JPS6025854B2 - Display element drive circuit - Google Patents

Description

[Detailed description of the invention] The present invention relates to a driving circuit for a light emitting display element.

2. Description of the Related Art In various machines and devices such as televisions and elevators, many display devices are used to display various operating states. As a conventional display device, for example, as shown in FIG. 1 (a is a front view, b is a side view), there is a push button switch whose button head emits light.

That is, in FIG. 1, the switch is turned on or off by pushing the button 1 toward the switch body 2. In conjunction with this operation, the light emitting diode 3 (or light bulb, etc.) lights up, and the light passes through the transparent plastic that makes up the button 1 and is emitted from the front of the button 1, making it appear as if the head of the button 1 appears to be emitting light. Note that 4 in FIG. 1 is a terminal for wiring.
The push-button type display device described above has a complicated structure, it is difficult to make the low light emitting part large, and the depth of the device becomes large. However, there are drawbacks such as multiple installations on the same plane. As a device that has improved the above-mentioned drawbacks, there is a display device having a capacitance change detection type sensor as shown in FIG. 2 (a is a front view, b is a side view and a circuit diagram). That is, in FIG. 2, the detection circuit 7 detects a capacitance change between the sensor panel 5, which also serves as a display section, and the ground plane (for example, a capacitance change due to a person touching the front surface of the sensor panel 5), and the signal is detected by the detection circuit 7. By turning on and off the switching circuit 8, the light emitting diode 6 (or light bulb) is made to blink, and light is emitted forward via the sensor panel 5. In addition, in FIG. 2, 9 is a power supply. Capacitance change detection type display devices such as those mentioned above are currently widely used in elevators, etc., but even in the case of this device, it is difficult to display a large area, and it is necessary to install light bulbs, etc., which increases the depth. There is a problem above. SUMMARY OF THE INVENTION An object of the present invention is to provide a display element drive circuit for solving the above-mentioned drawbacks of the prior art and realizing a display device that is thin, capable of large-area display, and easy to mount.

The gist of the present invention is to use a thin display element (electroluminescent element, liquid crystal display element, electrochromic element, etc.) as a display element and sensor, and use a counter electrode (or electrodes arranged in parallel) of the element as a capacitive detection type sensor. The problem that arises when used as an electric motor is solved by a special drive circuit.

Hereinafter, problems when electrodes of a thin display element are directly used as a sensor will be explained using an electroluminescent element (hereinafter abbreviated as an EL element) as an example.

FIG. 3 is an example diagram of an EL element drive circuit.

In Fig. 3, 10 is the capacitance when the human body contacts the electrodes of the EL elements 14 through the panel (the capacitance between the electrode and the finger is about several pF), and 11 is the impedance of the human body. (At 50-60Hz, it is a sufficiently small value compared to the impedance of 10) 12 is hum noise induced in the human body, 13 is a switching element, 14 is an EL element,
15 is an AC power source for driving the EL element. The circuit shown in FIG. 3 detects the voltage change at point P that occurs when a human body contacts the electrode of the EL element 14 through the panel (the detection circuit is not shown), thereby turning on the switching element 13. As a result, a current 15' flows from the AC power source 15 to the EL element 14, causing it to emit light.

However, the EL element 14 is constructed by sandwiching a dielectric layer between electrodes, and the capacitance between the electrodes is 100 F.
There is also a degree of /. On the other hand, when the human body contacts the electrode through the panel, the capacitance (10 above) is usually only a few pF, so the voltage change at point P is extremely small. .

For example, FIG. 4 is an equivalent circuit of FIG. 3, with O, Z, .
, Z, 3, and ZM have impedances of 10, 11, 13, and 14, respectively (however, Z, 3 is the interelectrode capacitance of the switching element 13 and is about 3 pF), and V.

is the hum noise of the human body. In Figure 4, 50Hz
The voltage Vp of P at is Z13 Otsu 4 Vp=Otsu 3 Otsu 40 (Z, 30 Z, 4).

Twelve. )V. It becomes 21 hV. Therefore, the detection circuit needs to detect changes of about 1 hV,
Considering the variations in each element, noise, etc., it is difficult to detect a change at an extremely small level of about 1 hV, and it has not been possible to put it into practical use.

The present invention solves the above problem by configuring the device to detect changes in resonance frequency due to human contact.

A detailed description will be given below based on the drawings. FIG. 5 is a front view of an example of the EL element used in the present invention, and FIG. 6 is A of FIG.
-A' sectional view.

In FIGS. 5 and 6, first, a transparent glass substrate 1
6 (e.g. 40 x 4 ribs) by forming one 03 nesa film (e.g. film thickness 2000△, sheet resistance 1500/base) on one side, and then removing the nesa film leaving a predetermined pattern by etching. Electrodes 17 are formed. Next, the display layer 18 is formed by screen printing using a phosphor printing paste for electroluminescence. The thickness of the display layer 18 is desirably about 10 to 40 m, since the dielectric strength will be insufficient if it is less than 10 m, and a high voltage will be required to obtain sufficient light emission if it is more than 40 m. . Next, a counter electrode 19 is formed by aluminum vapor deposition.

The above device emits light by applying an alternating current or square wave electric field between the electrodes 17 and 19. Next, the principle of the detection circuit will be explained.

FIG. 7 is a diagram showing the principle of the detection circuit.

In FIG. 7, a coil 20, an EL element 22, a coil 2
1 and the capacitor 23 constitute a resonant circuit. Further, 24 indicates the capacitance when a human body contacts the electrode (point B) of the EL element 22 through the panel. FIG. 8 is a band characteristic diagram at point B of the signal applied to point A in the above resonant circuit, and curves 25, 26, and 27 each have a capacitance of 2
The characteristics when 4 is 0.3 pF and 8 pF are shown.

As can be seen from Figure 8, when the capacity 24 is 0, 8MHZ
A peak of resonance, which has not been seen above, occurs below the IMHZ in the case of 3 pF and 5 pF.

A sensor can be constructed by utilizing this large change. Note that, as shown in FIG. 9, when the coil 21 in FIG. 7 is omitted, the band characteristic does not change at all with respect to a change in the capacitance 24. Furthermore, as shown in FIG. 10, when the coil 20 is omitted, the band characteristics do not change at all with respect to changes in the capacitance 24. On the other hand, if the capacitor 23 connected in parallel with the switching element 13 is omitted, as shown in FIG.
1 and the interelectrode capacitance of the switching element 13 is a resonance point 28 due to the coils 20, 21 and the capacitance 24.
Since it occurs in the vicinity of scratches, it tends to cause problems with sensor function.

Therefore, the capacitance 2 is sufficiently smaller than the capacitance of the EL element 22 and sufficiently larger than the interelectrode capacitance of the switching element 13.
4 must be connected in parallel with the switching element 13. Note that when the size of the capacitor 24 is made to be approximately the same as the capacitance of the EL element 22, even when the switching element 13 is off, an electric field divided by the capacitance ratio of both is applied to the EL element 22, and the EL element 22 is The element 22 may light up slightly. Of course, when the switching element 13 is turned on, the EL element 22 is completely illuminated. Next, an explanation will be given based on an example.

FIG. 12 is a block diagram of an embodiment of the present invention.

In FIG. 12, 30 is the resonant circuit shown in FIG. 7, and 31
32 is an oscillation circuit, 32 is a narrow band pass filter, and 33 is a detection circuit.

Note that the passband of the narrowband bandpass filter 32 is set to a range near the resonance point of the capacitor 24 (1 and 1 and 2 in the example of FIG. 8). Next, the operation will be explained.

First, when the human body is not in contact with the electrode of the EL element, the oscillation frequency of the oscillator composed of the resonant circuit 30 and the oscillation circuit 31 is at a low band (below 1 Hz), as can be seen from FIG. , outside the passband of the narrowband bandpass filter 32.

Therefore, the detection circuit 33 has no input and therefore no output. Next, when the human body comes into contact with the electrode of the EL element, the resonant frequency of the resonant circuit 30 changes, and the oscillation frequency of the oscillation circuit 31 falls within the passband of the narrowband pass filter 32.

Therefore, the detection circuit 33 sends out an output. By controlling the switching element 13 shown in FIG. 7 using this world power, it is possible to light up the EL element. Note that depending on the state of contact between the EL element and the human body (for example, when the capacitance increases due to strong pressure on the EL element), the capacitance 24 in FIG. 7 may become too large and the oscillation frequency may deviate from the passband. However, even in that case, there is always a time when the capacitance 24 is small at the beginning of contact, and the detection circuit 33 sends out an output at that time, so it is possible to memorize it by connecting a flip-flop circuit or the like after the detection circuit 33. .

Next, FIG. 13 is a diagram showing a second embodiment of the present invention.

In the circuit shown in FIG. 13, a narrow band 32 is inserted between the resonant circuit 30 and the oscillation circuit 31, and the human body
It is constructed so that it oscillates only when it comes into contact with the element. Other operations are the same as in FIG. 12. next,
FIG. 4 is a diagram showing a third embodiment of the present invention.

The circuit shown in FIG. 14 is configured so that a sensor oscillator 34 is connected in series with an EL element driving power source 35, and changes in the resonance output of the resonance circuit 30 depending on the presence or absence of human body contact are detected.

Note that a white noise generator may be used as the sensor oscillator 34. Next, FIG. 15 is a circuit diagram of an embodiment of the present invention, showing a specific circuit of the block diagram of FIG. 13.

In FIG. 15, the resonant circuit 3 is the same as the circuit in FIG. 7, and the same reference numerals as in FIG. constitutes an oscillator together with the resonant circuit 30, and sends out an output outside the band when the human body is not in contact with the EL element 22, and sends out an output within the band when the human body is in contact with the EL element 22.

Further, the narrowband bandpass filter 32, which is composed of two buffer circuits, three coils, and three capacitors, selectively passes the output of the oscillator when the human body contacts the EL element 22.

And a detection circuit 3 consisting of a diode and a capacitor
3 detects the output of the narrow band pass filter 32,
It is sent out from the output terminal 36. The output obtained from this output terminal 36 is, for example, a flip-flop.

The signal is applied to a processing circuit 37 using a circuit or the like to perform processing according to the operation mode of the display element, and the resulting signal is applied to the control input terminal 38 of the resonance circuit 30 to control the switching element 1.
By controlling 3, the EL element 22 can be made to blink in any operation mode. Examples of the above operation modes include {i} the light turns on only while the finger is touched and turns off when the finger is removed; {o} the light turns on when the finger is touched;
The light goes off after a certain period of time, and turns on when you touch it with your finger.
It is conceivable that the light will continue to turn on even when the finger is removed, and turn off when the finger is touched again, but the processing circuit 37 that has such a function is a combination of known circuits such as a flip-flop circuit and a timer circuit. This can be easily realized by

Next, FIG. 16 is a configuration diagram of the resonant circuit 30 when lighting a plurality of EL elements.

As shown in FIG. 16, the drive power source 15 and the coil 20'
Coils 21', 21''..., EL elements 22', 22..., capacitors 23', 23
"..., switching elements 13', 13"... may be connected in parallel.

In the above description, an example is given in which an EL element is used as a display element, but the present invention can be similarly applied to a case where a liquid crystal element, an electrochromic element, or the like is used.

As explained above, according to the present invention, it is possible to use the electrodes of a thin display element as a sensor, so it becomes extremely thin and easy to install, improving mounting efficiency, and the entire surface of the sensor Since it becomes a light emitting body, it has the effect of easily realizing a large area.

[Brief explanation of drawings]

Figures 1 and 2 are an example of a conventional device, Figure 3 is an example of an EL element drive circuit, Figure 4 is an equivalent circuit diagram of Figure 3, and Figure 5 is a thin display element used in the present invention. FIG. 6 is a sectional view taken along the line A-A' in FIG. 5, FIG. 7 is a principle diagram of the present invention, FIGS.
2 to 14 are block diagrams of embodiments of the present invention, FIG. 15 is a circuit diagram of an embodiment of the present invention, and FIG. 16 is a circuit diagram for lighting a plurality of EL elements. Explanation of symbols, 1...Button, 2...Switch body, 3...Light emitting diode, 4...
・Terminal, 5...Sensor panel, 6...
Light emitting diode, 7...Detection circuit, 8...
Switching circuit, 9...Power supply, 10...Capacitance upon contact, 11...Capacitance of human body, 12...
Hum noise, 13... Switching element, 14...
...EL element, 15...AC power supply, 15'...
...Current, 16...Glass substrate, 17...Electrode, 18...Display layer, 19...Counter electrode, 2
0, 21... Coil, 22... EL element,
23... Capacitor, 24... Capacity at the time of contact, 25
~27...Characteristic curve, 28,29...
Resonance point, 30... Resonance circuit, 31...
Oscillation circuit, 32...Narrowband bandpass filter, 33 Detection circuit, 34...Sensor oscillator, 3
5...Power supply for driving EL element, 36...
Output terminal, 37...processing circuit, 38...control input terminal. 1 figure 2 figure 3 figure 4 figure 5 figure 6 figure off figure 8 figure 9 figure

Claims (1)

[Claims] 1 Parallel circuit of switching element and capacitor, 1st
A resonant circuit formed by connecting a coil, a thin display element, a second coil, and a power supply in series, and detecting a change in the resonant frequency of the resonant circuit that occurs when a human body approaches or contacts an electrode of the thin display element. What is claimed is: 1. A display element drive circuit comprising: a detection circuit for controlling the switching element; and a circuit for controlling opening and closing of the switching element in a predetermined operation mode according to the output of the detection circuit.