JPH0229121A - Touch switch - Google Patents

Abstract

PURPOSE:To improve the temperature stability by providing a feedback path comprising an inverse amplifier, a contact plate, a capacitor and two resistors so as to act the contact plate as an equivalent capacitor. CONSTITUTION:Two resistors R1, R2 connected in series are connected between an output terminal and an inverting input terminal (a) of an inverse amplifier Z, a capacitor C is connected between the connecting point of the resistors R1, R2 and the ground terminal and the contact plate P is connected to the inverting input terminal (a). Thus, even if a human body P is in contact with the contact plate P and a capacitance is caused with the common path, the oscillation circuit is oscillated in terms of the 2nd order differential equation. Then each circuit constant is decided so that a 2nd order differential equation has oscillatory solutions. Thus, the temperature stability is enhanced and even if the amplifier chip is heated by using a solder iron, the oscillated amplitude does not cause the temperature instability.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an oscillator for touch switches. In other words, when one human body comes into contact with the contact plate,
This relates to an oscillator whose oscillation state changes.

■Conventional technology Various types of touch switches have been proposed.

The performance required of touch switches is higher reliability than mechanical switches. It is important that the device does not malfunction due to noise or leakage current.

Therefore, it can be said that the method using the human body as an antenna and the method based on detecting leakage current due to contact with the human body lack reliability.

By the way, there is a capacitive touch switch method that responds to the capacitance of the human body.

This method allows the surface of the contact plate to be covered with a dielectric insulator. It is also resistant to noise.

In this way, it can be said that the capacitive touch switch is an excellent method in principle. However, conventional capacitive touch switches have the disadvantage of lacking temperature stability.

1. OBJECTS OF THE INVENTION An object of the present invention is to provide a capacitive touch switch with high temperature stability and high reliability.

A second object of the present invention is to provide a touch switch circuit that does not require delicate adjustment of circuit constants and is easy to manufacture and provides stable manufacturing quality.

1. Configuration of the present invention The present invention is configured as follows.

The oscillator of the present invention comprises an inverting amplifier (Z) and a contact plate (
This is a feedback oscillator with a feedback path consisting of a capacitor (P), a capacitor, and two resistors. The contact plate (P) acts as an isometric capacitor.

Between the output terminal of the inverting amplifier (Z) and the 1 inverting input terminal (a), two resistors (R1) and a resistor (
R2) is connected.

The capacitor (C) is connected between the connection point of the resistor (R1) and the resistor (R2) and the ground terminal, or between the inverting input terminal (a) and the ground terminal.

In the first case, a capacitor (C) is connected between the junction of resistors (R1) and (R2) and the ground terminal, and a contact plate (P) is connected to the inverting input terminal (a). There is.

In the second case, the capacitor (C) is connected to the inverting input terminal (a
) and the ground terminal, and the contact plate (P)
is connected to the connection point between the resistor (R1) and the resistor (R2).

The above is the basic configuration of the present invention.

■Explanation A good way to increase reliability against touch switch failures is to limit the passive components used in the 5 circuits to resistors and capacitors. Furthermore, if a passive circuit is constructed using only CR, it becomes easier to manufacture the circuit using a printing and baking method.

From this point of view, one aspect of the present invention constitutes a passive circuit using only CR.

The circuit of the present invention constitutes a CR delayed phase oscillation circuit.

When the human body does not touch the contact plate and the capacitance between the contact plate and the common electrical circuit (power line or ground line) is zero, the oscillation circuit of the present invention is expressed by a -order differential equation and does not oscillate. Impossible.

When a human body comes into contact with the contact plate and capacitance is generated between the contact plate and the common electric circuit, the oscillation circuit of the present invention becomes a second-order differential equation and can oscillate.In the present invention, this second-order differential equation has an oscillating solution. Define each circuit constant as follows.

1 and 2 are circuit diagrams showing the most basic configuration of the present invention. FIG. 3 is the same as a 0 equivalent circuit in which one of the resistors in FIG.

FIG. 4 is an equivalent circuit of FIG. 1, FIG. 2, and FIG. 3.

The capacitance formed by the contact plate and the human body is shown as an isometric capacitor.

■Analysis using mathematical formulas Trying to analyze the amplifier by replacing it with a mathematical approximation model. The 0th order shown below is based on an approximation in which the amplification factor is a constant. If the amplification factor is set as a constant, a good approximation cannot be obtained.

Vout=-A-Vin The amplifier is an inverting amplifier and A is a positive constant.

When FIG. 4 is described mathematically, it becomes equation (1).

R8 and R2 are the resistance values of the resistors (R1) and (R2).

One of C and C2 is the capacitance caused by the contact plate and the human body, and the other is the capacitance of the capacitor (C).

+(1+A)Vout=O---------------
(1) This equation does not give a good approximation, and the phase rotation of the amplification factor cannot be ignored.

■Attempt to express the phase rotation of an amplifier using an operator amplification factor.

The following equation will be called the operator amplification factor as the amplification factor.

Replaced with m=GcOSθ and hω=Gsinθ.

Assuming that the gain G is positive, m is positive in a range where the phase delay is up to 90''.

When the phase delay exceeds 90'', m becomes negative.

h is always positive within the phase delay range of 00 to 180'.

■If Figure 4 is expressed in terms of operator amplification factors, the following equations m, h
is a constant selected according to the characteristics and operating frequency of the amplifier. The response to a sinusoidal input is f.

Vout=A−sin(J)t=m°Sin
ωt −h−ωco sωt This equation can be rewritten as the following equation.

Vout=G-sin (ωt-θ) G represents gain, and θ represents phase rotation.

In this formula Equation (2) is in good agreement with experimental facts.

Equation (2) is a second-order differential equation, and the conditions for having a vibrational solution can be easily found.

In the present invention, circuit constants are determined so that the second-order differential equation has an oscillatory solution. The operating principle is that when the human body does not touch the contact plate and C1 or C2 is zero, the two equations become a first-order differential equation and no oscillation occurs.

Set the circuit constants so that the coefficient of the second term is negative, and
Setting the operating frequency so that the coefficient of the term is positive is a necessary condition for oscillation.

As mentioned above, h is within the range where the phase delay is up to 180°.
o is 0m in the range of phase delay up to 90' m >
It is O. If the amplifier is used in this range, the third
The coefficient of the term is definitely positive.

In order to make the coefficient of the second term negative, there must be a sufficiently large h. There is a lower limit to the degree of amplification for zero oscillation.

If the amplifier is a non-inverting amplifier, the conditions for oscillation are not satisfied.

The present invention requires stable oscillation when both the capacitances of C1 and C2 are not zero.

For a touch switch circuit with good temperature stability, it is important to avoid operating regions where the coefficient of the second term and the coefficient of the third term become positive or negative due to variations in amplifier parameters. .

■The present invention connects either C1 or C2 to the contact plate (
P) and the capacitance formed by the human body. When either C1 or C2 is zero, (2
) is a first-order differential equation and will not oscillate.

When neither C8 nor C2 is zero, (2)
The equation becomes a second-order differential equation and oscillates.

In the present invention, circuit constants are determined so that a second-order differential equation has an oscillatory solution.

The operating principle of the present invention can be summarized as above.

-Features of the invention.

The oscillator circuit for the touch switch of the present invention has very good temperature stability and can realize very high sensitivity.

a; The strength of oscillation is (coefficient of the second term) in equation (2)
The larger the value of /(coefficient of the first term) is negative, the larger the value becomes.

The value of the second term is always set to be negative, and in order to increase the value of (coefficient of the second term)/(coefficient of the first term), the value of the coefficient of the first term needs to be small. .

If the value of the first term is zero, equation (2) becomes a first-order differential equation and does not oscillate. When the value of the first term becomes a small positive value, the circuit of FIG. 4 suddenly transitions to a strong oscillation state.

For this reason, the small capacitance formed between the human body, the contact plate and the common electrical path is not a disadvantage.

Therefore, the touch switch of the present invention can achieve extremely high sensitivity.

Further, the oscillation state operates to transition between a binary state of a stopped state and a strong oscillation state. This is preferred as a switch operation.

b; Furthermore, in order to increase the sensitivity, the product of resistors R8 and R2 may be increased. This is C1 or C,! in the coefficient of the first term of equation (2). This means that the coefficient of change of is set to a large value.

Conversely, in order to lower the sensitivity, the R1/R2 product may be reduced.

C; Amplifier parameters change depending on temperature,
In order to improve temperature stability, the sign of the coefficient of the differential equation (2) mentioned above should be unaffected by changes in the parameters of the amplifier. It is easy to make the code unaffected by changes in the amplifier parameters.

Therefore, the touch switch of the present invention can achieve extremely high temperature stability.

1. When C and R are added and connected to the circuit of the present invention, the order of the differential equation increases. However, connecting additional Cs and R's only increases redundancy; special care must be taken to ensure that the poles due to the additionally connected CRs converge. It only causes instability in switch operation.

■Effects of the present invention As described below, the present invention has excellent performance such as temperature stability, noise resistance, high sensitivity, and low cost.

a; The temperature stability of the present invention is extremely high, and even if the amplifier chip is heated with a soldering iron, no temperature instability will occur in the oscillation amplitude value.

b; Oscillation transitions very clearly between a stopped state and a strong oscillation state. The amplitude value in the oscillation state is close to the power supply voltage, and can be easily distinguished from the oscillation stopped state. Therefore, A
Extremely resistant to malfunctions caused by noise from C power lines, etc.

C: The present invention can easily achieve high sensitivity.

If the Rl' R2 product is set large, the switch can be operated without contact. In other words, it can also be used as a door switch to detect the approach of a human body.

Furthermore, by setting R1 and R2 to a small value, the switch can be operated only in response to reliable contact.

d; the circuit of the invention arranges the contact plates crosswise;
It is also possible to have a configuration in which when an intersection is touched, the touched point is detected.

[Brief explanation of the drawing]

1 and 2 are circuit diagrams of the oscillation circuit of the present invention. FIG. 3 is a circuit diagram of the present invention in which one of the resistors in FIGS. 1 and 2 is replaced by an output resistor of an amplifier. FIG. 4 is an equivalent circuit diagram of FIG. 1, FIG. 2, and FIG. 3 in which the capacitance formed by the touch plate and the human body is replaced by an isometric capacitor. FIG. 5 is an example of a redundant circuit. R2 Mei 21 Kaku

Claims (3)

[Claims] (1) Equipped with an inverting amplifier (Z) and a contact plate (P)
A feedback oscillator having a feedback path consisting of a capacitor and two resistors, and two resistors (R1) connected in series between the output terminal of the inverting amplifier (Z) and the inverting input terminal (a). and resistance (R
2) is connected, (a) capacitor (C) is connected to resistor (R1) and resistor (R2)
(b) The contact plate (P) is the oscillation circuit of the touch switch connected to the inverting input terminal (a). (2) Equipped with an inverting amplifier (Z) and a contact plate (P)
A feedback oscillator having a feedback path consisting of a capacitor and two resistors, and two resistors (R1) connected in series between the output terminal of the inverting amplifier (Z) and the inverting input terminal (a). and resistance (R
2) are connected, (a) the capacitor (C) is connected between the inverting input terminal (a) and the ground terminal, and (b) the contact plate is the connection point between the resistor (R1) and the resistor (R2). Touch switch oscillation circuit connected to. (3) The touch switch oscillation circuit according to claim 1 or 2, wherein one of the resistors (R1) and (R2) is replaced by an output resistor of an amplifier (Z).