Touch-Pad Digital Computer Pointing-Device

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 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 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 displacement of the elongated member from a pre-established neutral position into a continuous movement of the cursor displayed on a computer's screen. Consequently, a displacement 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 direction and speed of the cursor's movement. Therefore, several successive joystick displacements may be required to position 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 tablet's working surface and positions on the computer's display screen requires that an adequately high resolution digitizer be a physically large device. Consequently, generally 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 digitizer 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 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 continued cursor motion can occur upon activation of a mechanical "drag switch," disposed beneath the touch-pad, in combination 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 continued cursor motion. Consequently, at times the touch-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 motion reduces the amount of touch-pad active area that provides relative cursor positioning.

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 computer'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-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 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 conditions such as temperature, humidity, and atmospheric pressure.

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 computer 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-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 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-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 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 subsequently 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 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 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 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 computer 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 from the following detailed description of the preferred embodiment as illustrated in the various drawing figures.

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 embodiment 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 integrated 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 functions.

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.

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. Immediately adjacent disks 64 are spaced approximately 0.11 inches apart, which is also the spacing between immediately adjacent X-axis sensing-traces 56. An annularly-shaped terminal eyelet 66 terminates both ends of each X-axis sensing-trace 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 eyelets 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 illustrates that the diodes 94 and PNP transistors 104, together 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 ("k.OMEGA.") 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 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 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 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 having 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 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-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 potential. 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 diode 126. "Back-biasing" of the diode 126, consequently, forces virtually all the electrical current to flow more slowly through only the 390 k.OMEGA. 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 segment 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-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 waveform 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. A reference voltage VRef, having a potential 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 electrical potential present at its inverting input 182 is significantly less than VRef, or is significantly greater than VRef. The threshold voltages for changing state by the comparators 184 are depicted in FIG. 4 by dashed, parallel comparator 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 waveform 176, the electrical potential present at an output 192 of the comparator 184 depicted in a comparator-output waveform 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 respectively 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) megahertz ("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 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 finger 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 finger 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 fifty-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, i.e. that indicates whether or not a finger 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 executed by the microprocessor 218 senses the condition of the active area 22 by transmitting control signals to the inverters 134 via the charge-X-axis-trace line 136 or the charge-Y-axis-trace line 138, to the four (4) X-axis clock-gating circuits 212 and the three (3) Y-axis clock-gating circuits 214 via the clock signal-line 216, and to the four (4) counters 236 via the counter-reset signal-line 238; and by exchanging data with the counters 236, a X-axis decoder 262, and a Y-axis decoder 264 via an address-and-data bus 266. Data stored into the X-axis decoder 262 and the Y-axis decoder 264 by the computer program executed by the microprocessor 218 are decoded to provide signals for selecting individual PNP transistors 104. The signals generated by the X-axis decoder 262 and the Y-axis decoder 264 for selecting individual PNP transistors 104 are transmitted from the X-axis decoder 262 to the X-axis PNP transistors 104 via the X-axis select lines 162a through 162x, and are transmitted from the Y-axis decoder 264 to the Y-axis PNP transistors 104 via the Y-axis select lines 164a through 164r.

To initiate sensing the condition of the active area 22, the computer program executed by the microprocessor 218 transmits control signals via either the charge-X-axis-trace line 136 or the charge-Y-axis-trace line 138 either to all four (4) of the X-axis inverters 134 or to all three (3) Y-axis inverters 134 to activate either all four (4) X-axis capacitance-charging lines 108 or all three (3) Y-axis capacitance-charging lines 112. Concurrently, the computer program executed by the microprocessor 218 stores data via the address-and-data bus 266 into either the X-axis decoder 262 or into the Y-axis decoder 264. The X-axis decoder 262 or the Y-axis decoder 264 respectively decodes such data to select for charging one X-axis sensing-trace 56 or Y-axis sensing-trace 76 out of each group of six (6) X-axis sensing-traces 56 or Y-axis sensing-traces 76. Subsequently, the computer program executed by the microprocessor 218 terminates charging of the four (4) selected X-axis sensing-traces 56 or the three (3) selected Y-axis sensing-traces 76 by changing the line-charging-pulse waveform 172 present either on the charge-X-axis-trace line 136 or on the charge-Y-axis-trace line 138 from a high to a low potential, while concurrently releasing the counters 236 by changing the counter-reset-signal waveform 242 present on the counter-reset signal-line 238 from a high to a low potential. At the end of the discharge interval, the computer program executed by the microprocessor 218 stores data via the address-and-data bus 266 either into the X-axis decoder 262 or into the Y-axis decoder 264 which de-selects the X-axis sensing-traces 56 or the Y-axis sensing-traces 76, while concurrently retrieving via the address-and-data bus 266 the counts then present in each of the four (4) counters 236.

In this way the computer program executed by the microprocessor 218 repetitively scans all the X-axis sensing-traces 56 and then all the Y-axis sensing-traces 76 to determine X and Y coordinates at which one or more fingers contact the active area 22. If in sensing the condition of the active area 22 the computer program executed by the microprocessor 218 senses finger contact at two or more immediately adjacent X-axis sensing-traces 56 or immediately adjacent Y-axis sensing-traces 76, it filters such data to assign a unique X-axis and/or Y-axis coordinate to each finger contact. Moreover, the computer program executed by the microprocessor 218 may also analyze sensing finger contact at two or more immediately adjacent X-axis sensing-traces 56 or Y-axis sensing-traces 76 to evaluate how much finger pressure is applied to the active area 22.

If the computer program executed by the microprocessor 218 does not sense a finger contact with the touch-pad 20 it begins recording data that indicates the capacitance of the X-axis sensing-trace 56 and the Y-axis sensing-trace 76 in the absence of a finger contact. If there is no finger contact throughout a time interval that exceeds 2 milliseconds, preferably 5 milliseconds, the computer program then adjusts data values stored in the RAM 254 which specify a threshold for sensing a finger contact with the active area 22. In this way, the touch-pad 20 compensates for changes in environment surrounding the touch-pad such as temperature, humidity, and atmospheric pressure.

In addition to sensing individual and multiple finger contacts to the active area 22 of the touch-pad 20, the computer program executed by the microprocessor 218 also exchanges data with the computer 42 via the cable 36 and the serial-port connector 38. In effecting such exchanges of data with the computer 42, the computer program executed by the microprocessor 218 emulates operation of a conventional mouse or trackball. Accordingly, the touch-pad 20 may be used with any computer 42 with which a conventional mouse or trackball may be used.

While the touch-pad 20 has been described thus far as a unit separate and distinct from the computer 42, it is readily apparent that the touch-pad 20 may be physically incorporated into a laptop or notebook computer 42. Incorporation of the touch-pad 20 into a computer 42 permits directly coupling both an external keyboard 268 to a host computer main printed circuit board ("PCB") 274, and the touch-pad 20 to a primary serial port 272 of the main PCB 274, as depicted in FIGS. 5. However, the touch-pad 20 thus incorporated into the computer 42 may also provide a secondary serial port 276 for coupling to the computer 42 an external auxiliary input device 278 such as a mouse or trackball. If the active area 22 provides a secondary serial port 276 for a computer 42, the computer program executed by the microprocessor 218 in addition to communicating with the computer 42 via the cable 36 and the serial-port connector 38, also exchanges data with the auxiliary input device 278 For a computer 42 having the configuration depicted in FIG. 5, both the touch-pad 20 and the auxiliary input device 278 are active, and either may be used as an input device to the computer 42. However, if both the touch-pad 20 and the auxiliary input device 278 attempt to provide input data to the computer 42 simultaneously, input data from the touch-pad 20 takes precedence over that from the auxiliary input device 278. Moreover, the auxiliary input device 278 may be "hot plugged" into the secondary serial port 276 during execution of computer programs by a microprocessor included in the main PCB 274 without adversely impacting the operation of such computer programs, and to immediately commence operation as an input device for controlling cursor position.

The touch-pad 20 of the present invention is capable of sensing and resolving concurrent contacts of multiple fingers to the active area 22. That is, as the computer program executed by the microprocessor 218 repetitively scans the X-axis sensing-traces 56 and the Y-axis sensing-traces 76, if two or more fingers concurrently contact the active area 22, the computer program senses contacts either at two different X-axis locations on the active area 22, or at two different Y-axis locations, or at two different X-axis and two different Y-axis locations. The ability of the computer program executed by the microprocessor 218 to sense concurrent multi-finger contacts with the active area 22 permits the touch-pad 20 to perform a variety of useful functions in response to such multi-finger contacts at different specific locations within the active area 22.

Referring now to FIG. 6, depicted there is an elevational view of the display screen 44 of the computer 42 depicted in FIG. 1 on which appears a window-outline 282 generated by a GUI. Window operations commonly permitted by a GUI include either moving the window-outline 282 to another location on the display screen 44, or changing the size of the window-outline 282. FIG. 6 graphically illustrates changing the size of the window-outline 282 by positioning a double-headed arrow 284 at a lower right-hand corner 286 of the window-outline 282. Once the double-headed arrow 284 appears on the display screen 44, performing a "drag-lock" operation by concurrently pressing both one button of a conventional mouse or trackball while moving either the mouse or the trackball permits enlarging or reducing the size of the window-outline 282, as indicated by the dashed-line window-outlines 282a and 282b. Due to the small physical size of the active area provided by touch-pads, it is awkward to perform a drag-lock operation by pressing one button of a conventional touch-pad while concurrently moving a finger across the conventional touch-pad's active area.

Referring now to FIG. 7, the touch-pad 20 of the present invention permits performing a drag-lock operation easily by contacting one finger to the active area 22 while concurrently contacting a second finger within a pre-established specific location in the active area 22. Specifically, a concurrent second finger contact 292a or 292b, respectively illustrated by dashed-line circles in FIG. 7, in either a lower left-hand corner 294 or a lower right-hand corner 296 of the active area 22, respectively demarcated in FIG. 7 by dashed-lines, initially activates a drag-lock operating mode of the touch-pad 20. After the touch-pad 20 enters its drag-lock operating mode, it remains in that operating mode even if finger contact with the active area 22 ceases. However, a subsequent finger contact within either the lower left-hand corner 294 or the lower right-hand corner 296 of the active area 22 while another finger contacts some other area on the active area 22 deactivates the drag-lock operating mode.

Moreover, in response to concurrent finger contacts both within the lower left-hand corner 294 and within the lower right-hand corner 296 which persist for a pre-established time-interval longer than one-half second, preferably one second, the touch-pad 20 transmits a control signal to the computer 42 via a normally unused pin in the serial-port connector 38. A power management computer program executing within the computer 42 that senses transmission of this control signal by the touch-pad 20 can respond to the signal by activating a low-power suspend operating mode of the computer 42, if the computer 42 is not already operating in the suspend operating mode. Conversely, if the computer 42 is already operating in the suspend operating mode, then, in response to the control signal, the computer program executed by the computer 42 deactivates the low-power suspend operating mode.

In addition to the pre-established specific locations in the lower left-hand corner 294 and the lower right-hand corner 296, the touch-pad 20 also includes five (5) additional pre-established specific locations arranged in a horizontal row along an upper edge 302 of the active area 22. Concurrent finger contacts with particular pairs of these specific locations which persist for a pre-established time-interval longer than one-half second, preferably one second, alter particular operating characteristics of the touch-pad 20. Thus, a first finger contact 304 and a second finger contact 306, respectively illustrated by dashed-line circles in FIG. 7, in an upper right-hand corner 308 and in an upper left-hand corner 312 of the active area 22, respectively demarcated in FIG. 7 by dashed-lines, which persist for the pre-established time-interval select either a greater or a lesser increase in cursor translation for the same finger contact movement speed. That is, if the active area 22 is operating with the lesser increase in cursor translation when the finger contacts 304 and 306 occur, then the touch-pad 20 establishes the greater increase in cursor translation for the same contact movement speed. Conversely, if the active area 22 is operating with the greater increase in cursor translation when the finger contacts 304 and 306 occur, then the touch-pad 20 establishes the lesser increase in cursor translation.

A first finger contact 304 in the upper right-hand corner 308 concurrent with a second finger contact 314 in a pre-established specific location 316 of the active area 22 which persist for the pre-established time-interval interchanges X and Y coordinate axes of the touch-pad 20.

A first finger contact 304 in the upper right-hand corner 308 concurrent with a second finger contact 318 in a pre-established specific location 322 of the active area 22 which persist for the pre-established time-interval alters a pre-established threshold for sensing finger contact with the active area 22. Specifically, the touch-pad 20 operates either with a lower pre-established threshold for sensing finger contact with the active area 22 or with a higher pre-established threshold for sensing finger contact. If the touch-pad 20 is operating with the lower pre-established threshold for sensing finger contact when the concurrent contacts occur which persist throughout the pre-established time-interval, then the touch-pad 20 establishes the higher pre-established threshold for sensing finger contact. Conversely, if the touch-pad 20 is operating with the higher pre-established threshold for sensing finger contact when the concurrent contacts occur which persist throughout the pre-established time-interval, then the touch-pad 20 establishes the lower pre-established threshold for sensing finger contact in response to the concurrent first finger contact 304 and second finger contact 318.

A first finger contact 304 in the upper right-hand corner 308 concurrent with a second finger contact 324 in a pre-established specific location 326 of the active area 22 which persist for the pre-established time-interval activates or deactivates all the special operating modes of the touch-pad 20. Specifically, if the touch-pad 20 is operating in a mode in which it does not respond to concurrent contacts within another pair of pre-established specific locations for a pre-established time-interval, then the touch-pad 20 activates an operating mode in which it responds to contacts with other pairs of pre-established specific locations for the pre-established time-interval, in addition to concurrent finger contacts with the upper right-hand corner 308 and with the immediately adjacent pre-established specific location 326. Conversely, if the touch-pad 20 is operating in a mode in which it responds to concurrent contacts within another pair of pre-established specific locations for a pre-established time-interval, then the touch-pad 20 deactivates that operating mode after sensing concurrent contacts with the upper right-hand corner 308 and with the immediately adjacent pre-established specific location 326.

In addition to sensing and responding to multi-finger contacts to the active area 22, the touch-pad 20 also senses both a direction and a velocity at which a finger contact moves across the active area 22. If the velocity at which a contact moves across the active area 22 exceeds a pre-established threshold of at least 1 inch per second, and preferably 5 inches per second, then the touch-pad 20 transmits data to the computer 42 which causes a cursor to continue moving across the display screen 44 in a direction fixed by an initial direction of contact movement across the active area 22. Moreover, as long as finger contact with the active area 22 persists, the touch-pad 20 continues transmitting data which causes the cursor to continue moving even if such contact with the active area 22 subsequently slows down or becomes stationary.

Similarly, if the computer program executed by the microprocessor 218 senses that finger contact pressure with the active area 22 exceeds a pre-established threshold while moving across the active area 22, then, similar to sensing a finger contact motion in excess of a pre-established threshold velocity, the touch-pad 20 also transmits data to the computer 42 which causes a cursor to continue moving across the display screen 44 in a direction fixed by an initial direction of contact movement across the active area 22. Moreover, as long as finger contact with the active area 22 persists, the touch-pad 20 continues transmitting data which causes the cursor to continue moving even if such contact with the active area 22 subsequently slows down or becomes stationary.

Computer Program

Set forth below is a listing of a copyrighted computer program executed by the microprocessor 218 in controlling the operation of the touch-pad 20. The copyright owner hereby grant others a right to reproduce copies of the patent document including the computer program or of the patent disclosure exactly as it appears in the files of the United States Patent and Trademark Office, but otherwise reserve all copyright rights whatsoever. ##SPC1##

Although the present invention has been described in terms of the presently preferred embodiment, it is to be understood that such disclosure is purely illustrative and is not to be interpreted as limiting. For example, while a 80C51 has been disclosed as the preferred microprocessor 218, which in conjunction with the computer program executed by the microprocessor 218 provides means for sensing finger contacts with the active area 22 while also providing a computer port interface means to the computer 42 and the secondary serial port 276 for coupling the auxiliary input device 278 to the computer 42, there exist various other equivalent devices which may be employed for effecting the same operations as those performed by the microprocessor 218. Accordingly, those skilled in the art will recognize that the microprocessor 218 may alternatively be implemented with various different models of microprocessors other than the 80C51, or might also be replaced with a custom designed ASIC or with an appropriately programmed field programmable gate array ("FPGA"). Consequently, without departing from the spirit and scope of the invention, various alterations, modifications, and/or alternative applications of the invention will, no doubt, be suggested to those skilled in the art after having read the preceding disclosure. Accordingly, it is intended that the following claims be interpreted as encompassing all alterations, modifications, or alternative applications as fall within the true spirit and scope of the invention.