JP2009193139A - Proximity detector and detection method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a proximity detector for detecting an accurate position by eliminating the influence of noise with a relatively simple configuration in a proximity sensor for detecting the approach of an object by the capacitance of an electrode. <P>SOLUTION: By adding an internal capacitor to a differential electrode, capacitance is obtained from the frequency of a comparison oscillation means obtained by compositing three feedbacks, thus detecting the difference in the capacitance of the differential electrode by in-phase charge/discharge and the sum of the capacitance by inverse-phase charge/discharge by the similar operation and accurately detecting the capacitance of individual element electrodes of the differential electrode. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a proximity detection apparatus and method for detecting the approach and position of an object such as a human finger by electrostatic capacitance.

  It is known that when an object having a capacitance such as a person approaches the electrode, the apparent capacitance of the electrode increases. By applying this principle, proximity detection devices such as electrostatic touch sensors have been put into practical use.

  In such a proximity detection device, in order to detect the capacitance of the electrode, the apparent capacitance of the electrode is obtained from the relationship between the voltage and charge during charging or discharging of the electrode. However, since the increase in the capacitance of the electrode due to the approach of a person or the like is a minute value of about 1 pF, an accurate capacitance that removes noise from the characteristics of one-time charge or discharge to the capacitance of the electrode. It is difficult to seek. For this reason, it is common to improve the detection accuracy of capacitance by accumulating charge / discharge characteristics by repeatedly charging / discharging the electrode by applying an alternating current or switching a switch (for example, Patent Document 1).

  In the conventional proximity detection apparatus, a method of detecting the approach of an object based on a difference in capacitance with a reference electrode by differential detection is widely used in order to remove the influence of noise on the electrode.

  However, when a display device and a transparent proximity detection device are used in an overlapping manner, if the display region and the detection region of the proximity detection device are substantially the same and the reference electrode is arranged at a position different from the display region, There was a problem that noise could not be removed efficiently. Further, when the reference electrode is arranged in the detection region, there is a problem that the capacity of the reference electrode also changes due to the approach of the object and cannot be removed accurately.

In order to solve this problem, there is a method for detecting the capacitance obtained by removing each noise of the differential electrode from the capacitance difference of the differential electrode due to the in-phase charge / discharge differential and the sum of the capacitance due to the reverse phase charge / discharge differential .
JP-A-8-194025

  However, the conventional method using both in-phase charge / discharge differential and reverse-phase charge / discharge differential, as shown in FIG. 2, accumulates charge repeatedly charged in the differential electrode in a capacitor having a large capacitance, Since the capacitance was detected by the voltage of the storage capacitor, a large-capacity capacitor was required, and it was a problem when trying to configure it inexpensively by saving space using an integrated circuit etc. .

  There was also a method of applying an AC waveform to the differential electrode and obtaining the capacitance from the voltage drop due to the filter using the capacitance of the differential electrode, but this method uses a sinusoidal oscillation circuit or filter circuit. In addition, analog circuits such as a detection circuit and an A / D conversion circuit are necessary, and there is a problem that the circuit scale increases.

  As described above, the conventional proximity detection apparatus and method have a problem that the circuit scale becomes large. Accordingly, an object of the present invention is to solve this problem and to realize a proximity detection apparatus or method that can remove noise without using a reference electrode with a relatively simple configuration.

  A proximity detection device according to the present invention includes a differential electrode that detects an approach of an object as a change in capacitance, a capacitance detection means that determines a capacitance of the differential electrode, and an object that is assumed from the capacitance. Proximity calculation means for detecting the approach of. The capacitance detecting means compares the difference waveform obtained by the subtracting means for obtaining a difference between the terminal waveforms of the differential electrodes and the difference waveform obtained by the subtracting means, and applies feedback to both terminals of the differential electrodes by resistors. And a measurement means for obtaining a value corresponding to the period of the oscillation waveform from the comparison oscillation means.

  According to the present invention, it is possible to realize a proximity detection apparatus or method that removes noise without using a reference electrode with a relatively simple configuration.

  A proximity detection device according to the present invention includes a differential electrode that detects an approach of an object as a change in capacitance, a capacitance detection means that determines a capacitance of the differential electrode, and an object that is assumed from the capacitance. It is comprised with the proximity calculating means which detects approach of these. The capacitance detecting means compares the difference waveform obtained by the subtracting means for obtaining the difference between the terminal waveforms of the differential electrodes and the subtracting means, and applies feedback to both terminals of the differential electrode by resistance. And a measurement means for obtaining a value corresponding to the period of the oscillation waveform from the comparison oscillation means.

  A preferred embodiment of the present invention will be described with reference to FIG.

  In FIG. 1, a differential electrode 1 is composed of a positive element electrode and a negative element electrode as in a conventional proximity detection device, and increases the apparent capacitance when an object to be detected approaches.

  The electrostatic capacitance detection means 2 detects the sum and / or difference of the electrostatic capacitances of the positive and negative element electrodes constituting the differential electrode. However, the capacitance here does not necessarily need to be an absolute value of the capacitance. This is because, for proximity detection, it is only necessary to obtain a value that changes in accordance with a change in capacitance such as the period of the oscillation waveform.

  In the proximity calculation means 3, when the value of the capacitance obtained by removing the noise obtained by the capacitance detection means becomes larger than a preset value, it is detected as an approach of an object assumed in advance.

  Further, the capacitance detecting means 2 includes a subtracting means for removing noise common to both the elementary electrodes, a comparator having hysteresis characteristics, a comparative oscillating means for oscillating by a feedback resistor, and an oscillation waveform from the comparative oscillating means. Measuring means for obtaining a value corresponding to the capacitance, such as the period of. Here, since the positive element electrode and the negative element electrode are arranged in the vicinity, the influence of the external noise is also similar, so that the noise is largely removed by the subtracting means.

  An example of the internal configuration of this capacitance detection means is shown in FIG. In the example of FIG. 4, since the negative phase oscillation waveform is applied to the positive elementary electrode 4 and the negative elementary electrode 5 via a resistor, subtraction by the subtracting means 6 is performed while removing noise. A charge / discharge waveform corresponding to the capacitance of both element electrodes or the sum of the changes can be obtained.

  Here, the comparison oscillation means 15 includes, for example, a comparator 7 having hysteresis characteristics as shown in FIG. 5, a feedback resistance Rp (8) to the positive element electrode, and a feedback resistance Rm (9) to the negative element electrode. And composed. The feedback here is a negative feedback on both the positive and negative electrode sides in order to oscillate stably. Further, the values of the feedback resistors Rp and Rm are set so that the time constant due to the positive element electrode and the feedback resistor Rp is substantially the same as the time constant due to the negative element electrode and the feedback resistor Rm.

  Although the measuring means 10 obtains the period of the oscillation signal by counting the clock, it goes without saying that the frequency may be obtained by counting the oscillation signal for a certain period.

  Another example of the capacitance detection means is shown in FIG. In the example of FIG. 6, the positive electrode 4 and the negative electrode 5 are charged and discharged in the same phase and subtracted to detect the difference in capacitance between the two electrodes from which noise has been removed. It is. However, in this case, since the charge and discharge to both element electrodes are in phase, the basic oscillation waveform itself is removed simultaneously with the removal of noise by subtraction. Accordingly, the waveform from the subtracting means 6 is only a component corresponding to the difference in capacitance between the two elementary electrodes. For this reason, as shown in FIG. 7, the comparison oscillation means 15 is provided with a feedback resistor Ri (12) and a capacitor Ci (13), and feeds back to the comparator 7 via the adder 16. Even when the capacitances of both the element electrodes are exactly the same and the output of the subtracting means 6 is always 0, oscillation is performed. In other words, the feedback by the feedback resistor Ri is a negative feedback and always oscillates stably.

  Here, for example, when the charge and discharge of the capacitor Ci and both element electrodes are in phase, and the subtraction means subtracts the charge / discharge waveform of the negative element electrode from the charge / discharge waveform of the positive element electrode, The feedback resistor Rp (8) is a negative feedback like the feedback by the feedback resistor Ri (12) to the capacitor Ci (13), and the feedback by the feedback resistor Rm (9) to the negative element electrode is subtracted. Therefore, it is a positive feedback. Two of the same three feedbacks are negative feedback, one is positive feedback, and the negative feedback is strong, so that it oscillates stably.

  In this case, for example, when an object to be detected approaches the positive elementary electrode and the capacitance becomes larger than that of the negative elementary electrode, the polarity of the feedback to the positive elementary electrode and the capacitor Ci is the same. The oscillation period becomes longer as if becomes larger. Conversely, when the negative element electrode becomes larger, it can be considered that the subtraction means has multiplied by −1. Therefore, the polarity of the feedback to the negative element electrode and the capacitor Ci is opposite. It works to shorten the oscillation period.

  However, this relationship is based on the premise that the time constant due to the feedback resistor Ri and the capacitor Ci is substantially the same as the time constant due to the capacitance of the two electrodes and the feedback resistors Rp and Rm. Specifically, if the ratio of these three values is larger than 0.5 times and smaller than 2.0 times, it functions effectively.

  Note that the multiplication means 14 in FIG. 6 can change the sensitivity for detecting the difference in capacitance between the two elementary electrodes by further multiplying the subtracted waveform by a coefficient. However, this multiplication means is not always necessary, and may be provided only when it is desired to change the sensitivity. Further, this multiplication means is not necessarily provided after subtraction, and it is the same even if it is provided before subtraction by the subtraction means.

  Moreover, the measuring means in FIG. 6 is the same as the measuring means in FIG.

  Still another example of the capacitance detecting means is shown in FIG. In the example of FIG. 8, the charge and discharge in the same phase and the charge and discharge in the opposite phase are performed on the positive and negative element electrodes in a time-sharing manner, and the capacitance of both element electrodes from which noise is removed by subtraction is obtained. The sum and difference are detected. This is because if both the sum and the difference are known, the capacitances of the positive and negative element electrodes can be easily obtained by addition and subtraction.

  Here, the configuration and operation for obtaining the difference in capacitance between the two elementary electrodes by in-phase charge / discharge are the same as in the example of FIG.

  However, in the case of reverse-phase charge / discharge, the following points are different from the example shown in FIG. In the case of the example shown in FIG. 4, there is no feedback resistor and capacitor inside the comparison oscillation means 15, and both feedbacks to both element electrodes are negative feedbacks. On the other hand, in the example of FIG. 8, even in the case of reverse phase charge / discharge, the feedback resistor Ri and the capacitor Ci are used as in the example of FIG. However, the feedback by the feedback resistors Rp (8) and Rm (9) to both element electrodes is a negative feedback, and the feedback by the feedback resistor Ri to the capacitor Ci is a positive feedback. By doing so, oscillation is caused by two negative feedbacks and one positive feedback, and the operations of the electrostatic capacity difference due to in-phase charging / discharging and the electrostatic capacity difference due to reverse phase charging / discharging become substantially the same. For this reason, the in-phase charge / discharge frequency and the reverse-phase charge / discharge frequency are almost equal, and the frequency change for the same capacity change is almost the same. By adding and subtracting from the sum, the capacitance of each elemental electrode can be calculated more accurately.

  Thus, in the case of in-phase charge / discharge, the feedback by the feedback resistors Rp, Rm to the both element electrodes is a negative feedback and the feedback in the comparison oscillation means is a positive feedback. One of the feedbacks by the feedback resistors Rp and Rm to the electrodes may be positive feedback, the other may be negative feedback, and the feedback inside the comparison oscillation means may be negative feedback. Whether to apply positive feedback or negative feedback is easily determined by connecting the positive logic output or the negative logic output of the comparator of the comparison oscillation means to each of the three feedback resistors Rp, Rm, Ri. Can be controlled. Alternatively, it goes without saying that the logic may be inverted by exclusive OR.

  The measuring means 10 in FIG. 8 is the same as the measuring means in FIG.

  In the above, for the sake of convenience of explanation, an example in which the subtracting means, the adding means, and the multiplying means are separated has been shown. However, these functions can be realized by changing the order or realizing them together by one arithmetic means. It goes without saying that any means and method that can be used may be used.

  In the above, the case of the proximity detection device that detects the approach of an object by the pair of differential electrodes shown in FIG. 1 has been described. Similarly, as shown in FIG. 3, by using a plurality of differential electrodes, It goes without saying that the present invention can be applied to a proximity detection device that can detect not only the approach but also the position.

  As described above, the proximity detection device according to the present invention is relatively simple without using a large-capacity accumulation capacitor or a complicated analog circuit by providing a stable oscillation means inside and synthesizing three feedbacks. With this configuration, it is possible to realize a proximity detection apparatus or method that can detect noise and accurately detect the approach and position of an object without the need for a reference electrode.

The block diagram which shows the 1st Example of the proximity detection apparatus which concerns on this invention Connection diagram of capacitance detection means of a conventional proximity detector The block diagram which shows the other Example of the proximity detection apparatus which concerns on this invention The block diagram which shows the example of the electrostatic capacitance detection means which concerns on this invention Connection diagram showing an example of a comparator according to the present invention The block diagram which shows the example of the electrostatic capacitance detection means which concerns on this invention Internal connection diagram showing an example of comparative oscillation means according to the present invention The block diagram which shows the example of the electrostatic capacitance detection means which concerns on this invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Differential electrode 2 Capacitance detection means 3 Proximity calculation means 4 Positive elementary electrode 5 Negative elementary electrode 6 Subtraction means 7 Comparator 8, 9, 12 Feedback resistance 10 Measuring means 13 Capacitor 14 Multiplication means 15 Comparative oscillation means 16 Adder

Claims (10)

A proximity detection device that detects the approach or position of an object by a change in capacitance of a differential electrode,
One or more differential electrodes that change the apparent capacitance due to the approach of the object;
Capacitance detecting means for detecting a value corresponding to the capacitance of the differential electrode;
Proximity calculation means for detecting the approach or position of the object from a value according to the capacitance,
The capacitance detecting means includes a subtracting means for obtaining a difference between the waveforms of the differential electrodes, a comparison oscillating means having a hysteresis characteristic for comparing the differences in the waveforms, and an output of the differential oscillating means. A proximity detection device comprising: first and second feedback resistors that charge and discharge each.   The capacitance detecting means includes a power storage means different from the differential electrode, and a third feedback resistor that charges and discharges the power storage means by an output of the comparative oscillation means. The proximity detection device according to 1.   Any one of the two feedbacks by the first and second feedback resistors to the differential electrode and the feedback by the third feedback resistor to the storage means is a positive feedback, and the other two are negative feedbacks. The proximity detection device according to claim 2, wherein   A capacitance of a positive elementary electrode constituting the differential electrode, a time constant due to the first feedback resistance to the positive elementary electrode, and a capacitance of a negative elementary electrode constituting the differential electrode, Among the time constant due to the second feedback resistance to the negative element electrode, and the longest time constant among the capacitance of the power storage means and the time constant due to the third feedback resistance to the power storage means, 3. The proximity detection apparatus according to claim 2, wherein a ratio with a short time constant is larger than 0.5 times and smaller than 2.0.   The proximity detection apparatus according to claim 1, wherein the capacitance detection unit includes a multiplication unit. A proximity detection method for detecting the approach or position of an object by a change in capacitance of a differential electrode,
A capacitance detecting step of detecting a value corresponding to the capacitance of the differential electrode or electrodes that change the apparent capacitance due to the approach of the object;
A proximity calculation step of detecting the approach or position of the object from a value according to the capacitance,
The capacitance detection step includes a subtraction step for obtaining a difference in waveform of the differential electrode, a comparison oscillation step for comparing the waveform difference to oscillate, and an output of the comparison oscillation step for each of the differential electrodes. And a step of charging and discharging via a feedback resistor.   The proximity detection method according to claim 6, wherein the capacitance detection step charges / discharges the output of the comparison oscillation step to a power storage unit different from the differential electrode via a feedback resistor.   8. One of two feedbacks by a feedback resistor to the differential electrode and feedback by a feedback resistor to the power storage means is a positive feedback, and the other two are negative feedbacks. The proximity detector described in 1.   A capacitance of a positive elementary electrode constituting the differential electrode, a time constant due to the first feedback resistance to the positive elementary electrode, and a capacitance of a negative elementary electrode constituting the differential electrode, Among the time constant due to the second feedback resistance to the negative element electrode, and the longest time constant among the capacitance of the power storage means and the time constant due to the third feedback resistance to the power storage means, The proximity detection method according to claim 7, wherein a ratio with a short time constant is larger than 0.5 times and smaller than 2.0.   The proximity detection method according to claim 6, wherein the capacitance detection method includes a multiplication step.

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