Filed on behalf of TPK Touch Solutions Inc.
`
`Case IPR2013-00568
`Declaration of Joshua R. Smith
`
`UNITED STATES PATENT AND TRADEMARK OFFICE
`
`________________
`
`BEFORE THE PATENT TRIAL AND APPEAL BOARD
`
`________________
`
`WINTEK CORPORATION
`Petitioner,
`
`v.
`
`TPK TOUCH SOLUTIONS INC.
`Patent Owner
`________________
`
`Case IPR2013-00568
`U.S. Patent No. 8,217,902
`
`DECLARATION OF JOSHUA R. SMITH IN SUPPORT OF PATENT
`OWNER’S RESPONSE PURSUANT TO 37 C.F.R. § 42.120
`
`TPK 2002
`Wintek v. TPK Solutions
`IPR2013-00568
`
`

`

`Case IPR2013-00568
`Declaration of Joshua R. Smith
`
`TABLE OF CONTENTS
`
`I.
`
`II.
`
`III.
`
`IV.
`
`INTRODUCTION ..............................................................................................1
`
`BACKGROUND AND QUALIFICATIONS ..................................................2
`
`PERSON OF ORDINARY SKILL IN THE ART ...........................................7
`
`TECHNOLOGY BACKGROUND ..................................................................8
`
`A.
`
`B.
`
`Capacitance and Capacitive Touch Panels.............................................8
`
`Self-Capacitance-Based Touch Panels.................................................14
`
`1.
`
`2.
`
`3.
`
`Measuring Self-Capacitance.......................................................14
`
`Detecting a Touch Position by Measuring Self-
`Capacitance..................................................................................16
`
`Drawbacks of Self-Capacitance Systems Available at the
`Time of the ’902 Invention.........................................................17
`
`C. Mutual Capacitance-Based Touch Panels ............................................19
`
`1.
`
`2.
`
`3.
`
`4.
`
`Measuring Mutual Capacitance..................................................19
`
`Detecting a Touch Position by Measuring Mutual
`Capacitance..................................................................................21
`
`Conductor Layout in Self-Capacitance and Mutual
`Capacitance Systems...................................................................24
`
`Drawbacks of Mutual-Capacitance Systems Available at
`the Time of the ’902 Invention...................................................28
`
`V.
`
`THE ’902 PATENT..........................................................................................29
`
`A.
`
`B.
`
`The Invention of the ’902 Patent ..........................................................29
`
`Interpretation of Terms in the ’902 Patent ...........................................35
`
`VI. ANALYSIS OF THE PRIOR ART.................................................................39
`
`A.
`
`Fujitsu .....................................................................................................39
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`Case IPR2013-00568
`Declaration of Joshua R. Smith
`
`B.
`
`Binstead ..................................................................................................43
`
`C. Miller ......................................................................................................46
`
`D.
`
`E.
`
`Seguine ...................................................................................................53
`
`Bolender .................................................................................................54
`
`VII. VALIDITY OF THE ’902 PATENT ..............................................................54
`
`A.
`
`Asserted Anticipation Based on Fujitsu – Claims 1-15, 24, 32,
`34, 36-40, 42, 43, 46-58, and 60-67......................................................54
`
`1.
`
`2.
`
`Fujitsu Does Not Disclose “Conductor Assemblies”
`Comprising “Conductor Cells” and “Conduction Lines”.........54
`
`Fujitsu Does Not Disclose “Signal Transmission Lines
`Formed on the Surface of the Substrate”...................................59
`
`B.
`
`C.
`
`Asserted Obviousness Based on Fujitsu and Binstead – Claims
`11-15, 34, 43, 51, 60, and 67.................................................................63
`
`Asserted Obviousness Based on Fujitsu and Miller – Claims 17-
`22, 25-29, 35, 44, and 68.......................................................................65
`
`1.
`
`2.
`
`3.
`
`4.
`
`The Proposed Combination of Fujitsu and Miller Does
`Not Disclose All the Limitations of the Challenged
`Claims. .........................................................................................66
`
`Miller Contains No Teaching, Suggestion or Motivation
`of Implementing Mutual Capacitance in a Single-Layer
`Solution........................................................................................67
`
`Fujitsu Contains No Teaching, Suggestion or Motivation
`of Detecting a Position of Touch by Measuring a Change
`in Capacitance Between Conductor Elements. .........................70
`
`Combining the Electrode Structure of Fujitsu with the
`Measurement of Mutual Capacitance in Miller Would
`Result in an Unworkable System. ..............................................73
`
`D.
`
`Asserted Obviousness Based on Fujitsu and Seguine – Claims
`5, 10, 15, 21, 29, 39, 50, 57, and 64......................................................79
`
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`Case IPR2013-00568
`Declaration of Joshua R. Smith
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`E.
`
`Objective Evidence of Non-Obviousness.............................................81
`
`VIII. CONCLUSION.................................................................................................86
`
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`

`Case IPR2013-00568
`Declaration of Joshua R. Smith
`
`Declaration of Joshua R. Smith
`In Support of Patent Owner’s Response Pursuant to 37 C.F.R. § 42.120
`
`I.
`
`INTRODUCTION
`
`I, Joshua R. Smith, declare as follows:
`
`1.
`
`I am over 18 years of age and otherwise competent to make this
`
`Declaration.
`
`2.
`
`I have been retained as an expert witness to provide testimony on
`
`behalf of TPK Touch Solutions Inc. (“TPK”) as part of the above-captioned inter
`
`partes review proceeding. I make this Declaration based upon facts and matters
`
`within my own knowledge or on information provided to me by others. I am being
`
`compensated for my time in connection with this proceeding at a rate of $400 per
`
`hour.
`
`3.
`
`I understand that the Patent Office has instituted a review of claims 1-
`
`19, 21, 22, 24-27, 29, and 31-68 of U.S. Patent No. 8,217,902 (“the ’902 patent”),
`
`and that the review is based on four references. In particular, I understand the
`
`Board granted the Petition on the following grounds:
`
`A.
`
`Anticipation of claims 1-15, 24, 32, 34, 36-40, 42, 43, 46-58, and 60-
`
`67 based on Japanese Patent Application 60-75927 to Fujitsu
`
`(“Fujitsu”);
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`Case IPR2013-00568
`Declaration of Joshua R. Smith
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`B.
`
`Obviousness of claims 11-15, 34, 43, 51, 60, and 67 based on the
`
`combination of Fujitsu and U.S. Patent No. 6,137,427 to Binstead
`
`(“Binstead”);
`
`C.
`
`Obviousness of claims 17-22, 25-29, 35, 44, and 68 based on the
`
`combination of Fujitsu and U.S. Patent No. 5,374,787 to Miller
`
`(“Miller”); and
`
`D.
`
`Obviousness of claims 5, 10, 15, 16, 31, 39, 41, 45, 50, 57, and 64
`
`based on the combination of Fujitsu and U.S. Patent Pub. No.
`
`2007/0229469 to Seguine (“Seguine”); and
`
`E.
`
`Obviousness of claims 33 and 59 based on the combination of Fujitsu
`
`and U.S. Patent Pub. No. 2005/0030048 to Bolender (“Bolender”).
`
`4.
`
`In addition to the present Declaration, I have prepared a separate
`
`declaration pertaining to IPR2013-00567, which involves different grounds of
`
`rejection for certain claims of the ’902 patent.
`
`II.
`
`BACKGROUND AND QUALIFICATIONS
`5.
`I am a tenured Associate Professor, jointly appointed in the
`
`departments of Electrical Engineering, and Computer Science and Engineering, at
`
`the University of Washington in Seattle. In 2013, the Paul G. Allen Family
`
`Foundation named me an Allen Distinguished Investigator. I am the Theme
`
`Leader for Low Power Sensing and Computing in the Intel Science and
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`Case IPR2013-00568
`Declaration of Joshua R. Smith
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`Technology Center for Pervasive Computing. I am Thrust Leader for
`
`Communications and Interface in the National Science Foundation-funded
`
`Engineering Research Center on Sensorimotor Neural Engineering.
`
`6.
`
`I received Ph.D and S.M. degrees from the Massachusetts Institute of
`
`Technology in 1999 and 1995 respectively. I received an M.A. in Physics from the
`
`University of Cambridge in 1997 (originally conferred as a B.A. in 1993). I
`
`received a B.A. in Computer Science and Philosophy from Williams College in
`
`1991. My Ph.D thesis research concerned capacitive sensing. In particular, it
`
`focused on sensing and interpretation of capacitance measurements in order to
`
`infer geometrical information about human hands, for input device applications.
`
`The sensors I developed are more sensitive than today’s commercial capacitive
`
`sensors; they work at much greater range than today’s touch sensors. They can
`
`detect body parts in a non-contact fashion.
`
`Non-contact tracking of two hands in three dimensions.
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`Case IPR2013-00568
`Declaration of Joshua R. Smith
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`7.
`
`One application I explored in the course of my Ph.D thesis was the
`
`use of capacitive sensing for airbag safety. The technology I developed uses
`
`mutual capacitance measurements to detect out-of-position occupants and suppress
`
`airbag firing when a dangerous body pose is detected. The technology was
`
`licensed by NEC, now Elesys/Honda, and has been incorporated in every Honda
`
`car made since the year 2000. The technology was also incorporated into 4.5
`
`million cars manufactured by General Motors.
`
`8.
`
`After finishing my Ph.D, I was hired to start a hardware research lab
`
`for a small software company called the Escher Group. When I joined, the
`
`company was privately held, with no outside investors other than the founders;
`
`while I was there a portion of the company was sold to a private equity firm, and
`
`now it is publicly traded on the London Stock Exchange. The Escher Group’s
`
`primary product is postal counter automation software. This software was used to
`
`perform a variety of counter transactions at post offices around the world, most
`
`notably the U.K. Post Office, where 40,000 workstations were deployed. In
`
`addition to mail-related transactions, in the U.K. the software is used to perform
`
`financial and other transactions, such as distribution of welfare benefits. The
`
`system integrator partner responsible for deploying the hardware in some of these
`
`large projects was Fujitsu.
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`Case IPR2013-00568
`Declaration of Joshua R. Smith
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`9.
`
`The U.K. Post Office postal counter automation system was one of the
`
`first large commercial deployments of touch screens. Because of the commercial
`
`importance of touch screens to Escher’s business, I worked on developing new,
`
`improved forms of touch screen sensing technology. I developed a new type of
`
`mutual-capacitance-based touch screen that detected the user’s finger before
`
`contact. This allows an interaction that present day touch screens do not support
`
`(but ordinary computer mice do): the user can hover the pointer over a
`
`icon/button/hyperlink without clicking; context sensitive help pops up, indicating
`
`what will happen if the link were to be clicked.
`
`10.
`
`In the course of developing the new touch screen research prototypes,
`
`I designed and had fabricated several different ITO electrodes, and the electronics
`
`to drive them.
`
`Prototype non-contact touch screen showing raw sensor values
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`Case IPR2013-00568
`Declaration of Joshua R. Smith
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`Prototype non-contact touch screen being used for icon selection
`
`11. As a researcher and professor of electrical engineering, I have
`
`authored more than 90 technical journal and conference articles, and edited one
`
`book. My papers have won 8 best paper awards, including the Best Paper Award
`
`at the 2009 IEEE International Conference on RFID, for “A Capacitive Touch
`
`Interface for Passive RFID Tags.” I won the best paper award again at the same
`
`conference this year, 2014. I won a Best Paper Award at the 2012 ACM
`
`Conference on Ubiquitous Computing (“Ubicomp 2012”) for “An Ultra-Low-
`
`Power Human Body Motion Sensor Using Static Electric Field Sensing.” In 2013,
`
`I won the Best Paper Award at the ACM SIGCOMM 2013, a very selective
`
`conference, for a paper that introduced a completely new way communicate.
`
`12. Additionally, I was named a Herchel Smith Scholar at the University
`
`of Cambridge, and recognized as a Motorola Fellow during my time at MIT.
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`Case IPR2013-00568
`Declaration of Joshua R. Smith
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`13.
`
`I have 24 issued U.S. patents, numerous foreign patents, and
`
`numerous patents pending. These patents cover the following subject areas:
`
`capacitive sensing, electronic textile sensing, document security, Radio Frequency
`
`Identification sensing, power harvesting, wireless power transfer, and mailpiece
`
`tracking.
`
`14. My qualifications for forming the opinions set forth in this report are
`
`listed in this section and in Ex. 2003, which is my curriculum vitae. Ex. 2003 also
`
`includes a list of my publications.
`
`III. PERSON OF ORDINARY SKILL IN THE ART
`
`15. As a result of my more than 20 years experience with capacitive
`
`sensor technology and design, I am intimately familiar with the subject matter of
`
`the ’902 patent and competent to provide expert opinions on both the patent and
`
`the teachings of the prior art references at issue.
`
`16.
`
`In connection with this matter, I have reviewed the ’902 Patent, the
`
`prior art referenced in the Petition, and the Exhibits cited in this declaration.
`
`17.
`
`In my opinion, a person of ordinary skill in the art of touch sensor
`
`technology as described in the ’902 Patent as of April 27, 2007, would have at least
`
`a bachelor of science degree in electrical engineering or a similar degree and at
`
`least 2 years of experience in the design of touch sensors.
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`Case IPR2013-00568
`Declaration of Joshua R. Smith
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`IV. TECHNOLOGY BACKGROUND
`18.
`In this section, I provide an overview of the state of the art in touch
`
`sensor technology at the time the ’902 patent was filed, August 21, 2007.
`
`A.
`
`19.
`
`Capacitance and Capacitive Touch Panels
`
`The ’902 patent concerns capacitive sensing, which has existed in
`
`some form since the work of the inventor Theremin in the 1920s. Capacitive touch
`
`sensing has existed in recognizable form since the 1960s.
`
`20.
`
`Before capacitive touch sensing matured, “resistive” sensing was the
`
`predominant touch panel technology. Resistive touch technology, including the
`
`commonly known “four-wire resistive” touchscreen, is characterized by layers of
`
`resistive material. A voltage difference is applied across one of the layers; because
`
`the material is resistive, this results in a voltage gradient across the material. When
`
`a finger presses the two layers together, they make contact at a location, now
`
`“tagged” with a particular voltage. Thus the contact point can be determined by
`
`taking an electrical measurement at the “tagged” location.
`
`21. Other forms of non-capacitive touchscreen technology include
`
`acoustic pulse recognition touch panels, which detect touch by measuring the
`
`phase shift of acoustic waves generated by a finger touching the screen, and optical
`
`touch sensors, which detect disruptions in a grid of infrared light across the surface
`
`of the panel.
`
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`Case IPR2013-00568
`Declaration of Joshua R. Smith
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`22.
`
`Capacitive touch panels became an attractive alternative to resistive
`
`and other known technologies for a variety of reasons, including reliability,
`
`performance, and cost.
`
`23.
`
`Capacitive touch panels detect the location of touch as a function of a
`
`change in capacitance. Capacitance is a measure of the ability of an arrangement
`
`of conductors to store charge in response to an applied voltage. One simple
`
`example illustrating capacitance is a parallel plate capacitor. A parallel plate
`
`capacitor consists of two conductive “plates” separated by an insulator or
`
`dielectric.
`
`24. A capacitor is defined by the equation Q=CV, which relates the stored
`
`charge Q between the plates to the voltage V or potential difference across the
`
`plates:
`
`25.
`
`From the relationship above, we see that for higher values of C, the
`
`capacitor is able to store more charge given the same potential difference applied
`
`across the plates.
`
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`Case IPR2013-00568
`Declaration of Joshua R. Smith
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`26.
`
`The capacitance C varies as a function of the overlapping area A of
`
`the conductive plates, the distance d between the plates, and the electrical
`
`properties of the insulating material between the plates, represented by the
`
`dielectric constantߝ଴:
`
`As the area of overlap between the two conductive plates increases, the
`
`capacitance, or ability to store charge, also increases. As the distance between the
`
`plates increases, however, the capacitance decreases.
`
`27.
`
`To understand capacitive sensing, it is also important to understand
`
`the relationship between capacitance and current. If we assume that capacitance C
`
`is constant, then differentiating with respect to time both sides of the equation
`
`ܳ=ܥܸ results inௗொௗ௧=ܥௗ௏ௗ௧. The left-hand side of the equation,ௗொௗ௧, represents the
`
`change in charge with respect to time, which by definition is equal to current Ic
`
`flowing through the circuit and into the capacitor:
`
`10
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`Case IPR2013-00568
`Declaration of Joshua R. Smith
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`Looking at the above figure, it may be intuitive to think that current does not flow
`
`through the capacitor given that its two plates are separated by an insulator. But
`
`this raises the following question: How does current Ic continue to flow through
`
`the remainder of the circuit? The answer is that as current Ic from the voltage
`
`source flows into upper conductor plate, it results in charge Q+ accumulating on
`
`the plate. As the charge accumulates, it causes an electric field to propagate from
`
`the upper plate to the lower plate, represented by the downward arrows in the
`
`figure above. The electric field results in a charge Q- accumulating (or, more
`
`physically, depletion of charge Q+) on the lower plate, and as this charge
`
`accumulates (or depletes, depending on sign conventions), it induces a current to
`
`flow out of the lower plate.
`
`28.
`
`Thus, while no electrons actually flow between the capacitor plates,
`
`the presence of the electric field provides a fictitious “displacement current” Id that
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`Case IPR2013-00568
`Declaration of Joshua R. Smith
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`causes a current Ic to flow out of the capacitor, equal in value to the current Ic
`
`flowing into the capacitor:
`
`29.
`
`The “displacement current” is so called because Maxwell, seeking a
`
`mechanical explanation for electromagnetic phenomena, imagined that the current
`
`was caused by displacement of the Ether. We typically measure the displacement
`
`current as the time-varying current induced in one conductor plate by a time
`
`varying voltage applied to a second conductor plate, multiplied by the capacitance
`
`between the plates, orܫௗ=ܥௗ௏ௗ௧. Going back to our original equationܳ=ܥܸ, we
`can see the following relationships: ݀ܳ݀ݐ=ܥܸ݀݀ݐ
`ܫ஼=݀ܳ݀ݐ
`ܫௗ=ܥܸ݀݀ݐ
`ܫ஼=ܫௗ
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`Case IPR2013-00568
`Declaration of Joshua R. Smith
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`30.
`
`Thus, the current Ic flowing through the circuit wires and into (and out
`
`of the capacitor) is equal to the displacement current Id.
`
`31.
`
`In realistic everyday situations – and in particular in touch screen
`
`sensing – we do not have ideal parallel plate capacitors to measure. Nevertheless,
`
`a parallel plate capacitor can be a useful guide to the intuition in understanding the
`
`behavior of more complex geometries. For instance, in a touch panel with
`
`conductive electrodes, each electrode can be viewed as a “plate” in a capacitor.
`
`The opposing plate can be any number of references, including ground, another
`
`electrode, or a stylus or finger. The varying capacitive effects between each of
`
`these “plates” can be measured and compared to detect a position of touch.
`
`32. Different forms of capacitive touch panels measure capacitance (and
`
`changes in capacitance) to detect touch locations in different ways. In surface
`
`capacitive touch panels, the introduction of a finger disrupts the ground
`
`capacitance of a conductive coating covering the entire surface of the panel. The
`
`presence of the finger causes current to flow across the surface toward the contact
`
`point, the location of which is sensed by measuring the changes in voltage at the
`
`four corners of the screen. In projected capacitive touch panels, the introduction
`
`of a finger generates capacitive effects in one or more discrete electrodes
`
`distributed across the panel. These effects are measured to determine the location
`
`of the affected electrodes, and therefore the position of the touch.
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`Case IPR2013-00568
`Declaration of Joshua R. Smith
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`33.
`
`There are two types of projected capacitive touch panels—those that
`
`measure self-capacitance (the capacitance between an electrode and ground), and
`
`those that measure mutual capacitance (the capacitance between two discrete
`
`electrodes). The ’902 Patent discloses a mutual-capacitance based projected
`
`capacitive touch panel. In the following section, I will describe the operation of
`
`both forms of projected capacitive touch panels, and the design considerations
`
`specific to each form.
`
`B.
`
`Self-Capacitance-Based Touch Panels
`
`1. Measuring Self-Capacitance
`Self-capacitance –based touch sensors measure the change of
`
`34.
`
`capacitance between a single conductor electrode and ground. Given a time-
`
`varying voltage source, every electrode has a baseline, or steady-state (no touch)
`
`capacitance Cs to ground, as shown below:
`
`(Ex. 2004 (Walker, Fundamentals of Projected-Capacitive Touch Technology
`
`(2014) at 10 (modified).) If a time-varying voltage is applied to the capacitor, then
`
`the capacitance has an associated current, is traveling through the electrode to
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`Case IPR2013-00568
`Declaration of Joshua R. Smith
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`ground. This current can be calculated as the current traveling into the capacitor Ic,
`
`or the displacement current Id, both of which are discussed above. To measure
`
`steady-state self-capacitance within a sensor, we connect a sensing circuit to each
`
`individual electrode and measure the electrode’s current to ground.
`
`35. When a user touches the self-capacitance sensor, he creates an
`
`additional path to ground, thereby increasing the total capacitance between the
`
`electrode and ground by an amount CH. This also increases the current traveling
`
`through the electrode to ground by an amount iH:
`
`(Id.)
`
`36.
`
`The self-capacitance sensing circuit measures the increase in current
`
`traveling through the electrode, and thus the increase in capacitance between the
`
`electrode and ground, and determines that a user has touched the conductor.
`
`37.
`
`To summarize, self-capacitance can be measured by applying a time
`
`varying voltage signal to an electrode and measuring how much current flows into
`
`that electrode, and thus, indirectly, how much flows out of that electrode to ground.
`
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`Case IPR2013-00568
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`
`Detecting a Touch Position by Measuring Self-Capacitance
`2.
`Commercial touch panels that utilize the principle of self-capacitance
`
`38.
`
`typically comprise an X-Y array of conductor electrodes as shown below:
`
`(Ex. 2001 (Barrett & Omote, Projected-Capacitive Touch Technology (2010) at 17
`
`(modified).) In operation, each conductor X0-X3 and Y0-Y3 is connected to a time-
`
`varying voltage source that generates the steady state current through the
`
`conductor. The conductors are also connected to X-side and Y-side scanning
`
`circuits that cycle sequentially through each conductor, measuring that conductor’s
`
`current-to-ground.
`
`39. When a user touches the surface of the structure at the intersection of
`
`X2 and Y0, as indicated by the green check mark in the figure above, the X-side
`
`scanning circuit will detect an increase in current to ground for the X2 conductor,
`
`and the Y-side scanning circuit will detect an increase in current to ground for the
`
`Y0 conductor. The scanning circuits will report these X and Y measurements to a
`
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`Case IPR2013-00568
`Declaration of Joshua R. Smith
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`controller programmed with software to interpret the measurements as a location of
`
`touch.
`
`40.
`
`In an ideal system, the current sensed on one conductor, which we
`
`refer to as the “signal,” is due only to the voltage applied to that conductor. In
`
`reality, this is not the case because unwanted capacitive coupling, or parasitic
`
`capacitance, between conductors induces additional, unwanted current in the
`
`sensor. The unwanted current is referred to as “noise,” and this noise interferes
`
`with and therefore degrades the signal we are trying to measure. We often
`
`characterize a capacitive touch sensor’s effectiveness by its signal-to-noise ratio
`
`(“SNR”).
`
`41.
`
`To achieve a desired high SNR in any capacitive touch sensor, the
`
`sensor should seek to minimize the potential for parasitic capacitance. In the case
`
`of a self-capacitance system, any capacitance between conductors is considered
`
`parasitic capacitance and presents the potential to degrade the system’s SNR.
`
`3.
`
`Drawbacks of Self-Capacitance Systems Available at the
`Time of the ’902 Invention
`
`42.
`
`From the discussion above, we can see a number of disadvantages of
`
`self-capacitance touch sensors.
`
`43.
`
`First, because the conductors in a self-capacitance system operate
`
`independently of each other, each conductor requires both a drive circuit (to apply
`
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`Case IPR2013-00568
`Declaration of Joshua R. Smith
`
`a voltage to the conductor) and a sense circuit (to measure the resulting current in
`
`the conductor). Because the sense circuitry is typically connected to a large drive
`
`signal, it may in some cases be difficult to take sensitive measurements.
`
`44. Another well-known shortcoming of self-capacitance systems is that
`
`they do not perform reliably when two touches occur simultaneously. In the
`
`terminology of today’s capacitive touch sensing, a self-capacitance system is
`
`incapable of reliably interpreting "multi-touch," in which, for example, a finger and
`
`thumb might be used simultaneously to generate a pinch gesture.
`
`45.
`
`The figure below helps explain this shortcoming:
`
`Y7
`
`Y18
`
`F1
`
`X9
`
`F2
`
`X20
`
`Suppose that there are actually fingers at locations F1 and F2. These finger
`
`locations correspond to coordinate pairs (X=9, Y=7) and (X=20,Y=18). Because
`
`of finger F1, the row sensor labeled Y7 will detect an object when it is
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`interrogated. Similarly, row sensor Y18 will also detect an object. Similarly, X9
`
`and X20 will detect objects. Unfortunately, with self-capacitance based sensing,
`
`there is no way to reliably associate any given X measurement with the correct Y
`
`measurement. The “ghost” finger configuration (illustrated in the figure with
`
`dotted circles) gives the exact same sensor readings as the true finger configuration
`
`(illustrated with solid circles labeled F1 and F2).
`
`C. Mutual Capacitance-Based Touch Panels
`
`1. Measuring Mutual Capacitance
`46. Unlike self-capacitance, mutual capacitance does not refer to the
`
`capacitance between a single electrode and ground—instead, as its name implies,
`
`mutual capacitance is formed between two electrodes, typically at their
`
`intersection.
`
`47.
`
`This principle is illustrated in U.S. Patent No. 7,920,129 (Ex. 2005),
`
`assigned to Apple Inc. and filed in January 2007. Figure 3 of Exhibit 2005 shows
`
`a two-layer sensor layout with column traces 304 and row traces 306 formed on
`
`opposite sides of a substrates 310. Figure 2a illustrates that a steady-state
`
`capacitance Csig exists at the intersection of each row trace and each column trace.
`
`Accordingly, when a time-varying voltage is applied to a row trace, the steady-
`
`state capacitance Csig at each intersection induces a current in each corresponding
`
`column trace.
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`(Ex. 2005 at Figs. 3 and 2a (modified).)
`
`48.
`
`Figure 2b shows the steady-state capacitance Csig at the intersection of
`
`a row trace 204 and a column trace 206 (seen head-on) in greater detail.
`
`As shown, the steady-state capacitance Csig is a function of the electric field
`
`generated at the intersection of the traces, represented by electric field lines 208.
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`49.
`
`Figure 2c illustrates the capacitive effect of a user touching the sensor
`
`near an intersection.
`
`The user’s finger draws away some of the electric field between the row and
`
`column traces, reducing the capacitance Csig. From Exhibit 2005, therefore, we can
`
`see that a user’s touch in a mutual capacitance system causes a decrease from the
`
`steady-state capacitance between two conductors, as opposed to a self capacitance
`
`system where we detect an increase over the steady-state self-capacitance between
`
`a conductor and ground.
`
`2.
`
`Detecting a Touch Position by Measuring Mutual
`Capacitance
`
`50. Mutual capacitance can be used to detect a touch position in a number
`
`of ways.
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`51.
`
`In one method, a driving circuit applies a time-varying voltage to an X
`
`electrode (indicated by a green arrow in the figure above), then scans each Y
`
`electrode to measure the current due to the mutual capacitance at each intersection
`
`between the charged X electrode and a Y electrode (indicated by a red arrow).
`
`52. When a user touches the surface of the structure at the intersection of
`
`X2 and Y0, as indicated by the green check mark in the figure above, the user’s
`
`finger will reduce the mutual capacitance at the intersection of the X2 and Y0
`
`electrodes. Accordingly, when the X2 electrode is driven, a scanning circuit will
`
`detect that the current flowing through Y0 is lower than then the current of other
`
`electrodes in the Y direction. This allows a sensing circuit to identify a touch at
`
`this intersection.
`
`53.
`
`The method described above differs from self-capacitance touch
`
`panels, where each X conductor and each Y conductor is driven independently and
`
`scanned independently. This arises from the need to measure self-capacitance
`
`between each conductor and ground. By contrast, a mutual capacitance sensor
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`measures capacitance between two conductors by applying a time-varying voltage
`
`signal to one conductor, and sensing the current induced on the other conductor.
`
`Accordingly, in mutual-capacitance systems, one set of conductors is often referred
`
`to as “driving,” while the other set is referred to as “sensing.”
`
`54.
`
`By sensing with pairs of electrodes, a mutual-capacitance-based
`
`system has the ability to provide more information than a self-capacitance system.
`
`Given N row electrodes and M column electrodes, a mutual capacitance-based
`
`system can provide on the order ofܰ×ܯ data points (i.e., one point for each
`intersection), while a self-capacitance system provides only on the order ofܰ+ܯ
`
`data points (i.e., one point for each conductor). By effectively measuring
`
`capacitance at each intersection of conductors, a mutual-capacitance-based touch
`
`panel that uses this sensing methodology can solve the problem of “ghost points”
`
`and allow the system to correctly identify the locations of multiple simultaneous
`
`touches.
`
`55.
`
`To achieve the desired capacitive effects, the standard mutual-
`
`capacitance touch panels that were available at the time of the ’902 Patent relied on
`
`a two-layer structure as shown in Figure 3 of the ’129 patent above. As discussed
`
`below, several design considerations differentiate these panels from those that
`
`measured self-capacitance.
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`3.
`
`Conductor Layout in Self-Capacitance and Mutual
`Capacitance Systems
`
`56.
`
`To maximize performance, a designer of a projected capacitive touch
`
`system must carefully balance a number of interrelated considerations, including,
`
`inter alia:
`
`
`
`
`
`
`
`
`
`
`
`the steady-state or baseline capacitance of or between the conductor
`elements which are used to sense a touch position;
`
`the “contrast” capacitance, or the ability of a finger or other object to
`affect the baseline capacitance;
`
`the parasitic capacitance, or the level of “noise” attributable to
`undesired capacitive effects within the structure;
`
`the resolution and speed of the sensing structure, and
`
`the visual appearance of the sensor, including size, weight and
`transparency.
`
`57.
`
`These considerations are different in the self-capacitance and mutual-
`
`capacitance contexts. While the electrode arrays in self- and mutual-capacitance
`
`systems may hypothetically contain superficial similarities, the dynamics of the
`
`electric fields would look different depending on the type of capacitive sensing
`
`used. Accordingly, the properties that one optimizes to achieve the best
`
`performance will vary depending on whether the system relies on self-capacitance
`
`or mutual capacitance to detect a position of touch.
`
`58.
`
`Self-capacitance touch pa