOUCH
`SENSOR
`PANEL
`1224
`
`FIG. 12C
`
`TRACKPAD
`1224
`
`DELL EXHIBIT 1005 PAGE 13
`
`DELL EXHIBIT 1005 PAGE 13
`
`

`

`US 2010/0060608 A1
`
`Mar. 11, 2010
`
`CORRECTION OF PARASITIC
`CAPACITANCE EFFECT N TOUCH SENSOR
`PANELS
`
`FIELD OF THE INVENTION
`0001. This relates generally to multi-touch sensor panels
`that utilize an array of capacitive sensors (pixels) to detect and
`localize touch events, and more particularly, to the correction
`of pixels having distorted readings when touch events are
`generated by a poorly grounded object.
`
`BACKGROUND OF THE INVENTION
`0002 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 pan
`els, touch screens and the like. Touch screens, in particular,
`are becoming increasingly popular because of their ease and
`Versatility of operation as well as their declining price. Touch
`screens 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. Touch screens can allow a user to perform
`various functions by touching the touch sensor panel using a
`finger, stylus or other object at a location dictated by a user
`interface (UI) being displayed by the display device. In gen
`eral, touch screens can recognize a touch event and the posi
`tion 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.
`0003 Touch sensor panels can, in some embodiments, be
`formed from a matrix of drive lines (e.g., row traces) sepa
`rated by a dielectric material from a plurality of sense lines
`(e.g., column traces), with sensors or pixels created at each
`crossing point of the drive and sense lines. Touch sensor
`panels can alternatively be arranged in any number of orien
`tations or dimensions, including, but not limited to, diagonal,
`concentric circles, spiral, three-dimensional, or random ori
`entations. In order to detect and identify the location of a
`touch on a touch sensor panel, stimulation signals are pro
`vided to the drive lines causing the sense lines to generate
`signals indicative of touch output values. By knowing the
`timing of the stimulation signals to specific drive lines relative
`to the signals read out of the sense lines, processor(s) can be
`used to determine where on the touch sensor panel a touch
`occurred.
`0004. When the object touching the touch sensor panel is
`poorly grounded, touch output values read out of the sense
`lines may be erroneous, false, or otherwise distorted. The
`possibility of such erroneous, false, or otherwise distorted
`signals is further increased when two or more simultaneous
`touch events occur on the touch sensor panel.
`
`SUMMARY OF THE INVENTION
`0005 Present application relates to compensation of pix
`els that generate false, erroneous, or otherwise distorted touch
`output readings (so-called “negative pixels) due to poor
`grounding of the object touching the touch sensor panel.
`0006 Erroneous detection of what appears to be negative
`touch event(s) may occur when a user is touching one or more
`
`locations on the touch sensor panel but fails to also be in good
`contact with another part of the device including the touch
`sensor panel. To compensate for these erroneous readings,
`sense lines of the touch sensor panel can include reverse
`driving circuits to facilitate calculation of an object-to
`ground capacitance. This capacitance is periodically calcu
`lated during normal operation of the touch sensor panel to
`identify when the touch sensor panel is being touched under
`poor grounding conditions. If the calculated object-to-ground
`capacitance indicates the presence of a poor grounding con
`dition, then the object-to-ground capacitance and detected
`pixel touch output values are used to estimate new pixel touch
`output values in an iterative manner. These new values rep
`resent estimates of the actual pixel touch output values and
`are used in place of the detected pixel touch output values to
`actually determine touch event(s). Accordingly, improved
`accuracy is provided for determining touch event(s) on a
`touch sensor panel.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`0007 FIG. 1 illustrates an exemplary touch sensorpanel in
`accordance with embodiments of the invention.
`0008 FIG. 2 illustrates a close-up of a single exemplary
`pixel of the touch sensor panel with an impending touch event
`by a finger in accordance with embodiments of the invention.
`0009 FIG. 3 illustrates an alternative embodiment of the
`touch sensor panel in accordance with embodiments of the
`invention.
`(0010 FIGS. 4A-4D illustrate exemplary conceptually
`equivalent electrical circuits corresponding to a single pixel
`of the touch sensor panel under different touch and grounding
`conditions in accordance with embodiments of the invention.
`0011
`FIG. 5A illustrates a simultaneous multiple touch
`event occurring on the touch sensor panel in accordance with
`embodiments of the invention.
`0012 FIG. 5B illustrates an exemplary image map show
`ing a three-dimensional view of the phenomenon of negative
`pixels corresponding to the simultaneous touch event illus
`trated in FIG. 5A.
`0013 FIG. 6A illustrates a circuit diagram representative
`of a single pixel of the touch sensor panel showing a reverse
`Voltage source and inherent capacitance in accordance with
`embodiments of the invention.
`0014 FIG. 6B illustrates a circuit diagram representative
`of a single pixel during normal operation in accordance with
`embodiments of the invention.
`0015 FIG. 7 illustrates a flow diagram for determining an
`average panel lumped parasitic capacitance for the column in
`accordance with embodiments of the invention.
`0016 FIG. 8 illustrates a flow diagram for determining the
`average ground capacitance during normal operation in
`accordance with embodiments of the invention.
`0017 FIG. 9 illustrates a flow diagram for correcting para
`sitic capacitance effects during normal operation of the
`device in accordance with embodiments of the invention.
`0018 FIG. 10 illustrates a convergence plot relative to the
`number of iterations of the actual pixel touch output values
`estimation in accordance with embodiments of the invention.
`0019 FIG. 11 illustrates an exemplary computing system
`that can include one or more of the embodiments of the
`invention.
`0020 FIG. 12A illustrates exemplary mobile telephone
`that can include the computing system shown in FIG. 11 in
`accordance with embodiments of the invention.
`
`DELL EXHIBIT 1005 PAGE 14
`
`DELL EXHIBIT 1005 PAGE 14
`
`

`

`US 2010/0060608 A1
`
`Mar. 11, 2010
`
`0021 FIG.12B illustrates exemplary digital media player
`that can include the computing system shown in FIG. 11 in
`accordance with embodiments of the invention.
`0022 FIG. 12C illustrates exemplary personal computer
`that can include the computing system shown in FIG. 11 in
`accordance with embodiments of the invention.
`
`DETAILED DESCRIPTION OF THE PREFERRED
`EMBODIMENTS
`0023. In the following description of preferred embodi
`ments, reference is made to the accompanying drawings
`which form a parthereof, and in which it is shown by way of
`illustration specific embodiments in which the invention 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 embodiments of this inven
`tion.
`0024. Embodiments of the invention relate to correction of
`erroneous detection of touch event(s) on a touch sensor panel.
`Erroneous detection of what appears to be negative touch
`event(s) (e.g., so-called “negative pixels') may occur when a
`user is touching one or more locations on the touch sensor
`panel but fails to also be in good contact with another part of
`the device including the touch sensor panel. To compensate
`for these erroneous readings, sense lines of the touch sensor
`panel can include reverse driving circuits to facilitate calcu
`lation of an object-to-ground capacitance. This capacitance is
`periodically calculated during normal operation of the touch
`sensor panel to identify when the touch sensor panel is being
`touched under poor grounding conditions. If the calculated
`object-to-ground capacitance indicates the presence of a poor
`grounding condition, then the object-to-ground capacitance
`and detected pixel touch output values are used to estimate
`new pixel touch output values in an iterative manner. These
`new values represent estimates of the actual pixel touch out
`put values and are used in place of the detected pixel touch
`output values to actually determine touch event(s). Accord
`ingly, improved accuracy is provided for determining touch
`event(s) on a touch sensor panel.
`0025. Although embodiments of the invention may be
`described and illustrated herein in terms of mutual capaci
`tance touch sensor panels, it should be understood that
`embodiments of this invention are not so limited, but are
`additionally applicable to self-capacitance sensor panels, and
`both single and multi-touch sensor panels in which detection
`errors occur due to poor grounding conditions. The touch
`sensor panel may be implemented with a display, trackpad.
`trackball, or a variety of other touch sensing Surfaces where
`determination of location and/or intensity of touch would be
`relevant.
`0026 FIG. 1 illustrates an exemplary touch sensor panel
`100 according to embodiments of the invention. Touch sensor
`panel 100 includes an array of pixels 106 that can be formed
`by a two-layer electrode structure separated by a dielectric
`material. One layer of electrodes comprises a plurality of
`drive lines 102 positioned perpendicular to another layer of
`electrodes comprising a plurality of sense lines 104. The
`pixels 106 (also referred to as sensors) can be formed at the
`crossing points of the drive lines 102 and sense lines 104, with
`each of the pixels 106 having an associated mutual capaci
`tance 114 (also referred to as coupling capacitance).
`0027 Drive lines 102 (also referred to as rows, row traces,
`or row electrodes) can be activated by stimulation signals
`provided by respective drive circuits 108. Each of the drive
`
`circuits 108 includes an alternating current (AC) voltage
`Source referred to as a stimulation signal Source. The stimu
`lation signals from the drive circuits 108 may also be referred
`to as forward driving signals or forward stimulation signals.
`Senselines 104 (also referred to as columns, column traces, or
`column electrodes) can be activated by stimulation signals
`provided by respective reverse voltage sources 112 coupled to
`an input of its respective sense amplifier 110. Such stimula
`tion signals may also be referred to as reverse driving signals
`or reverse stimulation signals. The reverse Voltage sources
`comprise AC Voltage sources. The sense amplifiers 110 may
`also be referred to as charge amplifiers or trans-conductance
`amplifiers.
`0028. To sense touch event(s) on the touch sensor panel
`100, each of the drive lines 102 can be sequentially stimulated
`by the drive circuits 108, and the sense amplifiers 110 detect
`the resulting voltage values from the sense lines 104. The
`detected Voltage values are representative of pixel touch out
`put values, indicating the pixel location(s) where the touch
`event(s) occurred and the amount of touch that occurred at
`those location(s).
`0029 FIG. 2 illustrates a close-up of a single exemplary
`pixel 106 with an impending touch event by a finger 200.
`When the pixel 106 is not touched by an object, an electric
`field (shown as fringing electric field lines 202) can beformed
`between the drive line 102 and the sense line 104 via a
`dielectric material. Some of the electric field lines 202 can
`extend above the drive and sense lines 102, 104 and even
`above a cover 204 located over the touch sensor panel 100.
`When an object, such as the finger 200, touches the pixel 106
`(or a location near the pixel 106), the object blocks some of
`the electric field lines 202 extending above the cover 204.
`Such blockage or interruption of the electronic field lines 202
`changes the capacitance associated with the pixel 106, which
`changes the current flow from the drive line 102 to the sense
`line 104 (current is proportional to capacitance), and which in
`turn changes the Voltage value (or charge coupling) detected
`at the sense line 104.
`0030. The touch sensor panel 100 illustrated in FIG. 1 is
`arranged according to a Cartesian coordinate system. In alter
`nate embodiments, the touch sensor panel 100 may be
`arranged in any number of orientations or dimensions, includ
`ing, but not limited to, diagonal, concentric circles, spiral,
`three-dimensional, or random orientations. For example,
`FIG.3 illustrates a touch sensor panel 300 arranged according
`to a polar coordinate system. The touch sensor panel 300
`comprises a plurality of radially extending drive lines 302 and
`a plurality of concentrically arranged sense lines 304. At the
`crossing points of the drive lines 302 and sense lines 304 can
`be formed pixels 306 having an associated mutual capaci
`tance Cs. The drive lines 302 are driven by driving circuits
`308. The sense lines 304 are detected by sense amplifiers 310.
`0031 Whena touch event occurs on the touch sensorpanel
`100, capacitive coupling other than that described above may
`occur. These other capacitive couplings can be of a magnitude
`significant enough to be undesirable and can lead to errone
`ous, false, or otherwise distorted pixel touch output values.
`Parasitic capacitance can be introduced when the object
`touching the touch sensor panel 100 is poorly grounded. For
`purposes of this application, "poorly grounded may be used
`interchangeably with “ungrounded.” “not grounded,” “not
`well grounded,” “isolated,” or “floating and includes poor
`grounding conditions that exist when the object is not making
`a low resistance electrical connection to the ground of the
`
`DELL EXHIBIT 1005 PAGE 15
`
`DELL EXHIBIT 1005 PAGE 15
`
`

`

`US 2010/0060608 A1
`
`Mar. 11, 2010
`
`device employing the touch sensor panel. As an example, if
`the device employing the touch sensor panel 100 is placed on
`a table and the object only touches the device on the touch
`sensor panel 100, then a poor grounding condition may exist
`for that touch event. Conversely, if the object touches the
`touch sensor panel 100 and another part of the device (e.g., the
`object is holding the device and is in contact with the back of
`the device), then a good grounding condition exists and the
`impact of parasitic capacitance is negligible.
`0032. The presence of parasitic capacitance under poor
`grounding conditions can distort pixel touch output values in
`at least two ways. First, the change in the pixel touch output
`value measured for the touched pixel 106 can be less than it
`actually should be. Thus, the device employing the touch
`sensor panel 100 erroneous believes a lesser degree of touch
`occurred at the pixel 106 than in actuality. Second, when more
`than one simultaneous touch event is caused by the same
`poorly grounded object, pixel(s) 106 that were not actually
`touched may register having received a negative amount of
`touch (a “negative pixel at a phantom location). Sensing
`negative pixels at phantom locations may be problematic
`when the touch sensorpanel 100 is operable to capture inputs,
`for example, for a graphical user interface (GUI). Negative
`pixels are described in U.S. patent application Ser. No.
`11/963,578 filed on Dec. 21, 2007 and entitled “Negative
`Pixel Compensation, the contents of which are incorporated
`by reference herein in its entirety.
`0033 FIGS. 4A-4D illustrate exemplary conceptually
`equivalent electrical circuits corresponding to a single pixel
`106 under different touch and grounding conditions. In FIGS.
`4A-4D, the reverse voltage source 112 included on the sense
`line 104 is not shown, as the voltage value would be zero
`during touch sensing operations.
`0034. The circuit illustrated in FIG. 4A is representative of
`a no touch scenario. The drive circuit 108 applies a stimula
`tion signal V to the drive line 102. The stimulation signal can
`comprise an AC Voltage signal having a variety of amplitude,
`frequency, and/or waveform shape. For example, the stimu
`lation signal may comprise a sinusoidal 18 Vpp signal. With
`no object interrupting the electric field lines, the characteristic
`mutual capacitance 114 comprises the charge coupling
`detected at the sense amplifier 110. In FIG. 4A, the mutual
`capacitance 114 is denoted as Cs and a feedback capaci
`tance 400 is denoted as C. The resulting (no touch) pixel
`touch output value 402 (V) at the output of the sense ampli
`fier 110 can be expressed as:
`(1)
`V-VIXCso Ca
`0035. The circuit illustrated in FIG.4B is representative of
`an object, such as the finger 200, touching the pixel 106 (or
`near the pixel 106). When a stimulation signal V is applied to
`the drive line 102, similar to that discussed above for FIG. 4A,
`and with the object blocking some of the electric field lines
`between the drive line 102 and sense line 104, the character
`istic mutual capacitance 114 is reduced and becomes a touch
`capacitance 404. The capacitance is reduced by Cso says
`and the touch capacitance 404 can be denoted as Cs-Cs.
`sys. As an example, the mutual capacitance 114 (e.g., with
`no touch) may be approximately 0.75 picoFarad (pF) and the
`touch capacitance 404 (e.g., with touch) may be approxi
`mately 0.25 pF.
`0036 Introduction of touch not only changes the charge
`coupling at the pixel 106 from the mutual capacitance 114 to
`the touch capacitance 404, but undesirable capacitance cou
`
`plings called parasitic capacitance can also be introduced.
`Parasitic capacitance comprises a touch and drive capacitance
`406 (C) in series with a touch and sense capacitance 408
`(Cs). Also shown in FIG. 4B is a ground capacitance 410
`(C) (also referred to as an object-to-ground capacitance)
`comprising inherent capacitance associated with the device
`and an inherent capacitance associated with the object. The
`circuit illustrated in FIG. 4C is equivalent to the circuit shown
`in FIG. 4B. In FIG. 4C, a negative capacitance 414 (C) is
`equivalent to the combination of the touch and drive capaci
`tance 406, touch and sense capacitance 408, and ground
`capacitance 410 in FIG. 4B. The negative capacitance 414 can
`be expressed as:
`(2)
`CNEG-CADXCFs (CFD+CFs-CoND)
`0037. When the object touching the pixel 106 is well
`grounded because, for example, the object is also touching a
`bezel, backside, or other part of the device employing the
`touch sensor panel 100, the ground capacitance 410 is a large
`value relative to the touch and drive capacitance 406 and the
`touch and sense capacitance 408. (Ground capacitance 410
`(C) undergood grounding conditions can be on the order
`of 100 pF.) The large value of the ground capacitance 410
`results in the negative capacitance 414 being a negligible
`value (notice C in the denominator in Equation (2)). The
`touch and drive capacitance 406 has the effect of increasing
`the drive current of the drive circuit 108, while the touch and
`sense capacitance 408 has the effect of being shunted by the
`virtual ground of the sense amplifier 110. Thus, a circuit
`illustrated in FIG. 4D is representative of the object touching
`the pixel 106 undergood grounding conditions. The resulting
`(good ground) pixel touch output value 416 (denoted as
`V-V) at the output of the sense amplifier 110 is proportion
`ally smaller relative to the (no touch) pixel touch output value
`402 and can be expressed as:
`(3)
`V-V. (VIXCso CFB)-(VIXCso stNSE/CFB)
`0038. In contrast, when the object touching the pixel 106 is
`under poor grounding conditions, the negative capacitance
`414 is no longer negligible. The touch and sense capacitance
`408 is no longer shunted to ground. The ground capacitance
`410 can be on the same order as the touch and drive capaci
`tance 406 and touch and sense capacitance 408. (Ground
`capacitance 410 (C) underpoor grounding conditions can
`be on the order of 1 pF.) The negative capacitance 414 causes
`the voltage detected at the sense amplifier 110 to be higher by
`an amount V, than under good grounding conditions:
`
`0039. The (poor ground) pixel touch output value 418 can
`be expressed as V-V-V. The parasitic effect on the actual
`pixel touch output value is in the opposite direction of the
`intended touch capacitance change. Hence, a pixel experienc
`ing touch underpoor grounding conditions may detect less of
`a touch than is actually present.
`0040 FIGS. 5A-5B illustrate a simultaneous multiple
`touch event occurring on the touch sensor panel 100 in accor
`dance with embodiments of the invention. Two fingers are
`touching two different spots on the touch sensor panel 100, at
`the pixel intersected by drive line D0 and sense line S1 (P.
`S1) and at the pixel intersected by drive line D2 and sense line
`S2 (Ps). Under poor grounding conditions, there is para
`sitic capacitance at each of Pros and P2s2 as discussed
`above. In addition, negative pixels can be registered at the
`pixel (phantom location) intersected by drive line D0 and
`
`DELL EXHIBIT 1005 PAGE 16
`
`DELL EXHIBIT 1005 PAGE 16
`
`

`

`US 2010/0060608 A1
`
`Mar. 11, 2010
`
`sense line S2 (P,post) and at the pixel (phantom location)
`intersected by drive line D2 and sense line S1 (Ps).
`I0041) When drive line D0 is simulated, charge from Poo.
`S1 is coupled on the finger touching over Post. Instead of
`being shunted to ground, Some charge is coupled back onto
`sense line S1 and also the user's other finger touching the
`touch sensor panel (e.g., onto sense line S2). If the user was
`properly grounded, the finger over P.s would not cause
`charge to be coupled onto sense line S2 because drive line D2
`would not be stimulated at the same time as drive line D0. The
`net effect is that with drive line D0 simulated, the sense
`amplifiers 110 senses a touch event at sense lines S1 and S2
`(e.g., Pools and Pools2). Actual touch at Po2S2 similarly
`causes charge to be coupled to senseline S1 through the user's
`hand. Thus, when drive line D2 is stimulated, the sense ampli
`fiers 110 senses a touch event at sense lines S1 and S2 (e.g.,
`Pro2.si and PD2.S2).
`0042 Unintended charge coupling back on sense lines S1
`and S2 reduces the apparent touch detected at touch locations
`Pros and P2s2. The charge coupling across the user's
`fingers to other sense lines can also weaken adjacent pixels
`not being touched, to the point where output readings indica
`tive of a negative amount of touch (a negative pixel) can be
`erroneously produced. Negative pixilation is made worse if
`there are multiple pixels being touched along the same drive
`line being stimulated, because then even more charge can be
`coupled onto other sense lines being simultaneously touched.
`0043 FIG. 5B illustrates an exemplary image map show
`ing a three-dimensional view of the phenomenon of negative
`pixels corresponding to the simultaneous touch event illus
`trated in FIG. 5A. In FIG. 5B, positive output values are
`associated with locations of true touch (e.g., Pidos and PD2,
`S2) and negative output values are associated with locations of
`negative touch (e.g., ProS2 and PD2.s).
`0044 According to embodiments of the invention, para
`sitic capacitance correction can be performed for the touch
`sensor panel 100 by calculating an average ground capaci
`tance, and then using the measured pixel touch output values
`and the average ground capacitance to estimate actual pixel
`touch output values. The estimated actual pixel touch output
`values are used to determine touch event(s) on the touch
`sensor panel 100.
`0045 Prior to start of normal sensing operations of the
`touch sensor panel 100, the panel 100 (and the device includ
`ing the panel 100) undergoes calibration, baseline measure
`ments, and parameter setup. In particular, in order to perform
`parasitic capacitance correction in accordance with embodi
`ments of the invention, an average panel lumped parasitic
`capacitance for the column (e.g., the sense line) is determined
`during calibration. A circuit diagram representative of any
`single pixel 106 of the touch sensor panel 100 is illustrated in
`FIG. 6A, showing capacitance inherent to the touch sensor
`panel 100 including a panel lumped parasitic capacitance 600
`for the row (C) and a panel lumped parasitic capacitance
`602 for the column (Cs). Panel lumped parasitic capacitance
`600 for the row (C) comprises the parasitic capacitance of
`the drive line within the touch sensor panel to the local
`ground. Panel lumped parasitic capacitance 602 for the col
`umn (Cs) comprises the parasitic capacitance of the sense
`line within the touch sensor panel to the local ground. Touch
`and drive capacitance 406 (C) comprises the parasitic
`capacitance of the drive line through the touch sensor panel to
`the touch object (for example, the user's finger). Touch and
`sense capacitance