United States Patent [19J
`Duet al.
`
`111111111111111111111111111111111111111111111111111111111111111111111111111
`US005856822A
`[11] Patent Number:
`[45] Date of Patent:
`
`5,856,822
`Jan. 5, 1999
`
`[54]
`
`[75]
`
`TOUCH-PAD DIGITAL COMPUTER
`POINTING-DEVICE
`
`Inventors: Sterling S. Du, Palo Alto; Yung-Yu
`Joe Lee, San Jose, both of Calif.
`
`[73]
`
`Assignee: 02 Micro, Inc., Santa Clara, Calif.
`
`[21]
`
`[22]
`
`[51]
`[52]
`[58]
`
`[56]
`
`Filed:
`
`Appl. No.: 549,422
`Oct. 27, 1995
`....................................................... G09G 5/08
`Int. Cl. 6
`U.S. Cl. ........................... 345/145; 345/157; 345/173
`Field of Search ..................................... 345/157, 158,
`345/159, 173, 174, 175, 179, 180, 145
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`3/1988 Watanabe ................................ 345/157
`4/1994 Gerpheide ............................... 345/174
`7/1994 Logan et a!. ............................ 345/157
`6/1995 Ho et a!. ................................. 345/158
`
`4,734,685
`5,305,017
`5,327,161
`5,424,756
`
`OTHER PUBLICATIONS
`Diehl, Stanford, "Touchpads to Navigate By," Byte, p. 150,
`Oct. 1995.
`
`Primary Examiner-Steven 1. Saras
`Assistant Examiner-David Lewis
`Attorney, Agent, or Firm-Donald E. Schreiber
`
`[57]
`
`ABSTRACT
`
`A touch-pad digital computer pointing-device, for control(cid:173)
`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-finger con(cid:173)
`tacts occur. Multi-finger contacts with the active area acti(cid:173)
`vate or deactivate a drag-lock operating mode, computer
`power conservation, and other touch-pad operating charac(cid:173)
`teristics such as the touch-pad's sensitivity to finger contact.
`The touch-pad also senses a velocity and direction for finger
`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 fixed by the
`initial direction of contact movement across the active area.
`While there is no finger 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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`RingCentral Ex-1027, p. 1
`RingCentral v. Estech
`IPR2021-00574
`
`

`

`U.S. P a t e n t
`U.S. Patent
`
`Jan. 5, 1999
`Jan. S, 1999
`
`Sheet 1 of 5
`S h e e t 1 o f 5
`
`5,856,822
`5,856,822
`
`! 20
`F/G. 1
`
`
`
`RingCentral Ex-1027, p. 2
`RingCentral Ex-1027,p. 2
`RingCentral v. Estech
`RingCentral v. Estech
`IPR2021-00574
`IPR2021-00574
`
`

`

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`RingCentral Ex-1027, p. 3
`RingCentral v. Estech
`IPR2021-00574
`
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`RingCentral Ex-1027, p. 4
`RingCentral v. Estech
`IPR2021-00574
`
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`

`

`U.S. Patent
`
`Jan. 5, 1999
`
`Sheet 4 of 5
`
`5,856,822
`
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`RingCentral Ex-1027, p. 5
`RingCentral v. Estech
`IPR2021-00574
`
`

`

`U.S. Patent
`
`Jan. 5, 1999
`
`Sheet 5 of 5
`
`5,856,822
`
`274
`
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`RingCentral Ex-1027, p. 6
`RingCentral v. Estech
`IPR2021-00574
`
`

`

`5,856,822
`
`1
`TOUCH-PAD DIGITAL COMPUTER
`POINTING-DEVICE
`
`BACKGROUND OF THE INVENTION
`
`15
`
`2
`digitizer be a physically large device. Consequently, gener(cid:173)
`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(cid:173)
`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 finger's movement across the
`10 touch-pad's active area. Similar to a trackball, touch-pads
`occupy only a small, fixed 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 finger strokes
`across the touch-pad's active area. To address this particular
`limitation of touch-pads, U.S. Pat. No. 5,327,161 ("the '161
`patent"), which issued on an application filed 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 finger movement across the touch-pad's active area
`halts. This patent discloses that continued cursor motion
`occurs if a finger 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(cid:173)
`ued cursor motion can occur upon activation of a mechanical
`"drag switch," disposed beneath the touch-pad, in combi-
`30 nation a finger 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
`35 continued cursor motion. Consequently, at times the touch(cid:173)
`pad disclosed in the '161 patent may exhibit difficulty in
`positioning a cursor analogous to the difficulty sometimes
`experienced with a joystick. Moreover, dedication of the
`touch-pad's border area for sensing only continued cursor
`40 motion reduces the amount of touch-pad active area that
`provides relative cursor positioning.
`
`1. Field of the Invention
`The present invention relates generally to pomtmg(cid:173)
`devices used in conjunction with digital computer displays,
`and, more particularly, to small touch-pads which, in
`response to a finger'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 filter 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 filtering
`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 fixed and one rolls the ball directly with a finger.
`Consequently, a trackball enjoys an advantage over a mouse
`in that it requires only a fixed amount of space on a desk, or
`in a laptop or notebook personal computer. However, a
`trackball experiences problems with contamination because 45
`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 finger.
`A joystick is an elongated member that usually protrudes
`upward from a fixed base. A joystick converts a displace(cid:173)
`ment of the elongated member from a pre-established neu(cid:173)
`tral position into a continuous movement of the cursor
`displayed on a computer's screen. Consequently, a displace(cid:173)
`ment of the joystick does not provide absolute control over 55
`the cursor's position as does the movement of a mouse or
`trackball. Rather, at best a joystick controls only the direc(cid:173)
`tion and speed of the cursor's movement. Therefore, several
`successive joystick displacements may be required to posi(cid:173)
`tion a cursor at a desired location on a computer's screen.
`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(cid:173)
`let's working surface and positions on the computer's dis(cid:173)
`play screen requires that an adequately high resolution
`
`20
`
`25
`
`50
`
`SUMMARY OF THE INVENTION
`An object of the present invention is to provide a touch(cid:173)
`pad that requires no border area or a mechanical drag switch
`for effecting continuous cursor movement across a comput(cid:173)
`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(cid:173)
`finger 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
`60 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
`65 touch-pad that adapts its operation to environmental condi(cid:173)
`tions such as temperature, humidity, and atmospheric pres-
`sure.
`
`RingCentral Ex-1027, p. 7
`RingCentral v. Estech
`IPR2021-00574
`
`

`

`5,856,822
`
`4
`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
`10 plugged into the computer's second serial port while com(cid:173)
`puter programs are executing, i.e 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
`15 from the following detailed description of the preferred
`embodiment as illustrated in the various drawing figures.
`
`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 finger 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(cid:173)
`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(cid:173)
`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 specific locations within the
`active area which permit access to special touch-pad func-
`45 tions.
`
`3
`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.
`Briefly the present invention is a touch-pad digital com(cid:173)
`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-finger contacts. Furthermore,
`the touch-pad senses and resolves respective locations
`within the active area at which concurrent multi-finger
`contacts occur. A computer port interface, included in the
`touch-pad, responds to finger contacts with the active area
`by transmitting data to a digital computer that indicates a
`finger 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(cid:173)
`lock operating mode if the touch pad senses a first contact
`with the active area while concurrently sensing a second
`contact within a pre-established specific location in the 30
`active area. Alternatively, if the touch-pad is presently
`operating in a drag-lock operating mode, while one finger
`contacts another area on the touch-pad a subsequent contact
`with the pre-established specific location deactivates the
`drag-lock operating mode.
`The touch-pad also responds to concurrent multi-finger
`contacts within pre-established specific locations in the
`active area that persist throughout a pre-established time(cid:173)
`interval. In one instance, such touch-pad operation transmits
`a control signal to a digital computer coupled to the touch- 40
`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 finger 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- 50
`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 55
`screen in a direction fixed 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 finger contact. The touch-pad 60
`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.
`A touch-pad in accordance with the present invention may
`be implemented in two distinctly different embodiments. In
`
`35
`
`20
`
`25
`
`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
`65 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.
`
`RingCentral Ex-1027, p. 8
`RingCentral v. Estech
`IPR2021-00574
`
`

`

`5,856,822
`
`5
`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(cid:173)
`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 10
`end of which is a solid, circularly-shaped disk 64. Immedi(cid:173)
`ately adjacent disks 64 are spaced approximately 0.11 inches
`apart, which is also the spacing between immediately adja(cid:173)
`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(cid:173)
`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 20
`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. TheY-axis sensing-traces 76 are aligned 25
`parallel to aX-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- 30
`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 andY-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 andY-axis sensing(cid:173)
`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(cid:173)
`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(cid:173)
`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(cid:173)
`trates that the diodes 94 and PNP transistors 104, together
`
`6
`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 specific
`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 first terminal of a 390 kilo-ohm ("kQ") resistor 122, and
`to an anode 124 of a diode 126. A cathode 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 vee, 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 164r.
`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
`35 capacitance-charging lines 112. The emitters 106 of the six
`(6) PNP transistors 104 connected to the X-axis capacitance(cid:173)
`charging line 108 or to theY-axis capacitance-charging line
`112 receive the electrical potential present thereon. To
`turn-on a particular PNP transistors 104, a negative potential
`40 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 theY-axis capacitance(cid:173)
`charging line 112 to the selected X -axis sensing -trace 56 or
`45 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(cid:173)
`ing a high electrical potential and the line-selection-pulse
`50 waveform 174 initially having a low electrical potential, the
`trace-voltage waveform 176 present on the X-axis sensing(cid:173)
`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
`55 sensing-trace 76, electrical current flows 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-
`60 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 theY-axis sensing-trace 76
`immediately begins discharging back toward ground poten-
`65 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
`
`RingCentral Ex-1027, p. 9
`RingCentral v. Estech
`IPR2021-00574
`
`

`

`5,856,822
`
`7
`diode 126. "Back-biasing" of the diode 126, consequently,
`forces virtually all the electrical current to flow more slowly
`through only the 390 kQ resistor 122.
`If there exists no finger 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- 10
`ment 176a of the trace-voltage waveform 176. However, if
`finger 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(cid:173)
`trace 56 or Y-axis sensing-trace 76 increases, and therefore
`the electrical potential on the X-axis sensing-trace 56 or 15
`Y-axis sensing-trace 76 discharges more slowly as indicated
`by a dashed-line segment 176b of the trace-voltage wave(cid:173)
`form 176.
`Referring again to FIG. 3b, each of the X-axis
`capacitance-charging lines 108 and Y-axis capacitance(cid:173)
`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. A reference voltage VRef, having a poten(cid:173)
`tial approximately one-half that of vee, 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(cid:173)
`trical potential present at its inverting input 182 is signifi(cid:173)
`cantly less than VRef, or is significantly greater than VRef.
`The threshold voltages for changing state by the compara(cid:173)
`tors 184 are depicted in FIG. 4 by dashed, parallel com(cid:173)
`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(cid:173)
`form 176, the electrical potential present at an output 192 of
`the comparator 184 depicted in a comparator-output wave(cid:173)
`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(cid:173)
`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(cid:173)
`output waveform 194 returns to a low potential.
`Referring now to FIG. 3a, the electrical potentials respec(cid:173)
`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(cid:173)
`gating circuit 212, or of anY-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(cid:173)
`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
`
`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(cid:173)
`output-signal waveform 224 in FIG. 4. The X-axis clock(cid:173)
`gating c