111111
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`1111111111111111111111111111111111111111111111111111111111111
`US007821502B2
`
`c12) United States Patent
`Hristov
`
`(10) Patent No.:
`(45) Date of Patent:
`
`US 7,821,502 B2
`Oct. 26, 2010
`
`(54) TWO-DIMENSIONAL POSITION SENSOR
`
`2007/0008299 AI
`
`112007 Hristov
`
`(75)
`
`Inventor: Luben Hristov, Southampton (GB)
`
`(73) Assignee: Atmel Corporation, San Jose, CA (US)
`
`( *) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 912 days.
`
`(21) Appl. No.: 11/428,670
`
`(22) Filed:
`
`Jul. 5, 2006
`
`(65)
`
`Prior Publication Data
`
`US 2007/0008299 Al
`
`Jan. 11,2007
`
`Related U.S. Application Data
`
`FOREIGN PATENT DOCUMENTS
`
`EP
`
`0609021 A
`
`8/1994
`
`OTHER PUBLICATIONS
`
`IBMTechnica!DisclosureBulletin, vol. 21, No.10, Mar. 1979, N.D.
`Lupat et a!. "One layer optically transparent keyboard for input
`display", p. 3904 to 3906.
`"Chinese Application Serial No. 200610143149.0 Office Action
`Mailed Oct. 9, 2009", 6 pgs.
`Serial
`Application
`200610143149.0,
`"Chinese
`200610143149.0, Office Action mailed Apr. 10, 2009", 8 pgs.
`* cited by examiner
`Primary Examiner-Srilakshmi K Kumar
`(74) Attorney, Agent, or Firm-Schwegman, Lundberg &
`Woessner, P.A.
`
`No.
`
`(60) Provisional application No. 60/697,613, filed on Jul. 8,
`2005.
`
`(57)
`
`ABSTRACT
`
`(51)
`
`Int. Cl.
`G06F 31041
`(2006.01)
`G06F 31044
`(2006.01)
`(52) U.S. Cl .
`.................................... 345/173; 178/18.06
`(58) Field of Classification Search ................. 345/156,
`345/173-178; 178/18.01' 18.06
`See application file for complete search history.
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`4,550,221 A
`4,954,823 A
`5,463,388 A *
`5,730,165 A
`5,844,506 A
`5,861,583 A
`6,288,707 B1
`6,466,036 B1
`
`10/1985 Mabusth
`9/1990 Binstead
`10/1995 Boie et al ..................... 341133
`3/1998 Philipp
`12/1998 Binstead
`111999 Schediwy et al.
`912001 Philipp
`10/2002 Philipp
`
`A capacitive position sensor for determining the position of
`an object along first and second directions is described. The
`sensor comprises a substrate having an arrangement of elec(cid:173)
`trodes mounted on a single surface thereof. The electrodes are
`arranged so as to define an array of sensing cells arranged in
`columns and rows to form a sensing area. Each of the sensing
`cell including a column sensing electrode and a row sensing
`electrode with the column sensing electrodes of sensing cells
`in the same column being electrically coupled together and
`the row sensing electrodes of sensing cells in the same row
`also being electrically coupled together. Row sensing elec(cid:173)
`trodes of sensing cells at opposing ends of at least one of the
`rows are connected together by an electrical connection made
`outside of the sensing area so that there is no requirement for
`electrical connections to cross within the sensing area, thus
`providing a capacitive position sensor having a sensing area
`with electrodes on only one side of a substrate.
`
`24 Claims, 8 Drawing Sheets
`
`-X I -Y1
`-X2 lUlli]Y2
`li!BX3
`iil!?Jj'jY3
`QX4 fZ2!Y4
`~Y5
`
`EXHIBIT 1004
`IPR Petition for U.S. Patent No. 8,004,497
`
`

`

`US. Patent
`
`Oct. 26, 2010
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`US. Patent
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`0a. 26, 2010
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`US 7,821,502 B2
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`US‘ Patent
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`US 7,821,502 B2
`
`1
`TWO-DIMENSIONAL POSITION SENSOR
`
`BACKGROUND OF THE INVENTION
`
`The invention relates to a capacitive position sensor for
`determining the position of an object Within a tWo-dimen
`sional sensing area.
`The use of tWo-dimensional touch-sensitive position sen
`sors is becoming more common. Examples include the use of
`position sensors in laptop computers in place of mouse point
`ing devices, as control panels for receiving user inputs to
`control an appliance, or particularly as a glass touchscreen
`apparatus having an X-Y coordinate output. Some applica
`tions require a clear sensing layer so that a display can be
`vieWed beneath the screen, While others only require an
`opaque touch surface, for example for a keypanel on a kitchen
`appliance or a PC peripheral.
`Touch-sensitive position sensors are frequently preferred
`to mechanical devices because they provide for a more robust
`interface and are often considered to be more aesthetically
`pleasing. Furthermore, because touch-sensitive position sen
`sors require no moving parts to be accessible to a user, they
`are less prone to Wear than their mechanical counterparts and
`can be provided Within a sealed outer surface. This makes
`their use Where there is a danger of dirt or ?uids entering a
`device being controlled particularly attractive.
`There exists a large body of art involving 2D touchpanels
`and screens. They can be generally divided into tWo classi?
`cations: those that report an X-Y coordinate of a more or less
`continuous nature (‘XY’ type), and those that have a discrete
`sensing surface (‘discrete’ type) having prede?ned key areas
`that are ?xed by physical geometry. The XY type ?nd domi
`nant use over LCD or other display types While the latter ?nd
`use in ?xed function key panels. There are exceptions to this,
`for example touchpad surfaces on laptops report XY position
`but are opaque. XY types invariably involve a sensing surface
`on the user-side or ‘?rst surface’ of the touch area. For
`example, both continuous resistive and capacitive touch
`screens involve a sensing layer that must be either physically
`depressed by the user or touched almost directly, or at most
`through a thin layer of insulation (as in mouse touchpads).
`These types require that the product have a beZel opening to
`alloW direct or near-direct contact by the user With the sensing
`layer. A signi?cant disadvantage of these types is that there
`has to be an opening in the panel, Which requires sealing
`against moisture and dirt and hence is expensive to mount.
`Furthermore the sensing layer is directly exposed to abuse
`and can be easily damaged by sharp objects or abrasion.
`While robust capacitive types are knoWn Which have buried
`Wires inside a glass layer (eg US. Pat. No. 5,844,506), these
`still require a beZel opening in a panel Which must be sealed,
`and require tWo sensing layers as a matrix due to the need to
`cross X andY conductors. Furthermore these screens are very
`expensive to produce and in fact cannot be produced on a
`mass scale; additionally the sensing circuitry is knoWn to be
`complex and expensive.
`In the ?eld of discrete touch buttons, it has been knoWn for
`some time that capacitive keys can be placed behind a solid
`surface having no requirement for a beZel opening. HoWever
`these types only provide for limited resolution, as prede?ned
`by the location of discrete electrode shapes. An example of
`this can be found in US. Pat. No. 4,954,823, FIGS. 4 and 6.
`While it is Well knoWn that these electrodes can be made of a
`single layer of clear conductor such as Indium Tin Oxide
`(‘ITO’) to alloW placement over a beZel-less display, for
`example by the application of the layer as a ?lm on the back
`of a subsection of a panel, nevertheless the technology is
`
`20
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`2
`limited to discrete touch areas based on the number, siZe, and
`placement of discrete electrodes.
`FIG. 1 schematically shoWs in plan vieW a touch pad 2 of
`the type described in US. Pat. No. 4,954,823, but laid out in
`an orthogonal array. The touch pad 2 comprises a grid of
`discrete electrodes 4 mounted on an insulating substrate 6.
`Each electrode is connected to a channel of capacitance mea
`surement circuitry in a controller 8. US. Pat. No. 5,463,388
`describes this geometry in passing in conjunction With its
`FIG. 1, to shoW hoW such an array can be used to determine a
`position of an object proximate the sensing layer via a method
`of determining a centroid of the signals from each pad. HoW
`ever U.S. Pat. No. 5,463,388 fails to shoW hoW to implement
`such a design and describes instead a matrix of conductors
`along With a centroidal calculation of continuous X-Y posi
`tion. In fact it is not practical to have so many sensing chan
`nels as one per sense pad, and a matrix arrangement is much
`more e?icient as described beloW.
`FIG. 2 schematically shoWs a position sensor 12 based on
`a matrix of conductors as described in US. Pat. No. 5,463,
`388. The position sensor 12 comprises a number of vertically
`aligned strip electrodes (columns) 14 mounted on an upper
`surface of an insulating substrate 16 and a number of hori
`Zontally aligned strip electrodes (roWs) 15 mounted on an
`opposing loWer surface of the insulating substrate. Each ver
`tical strip electrode is connected to a channel of capacitance
`measurement circuitry in a controller 18. Thus, this type of
`position sensor alloWs an X-Y coordinate output of a continu
`ous nature by means of calculation of a centroid of capaci
`tance among the roWs and columns rather than among dis
`crete pads. HoWever this type requires tWo sensing layers so
`that the matrix traces canbe routed, and does not alloW the use
`of optically clear materials.
`The ideal touch surface Would eliminate the need for a
`beZel opening (or at least, make it optional), have an inexpen
`sive sensing surface that is applied to the rear of the panel
`surface that can project through a reasonable thickness of
`panel material (eg up to 4 mm of glass or plastic), optionally
`require only one sensing layer With no crossovers in the
`sensing region, be usable With clear sensing layers such as
`ITO, have an XY type of output, and have a compact, inex
`pensive driver circuit. This set of ideal goals has not been
`achieved With any knoWn prior art.
`
`SUMMARY OF THE INVENTION
`
`According to a ?rst aspect of the invention there is provided
`a capacitive position sensor for determining the position of an
`object in a sensing area, the sensor comprising a substrate
`having a surface With an arrangement of electrodes mounted
`thereon, Wherein the electrodes de?ne an array of sensing
`cells arranged in columns and roWs to form the sensing area,
`each sensing cell including a column sensing electrode and a
`roW sensing electrode, the column sensing electrodes of sens
`ing cells in the same column being electrically coupled
`together and the roW sensing electrodes of sensing cells in the
`same roW being electrically coupled together, Wherein roW
`sensing electrodes of sensing cells at opposing ends of at least
`one of the roWs are electrically coupled to one another by
`respective roW Wrap -around connections made outside of the
`sensing area.
`Thus a position sensor having electrodes on only a single
`layer of a substrate can be provided. Furthermore, because the
`position sensor employs an intersecting array of columns and
`roWs of sensing electrodes (i.e. a matrix), feWer measurement
`channels are required than With sensors based on an array of
`discrete electrodes.
`
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`US 7,821,502 B2
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`3
`Because the position sensor is based on sensing electrodes
`on only a single surface, it can be cheaper to manufacture than
`knoWn double-sided position sensors. This also means the
`sensing electrodes can be deposited directly onto a surface for
`Which the opposing surface is inaccessible (e. g. a display
`screen). The sensing electrodes can also be deposited on an
`inside surface of a device housing, thus removing the need for
`any protective covering that might be required if electrodes
`Were also required to be on the outer surface.
`The electrical roW Wrap-around connections may comprise
`a conductive trace mounted on the substrate. This alloWs the
`connection outside of the sensing area to be made in the same
`processing step as the sensing electrodes Within it. Alterna
`tively, the roW Wrap-around connections may be made by a
`free Wire appropriately connected to the respective roW sens
`ing electrodes.
`The column sensing electrodes of a column of sensing cells
`at an edge of the sensing area may be electrically coupled to
`one another by column Wrap-around connections made out
`side of the sensing area in a similar fashion.
`The position sensor may further comprise a plurality of
`capacitance measurement channels connected to respective
`ones of the roWs of roW sensing electrodes and the columns of
`column sensing electrodes, Wherein each measurement chan
`nel is operable to generate a signal indicative of a capacitance
`betWeen its associated column or roW of sensing electrodes
`and a system ground.
`In addition, the position sensor may further comprise a
`processor operable to determine the position of the object
`along the ?rst direction by comparing signals from the col
`umns of column sensing electrodes and along the second
`direction by comparing signals from the roWs of roW sensing
`electrodes.
`This alloWs the determination of the position of a touch to
`be made using otherWise conventional circuitry connected to
`the sensing elements.
`The capacitance measurement channels may comprise
`charge transfer circuitry since this provides a reliable and
`robust Way to measure capacitances of the level that might be
`expected in a typical implementation. HoWever, other forms
`of capacitance measurement circuitry may equally be used. In
`general it is preferential to use a capacitive driver circuit that
`drives all the roWs and column connections in a substantially
`phase-synchronous manner so as to prevent the electric ?elds
`from cross-loading into adjacent roWs and columns. This is
`described also in Us. Pat. No. 5,463,388, Where all the roWs
`and column conductors are driven by a single oscillator.
`The sensing cells may be arranged into three or four col
`umns. This can provide a position sensor With su?icient reso
`lution over a typically siZed sensing area for most applica
`tions.
`The column and roW sensing electrodes in each sensing cell
`may be interleaved With one another (e. g. by spiraling around
`one another or being interlaced/intertwined), especially in
`designs Where the roW and column spacing is larger than that
`of a typical ?nger. This provides for a much more uniform
`blend of signals from the X andY drives in each intersecting
`location, alloWing better position reporting With respect to a
`?nger touching the overlying surface. This is described also in
`Us. Pat. No. 5,463,388, for example FIG. 2. In layouts Where
`the roW and column spacings are similar to or smaller than a
`human ?nger it is su?icient to use other arrangements of
`electrode pattern, for example an array of diamond shapes as
`shoWn in FIG. 8 and described further beloW.
`The position sensor may include a transparent substrate
`and transparent electrodes (e. g. formed from Indium Tin
`Oxide (ITO) deposited on the substrate). This alloWs it to be
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`placed over a display screen Without obscuring What is dis
`played beneath. Thus the display screen might be con?gured
`to display “virtual” buttons to a user that may be selected by
`the user placing their ?nger over the appropriate part of the
`display adjacent the position sensor. The position of the user’ s
`touch can then be compared With the positions of the “virtual”
`buttons being displayed to determine Which one has been
`selected.
`According to a second aspect of the invention there is
`provided a device comprising a position sensor according to
`the ?rst aspect of the invention. The position sensor may be
`used in many types of device. For example the device may be
`a portable/hand-held device, eg a personal data assistant
`(PDA), a multimedia player, a mobile (cell) phone, a re
`con?gurable remote controller, or a still camera or video
`camera, for example With the position sensor overlaying a
`display. Alternatively, the position sensor could equally be
`used in larger scale devices such as kitchen appliances,
`kiosks, and the like. Opaque versions can be fashioned for use
`in PC-style trackpads, keypads, and other human interface
`devices as are Well knoWn in the art.
`According to a third aspect of the invention there is pro
`vided a method of constructing a capacitively sensitive sur
`face disposed on a substrate Which reports an X-Y coordinate
`position of an object Within an active sensing region When the
`object is adjacent to said surface, comprising the steps of: (a)
`depositing a single layer of patterned conductive material in
`the active sensing region, the pattern comprising roWs and
`columns of electrodes connected to individual ones of capaci
`tive sensing channels, and Wherein at least one roW or column
`is broken into a plurality of segments Within the active region;
`(b) connecting the broken segments together With an electri
`cal conductor, Wherein the conductor is made to lie outside of
`the active sensing region; (c) connecting the roWs and col
`umns to individual sensing channels of a multi-channel
`capacitive sensor circuit having multiple outputs representing
`amplitudes of capacitance on the roWs and columns; and (d)
`providing a processor operable to process the multiple out
`puts to determine a coordinate position of the adjacent object
`as an XY location.
`The processor may be operable to compensate for position
`distortion introduced by the physical geometry of the pat
`terned conductive material.
`The processor may also be operable to calculate a centroid
`of the signals across roWs and a centroid of the signals across
`columns.
`According to a fourth aspect of the invention there is pro
`vided a capacitive position sensor for determining the posi
`tion of an object in a sensing area, the sensor comprising a
`substrate having a surface With an arrangement of conductive
`electrodes mounted thereon, Wherein the electrodes de?ne an
`array of sensing cells arranged in columns and roWs to form
`the sensing area, each sensing cell including a column sensing
`electrode and a roW sensing electrode, the column sensing
`electrodes of sensing cells in the same column being electri
`cally coupled together and the roW sensing electrodes of
`sensing cells in the same roW being electrically coupled
`together, Wherein at least one column sensing electrode com
`prises a continuous spine Within the sensing area, and the at
`least one other column is made electrically continuous via
`connections external to the sensing area.
`
`

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`US 7,821,502 B2
`
`5
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`For a better understanding of the invention and to show
`hoW the same may be carried into effect reference is noW
`made by Way of example to the accompanying drawings in
`Which:
`FIG. 1 schematically shoWs in plan vieW a knoWn tWo
`dimensional capacitive position sensor;
`FIG. 2 schematically shoWs in plan vieW another knoWn
`tWo-dimensional capacitive position sensor;
`FIG. 3 schematically shoWs in plan vieW a tWo-dimen
`sional capacitive position sensor according to an embodiment
`of the invention;
`FIG. 4 schematically shoWs in perspective vieW a device
`including the position sensor of FIG. 3;
`FIGS. 5A and 5B are graphs schematically shoWing
`capacitance as function of column number (FIG. 5A) and roW
`number (FIG. 5B) of sensing cells used to determine the
`position of an object adjacent the position sensor of the device
`shoWn in FIG. 4;
`FIG. 6 schematically shoWs in plan vieW the tWo-dimen
`sional capacitive position sensor and display screen of the
`device shoWn in FIG. 4;
`FIGS. 7 and 8 schematically shoW inplan vieW tWo-dimen
`sional capacitive position sensors according to other embodi
`ments of the invention;
`FIG. 9 schematically shoWs in plan vieW reported positions
`compared to actual positions for an object adjacent a position
`sensor according to an embodiment of the invention; and
`FIG. 10 schematically shoWs in plan vieW a display of the
`outlines of desired key positions compared to the outlines of
`reported key positions for a position sensor according to an
`embodiment of the invention.
`
`DETAILED DESCRIPTION
`
`FIG. 3 schematically shoWs in plan vieW a tWo-dimen
`sional touch-sensitive capacitive position sensor 22 accord
`ing to an embodiment of the invention. The position sensor 22
`is operable to determine the position of an object along a ?rst
`(x) and a second (y) direction, the orientation of Which are
`shoWn toWards the top left of the draWing. The sensor 22
`comprises a substrate 24 having an arrangement of sensing
`electrodes 26 mounted thereon. The sensing electrodes 26
`de?ne a sensing area Within Which the position of an object
`(eg a ?nger or stylus) adjacent the sensor may be deter
`mined. The substrate 24 is of a transparent plastics material
`and the electrodes are formed from a transparent ?lm of
`Indium Tin Oxide (ITO) deposited on the substrate 24 using
`conventional techniques. Thus the sensing area of the sensor
`is transparent and can be placed over a display screen Without
`obscuring What is displayed behind the sensing area. In other
`examples the position sensor may not be intended to be
`located over a display and may not be transparent; in these
`instances the ITO layer may be replaced With a more eco
`nomical material such as a copper laminate PCB, for
`example.
`The pattern of the sensing electrodes on the substrate 24 is
`such as to divide the sensing area into an array (grid) of
`sensing cells 28 arranged into roWs and columns. (It is noted
`that the terms “roW” and “column” are used here to conve
`niently distinguish betWeen tWo directions and should not be
`interpreted to imply either a vertical or a horizontal orienta
`tion.) By Way of example one of the sensing cell 28 is iden
`ti?ed by a dotted outline in FIG. 3. In this position sensor
`there are four columns of sensing cells aligned With the y-di
`rection and ?ve roWs of sensing cells aligned With the x
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`direction (tWenty sensing cells in total). The top-most roW of
`sensing cells for the orientation shoWn in FIG. 3 is referred to
`as roW y1, the next one doWn as roW y2, and so on doWn to roW
`y5. The columns of sensing cells are similarly referred to from
`left to right as columns x1 to x4. Thus the sensing cell 28
`shoWn With a dotted outline in FIG. 3 is at the intersection of
`roW y1 and column x3.
`Each sensing cell includes a roW sensing electrode 30 and
`a column sensing electrode 32. The roW sensing electrodes 30
`and column sensing electrodes are arranged Within each sens
`ing cell 28 to interleave With one another (in this case by
`squared spiraling around one another), but are not galvani
`cally connected. Because the roW and column sensing elec
`trodes are interleaved (intertWined), an object adjacent a
`given sensing cell can provide a signi?cant capacitive cou
`pling to both sensing electrodes irrespective of Where in the
`sensing cell the object is positioned. The characteristic scale
`of interleaving may be on the order of, or smaller than, the
`capacitive footprint of a typical object to be detected to pro
`vide the best results. The siZe and shape of the sensing cell 28
`can be comparable to that of the object to be detected or larger
`(Within practical limits).
`The roW sensing electrodes 30 of all sensing cells in the
`same roW are electrically connected together to form ?ve
`separate roWs of roW sensing electrodes. Similarly, the col
`umn sensing electrodes 32 of all sensing cells in the same
`column are electrically connected together to form four sepa
`rate columns of column sensing electrodes.
`The column sensing electrodes in column x2 are connected
`to one another by a connection 51, also referred to as a spine,
`made Within the sensing area by a part of one of the electrodes
`deposited on the substrate and Which runs betWeen columns
`x2 and x3. This connection runs the length ofthe sensing area.
`Thus a single continuous conductive electrode deposited on
`the substrate 24 provides the column sensing electrodes 32 of
`all of the sensing cells in column x2 and their interconnec
`tions. The column sensing electrodes in column x3 are simi
`larly connected to one another by a connection 53 made
`Within the sensing area, again running betWeen columns x2
`and x3 as a spine. Thus again a single continuous conductive
`electrode deposited in the substrate 24 provides the column
`sensing electrodes 32 of all of the sensing cells in column x3
`and their interconnections.
`The roW sensing electrodes 30 in columns x1 and x2 of roW
`y2 are also connected together by a connection made Within
`the sensing area. Thus a single continuous conductive elec
`trode 34 deposited on the substrate 24 provides the roW sens
`ing electrodes of the sensing cells in columns x1 and x2 of roW
`y2 and their interconnection. The roW sensing electrodes in
`columns x3 and x4 of roW y2 are similarly connected together
`by a connection made Within the sensing area so that a single
`continuous electrode 36 again provides these roW sensing
`electrodes and their interconnection. HoWever, because of the
`on-substrate connections (spines) running betWeen columns
`x2 and x3 to connect betWeen their respective column sensing
`electrodes, the roW sensing electrodes in columns x1 and x2
`of roW y2 cannot be connected to the roW sensing electrodes
`in columns x3 and x4 of roW y2 by a connection made on the
`surface of the substrate. Thus a connection 38 betWeen the
`roW sensing electrodes at opposing ends of this roW (i.e. in
`columns x1 and x4) is provided outside of the sensing area.
`The connection 38 runs around the outside of the sensing area
`to connect the electrode 34 providing the roW sensing elec
`trodes in columns x1 and x2 of roW y2 With the electrode 36
`providing the roW sensing electrodes in columns x3 and x4 of
`roW y2. Thus all roW sensing electrodes in this roW are elec
`trically connected together. Similar Wrap -around connections
`
`

`

`US 7,821,502 B2
`
`7
`outside of the sensing area are made to ensure the respective
`roW sensing electrodes of the other roWs are connected
`together. It is noted that although one is shoWn in FIG. 3, a
`connection outside of the sensing area betWeen the roW sens
`ing electrodes at opposing ends of roW y1 is not required
`because the spines connecting betWeen the column sensing
`electrodes of columns X2 and X3 need not extend to the very
`edge of the sensing area and a connection running along the
`top edge of the sensing area could be used to connect betWeen
`the roW sensing electrodes in roW y1 (not shoWn).
`Each column sensing electrode in column X1 is formed
`from a separate electrode on the substrate. These separate
`electrodes are connected together by connections 40 made
`external to (i.e. outside of) the sensing area. The column
`sensing electrodes in column X4 are connected together by
`connections 41 in a similar manner to those of column X1. In
`this fashion the outer tWo columns can be discontinuous
`Within the sensing area to alloW access by roW electrodes into
`cells, yet the columns are nevertheless made Whole.
`In this eXample the various connections made outside of
`the sensing area betWeen the roW sensing electrodes in sens
`ing cells at opposing ends of the respective roWs and the
`column sensing electrodes in the columns at the periphery of
`the sensing area are formed from free Wires attached to the
`electrodes of the sensing area as appropriate using conven
`tional techniques. Because the connections are established by
`free Wires, no di?iculties arise from the need for the connec
`tions made outside of the sensing area to cross one another in
`places. In an alternative design the connections made outside
`of the sensing area may be provided by conductive traces on
`the substrate similar to the electrodes forming the sensing
`ar