JP3102411B2 - Driving circuit for organic thin film EL device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an organic thin film E utilizing the electroluminescence (EL) phenomenon of an organic thin film.
The present invention relates to a driving circuit for an L element, and more particularly to a driving circuit for an organic thin film EL used when displaying a character or a figure by driving an EL element in a matrix.

[0002]

2. Description of the Related Art When a certain kind of organic thin film is sandwiched between an anode and a cathode, when current is applied, holes and electrons injected from the respective electrodes are recombined in the organic thin film, and the energy at that time causes a light emission phenomenon. It is known to occur. This phenomenon is called an organic thin film EL, and can be driven by a DC voltage of several volts to several tens of volts, has higher luminous efficiency than other display devices, and has advantages such as a thin and light body. Therefore, research is being actively conducted toward application to various light emitting devices.

[0003] This EL phenomenon occurs even when the organic thin film capable of emitting light (hereinafter, referred to as an organic light emitting thin film layer) is a single layer. It is necessary to improve the efficiency of injecting carriers into the layer. Therefore, for the purpose of reducing the height of the energy barrier between the electrode and the organic light-emitting thin film layer and facilitating the transfer of carriers to the organic light-emitting thin film layer, a carrier injection layer or A laminated structure to which a carrier transport layer is added has been proposed. For example, JP
JP-A-6-314 discloses a structure of an anode / organic hole transport layer / organic light emitting thin film layer / cathode disclosed in JP-A-7-51781.
No. 594 / A plurality of organic hole injection / transport layers /
A laminated structure such as a structure of an organic light emitting thin film layer / a plurality of organic electron injection / transport layers / a cathode is exemplified. Note that the stacking order may be the reverse of these examples. FIG. 5 shows the anode / organic hole transport layer / organic light emitting thin film layer /
A cross section of a general organic EL device having a laminated structure having a cathode and a method of applying a voltage to the device are shown.

Referring to FIG. 5, an organic thin film EL shown in FIG.
As a material constituting the device, first, since the electrode must take out light from the organic light emitting thin film layer, at least either the negative or positive electrode needs to have translucency. In many cases, a film of indium tin oxide (ITO) or a thin film of gold is used for the anode 31. On the other hand, for the cathode 34, a material having a small work function is selected for the purpose of reducing the height of the electron injection barrier, and a metal film of magnesium, aluminum, indium, or the like, or an alloy film of these metals is used. For the organic hole transport layer 32, an aromatic tertiary amine, a porphyrin derivative, or the like is used. For the organic light emitting thin film layer 33, an 8-hydroxyquinoline metal complex, a butadiene derivative, a benzoxadol derivative, or the like is used. . Although not used in the illustrated organic thin film EL device, in the case of a structure having an organic electron transporting layer, a naphthalimide derivative, a perylenetetracarboxylic acid diimide derivative, a quinacridone derivative, or the like is used for the structure. The electrodes and the organic thin film layer can be formed on a supporting substrate such as a glass or resin film by a dry film forming method such as vacuum evaporation or sputtering, or by spinning a solution obtained by dispersing or dissolving the above-described material in a resin or a solvent. It is formed by sequentially laminating by a wet film forming method such as coating or dipping. When a light-transmitting electrode (in this case, the anode 31) is formed on the first layer, it is necessary that the support substrate 30 also be light-transmitting.

By the way, when a voltage is applied to the EL element configured as described above, a voltage-current characteristic similar to a diode as shown in FIG. 6 is exhibited. Therefore, current driving is generally performed to drive the element.

As a device to which the organic thin film EL having the above-described structure and electrical characteristics is applied, conventionally, the organic thin film EL element structure exemplified above is used as a unit pixel, and the unit pixel is formed on a single supporting substrate by a plane. There has been proposed a flat light-emitting organic thin-film EL display which is two-dimensionally arranged and driven by a matrix. One example (conventional example 1) is disclosed in JP-A-7-36.
No. 410 discloses this. That is, referring to FIG. 7, which shows a principle circuit diagram of the driving circuit of the conventional example 1 according to the above publication, the display panel 10 is driven by an X driver 12 and a Y driver 14. Signal electrodes 16-0, 16-1, 16-
2,... And scanning electrodes 18-0, 1 from the Y driver 14.
.. Constitute a matrix of the display panel 10. The light emitting elements 20 are connected to the respective intersections of the matrix. The X driver 12 includes constant current sources 22-0, 22-1, 22-2,..., And these constant current sources 22-0, 22-1, 22-2,. While receiving the pulse signal 26, the power supply voltage (= + V) is received, and the signal electrode 16−
A constant current for lighting the light emitting element is output to 0, 16-1, 16-2,... Further, the Y driver 14 includes switch elements 28-0, 28-1,..., Which are turned on and off by a control signal 29 from the control computer 24, and scan electrodes 18-0, 18-. The matrix drive is performed by connecting 1,... To the ground or cutting off from the ground.

FIG. 11 shows a more specific circuit configuration of FIG. 7 described above. In FIG.
The video signal is supplied to a shift register 38 as a memory via an A / D converter 36, and the shift register 38 includes a plurality of flip-flop circuits (hereinafter, referred to as FFs) 44 to 44. The signal from the FF in the shift register 38 is supplied to the PWM modulators 48 to 48 via the FFs 46 to 46 in the X driver 40. Signals (analog signals indicating pulse widths corresponding to luminance data) from the PWM modulators 48 to 48 are applied to the signal electrodes A0, A1, A2, A
, While the FF 50 in the Y driver 34
Signals from the scanning electrodes K0, K1, K2, K3,.
, And these signal electrodes A0, A1, A2, A3,.
, And the scanning electrodes K0, K1, K2, K3,... Constitute a matrix of the display panel 30. In the display panel 30, the signal electrodes A0, A1, A2, A3,.
At the intersection with 0, K1, K2, K3,..., The signal electrodes A0,
A1, A2, A3,... And scanning electrodes K0, K1, K2, K3,
Are connected to the light-emitting elements 52 to 52.

A timing generator 42 as a controller receives a horizontal synchronizing signal and a vertical synchronizing signal,
It outputs signals SCLK, LCLK, FPUL, and FCLK. The signal SCLK is supplied to the FFs 44 to 44 in the A / D converter 36 and the shift register 38, the signal LCLK is supplied to FFs 46 to 46 in the X driver 40, and the signals FPUL and FCLK are supplied to the FFs 50 to 46 in the Y driver 34. 50.

The timing chart of the X driver shown in FIG. 12A will be described with reference to the drawings. Each time the A / D converter 36 A / D converts a video signal and samples it, an A signal is output.
The / DATA-converted data DATA is sequentially shifted to the FFs 44 to 44 in the shift register 38 by the signal SCLK. When all of the data DATA for one horizontal synchronization period is sent to the FFs 44 to 44, the data in the FFs 44 to 44 is changed to the F in the X driver 32 by the signal LCLK.
The signals are supplied to the PWM modulators 48 to 48 via F46 to F46. The PWM modulators 48 to 48 convert the transmitted data into PWM signals.
M-modulate, and apply a pulse having a length corresponding to the data to the signal electrode A
0, A1, A2, A3, ... are output.

The timing chart of the Y driver shown in FIG. 1B will be described. The signal FPUL goes to the “High” level once during the vertical synchronization period, and the signal FPUL is turned on by the signal FCLK.
UL pulses are applied to scan electrodes (lines) K0, K1, K2, K
It is sequentially transferred to 3, ... Then, the scanning line K0
When (n = 0, 1, 2, 3,...) Is at the “High” level,
The line K0 is turned on. The signal FC
LK outputs a pulse once in one horizontal synchronization period, and outputs a signal FP.
UL outputs a pulse once in one vertical synchronization period.

As described above, Japanese Patent Application Laid-Open No. 7-364
No. 10 discloses a method of driving a matrix light emitting element by constant current driving.

Next, JP-A-3-157690 discloses that
The second type conventionally used for driving a thin film EL display
An example of the second method (conventional example 2) is disclosed. That is, when gradation display is performed by applying a pulse width modulation method to a display device EL in which an EL element is interposed between a plurality of scanning electrodes arranged in a direction crossing each other and a plurality of data electrodes. This is a driving method in which a pulse voltage having a waveform in which the peak value of the front part of the pulse is higher than the peak value of the rear part of the pulse is used as the voltage applied to each picture element on the selected scanning electrode. Referring to FIG. 8 showing a pulse waveform in the driving method of Conventional Example 2, FIG.
8B shows a pulse waveform in the light emission state of the intermediate luminance BX, and FIG. 8C shows a pulse waveform in the non-light emission state (luminance BO). Is shown. Here, a ramp voltage having a waveform in which the peak value decreases from the pulse front to the pulse rear is used. The driving method of Conventional Example 2 is mainly used for an EL display having a first field and a second field and driven by an AC voltage, and operates an EL element at an effective voltage (Vw2) near a threshold value. In order to perform a gradation display without uneven brightness when this is performed, a high voltage (Vw1) is applied to the EL element in the first stage of light emission, and the electric charge accumulated in the light emitting layer of the EL element constituting the pixel The present invention is directed to a method of driving an EL element by using an AC voltage, with the object of eliminating light emission and causing light emission not affected by accumulated charges.

[0013]

The first problem in the above-mentioned prior art is that the flat emission type organic thin film E of the prior art 1 is used.
In the L display, a constant current drive signal is supplied to a signal electrode in accordance with an input signal. However, when driven by a square pulse signal at this time, the rise of the pulse is delayed, and the luminance does not increase. . Organic thin film EL
Since the device has a junction capacitance, if it is driven with a constant current, it first charges the capacitance and then shifts to the light emission operation.
This is because it takes time for the voltage to increase until the start of light emission.

In order to simplify the explanation and facilitate understanding, one pixel is extracted from the circuit diagram shown in FIG. That is, it is driven by the configuration. Here, when the organic EL element 20 is driven by the square-wave pulse signal 26, the OA in the voltage waveform shown in FIG.
A pulse voltage indicated by PQ is applied. In FIG. 10, a voltage VF on the vertical axis is a forward voltage of the EL element,
The voltage Va is a voltage at which the EL element starts emitting light. The time ta on the horizontal axis is the time from the start of driving with a pulse to the start of light emission. The time T is a time during which a driving pulse is applied to the EL element, and is, for example, 1/64 duty and repetition frequency 1 in dynamic lighting.
If driven at 50 Hz, T is about 104 μs.

Referring to FIG. 10, although the driving pulse is originally applied for the period T, the EL element actually emits light for the time (T-ta). It can be seen that the luminance of the image becomes darker by the time ta. A specific example is that the element size of the EL element is 0.52
In the case of mm × 0.52 mm, the junction capacitance is about 670 pF, and the time ta is about 30 μs. This time ta =
30 μs is a value that cannot be ignored compared to the time T = 104 μs. Since the peak luminance is 13800 cd / m ² (at the time of direct current), the average luminance is 216 cd / m ^{2, but} is greatly reduced to 126 cd / m ² . As the size of the matrix becomes larger and the duty becomes smaller, the time T becomes shorter without changing the time ta. And
When ta> T, light emission becomes impossible.

Next, a second problem in the conventional technology is as follows.
In the flat emission type organic thin film EL display of Conventional Example 1,
This means that the life of the EL element is shortened.
The luminance of the organic EL element is determined by the current. For this reason, as described above, in order to obtain the required luminance while the rising of the driving pulse is slow, the current value must be increased more than necessary, and more current must be passed to the EL element. As a result, the temperature of the EL element rises, and the deterioration of the element is accelerated.

Accordingly, an object of the present invention is to provide an organic thin film EL which can prevent a decrease in luminance even when a capacitive element is driven.
It is to provide a driving circuit of the element.

Another object of the present invention is to extend the life of the organic thin film EL device.

[0019]

According to the present invention, there is provided a driving circuit for an organic thin film EL device, comprising: a plurality of organic thin films including a light emitting layer made of an organic substance and a signal electrode and a scanning electrode at least one of which sandwiches the light emitting layer. In a drive circuit of an organic thin film EL element for matrix driving of an EL element, a current drive means for supplying a constant current drive signal to the signal electrode according to an input signal, and a pulse synchronized with an output of the current drive means And a charging circuit that charges a junction capacitance of the organic thin-film EL element to a predetermined potential by an output of the pulse generator.

The driving circuit of the organic thin-film EL device of the present invention comprises:
A current driving means for supplying a constant current driving signal for driving the EL element is provided with a charging circuit for charging the EL element to a predetermined potential when the driving of the EL element rises by an output of the pulse generator. For this reason, the drive rise of the EL element can be accelerated, and the luminance can be prevented from lowering even in a capacitive element.

[0021]

Next, an embodiment of the present invention will be described with reference to the drawings. First, the basic operation of the first embodiment of the present invention will be described. FIG. 1 is a block diagram showing the operation principle of the present invention, in which one pixel is extracted from a circuit for driving a matrix element. Referring to FIG. 1, charging circuit 2 has switching element 3. The pulse generator 1 has a driving pulse 2
The trigger is applied by 6 and a pulse of a period tb which is very short as compared with the drive pulse period T is output to make the switching element 3 conductive. When the switching element 3 conducts, the power supply voltage + V is directly applied to the EL element. Then, the current limited by the constant current source 22 flows to the EL element 20 in a state where the limitation is removed, and the EL element 20
Is rapidly charged. The on-period tb of the switching element is set in advance to a period in which only the junction capacitance of the EL element 20 is charged. At this time, drive pulse 2
6 also drives the constant current source 22, so that the EL element 2
The current flowing into 0 becomes a state in which the drive pulse and the current by the switching element are added.

FIG. 2 shows a pulse waveform applied to the EL element 20 in this embodiment. Referring to FIG. 2, in the driving method using the constant current of Conventional Example 1, the OAP shown in FIG.
In the present embodiment, the OBPQ is driven by the pulse having the waveform indicated by Q.
It is driven in the state of. Rise period τ of pulse OBPQ
Is determined by a time constant determined by the ON resistance of the switching element 3 and the junction capacitance of the EL element 20, and is a time sufficiently shorter than the pulse width T. Therefore, the decrease in luminance due to this period τ is practically ignored. It is a level that can be done.
As a specific example, if driving is performed at 1/64 duty and repetition frequency of 150 Hz in dynamic lighting, the drive pulse application period T is about 104 μs.
The rising period τ of the pulse OBPQ differs depending on the voltage applied to the EL element 20 and the on-resistance of the switching element 3. For example, if a value of τ = about 2 μs (the voltage applied to the element and the period tb) is selected, the average Brightness is 126c
d / m ² (luminance in Conventional Example 1) to 211 cd / m
^It is improved to ² , and practically there is almost no problem.

It should be noted that any voltage other than the power supply voltage can be applied to the EL element.

Next, a second embodiment of the present invention will be described. FIG. 3 is a block diagram showing a configuration of the second exemplary embodiment of the present invention. The difference from the first embodiment is that a current modulation circuit 4 for modulating the current of the constant current source 22 is provided. The current modulation circuit 4 includes, for example, as shown in FIG. 4, a constant current source 22 used in FIG. 1 and a switching element (transistor) 5 as a charging circuit attached thereto.

Referring to FIG. 4, power supply voltage + V is supplied to constant current source 22 having a current mirror configuration. The transistors 90 and 91 in the constant current source 22 have a reference current Iref.
Is supplied. The constant current from the constant current source 22 is supplied to the EL element 20 via the transistor 92. The transistor 92 flows or cuts off a constant current to the EL element 20 in accordance with the drive pulse 26 applied to the base. Here, the value of the constant current flowing through the EL element 20 is the resistance 9
3 and the resistor 94. The switching transistor 5 is connected to one of the resistors 93 that determines the current value so that both ends thereof can be short-circuited. The switching transistor 5 is connected through an inverter 6 so as to be turned on by a pulse tb generated by the pulse generator 1. In the present embodiment, a charging circuit is configured by the switching transistor 5 and the inverter 6.

Assuming that a pulse having a width tb is generated by the pulse generator, the switching transistor 5 is turned on for a period tb, and the resistor 93 is short-circuited. Then
Since the resistor 93 of the resistors 93 and 94 for setting the current value is short-circuited, the total resistance value is reduced, and the increased current determined by the resistor 94 flows toward the EL element 20. Thus, the current modulation circuit 4 functions to increase the value of the current flowing through the EL element by the period tb.

In the second embodiment, the state of the pulse applied to the EL element is the state indicated by OBPQ in FIG. 2, as in the first embodiment. And
The rising period τ of this pulse is determined by a time constant determined by the on-resistance of the switching transistor 5 and the junction capacitance of the EL element, and is set to a time sufficiently shorter than the driving pulse width T as in the first embodiment. Can be set. That is, if the ratio of the resistance 93 to the resistance 94 and the period of the output tb of the pulse generator are adjusted to about τ = 2 μs,
Since the time is sufficiently short with respect to the entire pulse width T = 104 μs, the decrease in luminance is at a level that causes almost no problem. FIG. 13 shows a configuration of a drive circuit of an organic thin film EL element having a matrix structure to which the present invention is applied.

In FIG. 13, the X driver 60 includes column lines (signal electrodes) C1, C2, C3,.
, And the Y driver 61 drives the row lines (scanning electrodes) R1, R2, R3,... Of the EL panel 62. The X driver 60 has a data signal (XDATA) generated by the data generator 64 and a timing generator 65.
X driver timing signals (XCLK, X
STB, PGEN) is input. In addition, Y driver 6
To 1, a Y driver timing signal (YCLK, YSTB, etc.) generated by the timing generator 65 is input. 4, the data signal (XDATA) is a signal that determines Iref in FIG. 4, and XSTB is a drive pulse in a period T in FIG. 4.

The constant current driver 6 is provided inside the X driver 60.
The circuit according to the present invention (the first and second embodiments shown in FIG. 4 and the like) is connected to one output one circuit at a time. The PGEN generated by the timing generator 65 corresponds to the output of the pulse generator 1 shown in FIGS. 3 and 4, and inputs a pulse of the period tb to the current modulation circuit. At the time when XSTB and PGEN are output from the timing generator 65, there is no difference between the rises of both pulses if both pulses rise at the same time. However, XSTB is output from the constant current drive unit 66 of the X driver 60 as a drive pulse of the organic EL. At this point, the rise of the drive pulse (XSTB) is delayed due to the junction capacitance of the EL element. Therefore, if the current modulation circuit of the present invention is operated using the PGEN having the pulse width tb that has risen at the same time, almost The EL element can be driven without delay in rising. Specifically, it can be started up with a delay of about 2 μs as described above.

FIGS. 14 to 17 show timing charts of the output signals of the X driver 60 and the Y driver 61. FIG.
14 to 17 show driving waveforms of the X driver and the Y driver. In these figures, the EL element is turned on when the waveform of the Y driver is at the L level and the waveform of the X driver is at the H level.

FIG. 14 shows driving waveforms of the conventional X driver and Y driver. The inside of the X driver 60 is configured by a conventional circuit as shown in FIG. From the Y driver 61, drive pulses for one horizontal period T are sequentially output without overlapping each other, such as R1, R2, R3,. In the case of the conventional example shown in FIG.
The delay is caused by the junction capacitance of the L element.

FIG. 15 shows driving waveforms of the X driver and the Y driver when the present invention is applied. By adding the charging circuit of the present invention, the rise of the driving waveform of the X driver is improved. This is as described in FIG.

FIG. 16 shows a case where the present invention is applied.
In the case where there is a screen in which the H level is continuous at the output of the X driver as in (e), the charge of the EL element is not discharged, and if the charge is performed by the charging circuit of the present invention, it is charged more than necessary. As shown in FIG. 16 (e), the level rises to the vicinity of Vcc, the brightness becomes bright, and a phenomenon that a difference in brightness from the case where the luminance rises from the L level occurs.

As a third embodiment, as shown in FIG. 17, this phenomenon is improved by shortening the L level period of one horizontal period from T by tc. As described above, when the period of the Y driver is shortened, the time for which the EL element is turned on is shortened, and the waveform of the X driver has a transparent space for each pulse as shown in (d), (e), and (f). When charging is performed by the charging circuit, the charging is not performed more than necessary, and the phenomenon that the screen luminance differs between when the H level is continuous and when it is not the same can be improved.

In order to set the drive pulse of the Y driver to the period (T-tc) as shown in FIG. 17, it is only necessary to change the pulse width of YSTB of the timing generator 65 from T to (T-tc). At this time, the time of tc is the time of the organic EL.
This is the time until the electric charge charged in the element is sufficiently discharged. However, if the value of tc is too long, the luminance is reduced. Therefore, the value of tc is determined in consideration of a decrease in luminance. Specifically, at the time of the falling PQ of the pulse in FIG. 2, the duty is 1/64, the driving cycle is 150 Hz, and the pulse amplitude is 10 V
In this case, since the time was about 7 μs, the value of tc was 1
If the value of T is about 104 μs, the decrease in luminance falls within 10% or less.

As a specific circuit in the timing generator 65 for setting the drive pulse of the Y driver to a period (T-tc) as shown in FIG. 17, for example, FIG.
If the circuits (a) and (b) are used, the period T
−tc). FIG. 18A shows a case where a pulse in a period T is shortened to a period (T-tc) using a monostable multivibrator. FIG.
(B) is to create the pulse of the period (T-tc) by taking the logical sum of the pulse of the period T and the pulse of the period tc. By using such a circuit, the pulse width of YSTB of the timing generator 65 can be easily changed from T to (T−t
It can be changed to c).

[0037]

As described above, according to the present invention, the current driving means for supplying a constant current driving signal for driving the EL element to the driving circuit of the organic thin film EL element is provided by the output of the pulse generator. A charging circuit is provided for charging the EL element to a predetermined potential when the element starts driving.

If the effect of the charging circuit is too large depending on the contents of the screen and the luminance differs between the case where the EL element is continuously turned on and the case where the EL element is not continuous, the pulse width of the scanning side pulse is set to 1 Make it shorter than the scanning period.

Thus, according to the present invention, when the signal electrode is driven at a constant current by a square-wave pulse signal in response to an input signal, a decrease in luminance can be suppressed even if the EL element is capacitive. This is because the junction capacitance of the EL element can be charged in a very short time, and the EL element can be driven without delaying the rise of the pulse.

Further, according to the present invention, the life of the EL element can be extended. This is because it is not necessary to supply a large amount of current in order to obtain the required luminance while the rising of the driving pulse is slow, and the unnecessary rise in the temperature of the EL element is suppressed.

Further, when the period of the scanning pulse is shortened,
This is because the time during which the EL element is illuminated is shortened, and there is a gap between the drive pulses little by little, so that when the battery is charged by the charging circuit of the present invention, the battery is not charged more than necessary.

[Brief description of the drawings]

FIG. 1 is a block diagram of one pixel according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a pulse waveform according to the first embodiment.

FIG. 3 is a block diagram of one pixel according to the second embodiment of the present invention;

FIG. 4 is a transistor-level circuit diagram for one pixel according to the second embodiment;

FIG. 5 is a diagram showing a structure of an example of an organic thin-film EL element and a voltage application method.

FIG. 6 is a diagram showing an example of a current-voltage characteristic of an organic thin film EL device.

FIG. 7 is a circuit diagram of a drive circuit of the display device of Conventional Example 1.

FIG. 8 is a diagram showing a pulse driving waveform of the EL element of Conventional Example 2.

FIG. 9 is a block diagram of one pixel in Conventional Example 1.

FIG. 10 is a diagram showing a pulse waveform in Conventional Example 1.

FIG. 11 is a diagram showing a circuit configuration of a display device of Conventional Example 1.

FIG. 12 is a diagram showing a timing chart of the display device of Conventional Example 1.

FIG. 13 is a diagram illustrating an overall configuration of a drive circuit according to an embodiment of the present invention.

FIG. 14 is a diagram showing a timing chart of a conventional driving circuit.

FIG. 15 is a diagram showing a timing chart of the drive circuit according to the second embodiment of the present invention.

FIG. 16 is a diagram showing a timing chart of the driving circuit of the present invention.

FIG. 17 is a diagram illustrating a timing chart of the drive circuit according to the third embodiment of the present invention.

FIG. 18 is a diagram illustrating a part of a drive circuit according to a third embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 1 pulse generator 2 charging circuit 3 switching element 4 current modulation circuit 5 switching element 6 inverter 20 organic thin film EL element 22 constant current source 26 drive pulse 30 display panel 32 X driver 34 Y driver 36 A / D converter 38 shift register (memory ) 42 controller 44 flip-flop 46 flip-flop 48 PWM modulator 50 flip-flop 52 light emitting element 60 X driver 61 Y driver 62 EL panel 64 data generator 65 timing generator 66 constant current driver 90, 91 transistor 92 transistor 93, 94 , 95 resistance

Continuation of the front page (56) References JP-A-1-124997 (JP, A) JP-A-3-35289 (JP, A) JP-A-3-20779 (JP, A) JP-A 64-82096 (JP) , A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G09G 3/30 G09G 3/20 H05B 33/08

Claims (4)

(57) [Claims] An organic thin-film EL element driving circuit for driving a plurality of organic thin-film EL elements including a signal electrode and a scanning electrode, at least one of which sandwiches an organic thin-film light-emitting layer, in a matrix, according to an input signal. Current driving means for supplying a constant current driving signal to the signal electrode, a pulse generator for outputting a pulse synchronized with the output of the current driving means, and a junction capacitance of the organic thin film EL element by an output of the pulse generator. the have a charging circuit for charging to a predetermined potential, before
The charging time by the charging circuit is determined by the pulse of the current driving means.
A driving circuit for an organic thin-film EL element, wherein the driving circuit is shorter than the output time . 2. The charging circuit has a switching element, activates the switching element by an output of the pulse generator, and has a time constant determined by an on-resistance of the switching element and a junction capacitance of the organic thin film EL element. 2. The driving circuit according to claim 1, wherein the organic thin film EL element is charged to a predetermined potential. 3. A driving circuit of an organic thin-film EL element for driving a plurality of organic thin-film EL elements including a light-emitting layer made of an organic material and a signal electrode and a scanning electrode at least one of which sandwiches the light-emitting layer, in a matrix. A current driving unit that supplies a constant current driving signal to the signal electrode in accordance with an input signal; a pulse generator that outputs a pulse synchronized with an output of the current driving unit; and the organic thin film according to an output of the pulse generator. A charging circuit for charging a junction capacitance of the EL element to a predetermined potential, wherein the organic thin-film EL element is charged between a driving pulse for driving the arbitrary one scanning electrode and a driving pulse for the next scanning electrode. A driving circuit for an organic thin-film EL device, characterized in that a period for discharging the generated electric charge is provided. 4. A period in which the electric charge is discharged is a period between a drive pulse for driving any one of the scan electrodes reduced by a predetermined period and a drive pulse for the next scan electrode. 4. The driving circuit for an organic thin-film EL device according to claim 3 , wherein