USO05767458A
`[11] Patent Number:
`[45] Date of Patent:
`
`5,767,458
`Jun. 16,1998
`
`Tajin' et al. ............................. .. 178/20
`
`4,752,655
`5,225,636
`
`
`
`Protheroe Duwaer ...... ..
`
`..
`
`6/ 1988
`7/1993
`7/1993
`5,359,156 10/1994
`Chan et a1. 6/1996 Katabami .
`
`United States Patent 1191
`Koolen
`
`[54]
`
`LOW-PASS FILTER OF GRAPHICAL
`TABLET HAS CUT-OFF FREQUENCY
`LOWER THAN SAMPLING FREQUECY
`
`[75]
`
`Inventor:
`
`Gerardus J.K.M. Koolen. Eindhoven.
`Netherlands Antilles
`
`[73] Assignee: U.S. Philips Corporation. New York.
`NY.
`
`Appl. No.: 603,958
`[21]
`[22]
`Filed:
`Feb. 20, 1996
`Foreign Application Priority Data
`[30]
`Feb. 21, 1995 [EP]
`European Pat. O?'.
`
`95200432
`
`[51] Int. (:1.6 ............................ .. G08C 21/00; 6096 3/02
`[52] U.S. Cl. ............................ .. 178/18; 178/19; 345/173;
`345/174
`[58] Field of Search ................................ .. 178/18. 19. 20;
`345/173. 174, 179
`
`[56]
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`
`
`2/1997 Fukuzaki .... ..
`
`FOREIGN PATENT DOCUMENTS
`
`9424648 10/1994 WIPO .
`
`Primary Examiner—Curtis Kuntz
`Assistant Examiner-Vijay Shankar
`[57]
`ABSTRACT
`
`A graphical tablet includes a pair of parts to be brought into
`electrical contact with one another under user-interaction.
`Electrical signals are generated indicative of X and Y
`coordinates of the contact. The signals are ?ltered by a
`low-pass ?lter. The ?ltered X and Y signals are sampled with
`a particular sampling frequency and are held in separate X
`and Y holding circuits. The cut-01f frequency of the ?lter is
`at least part of the time substantially lower than the sampling
`frequency. as each holding circuit has to settle for only
`increments and decrements relative to its stored sample
`value. Thus the spectrum of noise rejection is widened with
`respect to the prior art.
`
`4,581,483 4/1986 Ralston
`
`4,616,107 10/1986 Abe . . . . .
`
`. . . . . . . .
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`. . . . . . . .
`
`. . . . .. 178/18
`
`. . . .. 178/19
`
`11 Claims,2Drawing Sheets
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`
`GOOGLE Ex. 1017
`Google v. Philips
`
`

`

`US. Patent
`
`Jun. 16, 1998
`
`Sheet 1 0f 2
`
`5,767,458
`
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`
`GOOGLE Ex. 1017
`Google v. Philips
`
`

`

`US. Patent
`
`Jun. 16, 1998
`
`Sheet 2 of 2
`
`5,767,458
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`
`GOOGLE Ex. 1017
`Google v. Philips
`
`

`

`1
`LOW-PASS FILTER OF GRAPHICAL
`TABLET HAS CUT-OFF FREQUENCY
`LOWER THAN SAIVIPLING FREQUECY
`
`5 .767,458
`
`2
`could be reduced by synchronizing the operation of the
`tablet with that of the display. The tablet then is active only
`during time slots wherein the display is relatively quiet.
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`20
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`25
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`
`BACKGROUND OF THE INVENTION
`1. Field of the Invention
`The invention relates to a data processing system with a
`data input device for enabling entering respective data into
`the system upon user-interaction at respective ?rst and
`second coordinates relative to the device. The device
`includes generating means for generating signals indicative
`of the ?rst and second coordinates. low-pass ?lter means for
`?ltering of the signals. and sampling means for sampling of
`the ?ltered signals with a sampling frequency.
`2. Background Art
`Graphical user-interfaces have become widespread in the
`?eld of data input devices as highly suitable means to
`communicate with a data processing system. Examples of
`graphical user-interfaces are touch screens and graphical
`tablets that enable a user to selectively enter data into the
`system by touching a screen at predetermined locations and
`by manipulating a stylus contacting the surface of the tablet.
`respectively. US. Pat. No. 5.231.381 (PHN 13.100) dis
`closes an attractive example wherein a touch screen and a
`graphical tablet are combined with an LCD into a multiple
`purpose graphical user-interface device. The touch screen
`and graphical tablet have functionally different detection
`mechanisms so as to avoid mutual interference. As the
`present invention relates particularly. but not exclusively. to
`user-interfaces that include a graphical tablet. some well
`known examples of detection mechanisms used in graphical
`tablets are discussed below.
`A ?rst example of graphical tablet probes with a stylus a
`DC voltage established across an electrically resistive layer.
`The DC voltage has a gradient in a particular direction so as
`to unambiguously associate the voltage level with a coor
`dinate in that direction. Such tablet is referred to herein
`below as a resistive tablet. Sec. e.g.. international applica
`tion WO 94/24648. A second example of graphical tablet
`employs a top ?lm resistor facing a bottom ?lm resistor. A
`stylus is used to depress the top ?lm to bring it into electrical
`contact with the bottom ?lm. A voltage gradient is estab
`lished across one of the ?lms and the other ?lm is used to
`measure the voltage at the contact point. The measured
`voltage is representative of the location of the point of
`contact. Such tablet is referred to herein below as a mem
`brane tablet.
`The accuracy of both resistive and membrane tablets is
`found to be hampered by all sorts of noise. One of the major
`sources of noise is considered to be contact noise. stemming
`from a wildly varying resistance of the contacting parts. such
`as stylus and resistive layer of the resistive tablet. and the
`?lms of the membrane tablet. The contact resistance typi
`cally sweeps across a range of l ohmto 100K ohms. i.e.. ?ve
`orders of magnitude. The variation is thought to derive at
`least partly from the contacting surfaces being physically
`inhomogeneous. e.g.. having a rough uneven surface at the
`relevant scale.
`Another major noise source that affects accuracy is the
`display with which such tablets usually are combined to
`serve as a visual feedback. For example. in case of the
`display including an LCD. the so-called M-signal causes
`radiation that is picked up by the resistive layers or by at
`least one of the ?lms. The undesirable effects of noise are
`somewhat mitigated by use of ?lters such as a low-pass ?lter
`either in software or in hardware. The radiation noise etfects
`
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`OBJECT OF THE INVENTION
`
`It is. inter alia. an object of the invention to provide a data
`processing system with a low-cost. high-performance
`graphical user-interface device whose accuracy is higher
`than that of the conventional devices.
`
`SUMMARY OF THE INVENTION
`
`To this end. the invention provides a system as speci?ed
`in the preamble. characterized by the following features. The
`sampling means comprises ?rst holding means for holding a
`?rst sample associated with a value of the ?rst coordinate.
`and second holding means for holding a second sample
`associated with a value of the second coordinate. The device
`further comprises ?lter control means operative to decrease
`at least temporarily a cut-0E frequency of the ?lter means
`substantially below the sampling frequency.
`The inventor has recognized that dividing the sampling
`means into separate holding means for each coordinate
`individually enables decreasing the settling time with
`respect to a single holding means used for both coordinates
`alternately. This owes to the fact that a particular one of the
`holding means is permitted to retain its previous sample
`value and only needs to adapt to an increment or decrement
`for the next value. That is. each holding means only needs
`a time for the dilferential value to settle. In operational use
`of the graphical tablet for input of. e.g.. handwriting. con
`secutive samples will di?'er only marginally. According to
`the invention. the cut-off frequency can be lowered well
`below the sampling frequency. i.e.. the rate at which each of
`the holding means is supplied with samples. As a
`consequence. the bandwidth is decreased to reject a wider
`band of noise. Note that this is impossible for a device using
`a single sample-and hold circuit for handling X and Y
`coordinates alternately. as the full sample value must be
`allowed to settle each sampling cycle after reset.
`When the user starts entering data. or when the user enters
`data in the form of intermittent dots. the full settling time is
`needed so that the full sample value can be acquired. This
`requires temporarily raising the cut-off frequency to or
`above the sampling frequency. Accordingly. the inventor has
`realized that the cutoff frequency therefore is preferably
`varied in the following manner. When the input device does
`not receive a stimulus from the user the cut-off frequency is
`zero. i.e.. the ?lter means is off. Upon detection of the
`stimulus. the cut-otf frequency is initially raised to a high
`value. preferably much higher than the sampling frequency.
`Subsequently. the cut-off frequency is lowered to well below
`the sampling frequency.
`Typically. low-pass ?lter means comprises an integrating
`network with a resistance between input and output and a
`capacitance connected to the output. In the invention the ?rst
`and second holding means comprise ?rst and second
`capacitances. respectively. that are selectively connected to
`the ?lter’s resistance via controlled switches so as to merge
`the holding means with the ?lter means. The effective cut-off
`frequency now can be varied by changing the duty cycle of
`the signal controlling the switches. The duty cycle control is
`preferably made dependent on the initialization of the user
`interaction. The duty cycle then is ?rst made large. e.g..
`100% and thereupon decreased to. say. 10%.
`Preferably. the ?lter control means is operative to control
`the cut-01f frequency in dependence on a noise-related
`
`GOOGLE Ex. 1017
`Google v. Philips
`
`

`

`5,767.45 8
`
`3
`quantity. For example. the device may include a pair of parts
`operative to be brought into electrical contact with one
`another under user-interaction for enabling generation of the
`signals indicative of the ?rst and second coordinates of the
`contact relative to the device. The ?lter control means then
`may control the cut-off frequency in dependence on a
`contact resistance of said parts. Alternatively. or subsidian'ly.
`the cut-01f frequency could be controlled in dependence on
`the radiation noise of a display integrated with the data input
`device. An elegant manner to achieve the dependence on
`contact resistance is to functionally integrate the contact
`resistance with the low-pass ?lter means. When the contact
`resistance increases. the bandwidth should decrease in order
`to reduce the eifects of contact noise. The inventor has
`recognized the fact that this functional integration can be
`applied to. among other things. both the resistive tablet and
`the membrane tablet discussed above. The principle of the
`invention also can be applied to a variety of touch screens.
`
`10
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`4
`connected to a respective one of holding means 116 and 118.
`The rate at which each of holding means 116 and 118 is
`supplied with sample values is the sampling frequency.
`Filter control means 122 is provided to decrease at least
`temporarily a cut-01f frequency of ?lter means 112 substan
`tially below the sampling frequency.
`Each of holding means 116 and 118 is permitted to retain
`its previous sample value and only needs to adapt to an
`increment or decrement for the next value. thus enabling the
`cut-01f frequency to be lower than the sampling frequency.
`Filter control means 122 may simply ?x the cut-off fre
`quency at a value substantially below the sampling fre
`quency. This. however. may hamper initialization of data
`entry. as the content of holding means 116 and 118 ?rst has
`to be brought into the capture range for the short settling
`time required for decrements and increments. Preferably.
`?lter control means 122 comprises contact detection means
`124 for temporarily having the cut-o? frequency raised to or
`above the sampling frequency when initializing contact
`between parts 106 and 108. This could be achieved by. for
`example. control of the duty cycle of the signal that controls
`switch 120.
`
`Resistive tablet
`FIG. 2 is a diagram of a ?rst example of an input device
`200 for use in system 100 of FIG. 1. Device 200 is a resistive
`graphical tablet comprised of a resistive ATO layer 106 and
`a stylus 108. here electrically represented by its contact
`resistor 108. DC voltage sources 202 and 203 are controlled
`in operational use to establish a voltage gradient across ATO
`layer 106. Tablet 200 is operated upon by the user through
`stylus 108 that probes the voltage at a point of contact 204
`with ATO layer 106. The X coordinate of the point of contact
`204 between stylus 108 and ATO layer 106 has a voltage
`determined by the voltage divider made up of resistors 206
`and 208 that represent portions of layer 106 at the left and
`right hand side of stylus 108. The resistances of resistors 206
`and 208 depend on the location of point 204 relative to layer
`106. A similar argument applies to the Y coordinate. Opera
`tion so far is well known in the art so that FIG. 1 shows only
`a single dimension of layer 106 in order to not obscure the
`drawing. Stylus 108 is electrically coupled to an ampli?er
`210. preferably having a high input impedance 212 to reduce
`the load. The voltage at contacting point 204 determines the
`voltage across input impedance 212 and. therefore. the
`output signal of ampli?er 210. The output of ampli?er 210
`is connected to an AID converter 218 whose output is
`supplied to a microcontroller 220. Microcontroller 220
`thereupon furnishes data to PC 102.
`Capacitors 116 and 118 are connected across impedance
`212 through switches 214 and 216. Switches 214 and 216
`are operated alternately to allow charge to accumulate on
`capacitors 116 and 118 that is representative of the X and Y
`coordinates. respectively. of point 204. Functionally. capaci
`tors 116 and 118 serve both as holding means 116 and 118
`illustrated in FIG. 1 and as an integral part of ?lter means
`112. Capacitors 116 and 118 have capacitances of. e.g.. l-10
`nF. Filter means 112 in device 200 is comprised of contact
`resistor 108 and capacitors 116 and 118 that are alternately
`connected to resistor 108. When stylus 108 physically
`contacts ATO layer 106. contact resistance 108 may vary
`between 1 ohm and 100K ohm due to surface irregularities
`of the contacting surfaces of stylus 108 and layer 106. The
`functional integration of resistor 108 with ?lter means 112
`renders the bandwidth of ?lter means 112 dependent on the
`contact resistance 108. The bandwidth is reduced when
`contact resistance 108 increases. Thus the eiTects of contact
`
`DESCRIPTION OF THE DRAWINGS
`The invention is explained below in further detail and by
`way of example with reference to the accompanying
`drawing. wherein
`FIG. 1 is a block diagram of a system in the invention;
`FIG. 2 is a diagram of a resistive tablet in the invention;
`and
`FIG. 3 is a diagram of membrane tablet in the invention.
`Throughout the drawing like reference symbols indicate
`corresponding or similar features.
`
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`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`
`Block diagram of general system
`FIG. 1 is a block diagram of a system 100 according to the
`invention. System 100 comprises a data processing appara
`tus 102. such as a PC. and a data input device 104 that is
`coupled to or functionally integrated with apparatus 102.
`Device 104 is comprised of a ?rst part 106 and a second part
`108 that are to be brought into electrical contact with one
`another under user-interaction. Device 104 is. for example.
`a graphical tablet to enable entering data with a stylus. Parts
`106 and 108 are. for example. a stylus and a resistive layer.
`or two ?lm resistors as explained above. Establishing the
`electrical contact causes generating means 110 to generate
`electrical signals indicative of an X coordinate and an Y
`coordinate relative to device 104. As this mechanism is
`known. reference is made to the general background art of
`graphical tablets for further information.
`Device 104 also includes low-pass ?lter means 112 for
`?ltering of the signals. and sampling means 114 coupled to
`an output of ?lter means 112 for sampling of the ?ltered
`signals with a sampling frequency. Filter means 112 and
`sampling means 114 are drawn as separate functionalities
`but may be physically merged as explained above. Sampling
`means 114 comprises ?rst holding means 116 for holding a
`?rst sample associated with a value of the X coordinate. and
`second holding means 118 for holding a second sample
`associated with a value of the Y coordinate. FIG. 1 shows a
`single ?lter means 112 connected to ?rst and second holding
`means 116 and 118 via a single switch 120 controlled by a
`controller (not shown) in device 104. Filter means 112 may
`be comprised of a single low-pass ?lter. Alternatively.
`generator 110 may supply each respective one of the signals
`representing the X and Y coordinates to a respective one of
`a pair of low-pass ?lters that in turn have a respective output
`
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`GOOGLE Ex. 1017
`Google v. Philips
`
`

`

`5,767.45 8
`
`5
`noise are drastically reduced. A resistor 221 of. e.g.. 10K
`ohm is inserted between stylus 108 and ampli?er 210 to set
`an upper limit to the cut-01f frequency.
`Initial contact between stylus 108 and layer 106 is deter
`mined with help of a series connection of a switch 222 and
`a resistor 224 arranged in parallel to high input resistance
`212 of ampli?er 210. and with help of sources 203. Initially.
`the voltage of layer 106 is made uniformly high throughout
`layer 106 by appropriate control of sources 202 and 203.
`Switch 222 is turned on. When stylus 108 contacts layer 106.
`stylus 108 closes the electrical circuit and ampli?er 210
`experiences a detectable voltage jump as a sign that elec
`trical contact has been made. Thereupon. switch 222 is
`turned off to start the coordinate detection as explained
`above. The effective cut-off frequency is changed during this
`operation by control of the duty cycle of the signals supplied
`by ?lter control means 122 to switches 120.
`Filter control means 122 is shown as a separate feature.
`Note that ?lter control means 122. the control of switches
`214. 216 and 222. and the control of voltage sources 202 and
`203 may all be integrated in a single controller. e.g.. con
`troller 220. comprising dedicated control software.
`
`15
`
`Membrane tablet
`
`FIG. 3 is a diagram of a second example of an input
`device 300 for use in system 100. Device 300 is a membrane
`graphical tablet comprised of a top ?lm resistor 106 facing
`a bottom ?lm resistor 108. In order to depress top ?lm 106
`to bring it into electrical contact with bottom ?lm 108 a
`stylus (not shown) can be used. By pair-wise control of
`switches 302. 304. 306 and 308. a voltage gradient is
`established across one of ?lm resistors 106 and 108. the
`other then being used to measure the voltage at a contact
`point. The measured signal voltages are representative of the
`coordinates of the point of contact. The signals are supplied
`via alternately controlled switches 120 to capacitors 116 and
`118. Capacitors 116 and 118 function as holding means 116
`and 118 of FIG. 1. In addition. capacitors 116 and 118 form
`?lter means 112 together with the contact resistance of ?lm
`resistors 106 and 108. Similar as to device 200 of FIG. 2.
`integrating the contact resistance in ?lter means 112 selec
`tively reduces bandwidth with increasing resistance. Capaci
`tors 116 and 118 have capacitanees of. say. 100 nF. Addi
`tional resistors 310 and 312 of. e.g.. 10K ohm. may be
`included to set a lower limit to the effective contact resis
`tance. The voltages across capacitors 116 and 118 are
`supplied to controller 220. preferably via A/D converters
`(not shown).
`Initial contact between ?lm resistors 106 and 108 is
`detected via switch 314 and resistor 316 in. for example. the
`following manner. Initially. switches 120. 304. 306 and 308
`are turned oif and switch 314 is on. When switch 302 is on.
`?lm 106 is charged to a high voltage. Upon contact with ?lm
`108 a current will ?ow to ground via ?lm 108. switch 314
`and resistor 316. Resistor 316 has a resistance of. e.g.. 10K
`ohm. The voltage across the series connection of switch 314
`and resistor 316 is fed to controller 220 via an AID converter
`(not shown) and is indicative of contact detection. Filter
`control means 122 thereupon is enabled to raise the e?’ective
`the cut-off frequency. e.g.. by control of the duty cycle of the
`signal governing switches 120. Thereupon. coordinate
`detection is started as explained above and after the ?rst
`samples being acquired the effective cut-o? frequency is
`lowered to well below the sampling frequency.
`Filter control means 122 here is shown as a separate
`feature. Note that ?lter control means 122. and the control of
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`switches 302. 304. 306. 308. 314 may all be integrated in
`controller 220 comprising dedicated control software.
`What is claimed is:
`1. A data processing system with a data input device for
`enabling entering respective data into the system upon
`user-interaction at respective ?rst and second coordinates
`relative to the device. and wherein the device includes:
`generating means for generating signzds indicative of the
`?rst and second coordinates;
`low-pass ?lter means for ?ltering of the signals;
`sampling means for sampling of the ?ltered signals with
`a sampling frequency;
`characterized in that
`the sampling means comprises:
`?rst holding means for holding a ?rst sample associated
`with a value of the ?rst coordinate;
`second holding means for holding a second sample
`associated with a value of the second coordinate;
`the device comprises ?lter control means operative to set
`a cut-0E frequency of the ?lter means initially to
`substantially at least the sampling frequency upon
`detection of the user-interacn'on and to subsequently
`decrease the cut-off frequency substantially below the
`sampling frequency.
`2. The system of claim 1. wherein the ?rst and second
`holding means are functionally and selectively merged with
`the low-pass ?lter means via ?rst and second switches
`controlled via ?rst and second control signals. respectively.
`3. The system of claim 1. wherein the ?lter control means
`comprises means for temporarily having the cut-off fre
`quency raised to or above the sampling frequency at initial
`ization of the user-interaction.
`4. The system of claim 2. wherein the ?lter control means
`comprises means for temporarily having an effective cut-o?’
`frequency raised to or above the sampling frequency at
`initialization of the user-interaction. the means being opera
`tive to control a duty-cycle of the control signals.
`5. The system of claim 1. wherein the ?lter control means
`is operative to control the cut-off frequency in dependence
`on a noise-related quantity.
`6. The system of claim 5. wherein:
`the device includes a pair of parts operative to be brought
`into electrical contact with one another under user
`interaction for enabling generation of the signals
`indicative of the ?rst and second coordinates of the
`contact relative to the device;
`the ?lter control means controls the cut-o? frequency in
`dependence on a contact resistance of said parts.
`7. The system of claim 6. wherein the ?lter control means
`comprises the contact resistance being functionally inte
`grated with the low-pass ?lter means.
`8. The system of claim 6. wherein the ?lter control means
`comprises means for temporarily having the cut-off fre
`quency raised to or above the sampling frequency at initial
`ization of contact between the parts.
`9. The system of claim 8. wherein the ?lter control means
`comprises means for temporarily having an eifective cut-o?‘
`frequency raised to or above the sampling frequency at
`contact between the parts being initialized. the means being
`operative to control a duty-cycle of the control signals.
`10. A data input device for use in the system of claim 1.
`11. A data processing system with a data input device for
`enabling entering respective data into the system upon
`user-interaction at a coordinate relative to the device. and
`wherein the device includes:
`
`GOOGLE Ex. 1017
`Google v. Philips
`
`

`

`5,767,458
`
`8
`
`7
`generating means for generating signal indicative of the
`wofdillate;
`low-pass ?lter means for ?ltering of the signal;
`_
`.
`.
`,
`sampling means for sampling of the ?ltered slgnal Wlth a 5
`sainpling fr?qucncy- Wh?rein the samPling means 00m‘
`P115651
`holding means for holding a sample associated with a
`value of the coordinate; and
`
`wherein
`the device comprises ?lter control means operative to set
`a cut'o? frequency of the ?lter means initially to
`substantially at least the sampling frequency upon
`detection of the user-interaction and to subsequently
`decrease the cut-off frequency substantially below the
`sampling frequency.
`
`*
`
`* * *
`
`*
`
`GOOGLE Ex. 1017
`Google v. Philips
`
`