JPH0748140B2 - Driving method of display device - Google Patents

Abstract

PURPOSE:To make all picture elements to illuminate with the same brightness for the same display data by correcting and setting the pulse width of modulating voltages large or previously by the increment in the pulse width of modulating voltages applied to the picture elements owing to the influence of the line resistance of data-side electrodes. CONSTITUTION:The modulating voltages applied to the data-side electrodes X1-Xn are corrected by decreasing or increasing the pulse width in the line sequence of scanning-side electrodes Y1-Ym. Namely, the pulse width of the modulating voltages is corrected and set wide or narrow by the increment or decrement in the pulse width of the modulating voltages applied to the picture elements owing to the influence of the line resistance of the data-side electrodes X1-Xn. Consequently, all the picture elements illuminates with the same brightness for the same display data.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving method of a display device such as a capacitive flat matrix display panel (hereinafter referred to as a thin film EL display device).

2. Description of the Related Art For example, a double-insulation (or three-layer structure) thin film EL device is constructed as follows.

As shown in FIG. 7, a strip-shaped transparent electrode 2 made of In ₂ O ₃ is provided in parallel on a glass substrate 1 and, for example, Y ₂
Dielectric material 3a such as O ₃ , Si ₃ N ₄ , Al ₂ O ₃ and EL material 4 consisting of ZnS doped with activator such as Mn and Y ₂ O ₃ , Si ₃ N as above
Dielectric materials 3b such as ₄ , TiO ₂ and Al ₂ O ₃ are sequentially laminated using a thin film technique such as a distillation method and a sputtering method to a film thickness of 500 to 10000Å to form a three-layer structure, on which the transparent electrode is formed. A strip-shaped back electrode 5 made of Al (aluminum) is provided in parallel in a direction orthogonal to 2.

Since the thin film EL element has the EL material 4 sandwiched between the dielectric materials 3a and 3b between its electrodes, it can be regarded as a capacitive element in terms of an equivalent circuit. Also, this thin film EL
As is clear from the voltage-luminance characteristic shown in FIG. 8, the 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.

Basic display driving of a thin film EL display device using the thin film EL element as a display panel is performed by using one of the transparent electrode 2 and the back electrode 5 of the thin film EL element as a scanning side electrode and the other as a data side electrode, and a data side electrode. A modulation voltage corresponding to display data for determining light emission / non-light emission is applied to the scanning side electrode, and a writing voltage is applied to the scanning side electrode line-sequentially. By this display driving, a superimposing effect or a canceling effect of the writing voltage and the modulation voltage is generated in the pixel portion where the scanning side electrode and the data side electrode of the EL layer 4 intersect, and the pixel has a light emission threshold value. A voltage equal to or higher than the voltage or equal to or lower than the light emission threshold voltage (hereinafter referred to as an effective voltage) is applied, whereby each pixel is in a light emitting / non-light emitting state and a predetermined display is obtained.

Conventionally, in such a thin film EL display device, as a driving method for performing gradation display in which the brightness of each pixel is changed in a plurality of stages, the pulse width of the modulation voltage applied to the data side electrode is gradation display data (brightness data). There is known a pulse width modulation method in which the area of the effective voltage applied to the pixel is controlled by changing the pulse width modulation method according to.

However, in the driving method described above, when a transparent electrode having a high line resistance is used as the data-side electrode, the modulation voltage applied to the data-side electrode is affected by the line resistance, As described below, there is a problem that a luminance difference occurs between pixels.

FIG. 9 is a connection configuration diagram showing the display panel 6 of the thin-film EL display device and a part of its drive circuit for explaining the cause of such a brightness difference. In FIG. 9, each data-side electrode 7a, 7b is an output of a data-side drive circuit for applying a modulation voltage V _M to the data-side electrode 7a, 7b at the electrode end portion pulled out to the upper side of the same figure. Ports 8a and 8b are connected to each other. On the other hand, a plurality of scanning side electrodes 9a, 9b, 9c, 9d are arranged in parallel to each other in a direction orthogonal to these data side electrodes 7a, 7b, and each scanning side electrode 9a-9d is on the left side of FIG. At the drawn electrode ends, write voltage -V _W
Output port 10a, 10b of the scanning side drive circuit for applying
10c and 10d are connected respectively. In FIG. 9, the line resistance in the middle of each data side electrode 7a, 7b is indicated by a resistance R.

In the thin film EL display device having the above structure, for example, in order to cause the two pixels 11A and 11D located on the data side electrode 7a to emit light with the same brightness, the scanning side electrode 10a has a light emission threshold voltage Vth.
Is applied to the data side electrode 7a from the output port 8a of the data side drive circuit in the case where the write voltage −V _W corresponding to is applied and the same write voltage −V _W is applied to the scanning side electrode 10d. It is assumed that a voltage having the same waveform is applied as the modulation voltage V _M.

In the pixel 11A located near the output port 8a, the line length of the data-side electrode 7a from the output port 8a to the pixel 11A is short, so that it is hardly affected by the line resistance, and therefore the pixel 11A has the same configuration as that shown in FIG. As shown in (1), a voltage having substantially the same waveform as the modulation voltage V _M output from the output port 8a is applied. At this time, from the output port 10a of the scanning side driving circuit to the scanning side electrode 9a, as shown in FIG.
When the write voltage -V _W having a waveform as shown in FIG. 10 is applied, the effective voltage having the waveform shown in FIG. 10 (3) is applied to the pixel 11A.

On the other hand, the pixel 11 located far from the output port 8a
In D, the data side electrode 7a from the output port 8a to the pixel 11D
Since the line length is long and the line resistance R between them becomes large, the modulation voltage V _M is greatly affected by the line resistance R. Therefore, as shown in FIG. 11 (1), the pixel 11D is applied with a voltage having an integral waveform such that the modulation voltage V _M output from the output port 8a is passed through the integrator circuit.
At this time, when the write voltage −V _W having a waveform as shown in FIG. 11 (2) is applied from the output port 10d of the scan side drive circuit to the scan side electrode 9d, the pixel 11D is shown in FIG. The effective voltage having the waveform shown in () is applied.

Of the effective voltages applied to the pixels 11A and 11D, the voltage that substantially contributes to light emission is the light emission threshold voltage Vth or higher, so the waveforms of FIG. 10 (3) and FIG. 11 (3) Is compared with the light emission threshold voltage Vth or higher,
The area of the waveform in FIG. (3) is wider by the shaded area. Since this difference in area becomes the difference in brightness as it is, the pixel 11D becomes brighter than the pixel 11A even though the pixels 11A and 11D were supposed to emit light at the same brightness. become.

That is, even if the modulation voltage V _M having the same waveform is applied, the pixels closer to the output port become darker and the pixels farther from the output port become brighter. There is a difference in brightness between the images, which deteriorates the display quality.

Therefore, an object of the present invention is to provide a driving method of a display device capable of causing each pixel to emit light with uniform brightness for the same gradation display data without being affected by the line resistance of the data side electrode. That is.

Means for Solving the Problems According to the present invention, a dielectric layer is interposed between a plurality of scanning side electrodes and a plurality of data side electrodes arranged in directions intersecting with each other,
A modulation voltage with a pulse width changed according to display data is applied to the data-side electrode from one electrode end side, while a writing voltage is applied line-sequentially to the scanning-side electrode to connect with the scanning-side electrode. In a method of driving a display device in which each pixel formed of a dielectric layer at a portion where the data-side electrode intersects is brought into a non-light-emitting state and a light-emitting state in which luminance is different over several steps, a modulation voltage applied to the data-side electrode is applied. Then, the pulse width is corrected so as to be sequentially decreased or increased according to the line sequence of the scanning side electrodes so that all pixels have the same brightness for the same display data. It is a driving method.

Operation According to the present invention, the pulse width of the modulation voltage is set to be wider or narrower in advance by the amount that the pulse width of the modulation voltage applied to the pixel increases or decreases due to the influence of the line resistance of the data side electrode. Therefore, all pixels emit the same brightness for the same display data.

Embodiment FIG. 1 is a block diagram showing a schematic structure of a thin film EL display device to which a driving method according to an embodiment of the present invention is applied. In the figure, the display panel 13 is composed of a thin film EL element,
Since its specific configuration is the same as the configuration described in the related art, its description is omitted here. A plurality of scanning-side electrodes Y1, Y2, ..., Y arranged on the display panel 13
m−1, Ym (hereinafter, represented by reference numeral Y for any scanning side electrode) are connected to the scanning side drive circuit 14 provided on the right side of FIG. Also, a plurality of data side electrodes arranged in a direction orthogonal to the scan side electrodes Y1 to Ym.
Xn-1, X2, ..., Xn−1, Xn (hereinafter, any data-side electrode is represented by symbol X) are connected to a data-side drive circuit 15 provided on the upper side of FIG.

In the scan side drive circuit 14, the output port 16 is individually connected to each of the scan side electrodes Y1 to Ym, and the write voltage −V _W from the power supply 17 is supplied to each of the scan side electrodes Y1 to Ym through the output port 16. Is selectively applied to. Each of these output ports 16 is connected to the shift register 18, and in order to set the scanning side electrodes Y1 to Ym in the shift register 18 in line sequential order in synchronization with the clock CLK3 input from the clock input terminal of the shift register 18. Of the scan data S-DATA is transferred, whereby each output port 16 is turned on in accordance with the line order of the scan side electrodes Y1 to Ym.

On the other hand, in the data side driving circuit 15, each data side electrode X1 to Xn
The output port 19 is individually connected to the output port 19, and the modulation voltage V _M is supplied from the power supply 20 via the output port 19 to each electrode on the data side.
It is selectively applied to X1 to Xn. Further, depending on the setting state of the output port 19, the data side electrodes X1 to Xn are clamped to the ground.

These output ports 19 are connected to the comparator 21. The comparator 21 is connected to the shift register 23 via the latch circuit 22. The shift register 23 is a circuit for performing a shift operation in synchronization with the clock CLK1 input from its clock input terminal and transferring the gray scale display data corresponding to each of the data side electrodes X1 to Xn, and transfers it to the shift register 23. After being processed, it is sent to the comparator 21.

The comparator 21 has a function of comparing the 3-bit parallel data supplied from the counter 24 with the gradation display data supplied from the latch circuit 22 to determine the gradation width corresponding to the gradation display data. In FIG. 1, each pixel on the display panel 13 is equivalently represented by a capacitor.

FIG. 3 is a block diagram showing a correction circuit for correcting the luminance difference between pixels caused by the line resistance of the data side electrodes X1 to Xn. In the correction circuit shown in FIG. 3, the clock generator 25 is a circuit for generating a basic clock CLK for determining the gradation width according to the gradation display data, and is operable by an enable signal CLKE given from its input terminal. To be done.

A delay circuit 26, which delays the basic clock CLK by a predetermined amount and provides it as the clock CLK2 of the counter 24 of the data side drive circuit 15, is connected to the next stage of the clock generator 25. A scanning line position detection circuit 27 is connected to the delay circuit 26. Scan line position detection circuit
27 has a function of counting up and a function of counting down the horizontal synchronizing signal HD input from the input terminal 31 as a clock, and is reset by the vertical synchronizing signal VD input from the input terminal 32.

The count-up signal or count-down signal of the scanning line position detection circuit 27 is sent to the delay circuit 26, and the delay circuit 26 performs delay processing by an amount according to the signal. A signal EDD for determining which of the count-up signal and the count-down signal described above to be sent to the delay circuit 26 is input to the input terminal 33 of the scanning line position detection circuit 27.
In this embodiment, the signal EDD is set to "L" level, and the delay circuit 26 is supplied with the countdown signal. When the signal EDD is set to "H" level, a count-up signal is sent to the delay circuit 26.

Next, the basic operation of the thin film EL display device shown in FIG. 1 will be described with reference to the timing chart shown in FIG.

The shift register 23 of the data side drive circuit 15 has a clock
The gradation display data is transferred in the form of a 3-bit binary code in synchronization with CLK1. The 3-bit gradation display data is temporarily held by the latch circuit 22. Under this condition, when the clear signal ▲ ▼ input to the comparator 21 and the counter 24 until then is released as shown in FIG. 2 (1) (time t1), it is held in the latch circuit 22. The data side electrode X corresponding to the data of "0" in the gray scale display data is clamped to the ground, and all the data side electrodes X corresponding to the other data are raised to the modulation voltage V _M.

Now, for example, the data side electrodes X1 and X of the data side drive circuit 15
It is assumed that the gradation display data "0", "2", "4", "7" are applied to the output ports 19 corresponding to 2, Xn-1, Xn, respectively. At this time, the output port 19 of the data side electrode X1
Is cleared to the ground simultaneously with the release of the clear signal ▲ ▼, and the waveform shown in FIG. That is, the gradation width is set to zero.

Further, at the output port 19 of the data-side electrode X2, the count value of the clock CLK2 (see FIG. 2 (2)) counted by the counter 24 is compared with the gradation display data “2” by the comparator 21, and the count value is “ It is clamped to the ground at the timing of "2" (time t2), and the gradation width T2 of the waveform shown in FIG. 2 (4) is set. Similarly, the data side electrode
The output port 19 of Xn-1 is clamped to the ground at the timing (time t3) when the count value of the counter 24 becomes "4", and the gradation width T4 of the waveform shown in FIG. 2 (5) is set. . The output port 19 of the data side electrode Xn is also clamped to the ground at the timing (time t4) when the count value of the counter 24 becomes “7”, and the gradation width T7 of the waveform shown in FIG. 2 (6) is set. To be done. Therefore, the modulation voltage V _M having a pulse width corresponding to the gradation display data “0”, “2”, “4”, “7” is applied to each of the data side electrodes X1, X2, Xn−1, Xn. Will be.

On the other hand, in the scanning side drive circuit 14, only one of all the output ports 16 is turned on while the clear signal ▲ ▼ is released in the data side drive circuit 15, and one scanning side electrode corresponding to this is turned on. The write voltage −V _W is applied only to Y.

By repeating the above operation in line-sequential order of the scanning-side electrodes Y, the pixels located on each scanning-side electrode Y emit light or do not emit light with the brightness according to the gradation display data, and the brightness as a whole is increased. A screen with gradation is displayed on.

Next, the brightness correction operation by the correction circuit shown in FIG. 3 will be described with reference to the timing chart shown in FIG.

The clock generator 25 outputs a basic clock CLK having a waveform shown in FIG. 4 (1) which is a basis for determining the gradation width. In the scanning line position detection circuit 27, after the vertical synchronizing signal VD is received and reset, the horizontal synchronizing signal HD is used as a clock to count down. In this countdown operation, the number "m" of horizontal synchronizing signals HD for one field is set as an initial value. When the first horizontal synchronizing signal HD in one field is counted, the countdown signal “m−1” is sent to the delay circuit 26. In the delay circuit 26, the basic clock CLK is delayed by an amount corresponding to the countdown signal "m-1" as shown in FIG. 4 (2), and the clock is applied to the counter of the data side drive circuit 15. Given as 24 clocks CLK2.

In this case, since the countdown signal "m-1" is large, the delay amount Ta of the clock CLK2 with respect to the basic clock CLK is Ta.
Is also big. Therefore, in the data side drive circuit 15, the timing at which the counter 24 starts counting the clock CLK2 is greatly delayed, and the pulse width tA larger than the pulse width tA corresponding to the grayscale data by the delay amount Ta described above.
The modulation voltage V _{M of} + Ta is applied.

FIG. 5 shows the waveform of the applied voltage to the pixel A at the intersection of the first scanning side electrode Y1 and the data side electrode X1 at this time. 5 (1) shows the waveform of the modulation voltage V _M applied from the data side electrode X1, and FIG. 5 (2) shows the light emission threshold voltage Vth applied from the first scanning side electrode Y1. The waveform of the corresponding write voltage −V _W is shown. At this time, the effective voltage applied to the pixel A has a waveform as shown in FIG.

That is, as described above, the pixel A has a delay amount Ta of the clock CLK2 rather than the pulse width tA corresponding to the gradation display data.
Since a modulation voltage V _M with a pulse width tA + Ta that is as wide as possible is applied, only the area shaded in FIG. 5 (3) is the area above the light emission threshold voltage Vth that contributes to light emission at the effective voltage. Is increased, and the brightness is corrected to be higher by the increased area.

In the correction circuit of FIG. 3, the scanning line position detection circuit 27
When the countdown signal of "CLK" advances and the countdown signal becomes "m-m", that is, "0", the delay amount applied by the delay circuit 26 becomes zero, and the basic clock CLK2 of the clock CLK2.
The amount of delay with respect to is also zero. Therefore, in the data side drive circuit 15, the timing for starting the counting of the clock CLK2 in the counter 24 is not delayed, the modulation voltage V _M is applied monkey pulse width tA corresponding to the gradation display data. In this case, since the countdown signal of the scanning line position detection circuit 27 is “m−m”, the writing voltage − is applied to the scanning side electrode Ym.
V _W is applied.

FIG. 6 shows a pixel B at the intersection position of the m-th scanning-side electrode Ym at this time and the same data-side electrode X1 as described above.
The waveform of the applied voltage with respect to is shown. Of which, the sixth
Figure (1) shows the modulation voltage V applied from the data electrode X1.
_M shows an integral waveform affected by the line resistance of the transparent electrode, and FIG. 6 (2) shows a writing voltage −V _M corresponding to the light emission threshold voltage Vth applied from the mth scanning-side electrode Ym.
Shows the waveform of. Therefore, at this time, the pixel B
The effective voltage applied to has a waveform as shown in FIG.

Since the pixel B in this case is located far from the output port 19, it is greatly affected by the line resistance, and the applied modulation voltage V _M has an integrated waveform as shown in FIG. 6 (1), and emits light at the effective voltage. Of the contributing light emission threshold voltage Vth or higher, the shaded portion in FIG. 6C increases.

However, at this time, the same gradation display data as that of the pixel A located on the first scanning-side electrode Y1 described above is used for the next pixel B.
If it is also set to, the pulse width tA + which is larger than the pulse width tA corresponding to the gradation display data as described above.
The area increase shown by hatching in FIG. 5 (3) in the effective voltage in the case of the pixel A to which the Ta modulation voltage V _M is applied is shown in FIG. 6 (3) in the effective voltage applied to the pixel B. )
Is almost equal to the area increase due to the influence of the line resistance shown by hatching. That is, the pixels A and B located on the same data side electrode X1 have the same brightness for the same gradation display data.

The correction amount of the above-described brightness correction is the scanning line position detection circuit.
The value of the countdown signal is determined according to the value of the countdown signal 27, and the value of the countdown signal indicates the position of the scanning side electrode Y to which the writing voltage −V _W is applied at that time. However, the correction amount of the brightness correction decreases in line-sequential order of the scanning side electrode Y, and the sum of the increase in brightness due to the influence of the line resistance and the increase in brightness due to the brightness correction is always constant.

In this way, the same brightness can be obtained for the same gradation display data among the pixels over the entire screen.

In the present embodiment, as shown in FIG. 5 and FIG. 6, the application timing of the modulation voltage V _M as the rising portion of the modulation voltage V _M from the portion contributing to light emission is out of the effective voltage applied to the pixel Therefore, when the modulation voltage V _M is affected by the line resistance and becomes an integral waveform, its rising portion does not pose a problem. On the other hand, when the trailing edge of the modulation voltage V _M to set the application timing of the modulation voltage V _M to deviate from the portion contributing to light emission of the effective voltage,
The falling part of the integrated waveform does not matter, but this time the rising part does matter. Contrary to the case of the above-mentioned embodiment, the rising portion of this integral waveform works so as to reduce the area of the effective voltage applied to the pixel as the influence of the line resistance increases. Therefore, the luminance correction in this case is performed in this embodiment. The opposite is true. That is, the signal ED applied to the input terminal of the scanning line position detection circuit 27 shown in FIG.
Contrary to the above embodiment, D may be set to the "H" level.

As described above, according to the driving method of the display device of the present invention,
Since the pulse width of the modulation voltage applied to the pixel increases due to the influence of the line resistance of the data-side electrode, the pulse width of the modulation voltage is corrected and set in advance. Can emit light with the same brightness.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of a thin film EL display device to which a driving method according to an embodiment of the present invention is applied, FIG. 2 is a timing chart showing its basic operation, and FIG. FIG. 4 is a block diagram showing a schematic configuration of a correction circuit for correcting the brightness of the display device, FIG. 4 is a timing chart showing the operation of the correction circuit, and FIG. 5 is on the first scanning side electrode of the thin film EL display device. 6 is a waveform diagram showing the voltage applied to the pixel located on the pixel, FIG. 6 is a waveform diagram showing the voltage applied to the pixel located on the m-th scanning side electrode of the thin film EL display device, and FIG. Partially cutaway perspective view, FIG. 8 is a graph showing applied voltage-luminance characteristics of a thin film EL element, and FIG. 9 is a circuit diagram showing a schematic configuration of a main part of a thin film EL display device to which a conventional driving method is applied. , Fig. 10 shows the scanning side voltage near the output port of the thin film EL display device. Waveform diagram showing the voltage applied to the pixel located above, FIG. 11 is a waveform diagram showing voltages applied to pixels located farther scanning side on the electrode from the output port of the thin film EL display device. 13 ... Display panel, 14 ... Scan side drive circuit, 15 ... Data side drive circuit, X1 to Xn ... Data side electrode, Y1 to Ym ... Scan side electrode, 25 ... Clock generator, 26 ... Delay circuit, 27
... Scan line position detection circuit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hiroshi Kishishita 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Within Sharp Corporation (72) Hisashi Kamiide 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Within Sharp Corporation (56) Reference JP-A-59-228698 (JP, A) JP-A-59-121390 (JP, A) JP-A-59-53891 (JP, A)

Claims (1)

[Claims] 1. A dielectric layer is interposed between a plurality of scanning-side electrodes and a plurality of data-side electrodes arranged in a direction intersecting with each other, and the data-side electrode is provided with a display data from one electrode end side thereof. While applying the modulation voltage with the pulse width changed, the writing voltage is applied line-sequentially to the scanning side electrode,
In a driving method of a display device in which each pixel formed of a dielectric layer at a portion where a scanning side electrode and a data side electrode intersect is brought into a non-light emitting state and a light emitting state in which luminance is different over several steps, a voltage is applied to a data side electrode. The pulse width of the modulation voltage is sequentially decreased or increased in accordance with the line sequence of the scanning-side electrodes so that all pixels have the same brightness for the same display data. Method for driving display device.