United States Patent [191
`Evans
`
`[11] Patent Number:
`[45] Date of Patent:
`
`4,806,709
`Feb. 21, 1989
`
`[54] METHOD OF AND APPARATUS FOR
`SENSING THE LOCATION, SUCH AS
`COORDINATES, OF DESIGNATED POINTS
`ON AN ELECTRICALLY SENSITIVE
`TOUCH-SCREEN SURFACE
`[75] Inventor:
`Blair Evans, Idlewild, Mich.
`[73] Assignee: Microtouch Systems, Inc., Woburn,
`Mass.
`[21] Appl. No.: 53,849
`[22] Filed:
`May 26, 1987
`
`[51] Int. Cl.4 ............................................ .. G08C 21/00
`[52] US. Cl. .................................................... .. 178/19
`[58] Field of Search .................. .. 178/ 18, 19; 340/706,
`340/712
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`Development System Operators Manual”, Newton
`ville, Mass., May 1983.
`Sierracin/Intrex Products, “Transparent Electrically
`Conductive Film”.
`Sierracin/Intrex Products, “TransFlexzUnique Con
`cepts in Membrane Switches, EMI Shielding and LCD
`Heaters”.
`Sun-Flex Co., Inc. “Touchpen On-Screen Digitizer”,
`Novato, Calif.
`
`Primary Examiner-Stafford D. Schreyer
`Attorney, Agent, or Firm-Rines and Rines; Shapiro and
`Shapiro
`
`ABSTRACT
`[57]
`A method and apparatus are disclosed for determining
`the location of a designated point on an electrically
`sensitive touch-screen surface while minimizing aberra
`tions introduced by non-uniformity in the ?eld applied
`to the surface, by attaching a plurality of ?eld-produc
`ing discrete point electrodes to widely spaced points on
`the surface in a predetermined geometric pattern and by
`measuring the currents drawn from the point electrodes
`upon the capacitive touching of a designated location
`on the surface.
`
`
`
`4,198,539 4/1980 Pepper, Jr. 4,220,815 9/1980 Gibson et a1. .... ..
`
`3,911,215 10/1975 Hurst et al. ......................... .. 178/18
`178/18
`178/18
`307/116
`
`4,233,522 11/1980 Grummer et a1. .
`4,293,734 10/1981 Pepper, Jr.
`..... .. 178/18
`4,353,552 10/1982 Pepper, Jr. .
`273/85
`4,371,746 2/ 1983 Pepper, Jr. . . . . .
`. . . . . .. 178/18
`4,680,429 7/1987 Murdock et a1. ................... .. 178/19
`
`OTHER PUBLICATIONS
`Interaction Systems, Inc., “The TK-lOOO CRT Touch
`
`36 Claims, 2 Drawing Sheets
`
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`
`Exhibit 2019 - Page 1 of 9
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`

`
`US. Patent Feb. 21, 1989
`
`‘Sheet 1 of2
`
`4,806,709
`
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`Exhibit 2019 - Page 2 of 9
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`

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`U.S. Patent
`
`Feb. 21, 1989
`
`Sheet 2 0f2
`
`4,806,709
`
`Exhibit 2019 - Page 3 of 9
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`Exhibit 2019 - Page 3 of 9
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`

`
`1
`
`METHOD OF AND APPARATUS FOR SENSING
`THE LOCATION, SUCH AS COORDINATES, OF
`DESIGNATED POINTS ON AN ELECI‘RICALLY
`SENSITIVE TOUCH-SCREEN SURFACE
`
`5
`
`10
`
`25
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`4,806,709
`2
`(ISI), 24 Munroe Street, Newtonville, Mass, as de
`scribed in their May, 1983, publication entitled “The
`TK-lOOO CRT Touch Development System Operators
`Manual”. This screen sensor has four linear bar elec
`trodes, each extending approximately the entire length
`of one of the four sides of the rectangular screen sensor
`surface. Although solving the screen transparency
`problem inherent in previously mentioned circular elec
`trodes, certain dif?culties are inherent in the linear bar
`type of screen sensor. The vertical pair of opposing
`electrodes, if used in the absence of a horizontal pair,
`creates a regular horizontal electric ?eld across the
`surface, enabling the touching of a point of the ?eld to
`establish the exact distance from each vertical bar with
`simple computations, and therefore providing high res
`olution horizontal location sensing on the surface. The
`use of a second set of horizontally oriented linear elec
`trodes, however, at the top and the bottom of the
`screen, creates a non-orthogonal electrical distortion in
`the horizontal electrical ?eld in the regions along the
`horizontal bar electrodes, causing sensing aberrations
`due to the lack of a regular ?eld near the electrodes.
`Such distortion, producing sensing aberration, usually is
`more severe at the corners where the orthogonal bar
`electrodes reach closest proximity to each other. Pre- or
`post-distortion circuiting is used to try to reduce the
`effects of tis aberration, but at additional complexity
`and not to the degree desired.
`Modi?cation of the solid bar electrode con?guration
`has been proposed, including segmenting the bar elec
`trodes into a plurality of successive sections along each
`edge of a surface, such as in the TransFlex TM screen
`produced by Sierracin/Intrax Products, 20500 Plum
`mer Street, Chatsworth, Calif. 91311, and shown in
`their publications “Transparent Electrically Conduc
`tive Film” and “TransFlex TM Unique Concepts in
`Membrane Switches, EMI Shielding and LCD Heat
`ers”, and also in U.S. Pat. Nos. 4,293,734, 4,353,552 and
`4,371,746. Such use of multiple closely spaced linearly
`arranged successive electrode sections is, however,
`subject to the same above-described attendant aberra
`tion disfunctions as the solid bar electrodes.
`Curved bar electrode con?gurations have also been
`suggested which may also be used in conjunction with
`curvilinear patterns of successive electrode sections as
`described, for example, in U.S. Pat. No. 4,198,539. The
`curved bar electrode system, however, is also subject to
`the ?eld distortion and resulting sensing aberration near
`the electrodes, including particularly the lack of corner
`resolution, as described for the linear bar electrodes.
`The present invention obviates the above-described
`limitations and disadvantages of prior touch screens.
`The invention reduces the electrodes to just widely
`separated “points” or very small discrete regions and
`enables the use of a minimal number of such point elec
`trodes at that. The widely spaced point or discrete elec
`trodes are coupled to a uniform resistive surface, with
`each point electrode of suf?ciently small surface area
`and located at such a remote distance from the other
`point electrodes, that a regular electric ?eld may be
`produced over the complete screen surface, minimizing
`any possible ?eld distortions produced by the electrodes
`thereon. Speci?cally, in a preferred or best mode, four
`point electrodes are employed, one at each corner or
`edge of the screen sensor surface, with each point elec
`trode thus as far from any other point electrode as is
`physically possible. Multiple overlapping or partially
`overlapping geometric patterns of comer-located point
`
`40
`
`The present invention relates to methods of and appa
`ratus for sensing the location, such as coordinates, of
`designated points on an electrically sensitive touch
`screen surface, such as capacitive touch-screen sensors
`and the like, being more particularly directed to reduc
`ing aberrations in linearity in the electrical sensing of
`locations over a large touch-screen surface, and to re
`ducing cost of sensor manufacture.
`Prior techniques for sensing discrete location on an
`electrically sensitive touch-screen surface include both
`resistive and capacitive methods. Resistive sensors gen
`erally have two surfaces, as of plastic and glass, at least
`one of which is deformable towards the other, with
`uniform or uniformly patterned coatings of a resistive
`material sandwiched therebetween. When pressure is
`applied to the ?exible surface at a point, as by a stylus or
`?nger, it deforms towards the opposing surface estab
`lishing contact between the opposing surfaces and
`thereby allowing sensing of the point of pressure. Such
`resistive sensors are described, for example in U.S. Pat.
`Nos. 3,911,215 and 4,220,815.
`One disadvantage of the resistive screen sensor is the
`high cost of construction of the complex sandwich.
`Additional disadvantages include diminishing optical
`clarity when applied over a display device, such as a
`cathode ray tube. Finally, the durability of the resistive
`sensor is less than ideal in view of the susceptibility of
`the screen to cutting or scratching as with the nail of a
`?nger or a sharp stylus, andbecause of fatigue problems
`in deformation.
`Capacitive screens, on the other hand, generally mini
`mize or ameliorate some of the aforementioned disad
`vantages of resistive screens. Such capacitive screen
`sensors usually require a single surface, such as glass,
`cloth or plastic, with a uniform resistive material coated
`or fused to one face of the surface, with the ?nger or a
`stylus establishing capacitive sensing when applied to
`the surface. Multiple electrodes are attached to the
`resistive material to render the screen electrically oper
`ative. Capacitive ?nger or stylus presence perturbs the
`electric ?eld produced in the resistive material by the
`electrodes, enabling sensing so as to determine the posi
`tion of the ?nger or stylus on the screen sensor. Among
`the numerous capacitive screen sensors that have been
`proposed is the arrangement described in U.S. Pat. No.
`4,233,522, for example, which includes an array of
`touch-sensitive electrode switch cells, such as circular
`electrodes located on the screen surface. Touching the
`surface causes distortion of the electric ?eld in the prox
`imity of the nearest electrode, such distortion being
`greater than that near the other electrodes, thereby
`designating the nearest electrode as the area of the point
`of touching. Such a system inherently discretely divides
`the surface of the screen sensor into areas at least as
`large as the electrodes, preventing use for ?ne resolu
`tion. To obtain reasonable resolution, therefore, a large
`number of electrodes is needed, adding cost and com
`plexity. Finally using electrodes on the sensing face of
`the screen sensor reduces the viewing clarity for under
`65
`lying display screens.
`Another type of electrode con?guration for a capaci
`tive screen sensor is that of Interaction Systems, Inc.
`
`45
`
`60
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`Exhibit 2019 - Page 4 of 9
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`q
`3
`electrodes can, if desired, be used to achieve optimum
`resolution near any particular area of the sensor, as will
`later be described in more detail. Additional point elec
`trodes may also be placed for special effects along the
`side edges of the geometric patterns. The point elec
`trodes, moreover, need not be located exclusively at
`edge or corner locations with respect to the sensor
`surface, but may be arranged in any geometric shape
`which maintains symmetry with the sensor shape, suf?
`cient to produce a regular ?eld over the entire sensor
`surface. Preferably a regular geometric shape using at
`least three discrete electrodes may be used to provide
`optimum location sensing with a minimum of distortion
`over the entire sensing surface. Additional discrete
`point electrodes may be used to provide greater resolu
`tion of sensing, especially in the area near one of the
`discrete electrodes where some measurement ambiguity
`may occur. Such ?exibility in electrode placement pro
`vides a substantial advantage over previous capacitive
`touch-screen sensors in that the previous touch-screen
`sensors limited the sensing area to within the area
`bounded by the ?eld-producing electrodes. The present
`invention does not require such limitation. Since a regu
`lar ?eld is produced over the entire surface area of the
`screen sensor, and the discrete electrodes are not used
`to bound the regular ?eld, due to the minimal ?eld
`distortion around the discrete electrodes, location sens
`ing can be successfully accomplished both within and
`without the area bounded by the discrete electrodes.
`Additionally, the sensing apparatus of the invention
`compares the draw of alternating ?eld current from
`each of the point electrodes, thus providing a wide
`dynamic range of capacitance that can be effectively
`sensed. This will also permit the use of dielectric mate
`rial separating the uniform resistive coating on the
`screen sensor surface from the stylus or ?nger used to
`designate a desired point or location on the surface
`without signi?cant loss of resolution or sensitivity.
`It is accordingly an object of the present invention to
`provide a new and improved method of and apparatus
`for touch-screen sensing, providing reduction in aberra
`tion produced in the sensing of discrete locations on the
`screen surface, and that shall not be subject to the
`above-mentioned prior art limitations, but that, to the
`contrary, provide a simple, durable and inexpensive
`means for accurately sensing the discrete location of
`indicated points on the sensing surface.
`A further object is to provide such a novel method
`and apparatus that have suf?cient clarity and transpar
`ency of screen sensor surface to provide clear viewing
`through the screen sensor when mounted over a display
`surface.
`A further object is to provide a novel method of and
`apparatus for capacitively sensing the location of a
`designated point on a sensor surface both inside and
`outside of the area bounded by the ?eld-producing
`electrodes, where desired.
`A still further object is to provide a novel method of
`and apparatus for providing an improved degree of
`sensing resolution in a capacitive touch-screen sensor.
`An additional object is to provide a novel capacitive
`touch-screen sensor that is useful over a wide range of
`capacitance, automatically compensating for variations
`in touch impedance, and useful with intervening mate
`rial between the sensor surface and the stylus, if desired,
`to designate location on the surface-all without sub
`stantial loss in resolution or sensitivity.
`
`4,806,709
`4
`Other and further objects will be explained hereinaf
`ter and are more particularly delineated in the appended
`claims.
`In summary, however, from one of its important
`aspects, the invention embraces a method of reducing
`the aberrations produced by irregular electric ?elds
`produced on touch-sensing surfaces and the like, that
`comprises, applying a plurality of discrete point elec
`trodes to widely separated points of the surface in a
`predetermined geometric pattern, driving the point
`electrodes with a common alternating-current voltage
`to generate a regular electric ?eld over the surface, and
`simultaneously measuring the currents drawn through
`the point electrodes upon the capacitive touching of a
`designated point on the surface to locate such desig
`nated point. Preferred details, best mode embodiments
`and other features are hereinafter described.
`The invention will now be described with reference
`to the accompanying drawings:
`FIG. 1 of which is a schematic block diagram of an
`illustrative type of capacitive touch-screen sensor
`showing a four and eight electrode con?guration and
`position sensing between the electrodes;
`FIG. 2 is a longitudinal section of a capacitive touch
`screen sensor partially covered by an intervening dis—
`play material;
`FIG. 3 is a schematic diagram of the discrete elec
`trode drivers of the four-electrode con?guration illus
`trated in FIG. 1; and
`FIG. 4 is a three-electrode con?guration, similar to
`FIG. 1, showing position sensing beyond the bound
`aries bordered by the electrodes.
`Referring to FIG. 1, a capacitive touch-screen sensor,
`generally designated 1, is provided with a screen 2
`shown in longitudinal section in FIG. 2. The screen 2 is
`preferably made of a rigid transparent material, such as
`a plastic or glass sheet 3, FIG. 2, with a uniform coating
`of resistive material 4, such as a coating of Indium Tin
`Oxide (ITO), fused to the screen 2, of a suf?ciently
`minimal thickness to provide transparent clarity
`through the coating 4. The coating 4 may be on either
`side of the sheet 3 but is preferably placed on the front
`(bottom surface of the sheet 3 in FIG. 2) to provide for
`maximum sensitivity to touch. The screen 2 may also be
`adapted with a partial or complete cover sheet 5, which
`can be made of dielectric material, such cover sheet 5
`permitting ?xed visual information on the screen 2 dur
`ing use. Preferably, the cover sheet 5 is substantially
`transparent to allow viewing through both the cover
`sheet and the screen 2, and the cover sheet 5 is suf?
`ciently thin to permit electrical capacitive touching
`contact between a stylus S, such as a ?nger, and the
`screen 2, as shown in FIG. 1.
`Fixed in electrical contact to the resistive material
`coating 4 are a plurality of discrete electrodes E of
`predetermined size. The electrodes E should be of a
`suf?ciently small size so as to minimize the area on the
`surface of screen 2 which is in close proximity to the
`electrodes and therefore subject to distortion, while
`being of suf?ciently large size to minimize contact resis
`tance with the coating 4. It has been found that a circu
`lar dot or “point” electrode with a diameter of between
`0.031 and 0.250 inches is acceptable with a preference
`for a point electrode of 0.125 inches in cross-dimension
`or diameter. As the electrical distortion produced by
`the presence of the electrode exists substantially for
`only a few cross-sections or diameters from the elec
`trode, such discrete point electrodes widely separated
`
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`Exhibit 2019 - Page 5 of 9
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`10
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`4,806,709
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`6
`in effect an operational ampli?er (op.amp.) A1—A4 with
`from each other-that is much more than a few diame
`ters away on the surface—provide for a substantially
`some respective impedance Z1-Z4, such as provided by
`distortion-free electrical ?eld over the surface of the
`matched resistors on its output terminal, and a feedback
`arrangement. The feedback arrangement maintains the
`screen 2.
`Each point electrode E is provided with an electri
`voltage driving the electrodes E1—E4. The difference
`cally conductive wire W, the wires being connected to
`between the voltages at the output of the op.amps.
`a driver circuit for providing an electrical signal to each
`A1—A4, designated as respective voltages Vol-V04, and
`point electrode E which produces a regular electric
`the input voltage V, is the same as the voltage across the
`corresponding impedances Z1-Z4, giving an indication
`?eld on the coating 4 of the screen 2 of the touch-screen
`sensor 1. More specifically, and in reference to FIG. 1,
`of the current drawn by each electrode E1-E4. That
`the screen 2 is provided with a ?rst set of four point
`voltage Vol-V04 is passed to the gain control block 9
`electrodes E1-E4, each connected by a conductive wire
`and shown in FIG. 1.
`The quantity of interest for determination of location
`W1-W4 to a driver circuit or series of drivers 6, as will
`be discussed in more detail in reference to FIG. 3. The
`is the voltage V": V,,-V,, where V0,, represents the
`four point electrodes E1—E4 are positioned near the four
`voltages Vol-V04, and V, is the reference voltage al
`ready discussed. Additionally, Vn=K l/Rn' where
`corners of the square screen 2, having a regular square
`geometric form, and are widely separated from one
`Rn=f(D,,) with R” being the impedance between the
`electrode En and the touch point P; D", the distance
`‘ another. The screen 2 is also provided with a second set
`of four discrete widely separated point electrodes
`from electrode E” to the touch point P; K, a proportion
`E5-E3 each connected by a respective wire W5-W8 to a
`ality factor that, although variable, is common to all
`outputs; and f(D,,) referring to a simple function of the
`driver circuit in a manner similar to wires W1-W4, and
`also connected to drivers 6 as will be explained in more
`touch screen, such as an x, y coordinate axis function.
`detail hereinafter.
`Therefore, the voltage V" is proportional to the recipro
`Referring again to FIG. 1, the drivers 6 are electri
`cal of the resistance between the electrode En and the
`cally connected by four output wires W1-W4 to the
`touch point P. Since the proportionality constant is
`determined by the impedances Z1-Z4, the impedances
`respective point electrodes Er-E4 on the screen 2, as
`noted above, for driving the screen 2 to produce a regu
`Z1-Z4 and therefore the corresponding drivers 6 must
`lar electric ?eld over the screen 2, and four output wires
`be matched, and the quality of the coupling between the
`which drive the sensor measurement circuitry of the
`screen 2 and ground must be equal for each of the driv
`touch-screen sensor 1. More speci?cally, the drivers 6
`ers 6 since they have a common touch point P on the
`are provided with an AC voltage V, from an AC source
`screen 2. The voltage measured for each electrode
`7. The AC source 7 is electrically connected to the
`E1—E4, therefore, is proportional to the reciprocal of the
`drivers 6, a ground 8 and a gain control circuit 9. The
`total impedance, and the impedance is a simple function
`AC source 7 provides to the drivers 6 a high frequency
`of the distance from each electrode E1-E4 to the touch
`point P.
`sine wave of approximately lO-SO kilohertz and the
`drivers 6, in turn, drive each electrode E1—E4 on the
`To provide for a wide dynamic range of touch capac
`screen 2 to a constant amplitude sine wave. The drivers
`itance that can be used to determine location of a desig
`6 also provide a mechanism for measuring the current
`nated point P on the screen 2, the gain control block 9
`drawn through the electrodes E1-E4, so if all the elec
`maintains the largest of the measured voltages to within
`trodes E1-E4 are driven at the same voltage, the output
`a predetermined percentage of the full scale signal for
`from each of the drivers will be the different currents
`the AC to DC converter 10. This allows the capacitive
`that correspond to the voltages of the electrodes E1—E4.
`touching, for sensing between the screen 2 and ground
`These current-draw signals go to two paths. One path is
`to the ?nger or other stylus S, to vary by at least three
`a gain control block 9 which takes those four measure
`orders of magnitude. More speci?cally, if a ?nger of a
`ment signals, feeds them back through any conventional
`human hand is used as the stylus S, because of the vari
`computational circuit (which is shown as part of gain
`ables including the size of the person, moisture content
`control block 9) which causes the reference voltage
`of the skin and quality of the touching between the
`supplied from the AC source 7 to increase or decrease
`touch screen 2 and ground to the ?nger, the touch ca
`in magnitude sufficient to keep the four point electrode
`pacitance is very variable. Also, the ?nger (stylus) may
`inject voltage into the screen 2 causing signal distortion.
`currents within some predetermined range. In the sec
`ond path, the signals are transferred to an analog-to
`The simultaneous reading and driving of the electrodes
`digital (AC/DC) converter block 10 which takes the
`removes the sensing difficulties inherent in such prob
`lO-5O kHz sine wave, converts it to a DC voltage corre
`lems and also minimizes extraneous electronic noise on
`sponding to its amplitude and from there through a
`the system, since only electrical comparisons between
`computational circuit and an analog-to-digital con
`electrode signals are made, and such common noise will
`verter (ADC) 11 and to a microcomputer 12 to compute
`be minimized. To limit the range of AC-to-DC conver
`and determine actual coordinates of a point P desig
`sion, a voltage sum technique is therefore used.
`nated by capacitive touching of the stylus S on the
`Under such a technique, the voltages V0,, are summed
`screen 2. Coordinates are obtained by measuring the
`and kept within a preselected range. Since the voltages
`signals representing current drawn through each elec
`V0,, are proportional to shared currents, as described
`trode E1—E4, such signals being directly dependent
`previously, the maximum differences would be one, if
`upon the distance from each electrode E1-E4 to the
`an electrode E were being touched (one current would
`capacitively touched point P, in a manner later de
`be maximum, while the others are zero). The opposite
`scribed in more detail.
`case would be the center point of screen 2, equidistant
`Referring now to FIG. 3, which is a schematic dia
`from all electrodes E1-E4. It is important to note that
`gram of the drivers 6, such are provided with a refer
`only the differences and ratios thereof between the
`'ence voltage V, supplied from the AC source 7, as
`different currents drawn through the electrodes E1-E4
`shown in FIG. 1. Each driver in this implementation is
`is utilized. The actual magnitude of the currents is not of
`
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`Exhibit 2019 - Page 6 of 9
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`4,806,709
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`tion. For example, if the designated point P were near a
`importance in determining point P location. Thus a
`measurement ambiguity, the other three electrodes
`wide dynamic range of electrical characteristics, specif
`ically capacitance, can be sensed and the system will
`E1-E3 are suf?cient accurately to determine the loca
`automatically compensate for variations in touch impe
`tion of point P. However, the additional pattern of
`dance. By using a gain control circuit, such automatic
`electrodes E5-Eg provides a high resolution check, as
`compensation may actually be accomplished before the
`none of the electrodes E5-E3 is close enough to point P
`current drawn through the electrodes E1-E4 is mea
`to provide resolution distortion. Therefore, in this
`sured.
`method of operation, the drivers 6 would alternately
`Referring now to FIG. 4, a screen 2 is shown with a
`drive each pattern of electrodes E1—E4 and E5-Eg to
`three-electrode E9-E11 con?guration, being the mini
`provide high resolution, low error sensing of point P.
`mum number of electrodes for sensing two-dimensional
`The second mode of operation provides that all eight
`coordinates on the surface of screen 2, forming the
`electrodes be driven simultaneously, which would re
`corner boundaries of a triangular geometric pattern.
`quire another set of drivers (not shown), similar to driv
`Each electrode E9-E11 is connected by a corresponding
`ers 6, to be connected to the electrodes E5-Eg. Since
`wire W9—W11 to drivers in a manner similar to that
`eight electrodes E1—E3 provide for a substantial number
`described for FIG. 1. FIG. 4 also has a designated point
`of Intersecting curvilinear segments, as previously de
`P, designated by capacitive touching with a stylus S,
`scribed, a high degree of resolution of sensing is pro
`such as a finger, to the designated point P on the screen
`vided.
`2.
`Other modes are contemplated such that any geomet
`As a graphical example of how location of a desig
`ric pattern bounded by three or more electrodes B may
`nated point P is sensed, and in reference to FIG. 4, a
`be driven simultaneously and may be driven alternately
`comparison or ratio of currents between the electrodes
`with any other pattern of three or more electrodes E.
`is established. Speci?cally, there is a locus of points, at
`Such geometric patterns of electrodes E may be regular
`least partially on the screen 2, that when capacitively
`or irregular, overlapping or not overlapping, and in
`touched will produce the same ratio of current drawn
`25
`each case such a pattern of point electrodes will locate
`through any two speci?c electrodes E. As an example,
`a designated point P, whether within or without such
`the locus of points having a single current draw ratio
`geometric patterns, on the screen surface 2. Care should
`between electrodes E9 and E10 has a curvilinear seg
`ment E9E10 that passes through the designated point P.
`be taken to minimize the number of electrodes E and
`widely separate them such that minimal inter-electrode
`In a similar manner, the ratios between electrodes E10
`and E11 and E9 and E11 have curvilinear segments E1
`distortion results.
`0E11 and E9E11, respectively, each constrained to pass
`Mathematically, the four electrode square con?gura
`through the designated point P. Each of the three curvi
`tion shown in FIG. 1 can also be de?ned. The sensor
`linear segments EgEw, E1OE11 and E9E11 share only one
`impedance Rn between the electrode En and the touch
`common point of intersection, that point being the des
`point P is a function of the distance D,, between the
`ignated point P. As shown, the designated point P may
`electrode E,, and the touch point P, R,,=f(D,,). Said
`be located, even outside of the triangular geometric
`function, f(D,,), is predetermined by sensor screen con
`pattern bounded by the electrodes E9—E11. Additional
`struction and the geometry of the electrodes E. The
`point electrodes E, not shown on FIG. 4, would pro
`voltages that come out of the drivers V", which has
`vide additional or redundant curvilinear segments and
`been previously de?ned as VQ,,-V,, are proportional to
`such additional electrodes would especially be useful
`the reciprocal of the sensor impedance Rn, V,,=K/Rn.
`when the designated point P is near an area of measure
`The distance D" may therefore be related to the driver
`ment ambiguity. In such a situation, the other elec
`voltage V": V,,=1/f(D,,) or Dn=f-1(1/V ,1). Since the
`trodes, not being subject to the same measurement am
`ratio between the distances from any two electrodes E
`biguity, would be used in the above-described manner
`is a measured value, the location f the designated point
`to resolve and locate the designated point P. Such an
`P becomes a basic distance formula on the distances D”.
`additional or redundant discrete electrode con?gura
`A, B, C and D are the square of the distances that are
`tion is shown in FIG. 1.
`represented by the voltages that come out of the driver
`FIG. 1, as before mentioned, shows a four-electrode
`6. Electrodes A to D: l/Vn2 where
`E1-E4 con?guration connected to drivers 6 and a sec
`ond four electrode E5-E8 con?guration connected to
`drivers. Such a system can be used in at least two
`modes. The ?rst provides two independent four elec
`trode E con?gurations that are alternately scanned; that
`is, the drivers 6 drive the electrodes E1—E4 and, after the
`location of point P is determined but before the desig
`nated point P has changed, the same drivers 6 would
`drive electrodes 135-133 in a partially overlapping inte
`rior surface arrangement. It should be noted that the
`point P is located within the square geometric pattern
`bounded by electrodes E1—E4 and outside of the square
`geometric pattern bounded by electrodes E5-E3. In
`both cases, whether inside or outside the square geo
`metric pattern bounded by the electrodes E1—E4 or
`E5-Eg, the designated point P can be sensed and located
`65
`by the capacitive touch-screen sensor 1. Using the two
`partially overlapping square geometric patterns pro
`vides for redundant error checking for enhanced resolu
`
`in reference to voltages for each of the electrodes E,
`where A is the voltage of E2, B is the voltage of E3, C
`is the voltage of E4 and D is the voltage E1.
`Therefore the distance from each of the four elec
`trodes E1—E4 to the designated touch point P, in terms
`of the four measurements de?ned above are:
`
`A = 1/1/12 c = 1/V32
`
`B = I/VZZ D = 1/V42
`
`40
`
`60
`
`Exhibit 2019 - Page 7 of 9
`
`

`
`4, 806,709
`
`:
`
`where K is the previously de?ned proportionality fac- 5
`tor and X and Y refer to coordinates on an x,y coordi
`nate axis planar surface. Since the sum of opposite diag
`onals of a rectangle are constant
`
`Now de?ne the quantities S and T as follows:
`
`so T=KS. Therefore,
`
`XiY
`
`and
`
`Also, L2+M2=P2; so P1T2-—2T+4=0. This, de?ning a
`quadratic equation, becomes;
`
`20
`
`25
`
`10
`1. A capacitive touch-screen sensor apparatus for
`providing high resolution sensing of a designated point
`on a touch-screen surface having, in combination:
`a rigid uniformly electrically conductive surface;
`a plurality of discrete point electrodes widely sepa
`rate from one another on the surface;
`alternating current driver means connected to the
`point electrodes for driving the electrodes with
`matched drive signals to produce a regular electric
`?eld over the surface;
`?rst circuit means for separately sensing the respec
`tive currents drawn through the point electrodes in
`response to the capacitive touching of a designated
`point on the surface and producing in accordance
`with each sensed current a signal representing the
`distance from the designated point to the corre
`sponding electrode; and
`second circuit means for determining from the dis
`tame