JP2002343561A - Drive circuit of organic electroluminescence element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a drive circuit that can prolong the life by suppressing the deterioration of the strength of the light-emission by applying to the organic electroluminescence element that performs a so-called simple matrix type display. SOLUTION: This is an organic electroluminescence element in which a plurality of positive electrodes A1-A3 and a plurality of negative electrodes B1-B4 cross opposed to each other and an organic layer having at least a luminous layer is interposed between both electrodes, and by using the negative electrodes B1-B4 as a scanning line, all of the scanning lines are scanned as one field by a prescribed frequency and any of the negative electrodes B1-B4 is selected one by one, and, synchronizing with this, a drive source is connected to the positive electrodes A1-A3. Thereby, the crossing points of both electrodes emit light as a picture element. After the scanning of the above one field, a reverse voltage Vk is impressed simultaneously on all of the above picture elements for a certain time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a driving circuit for an organic electroluminescent device (OLED) for performing a so-called simple matrix type display.

[0002]

2. Description of the Related Art OL having a light emitting layer composed of an organic compound
EDs have been attracting attention for realizing direct-current low-voltage driving. For example, Japanese Patent Publication No. 6-32307 discloses that an indium tin oxide (ITO) semi-transparent film is formed on the upper surface of a transparent glass substrate. An anode is formed, and a hole injection layer, a light emitting layer, and a cathode made of a coating of aluminum (Al) are sequentially formed thereon, and a power source is connected between the anode and the cathode. The disclosed structure discloses that the generated holes are transmitted to an interface between the hole injection layer and the light emitting layer, where the holes are combined with the electrons transmitted from the cathode and emit visible light.

In the OLED, the anode and the cathode are formed in a plurality of strips, respectively, and the anode and the cathode are arranged in a lattice. Each intersection point is defined as a light emitting point (pixel).
Either the anode or the cathode is sequentially selected and scanned at predetermined time intervals, and the other is driven by a DC constant current circuit as a driving source in synchronization with the scanning, so that any of the pixels emits light. An OLED for performing a so-called simple matrix type display and a driving circuit thereof are known.

[0004]

In such an OLED, when used for a long period of time, charge accumulates at the interface between the hole injection layer and the light emitting layer, so that the intensity of light emission in the element decreases. There was a problem.

In order to solve such a problem, for example, Japanese Patent No. 2666648 (prior art) discloses an OLED having at least one set of a counter electrode, an organic hole injection layer, and an organic light emitting layer. A technique for applying power of the opposite polarity is disclosed.

According to this prior art, it is possible to extend the life of the OLED by maintaining the initial light emission intensity for a long time, but it shows only general applicability, and it has recently been put to practical use. There has been no known driving circuit suitable and specific for an OLED which performs a so-called simple matrix type display.

The present invention has been made by paying attention to such a point, and is applied to an OLED which performs a so-called simple matrix type display, whereby a drive circuit capable of suppressing a decrease in light emission intensity and extending a life. The purpose is to provide.

[0008]

According to a first aspect of the present invention, there is provided an OLED drive circuit, wherein a plurality of anodes and a plurality of cathodes intersect while facing each other. An organic layer having at least a light-emitting layer is interposed between the two electrodes, and one of the two electrodes is used as a scanning line and all of the scanning lines are scanned as a field at a predetermined frequency to sequentially select one of the scanning lines. A driving circuit for an organic electroluminescent device that emits light by using a point of intersection where the two electrodes intersect as a pixel by connecting a driving source to the other while synchronizing with the driving source. And a reverse voltage is applied at the same time.

According to a second aspect of the present invention, a plurality of anodes and a plurality of cathodes intersect while facing each other, an organic layer having at least a light emitting layer is interposed between the two electrodes, and one of the two electrodes is connected to a scanning line. By scanning all of these scanning lines at a predetermined frequency as one field, one of the scanning lines is sequentially selected, and a driving source is connected to the other in synchronization with the scanning lines, thereby intersecting the intersection of the two poles. Is a driving circuit of an organic electroluminescent element that emits light by using a pixel as a pixel, and applies a reverse voltage to all of the pixels simultaneously for a predetermined time during the one-field scanning.

According to a third aspect of the present invention, a plurality of anodes and a plurality of cathodes intersect while facing each other, an organic layer having at least a light emitting layer is interposed between the two electrodes, and one of the two electrodes is connected to a scanning line. By scanning all of these scanning lines at a predetermined frequency as one field, one of the scanning lines is sequentially selected, and a driving source is connected to the other in synchronization with the scanning lines, thereby intersecting the intersection of the two poles. Is a driving circuit for an organic electroluminescent element that emits light by using a pixel as a pixel, and applies a reverse voltage to all of the pixels simultaneously for a predetermined time after the one-field scanning.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described based on embodiments shown in the accompanying drawings.

FIGS. 1 to 3 show a driving circuit according to an embodiment, in which a row (horizontal direction) × a column (vertical direction) = 3 × 4 = 12
1 shows a case where the number of pixels is two. For example, when such an OLED is used as a display device that displays numbers such as a odometer or a clock of a vehicle in one line, the number of the rows is determined by the number of digits to be displayed, and the number of the columns is about 16 .

A1 to A3 are anodes, B1 to B4 are cathodes, E
The pixels 11 to E34 are located at the intersections of the anodes A1 to A3 and the cathodes B1 to B4 and emit light.
E34 to E34 are represented by equivalent circuits of light emitting elements each having diode characteristics and a parasitic capacitance connected in parallel to the light emitting elements. In the following description and drawings, pixels E11 to E34 are shown.
Are shown as a light emitting element D and a parasitic capacitance C for an arbitrary pixel Exx. Anodes A1
The drive circuit 10 is connected to A3, and the scanning circuit 20 is connected to the cathodes B1 to B4.

A drive voltage circuit 30 for outputting a drive voltage Va is connected to the drive circuit 10, and switches 11 to 1 for selecting the anodes A1 to A3 are provided between the drive circuit 10 and the anodes A1 to A3.
When the switches 11 to 13 are turned “ON”, the DC constant current circuits 14 to 16 serving as driving sources for driving are connected to the anodes A1 to A3.

The scanning circuit 20 has switches 21 to 24 for sequentially scanning the cathodes B1 to B4 as scanning lines. One end of each of the switches 21 to 24 is connected to the driving voltage circuit 3
A reverse voltage terminal to which a cut-off voltage Vk volt supplied from 0 is applied, and the other end is connected to a ground terminal of 0 (zero) volt. These switches 21 to 24 are sequentially connected to the reverse voltage terminal (not selected). ) And the ground terminal (selection).

The drive circuit 10 and the scanning circuit 2
The control of 0 is controlled by the display control circuit 40. In the drawings, the switches 11 to 1 of the drive circuit 10 are shown.
3, the current Id is supplied from the current circuits 14 to 16 to the pixel E1.
The case where the voltage is applied to any of 1 to 34 is displayed as “ON”, and the case where no voltage is applied is displayed as “OFF”. Also, the scanning circuit 2
For the switches 21 to 24 of 0, the ones connected to the one being scanned among the anodes B1 to B4 are displayed as “selected”, and those not scanned are displayed as “non-selected”. As a result, only one of the pixels E11 to E34 in which the drive circuit 10 is “ON” and the scanning circuit 20 is “selected” emits light.

The control of light emission by such a driving circuit will be described below. In the following, the pixels B22 and E32 emit light by scanning the cathode B2 as a scanning line, and then the cathode B3
Will be described when the pixels E13 and E33 emit light.

In order to scan the cathode B2 to emit light from the pixels E22 and E32, as shown in FIG. 1, the switch 22 of the scanning circuit 20 is switched to the ground terminal on the selection side, and the cathode B2 scans. Have been. The other switches 21, 23, and 24 are switched to the non-selection reverse voltage terminals. Therefore, the potential of the scanning circuit 20 on the pixel side is 0 volt for the switch 22 and Vk volt for the others.

The current circuits 15 and 16 are connected to the anodes A2 and A3 by the switches 12 and 13 of the drive circuit 10, while the other switches 11 are connected to the ground terminal. Therefore, the potential on the pixel side of the drive circuit 10 is Vf volt, which is the predetermined potential of the switches 12 and 13, and the other is 0 volt.

At this time, the pixels E22, E22,
Only E32 is forward biased and the current circuits 15, 1
6, a drive current Id flows from the pixels E22 and E22.
The charge amount Qon of 32 is C × Vf. On the other hand, the charge amount Qoff of the other pixels corresponding to the non-selected portions is C × Vc, and since Vc is the difference between Vk and Vf, the charge amount Qoff is lower than Vf and has a relationship of Qon> Qoff. The other pixels do not emit light, and almost no current flows in the pixels at the non-selected places.

Next, by scanning the cathode B3, the pixels E13 and E13 are scanned.
In order to make 33 emit light, as shown in FIG.
The switch 23 of 0 is switched to the ground terminal on the selection side, and the cathode B3 is scanned. The other switches 21, 22, and 24 are switched to the reverse voltage terminal on the non-selection side. Therefore, the potential on the pixel side of the scanning circuit 20 is 0 volt for the switch 22 and Vk boiling for the others.

The current circuits 14 and 16 are connected to the anodes A1 and A3 by the switches 11 and 13 of the drive circuit 10, while the other switches 12 are connected to the ground terminal. Therefore, the potential on the pixel side of the drive circuit 10 is Vf volt, which is a predetermined potential of the switches 11 and 13, and the other is 0 volt.

At this time, the pixels E13,
Only E33 is forward biased and the current circuits 14,1
6, the drive current Id flows from the pixels E13 and E13.
The charge amount Qon of 33 is C × Vf. On the other hand, the charge amount Qoff of the other pixels corresponding to the non-selected portions is C × Vc, and since Vc is the difference between Vk and Vf, the charge amount Qoff is lower than Vf and has a relationship of Qon> Qoff. The other pixels do not emit light, and almost no current flows in the pixels at the non-selected portions.

Since the scanning of all the cathodes B1 to B4 is completed, that is, the reverse voltage Vk is simultaneously applied to all the pixels Exx for a certain period of time after one field scanning.
As shown in FIG. 3, the switches 11 to 11 of the drive circuit 10
Reference numeral 13 is connected to a ground terminal, and switches 21 to 23 of the scanning circuit 20 are switched to a reverse voltage terminal which is a non-selection side. These operations are performed by the display control circuit 40.

As a result, in all the pixels Exxx, the charges accumulated at the interface between the hole injection layer and the light emitting layer are released by the application of the reverse voltage Vk, and the pixels Exxx return to the initial state (reset operation). Therefore, the deterioration due to the charge can be improved.

Such a reset operation may be performed after completion of the one-field scanning (during the switching from the cathode B4 to the cathode B1), or at any time during the one-field scanning. (For example, during the switching from the cathode B2 to the cathode B3), or may be performed not only during the one-field scanning but also during the scanning, that is, a plurality of field scanning (for example, one field is performed twice). After scanning, a reverse voltage Vk may be simultaneously applied to all of the pixels Exx for a certain period of time.

Although FIGS. 1 to 3 show an example in which the DC constant current circuits 14 to 16 are used as the driving source, the present invention can also be realized by using a DC constant voltage circuit.

The time Tk for applying the reverse voltage Vk is:
Although determined by the characteristics of the OLED, the time Tk for applying the reverse voltage Vk is desirably set to a short time since all the pixels Exx are in a non-light emitting (non-display) state. It is conceivable to set the time to be equal to or shorter than the time T1 for driving one line, which is one of the lines.

That is, while one of the lines is being scanned, the other line is not scanned. Therefore, the time T1 for driving the one line is that the pixel Exx is in the light emitting (display) state. The time is set to a minimum time that can be recognized by the user, and at the time Tk when the reverse voltage Vk is applied, all of the pixels Exx are in a non-display state at the same time. Exceeding the value is considered undesirable.

[0030]

According to the first to third aspects of the present invention, the positive voltage is applied to all the pixels of the organic electroluminescent element which performs a so-called simple matrix type display having a plurality of pixels by applying a reverse voltage to all the pixels. Electric charges accumulated at the interface between the hole injection layer and the light emitting layer are released, whereby it is possible to provide an OLED drive circuit capable of suppressing a decrease in light emission intensity of the pixel and extending the life. .

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention.

FIG. 2 is a circuit diagram of the same.

FIG. 3 is a circuit diagram of the same.

[Explanation of symbols]

 A1 to A3 Anode B1 to B4 Cathode E11 to E34 Pixel 10 Drive circuit 20 Scan circuit 30 Drive voltage circuit 40 Display control circuit

Claims (3)

[Claims] 1. A plurality of anodes and a plurality of cathodes intersect while facing each other, an organic layer having at least a light emitting layer is interposed between the two electrodes, and one of the two electrodes is used as a scanning line, and all of the scanning lines are set to one. By scanning at a predetermined frequency as a field, one of the scanning lines is sequentially selected, and a driving source is connected to the other in synchronization with the scanning line, so that an intersection of the two electrodes intersects the pixel to emit light. A driving circuit for driving a light emitting element, wherein a reverse voltage is simultaneously applied to all of the pixels for a predetermined time during the scanning. 2. A plurality of anodes and a plurality of cathodes intersect while facing each other, an organic layer having at least a light-emitting layer is interposed between the two electrodes, and one of the two electrodes is used as a scanning line and all of the scanning lines are set to one. By scanning at a predetermined frequency as a field, one of the scanning lines is sequentially selected, and a driving source is connected to the other in synchronization with the scanning line, so that an intersection of the two electrodes intersects the pixel to emit light. A driving circuit for an organic electroluminescent element, wherein a reverse voltage is simultaneously applied to all of the pixels for a predetermined time during the one-field scanning. 3. A plurality of anodes and a plurality of cathodes intersect while facing each other, an organic layer having at least a light-emitting layer is interposed between the two electrodes, and one of the two electrodes is used as a scanning line and all of the scanning lines are set to one. By scanning at a predetermined frequency as a field, one of the scanning lines is sequentially selected, and a driving source is connected to the other in synchronization with the scanning line, so that an intersection of the two electrodes intersects the pixel to emit light. A driving circuit for an organic electroluminescent element, wherein a reverse voltage is simultaneously applied to all of the pixels for a predetermined time after the one-field scanning.