United States Patent [19]
`Du et al.
`
`USOO5856822A
`[11] Patent Number:
`[45] Date of Patent:
`
`5,856,822
`Jan. 5, 1999
`
`[54] TOUCH-PAD DIGITAL COMPUTER
`POINTING-DEVICE
`
`[75] Inventors: Sterling S. Du, Palo Alto; Yung-Yu
`Joe Lee, San Jose, both of Calif.
`
`[73] Assignee: 02 Micro, Inc., Santa Clara, Calif.
`
`[21] Appl. No.: 549,422
`[22] Filed:
`Oct‘ 27’ 199 5
`
`IIlt- Cl-6 ..................................................... ..
`U-S- Cl- ......................... ..
`[58] Field Of Search ................................... .. 345/ 157, 158,
`345/159, 173, 174, 175, 179, 180, 145
`_
`References Clted
`US PATENT DOCUMENTS
`
`[56]
`
`5:327:161
`5,424,756
`
`gjta?idee """"""""""""""""" " 345/157
`7/1994 102211 et at". ......................
`345/157
`6/1995 H0 et al. ............................... .. 345/158
`
`OTHER PUBLICATIONS
`
`Diehl, Stanford, “Touchpads to Navigate By,” Byte, p. 150,
`Oct. 1995.
`
`Primary Examiner—Steven J. Saras
`Assistant Examiner—David Lewis
`Attorney, Agent, or Firm—Donald E. Schreiber
`
`[57]
`
`ABSTRACT
`
`A touch-pad digital computer pointing-device, for control
`ling a position of a cursor appearing on a display screen of
`a digital computer, senses and resolves respective locations
`Within an active area at Which concurrent multi-?nger con
`tacts occur. Multi-?nger contacts With the active area acti
`Vate or deactivate a drag-lock Operating mode, Computer
`power Conservation, and other touch-pad Operating Charac
`teristics such as the touch-pad’s sensitivity to ?nger contact,
`The touch-pad also senses a velocity and direction for ?nger
`contact With the active area for use in transmitting data to the
`computer Which effects continuous cursor movement across
`the computer’s display screen in a direction ?xed by the
`initial direction of contact movement across the active area.
`While there is no ?nger contact With the active area, the
`touch'pad monitors the active area and adjusts its Operation
`to compensate for Changes in the Surrounding environment
`such as changes in temperature, humidity and atmospheric
`pressure.
`
`1 Claim, 5 Drawing Sheets
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`TCL EXHIBIT 1024
`Page 1 of 42
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`

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`U.S. Patent
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`Jan. 5, 1999
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`Sheet 1 of5
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`5,856,822
`
`FIG. 1
`
`O E F
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`TCL EXHIBIT 1024
`Page 2 of 42
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`

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`U.S. Patent
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`Jan. 5, 1999
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`Sheet 2 of5
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`5,856,822
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`TCL EXHIBIT 1024
`Page 3 of 42
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`U.S. Patent
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`Jan. 5, 1999
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`Sheet 3 of5
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`5,856,822
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`TCL EXHIBIT 1024
`Page 4 of 42
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`

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`U.S. Patent
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`Jan. 5, 1999
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`Sheet 4 of5
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`5,856,822
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`TCL EXHIBIT 1024
`Page 5 of 42
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`TCL EXHIBIT 1024
`Page 6 of 42
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`1
`TOUCH-PAD DIGITAL COMPUTER
`POINTING-DEVICE
`
`BACKGROUND OF THE INVENTION
`
`1. Field of the Invention
`The present invention relates generally to pointing
`devices used in conjunction With digital computer displays,
`and, more particularly, to small touch-pads Which, in
`response to a ?nger’s movement across a touch-pad’s active
`area, cause motion of a cursor across a computer’s display
`screen.
`2. Description of the Prior Art
`Pointing-devices for controlling a cursor on a digital
`computer’s display screen are essential for using a computer
`that employs a graphic user interface (“GUI”). Various
`different types of pointing-devices are available such as
`mice, trackballs, joysticks, digitiZer tablets and touch-pads.
`Each of these different devices exhibits certain limitations.
`For example, operating a mouse requires an appreciable
`amount of free area on a relatively smooth Work surface
`immediately adjacent to the computer. Sliding, i.e.
`translating, a mouse across such a Work surface rolls a ball
`that is secured Within the mouse, and that contacts the
`surface. Rolling of the ball Within the mouse effects a
`corresponding movement of the cursor across the display
`screen. Moreover, a computer program that receives the
`mouse’s output signal may ?lter the mouse’s signal to
`provide special effects. For example, the same translation of
`a mouse may move the cursor a greater or lesser distance
`across the computer’s screen depending upon the speed of
`the mouse’s translation. HoWever, even With such ?ltering
`and even With an appreciable amount of free Work surface
`area, achieving a desired cursor movement frequently
`requires lifting the mouse and moving it through the air
`Without touching the Work surface.
`A trackball essentially is a mouse turned upside doWn.
`Consequently, rather than rolling a ball by translating the
`trackball’s base across a surface, the trackball’s base
`remains ?xed and one rolls the ball directly With a ?nger.
`Consequently, a trackball enjoys an advantage over a mouse
`in that it requires only a ?xed amount of space on a desk, or
`in a laptop or notebook personal computer. HoWever, a
`trackball experiences problems With contamination because
`it must have an upWard facing opening around the ball
`through Which dust particles may enter its mechanism.
`Trackballs may also experience contamination problems if
`they are manipulated by a dirty ?nger.
`A joystick is an elongated member that usually protrudes
`upWard from a ?xed base. A joystick converts a displace
`ment of the elongated member from a pre-established neu
`tral position into a continuous movement of the cursor
`displayed on a computer’s screen. Consequently, a displace
`ment of the joystick does not provide absolute control over
`the cursor’s position as does the movement of a mouse or
`trackball. Rather, at best a joystick controls only the direc
`tion and speed of the cursor’s movement. Therefore, several
`successive joystick displacements may be required to posi
`tion a cursor at a desired location on a computer’s screen.
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`As contrasted With a mouse, a trackball, or a joystick; a
`digitiZer tablet permits immediately specifying, usually
`using a special stylus, an exact position at Which a cursor is
`to be located on a computer’s display screen. HoWever, the
`one-to-one correlation betWeen positions on a digitiZer tab
`let’s Working surface and positions on the computer’s dis
`play screen requires that an adequately high resolution
`
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`digitiZer be a physically large device. Consequently, gener
`ally a digitiZer tablet is unsuitable for use With a laptop or
`notebook personal computer.
`Particularly for laptop or notebook personal computers,
`touch-pads alleviate many of the problems experienced With
`other types of pointing-devices. Touch-pads are small digi
`tiZer tablets that, similar to a mouse or trackball, provide
`relative rather than absolute control over a cursor’s position
`usually in response to a ?nger’s movement across the
`touch-pad’s active area. Similar to a trackball, touch-pads
`occupy only a small, ?xed amount of Work surface area.
`Moreover, a touch-pad may be sealed so it doesn’t suffer
`from the contamination problems generally experienced by
`trackballs. HoWever, because a touch-pad is physically
`small, effecting large cursor movements across a computer’s
`display screen may require several successive ?nger strokes
`across the touch-pad’s active area. To address this particular
`limitation of touch-pads, US. Pat. No. 5,327,161 (“the ’161
`patent”), Which issued on an application ?led by James D.
`Logan and Blair Evans, discloses a touch-pad Which, similar
`to a joystick, causes a cursor on a computer’s display screen
`to continue moving in a pre-established direction even
`though ?nger movement across the touch-pad’s active area
`halts. This patent discloses that continued cursor motion
`occurs if a ?nger moving across the touch-pad’s active area
`enters a pre-established border area at the perimeter of the
`active area. Alternatively, this patent discloses that contin
`ued cursor motion can occur upon activation of a mechanical
`“drag sWitch,” disposed beneath the touch-pad, in combi
`nation a ?nger movement across the touch-pad’s active area.
`A limitation of the techniques for simulating a large
`touch-pad active area disclosed in the ’161 patent are that
`inadvertently entering the border area, or inadvertently
`pressing too hard on the touch-pad, automatically triggers
`continued cursor motion. Consequently, at times the touch
`pad disclosed in the ’161 patent may exhibit dif?culty in
`positioning a cursor analogous to the dif?culty sometimes
`experienced With a joystick. Moreover, dedication of the
`touch-pad’s border area for sensing only continued cursor
`motion reduces the amount of touch-pad active area that
`provides relative cursor positioning.
`
`SUMMARY OF THE INVENTION
`An object of the present invention is to provide a touch
`pad that requires no border area or a mechanical drag sWitch
`for effecting continuous cursor movement across a comput
`er’s display screen.
`Another object of the present invention is to provide a
`touch-pad that provides both continuous cursor movement
`across a computer’s display screen, and relative cursor
`positioning throughout the touch-pad’s entire active area.
`Another object of the present invention is to provide a
`touch-pad that does not require pressing a key to effect
`drag-lock operation.
`Another object of the present invention is to provide a
`touch-pad that can accept and utiliZe simultaneous multi
`?nger contacts With the touch-pad’s active area.
`Another object of the present invention is to provide a
`touch-pad that permits operator control over a laptop or
`notebook computer’s poWer management capabilities.
`Another object of the present invention is to provide a
`touch-pad that provides direct touch-pad control of the
`touch-pad’s operating characteristics.
`Another object of the present invention is to provide a
`touch-pad that adapts its operation to environmental condi
`tions such as temperature, humidity, and atmospheric pres
`sure.
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`Another object of the present invention is to provide a
`touch-pad for laptop or notebook computers that facilitates
`adding an external mouse or trackball as an auxiliary input
`device.
`Another object of the present invention is to provide a
`touch-pad for laptop or notebook computers that permits
`adding an external mouse or trackball as an auxiliary input
`device While maintaining operation of all active computer
`programs.
`Another object of the present invention is to provide a
`touch-pad for attachment to a host computer that includes
`the preceding advantages, and Which does not require the
`use of a driver computer program executed by the host
`computer.
`Brie?y the present invention is a touch-pad digital com
`puter pointing-device that permits controlling a position of
`a cursor appearing on a display screen of a digital computer.
`The touch-pad includes an active area that responds to both
`single and concurrent multi-?nger contacts. Furthermore,
`the touch-pad senses and resolves respective locations
`Within the active area at Which concurrent multi-?nger
`contacts occur. A computer port interface, included in the
`touch-pad, responds to ?nger contacts With the active area
`by transmitting data to a digital computer that indicates a
`?nger contact in the active area.
`Accordingly, if the touch-pad is not presently operating in
`a drag-lock operating mode, the touch-pad activates a drag
`lock operating mode if the touch pad senses a ?rst contact
`With the active area While concurrently sensing a second
`contact Within a pre-established speci?c location in the
`active area. Alternatively, if the touch-pad is presently
`operating in a drag-lock operating mode, While one ?nger
`contacts another area on the touch-pad a subsequent contact
`With the pre-established speci?c location deactivates the
`drag-lock operating mode.
`The touch-pad also responds to concurrent multi-?nger
`contacts Within pre-established speci?c locations in the
`active area that persist throughout a pre-established time
`interval. In one instance, such touch-pad operation transmits
`a control signal to a digital computer coupled to the touch
`pad. The computer, particularly a laptop or notebook
`computer, may respond to this control signal by activating or
`deactivating a loW-poWer “suspend” operating mode. In
`other instances, such touch-pad operation alters various
`touch-pad operating characteristics such as the touch-pad’s
`sensitivity to ?nger contact.
`The touch-pad also senses a velocity and direction at
`Which a contact to the touch-pad moves across the active
`area. If the contact velocity exceeds a pre-established
`threshold, the touch-pad alters a characteristic of data sub
`sequently transmitted to the digital computer. In particular,
`after sensing such a high velocity contact With the active
`area, upon the contact’s subsequently sloWing doWn or even
`becoming stationary, the touch-pad alters the transmitted
`data to effect continuous cursor movement across the display
`screen in a direction ?xed by the initial direction of contact
`movement across the active area.
`If the touch-pad is not sensing a contact With the active
`area, the touch-pad also records a quantity indicative of the
`response of the active area to ?nger contact. The touch-pad
`then uses the recorded quantity in adjusting a threshold for
`sensing a subsequent contact With the active area. In this
`Way the touch-pad compensates for changes in environment
`surrounding the touch-pad such as temperature, humidity
`and atmospheric pressure.
`Atouch-pad in accordance With the present invention may
`be implemented in tWo distinctly different embodiments. In
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`one embodiment, the touch-pad is external to the digital
`computer and communicates With the digital computer
`through the computer’s serial port. In another embodiment,
`particularly useful for a laptop or notebook computer, the
`touch-pad is physically incorporated into the computer’s
`structure. In such an integrated embodiment, the touch-pad
`also provides a second serial port for coupling a mouse or
`trackball that is external to the laptop or notebook computer.
`Moreover, such an external auxiliary input device may be
`plugged into the computer’s second serial port While com
`puter programs are executing, ie the auxiliary input device
`may be “hot plugged” into the computer.
`These and other features, objects and advantages Will be
`understood or apparent to those of ordinary skill in the art
`from the folloWing detailed description of the preferred
`embodiment as illustrated in the various draWing ?gures.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a perspective vieW depicting a touch-pad digital
`computer pointing-device in accordance With the present
`invention that is adapted for coupling to a serial port of a
`laptop or notebook computer also depicted in FIG. 1;
`FIG. 2 is an exploded, perspective vieW of a preferred
`embodiment of an active area of the touch-pad depicted in
`FIG. 1 that employs capacitance for sensing ?nger contact
`With the active area;
`FIG. 3, consisting of FIGS. 3a and 3b, is a block diagram
`depicting electronic circuits included in a preferred embodi
`ment of the touch-pad that employs capacitance sensing;
`FIG. 4 is a timing diagram depicting Waveforms that
`occur Within the electronic circuits depicted in FIG. 3 as
`those circuits capacitively sense a contact to the touch-pad’s
`active area as depicted in FIG. 2;
`FIG. 5 is a block diagram depicting a computer having a
`touch-pad in accordance With the present invention inte
`grated therein;
`FIG. 6 is a elevational vieW of a computer display screen
`taken along the line 6—6 in FIG. 1 that graphically depicts
`a drag-lock operation; and
`FIG. 7 is a plan vieW depicting the touch-pad’s active area
`illustrating pre-established speci?c locations Within the
`active area Which permit access to special touch-pad func
`tions.
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENT
`
`Referring noW to FIG. 1, depicted there is a touch-pad in
`accordance With the present invention referred to by the
`general reference character 20. The touch-pad 20 includes a
`2.64 inch by 2.0 inch active area 22 that is surrounded by an
`escutcheon 24. Disposed at opposite ends of a relatively
`Wide front edge 26 of the escutcheon 24 are respectively a
`left button 32 and a right button 34. The left and right
`buttons 32 and 34 operate the same as left and right buttons
`on a conventional digital computer mouse or trackball. The
`touch-pad 20 also includes a cable 36 one end of Which
`passes through a rear edge 37 of the escutcheon 24. Secured
`to the other end of the cable 36 is a serial-port connector 38.
`The serial-port connector 38 permits connecting the touch
`pad 20 to a serial port of a digital computer such as a laptop
`or notebook computer 42 depicted in FIG. 1. The computer
`42 includes a display screen 44 that is secured Within an
`upper half 46 of the computer 42. During execution of a
`computer program that employs a GUI, a cursor appears on
`the display screen 44.
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`Referring noW to FIG. 2, the active area 22 consists of a
`double sided printed circuit board 52, depicted With dashed
`lines, that is approximately seventy one-hundredths (0.070)
`of an inch thick. The printed circuit board 52 has an upper
`surface 54 on Which are preferably formed tWenty-four (24)
`parallel, elongated, electrically-conductive X-aXis sensing
`traces 56. The X-aXis sensing-traces 56 are aligned parallel
`to a Y-aXis 58 of the active area 22. As more clearly depicted
`in FIG. 3b, each X-aXis sensing-trace 56 includes a repeating
`pattern consisting of a rectangularly-shaped bar 62 at one
`end of Which is a solid, circularly-shaped disk 64. Immedi
`ately adjacent disks 64 are spaced approximately 0.11 inches
`apart, Which is also the spacing betWeen immediately adja
`cent X-aXis sensing-traces 56. An annularly-shaped terminal
`eyelet 66 terminates both ends of each X-aXis sensing-trace
`15
`56 to permit forming an electrical connection thereto. A
`separate guard ring 68, Which surrounds the X-aXis sensing
`traces 56, may also be disposed on the upper surface 54 of
`the printed circuit board 52. If the printed circuit board 52
`includes the guard ring 68, the guard ring 68 is electrically
`connected to circuit ground.
`Referring again to FIG. 2, the printed circuit board 52 has
`a loWer surface 74 on Which are preferably formed eighteen
`(18) parallel, elongated, electrically-conductive Y-aXis
`sensing-traces 76. The Y-aXis sensing-traces 76 are aligned
`parallel to a X-aXis 78 of the active area 22. As more clearly
`depicted in FIG. 3b, each Y-aXis sensing-trace 76 includes a
`repeating pattern consisting of a rectangularly-shaped bar 82
`at one end of Which is an annularly-shaped eyelet 84. Similar
`to the X-aXis sensing-traces 56, immediately adjacent eye
`lets 84 are spaced approximately 0.11 inches apart, Which is
`also the spacing betWeen immediately adjacent Y-aXis
`sensing-traces 76. An annularly-shaped terminal eyelet 86
`terminates both ends of each Y-aXis sensing-trace 76 to
`permit forming an electrical connection thereto.
`As depicted in FIG. 3b, one terminal eyelet 66 and one
`terminal eyelet 86 respectively of each of the X-aXis
`sensing-traces 56 and Y-aXis sensing-traces 76 connects to a
`cathode 92 of a diode 94. Anodes 96 of each of the diodes
`94 connect in parallel to circuit ground 98. The other
`terminal eyelet 66 and other terminal eyelet 86 respectively
`of each of the X-aXis sensing-traces 56 and Y-aXis sensing
`traces 76 connects to a collector 102 of a PNP transistor 104.
`An emitter 106 of each of the PNP transistors 104 connects
`in parallel respectively either to a X-aXis capacitance
`charging line 108, or to a Y-aXis capacitance-charging line
`112. In the preferred embodiment of the touch-pad 20 there
`are four (4) X-aXis capacitance-charging lines 108 and three
`(3) Y-aXis capacitance-charging lines 112. Each of the
`X-aXis capacitance-charging lines 108 and Y-aXis
`capacitance-charging lines 112 connects in parallel to the
`emitters 106 of siX (6) PNP transistors 104. The collectors
`102 of the siX (6) PNP transistors 104 connect respectively
`to siX (6) immediately adjacent X-aXis sensing-traces 56 or
`Y-aXis sensing-traces 76. In this Way, the tWenty-four (24)
`X-aXis sensing-traces 56 are subdivided by the X-aXis
`capacitance-charging lines 108 into four (4) independent
`groups each one of Which includes siX (6) X-aXis sensing
`traces 56, While the eighteen (18) Y-aXis sensing-traces 76
`are subdivided by the Y-aXis capacitance-charging lines 112
`into three (3) independent groups each one of Which also
`includes siX (6) Y-aXis sensing-traces 76.
`As illustrated in FIG. 3b, the diodes 94 and the PNP
`transistors 104 are all enclosed betWeen a dashed line 114
`and a dashed line 116. Enclosing the diodes 94 and the PNP
`transistors 104 betWeen the dashed lines 114 and 116 illus
`trates that the diodes 94 and PNP transistors 104, together
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`With all other components of the touch-pad 20 depicted in
`FIG. 3 that are located betWeen the dashed lines 114 and 116,
`are preferably all included in a single application speci?c
`integrated circuit (“ASIC”).
`Each of the X-aXis capacitance-charging lines 108 and
`each of the Y-aXis capacitance-charging lines 112 connects
`to a ?rst terminal of a 390 kilo-ohm (“k9”) resistor 122, and
`to an anode 124 of a diode 126. Acathode 128 of each of the
`diodes 126 and a second terminal of each resistor 122
`connect in parallel to an output 132 of an inverter 134. As
`illustrated in FIG. 3b, the resistors 122 and the diodes 126
`are outside the dashed lines 114 and 116, and are therefore
`preferably eXcluded from the ASIC. Depending upon the
`state of a logic signal supplied either via a charge-X-aXis
`trace line 136 or via a charge-Y-aXis-trace line 138 to an
`input 142 of each inverter 134, the electrical potential
`present at the output 132 of each inverter 134 is either near
`ground potential or near VCC, Which is a negative voltage.
`A base 146 of each of the PNP transistors 104 is coupled
`through a resistor 152 to an anode 154 of a diode 156. A
`cathode 158 of each of the diodes 156 is coupled either to
`one (1) of tWenty-four (24) X-aXis select lines 162a through
`162x, or to one (1) of eighteen (18) Y-aXis select lines 164a
`through 1641'.
`FIG. 4 depicts voltage Waveforms that occur Within the
`electronic circuits depicted in FIG. 3. A line-charging-pulse
`Waveform 172 illustrates an electrical potential present at the
`input 142 to any of the inverters 134. As described above,
`While the input 142 is at a high electrical potential, the
`electrical potential at the output 132 of the inverter 134 is
`negative. The negative potential present at the output 132 is
`coupled through the parallel connected resistor 122 and
`diode 126 from the output 132 either to one of the X-aXis
`capacitance-charging lines 108, or to one of the Y-aXis
`capacitance-charging lines 112. The emitters 106 of the siX
`(6) PNP transistors 104 connected to the X-aXis capacitance
`charging line 108 or to the Y-aXis capacitance-charging line
`112 receive the electrical potential present thereon. To
`turn-on a particular PNP transistors 104, a negative potential
`line-selection-pulse Waveform 174 is applied to the cathode
`158 of one of the diodes 156. Turning-on the PNP transistor
`104 couples the negative potential present on the X-aXis
`capacitance-charging line 108 or on the Y-aXis capacitance
`charging line 112 to the selected X-aXis sensing-trace 56 or
`Y-aXis sensing-trace 76. A trace-voltage Waveform 176 in
`FIG. 4 illustrates the electrical potential thus imposed on the
`selected X-aXis sensing-trace 56 or Y-aXis sensing-trace 76.
`Upon the line-charging-pulse Waveform 172 initially hav
`ing a high electrical potential and the line-selection-pulse
`Waveform 174 initially having a loW electrical potential, the
`trace-voltage Waveform 176 present on the X-aXis sensing
`trace 56 or on the Y-aXis sensing-trace 76 immediately
`begins charging toWard a negative VCC potential. During
`such charging of the X-aXis sensing-trace 56 or Y-aXis
`sensing-trace 76, electrical current ?oWs primarily through
`the diode 126 of the parallel connected diode 126 and
`resistor 122. Consequently, the X-aXis sensing-trace 56 or
`the Y-aXis sensing-trace 76 charges comparatively sWiftly
`toWard the VCC potential. Subsequently, When the line
`charging-pulse Waveform 172 returns to a loW electrical
`potential While the line-selection-pulse Waveform 174
`remains at a loW potential, the electrical potential present on
`the X-aXis sensing-trace 56 or on the Y-aXis sensing-trace 76
`immediately begins discharging back toWard ground poten
`tial. HoWever, during such discharging of the X-aXis
`sensing-trace 56 or Y-aXis sensing-trace 76, the diode 126 is
`“back-biased,” Which prevents current flow through the
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`diode 126. “Back-biasing” of the diode 126, consequently,
`forces virtually all the electrical current to How more slowly
`through only the 390 kQ resistor 122.
`If there exists no ?nger contact With the active area 22
`immediately adjacent to the selected X-axis sensing-trace 56
`or Y-axis sensing-trace 76, then the capacitance of the X-axis
`sensing-trace 56 or Y-axis sensing-trace 76 is loWer, and
`therefore the electrical potential on the X-axis sensing-trace
`56 or Y-axis sensing-trace 76 discharges more quickly
`toWard ground potential as indicated by a dashed-line seg
`ment 176a of the trace-voltage Waveform 176. HoWever, if
`?nger contact With the active area 22 exists immediately
`adjacent to the X-axis sensing-trace 56 or to the Y-axis
`sensing-trace 76, then the capacitance of the X-axis sensing
`trace 56 or Y-axis sensing-trace 76 increases, and therefore
`the electrical potential on the X-axis sensing-trace 56 or
`Y-axis sensing-trace 76 discharges more sloWly as indicated
`by a dashed-line segment 176b of the trace-voltage Wave
`form 176.
`Referring again to FIG. 3b, each of the X-axis
`capacitance-charging lines 108 and Y-axis capacitance
`charging lines 112 connects respectively to an inverting
`input 182 of a comparator 184. Consequently, the touch-pad
`20 includes seven (7) comparators 184, four (4) comparators
`184 for the four (4) groups of X-axis sensing-traces 56, and
`three (3) comparators 184 for the three (3) groups of Y-axis
`sensing-traces 76. Areference voltage VRef, having a poten
`tial approximately one-half that of VCC, is supplied to a
`non-inverting input 186 of each of the comparators 184.
`Each of the comparators 184 exhibits hysteresis so the
`comparators 184 do not change state either until the elec
`trical potential present at its inverting input 182 is signi?
`cantly less than VRef, or is signi?cantly greater than VRef.
`The threshold voltages for changing state by the compara
`tors 184 are depicted in FIG. 4 by dashed, parallel com
`parator threshold-lines 188a and 188b. Thus, as the X-axis
`sensing-trace 56 or the Y-axis sensing-trace 76 initially
`begins charging, as illustrated by the trace-voltage Wave
`form 176, the electrical potential present at an output 192 of
`the comparator 184 depicted in a comparator-output Wave
`form 194 remains at a loW potential until the trace-voltage
`Waveform 176 descends beloW the loWer comparator
`threshold-line 188a. After the trace-voltage Waveform 176
`crosses the comparator threshold-line 188a, the comparator
`output Waveform 194 changes to a high electrical potential,
`and remains at that high potential until the trace-voltage
`Waveform 176 subsequently rises above the comparator
`threshold-line 188b. After the trace-voltage Waveform 176
`crosses the comparator threshold-line 188b, the comparator
`output Waveform 194 returns to a loW potential.
`Referring noW to FIG. 3a, the electrical potentials respec
`tively present at each output 192 of the comparators 184 are
`respectively coupled either by an X-axis comparator-output
`signal-line 202 or by a Y-axis comparator-output signal-line
`204 to an input 206 respectively either of an X-axis clock
`gating circuit 212, or of an Y-axis clock-gating circuit 214.
`Each X-axis clock-gating circuit 212, of Which there are four
`(4) (one X-axis clock-gating circuit 212 for each group of six
`(6) X-axis sensing-traces 56), receives an eight (8) mega
`hertZ (“MHZ”) clock signal via a clock signal-line 216 from
`a 80C51 microprocessor 218. Analogously, each Y-axis
`clock-gating circuit 214, of Which there are three (3) (one
`Y-axis clock-gating circuit 214 for each group of six (6)
`Y-axis sensing-traces 76), also receives the 8 MHZ clock
`signal from the microprocessor 218 via the clock signal-line
`216.
`While the electrical potential present at the output 192 of
`the comparator 184 remains loW as indicated by the
`
`10
`
`15
`
`25
`
`35
`
`45
`
`55
`
`65
`
`8
`comparator-output Waveform 194 in FIG. 4, the X-axis
`clock-gating circuit 212 or the Y-axis clock-gating circuit
`214 blocks the 8 MHZ clock signal from reaching a clock
`output 222. HoWever, When the trace-voltage Waveform 176
`descends beloW the comparator threshold-line 188a and the
`comparator-output Waveform 194 changes to a high
`potential, the X-axis clock-gating circuit 212 or the Y-axis
`clock-gating circuit 214 transmits the 8 MHZ clock signal to
`their respective clock outputs 222 as indicated by a clock
`output-signal Waveform 224 in FIG. 4. The X-axis clock
`gating circuit 212 or the Y-axis clock-gating circuit 214
`continues transmitting the 8 MHZ clock signal to the clock
`output 222 until the trace-voltage Waveform 176 again rises
`above the comparator threshold-line 188b and the
`comparator-output Waveform 194 returns to a loW electrical
`potential. As is readily apparent from FIG. 4, if there does
`not exist a ?nger contact to the active area 22 immediately
`adjacent to the X-axis sensing-trace 56 or Y-axis sensing
`trace 76, the X-axis clock-gating circuit 212 or the Y-axis
`clock-gating circuit 214 transmits feWer clock pulses from
`the clock output 222 than are transmitted if a ?nger contacts
`the active area 22 immediately adjacent to the X-axis
`sensing-trace 56 or Y-axis sensing-trace 76.
`Referring again to FIG. 3a, the clock outputs 222 of each
`of the X-axis clock-gating circuits 212 and of the Y-axis
`clock-gating circuits 214 are respectively connected either to
`a X-axis clock-input 232 or to a Y-axis clock-input 234 of a
`tWo-hundred and ?fty-six (256) bit counter 236, of Which
`four (4) are included in the touch-pad 20. Each counter 236
`receives a counter reset signal from the microprocessor 218
`via a counter-reset signal-line 238. While the electrical
`potential on the counter-reset signal-line 238 remains at a
`high potential, as illustrated by the counter-reset-signal
`Waveform 242 in FIG. 4, the counters 236 do not respond to
`clock signals present at the X-axis clock-input 232 or the
`Y-axis clock-input 234. HoWever, When the counter-reset
`signal Waveform 242 changes to a loW potential concurrent
`With the line-charging-pulse Waveform 172 also changing to
`a loW potential, the counters 236 begin counting 8 MHZ
`clock pulses present either at their X-axis clock-input 232 or
`at their Y-axis clock-input 234. Moreover, the counters 236
`then continue counting 8 MHZ clock pulses until the trace
`voltage Waveform 176 rises above the comparator threshold
`line 188b. Thus, When the line-selection-pulse Waveform
`174 returns to a high potential each of the counters 236 holds
`a count that indicates the capacitance of the selected X-axis
`sensing-trace 56 or Y-axis sensing-trace 76, ie that indi
`cates Whether or not a ?nger contacted the active area 22
`immediately adjacent to the X-axis sensing-trace 56 or
`Y-axis sensing-trace 76.
`As illustrated in FIG. 3a, the microprocessor 218, Which
`preferably is an 80C51 microprocessor manufactured by
`Intel Corporation of Santa Clara, Calif., includes both a read
`only memory (“ROM”) 252, and a random access memory
`(“RAM”) 254. The ROM 252 stores a computer program
`executed by the microprocessor 218 While the RAM 254
`stores temporary data used by the computer program in
`controlling the operation of the touch-pad 20, and in
`exchanging communications With a digital computer via the
`cable 36 and serial-port connector 38. As is Well knoWn to
`those skilled in the art, the serial-port connector 38 and cable
`36 also supply electrical poWer to the touch-pad 20 to
`energiZe its operation.
`The computer program execute