U.S. patent application number 12/433513 was filed with the patent office on 2009-11-05 for touch input device.
This patent application is currently assigned to TPO DISPLAYS CORP.. Invention is credited to John Richard AYRES, Nicola BRAMANTE, Martin John EDWARDS.
Application Number | 20090273572 12/433513 |
Document ID | / |
Family ID | 40904677 |
Filed Date | 2009-11-05 |
United States Patent
Application |
20090273572 |
Kind Code |
A1 |
EDWARDS; Martin John ; et
al. |
November 5, 2009 |
TOUCH INPUT DEVICE
Abstract
A touch sensor input device includes a first and second array of
electrodes, the electrodes in the first array being orthogonal to
the electrodes in the second array. A capacitor sensing arrangement
senses an electrode capacitance signal which varies in the presence
of a touch input. The capacitance signals for groups of electrodes
in each array are combined in order to derive respective individual
sense signals. This arrangement has electrodes with a finer
resolution than the sensing resolution, and this gives improved
ability to sense accurately the position of the touch input.
Inventors: |
EDWARDS; Martin John;
(Crawley, GB) ; AYRES; John Richard; (Reigate,
GB) ; BRAMANTE; Nicola; (Cambridge, GB) |
Correspondence
Address: |
LIU & LIU
444 S. FLOWER STREET, SUITE 1750
LOS ANGELES
CA
90071
US
|
Assignee: |
TPO DISPLAYS CORP.
Chu-Nan
TW
|
Family ID: |
40904677 |
Appl. No.: |
12/433513 |
Filed: |
April 30, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61125917 |
Apr 30, 2008 |
|
|
|
61125963 |
Apr 30, 2008 |
|
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Current U.S.
Class: |
345/173 |
Current CPC
Class: |
G06F 3/0446 20190501;
G06F 3/047 20130101; G06F 3/0412 20130101 |
Class at
Publication: |
345/173 |
International
Class: |
G06F 3/041 20060101
G06F003/041 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 12, 2009 |
EP |
09152695.4 |
Claims
1. A display device with touch sensor input, the display device
comprising an array display pixels or an array of display
sub-pixels with groups of sub-pixels together defining respective
display pixels, the device comprising: a display layer; and a touch
sensor input device over the display layer for enabling a touch
input to the device, wherein the touch sensor input device
comprises: a first and second array of electrodes, the electrodes
in the first array being orthogonal to the electrodes in the second
array; and a capacitor sensing arrangement for sensing an electrode
capacitance signal which varies in the presence of the touch input,
wherein the electrode capacitance signals for groups of the
electrodes in each array are combined in order to derive respective
individual sense signals, wherein the pitch of the electrodes of
the first and second array is the same as a pixel or sub-pixel
pitch of the display device.
2. The device as claimed in claim 1, wherein some electrodes of one
or both of the first and second arrays of electrodes function as
dummy electrodes which are not used in any of the groups of
electrodes and thereby are not used to derive any individual sense
signals.
3. The device as claimed in claim 1, wherein each group of
electrodes comprises an adjacent group of electrodes.
4. The device as claimed in claim 1, wherein each group of
electrodes comprises a group of electrodes which are not an
adjacent block of electrodes.
5. The device as claimed in claim 4, wherein the different
individual sense signals are each derived from different
electrodes, so that no electrode is used to derive multiple
different sense signals.
6. The device as claimed in claim 1, wherein the electrodes of a
group are physically electrically connected together.
7. The device as claimed in claim 1, wherein not all electrodes of
a group are physically electrically connected together, and the
combination is at least in part implemented by signal
processing.
8. The device as claimed in claim 1, wherein the arrays of
electrodes each comprise straight electrode lines, with enlarged
portions along the lines, with a spacing between the enlarged
portions corresponding to the pitch between the electrode lines of
other array, the enlarged portions in one array having a different
size to the enlarged portions in the other array.
9. The device as claimed in claim 8, wherein the enlarged portions
are diamond shapes.
10. The device as claimed in claim 1, wherein the two electrode
arrays have the same pitch.
11. The device as claimed in claim 1, further comprising a colour
filter arrangement.
12. The device as claimed in any preceding claim, wherein the touch
sensor input device comprises a glass substrate between the first
and second arrays of electrodes, and an anti-scratch coating over
the second electrode array, which is on the opposite side of the
glass substrate to the display layer.
13. The device as claimed in claim 1, wherein the display layer
comprises a liquid crystal layer.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application No. 61/125,917, filed on Apr. 30, 2008, and U.S.
Provisional Application No. 61/125,963, filed on Apr. 30, 2008, the
entirety of which are incorporated by reference herein.
[0002] This application claims priority of EP Patent Application
No. 09152695.4, filed on Feb. 12, 2009, the entirety of which is
incorporated by reference herein.
BACKGROUND OF THE INVENTION
[0003] 1. Field of the Invention
[0004] This invention relates to touch input devices, for example
for use in display devices with touch screens.
[0005] 2. Description of the Related Art
[0006] Touch screens are becoming increasingly common in consumer
electronics applications where an LCD display is present in a
device e.g. mobile phone, PDA or camera. User interaction via a
touch screen saves the space required for key inputs and therefore
allows a larger display area for a given size of device. The touch
screen provides a 2D position sensing function, and it can be used
generally as a means of controlling or interacting with
devices.
[0007] Of the possible physical effects used to locate the
"touched" position on such a screen, sensing the capacitance change
induced between orthogonal sets of electrodes, or between a
grounded stylus and individual electrodes, promises the highest
resolution whilst integrating most easily with existing
manufacturing processes.
[0008] Typically the electrodes of a high resolution 2D capacitance
sensor are laid out in a matrix pattern of intersecting orthogonal
electrodes, indicated as electrodes 10a and 10b in FIG. 1. The
electrodes may be formed using two isolated layers of a transparent
conducting material such as indium tin oxide (ITO). As the object
moves over the electrodes, the capacitance between the electrodes
and the object and the capacitance between the electrodes varies.
Sensing circuits which connect to the electrodes are able to detect
changes in these capacitances which can then be interpreted to
determine the position of the object.
[0009] Typically position sensors are combined with displays in the
form of an overlay providing touch or stylus input. Sensors based
on capacitance sensing consist of sets of electrodes which are
connected to drive and/or sensing circuits. The location of an
object, for example a stylus or a finger, is detected by measuring
changes in the capacitances associated with the electrodes and the
object.
[0010] In FIG. 1, the electrodes are shown as narrow lines, however
the outline of the electrodes may be varied depending on the
detailed operation of the sensor. For example in order to increase
the capacitances between the sense electrodes and the object it may
be preferable to use wider electrodes for example as shown in FIG.
2.
[0011] In this case, the electrodes consist of diamond shapes which
are joined at their vertices to form horizontal and vertical sense
electrodes.
[0012] The electrodes are in the form of straight electrode lines
20a,20b, with enlarged diamond shaped portions 22a,22b along the
lines. The pitch of the diamonds 22a,22b (i.e. the distance between
the diamond centres) corresponds to the pitch of the electrode
lines of the other array, so that a regular array is defined.
[0013] The area presented by the electrodes is substantially
increased compared to FIG. 1 resulting in higher capacitance values
which can be more easily measured.
[0014] In the case where the sensor is combined with a matrix
display device, the number of sense electrodes is likely to be
lower than the number of rows and columns of pixels within the
display but interpolation techniques can be used to determine the
position of the object when it lies at intermediate positions
between the centres of the sense electrodes.
[0015] A concern that arises when locating sense electrode
structures in the optical path of a matrix display device is that
the pattern of the sense electrodes may be visible as a variation
of brightness over the surface of the display. For example, a
conducting layer of ITO might typically have a transmission of 95%.
Brightness variations of only 1% can be seen by the eye
particularly when they have a linear or repetitive structure making
it likely that under some circumstances the electrode pattern will
be visible to the person viewing the display. The presence of the
sense electrodes may therefore degrade the quality of the displayed
images particularly when moving images are being viewed.
[0016] A further concern is that when the object to be sensed is
significantly smaller than the sense electrode pitch, this will
affect the way in which the capacitance values change with the
position of the object, making it difficult to uniquely locate the
position of the object when it is centred on one of the sense
electrodes.
[0017] For example, FIG. 3 shows in more detail part of the
electrode layout and the corresponding cross section is shown in
FIG. 4.
[0018] FIG. 3 shows a line X-X along the centre of one of the
electrode rows. When the stylus 40 is located at the centre of the
line X-X as indicated in FIG. 4 (i.e. at the middle of one of the
diamonds in the row direction electrodes 30b,32b), it will have a
relatively large effect on the capacitances associated with the row
direction sense electrodes 30b,32b (these will be termed B
electrodes in the following description) but a much smaller effect
on the capacitances associated with the adjacent column electrodes
30a,32a (these will be termed A electrodes in the following
description). This may make it difficult to detect the location of
the stylus on one set of electrodes, for example the A electrodes,
when the stylus is centred over one of the other set of electrodes,
for example the B electrodes. In particular, from this starting
point, movement of the stylus along the column direction has much
less effect on the capacitance than movement of the stylus along
the row direction.
[0019] This is illustrated graphically by FIG. 5 which shows an
estimate of the capacitance between a stylus and the sense
electrodes when moving either side of the centre of the line X-X.
Curve 50 represents the capacitance between the stylus and the B
(row) electrode and the curves 52 and 54 represent the capacitance
between the stylus and the two A (column) electrodes to either
side.
[0020] For the graph of FIG. 5, it is assumed that the stylus 40
has a tip diameter of 1 mm and the diamond shapes of the sense
electrode arrangements have a side with a length of 4.2 mm (this is
dimension L shown in FIG. 3).
[0021] In FIG. 5, the x-axis shows the position along the line X-X.
Position 0 corresponds to the centre of a diamond 32b (as shown in
FIG. 4). Thus, this position corresponds to the maximum capacitance
to the row direction sense electrodes 30b,32b. When moving to the
side, the capacitance to the row direction sense electrode drops
(curve 50), but the capacitance one of the column direction sense
electrodes increases (curves 52 and 54).
[0022] It can be seen that when the stylus 40 is centred on the
line X-X, the capacitance between the stylus and the adjacent A
electrodes falls to a low level as most of the electric field lines
between the stylus and the sense electrode terminate on the B sense
electrode. This will make it difficult to detect which of the A
electrodes the object is closest to.
[0023] In general, the way in which the capacitances associated
with the sense electrodes vary with the position of the object
depends on the dimensions and the shape of the sense electrodes.
However, the electrode shape required to produce the desired sensor
characteristics may not be consistent with the pattern required to
minimize the visibility of the sense electrodes. Reducing the
visibility of the electrodes is particularly important when the
sensor is combined with a display device.
SUMMARY OF THE INVENTION
[0024] According to the invention, there is provided a display
device with touch sensor input, the display device comprising an
array display pixels or an array of display sub-pixels with groups
of sub-pixels together defining respective display pixels, the
device comprising: a display layer; and a touch sensor input device
over the display layer for enabling a touch input to the device,
wherein the touch sensor input device comprises: a first and second
array of electrodes, the electrodes in the first array being
orthogonal to the electrodes in the second array; and a capacitor
sensing arrangement for sensing an electrode capacitance signal
which varies in the presence of the touch input, wherein the
electrode capacitance signals for groups of the electrodes in each
array are combined in order to derive respective individual sense
signals, wherein the pitch of the electrodes of the first and
second array is the same as a pixel or sub-pixel pitch of the
display device.
[0025] In one example, each group of electrodes comprises an
adjacent group of electrodes. This means that each sense electrode
is effectively an arrangement of electrodes spread over an area
using a higher resolution array of electrodes. The high resolution
electrodes can thus be considered to be sub-electrodes. Because
these sense sub-electrodes have a finer resolution than the
resolution being sensed (for example finer than size of the object
being detected), there is a more gradual shift in capacitance
change from one sense electrode arrangement to the next as the
input moves. However, the sense electrode arrangements can still
occupy a small area and therefore the effect of the touch sensor
device on the output of an underlying display device can be
minimised. The touch sensor capacitance signal is stronger when the
input position is between sense electrode arrangement
positions.
BRIEF DESCRIPTION OF DRAWINGS
[0026] The invention can be more fully understood by reading the
subsequent detailed description and examples with references made
to the accompanying drawings, wherein:
[0027] FIG. 1 shows a first known arrangement of electrodes for a
touch sensor device.
[0028] FIG. 2 shows a second known arrangement of electrodes for a
touch sensor device.
[0029] FIG. 3 shows a portion of FIG. 2 and is used to explain a
problem with the arrangement of FIG. 2.
[0030] FIG. 4 shows how the input device interacts with the touch
sensor device, again to explain a problem with the arrangement of
FIG. 2.
[0031] FIG. 5 is a graph to explain the problem with the
arrangement of FIG. 2.
[0032] FIG. 6 shows one example of known structure for a display
device with touch sensor input and to which the invention can be
applied.
[0033] FIG. 7 shows a first arrangement of electrodes for a touch
sensor device of the invention.
[0034] FIG. 8 shows a second arrangement of electrodes for a touch
sensor device of the invention.
[0035] FIG. 9 shows a portion of FIG. 8 and is used to explain the
advantage of the invention.
[0036] FIG. 10 shows how the input device interacts with the touch
sensor device, again to explain the advantage of the invention.
[0037] FIG. 11 is a graph to explain the advantage of the
invention.
[0038] FIG. 12 defines the pitches of the sensor electrodes of the
invention.
[0039] FIG. 13 shows how the pitches of the sensor electrodes of
the invention can be matched to a colour filter arrangement.
[0040] FIG. 14 shows how the capacitance between a stylus and a
single sub-electrode varies with the position of the stylus
relative to the centre of the sub-electrode.
[0041] FIG. 15 shows an example of a sub-electrode grouping of the
invention which is not based on adjacent groups of
sub-electrodes.
[0042] FIG. 16 shows a target profile for the dependence of
capacitance on stylus position and the approximation to this
characteristic which is achieved using the sub-electrode grouping
shown in FIG. 15.
[0043] FIG. 17 shows how a number of the sub-electrode groups of
FIG. 15 can be positioned parallel to one another in order to form
a set of sense electrodes.
[0044] FIG. 18 shows the resulting capacitance verses object
position characteristics for the three adjacent sense electrodes of
FIG. 17.
DETAILED DESCRIPTION OF INVENTION
[0045] The following description is of the contemplated mode of
carrying out the invention. This description is made for the
purpose of illustrating the general principles of the invention and
should not be taken in a limiting sense. The scope of the invention
is determined by reference to the appended claims.
[0046] Wherever possible, the same reference numbers are used in
the drawings and the descriptions to refer to the same or like
parts.
[0047] The invention provides a touch sensor input device in which
capacitive sensing electrodes are arranged as connected groups of
electrodes, so that the individual electrodes have smaller pitch
than the sensing resolution. This improves the ability to determine
uniquely the location of a touch input for all positions. The
smaller electrode pitch matches the design of the display, so that
visual artefacts caused by the sense electrode structure are
reduced.
[0048] Before explaining the invention in detail, an example will
be provided of the type of device to which the invention can be
applied. FIG. 6 shows one example of known layer structure for a
display device with capacitance touch sensor input and to which the
invention can be applied.
[0049] Part of the display is shown schematically as 60, and this
includes at least a display layer. The precise design of display
panel is not material to the invention, and for this reason, a
detailed description of the display panel is not provided.
Typically, the display structure is a liquid crystal display
comprising a layer of liquid crystal material sandwiched between
substrates. For active matrix displays, the substrates comprise a
lower active plate and an upper passive plate. The passive plate
for example carries a common electrode. The common electrode is
shown as 62, and is a common ground plane in the form of a
transparent conducting layer that is present on the colour filter
layer 64. Below the common electrode 62 is the layer of liquid
crystal sitting on the active glass plate, indicated generally as
reference 61.
[0050] Above the colour filter layer 64 is a combination of a
planarising dielectric layer 66 and the Y-sense electrode
arrangements 68 for the touch sensor.
[0051] The layers 62,64,66,68 are, in practice, deposited on the
substrate 70. The top substrate 70 thus functions as the top
passive plate for the display device as well as the support
structure for the touch sensor device.
[0052] The X sense electrode arrangements 72 are provided on the
opposite side of the substrate 70 to the Y sense electrode
arrangements 68, and a light polarising layer and an anti scratch
layer 74 are provided as the top surface. These are conventional
layers for LCD touch screens. The stylus or finger that provides
the user touch interaction touches the surface of the anti scratch
layer and is shown as 76.
[0053] FIG. 6 thus shows a display structure with a touch sensor
structure on top of the display structure. It will be appreciated
that some components of the display structure are integrated with
the touch sensor, such as the glass substrate 70, light polarizing
layer, anti scratch layer 74 and colour filters 64. Thus, the
structure does not have separately defined display parts and touch
sensor parts. However, the general display function (i.e.
modulation or production of light) is beneath the general touch
sensor function, and the description and claims should be
understood accordingly.
[0054] FIG. 6 represents just one possible integrated structure. A
further level of integration would be to move the X sense electrode
arrangements inside the display (i.e. between the substrates).
However this would reduce the influence of the stylus on the XY
capacitance. FIG. 6 represents the first step towards integrating
the touch sensor into the display, but the invention applies
equally to designs with a greater level of integration of the touch
sensor function with the display function.
[0055] A first way in which the proposed method is applied to the
sense electrode structures of FIG. 1 and FIG. 2 is illustrated in
FIG. 7 and FIG. 8. In these examples, each sense electrode
arrangement is made up of a connected group of four sub-electrodes,
although in practice a larger number of sub-electrodes may be used.
The connection between the electrodes of the group can be by a
physical electrical connection as shown in FIGS. 7 and 8.
[0056] The structure of the sub-electrodes is shown as being
similar to that of the original sense electrodes although this does
not have to be the case. Sensing electrodes are created by
electrically connecting groups of adjacent sub-electrodes at the
periphery of the sensing area. The position of an object can be
determined by comparing the capacitances associated with the
vertical A electrodes 84a or 84b in order to determine the
horizontal position and by comparing the capacitances associated
with the horizontal B electrodes 80a or 80b in order to determine
the vertical position of the object.
[0057] FIG. 7 shows individual horizontal (i.e. row) electrodes 80a
in the form of bars, which are connected in groups 82a. Each
individual horizontal electrode can be considered as a
sub-electrode, and each group 82a can be considered as a combined
sense electrode arrangement or structure. Likewise, the individual
vertical (i.e. column) electrodes 84 are connected in groups
86a.
[0058] FIG. 8 shows individual horizontal (i.e. row) electrodes in
the form of bars with diamonds (as shown in FIG. 2), which are
again connected in groups 82b, and the individual vertical (i.e.
column) electrodes 84b in the form of bars with diamonds also
connected in groups 86b.
[0059] The benefit of the use of sub-electrodes is illustrated by
FIGS. 9, 10 and 11.
[0060] FIG. 9 shows an enlarged portion of the arrangement of FIG.
8, and shows the axis X-X along which stylus movement is modelled.
A cross section of the sense electrode structure is illustrated in
FIG. 10, showing the stylus 40 and individual sub-electrodes
80b,84b.
[0061] FIG. 11 shows how the estimated capacitance between a stylus
and the sense electrode arrangements varies with the position of
the stylus 40 (as shown in FIG. 10) along the line X-X shown in
FIG. 9.
[0062] As the stylus is moved along the line X-X, there is no
significant change in the capacitance between the stylus and the
group 82b of horizontal electrodes (which group functions as a row
sense electrode arrangement) as indicated by the curve 110, whereas
the capacitance to three sequential groups 86b of vertical
electrodes (which group functions as a vertical sense electrode
arrangement) varies smoothly with a significant capacitance to at
least one of the electrodes for all positions. The plots for three
adjacent vertical sense electrode arrangements are shown as plots
112,114,116.
[0063] The repeat pitch of the sub-electrode pattern is shown in
FIG. 12 as P.sub.SUB.sub.--.sub.A in the horizontal direction and
P.sub.SUB.sub.--.sub.B in the vertical direction. When the
electrodes are formed in front of a display, the pitch of the
sub-electrodes is matched to the repeat pitch of the display
pixels. This reduces image artefacts, as all pixels are then
affected equally.
[0064] FIG. 13 shows a possible layout for the colour pixels of an
active matrix display with a repeat pitch of P.sub.RGBH in the
horizontal direction and P.sub.RGBV in the vertical direction. The
colour pixels are arranged as red (R), green (G) and blue (B)
columns of pixels. In order to minimise the visibility of the
capacitance sensor electrodes, the pitches of the sub-electrode
pattern and the display pixel pattern should be matched so that
P.sub.SUB.sub.--.sub.A=P.sub.RGBH and
P.sub.SUB.sub.--.sub.B=P.sub.RGBV.
[0065] In the examples above, adjacent sub-electrodes are formed
into groups. An alternative approach is for the grouping of the
sub-electrodes to be changed in order to modify the characteristics
of the capacitance sensor, namely how the capacitances which are
measured by the sensor vary with the properties of the objects to
be sensed such as size and position.
[0066] To illustrate this approach, a sensor is considered based on
measurement of the capacitance between the sense electrodes and the
object to be sensed such as a stylus or finger (as opposed to
measurement of the capacitance between sense electrodes). The
sub-electrodes can be arranged in a grid pattern such as that
illustrated in FIG. 1 or 2. When the object, for example a grounded
conducting stylus, is brought close to one of the sense electrodes
the capacitance between the sense electrode and that object
increases. This is illustrated in FIG. 14 which shows an estimate
of how the capacitance between a stylus and a single sub-electrode
varies with the position of the stylus relative to the centre of
the sub-electrode on an axis which is perpendicular to the
sub-electrode. As the stylus moves towards the sub-electrode the
capacitance increases reaching a peak when the stylus is directly
over the sub-electrode. In this example, the width of the
sub-electrode is approximately 0.1 mm and the diameter of the
stylus is 1.5 mm.
[0067] Adjacent sub-electrodes have a similar variation of
capacitance to the stylus with stylus position but offset by a
distance corresponding to the separation of the sub-electrodes.
Each sense electrode can be formed by electrically connecting a
respective group of sub-electrodes as explained above. The
variation of capacitance between the sense electrode and the stylus
with the position of the stylus relative to the centre of the sense
electrode can be then be obtained by summing the contributions to
the capacitance from the sub-electrodes within the group.
[0068] FIG. 15 shows an example of a sub-electrode grouping which
is not based on adjacent groups of sub-electrodes, but instead
takes a set of sub-electrodes so that a desired capacitance
function is obtained. The sub-electrodes are numbered in FIG. 15
relative to the centre sub-electrode, with sub-electrodes having a
positive index on the right and sub-electrodes having a negative
index on the left.
[0069] The sense electrode which is centred on sub-electrode 0 is
formed by connecting sub-electrodes +3, -3, +19, -19, +20, -20, +22
and -22. The variation of the capacitance between the sense
electrode and the stylus depending on the stylus position relative
to the centre of sub-electrode 0 is shown in FIG. 16.
[0070] In FIG. 16, the plot 160 indicates the target profile for
the dependence of capacitance on stylus position while the plot 162
shows the approximation to this characteristic which is achieved
using the sub-electrode grouping shown in FIG. 15. This shows that
by appropriately grouping the sub-electrodes it is possible to
substantially modify the characteristics of the sense
electrode.
[0071] In order to sense the position of an object over an area it
is necessary to use multiple sense electrodes. FIG. 17 shows how a
number of the sub-electrode groups can be positioned parallel to
one another in order to form a set of sense electrodes. In this
example, the pitch of the sense electrodes is equal to 30 times the
pitch of the sub-electrodes. Thus, the sub-electrodes are much more
closely spaced than the sensing resolution. The pitch of the sense
electrodes determines the sensing resolution. Furthermore, the
sub-electrodes groups overlap with each other. This means that each
sense electrode uses sub-electrodes spanning a certain width, and
this width is greater than the distance between sense electrodes.
This can be seen clearly in FIG. 17.
[0072] For this particular sub-electrode group pattern and sense
electrode pitch, it is convenient that no sub-electrodes are
required to be part of more than one group.
[0073] However, this does not have to be the case. Sub-electrodes
can be used in multiple sense electrodes, by time multiplexing the
sub-electrode between different groups or by combining the data
from the sub-electrodes to form virtual groups at the signal
processing stage. This is discussed further below. These measures
mean that a sub-electrode can be part of two different sense
electrodes, either because the sub-electrode signals are combined
at different times to form the different sense electrode signals,
or else because the sense electrode signals are obtained using
signal processing (this is discussed further below).
[0074] An estimate of the resulting capacitance verses object
position characteristics for three adjacent sense electrodes, as
illustrated in FIG. 17, is shown in FIG. 18. The capacitance
profile 180a, 180b and 180c associated with each sense electrode is
of the same shape but is shifted in position on the horizontal axis
by an amount equal to the sense electrode pitch.
[0075] The example of the capacitance verses object position
profile generated by grouping sub-electrodes is purely for
illustration. In practice, the choice of profile and therefore
grouping may be made on criterion such as maximising the signal to
noise ratio for the signals derived from the sense electrode or
simplifying the signal processing required to convert the sense
electrode data to object position.
[0076] In the example of the sub-electrode grouping shown, the
pattern of sub-electrodes which forms a group is symmetrical about
its centre. However there may be occasions when it is preferable to
have an asymmetrical pattern of sub-electrodes forming a group. For
example, it may be beneficial to vary the pattern of the
sub-electrode grouping over the area of the sensor, as an example
it may be advantageous to use different sub-electrode group
patterns close to the edges of the sensor in order to ensure
consistent performance to the edge of the area being sensed where
the sense electrode groups might be truncated.
[0077] There may be some sub-electrodes which are not used for
sensing the object because they are not included in any of the
sense electrode groups. Although they are not used for sensing
these sub-electrodes can still be present in order to reduce the
visibility of the sense electrodes by producing a electrode pattern
which is uniform over the areas of the sensor. These sub-electrodes
can be considered to be dummy electrodes.
[0078] As explained above, where the sensor is combined with a
display this uniform repeating pattern is matched to that of the
display. The unused sub-electrodes should however be electrically
treated in such a way as to minimise any interference or
degradation of the measurements made on the sub-electrodes which
are being used for sensing. In most circumstances, this means that
the unused sub-electrodes should be connected to a low impedance,
for example they could be connected to ground.
[0079] In the examples above, both for adjacent groups of
sub-electrodes and non-adjacent groups, it has been shown that the
sub-electrodes are connected into groups with the connections
between the sub-electrodes hard-wired using a conductor like a
metal line or wire. Alternatively it may be sufficient to
indirectly couple the sub-electrodes within the group via a
capacitor or other electrical component allowing electrical charge
to pass between the sub-electrodes in the group.
[0080] Furthermore it is possible to connect the sub-electrodes
which form a group in a virtual manner to form virtual sense
electrodes. In this case, there would not be a direct electrical
connection between the sub-electrodes within the group. Instead
data would be obtained from individual sub-electrodes or small
groups of sub-electrodes (groups containing a smaller number of
sub-electrodes than the number required to form the sense
electrode) and this data would be combined in a signal processing
operation to derive a signal representing the data that would be
obtained from the full group of sub-electrodes. Thus, the important
point is that signals for a group of sub-electrodes are combined to
form a sense electrode signal, and this combination can be by
physical connection or by signal processing. Thus, the device may
be arranged so that not all electrodes of a group are physically
connected together, and the combination of electrode signals is at
least in part implemented by signal processing.
[0081] The measurements of the capacitances associated with the
sub-electrodes or sub-electrode groups are preferably made
simultaneously as this reduces the overall measurement time.
Alternatively, the measurements may be made in a time sequential
manner.
[0082] The capacitance sensing arrangement has not been described
in detail, as an existing conventional arrangement can be used. The
capacitor sensing arrangement is for sensing either a capacitance
between pairs of electrodes, with one electrode of each sensed pair
being from each electrode array, or for sensing a capacitance
between an electrode and a grounded stylus.
[0083] The invention is applicable to capacitance measurement touch
sensor input devices based on capacitance sensing, particularly for
matrix displays, such as AMLCDs or AMOLEDs.
[0084] The electrode pitch is preferably the same as the sub-pixel
pitch (i.e. the pitch of the R, G, B sub-pixels). However, it may
be the same as the overall pixel pitch, as there will still be a
uniform affect on each pixel. Of course, some displays may not have
sub pixels, for example colour sequential displays may use the same
pixels for different colours in a time sequential manner.
[0085] In some examples, the groups of electrodes used to form a
sense line may extend across a large number of sub-electrodes, for
example at least 3, 5 or even 8 sub-electrode lines each side of a
central sub-electrode line.
[0086] Various modifications will be apparent to those skilled in
the art.
[0087] While the invention has been described by way of example and
in terms of the preferred embodiments, it is to be understood that
the invention is not limited to the disclosed embodiments. To the
contrary, it is intended to cover various modifications and similar
arrangements (as would be apparent to those skilled in the art).
Therefore, the scope of the appended claims should be accorded the
broadest interpretation so as to encompass all such modifications
and similar arrangements.
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