U.S. patent application number 14/883821 was filed with the patent office on 2016-05-19 for display apparatus, method for driving display apparatus, and pointing device.
The applicant listed for this patent is Japan Display Inc.. Invention is credited to Kohei AZUMI, Fumitaka GOTOH, Makoto HAYASHI, Shinya IUCHI, Yoshitoshi KIDA.
Application Number | 20160139730 14/883821 |
Document ID | / |
Family ID | 55961667 |
Filed Date | 2016-05-19 |
United States Patent
Application |
20160139730 |
Kind Code |
A1 |
KIDA; Yoshitoshi ; et
al. |
May 19, 2016 |
DISPLAY APPARATUS, METHOD FOR DRIVING DISPLAY APPARATUS, AND
POINTING DEVICE
Abstract
In a display apparatus, a touch panel where driving and sensing
electrodes face each other across a dielectric substance outputs a
detection signal from the sensing electrode in synchronization with
a driving signal applied to the driving electrode. A pointing
device points to a position on a touch surface of the touch panel.
A detection assisting device includes an inverting circuit for
obtaining a detection driving signal corresponding to the driving
signal and inverting the phase thereof to generate an inversion
signal, and outputs the inversion signal to the sensing electrode
via the pointing device. A control device applies the driving
signal to the driving electrode, obtains the detection signal
generated at the sensing electrode according to the mutual
capacitance between the driving and sensing electrodes and the
inversion signal, and detects the pointing device in contact with
or proximity to the touch panel based on the detection signal.
Inventors: |
KIDA; Yoshitoshi; (Tokyo,
JP) ; HAYASHI; Makoto; (Tokyo, JP) ; AZUMI;
Kohei; (Tokyo, JP) ; IUCHI; Shinya; (Tokyo,
JP) ; GOTOH; Fumitaka; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Japan Display Inc. |
Tokyo |
|
JP |
|
|
Family ID: |
55961667 |
Appl. No.: |
14/883821 |
Filed: |
October 15, 2015 |
Current U.S.
Class: |
345/174 |
Current CPC
Class: |
G06F 3/03545 20130101;
G06F 3/0383 20130101; G06F 3/044 20130101; G06F 3/0416 20130101;
G06F 3/0445 20190501 |
International
Class: |
G06F 3/041 20060101
G06F003/041; G06F 3/044 20060101 G06F003/044; G06F 3/0354 20060101
G06F003/0354 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 19, 2014 |
JP |
2014-234104 |
Claims
1. A display apparatus comprising: a touch panel including a
driving electrode and a sensing electrode that faces at least a
part of the driving electrode across a dielectric substance, the
touch panel being configured to output a detection signal from the
sensing electrode in synchronization with a driving signal applied
to the driving electrode; a pointing device configured to point to
a position on a touch surface of the touch panel; a detection
assisting device including an inverting circuit configured to
obtain a detection driving signal corresponding to the driving
signal detected by the pointing device and generate an inversion
signal by inverting a phase of the detection driving signal, the
detection assisting device being configured to output the inversion
signal to the sensing electrode via the pointing device; and a
control device configured to apply the driving signal to the
driving electrode, obtain the detection signal that is generated at
the sensing electrode according to a mutual capacitance between the
driving electrode and the sensing electrode and the inversion
signal, and detect the pointing device in contact with or proximity
to the touch panel based on the detection signal.
2. The display apparatus according to claim 1, wherein the
detection assisting device is provided in the pointing device.
3. The display apparatus according to claim 1, wherein the
detection assisting device further includes an amplifier circuit
configured to amplify the inversion signal by a predetermined gain,
and the detection assisting device outputs the amplified inversion
signal to the sensing electrode via the pointing device.
4. The display apparatus according to claim 3, wherein the pointing
device detects whether or not the pointing device is in contact
with the touch surface, and notifies the detection assisting device
of a detection result, and the detection assisting device switches
an amplification level for amplifying the inversion signal based on
the detection result, by setting a gain of the amplifier circuit to
a first gain when the pointing device is in contact with the touch
surface and by setting the gain of the amplifier circuit to a
second gain when the pointing device is not in contact with the
touch surface.
5. The display apparatus according to claim 1, wherein the
detection assisting device further includes: a frequency selection
circuit configured to compare a signal component included in the
detection driving signal with a frequency of the driving signal,
select a first signal having a same frequency as the driving
signal, and output the first signal to the inverting circuit; and
an adder circuit configured to add a second signal having a
frequency different from a frequency of the driving signal to a
first inversion signal, which is obtained by inverting a phase of
the first signal by the inverting circuit, in order to correct the
first inversion signal to generate a correction inversion signal,
and the detection assisting device outputs the correction inversion
signal to the sensing electrode via the pointing device.
6. The display apparatus according to claim 5, wherein the control
device includes a noise detection unit configured to collate the
detection signal with predefined noise information, change a
frequency of the driving signal when determining that noise is
included in the detection signal, and notify the detection
assisting device of the changed frequency, the detection assisting
device obtains the changed frequency, and the frequency selection
circuit uses the changed frequency for selection of a signal
component included in the detection driving signal.
7. The display apparatus according to claim 1, wherein the
detection assisting device further includes a phase adjustment
circuit configured to compare a phase of an auxiliary signal to be
output to the sensing electrode via the pointing device with a
phase of the detection driving signal, determine whether or not an
amount of phase delay of the auxiliary signal relative to the
detection driving signal is within a predetermined allowable range,
and align the phase of the auxiliary signal with the phase of the
detection driving signal when the amount of phase delay exceeds the
allowable range.
8. A method for driving a display apparatus, the display apparatus
including a touch panel and a pointing device, the touch panel
including a driving electrode and a sensing electrode that faces at
least a part of the driving electrode across a dielectric
substance, the touch panel being configured to output a detection
signal from the sensing electrode in synchronization with a driving
signal applied to the driving electrode, the pointing device being
configured to point to a position on a touch surface of the touch
panel, the method comprising: applying, by a control device, the
driving signal to the driving electrode; obtaining, by a detection
assisting device, a detection driving signal corresponding to the
driving signal detected by the pointing device; generating, by the
detection assisting device, an inversion signal by inverting a
phase of the detection driving signal; outputting, by the detection
assisting device, the inversion signal to the sensing electrode via
the pointing device; obtaining, by the control device, the
detection signal generated at the sensing electrode according to a
mutual capacitance between the driving electrode and the sensing
electrode and the inversion signal; and detecting, by the control
device, the pointing device in contact with or proximity to the
touch panel based on the detection signal.
9. A pointing device for pointing to a position on a touch surface
of a touch panel including a driving electrode and a sensing
electrode that faces at least a part of the driving electrode
across a dielectric substance, the touch panel being configured to
output a detection signal from the sensing electrode in
synchronization with a driving signal applied to the driving
electrode, the pointing device comprising: an inverting circuit
configured to detect a detection driving signal corresponding to
the driving signal and generate an inversion signal by inverting a
phase of the detection driving signal; and an output unit
configured to output the inversion signal to the sensing electrode,
wherein the pointing device causes, when the driving signal is
applied to the driving electrode, the sensing electrode to generate
the detection signal according to a mutual capacitance between the
driving electrode and the sensing electrode and the inversion
signal.
Description
CROSS REFERENCES TO RELATED APPLICATIONS
[0001] The present application claims priority to Japanese Priority
Patent Application JP 2014-234104 filed in the Japan Patent Office
on Nov. 19, 2014, the entire content of which is hereby
incorporated by reference.
BACKGROUND
[0002] The embodiments discussed herein relate to a display
apparatus, a method for driving a display apparatus, and a pointing
device.
[0003] A display apparatus with a touch panel, which a user touches
with a finger, a stylus, or the like, to input information, is used
in various fields. As one of such touch panel systems, an
electrostatic-capacitance type touch panel capable of reducing the
power consumption is known. When the area of a screen of a touch
panel is small, the capability of inputting using a stylus with a
narrow tip is preferred. However, in the electrostatic-capacitance
type touch panel, a stylus with a narrow contact area has a poor
contact-detection sensitivity because the electrostatic capacitance
generated at a contact portion needs to be equal to or greater than
a predetermined level. Then, in order to improve operability, there
is proposed a display apparatus with a stylus that outputs an
active signal toward a detection unit. (See, for example, Japanese
Laid-open Patent Publication No. 2013-58198).
SUMMARY
[0004] The embodiments discussed herein provide a display apparatus
capable of reliably detecting the presence or absence of touch, a
method for driving the display apparatus, and a pointing
device.
[0005] According to an aspect of the embodiments, there is provided
a display apparatus including: a touch panel including a driving
electrode and a sensing electrode that faces at least a part of the
driving electrode across a dielectric substance, the touch panel
being configured to output a detection signal from the sensing
electrode in synchronization with a driving signal applied to the
driving electrode; a pointing device configured to point to a
position on a touch surface of the touch panel; a detection
assisting device including an inverting circuit configured to
obtain a detection driving signal corresponding to the driving
signal detected by the pointing device and generate an inversion
signal by inverting a phase of the detection driving signal, the
detection assisting device being configured to output the inversion
signal to the sensing electrode via the pointing device; and a
control device configured to apply the driving signal to the
driving electrode, obtain the detection signal that is generated at
the sensing electrode according to a mutual capacitance between the
driving electrode and the sensing electrode and the inversion
signal, and detect the pointing device in contact with or proximity
to the touch panel based on the detection signal.
[0006] The object and advantages of the invention will be realized
and attained by means of the elements and combinations particularly
pointed out in the claims.
[0007] It is to be understood that both the foregoing general
description and the following detailed description are exemplary
and explanatory and are not restrictive of the invention.
[0008] Additional features and advantages are described herein, and
will be apparent from the following Detailed Description and the
figures.
BRIEF DESCRIPTION OF THE FIGURES
[0009] FIG. 1 illustrates an example of the configuration of a
display apparatus of a first embodiment;
[0010] FIG. 2 illustrates an example of the configuration of a
display apparatus of a second embodiment;
[0011] FIG. 3 illustrates an example of the configuration of a
control device of the second embodiment;
[0012] FIG. 4 illustrates an example of the configuration of a TPIC
of the second embodiment;
[0013] FIG. 5 illustrates an example of the output signal of an
integration circuit in response to a driving signal;
[0014] FIG. 6 illustrates an example of the configuration of a
stylus of the second embodiment;
[0015] FIGS. 7A and 7B illustrate an example of a noise
pattern;
[0016] FIG. 8 is a flow chart illustrating a touch detection
procedure of the display apparatus of the second embodiment;
[0017] FIG. 9 illustrates an example of the configuration of a
second detection assisting circuit of a display apparatus of a
third embodiment;
[0018] FIG. 10 illustrates an example of the configuration of a
third detection assisting circuit;
[0019] FIG. 11 illustrates an example of the configuration of a
fourth detection assisting circuit of a display apparatus of a
fourth embodiment; and
[0020] FIG. 12 illustrates a relationship between an input signal
and an output signal of a phase adjustment circuit.
DETAILED DESCRIPTION
[0021] Several embodiments will be described below with reference
to the accompanying drawings, wherein like reference numerals refer
to like elements throughout.
[0022] Note that the disclosed embodiments are just one example,
and thus the appropriate modifications that may be readily
conceived to those skilled in the art without departing from the
spirit of the embodiments shall be included in the scope of the
embodiments. Moreover, for clarity of description, in the drawings
the width, thickness, shape, and the like of each unit may be
schematically illustrated as compared with the actual embodiments,
but the width, thickness, shape, and the like of each unit are just
one example and shall not limit the interpretation of the
embodiments.
[0023] Moreover, in the embodiments and the drawings, components
similar to those described in regard to a drawing thereinabove may
be marked with like reference numerals to omit the detailed
description as appropriate.
First Embodiment
[0024] A display apparatus of a first embodiment is described using
FIG. 1. FIG. 1 illustrates an example of the configuration of the
display apparatus of the first embodiment.
[0025] A display apparatus 1 illustrated in FIG. 1 includes a touch
panel 2, an image display panel 3, a control device 4, a pointing
device 5, and a detection assisting device 6.
[0026] The touch panel 2 includes a driving electrode 2a and a
sensing electrode 2b that faces at least a part of the driving
electrode 2a across a dielectric substance, in which the sensing
electrode 2b is arranged on a touch surface side of the touch panel
2. In the touch panel 2, a plurality of driving electrodes 2a and a
plurality of sensing electrodes 2b are arranged such as to cover
the touch surface area. Hereinafter, a configuration of the driving
electrode 2a and sensing electrode 2b will be described, in which a
part of the driving electrode 2a and a part of the sensing
electrode 2b cross each other to form a facing portion, but the
same applies to the other driving electrodes and sensing
electrodes.
[0027] The facing portion at which the driving electrode 2a and the
sensing electrode 2b face each other has a first capacitance formed
by the driving electrode 2a, the dielectric substance, and the
sensing electrode 2b. When a driving signal Tx of a square waveform
is applied to the driving electrode 2a, a detection signal Rx may
be detected by the sensing electrode 2b in synchronization with the
driving signal Tx. That is, when the driving signal Tx is applied
to the driving electrode 2a, an electric charge corresponding to
the mutual capacitance between the driving electrode and the
sensing electrode is accumulated in the sensing electrode 2b. If
the charge amount in the sensing electrode 2b is extracted as the
detection signal Rx, the mutual capacitance between the driving
electrode and the sensing electrode may be measured. Because the
mutual capacitance differs between when the pointing device 5 is in
contact with or proximate to the touch panel 2 and when the
pointing device 5 is apart from the touch panel 2, the presence or
absence of the touch of the pointing device 5 may be also detected
by measuring the mutual capacitance. In FIG. 1, the driving
electrode 2a and sensing electrode 2b have belt-like shapes
extending in mutually orthogonal directions of the touch panel 2,
respectively, and the facing portion is formed at a place where the
driving electrode 2a and the sensing electrode 2b cross each other,
but the embodiments are not limited thereto.
[0028] The image display panel 3 includes a planar display surface,
and displays an image based on a display signal output from the
control device 4.
[0029] The control device 4 is connected to the image display panel
3, the driving electrode 2a, and the sensing electrode 2b, and
performs a display control to display an image on the image display
panel 3 and a detection control to detect the touch of the pointing
device 5. In the detection control, the driving signal Tx of a
square waveform is applied to the driving electrode 2a and the
detection signal Rx is obtained from the sensing electrode 2b. From
the sensing electrode 2b, the detection signal Rx having a rising
edge and a falling edge each being in synchronization with the
timing of potential change of the driving signal Tx is output.
[0030] The pointing device 5 points to a position on the touch
surface of the touch panel 2. The pointing device 5 in contact with
or proximate to the touch panel 2 is electrically connected or
coupled to the touch panel 2 to form a second capacitance. A
detection driving signal Td obtained by detecting the driving
signal Tx that is input via the sensing electrode 2b of the touch
panel 2 in contact with or proximate to the pointing device 5 is
output to the detection assisting device 6. Moreover, the pointing
device 5 obtains an inversion signal RTd from the detection
assisting device 6, and outputs it to the sensing electrode 2b
using a capacitive coupling between an output circuit of the
pointing device 5 and the sensing electrode 2b, or the like.
[0031] The detection assisting device 6 includes an inverting
circuit 6a, obtains the detection driving signal Td from the
pointing device 5, generates the inversion signal RTd by inverting
the phase of the detection driving signal Td, and outputs it to the
pointing device 5. Note that the detection assisting device 6 may
be provided inside another device. For example, it may be provided
in the pointing device 5 or the control device 4.
[0032] A touch detection operation of such a display apparatus 1 is
described. Hereinafter, a state where the pointing device 5 is in
contact with or proximate to the touch panel 2 is referred to and
described as a "touch state", while a state where the pointing
device 5 is neither in contact with nor proximate to the touch
panel 2 is referred to and described as a "non-touch state".
[0033] When the pointing device 5 is in the non-touch state, the
mutual capacitance between the driving electrode 2a and the sensing
electrode 2b corresponds to the first capacitance. When the driving
signal is applied to the driving electrode 2a by the control device
4, an electric field corresponding to the first capacitance will be
generated between the driving electrode and the sensing electrode.
On the other hand, when the pointing device 5 is in the touch
state, a part of the electric field is generated also between the
pointing device 5 and the sensing electrode 2b due to the second
capacitance between the pointing device 5 and the sensing electrode
2b. As a result, the electric field between the driving electrode
and the sensing electrode decreases and the mutual capacitance also
decreases. Furthermore, the inversion signal RTd having a phase
opposite to the phase of the driving signal Tx is output to the
sensing electrode 2b via the pointing device 5 from the detection
assisting device 6. The inversion signal RTd acts in the direction
assisting the signal change of the detection signal Rx due to the
pointing device 5, via the capacitive coupling between the pointing
device 5 and the sensing electrode 2b.
[0034] As described above, in the detection signal Rx, a signal
component of the inversion signal RTd is superposed on a signal
component (referred to as a detection signal Rx0) corresponding to
the mutual capacitance between the driving electrode and the
sensing electrode. Therefore, the signal strength of the detection
signal Rx is increased as compared with the detection signal Rx0
simply corresponding to the mutual capacitance between the driving
electrode and the sensing electrode. In the control device 4, the
presence or absence of touch may be reliably detected by detecting
the touch state of the pointing device 5 using the detection signal
Rx whose signal strength has been increased in this manner.
Second Embodiment
[0035] Next, a display apparatus of a second embodiment is
described.
[0036] FIG. 2 illustrates an example of the configuration of the
display apparatus of the second embodiment.
[0037] A display apparatus 10 of the second embodiment includes a
touch panel 20, an image display panel 30, a display control
circuit 35, a touch-panel control circuit (hereinafter, referred to
as a TPIC) 40, a stylus 50, and a control device 60. The display
control circuit 35, the TPIC 40, and the control device 60 perform
a part of the procedure of the control device 4 illustrated in FIG.
1, respectively. Moreover, the detection assisting device 6
illustrated in FIG. 1 is mounted as a detection assisting circuit
51 inside the stylus 50.
[0038] The touch panel 20 is a mutual-capacitance detection type
touch panel that includes a plurality of belt-like driving
electrodes 21 extending in the horizontal direction in FIG. 2 and a
plurality of belt-like sensing electrodes 22 extending in the
direction perpendicular to the extending direction of the driving
electrode 21. The sensing electrode 22 is arranged on the touch
surface side of the touch panel 20, while the driving electrode 21
is arranged in a lower layer of the sensing electrode 22 across a
dielectric substance. The driving electrode 21 and the sensing
electrode 22 cross each other in a plan view, and at the
intersection, a facing portion where the driving electrode 21 and
the sensing electrode 22 face each other is formed. The facing
portion serves as a touch sensor, and in the touch panel 20, facing
portions are arranged in a matrix so as to be able to detect a
touch position of the stylus 50. The TPIC 40 outputs to the control
device 60 the touch information including the detected presence or
absence of the touch of the stylus 50 and the position of the
stylus 50 when touch has been detected.
[0039] The image display panel 30 is configured as the so-called
in-cell type, i.e., integrated with the touch panel 20. In the
in-cell type configuration, the driving electrode 21 of the touch
panel 20 and the common electrode of a liquid crystal display
element are shared. Note that the touch panel 20 and the image
display panel 30 may be separately formed and then bonded with an
adhesive or the like.
[0040] The display control circuit 35 performs a display control
among the processing functions of the control device 4. The display
control circuit 35 receives an image signal from the control device
60 to generate a display signal, thereby performing the display
control of the image display panel 30.
[0041] The TPIC 40 performs a detection control to detect the touch
of the stylus 50, among the processing functions of the control
device 4. In accordance with an instruction from the control device
60, the TPIC 40 sequentially selects the driving electrode 21 to
supply a driving signal of an AC square waveform driving signal.
Then, the TPIC 40 detects the presence or absence of the touch of
the stylus 50 and the position of the stylus 50 when the stylus 50
is in the touch state, based on the detection signal of the sensing
electrode 22 at that time.
[0042] The stylus 50 is one embodiment of the pointing device 5,
and in the second embodiment, the stylus 50 includes the detection
assisting circuit 51. The detection assisting circuit 51 generates
an auxiliary signal ARx whose phase is opposite to the phase of the
driving signal Tx, based on the detection driving signal Td
corresponding to the driving signal Tx that is detected when the
tip of the stylus 50 approaches the touch panel 20, and outputs the
auxiliary signal ARx to the sensing electrode 22. The auxiliary
signal ARx refers to a signal for increasing the signal strength of
the detection signal Rx including the inversion signal RTd
illustrated in FIG. 1.
[0043] The control device 60 controls the whole display apparatus
10.
[0044] Each unit of such a display apparatus 10 is described.
[0045] First, the control device 60 configured to control the whole
apparatus is described. FIG. 3 illustrates an example of the
configuration of the control device of the second embodiment.
[0046] The control device 60 is controlled by a CPU (Central
Processing Unit) 61. A RAM (Random Access Memory) 62, a ROM (Read
Only Memory) 63, and a plurality of peripheral devices are
connected or coupled to the CPU 61 via a bus 83.
[0047] The RAM 62 is used as the main storage device of the control
device 60. At least part of the program of an OS (Operating System)
and the application program executed by the CPU 61 are temporarily
stored in the RAM 62. Moreover, various types of data needed for
processing by the CPU 61 are stored in the RAM 62.
[0048] The ROM 63 is a nonvolatile semiconductor memory and used as
a secondary storage device of the control device 60, and stores the
information that need not to be updated. For example, the program
of an OS, application programs, and various types of data are
stored in the ROM 63. Note that a semiconductor memory, such as a
flash memory, may be used as the secondary storage device.
[0049] The peripheral devices connected or coupled to the bus 83
include the display control circuit 35, the TPIC 40, and a
communication interface 81.
[0050] The image display panel 30 is connected or coupled to the
display control circuit 35.
[0051] The touch panel 20 is connected or coupled to the TPIC 40.
The TPIC 40 detects a touch state of the stylus 50 based on an
instruction of the CPU 61. Moreover, the TPIC 40 calculates the
coordinate of a touch position, and outputs the touch information
including the coordinate of a touch position to the CPU 61 via the
bus 83.
[0052] The communication interface 81 is connected or coupled to a
network 90, and transmits and receives data to and from another
computer or telecommunication device via the network 90. Moreover,
if the stylus 50 is connected or coupled to the network 90, the
communication interface 81 may transmit and receive data to and
from the stylus 50 via the network 90.
[0053] With such a configuration, the processing function of the
control device 60 may be realized.
[0054] Next, the configuration of the TPIC 40 is described. FIG. 4
illustrates an example of the configuration of the TPIC of the
second embodiment. FIG. 4 illustrates the TPIC 40 and the outline
of the cross section of a facing portion of the touch panel 20.
[0055] The TPIC 40 includes a drive control circuit 41, an A/D
(analog/digital) conversion circuit 42, and a signal processing
circuit 43, and performs a detection control to detect the touch of
the stylus 50. Upon detection of a touch, the TPIC 40 detects the
coordinate of a touch position and notifies the control device 60
of the coordinate. The drive control circuit 41 applies the driving
signal Tx of an AC square waveform of a predetermined frequency to
the driving electrode 21. The A/D conversion circuit 42 operates in
synchronization with the drive control circuit 41, and receives the
detection signal Rx in accordance with the mutual capacitance
between the driving electrode and the sensing electrode and with
the auxiliary signal ARx, and converts the detection signal Rx to
the detection data Vdet. The A/D conversion circuit 42 is provided
for each sensing electrode 22, and converts the detection signal Rx
of the corresponding sensing electrode 22 to digital data. The
signal processing circuit 43 receives the detection data Vdet
converted by each A/D conversion circuit 42, and performs a
procedure of detecting the touch of the stylus 50 and identifying
the coordinate of a touch position of the stylus 50, based on the
detection data Vdet across the whole touch surface.
[0056] Each processing unit is described following a signal
flow.
[0057] In a period during which the driving electrode 21 to be
shared as the common electrode of the image display panel 30 is not
operating as the common electrode, within one frame period, the
drive control circuit 41 sequentially applies the driving signal Tx
to a plurality of driving electrodes 21. For example, the drive
control circuit 41 selects the driving electrodes 21 illustrated in
FIG. 2 in the order of #1, #2, #3, #4, and #5, . . . , and
sequentially applies the driving signal Tx. The driving signal Tx
is applied to each driving electrode 21 multiple times within one
frame period. The driving signal Tx may be continuously applied to
the selected driving electrode 21 multiple times.
[0058] In the touch panel 20, due to the driving signal Tx applied
to the driving electrode 21, an electric current in accordance with
the mutual capacitance between the driving electrode 21 and the
sensing electrode 22 flows to the sensing electrode 22. As
illustrated in FIG. 4, in the facing portion of the driving
electrode 21 and sensing electrode 22, an electrostatic capacitance
C1 (hereinafter, referred to as a capacitance C1) is formed by the
driving electrode 21, the sensing electrode 22, and the dielectric
substance therebetween. In the non-touch state of the stylus 50,
when the driving signal Tx of an AC square waveform is applied to
the driving electrode 21, an electric current in accordance with
the capacitance C1 flows to the sensing electrode 22, and is output
to the A/D conversion circuit 42 as the detection signal Rx. On the
other hand, in the touch state of the stylus 50, a capacitance C2
formed between the stylus 50 and the sensing electrode 22 is added
in series to the capacitance C1. Then, when the driving signal Tx
of an AC square waveform is applied to the driving electrode 21, an
electric field will be generated not only between the driving
electrode and the sensing electrode but also between the driving
electrode and the stylus. The electric field between the driving
electrode and the sensing electrode decreases as compared with that
in the non-touch state. Accordingly, the detection signal Rx0 has a
value smaller than the value in the non-touch state. Furthermore,
from the stylus 50, the auxiliary signal ARx generated by the
detection assisting circuit 51 is output to the sensing electrode
22. As a result, the detection signal Rx, whose signal change has
been strengthened by superimposing the signal component of the
auxiliary signal ARx on the detection signal Rx0, is obtained. As
described above, the auxiliary signal ARx output from the stylus 50
strengthens the signal change of the detection signal Rx due to the
capacitance, which the stylus 50 forms between the stylus 50 and
the driving electrodes 21, thereby making more noticeable a
difference between the detection signal Rx in the touch state and
the detection signal Rx in the non-touch state. The detection
signal Rx is generated in a plurality of sensing electrodes 22,
respectively, and is output to the A/D conversion circuit 42.
[0059] The A/D conversion circuit 42 includes an integration
circuit 421, an ADC (Analog to Digital Converter) 422, and an FIR
(Finite Impulse Response) 423, and extracts the detection signal Rx
in synchronization with the drive control circuit 41, and
generates, from the detection signal Rx, the detection data Vdet to
be used in the signal processing circuit 43. Note that only one A/D
conversion circuit 42 is illustrated in FIG. 4, but the A/D
conversion circuit 42 is provided corresponding to each of a
plurality of sensing electrodes 22. Alternatively, a plurality of
sensing electrodes 22 and the A/D conversion circuit 42 may be
connected, for example, via a multiplexer, so that the sensing
electrode 22, from which the detection signal is received, may be
sequentially switched in accordance with the driving electrode 21
selected by the drive control circuit 41.
[0060] The integration circuit 421 outputs a voltage value obtained
by integrating the detection signal Rx. In the non-touch state of
the stylus 50, when the driving signal is applied to the driving
electrode 21, an electric current flows in a path from the driving
electrode 21 to the capacitance of the integration circuit 421
through the capacitance C1 and the sensing electrode 22, so that
the output voltage of the integration circuit 421 decreases. In
contrast, in the touch state of the stylus 50, the capacitance
between the driving electrode and the sensing electrode decreases
and also the output signal of the stylus 50 is added, so that the
electric current flowing into the integration circuit 421 decreases
to cause a difference in the output voltage drop of the integration
circuit 421.
[0061] FIG. 5 illustrates an example of the output signal of the
integration circuit in response to the driving signal.
[0062] (A) illustrates the waveform in one clock interval of the AC
square waveform of the driving signal Tx. (B) illustrates the
waveform of the output voltage of the integration circuit when the
stylus 50 is in the non-touch state. (C) illustrates the waveform
of the output voltage of the integration circuit when the stylus 50
is in the touch state. Both (B) and (C) correspond to one clock
interval of (A).
[0063] As illustrated in FIG. 5, in the rising edge of the driving
signal Tx, an electric current flows in the path from the driving
electrode 21 to the capacitance of the integration circuit 421
through the mutual capacitance and sensing electrode 22, so that
the output voltage of the integration circuit 421 drops. In the
falling edge of the driving signal Tx, the output voltage of the
integration circuit 421 rises.
[0064] Here, the maximum value in the negative direction of the
output voltage of the integration circuit when the stylus 50 is in
the non-touch state illustrated in (B) is defined as a baseline Vb.
Similarly, the maximum value in the negative direction of the
output voltage of the integration circuit when the stylus 50 is in
the touch state illustrated in (C) is defined as a baseline Vx. As
described above, the magnitude of the mutual capacitance is larger
in the non-touch state than in the touch state, and furthermore in
the touch state, the auxiliary signal ARx whose phase is opposite
to the phase of the driving signal is output from the stylus 50 to
the sensing electrode 22. Accordingly, the difference between the
baseline Vb in the non-touch state and the baseline Vx in the touch
state is large enough to be used in determining whether the state
is the touch state or the non-touch state. In the second
embodiment, whether the state is the touch state or the non-touch
state is determined, based on a difference (a signal component Vs
in FIG. 5) in the output voltage of the integration circuit between
the touch state and the non-touch state. Note that, as illustrated
in FIG. 5, also when the driving signal falls, the signal component
may be similarly detected.
[0065] Returning to FIG. 4, the description continues.
[0066] The ADC 422 includes a sample/hold circuit, and
samples/holds the peak value of a signal that has been integrated
by the integration circuit 421, and A/D-converts the sampled/held
peak value to a digital signal. With the ADC 422, Vb in the
non-touch state and Vx in the touch state illustrated in FIG. 5 are
calculated.
[0067] The FIR 423 performs an averaging process to reduce unwanted
noise included in the signal generated by the ADC 422.
[0068] In this manner, in the A/D conversion circuit 42, the
detection data Vdet is generated based on the detection signal Rx
that is output from the sensing electrode 22 when the driving
signal Tx is applied to the driving electrode 21. The detection
data Vdet indicates the mutual capacitance between the driving
electrode and the sensing electrode at that time point. The
magnitude of the mutual capacitance is larger in the non-touch
state than in the touch state. Accordingly, the magnitude of the
detection data Vdet differs between the non-touch state and the
touch state. The measured detection data Vdet is output to the
signal processing circuit 43.
[0069] The drive control circuit 41 applies the driving signal Tx
selectively to the driving electrode 21. In the A/D conversion
circuit 42, the detection data Vdet is generated in all the sensing
electrodes 22 in synchronization with the application of the
driving signal Tx. The above-described procedure is performed on
all the driving electrodes 21 to generate the detection data Vdet
of all the facing portions formed in the touch panel 20.
[0070] The signal processing circuit 43 includes a baseline storage
unit 431, a signal value calculation unit 432, a noise detection
unit 433, and a coordinate calculation unit 434. The detection data
Vdet of all the facing portions where the driving electrode 21 and
the sensing electrode 22 face each other are input to the signal
processing circuit 43.
[0071] The baseline storage unit 431 stores, as the baseline Vb,
the detection data Vdet of the A/D conversion circuit 42 when the
stylus 50 is in the non-touch state. The baseline Vb is
appropriately updated by the signal calculation unit 432.
[0072] Based on the detection data Vdet obtained from the A/D
conversion circuit 42 and on the baseline Vb stored in the baseline
storage unit 431, the signal value calculation unit 432 calculates
the signal component Vs due to the presence of the stylus 50
included in the detection data Vdet and determines whether the
stylus 50 is in the touch state or in the non-touch state.
Specifically, the signal value calculation unit 432 calculates a
difference (Vdet-Vb) between the detection data Vdet obtained from
the A/D conversion circuit 42 and the baseline Vb, and compares the
calculated signal value Vs with a threshold. If the signal value Vs
is equal to or less than the threshold, the signal value
calculation unit 432 determines that the stylus 50 is in the
non-touch state. If the signal value Vs exceeds the threshold, the
signal value calculation unit 432 determines that the stylus 50 is
in the touch state. Moreover, when the signal value calculation
unit 432 determines that the stylus 50 is in the non-touch state,
the baseline Vb may be updated with the value of the detection data
Vdet at this time. Appropriate updating of the baseline Vb also
allows responding to the case where the baseline value has shifted
due to a change or the like of the operating environment, and
allows an accurate touch detection to be performed.
[0073] The noise detection unit 433 analyzes the signal value Vs in
the touch surface area that is calculated by the signal value
calculation unit 432, and determines whether or not noise is
included in the signal value Vs in the touch surface area. For
example, the noise detection unit 433 compares an assumed noise
pattern of an AC charger noise or the like with the signal value Vs
in the touch surface area to determine whether or not the noise
pattern has been detected. When noise is detected, the drive
control circuit 41 may be instructed to change the frequency of the
driving signal Tx.
[0074] When the calculated signal value Vs indicates the touch
state, the coordinate calculation unit 434 detects a position
coordinate indicative of the touch state. Using the signal value Vs
(=Vdet-Vb) of a signal whose noise has been removed by the noise
detection unit 433, a distribution state of the facing portions
indicative of the touch state is analyzed to determine the position
coordinate. The method for determining a position coordinate is
appropriately selected in accordance with the operating state or
the like. For example, the center of gravity of an area where
facing portions indicate the touch state may be calculated and set
as the position coordinate. Alternatively, the position coordinate
may be determined based on a signal whose calculated signal value
Vs is higher. Moreover, as needed, a tracking process to associate
the detected position coordinate with the previously detected
position coordinate may be performed. The presence or absence of
touch and the position coordinate of the touch are output to the
control device 60 as the touch information.
[0075] Note that, in the second embodiment, the signal processing
circuit 43 is provided inside the TPIC 40, but a similar procedure
may be performed by the control device 60. Moreover, a part of the
procedure of the signal processing circuit 43 may be performed by
the control device 60.
[0076] Next, the stylus is described. FIG. 6 illustrates an example
of the configuration of the stylus of the second embodiment.
[0077] The stylus 50 includes a detection assisting circuit 51, a
pen-point detection unit 52, and a pen-point output unit 53.
[0078] The detection assisting circuit 51 includes an inverting
circuit 511 and an amplifier circuit 512. The inverting circuit 511
inverts an electric potential change of the detection driving
signal Td input from the pen-point detection unit 52 to generate an
inversion signal. The amplifier circuit 512 generates an amplified
inversion signal by amplifying the inversion signal input from the
inverting circuit 511 by a predetermined gain, and outputs the
amplified inversion signal to the pen-point output unit 53 as the
auxiliary signal ARx.
[0079] The pen-point detection unit 52 is formed at a tip part of
the stylus 50 that is pointed to the touch panel 20. Then, the
pen-point detection unit 52 detects an electric potential change of
the driving signal Tx applied to the driving electrode 21 and
outputs the detection driving signal Td to the inverting circuit
511.
[0080] The pen-point output unit 53 is formed at a tip part of the
stylus 50, as with the pen-point detection unit 52. Then, the
pen-point output unit 53 outputs the auxiliary signal ARx generated
by the amplifier circuit 512 to the sensing electrode 22.
[0081] In the stylus 50 of such a configuration, when the stylus 50
approaches the touch panel 20, an electric potential change of the
driving signal Tx of the touch panel 20 is detected via the
pen-point detection unit 52. If the distance between the stylus 50
and the sensing electrode 22 is the same, the signal level of the
detected detection driving signal Td is determined in accordance
with the distance between the sensing electrode 22 and the driving
electrode 21 which the driving signal Tx is applied to. For
example, assume that among the driving electrodes 21 of #1 to #5
illustrated in FIG. 2, the stylus 50 is proximate to #3. As the
driving signal Tx is applied sequentially from #1, the potential
level of the detection driving signal Td detected by the stylus 50
becomes the maximum when the driving signal Tx is applied to #3,
and as the position where the driving signal Tx is applied departs
from #3, the potential level decreases. In the stylus 50, the
auxiliary signal ARx obtained by inverting and amplifying the
detected electric potential change by the detection assisting
circuit 51 is output from the pen-point output unit 53.
Accordingly, the auxiliary signal ARx weakly assists the signal to
change when the driving signal Tx is applied to a place away from
the stylus 50, while when the driving signal Tx is applied to a
place proximate to the stylus 50, the auxiliary signal ARx strongly
assists the signal to change. Therefore, the signal strength of the
detection signal Rx may be increased.
[0082] As described above, in the display apparatus 10, the use of
such a stylus 50 for the manipulation input in the mutual
capacitance type touch panel 20 allows the signal strength of the
detection signal Rx to be increased. As a result, a difference in
the signal change between the touch state and the non-touch state
increases, and therefore even the stylus 50 with a small contact
area may reliably detect the presence or absence of touch.
Moreover, because the signal strength is increased in the driving
electrode 21 closer to a touch position, the touch position may be
more reliably detected. In particular, in the case of the in-cell
type touch panel, because the distance between the driving
electrode 21 and the sensing electrode 22 increases, the magnitude
of the driving signal Tx reaching the sensing electrode 22
decreases to make the touch detection difficult. However, because
the display apparatus 10 allows the signal strength to be
increased, even an in-cell type touch panel may reliably detect a
touch.
[0083] Note that the gain of the amplifier circuit 512 is
appropriately set so that the potential level of the auxiliary
signal ARx becomes the optimum. Moreover, the gain setting of the
amplifier circuit 512 may be switched depending on whether or not
the stylus 50 is in contact with a touch surface. For example, a
pressure detection mechanism is provided in the pen-point detection
unit 52 to detect whether or not the pen point of the stylus 50 is
in contact with the touch surface. Between when a current flowing
when the pen-point detection unit 52 is in contact with the touch
surface is detected and when the pen-point detection unit 52 is up
in the air of the touch surface, the gain of the amplifier circuit
512 is switched to change the amplification level, thereby
controlling the pointing input when the pen-point detection unit 52
is up in the air of the touch surface. Once the gain when the
pen-point detection unit 52 is up in the air of the touch surface
is reduced, the pointing input is not allowed if the stylus 50 is
not in contact with the touch surface, thereby preventing a wrong
input. On the other hand, if the gain is increased, the pointing
input when the pen-point detection unit 52 is up in the air of the
touch surface may be reliably performed.
[0084] Because the driving signal Tx applied to the driving
electrode 21 is input to the stylus 50 through the path from the
dielectric substance to the capacitance between the stylus and the
sensing electrode through the sensing electrode 22, noise may mix
into the detection driving signal Td midway along the path. For
example, noise, i.e., the so-called AC charger noise, which is
generated from a low-cost charger when the charger is connected to
the display apparatus 10, might be added.
[0085] FIGS. 7A and 7B illustrate an example of the noise
pattern.
[0086] A black area illustrated in FIGS. 7A and 7B indicates a
place where the touch of the stylus 50 is detected. Both the
example of a pattern without noise of FIG. 7A and the example of a
pattern with noise of FIG. 7B illustrate the case where the stylus
50 touches the same position of the touch panel 20.
[0087] In the case without noise illustrated in the example of the
pattern without noise of FIG. 7A, touch is detected only at one
area P1. The area P1 is the place touched by the stylus 50. In the
case of such a pattern, the coordinate of a touch position may be
easily calculated.
[0088] In contrast, in the case with noise illustrated in the
example of the pattern with noise of FIG. 7B, touch is detected at
a plurality of areas N1, N2, N3, and N4 around an area P2. The area
P2 is the place touched by the stylus 50, and the areas N1, N2, N3,
and N4 are noises. In the state where such a pattern is generated,
the detection accuracy of a touch position will decrease.
[0089] Then, in the display apparatus 10, the signal processing
circuit 43 performs a procedure of analyzing the signal value Vs
obtained from the detection signal Rx, detecting noise, and
reducing the noise.
[0090] The noise detection unit 433 compares the touch information
across the whole touch surface of the touch panel 20 obtained from
the signal value calculation unit 432 with a predicted noise
pattern of an AC charger noise or the like to determine whether or
not noise is generated. In this connection, one or more noise
patterns are predicted, and the noise detection unit 433 compares
the touch information with each of these noise patterns. When the
noise detection unit 433 determines that noise is generated, then
in order to prevent a reduction of the touch position detection
accuracy due to such noise, the display apparatus 10 switches the
frequency of the driving signal Tx and notifies the drive control
circuit 41 of a new driving signal frequency Txf. If the frequency
of a periodically generated noise, such as an AC charger noise, is
close to the frequency of the driving signal Tx, the noise will be
superposed on the detection signal Rx. Then, by switching the
frequency of the driving signal Tx to a frequency different from
the frequency of the AC charger noise, the driving signal may be
distinguished from the noise and the noise superposed on the
detection signal Rx may be reduced.
[0091] A touch detection procedure in the display apparatus 10 of
such a configuration is described using a flow chart. FIG. 8 is a
flow chart illustrating the touch detection procedure of the
display apparatus of the second embodiment. The display apparatus
10 starts to operate and activates the touch detection procedure to
start the processing by the TPIC 40.
[0092] (Step S01) During activation, the TPIC 40 sets the driving
signal frequency Txf to a predetermined initial value to initialize
the frequency of the driving signal Tx.
[0093] (Step S02) The TPIC 40 determines whether or not the current
period is the processing period for performing the touch detection.
The touch detection is performed in a period during which the
driving electrode 21 is not operating as the common electrode for
display. If the current period is the processing period, the
procedure proceeds to step S03. If the current period is not the
processing period, the procedure waits till the next processing
period starts.
[0094] (Step S03) Because the current period is the processing
period, the TPIC 40 performs the touch detection procedure. In the
touch detection procedure, the driving signal Tx is sequentially
applied to the driving electrode 21 by the drive control circuit
41, and the detection signal Rx is received from the sensing
electrode 22. The received detection signal Rx is converted to the
detection data Vdet by the A/D conversion circuit 42. In the touch
detection procedure, the detection data Vdet in all the facing
portions where the driving electrode 21 and the sensing electrode
22 cross each other are obtained.
[0095] (Step S04) The TPIC 40 determines whether or not the current
touch detection procedure is the procedure during activation. If
the current procedure is the procedure during activation, the
procedure proceeds to step S05. If the current procedure is not the
procedure during activation, the procedure proceeds to step
S06.
[0096] (Step S05) Because the current procedure is the procedure
during activation, the TPIC 40 sets the value of the detection data
Vdet to the baseline Vb and stores the value into the baseline
storage unit 431. The detection data Vdet, by which the stylus 50
is assumed to be in the non-touch state, is set to the baseline
Vb.
[0097] (Step S06) The TPIC 40 calculates the signal component Vs
using the baseline Vb stored in the baseline storage unit 431 and
the detection data Vdet obtained through the touch detection
procedure. The signal component Vs is obtained by calculating a
difference (Vs=Vdet-Vb) between the detection data Vdet and the
baseline Vb.
[0098] (Step S07) The TPIC 40 compares the calculated signal
component Vs with a threshold. The comparison between the signal
component Vs and the threshold is performed on all the signal
components Vs calculated for each facing portion. When there is any
signal component Vs satisfying "the signal component Vs>the
threshold", the procedure proceeds to step S08. When there is not
any signal component Vs satisfying "the signal component Vs>the
threshold", the procedure proceeds to step S11.
[0099] (Step S08) When the signal component Vs is larger than the
threshold, the TPIC 40 collates the obtained detection data Vdet
with a pre-registered noise pattern to determine whether or not
noise is included in the detection data Vdet. When the TPIC 40
determines that there is noise, the procedure proceeds to step S12.
When the TPIC 40 determines that there is no noise, the procedure
proceeds to step S09.
[0100] (Step S09) When having determined that there is no noise,
the TPIC 40 calculates the coordinate value of the touch position
based on the signal component Vs.
[0101] (Step S10) The TPIC 40 outputs the calculated coordinate
value of the touch position to the control device 60 and then the
procedure proceeds to step S02.
[0102] (Step S11) When the signal component Vs is less than the
threshold, the TPIC 40 determines that the detection data Vdet
indicates the non-touch state. The TPIC 40 updates the baseline
storage unit 431 with new detection data Vdet as the baseline Vb,
and the procedure proceeds to step S02.
[0103] (Step S12) When having determined that there is noise, the
TPIC 40 switches the frequency (driving signal frequency Txf) of
the driving signal Tx to a frequency of a different value in order
to reduce noise, and the procedure proceeds to step S02.
[0104] By executing the above procedure, the TPIC 40 detects that
the stylus 50 has touched the touch panel 20 and obtains the
coordinate value of the touched position. In the state where the
stylus 50 is in touch with the touch panel 20, because the
auxiliary signal ARx whose phase is opposite to the phase of the
driving signal Tx is output to the sensing electrode 22 from the
stylus 50, the signal component Vs has a large value as compared
with the case where the stylus 50 does not output the auxiliary
signal ARx. Therefore, the presence or absence of touch may be
reliably detected.
[0105] Moreover, when a noise pattern is detected in the obtained
signal component Vs, the frequency of the driving signal Tx is
switched so as to reduce noise. As a result, the influence from
noise, such as an AC charger noise, may be reduced.
[0106] Note that, in the above, a case has been described, where an
input operation is performed on the touch panel 20 using the stylus
50. However, the touch panel 20 is a mutual capacitance type touch
panel, and therefore the touch panel 20 may be naturally
manipulated with a finger in contact with or proximate to the touch
surface. In this case, because a finger may secure a sufficient
contact area in the touch surface, the presence or absence of touch
may be reliably detected even if the auxiliary signal ARx is not
output to the sensing electrode 22.
Third Embodiment
[0107] In the second embodiment, in order to reduce noise, such as
an AC charger noise, the driving signal frequency Txf is switched
by the TPIC 40 when a noise pattern is detected. In a third
embodiment, furthermore a procedure of reducing noise is performed
in the stylus 50.
[0108] Hereinafter, a display apparatus of the third embodiment is
described using FIG. 9. In the third embodiment, the detection
assisting circuit 51 of the stylus 50 of the second embodiment is
replaced with a new configuration. Because other configurations are
the same as those of the second embodiment, only a new detection
assisting circuit is described.
[0109] FIG. 9 illustrates an example of the configuration of a
second detection assisting circuit of a display apparatus of the
third embodiment.
[0110] A second detection assisting circuit 54 of the third
embodiment is a replacement of the detection assisting circuit 51
of the second embodiment. The same number is attached to the same
element as the detection assisting circuit 51 to omit the
description thereof.
[0111] The second detection assisting circuit 54 includes a
frequency selection circuit 541, an inverting circuit 511, an
amplifier circuit 512, an amplifier circuit 542, and an adder
(adder circuit) 543.
[0112] The frequency selection circuit 541 selects the output
destination for each signal component according to whether the
frequency of a signal component included in the input detection
driving signal Td is the driving signal frequency Txf or another
frequency. The signal component includes, first of all, a signal
component corresponding to the driving signal Tx included in the
detection driving signal Td. When there is no noise generated, the
signal component included in the detection driving signal Td
includes only the signal component corresponding to the driving
signal Tx. The signal component whose frequency matches the driving
signal frequency Txf is referred to as a first signal, for
convenience. When there is any noise generated, the detection
driving signal Td includes a noise component in addition to the
first signal. The signal including noise has a frequency different
from the driving signal frequency Txf. The signal including noise
is referred to as a second signal. Based on such a difference in
frequency, the frequency selection circuit 541 sorts the signal
components of the detection driving signal Td in accordance with
the frequency, and outputs the first signal to the inverting
circuit 511 and outputs the second signal to the amplifier circuit
542.
[0113] The inverting circuit 511 and amplifier circuit 512 invert
and amplify an electric potential change of the first signal
included in the received detection driving signal Td and then
output the resulting electric potential change to the adder
543.
[0114] The amplifier circuit 542 amplifies an electric potential
change of the second signal included in the input detection driving
signal Td as it is, and then outputs the resulting electric
potential change to the adder 543. The signal component whose
electric potential change is amplified as it is will serve, when
output to the sensing electrode 22, as a correction signal for
reducing the noise included in the driving signal Tx.
[0115] The adder 543 adds the first inversion signal obtained by
inverting a phase of the first signal received via the amplifier
circuit 512, and the correction signal received via the amplifier
circuit 542 to generate a correction inversion signal, and outputs
the correction inversion signal from the pen-point output unit 53
as the auxiliary signal ARx.
[0116] In such a second detection assisting circuit 54, the
frequency selection circuit 541 separates a signal component of the
first signal included in the detection driving signal Td from a
signal component of the second signal included in the detection
driving signal Td. The first signal of the same frequency as that
of the driving signal Tx is inverted and amplified by the inverting
circuit 511 and amplifier circuit 512 to generate the first
inversion signal. On the other hand, the second signal that is a
noise component is amplified by the amplifier circuit 542, without
being inverted, to generate the correction signal for correcting a
noise component included in the detection signal Rx. The adder 543
adds the first inversion signal and the correction signal to
generate a correction inversion signal, and outputs the correction
inversion signal to the sensing electrode 22 as the auxiliary
signal ARx. Such an auxiliary signal ARx is output to the sensing
electrode 22, so that the strength of a signal component related to
touch detection included in the detection signal Rx may be
increased to reduce the noise component.
[0117] As a result, the presence or absence of touch may be
reliably detected under noisy environments.
[0118] Note that, as illustrated in FIG. 8, when a configuration is
employed, in which the driving signal frequency Txf is switched
when noise is detected, the frequency selection circuit 541 needs
to notify the stylus 50 side from the TPIC 40 side of the driving
signal frequency Txf when noise is detected. A configuration is
described, in which the second detection assisting circuit 54 is
provided with a function to provide the notification of the driving
signal frequency Txf.
[0119] FIG. 10 illustrates an example of the configuration of a
third detection assisting circuit.
[0120] A third detection assisting circuit 55 illustrated in FIG.
10 has a configuration, in which a frequency receiving circuit 551
is added to the second detection assisting circuit 54. The
frequency receiving circuit 551 receives the detection driving
signal Td, separates the notification of the driving signal
frequency Txf included in the detection driving signal Td, from the
detection driving signal Td. Then, the frequency receiving circuit
551 notifies the frequency selection circuit 541 of the obtained
driving signal frequency Txf. In the frequency selection circuit
541, the notified driving signal frequency Txf is stored into a
storage unit and is referred to when the component of the detection
driving signal Td is separated in accordance with frequency.
[0121] On the TPIC 40 side, the drive control circuit 41 that
obtained the new driving signal frequency Txf from the noise
detection unit 433 switches the driving signal frequency Txf, and
superimposes the notification of the switched driving signal
frequency Txf onto the driving signal Tx and outputs the resulting
driving signal Tx.
[0122] The notification of the driving signal frequency Txf is
performed continuously after the initialization of the driving
signal frequency Txf of step S01 and after the switching of the
driving signal frequency Txf of step S12, for example, in the
signal processing procedure illustrated in FIG. 8. Moreover, for
the purpose of notification of the driving signal frequency Txf,
data communication may be performed in a period during which the
touch detection is not being performed via the driving electrode 21
or sensing electrode 22. The notification of the driving signal
frequency Txf superposed on the driving signal Tx is input from the
pen-point detection unit 52 to the third detection assisting
circuit 55 through the driving electrode 21, the first capacitance,
and the sensing electrode 22 when the stylus 50 approaches the
sensing electrode 22.
[0123] Note that the method for transferring the driving signal
frequency Txf from the TPIC 40 to the stylus 50 is not limited to
the method performed via the detection driving signal Td between
the sensing electrode 22 and the stylus 50, but may be performed
via the communication interface 81, for example.
Fourth Embodiment
[0124] In the second embodiment and the third embodiment, a phase
delay due to the signal processing inside the stylus 50 is assumed
to be negligible. For example, in the second embodiment, the
detection driving signal Td detected by the pen-point detection
unit 52 is inverted by the inverting circuit 511 and amplified by
the amplifier circuit 512 and serves as the auxiliary signal ARx,
and is then just output from the pen-point output unit 53, and
therefore there may be almost no phase delay generated inside the
stylus 50. Accordingly, a phase difference between a signal
component corresponding to the mutual capacitance between the
driving electrode and the sensing electrode, the signal component
being detected by the sensing electrode 22 in synchronization with
a signal detected by the pen-point detection unit 52, and the
auxiliary signal ARx may be negligible.
[0125] However, when the phase delay inside the stylus 50
increases, the phase difference between a signal component included
in the detection signal Rx and detected by the sensing electrode
22, corresponding to the mutual capacitance between the driving
electrode and the sensing electrode, and a signal component of the
auxiliary signal ARx increases, which may cause a malfunction in
the TPIC 40 that uses the detection signal Rx.
[0126] In the fourth embodiment, the detection assisting circuit 51
of the first embodiment includes a circuit for aligning the phase
of the auxiliary signal ARx output from the pen-point output unit
53 with the phase of the detection driving signal Td of the
pen-point detection unit 52.
[0127] Hereinafter, a display apparatus of the fourth embodiment is
described using FIG. 11.
[0128] FIG. 11 illustrates an example of the configuration of the
fourth detection assisting circuit of the display apparatus of the
fourth embodiment.
[0129] A fourth detection assisting circuit 56 illustrated in FIG.
11 has a configuration, in which a phase adjustment circuit 561 is
added to the detection assisting circuit 51 illustrated in FIG. 6.
The description of the same element as that of the detection
assisting circuit 51 is omitted.
[0130] The phase adjustment circuit 561 receives the detection
driving signal Td input from the pen-point detection unit 52 and
the auxiliary signal ARx output by the amplifier circuit 512, and
monitors the phase delay of the auxiliary signal ARx relative to
the detection driving signal Td. Then, when the amount of phase
delay exceeds a predetermined amount, the phase adjustment circuit
561 adjusts to align the phase of the auxiliary signal ARx with the
phase of the detection driving signal Td. The phase of the
auxiliary signal ARx is shifted to align the edge of the waveform
thereof with the edge of the next detection driving signal Td. When
the amount of phase delay does not exceed a predetermined amount,
the phase of the auxiliary signal ARx is output as it is without
being shifted.
[0131] FIG. 12 illustrates a relationship between the input signal
and output signal of the phase adjustment circuit. 1 clk indicates
one period of the detection driving signal Td.
[0132] As illustrated in FIG. 12, the output of the amplifier
circuit 512 has a phase delay relative to the detection driving
signal Td. An allowable range of the phase delay is set to the
phase adjustment circuit 561 in advance, and whether or not to
align the phase of the auxiliary signal ARx with the phase of the
detection driving signal Td is determined based on the allowable
range.
[0133] In (A) of FIG. 12, an output whose phase delay is within an
allowable range indicates the output of the phase adjustment
circuit 561 when the phase of the output signal of the amplifier
circuit 512 is within an allowable range (A). Because the phase
delay is within the allowable range (A), the output of the
amplifier circuit 512 is output without delaying the phase thereof,
as it is, as the auxiliary signal ARx.
[0134] In (B) of FIG. 12, an output whose phase delay exceeds an
allowable range indicates the output of the phase adjustment
circuit 561 when the phase of the output signal of the amplifier
circuit 512 exceeds an allowable range (B). Because the phase delay
exceeds the allowable range (B), the phase of the output of the
amplifier circuit 512 is delayed in align with the edge of the
detection driving signal Td after 1 clk, and is then output as the
auxiliary signal ARx.
[0135] As described above, the phase adjustment circuit 561 is
provided and the phase of the auxiliary signal ARx is aligned with
the phase of the detection driving signal Td, so that the phase of
the auxiliary signal ARx synchronizes with the phase of a signal
component corresponding to the mutual capacitance between the
driving electrode and the sensing electrode in the sensing
electrode 22. As a result, the malfunctions in the TPIC 40 due to a
phase delay of the auxiliary signal ARx may be reduced.
[0136] Note that, in the fourth embodiment, a phase delay is
detected and the phase is shifted, but the phase of the auxiliary
signal ARx may be always delayed in align with the edge of the next
detection driving signal Td.
[0137] Note that the above-described processing functions may be
implemented on a computer. In that case, a program describing the
processing content of a function which each display apparatus needs
to have is provided. A computer system executes those programs,
thereby providing the above-described processing functions. The
programs may be stored in computer-readable media. Such
computer-readable storage media include magnetic storage
apparatuses, optical discs, magneto-optical storage media,
semiconductor memory devices, and other non-transitory storage
media. The examples of the magnetic storage apparatuses include a
hard disk drive (HDD; Hard disk Drive), a flexible disc (FD), and a
magnetic tape. The examples of the optical disc include a DVD
(Digital Versatile Disc), a DVD-RAM, a CD (Compact Disc)-ROM, and a
CD-R (Recordable)/RW (ReWritable). The examples of the
magneto-optical storage medium include an MO (Magneto-Optical
disc).
[0138] When a program is distributed, portable storage media, such
as a DVD and a CD-ROM, on which the program is recorded, are sold,
for example. Moreover, network-based distribution of software
programs may also be possible, in which case program files are
stored in a storage apparatus of a server computer for downloading
to other computers via a network.
[0139] A computer executing a program stores, in its storage
devices, for example, programs stored in a portable storage medium
or programs transferred from a server computer. The computer reads
a program from the storage device and executes a procedure
according to the program. Note that the computer may also read a
program directly from the portable storage medium and execute a
procedure according to the program. Another alternative method is
that the computer executes programs as they are downloaded from a
server computer connected via a network.
[0140] Moreover, at least some of the above-described processing
functions may be realized by an electronic circuit, such as DSP
(Digital Signal Processor), an ASIC (Application Specific
Integrated Circuit), or a PLD (Programmable Logic Device).
[0141] In the embodiments, a liquid crystal display apparatus has
been illustrated as an example of the disclosure, but other
application examples include all the flat panel type display
apparatuses, such as an organic EL (ElectroLuminescence) display
apparatus, other self-luminous display apparatuses, or an
electronic paper type display apparatus with an electrophoresis
element and the like. Moreover, it is needless to say that the
embodiments may be applicable to the small, middle to large type
display apparatuses without specifically limiting the size of the
display apparatus.
[0142] Moreover, in the above-described first to fourth
embodiments, needed constituent elements may be appropriately
combined in accordance with the specification and the like of a
product.
[0143] (1) According to an embodiment disclosed herein, there is
provided a display apparatus including: a touch panel including a
driving electrode and a sensing electrode that faces at least a
part of the driving electrode across a dielectric substance, the
touch panel being configured to output a detection signal from the
sensing electrode in synchronization with a driving signal applied
to the driving electrode; a pointing device configured to point to
a position on a touch surface of the touch panel; a detection
assisting device including an inverting circuit configured to
obtain a detection driving signal corresponding to the driving
signal detected by the pointing device and generate an inversion
signal by inverting a phase of the detection driving signal, the
detection assisting device being configured to output the inversion
signal to the sensing electrode via the pointing device; and a
control device configured to apply the driving signal to the
driving electrode, obtain the detection signal that is generated at
the sensing electrode according to a mutual capacitance between the
driving electrode and the sensing electrode and the inversion
signal, and detect the pointing device in contact with or proximity
to the touch panel based on the detection signal.
[0144] (2) According to an embodiment disclosed herein, there is
provided the display apparatus according to (1), in which the
detection assisting device is provided in the pointing device.
[0145] (3) According to an embodiment disclosed herein, there is
provided the display apparatus according to (1), in which the
detection assisting device further includes an amplifier circuit
configured to amplify the inversion signal by a predetermined gain,
and the detection assisting device outputs the amplified inversion
signal to the sensing electrode via the pointing device.
[0146] (4) According to an embodiment disclosed herein, there is
provided the display apparatus according to (3), in which the
pointing device detects whether or not the pointing device is in
contact with the touch surface, and notifies the detection
assisting device of a detection result, and the detection assisting
device switches an amplification level for amplifying the inversion
signal based on the detection result, by setting a gain of the
amplifier circuit to a first gain when the pointing device is in
contact with the touch surface and by setting the gain of the
amplifier circuit to a second gain when the pointing device is not
in contact with the touch surface.
[0147] (5) According to an embodiment disclosed herein, there is
provided the display apparatus according to (1), in which the
detection assisting device further includes: a frequency selection
circuit configured to compare a signal component included in the
detection driving signal with a frequency of the driving signal,
select a first signal having a same frequency as the driving
signal, and output the first signal to the inverting circuit; and
an adder circuit configured to add a second signal having a
frequency different from a frequency of the driving signal to a
first inversion signal, which is obtained by inverting a phase of
the first signal by the inverting circuit, in order to correct the
first inversion signal to generate a correction inversion signal,
and the detection assisting device outputs the correction inversion
signal to the sensing electrode via the pointing device.
[0148] (6) According to an embodiment disclosed herein, there is
provided the display apparatus according to (5), in which the
control device includes a noise detection unit configured to
collate the detection signal with predefined noise information,
change a frequency of the driving signal when determining that
noise is included in the detection signal, and notify the detection
assisting device of the changed frequency, the detection assisting
device obtains the changed frequency, and the frequency selection
circuit uses the changed frequency for selection of a signal
component included in the detection driving signal.
[0149] (7) According to an embodiment disclosed herein, there is
provided the display apparatus according to (1), in which the
detection assisting device further includes a phase adjustment
circuit configured to compare a phase of an auxiliary signal to be
output to the sensing electrode via the pointing device with a
phase of the detection driving signal, determine whether or not an
amount of phase delay of the auxiliary signal relative to the
detection driving signal is within a predetermined allowable range,
and align the phase of the auxiliary signal with the phase of the
detection driving signal when the amount of phase delay exceeds the
allowable range.
[0150] (8) According to an embodiment disclosed herein, there is
provided a method for driving a display apparatus, the display
apparatus including a touch panel and a pointing device, the touch
panel including a driving electrode and a sensing electrode that
faces at least a part of the driving electrode across a dielectric
substance, the touch panel being configured to output a detection
signal from the sensing electrode in synchronization with a driving
signal applied to the driving electrode, the pointing device being
configured to point to a position on a touch surface of the touch
panel. The method includes: applying, by a control device, the
driving signal to the driving electrode; obtaining, by a detection
assisting device, a detection driving signal corresponding to the
driving signal detected by the pointing device; generating, by the
detection assisting device, an inversion signal by inverting a
phase of the detection driving signal; outputting, by the detection
assisting device, the inversion signal to the sensing electrode via
the pointing device; obtaining, by the control device, the
detection signal generated at the sensing electrode according to a
mutual capacitance between the driving electrode and the sensing
electrode and the inversion signal; and detecting, by the control
device, the pointing device in contact with or proximity to the
touch panel based on the detection signal.
[0151] (9) According to an embodiment disclosed herein, there is
provided a pointing device for pointing to a position on a touch
surface of a touch panel including a driving electrode and a
sensing electrode that faces at least a part of the driving
electrode across a dielectric substance, the touch panel being
configured to output a detection signal from the sensing electrode
in synchronization with a driving signal applied to the driving
electrode. The pointing device includes: an inverting circuit
configured to detect a detection driving signal corresponding to
the driving signal and generate an inversion signal by inverting a
phase of the detection driving signal; and an output unit
configured to output the inversion signal to the sensing electrode,
wherein the pointing device causes, when the driving signal is
applied to the driving electrode, the sensing electrode to generate
the detection signal according to a mutual capacitance between the
driving electrode and the sensing electrode and the inversion
signal.
[0152] All examples and conditional language provided herein are
intended for the pedagogical purposes of aiding the reader in
understanding the invention and the concepts contributed by the
inventor to further the art, and are not to be construed as
limitations to such specifically recited examples and conditions,
nor does the organization of such examples in the specification
relate to a showing of the superiority and inferiority of the
invention. Although one or more embodiments of the present
invention have been described in detail, it should be understood
that various changes, substitutions, and alterations could be made
hereto without departing from the spirit and scope of the
invention.
[0153] It should be understood that various changes and
modifications to the presently preferred embodiments described
herein will be apparent to those skilled in the art. Such changes
and modifications can be made without departing from the spirit and
scope of the present subject matter and without diminishing its
intended advantages. It is therefore intended that such changes and
modifications be covered by the appended claims.
* * * * *