JP2006222022A - Capacitance type switch device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a capacitance type switch device a noise countermeasure for which can be achieved with a simple circuit and electrode configuration. <P>SOLUTION: Adjacent capacitance type switches are alternately connected to an input plus terminal and an input minus terminal of a differential amplifier 10. In this situation, even if the respective capacitance type switches are affected by exogenous noises and consequently output noise signals, the differential amplifier 10 can reject the noise signals and only detection signal output from the capacitance type switches for performing the detection can be detected. Therefore, a detection accuracy of the capacitance type switch is improved and an accurate stroke position of an electronic keyboard instrument can be detected. Consequently, since the noise signals caused by the exogenous noises can be rejected only by using the differential amplifier 10, a noise rejection device can be configured easily and the noise counter measure can be achieved inexpensively. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a capacitive switch device for detecting, for example, a keystroke of an input device such as a keyboard or an electronic keyboard instrument, and removes the influence of external noise.

Conventionally, as a device for detecting a keystroke of an input device such as a keyboard or an electronic keyboard instrument, there is one using a capacitive switch as described in, for example, Japanese Patent Application Laid-Open No. 9-204846. This capacitive switch is provided with a drive-side fixed electrode and a sense-side fixed electrode on a substrate, and a movable electrode connected on the drive-side fixed electrode and the sense-side fixed electrode (movable in response to pressing of a key) By pressing the electrode) toward the fixed electrode, an electrostatic capacity corresponding to the pressing stroke of the movable electrode is formed between the movable electrode and the sense-side fixed electrode. Based on this capacitance, it was detected that the key was pressed.
In addition, the drive-side fixed electrode and the sense-side fixed electrode (hereinafter simply referred to as a fixed electrode) of the capacitance type switch are planar electrodes having a predetermined size formed on the substrate, and are used to prevent external noise. easily influenced. For this reason, the capacitive switch is covered with a shield plate to prevent the influence of external noise.
JP-A-9-204846

  However, in the conventional noise countermeasures for the capacitance type switch, there is a problem that the structure for noise countermeasures becomes complicated, for example, it is necessary to provide a shield plate on the capacitance type switch. there were.

  In view of the above problems, an object of the present invention is to provide a capacitance type switch device that can achieve noise countermeasures with a simple circuit and electrode configuration.

  The present invention relates to a capacitance type switch device that detects a capacitance by sequentially inputting a trigger signal from a trigger signal output unit to a plurality of capacitance type switches whose capacitance changes in accordance with the amount of pressing. The input side positive terminal and the input side negative terminal have a differential amplifier that outputs the difference between the input signals input to the input side positive terminal and the input side negative terminal, and the adjacent capacitive switch The differential amplifier is alternately connected to the input side plus terminal and the input side minus terminal, and the output of the differential amplifier is used as the output of the capacitive switch to which the trigger signal is input.

According to the present invention, the adjacent capacitive switches are alternately connected to the input side plus terminal and the input side minus terminal of the differential amplifier, so that the noise signal is detected from the capacitance type switch to be detected due to the influence of external noise. Even when the is output, similar noise signals are also output from the adjacent capacitive switches due to the effects of external noise, so the signals output from these capacitive switches by the differential amplifier By taking the difference, only the noise signal is removed, and the capacitance detection circuit can detect the capacitance of the capacitance type switch based on the detection signal not including the noise signal.
As described above, since the noise signal due to the external noise can be removed using the differential amplifier, the noise countermeasure can be achieved with a simple circuit and electrode configuration.

Next, embodiments of the present invention will be described by way of examples.
The present embodiment is an example in which the capacitive switch device is applied to a switch for detecting a keystroke of an electronic keyboard instrument.
First, the capacitance type switch will be described.
FIG. 1 shows a cross section of the capacitive switch, and FIG. 2A shows only the fixed electrode of the capacitive switch.
On the substrate 2, a sense side fixed electrode 4 and a drive side fixed electrode 5 (hereinafter referred to as fixed electrodes 4 and 5) are formed. The fixed electrodes 4 and 5 are formed in a semicircular shape as shown in FIG. 2A, and the two fixed electrodes 4 and 5 face each other with their strings facing each other with a slight gap therebetween. Is placed on top.
The fixed electrodes 4 and 5 are covered with an insulator 3.

On the upper surface of the insulator 3, a movable electrode 6 formed of a spring is provided at a position corresponding to the fixed electrodes 4 and 5. The movable electrode 6 is covered with a rubber 7.
A key of an electronic keyboard instrument (not shown) is positioned above the rubber 7 in the figure, and when the key is pressed, the top of the rubber 7 approaches the substrate 2 side while compressing the movable electrode 6.
The substrate 2, the insulator 3, the fixed electrodes 4 and 5, the movable electrode 6, and the rubber 7 constitute a capacitance type switch 1.

A predetermined capacitance is formed between the drive side fixed electrode 5 and the movable electrode 6 and between the sense side fixed electrode 4 and the movable electrode 6.
Since the electrostatic capacity changes when the rubber 7 is pressed, the key stroke can be detected by detecting the electrostatic capacity.
The method for detecting the capacitance of the capacitance type switch 1 is the same as that described in Japanese Patent Laid-Open No. 9-204846, and a description thereof will be omitted.

Next, a circuit configuration of a capacitive switch that detects a keystroke of an electronic keyboard instrument will be described.
FIG. 3 shows a circuit configuration of the capacitance type switch.
The electrostatic capacitance type switch 1 (1A to 1F) is provided for each key of the electronic keyboard instrument. In the present embodiment, it is assumed that the number of keys of the electronic keyboard instrument is six and the capacitance switches 1A to 1F are provided for each key.
Among the capacitive switches 1A to 1F arranged in one row, the sense-side fixed electrodes of the capacitive switches 1A, 1C, and 1E are connected to the input-side plus terminal of the differential amplifier 10, and the electrostatic capacitance The sense-side fixed electrodes of the expression switches 1B, 1D, and 1F are connected to the input-side minus terminal of the differential amplifier 10.
As described above, the capacitive switches 1A to 1F arranged in one row are alternately connected to the input-side plus terminal and the input-side minus terminal of the differential amplifier 10.

  A trigger signal is sequentially input to the drive-side fixed electrodes of the capacitive switches 1A to 1F from the trigger output unit 14 described later for each switch. The detection signals output from the capacitive switches 1 </ b> A to 1 </ b> F pass through the differential amplifier 10, so that the noise signal due to the influence of external noise is removed, and the detection signal without noise is input to the capacitance detection circuit 11. The Details of noise signal removal will be described later.

The capacitance is detected from the detection signal by the capacitance detection circuit 11, and the detected capacitance is input to the CPU 13 after analog-digital conversion is performed by the AD converter 12.
The CPU 13 calculates the key stroke position from the input capacitance value and outputs the calculation result to the sound source 15.
The sound source 15 outputs a sound corresponding to the input key stroke position.

The CPU 13 includes a trigger output unit 14.
The trigger output unit 14 outputs a trigger signal to the capacitance type switch that detects the capacitance, and sequentially outputs the trigger signal to the capacitance type switches 1A to 1F.
Here, the trigger output unit 14 outputs the trigger A to the capacitive switches 1A, 1C, and 1E connected to the input side plus terminal of the differential amplifier 10, and the input side minus of the differential amplifier 10 is output. A trigger B is output to the capacitive switches 1B, 1D, and 1F connected to the terminals. Note that the trigger B is obtained by inverting the signal level of the trigger A.

Next, the removal operation of the noise signal mixed in the detection signal output from the capacitance type switch will be described.
First, in the state where the trigger signal is not output from the trigger output unit 14, if there is external noise around the capacitive switches 1 </ b> A to 1 </ b> F, noise due to the influence of the external noise from the electrostatic capacitance switches 1 </ b> A to 1 </ b> F. A signal is output.
A noise signal Y, which is a collection of noise signals output from the capacitive switches 1A, 1C, and 1E, is input to the input side plus terminal of the differential amplifier 10, and the capacitance type switch is input to the input side minus terminal. A noise signal Y that is a collection of noise signals output from 1B, 1D, and 1F is input.

Here, since the capacitive switch 1A and the capacitive switch 1B are adjacent to each other, they are affected by external noise to the same extent and are output from the capacitive switch 1A and the capacitive switch 1B. Noise signals can be considered the same.
Similarly, the noise signals output from the capacitive switches 1C and 1D can be regarded as the same, and the noise signals output from the capacitive switches 1E and 1F can be regarded as the same.
Therefore, the noise Y output from the capacitive switches 1A, 1C, and 1E is the same as the noise signal Y output from the capacitive switches 1B, 1D, and 1F.
In this way, the number of capacitive switches connected to the input side plus terminal and the input side minus terminal of the differential amplifier 10 is the same, and the capacitance type switches are alternately connected to the input side plus terminal and the input side minus terminal. By connecting, the noise signal input to the input side plus terminal and the input side minus terminal of the differential amplifier 10 can be made the same.

When the trigger output unit 14 outputs the trigger A to the capacitive switch 1A in the state where there is external noise around the capacitive switches 1A to 1F, the detection signal X is output from the capacitive switch 1A. The detection signal X is output to the input side plus terminal of the differential amplifier 10. At the same time, the noise signal Y due to the influence of external noise is input to the input side plus terminal and the input side minus terminal of the differential amplifier 10 respectively.
Since the differential amplifier 10 outputs the signal difference between the input-side plus terminal and the input-side minus terminal, only the detection signal X from which the noise signal Y has been removed is output from the differential amplifier 10.

  Further, by inputting a trigger B whose level is inverted from the trigger A to the capacitive switches 1B, 1D, and 1F connected to the input side negative terminal of the differential amplifier 10, the capacitive switch 1A, The polarity of the detection signal output from the differential amplifier 10 can be matched between 1C and 1E and the capacitive switches 1B, 1D, and 1F.

  The present embodiment is configured as described above, and by connecting adjacent electrostatic capacity type switches alternately to the input side positive terminal and the input side negative terminal of the differential amplifier 10, each electrostatic capacity type switch becomes an external noise. Even if a noise signal is output due to the influence of the above, it is possible to remove the noise signal by the differential amplifier 10, and it is possible to detect only the detection signal output from the capacitive switch that performs detection. Therefore, the detection accuracy of the capacitive switch is improved, so that the accurate stroke position of the key of the electronic keyboard instrument can be detected.

  Further, the trigger output unit 14 receives a trigger signal input to the capacitive switch connected to the input-side minus terminal of the differential amplifier 10, and the capacitive switch connected to the input-side plus terminal of the differential amplifier 10. By using a signal in which the level of the trigger signal input to is inverted, the polarity of the detection signal output from the differential amplifier 10 can be matched for all the capacitive switches.

In addition, since the noise signal generated due to the external noise can be removed simply by providing the differential amplifier 10, the noise signal removing device can be configured simply, and noise countermeasures can be taken at low cost.
Furthermore, since the detection signal output from the differential amplifier 10 is not affected by external noise, the detection signal is not fluctuated by the noise signal. Therefore, when the detection result of the capacitive switch 1 is used in an analog manner (for example, when a plurality of stroke positions are detected in one stroke of the key as in this embodiment), the stroke position can be accurately detected. Such an effect is particularly high.

In the present embodiment, when the number of keys of the electronic keyboard instrument is an odd number, or even when it is evenly spaced, one dummy capacitance type switch without a key is added, The number of capacitive switches connected to the input side plus terminal and the input side minus terminal of the differential amplifier 10 may be the same.
As shown in FIG. 2A, the fixed electrodes 4 and 5 have a semicircular shape. However, the shape is not limited to this. For example, as shown in FIG. The drive side fixed electrode 5A having a donut shape that is partially cut around the sense side fixed electrode 4A may be provided.

Next, as an application example, a case where the capacitance type switch device is applied to a keyboard such as a personal computer will be described.
FIG. 4 is a diagram showing a circuit configuration when the electrostatic capacity type switch is applied to a keyboard.
In the figure, the capacitance detection circuit, the AD converter, and the like are omitted, and only the peripheral portion of the capacitance type switch is shown.
When the number of the capacitive switches 1 is increased because they are provided corresponding to the keys of the keyboard, first, as shown in the figure, each of the capacitive switches 1 (1Aa, 1Ba...) It is divided into vertical columns in the order of column and C column, and the analog switching switch 22 can switch the connection to every other column in the order of column A and column C in the order of column A and column C in the same way. The switch 23 can switch the connection to the negative terminal of the differential amplifier 10 every other column in the order of the B column and the D column.
Note that the analog changeover switches 22 and 23 are always adjacent to each other, for example, when the analog changeover switch 22 selects the A column, the analog changeover switch 23 selects the B column. The selected column is selected.

Next, as shown in the figure, the capacitance type switches 1 are divided into horizontal rows in the order of a row, b row, and c row, and the input destination capacitance type of the trigger A output from the trigger output unit 14A. The switch can be sequentially switched for each row by the analog selector switch 20, and similarly, the input destination capacitance type switch of the trigger B can be sequentially switched for each row by the analog selector switch 21.
The trigger A is inputted only to the capacitance type switches 1Aa, 1Ca, 1Ea, 1Ab,... Connected to the input side plus terminal of the differential amplifier 10, and the trigger B is inputted to the input side minus terminal of the differential amplifier 10. Are input only to the capacitance type switches 1Ba, 1Da, 1Fa,.

With this configuration, for example, when detecting the electrostatic capacitance of the capacitive switch 1Aa in the A column, the analog selector switch 22 selects the A column and the analog selector switch 23 selects the B column. The analog changeover switch 20 switches the row to which the trigger A is input. As a result, the noise signal output from the capacitive switch in the A row by the differential amplifier 10 and the noise signal output from the capacitive switch in the B row are canceled out, and the noise signal is removed in the same manner as described above. Only the detected signal obtained can be obtained.
Other than the analog changeover switches 20 to 23, other changeover devices can be used as long as the input / output destinations of signals can be changed.

  Needless to say, the present invention is not limited to the electronic keyboard musical instruments and keyboards described above, and can be applied to various devices including switches, such as a capacitive switch device used as a switch of another pointing device.

It is a figure which shows the cross section of an electrostatic capacitance type switch. It is a figure which shows only the fixed electrode of an electrostatic capacitance type switch. It is a figure which shows the circuit structure of an electrostatic capacitance type switch. It is a figure which shows the circuit structure at the time of applying an electrostatic capacitance type switch to a keyboard.

Explanation of symbols

1, 1A, 1B, 1C, 1D, 1E, 1F Capacitive switch 2 Substrate 3 Insulator 4, 4A Sense side fixed electrode 5, 5A Drive side fixed electrode 6 Movable electrode 7 Rubber 10 Differential amplifier 11 Capacitance Detection circuit 12 AD converter 13 CPU
14 Trigger Output Unit 15 Sound Source 20-23 Analog Change Switch

Claims (4)

In the capacitance type switch device that detects a capacitance by sequentially inputting a trigger signal from a trigger signal output unit to a plurality of capacitance type switches whose capacitance changes in accordance with the amount of pressing,
It has a differential amplifier that has an input side plus terminal and an input side minus terminal, and outputs a difference between input signals inputted to the input side plus terminal and the input side minus terminal,
The adjacent capacitive switches are alternately connected to the input side plus terminal and the input side minus terminal of the differential amplifier, and the output of the differential amplifier is used as the output of the capacitive switch to which the trigger signal is input. A capacitive switch device characterized by the above. The trigger output unit has a signal level between the capacitance type switch connected to the input side plus terminal of the differential amplifier and the capacitance type switch connected to the input side minus terminal of the differential amplifier. 2. The capacitance type switch device according to claim 1, wherein a trigger signal in which is inverted is input. The number of the capacitive switches connected to the input side plus terminal of the differential amplifier is equal to the number of the capacitive switches connected to the input side minus terminal of the differential amplifier. The electrostatic capacity type switching device according to claim 1 or 2. 4. The capacitive switch according to claim 1, wherein the capacitive switch detects any one of a keystroke of an electronic keyboard instrument, a keystroke of a keyboard, and a switch operation of a pointing device. Capacitive switch device.

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