JP2004102077A - Display device and its driving method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To drive an organic light emitting device by setting proper driving voltage corresponding to a change in ambient temperature. <P>SOLUTION: A display device 100 is composed of a display circuit 10 and a control circuit 50. The control circuit 50 is equipped with: a control part 51 which controls a driving part 30 for driving cathodes which serve as scanning electrodes; and a driving part 40 for driving anodes which serve as data electrodes. The control part 51 successively scans the scanning electrodes, selects a data electrode, and lights up a prescribed light emitting device. The control part 51 drives the data electrodes in the manner that a constant electric current is supplied to an organic light emitting device in accordance with the change in the ambient temperature of a display device. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a display device and a driving method thereof, and more particularly, to a display device which is a passive matrix type display using an organic light emitting element and a driving method thereof.
[0002]
[Prior art]
In recent years, as a flat panel display replacing a liquid crystal display, an organic EL display using an organic EL (Electro Luminescence) element in a pixel portion has attracted attention. The organic EL display is a self-luminous element, has high visibility and can be driven at a low voltage, and has been actively studied for practical use. The organic EL element has an organic layer containing an organic compound that emits light when an electric field is applied, and an anode and a cathode sandwiching the organic layer. Some organic compounds utilize fluorescence due to singlet excitation and phosphorescence due to triplet excitation.
[0003]
As a driving method for driving each pixel portion of the organic EL display, a passive matrix type and an active matrix type are known as in the liquid crystal display. The passive matrix type has advantages such as low cost and high yield because of its simple structure.
[0004]
The passive matrix type display includes a plurality of anodes on a transparent substrate, a plurality of cathodes intersecting the anodes, and an organic layer sandwiched between the anodes and the cathodes. One pixel portion is formed with the light emitting element in the intersection region of the anode and the cathode as one unit, and a plurality of the pixel portions are arranged to form a display portion. The anode and the cathode are extended from the display section to the periphery of the transparent substrate to form a connection section. A display circuit is configured by connecting the drive unit and the display unit via the connection unit. A display device is configured by connecting a display circuit and a control circuit that converts an image signal input from the outside and controls a driving unit.
[0005]
The cathode is a scanning electrode, which is at the ground potential when selected, and at the power supply potential when not selected. The anode is a data electrode, which is connected to a constant current source when selected, and is at the ground potential when not selected. The control circuit controls the driving unit to sequentially select the scanning electrodes line by line, select pixels on the selected line by the data electrodes, and turn on the light emitting elements. In this manner, the lighting is performed for each scanning electrode by sequential scanning, and this is superimposed over one frame of the image signal to display an image. When both the scanning electrode and the data electrode are not selected, the light emitting element is reverse-biased, and at the time of lighting, is forward biased. Further, the light emitting element may become zero bias depending on the selection state of the electrode.
[0006]
The performance of the organic light emitting device is deteriorated by using it for a long period of time, and the forward voltage drop increases. If the forward drop voltage increases, it is not possible to obtain the required luminance. Therefore, in an initial state in which the organic light emitting element does not deteriorate, the driving voltage is set to be high in advance. However, if the drive voltage is set high in advance, power consumption increases. For example, it is necessary to measure the voltage drop of the organic light emitting element and set the drive voltage according to the measured voltage drop. (For example, see Patent Document 1).
[0007]
[Patent Document 1]
JP-A-7-36409 (paragraph number 0029, FIGS. 5 and 8)
[0008]
[Problems to be solved by the invention]
However, in the organic light emitting device, the voltage drop in the forward direction changes depending on the temperature as well as the aging described above. Further, even in the case of organic light emitting elements formed on the same glass substrate such as an organic EL display, the temperature characteristics of the individual organic light emitting elements vary greatly. Further, when a vertical display is configured, the temperature of the organic light emitting element differs between the lower part and the upper part of the display unit, and as a result, the voltage drop may be different for each organic light emitting element.
[0009]
Therefore, only by setting the drive voltage by measuring the drop voltage of a specific organic light emitting element as in the method described in Patent Document 1 described above, it is not possible to set the drive voltage with respect to temperature change with high accuracy. There is a problem that the display quality is deteriorated due to the variation for each organic light emitting element.
[0010]
The present invention has been made in view of such a problem, and an object of the present invention is to set an appropriate driving voltage with respect to a change in ambient temperature and reduce power consumption while maintaining display image quality. And a method for driving the display device.
[0011]
[Means for Solving the Problems]
In order to achieve such an object, the present invention is directed to a first aspect of the present invention, in which m first sets of electrodes which are scanning electrodes and which are parallel to each other, intersect with the first set of electrodes. N second sets of electrodes arranged in parallel with each other (m and n are integers) are arranged at each of intersections between the first set of electrodes and the second set of electrodes, and A display device having an organic light emitting element connected thereto, comprising a control means for sequentially scanning the first set of electrodes, selecting the second set of electrodes, and lighting a predetermined organic light emitting element; The means drives the second set of electrodes such that a constant current can be supplied to the organic light emitting element in response to a change in the ambient temperature of the display device.
[0012]
According to a second aspect of the present invention, in the display device according to the first aspect, a detecting unit that detects the ambient temperature, a power supply voltage value of a constant current source that supplies a constant current to the organic light emitting element, A storage unit for storing the power supply voltage value stored in the storage unit in accordance with the ambient temperature detected by the detection unit; Are driven.
[0013]
According to a third aspect of the present invention, the detecting means according to the second aspect includes a plurality of temperature detecting elements disposed on a substrate on which the organic light emitting element is formed, and a detecting unit that detects the temperature detected by the temperature detecting elements. And an arithmetic unit for calculating an average of the values.
[0014]
According to a fourth aspect of the present invention, there are provided a first set of m parallel electrodes, which are scanning electrodes, and a second set of n parallel electrodes arranged to intersect with the first set of electrodes. (Where m and n are integers), and a driving method of a display device having an organic light emitting element disposed at each intersection of the first set of electrodes and the second set of electrodes and connected to each of the electrodes A detecting step of detecting an ambient temperature of the display device, and a power supply voltage value of a constant current source that supplies a constant current to the organic light emitting element and an ambient temperature in accordance with the ambient temperature detected by the detecting unit. A reading step of reading out the power supply voltage value from a storage unit for attaching and storing, and sequentially scanning the first set of electrodes, selecting the second set of electrodes, and reading the power supply voltage value read out in the reading step. By supplying a constant current to the predetermined organic light emitting element, Characterized by comprising a driving step of.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0016]
FIG. 1 is a configuration diagram showing a display circuit according to one embodiment of the present invention. The display circuit 10 includes a plurality of anodes 21 that are a first set of electrodes parallel to each other, a plurality of cathodes 22 that are a second set of electrodes parallel to each other that intersect with the anode 21, and the anode 21 and the cathode 22. A display unit 20 having a light emitting element sandwiched between an anode 21 and a cathode 22 at a crossing position, a driving unit 30 for driving the cathode 22 as a scanning electrode, and a driving unit 40 for driving the anode 21 as a data electrode And
[0017]
With such a configuration, the drive unit 30 drives the cathode 22 under the control of the control circuit so that the cathode 22 has the ground potential when selected and the power supply potential when not selected. The drive unit 40 is connected to a constant current source when selected, and controls the anode 21 to be at the ground potential when not selected, under the control of the control circuit.
[0018]
FIG. 2 is a block diagram showing a display device according to one embodiment of the present invention. The display device 100 includes a display circuit 10 and a control circuit 50, and displays an image signal from a general-purpose computer 60 or the like on the display circuit 10. The control circuit 50 includes a control unit 51 that controls the driving units 30 and 40, a conversion unit 52 that converts an externally input image signal such as a general-purpose computer 60 into an analog-to-digital signal, and transmits the image signal to the control unit 51. And a table 53 corresponding to a storage unit in which control data is stored. In addition, a sensor 54 for detecting the ambient temperature is provided, and the details will be described later.
[0019]
With such a configuration, when a digitally converted image signal is input, the control unit 51 sequentially scans the cathode 22 as a scan electrode, selects the anode 21 as a data electrode for each scan electrode, and performs predetermined light emission. Light the element. At this time, the control unit 51 measures the ambient temperature with the sensor 54, obtains the power supply voltage value of the drive unit 40 with reference to the table 53, and drives the anode 21 which is a data electrode.
[0020]
FIG. 3 shows the relationship between the voltage drop of the organic light emitting element and the power supply voltage of the driving unit. The voltage drop A of the organic light emitting device is high on the low temperature side and low on the high temperature side. The voltage value obtained by adding the voltage drop of the constant current source capable of supplying a constant current to the organic light emitting element is the power supply voltage value B. Since the voltage drop of the constant current source also changes depending on the temperature, the difference between the voltage drop A and the power supply voltage value B is not always constant. The correspondence table between the ambient temperature and the power supply voltage value B is stored in the table 53 of the control circuit 50.
[0021]
The detecting means for detecting the ambient temperature uses the sensor 54 of the control circuit 50. For example, a plurality of temperature detecting elements may be arranged on the display unit 20 of the display circuit 10. By averaging the detection values detected by the plurality of temperature detection elements and referring to the table 53 to determine the power supply voltage value of the drive unit 40, it is possible to perform more accurate control.
[0022]
According to the present embodiment, since an appropriate drive voltage is set for a change in the ambient temperature, there is no need to set a high drive voltage in advance. Therefore, display quality can be maintained without increasing current consumption in the constant current source.
[0023]
【The invention's effect】
As described above, according to the present invention, the data electrode is driven at a predetermined power supply voltage value so that a constant current can be supplied to the organic light emitting element in response to a change in the ambient temperature of the display device. It is possible to reduce the power consumption while maintaining the display image quality by setting an appropriate drive voltage in response to the change.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing a display circuit according to an embodiment of the present invention.
FIG. 2 is a block diagram showing a display device according to one embodiment of the present invention.
FIG. 3 is a diagram for explaining a relationship between a voltage drop of an organic light emitting element and a power supply voltage of a driving unit.
[Explanation of symbols]
Reference Signs List 10 display circuit 20 display unit 21 anode 22 cathode 30, 40 drive unit 50 control circuit 51 control unit 52 conversion unit 53 table 54 sensor 60 general-purpose computer 100 display device

Claims (4)

A first set of m parallel electrodes, which are scanning electrodes, and a second set of n parallel electrodes arranged intersecting the first set of electrodes (m and n are integers); A display device, comprising: an organic light emitting element disposed at each of intersections of the first set of electrodes and the second set of electrodes, and connected to each of the electrodes.
Controlling means for sequentially scanning the first set of electrodes, selecting the second set of electrodes, and lighting a predetermined organic light emitting element;
The display device, wherein the control means drives the second set of electrodes so that a constant current can be supplied to the organic light emitting element in response to a change in ambient temperature of the display device. Detecting means for detecting the ambient temperature;
A power supply voltage value of a constant current source that supplies a constant current to the organic light emitting element, and a storage unit that stores the ambient temperature in association with each other,
2. The control unit according to claim 1, wherein the control unit reads the power supply voltage value stored in the storage unit and drives the second set of electrodes according to the ambient temperature detected by the detection unit. 3. The display device according to the above. The detection unit includes a plurality of temperature detection elements disposed on a substrate on which the organic light emitting element is formed, and a calculator that calculates an average of detection values detected by the temperature detection elements. The display device according to claim 2. A first set of m parallel electrodes, which are scanning electrodes, and a second set of n parallel electrodes arranged intersecting the first set of electrodes (m and n are integers); A method for driving a display device, comprising: an organic light emitting element disposed at each of intersections of the first set of electrodes and the second set of electrodes, and connected to each of the electrodes.
A detecting step of detecting an ambient temperature of the display device;
Reading the power supply voltage value from a storage unit that stores a power supply voltage value of a constant current source that supplies a constant current to the organic light emitting element and an ambient temperature in association with the ambient temperature detected by the detection unit; Steps and
A drive for sequentially scanning the first set of electrodes, selecting the second set of electrodes, and supplying a constant current to the predetermined organic light emitting element by the power supply voltage value read in the reading step to light the organic light emitting element And a step of driving the display device.

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