U.S. patent application number 13/752655 was filed with the patent office on 2013-05-30 for touch sensor and operating method thereof.
This patent application is currently assigned to ATLab Inc.. The applicant listed for this patent is ATLab Inc.. Invention is credited to Sang-Yun HAN, Jae-Surk HONG, Duck-Young JUNG, Byung-Joon MOON.
Application Number | 20130134995 13/752655 |
Document ID | / |
Family ID | 42629971 |
Filed Date | 2013-05-30 |
United States Patent
Application |
20130134995 |
Kind Code |
A1 |
MOON; Byung-Joon ; et
al. |
May 30, 2013 |
TOUCH SENSOR AND OPERATING METHOD THEREOF
Abstract
A touch sensor includes: a pulse signal generator for generating
a pulse signal of which pulse width is calibrated in response to a
control code; a pulse signal transmitter for transmitting the pulse
signal when a touch object is out of contact with a touch pad and
stopping transmitting the pulse signal when the touch object is in
contact with the touch pad; a pulse signal detector for detecting
the pulse signal transmitted through the pulse signal transmitter;
and a controller recognizing a non-contact state and adjusting the
control code to calibrate the pulse width of the pulse signal when
the pulse signal detector detects the pulse signal. In the
above-described configuration, the contact of the touch object with
the touch pad can be sensed more precisely, and the occurrence of a
malfunction in the touch sensor due to changed operating conditions
can be prevented.
Inventors: |
MOON; Byung-Joon;
(Yongin-si, KR) ; HAN; Sang-Yun; (Yongin-si,
KR) ; HONG; Jae-Surk; (Yongin-si, KR) ; JUNG;
Duck-Young; (Yongin-si, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ATLab Inc.; |
Yongin-si |
|
KR |
|
|
Assignee: |
ATLab Inc.
Yongin-si
KR
|
Family ID: |
42629971 |
Appl. No.: |
13/752655 |
Filed: |
January 29, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12710939 |
Feb 23, 2010 |
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13752655 |
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12297401 |
Oct 16, 2008 |
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PCT/KR2007/002134 |
May 1, 2007 |
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12710939 |
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Current U.S.
Class: |
324/676 |
Current CPC
Class: |
G06F 3/04182 20190501;
G06F 3/044 20130101; G01R 27/2605 20130101; H03K 2217/96072
20130101; H03K 17/962 20130101 |
Class at
Publication: |
324/676 |
International
Class: |
G01R 27/26 20060101
G01R027/26 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 22, 2006 |
KR |
10-2006-0056539 |
Feb 23, 2009 |
KR |
10-2009-0014944 |
Claims
1. A capacitance measurement circuit comprising: a pulse signal
generator for varying a pulse width of a clock signal in response
to a capacitance value, and generating a pulse signal; a pulse
signal transmitter including a pad through which a capacitance is
externally received, the pulse signal transmitter being configured
to or not to transmit the pulse signal in response to the
capacitance applied through the pad; a pulse signal detector for
periodically detecting the pulse signal applied through the pulse
signal transmitter, and outputting a detection signal; a counter
for gradually increasing or decreasing and outputting a counter
value according to predetermined rules in response to the detection
signal; and a digital filter for filtering the counter value and
outputting the capacitance value.
2. The circuit of claim 1, wherein the pulse signal generator
comprises: a clock signal generator for generating the clock
signal; a variable delay chain for variably delaying the clock
signal according to the capacitance value; an inverter for
inverting and outputting the output signal of the variable delay
chain; and an AND gate for performing a logic AND on the clock
signal and the output signal of the inverter, and generating the
pulse signal having a pulse width corresponding to a delay time of
the clock signal.
3. The circuit of claim 1, wherein the pulse signal transmitter
further comprises a resistor connected between the pulse signal
generator and the pulse signal detector and configured to inhibit
transmission of the pulse signal along with the capacitance applied
through the pad.
4. The circuit of claim 1, wherein the pulse signal detector
comprises: a T-flip-flop for detecting the pulse signal in response
to the clock signal, and generating an output signal that toggles
in response to the pulse signal; and a period determiner for
determining whether the output signal of the T-flip-flop
periodically toggles, and outputting the detection signal.
5. The circuit of claim 4, wherein the T-flip-flop comprises: an
SR-flip-flop for outputting the detection signal in response to the
pulse signal applied to one of a set terminal and a reset terminal;
a D-flip-flop for latching and outputting the detection signal in
response to the clock signal; and a multiplexer for selecting one
of the set terminal and the reset terminal in response to the
output signal of the D-flip-flop, and transmitting the pulse signal
to the selected terminal.
6. The circuit of claim 1, wherein the counter gradually increases
or decreases the capacitance value in response to the detection
signal by a predetermined unit and outputs the capacitance
value.
7. The circuit of claim 1, wherein when the detection signal is
continuously applied at a high level or low level, the counter
varies the capacitance value by a variation unit of the capacitance
value and gradually increases or decreases and outputs the
capacitance value.
8. The circuit of claim 1, wherein the digital filter is an LPF or
BPF configured to receive and stabilize the counter value, remove a
noise, and output the capacitance value.
9. The circuit of claim 1, wherein the counter and the digital
filter are embodied in software.
Description
[0001] The present invention relates to U.S. Pat. No. 7,605,805
which was applied by the same applicant.
TECHNICAL FIELD
Background Art
[0002] The present invention relates to a touch sensor, and more
particularly, to a touch sensor capable of sensing whether or not a
touch object is in contact with the touch sensor using an
electrostatic capacitance of the touch object.
[0003] Korean Patent Application No. 2005-23382 discloses a touch
sensor as shown in FIG. 1, which senses whether or not a touch
object is in contact with the touch sensor by varying a difference
in delay time between a touch signal and a reference signal using
the electrostatic capacitance of the touch object.
[0004] Referring to FIG. 1, the touch sensor includes a reference
signal generator 10, a first signal generator 21, a second signal
generator 22, a touch signal generator 30, and a low pass filter
(LPF) 40. Specifically, the reference signal generator 10 generates
a reference signal ref_sig. The first signal generator 21, which
includes a resistor R11 and a capacitor CAP, delays the reference
signal ref_sig by a constant delay time irrespective of whether or
not the touch object is in contact with the touch sensor, and
generates a first signal sig1. The second signal generator 22,
which includes a resistor R12 and a touch pad PAD, delays the
reference signal ref_sig by a variable delay time according to the
electrostatic capacitance of the touch object and generates a
second signal sig2. The touch signal generator 30, which includes a
D-flip-flop, latches the second signal sig2 in response to the
first signal sig1 and generates a touch signal con_sig. The LPF 40
filters the touch signal con_sig and outputs a filtered signal.
[0005] The touch signal generator 30 generates a touch signal
con_sig having a first level when the touch object is brought into
contact with the touch pad PAD and the second signal sig2 has a
longer delay time than the first signal sig1. On the other hand,
the touch signal generator 30 generates a touch signal con_sig
having a second level when the touch object is out of contact with
the touch pad PAD and the second signal sig2 has a shorter delay
time than the first signal sig1.
[0006] As described above, the touch sensor of FIG. 1 varies a
difference in delay time between the first signal sig1 and the
second signal sig2 depending on whether or not the touch object is
in contact with the touch pad PAD.
[0007] However, when the touch pad PAD has poor touch sensitivity
or the touch object has very small electrostatic capacitance, a
difference in delay time between the first signal sig1 and the
second signal sig2 cannot be sufficiently varied, so that a
malfunction may occur in the touch sensor.
[0008] Furthermore, the impedance of a circuit device included in
each of the first and second signal generators 21 and 22 and a
delay difference between the first and second signals sig1 and sig2
may vary with operating conditions of the touch sensor, such as an
operating power supply voltage and the temperature and humidity of
the atmosphere.
[0009] However, although the impedance of the circuit device
included in each of the first and second signal generators 21 and
22 is changed according to the operating conditions, the
conventional touch sensor provides no calibration element. As a
result, the operating characteristics of the touch sensor are
varied according to the operating conditions and, what is worse, a
malfunction may occur in the touch sensor.
DISCLOSURE
Technical Problem
[0010] The present invention is directed to a touch sensor and a
method of operating the same in which the contact of a touch object
with the touch sensor is precisely sensed.
[0011] Also, the present invention is directed to a touch sensor
and a method of operating the same in which the occurrence of a
malfunction due to changed operating conditions may be
prevented.
[0012] Furthermore, the present invention is directed to a
capacitance measurement circuit capable of reducing the influence
of a noise.
Technical Solution
[0013] One aspect of the present invention provides a touch sensor
including: a pulse signal generator for generating a pulse signal
of which pulse width is calibrated in response to a control code; a
pulse signal transmitter for transmitting the pulse signal when a
touch object is out of contact with a touch pad and stopping
transmitting the pulse signal when the touch object is in contact
with the touch pad; a pulse signal detector for detecting the pulse
signal transmitted through the pulse signal transmitter; and a
controller for recognizing a non-contact state and adjusting the
control code to calibrate the pulse width of the pulse signal when
the pulse signal detector detects the pulse signal.
[0014] In an embodiment of the present invention, the pulse signal
transmitter may include: a resistor; and the touch pad charged or
discharged with the pulse signal according to a resistance of the
resistor and an electrostatic capacitance of the touch object to
inhibit the transmission of the pulse signal.
[0015] In another embodiment, the pulse signal transmitter may
include: a variable resistor of which a resistance varies with the
control code; and the touch pad charged or discharged with the
pulse signal according to the varied resistance of the variable
resistor and the electrostatic capacitance of the touch object to
inhibit the transmission of the pulse signal when the touch object
is in contact with the touch sensor.
[0016] In an embodiment of the present invention, the pulse signal
generator may include: a clock signal generator for generating a
clock signal; and a counter of which a counting value is set
according to the control code and counting by the counting value in
response to the clock signal to vary the pulse width of the pulse
signal.
[0017] In another embodiment, the pulse signal generator may
include: a clock signal generator for generating a clock signal; a
signal delay unit for varying the delay time of the clock signal
according to the control code; an inverter for inverting an output
signal of the signal delay unit; and a logic gate for performing a
logic AND operation on the clock signal and an output signal of the
inverter to generate the pulse signal having a pulse width
corresponding to the delay time of the clock signal.
[0018] Another aspect of the present invention provides a method of
operating a touch sensor.
[0019] The method includes: generating a pulse signal having a
predetermined pulse width; transmitting the pulse signal when a
touch object is out of contact with a touch pad and stopping
transmitting the pulse signal when the touch object is in contact
with the touch pad; recognizing a non-contact state when the pulse
signal is transmitted and recognizing a contact state when the
pulse signal is not transmitted; and calibrating the pulse width of
the pulse signal in the non-contact state.
[0020] In an embodiment of the present invention, calibrating the
pulse width of the pulse signal in the non-contact state may
include: obtaining a critical pulse width at which the pulse signal
is not transmitted by gradually decreasing the pulse width of the
pulse signal from the maximum value; obtaining a calibrated pulse
width by adding a margin pulse width to the critical pulse width
when a difference between the current critical pulse width and a
critical pulse width obtained in the previous calibration operation
is within the permitted limit; and calibrating the pulse width of
the pulse signal to the calibrated pulse width.
[0021] In another embodiment of the present invention, calibrating
the pulse width of the pulse signal in the non-contact state may
include: obtaining a critical pulse width at which the pulse signal
is not transmitted by gradually decreasing the pulse width of the
pulse signal from the sum of a pulse width obtained in the previous
calibration operation and the permitted limit; obtaining a
calibrated pulse width by adding a margin pulse width to the
critical pulse width when a difference between the current critical
pulse width and a critical pulse width obtained in the previous
calibration operation is within the permitted limit; and
calibrating the pulse width of the pulse signal to the calibrated
pulse width.
[0022] In yet another embodiment of the present invention,
calibrating the pulse width of the pulse signal in the non-contact
state may include: obtaining a critical pulse width at which the
pulse signal is not transmitted by increasing and decreasing the
pulse width of the pulse signal using a successive approximation
method; obtaining a calibrated pulse width by adding a margin pulse
width to the critical pulse width when a difference between the
current critical pulse width and a critical pulse width obtained in
the previous calibration operation is within the permitted limit;
and calibrating the pulse width of the pulse signal to the
calibrated pulse width.
Advantageous Effects
[0023] As described above, a touch sensor is capable of confirming
if a touch object is in contact with a touch pad depending on
whether a pulse signal is transmitted or not, so that the touch
sensor can perform a touch sensing operation more precisely. Also,
the pulse width of the pulse signal is periodically adjusted to
operating conditions, thus preventing the occurrence of a
malfunction in the touch sensor due to changing operating
conditions. As a result, the operating reliability of the touch
sensor can be enhanced.
DESCRIPTION OF DRAWINGS
[0024] FIG. 1 is a detailed circuit diagram of a conventional touch
sensor;
[0025] FIG. 2 is a block diagram of a touch sensor according to an
exemplary embodiment of the present invention;
[0026] FIG. 3 is a detailed circuit diagram of a touch sensor
according to an exemplary embodiment of the present invention;
[0027] FIG. 4 is a detailed circuit diagram of a touch sensor
according to another exemplary embodiment of the present
invention;
[0028] FIG. 5 shows a correlation between the delay time of a
signal delay unit of FIG. 4 and the pulse width of a pulse
signal;
[0029] FIG. 6 is a detailed circuit diagram of a touch sensor
according to yet another exemplary embodiment of the present
invention;
[0030] FIG. 7 is a detailed circuit diagram of a signal delay unit
SIGD according to an exemplary embodiment of the present
invention;
[0031] FIG. 8 is a circuit diagram of a pulse signal transmitter
according to another exemplary embodiment of the present
invention;
[0032] FIG. 9 is a flowchart illustrating a method of operating a
touch sensor according to an exemplary embodiment of the present
invention;
[0033] FIG. 10 is a flowchart illustrating a calibration operation
(step S10) of FIG. 9 according to an exemplary embodiment of the
present invention;
[0034] FIG. 11 is a flowchart illustrating a calibration operation
(step S10) of FIG. 9 according to another exemplary embodiment of
the present invention;
[0035] FIG. 12 is a flowchart illustrating a calibration operation
(step S10) of FIG. 9 according to yet another exemplary embodiment
of the present invention;
[0036] FIG. 13 is a graph illustrating a method of finding a
critical pulse width in the calibration operation of FIG. 12;
[0037] FIG. 14 is a circuit diagram of a capacitance measurement
circuit configured to sense a contact state according to an
exemplary embodiment of the present invention;
[0038] FIG. 15 is a circuit diagram of the capacitance measurement
circuit including a delay time calculator/data generator of FIG.
14;
[0039] FIGS. 16 through 18 are diagrams illustrating operations of
the capacitance measurement circuit of FIG. 15;
[0040] FIG. 19 is a circuit diagram of a capacitance measurement
circuit according to another exemplary embodiment of the present
invention; and
[0041] FIG. 20 is a circuit diagram of a toggle circuit of a
T-flip-flop of FIG. 19.
MODE FOR INVENTION
[0042] Hereinafter, exemplary embodiments of the present invention
will be described in detail. However, the present invention is not
limited to the exemplary embodiments disclosed below, but can be
implemented in various types. Therefore, the present exemplary
embodiments are provided for complete disclosure of the present
invention and to fully inform the scope of the present invention to
those ordinarily skilled in the art.
[0043] FIG. 2 is a block diagram of a touch sensor according to an
exemplary embodiment of the present invention.
[0044] Referring to FIG. 2, the touch sensor may include a pulse
signal generator 1, a pulse signal transmitter 2, a pulse signal
detector 3, and a controller 4.
[0045] Specifically, the pulse signal generator 1 receives a code
value of a control code "code" from the controller 4, sets the
pulse width of a pulse signal "pul" according to the code value of
the control code "code", and generates the pulse signal "pul" with
the set pulse width.
[0046] The pulse transmitter 2 includes a touch pad PAD in which a
touch object having a predetermined electrostatic capacitance
contacts. The pulse transmitter 2 directly transmits the pulse
signal "pul" to the pulse signal detector 3 when the touch object
is out of contact with the touch pad PAD, while the pulse
transmitter 2 transmits the pulse signal "pul" not to the pulse
signal detector 3 but to the touch pad PAD when the touch object is
in contact with the touch pad PAD.
[0047] In this case, the touch object may be any object having a
predetermined electrostatic capacitance, for example, a human body
in which a lot of charges may be accumulated.
[0048] The pulse signal detector 3 receives the pulse signal "pul"
from the pulse signal transmitter 2, detects the pulse signal
"pul", and transmits the detection result to the controller 4.
[0049] The controller 4 generates an output signal "out" based on
the detection result of the pulse signal detector 3 and outputs the
output signal "out" to an external apparatus, so that the external
apparatus can be informed of whether the touch object is in contact
with the touch pad PAD or not. Also, the controller 4 periodically
performs a calibration operation such that the pulse width of the
pulse signal "pul" is adjustable to the current operating
conditions in a non-contact state.
[0050] In FIG. 2, the impedance of a circuit device included in
each of the pulse signal generator 1 and the pulse signal
transmitter 2 of the touch sensor and the touch sensitivity of the
touch pad PAD may vary with operating conditions, such as an
operating power supply voltage and the temperature and humidity of
the atmosphere. Thus, the range of the pulse width in which the
pulse signal detector 3 can detect the pulse signal "pul"
transmitted by the pulse signal transmitter 2 also varies with the
operating conditions of the touch sensor.
[0051] Therefore, the controller 4 of the present invention varies
the pulse width of the pulse signal according to the operating
conditions so that the pulse signal detector 3 can always precisely
detect the pulse signal "pul" transmitted by the pulse signal
transmitter 2, thus preventing the occurrence of a malfunction in
the touch sensor due to variable operating conditions.
[0052] FIG. 3 is a detailed circuit diagram of a touch sensor
according to an exemplary embodiment of the present invention.
[0053] Referring to FIG. 3, the pulse signal generator 1 may
include a clock signal generator GEN and a settable down counter
SDC, the pulse signal transmitter 2 includes a resistor R and a
touch pad PAD, and the pulse signal detector 3 is embodied by a
T-flip-flop TFF.
[0054] The clock signal generator GEN generates a clock signal
"clk" and transmits the clock signal "clk" to the settable down
counter SDC.
[0055] The settable down counter SDC generates a pulse signal "pul"
of which pulse width varies according to a code value of a control
code "code" transmitted from the controller 4. Specifically, the
settable down counter SDC of which a count value is set according
to the code value of the control code "code", leads the pulse
signal "pul" to make an upward (downward) transition at the start
of a counting operation, and leads the pulse signal "pul" to make a
downward (upward) transition at the end of the counting operation,
so that the pulse width of the pulse signal "pul" may vary with the
code value of the control code "code".
[0056] The resistor R has a predetermined resistance and obtains
the electrostatic capacitance of a touch object that is in contact
with the touch pad PAD. Thus, when the touch object is in contact
with the touch pad PAD, the resistor R and the touch pad PAD are
charged or discharged with the pulse signal "pul" according to the
resistance of the resistor R and the electrostatic capacitance of
the touch object, and the transmission of the pulse signal "pul" to
the T-flip-flop TFF is inhibited. On the other hand, when the touch
object is out of contact with the touch pad PAD, the resistor R and
the touch pad PAD are neither charged nor discharged with the pulse
signal "pul", and the pulse signal "pul" is transmitted to the
T-flip-flop TFF.
[0057] When receiving the pulse signal "pul", the T-flip-flop TFF
is synchronized with a rising edge or falling edge of the pulse
signal "pul" and toggles an output signal. When receiving no pulse
signal "pul", the T-flip-flop TFF does not toggle the output
signal.
[0058] When the T-flip-flop TFF outputs the toggled output signal,
the controller 4 externally outputs an output signal "out" for
informing a user of non-contact of the touch object with the touch
pad PAD. When the T-flip-flop TFF does not output the toggled
output signal, the controller 4 externally outputs an output signal
"out" for informing the user of contact of touch object with the
touch pad PAD.
[0059] As described above, the touch sensor of FIG. 3 allows or
inhibits the transmission of the pulse signal "pul" depending on
whether the touch object contacts the touch pad PAD, so that a user
can easily and precisely confirm the contact or non-contact of the
touch object with the touch pad PAD.
[0060] FIG. 4 is a detailed circuit diagram of a touch sensor
according to another exemplary embodiment of the present
invention.
[0061] Referring to FIG. 4, a pulse signal transmitter 2, a pulse
signal detector 3, and a controller 4 are respectively the same as
those of FIG. 3, but a pulse signal generator 1' includes a clock
signal generator GEN, a signal delay unit SIGD, an inverter I, and
an AND gate AND, unlike FIG. 3.
[0062] In FIG. 4, the same reference numerals are used to denote
the same elements as in FIG. 3 and thus, a detailed description of
the same elements will be omitted here.
[0063] The clock signal generator GEN generates a clock signal
"clk" and transmits the clock signal "clk" to each of the signal
delay unit SIGD and the AND gate AND.
[0064] The signal delay unit SIGD varies the delay time of the
clock signal "clk" in response to a code value of a control code
"code" transmitted from the controller 4.
[0065] The inverter I receives a delayed clock signal "dclk" from
the signal delay unit SIGD, inverts the delayed clock signal
"dclk", and outputs an inverted clock signal "/dclk".
[0066] The AND gate AND performs a logic AND operation on the clock
signal "clk" transmitted from the clock signal generator GEN and
the clock signal "/dclk" output from the inverter I and generates a
pulse signal "pul" having a pulse width corresponding to the delay
time of the signal delay unit SIGD.
[0067] For example, as illustrated in FIG. 5, when the delay time
of the signal delay unit SIGD is "vdt", the delay time of the clock
signal "/dclk" transmitted through the signal delay unit SIGD and
the inverter I also becomes "vdt". Thus, the AND gate AND performs
a logic AND operation on the clock signals "clk" and "/dclk" and
generates a pulse signal "pul" having a pulse width corresponding
to the delay time "vdt" of the signal delay unit SIGD.
[0068] As described above, in the touch sensor of FIG. 4, the pulse
signal generator 1', which includes the clock signal generator GEN,
the signal delay unit SIGD, the inverter I, and the AND gate AND,
generates the pulse signal "pul" of which pulse width varies with
the code value of the control code "code", so that the pulse signal
transmitter 2, the pulse signal detector 3, and the controller 4
can operate in the same manner as described with reference to FIG.
3.
[0069] FIG. 6 is a detailed circuit diagram of a touch sensor
according to yet another exemplary embodiment of the present
invention.
[0070] Referring to FIG. 6, a pulse signal generator 1' and a pulse
signal transmitter 2 are respectively the same as those of FIG. 4,
but a pulse signal detector 3' is embodied by a D-flip-flop
DFF.
[0071] In FIG. 6, the same reference numerals are used to denote
the same elements as in FIG. 4 and thus, a detailed description of
the same elements will be omitted here.
[0072] The D-flip-flop DFF receives a clock signal "clk" output
from a clock signal generator GEN as a clock, and receives a pulse
signal "pul" as data. When receiving the pulse signal "pul", the
D-flip-flop DFF is synchronized with a falling edge (or rising
edge) of the clock signal "clk", latches the pulse signal "pul",
and generates a high signal. When receiving no pulse signal "pul",
the D-flip-flop DFF does not latch any signal and generates a low
signal.
[0073] Thus, a controller 4 confirms non-contact of a touch object
with a touch pad PAD when the D-flip-flop DFF generates the high
signal, and confirms contact of the touch object with the touch pad
PAD when the D-flip-flop DFF generates the low signal.
[0074] As described above, in the touch sensor of FIG. 6, the
D-flip-flop DFF may vary the level of the output signal depending
on whether or not the touch object contacts the touch pad PAD, so
that the controller 4 can easily confirm the contact or non-contact
of the touch object with the touch pad PAD.
[0075] FIG. 7 is a detailed circuit diagram of a signal delay unit
SIGD according to an exemplary embodiment of the present
invention.
[0076] Referring to FIG. 7, the signal delay unit SIGD includes a
driver D, which is connected to a signal input terminal "clk", and
a plurality of delay cells DC1 to DCn, which are connected in
series between the driver D and a signal output terminal "dclk",
and each of the delay cells DC1 to DCn includes a multiplexer "mux"
and inverters I1 and I2.
[0077] The driver D buffers a clock signal "clk" and transmits the
buffered signal to the delay cells DC1 to DCn.
[0078] The multiplexers "mux" select the delay cells (e.g., the
delay cells DC2 to DC0) to perform delay operations in response to
code values c0 to cn of a control code "code", and the multiplexers
"mux" and the inverters I1 and I2 included in the selected delay
cells DC2 and DC0 delay the clock signal "clk" by a predetermined
delay time.
[0079] As described above, the signal delay unit SIGD varies the
number of delay cells to delay the clock signal "clk" according to
the code value of the control code "code" and varies the delay time
of the clock signal "clk", so that the inverter I and an AND gate
AND can generate a pulse signal "pul" having a pulse width
corresponding to the delay time of the clock signal "clk".
[0080] Also, the touch sensor according to the present invention
may employ a variable resistor of FIG. 8 instead of the resistor R
included in the pulse signal transmitter 2, so that the controller
4 can control the resistance of the variable resistor to vary the
touch sensitivity of the touch pad PAD.
[0081] FIG. 8 is a circuit diagram of a pulse signal transmitter
according to another exemplary embodiment of the present
invention.
[0082] Referring to FIG. 8, the pulse signal transmitter includes a
variable resistor VR and a touch pad PAD. The variable resistor VR
includes a plurality of drivers D0 to Dn, which are respectively
connected between a pulse input terminal "pul" and a plurality of
corresponding resistors R0 to Rn, and the plurality of resistors R0
to Rn are connected in series to the touch pad PAD.
[0083] In this case, a controller (not shown) further provides a
control code code' for controlling the resistance of the variable
resistor VR in addition to a control code "code" for varying the
pulse width of the pulse signal "pul" during a calibration
operation.
[0084] Thus, the variable resistor VR determines the number of
resistors to which the pulse signal "pul" is transmitted through
the drivers D0 to Dn, of which operations are controlled in
response to code values c0' to cn' of the control code code'. In
other words, the variable resistor VR varies the entire resistance
according to the code value of the control code code' and also
varies an RC time constant with the electrostatic capacitance of
the touch pad PAD.
[0085] Thus, charging/discharging characteristics of the touch pad
PAD vary with the RC time constant, which is varied by the variable
resistor VR, and the touch sensitivity of the touch pad PAD finally
depends on the varied charging/discharging characteristics
thereof.
[0086] Therefore, the pulse signal transmitter of FIG. 8 may vary
the touch sensitivity of the touch pad PAD according to the code
value of the control code code' transmitted from the controller
4.
[0087] As described above, the touch sensor according to the
present invention may vary not only the pulse width of the pulse
signal "pul" but also the touch sensitivity of the touch pad PAD to
the touch object according to the current operating conditions,
thus enhancing the preciseness of a calibration operation.
[0088] FIG. 9 is a flowchart illustrating a method of operating a
touch sensor according to an exemplary embodiment of the present
invention.
[0089] When the touch sensor starts its operation, the pulse signal
generator 1 generates a pulse signal "pul" having a predetermined
pulse width and outputs the pulse signal "pul" to the pulse signal
transmitter 2 in step S1.
[0090] When a touch object is brought into contact with a touch pad
PAD, the pulse signal transmitter 2 stops the transmission of the
pulse signal "pul" in step S2. When the touch object is out of
contact with the touch pad PAD, the pulse signal transmitter 2
transmits the pulse signal "pul" to the pulse signal detector 3 in
step S3.
[0091] Then, the controller 4 confirms if the pulse signal "pul" is
transmitted through the pulse signal detector 3 in step S4. As a
result, when the pulse signal "pul" is not transmitted, the
controller 4 informs a user or an external apparatus that the touch
object contacts the touch pad PAD in step S5. Thereafter, the
controller 4 resets a "non-contact cumulative time" in step S6 and
returns to step S1 to perform a new touch sensing operation.
[0092] On the other hand, when it is confirmed in step S4 that the
pulse signal "pul" is transmitted, the controller 4 informs the
external apparatus that the touch object is out of contact with the
touch pad PAD in step S7 and confirms if a calibration period comes
in step S8.
[0093] As a result, when it is confirmed in step S8 that the
calibration period has not come yet, the controller 4 increases the
current "non-contact cumulative time" as much as one unit in step
S9 and returns to step S1 to perform a new touch sensing
operation.
[0094] On the other hand, when it is confirmed in step S8 that the
calibration period has come, the controller 4 performs a
calibration operation such that the pulse width of the pulse signal
"pul" is adjustable to the current operating conditions in step
S10. The calibration of the pulse signal "pul" in step S10 will be
described in more detail with reference to FIGS. 10 through 12.
[0095] When step 10 is finished, the controller 4 resets the
current "non-contact cumulative time" and returns to step S1 to
perform a new touch sensing operation using the pulse signal "pul"
having a calibrated pulse width.
[0096] FIG. 10 is a flowchart illustrating a calibration operation
(step S10) of FIG. 9. In FIG. 10, a pulse width appropriate for the
current operating conditions may be obtained by gradually
decreasing the pulse width of the pulse signal "pul" from the
maximum value.
[0097] First, the controller 4 confirms if a "non-contact
cumulative time" is equal to or larger than a "non-contact
confirmation time" in step S1-1 in order to confirm if the current
operating conditions are conditions under which the calibration of
a pulse signal "pul" is normally performed (namely, if the touch
object is out of contact with the touch pad PAD).
[0098] When the "non-contact cumulative time" is less than "the
non-contact confirmation time", the controller 4 confirms that the
touch object is in contact with the touch pad PAD and cancels the
calibration operation in step S1-2 and ends the control
sequence.
[0099] On the other hand, when the "non-contact cumulative time" is
equal to or larger than the "non-contact confirmation time", the
controller 4 confirms that the touch object is out of contact with
the touch pad for a predetermined duration of time, and fixes the
current output state in step S1-3 such that any malfunction does
not occur in an external apparatus due to an output signal of the
touch sensor during the calibration operation.
[0100] Thereafter, the controller 4 sets the pulse width of the
pulse signal "pul" to the maximum value in step S1-4 and confirms
if the pulse signal "pul" is transmitted through the pulse signal
transmitter 2 to the controller 4 in step S1-5.
[0101] When the pulse signal "pul" is transmitted, the pulse width
of the pulse signal "pul" is reduced by one unit in step S1-6 and
the controller 4 returns to step S1-5. Thus, the pulse width of the
pulse signal "pul" is gradually reduced until the pulse signal
"pul" is not transmitted.
[0102] When the pulse signal "pul" is not transmitted, the
controller 4 obtains the current pulse width as a critical pulse
width in step S1-7 and confirms if a difference between the current
critical pulse width and a critical pulse width obtained in the
previous calibration operation exceeds a permitted limit in step
S1-8. Here, the permitted limit is a value that can be determined
by a user to confirm if the calibration of the pulse signal "pul"
is normally performed.
[0103] When the difference between the current critical pulse width
and the critical pulse width obtained in the previous calibration
operation exceeds the permitted limit, the controller 4 confirms
that the calibration condition is not satisfied and cancels the
calibration operation in step S1-2 and ends the control
sequence.
[0104] On the other hand, when the difference between the current
critical pulse width and the critical pulse width obtained in the
previous calibration operation is within the permitted limit, the
controller 4 confirms that the calibration operation is performed
under normal conditions and obtains a calibrated pulse width
appropriate for the current operating conditions in step S1-9 by
adding a margin pulse width to the current critical pulse width.
Here, the margin pulse width is a value that can be set by a user
based on the touch sensitivity of the touch pad PAD. Thus, the
calibrated pulse width becomes the minimum pulse width that enables
the pulse signal detector 3 to detect if the pulse signal "pul" is
transmitted under the current operating conditions.
[0105] Thereafter, the controller 4 calibrates the pulse signal
"pul" to the calibrated pulse width in step S1-10, ends the
calibration operation, and enters step S11 of FIG. 9.
[0106] FIG. 11 is a flowchart illustrating a calibration operation
(step S10) of FIG. 9 according to another exemplary embodiment of
the present invention.
[0107] In FIG. 11, a pulse width appropriate for the current
operating conditions may be obtained by gradually decreasing the
pulse width of the pulse signal "pul" from the sum of the pulse
width obtained in the previous calibration operation and the
permitted limit.
[0108] In other words, the controller 4 sets the pulse width of the
pulse signal "pul" to the sum of the pulse width obtained in the
previous calibration operation and the permitted limit in step
S1-4', unlike in step S1-4 of FIG. 10. Thereafter, the pulse width
of the pulse signal "pul" is gradually reduced in steps S1-5 and
S1-6.
[0109] As described above, the calibration operation of FIG. 11
aims to obtain the calibrated pulse width appropriate for the
current operating conditions like the calibration operation of FIG.
10, but the searchable range of the pulse width is restricted to
accelerate the calibration operation.
[0110] FIG. 12 is a flowchart illustrating a calibration operation
(step S10) of FIG. 9 according to yet another exemplary embodiment
of the present invention
[0111] In FIG. 12, a pulse width appropriate for the current
operating conditions may be obtained using a successive
approximation method, which is being widely adopted in the
analog-to-digital converter (ADC) field.
[0112] First, the controller 4 performs the same operations as in
steps S1-1 to S1-3 of FIG. 10. Thereafter, the pulse width of the
pulse signal "pul" is set to a half "mid" of the maximum value
"max", and a pulse-width change unit .DELTA.pul is set to an
intermediate value between the half-maximum value "mid" and the
maximum value "max" in step S2-1.
[0113] When the pulse signal "pul" is not transmitted in step S2-2,
the controller 4 increases the pulse width of the pulse signal
"pul" by pulse-width change unit .DELTA.pul and makes the
pulse-width change unit .DELTA.pul by half in step S2-3 and returns
to step S2-2 again. That is, the controller 4 repeats steps S2-2
and S2-3 until the pulse signal "pul" is transmitted to the
controller 4 so that the pulse width of the pulse signal "pul" is
gradually increased while increasing.
[0114] As a result, when the pulse signal "pul" is finally
transmitted in step S2-2, the controller 4 reduces the pulse width
of the pulse signal "pul" by the preset pulse-width change unit
.DELTA.pul and makes the pulse-width change unit .DELTA.pul by half
in step S2-4 and confirms if the pulse signal "pul" is transmitted
in step S2-5. That is, the controller 4 repeats steps S2-4 and S2-5
until the pulse signal "pul" is not transmitted to the controller 4
so that the pulse width of the pulse signal "pul" is gradually
decreased.
[0115] The controller 4 repeats steps S2-2 and S2-5 several times
until the pulse width of the pulse signal "pul" is converged to a
specific value in step S2-6, as shown in FIG. 13. Thus, when the
pulse width of the pulse signal "pul" is converged to the specific
value, the controller 4 obtains the specific value as a critical
pulse width in step S2-7.
[0116] In step S2-6, the pulse width is converged to the specific
value by repeating a process of gradually increasing the pulse
width through steps S2-2 and S2-3, as shown in FIG. 13, and a
process of gradually decreasing the pulse width through steps S2-4
and S2-5.
[0117] The controller 4 confirms if a difference between the
current critical pulse width and the critical pulse width obtained
in the previous calibration operation exceeds a permitted limit in
step S2-8. When the difference between the current critical pulse
width and the critical pulse width obtained in the previous
calibration operation exceeds the permitted limit, the controller 4
confirms that the calibration is not satisfied and cancels the
calibration operation in step S1-2 and ends the control
sequence.
[0118] On the other hand, when the difference between the current
critical pulse width and the critical pulse width obtained in the
previous calibration operation is within the permitted limit, the
controller 4 confirms that the calibration operation is performed
under normal conditions and obtains a calibrated pulse width
appropriate for the current operating conditions in step S2-6 by
adding a margin pulse width to the current critical pulse
width.
[0119] Thereafter, the controller 4 calibrates the pulse signal
"pul" to the calibrated pulse width in step S2-7, ends the
calibration operation, and enters step S11 of FIG. 9.
[0120] As described above, the calibration operation of FIG. 12
aims to obtain a calibrated pulse width appropriate for the current
operating conditions and calibrate the pulse width of the pulse
signal "pul", like the calibration operation of FIG. 10. It is
natural that the decision step whether or not the pulse signal is
transmitted can be done by a sequence way such as, not limited, a
train of the same pulse width.
[0121] The touch sensor senses only the contact or non-contact of
the touch object and output an output signal but does not output a
capacitance of the touch object. However, in some cases, the touch
sensor not only senses the contact or non-contact of the touch
object with the touch pad PAD but also may have to measure the
capacitance in order to measure the intensity of the contact. Also,
a portable device including the touch sensor may be affected by
frequent environmental changes due to its characteristics. Thus,
the touch sensor should be configured to lessen the influence of
various noises caused by the environmental changes in order to
inhibit malfunction from occurring in the portable device due to
the noises.
[0122] FIG. 14 is a circuit diagram of a capacitance measurement
circuit configured to sense a contact state according to an
exemplary embodiment of the present invention.
[0123] The capacitance measurement circuit of FIG. 14 includes a
reference signal generator 110, a variable delay unit 130, a fixed
delay unit 130, and a delay time calculator/data generator 140. The
reference signal generator 110 may be embodied by a clock
generation circuit configured to generate a clock signal having a
predetermined period as a reference signal ref_sig.
[0124] The variable delay unit 120 includes a variable delay chain
VDC and a resistor R1, which are connected in series between the
reference signal generator 110 and the delay time calculator/data
generator 140. Also, the variable delay unit 120 includes a pad PAD
connected between the resistor R1 and the delay time
calculator/data generator 140 and configured to externally receive
a capacitance value. The variable delay chain VDC variably delays
and outputs the reference signal ref_sig in response to a code
value Code fed back and applied by a delay pump 142. The resistor
R1 and the pad PAD receive the variably delayed reference signal
ref_sig from the variable delay chain VDC, delay the variably
delayed reference signal ref_sig according to the resistance of the
resistor R1 and the capacitance value applied through the pad PAD,
and output a sensing signal "sen" to the delay time calculator/data
generator 140.
[0125] The fixed delay unit 130 includes a fixed delay chain FDC
and a resistor R2, which are connected in series between the
reference signal generator 110 and the delay time calculator/data
generator 140 in parallel to the variable delay unit 120. The fixed
delay chain FDC receives a reference delay value Nref required for
controlling a zero point of a code value Code applied to the
variable delay chain VDC in order to compensate for an offset
capacitance of the pad PAD and maximize a measurement range of the
capacitance value. The fixed delay chain FDC delays the reference
signal ref_sig in response to the reference delay value Nref and
outputs the delayed reference signal ref_sig. The resistor R2
further delays the delayed reference signal ref_sig output by the
fixed delay chain FDC and outputs a fixed reference signal "ref" to
the delay time calculator/data generator 140.
[0126] Each of the fixed delay chain FDC and the variable delay
chain VDC may include a plurality of delay cells like the signal
delay unit SIGD of FIG. 7. Each of the plurality of delay cells may
include a single multiplexer MUX and two inverters. The fixed delay
chain FDC selects delay cells configured to delay the reference
signal ref_sig in response to the reference delay value Nref, and
the variable delay chain VDC selects delay cells configured to
delay the reference signal ref_sig in response to the code value
Code.
[0127] The delay time calculator/data generator 140 includes a
phase detector 141 and the delay pump 142. The phase detector 141
determines whether the phase of the sensing signal "sen" leads or
trails that of the fixed reference signal "ref" and outputs a
detection signal "det". The delay pump calculates a capacitance
value CV in response to the detection signal "det" and ups or downs
and outputs the code value Code in response to the calculated
capacitance value CV.
[0128] In the capacitance measurement circuit of FIG. 14, each of
the variable delay chain VDC and the fixed delay chain FDC of the
variable delay unit 120 and the fixed delay unit 130 directly
receives the reference signal ref_sig from the reference signal
generator 110. Thus, since the pad PAD configured to externally
receive the capacitance is interposed between the variable delay
chain VDC configured to receive the fed-back capacitance value CV
and the delay time calculator/data generator 140 configured to
output the capacitance value CV, the pad PAD is disposed within a
feedback loop.
[0129] Although noises may occur in the capacitance measurement
circuit, there are frequent cases where external noises are applied
through the pad PAD. Thus, it is most efficient to remove the
external noises applied through the pad PAD in order to reduce the
noises. Also, in the capacitance measurement circuit of FIG. 14,
the pad PAD through which a capacitance is externally applied is
connected to the inside of a feedback loop. When the pad PAD is
connected to the inside of the feedback loop, the noises may be
attenuated due to the characteristics of the feedback loop.
[0130] FIG. 15 is a circuit diagram of the capacitance measurement
circuit having the delay time calculator/data generator of FIG. 14.
Since a reference signal generator 110, a variable delay unit 120,
and a fixed delay unit 130 of FIG. 15 are the same as in FIG. 14, a
description thereof will be omitted here.
[0131] In a delay time calculator/data generator 140 of FIG. 15, a
phase detector 141 is embodied by a D-flip-flop DFF, and a delay
pump 142 includes a counter CNT and a subtracter "sub". The
D-flip-flop DFF latches a sensing signal "sen" in synchronization
with one of rising and falling edges of a fixed reference signal
"ref" and outputs the latched sensing signal "sen". The D-flip-flop
DFF outputs a low-level detection signal "det" when the sensing
signal "sen" is not delayed with respect to the fixed reference
signal "ref", and outputs a high-level detection signal "det" when
the sensing signal "sen" is delayed with respect to the fixed
reference signal "ref". The delay pump 142 increases a code value
Code when the detection signal "det" drops to a low level, and
decreases the code value Code when the detection signal "det" rises
to a high level. In other words, the delay pump 142 performs a
negative feedback function and controls such that the phase of the
sensing signal "sen" output by the variable delay unit 120 is equal
to that of the fixed reference signal "ref" output by the fixed
delay unit 130. A delay offset may occur due to the pad PAD between
the fixed delay unit 130 and the variable delay unit 120. When the
delay offset exceeds a control range of a variable delay chain VDC,
the capacitance measurement circuit of FIG. 15 departs from a
normal operation range. In this case, a reference delay value Nref
of the fixed delay unit 130 compensates for an offset capacitance
so that the code value Code of the variable delay chain can be
within a variable delay range. Although FIG. 15 shows the
D-flip-flop DFF as an example of the phase detector 141, it is
natural that the phase detector 141 can be embodied by another
logic circuit.
[0132] The counter CNT is an up/down counter configured to up or
down and output the capacitance value CV in response to the
detection signal "det". The counter CNT may up or down the
capacitance value CV by one bit according to the level of the
detection signal "det". In this case, however, when a large
capacitance is applied through the pad PAD, a long time is taken to
measure the capacitance. In order to solve this problem, the
counter CNT does not up or down the capacitance value CV by one bit
but may up or down and output the capacitance value CV in
proportion to multipliers of 2, that is, in the order of one bit,
two bits, four bits, and eight bits, in response to continuous
application of high-level or low-level detection signals "det".
Alternatively, the counter CNT may up and down the capacitance
value CV according to predetermined rules in response to the
continuous application of high-level or high-level detection
signals "det". Although it is illustrated that the counter CNT
receives the detection signal "det" in response to the fixed
reference signal "ref", the counter CNT may receive the detection
signal "det" in response to the reference signal ref_sig.
[0133] The subtracter "sub" subtracts the capacitance value CV from
the reference delay value Nref and outputs the code value Code.
Thus, the capacitance value CV refers to a total capacitance value
applied to the pad PAD. When the capacitance value applied to the
pad PAD is increased, a feedback loop including the phase detector
141 and the delay pump 142 reduces the code value Code by as much
as an increment in capacitance applied through the pad PAD and
reduces the delay amount of the variable delay chain. Also, when
the capacitance value applied to the pad PAD is reduced, the
feedback loop increases the code value Code by as much as a
decrement in capacitance applied through the pad PAD and increases
the delay amount of the variable delay chain. As a result, the
feedback loop controls such that the phase of the sensing signal
"sen" is equal to that of the fixed reference signal "ref" applied
to phase detector 141, so that the capacitance value CV may
correspond to the capacitance applied to the pad PAD.
[0134] Although it is described here that the reference delay value
Nref applied to the subtracter "sub" is the same as a signal
required to control the fixed delay chain FDC, the subtracter "sub"
and the fixed delay chain FDC may be controlled differently. Also,
although it is described that the capacitance measurement circuit
of FIGS. 14 and 15 includes the fixed delay chain FDC, the fixed
delay chain FDC may be omitted.
[0135] FIGS. 16 through 18 are diagrams illustrating operations of
the capacitance measurement circuit of FIG. 15. Initially, FIG. 16
shows variations in a sensing signal "sen" and a detection signal
"det" when a capacitance is applied to a pad PAD.
[0136] Since a reference signal ref_sig is delayed by a fixed delay
unit 130 for a fixed delay time and output as a fixed reference
signal "ref", the fixed reference signal ref has the same cycle as
the reference signal ref_sig. Since a capacitance value CV is 0
during an initial operation of the capacitance measurement circuit,
an initial code value Code is equal to a reference delay value
Nref, and the time taken for the variable delay chain VDC to delay
the reference signal ref_sig is equal to the time taken for the
fixed delay chain FDC to delay the reference signal ref_sig. Thus,
during the initial operation of the capacitance measurement
circuit, the sensing signal "sen" is delayed with respect to the
fixed reference signal ref due to the capacitance of the pad PAD
and output to the D-flip-flop DFF.
[0137] Since the sensing signal "sen" is delayed with respect to
the fixed reference signal "ref", the sensing signal "sen" is at a
high level at a falling edge of the fixed reference signal "ref",
and the detection signal "det" is output at a high level. Since the
detection signal "det" is at a high level, the counter CNT ups the
capacitance value CV and outputs 1. Since the subtracter "sub"
subtracts the capacitance value CV from the reference delay value
Nref and output the subtraction result, the code value Code is
pumped down and output as a reference delay value (Nref)-1.
[0138] The variable delay chain VDC reduces the delay time of the
reference signal ref_sig in response to the code value Code and
outputs the sensing signal "sen". As the delay time of the sensing
signal "sen" decreases, a difference in delay time between the
sensing signal "sen" and the fixed reference signal "ref" also
decreases. When the difference in delay time between the sensing
signal "sen" and the fixed reference signal "ref" is gradually
reduced until the delay time of the sensing signal "sen" is equal
to or shorter than that of the fixed reference signal "ref" at a
time point t1, the D-flip-flop DFF drops the detection signal "det"
to a low level.
[0139] Thereafter, when a capacitance is externally applied through
the pad PAD at a time point t2, the sensing signal "sen" is further
delayed due to the applied capacitance, and the D-flip-flop DFF
outputs a high-level detection signal "det". When the detection
signal "det" is output at a high level, the capacitance value CV is
gradually increased until the delay time of the sensing signal
"sen" is equal to or shorter than that of the fixed reference
signal "ref" at a time point t3 as described above. Thereafter, the
capacitance value CV may be oscillated.
[0140] FIG. 17 shows a variation in capacitance value CV of a
capacitance measurement circuit including a counter CNT configured
to up or down the capacitance value CV by one bit, and FIG. 18
shows a variation in capacitance value CV of a capacitance
measurement circuit including a counter CNT configured to down or
down the capacitance value CV according to predetermined rules.
[0141] Since the counter CNT performs a count-up or count-down
operation by one bit in FIG. 17, when a large capacitance is
applied through the pad PAD, it takes a long amount of time for the
capacitance value CV to be equal to the applied capacitance.
However, since the counter CNT performs the count-up or count-down
operation by one bit, even if a large noise is temporarily applied,
the capacitance value CV has only a variation of 1 bit. Thus, the
influence of the noise on the capacitance value CV is
immaterial.
[0142] FIG. 18 illustrates a case where the counter CNT ups or
downs the capacitance value CV according to a rule that when a
detection signal "det" is applied at a high level or low level
three times in succession, a bit number to be upped or downed is
increased. Specifically, when the detection signal "det" is applied
at a high level in succession, the counter CNT increases a bit
number to be upped once every three times. For example, when the
detection signal "det" is applied at a high level or low level in
succession, the capacitance value CV is varied by one bit three
times and then varied by 2 bits next three times. Also, when the
detection signal "det" is dropped to a low level, the counter CNT
reduces a bit number to be upped or downed and downs the
capacitance value CV. Thus, even if a large capacitance is applied,
the counter CNT may indicate the capacitance value CV in a short
amount of time. Although the capacitance value CV of FIG. 18 may
vary within a greater range than the capacitance value CV of FIG.
17 in the case of occurrence of a noise, the influence of the noise
on the capacitance value CV is small because the variation range of
the capacitance value CV of FIG. 18 is small. In particular, since
the pad PAD is disposed within the feedback loop, the variable
delay chain VDC directly receives a noise-free reference signal
ref_sig and delays and outputs the reference signal ref_sig in
response to the code value Code, which is obtained in consideration
of a noise and applied through the pad PAD, so that the noise can
be attenuated due to the characteristics of the feedback loop.
[0143] Although it is described that the data generator 140
includes a D-flip-flop DFF and an up/down counter CNT and gradually
ups or downs the capacitance value CV, the data generator 140 may
count a difference in delay time between the fixed reference signal
ref and the sensing signal "sen" and immediately output the
capacitance value CV applied to the pad PAD.
[0144] Furthermore, the delay pump 142 may further include a
digital filter configured to filter and output a capacitance value
CV in order to remove a noise. In the above-described embodiments,
since the capacitance value CV is output within a limited variation
range, a variation range of a code value Code is also limited.
However, when the code value Code is varied with a predetermined
range or more, it is determined that a noise is included. Thus, the
delay pump 142 may further include a digital low-pass filter (LPF)
or digital band-pass filter (BPF) as the digital filter which
receives and filters the code value Code from the subtracter "sub"
and outputs the variable delay chain VDC. Also, it is natural that
the same effect can be obtained by filtering the capacitance value
CV without filtering the code value Code. The digital filter may be
used to control not only noise characteristics of the capacitance
measurement circuit but also the characteristics of the feedback
loop. Furthermore, when a difference in delay time between the
fixed reference signal ref and the sensing signal "sen" is
sufficiently reduced to stabilize the feedback loop, the
capacitance value CV is oscillated by +1/-1 bit. However, the
oscillation of the capacitance value CV may be fixed using the
digital filter. That is, the digital filter may have hysteresis
characteristics to prevent minute oscillation of the capacitance
value CV in a steady state.
[0145] Furthermore, the counter CNT and the digital filter may be
embodied in not only hardware but also software.
[0146] FIG. 19 is a circuit diagram of a capacitance measurement
circuit according to another exemplary embodiment of the present
invention. Since a pulse signal generator 1' and a pulse signal
transmitter 2 of the capacitance measurement circuit have the same
configurations as in FIG. 4, a detailed description thereof will be
omitted.
[0147] Also, the pulse signal detector 3 of FIG. 4 adopts only the
T-flip-flop TFF. However, as described above, most noises are
frequently applied through the pad PAD. Since the T-flip-flop TFF
of FIG. 4 is directly connected to the pad PAD, when a noise is
applied to a pulse signal "pul" through the pad PAD, there is a
possibility that the T-flip-flop TFF may be toggled at least once
in response to one pulse signal "pul". The T-flip-flop TFF should
be toggled only once in response to one pulse signal "pul" so that
a period determiner 232 of FIG. 19 can accurately determine the
periodicity of the pulse signal "pul". In order to solve the
above-described problem, the T-flip-flop TFF of FIG. 19 may be
embodied by the toggle circuit of FIG. 20 to be toggled only once
in response to one pulse signal "pul".
[0148] In a pulse signal detector 230 of FIG. 19, since the
T-flip-flop 231 receives the pulse signal "pul" in response to the
clock signal "clk", an output signal of the T-flip-flop 231 is not
toggled due to a noise. Also, the pulse signal detector 230 of FIG.
19 may further include the period determiner 232 configured to
determine whether the output signal of the T-flip-flop 231 is
periodically toggled. The period determiner 232 determines whether
the output signal of the T-flip-flop 231 periodically toggles in
response to the clock signal "clk", outputs a low-level detection
signal "det" when the output signal of the T-flip-flop 231
periodically toggles, and outputs a high-level detection signal
"det" when the output signal of the T-flip-flop 231 does not
periodically toggles.
[0149] Unlike the touch sensor of FIG. 4 capable of sensing only a
contact or non-contact state, the capacitance measurement circuit
of FIG. 19 should measure a capacitance applied through the pad PAD
and output a capacitance value CV, and thus the delay pump 240
includes a counter 241 and a digital filter 242 like the
capacitance measurement circuit of FIG. 15. The counter 241 is an
up/down counter, which receives the detection signal "det" in
response to the clock signal "clk" and ups or downs and outputs a
counter value Cout by one bit or according to predetermined rules.
As described above, the digital filter 242 is used to control the
characteristics of a feedback loop along with the noise
characteristics of the capacitance measurement circuit. The digital
filter 242, which has hysteresis characteristic, filters the
counter value Cout and outputs the capacitance value CV to prevent
oscillation of the capacitance value CV.
[0150] Although it is described that the counter 241 receives the
detection signal "det" in response to the clock signal "clk", when
the counter 241 is a non-synchronous counter, the counter 241 may
not receive the clock signal "clk". Also, the period determiner 232
may use other signals than the clock signal "clk" in order to
determine whether the output signal of the T-flip-flop 231
periodically toggles.
[0151] In FIG. 19, the variable delay chain VDC variably delays and
outputs the clock signal "clk" in response to the capacitance value
CV.
[0152] FIG. 20 is a circuit diagram of a toggle circuit of the
T-flip-flop of FIG. 19. The toggle circuit includes a single
multiplexer Mux 331, an SR-flip-flop SRF 332, and a D-flip-flop DFF
333.
[0153] The multiplexer 331 may receive a pulse signal "pul" in
response to the output signal of the D-flip-flop 333 and applies
the pulse signal "pul" to a set terminal S or reset terminal R of
the SR-flip-flop 332. The multiplexer 331 applies the pulse signal
"pul" to the set terminal S when the detection signal "det" is
applied at a low level, and applies the pulse signal "pul" to the
reset terminal R when the detection signal "det" is applied at a
high level.
[0154] The SR-flip-flop 332 maintains the level of the previous
detection signal "det" when no pulse signal is applied from the
multiplexer 331, outputs a high-level detection signal "det" to the
delay pump 340 when a high-level signal is applied to the set
terminal S, and outputs a low-level detection signal "det" when a
high-level signal is applied to the reset terminal R.
[0155] The D-flip-flop 333 latches the detection signal "det" in
response to the clock signal "clk" applied from the clock signal
generator 311 and outputs the latched signal to the multiplexer
331. The D-flip-flop 333 latches the detection signal "det" in
response to the clock signal "clk" and determines whether the
output signal of the multiplexer 331 is applied to the set terminal
S or reset terminal R of the SR-flip-flop 332.
[0156] According to the present invention as described above, a
touch sensor is capable of confirming if a touch object is in
contact with a touch pad depending on whether a pulse signal is
transmitted or not, so that the touch sensor can perform a touch
sensing operation more precisely. Also, the pulse width of the
pulse signal is periodically adjusted to operating conditions, thus
preventing the occurrence of a malfunction in the touch sensor due
to changed operating conditions. Thus, the operating reliability of
the touch sensor can be enhanced. Furthermore, in a capacitance
measurement circuit configured to detect a contact state according
to exemplary embodiments, a pad through which a capacitance is
externally applied is disposed within a feedback loop, and a
capacitance value is gradually increased or reduced. As a result,
the influence of a noise applied through the pad on the capacitance
value can be reduced, thus enabling measurement of a precise
capacitance value.
[0157] While the invention has been shown and described with
reference to certain exemplary embodiments thereof, it will be
understood by those skilled in the art that various changes in form
and details may be made therein without departing from the spirit
and scope of the invention as defined by the appended claims.
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