JP2728582B2 - Driving method of EL display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art For example, a double insulation type (or a three-layer structure)
The thin film EL device 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
A dielectric material ₃ such as ₂ O ₃ , Si ₃ N ₄ , Al ₂ O ₃ , an EL layer 4 made of ZnS doped with an activator such as Mn, and a dielectric material 3 similar to the above are thin films formed by vapor deposition, sputtering or the like. A three-layer structure is formed by sequentially laminating a film having a thickness of 500 to 10000 ° using a technique, and a plurality of strip-shaped back electrodes 5 made of Al ₂ O ₃ are provided in parallel in a direction perpendicular to the transparent electrode 2. I have.

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

Heretofore, for a display device using such a thin film EL element, the present applicant has proposed a driving device for reducing power consumption when a modulation voltage is supplied. In this drive device, a scan-side drive IC including a transistor for applying a negative voltage to the data-side electrode and a transistor for applying a positive voltage to the data-side electrode is provided as a drive circuit for the scan-side electrode. A driving circuit includes a transistor for charging and discharging a modulation voltage to the EL layer, and a data-side driving IC in which a diode is connected in a direction opposite to the current direction of each transistor. On the data side, charging and discharging are performed according to display data. On the scanning side, so-called field inversion driving is performed using an N-channel transistor and a P-channel transistor while performing modulation driving using a transistor. Further, the characteristics of a writing voltage waveform applied to a 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 (drive signal) with good symmetry can be applied to the EL layer, and the reliability is excellent.

[0005]

In the case where display driving of an EL display device is performed using the above-described driving device, when a writing voltage is applied to a scanning-side electrode, the driving voltage on the scanning-side electrode (one horizontal line) is increased. If the number of luminescent picture elements is large, EL
When the write current to the layer increases, the write voltage waveform becomes dull, the light emission luminance decreases, and when the number of light emitting picture elements is small, EL
Since the write current to the layer is reduced, the dullness of the write voltage waveform is small, and the decrease in light emission luminance is small. Therefore, 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 luminance difference between the light emitting picture elements.

In the conventional driving device, 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. Affects brightness.

[0007] In an EL display device, for example, a $ 200
It is driven by applying a relatively high voltage of V or higher. Here, a case where a voltage of 220 V is applied to the EL layer to drive (emit) light will be described. As the modulation voltage on the data side electrode,
A voltage of 0 V or +60 V is selectively applied. In the first field in which a positive (+) write voltage is applied, a voltage of +220 V is applied as a write voltage, and 0 V is applied to the data side electrode corresponding to the picture element to emit light and to the data side electrode corresponding to the picture element not to emit light. A +60 V modulation voltage is applied. +220 for the picture element to emit light
A voltage of +160 V is applied to each of the V and the picture element that does not emit light, and only the picture element that emits light to which the voltage of +220 V is applied is driven (emitted).

A second method for applying a negative (-) write voltage;
In the field, a voltage of -160 V 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 60 V and a voltage of 0 V are applied to the data-side electrodes corresponding to the picture elements that do not emit light, respectively. As a result, -220 V is applied to a picture element to emit light, and -160 V is applied to a picture element not to emit light.
V will be applied respectively, and -220V
Only the picture elements that emit light to which a voltage is applied are driven (light emission)
Is done.

SUMMARY OF THE INVENTION An object of the present invention is to improve the second field in which a positive write voltage is applied when a modulation voltage other than 0 V is applied to a picture element to emit light, and light emission due to a difference in the number of light emitting picture elements. An object of the present invention is to provide a driving method of an EL display device which can reduce a difference in luminance and improve display quality.

[0010]

SUMMARY OF THE INVENTION The present invention relates to a method in which a scanning electrode and a data electrode are arranged in a direction intersecting each other.
For a display device having an L layer interposed, a first field for applying a positive write voltage and a second field for applying a negative write voltage to the scan electrode with reference to the data electrode are provided. Alternately, the modulation voltage or 0 is applied to the data side electrode according to the display data when the write voltage is applied.
In a method for driving an EL display device applying a voltage of V,
In the second field, a modulation voltage is applied to the data-side electrode after a lapse of time until a write current due to the application of the write voltage has finished flowing through the EL layer, and the modulation method is applied to the data-side electrode.

[0011]

According to the present invention, the writing voltage is applied to the scanning electrode, and after the lapse of a period until the writing current by the application of the writing voltage stops flowing to the EL layer, that is, the writing voltage waveform rises sufficiently. Later, a modulation voltage is applied to the data side electrode. As a result, the voltage waveform applied to the picture element to be illuminated is a portion that is not affected by the load, so that the difference in luminous brightness due to the difference in the number of illuminated picture elements is reduced, and display unevenness on one screen is eliminated.

[0012] A first write voltage applying a positive polarity write voltage is used.
In the field, a modulation voltage other than 0 V is applied to the picture element which does not emit light. The application timing at this time is almost the same as in the related art. And light is emitted for a short time). In the first field, the write voltage itself is a large value, and there is little voltage blunting due to 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 breakdown voltage driving IC.
20 and 30 (hereinafter referred to as scanning-side driving ICs) and data-side high-withstand-voltage driving ICs (hereinafter referred to as data-side driving ICs)
40 and 50 are connected. The scanning side drive ICs 20 and 30 are connected to potential switching circuits 100 and 200, and the data side drive ICs 40 and 50 are connected to a modulation voltage supply circuit 300 and a data inversion control circuit 400.

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

The scanning drive ICs 20 and 30 are provided with the thin film E
This is a driving circuit corresponding to each of odd-numbered lines and even-numbered lines of the Y-direction electrode of the L display device 10. Scan driver IC
In the odd line in FIG. 20, a transistor NTodd (odd) for applying a negative voltage to the data side electrode
= 1, 3,..., J−1) and a transistor PTodd for applying a positive voltage, and diodes NDodd, PDodd for flowing currents in opposite directions are connected to the respective transistors NTodd, PTodd. You.

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

The logic circuits 21 and 31 are circuits such as shift registers in each of the scanning-side driving ICs 20 and 30.

The data-side driving 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 bisected near the center of the screen, and the lower data-side electrodes X1 to Xi in FIG.
Are controlled by a data-side drive IC 40, and the upper data-side electrodes X1 to Xi in FIG.

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, or a PNP transistor. Switching elements (hereinafter simply referred to as transistors) UT1 to UTi, one of which is a data side electrode X
1 to Xi, the other side is grounded, and an N-channel NOSFET having a pull-down function, a thyristor, an 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 transistors UT and DT; DD1 to DDi, and turning on of the transistors UT and DT Inverting circuit UR for controlling / off
1 to URi; DR1 to DRi. The components 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 is connected to the scanning drive I
This is a circuit for switching the pull-down common line potentials of C20 and C30. A negative write voltage of -160V (-Vw + 1 / 2V) is supplied by a control signal NSC provided from the display control circuit.
m) and 0V.

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

The modulation voltage supply circuit 300 switches the switch S by a control signal T2 given from the display control circuit 500.
Turn on W4 and apply 1/2 modulation voltage 30 to capacitor Cm.
V (1 / 2Vm), 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, whereby the modulation voltage of 60 V (V
m), and is connected to the data side driving IC 40 through a switch SW5 controlled by a control signal T3. On the other hand, when the switch SW4 is turned on 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. It is also a circuit that accumulates.

The data inversion control circuit 400 converts the display data DATA given from the display control circuit into an inversion control signal RE.
This is a data inversion control circuit that is inverted by VERCE.

FIG. 2 is an enlarged perspective view showing the structure of the thin film EL display device 10. In _{2 on} the surface of the glass substrate 1
O ₃ is provided in parallel a plurality of strip-like transparent electrodes 2 made of, from on the example Y ₂ O _3, Si ₃ N _4, Al ₂ O ₃ dielectric material 3, such as, Mn doped with active agents such as ZnS The EL layer 4 and the dielectric substance 3 similar to those described above are successively formed in a thickness of 500 to 10 using a thin film technique such as an evaporation method or a sputtering method.
A plurality of band-shaped back electrodes 5 made of An ₂ O ₃ are provided in parallel with each other in a direction perpendicular to the transparent electrode 2 by laminating to a thickness of 000 °.

Since the thin-film EL display device 10 has the EL layer 4 interposed between its electrodes with the dielectric material 3 interposed therebetween, it can be regarded as a capacitive element in an equivalent circuit. The thin-film EL display device is driven by applying a relatively high voltage of about 200 V, as is apparent from the voltage-luminance characteristics shown in FIG. The thin-film EL display device 10 is characterized in that it emits high-luminance light by 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 driving 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 selected scanning electrode by the line sequential driving. Further, in this driving device, the polarity of a writing voltage applied to a picture element is inverted for each line and driving is performed.
The drive timing of one line for turning on only the 30 pull-down transistors NTn and applying a negative write pulse to the picture element on the electrode line is called N drive timing, and is connected to the scanning-side selection electrode. The pull-up transistor PTn of the scanning side driving ICs 20 and 30
The drive timing of one line in which only one is turned on and a positive write pulse is applied to the picture element on that electrode line is referred to as P drive timing.

The driving of the data-side electrodes is basically performed by switching the voltage applied to each data-side electrode between Vm and 0 V 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 of one line is transferred, the data is latched by the control signal DLS, and the transistors UT and DT of the data side driving IC 40 are turned on by the latched data. The modulation voltage Vm is not applied, and the modulation voltage supply circuit 300 performs stepwise charging from the potential 1/2 Vm to the potential Vm, reducing power consumption to 3/4 of the case where stepwise charging is not performed, In addition, by charging a part of the electric charge stored in the EL layer 4 at the time of the potential of 1/2 Vm to the external capacitor Cm through the diode Dr, it is reused as a part of the driving energy when the modulation voltage Vm is applied. Further, the power consumption when the modulation voltage is supplied is reduced.

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

Next, each driving period will be described.

(A) NP field Discharge period (TN1) in N drive The switches SW1 and SW are controlled by the control signals NSC and PSC.
2 is turned off and the common line is set to 0V, and then the scanning side driving IC
By turning off all the transistors NT and PT of the transistors 20 and 30, all the 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. The capacitor Cm is charged through the diode Dr and from the 1/2 Vm power supply through the diode Dm. As a result, the potential of the electrode connected to the selected picture element of the data side electrode becomes 1
/ 2Vm.

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

Write period (TN2) in N drive The data side drive IC 40 continues to drive the discharge period TN1 in the above N drive, turns on the switch SW5 of the modulation voltage supply circuit 300 by the control signal T3, and sets the floating state. To the potential 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 to raise the potential to the potential Vm.

After the charging current by the modulation voltage Vm has finished flowing, only the drive circuit portion connected to the selected scan electrode turns on the transistor NTn, and the other scan side drive I
The transistors NT and PT in C20 and C30 are all 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 scanning side drive ICs 20 and 30.

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

Thus, the electrode potential including the selected picture element on the data side becomes Vm. At the same time, a negative write voltage −Vw + ／ Vm is applied to the selected scan electrode, so that the selected picture element is

[0039]

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

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

[0041]

## EQU00002 ## 0V-(-Vw + 1 / 2Vm) = Vw-1 / 2Vm is applied, but does not emit light because it is lower than the light emission threshold voltage Vw.

The picture elements on the scanning-side non-selection electrode line change from 0 V to 60 V depending on the ratio between the data-side selection electrode and the non-selection electrode because the scanning-side electrode is in a floating state.

Discharge Period (TP1) in P Drive Except for turning on / off the transistors UT and DT of the data drive IC 40 in accordance with the inverted data of the display data DATA, the discharge period (T1) in N drive of the NP field
The same drive as in N1) is performed.

Write period (TP2) in P drive The data drive IC 40 continues to 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 the floating state to the 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 is raised to the potential Vm.

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

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

[0047]

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

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

[0049]

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

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

Write period (TP4) in P drive Except that the selection electrode on the scan side is selected from the odd number side,
Driving similar to the writing period (TP2) in the P driving of the field is performed.

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

Write period (TN4) in N drive Except that the selection electrode on the scanning side is selected from the even number side, NP
Driving similar to the writing period (TN2) in 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 write voltage from the scanning side are almost simultaneously. However, in the driving device according to the present invention, when the negative write voltage is applied to the data electrode, the data side is clamped in the same manner, but the timing of applying the modulation voltage is performed after the write drive. . That is, since the current is stopped when the charging current flows for a certain period of time due to the capacitive load, the modulation voltage is applied thereafter.

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. In FIG. 6, points A and B correspond to picture elements A and B in FIG.

As shown in FIG. 6A, in the conventional driving device, the same negative write voltage Vw (= −160) is used.
Even if V) is applied to the scanning electrodes Y1 and Y3, respectively, the application of the modulation voltage Vm and the writing voltage Vw are at the same timing, so that the difference in the writing voltage dullness due to the difference in the number of light emitting picture elements per scanning line causes light emission. Appears as a difference in luminance. Therefore, the luminance of the picture element B is lower than that of the picture element A.

On the other hand, as shown in FIG. 6 (2), in the driving device of the present invention, when the writing voltage is applied, the threshold voltage is not exceeded and the light emission does not occur, so that the waveform is less dull and the writing pulse sufficiently rises. Since the modulation voltage is applied later, the waveforms of the picture elements A and B at the time of light emission (after exceeding the threshold voltage) become the same.

As described above, according to the present embodiment, the thin film EL
The brightness unevenness between the scanning lines caused by the difference in the writing pulse due to the difference in the number of light emitting picture elements per scanning line of the display device 10 can be significantly reduced, the display quality can be improved, and the useful thin film EL can be used. A driving 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 configuration of the data side electrode is divided into an odd side and an even side as shown in FIG. 8A, the data-side electrode is divided on one side as shown in FIG. 8A, or divided vertically at the center of the matrix as shown in FIG. 8B, and extracted from both sides. The effect is great for a thin-film EL display device that is not easily affected by the resistance of the data-side electrode.

[0060]

As described above, according to the present invention, a writing voltage is applied to the scanning electrode, and after a period of time from when the writing current due to the application of the writing voltage stops flowing to the EL layer,
That is, since the modulation voltage is applied to the data electrode after the write voltage waveform has sufficiently risen, the voltage waveform applied to the picture element to emit light is a portion which is not affected by 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 the drawings]

FIG. 1 is a thin film EL display device 10 according to an embodiment of the present invention.
FIG. 2 is a circuit diagram showing a configuration of a driving device of FIG.

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 illustrating the operation of the driving device shown in FIG.

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

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

FIG. 7 is a diagram illustrating an example of a method of extracting a data-side electrode.

FIG. 8 is a diagram illustrating an example of a method of extracting a data-side electrode that is not easily affected by the resistance of the data-side electrode.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 glass substrate 2 transparent electrode 3 dielectric material 4 EL layer 5 back electrode 10 thin-film EL display device 20, 30 scan-side drive IC 21, 31, 41, 51 logic circuit 40, 50 data-side drive IC 100, 200 potential switching circuit 300 Modulation voltage supply circuit 400 Data inversion control circuit 500 Display control circuit

Claims (1)

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