U.S. patent application number 16/129863 was filed with the patent office on 2019-01-10 for position-sensing and force detection panel.
The applicant listed for this patent is ATMEL CORPORATION. Invention is credited to John Stanley Dubery, Peter Sleeman.
Application Number | 20190012035 16/129863 |
Document ID | / |
Family ID | 46083119 |
Filed Date | 2019-01-10 |
United States Patent
Application |
20190012035 |
Kind Code |
A1 |
Sleeman; Peter ; et
al. |
January 10, 2019 |
Position-Sensing and Force Detection Panel
Abstract
Disclosed is a touch position sensor. Force detection circuitry
can be included with the position sensor, for example, to determine
an amount of force applied to a touch panel of the sensor.
Inventors: |
Sleeman; Peter;
(Waterlooville, GB) ; Dubery; John Stanley;
(Basingstoke, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ATMEL CORPORATION |
Chandler |
AZ |
US |
|
|
Family ID: |
46083119 |
Appl. No.: |
16/129863 |
Filed: |
September 13, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14981510 |
Dec 28, 2015 |
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16129863 |
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12959166 |
Dec 2, 2010 |
9223445 |
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14981510 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G06F 3/044 20130101;
G06F 3/04164 20190501; G01L 1/14 20130101; G01L 5/228 20130101;
G01L 1/205 20130101; G06F 3/0414 20130101; G06F 2203/04105
20130101; G06F 3/0416 20130101 |
International
Class: |
G06F 3/041 20060101
G06F003/041; G06F 3/044 20060101 G06F003/044; G01L 1/14 20060101
G01L001/14; G01L 5/22 20060101 G01L005/22; G01L 1/20 20060101
G01L001/20 |
Claims
1.-17. (canceled)
18. A sensor, comprising: a voltage driver operable to provide an
alternating voltage; an integrator circuit; a first variable
resistance element coupled to a first output of the voltage driver
and an input of the integrator circuit, wherein the integrator
circuit is operable to measure a parameter of the first variable
resistance element over a period of time; and circuitry operable to
determine, based on the measured parameter, an amount of force
applied to a touch sensing panel.
19. The sensor of claim 18, wherein the parameter is current
flowing through the variable resistance element.
20. The sensor of claim 18, further comprising a bias resistance
element connected in parallel with the first variable resistance
element.
21. The sensor of claim 18, further comprising a limiting
resistance element connected in series with the first variable
resistance element,
22. The sensor of claim 18, further comprising a second variable
resistance element coupled with a second output of the voltage
driver and the input of the integrator circuit.
23. The sensor of claim 22, further comprising a bias resistance
element connected in parallel with the second variable resistance
element.
24. The sensor of claim 22, further comprising a limiting
resistance element connected in series with the second variable
resistance element.
25. The sensor of claim 18, wherein the first input of the
integrator circuit is at a voltage between a first voltage and a
second voltage of the alternating voltage provided by the voltage
driver.
26. The sensor of claim 18, wherein the circuitry is operable to
determine an amount of force applied to the sensor using a
differential measurement.
27. The sensor of claim 18, wherein the circuitry is further
operable to determine a location in a sensing area of the touch
sensing panel associated with the determined amount of force.
28. A circuit, comprising: a voltage driver operable to provide an
alternating voltage: an integrator circuit; a first resistive force
sensitive element coupled to a first output of the voltage driver;
a first bias resistance element connected in parallel with the
first resistive force sensitive element; and a first limiting
resistance element connected in series with the first resistive
force sensitive element and the first bias resistance element, and
coupled to an input of the integrator circuit.
29. The circuit of claim 38, further comprising: a second resistive
force sensitive resistance element coupled to a second output of
the voltage driver; a second bias resistance element connected in
parallel with the second resistive force sensitive element; and a
second limiting resistance element connected in series with the
second resistive force sensitive element and the second bias
resistance element, and coupled to the input of the integrator
circuit.
Description
BACKGROUND
[0001] A position sensor can detect the presence and location of a
touch by a finger or by an object, such as a stylus, within an area
of an external interface of the position sensor. In a touch
sensitive display application, the position sensor enables, in some
circumstances, direct interaction with information displayed on the
screen rather than indirectly via a mouse or touchpad. Position
sensors can be attached to or provided as part of devices with a
display. Examples of displays include, but are not limited to,
computers, personal digital assistants (PDAs), satellite navigation
devices, mobile telephones, portable media, players, portable game
consoles, public information kiosks, and point of sale systems.
Position sensors have also been used as control panels on various
appliances.
[0002] There are a number of different types of position sensors.
Examples include, but are not limited to, resistive touch screens,
surface acoustic wave touch screens, capacitive touch screens, and
the like. A capacitive touch screen, for example, may include an
insulator coated with a transparent conductor in a particular
pattern. When an object, such as a finger or a stylus, touches the
surface of the screen them is a change in capacitance. This change
in capacitance is sent to a controller for processing to determine
the position where the touch occurred.
[0003] In a mutual capacitance configuration, for example, an array
of conductive drive electrodes or lines and conductive sense
electrodes or lines can be used to form a touch screen having
capacitive nodes. A node may be formed at each intersection of a
drive electrode and a sense electrode. The electrodes cross at the
intersections but are separated by an insulator so as to not make
electrical contact. In this way, the sense electrodes are
capacitively coupled with the drive electrodes at the intersection
nodes. A pulsed or alternating voltage applied on a drive electrode
will therefore induce a charge on the sense electrodes that
intersect with the drive electrode. The amount of induced charge is
susceptible to external influence, such as from the proximity of a
nearby finger. When an object approaches the surface of the screen,
the capacitance change at every individual node on the grid can be
measured to determine the location or position of the object.
SUMMARY
[0004] Disclosed axe various examples of a touch sensor that
includes exemplary force detection circuitry. The force detection
circuity can be used to determine an amount of force applied to the
sensor.
BRIEF DESCRIPTION OF THE FIGURES
[0005] The figures depict one or more implementations in accordance
with the present teachings, by way of example only, not by way of
limitation. In the figures, like reference numerals refer to the
same or similar elements.
[0006] FIG. 1 illustrates schematically a cross-sectional view of a
touch sensitive panel;
[0007] FIG. 2 illustrates schematically a plan view of conductors
of the touch sensitive position-sensing panel of FIG. 1 together
with a controller of a touch sensitive panel;
[0008] FIG. 3 is a circuit diagram of a first example of a force
sensor useable together with the controller of a touch sensor;
[0009] FIG. 4 is a circuit diagram of a second example of a force
sensor useable together with the controller of a touch sensor;
and
[0010] FIG. 5 is a circuit diagram of a third example of a force
sensor useable together with a controller of a touch sensor.
DETAILED DESCRIPTION
[0011] In the following detailed description, numerous specific
details are set forth by way of examples in order to explain the
relevant teachings. In order to avoid unnecessarily obscuring
aspects of the present teachings, those methods, procedures,
components, and/or circuitry that are well-known to one of ordinary
skill in the art have been described at a relatively high
level.
[0012] Reference now Is made In detail to the examples illustrated
in the accompanying figures and discussed below.
[0013] A display may be overlaid with a touch position-sensing
panel, to implement a touch sensitive display device. The display
may include various forms. Examples include, but are not limited to
liquid crystal displays such as an active matrix liquid crystal
display, an electroluminescent display, an electrophoretic display,
a plasma display, cathode-ray display, an OLED display, or the
like. It will be appreciated that light emitted from the display
should be able to pass through the position-sensing panel with
minimal absorption or obstruction
[0014] FIG. 1 illustrates an exemplary touch position-sensing panel
1 which overlies a display 2. Although the force sensing may be
used in touch sensors implementing other types of touch sensing,
for discussion purposes, the drawing shows an example of a
structure that may be used to implement a mutual capacitance type
touch sensitive panel.
[0015] In the illustrated example, the panel 1 includes a substrate
3 having a surface on each side. The panel 1 includes a first
number of electrodes 4(X) and a second number of electrodes 5(Y)
provided on the opposite surfaces of the substrate 3. The substrate
3 is also provided adjacent to the display 2 such that one
electrode 4(X) is between the display 2 and the substrate 3. An air
gap is formed between the display 2 and the first electrode 4(X). A
transparent adhesive layer 6 is between the second electrode 5(Y)
and a transparent covering sheet 7.
[0016] In other examples, the touch position-sensing panel 1 may
have a second substrate (not shown). With a second substrate, a
touch position-sensing panel may have a transparent panel, a first
adhesive layer on the panel, a first electrode layer forming first
electrodes, a first substrate, a second adhesive layer, a second
electrode layer forming second electrodes, and the second
substrate. In such an example, the first conductive electrode layer
is attached to the first substrate and the second conductive
electrode layer is attached to the second substrate.
[0017] Returning to the illustrated example of FIG. 1, substrate 3,
which forms a core of the exemplary touch sensitive
position-sensing panel 1, can be formed from a transparent,
non-conductive material such as glass or a plastic. Examples of
suitable plastic substrate materials include, but are not limited
to Polyethylene terephthalate (PET), Polyethylene Naphthalate
(PEN), or polycarbonate (PC).
[0018] In the mutual capacitance example, electrodes 4(X) are drive
electrodes provided on one surface of the substrate 3, and
electrodes 5(Y) are sense electrodes provided on the opposing
surface of the substrate 3. Capacitive sensing channels are formed
at the capacitive coupling nodes which exist in the localized
regions surrounding where the first and second electrodes 4(X) and
5(Y) cross over each other and are separated by the
riots-conductive substrate 3.
[0019] Transparent covering sheet 7 is provided over the substrate
3 and electrodes 5(Y) and may be joined thereto using various
methods and materials. One exemplary implementation is a
pressure-sensitive adhesive. In one example, the covering sheet 7
may be glass, polycarbonate, or PMMA.
[0020] Indium-tin-oxide (ITO) is an example of a clear conductive
material that can be used so form either one or both sets of
electrodes 4(X) and 5(Y) in the example of FIG. 1. Alternatively,
any other clear conductive material may be used, such as other
inorganic and organic conductive materials, such as
Antimony-tin-oxide (ATO), tin oxide, PEDOT or other conductive
polymers, carbon nanotube or metal nanowire impregnated materials,
and the like, Farther, opaque metal conductors may be used such as
a conductive mesh, which may be of copper, silver or other
conductive materials.
[0021] With reference to FIG. 2, drive electrodes 4(X) and sense
electrodes 5(Y) are formed by solid areas of ITO. Sensing area 10
of the position sensing panel 1, denoted by the dotted line in FIG.
2, encompasses a number of the intersections 11 formed by the drive
electrodes 4(X) and sense electrodes (5)Y. In the example, the gaps
between adjacent X electrode bars arc made narrow. This may enhance
the ability of the electrodes 4(X) to shield against noise arising
from the underlying display 2 shows in FIG. 1. In some examples,
90% or more of the sensing area 10 is covered by ITO. In an example
like that shown in FIG. 2, the gap between adjacent drive
electrodes 4(X) may 200 microns or less.
[0022] In one example, each drive electrode 4(X) forms channels
with a number of the sense electrodes 5(Y) on an adjacent plane. As
mentioned previously, there are intersections 11 where the drive
electrodes 4(X) cross over the sense electrodes 5(Y).
[0023] A drive electrode connecting line 12 is in communication
with a respective drive electrode 4(X). A sense electrode
connecting line 13 is in communication with a respective sense
electrode 5(Y). The patterns of the connecting lines are shown by
way of an example only. The drive electrode connecting lines 12 and
the sense electrode connecting lines 13 are connected to a control
unit 20.
[0024] In some examples, the change in capacitance at the node
formed at each intersection 11 of drive electrode 4(X) and sense
electrode 5(Y) when an object touches the surface of the panel 1
can be sensed by the control unit 20. The control unit 20 applies
pulsed or alternating voltages to the drive electrodes 4(X) through
the drive electrode connecting lines 12. The control unit 20
measures the amount of charge induced on the sense electrodes 5(Y)
through the sense electrode connecting lines 13. The control unit
20 determines that a touch has occurred and the location of the
touch based upon the changes its capacitance sensed at one or more
of the nodes 11.
[0025] In some examples, the amount of charge induced on a sense
electrode 5(Y) can be measured by a current integrator circuit 22
incorporated in the control unit 20. The current integrator circuit
22 can measure the accumulated charge on a capacitor at fixed time
intervals. The exemplary controller 20 includes a number "n" of
current integrators 22a, 22b, . . . 22n and a processor 23. Some of
these integrators are used in the processing of signals from the
sensing channels to detect touch on the touch position-sensing
panel 1.
[0026] Some touch sensor applications may take advantage of a
measurement of the amount of force applied to the touch
position-sensing panel 1. For such an application of the touch
sensor, a force sensor can be associated with the touch
position-sensing panel 1 and controller 20. The force sensor, in
some examples, measures the amount of force applied to the
transparent covering sheet 2 of the touch position-sensing panel 1.
The force sensor may be used to quantify or distinguish between
different types of touch events. For example, the force sensor can
measure the amount of force applied and cause the execution of a
first function if the force is below or equal to a threshold. The
force sensor can also measure the amount of force applied and cause
the execution of a second function if the force exceeds the
threshold.
[0027] With reference back to FIG. 1, a resistive force sensitive
element 30 can be used to measure the amount of force applied to
the panel. In one example, the resistive force sensitive element 30
can be arranged between the touch position-sensing panel 1 and a
supporting structure (not shown). In another example, the touch
position-sensing panel 1 is incorporated in a portable device with
the resistive force sensitive element 30 arranged between the touch
position-sensing panel 1 and a housing of the device.
[0028] The resistive force sensitive element 30, for example, may
be formed of a Quantum Tunneling Composite material (QTC). The DC
resistance of the QTC material varies in relation to applied force.
In one example, the force sensitive element 30 can be formed by
printing an ink containing the QTC material.
[0029] With reference back to FIG. 2, in some examples, the
resistive force sensitive element 30 can modulate the flow of
current into a current integrator circuit 22 of the control unit
20. The control unit 20 can include one or more current integrator
circuits 22 that are not used in touch sensing operations. One
exemplary controller 20 is the mXT224 sold by Atmel Corporation, of
San Jose Calif. Using such a controller 20 facilitates force
sensing by using existing circuitry of the control unit 20. Thus,
force sensing can be achieved, in some examples, without any
additional dedicated electronic conditioning circuitry such as bias
networks, amplifiers, analogue to digital converters, and the
like.
[0030] With reference to FIG. 3, a first exemplary circuit 32 that
includes a resistive force sensitive element 30 is shown and
described. The circuit 32 is in communication with an input of a
current integrator 22 of the control unit 20. The control unit 20
is connected to a ground rail 19 and a fixed voltage supply rail 23
that has a voltage V.sub.dd. A resistive force sensitive element 30
having a value R.sub.Q is connected between the fixed voltage
supply rail 23 and the current integrator input 21 of the control
unit 20. The current integrator input 21 acts as a virtual earth
having a voltage V.sub.n. Having the resistive force sensitive
element 30 and the control unit 20 both connected to the same
voltage supply rail 23 allows the circuitry within the control unit
20, which measures the integrated current value, to be referenced
to the voltage supply rail. This configuration may also allow the
measurement to be made ratiometric and substantially decoupled from
any changes in the supply rail voltage V.sub.dd. Although the
supply rail voltage V.sub.dd can be a fixed voltage, there may be
unintended fluctuations in the supply rail voltage V.sub.dd.
[0031] A limit resistor 24 having a value R.sub.L is connected in
series with the resistive force sensitive element 30, between the
fixed voltage supply rail 23, and the current integrator input 21.
The limit resistor may, for example, have a resistance value in the
range 100 .OMEGA. to 500 .OMEGA.. The limit resistor 24 R.sub.L
limits the maximum current flow through the resistive force
sensitive element 30 to the current integrator input 21 if the
resistance of the resistive force sensitive element 30 drops to a
low value. This configuration can prevent the current irons
exceeding a maximum value that can be accepted and measured by the
current integrator 22. The resistance of some QTC materials can
drop to a relatively low value when subjected to a large applied
force.
[0032] A bias resistor 25 having a value R.sub.B is connected
between the fixed voltage supply rail 23 and the limit resistor 24
in parallel with rise resistive force sensitive element 30. In some
instances, the resistance of some QTC materials can rise to a high
value when not subjected to an applied force. The bias resistor 25
provides a DC current path if the resistance of the resistive force
sensitive element 30 rises to a very high value. The bias resistor
25 may, for example, have a resistance value of 1 M.OMEGA. or
more.
[0033] In this configuration, the value of the current flow I.sub.n
into the integrator input 21 will be approximately:
I.sub.n=(V.sub.dd-V.sub.n)/((R.sub.Q*R.sub.B)/(R.sub.Q+R.sub.B))+R.sub.L)-
.
[0034] In this example, each of the values in this equation other
than I.sub.n and R.sub.Q are fixed. However, the current I.sub.n is
a function of change in the force sensitive resistance R.sub.Q.
Accordingly, the resistance value R.sub.Q of the resistive force
sensitive element can be determined from the value of the
accumulated charge obtained by integration of I.sub.n over a fixed
time as measured at the current integrator input 22. The value of
the applied force can in turn be determined from the resistance
value R.sub.Q of the resistive force sensitive element. The force
can be calculated based on the characteristic of the QTC material
using the calculated resistance. In some applications the force
applied may not need to be accurately calculated; instead a simple
threshold on the output of the integrator performing the force
measurement may be sufficient to provide information to the host
system.
[0035] The determined force cats be used to cause certain events to
occur in response thereto. For example, if the portable device is a
mobile phone and the force applied to an area of the touch
sensitive-position panel 1 exceeds a threshold value, then the
mobile phone may perform a first action. For example, the menu of
the mobile phone can return to a home screen. However, if the force
does not exceed the threshold, then the menu may not change or a
different action can occur. In addition, more than one threshold
can be used to trigger various events. Some events can be triggered
when a threshold is met and exceeded. Other events can be triggered
when the force is below or equal to the threshold. Some events can
be triggered when the threshold is exceeded. Other events can occur
when the force is below the threshold. Still further actions can be
performed based directly on the applied force Examples include, but
are not limited to, a zoom-in action may be applied where the level
of zoom being proportional to the applied force.
[0036] With reference to FIG. 4, another circuit 33 that includes a
QTC resistive force sensitive element 30 is shown and described.
The resistive force sensitive element 30 is in communication with a
control unit 20. The control unit 20 is connected to a ground rail
19 and a fixed voltage supply rail 23 that has a voltage
V.sub.dd.
[0037] In this example, the resistive force sensitive element 30
has a resistance R.sub.Q and is connected between a voltage driver
output 26 of the control unit 20 and at an input 21 of a current
integrator 22 of the control unit 20. The voltage driver output 26
supplies an alternating voltage varying between a high voltage and
a low voltage while the current integrator input 21 acts its a
virtual earth at a voltage midway between the high and low
voltages. In particular, the voltage driver output 26 supplies an
alternating voltage varying between a high voltage substantially
equal to the supply rail voltage V.sub.dd and a low voltage of
substantially zero volts at ground, while the current integrator
input 21 acts as a virtual earth at a voltage V.sub.n which is
approximately half of V.sub.dd. Although the alternating voltage is
a positive voltage relative to the ground voltage, the alternating
voltage is an alternating bi-polar voltage relative to the virtual
earth at the current integrator input. The voltage driver can also
drive one or more drive electrodes 4(X).
[0038] In this example, the current integrator input 21 voltage is
nominally midway between the high and low voltages of the
alternating voltage. However, other values of the current
integrator input voltage between the high and low voltages could be
used. The value of the current: integrator input voltage will
depend on how the alternating voltage varies with time.
[0039] In some examples, the voltage driver output 26 of the
control unit 20 used to supply the alternating voltage to the
resistive force sensitive element 30 may also be used to drive a
drive electrode 4(X) of the touch position sensing panel 1. In such
a configuration, the force sensor 30 may be shielded by being
placed behind a conductive ground plane, Other types of Shielding
can also be used. Shielding can prevent capacitive coupling that
can cause the force sensing element to become touch sensitive as
well as force sensitive. In various applications this may be
undesirable as the force sensor should respond to the force applied
not to the proximity of the object applying the force.
[0040] Supplying the force sensing element 30 with an alternating
voltage having values that are above and below the voltage of the
current integrator input 21 can allow the circuits within the
control unit 20 used to measure the integrated current value to
carry out differential measurement of the current flow through the
resistive force sensitive element 30. Such differential measurement
may facilitate noise cancellation for some types of noise.
[0041] A limit resistor 25 having a resistance R.sub.L is connected
between the voltage driver output 26 and the current integrator
input 21. The limit resistor 24 is connected in series with the
resistive force sensitive element 30.
[0042] A bias resistor 25 having a resistance R.sub.B is connected
between the voltage driver output 26 and the limit resistor 24. The
bias resistor 25 is connected in parallel with the resistive force
sensitive element 30.
[0043] The resistance value R.sub.Q of the resistive force
sensitive element can be determined from current values measured by
differential current measurement at the input 21 of the current
integrator 20. The value of the applied force can in turn be
determined from the resistance value R.sub.Q of the resistive force
sensitive element. The force can be determined based on the
characteristics of the QTC material using the calculated
resistance.
[0044] With reference to FIG. 5, another example of a circuit 34,
is shown and described. The circuit 34 includes three QTC resistive
force sensitive elements 30a, 30b, and 30c in communication with
the control unit 20. Also, the control unit 20 is connected to a
ground rail 22 and a fixed voltage supply rail 23 that has it
voltage V.sub.dd.
[0045] In this example, each of the resistive force sensitive
elements 30a, 30b, 30c is connected to a respective voltage driver
output 26a, 26b, 26c of the control unit 20. All of the resistive
force sensitive elements 30a, 30b, 30c, also are connected to an
input 21 of a current integrator 22 of the control unit 20. Each
voltage driver output 26a, 26b, 26c periodically supplies an
alternating voltage varying between a high voltage and a low
voltage. The current integrator input 21 acts as a virtual earth at
a voltage midway between the high and low voltages. In particular,
each voltage driver output 26a, 26b, 26c supplies an alternating
voltage varying between a high voltage equal to the supply rail
voltage V.sub.dd and a low voltage of zero volts at ground. In
addition, the current integrator input 21 acts as a virtual earth
at a voltage V.sub.n which is half of V.sub.dd. In some examples,
each voltage driver output 26a, 26b, 26c of the control unit 20
used to supply the alternating voltage to a resistive force
sensitive element 30a, 30b, 30c may also be used to drive a drive
electrode of the much position sensing panel.
[0046] The timing of the periodic operation of the three voltage
driver outputs 26a, 26b, 26c may be synchronized so that one of the
three voltage driver outputs 26a, 26b, 26c is emitting an
alternating voltage at any time. Accordingly, a single current
integrator input 21 can measure the current flow through each of
the resistive force sensitive elements 30a, 30b, 30c in turn.
[0047] A respective limit resistor 24a, 24b, 24c, is connected
between each voltage driver output 26a, 26b, 26c and the current
integrator input 21 in series with a respective resistive force
sensitive element 30a, 30b, 30c.
[0048] A respective bias resistor 25a, 25, 25c is connected between
each voltage driver output 26a, 26b, 26c and a respective limit
resistor 24a, 24b, 24c in parallel with a respective resistive
force sensitive element 30a, 30b, 30c.
[0049] The resistance value of each resistive force sensitive
element 30a, 30b, 30c can be determined from the respective current
values determined by differential current measurement at the
current integrator input 21 during the respective driver intervals.
For each force sensing element 30a, 30b, 30c, the value of the
applied force can in turn be determined from the determined
resistance value of the respective resistive force sensitive
element. The force can be determined based on the characteristics
of the QTC material using the calculated resistance.
[0050] In this example, the resistance values of three resistive
force sensitive elements 30a, 30b, 30c, are measured using a single
current integrator input 21. Other numbers of current integrators
22 can also be used.
[0051] As shown, the resistance values of multiple resistive force
sensitive elements 30a, 30b, 30c are measured using multiple
voltage driver outputs 26a, 26b, 26c and a single current
integrator input 21. In other examples, a single voltage driver
output 26 and multiple current integrator inputs 21 could be used.
In yet other examples, multiple voltage driver outputs 26 and
multiple current integrator inputs 21 could be used. For example, N
voltage driver outputs 26 and M current integrator inputs 21 could
be arranged to measure N.times.M resistive force sensitive elements
30.
[0052] In the previous examples, limit resistors 26 are shewn.
However, limit resistors 26 may not be included if the
characteristics of the resistive force sensitive element 30 are
such that the resistance of the resistive force sensitive element
is sufficiently high that the maximum current flow through the
resistive force sensitive element is acceptable to the current
integrator 22. Further, limit resistors 26 may not be used in the
illustrated circuits if the current integrators 22 include an
integral limit resistor.
[0053] In the illustrated examples, bias resistors 25 are used.
However, bias resistors 25 may not be included if the
characteristics of the resistive force sensitive element 30 are
such that the resistance of the resistive force sensitive element
30 is sufficiently low that a DC current path through the resistive
force sensitive element exists.
[0054] In the illustrated examples, force sensitive resistance
elements 30 provide a force sensor. However, other types of
resistive elements can also be used to provide additional sensing
functionality. For example, light dependent resistance elements,
infra red dependent resistance elements, or temperature dependent
resistance elements can also be used. Bach of these types of
elements provides one or more additional sensing features In
addition the position sensing provided by the drive electrodes 4(X)
and sense electrodes 5(Y).
[0055] In the illustrated example, the drive electrodes 4(X) and
the sense electrodes 5(Y) may be formed as two separate layers,
However, other arrangements arc possible. The mutual capacitance
touch position sensor can alternatively be formed as a single layer
device having co-planar drive electrodes and sense electrodes both
formed on the same surface of a single substrate.
[0056] In the illustrated examples, the drive electrodes 4(X) and
sense electrodes 5(X) may be rectangular strips. However, other
arrangements are possible. The shape of the drive and sense
electrodes and the interconnection between the channels of any
given electrode may be modified according to the type of touch wife
which the position sensing panel is intended to be used. For
example, the stripes may have saw-tooth or diamond shaped edges
with attendant, inter-stripe gaps to facilitate field interpolation
to aid in smoothing positional response.
[0057] The number of drive electrodes and sense electrodes shown is
by way of illustration only, and the number shown is trot
limiting.
[0058] While the above discussion used mutual capacitance drive
approaches tor the discussions of examples of the sensors that may
incorporate force sensors, self-capacitance drive adapted to
include force sensing by application of the technologies discussed
in the examples above.
[0059] Various modifications may be made to tire examples described
in the foregoing, and any related teachings may be applied in
numerous applications, only some of which have been described
herein. It is intended by the following claims to claim any and all
applications, modifications and variations that fall within the
true scope of the present teachings.
* * * * *