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`US. Patent
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`Dec. 20, 1994
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`Dec. 20, 1994
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`Page 13 of 26
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`1
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`5,374,787
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`2
`
`OBJECT POSITION DETECTOR
`
`This application is a continuation-in-part of co-pending
`application Ser. No. 07/895,934, filed Jun. 8, 1992 and
`assigned to the same assignee as the present invention.
`BACKGROUND OF THE INVENTION
`
`1. Field Of The Invention
`The present invention relates to object position sens-
`ing transducers and systems. More particularly, the
`present invention relates to object position recognition
`useful in applicatiOns such as cursor movement for com-
`puting devices and other applications.
`2. The Prior Art
`
`10
`
`15
`
`Optical approaches are also possible but are some-
`what limited for several reasons. All would require light
`generation 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 thumb or other finger
`for use as a pointing device to replace a mouse or track-
`ball. Desirable attributes of such a device are low
`power, low profile, high resolution, low cost, fast re-
`sponse, 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 electrodes.
`U.S. Pat. No. 4,550,221 to Mabusth teaches a capaci-
`tive tablet wherein the effective capacitance to “virtual
`groun ” 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 aver-
`aging over many cycles of the oscillating waveform.
`The problem of contamination is addressed by sensing
`when no finger was present, and applying a periodic
`calibration during such no-fmger—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 ar-
`rangement 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 ad-
`dress the effects of electrical interference.
`U.S. Pat. Nos. 4,686,332 and 5,149,919, to Greanias,
`teaches a stylus and finger detection system meant to be
`mounted on a CRT. As a finger detection system, it’s
`X/Y sensor matrix is used to locate the two matrix
`wires canying the maximum signal. With a coding
`scheme these two wires uniquely determine the location
`of the finger position to the resolution of the wire step-
`ping. For stylus detection, Greanias first coarsely lo-
`cates 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 different dipole phases and
`signal polarities. Assuming a predetermined matrix re»
`sponse to the object, the three measurements present a
`set of simultaneous equations that can be solved for
`poaition.
`U.S. Pat. No. 4,733,222 to Evans is the first to teach
`a (capacitance touch measurement system that interpo-
`lates to a high degree. Evans teaches a three terminal
`measurement system that uses a drive, sense and elec-
`trode signal set (3 signals) in its matrix, and bases the
`
`20
`
`25
`
`30
`
`35
`
`Numerous devices are available or have been pro«
`posed 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 de-
`vice, a trackball device does not require a surface across
`which it must be rolled. Trackball devices are still can
`pensive, have moving parts, and require a relatively
`heavy touch as do the 'mouse devices. They are also
`large in size and doe 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
`suffer from poor resolution, the sensor surface is ex. 40
`posed to the user and is thus subject to wear. In addi»
`tion, resistive-membrane touch sensors are relatively
`expensive. A one~surface approach requires a user to be
`grounded to the sensor for reliable operation. This can-
`not be guaranteed in portable computers. An example of 45
`a one-surface approach is the UnMouse product by
`MicroTouch, of Wilmington, Mass. A two-surface ap-
`proach 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. 3,497.61? to Ellis and many
`others The drawback of all such approaches is the high
`power consumption and the high coat of the resistive
`membrane employed.
`Surface Acoustic Wave (SAW) devices have poten-
`tial use as position indicators. However,
`this sensor
`technology is expensive and is not seasitive 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
`interesting position sensing technology, but suffer from
`several drawbacks. This approach may employ piezo-
`electric transducers. 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. a somewhat expensive
`because special sensors are required.
`
`55
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`Page 14 of 26
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`

`

`3
`measurement on the attenuation effect ofa finger on the
`electrode node signal (uses a capacitive divider phe-
`nomena). Evans sequentially scans thru each drive set
`to measure the capacitance. From the three largest
`responses an interpolation routine is applied to deter-
`mine finger position. Evans also teaches a zeroing tech-
`nique that allows “no-finger” levels to be cancelled out
`as part of the measurement.
`U.S. 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 effect ofa finger
`to modulate the drive signal. The touch matrix is se-
`quentially scanned to read each matrix lines response.
`An interpolatiorr program then selects the two largest
`adjacent signals in both dimensions to determine the
`finger location, and ratiometrically determines the ef-
`fective position from those 4 numbers.
`Gerpheide, PCI' application USN/04584, publica-
`tion No. W091f03039, applies to a touch pad system a
`variation of the virtual dipole approach of Greanias.
`Gerpheide teaches the application of an oscillating po-
`tential of a given frequency and phase to all electrodes
`on one side of the virtual dipoleand an oscillating po-
`tential 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 pres-
`ent, 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 gener-
`ating a balance signal that is zero when the capacitance
`does not vary with distance, it only senses the perimeter
`of the linger contact area, rather than the entire contact
`area Because the method relies on synchronous detec-
`tion 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 af-
`fected by electrical interference.
`It should also be noted that all previous touch pad
`inventions that used interpolation placed rigorous de-
`sign 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 inde-
`pendent calibration of all signal paths, which makes
`board layout. simpler and less constraining, 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 offset and scale
`differences among circuits.
`
`10
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`5,3?4,787
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`4
`The sequential scanning approach of previous sys-
`t-s also made them more siisceptible 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 posi-
`tion. Because the transfer curve is very sensitive to
`many parameters and is not a smooth linear curve as
`Greanias and Gerpheide assume, such approaches are
`limited in the amount of interpolation they can perform.
`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 electrodes are sensed simultaneously, and all
`column electrodes are sensed simultaneously.
`It is a further object of the present invention to pro-
`vide an electronic system that is sensitive to the entire
`area of contact of a finger with a capacitive tablet, and
`to provide as output the coordinates of some measure of
`the center of this contact area while remaining insensi-
`tive to the characteristic profile of the object being
`detected.
`
`It is a further object of the present invention to pro-
`vide an electronic system that provides as output some
`measure of area of contact of a finger with a capacitive
`tablet.
`
`BRIEF DESCRIPTION OF THE INVENTION
`
`With the advent of very high levels of integration, it
`has become possible to integrate many channels of dri-
`ving/sensing electronics into one integrated circuit,
`along with the control logic for operating them, and the
`interface electronics to allow the pointing device to
`communicate directly with a host microprocessor. The
`present invention uses adaptive analog techniques to
`overcome offset and scale differences between chan-
`nels, and can thus sense either transcapacitance or self-
`capacitance of all tablet rows or columns in parallel;
`This parallel-sensing capability, made possible by pro-
`viding one set of electronics per row or column, allows
`the sensing cycle to be extremely short, thus allowing
`fast reaponse while still maintaining immunity to very
`high levels of electrical interference.
`The present invention comprises a position-sensing
`technology particularly useful for applications where
`finger position information is needed, such as in com-
`puter “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” em
`bodiment, 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 sec-
`ond direction generally perpendicular to the first direc-
`tion. 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.
`
`Page 15 of 26
`Page 15 of 26
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`

`

`5,374,787
`
`6
`sor surface layer including a _top conductive trace layer
`and conductive pads connected to a bottom trace layer.
`FIG. 1b is a bottom view of the object position sensor
`transducer of FIG. Ia showing the bottom conductive
`trace layer.
`FIG. 1c is a composite view of the object position
`sensor transducer of FIGS. 1:: and 1!; showing both the
`top and bottom conductive trace layers.
`FIG. 10' is a cross-sectional view of the object posi-
`tion sensor transducer of FIGS. 1c—-1c
`
`FIG. 2 is a block diagram of sensor decoding elec-
`tronics which may be used with the sensor transducer in
`accordance with a preferred embodiment of the present
`invention.
`
`10
`
`15
`
`5
`Sensing electronics respond to the proximity of a
`finger to translate the capacitance changes of the con-
`ductors caused by finger proximity into position and
`touch pressure information. Its output is a simple X, Y
`and pressure value of the one object on its surface.
`Different prior art pad scan techniques have different
`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 interfer-
`ing electrical signal, greatly simplifying the signal pro-
`cessing and noise filtering.
`There are two drive/sense methods employed in the
`touch sensing technology of the present invention. Ac-
`cording 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 volt-
`ages of the Y lines are held at a constant voltage, with
`the complete set of sampled points simultaneously giv-
`ing 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 complete set of
`sampled points simultaneously giving a profile of the
`finger in the other dimension.
`According to a second drive/sense method, the volt-
`ages on all of the X lines of the sensor matrix are simul-
`taneously moved in a positive direction, while the volt~
`ages 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 direc—
`tion, 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 effect of any parasitic capaci-
`tance to ground. In both methods, the capacitive infor-
`mation from the sensing process provides a profile of
`the proximity of the finger to the sensor in each dimen-
`sion.
`_
`
`Both embodiments then take these profiles and calcu-
`late the centroid for X and Y position and integrate
`under the curve for the 2 pressure information. The
`pasition 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 infor-
`mation is available to discern simple multi-finger ges-
`tures 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 pres-
`ent invention is so much faster than prior art techniques.
`According to a firrther aspect of the invention, noise
`reduction techniques that are focused on reducing noise
`produced in typical computer environments are inte-
`grated into the system.
`According to yet another aSpect of the present inven-
`tion, a capacitance measurement technique which is
`easier to calibrate and implement is employed.
`
`FIG. 30 is a simplified schematic diagram of a charge
`integrator circuit which may be used in the present
`invention.
`
`FIG. 3b is a schematic diagram of an illustrative sche-
`matic diagram of the charge integrator circuit of FIG.
`30.
`
`20
`
`FIG. 4 is a timing of the operation of charge integra-
`tor circuit of FIGS. 30 and 3b.
`FIG, 5 is a schematic diagram of an illustrative filter
`and sample/hold circuit for use in the present invention.
`FIG. 6a is a schematic diagram of an illustrative mini-
`mum selector and subtractor circuit including peak
`rejection which may be employed in the present inven-
`tion, showing circuit details of four individual channels
`and their interconnection.
`
`FIG. 6b is a representation of what the output of the
`minimum selector and subtractor circuit of FIG.
`(it!
`would be like without the background level removed.
`FIG. 6c is a representation of the output of the mini-
`mum selector and subtractor circuit of FIG. 6a with the
`background level removed.
`FIG. 7 is a schematic diagram of an illustrative OTA
`circuit used in the minimum selector and subtractor
`circuit, showing how the outputs Pout and Zout are
`derived, and further showing a current sink and source
`Options, Poutn and Poutp, respectively, for the Pout
`output.
`FIG. 8 is a schematic diagram of an illustrative maxi-
`mum detector circuit which may be used in the present
`invention.
`
`FIG. 9a is a schematic diagram of an illustrative posi-
`tion encoder circuit which may be used in the present
`invention.
`
`FIG. 9b is a schematic diagram of an P-type OTA
`circuit which may be used in the position encoder cir-
`cuit of the present invention.
`FIG. 9c is a schematic diagram of an N—type OTA
`circuit which may be used in the position encoder cir-
`cuit of the present invention.
`FIG. 10 is a schematic diagram of an illustrative
`ZSurn circuit which may be used in the present inven-
`non.
`
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`55
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`DETAILED DESCRIPTION OF A PREFERRED
`EMBODIMENT
`
`This application is a continuation-in-part of co-pend-
`ing application Ser. No. 07/895,934, filed Jun. 8, 1992.
`The present invention continues the approach disclosed
`in the parent application and provides more unique
`features not previously available. These improvements
`provide increased sensitivity, and greater noise rejec-
`tion,
`increased data acquisition rate and decreased
`power consumption.
`
`BRIEF DESCRIPTION OF TI-IE'. DRAWINGS
`
`65
`
`FIG. la is a top view of an object position sensor
`transducer according to a presently preferred embodi-
`ment of the invention showing the object position sen-
`
`Page 16 of 26
`Page 16 of 26
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`5,374,787
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`7
`Those of ordinary skill in the art will realize that the
`following description of the present invention is illustra-
`tive only and not in any way limiting. Other embodi-
`ments 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 appli-
`cations 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 applications 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 in-
`vention canbe integrated into a computer motherboard
`to even further lower its cost in computer applicatioris.
`Similarly, in other applications the sensor can be part of
`an already existent circuit board.
`Because of its small size and low profile, the sensor
`technology of the present invention is useful in lap t0p
`or portable applications where volume is important
`consideration. The sensor technology of the present
`invention requires circuit board Space for only a single
`sensor interface chip that can interface directly to a
`micmprocessor, plus the area needed on the printed
`circuit board for sensing.
`The sensor material can be anything that allows cre-
`ation of a conductive X/Y matrix of pads. This includes
`not only standard PC board, but also flexible PC board,
`conductive elastomer materials, silk-screened conduc-
`tive lines, and piezoelectric Kynar plastic materials.
`This renders it useful as well in any portable equipment
`application or in human interface where the sensor
`needs to be molded to fit within the hand.
`The sensor can be conformed to any three dimen-
`sional surface. Copper can be plated in two layers on
`most any surface contour producing the sensor. This
`will allow the sensor to be adapted to the best ergo-
`nomic form needed for :1 application. This coupled With
`the “light-touch” feature will make it effortless to use in
`many applications. The sensor can also be used in an
`indirect manner, i.e. it can have a conductive foam over
`the surface and be used to detect any object (not just
`conductive) that presses against it’s surface.
`Small sensor areas are practical, Le, a presently con-
`ceived embodiment
`takes about 1.5"X 1.5" of area,
`however those of ordinary skill in the art will recognize
`that the area is Scalable for different applications. The
`matrix area is scaleable by either varying the matrix
`trace spacing or by varying the number of traces. Large
`sensor areas are practical where more information is
`needed.
`
`Besides simple X and Y position information, the
`sensor technology of the present invention also pro-
`vides finger pressure information. This additional di-
`mension of information may be used by programs to
`control special features such as “brush-vvidth" modes in
`Paint programs, special menu accesses, etc, allowing
`provision of a more natural sensory input to computers.
`It has also been found usefill for implementing “mouse
`click and drag” modes and for simple input gestlues.
`The user will not even have to touch the surface to
`generate the minimum reaction. This feature can greatly
`minimize user strain and allow for more flexible use.
`The sense system of the present invention depends on
`a transducer device capable of providing position and
`pressure information regarding the object contacting
`
`Page 17 of 26
`Page 17 of 26
`
`8
`top,
`lcula',
`the transducer. Referring first to FIGS.
`bottom, composite, and cross-sectional views, respec-
`tively, are shown of a presently-preferred touch sensor
`array for use in the present invention. Since capacitance
`is exploited by this embodiment of the present inven—
`tiou,
`the sensor surface is designed to maximize the
`capacitive coupling.
`A presently preferred sensor array 10 according to
`the present invention comprises a substrate 12 including
`a set of first conductive traces 14 diSposed on a top
`surface 16 thereof and run in a first direction to com-
`prise row positions of the sensor array 10. A set of
`second conductive traces 18 are disposed on a bottom
`surface 20 thereof and run in a second direction prefera-
`bly orthogonal to the first direction to form the column
`positions of the sensor array 10. The sets of first and
`second conductive traces 14 and 18 are alternately in
`ooutact with periodic sense pads 22 comprising en-
`larged areas, shown as diamonds in FIGS. lav-lo. While
`sense pads 22 are shown as diamonds in FIGS. lit—1c,
`any shape, such as circles, which allows close packing
`of the sense pads 22, is equivalent for purposes of this
`invention. As an arbitrary convention herein, the set of
`first conductive traces 14 will be referred to as being
`oriented in the "X” or “row” direction and may be
`referred to herein sometimes as “X lines” and the set of
`second conductive traces 18 will be referred to as being
`oriented in the “Y” or “column" direction and may be
`referred to herein sometimes as “Y lines”.
`
`The number and spacing of these sense pads 22 de-
`pends upon the resolution desired. For example, in an
`actual embodiment constructed according to the princi-
`ples of the present invention, a 0.10 inch center—to-cen-
`ter diamOnd-shaped pattern of sense pads disposed
`along a matrix of 15 rows and 15 columns of conductors
`is employed. Every other sense pad 22 in each direction
`in the pad pattern is connected to sets of first and second
`conductive traces 14 and 18 on the top and bottom
`surfaces 16 and 20, respectively of substrate 12.
`Substrate 12 may be a printed circuit board, a flexible
`circuit board or any of a number of available circuit
`interconnect technology structures. Its thickness is un-
`important as long as contact my be made therethrough
`from the set of second conductive traces 18 to their
`sense pads 22 on the top surface 16. The printed circuit
`board comprising substrate 12 can be constructed using
`standard industry techniques. Board thickness is not
`important. Connections from the sense pads 22 to the set
`of second conductive traces 18 may be made employing
`standard plated-through hole techniques well known in
`the printed circuit board art.
`In an alternate embodiment of the present invention,
`the substrate 12 may have a thickness on the order of
`0.005 to 0.010 inches. Then the diamonds on the top
`surface 16 and the plated thru holes that connect to the
`set of second conductive traces 18, can be omitted,
`further reducing the cost of the system.
`An insulating layer 24 is disposed over the sense pads
`22 on top surface 16 to insulate a human finger or other
`object therefrom. Insulating layer 24 is preferably a thin
`layer (i.e., approximately 5 mils) to keep capacitive
`coupling large and may comprise a material, such as
`mylar, chosen for its protective and ergonomic charac-
`teristics. The term “significant capacitive coupling” as
`used herein shall mean capacitive coupling having a
`magnitude greater than about 0.5 pF.
`There are two different capacitive effects taking
`place when a finger approaches the sensor array 10. The
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`9
`first capacitive effect is trans-capacitance, or coupling
`between sense pads 22, and the second capacitive effect .
`is self-capacitance, or coupling to virtual ground. Sens-
`ing circuitry is coupled to the sensor array 10 of the
`present invention and responds to changes in either or
`both of these capacitances. This is important because
`the relative sizes of the two capacitances change greatly
`depending on the user environment. The ability of the
`present invention to detect changes in both self capaci-
`tance and trans-capacitance results in a very versatile
`system having a wide range of applications.
`According to the preferred embodiment of the inven—
`tion, a position sensor system including sensor array 10
`and associated touch detector circuitry will detect a
`finger position on a matrix of printed circuit board
`traces via the capacitive effect of finger proximity to the
`sensor array 10. The position sensor system will report
`the X, Y position of a finger placed near the sensor
`array 10 to much finer resolution than the spacing be-
`tween the sets of first and second conductive traces 14
`and 18. The position sensor according to this embodi-
`ment of the invention will also report a 2 value propor-
`tional to the outline of that finger and hence indicative
`of the pressure with which the finger contacts the sur-
`face of insulating layer 24 over the sensor array 10.
`According to the presently preferred embodiment of
`the invention, a very sensitive,
`light-touch detector
`circuit may be provided using adaptive analog VLSI
`techniques. The circuit of the present invention is very
`robust and calibrates out process and syst