JP2014230226A - Capacitive coupling type electrostatic sensor - Google Patents

Abstract

In a touch switch that converts a change in capacitance into a frequency by a C / F conversion circuit, it is possible to prevent malfunction caused by synchronization or interference due to radio wave noise or power noise that is the same as or close to the generated frequency. Synchronous oscillation circuits (5, 6) for converting a signal generated by an oscillator (4) into a synchronized sin signal and a cos signal, respectively, and a member (101) forming an impedance and an electrode for connecting to the member And a current / voltage conversion circuit 15 that converts a current flowing through the member and the electrode into a voltage, and generates a DC signal by multiplying the converted voltage by the sin signal and the cos signal, respectively. Multiplying circuits 19 and 20 and low-pass filter circuits 21 and 22 for stabilizing the DC signal, respectively, and comparing the stabilized DC signal with a threshold value stored in advance in an arithmetic unit, Determine whether the touch switch is on or off. [Selection] Figure 2

Description

  The present invention relates to an input device using a capacitive coupling method as an input method.

Conventionally, a touch switch is known as an input device using a capacitive coupling method. The capacitive coupling touch switch includes a panel switch and a control board. Panel switches are made of acrylic film, glass or resin, and electrode films with silver paste or ITO (indium tin oxide) printed on the surface of the film (polyethylene terephthalate film: PET film) as switch electrodes. It is comprised of what is bonded to an insulating base material such as an adhesive (double-sided tape or the like). When a finger or hand approaches the switch electrode, a parallel plate capacitor is formed between the switch electrode and the finger or hand, and capacitance is generated. This change in capacitance is converted to a frequency by a C / F conversion circuit (a circuit that converts capacitance C to frequency F) formed by a capacitor C and a resistor R, and the frequency is converted into an input capture function (number of frequencies). Is replaced with digital data, and the on / off state of the touch switch is determined by arithmetic processing. When there are a plurality of switch electrodes, the selection of the switch electrodes is performed by a switching circuit provided for each switch electrode (see JP-A-2005-049882).
The touch switch using the capacitive coupling method uses a region that can be touched by a finger or hand through an insulating base material such as acrylic, glass, or resin as a switch electrode, and the finger or hand approaches the switch electrode. This is a digital input device that detects on / off of a touch switch.
The switch electrode is formed by printing an electrically conductive material on the surface of the PET film by a screen printing method to form an electrode film. Screen printing is a printing method that forms an image pattern by extruding ink using a squeegee (rubber spatula or metal spatula) from the space (screen plate) between the yarns called opening. Screen printing has long been rooted in Japan as a traditional craft such as printing and printing.
Further, the thickness of the completed image pattern is the same as the thickness of the screen plate used. Currently, screen printing has been established as an indispensable method in the electronics field, and screen printing is always used in the production of printed wiring boards, electronic components, flat panel displays, and automobile meters. It is known.

The switch electrode is printed on the surface of the PET film using a silver paste ink (substance is silver) ink or ITO (indium oxide) (substance is tin) ink by screen printing. Forming. The screen plate for forming the switch electrode has a thickness of 10 to 30 μm. Silver paste ink, which is a conductive material used in the screen plate, has a small resistance value, but still has an area resistance of several Ω to several hundred Ω / cm 2. Similarly, in the case of ITO (indium tin oxide) ink which is a conductive material, the resistance value is high and has an area resistance of several Ω to several kΩ / cm 2.
The switch electrode printed by the screen printing method has a printing speed determined by the moving speed of the squeegee, the viscosity of the ink, the expansion and contraction of the plate depending on the printing environment, and the size and thickness of the switch electrode for each printing are in units of several mm. It is said that it is difficult to make the variation in size and thickness zero by a difference of several μm. Therefore, the resistance value of the switch electrode for each printing is not constant, and it is difficult to suppress the variation in the resistance value for each printing to 0Ω.

  The frequency when a switch in which a switch electrode is formed on the electrode film is used as an input area of the touch switch can be expressed by t = 0.7 × C × R by the capacitor C and the resistor R. The switch electrode has a resistance value of ΔR. The frequency of the switch electrode is generated as a frequency obtained by adding the resistance value ΔR of the switch electrode to the resistance R. The frequency t can be expressed by t = 0.7 × C × (R + ΔR).

As shown in FIG. 1, the frequency when there are four switch electrodes will be obtained. When the switch switches of the switch electrodes are SW1 to SW4, the resistance values can be expressed as SW1 (resistance value: ΔR1), SW2 (resistance value: Δ2), SW3 (resistance value: Δ3), SW4 (resistance value: Δ4). The frequency of each switch electrode is SW1 frequency t = 0.7 × C × (R + ΔR1)
SW2 frequency t = 0.7 × C × (R + ΔR2)
SW3 frequency t = 0.7 × C × (R + ΔR3)
SW4 frequency t = 0.7 × C × (R + ΔR4)
It can be expressed as
Further, there is a variation in resistance value in units of several ohms to several tens of ohms for each screen printing. When the resistance value of variation is Δr, each frequency for each printing is SW1 frequency t = 0.7 × C × (R + Δ1 + Δr).
SW2 frequency t = 0.7 × C × (R + Δ2 + Δr)
SW3 frequency t = 0.7 × C × (R + Δ3 + Δr)
SW4 frequency t = 0.7 × C × (R + Δ4 + Δr)
It can be expressed as
In recent years, electronic circuits using digital technology have been widely used, and radio wave interference due to frequencies from low to high of digital signals is likely to occur.
For example, if you bring a radio receiver to the side of an appliance such as a TV, you will get noise and noise. This is because the radio receiver picks up the radio noise generated from the appliance.
In addition, when AC power is supplied to a radio receiver, noise may be mixed into the AC power line and picked up as power noise depending on the wiring of the household power supply. When an electric appliance such as a TV and a radio receiver are connected to the same AC power outlet, the radio receiver picks up the power supply noise generated from the connected electric appliance and the radio does not sound due to the noise. Cause malfunctions.
As countermeasures against the noise contamination in the living environment, there are countermeasures for preventing noise from being mixed into the device, or countermeasures for improving noise resistance so as not to cause a failure even when receiving noise.

However, under the living environment, since it is not known what kind of noise is mixed in the equipment, it is difficult to take measures against noise.
The method of converting the change in capacitance into a frequency by a C / F conversion circuit is to convert the change in capacitance into C
The frequency is converted into a frequency (t = 0.7 × C × (R + ΔR)) by the / F conversion circuit, and the change in the frequency is replaced with digital data by the input capture function. Since this system is operated using frequencies, the influence of mixing of frequencies, which are noises generated in the living environment, is unavoidable.

  In addition, the frequency generated when the electrode film in which the switch electrode is printed on the film is used as a touch switch in a method of converting the change in capacitance into a frequency using a C / F conversion circuit, It can be seen that different switch electrodes have different frequencies depending on the shape of the switch electrodes.

JP 2005/084982 A

In Patent Document 1, the change in capacitance is converted to a frequency by a C / F conversion circuit, and the frequency obtained by the switch electrode is the same as the radio noise or supply power that is the same or close to the frequency obtained by the switch electrode. Alternatively, when power supply noise having a close frequency is mixed, the frequency generated by the C / F circuit and the noise frequency are synchronized or interfere with each other. For this reason, the synchronization or interference between the frequency generated by the C / F circuit and the noise frequency becomes a state in which the capacitance does not change even when a finger or a person approaches the switch electrode, even though the finger touches the switch electrode. Therefore, the switch cannot be input, and a malfunction occurs.
Since the generated frequency of the switch electrode varies depending on the difference in size, the number of generated frequencies increases as the number of switch electrodes having different sizes increases. For this reason, malfunctions increase due to radio wave noise having the same frequency as the generated frequency or synchronization or interference due to power supply noise. In the method of converting the change in capacitance into a frequency by the C / F conversion circuit, the frequency of ± several tens KHz is not separated from the frequency of noise generated with respect to the frequency used by each switch electrode. Under the influence of noise, the frequency does not become a frequency at which the switch electrode is turned on even if the finger touches the switch electrode, and turned off even if the finger is released from the switch electrode.
For this reason, as the number of different frequencies used increases due to the difference in the size of the switch electrode, the range of frequencies at which the switch malfunctions due to the effect of noise widens, and countermeasures for preventing malfunctions due to the effect of noise are extremely important. It becomes difficult.

  In addition, the change in capacitance is replaced with digital data using the C / F conversion circuit, and the frequency is replaced with digital data by the input capture function (function for counting the number of frequencies), and the on / off state of the touch switch is determined by arithmetic processing. ing. By counting the number of frequencies with the input capture function, the number of frequencies changes for each switch electrode, and it is very difficult to keep the operation speed constant and increase the speed.

An electrode made of a conductive material is arranged on an insulator, and a signal generated by an oscillator is converted into a sin signal and a cos signal synchronized by a synchronous oscillation circuit, and the sin signal is applied to a member forming an impedance. Furthermore, the current applied to the electrode connected to the member, the current flowing through the member and the electrode is converted into a voltage by a current / voltage conversion circuit, the voltage converted by the current / voltage conversion circuit, and the sin signal And a cos signal are multiplied, the sin signal and the cos signal are converted into a DC signal by the multiplier circuit, the DC signal is stabilized by a low-pass filter circuit, and the stabilized DC signal By measuring the voltage and comparing the measured voltage with a threshold value stored in advance in the arithmetic unit, the touch switch is turned on or off. It proposes a capacitive coupling type electrostatic sensor for disconnection.

  In the present invention, even when switch electrodes having different resistance values are used, the true current value can be obtained by multiplying the output of the current / voltage conversion circuit by the multiplying circuit by the two of the sin signal and the cos signal having a phase difference of 90 degrees. Only the AC signal becomes a double AC frequency including the DC signal, and the double AC frequency disappears by passing through the low-pass filter, and only the DC signal is obtained. By measuring the DC signal, when the finger and the hand are separated from the switch electrode, that is, when the capacitance is small between the switch electrode and the finger and the hand, the finger and the hand are close to the switch electrode. In other words, when there is a large capacitance between the switch electrode and the finger and hand, the difference in the magnitude of the DC signal can be measured, and even if switch electrodes with different resistance values are used, the different frequencies Does not occur. Even when the switch electrode is connected, all the frequencies are higher than the frequency of the sin signal by multiplying by the multiplication circuit, and noise can be eliminated by passing the low-pass filter with the high frequency AC signal. For this reason, even if a noise frequency other than the frequency of the sin signal is mixed into the switch electrode, a capacitance is accurately generated between the switch electrode and the finger and hand, and the on / off state of the touch switch can be detected. it can.

  Furthermore, in order to detect mixing of the same noise frequency as the frequency of the sin signal, the occurrence of capacitance is detected without applying the sin signal to the switch electrode. When a change in capacitance is detected, it is determined that the same noise frequency is mixed, and the frequencies of the sin signal and the cos signal are changed.

  Moreover, the switch electrode of an electrode film used by the system which converts the change of an electrostatic capacitance into a frequency using a C / F conversion circuit can be used as a touch switch. That is, the minimum number of switch electrodes forming one touch switch can be used as one.

Switch electrode frequency. The input device block diagram of a present Example. The multiplication circuit waveform diagram of the present embodiment. The input signal level and phase difference diagram of a present Example. FIG. 4 is a diagram illustrating the relationship between a finger and a switch electrode during switch measurement according to the present embodiment. The sin signal multiplication waveform figure of a present Example. The input device block diagram at the time of the noise measurement of a present Example. The relationship figure of the finger | toe and switch electrode at the time of the noise measurement of a present Example. The general flowchart of a present Example. The memory block diagram of a present Example.

  In the present invention, even when switch electrodes having different resistance values are used, signals generated by an oscillator are transmitted as two sin signals by a synchronous transmission circuit and a cos signal having a phase difference of 90 degrees, and one of the sin signals is Via an amplifier circuit, an impedance is applied to a member (for example, a capacitor or a resistor), connected to the resistor R of the current / voltage conversion circuit via the member, and the amplified sin signal is Connect to the switch electrode to connect to. Panel switches are made of acrylic film, glass or resin, and electrode films with silver paste or ITO (indium tin oxide) printed on the surface of the film (polyethylene terephthalate film: PET film) as switch electrodes. It is comprised of what is bonded to an insulating base material such as an adhesive (double-sided tape etc.).

The other of the sin signals is connected to one of the two multiplication circuits, and the cos signal is connected to the other multiplication circuit. The output of the current / voltage conversion circuit is connected to two multiplication circuits via a band pass filter via an amplification circuit, and multiplied by a sin signal and a cos signal, respectively. Only an AC signal having a true current value has a double AC frequency including a DC signal, and becomes a DC signal by passing through a low-pass filter.
Noises other than the frequencies of the sin signal and the cos signal mixed into the switch electrode are all multiplied by the sin signal / cos signal to become an AC signal having a frequency higher than the frequency of the sin signal / cos signal. A DC voltage of 0 V can be obtained by passing through a low-pass filter sufficiently lower than the frequency.

Further, by controlling the frequency of the signal generated by the oscillator, the signal from the oscillator can be converted into a sin signal and a cos signal by the synchronous transmission circuit, and the frequency of the sin signal and the cos signal can be set. Since a bandpass filter can be provided to remove noise of harmonic components in the frequency band of the sin signal to be used, it is desirable to use a bandpass filter corresponding to the frequency of the sin signal.
Here, in an initialization state such as when the power is turned on, multiplication with the sin signal in a state where fingers and hands are sufficiently separated from the individual switch electrodes connected to the member connected to the member forming the impedance. From the detection signal Y obtained by multiplying the detection signal X by the cos signal and the cos signal, the vector value of the input signal is stored in the control device. The vector value at this time is called an offset value, the sine signal side is called an Xoffset value, and the cos signal side is called a Yoffset value. The offset value at this time is that a capacitor is formed between each switch electrode connected to a member (for example, a capacitor or a resistor) that constitutes an impedance for applying a sin signal via the amplifier circuit, and a finger and a hand. First, a member that forms an impedance in a state in which no current flows between each switch electrode and a finger, a hand, or the like, only a current that flows through the member that forms an impedance to which a sin signal is applied via an amplifier circuit. It is the value which measured the electric current which flows into.
When measuring the state of the finger and hand, etc. and the switch electrode, a capacitor is provided between the individual switch electrode that connects the sin signal that has passed through the amplifier circuit to the member that forms the impedance to be applied, and the finger and the hand. By being formed, a part of the current flowing through the member forming the impedance flows between the individual switch electrodes and the fingers and hands. The vector value of the input signal is stored from the detection signal X obtained by multiplication with the sin signal at that time and the detection signal Y obtained by multiplication of the cos signal. The difference between the vector value and the offset value is determined by the individual switch electrode and the finger and It is calculated by the formula route (square of (X-Xoffset) + square of (Y-Yoffset)) which is an alternative characteristic of the capacitance of the formed capacitor between the hand and the like.
If this calculated value is equal to or greater than the threshold value, it is determined that the touch switch is on, assuming that the finger and hand are close to the switch electrode. If the calculated value is equal to or less than the threshold value, the finger and hand are separated from the switch electrode. It is determined that the touch switch is off. Furthermore, by providing another threshold value, two threshold values corresponding to the on / off state of the touch switch before calculation can be used, and hysteresis control is performed on the on / off state of the touch switch with respect to the calculated value. It can also be done.
Similarly, other switch electrodes are also performed.
Here, in the case of measuring noise having the same frequency as the sin signal mixed into the switch electrode, the sin signal via the amplifier circuit is not applied to the individual switch electrodes connected to the impedance member and the impedance member. Measure in state. The offset value at that time is set to 0. At the time of measurement, the vector value of the input signal is changed from the detection signal Y obtained by multiplication with the sin signal to the expression signal (the square of X + the square of Y) from the detection signal Y obtained by multiplication of the cosine signal. When the value is equal to or greater than the value for determining the presence or absence of mixing, it is determined that noise is mixed and the frequency of the signal generated by the oscillator is changed.
Then, at the time of initialization, whether or not noise is mixed is determined as described above to determine whether or not there is noise of the same frequency as the sin signal that drives the switch electrode. In the case of noise mixing, the frequency of the signal generated by the oscillator is changed, the frequency of the sin signal and the cos signal is changed by the synchronous transmission circuit of the signal from the oscillator, and the presence / absence of noise mixing is determined again. If it is determined that there is no noise, the switch electrode is measured and the touch switch is turned on / off.

  Hereinafter, the present invention will be described in detail by way of examples. First, this embodiment will be described with reference to FIGS.

FIG. 2 shows a configuration diagram in the case of measuring on / off of the touch switch of the input device of this embodiment. First, the control device 2 sends signals to the CPU 3, the ROM 28 containing a program and constants (for example, a threshold), the RAM 29 containing a working memory, and the synchronous transmission circuits 5 and 6 that convert the signals into sin signals and cos signals. The oscillator 4 to be output, the switching circuit 8 for selecting the capacitors 101 to 104 for supplying the sin signal, the switch selection 27 for selecting the switches 81 to 84, and the switch electrode group to be connected when the capacitors 101 to 104 are selected 11 switch electrodes 111 to 114, a resistor 14 for measuring the current of the capacitors 101 to 104 and the switch electrodes 111 to 114, and a current-voltage conversion circuit 15 for detecting the voltage at both ends of the resistor 14 are connected to the switch 131. Switch selection circuit 26 for controlling the switching circuit 13 for selecting .about.134 and the switching circuit 13 A resistor 14 with one of which is GND connected to detect the current, a current-voltage conversion circuit 15 that detects a voltage across the resistor 14, an amplifier circuit 16 that amplifies the voltage of the current-voltage conversion circuit 15, and an amplifier circuit 16 And a switch selection 25 that controls the switching circuit 18 that selects any one of the band filters 171 to 173 of the bandpass filter circuit 17 corresponding to the frequency band of the sine signal from the bandpass filter circuit 17. And the sin signal from the synchronous transmission circuit 5 and the sin signal via any of the band filters 171 to 173 of the band pass filter circuit 17 are multiplied, and the signal via the low pass filter 21 is converted into digital data. The D conversion circuit 23, the cos signal from the synchronous transmission circuit 6, and the band pass filter circuit 17 The A / D conversion circuit 24 that multiplies the sin signal via any of the data 171 to 173 and converts the signal via the low-pass filter 22 into digital data, and the digital signals of the two A / D conversion circuits 23 and 24. It comprises an external I / F 30 that calculates data and outputs touch switch on / off information to the external processing device 31.
Therefore, in this embodiment, an example in which four touch switches are provided will be described. The input area 121 is an input area for generating a touch switch on / off information that is close to or away from the switch electrode 111 of the switch electrode group 11. Similarly, the input area 122 is close to the switch electrode 112. Or it is an input area for generating a separated state as on / off information of the touch switch, and the input area 123 is an input for generating a state close to or away from the switch electrode 113 as on / off information of the touch switch. The input area 124 is an input area for generating a state close to or away from the switch electrode 114 as on / off information of the touch switch. The user's finger 1 touches the switch electrodes 111 to 114 of the switch electrode group 11 printed with silver paste or ITO on the surface of the PET film constituting the panel switch 9. And the switch electrodes 111 to 114 are touched via a glass, resin, or the like.
In this embodiment, the input area and the switch electrode are described on a one-to-one basis. However, a plurality of switch electrodes may be used as one input area and may be generated as on / off information of one touch switch.
The description will be made assuming that the number of oscillation frequencies output from the oscillator 4 is three and the number of types of band-pass filters that pass the frequency band of the sin signal is three.
The oscillation frequency output from the oscillator 4 is set by the CPU 3 of the control device 2, and the signal output from the oscillator 4 is converted into a 90-degree phase difference between the sin signal and the cos signal from the two synchronous transmission circuits 5 and 6 and output. To do. When setting the oscillation frequency, any one of the bandpass filters 171 to 173 of the bandpass filter circuit 17 corresponding to the frequency band of the sin signal is controlled by the switch selection 25 to control the switches 181 to 183 of the switching circuit 18. Set to.
Then, the sin signal is connected by the amplifier circuit 7 to the switching circuit 8 for selecting a line to be applied to the switch electrodes 111 to 114 of the four switch electrode groups 11. A switch electrode group which controls the switching circuit 8 from the switch selection 27, selects any of the switches 81 to 84, applies to the capacitors 101 to 104 corresponding to the switches 81 to 84, and further connects via the capacitors 101 to 104. Also applied to the eleven switch electrodes 111-114. On the other hand, the capacitors 101 to 104 selected and applied and the switch electrodes 111 to 114 of the switch electrode group 11 are connected to the resistor 14 by controlling the switches 131 to 134 of the switching circuit 13 from the corresponding switch selection 26. . Then, although it is not described in GND or the present embodiment through the resistor 14, it is connected to a constant voltage such as a midpoint voltage of the sin signal to be applied, and the current flowing through the resistor 14 is measured.
At this time, the switch electrodes that are not connected are controlled by switching the switching circuit 8 from the switch selection 27 and the switching circuit 13 by the switch selection 26 so that they are left unconnected, or are applied although not described in this embodiment. Connect to a constant voltage such as the midpoint voltage of the sin signal.
The currents i1 to i4 flowing through the selected capacitors 101 to 104 and the switch electrodes 111 to 114 of the switch electrode group 11 are converted to voltages E1 to E4 by passing through the resistor 14, and amplified by the amplifier circuit 16. To do. Then, depending on the oscillation frequency output from the oscillator 4 by controlling the switching circuit 18 from the switch selection 25, it passes through any of the bandpass filters 171 to 173 of the bandpass filter circuit 17 corresponding to the band of the generated sin signal, Cut frequencies other than the passband of the sin signal frequency.
The frequency output from any of the bandpass filters 171 to 173 of the bandpass filter circuit 17 via the switching circuit 18 is input to the y side of the two multiplication circuits 19 and 20, respectively. A sin signal and a cos signal are input to the x side of the two multiplication circuits 19 and 20. As a result of the multiplication circuits 19 and 20 passing through the respective multiplication circuits 19 and 20, the noise signals are eliminated in the low-pass filters 21 and 22 that pass a very low frequency band, and a DC signal is taken out. . Each DC signal is converted into digital data by the A / D converters 23 and 24 of the control device 2 and input to the CPU 3. The CPU 3 inputs the digital data by sequentially controlling the switching circuit 8 and the switching circuit 13 via the switch selection 27 and the switch selection 26 in the order of the switch electrodes 111, 112, 113, and 114.

FIG. 3 (1) shows a waveform diagram of the multiplication circuits 19 and 20 in the case of measuring the on / off of the touch switch of this embodiment. A sin signal or a cos signal is input to the x-side inputs of the multiplication circuits 19 and 20. One side of the resistor 14 is connected to GND. The input on the y side includes a switching circuit 13, a resistor 14, a bandpass filter circuit 17, a sin signal that has passed through the amplifier circuit 7, a switching circuit 8, a switch electrode 111 of a switch electrode group 11 connected via a capacitor 101. Connection is made via the switching circuit 18.
For example, when a human finger or the like approaches the switch electrode 111 of the switch electrode group 11, the current i1 changes as the current flows from the switch electrode 111 of the switch electrode group 11 connected to the drive line via the finger or the like. Then, a change occurs in the potential difference E1 at both ends of the resistor 14, and the change is input to the y side of the multiplication circuits 19 and 20. The x-side and y-side input signals are multiplied, and only the AC signal of the true current value becomes a double AC frequency including the DC signal, and becomes a DC signal by passing through the following low-pass filters 21 and 22. Even if noise, which is another frequency component, is mixed into the switch electrode 111 of the switch electrode group 11, all noise frequencies are multiplied by the sin signal / cos signal into an AC signal having a frequency higher than that of the sin signal / cos signal. Therefore, the low-pass filters 21 and 22 that are sufficiently lower than the frequencies of the sin signal and the cos signal are not passed. In this way, it can be grasped that a human finger or the like is approaching the switch electrode 111.
FIG. 3B is a diagram in the case where a resistor R ′ is used instead of the capacitor 101 in FIG. If the impedance of the capacitor 101 and the resistor R ′ is the same, the value of the DC signal from the low-pass filters 21 and 22 differs from that of (1) in FIG. However, the magnitudes of the vectors are the same according to the equation in FIG.
FIG. 3 (3) is a diagram when the positions of the capacitor 101 and the electrode 111 in FIG. 3 (1) are changed. The operation is equivalent to (1) in FIG.

FIG. 4 shows the input signal level and phase difference diagram of the present invention. The input signal multiplied by the sin signal in the multiplication circuits 19 and 20 in FIG. 3 becomes a detection signal by sin through the low-pass filter 21, and the input signal multiplied by the cos signal becomes a detection signal by cos through the low-pass filter 22. become. Here, in a state of initialization such as when the power is turned on, a detection through the low-pass filter 21 is performed for multiplication with the sin signal in a state in which a human finger or the like is not in contact with the switch electrodes 111 to 114 of the switch electrode group 11. The signal X and the cos signal are multiplied from the detection signal Y by the low-pass filter 22 and measured via the A / D converters 23 and 24, and the measured value is used as a vector value. The value is called an offset value.
Then, the sin signal side of the offset value is the Xoffset value, and the cos signal side is the Yoffset value. When measurement is performed, the vector value and offset of the input signal are calculated from the detection signal X via the low-pass filter 21 and the detection signal Y via the low-pass filter 22 for multiplication with the sin signal at that time. The magnitude of the difference between the values is calculated as an equation root ((X−Xoffset) square + (Y−Yoffset) square). The phase difference is obtained from the formula arctangent ((X-Xoffset) / (Y-Yoffset)).
Obtaining and using the vector value and phase difference of the input signal is a very effective means for detecting position coordinates and the like that require accuracy.

  FIG. 5 shows the relationship between human fingers and switch electrodes. (1) in FIG. 5 is a case where the human finger is sufficiently separated from the switch electrode. Even if the human finger is sufficiently separated from the switch electrode 111 of the switch electrode group 11, a capacitance is generated between the finger and the switch electrode 101 of the switch electrode group A10. However, since there is a distance between the human finger and the switch electrode, the capacitance becomes very small, and the current Δi hardly flows from the switch electrode 111 of the switch electrode group 11 to the ground via the finger. As for the sin signal supplied via, current flows to the resistor 14 via the capacitor 101. Since the voltage of the sin signal from the current-voltage conversion circuit 15 that detects the voltage across the resistor 14 at this time is the same level as the initialization state at the time of power-on or the like, the subsequent amplifier circuit 16, band-pass filter circuit The signal that has passed through the multiplication circuits 19 and 20 and the low-pass filters 21 and 22 through the sine signal and the cos signal via any one of the 17 band filters 171 to 173 does not change from the initialization state when the power is turned on. .

FIG. 5 (2) shows a case where a human finger is close to the switch electrode 111.
The human finger and the switch electrode 111 of the switch electrode group 11 form a capacitor. Therefore, a capacitance is generated, and the current Δi starts flowing from the switch electrode 111 of the switch electrode group 11 to the ground via the finger. Loss Δi. Therefore, the sine signal supplied through the amplifier circuit 7 is turned on since the current Δi of a part of the current flowing through the resistor 14 flows from the switch electrode 111 to the ground through the capacitor 101 via the finger. The current is smaller than the initialization state such as time. The voltage of the sin signal from the current-voltage conversion circuit 15 that detects the voltage across the resistor 14 at this time has a smaller amplitude than the initial state when the power is turned on, and the subsequent amplifier circuit 16 and band-pass filter circuit. The amplitude of a signal that has passed through the multiplication circuits 19 and 20 and the low-pass filters 21 and 22 through any of the 17 band filters 171 to 173 and the low-pass filters 21 and 22 is greater than that of the initialization state when the power is turned on. Get smaller.

  The current i1 when the finger is sufficiently separated from the switch electrode 111 of the switch electrode group 11 is measured in advance, and the current i1 when the finger is close to the threshold is defined as the amount of change in current at which the touch switch 121 is turned on. Thus, it operates as a touch switch.

  FIG. 6 shows a sin signal multiplication waveform diagram. Multiplying a · sin α and b · sin α yields (a · sin α) · (b · sin α) = (a · b / 2) − (a · b · cos 2α) / 2, where only a · b / 2. Where added, there is a cos signal that is half the frequency doubled. If this calculation result passes through the low-pass filter 21 or 22 having a sufficiently low value, the cos signal becomes 0, and only a constant of a · b / 2 is obtained. Even if a noise frequency other than the frequency of a · sin α is mixed according to this equation, the noise frequency is cut and the influence of the noise frequency is eliminated.

  FIG. 7 is a configuration diagram of the input device in the case of measuring noise having the same frequency as the sin signal mixed into the switch electrode. The switches 81 to 84 of the switching circuit 8 are disconnected from the switch selection 27 in the configuration diagram of FIG. 2, and the sin signal is supplied from the amplifier circuit 7 to the capacitors 101 to 104 corresponding to the switches 81 to 84 of the switching circuit 8. The switch electrodes 111 to 114 of the switch electrode group 11 connected via 101 to 104 are not applied. In addition, the switch 131 of the switching circuit 13 is selected and connected from the switch selection 26, the other switches 132 to 134 are not connected, and the switch electrode 111 of the switch electrode group 11 is connected to the resistor 14 via the switch 131 of the switching circuit 13. The CPU 3 inputs digital data in a state of being connected to. FIG. 8 shows a relationship diagram when measuring noise having the same frequency as the sin signal mixed in the switch electrode in the state of FIG.

(1) in FIG. 8 is a case where there is no noise, and no current flows through the resistor 14. Therefore, the current-voltage conversion circuit 15, the amplification circuit 16, the band-pass filter circuit 17, the switching circuit 18, the multiplication circuits 19, 20 and the low-pass filter. The digital data to be measured is measured by the CPU 3 via the digital data 21 and 22 and the A / D converters 23 and 24.
(2) in FIG. 8 shows a case where there is noise having a frequency different from that of the sin signal. A current flows through the resistor 14, and the current-voltage conversion circuit 15, the amplification circuit 16, the band-pass filter circuit 17, the switching circuit 18, and the multiplication circuits 19, 20 However, the multiplication circuits 19 and 20 output only AC signals that do not contain a DC signal to the low-pass filters 21 and 22, but the low-pass filters 21 and 22 cut the AC signals. , 22 becomes GND, and the CPU 3 measures the GND digital data via the A / D converters 23, 24.
(3) in FIG. 8 is a case where there is noise having the same frequency as the sin signal, a current flows through the resistor 14, and the current-voltage conversion circuit 15, the amplification circuit 16, the band-pass filter circuit 17, the switching circuit 18, and the multiplication circuits 19, 20 The multiplication circuit 19 and 20 outputs an alternating current signal including a DC signal to the low-pass filters 21 and 22, the low-pass filters 21 and 22 cut the alternating current, and the low-pass filters 21 and 22 extract the DC signal. The CPU 3 measures the digital data via the A / D converters 23 and 24.

  Therefore, when the CPU 3 measures noise having the same frequency as that of the sin signal mixed in the switch electrode in FIG. 7, when the CPU 3 measures digital data other than the vicinity of the GND, the CPU 3 detects noise having the same frequency as that of the sin signal. The frequency of the sin signal and the cos signal is changed to a frequency different from the frequency of the noise by controlling the oscillation frequency of the oscillator 4, and the band-pass filter circuit 17 corresponding to the frequency band of the sin signal is used. Any one of the bandpass filters 171 to 173 is set by the switching circuit 18.

  The control flow will be described with reference to FIGS. 9 and 10. FIG. 9 shows the control flow of the first embodiment, and FIG. 10 shows the memory arranged in the ROM 28 and RAM 29 used for the control flow. First, the external I / F 30 connected to the external processing device 31 is initialized (S1) (S represents a step). Then, the variables H and I arranged in the RAM 29 are set to 0 (S2, S3).

Then, data of the I-th oscillation frequency in the data table HZ that stores three types of oscillation frequency data stored in the ROM 28 is set in the oscillator 4. Data for selecting one of the band filters 171 to 173 of the band-pass filter circuit 17 corresponding to the frequencies of the sin signal and the cos signal output from the two synchronous transmission circuits 5 and 6 is stored. The I-th data of the data table HZFIL is set to the switches 181 to 183 of the switching circuit 18 via the switch selection 25 (S4).
Next, in order to measure the digital data in the input area 121, the sin signal from the synchronous oscillator 5 from the oscillator 4 is applied to the switch electrode 111 of the switch electrode group 11 via the amplifier circuit 7 and measured. In the switching circuit 8 controlled via the switch selection 27, only the switch 81 is connected and controlled via the switch selection 26 so that the switch electrodes constituting the other touch switches are not applied and are not measured. In the switching circuit 13 to be set, only the switch 131 is connected and set. Then, the digital data through the A / D converter 23 measured by the sine signal from the synchronous transmitter 5 from the oscillator 4 and the A / D measured by the cos signal from the synchronous transmitter 6 from the oscillator 4 are used. The digital data via the D converter 24 is stored in the I-th one-dimensional array SW1_Xoffset and SW1_Yoffset arranged on the RAM 29 (S5).
Similarly, in order to measure the digital data in the input area 122, the sin signal from the synchronous oscillator 5 from the oscillator 4 is applied to the switch electrode 112 of the switch electrode group 11 via the amplifier circuit 7 and measured. In the switching circuit 8 controlled via the switch selection 27, only the switch 82 is connected and controlled via the switch selection 26 so that the switch electrodes constituting the other touch switches are not applied and are not measured. In the switching circuit 13 to be set, only the switch 132 is connected and set. Then, the digital data through the A / D converter 23 measured by the sine signal from the synchronous transmitter 5 from the oscillator 4 and the A / D measured by the cos signal from the synchronous transmitter 6 from the oscillator 4 are used. The digital data via the A / D converter 23 measured with the sin signal from the digital data via the D converter 24 is stored in the Ith of the one-dimensional arrays SW2_Xoffset and SW2_Yoffset arranged on the RAM 29 (S6). .
Similarly, in order to measure the digital data in the input area 123, the sin signal from the synchronous oscillator 5 from the oscillator 4 is applied to the switch electrode 113 of the switch electrode group 11 via the amplifier circuit 7 and measured. In the switching circuit 8 that is controlled via the switch selection 27, only the switch 83 is connected and control is performed via the switch selection 26 so that the switch electrodes constituting the other touch switches are not applied and are not measured. In the switching circuit 13 to be set, only the switch 133 is connected and set. Then, the digital data through the A / D converter 23 measured by the sine signal from the synchronous transmitter 5 from the oscillator 4 and the A / D measured by the cos signal from the synchronous transmitter 6 from the oscillator 4 are used. The digital data via the A / D converter 23 measured with the sin signal from the digital data via the D converter 24 is stored in the Ith of the one-dimensional arrays SW3_Xoffset and SW3_Yoffset arranged on the RAM 29 (S7). .
Similarly, in order to measure digital data in the input area 124, a sin signal from the synchronous oscillator 5 from the oscillator 4 is applied to the switch electrode 114 of the switch electrode group 11 via the amplifier circuit 7 and measured. In the switching circuit 8 controlled via the switch selection 27, only the switch 84 is connected and controlled via the switch selection 26 so that it is not applied to the switch electrodes constituting the other touch switches and is not measured. In the switching circuit 13 to be set, only the switch 134 is connected and set. Then, the digital data through the A / D converter 23 measured by the sine signal from the synchronous transmitter 5 from the oscillator 4 and the A / D measured by the cos signal from the synchronous transmitter 6 from the oscillator 4 are used. The digital data via the A / D converter 23 measured with the sine signal from the digital data via the D converter 24 is stored in the Ith of the one-dimensional arrays SW4_Xoffset and SW4_Yoffset arranged on the RAM 29 (S8). .
Similarly, in order to measure digital data of noise having the same frequency as the sin signal, the switch electrode 111 of the switch electrode group 11 is set for noise measurement. At this time, the sine signal from the synchronous oscillator 5 from the oscillator 4 is not applied to the switch electrode 111 via the amplifier circuit 7, but measurement is performed, the other switch electrodes are not applied, and In order to avoid measurement, the switches 81 to 84 are not connected in the switching circuit 8 controlled via the switch selection 27, and only the switch 131 is connected and set in the switching circuit 13 controlled via the switch selection 26. Then, the digital data through the A / D converter 23 measured by the sine signal from the synchronous transmitter 5 from the oscillator 4 and the A / D measured by the cos signal from the synchronous transmitter 6 from the oscillator 4 are used. The digital data via the D converter 24 is stored in the Ith of the one-dimensional arrays NOISE_Xoffset and NOISE_Yoffset arranged on the RAM 29 (S9). At this time, the digital data when there is no noise or noise having a frequency different from that of the sin signal indicates the digital data of GND_X and GND_Y in the vicinity of GND. The GND_X and GND_Y are arranged in advance on the ROM 28.
In S10, the value of the formula root ((NOISE_Xoffset I-th−GND_X) squared + (NOISE_Yoffset I-th−GND_Y) squared) is mixed with noise having the same frequency as the sin signal arranged on the ROM 28. If it is determined that it is equal to or greater than the threshold NOISE_MAX, the process proceeds to S12. If it is determined that the value is less, I is substituted for H (S11), and the process proceeds to S12.

Then, 1 is added to I (S12), and if I is less than 3, the process proceeds to S4, and if I is 3 or more, the process proceeds to S14. This loop from S3 to S13 represents calibration for measuring the offset value of the touch switch corresponding to the switch electrodes 111 to 124 corresponding to the three types of oscillation frequencies of the oscillator 4 when the power is turned on, and measuring noise. ing.
In S 14, the H-th oscillation frequency data in the data table HZ that stores three types of oscillation frequency data stored in the ROM 28 is set in the oscillator 4. Data for selecting one of the band filters 171 to 173 of the band-pass filter circuit 17 corresponding to the frequencies of the sin signal and the cos signal output from the two synchronous transmission circuits 5 and 6 is stored. The Hth data in the data table HZFIL is set to the switches 181 to 183 of the switching circuit 18 via the switch selection 25.

These S2 to S14 are steps for selecting a frequency free from noise having the same frequency as that of the sin signal at the time of activation.
In S15, the switch electrode 111 of the switch electrode group 11 is set for noise measurement in order to measure digital data of noise having the same frequency as the sin signal. At this time, the sine signal from the synchronous oscillator 5 from the oscillator 4 is not applied to the switch electrode 111 via the amplifier circuit 7, but measurement is performed, the other switch electrodes are not applied, and In order to avoid measurement, the switches 81 to 84 are not connected in the switching circuit 8 controlled via the switch selection 27, and only the switch 131 is connected and set in the switching circuit 13 controlled via the switch selection 26. Then, the digital data through the A / D converter 23 measured by the sine signal from the synchronous transmitter 5 from the oscillator 4 and the A / D measured by the cos signal from the synchronous transmitter 6 from the oscillator 4 are used. The digital data via the D converter 24 is stored in the Hth one-dimensional array NOISE_X, NOISE_Y arranged on the RAM 29. (S9)
S15 is a step of measuring noise having the same frequency as the sin signal.

  In S16, the value of the formula route ((NOISE_XHth-GND_X) square + (NOISE_YHth-GND_Y) squared) is mixed with noise having the same frequency as the sin signal arranged on the ROM 28. If it is less than the threshold NOISE_MAX and the value of the formula route (the square of (NOISE_Xoffset H th -GND_X) + (NOISE_Yoffset H th -GND_Y) square) is determined to be less than the threshold NOISE_MAX, the process proceeds to S17. In other cases, the process proceeds to S33.

Step S16 is a step of determining whether noise having the same frequency as that of the sin signal is mixed.
Next, in order to measure the digital data in the input area 121, the sin signal from the synchronous oscillator 5 from the oscillator 4 is applied to the switch electrode 111 of the switch electrode group 11 via the amplifier circuit 7 and measured. In the switching circuit 13 controlled only via the switch selection 27, only the switch 81 is connected to the other switch electrodes so as not to be applied and measured, and in the switching circuit 13 controlled via the switch selection 26. Only the switch 131 is connected and set. Then, the digital data through the A / D converter 23 measured by the sine signal from the synchronous transmitter 5 from the oscillator 4 and the A / D measured by the cos signal from the synchronous transmitter 6 from the oscillator 4 are used. The digital data via the D converter 24 is stored in the Hth one-dimensional array SW1_X, SW1_Y arranged on the RAM 29 (S17).
Similarly, in order to measure the digital data in the input area 122, the sin signal from the synchronous oscillator 5 from the oscillator 4 is applied to the switch electrode 112 of the switch electrode group 11 via the amplifier circuit 7 and measured. In the switching circuit 8 controlled via the switch selection 27, only the switch 82 is connected and controlled via the switch selection 26 so that the switch electrodes constituting the other touch switches are not applied and are not measured. In the switching circuit 13 to be set, only the switch 132 is connected and set. Then, the digital data through the A / D converter 23 measured by the sine signal from the synchronous transmitter 5 from the oscillator 4 and the A / D measured by the cos signal from the synchronous transmitter 6 from the oscillator 4 are used. The digital data via the A / D converter 23 measured with the sin signal from the digital data via the D converter 24 is stored in the Hth one-dimensional array SW2_X, SW2_Y arranged on the RAM 29 (S18). .
Similarly, in order to measure the digital data in the input area 123, the sin signal from the synchronous oscillator 5 from the oscillator 4 is applied to the switch electrode 113 of the switch electrode group 11 via the amplifier circuit 7 and measured. In the switching circuit 8 that is controlled via the switch selection 27, only the switch 83 is connected and control is performed via the switch selection 26 so that the switch electrodes constituting the other touch switches are not applied and are not measured. In the switching circuit 13 to be set, only the switch 133 is connected and set. Then, the digital data through the A / D converter 23 measured by the sine signal from the synchronous transmitter 5 from the oscillator 4 and the A / D measured by the cos signal from the synchronous transmitter 6 from the oscillator 4 are used. The digital data via the A / D converter 23 obtained by measuring the digital data via the D converter 24 using the sin signal is stored in the Hth one-dimensional array SW3_X, SW3_Y arranged on the RAM 29 (S19). .
Similarly, in order to measure digital data in the input area 124, a sin signal from the synchronous oscillator 5 from the oscillator 4 is applied to the switch electrode 114 of the switch electrode group 11 via the amplifier circuit 7 and measured. In the switching circuit 8 controlled via the switch selection 27, only the switch 84 is connected and controlled via the switch selection 26 so that it is not applied to the switch electrodes constituting the other touch switches and is not measured. In the switching circuit 13 to be set, only the switch 134 is connected and set. Then, the digital data through the A / D converter 23 measured by the sine signal from the synchronous transmitter 5 from the oscillator 4 and the A / D measured by the cos signal from the synchronous transmitter 6 from the oscillator 4 are used. The digital data via the A / D converter 23 measured with the sin signal from the digital data via the D converter 24 is stored in the Hth one-dimensional array SW4_X, SW4_Y arranged on the RAM 29 (S20). .
In S21, the value of the formula root ((SW1_XHth−SW1_XoffsetHth) squared + (SW1_YHth−SW1_YoffsetHth) squared) is equal to the switch electrode 111 with a finger and a hand nearby. If it is equal to or greater than the threshold SW1_ON_LEVEL arranged on the ROM 28 that is determined to be in contact, the process proceeds to S22, the touch switch SW1 corresponding to the switch electrode 111 is set to ON in the external I / F 30, and the process proceeds to S24. When it is less than the threshold SW1_ON_LEVEL, the process proceeds to S23, the touch switch SW1 corresponding to the switch electrode 111 is set to OFF in the external I / F 30, and the process proceeds to S24.
In S24, the value of the formula root ((SW2_XHth−SW2_XoffsetHth) squared + (SW2_YHth−SW2_YoffsetHth) squared) is the value when the finger and the hand touch the switch electrode 112 in the vicinity. If it is equal to or greater than the threshold value SW2_ON_LEVEL arranged on the ROM 28 that is determined to be present, the process proceeds to S25, the external I / F 30 is set to the touch switch SW2 corresponding to the switch electrode 112 being ON, and the process proceeds to S27. If it is less than the threshold SW2_ON_LEVEL, the process proceeds to S26, the external I / F 30 is set to the touch switch SW2 corresponding to the switch electrode 112 being OFF, and the process proceeds to S27.
In S27, the value of the formula root ((SW3_XHth−SW3_XoffsetHth) squared + (SW3_YHth−SW3_YoffsetHth) squared) is the value when the finger and the hand touch the switch electrode 113 in the vicinity. If it is equal to or greater than the threshold value SW3_ON_LEVEL arranged on the ROM 28 determined to be present, the process proceeds to S28, the touch switch SW3 corresponding to the switch electrode 113 is set to ON in the external I / F 30, and the process proceeds to S30. If it is less than the threshold SW3_ON_LEVEL, the process proceeds to S29, the external I / F 30 is set to the touch switch SW3 corresponding to the switch electrode 113 being OFF, and the process proceeds to S30.
In S30, the value of the formula root ((SW4_XHth−SW4_XoffsetHth) squared + (SW4_YHth−SW4_YoffsetHth) squared) is the value at which the switch electrode 114 finger and the hand are in contact with each other. If it is equal to or greater than the threshold value SW4_ON_LEVEL arranged on the ROM 28, it is determined that the touch switch SW4 corresponding to the switch electrode 114 is ON in the external I / F 30, and the process returns to S15. If it is less than the threshold SW4_ON_LEVEL, the process proceeds to S32, the external I / F 30 is set to the touch switch SW4 corresponding to the switch electrode 114 being OFF, and the process returns to S15.

These S17 to S32 are steps for measuring the switches.
Here, in S17 to S20, the sin side and cos side digital data corresponding to the switch electrodes 111 to 114 are temporarily stored in the FIFO buffer, and the digital data is measured a plurality of times and stored in the buffer. The average values obtained by subtracting the maximum value and the minimum value from the contents of SW1_X, SW1_Y, SW2_X, SW2_Y, SW3_X, SW3_Y, SW4_X, and SW4_Y are stored in the H-th to further cope with noise, so that the switch electrodes 111 to 114 The on / off information of the touch switches SW1 to SW4 corresponding to is improved.

  In S33, 1 is added to H. If H is less than 3, the process returns to S14. If H is 3 or more, H is set to 0 (S35), and the process returns to S14.

  These S33 to S35 and S14 are steps for changing the frequency of the sin signal to a different frequency when noise having the same frequency as the sin signal is mixed. In this embodiment, three different frequencies are sequentially changed, but the frequency may be changed using a random number.

1 finger 2 control device 3 CPU
DESCRIPTION OF SYMBOLS 4 Oscillator 5 Synchronous transmission circuit 6 Synchronous transmission circuit 7 Amplification circuit 8 Switching circuit 81 Switch 82 Switch 83 Switch 84 Switch 9 Panel switch 101 Capacitor 102 Capacitor 103 Capacitor 104 Capacitor 11 Switch electrode group 111 Switch electrode 112 Switch electrode 113 Switch electrode 114 Switch Electrode 121 Input area 122 Input area 123 Input area 124 Input area 13 Switching circuit 131 Switch 132 Switch 133 Switch 134 Switch 14 Resistance 15 Current-voltage converter 16 Amplifier circuit 17 Bandpass filter circuit 171 Bandpass filter 172 Bandpass filter 173 Bandpass Filter 18 switching circuit 181 switch 182 switch 183 switch 19 multiplication circuit 20 Calculation circuit 21 low-pass filter 22 low-pass filter 23 A / D converter 24 A / D converter 25 switch selection 26 switch selection 27 switch selection 28 ROM
29 RAM
30 External I / F
31 External processing device

Claims (1)

An electrode made of a conductive material is arranged on an insulator, and a signal generated by an oscillator is converted into a sin signal and a cos signal synchronized by a synchronous oscillation circuit, and the sin signal is applied to a member forming an impedance. Furthermore, the current applied to the electrode connected to the member, the current flowing through the member and the electrode is converted into a voltage by a current / voltage conversion circuit, the voltage converted by the current / voltage conversion circuit, and the sin signal And a cos signal are multiplied, the sin signal and the cos signal are converted into a DC signal by the multiplier circuit, the DC signal is stabilized by a low-pass filter circuit, and the stabilized DC signal By measuring the voltage and comparing the measured voltage with a threshold value stored in advance in the arithmetic unit, the touch switch is turned on or off. Capacitive coupling type electrostatic sensor, characterized in that the cross-sectional.

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