JPH06186929A - Method for driving el display device - Google Patents

Abstract

PURPOSE:To provide a method for driving an EL display device capable of reducing the difference in light emission luminance due to the difference in the number of light emitting pixels and improving display quality. CONSTITUTION:In the method for driving the EL display device 10 alternately setting a PN field applying a positive polarity write voltage to a scanning side electrode Y regarding a data side electrode X as a reference and an NP field applying a negative polarity write voltage for a display device constituted by lying an EL layer between the scanning side electrodes Y1-Yj and the data side electrodes X1-Xi arranged in the direction of intersecting each other, and applying a modulation voltage or 0V voltage to the data side electrode X according to display data at the time of applying the write voltage, the modulation voltage is applied to the data side electrode X after the time until when a write current due to the applying of the write voltage is ended to flow through the EL layer elapses.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of driving an AC drive type capacitive flat matrix display, that is, a thin film EL (electroluminescence) display device.

[0002]

2. Description of the Related Art For example, double insulation type (or three-layer structure)
The thin film EL element is configured as follows. As shown in FIG. 2, a plurality of strip-shaped transparent electrodes 2 made of In ₂ O ₃ are provided in parallel on the surface of a glass substrate 1 and, for example, Y
₂ O ₃ , Si ₃ N ₄ , Al ₂ O ₃ and other dielectric substances 3, ZnS doped with an activator such as Mn, and an EL layer 4 and the same dielectric substance 3 as described above are thin films formed by vapor deposition, sputtering, etc. Using a technique, the film is sequentially laminated to a film thickness of 500 to 10000Å to form a three-layer structure, and a plurality of strip-shaped back electrodes 5 made of Al ₂ O ₃ are provided in parallel in a direction orthogonal to the transparent electrode 2 on the three-layer structure. There is.

The thin-film EL device described above has the EL layer 4 sandwiched between the dielectric materials 3 between its electrodes, and therefore can be regarded as a capacitive device in terms of an equivalent circuit. Further, as can be seen from the voltage-luminance characteristics shown in FIG. 3, this thin film EL element is driven by applying a relatively high voltage of about 200V. This thin film EL element is characterized in that it emits light with high brightness due to an AC electric field and has a long life.

Conventionally, for the display device using such a thin film EL element, the applicant of the present application has proposed a driving device for the purpose of reducing the power consumption when the modulation voltage is supplied. In this driving device, as a driving circuit for the scanning side electrode, a scanning side driving IC including a transistor for applying a negative voltage and a transistor for applying a positive voltage to the data side electrode is provided. The drive circuit includes a transistor for charging and discharging a modulation voltage in the EL layer, and a data side drive IC in which a diode is connected in a direction opposite to the current direction of each transistor. The data side is for charging and discharging according to display data. While the transistor is used for modulation drive, on the scanning side, so-called field inversion drive is performed using the N-channel transistor and the P-channel transistor, and further, the characteristics of the write voltage waveform applied to the picture element for each scanning line are determined. Line-sequential driving is performed while reversing. As a result, the driving time for one horizontal period is short, and an AC pulse (driving signal) having good symmetry can be applied to the EL layer, which is excellent in reliability.

[0005]

When display driving of an EL display device is performed using the above driving device, when a writing voltage is applied to the scanning side electrode, the scanning side electrode (one horizontal line) If the number of light emitting picture elements is large, EL
When the write current to the layer increases, the write voltage waveform becomes dull, the emission brightness decreases, and when the number of light emitting pixels is small, EL
Since the write current to the layer is reduced, the waveform of the write voltage is less blunt, and the decrease in the emission brightness is small. For this reason, when scanning side electrodes (horizontal lines) having different numbers of light emitting picture elements are mixed in one screen, display unevenness occurs due to a difference in luminance of the light emitting picture elements.

In the conventional driving device, since the timing of applying the modulation voltage to the data-side electrode and the timing of applying the writing voltage to the scanning-side electrode are almost the same, the dulling of the writing voltage applied to the picture element during light emission directly causes light emission. It affects the brightness.

In an EL display device, the EL layer has a thickness of 200
Driving is performed by applying a relatively high voltage of V or more. Here, a case where a voltage of 220 V is applied to the EL layer to drive (emit) will be described. As the modulation voltage to the data side electrode,
A voltage of 0V or + 60V is selectively applied. In the first field in which a positive polarity (+) write voltage is applied, a voltage of +220 V is applied as a write voltage, 0 V is applied to the data side electrode corresponding to the pixel to emit light, and 0 V to the data side electrode corresponding to the pixel not to emit light. A modulation voltage of + 60V is applied. +220 for the picture elements that emit light
A voltage of + 160V is applied to each of the V and the picture elements which are not made to emit light, and only the picture elements which are made to emit light to which the voltage of + 220V is applied are driven (emits light).

Second for applying a negative polarity (-) write voltage
In the field, a voltage of -160V is applied as a writing voltage, and + is applied to the data side electrode corresponding to the picture element to emit light.
A voltage of 60V and a voltage of 0V are applied to the data-side electrodes corresponding to the pixels that do not emit light. -220V for the picture elements that emit light, and -160V for the picture elements that do not emit light.
The voltage of V will be applied respectively, and -220V
Only the picture elements that emit light are driven (light emission).
To be done.

An object of the present invention is to improve the second field in which a writing voltage having a positive polarity is applied, in which a modulation voltage other than 0 V is applied to the light emitting pixels, and the light emission is caused by the difference in the number of light emitting pixels. An object of the present invention is to provide a driving method of an EL display device capable of reducing a difference in brightness and improving display quality.

[0010]

According to the present invention, E is provided between a scanning side electrode and a data side electrode arranged in a direction intersecting with each other.
With respect to the display device configured with the L layer interposed, a first field for applying a positive writing voltage and a second field for applying a negative writing voltage to the scanning side electrode with reference to the data side electrode are provided. Alternately set, and when the write voltage is applied, the modulation voltage or 0 is applied to the data side electrode according to the display data.
In a driving method of an EL display device for applying a voltage of V,
In the second field, the EL display device driving method is characterized in that the modulation voltage is applied to the data side electrode after a lapse of time until the write current due to the application of the write voltage ends in the EL layer.

[0011]

According to the present invention, the write voltage is applied to the scanning side electrode, and the write voltage waveform rises sufficiently after the elapse of the period until the write current due to the application of the write voltage ends in the EL layer. After that, a modulation voltage is applied to the data side electrode. As a result, the voltage waveform applied to the picture element to be emitted becomes a part which is not affected by the load, so that the difference in light emission luminance due to the difference in the number of light emitting picture elements is reduced and the display unevenness on one screen is eliminated.

It should be noted that the first for applying a positive write voltage
In the field, a modulation voltage that is not 0 V is applied to the picture elements that do not emit light, but the application timing at this time is almost the same as in the conventional case (if the application timing of the modulation voltage is delayed, the high voltage for the delayed time is applied. Then, it will emit light for a short time). Further, in the first field, the write voltage itself is a large value, and there is little blunting of the voltage depending on the number of picture elements to emit light, and there is no problem.

[0013]

FIG. 1 is a circuit diagram showing an embodiment of the present invention. The thin film EL display device 10 includes a scanning side high withstand voltage drive IC.
(Hereinafter referred to as scanning side driving IC) 20, 30 and data side high withstand voltage driving IC (hereinafter referred to as data side driving IC)
40 and 50 are connected. The potential switching circuits 100 and 200 are connected to the scan side drive ICs 20 and 30, and the modulation voltage supply circuit 300 and the data inversion control circuit 400 are connected to the data side drive ICs 40 and 50.

The thin film EL display device 10 has an emission threshold voltage of 1
This is an EL display device of 90 V (Vw), and in FIG. 1, the X direction electrodes X1 to Xi are used as the data side electrodes, and the Y direction electrodes Y1 to Y1 are used.
Only the electrodes are shown with Yj as the scanning side electrode.

The scanning side drive ICs 20 and 30 are the thin film E.
The drive circuits correspond to the odd lines and the even lines of the Y-direction electrodes of the L display device 10, respectively. Scan side drive IC
In FIG. 20, the transistor NTodd (odd) that applies a negative voltage to the data-side electrode is applied to the odd line.
, 1, 3, ..., J-1) and a transistor PTodd for applying a positive voltage, and diodes NDodd and PDodd for flowing current in the opposite directions are connected to the respective transistors NTodd and PTodd. It

Further, in the scanning side driving IC 30, a transistor NTeven (even = 2, 4, ...,) for applying a negative voltage to the data side electrode is applied to even lines.
j) and a transistor PTe applying a positive voltage
ven are connected to each transistor NTeve
Diodes NDeven and PDeven for flowing a current in the opposite direction are connected to n and PTeven.

The logic circuits 21 and 31 are circuits such as shift registers in the scan side drive ICs 20 and 30.

The data side drive ICs 40 and 50 are circuits corresponding to the X direction electrodes of the thin film EL display device 10.
In this embodiment, the X-direction electrodes X1 to Xi are equally divided into two near the center of the screen, and the lower data side electrodes X1 to Xi in FIG.
Is controlled by the data side drive IC 40, and the upper data side electrodes X1 to Xi in FIG. 1 are controlled by the data side drive IC 50.

The data side drive ICs 40 and 50 have one side connected to each of the data side electrodes X1 to Xi and the other side connected to the modulation voltage supply circuit 300, and have a pull-up function such as a P-channel MOSFET, a thyristor, and a PNP transistor. Switching elements (hereinafter simply referred to as transistors) UT1 to UTi, one side of each data side electrode X
1 to Xi, the other side is grounded, and an N-channel NOSFET having a pull-down function, thyristor, NP
Switching elements such as N-type transistors (hereinafter simply referred to as transistors) DT1 to DTi, diodes UD1 to UDi for flowing current in the opposite direction to the respective transistors UT and DT; DD1 to DDi, and turning on of each transistor UT and DT Inversion circuit UR for controlling ON / OFF
1-URi; DR1-DRi. The constituent elements are controlled by logic circuits 41 and 51 such as shift registers in the data side driving ICs 40 and 50, respectively.

The potential switching circuit 100 has the scanning side drive I
A circuit for switching the pull-down common line potential of C20 and C30, and a negative write voltage of -160V (-Vw + 1 / 2V) in response to a control signal NSC supplied from the display control circuit.
m) and 0 V for the switch SW1.

The potential switching circuit 200 includes the scanning side drive I.
A circuit for switching the pull-up common line potentials of C20 and C30, and a positive write voltage 220V (Vw + 1 / 2Vm) by a control signal PSC provided from the display control circuit.
And a switch SW2 for switching between 0V and 0V.

The modulation voltage supply circuit 300 switches the switch S by the control signal T2 supplied from the display control circuit 500.
W4 is turned on and the capacitor Cm has a 1/2 modulation voltage of 30
V (1/2 Vm) is charged, and after charging, the switch SW4 is turned off by the control signal T2, and the switches SW3 and SW4 are turned on by the control signals T1 and T3 respectively, so that the modulation voltage 60 V (V
m), and is connected to the data side drive IC 40 through the switch SW5 controlled by the control signal T3. On the other hand, by turning on the switch SW4 by the control signal T2 after the thin film EL display device 10 emits light, a part of the energy stored in the thin film EL display device 10 is charged to the capacitor Cm through the diode Dr as a switch. Is also a circuit for accumulating.

The data inversion control circuit 400 inverts the display data DATA given from the display control circuit to the inversion control signal RE.
It is a data inversion control circuit which inverts by VERCE.

FIG. 2 is an enlarged perspective view showing the structure of the thin film EL display device 10. In ₂ is formed on the surface of the glass substrate 1.
A plurality of strip-shaped transparent electrodes 2 made of O ₃ are provided in parallel, and a dielectric material 3 such as Y ₂ O ₃ , Si ₃ N ₄ and Al ₂ O ₃ and ZnS doped with an activator such as Mn are formed on the transparent electrodes 2. The formed EL layer 4 and the same dielectric material 3 as described above are sequentially applied in the order of 500 to 10 by using thin film technology such as vapor deposition and sputtering.
A plurality of strip-shaped back electrodes 5 made of An ₂ O ₃ are provided in parallel in a direction perpendicular to the transparent electrode 2 by laminating it to a film thickness of 000Å to form a three-layer structure.

Since the thin film EL display device 10 has the EL layer 4 sandwiched between the dielectric materials 3 between its electrodes, it can be regarded as a capacitive element in an equivalent circuit. Further, as is clear from the voltage-luminance characteristic shown in FIG. 3, this thin film EL display device is driven by applying a relatively high voltage of about 200V. The thin film EL display device 10 is characterized in that it emits light with high brightness due to an AC electric field and has a long life.

FIG. 4 is a timing chart for explaining the operation of the driving device shown in FIG. 1, and FIG. 5 is a circuit diagram showing an equivalent circuit of the EL display device 10. The operation of the drive device shown in FIG. 1 will be described with reference to the timing chart of FIG.

Here, it is assumed that the scanning electrode Y1 including the picture element A shown in FIG. 5 is selected as the selective scanning electrode by line sequential driving. In addition, in this driving device, the polarity of the writing voltage applied to the picture element is inverted for each line for driving, but the scanning side driving IC 20 connected to the scanning side selection electrode,
The driving timing of one line in which only the pull-down transistor NTn of 30 is turned on and the negative writing pulse is applied to the picture element on that electrode line is called N driving timing, and is connected to the scanning side selection electrode. Pull-up transistor PTn of the scan side drive ICs 20 and 30
Only one is turned on, and the drive timing of one line for applying a positive write pulse to the picture element on that electrode line is called P drive timing.

The data-side electrode is basically driven by switching the voltage applied to each data-side electrode between Vm and 0V in a cycle of one horizontal period according to the display data DATA. Next, the switching timing will be described.

As shown in FIG. 4, after the data for one line is transferred, the data is latched by the control signal DLS, and even if the transistors UT and DT of the data side driving IC 40 are turned on by the latched data, the data is immediately turned on. The modulation voltage Vm is not applied, the stepwise charging is performed from the potential 1/2 Vm to the potential Vm by the modulation voltage supply circuit 300, and the power consumption is reduced to 3/4 that in the case where the stepwise charging is not performed. In addition, by charging a part of the electric charge accumulated in the EL layer 4 at the potential of 1/2 Vm to the external capacitor Cm through the diode Dr and reusing it as a part of driving energy when the modulation voltage Vm is applied next. Further, the power consumption when the modulation voltage is supplied is reduced.

The operation of such a drive device is roughly divided into two kinds of timings, an NP field (second field) and a PN field (first field), and the execution of these two fields is completed. Thus, the AC pulse necessary for light emission is closed for all the picture elements of the thin film EL display device 10. Further, each field (screen) is composed of two types of timings, N drive and P drive. In the NP field, N drive is executed for odd-numbered selection lines of the scanning side electrodes, and even number P drive is executed for the selected line of.
In the PN field, the opposite driving is executed. Further, the N drive and the P drive are each configured by a discharge period and an address period.

Next, each drive period will be described.

(A) Discharge period in NP field N drive (TN1) Switches SW1 and SW are controlled by control signals NSC and PSC.
2 is turned off and the common line is set to 0 V, then the scanning side drive IC
By turning off all the transistors NT and PT of 20 and 30, all electrodes on the scanning side are brought into a floating state.

At this time, in the data side driving IC, the switches SW3 and SW5 are turned off by the control signals T1 and T3, and the switch SW4 is turned on by the control signal T2, so that a part of the charges accumulated in the EL layer 4 is removed. The capacitor Cm is charged through the diode Dr and also from the 1/2 Vm power supply through the diode Dm. As a result, the electrode potential connected to the selected picture element of the data side electrode is 1
It becomes / 2Vm.

Thereafter, when the control signal DLS is input and the transistors UT and DT of the data side drive IC 40 are switched on / off, the switch S is activated by the control signal T3.
Turn off W5 and put it in a floating state. At the same time, when all the scanning side transistors PT and NT are turned on,
The electric charge of the EL layer 4 is discharged and the scanning-side electrode potential becomes 0V.

Write Period in TN Drive (TN2) The data side drive IC 40 continues driving in the discharge period TN1 in N drive described above, turns on the switch SW5 of the modulation voltage supply circuit 300 by the control signal T3, and is in a floating state. From the potential to 1/2 Vm, and then the switch SW3 is turned off by the control signal T2 and the control signal T
The switch SW4 is turned on by 1 and pulled up to the potential Vm.

After the charging current due to the modulation voltage Vm has finished flowing, the transistor NTn is turned on only in the drive circuit portion connected to the selective scan electrode, and the other scan side drive I
All the transistors NT and PT in C20 and C30 are turned off. At the same time, the switch SW2 is turned off by the control signal PSC and 0V is applied to the pull-up supply lines of the scan side drive ICs 20 and 30.

The pull-down common line of the scan side drive IC 20.30 is switched by the control signal NSC to the switch SW1.
Is turned on, the negative write voltage −Vw +
Apply 1/2 Vm.

As a result, the electrode potential including the selected picture element on the data side becomes Vm. At the same time, since the negative write voltage −Vw + 1 / 2Vm is applied to the selective scan electrode,

[0039]

## EQU1 ## Vm-(-Vw + 1 / 2Vm) = Vw + 1 / 2Vm is applied and light is emitted.

The non-selected picture element has a data side electrode potential of 0.
V, and as described above, since the negative write voltage −Vw + 1 / 2Vm is applied to the selective scan electrode, the non-selected pixel is

[0041]

## EQU00002 ## 0V-(-Vw + 1 / 2Vm) = Vw-1 / 2Vm is applied, but no light emission occurs because the light emission threshold voltage Vw or less.

As for the picture elements on the scanning side non-selection electrode line, since the scanning side electrode is in a floating state, it changes from 0V to 60V depending on the ratio of the selection electrode on the data side and the non-selection electrode.

Discharging Period in TP Field (TP1) Except for turning on / off the transistors UT and DT of the data side driving IC 40 according to the inverted data of the display data DATA, the discharging period (T in N driving in the NP field).
The same driving as N1) is performed.

Write Period (TP2) in P Drive The data side drive IC 40 continues the drive in the discharge period (TP1) in the above P drive, and turns on the switch SW5 of the modulation voltage supply circuit 300 by the control signal T3. Switching from floating state to potential 1/2 Vm,
Next, the switch SW3 is turned off by the control signal T2,
The switch SW4 is turned on by the control signal T1 and pulled up to the potential Vm.

After the charging current due to the modulation voltage Vm has finished flowing through the EL layer 4, the transistor PTn is turned on only in the drive circuit portion connected to the selective scan electrode, and the transistors UT, of the other scan side drive ICs 20 and 30 are connected. Turn off all PTs. At the same time, a switch SW is applied to the pull-up common line of the scan side drive ICs 20 and 30 by a control signal PSC.
2 is turned on and the positive polarity write voltage Vw + 1/2 Vm is applied. Further, 0V is applied to the pull-down common line of the scan side drive ICs 20 and 30 by turning off the switch SW1 by the control signal NSC.

As a result, the electrode potential including the selected picture element on the data side becomes 0V. At the same time, since the positive write voltage Vw + 1 / 2Vm is applied to the selective scan electrode,

[0047]

## EQU00003 ## (Vw + 1 / 2Vm) -0V = Vw + 1 / 2Vm is applied with the opposite polarity to the above-mentioned N drive write voltage, and light is emitted.

The non-selected pixel has a data-side electrode potential of Vm, and the positive write voltage Vw + 1 / 2Vm is applied to the selected scan electrode as described above.

[0049]

## EQU00004 ## (Vw + 1 / 2Vm) -Vm = Vw-1 / 2Vm is applied, but it does not emit light because it is less than or equal to the light emission threshold voltage Vw.

(B) Discharge period in PN field P drive (TP3) The same drive as in the discharge period (TP1) in NP field P drive is performed.

Write period in P drive (TP4) NP except that the select electrode on the scanning side is selected from the odd number side
The same driving as in the writing period (TP2) in the P driving of the field is performed.

Discharge period in N drive (TN3) The same drive as in the N drive discharge period (TN1) of the NP field is performed.

Write period in N drive (TN4) NP except that the select electrode on the scanning side is selected from the even number side
The same driving as in the writing period (TN2) in the N driving of the field is performed.

In the conventional driving device, the timing of applying the modulation voltage from the data side and the timing of applying the writing voltage from the scanning side are substantially the same. However, in the drive device according to the present invention, the data side is clamped at the same time when the negative write voltage is applied to the data side electrode, but the timing of applying the modulation voltage is performed after the write drive. . That is, since it is a capacitive load, the current stops when the charging current flows for a certain period of time, so the modulation voltage is applied after that.

FIG. 6 is a diagram showing the difference in each voltage waveform between the conventional driving device and the driving device of the present invention. Points A and B in FIG. 6 correspond to the picture elements A and B in FIG.

As shown in FIG. 6A, the conventional driving device has the same negative write voltage Vw (= -160).
V) is applied to the scanning-side electrodes Y1 and Y3 respectively, the modulation voltage Vm and the writing voltage Vw are applied at the same timing. Therefore, the difference in the writing voltage due to the difference in the number of light-emitting pixels per scan line causes light emission. It appears as a difference in brightness. Therefore, the luminance of the picture element B becomes darker than that of the picture element A.

On the other hand, as shown in FIG. 6B, in the driving device of the present invention, when the write voltage is applied, the threshold voltage is not exceeded and light emission does not occur, so that the waveform is not blunted and the write pulse rises sufficiently. Since the modulation voltage is applied later, the waveforms of the picture element A and the picture element B at the time of light emission (after exceeding the threshold voltage) become the same.

As described above, according to this embodiment, the thin film EL
It is possible to remarkably reduce the luminance unevenness between scanning lines due to the difference in the dullness of the writing pulse due to the difference in the number of light emitting pixels per scanning line of the display device 10, and it is possible to improve the display quality, which is a useful thin film EL. A drive device for a display device can be provided.

According to the present invention, in the case of a thin film EL display device in which the structure of the data side electrode is divided into an odd side and an even side as shown in FIG. As a result, the phenomenon that the emission brightness differs every other line occurs. Therefore, the data side electrode is divided into one side as shown in FIG. 8 (1) or vertically at the center of the matrix as shown in FIG. 8 (2) and taken out from both sides. The effect is great for the thin film EL display device which is hardly affected by the resistance component of the data side electrode.

[0060]

As described above, according to the present invention, the writing voltage is applied to the scanning side electrode, and after the period until the writing current due to the application of the writing voltage ends in the EL layer,
That is, since the modulation voltage is applied to the data side electrode after the write voltage waveform has risen sufficiently, the voltage waveform applied to the picture element to emit light is a portion where there is no influence of the load.
The difference in light emission luminance due to the difference in the number of light emitting picture elements is suppressed, and display unevenness on one screen is eliminated.

[Brief description of drawings]

FIG. 1 is a thin film EL display device 10 which is an embodiment of the present invention.
3 is a circuit diagram showing the configuration of the driving device of FIG.

2 is a partially cutaway perspective view of the thin film EL display device 10. FIG.

FIG. 3 is a graph showing a luminance characteristic with respect to an applied voltage of the thin film EL display device 10.

FIG. 4 is a timing chart explaining the operation of the drive device shown in FIG.

5 is a circuit diagram showing an equivalent circuit of the EL display device 10. FIG.

FIG. 6 is a waveform diagram showing respective waveforms of a conventional driving device and a driving device according to the present invention.

FIG. 7 is a diagram showing an example of how to take out a data side electrode.

FIG. 8 is a diagram showing an example of how to take out the data side electrode that is less susceptible to the resistance component of the data side electrode.

[Explanation of symbols]

 1 Glass Substrate 2 Transparent Electrode 3 Dielectric Material 4 EL Layer 5 Back Electrode 10 Thin Film EL Display Device 20, 30 Scanning Side Driving IC 21, 31, 41, 51 Logic Circuit 40, 50 Data Side Driving IC 100, 200 Potential Switching Circuit 300 Modulation voltage supply circuit 400 Data inversion control circuit 500 Display control circuit

Claims (1)

[Claims] 1. A display device having an EL layer interposed between a scanning side electrode and a data side electrode arranged in a direction intersecting with each other, wherein the scanning side electrode has a positive polarity with reference to the data side electrode. The first field for applying the write voltage and the second field for applying the negative write voltage are alternately set, and when the write voltage is applied, the modulation voltage or the voltage of 0 V is applied to the data side electrode according to the display data. In the driving method of an EL display device according to the present invention, in the second field, the modulation voltage is applied to the data-side electrode after a lapse of time until the write current due to the application of the write voltage ends in the EL layer. Device driving method.