JP2000221944A - EL display device driving method and EL display device - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To reduce luminance unevenness due to a difference in light emission luminance between adjacent scanning-side electrodes as well as luminance unevenness of the entire panel. Each time a display image changes, a pulse width setting map change circuit inputs a pulse width setting map data created in advance for the image and writes it into a pulse width setting map storage circuit. Pulse width control circuit 43
In the line-sequential scanning of the scanning electrode, the number of light emitting pixels on each scanning electrode is counted based on display data of a display image, and the pulse width of the scanning voltage is determined by comparing the counted value with the pulse width setting map. Set. The pulse width setting map is created such that the difference between the highest luminance and the lowest luminance is within 20% of the target luminance, and the difference in light emission luminance between adjacent scanning electrodes is within 10% of the target luminance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an EL (Electrolum)
The present invention relates to an EL display device driving method and an EL display device capable of reducing luminance unevenness generated when an image is displayed on a panel.

[0002]

2. Description of the Related Art An EL panel has an EL element (hereinafter, referred to as a pixel) at each intersection of a plurality of scanning electrodes arranged in a horizontal direction of the panel and a plurality of data electrodes arranged in a vertical direction of the panel. ) Is formed. And this E
In order to drive the L panel, a conventional simple matrix driving type EL display device includes a scanning-side electrode driving circuit that sequentially outputs a pulse-like scanning voltage having a constant width to the scanning-side electrode;
A data-side electrode driving circuit for outputting a pulse-like data voltage having a fixed width to the data-side electrode according to display data.

However, in an EL display device having such a configuration, when an image is displayed on an EL panel, as shown in FIG. 9, pixels formed along each scanning electrode (hereinafter, pixels on the scanning electrode are referred to as pixels on the scanning electrode). ) Depending on the number of light emitting pixels. That is, if the light emission luminance when all the pixels (for example, 100) on the scanning electrode emit light is 100%, the number of light emitting pixels is 2
The light emission luminance at 0 is 150%, and the light emission luminance at 1 light pixel is 200%, which is greatly changed.

FIG. 10 shows an image (excluding dashed lines) extending in a horizontal direction displayed on the EL panel by the EL display device. A black-out area indicates a non-emission pixel, and an unfilled area. Indicates a light emitting pixel.
Here, the light emitting pixel on the scanning electrode indicated by A, which has the smallest number of light emitting pixels on the scanning electrode, has the highest light emission luminance in the entire EL panel. In addition, the light emitting pixels on the scanning electrode denoted by B, D, F, and H in which all the pixels on the scanning electrode emit light have the lowest light emission luminance. As a result, a difference in light emission luminance occurs between the light emitting pixels on the scanning electrodes A to H, and a band-like pattern having a broken line as a boundary line appears in the light emitting pixel region.

[0005] Such a difference in luminance (hereinafter referred to as luminance unevenness) varies the load of the scanning-side electrode driving circuit in accordance with the number of light-emitting pixels on the scanning-side electrode. It is caused by changing. FIG. 11A shows a scanning voltage waveform applied to a scanning electrode having a large number of light emitting pixels, and FIG. 11B shows a scanning voltage waveform applied to a scanning electrode having a small number of light emitting pixels. Since the EL element which is a pixel can be regarded as a capacitive load due to its structure, the driving capability of the scanning-side electrode driving circuit becomes insufficient as the number of light emitting pixels increases,
Waveform distortion increases, such as the rising of the scanning voltage waveform. As a result, a difference occurs in the substantial light emission time during which a voltage equal to or higher than the light emission threshold (indicated by a dashed line in the figure) is applied to the light emitting pixel, and a difference appears in the light emission luminance. The difference in light emission luminance (see FIG. 9) differs depending on the driving capability of the scanning-side electrode driving circuit, the pulse width of the scanning voltage waveform, the driving voltage value, the number of pixels of the EL panel, the capacitance of the pixels, and the like.

In order to improve such luminance unevenness, there is provided an EL display device which employs a shadowing measure in which a pulse width of a scanning voltage output by a scanning electrode driving circuit is changed according to the number of light emitting pixels on the scanning electrode. is there. This shadowing countermeasure will be described with reference to FIGS.

FIG. 12A shows the relationship between the number of light emitting pixels and the relative luminance. The five thin solid lines shown in FIG.
It shows luminance characteristics when a scanning voltage having a specific pulse width up to ec is applied. It can be seen that the emission luminance increases as the pulse width increases, and the emission luminance decreases as the number of pixels emitted increases.

Therefore, the pulse width of the scanning voltage output from the scanning side electrode driving circuit is changed according to the number of light emitting pixels according to the pulse width setting map shown in FIG. As a result, the relationship between the number of light-emitting pixels and the relative luminance is corrected as shown by the thick solid line in FIG. 12A, and the difference in light-emitting luminance due to the difference in the number of light-emitting pixels is reduced.

[0009]

However, even in the EL display device in which the above-described shadowing countermeasures are taken, the scanning side electrode having the light emitting pixels before and after the dividing value of the number of the light emitting pixels divided in the pulse width setting map. When the pixels are close to each other, on the contrary, the difference in light emission luminance between the light emitting pixels on these scanning electrodes may increase, and may appear as uneven luminance on the EL panel. For example, in FIG. 12A, when the light emitting pixels are adjacent to 36 scanning electrodes and 37 scanning electrodes, the light emitting pixels on the former scanning electrodes are on the latter scanning electrodes. The pixel becomes relatively dark with respect to the light emitting pixel, and a horizontal streak is seen in the light emitting pixel portion on the two scanning electrodes.

In order to reduce such uneven brightness, FIG.
2 (b), the number of sections of the pulse width setting map is increased,
It is conceivable to switch the pulse width more finely according to the division of the number of light emitting pixels. However, in the above-described pulse width setting control on the premise of digital processing, there is a limit to the pulse width resolution due to a limitation on a system clock frequency supplied to a control circuit for controlling the scanning-side electrode driving circuit.

It is also conceivable that the control circuit of the scanning-side electrode driving circuit is constituted by an analog circuit so that the pulse width can be continuously and variably set with respect to the number of light emitting pixels. However, in this case, it is difficult to adjust the analog circuit for the EL panel or the analog circuit having manufacturing variations so that the EL display device has an optimum luminance characteristic, and the analog circuit is also complicated. It will be expensive.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to display an image defined on an EL panel. An object of the present invention is to provide a driving method of an EL display device and an EL display device which can reduce luminance unevenness due to a difference in light emission luminance.

[0013]

According to the driving method of the EL display device, the EL display device counts the number of light emitting pixels formed along each scanning side electrode during scanning by the scanning side electrode. Then, based on the count value and the pulse width setting map, the pulse width of the driving voltage to be applied to the luminescent pixel on the scanning side electrode is set. The EL display device controls the scanning voltage and the data voltage,
A drive voltage having a set pulse width is generated.

Thus, in the EL display device, the pulse width of the driving voltage is set to be wide when the number of light emitting pixels on the scanning side electrode is large, and when the number of light emitting pixels on the scanning side electrode is small, the driving is performed. Set the voltage pulse width narrow. On the other hand, when a drive voltage is applied to a pixel as a capacitive element, the pulse waveform becomes more rounded as the number of light-emitting pixels increases, and a substantial light-emitting time during which a voltage equal to or higher than a light-emitting threshold is applied to a light-emitting pixel. It has the property of becoming shorter. As a result, the substantial light emission time is substantially constant irrespective of the number of light emitting pixels on the scanning electrode, and the difference in light emission luminance caused by the difference in the number of light emitting pixels on the scanning electrode when viewed as a whole EL panel ( Brightness unevenness)
Decrease.

Further, in the present driving method, a pulse width setting map suitable for the image to be displayed on the EL panel is created in advance, and the EL display device sets the display target before starting display of the image. Validating the pulse width setting map created for the image to enable reference. According to this, since the EL display device sets the pulse width using the pulse width setting map suitable for each display target image, a display state suitable for each image can be obtained.

According to the driving method of the EL display device of the present invention, the pulse width setting map is created so that the emission luminance difference of the display target image is smaller than a predetermined value.
In this case, the predetermined value is set to such an extent that, for example, when the user looks at the EL panel, the luminance unevenness of the entire EL panel cannot be visually recognized. In this case, since a pulse width setting map is created for each image, it is easier to create a pulse width setting map for each image than when a uniform pulse width setting map is used for all displayed images. .

According to the driving method of the EL display device of the present invention, the pulse width setting map is created such that the light emission luminance difference between the adjacent scanning electrodes for the display target image is smaller than a predetermined value. Therefore, in addition to the uneven brightness of the EL panel as a whole, the uneven brightness particularly appearing in the form of fine stripes can be reduced to a predetermined amount or less.

According to the driving method of the EL display device of the present invention, the pulse width setting map adjusts the division value of the number of the luminous pixels divided according to the pulse width of the driving voltage, so that the luminous luminance difference can be reduced. Created to be smaller. Further, according to the driving method of the EL display device according to the fifth aspect,
The pulse width setting map is created by adjusting the pulse width of the drive voltage corresponding to each section of the number of divided light emitting pixels. As a result, the EL display device can reduce the light emission luminance difference by using the pulse width setting map that is divided into the minimum required number and has the minimum required pulse width resolution. As a result, the control circuit for setting the pulse width and the processing thereof are simplified, and the cost is reduced and the processing speed is improved.

According to the EL display device of the present invention, the pulse width setting map changing circuit validates the pulse width setting map corresponding to the image displayed on the EL panel by storing the map in the pulse width setting map storage circuit. The pulse width control circuit sets the pulse width of the driving voltage of the light emitting pixel based on the number of light emitting pixels on the scanning electrode and the stored pulse width setting map. The pulse width control circuit generates a drive voltage having the set pulse width by controlling the scan-side electrode drive circuit and the data-side electrode drive circuit.

Therefore, the pulse width control circuit can make the substantial light emission time in which the voltage applied to the light emission pixel is equal to or higher than the light emission threshold value substantially constant regardless of the number of light emission pixels on the scanning electrode. In addition, uneven brightness can be reduced. Further, in this case, since the pulse width control circuit uses the pulse width setting map corresponding to the display target image, the pulse width control map is not limited to the luminance unevenness of the entire EL panel, but also depends on the display image, for example, a part of the EL panel, for example, in the proximity scanning. Brightness unevenness appearing between the side electrodes can be sufficiently reduced.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment for displaying an image defined by an EL display device and a driving method thereof on an EL panel according to the present invention will be described below with reference to FIGS. FIG. 3 schematically shows a cross-sectional structure of the EL element. In the EL element 1 as a pixel, first, a transparent electrode 3 is provided on a glass substrate 2, and a thin film of a first insulating layer 4, a light emitting layer 5, and a second insulating layer 6 is sequentially formed thereon,
Further, it is formed by providing a back electrode 7 thereon. The EL element 1 having such a structure is electrically capacitive.

When a pulsed driving voltage (for example, 200 V) equal to or higher than the light emission threshold is applied between the transparent electrode 3 and the back electrode 7, the EL element 1 emits light, and the light is emitted from the glass substrate 2.
It can be taken out through. In this case, for the purpose of reducing the variation in the light emission intensity due to the polarity of the drive voltage, an alternating voltage drive in which the polarity of the drive voltage is inverted at every predetermined timing is performed as described later. Also, the back electrode 7
Is a transparent electrode, the emitted light can be extracted also from the back electrode 7 side.

FIG. 2 schematically shows an electrical configuration of the EL display device. In FIG. 2, the EL display device 8 includes an EL panel 9, a scanning-side electrode driving circuit 10, a data-side electrode driving circuit 11, and a control circuit 12.

In the EL panel 9, a plurality of transparent electrodes 3 are arranged at regular intervals along the horizontal direction of the panel as scanning electrodes 201, 202,... Are arranged at regular intervals along the vertical direction of the panel. . And the data side electrode 30.
Each of the intersections with the EL elements 111, 112,..., 1 as pixels having the structure shown in FIG.
Are formed in a matrix. In FIG. 2, the EL elements 111, 112,... Are represented by using symbols for capacitors.

The scanning side electrode driving circuit 10 includes the scanning side electrode 2
.., And outputs a pulse-like positive or negative scan voltage to 01, 202,..., And includes a scan driver IC 13 and scan voltage supply circuits 14, 15.

The scanning driver IC 13 is connected between a power supply line L 1 to which a voltage is supplied from the scanning voltage supply circuit 14 and a power supply line L 2 to which a voltage is supplied from the scanning voltage supply circuit 15.
A P-channel type MOSFET 21a and an N-channel type MOSFET 21b, and similar MOSFETs 22a and 22b,. Scanning electrodes 201, 202,... Are connected to the common connection points of the MOSFETs in each complementary connection.
.. Have a push-pull configuration.

The scanning side driver IC 13 is a MOS
A gate drive circuit 20 for driving the gates of the FETs 21a, 21b, 22a, 22b,. The control signal input from the control circuit 12 is supplied to the MOSFETs 21a, 21b, 22
a, 22b,... are turned on and off. The MOSFETs 21a, 21b, 22a, 22b,.
Are connected in parallel in a state where the parasitic diodes 21c, 21d, 22c, 22d,...

The scanning voltage supply circuit 14 includes a switch circuit, for example, switching elements 14a and 14b. These switching elements 14a, 14b
According to a control signal from the control circuit 12, only one of them is selectively turned on. When the switching element 14a is turned on, the scanning voltage supply circuit 14 outputs a DC voltage Vr (write voltage Vr) of, for example, 200 V to the power supply line L1, and when the switching element 14b is turned on, the scanning voltage supply circuit 14 supplies the power supply line L1. On the other hand, a ground voltage (0 V) is output.

The scanning voltage supply circuit 15 includes a switch circuit, for example, switching elements 15a and 15b. These switching elements 15a, 15b
According to a control signal from the control circuit 12, only one of them is selectively turned on. When the switching element 15b is turned on, the scanning voltage supply circuit 15 applies a DC voltage V of, for example, 45 V to the power line L2.
m (offset voltage Vm), and outputs a negative DC voltage (-Vr + Vm) to the power supply line L2 when the switching element 15a is turned on.

On the other hand, the data-side electrode drive circuit 11 is a circuit for outputting a pulse-like data voltage to the data-side electrodes 301, 302,... And is composed of a data-side driver IC 16 and a data voltage supply circuit 17.

The data-side driver IC 16 has the same configuration as the above-described scanning-side driver IC 13. That is, between the power supply lines L3 and L4 to which the voltage is supplied from the data voltage supply circuit 17, the data side electrodes 301 and 30 are connected.
MOSs each having a push-pull configuration for 2,.
FET 31a, 31b, MOSFET 32a, 32b,
... are connected. Also, the data side driver IC 16
The MOSFETs 31a, 31b, 32a, 3
Gate drive circuit 3 for driving each gate of 2b,.
0 is provided. On the other hand, the data voltage supply circuit 17
Outputs a DC voltage Vm (offset voltage Vm) to the power line L3 and a ground voltage (0 V) to the power line L4.
Is output.

The control circuit 12 is mainly composed of a microcomputer, and executes a pulse width setting process described later in accordance with a control program stored in a nonvolatile memory (not shown) in advance. .
FIG. 1 shows the configuration of the control circuit 12 as a schematic functional block diagram. 1, the control circuit 12 includes a pulse width setting map storage circuit 41, a pulse width setting map changing circuit 42, a pulse width control circuit 43, and a drive signal generation circuit 44.

The pulse width setting map changing circuit 42 inputs the pulse width setting map data of the display image transferred from an external device (not shown) and stores the data in a pulse width setting map constituted by a volatile memory such as a RAM. The data is written to the map storage circuit 41. Further, the pulse width control circuit 43 receives the display data of the display target image transferred from the external device and outputs a control signal for controlling the pulse width of the drive voltage. The control signal is supplied to the scanning driver IC 13, the scanning voltage supply circuits 14 and 15, the data driver IC 16, and the data voltage supply circuit 17 via the drive signal generation circuit 44.

Next, the operation of the present embodiment will be described. First, using the timing chart shown in FIG.
A driving method of the L display device 8 will be described. EL element 1
,.. And the data side electrodes 301, 30 in order to stably emit light.
2. It is necessary to apply an AC voltage between. Therefore, the EL display device 8 switches the switching elements 14a and 14b of the scanning voltage supply circuit 14 every scanning period (hereinafter, referred to as a field) for all the scanning electrodes of the EL panel 9.
And switching element 15 of scanning voltage supply circuit 15
a and 15b are respectively switched to alternately and repeatedly perform a positive field drive for applying a positive drive voltage and a negative field drive for applying a negative drive voltage to the EL elements 111, 112,. Inversion drive). One cycle of the display operation is completed by one positive field drive and one negative field drive.
Hereinafter, the positive field drive and the negative field drive will be described separately.

(Positive Field Drive) The control circuit 12 controls the switching elements 14a and 15 during the period of the positive field drive.
b is turned on, and the switching elements 14b and 15a are turned off. At this time, the power supply line L1 of the scanning driver IC 13 is at the write voltage Vr, and the power supply line L2 is at the offset voltage Vm. Also, the control circuit 12
MO on the P channel side in the data side driver IC 16
The SFETs 31a, 32a, ... are turned on. as a result,
The scanning electrodes 201, 202,...
, 22d,... become the offset voltage Vm, and the data side electrodes 301, 302,.
The offset voltage Vm is obtained through 1a, 32a,.
Therefore, in this state, all the EL elements 111, 112,
Are driven at 0 V and do not emit light.

Thereafter, the control circuit 12 turns on the MOSFET 21a of the scanning driver IC 13, and sets the voltage of the scanning electrode 201 in the first row to the writing voltage Vr (time t1). At this time, the other scanning electrodes 202, 203,.
Are MOSFETs 22a, 22b, 23a, 23b,.
Are kept in an off state, thereby bringing them into a floating state.

On the other hand, in the data side driver IC 17, the EL on the scanning side electrode 201 is determined based on the display data.
Of the elements 111, 112,..., The P-channel MOSFET (MOSFET 31a) connected to the data-side electrode of the EL element that emits light (eg, the EL element 111) is turned off, and the N-channel MOSFET (MOSFET 31) is turned off.
b) is turned on (time t1). In addition, E which does not emit light
MO on the P channel side connected to the data side electrode of the L element
The SFET is kept on and the N-channel MO
The SFET is kept off.

As a result, the EL element to emit light emits light when the voltage of the data side electrode becomes the ground voltage and a voltage Vr higher than the light emission threshold voltage Vth is applied between the electrodes. The EL element that does not emit light does not emit light because the voltage of the data electrode becomes the offset voltage Vm and a voltage (Vr-Vm) lower than the light emission threshold voltage Vth is applied between the electrodes.

After that, the control circuit 12
After turning off the scanning side electrode 201 to turn the scanning side electrode 201 into a floating state, the MOSFET 21b is turned on at time t2 to discharge the electric charges accumulated between the electrodes of the EL elements 111, 112,. All the upper EL elements 111, 112,... Do not emit light. In this case, the P connected to the data side electrode of the EL element to emit light
MOSFET on channel side (MOSFET 31a) and MOSFET on N channel side (MOSFET 31b)
Maintain the off state and the on state, respectively, from the time t1 for a pulse width set for the data side electrode, for example, 24 .mu.sec.

When the MOSFET 21a is turned on (time t1) in the scanning of the scanning electrode 201 described above, the voltage of the scanning electrode 201 gradually rises with a certain rise time, and eventually reaches the write voltage Vr. The rise time occurs because the MOSFET 21a drives the capacitive EL elements 111, 112,...
The longer the number of EL elements emitting light on the scanning side electrode 201 (hereinafter, referred to as the number of light emitting pixels), the longer the length. Then, as the rise time increases, the scanning side electrode 201
The timing at which this voltage exceeds the light emission threshold voltage Vth is delayed. Further, the voltage of the scanning electrode 201 when the MOSFET 21b is turned on also gradually decreases with a certain fall time.

Therefore, as described later, the control circuit 12
Is MOSFET2 after the MOSFET 21a is turned on.
The time until 1b is turned on, that is, the pulse width of the scanning voltage is changed based on the number of light emitting pixels and the pulse width setting map. Thereby, the substantial light emission time in which the voltage of the scanning electrode 201 exceeds the light emission threshold voltage Vth becomes substantially constant.

In FIG. 4, the time required for scanning one scanning electrode (for example, the time from time t1 to time t3) is set to, for example, 30 μsec, and the MOSFET
The width of the pulse for turning on 21a and 21b is longer than the rise time and the fall time.

Subsequently, the control circuit 12 starts scanning the scanning electrodes 202 in the second row from time t3. FIG. 4 shows a case where the EL element 121 is not lit. That is, the MOSFET 31a connected to the data side electrode 301 of the EL element 121 is maintained in an on state, and the MOSFET 31b is maintained in an off state. In this case, the voltage of the scanning electrode 202 of the EL element 121 becomes the write voltage Vr, and the voltage of the data electrode 301 becomes the offset voltage Vm. As a result, the EL element 121
Is the threshold voltage V at which the voltage between the electrodes (Vr-Vm) is
It does not emit light because it is smaller than th.

(Negative field driving) The control circuit 12 controls the switching elements 14a and 15 during the negative field driving.
b is turned off, and the switching elements 14b and 15a are turned on. At this time, the power line L1 of the scanning driver IC 13 is at the ground voltage, and the power line L2 is at the offset voltage (-Vr + Vm). The control circuit 12
Turns on the N-channel MOSFETs 31b, 32b,... In the data-side driver IC 16. As a result, the scanning electrodes 201, 202,... And the data electrodes 301, 302,. Therefore,
In this state, the driving voltages of all the EL elements 111, 112,.

Thereafter, the control circuit 12 performs line sequential scanning in the same manner as in the normal field driving. In this case, the control circuit 12 turns on the N-channel MOSFET connected to the scanning electrode in the sequentially selected row, and applies a voltage of (−Vr + Vm) to the scanning electrode. On the other hand, the control circuit 1
Reference numeral 2 turns on and off the P-channel and N-channel MOSFETs connected to the data electrode of the EL element to emit light, respectively, and sets the voltage of the data electrode to the offset voltage Vm. Further, the control circuit 12 keeps the P-channel side and N-channel side MOSFETs connected to the data side electrode of the EL element which does not emit light as OFF and ON, respectively, and keeps the voltage of the data side electrode at the ground voltage.

As a result, an EL element (for example, E
The L element 111) emits light when a voltage -Vr whose absolute value exceeds the light emission threshold voltage Vth is applied between its electrodes. In addition, an EL element which does not emit light (eg, EL element 121)
Does not emit light because a voltage (-Vr + Vm) whose absolute value is lower than the light emission threshold voltage Vth is applied between the electrodes.

Next, a method of variably setting the pulse width of the driving voltage in the above-described positive and negative field driving will be described with reference to FIGS. Each time the image displayed on the EL panel 9 changes, the pulse width setting map change circuit 42 inputs pulse width setting map data from an external device through an external interface (both not shown) before starting to display the image. The pulse width setting map stored in the pulse width setting map storage circuit 41 is rewritten with the input pulse width setting map.

The input pulse width setting map, which will be described in detail later, is created in advance so that the luminance unevenness of the image is reduced. The pulse width setting map, as illustrated in FIG.
2,... EL elements 111, 112,.
, And the scanning side driver IC1
., Or the number of light-emitting pixels and the data-side electrode 30 via the data-side driver IC 16.
1, 302,... Show the relationship with the pulse width of the data voltage to be output. Here, the pulse width setting map shown in FIG. 6 changes only the pulse width of the scanning voltage applied to the scanning electrodes 201, 202,.
The pulse width of the scan voltage applied to the data side electrodes 301, 302,... May be varied, or the pulse width of the scan voltage and the pulse width of the data voltage may be varied.

The pulse width control circuit 43 generates a control signal for performing the above-described field drive in order to display an image on the EL panel 9. In this case, the pulse width control circuit 43 sets the pulse width of the scanning voltage output from the scanning driver IC 13 and the pulse width of the data voltage output from the data driver IC 16 according to the flowchart shown in FIG.

That is, in FIG. 5, the pulse width control circuit 43 counts the number of light emitting pixels on the scanning side electrode based on the display data before outputting the scanning voltage to each scanning side electrode (step S1). The count value is compared with the pulse width setting map stored in the pulse width setting map storage circuit 41 (step S2). Then, the pulse width control circuit 43 sets the pulse widths of the scanning voltage and the data voltage based on the comparison result (Step S).
3).

When the pulse width is controlled in accordance with such a procedure, a scanning voltage having a wide pulse width is applied to the scanning-side electrode having a long rising time of the scanning voltage due to a large number of light emitting pixels, and light emission is performed. A scanning voltage having a narrow pulse width is applied to a scanning-side electrode having a small number of pixels and a short rising time of the scanning voltage. As a result, irrespective of the number of light emitting pixels of each scanning side electrode, the substantial light emitting time in which the scanning voltage exceeds the light emitting threshold voltage Vth is controlled to be substantially constant,
The uneven brightness of the EL panel 9 is reduced.

Next, a method of creating a pulse width setting map for sufficiently reducing the uneven brightness of the EL panel 9 will be described with reference to FIGS. First, a brightness map shown in FIG. 7 is created. This luminance map is obtained by measuring the relationship between the number of light emitting pixels on the scanning side electrode and the light emission luminance when a scanning voltage having a predetermined pulse width is applied to the scanning side electrode. The value of the pulse width discretely determined in this luminance map is determined based on the resolution at which the control circuit 12 can actually control the pulse width using the system clock of the microcomputer.

Subsequently, using this luminance map, FIG.
A reference pulse width setting map as shown in FIG. In this case, the pulse width setting map is created such that the emission luminance distribution of the EL element is within the range of 10% or less with respect to the target luminance regardless of the number of light emitting pixels on the scanning side electrode.

Subsequently, based on the luminance map created in this way and the reference pulse width setting map (see FIG. 12B), the luminance unevenness becomes smaller for each image displayed on the EL panel 9. A pulse width setting map (see FIG. 6) optimized so as to be generated is created. FIG. 8 shows a flowchart for creating the pulse width setting map. This creation process is performed manually by an operator or automatically performed by using a computer. Further, the pulse width of the scanning voltage may be made constant, and the pulse width of the data voltage may be varied.

In FIG. 8, first, the number of light emitting pixels of each scanning electrode is calculated based on image display data (step T1). Subsequently, the pulse width of the scanning voltage to be applied to the scanning side electrode is obtained from the calculated number of light emitting pixels of each scanning side electrode and the reference pulse width setting map (see FIG. 12). (See step T) to determine the light emission luminance at the pulse width and the number of light emission pixels.
2). Then, the emission luminances obtained for all the scanning electrodes are compared, and the difference between the maximum luminance and the minimum luminance (maximum luminance difference) is obtained.
Is within 20% of the target luminance (first condition), and the emission luminance difference between adjacent scanning electrodes is 10% of the target luminance.
It is determined whether the condition is within (second condition) (step T3). If these two conditions are both satisfied,
The reference pulse width setting map is adopted as it is as the pulse width setting map for the image, and the process ends.

On the other hand, if "NO" in the step T3, the reference pulse width setting map is changed, and the reference pulse width setting map is newly set as the pulse width setting map for the image (step T4). At the time of this change, attention is paid to two adjacent scanning electrodes having the largest difference in light emission luminance, and the pulse width setting map is changed so that the difference in light emission luminance is within 10%. As this changing method, a delimiting value of the number of light emitting pixels with respect to the pulse width (22, 36 in FIG. 6,
52,...) And a method of changing the pulse width without changing the delimiter. When changing, it is necessary to pay attention so that the first condition is satisfied.

The former method is effective when, for example, only the light emission luminance of the scanning electrode having the number of light emission pixels before and after the separation value does not satisfy the above condition. In the latter case,
This is an effective method when there are two or more scanning electrodes having the same number of light emitting pixels and only one of them does not satisfy the second condition.

After changing the pulse width setting map by any of the above-described methods, the process returns to step T2, and returns to step T2.
At 3, it is determined whether the first and second conditions are both satisfied. Then, for the display image, these 2
Steps T2 to T4 are repeated until a pulse width setting map that satisfies the two conditions is obtained.

The allowable values under the first and second conditions are set to 20% and 10% as an example.
In order to further reduce luminance unevenness, it is preferable to set these allowable values smaller. If it is difficult to satisfy these two conditions depending on the image, increase the number of sections of the pulse width setting map, or use a pulse width setting map for the image in which the difference in emission luminance is minimized within a possible range. It should be adopted as.

As described above, according to the present embodiment, E
For each image displayed on the L-panel 9, a pulse width setting map optimized so that the maximum luminance difference and the light emission luminance difference between the adjacent scanning electrodes are each equal to or smaller than a predetermined value is created. The change circuit 42 rewrites the pulse width setting map storage circuit 41 with the created pulse width setting map before starting display of each image. And
The pulse width control circuit 43 sets the pulse width of the scanning voltage using a pulse width setting map optimized for the display image.

Therefore, according to the EL display device 8, not only luminance unevenness when viewed as a whole EL panel 9 but also luminance unevenness in a partial region of the EL panel 9 such as between adjacent scanning electrodes is sufficiently obtained. This has the effect of reducing the appearance of streak (or band) patterns extending in the lateral direction of the panel.

Since the EL display device 8 uses the optimum pulse width setting map for each display image, the number of sections in the pulse width setting map is smaller than when the same pulse width setting map is used for all display images. And the resolution of the pulse width can be reduced. As a result, the configuration of the pulse width control circuit 43 can be simplified, and its design and manufacturing costs can be reduced. Further, since the processing of the pulse width control circuit 43 is reduced, the processing speed is improved.

(Other Embodiments) The present invention is not limited to the above-described embodiments, and the following modifications or extensions are possible. In the above embodiment, the pulse width setting map based on the number of light emitting pixels is used to change the pulse width of the drive voltage, but a pulse width setting map based on the number of non-light emitting pixels may be used. In the second condition for creating the pulse width setting map, the light emission luminance difference between adjacent scanning electrodes is used, but the light emission luminance difference between adjacent scanning electrodes may be used.

In the positive field driving shown in FIG.
The control circuit 12 keeps the timing at which the MOSFET on the P-channel side of the scanning driver IC 13 is turned on constant (30 μm).
every second), and by changing the timing at which the N-channel MOSFET is turned on, a scanning voltage having a predetermined pulse width is generated. In contrast, the control circuit 12
May generate a scanning voltage having a predetermined pulse width by changing the timing at which the N-channel MOSFET is turned on and changing the timing at which the P-channel MOSFET is turned on (the same applies to negative field driving). ). In addition, the EL display device 8 may employ a line inversion drive in which the polarity of the drive voltage applied to the EL elements 111, 112,.

[Brief description of the drawings]

FIG. 1 is a functional block diagram of a control circuit showing one embodiment of the present invention.

FIG. 2 is a schematic electrical configuration diagram of an EL display device.

FIG. 3 is a configuration diagram schematically showing a cross-sectional structure of an EL element.

FIG. 4 is a timing chart of a field drive.

FIG. 5 is a flowchart of a pulse width setting process.

FIG. 6 is a diagram showing a pulse width setting map.

FIG. 7 shows a luminance map.

FIG. 8 is a flowchart of a pulse width setting map creation process;

FIG. 9 is a diagram showing luminance characteristics with respect to the number of light emitting pixels in a conventional configuration.

FIG. 10 is an explanatory diagram of luminance unevenness appearing on an EL panel.

FIG. 11 is a waveform diagram of a scanning voltage.

12A is a diagram illustrating a luminance characteristic with respect to the number of light-emitting pixels after shadowing countermeasures, and FIG. 12B is a diagram illustrating a pulse width setting map.

[Explanation of symbols]

1, 111, 112,... Are EL elements (pixels), 8 is EL
A display device, 9 an EL panel, 10 a scanning-side electrode drive circuit, 11 a data-side electrode drive circuit, 41 a pulse width setting map storage circuit, 42 a pulse width setting map change circuit,
Reference numeral 43 denotes a pulse width control circuit, 201, 202,..., Scanning side electrodes, and 301, 302,.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hiroyuki Kinoshita 1-1-1, Showa-cho, Kariya-shi, Aichi Prefecture Inside Denso Corporation (72) Inventor Masahiko Nagata 1-1-1, Showa-cho, Kariya-shi, Aichi Prefecture Denso Corporation (72) Inventor Naoki Matsumoto 1-1-1, Showa-cho, Kariya-shi, Aichi F-term in DENSO Corporation (reference) 5C080 AA06 BB05 DD05 EE28 FF12 GG02 GG12 JJ02 JJ04 JJ05 JJ06 JJ07

Claims (6)

[Claims] 1. A pulse-like scanning voltage is sequentially applied to a plurality of scanning electrodes arranged on an EL panel, and a plurality of data electrodes arranged on the EL panel in synchronization with scanning of the scanning electrodes. A driving method of an EL display device for driving a pixel of the EL panel to display an image by applying a pulsed data voltage to the EL panel, wherein an image to be displayed on the EL panel is formed along the scanning electrode. Creating in advance a pulse width setting map indicating a relationship between the number of light emitting pixels of the pixel and a pulse width of a driving voltage to the light emitting pixel generated by the scanning voltage and the data voltage; Validating the pulse width setting map created for the image before displaying the image; and applying a scanning voltage to each of the scanning electrodes. Counting the number of light emitting pixels of pixels formed along the scanning side electrode before the scanning, and based on the count value and the validated pulse width setting map, a pulse corresponding to the number of light emitting pixels. Controlling the scan voltage and the data voltage to generate a drive voltage having a width.
A method for driving the L display device. 2. The method according to claim 1, wherein the pulse width setting map is created so that a difference between a light emitting pixel having a highest luminance and a light emitting pixel having a lowest luminance is smaller than a predetermined value. The EL according to claim 1,
A method for driving a display device. 3. The pulse width setting map includes, for a display target image, a luminescent pixel formed along the scanning electrode and a luminescent pixel formed along a scanning electrode close to the scanning electrode. 3. The light-emitting device according to claim 1, wherein the light-emitting luminance difference is made smaller than a predetermined value.
The driving method of the EL display device described in the above. 4. The pulse width setting map according to claim 2, wherein the pulse width setting map is created by adjusting a division value of the number of light-emitting pixels divided according to a pulse width of the driving voltage. Driving method of an EL display device. 5. The pulse width setting map according to claim 2, wherein the pulse width setting map is created by adjusting a pulse width of the driving voltage corresponding to each section of the number of divided light emitting pixels. Or a driving method of an EL display device. 6. An EL panel in which a plurality of pixels are formed by arranging a plurality of scanning electrodes and data electrodes, a scanning electrode driving circuit for outputting a pulsed scanning voltage to the scanning electrodes, A data-side electrode driving circuit that outputs a pulsed data voltage to the data-side electrode; a light-emitting pixel number of the pixels formed along the scanning-side electrode for an image to be displayed on the EL panel; A pulse width setting map storage circuit for storing a pulse width setting map indicating a relationship between the driving voltage generated by the data voltage and the pulse width of the driving voltage to the pixel, and a pulse stored in the pulse width setting map storage circuit A pulse width setting map changing circuit that changes a width setting map by a pulse width setting map corresponding to a display target image, and at the time of scanning by the scanning side electrode, Based on the pulse width setting map stored in the pulse width setting map storage circuit, the scan-side electrode drive circuit and the data-side electrode drive circuit to generate a drive voltage having a pulse width corresponding to the number of pixels. An EL display device comprising a pulse width control circuit for controlling the EL display device.