JP2002328650A - Drive circuit for organic electric field light emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a drive circuit for organic electric field light emitting elements whose operation is simplified and moreover, whose current consumption can be suppressed. SOLUTION: In this drive circuit for organic electric field light emitting elements, a plurality of anodes A1 to A3 and a plurality of cathodes B1 to B4 intersect while being confronted and organic layers having at least light emitting layers are interposed among both electrodes and one side of both electrodes is made to be scanning lines and performs light emission by making intersection where both electrodes intersect to be pixels E11 to E34 by connecting a driving source to other side of the electrodes in synchronization with scanning while scanning these scanning lines with a prescribed frequency. Then, the scanning lines which are connected to pixels which are not made to emit light in the pixels E11 to E34 are connected to high impedance and when performing an changeover to a next scanning line, the present and the next scanning lines and entire of the other side of both electrodes are connected to the same potential.

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]

The pixel of such an OLED can represent an equivalent circuit by a light emitting element exhibiting diode characteristics and a parasitic capacitance connected in parallel with the light emitting element. For this reason, there is a problem that the rising speed until the light emission is slow and high-speed scanning cannot be performed. In addition, since the parasitic capacitance of all the pixels connected to the anode must be charged, there is a problem that the current capacity of the driving source connected to each anode must be increased.

In order to solve such a problem, for example, Japanese Patent Application Laid-Open No. 9-232074 discloses a driving circuit (method) for performing the simple matrix type display at the time of switching to the next scanning line (the cathode). By connecting all of the scanning lines to a reset voltage of zero volt (or power supply voltage) once having the same potential, the parasitic capacitance of the pixel to be caused to emit light is reduced by the drive source via the drive line (the anode). And is simultaneously charged by the reverse bias voltage of the scanning line through the parasitic capacitance of the pixel that does not emit light, so that the pixel to be caused to emit light instantaneously rises to a potential at which both ends of the pixel can emit light. Therefore, a technology capable of emitting light instantaneously has been disclosed.

However, connecting all the scanning lines to the reset voltage having the same potential at the time of switching to the next scanning line is not preferable because the operation becomes complicated and the driving circuit becomes complicated. Further, since the power supply voltage is applied to the unselected scanning lines, an invalid charging current that does not contribute to light emission flows to the drive lines via the pixels, thereby increasing current consumption. There was a problem.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem of the prior art. It is an object of the present invention to provide a high-speed scanning from the start of supply of a driving current to the emission of light. Along with
An object of the present invention is to provide an OLED driving circuit whose operation is simplified and current consumption can be suppressed.

[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 while scanning one of the two electrodes as a scanning line at a predetermined frequency and connecting a driving source to the other in synchronization with the other, a crossing point where the two electrodes intersect is formed. A driving circuit for an organic electroluminescent device that emits light as a pixel, wherein the scanning line connected to a pixel that does not emit light is connected to a high impedance.

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. A driving circuit for an organic electroluminescent element 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 scanning at a predetermined frequency while scanning at a predetermined frequency, wherein the next scanning line At the time of switching to, at least the current scanning line and all of the other of the two electrodes are connected to the same potential.

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. A driving circuit for an organic electroluminescent element 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 scanning at a predetermined frequency while scanning at a predetermined frequency, wherein the next scanning line The current and the next scanning lines and all the other of the two electrodes are connected to the same potential at the time of switching to.

According to a fourth 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. A driving circuit for an organic electroluminescent element that emits light by using a point of intersection where the two poles intersect as a pixel by connecting a driving source to the other while scanning at a predetermined frequency while scanning at a predetermined frequency. Connect the scanning line leading to the ones not to be connected to high impedance,
At the time of switching to the next scanning line, at least the current scanning line and the other of the two electrodes are all connected to the same potential.

According to a fifth 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. A driving circuit for an organic electroluminescent element that emits light by using a point of intersection where the two poles intersect as a pixel by connecting a driving source to the other while scanning at a predetermined frequency while scanning at a predetermined frequency. Connect the scanning line leading to the ones not to be connected to high impedance,
At the time of switching to the next scanning line, the current and next scanning lines and the other of the two electrodes are all connected to the same potential.

In particular, the same potential is set to zero potential as described in claim 6 in claims 2 to 5.

As a result, it is possible to realize an OLED driving circuit whose operation is simplified and current consumption can be suppressed.

[0015]

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 rows (horizontal direction) × columns (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, DC constant current circuits 14 to 16 serving as a driving source 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 a high impedance terminal to which a high resistance is connected. The other end is connected to a 0 V (zero volt) ground terminal.
4 is sequentially switched to the high impedance terminal (unselected) and the ground terminal (selected).

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.

Control of light emission by such a driving circuit will be described. In the following, after scanning the cathode B2 as a scanning line to cause the pixels E22 and E32 to emit light, the cathode B3
Will be described when the pixels E13 and E3 emit light.

In order to make the pixels E22 and E32 emit light by scanning the cathode B2, 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 is scanned. Have been. The other switches 21, 23, and 24 are switched to non-selected high impedance terminals. Therefore, the scanning circuit 20
The pixel-side potential of the switch 22 is “0 V” for the switch 22 and “HI (high impedance)” for the others.

The current circuits 15, 16 are connected to the anodes A2, A3 by the switches 12, 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” where the switches 12 and 13 are at the predetermined potential.
And the others are “0v”.

At this time, the pixels 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 extremely lower than VF due to the influence of high impedance, the relationship of Qon> Qoff is established. The pixel emits no light, and almost no current flows through the pixel at the non-selected portion.

Next, the cathode B3 is scanned to scan the pixels E13 and E13.
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 non-selected high impedance terminals. Therefore, the scanning circuit 2
The potential on the pixel side of 0 is “0v” for the switch 22 and “HI” for the others.

The current circuits 14, 16 are connected to the anodes A1, A3 by the switches 11, 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” where the switches 11 and 13 are at the predetermined potential.
And the others are “0v”.

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 extremely lower than VF due to the influence of high impedance, the relationship of Qon> Qoff is established. The pixel does not emit light, and almost no current flows in the pixel at the non-selected portion.

Specifically, an OL having an overall area of 8 × 8 mm
When the element capacity of the ED is 2000 when the light emission start drive voltage VF = 4 V
In the case of 0 pF, if all the pixels E have an area of 0.6 × 0.6 mm, the parasitic capacitance C of an arbitrary pixel Exx becomes 20,000pF.
F ÷ (8 × 8 mm) × (0.6 × 0.6 mm) = 112 pF, and if the high impedance is 1000 MΩ, the time constant τ
Is 1000 MΩ × 112 pF = 112 ms. Incidentally, the light emission start drive voltage VF is not the line voltage VF but the pixel E
should use the voltage VE applied directly to xx,
VF is used as VE is substantially equal to VF.

The maximum value T of the time during which the light emission start voltage VF is applied to the pixel Exx when the pixel is not selected (the switch of the scanning circuit 20 is open) is 16 scanning lines (for example, cathodes) (line). ) And the frame frequency is 100H
When z and duty are 1/16, T = 1/100 Hz x 1/16 x 1
5 lines = 625 μsec × 15 lines = 9.4 ms.

Accordingly, since the maximum application time T of the pixel Exx at the time of non-selection is less than the time constant τ required for light emission, the pixel Exx at the time of non-selection does not emit light. When the area of the pixel Exx is reduced with the recent miniaturization of the display, the time constant τ is also reduced.
Even if the pixel Exxx has an area of 0.35 × 0.35 mm, the time constant τ is about 38.0 ms, and the maximum application time T
Since it is sufficiently longer than 9.4 ms, the pixel E
xx does not emit light.

As described above, the cathodes B2 and B3 are scanned to shift from FIG. 1 to FIG. 3, and the pixels E22 and E3 are scanned.
Light emission can be switched from 2 to the pixels E13 and E33. When the pixel is not selected, almost no current flows through the pixel Exx that does not emit light due to the high impedance terminal. Therefore, it is possible to suppress an invalid charging current that does not contribute to light emission and reduce the current consumption as compared with the related art. .

By the way, before shifting from FIG. 1 to FIG. 3,
As shown in FIG. 2, the potentials of the anodes A1 to A3 are made equal to the cathode B2 that has been scanned, that is, the switches 11 to 13 of the drive circuit 10 are connected to the ground terminal,
It is set to “0 V” which is the same as the switch 22 of the scanning circuit 20.

As a result, the cathode B2 and the anodes A1 to A3 have the same potential "0 V", so that the pixel E connected to the cathode B2
All the charge charges from 12 to E32 are discharged to zero.
Thus, it is possible to prevent a so-called pseudo light emission in which the charge is accumulated in the pixels E12 to E33 in a superimposed manner after the shift to FIG. In addition, since this step only requires the operation of the switches 11 to 13 of the drive circuit 10, the operation can be simplified.

In the step of FIG. 2, as shown in FIG. 4, the switch 23 of the scanning circuit 20 is switched to the ground terminal, and all the pixels E13 to E33 connected to the cathode B3 to be scanned next are all charged. Discharging the charges makes it possible to uniformly reduce the individual charged charges stored in the pixels E13 to E33 connected to the cathode B3 to zero, thereby making the rise time of the pixels E13 to E33 constant. . In addition, the switch 23 is switched to the ground terminal when scanning the cathode B3, so that the operation is not complicated.

Although FIGS. 1 to 4 have described the examples in which the DC constant current circuits 14 to 16 are used as the driving sources, the present invention can be realized in the same manner as described above by using a DC constant voltage circuit.

[0036]

According to the first, fourth, and fifth aspects of the present invention, almost no current flows to a pixel that does not emit light due to the high impedance terminal when it is not selected, and thus does not contribute to light emission. It is possible to realize a drive circuit that suppresses an invalid charging current and reduces current consumption as compared with the related art.

According to the second and fourth aspects of the present invention, there is provided a drive circuit capable of preventing a so-called pseudo light emission in which a charge is accumulated in a pixel in a superimposed manner and emits light despite being unselected. can do.

According to the third and fifth aspects of the present invention, it is possible to prevent the so-called pseudo light emission in which the charge is accumulated in the pixel in a superimposed manner and light is emitted although the pixel is not selected. Discharging all the charged charges for the selected pixels to be scanned also makes it possible to uniformly reduce the individual charged charges stored in those pixels to zero, and to drive the pixels so that the rise time of light emission of those pixels is constant. A circuit can be realized.

According to the sixth aspect of the present invention, it is sufficient to switch to the ground level in order to make the potential zero, so that it can be easily realized without preparing a special circuit separately.

[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.

FIG. 4 is a circuit diagram showing an application example of FIG. 2;

[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

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) // H05B 33/14 H05B 33/14 A

Claims (6)

[Claims] 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 while scanning at a predetermined frequency. In synchronization with this, a driving circuit for an organic electroluminescent element 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, and the scanning line that leads to a pixel that does not emit light among the pixels. A driving circuit for an organic electroluminescent device, wherein the driving circuit is connected to a high impedance. 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 while scanning at a predetermined frequency. A driving circuit of an organic electroluminescent element that emits light by using an intersection where the two electrodes intersect as a pixel by connecting a driving source to the other in synchronization with the other, and at least at the time of switching to the next scanning line, A driving circuit for an organic electroluminescent device, wherein a scanning line and all of the other of the two electrodes are connected to the same potential. 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 intervenes between the two electrodes, and one of the two electrodes is used as a scanning line while scanning at a predetermined frequency. A driving circuit of an organic electroluminescent element that emits light by using an intersection where the two electrodes intersect as a pixel by connecting a driving source to the other in synchronization with the current, and the current and the next at the time of switching to the next scanning line. A driving circuit for an organic electroluminescent device, wherein the scanning line and the other of the two electrodes are all connected at the same potential. 4. A plurality of anodes and a plurality of cathodes intersect while facing each other, an organic layer having at least a light emitting layer intervenes between the two electrodes, and one of the two electrodes is used as a scanning line while scanning at a predetermined frequency. In synchronization with this, a driving circuit for an organic electroluminescent element 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, and the scanning line that leads to a pixel that does not emit light among the pixels. A driving circuit for an organic electroluminescent device, wherein the driving circuit is connected to high impedance, and at least the current scanning line and all of the other electrodes are connected to the same potential at the time of switching to the next scanning line. 5. 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 while scanning at a predetermined frequency. In synchronization with this, a driving circuit for an organic electroluminescent element 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, and the scanning line that leads to a pixel that does not emit light among the pixels. A driving circuit for an organic electroluminescent device, wherein the driving circuit is connected to a high impedance, and the current and the next scanning line and all of the other electrodes are connected to the same potential when switching to the next scanning line. 6. The driving circuit for an organic electroluminescent device according to claim 2, wherein the same potential is set to zero potential.