(12) United States Patent
`Philipp
`
`USOO64525 14EB1
`(10) Patent No.:
`US 6,452,514 B1
`(45) Date of Patent:
`Sep. 17, 2002
`
`(54) CAPACITIVE SENSOR AND ARRAY
`
`(76) Inventor: Harald Philipp, 7 Cirrus Gardens,
`Hamble H
`hire SD31 4RH (GB
`ample Hampsnure
`(GB)
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`(*) Notice:
`
`(21) Appl. No.: 09/491,129
`1-1.
`(22) Filed:
`Jan. 26, 2000
`Related U.S. Application Data
`(60) Provisional application No. 60/117,326, filed on Jan. 26,
`1999.
`7
`
`5,973,623 A * 10/1999 Gupta et al. .................. 341/33
`6.256,022 B1 * 7/2001 Manaresi et al. ........ 178/18.06
`
`6.288.707 B1 * 9/2001 Philipp - - - - - - - - - - - - - - - - - - - - - - - - 341/22
`
`* cited by examiner
`
`Primary Examiner Timothy Edwards, Jr.
`(74) Attorney, Agent, or Firm-David Kiewit
`(57)
`ABSTRACT
`ProXimity of a body, which may be a user's finger, to an
`electrode pair is Sensed by a charge transfer capacitive
`measurement approach. The electrode pair thus acts as a key
`that can be arrayed with other electrode pairs to form a
`k
`d. k
`eypad, keyboard, linear slider control, or liquid level Sen
`Sor. In one embodiment of the invention each key is asso
`
`(51) Int. C. - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - HO3K 17/94
`
`ciated with
`
`alternating Voltage SOUCC and
`
`pair of
`
`(52) U.S. Cl. ......................... 341/33; 341/22; 178/18.06
`(58) Field of Search .................. 341/33, 22; 178/18.06,
`178/18.07; 200/343; 34.5/168
`
`(56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`4.550,221. A 10/1985 Mabusth
`4,651,133 A 3/1987 Ganesan et al.
`4,879,461. A 11/1989 Philipp
`5,543,591 A 8/1996 Gillespie et al.
`5,572.205 A 11/1996 Caldwell et al.
`5,730,165 A 3/1998 Philipp
`5.841,078 A 11/1998 Miller et al.
`5,861,583 A 1/1999 Schedivy et al.
`5,914,465. A
`6/1999 Allen et al. ................... 341/33
`
`electrodes mounted on or within a Solid dielectric Substrate
`or panel So as to be separated from each other by a gap. The
`Voltage Source is connected to a driven electrode, a Sampling
`charge detector is connected to a Second, receiving,
`electrode, and the output of the charge detector is, in turn,
`fed into a Signal processor. Disturbances in coupling
`between the two electrodes are detected through the solid
`Substrate or panel material when a Substance or object
`approaches or contacts the panel. The receiving electrode is
`a low-impedance node during the Sampling phase of the
`process, which aids in keeping the Sensor from being
`affected by wiring length or by extraneous objects near an
`output lead.
`
`10 Claims, 7 Drawing Sheets
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`4OO
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`Petitioner STMICROELECTRONICS, INC.,
`Ex. 1028, IPR2021-01161 Page 1 of 17
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`

`

`U.S. Patent
`US. Patent
`
`Sep. 17, 2002
`Sep. 17, 2002
`
`Sheet 1 of 7
`Sheet 1 0f 7
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`US 6,452,514 B1
`US 6,452,514 B1
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`
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`
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`Petitioner STMICROELECTRONICS, INC,
`
`EX. 1028,1PR2021-01161 Page 2 of 17
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`Petitioner STMICROELECTRONICS, INC.,
`Ex. 1028, IPR2021-01161 Page 2 of 17
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`

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`U.S. Patent
`
`Sep. 17, 2002
`
`Sheet 2 of 7
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`US 6,452,514 B1
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`109
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`FIC. 1 Ol
`1 11
`1 OB
`OUTPUT OF 101
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`SAMPLE GATE
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`X
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`1 00
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`CE-TN 105
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`1 O4
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`2O1
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`Petitioner STMICROELECTRONICS, INC.,
`Ex. 1028, IPR2021-01161 Page 3 of 17
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`

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`U.S. Patent
`
`Sep. 17, 2002
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`Sheet 3 of 7
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`US 6,452,514 B1
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`FIG. 3OL
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`
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`3O3
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`Petitioner STMICROELECTRONICS, INC.,
`Ex. 1028, IPR2021-01161 Page 4 of 17
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`U.S. Patent
`
`Sep. 17, 2002
`
`Sheet 4 of 7
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`US 6,452,514 B1
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`FIG. 4 OL
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`Y400
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`/
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`
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`109
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`Petitioner STMICROELECTRONICS, INC.,
`Ex. 1028, IPR2021-01161 Page 5 of 17
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`U.S. Patent
`US. Patent
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`Sep. 17, 2002
`Sep. 17, 2002
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`Sheet 5 of 7
`Sheet 5 0f 7
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`US 6,452,514 B1
`US 6,452,514 B1
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`Petitioner STMICROELECTRONICS, INC,
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`EX. 1028,1PR2021-01161 Page 6 of 17
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`Petitioner STMICROELECTRONICS, INC.,
`Ex. 1028, IPR2021-01161 Page 6 of 17
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`U.S. Patent
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`Sep. 17, 2002
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`Sheet 6 of 7
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`US 6,452,514 B1
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`103 of 16)
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`
`Petitioner STMICROELECTRONICS, INC.,
`Ex. 1028, IPR2021-01161 Page 7 of 17
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`U.S. Patent
`US. Patent
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`Sep. 17, 2002
`Sep. 17, 2002
`
`Sheet 7 of 7
`Sheet 7 0f 7
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`US 6,452,514 B1
`US 6,452,514 B1
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`
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`Petitioner STMICROELECTRONICS, INC,
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`EX. 1028,1PR2021-01161 Page 8 of 17
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`Petitioner STMICROELECTRONICS, INC.,
`Ex. 1028, IPR2021-01161 Page 8 of 17
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`

`

`1
`CAPACTIVE SENSOR AND ARRAY
`
`US 6,452,514 B1
`
`15
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`2
`is connected to a Voltage drive Source and the Second of each
`pair is connected to a charge detector. In the general case for
`a matrix there are X drive lines and Y charge detectors.
`Although a minimal matrix could comprise two drive lines
`and a Single charge detector, or Vice versa, an N by M matrix
`is expected to usually involve at least four keys, e.g., an
`X=2, Y=2 arrangement. It may be noted that arrangements
`having the same number of drive lines as they do charge
`detectors (hereinafter referred to as "square matrices”) are
`generally preferred because these yield the greatest number
`of keys for a given amount of circuitry and wiring. It may
`be noted that the terms matrix and Square have nothing to
`do with the physical form of the key matrix. The keys can
`be arrayed linearly, circularly, or randomly on a single
`Surface, or in any fashion desired on a plurality of Surfaces.
`Moreover, the keys do not have to be the same physical size
`or shape, Some can be large and circular, other Small and
`triangular, others medium and rectangular.
`In one embodiment of the invention, each key is associ
`ated with an alternating Voltage Source and a pair of elec
`trodes mounted on or within a Solid dielectric Substrate or
`panel So as to be separated from each other by a gap. The
`Voltage Source is connected to a first electrode, a Sampling
`charge detector is connected to the Second electrode, and the
`output of the charge detector is, in turn, fed into a signal
`processing means. Disturbances in coupling between the
`two electrodes are detected through the Solid Substrate or
`panel material when a Substance or object approaches or
`contacts the panel.
`In another embodiment of the invention, each key is
`asSociated with an alternating Voltage Source and a pair of
`electrodes So as to be separated from each other by a gap.
`The voltage Source is connected to a first electrode, a
`Sampling charge detector is connected to the Second
`electrode, and the output of the charge detector is, in turn,
`fed into a signal processing means. Disturbances in coupling
`between the two electrodes are detected when a Substance or
`object approaches or contacts the electrode Set directly,
`without an intervening Solid dielectric layer.
`In operation of a preferred embodiment of the invention
`an alternating voltage Source is connected to a first (X)
`electrode that projects a time-varying e-field acroSS a gap.
`This field is, at least in part, received by a Second, receiving
`(Y), electrode. The receiving electrode is connected to a
`Sampling charge detector which acts to Sample the change in
`the charge coupled acroSS the gap caused by the dV/dt of the
`pulsed Voltage. It is a feature of the invention that the
`receiving electrode is a low-impedance node during the
`Sampling phase of the process. This ensures that the charge
`coupled to the Second electrode does not cause an appre
`ciable Voltage rise on the Second electrode.
`Although it is believed that the foregoing recital of
`features and advantages may be of use to one who is skilled
`in the art and who wishes to learn how to practice the
`invention, it will be recognized that the foregoing recital is
`not intended to list all of the features and advantages.
`Moreover, it may be noted that various embodiments of the
`invention may provide various combinations of the herein
`before recited features and advantages of the invention, and
`that less than all of the recited features and advantages may
`be provided by some embodiments.
`BRIEF DESCRIPTION OF THE SEVERAL
`VIEWS OF THE DRAWING
`FIG. 1a is an electrical Schematic of one embodiment of
`the invention having an alternating Signal Source and an
`electrode pair.
`
`25
`
`CROSS REFERENCE TO RELATED
`APPLICATIONS
`This application claims the priority date of a U.S. Provi
`sional Application for Patent having Ser. No. 60/117,326,
`which was filed on Jan. 26, 1999
`BACKGROUND OF THE INVENTION
`1. Field of the Invention
`The invention pertains to the Sensing of matter in contact
`or in close proximity to a Surface. One Specific area of
`interest is in human interfaces, Such as Switches, keys, and
`keyboards, used for entry of data or for control of an
`apparatus or process. Another specific area of interest is the
`Sensing of inanimate matter Such as powders and fluids, as
`is done in the Sensing of the level or Volume of a fluent
`material in a container.
`2. Background Information
`The invention employs capacitance Sensing, and in par
`ticular a form of Sensing known as 'charge-transfer (or
`* QT) sensing which has been taught by the inventor in his
`U.S. Pat. No. 5,730,165, the disclosure of which is herein
`incorporated by reference. Charge transfer Sensing uses
`electronic Switch closures to induce a charge onto an elec
`trode. A disturbance in the resulting electric field is Sensed
`by measuring the amount of charge on the electrode and to
`thereby determine the change in capacitance at the electrode.
`Caldwell et al., in U.S. Pat. No. 5,572,205, teach a
`capacitive touch control System that is responsive to a user
`input Selection and that can be configured as a touch pad
`disposed on an electrically non-conducting Substrate, Such
`as glass ceramic electrical cook-top. A Source Signal having
`a primary frequency that is greater than 150 kHz, and
`preferably in the range of between 150 kHz and 500 kHz, is
`applied to one portion of their touch pad. The touch pad
`couples the electrical Signal to another portion of the touch
`pad in order to develop a detection Signal, which is decoded
`40
`in order to determine the presence of the capacitance of a
`user. The decoder preferably includes a peak detector com
`posed of a low gain circuit in order to avoid distortion of the
`detection Signal.
`BRIEF SUMMARY OF THE INVENTION
`In the present invention two or more electrodes are
`arranged to create an electric field transmitted through an
`adjacent dielectric which can be disturbed by the proximity
`of an object A charge transfer measurement circuit is con
`nected to one of the electrodes.
`Because one of the major anticipated applications of the
`invention is in keyboards used in data entry, the Sensing
`elements are Sometimes hereinafter referred to as keys. It
`will be understood that this is done to simplify the presen
`tation and to avoid reciting lists of known Sensing or
`Switching products that could employ the invention, and that
`key, when So used, represents a proximity detection Zone
`for any possible application.
`Thus, one aspect of the invention is the provision of
`apparatus and method for detecting proximity to an elec
`trode pair to form a key. Another aspect of the invention is
`the provision of apparatus and method for detecting proX
`imity to one or more of a matrix of electrodes So as to form
`a keypad, keyboard, Slider Switch analog, or level Sensor.
`The creation of a key matrix follows from the arrange
`ment of a plurality of electrode pairs, where one of each pair
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`3
`FIG. 1b is a partial Schematic depiction showing a Section
`of a Solid, fixed dielectric Substrate having two electrodes
`disposed thereon, or alternatively, two fixed electrodes adja
`cent to a moving dielectric material, Solid or fluid, which is
`to be Sensed.
`FIG. 1c is a schematic depiction of the waveform output
`by the alternating Signal generator of FIGS. 1a and 1b,
`wherein the Signal generator is a pulse Source.
`FIG. 1d is a schematic depiction of the waveform output
`by the alternating Signal generator of FIGS. 1a and 1b,
`wherein the Signal generator is a sinusoidal Source.
`FIG. 2a is a partly Schematic depiction similar to that of
`FIB. 1b, wherein a thin conductive film, Such as water, is
`shown on the dielectric Substrate.
`FIG.2b is an electrical schematic corresponding to FIG.
`2a.
`FIG. 3a is a partial Schematic depiction, Similar to those
`of FIGS. 1b and 2a, wherein a massive conducting body,
`Such as a container of water, is shown adjacent the elec
`trodes.
`FIG. 3b is an electrical schematic corresponding to FIG.
`3a
`FIG. 4a is an electrical Schematic of one embodiment of
`a charge transfer measurement circuit.
`FIG. 4b is a Schematic depiction of timing relationships
`used in the operation of the circuit of FIG. 4a.
`FIG.5a is an electrical Schematic of a second embodiment
`of a charge transfer measurement circuit.
`FIG. 5b is an electrical timing diagram for the circuit of
`FIG 5.
`FIG. 6 is an electrical Schematic of an X-Y multiplexed
`array of charge measurement circuits of the type depicted in
`FIG. 4a.
`FIG. 7 is an electrical schematic of an X-Y multiplexed
`array of charge measurement circuits of the type depicted in
`FIG 5.
`FIG. 8a is an electrical schematic of circuitry adapted to
`use both the leading and falling edges of the drive Signal.
`FIG. 8b is a schematic depiction of timing relationships in
`the operation of the circuit of FIG. 8a.
`FIG. 9 is a schematic depiction of a slider control or fluid
`level Sensing probe made according to the invention.
`DETAILED DESCRIPTION OF THE
`INVENTION
`Aschematic view of the simplest form of the invention is
`shown in FIGS. 1a, 1b, 1c and 1d. A key, or composite
`sensing element 10 comprises a first, drive, electrode 100
`driven by a signal generator 101, which in one embodiment
`can be a simple CMOS logic gate powered from a conven
`tionally regulated Supply 102 to provide a periodic plurality
`of Voltage pulses having Some Selected duration.
`Alternatively, the Voltage Source 101 can be a sinusoidal
`generator or generator of a cyclical Voltage having another
`Suitable waveform. In one embodiment, a dielectric material
`or substrate 103 Supports the drive electrode 100 as well as
`a Second, receiving, electrode 104 connected to a receiving
`circuit having a low impedance or 'virtual ground charac
`teristic as depicted in cursory, not literal, fashion by 113. A
`changing electric field 110 is generated in the dielectric 103
`on the rising 109 and failing 111 edges of the train of voltage
`cycles 108 applied to the driven electrode 100 FIG. 1c shows
`these as pulses, while 1d depicts sinusoidal waveforms,
`other waveforms Such as triangle waves, Slew-rate-limited
`
`4
`pulses, etc. can be used instead, for example, to SuppreSS
`radiated RFI. The nature of the waveform used is not crucial
`to the discussion of the operation of the invention. Through
`out the remainder of the discussion pulses are depicted for
`convenience, but these may just as easily be other wave
`forms for the above and other reasons, and thus the use of
`pulses or Square waves should not be construed as a limi
`tation with regard to any X-drive Voltage Source depicted in
`any figure or discussed in conjunction therewith.
`The receiving electrode 104 receives or sinks the e-field
`110 via a coupling capacitance 105 that is generally indi
`cated in the drawing with the symbol C, which results in
`current signal 114 due to the capacitive differentiation of 108
`by means of capacitance 105. An output lead 112 from the
`receiving electrode 104 conducts this current Signal to a
`charge measurement circuit described in conjunction with
`further figures. This differentiation occurs because of the
`equation governing current flow through a capacitor:
`
`where C is the inter-electrode capacitance and V is the
`drive Voltage. The amount of charge coupled acroSS each key
`during an edge transition is defined as the integral of the
`above equation over time, or:
`
`The charge coupled on these transitions, Q is independent
`of the rise time of V, which is an important result. Moreover,
`Q is proportional to the Voltage Swing on the drive elec
`trode 100 and the magnitude of the coupling capacitance 105
`between the driven 100 and receiving 104 electrodes. As is
`known in the art, the degree of coupling is dependent on the
`proximity, Size, geometry, and relative attitude of the two
`electrodes, the material composition of the Substrate
`dielectric, and the proximity of the composite Sense element
`to other objects, Such as fluids and human fingers. Inasmuch
`as Solid dielectrics, Such as plastic and glass, have a much
`higher dielectric constant than air, if the Substrate is thick
`enough the coupling between the two electrodes 100 and
`104 will principally be through the substrate.
`If an external contact is made with the composite Sense
`element by a conductive film 201, such as by a metal, or by
`an ionic aqueous fluid as shown in FIG. 2a, the coupling
`between the two electrodes will increase because the exter
`nal film will have coupled to it the Signal from the emitting
`electrode 100. The film will then act as a secondary radiator
`of the same Signal, and in turn will Strongly couple the same
`signal into the receiving electrode 104. FIG. 2b shows
`Schematically what occurs when Such a film is present. Two
`additional capacitors 202 and 203 are formed. One of these
`202 is from the drive electrode to the film, the other 203 is
`from the film to the receive electrode. These act in unison to
`increase the amount of capacitive signal coupling from the
`driven to the receiving electrode. These effects are prevalent
`in many situations where keypads or contact Sensors are to
`be used. For example, both outdoor controls exposed to
`condensing humidity and rain, and appliance keypads in
`kitchens must commonly contend with extraneous films. In
`Such instances the film should be ignored if at all possible in
`order to prevent false detection.
`In practice, electrodes 100 and 104 are typically
`interdigitated, which is known in the art to facilitate a higher
`amount of coupling of e-field from and to the respective
`electrodes via the dielectric layer. Interdigitation increases
`the effective gain of the key and reduces the need for higher
`gain amplification or higher levels of drive signal. Interdigi
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`Ex. 1028, IPR2021-01161 Page 10 of 17
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`S
`tation also tends to localize the fields in a more defined area
`and permits the key shape to cover a larger Surface than
`otherwise possible with Simple neighboring electrodes as
`depicted in FIG. 1a through FIG. 2b.
`If, on the other hand, external contact is made with the
`composite Sense element 10 by a large body, Such as a
`human, or perhaps by a large Volume of fluid as shown in
`FIG. 3a, the coupling of charge between 100 and 104 will be
`reduced because the large object has a Substantial capaci
`tance to earth 206 (or to other nearby structures whose path
`will complete to the ground reference potential of the
`circuitry controlling the Sense elements). This reduced cou
`pling occurs because the coupled e-field between the driven
`100 and receiving 104 electrodes is in part diverted away
`from the receiving plate 104 to earth. This is shown sche
`matically in FIG. 3b. Capacitances 301 and 302 are set up,
`which in conjunction with capacitance 304 from the third
`object to free Space or a local ground, and which act to Shunt
`the e-field away from the direct coupling 105 present
`between 100 and 104. The coupling capacitance 105 in FIG.
`3b is significantly less than is the corresponding coupling
`capacitance 105 of FIG 1a as a result of the diversion of field
`lines to the object 303. If the receive electrode 104 is
`connected to a virtual ground, then the effect of the added
`capacitance 302 will not be Significant. If the receiving
`electrode 104 is connected to a high impedance amplifier,
`then the effect of 302 can be significant, because it will act
`to reduce the signal on 104 even further.
`The difference in signal shift polarity between the above
`two scenarios of FIGS. 2a and 3a is significant and can be
`taken advantage of to create a robust Sense element which
`can detect and discriminate between Surface films and bulk
`materials or human fingers. In one case (e.g., FIG. 2a) the
`detected material causes a rise in Signal, while in the case of
`FIG. 3a, the detected material causes a decrease in Signal.
`It is preferred in most embodiments to use a Solid panel
`material 103 as an intervening layer between the electrodes
`and the material or object to be sensed. This is not only for
`purposes of concealment of the electrodes 100 and 104 and
`associated wiring, but also to allow the fields to mix within
`the panel prior to exiting into free Space. An overlying
`dielectric panel provides an efficient means of creating
`coupling capacitances 105,301 and 302, the latter two being
`Set up when Sensing an object, finger, or other Substance.
`In another embodiment, 103 of FIG. 1b is actually the
`Substance to be sensed, Such as a dielectric fluid (e.g. oil,
`petrol), or a moving Solid (e.g. a plastic encoder vane) that
`is directly contacting or very close to the electrodes. The
`presence of this fluid or Solid adjacent to 100 and 104 creates
`additional coupling 110 between the electrodes and
`increases Signal Strength, resulting in a higher level of
`C105, which can be readily detected. In this case the
`electrodes are mechanically affixed in Space or bonded to a
`non-critical dielectric Substrate for mechanical Stability (not
`shown in the context of FIG. 1b).
`Turning now to FIG. 4a, one finds a circuit based in part
`on the charge-transfer (“OT”) apparatus and methods dis
`closed in the inventor's U.S. Pat. No. 5,730,165. This circuit
`shows an implementation of a Sensor comprising electrodes
`100,104, and processing circuitry 400. The exemplar pro
`cessing circuitry 400 depicted in FIG. 4a comprises a
`Sampling Switch 401, a charge integrator 402 (shown here as
`a simple capacitor), an amplifier 403 and a reset switch 404,
`and may also comprise optional charge cancellation means
`405. The timing relationships between the electrode drive
`Signal from the Voltage Source 101 and the Sample timing of
`Switch 401, as shown in FIG. 4b, are provided by a suitable
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`Synchronizing means, which may be a microprocessor or
`other digital controller 408. In the implementation shown,
`the reset switch 404 is initially closed in order to reset the
`charge integrator 402 to a known initial state (e.g., Zero
`volts). The reset switch 404 is then opened, and at some time
`thereafter the Sampling Switch 401 is connected to charge
`integrator 402 via terminal 1 for an interval during which the
`Voltage Source 101 emits a positive transition, and thereafter
`reconnects to terminal 0, which is an electrical ground or
`other suitable reference potential. The voltage source 101
`then returns to ground, and the process repeats again. At the
`end of a repetition of 'n' of these cycles, (where n is a finite
`non-zero integer) the sampling Switch 401 is held at position
`0 while the voltage on the charge integrator 402 is measured
`by a measurement means 407, which may comprise an
`amplifier, ADC or other circuitry as may be appropriate to
`the application at hand. After the measurement is taken, the
`reset Switch 404 is closed again, and the cycle is restarted
`when next desired. The proceSS is referred to herein as being
`a measurement burst of length n. where n can range
`from 1 to any finite number. The circuit's sensitivity is
`directly related to 'n' and inversely to the value of the charge
`integrator 402.
`It should be understood that the circuit element designated
`as 402 provides a charge integration function that may also
`be accomplished by other means, and that the invention is
`not limited to the use of a ground-referenced capacitor as
`shown by 402. It should be self-evident to the practitioner
`that the charge integrator 402 can be an opamp-based
`integrator to integrate the charge flowing through the Y lines.
`Such integrators also use capacitors to Store the charge. It
`may be noted that although integrators add circuit complex
`ity they provide a more ideal Summing-junction load for Y
`Sense currents and more dynamic range. If a Slow speed
`integrator is employed, it may be necessary to use a separate
`capacitor in the position of 402 to temporarily store the
`charge at high Speed until the integrator can absorb it in due
`time, but the value of Such a capacitor becomes relatively
`non-critical compared to the value of the integration capaci
`tor incorporated into the opamp-based integrator.
`The circuit shown in FIG. 4a provides an important
`electrical feature, that of a virtual ground node on the Y
`line, which is sampled during the closure of 401 to position
`1. The charge integrator, whether a simple ground
`referenced capacitor or an opamp-based integrator, provides
`a Summing-junction attribute which, as discussed above , is
`invaluable for keeping the effects of interference and Stray
`capacitance of the Y connections low.
`Switch 401 should preferably connect Y lines 112 to
`ground when not actually Sampling charge to create an
`artificial ground plane on the matrix, thus reducing RF
`emissions, and also permitting the coupled charge of oppo
`Site polarity to that being Sensed by the charge integrator 402
`to properly dissipate and neutralize. If one were to omit
`grounding the Y lines between Sample pulses the System
`would be purely AC coupled and would quickly cease to
`function, because charge would be both pulled and pushed
`across 105 with no DC restoration. It is also possible to use
`a resistor to ground on the Y lines to accomplish the same
`effect between transitions of voltage sources 101. As an
`alternative to a single SPDT Switch 401, two independent
`Switches can be used if timed in an appropriate manner.
`Although there are many alternative approaches possible, it
`should be clear that an important feature of a preferred
`embodiment of the invention is the provision of means for
`restoring charge on the receiving plate 104 after each
`Sampling.
`
`Petitioner STMICROELECTRONICS, INC.,
`Ex. 1028, IPR2021-01161 Page 11 of 17
`
`

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`US 6,452,514 B1
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`As explained in the inventor's U.S. Pat. No. 5,730,165,
`there are many Signal processing options possible for the
`manipulation and determination of a detection or measure
`ment of Signal amplitude. The aforesaid patent also
`describes the gain relationship of the arrangement depicted
`in FIG. 4a, albeit in terms of a single electrode system. The
`gain relationship in the present case is the Same. The utility
`of a signal cancellation means 405 is described in the
`inventor's U.S. Pat. No. 4,879,461 as well as the U.S. Pat.
`No. 5,730,165 patent. The disclosure of U.S. Pat. No.
`4,879,461 is herein incorporated by reference. The purpose
`of signal cancellation is to reduce the Voltage (i.e. charge)
`buildup on the charge integrator 402 concurrently with the
`generation of each burst, So as to permit a higher coupling
`between the driven 100 and receiving 104 electrodes. One
`benefit of this approach is to allow a large Sensing area that
`is sensitive to small deviations in coupling between 100 and
`104 at a low cost. Such large Sense couplings are present in
`physically large, highly interdigitated electrodes used in
`human touch Sensing pads. Charge cancellation permits
`measurement of the amount of coupling with greater
`linearity, because linearity is dependent on the ability of the
`coupled charge from the driven 100 to the receiving 104
`electrode to be Sunk into a virtual ground node over the
`course of a burst. If the Voltage on the charge integrator 402
`were allowed to rise appreciably during the course of a burst,
`the Voltage would rise in inverse exponential fashion. This
`exponential component has a deleterious effect on linearity
`and hence on available dynamic range. There are numerous
`possible circuits disclosed in the inventor's previous capaci
`tance Sensing patents and patent applications that can
`accomplish charge cancellation, and all are applicable to the
`invention with at most minor variation.
`It may be noted that if the charge measurement circuit had
`a high impedance, the currents induced by dV/dt would
`become manifest as actual Voltage pulses on the receive
`electrode 104. Hence, the sensor would be susceptible to
`walk-by interference from other objects that came near the
`output lead 112 to the charge detector. An object placed near
`the wiring of 112 will absorb some of the signal from the
`wire and cause a reduction in Signal; this can look to the
`circuit exactly like a detection event, even when the object
`is not near the electrode Set. More importantly, the use of a
`high impedance circuit connected to the receive electrode
`104 will ensure that the length of wiring becomes a factor in
`determining the gain of the circuit, which is not good.
`Wiring will cause some of the signal to "bleed off capaci
`tively into free Space, adjacent wires, and ground, forming
`a capacitance divider circuit together with coupling capaci
`tance 105. The prior art shows numerous attempts to devise
`Strategies for eliminating or reducing the effect of parasitic
`capacitance on electrode coupling. The present invention,
`which uses a detector having a low impedance or 'virtual
`ground, Solves these problems by reducing Voltage Swings
`on the receive electrode 104 to inconsequential levels. A
`charge-transfer (“OT”) detector of the type shown in FIG. 4a
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`is easily the Simplest and least expensive method of imple
`menting a low impedance detector.
`The low impedance nature of the receiver circuit depicted
`in FIG. 4a derives not from the charge cancellation circuit
`405, but rather from the fact that the charge integrator 402
`absorbs charge during the Slew portion of the Signal on the
`driven electrode 100 without rising appreciably in voltage.
`The charge cancellation circuit 405 exists to reduce the
`voltage rise on 402 during a burst, in order to improve both
`linearity and Signal acquisition range, as described above.
`The timing diagram shown in FIG. 4b shows how the
`rising edges 109 of the signal on 100 are captured using a
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`signal controlling Switch 401. The Switch 401 connects to
`position 1 of the controlling Switch 401 before, during, and
`after the rising portion of drive signal 100. It is during the
`rising portion of 100, slew 109, that the charge is transferred
`acroSS the coupling capacitance 105. However, if water or
`other conductive films are present on the touch Surface,
`Some of the coupled energy will lag in phase with respect to
`the edges 109. This is due to the distributed RC nature of
`Such films. That is, the film receives an induced charge from
`the drive electrode 100 and the resulting induced currents
`flow through the resistive fluid sheet in two dimensions, and
`charge the parasitic capacitances associated there with. If the
`sampling Switch 401 is held in position 1 for a relatively
`long time after the rising slew 109 on the drive electrode 100
`has ended, the film will couple back to the receive electrode
`104 and thence through the sampling switch 401 any
`changes in charge due to the current distribution in the sheet.
`The conductive sheet will therefore increase the sampled
`Signal the longer 401 is held in position 1 after the rising
`slew of 100 is complete. This effect is also described in my
`U.S. Pat. No. 5,730,165 with regard to water films around a
`water Spout. It is better, in the presence of fluids, to discon
`nect Switch 401 very quickly from position 1 so as to limit
`t