JPH0120434B2 - - 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,
In particular, it relates to a new driving method that reduces variations in brightness due to the influence of electrode resistance while suppressing unnecessary power consumption.

(b) Conventional technology and problems AC is known as a type of flat display.
A drive-type EL display panel has transparent data electrodes arranged on a transparent glass substrate, and a light-emitting layer such as ZnS:Mn sandwiched between insulating layers on both sides.
Furthermore, it has a multilayer thin film structure in which metal scanning electrodes are formed on the upper insulating layer. The data electrodes and the scan electrodes are arranged in a matrix in directions perpendicular to each other, and display cells are defined at their opposing intersections, and the display cells are selected by the combined voltage of the scan pulse and data pulse selectively applied from both electrodes. is beginning to emit light. A refresh driving method is adopted in which, after once addressing the entire surface with such a selection pulse, a refresh pulse having a polarity opposite to that of the selection pulse is commonly applied to cause the address point to emit light again.

However, in the EL display panel having the above configuration, it is difficult to avoid that the electrode resistance of the transparent electrode on the substrate side, which is generally used as a data electrode, becomes higher than the electrode resistance of the metal scanning electrode on the back side. Transparent electrodes are usually formed as a mixed evaporated film (ITO) of tin oxide and indium oxide, but this transparent electrode film has a relatively high resistance, and 5 electrodes per 1 mm are formed with a width of 0.15 mm. When configuring a display pulse of ×1000 cells, an electrode length of 200 mm exhibits an electrode resistance of about 20 KΩ. As a result, a difference occurs in the rising waveform of the data pulse between the display cell on the connection end side to the data driver (the nearest cell) and the display cell far away from the connection end (the farthest cell), resulting in a difference in luminance. A problem was occurring.

These conventional problems will be explained in more detail with reference to the panel schematic diagram in FIG. 1, the panel equivalent circuit diagram in FIG. 2, and the drive voltage waveform diagram in _FIG . This shows a case where a display cell group is selected and emitted light. In FIGS. 1 and 2, 1 is a glass substrate, D ₁ to D ₁₀₀₀ are transparent data electrodes, S ₁ to _{S 1000} are metal scanning electrodes such as Al,
S _o is the display cell closest to the data pulse source (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), and r _d is the display cell per cell. The resistance value at the data electrode, CS indicates the cell capacitance, and as is clear from both figures, the CR circuit of the panel electrode resistance and panel cell capacitance seen from the data electrode forms a ladder circuit.
A large difference occurs in the CR time constant between a region close to the data pulse source and a region far away. Therefore, as is clear with reference to FIG. 3, the data voltage pulse DP supplied from the data pulse source to the data electrode _D1 shown in FIG. As shown in figure b, it is added in almost the same way, but at the electrode part far from it, it is shown in figure c.
It is added as a waveform with a sluggish rise as shown in the figure. Therefore, scanning electrodes S1 and _S1 shown in d and f of the same figure
There is a significant difference in the rise of the voltage waveform PS o of the nearest cell S _o in the panel in g, which is added by combining with the scanning voltage pulse SP of S ₁₀₀₀ , and the voltage waveform PS _{f of the farthest cell S f in} the panel, _h in the same figure. appears, especially the farthest cell S _f
In the case of , it has become difficult to obtain sufficient voltage to emit light, and recently the luminance has been lower than that of the cell S _o , resulting in the disadvantage that the luminance varies across all display cells. Note that the refresh pulse RP applied during the refresh period shown in FIG. 3 is applied from the low-resistance metal scanning electrode side, so no particular waveform problem occurs.

However, it is clear that the above-mentioned problem occurs in the same way when the length and size of the electrodes are different even if the electrode material is the same (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 that reduces variations in luminance due to the influence of electrode resistance of an EL panel while suppressing unnecessary power consumption.

(d) Structure of the Invention Briefly stated, the present invention aims to achieve the above-mentioned object by changing the rise of a selection pulse applied from the high-resistance electrode side of the opposing matrix electrodes of an EL display panel to a low-resistance one. This is characterized in that the pulse rises prior to the rise of the selection pulse applied from the electrode side, and during that time the non-selection electrodes on the low resistance side are placed in a floating state. As a result, the data pulse to the transparent data electrode is applied in advance in anticipation of the rise being blunted by the electrode resistance, so there is no difference in the effective combined pulse voltage applied to the recent cell and the farthest cell. There will be no
Furthermore, since the unselected scan electrodes are placed in a floating state, there is almost no unnecessary power consumption for charging the unselected cell capacitors, even though data pulses are applied early.

(e) Embodiments of the Invention Preferred embodiments of the invention will now be described in more detail with reference to FIGS. 4 and 5.

FIG. 4 is a diagram showing the driving voltage waveforms of various parts according to the present invention when the display cell group related to the data electrode D ₁ is caused to selectively emit light, as in the case of FIG. 3 above. The waveform a of the data pulse applied to the data electrodes is significantly different. In other words, in the case of this invention, the data voltage pulse DP is set to 1 in order to rise faster than the scanning pulse SP.
Address (write) time for display line (e.g.
16μsec) The waveform has a pulse width that is applied to the entire scanning voltage pulse SP.
It is set to be applied to the data electrodes 8 μsec prior to the rise of . Therefore, data voltage pulses for causing adjacent display cells on the same data electrode to emit light continuously are applied to the data electrodes as a substantially continuous waveform while adjacent scan electrodes are sequentially selected.

Thus, although the data voltage pulse applied to the data electrode site on the farthest cell Sf in the panel has a blunted rise as before, as shown in _FIG . In this case, the predetermined potential can already be reached. Therefore, as shown in Figure 4h, the composite voltage pulse PSf applied to the farthest cell Sf in the panel has almost the same shape as the voltage pulse PSn applied to the nearest cell Sn in the panel shown in Figure 4g, and the farthest cell Sf also has a sufficient voltage. It can emit light with high brightness. Thus, there is almost no difference in luminance between the nearest cell in the panel and the farthest cell in the panel.

On the other hand, if the unselected scan electrodes were clamped to the ground potential while addressing the cells to be displayed as described above, unnecessary charging current would flow to the cells associated with the unselected scan electrodes at the rise of the data pulse DP. flows, resulting in wasted power consumption.
Therefore, in the present invention, the non-selected scan electrodes are always kept in a floating state to have high impedance and prevent unnecessary charging current from flowing. In the voltage waveform of FIG. 4, the dotted line portion indicates a floating potential, and the potential of the non-selected scanning electrode floats depending on the selection state of the opposing data electrode.

FIG. 5 is a diagram showing a schematic configuration of an example of a drive circuit for driving as described above, in which horizontal scan electrodes Y ₁ to Y ₁₀₀₀ of the thin film EL display panel 10 are provided with scan drivers Q _S1 to Q, respectively. The scanning pulse generation circuit 11 connected to the scanning potential of -V _Na via _S1000 , and the Y _R
Refresh pulse generation circuit 12 connected to the potential of
is connected. A scanning signal S _S from a scanning shift register 13 and a refresh signal S _R from a refresh control circuit are supplied to the input side of each of the scanning drivers through an OR circuit 14 . Further, data drivers Q _d1 to Q _d1000 connected to the address potential V _a are connected to the transparent data electrodes X ₁ to X ₁₀₀₀ extending in the vertical direction on the panel 10, and these data drivers are connected to the shift register 15 for data address. They are driven in parallel by a signal from a latch circuit 16 that temporarily stores the parallel address signal S _a from the latch circuit 16 .

In such a configuration, a high resistance transparent data electrode
On the X ₁ to X ₁₀₀₀ side, a latch circuit 16 for signal storage is inserted in the address circuit, so even if the time required to input and output the data address signal for each scanning line to and from the shift register 15 is taken into account, the processing time is as shown in Figure 4a. The selected data drivers Q _d1 to Q _d1000 can be driven in one unit address time. On the other hand,
On the scan electrodes Y ₁ to Y ₁₀₀₀ side, the scan drivers are sequentially controlled to be conductive one by one by the scan signal S _s from the scan shift register 13, so that the scan pulse generation circuit 11 controlled at the same timing A scan voltage pulse of −V _NA of is applied to the selected scan voltage. During this time, the scan drivers connected to the non-scan electrodes are always in a non-conducting off state, and therefore the corresponding non-selected scan electrodes are substantially opened and placed in a floating state. Once the sequential addressing of all scan electrodes is completed in this way, a refresh signal S _R for common driving is introduced through the scan side OR circuit 14, and all scan drivers Q _s1 to _{Q s1000} are controlled to be in a conductive state. . At this timing, the refresh pulse generating circuit 12 applies a refresh pulse RP of opposite polarity to the scanning voltage pulse to all scanning electrodes, and the next address cycle begins.

Now, one embodiment of the present invention has been described above, but the lead time of the selection pulse applied to the high resistance electrode side depends on the scale of the panel, the magnitude of the resistance value, the required operating speed, etc. You can set it as appropriate. In addition, when the transparent electrode side is used as a scanning electrode, or when the length of the scanning electrode is significantly longer than the data electrode in a horizontally elongated display panel, the scanning electrode side has a high resistance. It is sufficient if the pulse is caused to rise in advance.

(f) Effects of the Invention As is clear from the above explanation, according to the driving method of the present invention, the cell voltage waveforms applied to the nearest cell in the panel and the farthest cell in the panel are made almost the same, and both cells are Of course, the luminance of all cells can be made uniform, and the display quality of the panel can be greatly improved without unnecessary power consumption. Therefore, the present invention is extremely advantageous when applied to EL panels for large displays.

[Brief explanation of drawings]

1, 2, and 3 are panel schematic diagrams, panel equivalent circuit diagrams, and drive waveform diagrams for explaining the conventional example; FIG. 4 is a drive voltage waveform diagram in one embodiment of the present invention; The figure is a diagram showing a schematic configuration of an example of a drive circuit. 1 is the substrate, S ₁ to S ₁₀₀₀ are scanning electrodes, D ₁ to _{D 1000} are data electrodes, DP is data pulse, SP is scanning pulse, PS _o is the composite voltage pulse of the latest cell S _o in the panel, PS _f is the panel The composite voltage pulse of the farthest cell S _f ,
10 is an EL display panel, Q _s1 to _{Q s1000} are scan drivers, 11 is a scan pulse generation circuit, 12 is a refresh pulse generation circuit, and Q _d1 to _{Q d1000} are data drivers.

Claims (1)

[Claims] 1. A display cell is formed by arranging a plurality of scanning electrodes and data electrodes having different resistance values so as to cross each other, and capacitively coupling a light emitting layer to the intersection of these electrodes. A selected voltage of a predetermined level is applied from both electrodes in a combined form to obtain display light emission.
In an EL display panel, when emitting display light to a selected display cell, the high resistance side is set so that the selection voltage applied to the selected display cell rises in advance for a sufficient period of time to reduce the influence of the electrode resistance. is applied with a composite voltage waveform of the voltage applied from the selection electrode at an early timing and the voltage applied from the selection electrode on the low resistance side that is superimposed on this previously applied voltage to give a full selection effect, and this selection A method for driving an EL display panel, characterized in that a non-selected electrode on a low resistance side is maintained in a floating state while a display cell emits display light.