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`US005543590A
`
`5,543,590
`[1 11 Patent Number:
`[191
`Umted States Patent
`
`Gillespie et al.~
`[45] Date of Patent:
`Aug. 6, 1996
`
`[54] OBJECT POSITION DETECTOR WITH
`EDGE MOTION FEATURE
`
`5,194,862
`5,327,161
`
`3/1993 Edwards .................................... 341/20
`7/1994 Logan et a1.
`............................ 345/157
`
`[75]
`
`Inventors: David Gillespie, Palo Alto; Timothy P.
`Allen, Los Gatos; Robert J. Miller,
`Fremont; FEdBI‘iCO Faggin, L03 AltOS,
`all Of Calif.
`[73] Assignec: Synaptics, Incorporated, San Jose,
`Cal”
`
`Primary Examiner~Stephen Chin
`Assistant Examiner—Kevin Kim
`Attorney, Agent, or Finn~D’A1essandro & Ritchie
`
`[57]
`
`ABSTRACT
`
`881” 2’ 1994
`Related U.S. Application Data
`
`[21] Appl. No.: 300,630
`.
`'
`[221 Filed
`
`A proximity sensor system includes a sensor matrix array
`having a characteristic capacitance on horizontal and verti-
`cal conductors connected to sensor pads. The capacitance
`changes as a function of the proximity of an object or objects
`to the sensor matrix. The change in capacitance of each node
`in both the X and Y directions of the matrix due to the
`[63] Continuation-input of Ser. No. 300,387, Sep. 2, 1994,
`-
`-
`-
`which is a continuation-in-part of Ser. No, 115,743, Aug. 31,
`approach of an 9b] ect ls converted to a set 0f voltages m the
`1993, Pat. No. 5,374,787, which is a continuation-impart of
`X and Y directions. These voltages are processed by ctr-
`Ser. No. 395,934. Jun. 8' 1992, abandoned.
`ffifiii°ogfffl°£fiflffff ET]? fefifesf‘ffitjf‘ifiogefl‘;
`Int. c1.6 .............................. eosc 21/00; 0096 5/00
`[51}
`[52] US. Cl.
`................................ 178/18; 345/174; 341/33 M“ “.
`.p
`‘
`".
`" 4°." “"
`p‘mm’”
`‘
`.
`and Y d11nens1ons. Neise reduction and background level
`[58] Field of Search .......................... 178/18, 19; 341/33,
`.
`.
`.
`.
`.
`.
`341I34; 345I173, 174
`setting techniques inherently available in the architecture are
`employed.
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`4,935,728
`
`6/1990 Kley ........................................ 340/709
`
`13 Claims, 15 Drawing Sheets
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`8
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`Wintek Exhibit 1023
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`US. Patent
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`Aug. 6, 1996
`
`Sheet 1 of 15
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`5,543,590
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`US. Patent
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`Aug. 6, 1996
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`Sheet 2 of 15
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`5,543,590
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`US. Patent
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`Aug. 6, 1996
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`Sheet 3 of 15
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`5,543,590
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`US. Patent
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`Aug. 6, 1996
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`Sheet 4 of 15
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`5,543,590
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`40
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`48-1
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`US. Patent
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`Aug. 6, 1996
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`Sheet 5 of 15
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`5,543,590
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`OUT
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`FIG. 4A
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`
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`US. Patent
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`Aug. 6, 1996
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`Sheet 6 of 15
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`5,543,590
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`US. Patent
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`Aug. 6, 1996
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`Sheet 7 of 15
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`5,543,590
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`50-1
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`50-2
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`50-3
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`FIG. 7
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`US. Patent
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`Aug. 6, 1996
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`Sheet 8 of 15
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`5,543,590
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`#150
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`166
`
`
`
`
`NUMERATOR
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`
`FIG. 8
`
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`US. Patent
`
`Aug. 6, 1996 '
`
`Sheet9of 15
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`5,543,590
`
`180
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`US. Patent
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`Aug. 6, 1996
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`Sheet 10 of 15
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`5,543,590
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`US. Patent
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`Aug. 6, 1996
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`Sheet 11 of 15
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`5,543,590
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`" Y CENTER
`
`YMIN
`
`I
`
`X CENTER
`
`240
`
`FIG. 11
`
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`
`FIG. 12
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`US. Patent
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`Aug. 6, 1996
`
`Sheet 12 of 15
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`5,543,590
`
`XG
`
`256
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`US. Patent
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`Aug. 6, 1996
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`Sheet 13 of 15
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`5,543,590
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`280
`
`PRE—
`VIOUSLY
`003m
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`290
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`US. Patent
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`Aug. 6, 1996
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`Sheet 14 of 15
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`5,543,590
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`
`
` PRE-
`VIOUSLY
`
`U?P
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`296 .
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`FIG. 148
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`US. Patent
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`Aug. 6, 1996
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`Sheet 15 of 15
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`5,543,590
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`310
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`
`
`
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`PRESS VIRTUAL
`
`MOUSE BUTTON
`
`
`RELEASE VIRTUAL
`MOUSE BUTTON
`
`318
`
`316
`
`FIG. 140
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`5,543,590
`
`1
`OBJECT POSITION DETECTOR WITH
`EDGE MOTION FEATURE
`
`RELATED APPLICATIONS
`
`This application is a continuation in part of application
`Ser. No. 08/300,387, filed Sep. 2, 1994, attomey’s Docket
`No. SYN-057A, which is a continuation-in-part of applica-
`tion Ser. No. 08/115,743, filed Aug. 31, 1993, now U.S. Pat.
`No. 5,374,787, which is a continuation—in-part of application
`Ser. No. 07/895,934, filed Jun. 8, 1992, abandoned.
`
`BACKGROUND OF THE INVENTION
`
`1. Field of the Invention
`
`The present invention relates to object position sensing
`transducers and systems. More particularly,
`the present
`invention relates to object position recognition useful in
`applications
`such as cursor movement
`for computing
`devices and other applications, and especially to cursor
`movement with enhanced edge-motion features.
`2. The Prior Art
`
`Numerous devices are available or have been proposed
`for use as object position detectors for use in computer
`systems and other applications. The most familiar of such
`devices is the computer “mouse”. While extremely popular
`as a position indicating device, a mouse has mechanical
`parts and requires a surface upon which to roll its position
`ball. Furthermore, a mouse usually needs to be moved over
`long distances for reasonable resolution. Finally, a mouse
`requires the user to lift a hand from the keyboard to make the
`cursor movement,
`thereby upsetting the prime purpose,
`which is usually typing on the computer.
`Trackball devices are similar to mouse devices. A major
`difference, however is that, unlike a mouse device, a track
`ball device does not require a surface across which it must
`be rolled. Trackball devices are still expensive, have moving
`parts, and require a relatively heavy touch as do the mouse
`devices. They are also large in size and do not fit well in a
`volume-sensitive application like a laptop computer.
`There are several available touch-sense technologies
`which may be employed for use as a position indicator.
`Resistive-membrane position sensors are known and used in
`several applications. However, they generally suifer from
`poor resolution, the sensor surface is exposed to the user and
`is thus subject to wear. In addition, resistive-membrane
`touch sensors are relatively expensive. A one-surface
`approach requires a user to be grounded to the sensor for
`reliable operation. This cannot be guaranteed in portable
`computers. An example of a one-surface approach is the
`UnMouse product by MicroTouch, of Wilmington, Mass. A
`two-surface approach has poorer resolution and potentially
`will wear out very quickly in time.
`Resistive tablets are taught by U.S. Pat. No. 4,680,430 to
`Yoshikawa, U.S. Pat. No. 3,497,617 to Ellis and many
`others. The drawback of all such approaches is the high
`power consumption and the high cost of the resistive mem-
`brane employed.
`Surface Acoustic Wave (SAW) devices have potential use
`as position indicators. However, this sensor technology is
`expensive and is not sensitive to light touch. In addition,
`SAW devices are sensitive to residue buildup on the touch
`surfaces and generally have poor resolution.
`Strain gauge or pressure plate approaches are an interest-
`ing position sensing technology, but suffer from several
`drawbacks. This approach may employ piezoelectric trans~
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`45
`
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`
`55
`
`60
`
`65
`
`2
`ducers. One drawback is that the piezo phenomena is an AC
`phenomena and may be sensitive to the user’s rate of
`movement.
`In addition, strain gauge or pressure plate
`approaches are somewhat expensive because special sensors
`are required.
`Optical approaches are also possible but are somewhat
`limited for several reasons. All would require light genera-
`tion which will require external components and increase
`cost and power drain. For example, a “finger-breaking”
`infra-red matrix position detector consumes high power and
`suffers from relatively poor resolution.
`There have been numerous attempts to provide a device
`for sensing the position of a thumb or other finger for use as
`a pointing device to replace a mouse or trackball. Desirable
`attributes of such a device are low power, low profile, high
`resolution, low cost, fast response, and ability to operate
`reliably when the finger carries electrical noise, or when the
`touch surface is contaminated with dirt or moisture.
`
`Because of the drawbacks of resistive devices, many
`attempts have been made to provide pointing capability
`based on capacitively sensing the position of the finger. U.S.
`Pat. No. 3,921,166 to Volpe teaches a capacitive matrix in
`which the finger changes the transcapacitance between row
`and column electrodes. U. S. Pat. No. 4,103,252 to Bobick
`employs four oscillating signals to interpolate x and y
`positions between four capacitive electrodes. U.S. Pat. No.
`4,455,452 to Schuyler teaches a capacitive tablet wherein
`the finger attenuates the capacitive coupling between elec-
`trodes.
`
`U.S. Pat. No. 4,550,221 to Mabusth teaches a capacitive
`tablet wherein the efi'ective capacitance to “virtual ground”
`is measured by an oscillating signal. Each row or column is
`polled sequentially, and a rudimentary form of interpolation
`is applied to resolve the position between two rows or
`columns. An attempt is made to address the problem of
`electrical interference by averaging over many cycles of the
`oscillating waveform. The problem of contamination is
`
`applying a periodic calibration during such no-finger—present
`periods. U.S. Pat. No. 4,639,720 to Rympalski teaches a
`tablet for sensing the position of a stylus. The stylus alters
`the transcapacitance coupling between row and column
`electrodes, which are scanned sequentially. U.S. Pat. No.
`4,736,191 to Matzke teaches a radial electrode arrangement
`under the space bar of a keyboard,
`to be activated by
`touching with a thumb. This patent teaches the use of total
`touch capacitance, as an indication of the touch pressure, to
`control
`the velocity of cursor motion. Pulsed sequential
`polling is employed to address the effects of electrical
`interference.
`to Greanias,
`U.S. Pat. Nos. 4,686,332 and 5,149,919,
`teaches a stylus and finger detection system meant to be
`mounted on a CRT. As a finger detection system, its X/Y
`sensor matrix is used to locate the two matrix wires carrying
`the maximum signal. With a coding scheme these two wires
`uniquely determine the location of the finger position to the
`resolution of the wire stepping. For stylus detection, Gre-
`anias first coarsely locates it, then develops a virtual dipole
`by driving all lines on one side of the object in one direction
`and all lines on the opposite side in the opposite direction.
`This is done three times with difi'erent dipole phases and
`signal polarities. Assuming a predetermined matrix response
`to the object,
`the three measurements present a set of
`simultaneous equations that can be solved for position.
`U.S. Pat. No. 4,733,222 to Evans is the first to teach a
`capacitance touch measurement system that interpolates to a
`
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`3
`high degree. Evans teaches a three terminal measurement
`system that uses a drive, sense and electrode signal set (3
`signals) in its matrix, and bases the measurement on the
`attenuation efl’ect of a finger on the electrode node signal
`(uses a capacitive divider phenomena). Evans sequentially
`scans through each drive set to measure the capacitance.
`From the three largest responses an interpolation routine is
`applied to determine finger position. Evans also teaches a
`zeroing technique that allows “no-finger" levels to be can-
`celled out as part of the measurement.
`US. Pat. No. 5,016,008 to Gruaz describes a touch
`sensitive pad that also uses interpolation. Gruaz uses a drive
`and sense signal set (2 signals) in the touch matrix and like
`Evans relies on the attenuation efiect of a finger to modulate
`the drive signal. The touch matrix is sequentially scanned to
`read the response of each matrix line. An interpolation
`program then selects the two largest adjacent signals in both
`dimensions to determine the finger location, and ratiometri-
`cally determines the effective position from those 4 num-
`bers.
`
`Gerpheide, PCT application US90/04584, publication No.
`W09l/03039, U. S. Pat. No. 5,305,017 applies to a touch pad
`system a variation of the virtual dipole approach of Green—
`ias. Gerpheide teaches the application of an. oscillating
`potential of a given frequency and phase to all electrodes on
`one side of the virtual dipole, and an oscillating potential of
`the same frequency and opposite phase to those on the other
`side. Electronic circuits develop a “balance signal" which is
`zero when no finger is present, and which has one polarity
`if a finger is on one side of the center of the virtual dipole,
`and the opposite polarity if the finger is on the opposite side.
`To acquire the position of the finger initially,
`the virtual
`dipole is scanned sequentially across the tablet. Once the
`finger is located, it is "tracked" by moving the virtual dipole
`toward the finger once the finger has moved more than one
`row or column.
`
`Because the virtual dipole method operates by generating
`a balance signal that is zero when the capacitance does not
`vary with distance, it only senses the perimeter of the finger
`contact area, rather than the entire contact area. Because the
`method relies on synchronous detection of the exciting
`signal, it must average for long periods to reject electrical
`interference, and hence it
`is slow. The averaging time
`required by this method,
`together with the necessity to
`search sequentially for a new finger contact once a previous
`contact is lost, makes this method, like those before it, fall
`short of the requirements for a fast pointing device that is not
`affected by electrical interference.
`It should also be noted that all previous touch pad
`inventions that used interpolation placed rigorous design
`requirements on their sensing pad. Greanias and Evans use
`a complicated and expensive drive, sense and electrode line
`scheme to develop their signal. Gruaz and Gerpheide use a
`two signal drive and sense set. In the present invention the
`driving and sensing is done on the same line. This allows the
`row and column sections to be symmetric and equivalent.
`This in turn allows independent calibration of all signal
`paths, which makes board layout simpler and less constrain—
`ing, and allows for more unique sensor topologies.
`The shortcomings of the inventions and techniques
`described in the prior art can also be traced to the use of only
`one set of driving and sensing electronics, which was
`multiplexed sequentially over the electrodes in the tablet.
`This arrangement was cost effective in the days of discrete
`components, and avoided ofiset and scale differences among
`circuits.
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`The sequential scanning approach of previous systems
`also made them more susceptible to noise. Noise levels
`could change between successive measurements,
`thus
`changing the measured signal and the assumptions used in
`interpolation routines.
`Finally, all previous approaches assumed a particular
`signal response for finger position versus matrix position.
`Because the transfer curve is very sensitive to many param-
`eters and is not a smooth linear curve as Greanias and
`Gerpheide assume, such approaches are limited in the
`amount of interpolation they can perform.
`In prior co-pending application Ser. No. 08/115,743, filed
`Aug. 31, 1993, now US. Pat. No. 5,374,789, a two-dimen-
`sional capacitive sensing system equipped with a separate
`set of drive/sense electronics for each row and for each
`column of a capacitive tablet is disclosed. All row electrodes
`are sensed simultaneously, and all column electrodes are
`sensed simultaneously. The sensed signals are processed by
`analog circuitry.
`It is thus an object of the present invention to provide a
`two-dimensional capacitive sensing system equipped with a
`separate set of drive/sense electronics for each row and for
`each column of a capacitive tablet, wherein all row elec-
`unA a" nnlnmn nlsnfrnrlae
`uuu u.” yununur yavveauuva
`trodes are sensed sin: ltancousl ',
`are sensed simultaneously.
`It is a further object of the present invention to provide an
`electronic system that
`is sensitive to the entire area of
`contact of a finger or other conductive object with a capaci-
`tive tablet, and to provide as output the coordinates of some
`measure of the center of this contact area while remaining
`insensitive to the characteristic profile of the object being
`detected.
`
`It is a further object of the present invention to provide an
`electronic system that provides as output some measure of
`area of contact of a finger or other conductive object with a
`capacitive tablet.
`Yet another object of the present invention is to provide a
`two-dimensional capacitive sensing system equipped with a
`separate set of drive/sense electronics for each row and for
`each column of a capacitive tablet, wherein all row elec-
`trodes are sensed simultaneously, and all column electrodes
`are sensed simultaneously and wherein the information
`defining the location of a finger or other conductive object
`is processed in digital form.
`It is a further object of the present invention to provide a
`two—dimensional capacitive sensing system wherein all row
`electrodes are sensed simultaneously, and all column elec—
`trodes are sensed simultaneously and wherein the location of
`a finger or other conductive object within a peripheral region
`of a sensing plane can optionally cause cursor “edge
`motion” on a display screen allowing control of large cursor
`excursions from a small sensing plane with a single gesture.
`
`BRIEF DESCRIPTION OF THE INVENTION
`
`With the advent of very high levels of integration, it has
`become possible to integrate many channels of driving]
`sensing electronics into one integrated circuit, along with the
`control logic for operating them, and the interface electron-
`ics to allow the pointing device to conununicate directly
`with a host microprocessor. The present
`invention uses
`adaptive analog techniques to overcome offset and scale
`diiferences between channels, and can thus sense either
`transcapacitance or self-capacitance of all
`tablet rows or
`columns in parallel. This parallel-sensing capability, made
`,possible by providing one set of electronics per row or
`
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`column, allows the sensing cycle to be extremely short, thus
`allowing fast response while still maintaining immunity to
`very high levels of electrical interference.
`The present invention comprises a position-sensing tech-
`nology particularly useful
`for applications where finger
`position information is needed,
`such as
`in computer
`“mouse” or trackball environments. However the position-
`sensing technology of the present invention has much more
`general application than a computer mouse, because its
`sensor can detect and report if one or more points are being
`touched. In addition, the detector can sense the pressure of
`the touch.
`
`According to a preferred embodiment of the present
`invention, referred to herein as a “finger pointer” embodi-
`ment, a position sensing system includes a position sensing
`transducer comprising a touch~sensitive surface disposed on
`a substrate, such as a printed circuit board,
`including a
`matrix of conductive lines. A first set of conductive lines
`runs in a first direction and is insulated from a second set of
`conductive lines running in a second direction generally
`perpendicular to the first direction. An insulating layer is
`disposed over the first and second sets of conductive lines.
`The insulating layer is thin enough to promote significant
`capacitive coupling between a finger placed on its surface
`and the first and second sets of conductive lines.
`
`Sensing electronics respond to the proximity of a finger,
`conductive object, or an object of high dielectric constant
`(i.c., greater than about 5)
`to translate the capacitance
`changes of the conductors caused by object proximity into
`digital information which is processed to derive position and
`touch pressure information. Its output is a simple X, Y and
`pressure value of the one object on its surface. In all
`descriptions herein, fingers are to be considered interchange-
`able with conductive objects and objects of high dielectric
`constant.
`
`Different prior art pad scan techniques have dilferent
`advantages in different environments. Parallel drive/sense
`techniques according to the present invention allow input
`samples to be taken simultaneously, thus all channels are
`affected by the same phase of an interfering electrical signal,
`greatly simplifying the signal processing and noise filtering.
`There are two drive/sense methods employed in the touch
`sensing technology of the present invention. According to a
`first and presently preferred embodiment of the invention,
`the voltages on all of the X lines of the sensor matrix are
`simultaneously moved, while the voltages of the Y lines are
`held at a constant voltage, with the complete set of sampled
`points simultaneously giving a profile of the finger in the X
`dimension. Next, the voltages on all of the Y lines of the
`sensor matrix are simultaneously moved, while the voltages
`of the X lines are held at a constant voltage to obtain a
`complete set of sampled points simultaneously giving a
`profile of the finger in the other dimension.
`According to a second drive/sense method, the voltages
`on all of the X lines of the sensor matrix are simultaneously
`moved in a positive direction, while the voltages of the Y
`lines are moved in a negative direction. Next, the voltages on
`all of the X lines of the sensor matrix are simultaneously
`moved in a negative direction, while the voltages of the Y
`lines are moved in a positive direction. This technique
`doubles the effect of any transcapacitance between the two
`dimensions, or conversely, halves the efi‘ect of any parasitic
`capacitance to ground. In both methods,
`the capacitive
`information from the sensing process provides a profile of
`the proximity of the finger to the sensor in each dimension.
`As presently preferred, both embodiments then take these
`profiles and derive a digital value representing the centroid
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`for X and Y position and derive a second digital value for the
`Z pressure information. The digital
`information may be
`directly used by a host computer. Analog processing of the
`capacitive information may also be used according to the
`present invention.
`The position sensor of these embodiments can only report
`the position of one object on its sensor surface. If more than
`one object is present, the position sensor of this embodiment
`computes the centroid position of the combined set of
`objects. However, unlike prior art, because the entire pad is
`being profiled, enough information is available to discern
`simple multi-finger gestures to allow for a more powerful
`user interface.
`
`According to another aspect of the present invention,
`several power reduction techniques which can shut down the
`circuit between measurements have been integrated into the
`system. This is possible because the parallel measurement
`technique according to the present invention is so much
`faster than prior art techniques.
`According to a further aspect of the invention, a variety of
`noise reduction techniques are integrated into the system.
`According to yet another aspect of the present invention,
`a capacitance measurement technique which is easier to
`calibrate and implement is employed.
`According to another aspect of the present invention,
`when the presence of a finger or other conductive object is
`sensed within a defined peripheral region of the sensing
`plane,
`the control of cursor motion may be changed to
`provide “edge motion” to allow control of large cursor
`excursions on a display screen from a single gesture
`executed on a small sensing plane.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is an overall block diagram of the capacitive
`position sensing system of the present invention.
`FIG. 2a is a top view of an object position sensor
`transducer according to a presently preferred embodiment of
`the invention showing the object position sensor surface
`layer including a top conductive trace layer and conductive
`pads connected to a bottom trace layer.
`FIG. 2b is a bottom view of the object position sensor
`transducer of FIG. 2a showing the bottom conductive trace
`layer.
`FIG. 20 is a composite View of the object position sensor
`transducer of FIGS. 2a and 21: showing both the top and
`bottom conductive trace layers.
`FIG. 2d is a cross~scctional view of the object position
`sensor transducer of FIGS. 2a—2c.
`
`FIG. 3 is a block diagram of sensor decoding electronics
`which may be used with the sensor transducer in accordance
`with a preferred embodiment of the present invention.
`FIG. 4a is a simplified schematic diagram of a charge
`integrator circuit which may be used in the present inven-
`tion.
`
`FIG. 4b is an illustrative schematic diagram of the charge
`integrator circuit of FIG. 4a.
`FIG. 5 is a timing diagram of the operation of charge
`integrator circuit of FIGS. 4a and 4b.
`FIG. 6 is a schematic diagram of an illustrative filter and
`sample/hold circuit for use in the present invention.
`FIG. 7 is a more detailed block diagram of a presently
`preferred arrangement of A/D converters for use in the
`present invention.
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`FIG. 8 is a block diagram of an illustrative arithmetic unit
`which may be used in the present invention.
`FIG. 9 is a block diagram of a calibration unit which may
`be used with the arithmetic unit of FIG. 8.
`FIG. 10 is a schematic diagram of a bias voltage gener-
`ating circuit useful in the present invention.
`FIG. 11 is a diagram of the sensing plane illustrating the
`edge motion feature of the object position sensor of the
`present invention.
`FIG. 12 is a schematic diagram illustrating hardware
`implementation of the determination of whether a finger or
`other object is present
`in the peripheral regions of the
`sensing plane.
`FIG. 13 is a schematic diagram illustrating hardware
`implementation of the edge motion feature of the present
`invention.
`
`FIGS. 14a—l4c are flow diagrams illustrating a process
`according to the present invention for recognizing tap and
`drag gestures.
`
`DETAILED DESCRIPTION OF A PREFERRED
`EMBODIMENT
`
`This application is a continuation—in-part of co-pending
`application Ser. No. 08/300,387, filed Sep. 2, 1994, which is
`a continuation—in—part of copending application Ser. No.
`08/115,743, filed Aug. 31, 1993, now US. Pat. No. 5,734,
`787, which is a continuation-in-part of co—pending applica-
`tion Ser. No. 07/895,934, filed Jun. 8, 1992. The present
`invention continues the approach disclosed in the parent
`applications and provides more unique features not previ—
`ously available. These improvements provide a more easily
`integrated solution, increased sensitivity, and greater noise
`rejection,
`increased data acquisition rate and decreased
`power consumption. The present invention allows for con-
`tinuous self calibration to subtract out the effects of envi-
`ronmental changes and allows for enhanced cursor control
`from edge motion on a sensing plane.
`Those of ordinary skill
`in the art will realize that the
`following description of the present invention is illustrative
`only and not in any way limiting. Other embodiments of the
`invention will readily suggest themselves to such skilled
`persons.
`
`The present invention brings together in combination a
`number of unique features which allow for new applications
`not before possible. Because the object position sensor of the
`present invention has very low power requirements, it is
`beneficial for use in battery operated or low power applica—
`tions such as lap top or portable computers. It is also a very
`low cost solution, has no moving parts (and is therefore
`virtually maintenance free), and uses the existing printed
`circuit board traces for sensors. The sensing technology of
`the present invention can be integrated into a computer
`motherboard to even further lower its cost
`in computer
`applications. Similarly, in other applications the sensor can
`be part of an already existent circuit board.
`the sensor
`Because of its small size and low profile,
`technology of the present invention is useful in lap top or
`portable applications where volume is an important consid~
`eration. The sensor technology of the present invention
`requires circuit board space for only a single sensor interface
`chip that can interface directly to a microprocessor, plus the
`area needed on the printed circuit board for sensing.
`Referring first to FIG. 1, a simplified block diagram of the
`capacitive position sensing system 6 of the present invention
`
`8
`is presented. Capacitive position sensing system 6 can
`accurately detemiine the position of a finger 8 or other
`conductive object proximate to or touching a sensing plane
`10. The capacitance of a plurality of conductive lines
`running in a first direction (e.g., “X") is sensed by X input
`processing circuitry 12 and the capacitance of a plurality of
`conductive lines running in a second direction (e.g., “Y”) is
`sensed by Y input processing circuitry 14. The sensed
`capacitance values are digitized in both X input processing
`circuitry 12 and Y input processing circuitry 14. The outputs
`of X input processing circuitry 12 and Y input processing
`circuitry 14 are presented to arithmetic unit 16, which uses
`the digital information to derive digital information repre—
`senting the position and pressure of the finger 8 or other
`conductive object relative to the sensing plane 10.
`The X, Y, and Z outputs of arithmetic unit 16 are di