JPS6051815B2 - Input circuit of small electronic device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to input circuits for small electronic devices.

Switches in small electronic devices not only increase the cost of the device, but also have an undesirable effect on the waterproof structure and design.

Therefore, as shown in FIG. 1, if a translucent or transparent Nesa membrane electrode 1 is provided on the surface of the windshield of the device and used as a switch electrode, the above-mentioned drawbacks can be improved.

FIG. 2a shows the most common electrode structure, in which a NESA film electrode 1 is deposited on a windshield 2, and a protective film 3 (for example, 5102) is formed on this NESA film electrode 1. A part of the Nesa membrane electrode 1 is not covered with the protective film 3, so that a switch input can be performed by directly touching this part with the human body. The opposing common electrodes are brought into contact with the human body via a case or the like. The input circuit in this case can be constructed extremely simply as shown in FIG. Inverter 4
The input terminal of is an insulated gate field effect transistor (hereinafter M
If the configuration is such that the input resistance is received at the gate of the OST (abbreviated as OST), its input resistance is extremely large, and its influence can be ignored.
The electrical resistance of the human body can normally be considered to be from several hundred ohms to several megaohms. Therefore, if the dividing resistor 5 is made sufficiently larger than this value, when the switch is short-circuited by the human body, the inverter 4 will The input terminal potential changes widely, and the logic state of the output changes.

This allows the input state of the switch to be detected. However, this method has a major drawback. That is, if the number of Nesa membrane electrodes 1 increases or the distance between the plurality of electrodes becomes narrower for some reason, there is a risk that the fingertip may touch an electrode other than the desired Nesa membrane electrode. With conventional contact-type input mechanisms, if your fingertip touches an electrode even slightly, it is determined that you have pressed a switch, so if you accidentally touch an unwanted electrode, it will result in an erroneous operation, which poses many practical problems. Furthermore, since the Nesa membrane electrode 1 is exposed, it is easily scratched when it is hit against a hard object, and there is also a risk of wire breakage. There was also a problem with corrosion caused by sweat. SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks and provide a reliable input circuit with a simple configuration. In order to achieve the above object, the present invention covers the part of the Nesa membrane electrode that touches the fingertip with a protective film, and detects switch input using the capacitance formed between the Nesa membrane electrode and the human body. .

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 4 shows an embodiment of the present invention, in which the NESA film electrode 1 is connected to the data input terminal of a data type flip-flop 9 (hereinafter abbreviated as D-FF), and the D-FF is connected via a resistor 8.
It is connected to the inverted clock input terminal of 9.

A clock φ is applied to the inverted clock input terminal, but
If the duty cycle of this clock φ is 50%, the potential at a certain level A as shown in FIG. It is difficult to detect the input because the input is close to the side (hereinafter referred to as ゜゜L゛). Therefore, in the present invention, as shown in FIG. 6, a clock φ having a relatively small duty cycle (or conversely, a relatively large clock φ) is applied. If the capacitor 7 is not formed, a waveform similar to that of the clock φ appears at a certain level A with a slight delay, and the value immediately before the fall of the clock φ is H, so the D-FF9
is always reading a high potential, so the output power of D-FF9 is high. Assuming that capacitor 7 is formed during time T, the waveform of level A will be blunted by the influence of resistor 8 and capacitor 7, but since the duty cycle is not 50%, it will necessarily deviate to one of the potentials.

In the case of FIG. 6, the deviation is to "L", so the output of the D-FF 9 becomes "L" with a slight delay. The capacitor 7 is formed by pressing a fingertip onto the protective film on the switch electrode, as shown in FIG. On the electrodes that are very close to each other
5, the capacitance formed in these electrodes is small and malfunctions are unlikely to occur.

FIG. 8 shows another embodiment of the present invention, in which the Nesa membrane electrode 1 is connected to H through a resistive element 10 and! to N channel M
Connected to L via OSTll.

The value of the resistance element 10 is set to be sufficiently larger than the on-resistance of the MOSTll.

As a result, as shown in Figure 9, at level A, there is a difference in time and constant between the rise and fall of the voltage, so even if a waveform with a duty cycle of 50% is used as the clock φ, there will be a sufficient deviation. You can get a rank. Unlike the case in Figure 4, D
- Reading into the FF is performed at the rising edge of the clock φ. In this example, when MOSTll is on, the resistance element 10
Current flows through it, affecting power consumption. 10th
The figure shows an embodiment that improves the above points, in which a P-channel MOSTl2 is inserted in series with the resistor element 10, and when MOSTll is on, MOSTl2 is turned off, thereby preventing the above-mentioned wasteful current from flowing. .

Note that the resistance element 10 is shown using the on-resistance of the channel of a P-channel MOST. The on-resistance of the MOST can be set large by increasing the channel length and decreasing the channel width. Therefore, if the on-resistance of MOSTl2 is designed to be large, the resistance element 10
Since the channel resistance of 2 is replaced, there is no need to provide a separate channel resistance. That is, in FIG. 11, the on-resistance of MOSTl2 is M
If it is designed to be sufficiently larger than that of OSTll, it is possible to achieve the above-mentioned objects 1-7 of the present invention.

It should be noted that the touch switch that is the subject of the present invention may be accidentally touched even when there is no intention to operate it, but if the touch switch is not pressed with some force, sufficient capacitance will not be formed between the switch electrode and the human body. This is advantageous compared to the contact type.

In the unlikely event that there is a strong possibility of erroneous operation, a lock switch that is linked to the input circuit is provided, and when the input circuit power button is in the locked state, the potential of the clock φ applied to the switch electrode is not fixed to prevent erroneous operation. You may. This can be achieved by simply implementing a gate method. Further, in the above description of the invention, it has been explained that the state of the switch electrode is once read by the D-FF, but it goes without saying that the state may be directly processed by other gate means. Furthermore, since the resistance elements are set to relatively large values, whether they are built into the integrated circuit or external components, if there is a risk of various problems occurring when the number of resistors increases, it is necessary to set them in the input circuit as shown in Figure 12. On the other hand, the problem can be solved by scanning the switch electrode connections.

An example of the drive waveforms of each part at this time is shown in FIG. Processing after the input circuit also uses scan signals Tl, T2...
It is possible to make a correspondence with each switch electrode using . As described above, according to the present invention, by covering the entire electrode with an insulating film, a switch input is detected only when the capacitance formed between the electrode and the human body exceeds a certain level. Even if some capacitance is formed between adjacent electrodes, it is possible to operate only the required switch by determining the capacitance value, thus creating a touch switch input circuit that is less likely to malfunction. I can do that.

Furthermore, since the plurality of electrodes are entirely covered with an insulating film, there is no need for the step of making holes in the insulating film, and a structure that is less prone to scratches and corrosion can be easily obtained. Moreover, it is possible to provide a practical compact electronic device that is excellent in terms of design and cost, and the effects are significant.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing a specific example of a small electronic device, FIG.
Fig. b is a cross-sectional view of the main part showing the switch structure to which the present invention applies, Fig. 3 is a partial circuit diagram showing a conventional input circuit, Fig. 4 is a partial circuit diagram showing an embodiment of the present invention, and Fig. 5 , FIG. 6 is a waveform diagram explaining the operation based on the embodiment of FIG. 4, FIG. 7 is an explanatory diagram showing the operating state of this embodiment, and FIG. 8 is a partial circuit showing another embodiment of the present invention. 9 are waveform diagrams explaining the operation of the embodiment shown in FIG. 8, FIGS. 10 and 11 are partial circuit diagrams showing other embodiments of the present invention, and FIG. 12 is a further embodiment of the present invention. A partial circuit diagram showing another embodiment, FIG.
FIG. 3 is a waveform diagram in the embodiment shown in the figure. 1... Nesa membrane electrode (Nesa membrane), 2... Windshield glass,
3... Protective film, 7... Capacitance, 8, 10... Resistance element, 9... Data type flip-flop, 11, 1
2. Field effect transistor.

Claims (1)

[Claims] 1. In a small electronic device having an input device having a structure in which a NESA membrane electrode formed on the upper surface of the windshield is protected by an insulating film, a plurality of the NESA membrane electrodes are formed on the upper surface of the windshield, and the plurality of NESA membrane electrodes are formed on the upper surface of the windshield. Covering the entire surface of the electrode with a common insulating film, and applying a signal to the Nesa film electrode via a resistive element,
An input device for a small electronic device, characterized in that it is provided with means for determining an input state by detecting a signal delay due to a capacitance formed between the Nesa membrane electrode and the human body surface and the resistive element. circuit.