JP6797765B2 - Capacitive touch switch module - Google Patents

Description

The present invention relates to a capacitive touch switch module, and more particularly to a capacitive touch switch module having an electrostatic protection circuit.

In home appliances, AV equipment, PC / OA equipment, industrial machines, and other electronic devices, a capacitive touch switch panel is used as one of the input means to each device. This capacitance type touch switch panel has a plurality of sensor electrodes, and the amount of change in the capacitance of the sensor electrodes in this touch switch panel is quantified, and when the numerical value exceeds a predetermined threshold value, a finger is used. Is connected to a microcomputer that determines that the contact has occurred.

When a finger touches the capacitive touch switch panel, static electricity may be discharged, which may cause the microcomputer to be destroyed. Therefore, an electrostatic discharge (hereinafter referred to as ESD) protection circuit is usually used between the touch switch panel and the microcomputer. FIG. 5 shows an example of a capacitance type touch switch module having such an ESD protection circuit. FIG. 5 is a block diagram of the touch switch module. The touch switch module 1a has an ESD protection circuit 4 between the touch switch panel 2 and the control microcomputer 3, and the protection circuit 4 is connected to a DC resistor 5 and a diode protection circuit 6 in order from the microcomputer side. There is.

Conventionally, with respect to the electrostatic protection circuit of a semiconductor integrated device, impurity diffusion for giving an electric potential to a substrate facing each other at a junction between a substrate and a well formed by arranging a first diode and a second diode close to each other. The distance between the layer and the impurity diffusion layer for applying an electric potential to the well, the impurity diffusion layer for applying an electric potential to the opposite substrate at the junction between the other substrate and the well, and the impurity diffusion layer for applying an electric potential to the well. There is known an electrostatic protection circuit that increases the resistance value of the electrostatic current path by making the distance from the impurity diffusion layer wider (Patent Document 1).

Japanese Unexamined Patent Publication No. 09-116097

However, for the capacitive touch switch module, there is a problem that the electrostatic protection circuit that increases only the resistance value of the electrostatic current path is insufficient. For example, in the protection circuit of a capacitance type touch switch panel module, protection is possible by increasing the DC resistance value, but there is an adverse effect that the detection sensitivity of the touch switch deteriorates by increasing the resistance straight, and resistance. There is a limit to raising the direct current. Further, as shown in FIG. 5, when a diode protection circuit is additionally mounted, it becomes strong against ESD and the microcomputer is rarely destroyed, but there is a problem that a malfunction occurs in another immunity test.

The present invention has been made in order to cope with this problem, ESD protection is also possible, and aims to provide a capacitive touch switch module having the ESD circuit that does not cause operation failure in other immunity test To do.

The capacitive touch switch module of the present invention includes a capacitive touch switch panel, a control microcomputer for controlling a signal from the capacitive touch switch panel, the capacitive touch switch panel, and the control microcomputer. An ESD protection circuit is arranged between the two, and in the ESD protection circuit, a resistance element and a noise current blocking element are connected, the resistance element is on the capacitance touch switch panel side, and the noise current blocking element is placed. It is characterized in that it is connected to each of the control microcomputers.

The capacitive touch switch module of the present invention is characterized in that the resistance element is a DC resistor or a ferrite bead.
Further, the impedances of the control microcomputer and the ESD protection circuit are substantially the same. Further, the noise current blocking element is a diode protection circuit.

The capacitive touch switch module of the present invention has the following effects because the resistance element is connected to the capacitive touch switch panel side and the noise current blocking element is connected to the control microcomputer side.
(1) It is possible to exert an effect on other immunities without impairing the ESD resistance.
(2) The impedance between the terminal on the control microcomputer side and the diode protection circuit is almost the same, and the current flowing through the control microcomputer (that is, the minute current that detects and controls the ON / OFF of the switch) is not disturbed by the noise current. Therefore, it is a key figure that does not cause malfunction even if it receives noise.
(3) It is possible to prevent abnormalities such as destruction of parts and program destruction inside the microcomputer, and it is possible to reduce the defective rate in the market and process.
(4) Since the impedances of the control microcomputer and the ESD protection circuit are substantially the same, the immunity characteristics can be improved. If the impedance of the control microcomputer terminal is higher than that of the ESD protection circuit, the current flowing on the microcomputer side may be affected and malfunction may occur.

It is a block diagram of the capacitive touch switch module of this invention. It is a figure which shows the flow of a surge current. It is a figure which shows the equivalent circuit of a diode circuit. It is a figure which shows the result of having measured the immunity characteristic. It is a block diagram of the capacitive touch switch module of the comparative example 1. FIG. It is a figure which shows the flow of the surge current of the comparative example 1. FIG. It is a figure which shows the result of having measured the immunity characteristic of the comparative example 1. It is a block diagram of the capacitive touch switch module of the comparative example 2. It is a block diagram of the capacitive touch switch module of the comparative example 3.

As an example, a block diagram of the capacitive touch switch module of the present invention is shown in FIG.
The capacitive touch switch module 1 includes a capacitive touch switch panel 2, a control microcomputer 3 for controlling a signal from the capacitive touch switch panel, a capacitive touch switch panel 2 and a control microcomputer 3. The ESD protection circuit 4 is arranged between the two. In the ESD protection circuit 4, a resistance element 5 such as a series resistor 5a and a noise current blocking element 6 including a diode circuit 6a are sequentially connected from the capacitance touch switch panel 2 side toward the control microcomputer 3 side. By connecting the touch switch panel 2 → series resistor 5a → diode circuit 6a → microcomputer 3 in this order, double ESD protection can be achieved by the series resistor 5a and the diode circuit 6a. In addition, no malfunction occurs in the immunity test. The immunity test in the present invention is a state of simulating the electrical stress such as ESD that the module is expected to receive in order to evaluate the resistance of the capacitive touch switch module to electrical stress such as ESD. A test in which a capacitive touch switch module is exposed and its behavior is observed. Further, the capacitive touch switch module of the present invention can sufficiently protect the diode circuit 6a and the microcomputer 3 by using a series resistor 5a having a large allowable current or a large pulse resistance characteristic.

Specifically, FIG. 2 shows the flow of surge current due to ESD when a 1 kΩ resistor is used as the series resistor 5a. The impedance Z _cpu of the control microcomputer 3 terminal is about 10Ω.
When noise is applied to the capacitive touch switch panel 2, a noise voltage is induced in the electrodes of the touch switch panel 2. The induced current I _noise flows due to this induced voltage, but by setting the impedance Z _{cpu of the} microcomputer terminal and the impedance Z _{D of the} diode circuit to the same level, the currents I _cpu and I _noise flowing through the microcomputer become substantially the same, and I The influence of _noise is reduced. In this way, noise is further suppressed by connecting a series resistor 5a between the touch switch panel 2 and the diode circuit 6a and using a resistor having a large allowable power for this resistor. As a result, the noise current flowing through the diode circuit 6a is suppressed, and the diode circuit 6a is not destroyed, so that the microcomputer is protected.

The equivalent circuit of the diode circuit is shown in FIG. When a surge on the positive side enters from the input side 7, the surge current on the positive side flows from the diode D1 through the Zener diode D2 to the ground line to protect the microcomputer.

As described above, the influence of I _noise can be reduced by making the impedance Z _cpu of the microcomputer terminal and the impedance Z _D of the diode circuit about the same. That is, if the impedances of the Z _cpu and the noise current blocking element 6 can be made similar, a varistor, a TVS, or the like can be used instead of the diode circuit 6a. Further, if the element can cut off the noise current I _noise , ferrite beads can be used instead of the series resistor 5a. Further, the noise resistance characteristics can be further improved by inserting a series resistance of about 100 kΩ on the microcomputer terminal side.

FIG. 4 is a diagram showing the results of measuring the immunity characteristics of the capacitive touch switch module 1 shown in FIG. The number of counts on the vertical axis is a numerical value of I _cpu , the number of references is a comparative value, and the touch switch is turned on when the number of counts is lower than the number of references to a certain level. Recognize that. The capacitive touch switch module 1 reacted when the switch 1 and the switch 2 were pressed, and no malfunction was observed.

As Comparative Example 1, a block diagram of the capacitive touch switch module 1a when the touch switch panel 2 → the diode circuit 6a → the series resistor 5a → the microcomputer 3 are connected in this order is shown in FIG. As the series resistor 5a, the diode circuit 6a, the touch switch panel 2 and the microcomputer 3, the same parts as those shown in FIG. 1 were used. Further, FIG. 6 is a diagram showing a flow of surge current due to ESD in FIG.
In FIG. 6, when noise is applied to the capacitive touch switch panel 2, a noise voltage is induced in the electrodes of the touch switch panel 2. When this induced voltage exceeds the protection voltage of the diode circuit 6a, a noise current I _noise flows between the electrode of the touch switch panel 2 and the diode circuit 6a. This current affects the current I _cpu flowing through the microcomputer. In order to protect the microcomputer 3, the resistance value of the series resistor 5a must be made larger than that of the diode circuit 6a. As a result, the influence of I _noise becomes large, which affects I _cpu , and the capacitance cannot be detected normally. If the capacitance cannot be detected normally, an error will occur in the ON / OFF determination of the touch switch panel 2. In addition, the switch operation causes a malfunction, which adversely affects other systems.

Capacitance The touch switch panel 2 is equivalent to a capacitor, and the microcomputer 3 converts the capacitance of the touch switch into the capacitance and the charge / discharge current (I _cpu ) into the capacitance at the ports (Rx, Tx). , Detecting. Even if the diode circuit 6a is mounted, malfunction does not occur when the noise is less than the protection voltage (about 5V) of the diode circuit 6a.
However, if excessive noise is applied, the diode circuit 6a may be destroyed. If the diode circuit 6a is destroyed, the series resistor 5a cannot protect it completely, and the microcomputer 3 itself may be destroyed.

FIG. 7 is a diagram showing the results of measuring the immunity characteristics of the capacitive touch switch module 1a shown in FIG. 5, and corresponds to FIG. The number of counts on the vertical axis is a numerical value of I _cpu , the number of references is a comparative value, and the touch switch is turned on when the number of counts is lower than the number of references to a certain level. Recognize that. When noise is applied to the capacitive touch switch module 1a and an abnormality in detecting I _cpu represented by n1 to n4 is observed, the microcomputer 3 becomes uncontrollable and the reference number shows an abnormal value. As a result, it was determined to be ON without pressing the switch, and a malfunction was observed.

As Comparative Example 2, FIG. 8 shows a capacitive touch switch module 1b when the touch switch panel 2 → the diode circuit 6a → the microcomputer 3 are connected in this order. FIG. 8A is a block diagram, and FIG. 8B is a diagram showing a flow of surge current due to ESD in FIG. 8A. The impedances of the microcomputer terminal and the diode circuit were set to the same level. The same touch switch panel 2 as shown in FIG. 1 was used.
In FIG. 8B, when noise is applied to the capacitive touch switch panel 2, a noise voltage is induced in the electrodes of the touch switch panel 2. When this induced voltage exceeds the protection voltage of the diode circuit 6a, a noise current I _noise flows between the electrode of the touch switch panel 2 and the diode circuit 6a. If this current becomes excessive, the diode circuit 6a may be destroyed, and the microcomputer 3 itself may be destroyed.

As Comparative Example 3, FIG. 9 shows a capacitive touch switch module 1c when the touch switch panel 2 → the series resistor 5a → the microcomputer 3 are connected in this order. 9 (a) is a block diagram, and FIG. 9 (b) is a diagram showing the flow of surge current due to ESD in FIG. 9 (a). The impedance of the protection circuit inside the microcomputer and the impedance of the microcomputer terminal were set to the same level. The same touch switch panel 2 as shown in FIG. 1 was used. Note that FIG. 9B shows a case where a protective diode circuit is provided inside the microcomputer 3 itself.
In FIG. 9B, when noise is applied to the capacitive touch switch panel 2, a noise voltage is induced in the electrodes of the touch switch panel 2. The noise current I _noise due to this noise voltage cannot be completely protected by the series resistor 5a and leads to the destruction of the microcomputer 3 itself.

The results of the above examples and each comparative example are summarized in Table 1.

Since the capacitive touch switch module of the present invention can exert an effect on immunity evaluation without impairing the ESD resistance characteristics, it can be used for all the capacitive touch switch modules.

1 Capacitive touch switch module 2 Capacitive touch switch panel 3 Control microcomputer 4 ESD protection circuit 5 Resistance element 6 Noise current cutoff element 7 Input side

Claims (4)

A electrostatic discharge protection circuit is arranged between the capacitive touch switch panel, the control microcomputer that controls the signal from the capacitive touch switch panel, and the capacitive touch switch panel and the control microcomputer. Capacitive touch switch module
In the electrostatic discharge protection circuit, a resistance element and a noise current cutoff element are connected, the resistance element is connected to the capacitance touch switch panel side, and the noise current cutoff element is connected to the control microcomputer side .
The resistance element is a DC resistance, and the noise current blocking element is a diode protection circuit.
A capacitive touch switch module characterized in that the impedances of the control microcomputer and the diode protection circuit are substantially the same . The capacitive touch switch module according to claim 1, wherein the resistance element is a ferrite bead. The capacitive touch switch module according to claim 1 or 2 , wherein the impedances of the control microcomputer and the electrostatic discharge protection circuit are substantially the same. The capacitive touch according to any one of claims 1 to 3, wherein the noise current generated in the capacitive touch switch panel and the current flowing through the control microcomputer are substantially the same. Switch module .