Europaisches Patentamt
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`European Patent Office
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`Office europeen des brevets
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`iii
`1111 iii
`111111111111111
`1111
`Publication number : 0 574 213 Al
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`12
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`EUROPEAN PATENT APPLICATION
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`0 Application number : 93304403.4
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`0 Date of filing : 07.06.93
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`e Int. CI 5: GOOK 11/16
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`0 Priority : 08.06.92 US 895934
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`0 Date of publication of application :
`15.12.93 Bulletin 93/50
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`0 Designated Contracting States :
`CH DE FR GB IT LI NL SE
`
`0 Applicant : SYNAPTICS, INCORPORATED
`2698 Orchard Parkway
`San Jose, California 95134 (US)
`
`0 Inventor : Miller, Robert J.
`1021, Washo Drive,
`Fremont, California 94539 (US)
`Inventor : Bisset, Stephen J.
`1426 Arbor Avenue
`Los Altos, California 94024 (US)
`
`0 Representative : Williams, Trevor John
`J.A. KEMP & CO. 14 South Square Gray's Inn
`London WC1R 5LX (GB)
`
`0 Object position detector.
`
`0 A proximity sensor system includes a sensor
`matrix array having a characteristic capacitance
`between horizontal and vertical 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
`approach of an object is converted to a set of
`voltages in the X and Y directions. These vol-
`tages are processed by analog circuitry to de-
`velop electrical signals representative of the
`centroid of the profile of the object, i.e., its
`position in the X and Y dimensions. The profile
`of position may also be integrated to provide
`Z-axis (pressure) information.
`
`-10
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`14141414141414141414'414141414
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`• • • • • 4, • • • • • • • • 22
`• • • • • • • • • • • • •
`• • • • • • • • • • • • • •
`• • • • • • • • • • • • • •
`• • + • • • • • • • • • • •
`• • • • • • • • • 4. • • • •
`•
`+ • • •
`• •
`• •
`• • •
`• •
`• 16
`• • • •
`4. •
`• •
`• •
`• • •
`• * • • • • • • • • * • • •
`• • • • • • • • • ••• • 4,
`4, • • • 4. • • • • • • • • +
`• • • + • • • • • • + 0 • •
`• • • • • • 0 • • • •• • •
`• • • • • • * • • • • • • •
`• • • * • • • • • • • • • •
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`FIG. 1a
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`Jouve, 18, rue Saint-Denis, 75001 PARIS
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`Exhibit 2018 - Page 01 of 35
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`Exhibit 2018 - Page 01 of 35
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`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 sen-
`sors useful in applications such as cursor movement
`for computing devices and other applications.
`
`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 (cid:9)
`most familiar of such devices is the computer
`"mouse". While extremely popular as a position indi-
`cating device, a mouse has mechanical parts and re-
`quires a surface upon which to roll its position ball.
`Furthermore, a mouse usually needs to be moved (cid:9)
`over long distances for reasonable resolution. Finally,
`a mouse requires the user to lift a hand from the key-
`board to make the cursor movement, thereby upset-
`ting the prime purpose, which is usually typing on the
`computer. (cid:9)
`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 expensive, have moving parts, and require a rel- (cid:9)
`atively 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 technol-
`ogies which may be employed for use as a position in- (cid:9)
`dicator. Resistive-membrane position sensors are
`known and used in several applications. However,
`they generally suffer from poor resolution, the sensor
`surface is exposed to the user and is thus subject to
`wear. In addition, resistive-membrane touch sensors (cid:9)
`are relatively expensive. A one-surface approach re-
`quires 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, (cid:9)
`MAAtwo-surface approach has poorer resolution and
`potentially will wear out very quickly in time.
`Surface Acoustic Wave (SAW) devices have po-
`tential use as position indicators. However, this sen-
`sor technology is expensive and is not sensitive to (cid:9)
`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 (cid:9)
`from several drawbacks. This approach may employ
`piezo-electric transducers. One drawback is that the
`piezo phenomena is an AC phenomena and may be
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`sensitive to the user's rate of movement. In addition,
`strain gauge or pressure plate approaches are a
`somewhat expensive because special sensors are re-
`quired.
`Optical approaches are also possible but are
`somewhat limited for several reasons. All would re-
`quire light generation which will require external com-
`ponents and increase cost and power drain. For ex-
`ample, a "finger-breaking" infra-red matrix position
`detector consumes high power and suffers from rela-
`tively poor resolution.
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`BRIEF DESCRIPTION OF THE INVENTION
`
`The present invention comprises a position-sens-
`ing technology particularly useful for applications
`where finger position information is needed, such as
`in computer "mouse" or trackball environments. How-
`ever 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 ad-
`dition, the detector can sensa the pressure of the
`touch.
`There are at least two distinct embodiments of
`the present invention. Both embodiments of the pres-
`ent invention include a sensor comprising a plurality
`of spaced apart generally parallel conductive lines
`disposed on a first surface.
`According to a first embodiment of the present in-
`vention, referred to herein as a "finger pointeC em-
`bodiment, a position sensing system Includes a pos-
`ition sensing transducer comprising a touch-sensitive
`surface disposed on a substrate, such as a printed cir-
`cuit 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 run-
`ning 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 in-
`sulating layer is thin enough to promote significant ca-
`pacitive coupling between a finger placed on its sur-
`face and the first and second sets of conductive lines.
`Sensing eledronics respond to the proximity of a
`finger to translate the capacitance changes between
`the conductors caused by finger proximity into posi-
`tion and touch pressure Information. Its output is a
`simple X, Y and pressure value of the one object on
`Its surface. The matrix of conductive lines are succes-
`sively scanned, one at a time, with the capacitive in-
`formation from that scan indicating how close a finger
`is to that node. That information provides a profile of
`the proximity of the finger to the sensor in each di-
`mension. The centroid of the profile is computed with
`that value being the position of the finger in that di-
`mension. The profile of position is also integrated with
`that result providing the Z (pressure) information. The
`position sensor of the first embodiment of the inven-
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`tion can only detect the position of one object on its
`sensor surface. If more than one object is present, the
`position sensor of this embodiment tries to compute
`the centroid position of the combined set of objects. (cid:9)
`According to a second embodiment of the pres-
`ent invention, a position sensing system includes a
`position sensing transducer as described herein.
`Sensing electronics respond to the.proximity of a fin-
`ger to translate the capacitance changes between (cid:9)
`the conductors running in one direction and those
`running in the other direction caused by finger prox-
`imity into position and touch pressure information.
`The sensing electronics of the second embodiment of
`the invention saves information for every node in its (cid:9)
`sensor matrix and can thereby give the full X/Y di-
`mension picture of what it is sensing. It thus has much
`broader application for richer multi-dimensional sens-
`ing than does the first "finger pointer' embodiment. In
`this embodiment, referred to herein as the "position (cid:9)
`matrix" approach, the x,y coordinate information can
`be used as input to a on-chip neural network proces-
`sor. This allows an operator to use multiple fingers,
`coordinated gestures, etc. for even more complex in-
`teractions. (cid:9)
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`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. la is a top view of an object position sensor
`transducer according to a presently preferred em- (cid:9)
`bodiment 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. 1b is a bottom view of the object position (cid:9)
`sensor transducer of FIG. la showing the bottom con-
`ductive trace layer.
`FIG. lc is a composite view of the object position
`sensor transducer of FIGS. la and 1 b showing both
`the top and bottom conductive trace layers. (cid:9)
`FIG. 1d is a cross-sectional view of the object
`position sensor transducer of FIGS. la-lc.
`FIG. 2 is a block diagram of sensor decoding elec-
`tronics which may be used with the sensor transducer
`in accordance with a first embodiment of the present (cid:9)
`invention.
`FIGS. 3a and 3b are graphs of output voltage ver-
`sus matrix conductor position which illustrate the ef-
`fect of the minimum detector.
`FIG. 4 is a simplified schematic diagram of an in- (cid:9)
`tegrating charge amplifier circuit suitable for use in
`the present invention.
`FIG. 5 is a timing diagram showing the relative
`timing of control signals used to operate the object
`position sensor system of the present invention with
`an integrating charge amplifier as shown in FIG. 4.
`FIG. 6a is a schematic diagram of a first alternate
`embodiment of an integrating charge amplifier circuit
`suitable for use in the present invention including ad-
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`ditional components to bring the circuit to equilibrium
`prior to integration measurement.
`FIG. 6b is a timing diagram showing the control
`and timing signals used to drive the integrating
`charge amplifier of FIG. 6a and the response of vari-
`ous nodes in the amplifier to those signals.
`FIG. 7a is a schematic diagram of a second alter-
`nate embodiment of an integrating charge amplifier
`circuit suitable for use in the present invention includ-
`ing additional components to bring the circuit to equi-
`librium prior to integration measurement.
`FIG. 7b is a timing diagram showing the control
`and timing signals used to drive the integrating
`charge amplifier of FIG. 7a and the response of vari-
`ous nodes in the amplifier to those signals.
`FIG. 8 is a schematic diagram of a minimum de-
`tector circuit according to a presently preferred em-
`bodiment of the invention.
`FIG. 9 is a schematic diagram of a maximum de-
`tector circuit according to a presently preferred em-
`bodiment of the invention.
`FIG. 10 is a schematic diagram of a linear vol-
`tage-to-current converter circuit according to a pre-
`sently preferred embodiment of the invention.
`FIG. 11 is a schematic diagram of a position en-
`coder centroid computing circuit according to a pre-
`sently preferred embodiment of the invention.
`FIG. 12 is a schematic diagram of a Z Sum circuit
`according to a presently preferred embodiment of the
`invention.
`FIG. 13 is a schematic diagram of a multiplier cir-
`cuit according to a presently preferred embodiment of
`the invention.
`FIG. 14 is a schematic diagram of a combination
`driving-point impedance circuit and receiving-point
`impedance circuit according to a presently preferred
`position matrix embodiment of the invention.
`FIG. 15 is a block diagram of a the structure of a
`portion of a sample/hold array suitable for use in the
`present invention.
`FIG. 16a is a block diagram of a simple version
`of a position matrix embodiment of the present inven-
`tion in which the matrix of voltage information is sent
`to a computer which processes the data.
`FIG. 16b is a block diagram of a second version
`of a position matrix embodiment of the present inven-
`tion employing a sample/hold array such as that de-
`picted in FIG. 15.
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`DETAILED DESCRIPTION OF A PREFERRED
`EMBODIMENT
`
`Those of ordinary skill in the art will realize that
`the following description of the present invention is il-
`lustrative only and not in any way limiting. Other em-
`bodiments of the invention will readily suggest them-
`selves to such skilled persons.
`The present invention brings together in combin-
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`ation 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 applications such as lap top or
`portable computers. It is also a very low cost solution,
`has no moving parts (and is therefore virtually main-
`tenance free), and uses the existing printed circuit
`board traces for sensors. The sensing technology of
`the present invention can be integrated into a comput-
`er motherboard to even further lower its cost in com-
`puter applications. Similarly, in other applications the
`sensor can be part of an already existent circuit
`board.
`Because of its small size and low profile, the sen-
`sor technology of the present invention is useful in lap
`top or portable applications where volume is impor-
`tant consideration. The sensor technology of the
`present invention requires circuit board space for only
`a single sensor interface chip that can interface di-
`rectly to a microprocessor, plus the area needed on
`the printed circuit board for sensing.
`The sensor material can be anything that allows
`creation of a conductive X/Y matrix of pads. This in-
`cludes not only standard PC board, but also flexible
`PC board, conductive elastomer materials, and piezo-
`electric Kynar plastic materials. This renders it useful
`as well in any portable equipment application or in hu-
`man interface where the sensor needs to be molded
`to fit within the hand.
`The sensor can be conformed to any three di-
`mensional surface. Copper can be plated in two lay-
`ers on most any surface contour producing the sen-
`sor. This will allow the sensor to be adapted to the
`best ergonomic form needed for a application. This
`coupled with the "light-touch" feature will make it ef-
`fortless 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 de-
`tect any object (not just conductive) that presses
`against it's surface.
`Small sensor areas are practical, i.e., a presently
`conceived embodiment takes about 1.5"x 1.5" of area,
`however those of ordinary skill in the art will recog-
`nize that the area is scalable for different applica-
`tions. 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-width" modes
`in Paint programs, special menu accesses, etc., al-
`lowing provision of a more natural sensory input to
`computers.
`The user will not even have to touch the surface
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`to generate the minimum reaction. This feature can
`greatly minimize user strain and allow for more flex-
`ible use.
`The sense system of the present invention de-
`pends on a transducer device capable of providing
`position and pressure information regarding the ob-
`ject contacting the transducer. Referring first to FIGS.
`1a-1d, top, bottom, composite, and cross-sectional
`views, respectively, are shown of a presently-prefer-
`red touch sensor array for use in the present inven-
`tion. Since capacitance is exploited by this embodi-
`ment of the present invention, the sensor surface is
`designed to maximize the capacitive coupling be-
`tween top (X) trace pads to the bottom (Y) trace pads
`in a way that can be maximally perturbed and coupled
`to a finger or other object placed above the surface.
`A presently preferred sensor array 10 according
`to the present invention comprises a substrate 12 In-
`cluding a set of first conductive traces 14 disposed on
`a top surface 16 thereof and run in a first direction to
`comprise rows of the array. A second set of conduc-
`tive traces 18 are disposed on a bottom surface 20
`thereof and run In a second direction preferably or-
`thogonal to the first direction to form the columns of
`the array. The top and bottom conductive traces 14
`and 18 are alternately in contact with periodic sense
`pads 22 comprising enlarged areas, shown as dia-
`monds in FIGS. la-1c. While sense pads 22 are
`shown as diamonds in FIGS. la-1c, any shape, such
`as circles, which allows close packing of the sense
`pads, is equivalent for purposes of this invention.
`The number and spacing of these sense pads 22
`depends upon the resolution desired. For example, in
`an actual embodiment constructed according to the
`principles of the present invention, a 0.10 inch center-
`to-center diamond-shaped pattern of conductive
`pads disposed along a matrix of 15 rows and 15 col-
`umns of conductors is employed. Every other sense
`pad 22 in each direction in the pad pattern is connect-
`ed to conductive traces on the top and bottom surfac-
`es 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 thick-
`ness is unimportant as long as contact may be made
`therethrough from the bottom conductive traces 18 to
`their sense pads 22 on the top surface 16. The print-
`ed circuit board comprising substrate 12 can be con-
`structed using standard Industry techniques. Board
`thickness is not important. Pad-to-pad spacing
`should preferably be minimized to something in the
`range of about 15 mils or less. Connections from the
`conductive pads 22 to the bottom traces 18 may be
`made employing standard plated-through hole tech-
`niques well known in the printed circuit board art.
`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 pre-
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`ferably a thin layer (i.e., approximately 5 mils) to keep
`capacitive coupling large and may comprise a mate-
`rial, such as mylar, chosen for its protective and ergo-
`nomic characteristics.
`There are two different capacitive effects taking
`place when a finger approaches the sensor array 10.
`The first capacitive effect is trans-capacitance, or
`coupling between sense pads 22, and the second ca-
`pacitive effect is self-capacitance (ground capaci-
`tance), or coupling to earth-ground. Sensing circuitry
`is coupled to the sensor array 10 of the present inven-
`tion 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 ca-
`pacitance and trans-capacitance results in a very ver-
`satile system having a wide range of applications.
`According to a first embodiment of the invention,
`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 trac-
`es via the capacitive effect of finger proximity to the
`sensor array 10. The position sensor system will re-
`port the X, Y position of a finger placed near the sen-
`sor array 10 to much finer resolution than the spacing
`between the row and column traces 14 and 18. The
`position sensor according to this embodiment of the
`invention will also report a Z value proportional to the
`outline of that finger and hence Indicative of the pres-
`sure with which the finger contacts the surface of in-
`sulating layer 22 over the sensing array 10.
`According to a 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 systematic er-
`rors. The detector circuit of the present invention will
`process the capacitive input information and provide
`digital information to a microprocessor.
`According to this embodiment of the invention,
`sensing circuitry is contained on a single sensor proc-
`essor integrated circuit chip. The sensor processor
`chip can have any number of X and Y "matrix" inputs.
`The number of X and Y inputs does not have to be
`equal. The Integrated circuit has a digital bus as out-
`put. In the illustrative example disclosed in FIGS. 1a-
`1d herein, the sensor array has 15 traces in both the
`Y and Y directions. The sensor processor chip thus
`has 15 X inputs and 15 Y inputs.
`The X and Y matrix nodes are successively scan-
`ned, one at a time, with the capacitive information
`from that scan indicating how close a finger is to that
`node. The scanned information provides a profile of
`the finger proximity in each dimension. According to
`this aspect of the present invention, the profile cen-
`troid is derived in both the X and Y directions and is
`the position in that dimension. The profile curve of
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`proximity is also integrated to provide the Z informa-
`tion.
`Referring now to FIG. 2, a block diagram of pre-
`sently preferred sensing circuitry 30 for use according
`to the present invention is shown. The sensing circui-
`try of this embodiment employs a driving-point impe-
`dance measurement for each X and Y line in the sens-
`ing matrix 10. The block diagram of FIG. 2 illustrates
`the portion of the sensing circuitry for developing sig-
`nals from one direction (shown as X in the matrix).
`The circuitry for developing signals from the other di-
`rection in the matrix is identical and Its interconnec-
`tion to the circuitry shown in FIG. 2 will be disclosed
`herein. The circuitry of FIG. 2 illustratively discloses
`an embodiment in which information from six X matrix
`lines X1 ... X6 are processed. Those of ordinary skill
`in the art will recognize that this embodiment is illus-
`trative only, and that actual embodiments fabricated
`according to the present invention may employ an ar-
`bitrarily sized matrix, limited only by technology con-
`straints.
`The driving-point capacitance measurement for
`each of X lines X1 ... X6 is derived from an integrating
`charge amplifier circuit. These circuits are shown in
`block form at reference numerals 32-1 through 32-6.
`The function of each of integrating charge amplifier
`circuits 32-1 through 32-6 is to develop an output vol-
`tage proportional to the capacitance sensed on its
`corresponding X matrix line.
`The driving-point capacitance measurement is
`made for all X (row) conductors 14 and all Y (column)
`conductors 18 in the sensor matrix array 10. A profile
`of the finger proximity mapped into the X and Y di-
`35 (cid:9) mension is generated from the driving-point capaci-
`tance measurement data. This profile is then used to
`determine a centrold in both dimensions, thereby de-
`termining the X and Y position of the finger.
`The output voltages of integrating charge ampli-
`fier circuits 32-1 through 32-6 are utilized by several
`other circuit elements and are shown for convenience
`in FIG. 2 as distributed by bus 34. Bus 34 is a six con-
`ductor bus, and those of ordinary skill in the art will
`recognize that each of its conductors comprises the
`output of one of integrating charge amplifiers 32-1
`through 32-6.
`The first of circuit elements driven by the outputs
`of integrating charge amplifier circuits 32-1 through
`32-6 Is linear voltage-to-current converter 36. The
`function of linear voltage-to-current converter 36 is to
`convert the output voltages of integrating charge am-
`plifiers 32-1 through 32-6 to currents for subsequent
`processing.
`The current outputs from linear voltage-to-cur-
`rent converter 36 are presented as inputs to X posi-
`tion encode circuit 38. The function of X position en-
`code circuit 38 is to convert the input information into
`a signal representing object proximity in the X dimen-
`sion of the sensor array matrix. According to a pre-
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`sently preferred embodiment of the invention, this cir-
`cuit will provide a scaled weighted mean (centroid) of
`the set of input currents. The result is a circuit which
`is a linear position encoder,having an output voltage (cid:9)
`which varies between the power supply rails. Be-
`cause it is a weighted mean, it averages all current in-
`puts and can in turn generate an output voltage which
`represents an X position with a finer resolution than
`the spacing of the X matrix grid spacing. (cid:9)
`The output voltage of X position encode circuit 38
`is presented to sample/hold circuit 40, the output of
`which, as is well known in the art, either follows the
`Input or holds a value present at the input depending
`on the state of its control input 42. The structure and (cid:9)
`operation of sample/hold circuits are well known in the
`art.
`The output of sample/hold circuit 40 drives the in-
`put of analog-to-digital (ND) converter 44. The output
`of ND converter 44 is a digital value proportional to (cid:9)
`the position of the object in the X dimension of the
`sensor array matrix 10.
`While the portion of the circuit described so far is
`useful for providing a digital signal indicating object
`position in one dimension, the addition of further cir- (cid:9)
`cuit elements yields a more useful device which is
`more immune to noise, detects and subtracts the no-
`object-proximate signal from the outputs of the sen-
`sors, and provides threshold detection of an ap-
`proaching object. (cid:9)
`The first of these additional circuit elements is
`minimum detector circuit 46. The function of minimum
`detector circuit 46 is to determine the level of signal
`representing ambient no-object-proximate to the sen-
`sor array matrix 10 and to provide a signal which may (cid:9)
`be fed back to integrating charge amplifiers 32-1
`through 32-6 to control their output voltages to effec-
`tively zero out the outputs of the amplifiers under the
`ambient condition. The output of minimum detector 46
`circuit is a voltage. This voltage is compared in opera- (cid:9)
`tional amplifier 48 with an adjustable voltage repre-
`senting a minimum threshold value VThmin. Through
`feedback to the integrating charge amplifiers 32-1
`through 32-6, amplifier 48 adjusts its output to bal-
`ance the output voltage of Minimum detector circuit (cid:9)
`46 with the voltage VThmin. Feedback'is controlled
`by P-channel MOS transistor 50, which allows the
`feedback to operate only when the PROCESS signal
`is active.
`FIGS. 3a and 3b are graphs of output voltage ver- (cid:9)
`sus matrix conductor position which illustrate the ef-
`fect of the minimum detector circuit 46. In order to bet-
`ter illustrate the effect of offset cancellation, FIGS. 3a
`and 3b show the outputs of integrating charge ampli-
`fiers from a fifteen row matrix, rather than from a six (cid:9)
`row matrix as is implied by FIG. 2. FIG. 3a shows the
`offset component of the voltage outputs of integrating
`charge amplifiers without the operation of minimum
`detector 46, and FIG, 3b shows the voltage outputs
`
`5
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`6
`
`with the offset having been zeroed out by the feed-
`back loop comprising minimum detector circuit 46, P-
`channel MOS transistor 50, and feedback conductor
`52.
`
`Anotheradditional circuit component is maximum
`detector circuit 54. The function of maximum detector
`circuit 54, working in co-operation with amplifier 56,
`OR gate 58, and AND gate 60 is to provide a MAX IN-
`TERRUPT signal. The MAX INTERRUPT signal
`alerts the microprocessor controlling the object sen-
`sor system of the present invention that an object is
`approaching the sensor array matrix 10. The amplifi-
`er 56 acts as a comparator which trips if the output
`voltage from maximum detector circuit 54 exceeds
`the threshold set by the voltage Vi-h„ax. When the out-
`put voltage from maximum detector circuit 54 exceeds
`the threshold, or the output voltage from the corre-
`sponding Y maximum detector (not shown) exceeds
`the threshold set for its corresponding amplifier, the
`output of OR gate 58 becomes true. That and a true
`SAMPLE signal at the second input of AND gate 60
`causes a true MAX INTERRUPT signal at its output.
`The Z Sum circuit 62 produces an output which is
`proportional to the pressure with which a finger is
`pressing on the sensor. This is done in both the X and
`Y dimensions by effectively integrating the areas un-
`der the curves of FIG. 3b. Referring again to FIG. 3b
`for illustration purposes, it can be seen that the width
`of the contact area in the X dimension of the sensor
`array 10 is from about X2 to X10.
`According to a presently preferred embodiment
`of the invention, Z Sum circuit 62 is configured to pro-
`duce an output voltage Vo. Output voltage Vo is a
`scaled function of all the input voltages.
`Since the outputs of the Z Sum circuits 62 in both
`the X and Y directions are proportional to the width
`of the pointing finger or other flexible object in the two
`dimensions of the sensor array matrix 10, the area of
`the finger or ot her flexible object is a reliable measure
`of the pressure with which the finger is contacting the
`surface of the sensor array matrix 20. The area may
`be calculated by multiplier circuit 64, having the out-
`put of the Z Sum circuit in the X dimension as one of
`its inputs and the output of the Z Sum circuit in the Y
`dimension as the other one of its inputs.
`A presently preferred embodiment of multiplier
`circuit takes two analog voltage inputs and performs
`an analog computation on those voltages to create a
`voltage output which is proportional to the product of
`the two input voltages. As shown in FIG. 2, a first input
`term is the output voltage of the X dimension Z Sum
`circuit 62 and a second input term is the output of the
`Y dimension Z Sum circuit (not shown). Those of or-
`dinary skill in the art will recognize that since multi-
`plication is commutative process and since the multi-
`plier inputs are symmetrical, it does not matter which
`of the X and YZ sum circuits contributes the first input
`term and which contributes the second input term.
`
`Exhibit 2018 - Page 06 of 35
`
`Exhibit 2018 - Page 06 of 35
`
`(cid:9)
`

`

`11 (cid:9)
`
`EP 0 574 213 Al
`
`12
`
`The output of multiplier circuit 64 is a voltage and
`drives a sample/hold circuit 66. Sample/hold circuit 66
`may be identical to sample/hold circuit 40 and may be
`driven by the same SAMPLE signal which drives sam-
`ple/hold circuit 40.
`The output of sample/hold circuit 66 drives the in-
`put of analog-to-digital (A/D) converter 68. A/D con-
`verter 68 may be identical to A/D converter 44. The
`output of A/D converter 68 is a digital value propo