(12) United States Patent
`Gerpheide et al.
`
`USOO673O863B1
`(10) Patent No.:
`US 6,730,863 B1
`(45) Date of Patent:
`May 4, 2004
`
`(54) TOUCHPAD HAVING INCREASED NOISE
`REJECTION, DECREASED MOISTURE
`SENSITIVITY, AND IMPROVEDTRACKING
`(75) Inventors: George Gerpheide, Salt Lake City, UT
`(US); Brian Taylor, Sandy, UT (US);
`Daniel Lee, Salt Lake City, UT (US)
`(73) Assignee: Cirque Corporation, Salt Lake City,
`UT (US)
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 361 days.
`
`s
`
`y
`
`s
`
`(*) Notice:
`
`a 149
`
`(21) Appl. No.: 09/603,417
`(22) Filed:
`Jun. 22, 2000
`O
`O
`Related U.S. Application Data
`(60) Provisional application No. 60/140,379, filed on Jun. 22,
`1999.
`(51) Int. Cl." ......................... G08C 21/00; G06K 11/06
`(52) U.S. Cl. ................................ 178/18.02; 178/2002;
`178/1806; 34.5/174
`(58) Field of Search ................................. 345/173-179.
`178/18.01, 18.02, 18.03, 18.05, 18.06, 18.07,
`18.08, 19.01, 19.03, 2001, 20.02, 20.03,
`2004
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`3,886,311 A 5/1975 Rodgers et al.
`4,071,691 A 1/1978 Pepper, Jr.
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`4,163,948 A 8/1979 Rieger et al.
`4,237,421. A 12/1980 Waldron
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`4,371,746 A 2/1983 Pepper, Jr.
`4,455,452 A 6/1984 Schuyler
`4,476.463 A 10/1984 Ng et al.
`4,495.485 A 1/1985 Smith
`4,528,684 A 7/1985 Iida et al.
`
`OC e a
`
`2
`
`a 2
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`4,587,378 A 5/1986 Moore
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`4,672,154 A 6/1987 Rodgers et al.
`4,680,430 A 7/1987 Yoshikawa et al.
`s: A
`E.
`t al.
`4,736,191 A 4/1988 Matzke et al.
`4,740,781. A
`4/1988 B
`4,743,895 A 5/1988 Rider
`4,803,709 A 2/1989 Kimata
`4,845,682 A 7/1989 Boozer et al.
`4,873,400 A 10/1989 Rapp et al.
`4,974,239 A 11/1990 Miwada
`4,975,830 A 12/1990 Gerpheide et al.
`4,993,053 A 2/1991 Itoh et al.
`5,033,068 A
`7/1991 Imai
`5,053,757 A 10/1991 Meadows
`5,073.908 A 12/1991 Cazaux
`(List continued on next page.)
`Primary Examiner Amr Ahmed Awad
`(74) Attorney, Agent, or Firm Morriss O'Bryant
`Compagni
`ABSTRACT
`(57)
`An improved touchpad and measurement circuitry for
`enabling input to a computer or other electronic device. The
`System includes an X electrode, a Y electrode, a common
`Sensing electrode, and a “water electrode, wherein these
`four separate electrodes can be implemented in various
`physical configurations to obtain the desired effects, wherein
`moisture and water droplets can be identified and compen
`Sated for So as not to interfere with the input of data, wherein
`noise rejection is achieved by using a time aperture filtering
`method, wherein an improved Scanning technique focuses
`Scanning around an identified input object, wherein an
`adaptive motion filter responds to the Speed and acceleration
`of an object being tracked, and wherein the measurement
`circuitry has an increased dynamic range enabling the touch
`pad to operate with greater tolerances to manufacturing
`variances.
`
`11 Claims, 3 Drawing Sheets
`
`
`
`
`
`WATER ELECTRODE N
`
`Sx
`
`X
`
`YELECTRODE
`
`4.
`
`O
`
`2
`
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`

`

`US 6,730,863 B1
`Page 2
`
`U.S. PATENT DOCUMENTS
`
`3/1993 Miller
`5.191,400 A
`4/1994 Gerpheide
`5,305,017 A
`7/1994 Logan et al.
`5,327,161. A
`... 178/18.02
`5,565,658 A * 10/1996 Gerpheide et al.
`5,631,666 A * 5/1997 Tagawa et al. ............. 34.5/104
`1/1999 Schedivy et al.
`5,861,583 A
`3/1999 Gillespie et al.
`5,880,411 A
`
`5,905,489 A * 5/1999 Takahama et al. .......... 345/174
`5,923,320 A * 7/1999 Murakami et al. .......... 345/179
`6,028,594 A
`2/2000 Inoue ...............
`... 34.5/173
`6,043,810 A
`3/2000 Kim et al. .................. 345/173
`6,229,528 B1 * 5/2001 Okajima et al. ............ 345/173
`6,366.866 B1
`4/2002 Kanagawa et al
`702/95
`2-Y/ / 2
`-
`
`- - - - - - - - - - -
`
`
`
`* cited by examiner
`
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`

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`U.S. Patent
`
`May 4, 2004
`
`Sheet 1 of 3
`
`US 6,730,863 B1
`
`74
`
`fC)
`
`T2
`
`- WATER ELECTRODE N
`Yx t!
`
`X I,
`
`YELECTRODE
`
`Fig. 1
`
`18
`
`16
`
`Fig. 2
`
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`

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`U.S. Patent
`
`May 4, 2004
`
`Sheet 2 of 3
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`US 6,730,863 B1
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`20
`
`Fig. 3
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`30
`
`SENSE
`
`-
`DRIVE
`
`REF
`D O-o-
`
`CONVERTER
`
`Fig. 4
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`

`

`U.S. Patent
`U.S. Patent
`
`May4, 2004
`
`Sheet 3 of 3
`
`US 6,730,863 B1
`US 6,730,863 B1
`
`ary
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`

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`1
`TOUCHPAD HAVING INCREASED NOSE
`REJECTION, DECREASED MOISTURE
`SENSITIVITY, AND IMPROVED TRACKING
`
`This application claims the benefit of Provisional appli
`cation Ser. No. 60/140,379 filed Jun. 22, 1999.
`
`BACKGROUND
`
`1. The Field of the Invention
`This invention relates generally to touchpad technology.
`Specifically, the invention is an improved System and appa
`ratus for utilizing a touchpad which is primarily used for
`cursor control on a computer display. The advantages of the
`invention relate generally to improved noise rejection,
`immunity to the effects of moisture on the touchpad Surface,
`increased manufacturing tolerances, an improved Scanning
`pattern, and an adaptive motion filter.
`2. The State of the Art
`The State of the art in capacitance Sensitive touchpad
`technology spans a variety of different technologies and
`methodologies for Sensing the location and movement of a
`pointing object as it moves acroSS a touchpad Surface. The
`means by which data can be input to a computer or other
`electronic apparatus are many. For example, one method of
`providing input is through manipulation of a cursor on a
`computer display. By controlling a cursor, the cursor can be
`caused to move icons or other objects on the display, Such
`as text, or Select buttons, hyperlinks or icons. In addition,
`discrete tappings on the touchpad Surface can be caused to
`actuate buttons or controls that are disposed beneath the
`cursor on the computer display. Another method of data
`input includes using gestures that can be recognized by
`programming routines disposed in the Software or firmware
`of the touchpad.
`However, regardless of whether the touchpad is being
`used for cursor control or any of the other methods of data
`input, touchpads are being called upon to be more versatile,
`and to operate more reliably, especially in adverse operating
`conditions and environments.
`The demands of data input reliability are especially
`becoming more critical. Touchpads are not only being used
`in many portable computers, but also in personal informa
`tion managers (PIMs) and personal digital assistants
`(PDAs). The desire to be mobile and at the same time
`connected to communications Services has consequently
`created the need for novel forms of data input. But new
`applications for the use of touchpads have brought more
`challenges for reliable performance. These challenges not
`only come from the devices in which they are used, but the
`environments in which they operate as well.
`For example, moisture on a touchpad Surface has always
`been a hindrance to reliable touchpad operation. But touch
`pads are not only being used in very humid climates, but also
`in inclement weather, where water droplets might Splash
`onto the touchpad Surface. State of the art touchpads perform
`poorly in these situations, again posing challenges to reliable
`touchpad performance.
`Weather and climate are not the only formidable problems
`for touchpads. For example, the electronic environment
`poses its own kind of challenges. Consider a portable
`computer that is operating on its own internal battery power
`Supply. The user might want to Save battery power by
`plugging into an AC outlet. The electronic noise generated
`by an AC power Source is very large, and can significantly
`impact the performance of a touchpad.
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`Another problem in the state of the art is inevitable when
`the touchpad is being used in a portable device. Power
`consumption will always be an issue when operating away
`from an AC or large DC power Source. However, touchpad
`circuitry has generally not been considered an area where
`power usage can be minimized. Nevertheless, it has been
`determined by the inventors that significant improvements in
`power conservation can be obtained.
`Accordingly, what is needed is an improved touchpad that
`is able to compensate for general electromagnetic noise
`(EMI) interference, as well as the more specific problems of
`noise from an AC power Source. It would also be an
`improvement to have increased immunity to the problems
`created for a touchpad when exposed to moisture and water
`droplets.
`Along with the noise and moisture problems identified
`above, there are other problems more general to touchpad
`performance. For example, manufacturing tolerances of the
`Sensing circuitry are not very forgiving in the State of the art.
`The result is that touchpads have required precision layout
`of Sensor electrodes. Without precision layout, the Sensing
`circuitry is not capable of compensating for variations in the
`layout. Thus, manufacturers have often had to use more
`costly PC boards to obtain the precise layout needed for
`reliable touchpad operation.
`Accordingly, it would be an improvement over the prior
`art to improve the performance of the Sensing circuitry Such
`that the circuitry could tolerate and compensate for greater
`variations in the layout of the Sensing electrodes. This can be
`accomplished by improving the dynamic range of the Sens
`ing circuitry.
`Another problem inherent to touchpads is locating a valid
`object on the touchpad Surface. The total number of mea
`Surements of the Sensing circuitry that are required to locate
`the valid object has a significant affect on power consump
`tion. Accordingly, it would an improvement over the prior
`art to have quicker Scanning algorithms, thereby enabling
`the Sensor circuitry to power down and thereby conserve
`power. It would also be an advantage over the prior art to be
`able to compensate for objects which are no longer consid
`ered to be valid objects on the touchpad Surface.
`Another reliability issue of touchpads lies in the Sensing
`circuitry. The prior art generally Scans for objects with a
`Single algorithm. In other words, there are no adjustments
`made in Scanning routines for objects that are moving
`rapidly or slowly.
`It would be an improvement over the prior art to utilize an
`adaptive motion filter which can compensate for the Speed at
`which an object on the touchpad Surface is moving. The
`advantage of this type of filtering is that the touchpad is
`capable of more precise Sensing when the object is moving
`Slowly, and keep pace with an object that is moving faster by
`using reduced filtering. Effectively, the resolution is
`decreased in exchange for keeping pace with the object
`being tracked.
`A last performance issue of prior art touchpads is con
`cerned with the Sampling of data from the Sensing elec
`trodes. Noise in the touchpad circuitry can prevent the
`Sensing circuitry from performing correctly.
`Therefore, it would be an advantage over the state of the
`art in touchpads to provide a filter which could compensate
`for noise and prevent false signals from affecting location
`calculations of the touchpad.
`OBJECTS AND SUMMARY OF THE
`INVENTION
`It is an object of the invention to provide a System and
`method for improved touchpad performance in the presence
`of moisture.
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`3
`It is another object to provide a System and method for
`improved touchpad performance when there is at least one
`water droplet on a touchpad Surface.
`It is another object to provide a System and method for
`improved touchpad performance through increased elec
`tronic noise rejection.
`It is another object to provide a System and method for
`improved touchpad performance through increased EMI and
`power Supply noise rejection.
`It is another object to provide a System and method for
`improved power conservation through an improved Scan
`ning routine used in the identification and tracking of objects
`on the touchpad Surface.
`It is another object to provide a System and method for
`improved identification of objects on a touchpad Surface So
`that eXtraneous objects can be more readily ignored by
`touchpad circuitry.
`It is another object to provide a System and method for
`improved touchpad performance regarding tracking of
`objects relative to Speed and acceleration by being able to
`adjust tracking resolution relative to the Speed of an object
`being tracked.
`It is another object to provide a System and method for
`improved tolerance to manufacturing variations by provid
`ing Sensing circuitry with an increased dynamic range.
`It is another object to provide a System and method for
`improved position detection by using time aperture filtering
`to reduce the effects of noise.
`The above objects are realized in a specific illustrative
`embodiment of a System and method including a touchpad
`and measurement circuitry for enabling input to a computer
`or other electronic device. The system includes an X
`electrode, a Y electrode, a common Sensing electrode, and a
`35
`“water electrode, where these four Separate electrodes can
`be implemented in various physical configurations to obtain
`the desired effects, wherein moisture and water droplets can
`be identified and compensated for So as not to interfere with
`the input of data, wherein noise rejection is achieved by
`using a time aperture filtering method, where an improved
`Scanning technique focuses Scanning around an identified
`input object, and where an adaptive motion filter responds to
`the Speed and acceleration of an object being tracked, and
`wherein the measurement circuitry has an increased
`dynamic range enabling the touchpad to operate with greater
`tolerances to manufacturing variances.
`In accordance with a first aspect of the invention, the
`touchpad disposes the water electrode as near to the Surface
`of the touchpad as is practical. In a preferred embodiment,
`the X or Y electrode is combined with the water electrode
`just beneath the touchpad Surface.
`In accordance with a Second aspect of the invention, the
`water electrode capacitively couples to water on the touch
`pad Surface to thereby balance the added capacitance
`between the drive (X and Y) electrodes and the common
`Sensing electrode.
`In accordance with a third aspect of the invention, a
`Scanning method is modified to more rapidly identify the
`presence of an input object Such as a finger. The Scanning
`pattern is then minimized around the location of the finger,
`eliminating the need to Scan the entire touchpad Surface until
`the finger is removed.
`In accordance with a fourth aspect of the invention, a
`quicker Scanning routine results in reduced power consump
`tion because the Sensing circuitry completes its locating and
`tracking task more efficiently.
`
`4
`In accordance with a fifth aspect of the invention, inherent
`imbalances within the touchpad Sensors are reduced to
`thereby enable the touchpad to be able to tolerate larger
`manufacturing discrepancies thereof.
`In accordance with a sixth aspect of the invention, a time
`aperture filter is used to more Selectively obtain position
`information of an object on the touchpad Surface, thereby
`reducing the deleterious affects of noise.
`In accordance with a Seventh aspect of the invention, the
`aperture filter Selectively obtains position information using
`a changing frequency, thereby further eliminating unwanted
`noise which is otherwise Synchronous with the Sampling rate
`of the time aperture filter.
`In accordance with an eighth aspect of the invention, an
`adaptive motion filter makes adjustments to a level of
`precision and a response rate relative to the Speed and
`acceleration of a tracked object.
`In accordance with a ninth aspect of the invention,
`improved identification of objects on a touchpad Surface
`enables the System to ignore extraneous objects.
`These and other objects, features, advantages and alter
`native aspects of the present invention will become apparent
`to those skilled in the art from a consideration of the
`following detailed description taken in combination with the
`accompanying drawings.
`
`BRIEF DESCRIPTION OF THE DRAWING
`FIG. 1 is a perspective and expanded illustration of the
`touchpad Surface and the electrode planes which is made in
`accordance with the presently preferred embodiment of the
`invention.
`FIG. 2 is a top view of an electrode plane which shows a
`preferred configuration of interleaving for the preferred two
`electrodes which are present thereon.
`FIG. 3 is a graphical view showing a waveform of a drive
`Signal which is applied to the X and Y electrodes as taught
`by the parent application.
`FIG. 4 is a circuit diagram which shows the preferred
`method of applying a time aperture filter to the measurement
`circuitry of the touchpad, to thereby prevent a Substantial
`portion of noise that affects the circuitry from interfering
`with the measurements.
`FIG. 5 is a block diagram which shows the relationship of
`the components within a capacitance Sensitive touchpad
`which is made in accordance with the principles of the
`presently preferred embodiment.
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`Reference will now be made to the drawings in which the
`various elements of the present invention will be given
`numerical designations and in which the invention will be
`discussed So as to enable one skilled in the art to make and
`use the invention. It is to be understood that the following
`description is only exemplary of the principles of the present
`invention, and should not be viewed as narrowing the claims
`which follow.
`The present invention makes significant improvements in
`the overall performance of a touchpad. However, while
`Some of the improvements are Specific to a capacitance
`Sensitive touchpad, other improvements are more general
`ized. Nevertheless, the presently preferred embodiment of
`the invention is a capacitance Sensitive touchpad having a
`plurality of electrodes disposed in a plurality of electrode
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`S
`planes or layers. The circuitry and operation thereof are
`presently integrated into the PEGASUS(TM) chip of Cirque
`Corporation.
`FIG. 1 shows that, in the presently preferred embodiment,
`two electrode planes 10, 12 are utilized. The figure is a
`profile view which exaggerates the thicknesses of the
`electrodes, and the distance between the electrode planes 10,
`12 and the touchpad surface 14. It is also preferred that a
`“water' electrode be incorporated into the top electrode
`plane 10. This placement is preferred as a result of the
`function of the water electrode. In order to capacitively
`couple to water on the touchpad Surface 14, the water
`electrode needs to be as close as possible to the touchpad
`surface 14 in order to minimize its size. The farther away
`from the touchpad surface 14 that the water electrode is
`positioned, the larger it must be.
`Advantageously, it is possible to dispose another elec
`trode in the electrode plane 10. Because it is also preferable
`to Separate the drive electrodes from the common Sensing
`electrode, the X or the Yelectrode is disposed therein. This
`is accomplished by interleaving or interdigitating the water
`electrode and the X or Y electrode. For the purposes of the
`preferred embodiment, the X electrode is Selected as Sharing
`the top electrode plane 10. The X electrode and the water
`electrode are shown “on end” in this view. It is also observed
`that only a few electrodes are illustrated in this figure. The
`actual number of electrodes is greater in an actual touchpad.
`This figure is for illustration purposes only.
`The Y electrode and the common Sensing electrode are
`disposed on the bottom electrode plane 12. The Yelectrode
`is interleaved with the common Sensing electrode to reduce
`the total number of electrode planes that are used. This
`results in a cost Savings, and reduced complexity in the
`design. The Y electrode and the common Sensing electrode
`are shown on a side edge, thus exposing only one of them
`in FIG. 1.
`FIG. 2 is a top view of an electrode plane. The figure is
`provided to illustrate one possible configuration of elec
`trodes on a surface thereof. What is important to note is that
`there are a plurality of “fingers' which are interleaved to
`thereby maximize the extent of coverage by an electrode
`acroSS the area of the touchpad. The figure illustrates a
`preferred configuration of interleaving which would occur
`on both of the electrode planes 10 and 12 of FIG. 1.
`For example, the electrode 16 could be the X electrode of
`the top electrode plane 10, and the electrode 18 could be the
`water electrode. It is noted that the thickness, placement, and
`number of electrode fingerS is not to be considered to be
`accurate. The figure is provided only to illustrate the concept
`of using interleaved electrodes to make maximum use of a
`Single electrode plane by combining electrodes.
`Furthermore, it is also noted that the water electrode is most
`likely to have fingers that are wider than the X, Y or common
`Sense electrodes. It has been determined that the water
`electrode is ideally given a maximum amount of Surface area
`possible in order to couple to any liquid that is present on the
`touchpad Surface.
`It is observed that this illustration also serves to show the
`configuration of the Y electrode and the common Sensing
`electrode. The Y electrode would be shown as 16, and the
`common Sensing electrode as 18. Of course, the orientation
`of the Y and the common sensing electrode would be
`perpendicular to the orientation shown for the X electrode
`and the water electrode.
`Another advantage of the present invention is the ability
`to cancel out any signal generated by water that is disposed
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`6
`on the touchpad Surface. Using the touch Sensing circuitry of
`the present invention, a drop of water increases measured
`capacitance, while a finger decreases measured capacitance.
`This fact is used to balance a positively driven side of a
`touchpad to a negatively driven Side of the touchpad pad,
`thereby enabling software to cancel out the effect of the
`water. For this reason the water electrode is said to “balance'
`out the added capacitance between the drive electrodes (X
`and Y), and the common Sensing electrode. In other words,
`by adding an electrode which is dedicated to Subtracting the
`influence of water, the drive and Sensing electrodes are able
`to function as desired without interference by the water
`droplet.
`It is noted that the water droplet which is being detected
`and canceled by using the “water electrode out can be Some
`other liquid. The purpose of detecting and canceling out the
`effect of a liquid on the touchpad Surface is Solely to increase
`reliability of a touchpad device under many different oper
`ating conditions. While it is more likely that water is going
`to be the liquid that is present on the touchpad Surface, it is
`not the only liquid which the “water electrode will detect.
`Noise rejection in touchpad circuitry is a very important
`issue for portable devices. Portable devices which incorpo
`rate a touchpad can often be operated using an internal
`power Supply or by plugging in to an external power Source.
`Unfortunately, an external power Source can generate a
`Significant amount of noise which is not filtered from the
`touchpad or other System circuitry. For reliable operation,
`the touchpad needs to be able to reject noise which will
`otherwise generate false readings to the electrodes.
`Advantageously, a time aperture filter is utilized to filter
`out noise. The basic principle of operation is to only take a
`measurement reading when it is known that data can be read.
`In other words, by ignoring all other Signal input except
`during a short measurement window, extraneous Signals will
`have a much Smaller opportunity to affect touchpad perfor
`CC.
`FIG. 3 is provided to illustrate the concept above.
`Specifically, a waveform is shown having a frequency at
`which the electrodes X and Y generate a signal. It was
`observed that the most useful measurement information
`from the position Sensing electrodes is obtained during a
`relatively short time period with respect to the total duration
`of the driven signal. The relatively short useful time period
`is indicated by time frame 20. In contrast, the entire time
`period from the beginning of one Sensing Signal being
`generated to the next is indicated by time frame 22. FIG. 3
`is not shown to Scale because time frame 20 is approxi
`mately /20th in size relative to time frame 22. More
`Specifically, time frame 22 is approximately 10 us, and time
`frame 20 is approximately 500 ns in the presently preferred
`embodiment.
`FIG. 4 is provided as an illustration of a circuit 30 which
`can be utilized to accomplish the desired filtering. The
`aperture is placed at the back end of a transconductance
`amplifier, or in front of the converter. The aperture is opened
`just prior to an electrode transition, enabling the change
`from the transition to be transferred into the converter. When
`the aperture time is completed, the aperture is closed by
`transferring or draining any remaining charge to a reference.
`The result is that only the charge or Signal that is related to
`an electrode event is passed to the converter, and all other
`Signals that would be noise generated are stopped or filtered
`away from the converter. In other words, most of the
`measurement Signal can be ignored, thereby minimizing the
`time frame in which noise is able to influence the measure
`ment being taken from the common Sensing electrode.
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`7
`It is also realized that a noise Signal that is Synchronous
`with the preferred time aperture filter might still interfere
`with the Sensing function. Accordingly, an alternative
`embodiment is to vary the frequency that is driving the
`electrodes, and thus the frequency of the aperture window in
`which measurements are taken. This would eliminate the
`possibility of allowing a time Synchronous signal to regu
`larly interfere with the measurement process.
`It is noted that the Sources of noise are many, but are often
`from power Sources.
`The presently preferred embodiment also includes an
`adaptive motion filter. The adaptive motion filter will adjust
`performance of the touchpad in accordance with the chang
`ing parameters of an object being tracked. These parameters
`include the aspects of Speed and acceleration.
`For example, consider a finger on a touchpad which is
`Slowly moving over the Surface. The present invention first
`determines the presence of the finger, and then determines an
`instantaneous Speed of the finger. A speed threshold value is
`set within Software of the touchpad. The Software provides
`a trade off in performance of the touchpad. If the finger is
`determined to be moving slowly because its speed is below
`the Speed threshold value, then it is more advantageous if the
`touchpad provides greater precision in tracking the position
`of the finger as opposed to providing more rapid updates of
`the finger position. This is because slow movement is
`generally the result of a finger more precisely controlling
`movement of a cursor on a computer display. At the very
`least, the need for providing precise movement control was
`recognized, and thus incorporated into the present invention.
`The relatively slower position updates of the finger location
`are also inherently not a problem for the Simple fact that the
`finger is moving slowly.
`In contrast, the Software provides the opposite trade offin
`performance of the touchpad if the finger is determined to be
`moving rapidly because its Speed is above the Speed thresh
`old value. It is more advantageous, for example, if the
`touchpad provides quicker response in updating its location
`on the touchpad, and therefore the corresponding location of
`a cursor on a computer display. The finger is probably
`moving the cursor to a new location or even dragging an
`object acroSS a desktop. Precision in this case is not as
`important as making Sure that the cursor is accurately
`displaying the last known and relatively leSS precise position
`of the finger on the touchpad. Furthermore, the relatively
`lower precision of the finger location is inherently not a
`problem for the Simple fact that the finger is moving So
`quickly.
`It is observed that the acceleration and deceleration of the
`finger on the touchpad Surface is handled by using the same
`Speed threshold value. The measurements taken of the finger
`to determine the relatively instantaneous Speed of the finger
`are more than adequate to make compensations on the fly as
`the finger accelerates to a relatively constant Speed, and then
`decelerates to a Stop.
`It is also observed that there can be more than one Speed
`threshold value. For example, there can be a lower Speed
`threshold, midrange Speed, and upper Speed threshold.
`Accordingly, the factors of precision and response could be
`modified at the for these three different areas, or for an even
`greater number of divisions of Speed. However, for
`Simplicity, the preferred embodiment operates under a
`Scheme which defines two possible levels of precision and
`response time.
`Another feature of the presently preferred embodiment is
`the improvement of a Scanning routine. The Scanning routine
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`US 6,730,863 B1
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`8
`refers to the function of detecting, identifying and tracking
`an object that touches the touchpad Surface. The present
`invention provides a Scanning function which is more effi
`cient and uses less power than Scanning functions of the
`prior art.
`When there are no objects being tracked on the touchpad
`Surface, the Scanning function of the presently preferred
`embodiment is in a wide Scan mode. In other words, all of
`the electrodes that can be driven are activated So that the
`presence of a new object can be detected at any location on
`the touchpad. For example, consider a finger which touches
`the Surface of the touchpad. The Scanning function detects
`the presence because of the decrease in capacitance between
`electrodes and the commonSense electrode at the location of
`the finger. This ability is present in the state of the art
`Scanning functions.
`However, one new feature of the Scanning function is the
`ability to then focus the Scanning function. In other words,
`instead of keeping all of the electrodes powered up, only the
`electrodes in the immediate vicinity of the detected object
`are kept active. This means that another object, Such as a
`finger, could also be placed on the touchpad Surface. AS long
`as the first object remains in contact with the touchpad
`surface, the new object will be ignored. Should the first
`object then be removed from the touchpad Surface, the
`Scanning routine immediately widens its Search pattern by
`again activating all of the electrodes. The Second object will
`be detected, and then the Scanning routine will again focus,
`deactivating the majority of the electrodes of the touchpad.
`Suppose, however, that the first object to be placed on the
`touchpad Surface is not a finger or Stylus, but a drop of water.
`The touchpad determines that the first object is a liquid
`because it increases the capacitance between the drive
`electrodes and the common Sense electrode, instead of
`decreasing it which occurs with objects that are used as input
`devices (a finger, Stylus, etc.). The water electrode is used to
`eliminate the effect of the water droplet. Advantageously,
`from that point on, the water droplet and its effect on the
`touchpad circuitry is ignored.
`The Situation might also arise where the water droplet
`moves. In this Scenario, its effect on the touchpad must again
`be compensated for, and its influence canceled out again.
`Therefore, as long as the water droplet is Stationary, its effect
`on the touchpad is able to be ignored. Movement of the
`water droplet requires recompensation.
`It should also be apparent that the addition of a Second, or