JPH0748136B2 - Display drive method - Google Patents

Abstract

PURPOSE:To reduce modulation power consumption by dividing scanning electrodes to groups each of which consists of plural scanning electrodes adjacent to one another and discharging all electric charges charged in a dielectric layer by a modulating potential at the time of terminating driving of each group. CONSTITUTION:Two-line scanning electrodes 12 adjacent to one another are divided to groups, and write pulses are given from a display control circuit 16 to respective electrodes 12 through a scanning driver circuit 13 in line sequence. Meanwhile, the period when each electrode 12 is selected is defined as one cycle and a modulating voltage which determines light emission or non- emission is given to each data electrode 14. Write pulses having the same polarity are given to two-line electrodes 12 in one group and write pulses having the opposite polarity are given after the completion of display of this group; and when display of this group is completed, 0V is given to all electrodes 14 at a time before switching to the next group to which write pulses having the opposite polarity are given. Thus, all electric charges charged in a display panel by the modulating voltage are completely discharged.

Description

TECHNICAL FIELD The present invention relates to a capacitive display device such as an AC drive type capacitive flat matrix display panel (hereinafter referred to as a thin film electroluminescence (abbreviated as EL) display device). Drive method for display.

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. 8, 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 layer 3a such as O ₃ , Si ₃ N ₄ and Al ₂ O ₃ , EL layer 4 made of ZnS doped with activator such as Mn and Y ₂ O ₃ and S as described above.
The dielectric material layer 3b such as i ₃ N ₄ , TiO ₂ , Al ₂ O ₃ etc. is sequentially applied by thin film technology such as vapor deposition method and sputtering method in the range of 500 to 10000Å
And a strip-shaped back electrode 5 of Al and Ni is provided in parallel in the direction orthogonal to the transparent electrode 2 on the three-layer structure.

Since the thin film EL element has the EL layer 4 sandwiched between the dielectric material layers 3a and 3b between its electrodes, it can be regarded as a capacitive element in terms of an equivalent circuit. Also, this thin film
As is clear from the voltage-luminance characteristics shown in FIG. 9, the EL 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 above 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 above thin film EL element as a scanning side electrode and the other as a data side electrode, and a data side electrode. This is performed by applying a writing voltage to the scanning side electrodes line-sequentially while applying a modulation voltage corresponding to display data for determining whether to emit light or not. By this display driving, a voltage equal to or higher than the light emission start voltage or the light emission start voltage is generated in the picture element portion of the EL layer 4 where the scanning side electrode and the data side electrode intersect, by the superimposing effect or the canceling effect of the writing voltage and the modulation voltage. Voltage below the voltage is applied,
A predetermined display can be obtained by making each picture element emit or not emit light.

As one method of driving such a display, a method called line inversion described below has been proposed in recent years. FIG. 11 is a schematic diagram showing a part of a thin film EL to which this display driving method is applied, with scanning side electrodes 6 _{n to} 6 _{n + 3} , data side electrodes 7 _m and 7 _{m + 1} and picture elements 8. FIG. 10 shows a timing chart of the display drive. In this display driving method, the polarity of the writing voltage applied to the picture element 8 is changed for each line of the scanning side electrode, and it is assumed that a positive writing voltage is applied to the scanning side electrode 6 _n in FIG. , Other scanning electrodes
6 _{n + 1} , 6 _{n + 2} and 6 _{n + 3} are applied with write voltages of negative, positive and negative polarities respectively, and the applied voltage waveforms are as shown in FIG. 10 (a). Further, the modulation voltage corresponding to the light emission in this case the data-side electrode 7 _m, when the data-side electrode 7 _{m + 1} shall be given a modulation voltage corresponding to the non-luminescent, each scanning-side electrodes 6 _n, 6 _{n +1, 6 n + 2, 6} n + 3 when the write voltage is applied, respectively, as the modulation voltage of the data side electrodes 7 _m is shown in Figure No. _{10 (b) 0V, V M} , 0V, V M And the data side electrode 7
On the contrary, the modulation voltage of _{m + 1} becomes V _M , 0V, V _M , 0V, respectively, as shown in FIG. 10 (c). Therefore, the picture element 8 included in the data-side electrode 7 _m has a different emission start voltage with a different polarity for each line of the scanning-side electrodes 6 _{n to} 6 _{n + 3} as shown by the solid line in FIG. As shown by the broken line, the scanning side electrodes 6 _{n to} 6 _n are applied to the picture elements 8 to which the above voltages are applied and which are included in the data side electrodes 7 _{m + 1.
A} voltage equal to or lower than the light emission start voltage having a different polarity is applied to each line of _{n + 3} . By performing such line inversion drive, variations in the light emission intensity on the display panel due to the applied voltage polarity are averaged and flicker is reduced.

However, in the case of the above display driving method, the polarity of the write voltage applied to the scanning side electrode is 1 of the scanning side electrode.
Since it changes from line to line, when, for example, the entire surface of the display panel is to be made to emit light, light emission / light emission occurs each time the selection of the scanning side electrode changes, as in the case of the data side electrode 7 _m shown in FIG. 10 (b). The modulation voltage that determines non-light emission must be switched and reapplied to all the data-side electrodes, and a large amount of charge and discharge is repeated each time, which increases the power consumption of the entire device. was there.

Therefore, an object of the present invention is to provide a display driving method capable of significantly reducing modulation power in display driving of a thin film EL display device or the like.

Means for Solving the Problems The present invention provides a capacitive display element having a plurality of scanning-side electrodes and a plurality of data-side electrodes arranged in directions intersecting with each other, in which a modulation potential corresponding to display data is provided on the data-side electrode. In this state, the writing potential is sequentially applied to the scanning side electrode,
In the display driving method of driving, one frame of display is performed by displaying the first field in which the writing potential of one polarity is applied to the scanning side electrode and displaying the second field in which the writing potential of the other polarity is applied to the scanning side electrode. After the display is completed, the scanning electrodes are grouped into a plurality of adjacent electrodes in each field, and the polarities of the write potentials applied to the scanning electrodes of each group are alternated between one polarity and the other according to the group order. In addition, the display driving method is characterized in that all electric charges charged in the dielectric layer are discharged by the modulation potential each time the driving of each group ends.

Operation According to the present invention, since there is generally a tendency that the variation of display data that determines light emission / non-light emission between adjacent scanning lines in a capacitive display element is small, a writing potential of the same polarity is applied. In the group of scanning side electrodes, when the driving is transferred from one scanning side electrode to the next adjacent scanning side electrode, the number of data side electrodes that need to be switched with the modulation voltage is small, and the switching of the modulation voltage is required. The power consumption required for the accompanying charging / discharging is reduced accordingly.

Embodiment FIG. 1 is a block diagram showing a schematic structure of a thin film EL display device to which a display driving method according to an embodiment of the present invention is applied, and FIG. 2 is a timing chart of the display driving method of this embodiment. Indicates. In FIG. 1, reference numeral 11 is a display panel composed of a thin film EL element, and since its specific configuration is the same as that described in the prior art, its description is omitted here. The scanning side electrode 12 of the display panel 11 is a scanning side driver circuit.
While the data side electrode 14 of the display panel 11 is connected to the data side driver circuit 15, the scan side driver circuit 13 and the data side driver circuit 15 are connected to the display control circuit 16 that controls these circuits. Has been done. In this display driving method, the first field is displayed and the second field is displayed.
The display of one field is performed by the display of the field. The driving of the thin film EL display device in the case of displaying the first field will be described below. The scanning-side electrodes 12 of the display panel 11 have two groups of scanning-side electrodes 12 that are adjacent to each other over the entire line, such that the first and second lines are one group and the third and fourth lines are one group. Grouping is performed, and each scanning side electrode is passed from the display control circuit 16 through the scanning side driver circuit 13.
While a writing pulse is applied to 12 in a line-sequential manner, a modulation voltage for determining light emission / non-light emission is applied to each data side electrode 14 with one period in which each scan side electrode 12 is selected as one cycle. At this time, a positive polarity write pulse is given to the first group, that is, the first and second scanning electrodes 12 of the scanning side electrodes 12, and the second group, that is, the third and fourth scanning pulses.
A negative polarity writing pulse is applied to the second scanning electrode 12. Similarly, as shown in FIG. 2A, the scanning side electrodes 12 _{2N + 1} , 12 of two lines of odd-numbered groups are similarly _processed.
A positive polarity write pulse is applied to _{2N + 2,} and a negative polarity write pulse is applied to the scanning side electrodes 12 _{2N + 3} and 12 _{2N + 4} of the next even-numbered group of two lines. Further, the modulation voltage corresponding to the light emission in this case for example the data side electrodes 14 _M, if the data-side electrode 14 _{M + 1} shall be given a modulation voltage corresponding to the non-luminescent, for 2 lines of the odd-numbered group When a positive write pulse is applied to the scanning side electrodes 12 _{2N + 1} and 12 _{2N + 2} , 0 V is applied as a modulation voltage to the data side electrode 14 _M as shown in FIG. V _M is applied to _{M + 1} as a modulation voltage as shown in FIG. 2 (c). On the other hand, when a negative polarity write pulse is applied to the scanning side electrodes 12 _{2N + 2} and 12 _{2N + 4} of the two lines of the next even-numbered group, a modulation voltage is applied to the data side electrode 14 _M as shown in FIG. ), V _M is the data side electrode 14 _{M + 1}
As a modulation voltage, 0V is applied to each of them as shown in FIG. That is, the modulation voltage applied to the data-side electrode 14 cannot be switched while the scanning-side electrodes 12 of the two lines in the same group are selected, as long as the display data determining light emission / non-light emission does not change. When the write pulse of the same polarity is given to the scanning line electrodes 12 of two lines of one group and the display of that group is completed, all the data side electrodes are given before moving to the next group to which the write pulse of the opposite polarity is given. 0V is given to 14 all at once, which causes the modulation voltage.
The V _M completely discharges all the charges charged in the display panel.

Since the display data generally tends to vary little between the adjacent scan lines of the display panel 11, as described above, the modulation voltage is applied while one group of scan side electrodes 12 is selected. Is 0V to V _M or V _M to 0V
The number of data-side electrodes 14 that switch to
The power consumption due to charging / discharging accompanying the switching of the modulation voltage is reduced accordingly.

FIG. 3 is a circuit diagram showing a simplified connection configuration between the data side driver circuit 15 and the display panel 11 in order to explain this principle. In the figure, reference numeral 17 is a shift register of the data side driver circuit 15, in which display data for determining the modulation voltage applied to each data side electrode 14 is stored. Further, the data side driver circuit 15 has one for each data side electrode 14.
A switch 18 associated with the pair 1 is provided, and each data-side electrode 14 is connected to the power source 19 having a power source voltage 2V ₀ corresponding to the modulation voltage V _M and the ground via the switch 18. Each picture element 20 of the display panel 11 is shown as a capacitor connected between the scanning side electrode 12 and the data side electrode 14 intersecting with the scanning side electrode 12.

FIG. 4 is a circuit diagram showing a specific configuration example of the switch 18 in FIG. 3, and includes two N-type MOS transistors 21 and 22 connected in series between the power supply 19 and the ground and the respective N-types.
Diodes 23 and 24 connected between the source and drain of the MOS transistors 21 and 22 and the respective N-type MOS transistors
It is composed of an inverter 25 connected between the gates of 21, 21, and the display data stored in the shift register 17 is input to the gate of the N-type MOS transistor 22, and the output corresponding to the display data is N-type. It is applied to each data side electrode 14 from the connection point of the MOS transistors 21 and 22.

In FIG. 3, among all the switches 18, the ones corresponding to the picture elements 20a and 20b are set in a state where the data side electrode 14 is connected to the power supply 19, and the other switches 18 connect the data side electrode 14 to the ground. The scanning side electrode 12
Is in a floating state, the electric charge q charged in each of the picture elements 20a, 20b, 20c at this time is q = CV ₀ (1). However, C is the equivalent capacity of each picture element 20a, 20b, 20c. The equivalent circuit of the above circuit is shown in FIG. 5, in which 26 is a group of picture elements 20 connected in parallel.
A and 20b are equivalently shown by a capacitor having a capacity of 5c, and 27 is an equivalent view of a pixel group 20c connected in parallel by a capacitor having a capacity of 5c.

If all the switches 18 are inverted from this state, that is, if the modulation voltage of all the data side electrodes 14 is switched, the energy required to charge each picture element 20a, 20b, 20c is Therefore, once all the data side electrodes 14 are connected to the ground, the energy required to recharge after discharging the charges charged in the picture elements 20a, 20b, 20c is It will be four times as much as. That is, in this operation,
An increase in power consumption due to an increase in the number of data-side electrodes 14 whose modulation voltage can be switched when driving is moved from one group of scanning-side electrodes 12 to the next group having a different write pulse polarity. And in this example,
After the driving of one group is completed, the charge charges of all the picture elements are once discharged, so that the increase in power consumption at this time can be suppressed.

On the other hand, from the previous state, one of the switches 18 corresponding to the picture element 20b of the picture element group 26 represented by the capacitor in FIG. 5 and the picture element group 27 represented by the capacitor in FIG. If only one of the switches 18 corresponding to one of the picture elements 20c is inverted, that is, if only the modulation voltage of the two data side electrodes 14 is switched, then the circuit of FIG. 3 is equivalent. As shown in FIG. 6, reference numeral 26 ′ in FIG. 6 equivalently shows a state in which the picture element group 26 excluding the picture element 20 b is connected in parallel with a capacitor having a capacitance of 4 c.
Reference numeral 27 'shows equivalently a state in which one element 20c is removed from the pixel group 27 and connected in parallel with a capacitor having a capacity of 4c. At the moment when the two display data are switched in this way, the picture element group 26 'and the picture element 20b holding the reverse voltage as shown in FIG. 6 are changed by the picture element group 26' and the picture element group 27 '. The picture elements 20c holding the reverse voltage are respectively charged by the picture element group 27 ', and the voltage V ₁ after charging is Becomes In other words, in this case, the charge / discharge is automatically performed in the picture elements 20a, 20b, 20c, and the potential is 3 / 5V ₀ , so once connect all the data side electrodes 14 to the ground. Then, after discharging the electric charges charged in the picture elements 20a, 20b, 20c, and then recharging, You will get the required energy. This behavior is
This corresponds to the charging / discharging operation when the selection is switched from one line to the next one line between the two scanning side electrodes 12 belonging to one group in this embodiment.

The above is the description of the first field, but in the second field, the polarity of the write pulse given to each group of the scanning-side electrodes 12 is reversed from that in the first field, and each data is written. The modulation voltage applied to the side electrode 14 is V when it is 0V in the first field.
_M is, to those was V _M 0V is supplied respectively, which AC driving entirety by is performed.

FIG. 7 is a graph showing a comparison between the modulation power consumption by the display driving method of this embodiment and the modulation power consumption by the conventional line inversion display driving method, in which the broken line graph (a) shows In the case of the example, the solid line graph (b) shows the case of the conventional example.

In this embodiment, the case where two lines of the scanning electrodes 12 are grouped into one group has been described.
The number of lines in the group may be more than that as long as flicker is not noticeable.

EFFECTS OF THE INVENTION As described above, according to the display driving method of the present invention, driving is performed from one scanning side electrode to an adjacent scanning side electrode within a group of scanning side electrodes to which a writing potential of the same polarity is applied. When moving, the number of electrodes on the data side that need to switch the modulation voltage can be small, and the modulation power consumption can be greatly reduced.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of a thin film EL display device to which a display driving method according to an embodiment of the present invention is applied.
FIG. 3 is a timing chart showing the display driving method,
FIG. 4 is a circuit diagram for explaining the effect of reducing the modulation power consumption by the display driving method, FIG. 4 is a circuit diagram showing a specific configuration of a switch in the circuit, and FIGS. FIG. 7 is an equivalent circuit diagram of the circuit, FIG. 7 is a graph showing the comparison of the modulation power consumption of the display driving method of the embodiment and the conventional display driving method, and FIG. 8 is a partially cutaway perspective view of the thin film EL element. FIG. 10 is a graph showing luminance characteristics with respect to applied voltage of the thin film EL element, FIG. 10 is a timing chart showing a conventional display driving method, and FIG. 11 is a schematic diagram of a thin film EL element to which the display driving method is applied. . 11 ... Display panel, 12 ... Scanning side electrode, 13 ... Scanning side driver circuit, 14 ... Data side electrode, 15 ... Data side driver circuit, 16 ... Display control circuit

Claims (1)

[Claims] 1. A capacitive display element having a plurality of scanning side electrodes and a plurality of data side electrodes arranged in directions intersecting with each other, wherein a scanning side is provided with a modulation potential corresponding to display data applied to the data side electrodes. The write potential is sequentially applied to the electrodes,
In the display driving method of driving, one frame of display is performed by displaying the first field in which the writing potential of one polarity is applied to the scanning side electrode and displaying the second field in which the writing potential of the other polarity is applied to the scanning side electrode. After the display is completed, the scanning electrodes are grouped into a plurality of adjacent electrodes in each field, and the polarities of the write potentials applied to the scanning electrodes of each group are alternated between one polarity and the other according to the group order. In addition, the display drive method is characterized in that all electric charges charged in the dielectric layer by the modulation potential are discharged after each group is driven.