US008773 146B1
`
`(12) United States Patent
`Hills et al.
`
`(10) Patent No.:
`(45) Date of Patent:
`
`US 8,773,146 B1
`Jul. 8, 2014
`
`(54) WATERPROOF SCANNING OFA
`CAPACTIVE SENSE ARRAY
`
`(75) Inventors: Michael Patrick Hills, Lynnwood, WA
`(US); Volodymyr Burkovskyy, Lviv
`(UA), Oleksandr Karpin, Lviv (UA).
`Seok Pyong Park, Gyeonggi-do (KR);
`Patrick Prendergast, Clinton, WA (US)
`
`rsr rr
`(73) Assignee: Cypress Semiconductor Corporation,
`San Jose, CA (US)
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 392 days.
`
`(*) Notice:
`
`(21) Appl. No.: 13/075,762
`(22) Filed:
`Mar. 30, 2011
`
`Related U.S. Application Data
`(60) Provisional application No. 61/325,124, filed on Apr.
`16, 2010.
`
`(51) Int. Cl.
`(2006.01)
`GOIR 27/26
`(2006.01)
`G06F 3/04
`3.08:
`ge
`st
`(2013.01)
`(52) seats
`AV e. we
`CPC .............. G0IN 27/22 (2013.01); conties
`1.
`USPC ........... 324/658; 324/662: 324/663:
`I 4
`(58) Field of Classification Search
`USPC ................... 324/662, 663, 658; 34.5/173, 174
`See application file for complete search history.
`
`(56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`6,283,504 B1* 9/2001 Stanley et al. ................ 28Of735
`6504,550 B1
`1/2003 Wilsonetal
`8,054,296 B2 * 1 1/2011 Land et al. .................... 345,173
`2005/0001633 A1
`1/2005 Okushima et al. ............ 324,658
`2008/0136792 A1
`6/2008 Peng et al.
`2008. O158146 A1
`7/2008 Westerman
`2008. O158174 A1
`7, 2008 Land et al.
`2008. O158182 A1
`7/2008 Westerman
`2009/0009485 A1* 1/2009 Bytheway ..................... 345,174
`2009/0073140 A1
`3/2009 Fujita et al.
`2009, O174676 A1
`7, 2009 Westerman
`SR 85. A. ck 129, Mid
`all
`. . . . . . . . . . . . . . . . . . . . . . . . . . .
`2010/0060608 A1
`3/2010 Yousefpor
`2010/0328262 A1* 12/2010 Huang et al. .................. 345,174
`2012/0050214 A1
`3/2012 Kremlin et al. ................ 345,174
`* cited by examiner
`
`345,174
`
`Primary Examiner — Amy He
`
`ABSTRACT
`(57)
`A water-resistant capacitance sensing apparatus comprising a
`plurality of capacitive sense elements and a capacitance sens
`ing circuit configured to measure both the mutual capacitance
`and self-capacitance on the plurality of capacitive sense ele
`mentS.
`A method for water-resistant capacitance sensing, the method
`comprising performing a self-capacitance scan and a mutual
`capacitance scan, and detecting, by a processing device, a
`presence of an object with the plurality of sense elements. The
`method further determines whether the detected presence of
`the object is legitimate.
`
`18 Claims, 9 Drawing Sheets
`
`Self Scan and
`Baseline Update
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`910
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`900
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`Timeout
`outer----
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`Baseline
`Update
`timeout?
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`940
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`Mutual Scan
`and Baseline
`Update
`
`Baseline Reset
`Logic
`
`Reset Self
`Baseline
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`955
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`920
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`Mutual Scan and
`Baseline logic
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`925
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`so
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`DELL EXHIBIT 1018 PAGE 1
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`

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`DELL EXHIBIT 1018 PAGE 2
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`U.S. Patent
`
`US 8,773,146 B1
`
`Mutual
`Capacitive
`Sense Array
`
`Receive
`electrode
`223
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`DELL EXHIBIT 1018 PAGE 3
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`

`

`U.S. Patent
`
`Jul. 8, 2014
`
`Sheet 3 of 9
`
`US 8,773,146 B1
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`DELL EXHIBIT 1018 PAGE 4
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`

`

`U.S. Patent
`
`Jul. 8, 2014
`
`Sheet 4 of 9
`
`US 8,773,146 B1
`
`Sense
`Element
`401(1)
`
`Sense
`Element
`403(1)
`
`Row 1
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`Sense
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`
`DELL EXHIBIT 1018 PAGE 5
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`

`

`U.S. Patent
`
`Jul. 8, 2014
`
`Sheet 5 Of 9
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`
`DELL EXHIBIT 1018 PAGE 6
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`

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`U.S. Patent
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`Jul. 8, 2014
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`U.S. Patent
`
`Jul. 8, 2014
`
`Sheet 9 Of 9
`
`US 8,773,146 B1
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`
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`Self Scan and
`Baseline Update
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`DELL EXHIBIT 1018 PAGE 10
`
`

`

`US 8,773,146 B1
`
`1.
`WATERPROOF SCANNING OFA
`CAPACTIVE SENSE ARRAY
`
`RELATED APPLICATION
`
`This application claims priority to U.S. Provisional Appli
`cation 61/325,124 filed Apr. 16, 2010, which is hereby incor
`porated by reference in its entirety.
`
`TECHNICAL FIELD
`
`This disclosure relates to the field of user interface devices
`and, in particular, to capacitive sense devices.
`
`BACKGROUND
`
`Capacitive touch sense elements may be used to replace
`mechanical buttons, knobs and other similar mechanical user
`interface controls. The use of a capacitive sense element
`allows for the elimination of complicated mechanical
`Switches and buttons, providing reliable operation under
`harsh conditions. Capacitive touch sense elements can be
`arranged in the form of a sense array for a touch-sense Sur
`face. When a conductive object, Such as a finger, comes in
`contact or close proximity with the touch-sense surface, the
`capacitance of one or more capacitive touch sense elements
`changes. The capacitance changes of the capacitive touch
`sense elements can be measured by an electrical circuit. The
`electrical circuit converts the measured capacitances of the
`capacitive touch sense elements into digital values.
`In practice, contemporary capacitive touch sense elements
`find use in a wide variety of modern customer applications
`including laptops, cell phones, and automotive applications,
`which may be exposed to widely varying environmental con
`ditions. For example, moisture, high humidity, or sharp
`changes in the ambient temperature may adversely affect the
`electrical characteristics of the capacitive touch sense ele
`ments, causing the tracking algorithms to report false touches
`or ignore real touches. This results in inaccurate and unreli
`able position tracking in many real-world applications.
`
`10
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`15
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`25
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`BRIEF DESCRIPTION OF THE DRAWINGS
`
`45
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`50
`
`The present invention is illustrated by way of example, and
`not of limitation, in the figures of the accompanying drawings
`in which:
`FIG. 1 is a block diagram illustrating one embodiment of
`an electronic system having a processing device for detecting
`a presence of a conductive object according to an embodi
`ment of the present invention.
`FIG. 2 is a block diagram illustrating one embodiment of a
`mutual capacitive touchpad sense array and a capacitance
`sensor that converts measured capacitances to touchpad coor
`dinates.
`FIG. 3 illustrates the electrical characteristics of a pair of
`55
`transmit-receive capacitive sense elements according to an
`embodiment of the present invention.
`FIG. 4 illustrates a top-side view of one embodiment of a
`sense array of sense elements for detecting a presence of a
`conductive object on the self-capacitive sense array of a
`touch-sense pad.
`FIG. 5A is a diagram illustrating the typical effect of water
`on a mutual capacitive sense array, according to an embodi
`ment of the invention.
`FIG. 5B is a diagram illustrating the typical effect of water
`on a self-capacitive sense array, according to an embodiment
`of the invention.
`
`60
`
`65
`
`2
`FIG. 6 is a diagram illustrating the electrical characteristics
`of a touch on a waterproof scanning array, according to an
`embodiment of the present invention.
`FIG. 7 is a diagram illustrating the effect of a water drop
`and touch on a waterproof scanning array, according to an
`embodiment of the present invention.
`FIG. 8 is a diagram illustrating the effect of a finger present
`at startup on a waterproof scanning array, according to an
`embodiment of the present invention.
`FIG. 9 is a flow chart of one embodiment of a method for
`waterproof scanning on a sense array with reduced power
`consumption, according to an embodiment of the present
`invention.
`
`DETAILED DESCRIPTION
`
`In the following description, for purposes of explanation,
`numerous specific details are set forth in order to provide a
`thorough understanding of the present invention. It will be
`evident, however, to one skilled in the art that the present
`invention may be practiced without these specific details. In
`other instances, well-known circuits, structures, and tech
`niques are not shown in detail, but rather in a block diagram
`in order to avoid unnecessarily obscuring an understanding of
`this description.
`Reference in the description to “one embodiment' or “an
`embodiment’ means that a particular feature, structure, or
`characteristic described in connection with the embodiment
`is included in at least one embodiment of the invention. The
`phrase “in one embodiment located in various places in this
`description does not necessarily refer to the same embodi
`ment.
`FIG. 1 is a block diagram illustrating one embodiment of
`an electronic system 100 having a processing device for
`detecting a presence of a conductive object according to an
`embodiment of the present invention. Electronic system 100
`includes processing device 110, touch-sense pad 120, touch
`sense slider 130, touch-sense buttons 140, host processor
`(“host') 150, embedded controller 160, and non-capacitive
`sense elements 170. The processing device 110 may include
`analog and/or digital general purpose input/output (“GPIO)
`ports 107. GPIO ports 107 may be programmable. GPIO
`ports 107 may be coupled to a Programmable Interconnect
`and Logic (“PIL), which acts as an interconnect between
`GPIO ports 107 and a digital block array of the processing
`device 110 (not shown). The digital block array may be con
`figured to implement a variety of digital logic circuits (e.g.,
`DACs, digital filters, or digital control systems) using, in one
`embodiment, configurable user modules (“UMs). The digi
`tal block array may be coupled to a system bus. Processing
`device 110 may also include memory, such as random access
`memory (“RAM) 105 and program flash 104. RAM 105 may
`be static RAM (“SRAM), and program flash 104 may be a
`non-volatile storage, which may be used to store firmware
`(e.g., control algorithms executable by processing core 102 to
`implement operations described herein). Processing device
`110 may also include a memory controller unit (“MCU’) 103
`coupled to memory and the processing core 102.
`The processing device 110 may also include an analog
`block array (not shown). The analog block array is also
`coupled to the system bus. Analog block array also may be
`configured to implement a variety of analog circuits (e.g.,
`ADCs or analog filters) using, in one embodiment, config
`urable UMs. The analog block array may also be coupled to
`the GPIO ports 107.
`As illustrated, capacitance sensor circuit ("capacitance
`sensor) 101 may be integrated into processing device 110.
`
`DELL EXHIBIT 1018 PAGE 11
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`15
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`3
`Capacitance sensor 101 may include analog I/O for coupling
`to an external component, such as touch-sense pad 120,
`touch-sense slider 130, touch-sense buttons 140, and/or other
`devices. Capacitance sensor 101 and processing device 110
`are described in more detail below.
`The embodiments described herein are not limited to
`touch-sense pads for notebook implementations, but can be
`used in other capacitive sensing implementations, for
`example, the sensing device may be a touch screen, a touch
`sense slider 130, or touch-sense buttons 140 (e.g., capaci
`tance sense buttons). In one embodiment, these sensing
`devices include one or more capacitive sense elements. The
`operations described herein are not limited to notebook
`pointer operations, but can include other operations, such as
`lighting control (dimmer), Volume control, graphic equalizer
`control, speed control, or other control operations requiring
`gradual or discrete adjustments. It should also be noted that
`these embodiments of capacitive sense implementations may
`be used in conjunction with non-capacitive sense elements,
`including but not limited to pick buttons, sliders (ex. display
`brightness and contrast), Scroll-wheels, multi-media control
`(ex. Volume, track advance, etc) handwriting recognition and
`numeric keypad operation.
`In one embodiment, the electronic system 100 includes a
`touch-sense pad 120 coupled to the processing device 110 via
`bus 121. Touch-sense pad 120 may include a multi-dimension
`sense array. The multi-dimension sense array includes mul
`tiple sense elements, organized as rows and columns. In
`another embodiment, the electronic system 100 includes a
`touch-sense slider 130 coupled to the processing device 110
`via bus 131. Touch-sense slider 130 may include a single
`dimension sense array. The single-dimension sense array
`includes multiple sense elements, organized as rows, or alter
`natively, as columns. In another embodiment, the electronic
`system 100 includes touch-sense buttons 140 coupled to the
`processing device 110 via bus 141. Touch-sense buttons 140
`may include a single-dimension or multi-dimension sense
`array. The single- or multi-dimension sense array may
`include multiple sense elements. For a touch-sense button, the
`sense elements may be coupled together to detect a presence
`of a conductive object over the entire Surface of the sensing
`device. Alternatively, the touch-sense buttons 140 may have a
`single sense element to detect the presence of the conductive
`object. In one embodiment, touch-sense buttons 140 includes
`a capacitive sense element. Capacitive sense elements may be
`used as non-contact sense elements. These sense elements,
`when protected by an insulating layer, offer resistance to
`severe environments.
`The electronic system 100 may include any combination of
`one or more of the touch-sense pad 120, touch-sense slider
`130, and/or touch-sense button 140. In another embodiment,
`the electronic system 100 may also include non-capacitance
`sense elements 170 coupled to the processing device 110 via
`bus 171. The non-capacitance sense elements 170 may
`include buttons, light emitting diodes (“LEDs), and other
`user interface devices, such as a mouse, a keyboard, or other
`functional keys that do not require capacitive sensing. In one
`embodiment, buses 171, 141,131, and 121 are embodied in a
`single bus. Alternatively, these buses may be configured into
`any combination of one or more separate buses.
`Processing device 110 may include internal oscillator/
`clocks 106 and communication block (“COM) 108. The
`oscillator/clocks block 106 provides clock signals to one or
`more of the components of processing device 110. Commu
`nication block 108 may be used to communicate with an
`65
`external component, such as a host processor 150, via host
`interface (“I/F) line 151. Alternatively, processing device
`
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`110 may also be coupled to embedded controller 160 to
`communicate with the external components, such as host 150.
`In one embodiment, the processing device 110 is configured
`to communicate with the embedded controller 160 or the host
`150 to send and/or receive data.
`Processing device 110 may reside on a common carrier
`substrate such as, for example, an integrated circuit (“IC) die
`substrate, a multi-chip module substrate, or the like. Alterna
`tively, the components of processing device 110 may be one
`or more separate integrated circuits and/or discrete compo
`nents. In one exemplary embodiment, processing device 110
`is a Programmable System on a Chip (“PSoCTM) processing
`device, manufactured by Cypress Semiconductor Corpora
`tion, San Jose, Calif. Alternatively, processing device 110
`may be one or more other processing devices known by those
`of ordinary skill in the art, such as a microprocessor or central
`processing unit, a controller, special-purpose processor, digi
`tal signal processor (DSP), an application specific inte
`grated circuit (ASIC), a field programmable gate array
`(“FPGA), or the like.
`It should also be noted that the embodiments described
`herein are not limited to having a configuration of a process
`ing device coupled to a host, but may include a system that
`measures the capacitance on the sensing device and sends the
`raw data to a host computer where it is analyzed by an appli
`cation. In effect the processing that is done by processing
`device 110 may also be done in the host.
`Capacitance sensor 101 may be integrated into the IC of the
`processing device 110, or alternatively, in a separate IC. Alter
`natively, descriptions of capacitance sensor 101 may be gen
`erated and compiled for incorporation into other integrated
`circuits. For example, behavioral level code describing
`capacitance sensor 101, orportions thereof, may be generated
`using a hardware descriptive language. Such as VHDL or
`Verilog, and stored to a machine-accessible medium (e.g.,
`CD-ROM, hard disk, floppy disk, etc.). Furthermore, the
`behavioral level code can be compiled into register transfer
`level (“RTL) code, a netlist, or even a circuit layout and
`stored to a machine-accessible medium. The behavioral level
`code, the RTL code, the netlist, and the circuit layout all
`represent various levels of abstraction to describe capacitance
`sensor 101.
`It should be noted that the components of electronic system
`100 may include all the components described above. Alter
`natively, electronic system 100 may include only some of the
`components described above.
`In one embodiment, electronic system 100 is used in a
`notebook computer. Alternatively, the electronic device may
`be used in other applications, such as a mobile handset, a
`personal data assistant (PDA), a keyboard, a television, a
`remote control, a monitor, a handheld multi-media device, a
`handheld video player, a handheld gaming device, or a control
`panel.
`FIG. 2 is a block diagram illustrating one embodiment of a
`mutual capacitive touchpad sense array (“sense array') 200
`comprising an NXM electrode matrix 225 and a capacitance
`sensor 101 that converts measured capacitances to touchpad
`coordinates. The mutual capacitance sense array 200 may be,
`for example, the touch-sense pad 120 of FIG. 1. The NXM
`electrode matrix 225 includes NxM electrodes (N receive
`electrodes and M transmit electrodes), which further includes
`transmit (“TX”) electrode 222 and receive (“RX”) electrode
`223. Each of the electrodes in NXM electrode matrix 225 is
`connected with capacitance sensor 101 by conductive traces
`250. In one embodiment, capacitance sensor 101 operates
`using a charge accumulation circuit, capacitive bridge
`
`DELL EXHIBIT 1018 PAGE 12
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`

`

`5
`divider, current versus Voltage shift measurement, or other
`method known by those skilled in the art.
`The transmit and receive electrodes in the NxM electrode
`matrix 225 are arranged so that each of the transmit electrodes
`intersects each of the receive electrodes. Thus, each transmit
`electrode is capacitively coupled with each of the receive
`electrodes. For example, transmit electrode 222 is capaci
`tively coupled with receive electrode 223 at the point where
`transmit electrode 222 and receive electrode 223 intersect.
`Because of the capacitive coupling between the transmit
`and receive electrodes, a TX signal (not shown) applied to
`each transmit electrode induces a current at each of the
`receive electrodes. For instance, when a TX signal is applied
`to transmit electrode 222, the TX signal induces an RX signal
`(not shown) on the receive electrode 223 in NxM electrode
`matrix 225. The RX signal on each of the receive electrodes
`can then be measured in sequence by using a multiplexor to
`connect each of the N receive electrodes to a demodulation
`circuit in sequence. The capacitance associated with each
`intersection between a TX electrode and an RX electrode can
`be sensed by selecting every available combination of TX
`electrode and RX electrode.
`When an object, such as a finger, approaches the NXM
`electrode matrix 225, the object causes a decrease in capaci
`tance affecting only some of the electrodes. For example, if a
`finger is placed near the intersection of transmit electrode 222
`and receive electrode 223, the presence of the finger will
`decrease the capacitance between the transmit electrode 222
`and receive electrode 223. Thus, the location of the finger on
`the touchpad can be determined by identifying both the
`receive electrode having a decreased capacitance and the
`transmit electrode to which the TX signal was applied at the
`time the decreased capacitance was measured on the receive
`electrode. Thus, by sequentially determining the capacitances
`associated with each intersection of electrodes in the NXM
`35
`electrode matrix 225 the locations of one or more inputs can
`be determined. The conversion of the induced current wave
`form to touch coordinates indicating a position of an input on
`a touch sense pad is known to those skilled in the art.
`Although the transmit and receive electrodes 222, 223,
`appear as bars or elongated rectangles in FIG. 2, alternative
`embodiments may use various tessellated shapes such as
`rhomboids, chevrons, and other useable shapes known by
`those skilled in the art. In one embodiment, the transmit and
`receive electrodes 222, 223, are diamonds, similar to the
`self-capacitive sense array 400 of FIG. 4 below.
`FIG. 3 illustrates the electrical characteristics of a pair
`TX-RX capacitive sense elements 300 (“TX-RX 300)
`according to an embodiment of the present invention. The
`TX-RX300 includes a finger 310, a TX electrode 350, an RX
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`electrode 355, and a capacitance sensor 101. The TX elec
`trode 350 includes an upper conductive plate 340 (“UCP
`340) and a lower conductive plate 360 (“LCP360'). The RX
`electrode 355 includes an upper conductive plate 345 (“UCP
`345) and a lower conductive plate 365 (“LCP 365').
`The capacitance sensor 101 is electrically connected to the
`upper conductive plates 340 and 345 of TX electrode 350 and
`RX electrode 355, respectively. The upper conductive plates
`340 and 345 are separated from the lower conductive plates
`360 and 365, respectively, by air, dielectric, or any non
`conductive material known to those skilled in the art. Simi
`larly, the upper conductive plates 340 and 345 are separated
`from one another by air or dielectric material. The finger 310
`and lower conductive plates 360 and 365 are electrically
`grounded.
`Each of the transmit and receive electrodes 350 and 355,
`respectively, has a parasitic capacitance C and a mutual
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`capacitance C. The parasitic capacitance of a sense element
`(TX/RX electrode) is the capacitance between the sense ele
`ment and ground. In the TX electrode 350, the parasitic
`capacitance is the capacitance between the UCP 340 and the
`LCP360 as depicted by C-330. In the RX electrode 355, the
`parasitic capacitance is the capacitance between the UCP 345
`and the LCP 365 as depicted by C. 335. The mutual capaci
`tance of a sense element is the capacitance between the sense
`element and other sense elements. Here, the mutual capaci
`tance is the capacitance between TX electrode 350 and RX
`electrode 355, denoted as C370.
`The proximity of an object, such as a finger 310, near the
`TX electrode 350 and RX electrode 355 may change the
`capacitance between the electrodes as well as the capacitance
`between the electrodes and ground. The capacitance between
`the finger 310 and the electrodes is shown in FIG.3 as C320
`and C325. C. 320 is the capacitance between the UCP 340
`and the finger 310. C. 325 is the capacitance between the
`UCP 345 and the finger 310. The magnitude of the change in
`capacitance induced by the finger 310 can be detected and
`converted to a Voltage level or a digital code that can be
`processed by a computer or other circuit as described above.
`In one exemplary embodiment, Cf ranges between 10-30
`picofarads (pF). Alternatively, other ranges may occur.
`The measured capacitance of the sense elements as seen
`from capacitance sensor 101 includes the parasitic and
`mutual capacitances C and C in addition to C. The base
`line capacitance may be described as the capacitance of the
`sense element when no input (i.e., a finger touch) is present, or
`C and C. The capacitance sensor 101 and supporting cir
`cuitry are configured to resolve a difference between the
`baseline capacitance and the capacitance including C, in
`order to accurately detect a legitimate presence of a conduc
`tive object. This is further discussed in FIG. 2 and is generally
`known to those skilled in the art.
`FIG. 4 illustrates a top-side view of one embodiment of a
`sense array of sense elements for detecting a presence of a
`conductive object 303 on the self-capacitive sense array 400
`of a touch-sense pad. Sense array 400 includes rows 404(1)-
`404(N) and columns 405(1)-405(M), where N is a positive
`integer value representative of the number of rows and M is a
`positive integer value representative of the number of col
`umns. Each row includes sense elements 403(1)-403(K),
`where K is a positive integer value representative of the num
`ber of sense elements in the row. Each column includes sense
`elements 401(1)-401(L), where L is a positive integer value
`representative of the number of sense elements in the column.
`Accordingly, the sense array is an NXM sense matrix. The
`NXM sense matrix, in conjunction with the capacitance sen
`sor 101 through conductive traces 402, is configured to detect
`a position of a presence of the finger (i.e., conductive object)
`310 in the x-, and y-directions. In reference to FIG. 3, the
`capacitance sensor 101 is connected between UCP 345 and
`LCP 365 to measure the self-capacitance of RX electrode
`355, according to one embodiment. In another embodiment,
`the sense array is a 1xM or Nx1 sense matrix that can be
`configured to operate as a touch-sense slider.
`Alternating sense elements in FIG. 4 correspond to X- and
`y-axis elements. The y-axis sense elements 403(1)-403(K)
`for each row 404(1)-404(N) are illustrated as black diamonds.
`The x-axis sense elements 401(1)-401(L) for each column
`405(1)-405(M) are illustrated as white diamonds. It should be
`noted that other shapes, such as hexagons, chevrons, or other
`tessellatable shapes known by those skilled in the art may be
`used for the sense elements.
`In one embodiment, the sense array 400 is arranged in
`conjunction with a liquid-crystal display (LCD) (not shown),
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`where the boundaries and dimensions of the LCD display are
`similar and align with the sense array 400. In another embodi
`ment, the mutual capacitive touchpad sense array 200 may
`also be arranged in conjunction with a display. Other types of
`displays may be used insteadofan LCD display. For example,
`other applicable display technologies include light emitting
`diodes (“LED), organic light emitting diodes (“OLED'),
`nanocrystal displays, carbon nanotube displays, plasma dis
`plays, or other flat panel technologies known by those skilled
`in the art.
`FIG. 5A is a diagram 500 illustrating the typical effect of
`water on a mutual capacitive sense array, according to an
`embodiment of the invention. The diagram 500 depicts the
`capacitance measured on a mutual capacitive sense array,
`Such as that shown in sense array 200, over changing envi
`ronmental conditions.
`At point A510, the sense array 200 is in its normal opera
`tion state with no touches, water, or other capacitance induc
`ing events. At point B520, a water droplet is introduced on the
`sense array 200. Water induces an increased measured capaci
`tance between electrodes on a mutual capacitive sense array.
`As a result, the sense array 200 experiences an increased
`measured capacitance in the presence of the water droplet,
`point C530. It should be noted that the measurements shown
`in FIGS. 5A-8 with respect to the measured capacitances are
`inverted to more easily describe the operation of the present
`invention. The quantitative amount of increased mutual
`capacitance depends upon the amount of water on the mutual
`capacitive sense array 200. At point D540, the water dropletis
`removed and the mutual capacitance sense array 200 returns
`to a normal “dry” state operational state, point E 550.
`FIG. 5B is a diagram 560 illustrating the typical effect of
`water on a self-capacitance sense array, according to an
`embodiment of the invention. The diagram 560 depicts the
`capacitance measures on a self-capacitance sense array, Such
`as that shown in sense array 400, over changing environmen
`tal conditions.
`At point A565, the sense array 400 is in its normal opera
`tional state with no touches, water, or other capacitance
`inducing events. At point B570, a water droplet is introduced
`on the sense array 400. In contrast to FIG. 5A, water has
`relatively little effect on measured capacitance in self-capaci
`tance sense arrays. To illustrate this property, the self capaci
`tance of the TX and RX electrodes 350, 355 of FIG. 3 are
`represented by capacitors C-330 and C-335, respectively. As
`shown, the introduction of water on the sense array does not
`create an alternative conduction path between the upper con
`ductive plates (UCP 340, 345) and lower conductive plates
`(LCP 360, 365) nor does it increase the capacitance between
`the upper and lower conductive plates. As a result, adding
`water on a self-capacitance sense arrays may have some, but
`no significant effect on the measured capacitance. At point
`C575, the measured self-capacitance slightly increases due to
`the water droplet. This may vary depending on the existence
`of shielding on the sense array 400, as further addressed
`below. At point D580, the self-capacitive sense array 400
`returns to a normal “dry” operational state after the water
`droplet is removed, point E 585.
`In alternative embodiments, the sense array 400 may have
`shielding. In standard driven shields, inactive electrodes
`(electrodes not currently being measured) are driven with the
`same waveform as the active electrodes by the driven shield,
`which may significantly reduce the effect of water on the
`sensor array. In grounded shielding, inactive electrodes are
`grounded by a grounded shield. In one embodiment,
`grounded and driven shields are used in conjunction with the
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`self-capacitive scan and would be appreciated by those of
`ordinary skill in the art with the benefit of this disclosure.
`FIG. 6 is a diagram 600 illustrating the electrical charac
`teristics of a touch on a waterproof scanning array, according
`to an embodiment of the present invention. The waterproof
`scanning array (not shown) alternately performs a mutual
`capacitance all-points addressable scan (“MC scan 611) and
`a self-capacitance single electrode scan (“SC scan 612). In
`one embodiment, the MC scan 611 and SC scan 612 have
`complimentary electrical properties when exposed to water
`as well as temperature (discussed below), and both exhibit a
`significant increase in capacitance with a touch. If one scan
`method detects a signal indicating a touch, but the other does
`not, no touch is reported. Thi