(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2008/0162996 A1
`Krah et al.
`(43) Pub. Date:
`Jul. 3, 2008
`
`US 2008O162996A1
`
`(54) MULTI-TOUCH AUTO SCANNING
`(75) Inventors:
`Christoph Horst Krah, Los Altos,
`
`Cupertino, CA (US); Thomas
`James Wilson, Pleasanton, CA
`(US)
`Correspondence Address:
`MORRISON & FOERSTER, LLP
`555 WEST FIFTH STREET, SUITE 3500
`LOS ANGELES, CA 90013-1024
`(73) Assignee:
`Apple, Inc., Cupertino, CA (US)
`
`(21) Appl. No.:
`
`11/650,040
`
`(22) Filed:
`
`Jan. 3, 2007
`
`Publication Classification
`
`(51) Int. Cl.
`G06F II/22
`G06F 3/04
`
`(2006.01)
`(2006.01)
`
`(52) U.S. Cl. ........................................... 714/27; 34.5/173
`
`A system and method for autonomously scanning a sensor
`panel device, such as a multi-touch panel, is disclosed. In one
`embodiment, the system and method disables a sensor panel
`processor after a first predetermined amount of time has
`elapsed without the sensor panel device sensing any events.
`One or more system clocks can also be disabled to conserve
`power. While the processor and one or more system clocks are
`disabled, the sensor panel device can periodically autono
`mously scan the sensor panel for touch activity. Accordingly,
`if one or more results from the autonomous scans exceed a
`threshold, the sensor panel device re-enables the processor
`and one or more clocks to actively scan the sensorpanel. If the
`threshold is not exceeded, then the sensor panel device con
`tinues to periodically autonomously scan the sensor panel
`without intervention from the processor. Furthermore, the
`sensor panel device can periodically perform calibration
`functions to account for any drift that may be present in the
`system.
`
`
`
`Peripherals
`104.
`
`130
`
`102
`
`MT Pane
`Processor
`
`Multi-touch Subsystem
`
`128
`
`.
`
`100
`
`1
`
`
`
`Host
`Processor
`
`
`
`Program
`Storage
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`Analog
`
`t
`
`Channel
`S
`
`Driver
`
`i. n Logic
`
`MT
`Subsystem
`Outputs
`116
`
`
`
`High Voltage Driver
`Decoder
`Levi Shifter
`120
`118
`
`
`
`
`
`MT Panel
`Row inputs
`122
`
`Control
`Signals
`
`
`
`Multi-TouchPanel
`
`
`
`C:
`Sig
`
`124
`
`Petitioners Samsung and Sony Ex-1005, 0001
`
`

`

`Patent Application Publication
`
`Jul. 3, 2008 Sheet 1 of 7
`
`US 2008/O162996 A1
`
`08' 1
`
`ZE I
`
`?SOH
`
`JOSS0001)
`
`| .JOSS30OJE
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`I "OI-|
`
`Petitioners Samsung and Sony Ex-1005, 0002
`
`

`

`Patent Application Publication
`
`Jul. 3, 2008 Sheet 2 of 7
`
`US 2008/0162996 A1
`
`Pulse Trai
`USe a
`216
`Vstim funn
`214
`
`U
`
`Ostray
`DC
`
`DC
`
`DC
`
`To Analog Channels
`FIG. 2A
`
`Column
`Dielectric Tige
`
`208
`
`Pixel
`
`
`
`Due to Finger
`A
`CSIG-ACSIG
`Electric
`- J
`Field Lines
`T
`
`Petitioners Samsung and Sony Ex-1005, 0003
`
`

`

`Patent Application Publication
`
`Jul. 3, 2008 Sheet 3 of 7
`
`US 2008/O162996 A1
`
`
`
`|?ued
`
`
`
`
`
`
`
`uo?eSueduuOO
`----008
`
`OVO
`õz?
`
`Petitioners Samsung and Sony Ex-1005, 0004
`
`

`

`emP
`
`b
`
`00
`
`a
`
`a
`
`m
`
`mond:
`
`m.8m.\
`.m9.90m32.5
`
`
`
`.m:5w:.._(“mu—JAWH—wc:..NQM.F2EOLKm553:3
`m.59:0Wmmfunny?
`ozo:3_rl/wlllx
`
`
`
`
`--:---..----:__..ISE=II£52W,59%>5.th1.:N.-"1A.mEoV
`
`.mQmOu>>Kumm>.szOQAu>w_‘
`.mmmmE=m>m_m0uc_-mad
`E_m"So-
`
`
`
`mIsanDE
`
`mImm>.NAN
`
`"mnTliM.AmwmiaNF.mdv
`
`8Iu.mANIxomNaimANIxoomm3ANIVSE.m3mSEzw>UIE..____
`
`
`:z.:::Ecomm\90mmk
`.mommk
`
`
`
`m1|N~.5Ill;
`
`
`
`Petitioners Samsung and Sony EX-1005, 0005
`
`Petitioners Samsung and Sony Ex-1005, 0005
`
`
`
`

`

`Patent Application Publication
`
`US 2008/O162996 A1
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`Petitioners Samsung and Sony Ex-1005, 0006
`
`

`

`Patent Application Publication
`
`Jul. 3, 2008 Sheet 6 of 7
`
`US 2008/O162996 A1
`
`5O2
`
`Active
`Mode
`
`
`
`Multi-touch
`Activity
`Detected
`
`
`
`5
`No
`Auto-SCan
`Enable
`
`Put PrOCeSSOr
`in Idle Mode
`
`51
`
`Turn Off
`System Clock
`
`
`
`512
`
`Turn Off High
`Frequency Oscillator
`
`
`
`
`
`Enable and Reset
`Sniff Timer
`
`Enable and Reset
`Calibration Timer
`
`FIG. 5
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`518
`Yes
`
`Interrupt
`Received
`2
`
`Sniff Time
`Exceeded
`?
`
`Calibration
`Time Exceedeg
`
`
`
`
`
`
`
`6
`52
`
`Turn On High
`Frequency Oscillator
`52 8
`Acquire Multi-touch
`Image
`
`
`
`Threshold
`ExCeeded
`
`52
`Turn On Clocks and
`Enable Processor
`
`Petitioners Samsung and Sony Ex-1005, 0007
`
`

`

`Patent Application Publication
`
`Jul. 3, 2008 Sheet 7 of 7
`
`US 2008/O162996 A1
`
`System
`POWer
`
`Time
`
`
`
`Cellular
`Telephone 736
`
`
`
`Digital
`Audio/Video
`gig.
`
`
`
`730 Display Device
`
`--- Other Computing
`System Blocks
`
`830 Display Device
`----- Other Computing
`System Blocks
`
`FIG. 7
`
`FIG. 8
`
`Petitioners Samsung and Sony Ex-1005, 0008
`
`

`

`US 2008/O 162996 A1
`
`Jul. 3, 2008
`
`MULTI-TOUCH AUTO SCANNING
`
`FIELD OF THE INVENTION
`0001. This relates generally to electronic devices (e.g.,
`touch screen devices) capable disabling various components
`(e.g., system clock and processor) during periods of inactiv
`ity, and, in particular, a system and method that initiates a low
`power auto-scan mode during periods of inactivity.
`
`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, touch panels, joysticks,
`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 may include a touch panel, which may be a clear panel
`with a touch-sensitive Surface. The touch panel may be posi
`tioned in front of a display screen so that the touch-sensitive
`surface covers the viewable area of the display screen. Touch
`screens may allow a user to make selections and move a
`cursor by simply touching the display screen via a finger or
`stylus. In general, the touch screen may recognize the touch
`and position of the touch on the display screen, and the
`computing system may interpret the touch and thereafter
`perform an action based on the touch event.
`0003. One limitation of many conventional touch panel
`technologies is that they are only capable of reporting a single
`point or touch event, even when multiple objects come into
`contact with the sensing Surface. That is, they lack the ability
`to track multiple points of contact at the same time. Thus,
`even when two points are touched, these conventional devices
`only identify a single location, which is typically the average
`between the two contacts (e.g. a conventional touchpad on a
`notebook computer provides such functionality). This single
`point identification is a function of the way these devices
`provide a value representative of the touch point, which is
`generally by providing an average resistance or capacitance
`value.
`0004 Moreover, a concern with many touch devices is the
`amount of power they consume when actively scanning a
`touch sensor panel. The high power consumption problem
`may be particularly important for hand-held devices, as a
`hand-held device's limited power supply can be readily con
`Sumed by actively scanning the touch sensor panel as well as
`processing those scans. These scans can be wasteful if there is
`no touch-activity on the panel for an extended period of time.
`0005. A possible remedy for a loss of power consumption
`during periods of inactivity is to shut down (i.e. turn off) the
`touch panel or touch panel device. But doing so can have
`several disadvantages. Such as consuming even more power
`when turning the touch panel back on (particularly if the
`period of inactivity is not an extended period of time) and the
`inconvenience to the user for having to wait for the touch
`panel to turn back on. Additionally, a user may forget to turn
`the touch panel off, so the device continues to actively scan
`the touch panel despite the user is not inputting any touch
`data.
`
`conserve power. Components that can be disabled include a
`touch-panel processor and system clock.
`0007 Another aspect of the multi-touch system relates to
`having an auto-scan mode that periodically scans a touch
`panel for touch events, without intervention from a multi
`touch processor. If predefined activity is detected, then the
`multi-touch processor can be enabled to actively scan the
`touch panel for touch events.
`0008 Another aspect of the multi-touch system relates to
`using a 'sniff mode to scan a touch panel for touch events
`after a predetermined amount of time has transpired. The
`multi-touch system can also have a calibration timer that
`automatically enables a multi-touch processor and system
`clocks to perform an active scan and calibration functions
`after a different predetermined amount of time has transpired.
`0009. Yet a further aspect of the multi-touch system relates
`to measuring stray capacitance in a touch panel sensor during
`an auto-scan mode.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`0010 FIG. 1 illustrates an exemplary computing system
`using a multi-touchpanel input device in accordance with one
`embodiment of the present invention.
`0011
`FIG. 2a illustrates an exemplary capacitive multi
`touch panel in accordance with one embodiment of the
`present invention.
`0012 FIG. 2b is a side view of an exemplary capacitive
`touch sensor or pixel is a steady-state (no-touch) condition in
`accordance with one embodiment of the present invention.
`0013 FIG. 2C is a side view of the exemplary capacitive
`touch sensor or pixel in a dynamic (touch) condition in accor
`dance with one embodiment of the present invention.
`0014 FIG. 3a illustrates an exemplary analog channel in
`accordance with one embodiment of the present invention.
`0015 FIG. 3b is a more detailed illustration of a virtual
`ground charge amplifier at the input of an analog channel, and
`the capacitance contributed by a capacitive touch sensor and
`seen by the charge amplifier in accordance with one embodi
`ment of the present invention.
`0016 FIG. 3c illustrates an exemplary V stim signal with
`multiple pulse trains each having a fixed number of pulses,
`each pulse train having a different frequency Fstim in accor
`dance with one embodiment of the present invention.
`0017 FIG. 4 is a block diagram illustrating auto-scan logic
`accordance with one embodiment of the invention.
`0018 FIG. 5 illustrates an auto-scan process implemented
`by the auto-scan logic of FIG. 6 in accordance with one
`embodiment of the invention.
`0019 FIG. 6 illustrates a 'sniff mode” power management
`profile in accordance with one embodiment of the invention.
`0020 FIG. 7 illustrates an exemplary mobile telephone
`that may include multi-touch panel, display device, and other
`computing system blocks in accordance with one embodi
`ment of the present invention.
`0021
`FIG. 8 illustrates an exemplary digital audio/video
`player that may include a multi-touch panel, a display device,
`and other computing system blocks in accordance with one
`embodiment of the present invention.
`
`SUMMARY OF THE INVENTION
`0006. A multi-touch touch system is disclosed herein. One
`aspect of the multi-touch touch system relates disabling com
`ponents of a touch-panel device during periods of inactivity to
`
`DETAILED DESCRIPTION OF THE PREFERRED
`EMBODIMENT
`0022. In the following description of preferred embodi
`ments, reference is made to the accompanying drawings
`
`Petitioners Samsung and Sony Ex-1005, 0009
`
`

`

`US 2008/O 162996 A1
`
`Jul. 3, 2008
`
`which form a parthereof, and in which it is shown by way of
`illustration specific embodiments in which the invention may
`be practiced. It is to be understood that other embodiments
`may be used and structural changes may be made without
`departing from the scope of the preferred embodiments of the
`present invention.
`0023. A plurality of touch sensors in a multi-touch panel
`can enable a computing system to sense multi-touch events
`(the touching of fingers or other objects upon a touch-sensi
`tive Surface at distinct locations at about the same time) and
`perform additional functions not previously available with
`touch sensor devices
`0024. Although some embodiments may be described
`herein in terms of capacitive touch sensors in a multi-touch
`panel, it should be understood that embodiments of the inven
`tion are not so limited, but are generally applicable to the use
`of any type of multi-touch sensortechnology that may include
`resistive touch sensors, Surface acoustic wave touch sensors,
`electromagnetic touch sensors, near field imaging touchsen
`sors, and the like. Furthermore, although the touch sensors in
`the multi-touch panel may be described herein in terms of an
`orthogonal array of touch sensors having rows and columns,
`it should be understood that embodiments of the invention are
`not limited to orthogonal arrays, but may be generally appli
`cable to touch sensors arranged in any number of dimensions
`and orientations, including diagonal, concentric circle, and
`three-dimensional and random orientations.
`0025. In general, multi-touch panels may be able to detect
`multiple touches (touch events or contact points) that occurat
`or about the same time, and identify and track their locations.
`Examples of multi-touch panels are described in Applicant's
`co-pending U.S. application Ser. No. 10/842,862 entitled
`“Multipoint Touchscreen.” filed on May 6, 2004 and pub
`lished as U.S. Published Application No. 2006/0097991 on
`May 11, 2006, the contents of which are incorporated by
`reference herein.
`0026 FIG. 1 illustrates computing system 100 using touch
`sensors according to one embodiment. Computing system
`100 may correspond to computing devices such as desktops,
`laptops, tablets or handhelds, including personal digital assis
`tants (PDAs), digital music and/or video players and mobile
`telephones. Computing system 100 may also correspond to
`public computer systems such as information kiosks, auto
`mated teller machines (ATM), point of sale machines (POS),
`industrial machines, gaming machines, arcade machines,
`vending machines, airline e-ticket terminals, restaurant res
`ervation terminals, customer service stations, library termi
`nals, learning devices, and the like.
`0027 Computing system 100 may include one or more
`multi-touch panel processors 102 and peripherals 104, and
`multi-touch subsystem 106. The one or more processors 102
`can be ARM968 processors or other processors with similar
`functionality and capabilities. However, in other embodi
`ments, the multi-touch panel processor functionality may be
`implemented instead by dedicated logic Such as a state
`machine. Peripherals 104 may include, but are not limited to,
`random access memory (RAM) or other types of memory or
`storage, watchdog timers and the like. Multi-touch subsystem
`106 may include, but is not limited to, one or more analog
`channels 108, channel scan logic 110 and driver logic 114.
`Channel scan logic 110 may access RAM 112, autonomously
`read data from the analog channels and provide control for the
`analog channels. This control may include multiplexing col
`umns of multi-touch panel 124 to analog channels 108. In
`
`addition, channel scan logic 110 may control the driver logic
`and stimulation signals being selectively applied to rows of
`multi-touch panel 124. In some embodiments, multi-touch
`Subsystem 106 may be integrated into a single application
`specific integrated circuit (ASIC).
`0028. Driver logic 114 can provide multiple multi-touch
`Subsystem outputs 116 and can presentaproprietary interface
`that drives high voltage driver, which is comprised of decoder
`120 and subsequent level shifter and driver stage 118,
`although level-shifting functions could be performed before
`decoder functions. Level shifter and driver 118 can provide
`level shifting from a low voltage level (e.g. CMOS levels) to
`a higher Voltage level, providing a better signal-to-noise
`(S/N) ratio for noise reduction purposes. Decoder 120 can
`decode the drive interface signals to one out of N outputs,
`whereas N is the maximum number of rows in the panel.
`Decoder 120 can be used to reduce the number of drive lines
`needed between the high voltage driver and multi-touch panel
`124. Each multi-touch panel row input 122 can drive one or
`more rows in multi-touch panel 124. In some embodiments,
`driver 118 and decoder 120 can be integrated into a single
`ASIC. However, in other embodiments driver 118 and
`decoder 120 can be integrated into driver logic 114, and in
`still other embodiments driver 118 and decoder 120 can be
`eliminated entirely.
`0029 Multi-touch panel 124 can in some embodiments
`include a capacitive sensing medium having a plurality of row
`traces or driving lines and a plurality of column traces or
`sensing lines, although other sensing media may also be used.
`The row and column traces may beformed from a transparent
`conductive medium, such as Indium Tin Oxide (ITO) or Anti
`mony Tin Oxide (ATO), although other transparent and non
`transparent materials, such as copper, can also be used. In
`Some embodiments, the row and column traces can beformed
`on opposite sides of a dielectric material, and can be perpen
`dicular to each other, although in other embodiments other
`non-orthogonal orientations are possible. For example, in a
`polar coordinate system, the sensing lines can be concentric
`circles and the driving lines can be radially extending lines (or
`vice versa). It should be understood, therefore, that the terms
`“row' and “column,” “first dimension' and “second dimen
`sion, or “first axis' and “second axis' as used herein are
`intended to encompass not only orthogonal grids, but the
`intersecting traces of other geometric configurations having
`first and second dimensions (e.g. the concentric and radial
`lines of a polar-coordinate arrangement). It should also be
`noted that in other embodiments, the rows and columns can be
`formed on a single side of a Substrate, or can beformed on two
`separate Substrates separated by a dielectric material. In some
`embodiments, the dielectric material can be transparent, Such
`as glass, or can beformed from other materials, such as mylar.
`An additional dielectric cover layer may be placed over the
`row or column traces to strengthen the structure and protect
`the entire assembly from damage.
`0030. At the “intersections” of the traces, where the traces
`pass above and below each other (but do not make direct
`electrical contact with each other), the traces essentially form
`two electrodes (although more than two traces could intersect
`as well). Each intersection of row and column traces can
`represent a capacitive sensing node and can be viewed as
`picture element (pixel) 126, which can be particularly useful
`when multi-touch panel 124 is viewed as capturing an
`“image' of touch. (In other words, after multi-touch sub
`system 106 has determined whether a touch event has been
`
`Petitioners Samsung and Sony Ex-1005, 0010
`
`

`

`US 2008/O 162996 A1
`
`Jul. 3, 2008
`
`detected at each touch sensor in the multi-touch panel, the
`pattern of touch sensors in the multi-touch panel at which a
`touch event occurred can be viewed as an “image' of touch
`(e.g. a pattern offingers touching the panel).) The capacitance
`between row and column electrodes appears as a stray capaci
`tance on all columns when the given row is held at DC and as
`a mutual capacitance Csig when the given row is stimulated
`with an AC signal. The presence of a finger or other object
`near or on the multi-touch panel can be detected by measuring
`changes to Csig. The columns of multi-touch panel 124 can
`drive one or more analog channels 108 (also referred to herein
`as event detection and demodulation circuits) in multi-touch
`Subsystem 106. In some embodiments, each column is
`coupled to one dedicated analog channel 108. However, in
`other embodiments, the columns may be couplable via an
`analog switch to a fewer number of analog channels 108.
`0031 Computing system 100 can also include host pro
`cessor 128 for receiving outputs from multi-touch panel pro
`cessor 102 and performing actions based on the outputs that
`may include, but are not limited to, moving an object such as
`a cursor or pointer, scrolling or panning, adjusting control
`settings, opening a file or document, viewing a menu, making
`a selection, executing instructions, operating a peripheral
`device connected to the host device, answering a telephone
`call, placing a telephone call, terminating a telephone call,
`changing the Volume or audio settings, storing information
`related to telephone communications such as addresses, fre
`quently dialed numbers, received calls, missed calls, logging
`onto a computer or a computer network, permitting autho
`rized individuals access to restricted areas of the computer or
`computer network, loading a user profile associated with a
`user's preferred arrangement of the computer desktop, per
`mitting access to web content, launching a particular pro
`gram, encrypting or decoding a message, and/or the like. Host
`processor 128 may also perform additional functions that
`may not be related to multi-touch panel processing, and can
`be coupled to program storage 132 and display device 130
`such as an LCD display for providing a user interface (UI) to
`a user of the device.
`0032 FIG. 2a illustrates exemplary capacitive multi
`touch panel 200. FIG. 2a indicates the presence of a stray
`capacitance Cstray at each pixel 202 located at the intersec
`tion of a row 204 and a column 206 trace (although Cstray for
`only one column is illustrated in FIG. 2 for purposes of
`simplifying the figure). Note that although FIG.2a illustrates
`rows 204 and columns 206 as being substantially perpendicu
`lar, they need not be so aligned, as described above. In the
`example of FIG. 2a, AC stimulus Vstim 214 is being applied
`to one row, with all other rows connected to DC. The stimulus
`causes a charge to be injected into the column electrodes
`through mutual capacitance at the intersecting points. This
`charge is Qsig CsigxVstm. Each of columns 206 may be
`selectively connectable to one or more analog channels (see
`analog channels 108 in FIG. 1).
`0033 FIG.2b is a side view of exemplary pixel 202 in a
`steady-state (no-touch) condition. In FIG.2b, an electric field
`of electric field lines 208 of the mutual capacitance between
`column 206 and row 204 traces or electrodes separated by
`dielectric 210 represents a signal capacitance Csig between
`the row and column electrodes and can cease a charge to be
`injected form a stimulated row to a column electrode. Since
`Csig is referenced to virtual ground, it also makes up a stray
`capacitance. For example, a total stray capacitance of a col
`umn electrode can be the sum of all signal capacitances Csig
`
`between a given column and all row electrodes. Assuming
`that CSig is for example 0.75 pF and a column electrode is
`intersected by fifteen row electrodes, the total stray capaci
`tance on that column electrode would be at least 15x0.75
`pF=11.25 pF. In reality, however, the total stray capacitance is
`likely larger due to a trace Stray capacitance of the column
`electrode to the multi-touch ASIC or other stray capacitances
`in the system.
`0034 FIG.2c is a side view of exemplary pixel 202 in a
`dynamic (touch) condition. In FIG. 2C, finger 212 has been
`placed near pixel 202. Finger 212 is a low-impedance object
`at signal frequencies, and represents an CA ground return
`path to via body capacitance Cbody. The body has a self
`capacitance to ground Cbody, which is a function of, among
`other things, body size and geometry. If finger 212 blocks
`some electric field lines 208 between the row and column
`electrodes (those fringing fields that exit the dielectric and
`pass through the air above the row electrode), those electric
`field lines are shunted to ground through the capacitance path
`inherent in the finger and the body, and as a result, the steady
`state signal capacitance Csig is reduced by Csig sense. In
`other words, the combined body and finger capacitance act to
`reduce Csig by an amount ACsig (which can also be referred
`to herein as Csig sense), and can act as a shunt or dynamic
`return path to ground, blocking some of the electric fields as
`resulting in a reduced net signal capacitance. The signal
`capacitance at the pixel becomes Csig-ACsig, where Csig
`represents the static (no touch) component and ACsig repre
`sents the dynamic (touch) component. Note that Csig-ACsig
`may always be nonzero due to the inability of a finger, palm or
`other object to block all electric fields, especially those elec
`tric fields that remain entirely within the dielectric material.
`In addition, it should be understood that as a finger is pushed
`harder or more completely onto the multi-touch panel, the
`finger can tend to flatten, blocking more and more of the
`electric fields, and thus ACsig can be variable and represen
`tative of how completely the finger is pushing down on the
`panel (i.e. a range from “no-touch' to “full-touch').
`0035 Referring again to FIG. 2a, as mentioned above,
`Vstim signal 214 can be applied to a row in multi-touch panel
`200 so that a change in signal capacitance can be detected
`when a finger, palm or other object is present. VStim signal
`214 can include one or more pulse trains 216 at a particular
`frequency, with each pulse train including of a number of
`pulses. Although pulse trains 216 are shown as square waves,
`other waveshapes such as sine waves can also be employed. A
`plurality of pulse trains 216 at different frequencies can be
`transmitted for noise reduction purposes to minimize the
`effect of any noise Sources. VStim signal 214 essentially
`injects a charge into the row via signal capacitance Csig, and
`can be applied to one row of multi-touch panel 200 at a time
`while all other rows are held at a DC level. However, in other
`embodiments, the multi-touch panel may be divided into two
`or more sections, with Vstim signal 214 being simultaneously
`applied to one row in each section and all other rows in that
`region section held at a DC voltage.
`0036) Each analog channel coupled to a column can pro
`vide a result representing a mutual capacitance between a row
`being stimulated and a column the row is connected to. Spe
`cifically, this mutual capacitance is comprised of the signal
`capacitance Csig and any change Csig sense in that signal
`capacitance due to the presence of a finger, palm or other body
`part or object. These column values provided by the analog
`channels may be provided in parallel while a single row is
`
`Petitioners Samsung and Sony Ex-1005, 0011
`
`

`

`US 2008/O 162996 A1
`
`Jul. 3, 2008
`
`being stimulated, or may be provided in series. If all of the
`values representing the signal capacitances for the columns
`have been obtained, another row in multi-touchpanel 200 can
`be stimulated with all others held at a DC voltage, and the
`column signal capacitance measurements can be repeated.
`Eventually, if Vstim has been applied to all rows, and the
`signal capacitance values for all columns in all rows have
`been captured (i.e. the entire multi-touch panel 200 has been
`“scanned'), a “snapshot' of all pixel values can be obtained
`for the entire multi-touchpanel 200. This snapshot data can be
`initially saved in the multi-touch. Subsystem, and later trans
`ferred out for interpretation by other devices in the computing
`system such as the host processor. As multiple Snapshots are
`obtained, saved and interpreted by the computing system, it is
`possible formultiple touches to be detected, tracked, and used
`to perform other functions.
`0037 FIG. 3a illustrates exemplary analog channel or
`event detection and demodulation circuit 300. One or more
`analog channels 300 can be present in the multi-touch sub
`system. One or more columns from a multi-touch panel can
`be connectable to each analog channel 300. Each analog
`channel300 can include virtual-ground charge amplifier 302,
`signal mixer 304, offset compensation 306, rectifier 332,
`subtractor 334, and analog-to-digital converter (ADC) 308.
`FIG. 3a also shows, in dashed lines, the steady-state signal
`capacitance Csig that can be contributed by a multi-touch
`panel column connected to analog channel 300 when an input
`stimulus V stim is applied to a row in the multi-touch panel
`and no finger, palm or other object is present, and the dynamic
`signal capacitance Csig-ACsig that can appear when a finger,
`palm or other object is present.
`0038 Vstim, as applied to a row in the multi-touch panel,
`can be generated as a burst of square waves or other non-DC
`signaling in an otherwise DC signal, although in some
`embodiments the square waves representing VStim can be
`preceded and followed by other non-DC signaling. If V stim is
`applied to a row and a signal capacitance is present at a
`column connected to analog channel300, the output of charge
`amplifier 302 can be pulse train 310 centered at Vref with a
`peak-to-peak (p-p) amplitude in the steady-state condition
`that is a fraction of the p-pamplitude of Vstim, the fraction
`corresponding to the gain of charge amplifier 302, which is
`equivalent to the ratio of signal capacitance Csig and pream
`plifier feedback capacitance Cfb. For example, if Vstim
`includes 18V p-p pulses and the gain of the charge amplifier
`is 0.1, then the output of the charge amplifier can be 1.8V p-p
`pulses. This output can be mixed in signal mixer 304 with
`demodulation waveform Fstim316.
`0039. Since the stimulation signal can be a square wave, it
`may be advantageous to use a sinusoidal demodulation wave
`form to remove the harmonics of the square wave. In order to
`reduce the stop band ripple of the mixer at a given stimulation
`frequency, it can be advantageous to use a Gaussian shaped
`sinewave. The demodulation waveform can have the same
`frequency as the stimulus VStim and can be synthesised from
`a Lookuptable, enabling generation of any shape of demodu
`lation waveform. Besides Gaussian shaped sinewaves, other
`waveshapes may be programmed to tune the filter character
`istics of the mixers. In some embodiments, Fstim316 may be
`tunable in frequency and amplitude by selecting different
`digital waveforms in the LUT 312 or generating the wave
`forms differently using other digital logic. Signal mixer 304
`may demodulate the output of charge amplifier 310 by sub
`tracting Fstim 316 from the output to provide better noise
`
`rejection. Signal mixer 304 may reject all frequencies outside
`the passband, which may in one example be about +/-30 kHz
`around Fstim. This noise rejection may be beneficial in noisy
`environment with many sources of noise, Such as 802.11,
`Bluetooth and the like, all having some characteristic fre
`quency that may interfere with the sensitive (femt-faradlevel)
`analog channel 300. Since the frequency of the signals going
`into the signal mixer can have the same frequency, the signal
`mixer may be thought of as a synchronous rectifier, such that
`the output of the signal mixer is essentially a rectified wave
`form.
`0040. Offset compensation 306 can then be applied to
`signal mixer output 314, which can remove the effect of the
`static Csig, leaving only the effect of ACsig appearing as
`result 324. Offset compensation 306 can be implemented
`using offset mixer 330. Offset compensation output 322 can
`be generated by rectifying Fstim316 using rectifier 332, and
`mixing rectifier output336 with analog Voltage from a digital
`to-analog converter (DAC)320 in offset mixer 330. DAC 320
`can generate the analog Voltage based on a digital value
`selected to increase the dynamic range of analog channel300.
`Offset compensation output 322, which can be proportional
`to the analog voltage from DAC 320, can then be subtracted
`from signal mixer output 314 using Subtractor 334, producing
`subtractor output 338 which can be representative of the
`change in the signal capacitance ACsig that occurs when a
`capacitive sensor on the row being stimulated has been
`touched. Subtractor output 338 is then integrated and can then
`be converted to a digital value by ADC 308. In some embodi
`ments, integrator and ADC functions are combined and ADC
`308 may be an integrating ADC, such as a sigma-delta ADC,
`which can sum a number of consecutive digital values and
`average them to generate result 324.
`0041
`FIG. 3b is a more detailed view of charge amplifier
`(a virtual ground amplifier) 302 at the input of an analog
`channel, and the capacitance that can be contributed by the
`multi-touch panel (see dashed lines) and seen by the charge
`amplifier. As mentioned above, there can be an inherent stray
`capacitance Cstray at each pixel on the multi-touch panel. In
`virtual grou