JP2002123216A - Driving method for light emission display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a driving method for a light emission display device small in power consumption. SOLUTION: In a driving method of a light emission display device in which light emitting elements are arranged at intersections of signal lines and scanning lines, and when the light emitting elements are made to emit light while scanning the scanning lines, whether the scanning of a scanning line is to be performed or not by the presence or absence of elements which are to emit light and which are on the selected scanning line.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for driving a light-emitting display device that can be used in fields such as display elements, flat panel displays, backlights, and interiors.

[0002]

2. Description of the Related Art In recent years, an organic electroluminescent device has attracted attention as one of new light emitting display devices. This element emits light when holes injected from the anode and electrons injected from the cathode are recombined in the organic light emitting layer sandwiched between both electrodes, and emits light at a low voltage with high luminance. Was first shown by Kodak CW Tang et al. (Appl. Phy
s. Lett. 51 (12) 21, pp. 913, 1987).

FIG. 2 is a sectional view showing a typical structure of an organic electroluminescent device. On a transparent anode 12 formed on a glass substrate 11, a hole transport layer 13, an organic light emitting layer 14, and a cathode 1
5 are stacked, and light emission generated by driving by the driving source 16 is extracted to the outside via the anode and the glass substrate. This light-emitting element has a rectifying property in which current flows when the anode has a positive polarity (forward bias direction) and emits light, and almost no current flows when the cathode has a positive polarity (reverse bias direction). Is common.

Such an organic electroluminescent device is thin, can emit high-luminance light under low-voltage driving, and can emit multicolor light by selecting an organic light-emitting material. It has been done.

FIG. 9 is an example of an equivalent circuit showing a simple matrix type display device using an organic electroluminescent device. m
× n organic electroluminescent elements 40 (EL) are composed of n signal lines 4
It is arranged at the electrical intersection of one and m scanning lines 42.
The signal line 41 and the scanning line 42 are respectively connected to the signal line switch 4
3 (DSW) and a scanning line switch 44 (SSW) are connected to a driving source 45, a reverse bias voltage source 46, or a reference potential (generally ground). The voltage value of the reverse bias voltage source is set to a value equal to or higher than the reference potential and substantially equal to the inter-terminal voltage of the light emitting element. The signal line 41 corresponds to the anode of the light emitting element, and the scanning line 42 corresponds to the cathode.

In such a display device, each light emitting element can emit light in a desired pattern by, for example, line-sequential driving. In FIG. 9, the light emitting elements ELi, j (1 ≦ i ≦
(m, 1 ≦ j ≦ n), only the scanning line SSWi is connected to the reference potential, and all other scanning lines are connected to the reverse bias (Vs). At this time, DSWj is connected to the driving source, and a signal current is input in synchronization with the scanning line. The signal current flows only through the light emitting element ELi, j in the forward direction due to the reverse bias of the scanning line, and emits light. To emit light from a plurality of elements on the selected scanning line, signal currents are simultaneously supplied from a plurality of signal lines corresponding to the light emitting pixels. If the above operation is repeated at high speed for other scanning lines, an image display can be performed by causing any combination of light emitting elements to emit light by the afterimage effect. The switching timing of the scanning line is determined by the frame frequency and the number of scanning lines of the display device.

In order to instantaneously supply a signal current of a pixel to emit light, there is a reset method disclosed in Japanese Patent Application Laid-Open No. 9-232074. In the reset method, a fixed reset period is provided when scanning is switched, and an operation of discharging electric charges accumulated in the parasitic capacitance of the light emitting element is performed.
In the reset period, the potential difference between both ends of the light emitting element is zero.
All signal lines and scanning lines are connected to the same voltage source or reference potential (earth).

The gradation expression in a light emitting display device is performed by modulating the magnitude of a signal current applied to an element or a time during which a signal is applied, and several methods have been considered. In the pulse width modulation method, as shown in FIG. 10, during a predetermined scanning period in which a pixel is selected, a signal current is constant, and gradation control is performed depending on a time ratio of the pulse width. On the other hand, in the pulse amplitude modulation, as shown in FIG. 11, gradation control is performed according to the magnitude of the current supplied during the scanning period.

In addition, a sub-field display method in which one frame is divided into sub-fields having a time width corresponding to a power of 2 and gradation control is performed by a combination of the sub-fields, and a sub-field display method in which an applied voltage is constant and a frame display is performed, There is a frame extraction method that performs key control.

[0010]

In the conventional method of driving a light-emitting display device, all the scanning lines are sequentially scanned in any signal input state. Therefore, every time the selection of the scanning line is switched, the reverse bias is applied. Power was being supplied from the power supply. Therefore, even when there is no element that emits light in the selected scanning line, extra charge / discharge to the parasitic capacitance of the light emitting element is performed, resulting in a problem of enormous power consumption. In the case where the size of the panel is increased or an image display with many non-light-emitting lines is performed, the power consumption becomes so large that it cannot be ignored.

An object of the present invention is to solve such a problem and to provide a driving method capable of reducing power consumption in a light emitting display device.

[0012]

That is, the present invention relates to a method of driving a light emitting display device in which light emitting elements are arranged at intersections of signal lines and scanning lines, wherein the light emitting elements emit light while scanning the scanning lines. In this case, a driving method of the light emitting display device is characterized in that whether or not scanning of the scanning line is performed is determined based on presence or absence of an element to emit light on a selected scanning line.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a driving method according to the present invention will be described below.

FIG. 1 shows an example of a light emitting display device according to the present invention.
Shown in The light emitting display portion 1 receives the input signal data 4 via the signal line drive circuit 5 and the scan line drive circuit 2 respectively.
And a scanning voltage determining means 3 for determining the reverse bias of the scanning line according to the input signal data.

Next, an operation of displaying a pattern by line-sequential driving according to the present driving method will be described with reference to equivalent circuits shown in FIGS. As an example, consider the case of displaying a 4 × 4 pattern shown in FIG. 4 for simplicity. The gray part in FIG. 4 is the light-emitting pixel 6, and the white part is the non-light-emitting pixel 7.
In the equivalent circuit, a light emitting pixel uses a diode and a non-light emitting pixel uses a capacitance symbol.

In FIG. 5, 4 × 4 organic electroluminescent elements 4
0 (EL) is arranged at an electrical intersection of the four signal lines 41 and the four scanning lines 42. The signal line 41 is connected to a driving source 45 or a reference potential via a signal line switch 43 (DSW), and the scanning line 42 is connected to a scanning line switch 44.
It is connected to a reverse bias voltage source 46 or a reference potential which can be varied by the scanning voltage determining means 3 via (SSW) (FIG. 5). Here, the reference potential is a ground potential of 0V. First, signal line switch 43 (DSW)
The scanning line switch 44 (SSW) is connected to the reference potential. When the reset method is used, the reset potential can be set arbitrarily. Hereinafter, a case where the reset potential is set to the reference potential will be described.

The scanning line is scanned from the state shown in FIG. 5 to emit a light-emitting pattern. Scanning is performed sequentially from the top of the pattern. First, the selected scanning line S1
Since the light emitting pixels shown in gray in FIG. 4 are present above, the scanning line S1 is scanned by connecting the scanning line switch SSW1 to the reference potential and connecting the other scanning lines to the reverse bias power supply Vs. (FIG. 6). At the same time, each signal line D1 to D4
To give a signal input corresponding to the light emission pattern,
DSW1 and DSW4 are switched and connected to the drive source 45. At this time, the current of the signal input flows through the light emitting pixel in the forward direction indicated by the arrow in the figure, and emits a predetermined light.
At this time, there are pixels charged on the signal lines D2 and D3 as shown by + and-in FIG. Next, as shown in FIG. 5, the switches DSW and SSW are switched to the reference potential to reset the electric charges charged in the parasitic capacitance of the light emitting element, and then the selection is switched to the scanning line S2. At this time,
Since no luminescent pixel exists on the scanning line S2, the scanning line S2
There is no need to perform 2 scans. That is, the scanning lines S1, S
3. By fixing all the scanning lines at the reference potential without applying the reverse bias Vs to S4, as a result, the scanning lines S2
Can be determined. As a result, it is possible to switch to the next scan without generating power consumption due to charging and discharging of the parasitic capacitance.

In the next scan (FIG. 7), since a luminescent pixel exists on S3, a reference potential is applied to the scan line S3, and a reverse bias Vs is applied to the other scan lines S1, S2 and S4. Similarly to the above-described procedure, the switches DSW and SSW are switched to the reference potential (FIG. 5), and after the charges charged in the parasitic capacitance are reset, the selection is switched to the scanning line S4. Also in this case, since there is no pixel that emits light on the scanning line S4,
As in the case of S2, the scanning of S4 is not performed, and all the signal lines and scanning lines may be kept at the reference potential (FIG. 5). By repeating the above operation, power consumption can be reduced and an arbitrary light emitting pattern can be displayed.

As described above, the light emission of the pixel on the scanning line,
It is a feature of the present invention that the voltage supplied to the scanning line is switched by non-emission, and a systematic determination is made as to whether or not to scan the scanning line. In particular, all pixels on the selected scanning line are non-emission. In the case of light emission, it is preferable that the voltage values supplied to all the scanning lines are equal until the scanning line having the next light-emitting pixel is scanned, and in particular, all the scanning lines are connected to the reference potential.

The scanning lines S1 to S according to the present invention described above.
8 shows examples of the voltage waveforms of FIG. In the scanning period of the scanning line S1, only S1 is connected to the reference potential to perform scanning, and the other scanning lines S2 to S4 are connected to the reverse bias Vs.
It is connected to the. Since it is not necessary to scan the scanning line S2 in the next scanning period of S2 after the reset period,
All the scanning lines maintain the reset reference potential. In the scanning period of the scanning line S3, only the scanning line S3 is connected to the reference potential, and the other scanning lines S1, S2, S
4, a reverse bias Vs is applied. After the reset period, in the scan period of S4, since it is not necessary to perform the scan as in the case of S2, all the scan lines are connected to the reset reference potential.

In the present invention, the resetting period is set to about several tens of μs or less at which all the charges accumulated in the parasitic capacitance are discharged, and the switching timing of the scanning line is set to a frame frequency of 30 Hz or more at which flicker does not appear. It is preferable to set the speed to a certain speed. The order of scanning is not particularly limited,
An interlace method of alternately selecting even lines and odd lines may be used. Note that, in the above example, the description has been given of a simple matrix type display device, but the driving method of the light emitting display device of the present invention does not limit the structures of the light emitting elements and electrodes. Preferably, it is used for a display device using a current-driven organic electroluminescent element as a light emitting element. Further, in the above-described embodiment, for simplicity, a pattern display example represented by the presence or absence of a light-emitting pixel has been described, but the gradation expression such as pulse width modulation or pulse amplitude modulation of signal input is not limited. . Each of the reverse bias voltage values is desirably set to the maximum voltage value of the input signal supplied to the signal line from the viewpoint of suppressing the current from flowing to the unselected pixels and reducing the power consumption.

[0022]

According to the driving method of the light emitting display device of the present invention,
In causing the light emitting element to emit light while scanning the scanning line,
Since it is possible to determine whether to perform scanning of a scanning line based on the presence or absence of an element to emit light on a selected scanning line, it is possible to reduce unnecessary power consumption due to charging and discharging of a parasitic capacitance on a light emitting display device. Became possible.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

FIG. 2 is a cross-sectional view illustrating a structural example of an organic electroluminescent element.

FIG. 3 is an electrical equivalent circuit showing a parasitic capacitance of a light emitting element.

FIG. 4 is a diagram showing an example of a display pattern.

FIG. 5 is an equivalent circuit illustrating an operation example of the light emitting display device according to the present invention.

FIG. 6 is an equivalent circuit illustrating an operation example of a light emitting display device according to the present invention.

FIG. 7 is an equivalent circuit illustrating an operation example of a light emitting display device according to the present invention.

FIG. 8 shows an example of a driving waveform of a scanning line according to the present driving method.

FIG. 9 is an equivalent circuit showing an example of a conventional simple matrix type display device.

FIG. 10 is a diagram showing a driving waveform of a pulse width modulation method.

FIG. 11 is a diagram showing a driving waveform of a pulse amplitude modulation method.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 light emitting display unit 2 scanning line drive circuit 3 scanning voltage determining means 4 input signal data 5 signal line drive circuit 6 light emitting pixel 7 non-light emitting pixel 11 glass substrate 12 anode 13 hole transport layer 14 organic light emitting layer 15 cathode 16, 45 drive Source 21 Capacitance (parasitic capacitance) 22, 40 Organic electroluminescent device 31, 41 Signal line 32, 42 Scan line 43 Signal line switch 44 Scan line switch 46 Reverse bias voltage source

Continued on front page F-term (reference) 3K007 AB00 BA06 DA01 DB03 EB00 GA02 5C080 AA06 BB05 CC03 DD26 FF12 JJ02 JJ03 JJ04 JJ06 KK02 KK52

Claims (4)

[Claims] 1. A method for driving a light emitting display device in which a light emitting element is arranged at each intersection of a signal line and a scanning line, wherein the light emitting element emits light while scanning the scanning line and is on a selected scanning line. A method for driving a light-emitting display device, comprising determining whether or not to perform scanning of the scanning line according to the presence or absence of an element to emit light. 2. The driving method for a light emitting display device according to claim 1, wherein when all of the light emitting elements on the selected scanning line do not emit light, the voltage supplied to all the scanning lines is equalized. Method. 3. The method according to claim 1, wherein when all of the light emitting elements on the selected scanning line do not emit light, all the scanning lines are connected to a reference potential. 4. The method according to claim 1, wherein the light emitting device is an organic electroluminescent device.