JPS6025853B2 - Display element drive circuit - Google Patents

Description

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

2. Description of the Related Art Many display devices for displaying various operating states are used in various machines and devices such as televisions and elevators.

As a subsidiary display device, for example, as shown in FIG. IL (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 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 radiates from the front of the button 1, making it appear as if the head of the button It appears to emit light. Note that 4 in FIG. 1 is a terminal for wiring.
In the push-button type display device as described above, the structure is complicated, the light emitting part is difficult to make large area, and the depth of the device is large. There are drawbacks such as the need for mounting holes and the need for multiple mounting on the same plane. As a display device that has improved the above-mentioned drawbacks, there is a display device having a static 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 (for example, a capacitance change due to a person touching the front surface of the sensor panel 5) between the sensor panel 5, which also serves as a display section, and the ground plane. The switching circuit 8 is turned on by the signal. When turned off, the light emitting diode 6 (or light bulb) blinks and emits light forward via the sensor panel 5. In addition, in FIG. 2, 9 is a power supply. Display devices that detect changes in capacitance as described above are currently widely used in elevators, etc. However, even with this device, it is difficult to display a large area, and the depth is also large because it requires the installation of light bulbs, etc. There is a problem with implementation. SUMMARY OF THE INVENTION An object of the present invention is to provide a display element driving 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 main point 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 to use a capacitive detection type electrode that is opposite to the element (or electrodes arranged in parallel). The problem that arises when used as a sensor 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 Figure 3, 1 is the capacitance when the Kawama human body key EL element 1 and 4's electrodes are in contact with each other via the panel (the capacitance between the electrode and the finger is approximately several pF), and 11 is the impedance of the human body. (For 50 to 60 days 2, the value is sufficiently small compared to the impedance of 10.) 12 is hum noise caused by the human body, 13 is a switching element, 14 is an EL element, and 15 is an MC power supply. 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 on the order of 100 F/.

On the other hand, when a human body contacts the electrode through the panel, the capacitance (10) is only a few pF, so the voltage change at point P is very small.

For example, FIG. 4 is an equivalent circuit of FIG. 3, and Z.

,Z,. , Z, 3, Z, 4 are respectively 10, 1 1, 1
3, 14 (however, Z, 3 is the interelectrode capacitance of the switching element 13, which is about 3 pF), and V. is the hum noise of the human body. In Figure 4, the voltage Vp at point P at 50Hz is Z13 Otsu 4Vp=Otsu 3 Otsu 40 (Z, 30 Z, 4) (Otsu.

10Z,. )V. It will be 21 hV. Therefore, the detection circuit needs to be able to detect changes of about 1 V, but considering the variations in each element, noise, etc., it is difficult to detect changes at the minimal level of about 1 hV, and it is difficult for practical use. There was no production.

The present invention solves the above problems by providing switching elements before and after the display element to increase the impedance of the circuit so that hum noise can be detected at a high level.

Hereinafter, the present invention will be explained in detail based on the drawings. FIG. 5 is a front view of an example of an EL element used in the present invention, and FIG. 6 is a cross-sectional view taken along line AA' in FIG.

In FIGS. 5 and 6, first, the transparent glass substrate 16
The electrode 17 is formed by forming a ln203 nesa film (for example, film thickness 2000A, sheet resistance 1500/m) on one side of a board (for example 40 x 4 sides), and then removing the nesa film leaving a predetermined pattern by etching. Form. Next, the display layer 18 is formed by screen printing using a phosphor printing paste for electroluminescence. Note that if the thickness of the display layer 18 is less than 10 rm, the dielectric strength will be insufficient, and if it is more than 40 rm, a high voltage will be required to obtain sufficient light emission, so it is desirable to set the thickness to about 10 to 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, FIG. 7 is a diagram showing the principle of the present invention.

In FIG. 7, when a human body contacts the electrode of the EL element 25 through the panel, the capacitance 21 is the capacitance of the human body, 22 is the hum noise of the human body, and 23 and 24 are provided at both ends of the EL element. 25 is an EL element, 26 is a discharging resistor connected in parallel with the EL element 25 (not required if the driving power source is an AC power source), and 27 is a driving It is a DC power supply.

In the circuit shown in FIG. 7, when the switching elements 23 and 24 open and close, a square wave electric field is applied to the EL element 25 and the E
The L element 25 emits light.

In the above circuit, the equivalent circuit when the switching elements 23 and 24 are off is as shown in FIG.

In FIG. 8, the combined impedance of the EL element 25 and the parallel resistor 26 is Z25, and the impedance of the capacitances 20 and 21 is Z, respectively, and the switching element 23
, 24 interelectrode capacitances are Z3,
Set it to Z4 and set the hum noise to V.

For example, hum noise V at 50 days 2. The voltage V^ at point A according to is Z4 (Z23 + Z25) V^ = Z4 (Z2 + Z meat) + (Z.

10Z, XZ3 40Z5) V. D becomes 1.3V. As described above, by inserting switching elements on both sides of the EL element and turning them off to increase the impedance of the circuit, it is possible to increase the hum noise at point A and make it detectable.

Next, FIG. 9 is a circuit diagram of an embodiment of the present invention based on the above principle. In FIG. 9, switching circuit 2
Reference numeral 9 is composed of transistor switching elements 34, 35, etc., and the two switching elements 34, 35 open and close in the same phase in response to a control signal applied to the control input terminal 28.

Next, the hum noise injected into point A by the human body coming into contact with the electrode of the EL element 25 through the panel is applied to the amplifier circuit 30 via the DC blocking capacitor 36, and is input to the amplifier circuit 30'. After the signal is amplified to an appropriate level, it is sent to a low-pass filter 31.

The low-pass filter 31 has a hum noise frequency (50~
60Hz) (for example, spike noise components due to shifts in switch timing between switching elements 34 and 35) are removed, and only hum noise components are output.

If the switching circuit consisting of transistors 37 and 38 is controlled by a signal obtained by rectifying this output by the rectifier circuit 32, the output terminal 33 will have a high level while hum noise is injected, and a low level when no hum noise is injected. A discrimination signal is obtained. This discrimination signal is applied to a processing circuit 39 using, for example, a flip-flop circuit, and performs processing according to the operation mode of the display element.

Then, by operating the oscillator 40 in accordance with the output of the processing circuit 39 and applying the oscillation output to the control input terminal 28 of the switching circuit 29 to open and close the switching elements 34 and 35, the EL element 25 can be set to any operating mode. You can make it blink by pressing -. The above operation modes include, for example, 'a) the light turns on only while the finger is touched and turns off when the finger is removed, {b) the light turns on when the finger is touched and turns off after a certain period of time, and the light turns off after a certain period of time; One conceivable example would be something that lights up when you touch it, continues to light up even when you remove your finger, and turns off when you touch it again, but the processing circuit 39 that has such a function is either a flip-flop circuit or a timer circuit. This can be easily realized by roughly combining known circuits such as the following.

In the case of FIG. 9, the output signal of the oscillator 40 is made into a square wave with a frequency sufficiently higher than the frequency of the hum noise (for example, 500 Hz), so that the EL element 25 is turned on using the DC power supply 27, and the EL element 25 is injected from point A. It is possible to accurately detect hum noise by distinguishing it from other signals.

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 or an electrochromic element 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, which makes it extremely thin and easy to install, and improves the mounting efficiency.Moreover, the entire surface of the sensor emits light. Since it becomes a 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. A front view of an example, FIG. 6 is a sectional view taken along line A-A' in FIG. 5, FIG. 7 is a diagram of the principle of the present invention, FIG. 8 is an equivalent circuit diagram of FIG. 7, and FIG. FIG. 2 is a circuit diagram of one embodiment. 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, IQ...Capacitance upon contact, 11...Capacitance of human body, 12.・・・・・・
Hum noise, 13...Switching element, 14
...EL element, 15 ...AC power supply, 1
5'... Current, 16... Glass substrate,
17... Electrode, 18... Display layer, 19...
...・Counter electrode, 20...Capacitance at the time of contact, 2
1... Human body capacitance, 22... Hum noise, 23... Switching element, 25...
...EL element, 26...Resistance, 27...
・DC power supply, 28...Control input terminal, 29...Switching circuit, 30...Amplification circuit, 31...
・Low pass filter, 32... Rectifier circuit, 33...
...Output terminal, 34, 35...Switching element,
36... Capacitor, 37, 38... Transistor 39... Processing circuit, 40... Oscillator. Spear l figure 2 figure 3 figure spear 4 figure O 5 figure ice 6 figure off figure 8 figure figure 9 figure

Claims (1)

[Claims] 1. A loop circuit formed by connecting in series a power supply, a first switching element, a thin display element, and a second switching element that opens and closes in the same phase as the first switching element;
A detection circuit that detects the hum noise injected when a human body approaches or contacts the electrode of the thin display element, and a circuit that controls opening and closing of the first and second switching elements in the same phase according to the output of the detection circuit. A display element drive circuit comprising: