JPH0120433B2 - - Google Patents

Description

[Detailed Description of the Invention] (a) Technical Field of the Invention The present invention relates to a method for driving an EL display panel,
More specifically, the present invention relates to a new driving method that reduces variations in luminance due to the influence of electrode resistance in an EL display panel equipped with matrix electrodes having different resistance values.

(b) Prior art and problems EL display panels, which are known as a type of flat display device, have a manganese-doped zinc sulfide (ZnS; Mn) luminescent layer sandwiched between insulating films in a sandwich-like pattern on both sides. Although it has a basic structure with scan electrodes and data electrodes arranged in a matrix on both sides, it is generally driven by AC refresh. However, such a display panel is
Attempts have been made to utilize the thin structure to apply it to large display panels, but because the data side electrode uses a transparent electrode made of a mixture of tin oxide and indium oxide, this material has high resistance properties. There was a problem in that the rising characteristics of the voltage waveforms applied to the cells differ between display elements (cells) that are close to the data power supply (driver) and display elements (cells) that are far away, resulting in differences in luminance. .

These conventional problems will be explained in more detail with reference to the panel schematic diagram in FIG. 1, the panel equalization circuit diagram in FIG. 2, and the drive voltage waveform diagram in FIG. ₃ . This shows a case in which a group of display cells to be displayed are selected and emitted light. 1 and 2, 1 is the substrate, D ₁ to _{D 1000} are data electrodes, S ₁ to _{S 1000} are scanning electrodes, and S _o is the display cell closest to the data power supply (hereinafter referred to as the nearest cell in the panel). ), S _f is the display cell furthest from the data power supply (hereinafter referred to as the farthest cell in the panel), rd is the resistance value at the data electrode per cell, and CS is the cell capacitance. The CR circuit of the panel electrode resistance and panel cell capacitance seen from the data electrode forms a ladder circuit, and there is a large difference in the CR time constant between parts near and far from the data power supply. Therefore, as is clear with reference to FIG. 3, the data voltage pulse DP supplied from the data power source to the data electrode _D1 shown in FIG. Although it is applied almost as is as a half-selection voltage with a waveform like this, it is applied as a half-selection voltage waveform with a slow rise at an electrode part far from the waveform as shown in c of the same figure. Therefore, the voltage waveform PS o of _{the nearest} cell S o in the panel g of the same figure and the voltage waveform PS _o of the nearest cell S _o in the panel h of the figure There is a significant difference in the rise of the composite voltage at the time of full selection between the voltage waveform PS _f of the farthest cell S _f , and in the case of the farthest cell S _f in particular, it has become difficult to obtain sufficient voltage to emit light, and recently the cell The emission brightness was lower than that of S _o , resulting in a disadvantage that the emission brightness varied across all display cells.

Incidentally, even if the electrode material is the same, the same problem occurs when the length and size of the electrodes are different (for example, a long electrode has a high resistance).

(c) Purpose of the Invention In view of the above-mentioned circumstances, the present invention aims to provide a driving method for reducing variations in luminance of an EL panel equipped with matrix electrodes having different resistance values. The purpose of the present invention is to provide a new driving method that can solve the problem of brightness variations due to the influence of electrode resistance on the side with a larger resistance value.

(d) Structure of the Invention Briefly stated, the present invention provides an electro-optical display effect to a selected display cell of an EL panel having data electrodes and scan electrodes having different resistance values. The selection voltage is applied at an early timing from the high-resistance electrode so that it rises in advance for a sufficient period of time to reduce the influence of the electrode resistance, and this pre-applied voltage is superimposed to give a full selection effect. It is characterized in that it is applied with a composite voltage waveform with the voltage applied from the low resistance electrode. As a result, the composite voltage waveform applied to the farthest cell in the panel becomes a sharp waveform at the time of full selection, and is almost the same as the composite voltage waveform of the nearest cell in the panel at the time of full selection, so the waveform between both cells becomes sharp. This will eliminate variations in brightness.

(e) Embodiments of the Invention Hereinafter, one embodiment of the present invention will be described in detail with reference to the drive voltage waveform shown in FIG. The driving example shown in FIG. 4 selectively causes the display cells related to the data electrode D ₁ to emit light similarly to the driving example shown in FIG. 3, but differs from the driving example in FIG. are significantly different. In other words, the data voltage pulse DP applied as a half-select voltage to the display cells along the selected data electrode rises faster than the scan voltage pulse SP applied as a half-select voltage to the display cells along the selected data electrode. The waveform has a pulse width that is applied to the address (writing) time for one display line (for example, 16 μsec), and specifically, it is applied to the data electrodes 8 μsec before the rise of the scanning voltage pulse SP. It is set as follows.

Therefore, although the data voltage pulse applied to the data electrode portion on the farthest cell S _f in the panel has a blunted rise as before, as shown in FIG. 4c, the scan voltage pulse is applied to the corresponding scan electrode S ₁₀₀₀ . At the time of full selection, a predetermined potential can be reached.
In other words, the voltage pulse applied to the farthest cell S _f in the panel
As shown in Fig. 4h, PS _f has a two-step rising waveform: the data voltage DP as the first voltage portion that rises in advance, and the scanning voltage SP that is superimposed thereon as the second voltage portion. , at the time of full selection, has almost the same shape as the applied voltage pulse P _o of the nearest cell S _o in the panel shown in g of the same figure. Therefore, in the farthest cell S _f , the reduction in brightness due to the influence of the electrode resistance no longer appears, and there is almost no difference in luminance between the nearest cell in the panel and the farthest cell in the panel.

In the above embodiment, the data voltage pulse as the first voltage portion has a pulse width equivalent to one cell address time, and is caused to rise significantly ahead of the scanning voltage pulse as the second voltage portion. However, since it is sufficient to advance the rise time to such an extent that the influence of the electrode resistance on the data electrode side can be ignored, it is possible to set the rise time a little later depending on the size and characteristics of the panel. In addition, if the length of the scanning electrode is made significantly longer than the data electrode in the shape of the data electrode and scanning electrode, the resistance value of the scanning electrode will be larger, so in this case, the voltage pulse applied to the scanning electrode should be applied in advance. All you have to do is stand up.

Further, in the above embodiment, a case was explained in which a half-selection voltage pulse of positive and negative polarities was applied from both the data electrode and the scan electrode to perform the selection operation.
The level of the voltage applied to both selection electrodes can be set relatively arbitrarily within a range where the combined voltage at the selection cell provides a full selection effect for display.

(f) Effects of the Invention As is clear from the above explanation, in short, the present invention, when applying a full selection voltage to a selected cell, applies the first voltage portion in advance for a sufficient period of time to ignore the influence of electrode resistance. The display effect is obtained by superimposing a second voltage portion on top of the voltage at the time of full selection. Since the cell voltage waveforms are almost the same, the luminance of both cells as well as all cells can be made uniform.
The display quality of the panel can be significantly improved. Therefore,
It would be extremely advantageous to apply this invention to an EL panel for large displays.

[Brief explanation of drawings]

1, 2, and 3 show a panel schematic diagram, a panel equivalent circuit diagram, and a drive waveform diagram for explaining a conventional example, and FIG. 4 shows a drive voltage waveform diagram in one embodiment of the present invention. 1: Substrate, D ₁ ~ D ₁₀₀₀ : Transparent data electrode, S ₁ ~
S ₁₀₀₀ : Scanning electrode, S _o : Nearest cell in panel, S _f :
Farthest cell in panel, DP: data voltage pulse,
SP: scanning voltage pulse.

Claims (1)

[Claims] 1. A scanning electrode and a data electrode having different resistance values, and applying a selected voltage of a predetermined level from both electrodes to a capacitive display element defined at the intersection of these electrodes in a combined form. to obtain electro-optical display effect
In an EL display panel, when giving an electro-optical display effect to a selected display element, the selected voltage applied to the selected display element is
A voltage is applied from the high-resistance side electrode at an early timing so that the voltage rises in advance for a sufficient time to reduce the influence of the electrode resistance, and a voltage from the low-resistance side electrode that is superimposed on this pre-applied voltage to give a full selection effect. A method for driving an EL display panel, characterized in that a voltage is applied with a composite voltage waveform with an applied voltage. 2. The data electrode is formed of a transparent material, and the voltage pulse applied to the transparent data electrode is applied at an earlier timing so as to rise earlier than the voltage pulse applied to the scanning electrode. As stated in claim 1
How to drive an EL display panel.