USOO85422O2B2
`
`(12) United States Patent
`Zhuang et al.
`
`(10) Patent No.:
`(45) Date of Patent:
`
`US 8,542,202 B2
`Sep. 24, 2013
`
`(54) ELECTRONIC DEVICE AND METHOD FOR
`DETERMINING ATOUCH INPUT APPLIED
`TO A CAPACTIVE TOUCH PANEL, SYSTEM
`NCORPORATED THEREN
`
`(75) Inventors: Zhiming Zhuang, Kildeer, IL (US);
`William P. Alberth, Jr., Prairie Grove,
`IL (US); Ken K. Foo, Gurnee, IL (US)
`
`(73) Assignee: Motorola Mobility LLC, Libertyville,
`IL (US)
`
`(*) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 703 days.
`
`(21) Appl. No.: 12/6.50,789
`
`(22) Filed:
`
`Dec. 31, 2009
`
`(65)
`
`Prior Publication Data
`US 2011 FO157O69 A1
`Jun. 30, 2011
`
`(2006.01)
`
`(51) Int. Cl.
`G06F 3/045
`(52) U.S. Cl.
`USPC .......................................................... 345/173
`(58) Field of Classification Search
`USPC .......................................................... 34.5/173
`See application file for complete search history.
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`2002/0089491 A1* 7/2002 Willig ........................... 345,173
`2005/0134292 A1
`6/2005 Knoedgen
`2007,0262969 A1* 11/2007 Pak ............................... 345,173
`2008. O157893 A1
`7, 2008 Krah
`2008. O158174 A1
`7/2008 Land et al.
`2008. O15817.6 A1
`7/2008 Land et al.
`2008. O158179 A1
`7, 2008 Wilson
`2008. O158182 A1
`7/2008 Westerman
`2008. O158.184 A1
`7/2008 Land et al.
`2008/0238881 A1 10, 2008 Perski et al.
`2008/0309622 A1 12/2008 Krah
`2009 OO32312 A1
`2/2009 Huang et al.
`* cited by examiner
`Primary Examiner — Quan-Zhen Wang
`Assistant Examiner — Tony Davis
`(57)
`ABSTRACT
`An electronic device is operable to determine a touch input
`applied to a capacitive touch panel system thereof So as to
`account for time-varying noise affecting the touch panel sys
`tem. The electronic device includes the touch panel system,
`an analog-to-digital conversion (ADC) unit, and a processing
`unit. The processing unit is operable to: receive digital signal
`values from the ADC unit representing capacitances detected
`by sensing points of the touchpanel system; adjust at least one
`of the digital signal values based at least on a time-varying
`noise to produce at least one noise-adjusted value; and deter
`mine the touch input based on the at least one noise-adjusted
`value. In one embodiment, the electronic device determines
`the time-varying noise prior to adjusting the digital signal
`values. In another embodiment, the time-varying noise is
`produced by a display panel of a touchscreen display that also
`includes the touch panel system.
`41 Claims, 11 Drawing Sheets
`
`ENTER
`
`APPLYXCITATIONSIGNALSTO
`SENSINGPOINTEXCITATION
`NODES
`
`SCANSENSINGPOINT OUTPUT
`NoSTOTECT OUTPUT
`SISNALS
`
`DETERMINECAPACITANCESAT
`SENSINGPOINTSBASED ON
`OUTPUTSIGNALS
`
`NORMALIZESENSED
`CAPACITANCEWALUESTO
`ACCOUNTFORSTATIC,
`SPATALVAN NOSE AND
`
`DETERMINEAWERAGE OF
`NORMALIZEWALUES
`
`COMPAREACHNORMALIZED
`WALUE TO AVERAGEWALUE
`
`
`
`NORMAZED
`WALUE GREATER THAN
`CLESS THAN)AVERAGE
`WALUE
`
`91?
`
`95
`
`SLOWOPERATION OF
`ELECTRONCNOISE SOURCE
`(E.G., DISPLAYPANEL)
`
`EXCLUDENORMALZED WALE
`FROMNOISEDETERMINATION
`SUBSET
`
`ADD NORMALZED WALUE TO
`NOISEDETERMINATIONSUBSET
`
`TRMINETIME WARYING
`NOSEFROMSUBSETAVERAGE
`
`928
`
`FILTER TIME-WARYINGNOISE
`WALUEFROMEACHSENSE
`CAPACTANCEWALUE
`
`
`
`DELL EXHIBIT 1027 PAGE 1
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`DELL EXHIBIT 1027 PAGE 1
`
`

`

`U.S. Patent
`
`Sep. 24, 2013
`
`Sheet 1 of 11
`
`US 8,542,202 B2
`
`100
`% 2
`Z2
`2
`to I
`I
`I
`I
`I
`I
`%
`%
`%
`% Z 2
`
`T
`
`2
`
`
`
`Z
`
`z T
`
`L
`
`T
`
`L
`
`T
`
`N
`
`DELL EXHIBIT 1027 PAGE 2
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`DELL EXHIBIT 1027 PAGE 2
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`

`

`U.S. Patent
`
`Sep. 24, 2013
`
`Sheet 2 of 11
`
`US 8,542,202 B2
`
`
`
`C C
`
`E-FIELD
`
`ICDRIVE SIGNAL
`
`(PRIOR ART)
`
`FIG. 2
`
`DELL EXHIBIT 1027 PAGE 3
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`DELL EXHIBIT 1027 PAGE 3
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`

`

`U.S. Patent
`
`Sep. 24, 2013
`
`Sheet 3 of 11
`
`US 8,542,202 B2
`
`DELECTRIC
`
`
`
`
`
`
`
`C
`
`IC TRANSMIT
`
`C RECEIVE
`
`307
`
`(PRIOR ART)
`
`FIG. 3
`
`DELL EXHIBIT 1027 PAGE 4
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`DELL EXHIBIT 1027 PAGE 4
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`

`

`U.S. Patent
`
`Sep. 24, 2013
`
`Sheet 4 of 11
`
`US 8,542,202 B2
`
`
`
`S
`
`g
`
`2622.
`22.
`&S
`N7N7N7N7N7N7N7N7N7
`S
`
`: DIELECTRIC
`LENS
`
`g
`
`IC TRANSMIT
`
`C RECEIVE
`
`401
`
`DISPLAYPANEL
`
`(PRIOR ART)
`
`FIG. 4
`
`DELL EXHIBIT 1027 PAGE 5
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`DELL EXHIBIT 1027 PAGE 5
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`

`

`U.S. Patent
`
`Sep. 24, 2013
`
`Sheet 5 of 11
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`US 8,542,202 B2
`
`
`
`s
`
`S 3 3 S.
`
`s 3 & 3 S.
`
`S
`
`d
`
`a
`
`DELL EXHIBIT 1027 PAGE 6
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`DELL EXHIBIT 1027 PAGE 6
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`

`

`U.S. Patent
`
`Sep. 24, 2013
`
`Sheet 6 of 11
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`US 8,542,202 B2
`
`
`
`TOUCH PANEL
`SYSTEM
`
`606
`
`607
`DISPLAY 6
`DISPLAYPANEL
`
`PROCESSING
`UNIT
`
`MEMORY
`
`615
`TOUCH INPUT
`DETERMINATION
`INSTRUCTIONS
`
`ADDITIONAL USER
`INTERFACE
`ELEMENTS
`
`FIG. 6
`
`DELL EXHIBIT 1027 PAGE 7
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`DELL EXHIBIT 1027 PAGE 7
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`

`

`U.S. Patent
`
`Sep. 24, 2013
`
`Sheet 7 of 11
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`US 8,542,202 B2
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`
`
`FIG. 7
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`DELL EXHIBIT 1027 PAGE 8
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`DELL EXHIBIT 1027 PAGE 8
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`

`

`U.S. Patent
`
`Sep. 24, 2013
`
`Sheet 8 of 11
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`US 8,542,202 B2
`
`ENTER
`
`801
`
`803
`
`805
`
`807
`
`DETECT CAPACITANCEAT
`SENSINGPOINTS
`
`
`
`
`
`
`
`DETERMINETIME-VARYING
`NOISE FROMNOISE SOURCE(S)
`
`ADJUST SENSED CAPACITANCE
`VALUES BASED ON DETERMINED
`NOISEWALUE
`
`DETERMINE TOUCH INPUT
`BASED ONNOISE-ADJUSTED
`VALUES
`
`FIG. 8
`
`DELL EXHIBIT 1027 PAGE 9
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`DELL EXHIBIT 1027 PAGE 9
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`

`

`U.S. Patent
`
`Sep. 24, 2013
`
`Sheet 9 of 11
`
`US 8,542,202 B2
`
`APPLY EXCITATION SIGNALS TO
`SENSING POINT EXCITATION
`NODES
`
`SCAN SENSINGPOINT OUTPUT
`NODESTO DETECT OUTPUT
`SIGNALS
`
`DETERMINE CAPACITANCESAT
`SENSING POINTS BASED ON
`OUTPUT SIGNALS
`
`NORMALIZE SENSED
`CAPACITANCEVALUESTO
`ACCOUNT FOR STATIC,
`SPATALVAN NOISE AND
`
`DETERMINEAVERAGE OF
`NORMALIZED VALUES
`
`COMPARE EACH NORMALIZED
`VALUE TO AVERAGE VALUE
`
`
`
`
`
`
`
`
`
`
`
`
`
`NORMALIZED
`VALUE GREATER THAN
`(LESS THAN) AVERAGE
`VALUE
`
`
`
`SLOW OPERATION OF
`ELECTRONIC NOISE SOURCE
`(E.G., DISPLAYPANEL)
`
`EXCLUDENORMALIZED WALUE
`FROM NOISEERMINATION
`
`NO
`ADD NORMALIZED WALUE TO
`NOISE DETERMINATION SUBSET
`
`919
`
`DETERMINE TIME-VARYING
`NOISE FROMSUBSETAVERAGE
`
`EXIT
`
`FILTER TIME-VARYINGNOISE
`VALUEFROMEACHSENSED
`CAPACITANCEVALUE
`
`00
`
`FIG. 9
`
`917
`
`915
`
`921
`
`923
`
`DELL EXHIBIT 1027 PAGE 10
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`DELL EXHIBIT 1027 PAGE 10
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`

`

`U.S. Patent
`
`Sep. 24, 2013
`
`Sheet 10 of 11
`
`US 8,542,202 B2
`
`
`
`SENSOR
`SCANNING
`
`
`
`617
`
`1001-O-G(n), B(n)
`
`DISPLAY
`OFF
`
`
`
`SENSOR
`SCANNING
`
`DISPLAY ON
`
`67
`
`DELL EXHIBIT 1027 PAGE 11
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`

`

`U.S. Patent
`
`Sep. 24, 2013
`
`Sheet 11 of 11
`
`US 8,542,202 B2
`
`SENSOR
`SCANNING
`
`
`
`DISPLAY ON
`
`67
`
`NOTOUCH
`CONDITION
`
`DELL EXHIBIT 1027 PAGE 12
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`

`

`US 8,542,202 B2
`
`1.
`ELECTRONIC DEVICE AND METHOD FOR
`DETERMINING ATOUCH INPUT APPLIED
`TO A CAPACTIVE TOUCH PANEL, SYSTEM
`NCORPORATED THEREN
`
`FIELD OF THE INVENTION
`
`The present invention relates generally to electronic
`devices and, more particularly, to determining a touch input
`applied to a capacitive touch panel system incorporated
`within an electronic device.
`
`10
`
`BACKGROUND
`
`2
`The application of a touch input signal to the touch panel
`system 100 may have different effects depending on the
`arrangement of the sensor grid. FIGS. 2 and 3 illustrate the
`effect of a touch input on electric fields and, therefore capaci
`tance, depending on whether the sensing points 102 are con
`figured to detect self-capacitance or mutual capacitance. For
`example, as illustrated in FIG. 2, the sensing points 102 may
`be arranged as a grid of sensors 203 that detect self-capaci
`tance relative to ground 204. As noted above, the sensors 203
`are typically protected by a flexible dielectric lens 201 that is
`touched by a user's finger 209 or an instrument, such as a
`stylus, pencil, toothpick, or other device. In operation, an
`excitation or drive signal 205 is supplied as a burst to the
`sensor 203 by an integrated circuit (IC) or other source. The
`drive signal is then removed and the amount of time required
`for the Voltage of the sensor 203 to decrease to Zero or some
`predetermined threshold is measured as the discharge time.
`As detailed above, the discharge time is directly related to the
`capacitance of the sensor 203.
`In the case of a sensor 203 configured to detect self-capaci
`tance, an electric field is created between the sensor 203 and
`ground 204 upon excitation of the sensor 203 by the excita
`tion signal 205. The electric field includes a quantity of elec
`tric field lines 207 or flux between the charged node or plate
`of the capacitive sensor 203 and ground 204. When a touch
`input is applied by a user's finger 209, more electric field lines
`211 are added from the sensor 203 to ground 204 due to the
`capacitive nature of the human body. Such additional electric
`field lines 211 result in an increase in the effective capacitance
`as detected by the sensor 203. The increase in capacitance
`causes a resulting increase in the discharge time of the sensor
`because, as noted above, the discharge rate of a capacitor
`varies as an inverse function of the capacitance (e.g., as
`capacitance increases, T increases, the exponential discharge
`rate decreases, and the duration of time required to discharge
`the capacitor increases).
`By contrast, a touch input has the effect of decreasing the
`effective capacitance where the sensing points 102 are con
`figured to detect mutual capacitance. For example, as illus
`trated in FIG.3, each sensing point 102 may be configured as
`two parallel sensors 301, 303 that sense the mutual capaci
`tance between them. In this case, an IC excitation signal 305
`applied to sensor 301 is received in attenuated form as a
`received signal 307 at sensor 303 based on the capacitance
`between the two sensors 301,303. The difference in potential
`between the two sensors 301, 303 in the presence of the
`applied excitation signal 305 causes an electric field to be
`generated between the two sensors 301,303. As illustrated in
`FIG. 3, the electric field includes electric field lines 309 or
`flux emanating from the charged sensor 301 and terminating
`at the receiving sensor 303. If a user touches the dielectric lens
`201 near the sensors 301,303, some of the electric field lines
`311 are redirected to the user's finger 209 due to the inherent
`capacitance between the user and ground. The redirection of
`the electric field lines 311 causes an effective reduction in the
`capacitance between the two sensors 301, 303. As is known,
`the impedance between the two sensors 301, 303 is inversely
`proportional to the capacitance between the two sensors 301,
`303. Therefore, as the capacitance decreases due to the pres
`ence of the touch input, the impedance of the capacitor
`increases and the level of the signal 307 received at the receiv
`ing sensor 303 decreases.
`In an ideal environment, sensing points 102 of touch panel
`systems 100 would only detect signals and capacitance
`changes resulting from touch inputs. However, due to the
`presence of the housing and various electronic components of
`electronic devices that include touchpanel systems 100, such
`
`15
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`25
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`30
`
`35
`
`Projected capacitive touch panel systems are well known.
`Such systems are typically employed in touchscreens of elec
`tronic devices, such as Smart phones, handheld gaming
`devices, global positioning system (GPS) devices, point-of
`sale credit/debit card machines, and so forth. Typically, pro
`jected capacitive touch panel systems utilize a grid of sensing
`points to sense changes in self capacitance (e.g., between a
`sensor and ground) or mutual capacitance (e.g., between two
`sensors) as a result of a touch input caused by a user touching
`an area of the panel. The grid sensors typically coincide with
`pixel locations where the touch panel system forms part of a
`touchscreen display.
`An exemplary touchpanel system 100 is illustrated in FIG.
`1. The touch panel system 100 includes a grid or matrix of
`sensing points 102 encased within a housing and covered by
`a protective dielectric lens. In the illustrated system 100,
`forty-eight (48) sensing points 102 are shown. The sensing
`points 102 are capacitive in nature and may be formed by
`overlapping conductors in a multilayer implementation or
`arranging conductors adjacent to one another in a single layer
`implementation. An excitation signal is applied to one or
`more excitation nodes 104 (X-X-7) and an output signal is
`detected at one or more output nodes 106 (Yo-Y). The output
`signals are proportional to the sensing point capacitances.
`For example, the charge of a capacitor with capacitance C
`at time t can be determined by the equation:
`40
`Q=CVe", where
`t=RC;
`R is the resistance associated with the capacitor (e.g.,
`inherent and terminal resistances); and
`V is the voltage of the capacitor when fully charged.
`Therefore, changes in the capacitance of a sensing point 102
`can be detected by measuring the change in the discharge time
`of the sensing point 102. The discharge time is measured by
`measuring the output Voltage decay as a function of time after
`application of an input signal burst. In a typical capacitive
`touch panel system 100, excitation signals are sequentially
`applied to each excitation node 104 and timers are used to
`measure the discharge times at the output nodes 106. For
`example, an excitation signal burst is applied to excitation
`node X and timers are used to measure the discharge times at
`all the output nodes 106 (Yo-Ys) to determine the capaci
`tances at the sensing points 102 defined by excitation node Xo
`and the output nodes 106 (Yo-Ys). Excitation signals are then
`sequentially applied to the other excitation nodes 104 (X-
`X) and the discharge times at the output nodes 106 (Yo-Ys)
`are measured to determine the capacitances at the remaining
`sensing points 102. In other words, the sensing points 102 are
`effectively scanned repeatedly to detect variations in capaci
`tance. Variation in the determined capacitances at one or more
`sensing points 102 may indicate a touch input in the area of
`the sensing points 102.
`
`45
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`

`

`3
`systems 100 are required to distinguish touch inputs from
`various noise Sources. For example, in a touchscreen display,
`a display panel is positioned in close proximity to the touch
`panel so that information can be displayed to the user as part
`of the touch panel user interface experience. An exemplary
`touchscreen display configuration is illustrated in FIG. 4. In
`the illustrated touchscreen display, a display panel 401 is
`positioned in close proximity below the touch panel system.
`In this case, the dielectric lens 201 would most likely be
`transparent so that the information displayed on the display
`panel 401 could be seen through the lens 201. The touch
`screen display gives the user the impression that he or she is
`selecting areas on the display panel 401, when instead the
`user is actually selecting areas of the touch panel system that
`correspond to the displayed areas of the display panel 401.
`Software within a processing unit of the electronic device
`employing the touchscreen display maps the areas of the
`touch panel system to the information displayed on the dis
`play panel 401 to achieve the function or result desired by the
`user based on the users touch input. Thus, accurately recog
`nizing where the user touched the touch panel system is
`critical to proper operation of the touch panel system or a
`touchscreen display incorporating it.
`Electronic components, such as display panels, generate
`spectral noise during operation. Such noise may be static
`(time-invariant) and/or may vary over time depending on the
`output of the electronic component. For example, the noise
`produced by a display panel. Such as a liquid crystal display
`(LCD) panel, varies overtime depending upon the colors and
`images displayed by the display panel, the refresh rate of the
`panels pixels, the resolution of the display panel, and the
`display panels backlight intensity. Placement of a noise
`producing, electronic component in close proximity to
`capacitive sensors 203,301,303, such as those employed in a
`capacitive touch panel system, creates parasitic capacitance
`between the noise-producing component (e.g., a display
`panel) and the touch panel sensors 203,301,303, which in
`turn creates time-varying noise in the touch panel system.
`FIG. 5 provides a graphical illustration of the spectral noise
`detected by a capacitive touch panel system due to noise
`produced by a display panel positioned in close proximity and
`directly below the touch panel system. As can be seen from
`the graph 500, the amplitude of the noise 503 is only about
`three decibels (3 dB) below the amplitude of the touch input
`501. Thus, the signal-to-noise ratio illustrated in FIG. 5 is
`only 3 dB. The signal-to-noise ratio would likely be even
`worse in touchscreen displays in which the touch panel sys
`tem is integrated directly into the display panel. Much higher
`signal-to-noise ratios are desired to improve touch input reso
`lution and facilitate higher sensing point Scanning speeds.
`As noted above, noise produced by a display panel typi
`cally comes in two forms—static (time-invariant) noise and
`time-varying noise. Prior art solutions have addressed filter
`ing and other compensation for static noise components to
`assist in improving signal-to-noise ratios. However, prior art
`Solutions have not adequately accounted for time-varying
`noise, which may be a significant noise Source especially in
`touchscreen displays.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`The accompanying figures, where like reference numerals
`refer to identical or functionally similar elements throughout
`the separate views and which together with the detailed
`description below are incorporated in and form part of the
`disclosure, serve to further illustrate various embodiments
`
`10
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`US 8,542,202 B2
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`4
`and to explain various principles and advantages all in accor
`dance with the present invention.
`FIG. 1 illustrates an exemplary, prior art touch panel sys
`tem showing a grid of sensing points.
`FIG. 2 illustrates an exemplary, prior art arrangement of a
`capacitive sensor for use as a sensing point in the capacitive
`touch panel system of FIG. 1 and configured to detect self
`capacitance.
`FIG. 3 illustrates an exemplary, prior art arrangement of
`capacitive sensors for use as a sensing point in the capacitive
`touch panel system of FIG. 1 and configured to detect mutual
`capacitance.
`FIG. 4 illustrates an exemplary, prior art touchscreen dis
`play configuration containing a display panel positioned in
`close proximity to the arrangement of capacitive sensors
`depicted in FIG. 3.
`FIG. 5 is a graphical illustration of spectral noise detected
`by a capacitive touch panel system due to noise produced by
`a display panel positioned in close proximity to the touch
`panel system.
`FIG. 6 is an electrical block diagram of an electronic device
`incorporating a touch panel system, in accordance with
`another exemplary embodiment of the present invention.
`FIG. 7 illustrates a smartphone embodiment of the elec
`tronic device of FIG. 6, which includes a touchscreen display
`in accordance with another exemplary embodiment of the
`present invention.
`FIG. 8 illustrates a logic flow diagram of steps executable
`by an electronic device to determine a touch input applied to
`a capacitive touch panel system of the electronic device, in
`accordance with one embodiment of the present invention.
`FIG. 9 illustrates a logic flow diagram of steps executable
`by an electronic device to determine a touch input applied to
`a capacitive touch panel system of the electronic device, in
`accordance with an alternative embodiment of the present
`invention.
`FIG. 10 is an exemplary touchscreen display illustrating
`determination of static, spatial-varying noise and static, spa
`tial-varying gain when a display panel of the touchscreen
`display is off, in accordance with one embodiment of the
`present invention.
`FIG. 11 illustrates determination of a touch input on the
`touchscreen display of FIG. 10 when a display panel of the
`touchscreen display is on, in accordance with various
`embodiments of the present invention.
`FIG. 12 illustrates determination of an absence of a touch
`input on the touchscreen display of FIG. 10 when a display
`panel of the touchscreen display is on, in accordance with a
`further embodiment of the present invention.
`Skilled artisans will appreciate that elements in the figures
`are illustrated for simplicity and clarity and have not neces
`sarily been drawn to scale. For example, the dimensions of
`Some of the elements in the figures may be exaggerated alone
`or relative to other elements to help improve the understand
`ing of the various embodiments of the present invention.
`
`DETAILED DESCRIPTION
`
`Generally, the present invention encompasses an electronic
`device and a method for determining a touch input applied to
`a capacitive touch panel system incorporated within the elec
`tronic device. The electronic device may be a computer, a
`Smart phone, a cellular phone, a handheld game system, a
`global positioning satellite (GPS) unit, a point-of-sale credit/
`debit card reader, or any other electronic device that includes,
`inter alia, a capacitive touch panel system, an analog-to
`digital conversion (ADC) unit, and a processing unit. The
`
`DELL EXHIBIT 1027 PAGE 14
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`DELL EXHIBIT 1027 PAGE 14
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`

`

`5
`touch panel system includes a plurality of sensing points that
`are operable to detect capacitances (e.g., self-capacitances or
`mutual capacitances) at the locations of the sensing points,
`which capacitances may have resulted from a touch input
`received from a user of the electronic device. The ADC unit is
`operably coupled to the sensing points and converts analog
`output signals from the sensing points to digital signal values
`that are usable by the processing unit.
`The processing unit is operably coupled to the ADC unit
`and operable in accordance with a set of operating instruc
`tions. In one embodiment, the processing unit is operable to
`receive digital signal values or sensed values from the ADC
`unit representing capacitances detected by the sensing points.
`The processing unit then adjusts one or more of the sensed
`values based at least on a time-varying noise (and optionally
`based on Static noise and gain) affecting the touch panel
`system and determines the touch input based on the noise
`adjusted value(s). The time-varying noise may be a common
`mode noise that similarly affects all the sensing points. In one
`embodiment, the processing unit is also operable to determine
`the time-varying noise prior to adjusting the sensed values.
`Alternatively, the time-varying noise may be determined
`separately and Supplied to the processing unit (e.g., via Stor
`age in memory). In another embodiment, the processing unit
`filters (e.g., digitally filters) the time-varying noise from the
`sensed values to produce the noise-adjusted values.
`In another embodiment, one or more of the sensing points
`may be located in the touch panel system such that they are
`protected from, and insusceptible to, application of a touch
`input (e.g., they may be covered by a blacked-out section of a
`screen or shielded by a grounded cover, Such as part of a
`housing Supporting the touch panel system). In such a case,
`the processing unit may be operable to determine a time
`varying noise affecting the touch panel system based on noise
`signals detected by the input-protected sensing points and
`processed through the ADC unit.
`In an alternative embodiment, the processing unit may be
`operable in accordance with the set of operating instructions
`to determine a time-varying noise affecting the touch panel
`system by adjusting one or more of the sensed values to
`account for static, spatial-varying noise and static, spatial
`varying gain to produce one or more adjusted values and then
`determining the time-varying noise value based on the
`adjusted value or values. For example, in one embodiment in
`which one or more input-protected sensing points are used to
`detect the time-varying noise, the processing unit may adjust
`only the sensed value or values from the input-protected
`sensing point or points. In an exemplary embodiment, the
`processing unit adjusts the sensed value from an input-pro
`tected sensing point by normalizing the sensed value to
`account for static, spatial-varying noise and static, spatial
`varying gain. For example, such normalization may be per
`formed by Subtracting the static, spatial-varying noise from
`the sensed value to produce a difference and dividing the
`difference by the static, spatial-varying gain to produce the
`time-varying noise value.
`Alternatively, when the sensing points that are not input
`protected are used to detect the time-varying noise, the pro
`cessing unit may adjust all of the sensed values resulting from
`the non-protected sensing points (which may include all of
`the sensing points of the touch panel system) to account for
`static, spatial-varying noise and static, spatial-varying gain.
`The processing unit may then determine an average of the
`adjusted values and compare each adjusted value to the aver
`age value to produce a plurality of comparison results. Based
`on the comparison results, the processing unit may determine
`a Subset of the adjusted values and then determine an average
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`of the Subset of adjusted values to produce the time-varying
`noise value. For example, in one embodiment, the processing
`unit may adjust the sensed values by normalizing them to
`account for static, spatial-varying noise and static, spatial
`varying gain. In Such a case, the processing unit may then
`determine an average of the normalized values to produce the
`average value and compare each of the normalized values to
`the average value to produce the comparison results. Based on
`the comparison results, the processing unit may determine a
`subset of the normalized values and then determine an aver
`age of the Subset of normalized values to produce the time
`varying noise value, which may be considered a common
`mode noise value when the time-varying noise value is Sub
`stantially constant over a Surface area of the touch panel
`system.
`In yet another embodiment, the processing unit may be
`further operable to adjust at least one of the sensed values
`based at least on the time-varying noise value by filtering the
`time-varying noise value from each of the sensed values to
`produce the noise-adjusted value(s). For example, the pro
`cessing unit may, in the digital domain, Subtract the time
`varying noise value or again-adjusted version thereof (e.g.,
`where the time-varying noise is affected by static, spatial
`varying gain) from each of the sensed values.
`In a further embodiment, the electronic device may also
`include at least one electronic noise source (e.g., a display
`panel) that is located proximate the touch panel system and is
`controllable by the processing unit. In such a case, the time
`varying noise affecting the touch panel system results at least
`in part from operation of the electronic noise Source. In this
`embodiment, the processing unit may be further operable, in
`accordance with the set of operating instructions, to deter
`mine whether a touch input is present based on the compari
`son results (i.e., the results of the comparisons of the adjusted
`(e.g., normalized) sensed values to the average of the adjusted
`sensed values). For example, a touch input may be deter
`mined to be present when the comparison results indicate that
`at least one of the adjusted sensed values is greater than the
`average of the adjusted sensed values by a predetermined
`threshold when the vast majority of the adjusted sensed val
`ues are less than or equal to the average value (e.g., where the
`sensing points of the touch panel system detect self-capaci
`tance) or at least one of the adjusted sensed values is less than
`the average of the adjusted sensed values by a different pre
`determined threshold when the vast majority of the adjusted
`sensed values are greater than or equal to the average value
`(e.g., where the sensing points of the touch panel system
`detect mutual capacitance). Responsive to a determination
`that a touch input is present, the processing unit may be
`further operable to slow operation of the electronic noise
`Source(s) on a temporary basis so as to cause noise produced
`thereby to be substantially less time dependent. Additionally,
`while operation of the electronic noise source is slowed, the
`processing unit may rescan the sensing points to detect
`capacitance values, adjust (e.g., normalize) the sensed values,
`determine an average of the adjusted sensed values, and com
`pare each of the adjusted values to the average value. In other
`words, the processing unit may, upon detecting that a touch
`input is present, attempt to cause the time-varying noise to
`become Substantially time-invariant or at least slow-changing
`in order to increase the accuracy of the noise measurement
`and thereby increase the likelihood offiltering the noise out of
`the touch panel system in order to more accurately determine
`the location of the touch input.
`For example, the electronic noise source may include a
`display panel that together with the touch panel system form
`a touchscreen display. In this case, operation of the display
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`panel causes time-varying noise in the touch panel system.
`Therefore, when the processing unit detects that a touch input
`is present based on the comparison results, the processing unit
`may slow operation of the electronic noise source by tempo
`rarily freezing operation of at least part of the display panel.
`For example, the processing unit may freeze or stop changes
`in the entire display panel or in a part of the display panel,
`Such as in an area Surrounding an estimated location of the
`touch input. The estimated location of the touch input may be
`determined as at least the area encompassing all sensing
`points having detected capacitances that resulted in adjusted
`(e.g., normalized) values which are greater than or less than
`(as applicable depending on the type of capacitance being
`detected by the sensing points) the average of all the adjusted
`values.
`In yet another embodiment, the sensing points may include
`a plurality of excitation nodes and a plurality of output nodes
`configured in a grid arrangement. In Such a case, the capaci
`tance at each sensing point may be detected by applying
`excitation signals to the excitation nodes, scanning the output
`nodes to detect corresponding output signals responsive to the
`excitation signals, and determining the capacitance at each
`sensing point based on a corresponding output signal. In this
`embodiment, the excitation signals may be identical and
`applied to each excitation node in a predetermined order one
`at a time and the output nodes may be scanned in a predeter
`mined order one at time, in a random order one at a time, in
`groups substantially simultaneously, or all Substantially
`simultaneously (e.g., at a common clock pulse or cycle, but
`due to inherent delays all output signals may not be detected
`at exactly the same time).
`In yet a further embodiment, the capacitance detected at a
`particular time and at a particular sensing point may be
`defined by the following equation:
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`where D(t) is the time-varying noise value, and N' is a quan
`tity of the Subset of normalized values and is less than or equal
`to N. R"(n,t) equals R(n,t)-B(n)/G(n) and is determined
`only for those sensing points for which a touch input is absent
`based on the comparison results.
`By providing an electronic device with the aforementioned
`functionality, the present invention facilitates accurate deter
`mination of a touch input to a touch panel system in the
`presence of time-varying noise. Such noise is present in many
`touch panel systems, especially those used to form touch
`screen displays. The positioning of a time-varying display
`panel in close proximity to a touch panel system, as is done in
`a touchscreen display, results in the injection of time-varying
`noise from the display panel into the touch panel system due
`to parasitic capacitance between the display panel and the
`touch panel sensing points. The amount of Such display
`induced noise is expected to increa