The present application is based on Japanese patent application No. 2011-062044 filed on Mar. 22, 2011, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
This invention relates to a capacitance detecting device and, in particular, relates to capacitance detecting device having a function of detecting the presence or absence of a noise.
2. Description of the Related Art
A capacitance detecting device is known that can prevent a false detection caused by an influence of electromagnetic noise. The capacitance detecting device includes a detecting electrode configured to detect a capacitance and a noise detecting electrode configured to detect an influence of the electromagnetic noise based on the capacitance, and has a configuration that detection by the detecting electrode is forbidden when a capacitance (a first count value) detected by the detecting electrode exceeds a predetermined first upper limit and a capacitance (a second count value) detected by the noise detecting electrode exceeds a predetermined second upper limit (for example, refer to JP-A-2008-80952).
As disclosed in JP-A-2008-80952, the noise detecting electrode for detecting the electromagnetic noise is equipped in addition to the detecting electrode for detecting the capacitance, such that the capacitance detecting device can be insusceptible to the electromagnetic noise.
However, the capacitance detecting device of JP-A-2008-80952 has a problem that it is highly constrained in design since it needs to have the additional noise detecting electrode other than the detecting electrode, and to provide the noise detecting electrode with the same characteristic such as easiness to receive a noise as the detecting electrode, e.g., by placing it adjacent to the detecting electrode.
Accordingly, it is an object of the invention to provide a capacitance detecting device that is capable of accurately detecting the presence or absence of a noise without the additional noise detecting electrode.
(1) According to one embodiment of the invention, a capacitance detecting device comprises:
a detecting electrode to form a capacitance;
an electrical current supply part to supply electrical current to the detecting electrode; and
a control part to set different conditions of the electrical current supplied from the electrical current supply part to the detecting electrode, and judge a presence or absence of an electromagnetic noise at the detecting electrode based on an output value of the detecting electrode under the different conditions.
In the above embodiment (1) of the invention, the following modifications and changes can be made.
(i) The control part comprises a comparison portion to compare the output values of the detecting electrode under the different conditions, and changes a threshold value in the comparison of the comparison portion.
(ii) The control part measures a time until the output value reaches the threshold value, and compares the measured time in the comparison portion so as to judge the presence or absence of the electromagnetic noise.
(iii) The control part determines the absence of the electromagnetic noise when the measured time is changed in proportion to amount of the change in the threshold value.
(iv) The control part determines the presence of the electromagnetic noise when the measured time is not changed in proportion to amount of the change in the threshold value.
(v) The threshold value comprises not less than three threshold values.
(vi) The capacitance detecting device is used as a capacitance type touch sensor or switch module.
Points of the Invention
According to one embodiment of the invention, a capacitance detecting device is constructed such that a threshold value (electrode voltage) is set to be different values such as values (Vth), (Vth/2) in case of comparing the electrode voltage (VEL) of a detecting electrode in a comparator, and the presence or absence of a noise is judged based on plural comparison results. Thus, noise detection at the detecting electrode can be performed without any additional hardware such as an electrode for detecting only a noise.
The preferred embodiments according to the invention will be explained below referring to the drawings, wherein:
Configuration of Capacitance Detecting Device 10
Here, the presence or absence of an electromagnetic noise means a state that an electromagnetic noise is applied or not applied to the detecting electrode 100 by an influence of circumference environment. In addition, the state of presence of an electromagnetic noise means a state that the measurement accuracy of the capacitance value is lowered so as to cause an adverse effect such as a false operation in the measurement of capacitance detection of the detecting electrode 100.
The detecting electrode 100 has a configuration that conductive members having a plate-like shape are arranged so as to face each other, and one electrode is connected to a ground level and another electrode is connected to an input terminal of a comparator OP1, a switch element SW1 configured to carry out a switching control of discharge and charge and the electrical current supply part 110 configured to charge. Here, in case that a constant electrical current (ICH) is supplied to the detecting electrode 100 in which electrical charge is zero so as to charge the detecting electrode 100, and a time (TC) until reaching a setting voltage (threshold value) (Vth) is measured, the capacitance (C) of the detecting electrode 100 is calculated by a formula of (C)=(ICH)×(TC) (Vth).
As shown in
The timer (timer counter) TM1 is configured to measure a time between a time when the charge to the detecting electrode 100 is started and a time when the electrode voltage (VEL) of the detecting electrode 100 reaches a setting voltage (threshold value) of the comparator OP1. In the embodiment, a timer housed in the microcomputer M1 is used, but a timer installed externally can be also used.
The comparator OP1 compares the electrode voltage (VEL) of the detecting electrode 100 and the setting voltage (threshold value) so as to output the output (VC) of the comparator that is inverted, and is connected to an input part of the timer TM1. The setting voltage (threshold value) of the comparator OP1 is appropriately changed to the threshold value (Vth), the threshold value (Vth/2) or the like by the microcomputer M1 so as to be set.
Further, a switching part (not shown) that is to be connected to the detecting electrode 100 only at the time of the charge to the detecting electrode 100 is installed in the electrical current supply part 110. In addition, as the electrical current supply part 110, an electrical current source that is capable of supplying a predetermined charge to the detecting electrode 100 during a predetermined period can be also used other than the constant electrical current source.
In
On the other hand, in a state that an electromagnetic noise is applied to the detecting electrode 100, as shown in
In a state that the noise is absent, from
Namely, in case that the threshold value of the comparator OP1 is a voltage (Vth), from
(C)=(ICH)×(TC)/(Vth)
In addition, in case that the threshold value of the comparator OP1 is a voltage (Vth/2), from
(C)=(ICH)×(TC/2)/(Vth/2).
Accordingly, in a state that the noise is absent, in any calculation result, the calculated values of capacitance (C) correspond with each other.
On the other hand, in a state that the noise is present, from
Namely, in case that the threshold value of the comparator OP1 is a voltage (Vth), from
(C)=(ICH)×(TC−ΔTNZ)/(Vth)
In addition, in case that the threshold value of the comparator OP1 is a voltage (Vth/2), from
(C′)=(ICH)×(TC/2−ΔTNZ)/(Vth/2).
Accordingly, in a state that the noise is present, the results calculated by the two formulae do not correspond with each other. This is due to the fact that the charge to the detecting electrode 100 by the constant electrical current source is varied by changing the setting of the threshold value, but the noise component is not varied.
Judging Presence or Absence of Noise
When the noise judgment flow of the capacitance detecting device 10 is started, first, the microcomputer M1 switches the switching SW1 on, and discharges electrical charge accumulated in the detecting electrode 100 (Step 1 shown in
The microcomputer M1 judges whether a predetermined time (td) has passed from the turning on of the switch element SW1. The predetermined time (td) is the reference signal (clock) (V2) shown in
The microcomputer M1 turns the switch element SW1 off, and starts to charge the constant electrical current (ICH) from the electrical current supply part 110 to the detecting electrode 100 by using the rising of the reference signal (V2) as a trigger (Step 3 shown in
The microcomputer M1 sets the threshold value voltage of the comparator OP1 to a voltage (Vth) so as to measure a time (Tc) by the timer TM1 (Step 4 shown in
The microcomputer M1 judges whether the rising (inversion) of the output (VC) of the comparator OP1 has been detected. If it has been detected, the procedure proceeds to the next step, on the other hand if it does not have been detected, the procedure returns to Step 3 so as to continue the measurement by the timer (Step 5 shown in
The microcomputer M1 turns the switch element SW1 on, and discharges electrical charge accumulated in the detecting electrode 100 (Step 6 shown in
The microcomputer M1 judges whether a predetermined time (td) has passed from the turning on of the switch element SW1 (Step 7 shown in
The microcomputer M1 turns the switch element SW1 off, and starts to charge the constant electrical current (ICH) from the electrical current supply part 110 to the detecting electrode 100 by using the rising of the reference signal (V2) as a trigger (Step 8 shown in
The microcomputer M1 sets the threshold value voltage of the comparator OP1 to a voltage (Vth/2) so as to measure a time (Tc′) by the timer TM1 (Step 9 shown in
The microcomputer M1 judges whether the rising (inversion) of the output (VC) of the comparator OP1 has been detected. If it has been detected, the procedure proceeds to the next step, on the other hand if it does not have been detected, the procedure returns to Step 8 so as to continue the measurement by the timer (Step 10 shown in
The microcomputer M1 judges whether the time (Tc) measured in Step 4 is equal to the time (Tc′) measured in Step 9, namely whether a formula of Tc=Tc′ is satisfied (Step 11 shown in
In case of Tc=2Tc′, by a judgment of no noise, for example, a noise judgment signal Sn is output from the microcomputer M1 as Lo (noise is absent) and the procedure returns to Step 1 (Step 12 shown in
In case of Tc≠2Tc′, by a judgment of noise, for example, a noise judgment signal Sn is output from the microcomputer M1 as Hi (noise is present) and the procedure returns to Step 1 (Step 13 shown in
The above-mentioned series of steps are carried out repeatedly, and the judgment of the presence or absence of the noise is always carried out until an interrupt discontinuation signal is input.
Detection of Touch Operation to the Detecting Electrode 100
For example, in
In case that as mentioned above, the presence or absence of the touch operation to the detecting electrode 100 is judged, the judgment of the presence or absence of the noise shown in the above-mentioned Step 1 to Step 13 is always carried out, thus the high accuracy judgment of the presence or absence of the touch operation can be carried out by that the judgment of the presence of the touch operation in case of the judgment of the presence of the noise is invalidated.
As shown in
In accordance with the capacitance detecting device 10 according to the embodiment of the invention, the following advantages can be provided.
(1) The capacitance detecting device 10 has a configuration that the setting threshold value is set to different values such as values (Vth), (Vth/2) in case of comparing with the electrode voltage (VEL) of the detecting electrode 100 in the comparator OP1, and the judgment of the presence or absence of the noise is carried out based on a plurality of the comparison results. Consequently, the noise detection can be carried out without adding a new hardware such as an electrode for noise detection only for the noise detection.
(2) Since the noise detection is carried out by the detecting electrode 100, the problem can be eliminated, that conditions such as ease of reception of a noise are varied by that the installation places are different from each other, for example, the problem caused by that an electrode for noise detection is installed separately can be eliminated. Due to this, it is not needed to adjust the conditions such as ease of reception of a noise, thereby the detection of the presence or absence of the noise can be easily carried out with a high degree of accuracy.
Although the invention has been described with respect to the specific embodiments for complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art which fairly fall within the basic teaching herein set forth. For example, the presence or absence of the noise can be also judged by means such as comparison of the values of integral of the electrode voltage (VEL) at a predetermined time, instead of comparison judgment of the times (TC), (TC′) measured by a timer based on the output of the comparator OP1. In addition, in the embodiment, the comparison in the comparator OP1 is carried out by varying the threshold value to the two kind of values (Vth), (Vth/2), but not limited to this, a plurality of comparisons based on not less than tree threshold values can be also carried out, thereby the detection of the presence or absence of the noise can be carried out with a higher degree of accuracy.
Number | Date | Country | Kind |
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2011-062044 | Mar 2011 | JP | national |