| United States Patent Application |
20120306802
|
| Kind Code
|
A1
|
|
McCracken; David Harold
|
December 6, 2012
|
DIFFERENTIAL CAPACITANCE TOUCH SENSOR
Abstract
A touch sensor is provided. The touch sensor includes at least two
capacitive sensing electrodes, each of the at least two capacitive
sensing electrodes having a surface area that is smaller than an area of
a touch from a user. The at least two capacitive sensing electrodes each
include a substrate, a single conductive element formed on the substrate,
and electronic circuitry coupled to the at least two capacitive sensing
electrodes for measuring a self-capacitance of the at least two
capacitive sensing electrodes. A position corresponding to the touch of a
user is determined by the electronic circuitry based on a difference of
the measured self-capacitance between the at least two capacitive sensing
electrodes.
| Inventors: |
McCracken; David Harold; (Aptos, CA)
|
| Serial No.:
|
154227 |
| Series Code:
|
13
|
| Filed:
|
June 6, 2011 |
| Current U.S. Class: |
345/174 ; 178/18.06 |
| Class at Publication: |
345/174 ; 178/18.06 |
| International Class: |
G06F 3/045 20060101 G06F003/045 |
Claims
1. A touch sensor, comprising: at least two capacitive sensing
electrodes, each of the at least two capacitive sensing electrodes having
a surface area that is smaller than an area of a touch from a user, the
at least two capacitive sensing electrodes comprising: a substrate; a
single conductive element formed on the substrate; and electronic
circuitry coupled to the at least two capacitive sensing electrodes for
measuring a self-capacitance of the at least two capacitive sensing
electrodes, wherein: a position corresponding to the touch of a user is
determined by the electronic circuitry based on a difference of the
measured self-capacitance between the at least two capacitive sensing
electrodes.
2. The sensor of claim 1, wherein: the at least two capacitive sensing
electrodes each have a rectangular shape and are arranged to be abutting.
3. The sensor of claim 1, wherein the at least two capacitive sensing
electrodes each have a trapezoidal shape and are arranged to be abutting.
4. The sensor of claim 1, wherein: the at least two capacitive sensing
electrodes comprises four capacitive sensing electrodes arranged around a
central area such that leading edges of the four capacitive sensing
electrodes are equidistant from the central area; and the electronic
circuitry determines a two-dimensional position corresponding to the
touch of a user based on a first difference of the measured
self-capacitance between two capacitive sensing electrodes arranged in a
first direction and a second difference of the measured self-capacitance
between two capacitive sensing electrodes arranged in a second direction.
5. The sensor of claim 4, further comprising: a switch coupled in the
central area, wherein the four capacitive sensing electrodes have a
trapezoidal shape and are arranged around the switch.
6. The sensor of claim 1, wherein: the at least two capacitive sensing
electrodes comprises four capacitive sensing electrodes, each of the at
least two capacitive sensing electrodes having a triangular shape and
having an equal surface area.
7. The sensor of claim 1, wherein the sensor is used as a user interface
device, the determined position corresponding to a position on a display.
8. The sensor of claim 1, wherein the sensor is used in a touch screen,
the determined position corresponding to a position on the touch screen.
9. A capacitive touch sensor, comprising: at least two capacitive
electrodes, the at least two capacitive electrodes each being formed on a
substrate and having a single electrode layer, wherein: the at least two
capacitive electrodes are arranged to oppose each other along an axis for
determining a touch position along the axis; circuitry coupled to the at
least two capacitive electrodes, the circuitry configured to determine a
differential self-capacitance between the at least two capacitive
electrodes.
10. The capacitive touch sensor of claim 9, wherein: the at least two
capacitive electrodes comprises four capacitive electrodes, a first
capacitive electrode arranged opposite a second capacitive electrode
along a first axis, and a third capacitive electrode arranged opposite a
fourth capacitive electrode along a second axis; and the circuitry
determines a touch position along the first axis by determining a
differential self-capacitance between the first and second capacitive
electrodes and determines a touch position along the second axis by
determining a differential self-capacitance between the third and fourth
capacitive electrodes.
11. The capacitive touch sensor of claim 10, further comprising: a fifth
capacitive electrode under the substrate, wherein: the circuitry
determines a touch position along a third axis based on a distance
between a user touch on a back of the sensor and the fifth capacitive
electrode.
12. The capacitive touch sensor of claim 10, further comprising: a fifth
capacitive electrode under the substrate; and a grounded plane positioned
opposite the fifth capacitive electrode with a space therebetween,
wherein: the circuitry determines a touch position along a third axis
based on a distance between the grounded plane and the fifth capacitive
electrode.
13. The capacitive touch sensor of claim 10, further comprising: a
plurality of switches arranged along a periphery of each of the
capacitive electrodes, the switches being coupled to the circuitry and
being configured to provide additional touch positional information to
the circuitry.
14. The capacitive touch sensor of claim 13, wherein the plurality of
switches are arranged such that each of the capacitive electrodes wraps
around one of the plurality of switches.
15. The capacitive touch sensor of claim 10, further comprising: a first
conductive ring coupled to a printed circuit board; a conductive
elastomer formed above the first conductive ring, the conductive
elastomer coupled to the circuitry; and a second conductive ring formed
above the conductive elastomer and coupled to the substrates of the
capacitive electrodes, wherein: a resistance of the conductive elastomer
changes based on a distance between the first and second conductive
rings; and the circuitry determines a pressure based on the resistance of
the conductive elastomer.
16. The capacitive touch sensor of claim 15, wherein the circuitry
determines a touch position along the first or second axis based on the
determined pressure.
17. The capacitive touch sensor of claim 15, wherein the circuitry
determines a position along a third axis based on the resistance of the
conductive elastomer.
18. The capacitive touch sensor of claim 10, wherein the capacitive touch
sensor is embedded in a touch screen device.
19. The capacitive touch sensor of claim 10, wherein the combined surface
area of the four electrodes is about the average surface area of a human
fingertip.
20. The capacitive touch sensor of claim 9, wherein the circuitry is
coupled to a display such that the determined touch position corresponds
to a position on the display.
21. The capacitive touch sensor of claim 9, wherein the circuitry rejects
substantially all of any common mode noise caused by an environment
around the capacitive touch sensor.
Description
BACKGROUND
[0001] 1. Technical Field
[0002] The present disclosure is related to capacitive touch sensors. In
particular, the present disclosure is related to capacitive touch sensors
which measure a differential self-capacitance between adjacent capacitive
touch sensors.
[0003] 2. Discussion of Related Art
[0004] Modern electronics often include a display and require a user
interface device or navigation device to interface with or navigate on
the display. Such navigation devices include the well-known mice and
trackballs that have been used for a long time. As modern electronics are
made more portable, the displays are becoming smaller, and the need for
smaller navigation devices is increasing. Some portable devices have
displays that use touch screens such that the navigation is made by
touching the display itself. Some portable electronics use small
trackballs or optical trackballs for interfacing with a display. However,
trackballs may be unreliable as debris from the environment can get into
the trackball rotation surface, impeding the rotation of the trackball.
Optical trackballs, which are more reliable than standard trackballs,
require a thick circuit board and lens, which increases the overall
thickness of a portable device. Moreover, optical trackballs require a
special lens that adds to fabrication costs. Furthermore, optical
trackballs require that the lens be exposed to the environment to sense a
user touch and, thus, may be easily damaged from external debris.
[0005] Capacitive touch sensors have been commonly used in touch screens
and as selection buttons in electronics. Conventional touch sensors based
on capacitive coupling use conductive plates typically made of Indium Tin
Oxide (ITO) or some other transparent material that is electrically
conductive. Several conductive elements separated by a dielectric may be
placed in the plane of a sensor panel to detect the position of a touch.
Such capacitive touch sensors may be typically fabricated using standard
semiconductor processing techniques, and can be easily mass produced.
Typically, capacitive touch sensors require multiple layers of Indium Tin
Oxide (ITO) and, in order to accurately measure a touch position in
multiple directions, often require conductive electrodes arranged in
special geometries coupled with extensive processing. Consequently,
despite the relative ease in manufacturing capacitive touch sensors, the
complex geometries of electrodes often required for positional accuracy
makes it difficult to scale the electrode sizes down to a level that is
ideal for user interface devices or navigation devices.
[0006] What is needed is capacitive touch sensor that can provide
exceptional positional accuracy when detecting a touch position and is an
ideal size for use as a navigational device.
SUMMARY
[0007] Consistent with some embodiments, there is provided a touch sensor.
The touch sensor includes at least two capacitive sensing electrodes,
each of the at least two capacitive sensing electrodes having a surface
area that is smaller than an area of a touch from a user. The at least
two capacitive sensing electrodes each include a substrate, a single
conductive element formed on the substrate, and electronic circuitry
coupled to the at least two capacitive sensing electrodes for measuring a
self-capacitance of the at least two capacitive sensing electrodes. A
position corresponding to the touch of a user is determined by the
electronic circuitry based on a difference of the measured
self-capacitance between the at least two capacitive sensing electrodes.
[0008] Further consistent with some embodiments, there is also provided a
capacitive touch sensor. The capacitive touch sensor includes at least
two capacitive electrodes, the at least two capacitive electrodes each
being formed on a substrate and having a single electrode layer. The at
least two capacitive electrodes are arranged to oppose each other along
an axis for determining a touch position along the axis and are coupled
to circuitry that is configured to determine a differential
self-capacitance between the at least two capacitive electrodes.
[0009] These and other embodiments will be described in further detail
below with respect to the following figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a diagram illustrating a differential capacitive touch
sensor system consistent with some embodiments.
[0011] FIG. 2 is a diagram illustrating a cross section of a sensor shown
in FIG. 1 across line according to some embodiments.
[0012] FIG. 3A is a diagram illustrating a capacitive touch sensor
consistent with some embodiments.
[0013] FIG. 3B is a diagram illustrating a partial shield formed on a
bottom surface of a substrate or PCB, consistent with some embodiments.
[0014] FIGS. 4A-4G are diagrams illustrating additional exemplary
electrode numbers and shapes for a capacitive touch sensor, consistent
with some embodiments.
[0015] FIG. 5 is a diagram of a user holding a system having a capacitive
touch sensor capable of three-dimensional position detection.
[0016] FIG. 6A is a diagram illustrating a capacitive touch sensor for
measuring a touch position in three dimensions, consistent with some
embodiments.
[0017] FIG. 6B is a cross-section of sensor 600 shown in FIG. 6A taken
along the line VI-VI'.
[0018] FIG. 6C is a cross-section of sensor 600 shown in FIG. 6A taken
along the line VI-VI'.
[0019] FIG. 7 is a diagram illustrating a capacitive touch sensor capable
of detecting a touch in three dimensions, consistent with some
embodiments.
[0020] FIG. 8 is a diagram illustrating a capacitive touch sensor that is
also capable of detecting a pressure of a touch, consistent with some
embodiments.
[0021] FIG. 9 is a diagram illustrating a touch screen having multiple
differential capacitive touch sensors, consistent with some embodiments.
[0022] FIGS. 10A, 10B, and 10C are diagrams illustrating measuring the
differential capacitance of adjacent differential capacitive sensors,
consistent with some embodiments.
[0023] FIG. 11 is a diagram illustrating a mutual-capacitive touch screen
that measures the differential capacitance of adjacent electrodes,
consistent with some embodiments.
[0024] FIG. 12 is a diagram illustrating a mutual capacitance touch screen
having a differential capacitance touch sensor, consistent with some
embodiments.
[0025] In the drawings, elements having the same designation have the same
or similar functions.
DETAILED DESCRIPTION
[0026] In the following description specific details are set forth
describing certain embodiments. It will be apparent, however, to one
skilled in the art that the disclosed embodiments may be practiced
without some or all of these specific details. The specific embodiments
presented are meant to be illustrative, but not limiting. One skilled in
the art may realize other material that, although not specifically
described herein, is within the scope and spirit of this disclosure.
[0027] Touch sensors may be of a variety of types, such as resistive,
capacitive, and electro-magnetic types, and may be used for numerous
applications, including selection, positioning, and navigation. One
particular touch sensor, capacitive touch sensor, may include a
conductive material such as Indium Tin Oxide (ITO), aluminum or copper,
which conducts continuous electrical current across a sensor element.
Capacitive touch sensors typically exhibit a precisely controlled field
of stored charge to achieve capacitance. The human body is also an
electrical device which has stored charge and therefore exhibits
capacitance. When a capacitive touch sensor's normal capacitance field
(its reference state) is altered by another capacitance field, e.g., by
the touch or near touch (hereinafter, touches will also include near
touches unless otherwise noted) of a person, capacitive touch sensors
measure the resultant distortion in the characteristics of the reference
field and send the information about the touch event to a touch
controller for mathematical processing. There are a variety of types of
capacitive touch controllers, including capacitance-to-digital converters
(CDC) which include Sigma-Delta modulators, charge transfer capacitive
touch controllers, and relaxation oscillator capacitive touch
controllers.
[0028] Conventional capacitive touch sensors use multiple electrode
layers, including a transmitter electrode layer coupled to an excitation
source, and a receiver electrode layer coupled to a
capacitance-to-digital converter (CDC). In operation, there is an
electric field formed between the transmitter electrode layer and the
receiver electrode layer, as well as a stray electric field that extends
from the transmitter electrode layer. The environment of the capacitive
touch sensor changes when a human enters the stray electric field, with a
portion of the electric field being shunted to ground instead of
terminating at the receiver electrode layer, resulting in a decrease in
capacitance at the receiver electrode layer. The resulting decrease in
capacitance is detected by the CDC and converted to digital data which
can be processed by a processor to provide an indication of a touch, a
selection, or a position.
[0029] Capacitive touch sensors may also include single electrode layer
capacitive touch sensors. Such single layer capacitive touch sensors
include a single layer of conductive material, typically ITO, formed on
an insulative substrate or printed circuit board (PCB). The single layer
of conductive material forms a capacitive electrode. The single layer
capacitive electrode may be protected from the environment using an
overlay of protective material, which may be a plastic such as
acrylonitrile-butadiene-styrene (ABS), for example. The single layer
electrode may then be coupled to circuitry for reading a capacitance
value from the single layer electrode. Moreover, the single layer
capacitive electrode may be divided into multiple electrodes by
patterning the ITO into separate electrodes, each of which may have a
separate coupling to circuitry, such as a CDC, for reading determining
the capacitance value on each electrode. The separate electrodes may be
patterned using etching or deposition techniques. Alternatively, multiple
single layer capacitive electrodes may be formed on an insulative
substrate or PCB.
[0030] FIG. 1 is a diagram illustrating a differential capacitive touch
sensor system consistent with some embodiments. As shown in FIG. 1,
system 100 includes a differential capacitive touch sensor 102 that is
coupled to a multiplexer 104 by one or more leads 106. According to some
embodiments, capacitive touch sensor 102 is a single electrode layer
capacitive touch sensor. However, according to other embodiments,
capacitive touch sensor 102 may be a conventional multiple electrode
layer capacitive touch sensor.
[0031] Capacitive touch sensor 102 includes multiple electrodes and,
consistent with some embodiments, each lead 106 couples an individual
electrode of sensor 102 to multiplexer 104. Consequently, in accordance
with such embodiments, the number of leads 106 will correspond to the
number of electrodes in sensor 102. However, according to other
embodiments, one or more leads 106 may couple one or more electrodes of
sensor 102 to multiplexer 104. Multiplexer 104 outputs a capacitance
value to capacitance to digital converter (CDC) 108 which, in turn,
converts the capacitance value relative to ground output by multiplexer
104 to a digital value. Consistent with some embodiments, CDC 108 coverts
a capacitance value to a digital value by transferring a charge between a
reference capacitor fabricated as part of CDC 108 and an electrode of
sensor 102. Further consistent with some embodiments, CDC 108 provides
digital conversion using a sigma-delta process to provide high resolution
and high frequency noise filtering.
[0032] System 100 also includes circuitry that acts as an analog front end
controller 110. Analog front end controller 110 may include a state
machine and/or other logic, and provides a channel select signal 112 to
multiplexer 104 for selecting a particular capacitance value from one or
more leads 106 to output to CDC 108. In addition, analog front end
controller may also provide a control signal 114 to CDC to control the
operation of the CDC to convert the input capacitance value to a digital
value. Analog front end controller 110 is coupled to, and controlled by,
a processor 116. Consistent with some embodiments, processor 116 may be a
microprocessor or microcontroller, and may be a separate device, such as
shown in FIG. 1, or may be embedded in analog front end controller 110.
[0033] According to some embodiments, processor 116 is further coupled to
a system 118. System 118 receives a signal 120 from processor which may
be related to a capacitance value output from sensor 102. For example,
sensor 102 may be a sensor for providing system navigation and, thus, may
be used to provide position information to system 118. In particular,
sensor 102 may be a navigation tool used to navigate and control a
display position of a cursor output on a display 124 of system 118.
Consistent with some embodiments, system 100 may be a system that is
formed on a single substrate or PCB, wherein wiring within the substrate
or PCB couple the discrete elements. In operation, processor 116 may
provide a command signal 122 to analog front end controller 110 to
convert the capacitance values from output from sensor 102 on leads 106
one at a time, and storing each value until all capacitance values have
been read from sensor 102. These capacitance values may then be converted
by processor 116 to a position value that is output to system 118. As
noted above, the converted capacitance values may correspond to a
position of a cursor displayed on display 124. However, the converted
capacitance values may also be used for other control functions, such as,
panning an image, selecting a displayed object, zooming in or out on
display 124. Consistent with some embodiments, processor 116 continuously
reads converted capacitance values output from CDC 108 through analog
front end controller 110, but may only output a position value to system
118 when the position changes. In other words, system 118 assumes that a
last reported position remains in effect until data processor 116
provides a position value to system 118 that is different than a previous
position value.
[0034] As previously noted, consistent with some embodiments, processor
116 may convert capacitance values to a position value that is output to
system 118. System 118 may then translate the position values to an
abstract domain which may correspond to, for example, display 124 coupled
to system 118. The translation of the position values typically requires
mapping the range and resolution of the capacitance values from sensor
102 to a position on display 124. Consistent with some embodiments, an
entire range of values that may be detected by sensor 102 may be mapped
to an entire range of display values for display 124. While mapping an
entire range of values that may be detected by sensor 102 to an entire
range of display values may provide an ability for a user using sensor
102 as a positioning device to be able to quickly move a cursor on
display 124 to any location on display 124, the quick movement of the
cursor comes with decreased positional precision and accuracy. To
increase accuracy at the expense of speed, the translation of the
detected position values can be scaled down. For example, 100%
translation scaling results in complete mapping of an entire range of
values detected by sensor 102 to an entire display range of display 124.
Scaling the translation to 50%, doubles the positional precision, but
only allows a user to direct a cursor across a half of display 124.
Similarly, scaling the translation to 25% means that a user's movement
from one end of sensor 102 to another end of sensor 102 only moves the
cursor across a quarter of display 124. Thus, consistent with some
embodiments, capacitance values from sensor 102 may be treated as a
displacement from a fixed starting position, such as a last detected
position, instead of a true positional value in order to achieve both
full range of movement and precision. Displacement from a fixed position
may be achieved by designating a last detected capacitance value
corresponding to a position on display 124 as being a last detected
position such that subsequent detected capacitance values are converted
to a position on display 124 with respect to a displacement from the last
detected capacitance value. For example, considering a 50% scaling when a
finger, stylus, or other object comes in contact with sensor 102 and
changes the capacitance thereof, the computer system or data processor
maps the capacitance value to a position displayed on display 124. If a
last touch display position corresponds to a position in the middle of
display 124, when an initial touch is detected on sensor 102 in a
position corresponding to an upper left corner of display 124, the
display position does not change. If the user then slides to the middle
of sensor 102, the display position will move toward the lower right
corner but stop at the halfway position. If the detected touch is then
lifted, repositioned at the upper left corner of sensor 102, and the same
slide repeated, the display position will move the rest of the distance
to the lower right corner. Treating capacitance values from sensor 102 as
a displacement from a last detected position allows a user to make
multiple "scrolling" movements across sensor 102 to position a cursor
from, for example, one side of display 124 to another side, while
providing greater positional accuracy and position.
[0035] FIG. 2 is a diagram illustrating a cross section of sensor 102
across line II-II' according to some embodiments. As shown in FIG. 2,
sensor 102 includes a single electrode layer 202 deposited on a
dielectric layer 204. Consistent with some embodiments, single electrode
layer 202 may be a metallic layer, such as a layer of Indium Tin Oxide
(ITO), and dielectric layer 204 may be a semiconductor substrate or a
printed circuit board (PCB). As shown in FIG. 2, electrode layer 202 is
coupled to multiplexer 104 by lead 106. If dielectric layer 204 is a PCB,
lead 106 may correspond to a trace on PCB, and multiplexer 106 may also
be integrated on PCB. According to some embodiments, electrode layer 202
may be covered by protective material 206, which may be a plastic shell
made from ABS, a clear epoxy or resin, or other material which protects
electrode layer 202 from the environment and also protect electrode layer
202 from electrostatic discharge. Moreover, protective material 206 may
be made thin enough such that protective material 206 does not interfere
with the capacitive sensing capabilities of electrode layer 202.
[0036] Consistent with some embodiments, capacitive touch sensor 102
measures self-capacitance. Measuring self-capacitance involves measuring
a change in capacitance of a system in response to the touch or near
touch of an object, such as a user's finger, that has its own
capacitance. In operation, capacitive touch sensor 102 has a system
capacitance G that, when an object is not touching, is equal to a
parasitic capacitance G from electrode layer 202. When a an object, such
as a user's finger, touches capacitive touch sensor 102, the object forms
a simple parallel plate capacitor with electrode layer 202 and the result
is an object capacitance C.sub.o, wherein the object capacitance C.sub.o
is proportional to the area of overlap between the object and electrode
layer 202. When the object is touching capacitive touch sensor 102, the
system capacitance C.sub.s is equal to the sum of the parasitic
capacitance C.sub.p and object capacitance C.sub.o. Because the parasitic
capacitance may be generally known, the system capacitance C.sub.s will
be proportional to an area of overlap between the object and electrode
layer 202, circuitry coupled to capacitive touch sensor 102, such as
processor 116, may determine the position on capacitive touch sensor 102
on which the touch is made, and can translate this position to a touch
position or a position on display 124. Using a single electrode layer 202
and measuring self-capacitance allows for the manufacture of a capacitive
touch sensor 102 that may be made much thinner than conventional multiple
electrode layer capacitive touch sensors.
[0037] FIG. 3A is a diagram illustrating a capacitive touch sensor 102
consistent with some embodiments. As shown in FIG. 3A, capacitive touch
sensor 102 includes two opposing single layer capacitive electrodes 304
and 308 formed on a substrate or PCB oriented along the y-axis and two
opposing single layer capacitive electrodes 302 and 306 oriented along
the x-axis. Consistent with some embodiments, capacitive touch sensor 102
includes an electrically non-conducting protective layer that, for
example, may be made of a plastic such as ABS (not shown). Each electrode
302-308 is coupled to multiplexer 104 by separate leads 106. As shown in
FIG. 3, electrodes 302-308 are triangular-shaped and each have the same
surface area, however, electrodes 302-308 may have any shape. Each of
electrodes 302-308 are electrically isolated from one another through
isolation 310. According to some embodiments, isolation 310 is formed by
a dielectric material to provide an insulator between electrodes 302-308.
According to other embodiments, isolation 310 may simply be a gap of a
predetermined width between electrodes 302-308. Consistent with some
embodiments, electrodes 304 and 308 are used to measure a touch position
in the y-direction and electrodes 302 and 306 are used to measure a touch
position in the x-direction.
[0038] Consistent with some embodiments, capacitive touch sensor 102
measures a differential self-capacitance between the electrodes in each
direction. That is, processor 116 determines a difference in the
self-capacitance between y-axis electrodes 304 and 308 and a difference
in the self-capacitance between x-axis electrodes 302 and 306. Processor
116 converts the differential self-capacitances in the x direction and
the y direction to determine a two dimensional position on capacitive
touch sensor 102 which may correspond to a position on display 124.
Measuring the differential self-capacitance between two opposing
capacitive electrodes provides advantages over conventional capacitive
touch sensors which measure mutual capacitance between one or more
capacitive electrode plates (multiple electrode layers) or even
capacitive touch sensors that measure only the individual
self-capacitance of each individual electrode. One of the advantages that
measuring the differential self-capacitance between two opposing
electrodes provides over conventional methods is providing very good
common mode noise rejection.
[0039] Using capacitive touch sensors to measure self-capacitance is
generally limited to measuring simple on/off behavior due to inherent
poor precision and noise, and requires the complex interleaving of many
electrode patterns to have nominal precision. Differential
self-capacitance, on the other hand, measures the difference between two
capacitive electrodes subjected to the same environment and can, thus,
extract a high-resolution signal in the presence of significant
common-mode noise. However, because the two opposing capacitive
electrodes used to measure differential self-capacitance are subjected to
the same environment, the common-mode noise resulting from the
environment will be present on the readings from each electrode and will
be removed from the reading when the difference between the two
electrodes is calculated. That is, the differential capacitance
calculated between two opposing electrodes effectively subtracts the
environmental noise that is common to both of the opposing capacitive
electrodes.
[0040] Returning to FIG. 3A, a processor 116 determines a differential
capacitance between capacitive electrodes 302 and 306 to determine a
touch position in the x-direction, and processor 116 determines a
differential capacitance between capacitive electrodes 304 and 308 to
determine a touch position in the y-direction. Thus, sensor 102 having
electrodes 302-308 may be used to determine a two-dimensional position
that is substantially free from common mode noise. That is, processor 116
calculates the differential capacitance in the x-direction C.sub.x as
being approximately C.sub.302-C.sub.306 and the differential capacitance
in the y-direction C.sub.y as being approximately C.sub.304-C.sub.308.
Consistent with some embodiments, sensor 102 may be used as a user
interface device, allowing a user to interface with system 118 and
navigate display 124, as discussed above. Further consistent with some
embodiments, sensor 102 having electrodes 302-308 may be fabricated to
have a small size, for example, approximately the size of a fingertip.
For example, sensor 102 may have a surface area of about 16 mm.sup.2 to
about 144 mm.sup.2.
[0041] Moreover, electrodes 302-308 may be formed on a substrate or PCB by
etching a top surface of substrate or PCB to form electrodes 302-308 or
by depositing conductive material onto the top surface of substrate or
PCB 302-308. Consistent with some embodiments, a shield may be formed on
the bottom surface of the substrate or PCB. FIG. 3B is a diagram
illustrating a partial shield formed on a bottom surface of a substrate
or PCB, consistent with some embodiments. Because the differential
capacitive sensing of sensor rejects common-mode noise, shielding is used
only to prevent grounding from the bottom of sensor 102 raising the
overall capacitance to a level that interferes with the determination of
whether sensor 102 is touched or not. Shield 310 is a partial shield
formed on a bottom side of the substrate or PCB, and shares the circuit
layer of the substrate or PCB, filling the empty areas of the bottom side
of the substrate or PCB. Shield 310 includes openings 312 for leads 106
to pass through, each of leads 106 being coupled to one of electrodes
302-308 and multiplexer 104. Shield 310 may be further coupled to analog
front end controller 110 for receiving an excitation signal based on a
capacitance level detected on electrodes 302-308 such that the shield 310
is driven to be at the same potential as electrodes 302-308. Driving
shield 310 at a potential equivalent to the potential on electrodes
302-308 increases the accuracy of touch detection by sensor 102 by
preventing sensor 102 from registering stray or parasitic capacitance on
electrodes 302-308 as being a touch when a user is not touching
electrodes 302-308.
[0042] According to some embodiments, sensor 102 does not include a shield
such as shield 310. To increase accuracy of detecting a user touch when
sensor 102 does not include a shield, processor 116 may implement an
algorithm for distinguishing between common-mode and differential
capacitance changes to automatically adjust the touch threshold to
compensate for background capacitance caused by stray or differential
capacitance in the vicinity of sensor 102. For example, processor 116 may
recognize nearly equal capacitance changes simultaneously on all of
electrodes 302-308 as a background change rather than a touch on sensor
102. Alternatively, or in combination, processor 116 may also recognize
patterns of capacitance changes that distinguish a user touch from stray
or parasitic capacitance changes. Consistent with some embodiments, the
apparent touch position based on capacitance differences between opposing
electrodes 302-308 varies considerably as, for example, a user finger
approaches the front of sensor 102. The apparent position due to stray or
parasitic capacitances may also vary. However, a plot of the finger
position against time produces a continuous curve, whereas a similar plot
for the stray and parasitic capacitances shows extreme direction
reversals and changes in position that can be differentiated from that of
the finger position. Consequently, processor 116 may implement algorithms
to differentiate capacitance changes caused by a user touch from
capacitance changes caused by stray or parasitic capacitance to allow the
fabrication of sensor 102 without shield 310. The fabrication of sensor
102 without shield 310 allows for a less complex fabrication and further
allows sensor 102 to be fabricated at a reduced thickness.
[0043] Although sensor 102 having electrodes 302-308 is shown as having
four triangular-shaped electrodes in FIG. 3A, sensor 102 may have
different numbers of electrodes in different shapes. FIGS. 4A-4G are
diagrams illustrating additional exemplary electrode numbers and shapes
for sensor 102. FIG. 4A is a sensor 401 having four capacitive electrodes
402, 404, 406, and 408 each having substantially identical surface areas.
As shown in FIG. 4A, electrodes 402-408 correspond to trapezoids having a
base along the edges of sensor 102. Consistent with some embodiments,
electrodes 402 and 406 correspond to electrodes for detecting a touch
position in the x-direction by determining a differential capacitance
between electrodes 402 and 406 and electrodes 404 and 408 correspond to
electrodes for detecting a touch position in the y-direction. by
determining a differential capacitance between electrodes 404 and 408.
[0044] FIGS. 4B, 4C, and 4D illustrate one-dimensional sensors, consistent
with some embodiments. As shown in FIG. 4B, sensor 409 includes two
triangular-shaped electrodes 410 and 412 arranged vertically to provide
position detection in the y-direction by determining a differential
capacitance between electrodes 410 and 412. Alternatively, electrodes 410
and 412 may be arranged horizontally to provide position detection in the
x-direction. As shown in FIG. 4C, sensor 413 includes trapezoidal-shaped
electrodes 414 and 416 arranged vertically to provide position detection
in the y-direction by determining a differential capacitance between
electrodes 414 and 416. Alternatively, electrodes 414 and 416 may be
arranged horizontally to provide position detection in the x-direction.
As shown in FIG. 4D, sensor 417 includes rectangular-shaped electrodes
418 and 420 arranged vertically to provide position detection in the
y-direction by determining a differential capacitance between electrodes
418 and 420. Alternatively, electrodes 418 and 420 may be arranged
horizontally to provide position detection in the x-direction.
[0045] FIG. 4E is a diagram illustrating a capacitive touch sensor 421
having four trapezoidal-shaped capacitive electrodes 422, 424, 426, and
428 surrounding a central sensor 430. Similar to sensor 401 shown in FIG.
4A, electrodes 422 and 426 are used to detect a touch position in the
x-direction by determining a differential capacitance between electrodes
422 and 426 and electrodes 424 and 428 are used to detect a touch
position in the y-direction by determining a differential capacitance
between electrodes 424 and 428. Consistent with some embodiments, central
sensor 430 may be a capacitive electrode, similar to capacitive
electrodes 422-428, or a tactile button, mechanical switch, or other
similar sensor device. Central sensor 430 may provide additional
functionality to the two-dimensional position sensing provided by sensor
421 in FIG. 4E. Such additional functionality includes providing
increased accuracy, a scrolling function, or a selection or tap
functionality to touch sensor 421.
[0046] FIG. 4F is a diagram illustrating a sensor 431 similar to sensor
102 shown in FIG. 3A, having triangular-shaped electrodes 432-438 for
providing positional detection in the x-direction and in the y-direction
by determining a differential self-capacitance between opposing
electrodes in the x and y-direction. However, sensor 431 in FIG. 4F
further provides an electrode ring 440 surrounding electrodes 432-438.
Consistent with some embodiments, electrode ring 440 is used to provide
greater positional detection accuracy at the edges and corners of sensor
431 than may be provided using triangular-shaped electrodes 432-438. As
can be seen in FIG. 4F, the overall electrode area of electrodes 432 and
438 at corner is small and, thus, accurate positional detection is
difficult to achieve at corner 442. Consequently, electrode ring 440
provides additional area surrounding corner 442 to provide greater
accuracy around corner 442, and other corners and edges of sensor 431.
Consistent with some embodiments, capacitance measured by ring electrode
440 may be measured as a differential capacitance, wherein the
capacitance measured by ring electrode 440 is compared with the closest
electrode of electrodes 432-438. According to other embodiments,
capacitance measured by ring electrode 440 may be measured as an absolute
value, and the absolute value may be interpreted by processor to provide
an indication of the amount of capacitance present at the edges which can
be used to compensate the differential capacitance readings obtained from
electrodes 432-438.
[0047] FIG. 4G is a sensor similar to sensor 421 shown in FIG. 4E, having
trapezoidal-shaped electrodes 422-428. However, as shown in FIG. 4G,
sensor 444 also includes dome switches 446 formed within a periphery of
trapezoidal-shaped electrodes 432-438, and a dome switch 448 in a center
of sensor 444 within a gap formed by the shorter parallel side of
trapezoidal-shaped electrodes 432-438. Consistent with some embodiments,
dome switches 446 and 448 may be formed on the same substrate or PCB as
trapezoidal-shaped electrodes 432-438, and may be used to provide tactile
feedback or coarse position indication for a user. Further consistent
with some embodiments, sensor 444 may be covered by a shell or plastic,
as discussed previously, such that the shell or plastic covering dome
switches 446 and 448 is thinner than the shell or plastic covering
trapezoidal-shaped electrodes 432-438 such that a uniform level surface
is provided to a user. Further consistent with some embodiments, dome
switches 446 may be arranged around the periphery of each of the
trapezoidal-shaped electrodes 432-438 such that each of the
trapezoidal-shaped electrodes 432-438 wrap around one of the plurality of
dome switches 446. Although electrodes 432-438 are illustrated in FIG. 4G
as being trapezoidal-shaped, the shape is not important, and electrodes
432-438 may have any shape, including but not limited to a triangular
shape or a rectangular shape.
[0048] Consistent with some embodiments, a capacitive touch sensor
measuring a differential self-capacitance of opposing electrodes to
determine a touch position in two dimensions, such as sensor 102, 401,
409, 413, 417, 421, 431, or 444, may be capable of detecting a position
in a third dimension as well. FIG. 5 is a diagram of a user holding a
system having a capacitive touch sensor capable of three-dimensional
position detection. As shown in FIG. 5, a user 502 is holding a
differential capacitive touch sensor system 504 in their hand 506. System
504 includes differential capacitive touch sensor 508 and circuitry (not
shown) encased within a housing 510 of system 504. The circuitry may
include a multiplexer, and analog front end controller, and a processor,
similar to system 100 shown in FIG. 1. Moreover, system 504 may be
coupled to a system having a display (not shown), wherein the user is
capable of navigating the display and selecting elements displayed on the
display using system 504. The coupling between system 504 and the
external system having a display may be a wired coupling or a wireless
coupling. Housing 510 may include a shell 512 that covers sensor 508.
Shell 512 includes flexible sides 514 and may be made of plastics, such
as ABS, or acrylics or other suitable materials, and may completely cover
sensor 508 such that sensor 508 is not exposed to the external
environment.
[0049] Consistent with some embodiments, sensor 508 is not internally
shielded allowing for the capacitance measured on the electrodes of
sensor 508 to be measurably altered based on a proximity of fingers 516
and 518 to a back side of sensor 508. Thus, when hand 506 firmly presses
on flexible shell 512, shell 512 deforms bringing fingers 516 and 518
closer to sensor 508 beneath shell 512, which increases the capacitance
measured on sensor 508 resulting from the proximity of fingers 516 and
518. In particular, the proximity capacitance increases the capacitance
detected on all of the electrodes of sensor 508 such that the uniform
increase in capacitance on all of the electrodes of sensor 508 may be
interpreted by the circuitry as movement in the z-direction. Similarly,
relaxing hand 506 will return shell 512 to its original shape and fingers
516 and 518 will move away from sensor 508 beneath shell 512 resulting in
a decrease in capacitance measured on all electrodes of sensor 508. The
z-direction sensing provided by system 502 allows a user to press down to
navigate in the z-direction or to use sensor 508 as a button for
selecting interactive elements displayed by a display coupled to system
502.
[0050] FIG. 6A is a diagram illustrating a capacitive touch sensor for
measuring a touch position in three dimensions, consistent with some
embodiments. As shown in FIG. 6A, sensor 600 includes capacitive
electrodes 602, 604, 606, and 608, formed on a substrate or PCB 610.
Electrodes 602-608 are coupled to circuitry (not shown) for determining
an x-y touch position. Consistent with some embodiments, capacitive
electrodes 602 and 606 detect a position in the x-direction by
determining a differential capacitance between electrodes 602 and 606,
and capacitive electrodes 604 and 608 detect a position in the
y-direction by determining a differential capacitance between electrodes
604 and 608. Although electrodes 602-608 are shown as being
triangular-shaped, electrodes 602-608 may be any shape, such as
trapezoids, as discussed herein. Sensor 600 further includes a driven
shield 612. Driven shield 612 is coupled to circuitry (not shown) that
drives shield 612 to the same potential as at least one of electrode
602-608 that is currently under test in order to prevent sensor 600 from
detecting stray or parasitic capacitances and only being activated when a
user is touching sensor 600. Sensor 600 further includes a z-axis
electrode 614 formed on an additional substrate or PCB layer 616. Z-axis
electrode 614 is also coupled to circuitry (not shown), wherein the
circuitry determines a change in the capacitance of z-axis electrode 614
based on a distance between a user's hand located behind the assembly and
z-axis electrode 614. Similar to sensor 504 in FIG. 5, sensor 600 may be
enclosed in a housing having a flexible shell such that when a user
presses firmly on sensor 600, the flexible shell is compressed, and the
user's finger or hand becomes closer to z-axis electrode 614 increasing
the measured capacitance on z-axis electrode 614. Although sensor 600 is
similar to sensor 504, sensor 600 is physically more complex than sensor
504 but may simplify associated signal processing by making z-axis
information independent of x- and y-axes.
[0051] FIG. 6B is a cross-section of sensor 600 shown in FIG. 6A taken
along the line VI-VI' enclosed in a flexible shell 510 and held by a
user's hand. When the user's thumb 506 presses on sensor 600, z-axis
electrode 614 moves closer to the user's finger 516 located behind the
assembly, increasing the capacitance seen on electrode 614. FIG. 6C is a
cross-section of sensor 600 shown in FIG. 6A taken along the line VI-VI'
enclosed in a flexible shell 510 and held by a user's hand similar to
FIG. 6B but with an additional ground plane 618 located on the inside of
shell 510 opposite z-axis electrode 614. Ground plane 618 may comprise
metallization of the shell itself or a separate conductive element.
Pressing firmly on sensor 600 moves z-axis electrode 614 closer to ground
plane 618, increasing the capacitance seen on electrode 614. The user's
finger 516 shown in FIG. 6B serves no electrical role. The more
consistent z-axis measurement environment of this compared to the
embodiment of FIG. 6B may afford a more consistent response and simplify
z-axis signal processing. This embodiment may also be used where the user
does not hold the assembly.
[0052] FIG. 7 is a diagram illustrating a capacitive touch sensor capable
of detecting a touch in three dimensions, consistent with some
embodiments. As shown in FIG. 7, sensor 700 includes four capacitive
electrodes 702, 704, 706, and 708. Consistent with some embodiments, a
differential capacitance between electrodes 702 and 706 may be measured
to determine a touch position in an x-direction and a differential
capacitance between electrodes 704 and 708 may be measured to determine a
touch position in a y-direction. Although electrodes 702-708 are shown as
having a triangular shape, the shape of electrodes 702-708 may be chosen
from any shape as long as electrodes 702-708 have the same surface area.
As shown in FIG. 7, sensor 700 includes an upper conductive ring 710 and
a lower conductive ring 712 separated by a conductive elastomer 714.
Electrodes 702-708 are separated from upper conductive ring by an
insulative layer 716, and lower conductive ring 712 is mounted on a
substrate or PCB 718. Upper and lower conductive rings 710 and 712
connect conductive elastomer 714 to circuitry (not shown) that measures
an electrical resistance of conductive elastomer 714. When a user presses
on a flexible shell enclosing sensor 700, the resistance through
conductive elastomer 714 decreases, which can be detected by circuitry to
determine a z-axis touch position.
[0053] FIG. 8 is a diagram illustrating a capacitive touch sensor that is
also capable of detecting a pressure of a touch, consistent with some
embodiments. As shown in FIG. 8, sensor 800 includes four capacitive
electrodes 802, 804, 806, and 808. Consistent with some embodiments, a
differential capacitance between electrodes 802 and 806 may be measured
to determine a touch position in an x-direction and a differential
capacitance between electrodes 804 and 808 may be measured to determine a
touch position in a y-direction. Although electrodes 802-808 are shown as
having a triangular shape, the shape of electrodes 802-808 may be chosen
from any shape as long as electrodes 802-808 have the same surface area.
Electrodes 802-808 may be formed on a substrate or PCB having an
insulative layer 810 and four conductive electrodes 812 on the underside
of insulative layer 810. Each of the four conductive electrodes 812 is
located in the middle of one side of the touch area. Sensor 800 also
includes an elastomer layer 814 comprising non-conductive portions 818
and four conductive portions 816. Sensor 800 further includes a substrate
or PCB 820 on which four conductive electrodes 822 are formed and on
which elastomer layer 814 and electrodes 802-808, and insulative layer
810 are mounted. Conductive electrodes 812, conductive elastomer portions
816, and conductive electrodes 822 are aligned
[0054] Consistent with some embodiments, sensor 800 combines properties of
both a touch sensor and a joystick by adding pressure sensing to the
accurate positional detection in the x- and y-direction provided by
electrodes 802-808. Similar to sensor 700 shown in FIG. 7, each aligned
pair of conductive electrodes 812 and 824 is connected to circuitry that
measures resistance and, particularly, the resistance of the conductive
elastomer 816 directly between the two electrodes, which varies with
pressure applied to sensor 800. By providing electrodes 812 and 824 and
conductive elastomer 816 at multiple locations, a pressure applied to
sensor 800 can be interpreted as movement in either the x or y direction
based on the changing resistance across elastomer layer 814. Thus, a user
can use sensor to provide both pressure-based displacement sensing,
similar to a joystick, and actual displacement, by measuring a touch
position through the differential capacitance on electrodes 802-808.
Alternatively, sensor 800 can be used to detect pressure applied to
sensor as being indicative as movement in the z-direction, similar to
sensor 700 of FIG. 7.
[0055] Moreover, the pressure and displacement sensing capabilities of
sensor 800 can be combined to improve a user's control when using sensor
800 as an input or navigation device. As discussed herein, with small
displacement input devices it is difficult to map the device input area
to the display area. With a one-to-one mapping, the user can traverse the
entire display with one slide of the finger but fine positioning is
impossible. The mapping can be changed to improve fine position but at
the expense of requiring multiple swipes to traverse the full display.
Variable mapping based on finger movement speed is feasible but is
non-intuitive for most users and takes time for the user to adapt. If the
user's slide across electrodes 802-808 is aborted by reaching the limit
of electrodes 802-808, the natural tendency is to push harder to
continue. The additional pressure provided by pushing harder could be
detected by sensor 800 and translated into additional movement in the x-
or y-direction.
[0056] Consistent with some embodiments, differential capacitive touch
sensors as described herein may be used as sensing elements in a touch
screen device. FIG. 9 is a diagram illustrating a touch screen having
multiple differential capacitive touch sensors, consistent with some
embodiments. As shown in FIG. 9, a touch screen 900 includes a plurality
of differential capacitive sensors 902 arranged in rows and columns to
substantially cover the surface area of a screen 904 of touch screen 900.
Each differential capacitive sensor 902 is coupled to circuitry 906,
which may include a multiplexer, by separate leads 908. Consistent with
some embodiments, each differential capacitive sensor 902 is fabricated
as a single electrode layer over a substrate or PCB. The single electrode
layer may be a conductive material such as indium tin oxide (ITO).
Differential capacitive sensors 902 measure a self-capacitance and,
further, a difference in capacitance between itself and a neighboring
sensor 902.
[0057] FIGS. 10A, 10B, and 10C are diagrams illustrating measuring the
differential capacitance of adjacent self-capacitive sensors, consistent
with some embodiments. As shown in FIG. 10A, a finger 1002 is touching an
approximate center point of self-capacitive sensor 902B, which is between
self-capacitive sensors 902A and 902C. When finger 1002 is at the center
point of sensor 902B, the effects of finger 1002 are detected at the
edges of both sensors 902A and 902C. If the distance 1004 between
adjacent sensors is too great, then the effects of finger 1002 would not
be felt at adjacent sensors 902A and 902C. Consequently, distance 1004
shown in FIG. 10A represents a minimum distance between sensors to
prevent dead spots. As shown in FIG. 10B, as finger 1002 moves towards
sensor 902A, the capacitive effects of finger 1002 are seen on sensor
902A and sensor 902B. Then, as finger 1002 moves back towards sensor
902B, the capacitive effects are seen on sensors 902A and 902B, as shown
in FIG. 10C. Consistent with some embodiments, circuitry 906 is
programmed with the distance between the middle of sensors 902A-902C and
maps the touch position of finger 1002 detected by sensors 902A-902C
absolutely to the underlying display.
[0058] Consistent with some embodiments, touch screen 900 provides
advantages over conventional touch screens as only one conductive layer
is required for sensor fabrication. Moreover, by measuring a differential
capacitance between adjacent sensors 902, common mode noise is
substantially rejected, as all sensors 902 are exposed to the same common
mode noise. Moreover, the wiring required for touch screen 900 is about
the same is required for a conventional mutual capacitance touch screen.
[0059] The concept of measuring the differential capacitance of adjacent
electrodes can be applied to a mutual-capacitive touch screen. FIG. 11 is
a diagram illustrating a mutual-capacitive touch screen that measures the
differential capacitance of adjacent electrodes, consistent with some
embodiments. As shown in FIG. 11, touch screen 1100 includes a grid of
horizontal electrodes 1102 and vertical electrodes 1104 separated by an
insulative layer. Horizontal and vertical mutual capacitance electrodes
1102 and 1104 are coupled to circuitry 1106 by leads 1108 coupled to each
electrode. A typical touch screen measures a mutual capacitance between
horizontal and vertical electrodes 1102 and 1104 such that a user touch
at the intersection of horizontal electrode 1102 and vertical electrode
1104 changes the capacitive coupling between the two. Typically, the
charge on the driven electrode is split between the reading electrode and
the grounded body of the user, effectively reducing coupling. Circuitry
1106 would recognize this change as a touch. In a conventional mutual
capacitance touch screen, position resolution is typically twice the
electrode spacing because a touch that appears on two adjacent electrodes
is interpreted as occurring exactly between the two. However, circuitry
1106 can achieve much higher resolution with touch screen 1100 by
measuring the differential capacitance between two adjacent electrodes in
the range of the capacitive influence caused by a user touch. The mutual
capacitance between horizontal and vertical electrodes 1102 and 1104
provides precise absolute positioning of low resolution while the
differential capacitance between adjacent horizontal or vertical
electrodes 1102 and 1104 provides high resolution that is made precise by
being referenced to the absolute positions determined by the grid. For
example, in FIG. 11, a vertical position of a user touch at user touch
area 1110 is determined by the offset from either of the horizontal
electrodes 1102 in the region indicated by the differential capacitance
therebetween. Similarly, the horizontal position could be determined by
the offset from either of the vertical electrodes 1104 in the region
indicated by the differential capacitance therebetween.
[0060] Thus, consistent with some embodiments, a differential capacitance
can be measured between adjacent pairs of horizontal or vertical
electrodes 1102 to provide accurate positioning on touch screen.
Moreover, this would require very little modification to touch screen
1100, as the modifications would only be implemented in circuitry.
Consequently, a conventional mutual capacitance touch screen having
horizontal and vertical electrodes 1102 and 1104 could be essentially
reprogrammed to measure differential capacitance between adjacent
electrodes. Alternatively, a user could designate only a finite area on
touch screen to measure differential capacitance, such as touch area
1110, such that the designated area can be used as a touch sensor for
providing mouse or trackball-like navigation on touch screen 1100. User
could designate the area through a command that would instruct circuitry
1106 to read touch area 1110 as an area of differential capacitance
measurement.
[0061] Consistent with some embodiments, a differential capacitance touch
sensor may be added to a conventional mutual capacitance touch screen to
provide a precise positional navigation device for a touch screen. While
the touch screen would be used for most applications, a differential
capacitance touch sensor could be used to provide mouse-like navigation
of a cursor on the touch screen. FIG. 12 is a diagram illustrating a
mutual capacitance touch screen having a differential capacitance touch
sensor, consistent with some embodiments. As shown in FIG. 12, touch
screen 1200 includes a grid of horizontal electrodes 1202 and vertical
electrodes 1204 separated by an insulative layer. Electrodes 1202 and
1204 are connected to circuitry 1206 by leads 1208. Circuitry 1206 uses
mutual capacitance coupling between horizontal and vertical electrodes to
determine the position of a touch. Touch screen 1200 also includes a
differential capacitance touch sensor 1210 coupled to circuitry 1206 by
leads 1212. Consistent with some embodiments, differential capacitance
touch sensor 1210 may include four triangular shaped single layer
electrodes 1214, 1216, 1218, and 1220, each measuring a differential
self-capacitance between opposing electrodes 1214 and 1218 and 1216 and
1220, similar to sensor 102 shown in FIG. 3. According to some
embodiments, differential capacitance touch sensor 1210 may measure a
touch position of a user to provide a mouse or trackball-like navigation
of touch screen 1200.
[0062] According to some embodiments, differential capacitance touch
sensor 1210 may be fabricated independently of horizontal and vertical
electrodes 1202 and 1204. Consistent with other embodiments, single layer
electrodes 1214-1220 may be coupled to horizontal and vertical electrodes
in order to reduce wiring. For example, each single layer electrode
1214-1220 may be coupled to a different horizontal or vertical electrode
1202 or 1204 by a conductor. The coupling would be chosen such that the
simultaneous appearance of a touch on all four could not happen under
normal operation and would, therefore, indicate that the user was
touching differential capacitance touch sensor 1210. Detecting this,
circuitry 1206 could switch to the differential capacitive position
measurement mode of operation for detecting signals from electrodes
1214-1220.
[0063] Consistent with embodiments described herein, a capacitive touch
sensor having at least one pair of opposing electrodes may be provided to
allow for the measuring of a differential capacitance between the at
least one pair of opposing electrodes providing a capacitive touch sensor
having improved precision and substantially complete common mode noise
rejection. Such a capacitive touch sensor may be used as a navigation
device for navigating on a display. Moreover, such a capacitive touch
sensor may be about the size of a human fingertip, providing an accurate,
yet compact, navigation device. Furthermore, capacitive touch sensors as
described herein may be formed on a substrate or PCB and, thus, may be
integrated onto the substrates or PCBs of existing devices. Capacitive
touch sensors as described herein may use electrodes having any shape,
and may be have additional electrodes formed on below the substrate or
PCB to allow for three-dimensional position sensing. Finally, capacitive
touch sensors as described herein may be used as touch position sensors
in touch screen devices. The examples provided above are exemplary only
and are not intended to be limiting. One skilled in the art may readily
devise other systems consistent with the disclosed embodiments which are
intended to be within the scope of this disclosure. As such, the
application is limited only by the following claims.
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