JP2007011218A - Display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a display device whose display life can be prolonged by compensating temporal luminance deterioration in an electrooptical element with simple constitution without setting restrictive conditions. <P>SOLUTION: The display device includes a display panel 100 including a plurality of organic EL elements arranged in a matrix nearby intersections of pluralities of scan electrodes and data electrodes crossing each other at right angles, a scan electrode driving circuit 200 and a data electrode driving circuit 300 which allow currents to flow selectively to those elements, and a constant voltage power source 400 which supplies the currents, and the scan electrodes and data electrodes are connected to the corresponding driving circuits by prescribed wiring lines. Wiring line resistance is properly adjusted to set a range of the resistance rate β' of the total resistance value Relall of organic EL elements which are connected in parallel and the total resistance value Rrall of wiring lines to 0.1≤β≤10, thereby prolonging the display life of the organic EL elements as electrooptical elements with simple constitution. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a display device including a display element whose light emission is controlled by an amount of current passed through an electro-optical element.

  Conventionally, an element whose light emission amount is controlled in accordance with the amount of current flowing through the element, for example, an LED (Light Emitting Diode) typified by an inorganic EL (Electro Luminescence) element or an organic EL element is used as an electro-optical element. There are display elements used. Here, in the present specification, the electro-optical element means an optical element by applying electricity such as FED (Field Emission Display), charge driving element, liquid crystal, E ink (Electronic Ink), in addition to the organic EL element. All the elements whose characteristics change will be referred to. In the following, an organic EL element is illustrated as an electro-optical element, but the same description can be made as long as the light emitting element controls the light emission amount according to the amount of current.

  A display using this organic EL element can emit light with a low voltage and low power consumption, and does not require a backlight. Therefore, it can be made thinner than a liquid crystal display, and in recent years, it is particularly applied to portable devices. Is attracting attention. As a method for driving the organic EL element, a simple matrix method and an active matrix method are known. The active matrix method is a thin film transistor (hereinafter referred to as “TFT”) used in each pixel circuit. ) And the current variation are difficult to control appropriately, and the manufacturing process is complicated and the yield is poor compared to the simple matrix method, so there are many problems in mass production. Therefore, the simple matrix method that can simplify the manufacturing process and reduce the manufacturing cost is often adopted, and a large number of mobile phone display devices and in-vehicle display devices using the simple matrix method are mass-produced. .

  In addition, this organic EL element control method includes a constant voltage control method using a constant voltage source and a constant current control method using a constant current source, depending on the form of a power source that supplies current to the organic EL element. It is divided roughly.

  The constant voltage type control method has a simpler circuit configuration of the power supply than the constant current type control method, so that the manufacturing cost can be reduced. However, in the constant voltage control method, as the internal resistance of the organic EL element increases over time due to element degradation such as reaction with moisture and oxygen, material decomposition, and film layer shape change, Since the voltage is constant, the current flowing through the organic EL element decreases. And it is known that the light emission luminance and the current flowing at the time of light emission are in a proportional relationship. From this, the light emission luminance of the organic EL element also decreases.

  On the other hand, in the constant current control method, control is performed so that a constant current flows through the organic EL element regardless of an increase in internal resistance with the passage of time. Therefore, the above-described decrease in light emission luminance due to a decrease in flowing current does not occur. However, since organic EL elements generally have a characteristic that the emission luminance for the same current value decreases with the passage of time (due to deterioration of the element), even in the constant current control method, the emission luminance with the passage of time. The decrease occurs.

  FIG. 12 is a diagram illustrating a decrease in light emission luminance over time of the organic EL element according to a constant voltage control method and a constant current control method. Curve A in the figure shows the case of the constant voltage type control method, and curve B shows the case of the constant current type control method. In addition, the normalized time shown in FIG. 12 is set to 1 when the normalized luminance in the constant voltage control method is halved (that is, 0.5). As shown in FIG. 12, the constant current control method can extend the display life of the display device than the constant voltage control method. The display life means a time until an element that emits light with a predetermined luminance reaches a luminance that cannot be used as a display device due to deterioration over time, that is, a time until the predetermined luminance is almost halved.

  In addition, it is well known that the display life of an organic EL element varies depending on the ambient temperature. Since the amount of heat generated increases as the amount of current flowing through the element during light emission increases, the display life also varies. It will be. However, since the light emission of the organic EL element is instantaneous in the simple matrix system, the heat generated by the organic EL element is quickly dissipated. Therefore, it is known that the display life of the organic EL element is determined by the time average current density (see, for example, Non-Patent Document 1).

For this reason, for example, a conventional driving voltage applied to the organic EL element is set to 3 [mA / cm ² ] as an average driving current flowing through the organic EL element, and a pulse voltage having a duty ratio of 10% or less is set to 4 V or less. There is a display device (see, for example, Patent Document 1). With this configuration, the display life of the organic EL element can be greatly extended. In addition, there is a conventional display device in which a capacitor is connected to an organic EL element, and the capacitor accumulates charges 50 times or more per second (see, for example, Patent Document 2).

  Here, the constant current type control method can extend the display life of the organic EL element, and the light emission luminance and the current flowing during light emission are in a proportional relationship. Widely used in displays that strictly require gradation reproducibility to display natural images, and exhibits excellent effects.

  On the other hand, a simple display that performs static binary (gradation) display, such as a display used for displaying a title song of a clock or a portable music player, requires a complicated circuit configuration. A constant current control type display is rarely adopted, and a constant voltage control type with a lower manufacturing cost is often adopted.

  By the way, the simple matrix type display is configured such that the wiring resistance is as close to 0 [Ω] as possible, regardless of whether the constant current control method or the constant voltage control method is employed. With this configuration, since the voltage drop due to the wiring resistance is close to 0, in the constant current control method, a voltage close to the power supply voltage (or the voltage obtained by subtracting the voltage drop of the driving IC) is applied to the organic EL element. Can be applied. And since an organic EL element shows a diode characteristic by the relationship between the voltage applied and light emission brightness or the flowing electric current, the light emission brightness can be made higher by increasing the voltage applied to the organic EL element. In addition, in the constant voltage control method, the emission luminance can be increased by increasing the voltage applied to the organic EL element, and the variation in the voltage drop due to the variation in the wiring resistance value for each wiring is suppressed. Variation in voltage applied to each organic EL element, that is, variation in luminance can be suppressed.

  For example, conventionally, there is a display device substrate (display panel) in which the width of the wiring increases as the distance from the power source increases (see Patent Document 3). Since the wiring resistance can be lowered by increasing the width of the wiring in this way, variations in voltage applied to each display element, that is, variations in luminance can be suppressed.

In addition, as a configuration for suppressing variations in luminance, a resistance element is conventionally provided in series with the organic EL element, and the resistance value of the resistance element is set to a predetermined ratio with respect to the internal resistance value of the organic EL element. Display devices, and display devices configured to draw scanning lines or data lines alternately in different directions (see Patent Documents 4 and 5).
JP 2002-299045 A JP 2000-276109 A JP 2004-246330 A JP 11-87053 A JP 2002-299045 A Seizo Miyata, et al., “Organic EL devices and their industrialization fronts”, NTS, November 1998, p. 225-226, p. 242-243

  Here, as described above, it is preferable to adopt a constant voltage control method with a low manufacturing cost for the simple type display. However, as shown in FIG. 12, this constant voltage control method is a constant current control method. Compared to this, it is difficult to extend the display life of the display device.

  In this regard, it is conceivable to extend the display life by driving the organic EL element under a predetermined driving condition as in the conventional display device disclosed in Patent Document 1 described above. However, since the conventional display device disclosed in Patent Document 1 has limited driving conditions, it may be extremely difficult to manufacture a device having a desired resolution and luminance.

  Here, an organic EL element as an electro-optical element is described as an example. However, the present invention is not limited to an organic EL element, and is similar to a light-emitting element whose light emission amount is controlled according to the amount of current flowing through the element. There is a problem.

  Therefore, the present invention compensates for the luminance degradation of the electro-optic element over time with a simple configuration without setting the limiting conditions for driving the electro-optic element such as the organic EL element as described above. It is an object of the present invention to provide a display device capable of extending the display life. Another object of the present invention is to provide a display device capable of extending the display life by compensating the time-dependent luminance deterioration of the electro-optic element with a simple configuration while suppressing variations in display luminance.

According to a first aspect of the present invention, the first and second electrodes, the electro-optical element that is disposed at the intersection of the first and second electrodes and emits light when an electric current is applied, and the electro-optical element should be applied A constant voltage power source for supplying current; first switch means for selectively grounding the first electrode; and a second switch for selectively applying a voltage from the constant voltage power source to the second electrode. A display device comprising:
The first resistance value Rs from the electro-optical element that emits light until it is grounded via the first switch means and the constant-voltage power source that is connected from the electro-optical element that emits light via the second switch means The second resistance value Rd up to is the ratio of the sum of the first resistance value Rs and the second resistance value Rd to the resistance value Rel at the time of light emission of the electro-optic element β (= (Rs + Rd) / Rel ), It is set to satisfy 0.1 ≦ β ≦ 10.

According to a second invention, in the first invention,
The first resistance value Rs and the second resistance value Rd are set to satisfy 0.1 ≦ β ≦ 9.0.

According to a third invention, in the second invention,
The first resistance value Rs and the second resistance value Rd are set to satisfy 0.1 ≦ β ≦ 5.0.

According to a fourth invention, in the first invention,
The first electrode is formed of a single metal layer, a laminated structure of Cr and Ta, a laminated structure of Cr and ITO, or a metal layer having a laminated structure of Cr, Ta, and ITO.

According to a fifth invention, in the first invention,
The second electrode is made of ITO.

According to a sixth invention, in the first invention,
A first wiring that connects the first electrode and the first switch means; and a second wiring that connects the second electrode and the second switch means;
By setting at least one of a wiring length, a wiring width, and a wiring sheet resistance value in at least one of the first and second wirings to a predetermined value, the first resistance value Rs and the second resistance value are set. A resistance value Rd is set.

A seventh invention is the sixth invention, wherein
A plurality of the first and second wirings are provided,
At least one of the first and second wirings is characterized in that the wiring resistances of the plurality of wirings are substantially the same because the wiring lengths of the plurality of wirings are substantially equal.

In an eighth aspect based on the sixth aspect,
A plurality of the first and second wirings are provided,
At least one of the first and second wirings is characterized in that a wiring width is determined in accordance with a wiring length in the plurality of wirings so that wiring resistances in the plurality of wirings are substantially the same.

According to a ninth invention, in the sixth invention,
A plurality of the first and second wirings are provided,
At least one of the first and second wirings is characterized in that wiring resistances in the plurality of wirings are substantially the same by determining a wiring depth according to a wiring length in the plurality of wirings.

A tenth aspect of the present invention is a first electrode that is a plurality of parallel electrodes extending in a predetermined direction, and a second electrode that is a plurality of parallel electrodes extending in a direction orthogonal to the first electrode; A plurality of electro-optic elements that form a plurality of pixels arranged in a matrix corresponding to the intersections of the first and second electrodes, and a constant-voltage power source that supplies a current to be passed through the electro-optic elements; , First switch means for selectively grounding the first electrode for each predetermined period, and second switch means for selectively applying a voltage from the constant voltage power source to the second electrode. A display device,
When the number of the second electrodes to which the voltage from the constant voltage power source is selectively applied by the second switch means within the predetermined period is X, all the electro-optical elements that emit light are A first resistance value Rs until grounded via one switch means and a third resistance until all light-emitting electro-optic elements are connected to the constant voltage power source via the second switch means The value (Rd / X) is a ratio of the sum of the first resistance value Rs and the third resistance value (Rd / X) to the total resistance value Reall of all the light-emitting electro-optic elements, β ′ (= ( Rs + Rd / X) / Relall), 0.1 ≦ β ′ ≦ 10 is set.

In an eleventh aspect based on the tenth aspect,
The first resistance value Rs and the third resistance value (Rd / X) are set to satisfy 0.1 ≦ β ′ ≦ 9.0.

In a twelfth aspect based on the eleventh aspect,
The first resistance value Rs and the third resistance value (Rd / X) are set to satisfy 0.1 ≦ β ′ ≦ 5.0.

In a thirteenth aspect based on the tenth aspect,
The first electrode is formed of a single metal layer, a laminated structure of Cr and Ta, a laminated structure of Cr and ITO, or a metal layer having a laminated structure of Cr, Ta, and ITO.

In a fourteenth aspect based on the tenth aspect,
The second electrode is made of ITO.

A fifteenth aspect of the invention is the tenth aspect of the invention,
A first wiring that connects the first electrode and the first switch means; and a second wiring that connects the second electrode and the second switch means;
By setting at least one of a wiring length, a wiring width, and a wiring sheet resistance value in at least one of the first and second wirings to a predetermined value, the first resistance value Rs and the third resistance value are set. A resistance value (Rd / X) is set.

In a fifteenth aspect based on the fifteenth aspect,
At least one of the first electrode and the second electrode is connected to a corresponding first or second wiring at an end which is a different side between two parallel electrodes.

In a fifteenth aspect based on the fifteenth aspect,
A plurality of the first and second wirings are provided,
At least one of the first and second wirings is characterized in that the wiring resistances of the plurality of wirings are substantially the same because the wiring lengths of the plurality of wirings are substantially equal.

In an eighteenth aspect based on the fifteenth aspect,
A plurality of the first and second wirings are provided,
At least one of the first and second wirings is characterized in that a wiring width is determined in accordance with a wiring length in the plurality of wirings so that wiring resistances in the plurality of wirings are substantially the same.

In a nineteenth aspect based on the fifteenth aspect,
A plurality of the first and second wirings are provided,
At least one of the first and second wirings is characterized in that wiring resistances in the plurality of wirings are substantially the same by determining a wiring depth according to a wiring length in the plurality of wirings.

In a twentieth invention according to the first or tenth invention,
The constant voltage power supply is a pulse power supply,
When the light emission voltage of the electro-optical element is set to 2 [V] to 20 [V], the current density Ael [mA / mA flowing through the electro-optical element with respect to the duty number Y (Y is a natural number) for driving the pulse power source. cm ² ] ratio γ (= Ael / Y) is defined within a range of 50 to 5.

The twenty-first invention is the twentieth invention,
When the light emission voltage of the electro-optic element is 2 [V] to 18.2 [V], the ratio γ is set within a range of 50 to 5.5.

According to a twenty-second aspect, in the twenty-first aspect,
When the light emission voltage of the electro-optical element is 2 [V] to 9.1 [V], the ratio γ is determined within a range of 50 to 11.

In a twenty-third aspect based on the first or tenth aspect,
The electro-optical element is controlled in gradation by binary so as to be in a light emitting state or a non-light emitting state.

According to a 24th aspect of the present invention, in the first or 10th aspect,
The electro-optic element is an organic electroluminescence element.

  According to the first aspect of the invention, the first resistance value Rs from the electro-optical element that emits light to the ground through the first switch means, and the second resistance means from the electro-optical element that emits light via the second switch means. The second resistance value Rd until connected to the constant voltage power supply is set to satisfy 0.1 ≦ β ≦ 10. Accordingly, for example, while taking into consideration the upper limit voltage to be applied to the electro-optic element, it is possible to extend the display life by compensating for the luminance deterioration with time of the electro-optic element with a simple configuration.

  According to the second aspect, since the first resistance value Rs and the second resistance value Rd are set to satisfy 0.1 ≦ β ≦ 9.0, for example, the manufacturing cost of the constant voltage power supply is reduced. While taking into account keeping it low, it is possible to extend the display life by compensating the luminance deterioration with time of the electro-optic element with a simple configuration.

  According to the third aspect, since the first resistance value Rs and the second resistance value Rd are set to satisfy 0.1 ≦ β ≦ 5.0, for example, the power consumption of the constant voltage power supply is reduced. The display life can be extended by compensating for the luminance deterioration with time of the electro-optic element with a simple configuration while keeping it low and taking into account the use of a commonly used power source.

  According to the fourth invention, the first electrode is made of one or more of Cr, Ta, and ITO. These metals do not require a structure to avoid corrosion due to oxidation, such as when Al is used, and can be easily formed, and are conventionally known as conductive materials, and the stability of the materials It is also preferable because it is excellent.

  According to the fifth aspect, the second electrode is made of ITO. However, in a general electro-optic element, when a current flows from the second electrode to the first electrode, light is emitted to the second electrode side. Since it is performed, the second electrode is preferably made of transparent ITO. Further, since a configuration for avoiding corrosion due to oxidation is not required as in the case of using Al, for example, it can be formed easily and is excellent in material stability.

  According to the sixth aspect of the invention, by setting at least one of the wiring length, the wiring width, and the wiring sheet resistance value in at least one of the first and second wirings to a predetermined value, the first resistance Since the value Rs and the second resistance value Rd are set, these resistance values can be set with a simple configuration.

  According to the seventh aspect, at least one of the first and second wirings has substantially the same wiring resistance in the plurality of wirings because the wiring lengths in the plurality of wirings are substantially equal. As a result, the luminance variation with time of the electro-optic element can be compensated for with a simple configuration while eliminating or reducing the luminance variation of each electro-optic element in the direction orthogonal to at least one of the first and second wirings. The display life can be extended.

  According to the eighth aspect, at least one of the first and second wirings has the wiring width determined according to the wiring length of the plurality of wirings, so that the wiring resistances of the plurality of wirings are substantially the same. As a result, the luminance variation with time of the electro-optic element can be compensated for with a simple configuration while eliminating or reducing the luminance variation of each electro-optic element in the direction orthogonal to at least one of the first and second wirings. The display life can be extended.

  According to the ninth aspect, at least one of the first and second wirings has a wiring depth determined according to a wiring length of the plurality of wirings, so that the wiring resistances of the plurality of wirings are substantially the same. . As a result, the luminance variation with time of the electro-optic element can be compensated for with a simple configuration while eliminating or reducing the luminance variation of each electro-optic element in the direction orthogonal to at least one of the first and second wirings. The display life can be extended.

  According to the tenth aspect of the invention, in the matrix type display device, the first resistance value Rs until all the light emitting electro-optic elements are grounded via the first switch means, and all the light emitting electricity. The third resistance value (Rd / X) from when the optical element is connected to the constant voltage power supply via the second switch means is set to satisfy 0.1 ≦ β ′ ≦ 10. Accordingly, as in the first aspect of the invention, for example, the upper limit voltage to be applied to the electro-optical element is taken into account, and the display lifetime is extended by compensating for the luminance deterioration with time of the electro-optical element with a simple configuration. be able to.

  According to the eleventh aspect of the invention, as with the second aspect of the invention, for example, it is possible to compensate for deterioration in luminance of the electro-optic element over time with a simple configuration while taking into account, for example, keeping the manufacturing cost of a constant voltage power supply low. Display life can be extended.

  According to the twelfth aspect, as in the third aspect, the power consumption of the constant voltage power supply is kept low, for example, while taking into account the use of a commonly used power supply, with a simple configuration. It is possible to extend the display life by compensating the luminance degradation of the electro-optic element over time.

  According to the thirteenth aspect, as with the fourth aspect, it can be formed easily, is conventionally known as a conductive material, and is excellent in the stability of the material.

  According to the fourteenth aspect of the invention, like the fifth aspect of the invention, it is preferably made of transparent ITO, and can be easily formed and is excellent in material stability.

  According to the fifteenth aspect, as in the sixth aspect, at least one of the wiring length, the wiring width, and the wiring sheet resistance value in at least one of the first and second wirings is set to a predetermined value. By setting, the first resistance value Rs and the third resistance value (Rd / X) are set, so that these resistance values can be set with a simple configuration.

  According to the sixteenth aspect of the present invention, at least one of the first and second electrodes is connected to the corresponding first or second wiring at the end portions that are different from each other between two parallel electrodes. ing. As a result, in a direction parallel to at least one of the first and second wirings, the luminance variation of each electro-optic element is averaged as a result, thereby eliminating or mitigating the luminance variation and simplifying the configuration. Thus, it is possible to extend the display life by compensating for the luminance deterioration of the electro-optic element over time.

  According to the seventeenth aspect, as in the seventh aspect, with a simple configuration, the luminance variation of each electro-optic element in the direction orthogonal to at least one of the first and second wirings is eliminated or reduced. The display life can be extended by compensating the luminance degradation of the electro-optic element over time.

  According to the eighteenth aspect, as in the eighth aspect, with a simple configuration, the luminance variation of each electro-optic element in the direction orthogonal to at least one of the first and second wirings is eliminated or reduced. The display life can be extended by compensating the luminance degradation of the electro-optic element over time.

  According to the nineteenth aspect, similar to the ninth aspect, with a simple configuration, eliminating or mitigating the luminance variation of each electro-optic element in the direction orthogonal to at least one of the first and second wirings. The display life can be extended by compensating the luminance degradation of the electro-optic element over time.

  According to the twentieth invention, the constant voltage power source is a pulse power source, the light emission voltage of the electro-optic element is 2 [V] to 20 [V], and the ratio γ is determined within the range of 50 to 5. Therefore, it is possible to extend the display life by suppressing the temperature rise that shortens the display life of the electro-optical element with a pulse power supply, and with a simple configuration, taking into account the upper limit voltage to be applied to the electro-optical element, for example. It is possible to further extend the display life by compensating for the luminance degradation of the electro-optic element over time.

  According to the twenty-first aspect, the light emission voltage of the electro-optic element is set to 2 [V] to 18.2 [V], and the ratio γ is set within the range of 50 to 5.5. The display life of the electro-optic element can be shortened and the display life can be extended, and for example, while taking into account the low manufacturing cost of the constant voltage power supply, the electro-optic element can be kept with a simple structure. It is possible to further extend the display life by compensating for a typical luminance deterioration.

  According to the twenty-second aspect, the light emission voltage of the electro-optic element is set to 2 [V] to 9.1 [V], and the ratio γ is set within the range of 50 to 11, so that, for example, the duty number Y is It is possible to extend the display life by suppressing the temperature rise that shortens the display life of the electro-optic element with the relatively used pulse power supply of 64, and taking into account, for example, keeping the manufacturing cost of the constant voltage power supply low. However, it is possible to further extend the display life by compensating for the luminance deterioration with time of the electro-optic element with a simple configuration.

  According to the twenty-third aspect of the invention, gradation control is performed with a binary voltage. According to this configuration, a display device for a mobile phone, which often incorporates the present display device that employs a simple matrix method that is less likely to cause variations in gradation display, that is simple in manufacturing process, and can be manufactured at low cost, A suitable display can be performed also in an in-vehicle display device.

  According to the twenty-third aspect of the present invention, a high-quality display device can be easily provided by using an organic electroluminescence element which is a typical electro-optical element.

  Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

<1. Principle>
As a premise for explaining the configuration of an embodiment of the present invention, the principle to be applied and the effects obtained in the present invention will be described.

FIG. 1 is a circuit diagram showing an electro-optical element when light is emitted alone. When the voltage applied from the power source to the illustrated electro-optic element is V, the resistance value when the electro-optic element has a predetermined luminance is Rel, and the current value is I, the Ohm's law The relationship between current, voltage, and resistance is expressed by the following equation (1).
V = I · Rel (1)

  FIG. 2 is a circuit diagram showing these elements when resistance elements are inserted in series with respect to the electro-optical elements in the circuit shown in FIG. Note that the deterioration characteristics of the electro-optic element are the same regardless of the connected resistance element. The resistance value at the time of light emission of this electro-optical element is Rel, and the resistance value (hereinafter referred to as “insertion resistance value”) of a resistance element (hereinafter referred to as “insertion resistance element”) inserted in series with respect to the electro-optical element is defined as When Rr is set, the voltage value V ′ can be determined such that the current value I ′ flowing through the electro-optic element is equal to the current value I. That is, the voltage value V ′ can be determined such that the light emission luminance of the electro-optical element shown in FIG. 2 is equal to the light emission luminance of the electro-optical element when the insertion resistance element is not inserted.

When the voltage value applied to the electro-optic element is Vel and the voltage value applied to the insertion resistance element (insertion resistance value Rr) at that time is Vr, the relationship between the current, voltage, and resistance is as follows from Ohm's law: It is expressed as equation (2).
V ′ = Vel + Vr
= I '. (Rr + Rel)
= I · (Rr + Rel) (2)

Since the current value I shown in the above equation (2) is expressed as I = Vel / Rel from the above equation (1), when this is substituted into the above equation (2), it is expressed as the following equation (3). Can do.
V ′ = Vel · (Rr + Rel) / Rel (3)

Here, when β is the resistance ratio between the insertion resistance value Rr and the resistance value Rel when the electro-optic element emits light (that is, the ratio of the insertion resistance value Rr to the resistance value Rel), β is replaced with the ratio of the partial pressure. Thus, it can be expressed as the following equation (4).
β = Rr / Rel
= (Vr / I ') / (Vel / I')
= Vr / Vel (4)

  As described above, the ratio β (= Rr / Rel) of the insertion resistance value Rr to the resistance value Rel at the time of light emission of the electro-optical element can also be expressed by the ratio Vr / Vel of the voltage values applied to these resistors.

At this time, the above equation (3) can be expressed as the following equation (5) when represented by β shown in the above equation (4).
V ′ = Vel · (β + 1) (5)

  FIG. 3 is a diagram showing an equivalent circuit diagram when one scan electrode is selected in the display device of the simple matrix system using the constant voltage control system. Here, as shown in FIG. 8 to be described later, the simple matrix display device selectively includes a display panel 100 including a plurality of organic EL elements arranged in a matrix, and the organic EL elements. A scan electrode driving circuit (also referred to as a common driver circuit or a row driver circuit) 200 and a data electrode driving circuit (also referred to as a segment driver circuit or a column driver circuit) 300 including a plurality of switch circuits for supplying a current, and supplying the current The display panel 100 includes scanning electrodes (cathode electrode lines) SL1 to SL64 parallel to each other, and data electrodes (anode electrode lines) DL1 to DL96 orthogonal to these, And an organic EL element 10 disposed in the vicinity of these intersections.

  The circuit shown in FIG. 3 has a configuration in which a plurality of the circuits shown in FIG. 2 are arranged in parallel to the power source. The characteristics of each wiring and each electro-optical element shown in FIG. The characteristics are similar to those of the wiring and each electro-optical element. Further, in the circuit shown in FIG. 3, the resistance values of the scan electrode and the data electrode itself not including the wiring are regarded as zero.

Here, the number of data electrodes contributing to the light emission of each electro-optical element (that is, connected to each light-emitting electro-optical element) is X, the current value flowing through each electro-optical element is I, and control is performed so that this current is conducted or cut off. Rd is the wiring resistance value of each data electrode including the wiring from the switch SW to each electro-optical element, Rs is the wiring resistance value of each scanning electrode including the wiring from each electro-optical element to the ground point, and When the resistance value at the time of light emission is Rel, the electro-optical element total resistance value Reall which is a combined resistance value in which only the internal resistances of the electro-optical elements at the time of light emission connected in parallel are connected in parallel is expressed by the following equation (6). Can be expressed as:
Relall = Rel / X (6)

Further, the wiring total resistance value Rall, which is a combined resistance value obtained by connecting only the wiring resistances of the data electrode and the scan electrode (its own resistance value is 0), is similarly expressed by the following equation (7). Can be expressed.
Rall = Rs + Rd / X (7)

Furthermore, when the resistance ratio between the total electro-optical element resistance value Rrel and the total wiring resistance value Rall (that is, the ratio of the total wiring resistance value Rall to the total electro-optical element resistance value Rell) is β ′, β ′ 8).
β ′ = Rall / Reall (8)

Further, since the above equation (8) can also be expressed by a voltage ratio in the same manner as the above equation (4), the voltage applied to the entire data electrode and the scanning electrode having the wiring total resistance value Rall is defined as Vall, When the voltage applied to the entire electro-optical element at the time of light emission having the resistance value Relall is Velall, β ′ can be expressed as the following equation (9).
β ′ = (I · X · Rall) / (I · X · Relall)
= Vall / Velall (9)

Further, in the circuit shown in FIG. 3, the wiring resistance value Rs of the scanning electrode including the wiring is set to 0, the power supply voltage is set to Vdd, the voltage applied to the electro-optical element when X = 1 is set to Vel, the data electrode and the scanning The voltage applied to the entire electrode is Vr, and the ratio is β. At this time, the power supply voltages Vdd and β can be expressed as in the following equation (10).
Vdd = Vel + Vr
= I ・ Rel + I ・ Rd
β = Vr / Vel (10)

Further, when the number of all data electrodes provided in the display device is Xmax and X = Xmax, the power supply voltage Vdd can be expressed as the following equation (11).
Vdd = I.X.Rel / X + I.X.Rd / X
= I ・ Rel + I ・ Rd
= Vel + Vr (11)

Here, β ′ when X = Xmax can be expressed by the following equation (12) from the above equation (9).
β ′ = (I · X · Rel / X) / (I · X · Rd / X)
= Vr / Vel (12)

  Therefore, since the above equation (10) and the above equation (12) are equal, when the wiring resistance value Rs of the scan electrode is 0, all the data electrodes are connected in parallel to the power supply in Xmax. β and β ′ have the same value, and the current value I does not change.

  This result is obtained when the wiring resistance value Rs of the scan electrode is 0, but when the wiring resistance value Rs of the scan electrode is larger than 0, the current depends on the number of data electrodes contributing to light emission. The value changes. An organic EL element, which is an electro-optical element, is known to have a proportional relationship between the light emission luminance and the flowing current. Therefore, a change in the flowing current value is a change in the light emission luminance. The maximum value of the changing emission luminance is called peak luminance, and the magnification of the maximum luminance with respect to the minimum luminance is called peak luminance ratio.

Here, when Rs> 0 and X = 1, the insertion resistance value Rr for the electro-optical element that emits light is equal to the wiring resistance value Rd of the data electrode (including wiring) and the scanning electrode (including wiring). Therefore, the voltage value Vr applied to these can be expressed as the following equation (13).
Vr = I · (Rs + Rd) (13)

From this equation (13), the power supply voltage Vdd can be expressed as the following equation (14).
Vdd = Vel + Vr
= I · Rel + I · (Rs + Rd) (14)

Further, when X = Xmax, the power supply voltage Vdd can be expressed as the following equation (15).
Vdd = I.X.Rel / X + I.X. (Rs + Rd / X)
= I.Rel + I.Rd + I.X.Rs (15)

Here, when X = Xmax, the voltage value applied to the electro-optic element is Vel ′, and when the voltage value applied to the total wiring resistance having the insertion resistance value Rr is Vr ′, Rs = 0. Referring to the above equation (14) and the above equation (15) when Rs> 0, it can be seen that Vr ′> Vr, and the power supply voltage Vdd is constant, so that Vel> Vel 'It can be seen that it is. Further, the current value I ′ flowing through the electro-optical element when X = Xmax is naturally smaller than the current value flowing through the electro-optical element when X = 1, so that I> I ′. Further, the voltage value Vr ′ can be expressed as the following equation (16).
Vr ′ = I ′ · X · (Rs + Rd / X) (16)

From the above equation (16), when X = Xmax, the power supply voltage Vdd can be expressed as the following equation (17).
Vdd = Vel ′ + Vr ′
= Vel '+ I'.X. (Rs + Rd / X) (17)

When this equation (17) is modified, the current value I ′ can be expressed as the following equation (18).
I ′ = (Vdd−Vel ′) / (Rd + X · Rs) (18)

Here, in general, an organic EL element that is an electro-optical element has an exponential approximate expression between a voltage applied to the element and a flowing current, and these voltages are applied when the applied voltage is about several volts. It is known that this relationship can be approximated by a quadratic function equation. Therefore, when the predetermined constants are a, b, and c, the current value I ′ can be expressed as the following equation (19).
I ′ = a · Vel ′ ² + b · Vel ′ + c (19)

Therefore, the voltage value Vel ′ can be expressed by the following equation (20) from the formula of the solution from the above equations (18) and (19).
Vel ′ = {− (b + 1 / (Rd + X · Rs))
+ √ {(b + 1 / (Rd + X · Rs)) ²
−4 · a · (c−Vdd / (Rd + X · Rs))}}
/ (2 · a) (20)

When the light emission luminance of the electro-optical element when X = 1 is L and the light emission luminance of the electro-optical element when X = Xmax is L ′, the peak luminance rate α is expressed by the following equation (21). Can be expressed in
α = L / L ′ (21)

Since the light emission luminance of the electro-optic element and the flowing current are in a proportional relationship, the peak luminance rate α can be expressed as the following equation (22).
α = I / I ′ (22)

  Further, when the peak luminance rate α is set to a desired value in advance, the wiring resistance value Rd of the data electrode (including wiring) and the wiring resistance value of the scanning electrode (including wiring) for realizing the peak luminance rate α. Rs is obtained by calculating the voltage value Vr ′ from the above equations (18), (19), and (22), and substituting the obtained voltage value Vr ′ for the above equations (13), (16), ( 22) to solve the simultaneous equations.

Since Vel> Vel ′ and Vr ′> Vr as described above, from the above formulas (8), (10), and (12), β ′ in the case of X = Xmax and the case of X = 1 The relationship with β in can be expressed by an inequality such as the following equation (23).
β ′ (= Vr ′ / Vel ′)> β (= Vr / Vel) (23)

  Therefore, referring to this equation (23), the resistance ratio β between the insertion resistance value Rr and the resistance value Rel at the time of light emission of the electro-optical element is large in the number of light-emitting electro-optical elements connected to one scanning electrode. You can see that it grows bigger.

Further, when the characteristics of the plurality of electro-optic elements and the related wiring resistance are all the same as described above, the sheet resistance value of the wiring is Rsh, the wiring length is L, and the wiring width is W, the wiring The resistance R is expressed as the following equation (24).
R [Ω] = Rsh [Ω / □ (square)] · L / W (24)

<2. Relationship between display life of electro-optic element and β>
Next, the relationship between the display life of the organic EL element, which is an electro-optical element, and the resistance ratio β (or β ′) of the insertion resistance value Rr and the resistance value Rel when the electro-optical element emits light will be described.

  The value of the internal resistance of the organic EL element at the initial light emission at a predetermined luminance (that is, when the light emission history is short) varies greatly depending on the light emission area and internal structure, but is usually 100 [Ω] to 20 [MΩ]. The value of the internal resistance of the organic EL element is calculated based on the relationship (characteristic) between the current density flowing through the inside and the luminance and the relationship (characteristic) between the current density and the voltage.

  It is well known that the internal resistance changes when the voltage applied to both ends of the organic EL element changes. The voltage applied to the organic EL element when it emits light varies depending on the element structure, but is usually about 2 [V] to about 20 [V]. Generally, when a voltage higher than 20 [V] is applied to the organic EL element, the organic EL element that has reached a high temperature due to heat that cannot escape to the outside deteriorates rapidly. In general, the organic EL element has a very thin film thickness of several tens of nanometers. Therefore, when a voltage higher than 20 [V] is applied, local electric field concentration is likely to occur due to the surface roughness of ITO (Indium Tin Oxide) or the like constituting the electrode of the organic EL element, causing dielectric breakdown. May be. From these things, it can be said that it is not preferable to apply a voltage higher than 20 [V] to a general organic EL element. Hereinafter, the relationship between the display lifetime and β in the organic EL element to which the voltage in the above-described range is applied will be described with reference to FIGS. 4 and 5.

  FIG. 4 is a diagram showing an equivalent circuit in which 220 organic EL elements are connected in parallel to a DC constant voltage power source. The equivalent circuit shown in FIG. 4 is different from the equivalent circuit when one scan electrode is selected in a simple matrix display device using the constant voltage control method as shown in FIG. This corresponds to a simple configuration in which the wiring resistance value Rs is 0 and X = 220.

  Here, under the following two different conditions A and B, a measurement is made of the change over time in the light emission luminance of the organic EL element in the circuit shown in FIG. Under these conditions A and B, organic EL elements having the same element configuration and element size are both used, and the resistance value Rel of the organic EL element at the initial light emission is 2.3 [MΩ]. In condition A, the power supply voltage (input voltage) Vdd is 4.3 [V], and the insertion resistance value Rr is 300 [kΩ]. Further, the power supply voltage (input voltage) Vdd in the condition B is 3.98 [V], and the insertion resistance value Rr is 5 [kΩ].

  FIG. 5 is a diagram showing a change with time of the normalized emission luminance of the organic EL element shown in FIG. 4 under the above conditions A and B. The vertical axis shown in FIG. 5 is the normalized light emission luminance of the organic EL element, and the horizontal axis is the normalization time with 1 as the time when the normalization luminance in the condition B is 0.5.

  Here, when the resistance ratio β (= Rr / Rel) in each of the above conditions is calculated, β = 0.13 in the condition A and β = 0.002 in the condition B. When the insertion resistance value Rr is very small compared to the resistance value Rel of the organic EL element as in the case of β = 0.002 in the condition B, the insertion resistance value Rr can be regarded as almost zero. Generally, in order to reduce power consumption, it is preferable that the insertion resistance value Rr can be regarded as 0 in this way. In the conventional display device, for example, each of the scan electrode, the data electrode, and the related wiring In many cases, the resistance value is configured to be as close to 0 as possible.

  In this respect, under the condition A where β = 0.13, the insertion resistance value is a value slightly exceeding 10% of the internal resistance value of the organic EL element. However, with reference to FIG. 5, it can be seen that a longer display life is obtained in condition A than in condition B. As the internal resistance increases due to deterioration of the organic EL element, the voltage applied to the resistance of the insertion resistance value Rr at the beginning of light emission is changed so as to be distributed to the organic EL element thereafter. It is considered that an increase in the voltage applied to the pixel causes a decrease in the luminance thereof to be relatively suppressed as compared with the case of condition B, resulting in an effect of extending the display life.

  Referring further to FIG. 5, the elapsed time until the normalized luminance reaches 0.5, that is, the display life of the organic EL element, is about 1.76 times longer in the condition A than in the condition B. . As can be seen from the above, when β is substantially equal to 0, for example, when β = 0.002 in the condition B, the insertion resistance value Rr is such that it can be regarded as substantially 0 with respect to the resistance Rel of the organic EL element. Since it is small, almost all the voltage from the power source is applied to the organic EL element. For this reason, the display life extension effect can hardly be expected. On the other hand, when β is a value in the vicinity of 0.1, that is, when β = 0.13 in the condition A, an effect of extending the display life can be actually obtained as described above. Therefore, it is considered that the lower limit value of β at which the display life extending effect can be significantly obtained must be at least 0.1 or more.

  Next, a change with time in the light emission luminance of the organic EL element when the pulse power source is used is measured. FIG. 6 is a diagram showing an equivalent circuit in which an organic EL element and an insertion resistor are connected in series to a pulse power supply. The pulse power supply shown in FIG. 6 provides a voltage indicating a pulse waveform having a duty ratio of 50% (that is, an on-potential determined only for a period of 50% in one cycle). This pulse power supply can also be said to be a constant voltage power supply in a broad sense.

  Here, the display lifetime of the light emission luminance of the organic EL element in the circuit shown in FIG. 6 is measured under four different conditions C, D, E, and F. Under these conditions C, D, E, and F, organic EL elements having the same element configuration and element size are used, and the resistance value Rel of the organic EL element in the initial light emission is 2.3 [kΩ]. In condition C, the insertion resistance value Rr is 0 [Ω], and no insertion resistance is provided. The insertion resistance value Rr in condition D is 51 [kΩ], the insertion resistance value Rr in condition E is 11.5 [kΩ], and the insertion resistance value Rr in condition F is 5.35 [kΩ]. Other conditions are the same for conditions C, D, E, and F. When the resistance ratio β (= Rr / Rel) is calculated in each of these conditions, β = 0 in the condition C, β = 0.045 in the condition D, and β = 0.20 in the condition E. In condition F, β = 0.43.

  FIG. 7 is a diagram showing a change with time of the normalized emission luminance of the organic EL element shown in FIG. 6 under the above conditions C, D, E, and F. The vertical axis shown in FIG. 7 is a value indicating how many times the display life in each condition is increased, assuming that the display life in condition C is 1. The horizontal axis is β.

  Referring to FIG. 7, since the display life under the condition D is almost the same as the display life under the condition C in which no resistance is inserted, the effect of extending the display life is almost obtained when β = 0.045. It can be seen that cannot be obtained. In addition, it can be seen that the display lifetime increases as the insertion resistance value increases, that is, as β increases as in the conditions E and F. Further, referring to FIG. 4 and FIG. 5 described above, instead of the constant voltage source shown in FIG. 4, a pulse power source having the above-described duty ratio is provided, and 220 organic EL elements are provided for this pulse power source. It is considered that the same effect can be obtained even in a circuit in which are connected in parallel.

  From the measurement results as described above, the effect of extending the life can be obtained by inserting a resistor in series with the organic EL element, regardless of whether it is a DC constant voltage power supply or a pulse power supply. It can be seen that β for significant appearance is about 0.1 or more.

In addition, as described above, the upper limit voltage suitable for application to the organic EL element is about 20 [V], so that it is connected in series with the insertion resistance when β is set to the minimum value at which a significant effect can be obtained. The voltage value V ′ at which the light emission luminance of the electro-optical element becomes equal to the light emission luminance of the electro-optical element when no resistor is inserted, that is, the power supply voltage (maximum value) V ′ is given by the above equation (5) By substituting Vel = 20 and β = 0.1, it can be determined that the voltage is about 22 [V]. Therefore, since V ′ = 20 and the minimum voltage for light emission of a general organic EL element is about 2 V, when Vel = 2, β is expressed by the following equation (25) from the above equation (5). It can be expressed as an inequality.
22 ≧ 2 (β + 1) (25)

From this equation (25), β ≦ 10. Since the minimum value of β for obtaining a significant effect is 0.1 as described above, the range of β can be expressed by an inequality such as the following equation (26).
0.1 ≦ β ≦ 10 (26)

Here, if Vel = 20 and β is made larger than 0.1, the power supply voltage V ′ becomes larger than 22 [V] from the above equation (5). However, if the power supply voltage V ′ becomes a very large voltage, the chip breakdown must be increased in order to increase the element breakdown voltage in the IC for performing switch control, resulting in an increase in manufacturing cost. . Considering this, the power supply V ′ is preferably 20 [V] or less. Considering this, if V ′ = 20 and Vel = 2, β can be expressed by an inequality such as the following equation (27) from the above equation (5).
20 ≧ 2 (β + 1) (27)

From this equation (27), β ≦ 9.0. As described above, since the minimum value of β for obtaining a significant effect is 0.1, the range of β can be expressed by an inequality such as the following equation (28).
0.1 ≦ β ≦ 9.0 (28)

  Similarly, when β is set to the minimum value at which a significant effect can be obtained and the power supply V ′ is set to a preferable maximum voltage value of 20 [V], the maximum light emission voltage Vel of the organic EL element is It can be calculated as 18.2 V from the equation (5).

Here, if the power supply voltage V ′ is 20 [V], the power consumption becomes very large, and the power supply voltage generally used is too high. In consideration of using the power supply used for the above, the power supply voltage V ′ is more preferably 12 V or less. Considering this, if V ′ = 12 and Vel = 2, β can be expressed by an inequality such as the following equation (29) from the above equation (5) as in the above equation (27). .
12 ≧ 2 (β + 1) (29)

From this equation (29), β ≦ 5.0. As described above, since the minimum value of β for obtaining a significant effect is 0.1, the range of β can be expressed by an inequality such as the following equation (30).
0.1 ≦ β ≦ 5.0 (30)

  Similarly, when β is set to the minimum value at which a significant effect can be obtained, and the power supply V ′ is set to 12 [V] which is a more preferable maximum voltage value, the maximum light emission voltage Vel of the organic EL element is It can be calculated as 10.9 V from the above equation (5).

  From the above, considering the upper limit voltage suitable for application to the organic EL element, the light emission voltage is preferably set in the range of 2 [V] to 20 [V], and the manufacturing cost of the power source, etc. , The light emission voltage is preferably set in the range of 2 [V] to 18.2 [V], and the light emission voltage is 2 [V] in consideration of reducing power consumption. ] To 10.9 [V] is more preferable.

  As described above, the range of β is preferably 0.1 ≦ β ≦ 10, more preferably 0.1 ≦ β ≦ 9.0, and further 0.1 ≦ β ≦ 5. 0.0 is more preferable.

  The same applies to the range of the resistance ratio β ′ between the electro-optic element total resistance value Rrelall and the wiring total resistance value Rall in the simple matrix type display device in which the organic EL elements are arranged in a matrix. Therefore, as in the case of β, the range of β ′ is preferably 0.1 ≦ β ′ ≦ 10, more preferably 0.1 ≦ β ′ ≦ 9.0, and still more preferably 0.00. It is more preferable that 1 ≦ β ′ ≦ 5.0.

  Here, in the display device according to an embodiment of the present invention described below, a resistance element is not inserted in series with respect to each organic EL element that is an electro-optical element, but a current is passed through the organic EL element. The wiring resistance from the power supply (specifically, the drive driver) connected to the scan electrode and the data electrode, typically one or more of the wiring sheet resistance value, the wiring length, and the wiring width. The β ′ is adjusted by adjusting appropriately. The present display device is thus configured to extend the display life. A display device according to an embodiment of the present invention configured as described above will be described with reference to the accompanying drawings.

<2. Configuration of display device>
<2.1 Overall configuration>
FIG. 8 is a diagram schematically illustrating the overall configuration of a display device according to an embodiment of the present invention. As shown in FIG. 8, this display device is a display device of a simple matrix system, and includes a display panel 100 including a plurality of organic EL elements arranged in a matrix, and a selection for these organic EL elements. A scan electrode driving circuit (also referred to as a common driver circuit or a row driver circuit) 200 and a data electrode driving circuit (also referred to as a segment driver circuit or a column driver circuit) 300 including a plurality of switch circuits for allowing current to flow, and the current And a constant voltage power source 400 for supplying power.

  The constant voltage power supply 400 outputs a determined DC power supply voltage Vdd (here 12 [V]) regardless of the load to be driven. Therefore, this display device employs the constant voltage control method described above, and the circuit configuration of the power supply is simpler than that of the constant current control method, so that the manufacturing cost can be reduced.

  The display panel 100 includes 64 scan electrodes (cathode electrode lines) SL1 to SL64 that are parallel to each other, 96 data electrodes (anode electrode lines) DL1 to DL96 that are orthogonal to each other, and in the vicinity of these intersections. A plurality of organic EL elements including the organic EL element 10 to be disposed.

  The display panel 100 has a multi-layer structure. For example, an ITO layer to be the data electrode is first formed on a glass substrate, and a hole transport layer made of α-NPD or the like is formed on the ITO layer. A light emitting layer made of a well-known organic light emitting material is formed thereon, and further a Cr single body, a laminated structure of Cr and Ta, a laminated structure of Cr and ITO, or a Cr, Ta and ITO, which is to be the scanning electrode. A metal layer having a laminated structure is formed. Since this configuration is well known, detailed description is omitted. In addition, a known anode buffer layer, electron transport layer, and the like may be further laminated at appropriate positions.

  In this multilayer structure, since light is emitted in the direction of the glass substrate when a current flows from the ITO layer to be the data electrode to the metal layer to be the scan electrode, the data electrode is preferably made of transparent ITO. . The material of the metal layer to be the scan electrode is not particularly limited. For example, when Al is used, a structure for avoiding corrosion due to oxidation is required. In this respect, the Cr, Ta, and ITO do not need such a configuration, and are conventionally known as conductive materials and excellent in material stability. It is preferably formed by a known laminated structure.

  As described above, since the scan electrode and the data electrode are orthogonal to each other, in this display device, only the portion where they overlap in the direction perpendicular to the display surface emits light. Here, the specific size of the light emitting portion is 240 μm in length and 240 μm in width, and the aperture ratio is 50%.

  Scan electrodes SL <b> 1 to SL <b> 64 are connected to scan electrode drive circuit 200, and are supplied with either power supply voltage Vdd or ground potential supplied from constant voltage power supply 400 by the switching operation of the switch circuit included in scan electrode drive circuit 200. Given selectively.

  That is, in one frame period for displaying one display screen, scan electrode driving circuit 200 sequentially selects one of scan electrodes SL1 to SL64 and applies a ground potential to scan electrodes that are not selected. Gives the power supply voltage Vdd. FIG. 8 shows a state where the scan electrode SL62 is selected.

  Note that in this specification, the ground potential refers to a common potential having a predetermined potential difference from the power supply voltage Vdd, and grounding a certain electrode means that the electrode is set to the common potential.

  The data electrodes DL1 to DL96 are connected to the data electrode drive circuit 300, and similarly to the scan electrode drive circuit 200, the power supply voltage supplied from the constant voltage power supply 400 by the switching operation of the switch circuit included in the data electrode drive circuit 300. Either Vdd or ground potential is selectively applied.

  Here, the data electrode driving circuit 300 includes the data electrodes DL1 to DL1 connected to one or more organic EL elements that should emit light among the plurality of organic EL elements connected to one scanning electrode selected by the scanning electrode driving circuit 200. A power supply voltage Vdd is applied to one or more of the DLs 96, and the other data electrodes are grounded. The data electrode drive circuit 300 repeats this operation every time a scan electrode is selected by the scan electrode drive circuit 200. FIG. 8 shows a state where the power supply voltage Vdd is applied to the data electrodes DL1 and DL2. Therefore, only the organic EL element 10 and the organic EL element on the right side thereof emit light here.

  Note that the scan electrode drive circuit 200 in this display device drives each scan electrode at 100 Hz, and the duty number is 64 times. The drive frequency is not particularly limited, but is preferably 60 Hz or more, which is a limit frequency that does not cause (or makes it difficult to) feel flicker to human eyes.

  Here, the display device may have an analog gradation control configuration in which the current flowing through the organic EL element that emits light is controlled by an analog amount, but in general, the constant voltage control method is different from the constant current control method. It is known that the gradation displayed by each organic EL element is likely to vary, and considering this, the configuration of analog gradation control is not necessarily preferable. Therefore, in the present embodiment, gradation is controlled by controlling the light emission time of the organic EL element by controlling the organic EL element with a binary voltage that makes the light emission state of a predetermined bright luminance or the non-light emission state of a predetermined dark luminance. It is assumed that a digital gradation control method for expressing is used. As described above, according to the configuration in which the gradation is controlled by the binary voltage, the present display device adopting a simple matrix system that is less likely to cause variations in gradation display, that has a simple manufacturing process, and that can reduce manufacturing costs. A suitable display can be performed also in a display device of a mobile phone or an in-vehicle display device that often incorporates.

  In addition, as a well-known method for performing gradation control using the above binary voltage, for example, a moving image having a halftone is divided into a plurality of weighted binary images and these are temporally superimposed. There are a method for displaying halftones (called a subfield method) and a method for controlling gradations of electro-optic elements having different light emitting areas with binary voltages. These well-known methods are adopted for this display device. Also good.

  Next, the display panel provided to connect scan electrodes SL1 to SL64 and data electrodes DL1 to DL96 in display panel 100 to scan electrode drive circuit 200 and scan electrode drive circuit 200 provided outside display panel 100. The 100 wirings will be described.

<2.2 Wiring configuration of display panel>
FIG. 9 is a plan view schematically showing the wiring configuration of the display panel 100. As shown in FIG. 9, below the display panel 100 in the figure, odd-numbered scan electrode connector 101 and even-numbered scan electrode connector 103 connected to scan electrode drive circuit 200 and data connected to data electrode drive circuit 300 are displayed. An electrode connector 102 is provided.

  Scan electrodes SL1, SL3,..., SL63 corresponding to odd rows among scan electrodes SL1 to SL64 are connected to one ends of corresponding scan electrode wirings Ls1, Ls3,. These scanning electrode wirings Ls1, Ls3,..., Ls63 each have a predetermined sheet resistance value, wiring length, and wiring width, and the other ends are connected to the odd-numbered scanning electrode connector 101. The sheet resistance value, wiring length, and wiring width will be described later.

  Similarly, among the scan electrodes SL1 to SL64, the scan electrodes SL2, SL4,..., SL64 corresponding to even rows are connected to one ends of the corresponding scan electrode wirings Ls2, Ls4,. . These scanning electrode wirings Ls2, Ls4,..., Ls64 similarly have predetermined sheet resistance values, wiring lengths, and wiring widths, and the other ends are connected to the odd scanning electrode connector 101.

  As described above, since the scan electrodes corresponding to the odd rows and the scan electrodes corresponding to the even rows among the scan electrodes SL1 to SL64 are connected to the scan electrode wirings corresponding to the left and right alternately, Variation in luminance can be reduced. That is, since the resistance of the scan electrode cannot be made completely zero, each organic EL element according to the wiring distance from each organic EL element connected to the scan electrode to the constant voltage power source 400 (via the scan electrode drive circuit 200). As a result of variations in the voltage applied to, the luminance also varies. Therefore, by connecting one end of the scan electrode to the scan electrode wiring alternately on the left and right for each row, the organic EL elements farthest from the constant voltage power source 400 in each scan electrode are alternately arranged at the left end or the right end for each row. can do. With this configuration, the luminance variations of the organic EL elements in the left and right direction of the display screen are averaged as a result, thereby reducing the luminance variations.

  The scan electrode SL1 is located farther from the odd scan electrode connector 101 than the scan electrode SL63, and similarly, the scan electrode SL2 is farther from the even scan electrode connector 103 than the scan electrode SL64. Due to the variation in the voltage applied to each organic EL element according to the wiring distance of each scanning electrode to the constant voltage power source 400 in the vertical direction, the luminance also varies. Therefore, a longer detour may be caused by a configuration in which, for example, the scanning electrode wiring connected to the scanning electrode at a closer position is bent to the left and right so that all the scanning electrode wirings Ls1 to Ls64 have the same wiring length. Use a wiring shape. As a result, the wiring resistances of all the scanning electrode wirings Ls1 to Ls64 can be made substantially the same, so that the luminance variation of each organic EL element in the vertical direction in the figure can be eliminated or alleviated.

  Further, instead of or together with this configuration, the scanning electrode wiring Ls1 connected to the scanning electrode SL1 disposed at the uppermost position in the drawing has the largest wiring width, and the scanning electrode SL64 disposed at the lowermost position in the drawing. By making the wiring width of the scanning electrode wiring Ls64 connected to the smallest, the wiring resistances of all the scanning electrode wirings Ls1 to Ls64 may be made substantially the same. That is, since the wiring length increases as the scanning electrode wiring connected to the scanning electrode located far from the odd scanning electrode connector 101 or the even scanning electrode connector 103 increases the wiring resistance, the wiring width is appropriately adjusted as described above. As a result, the wiring resistances of all the scan electrode wirings Ls1 to Ls64 can be made substantially the same. With this configuration, the luminance variation of each organic EL element in the vertical direction in the figure is eliminated or alleviated.

  Furthermore, instead of these components or together with these components, all the scan electrode wires Ls1 to Ls64 are adjusted by appropriately adjusting the wiring depth of each scan electrode wire (the film thickness of the wiring material in the direction perpendicular to the display surface). Can be made substantially the same. This is because the sheet resistance value of the wiring can be adjusted by adjusting the depth of the wiring. In practice, this configuration is preferably performed for fine adjustment to slightly increase or decrease the sheet resistance value by about 0.3 [Ω / □] due to restrictions on the manufacturing process or the like. Similarly, although there are restrictions on the manufacturing process and the like, the wiring resistance of all the scanning electrode wirings Ls1 to Ls64 can be made substantially the same by appropriately selecting the material of each scanning electrode wiring. This is because the sheet resistance value of the wiring can be adjusted by adjusting the resistivity of the wiring material. With these configurations, the luminance variation of each organic EL element in the vertical direction of the figure is eliminated or alleviated.

  Next, by appropriately setting the sheet resistance value, the wiring length, and the wiring width of the scanning electrode wiring and the data electrode wiring as described above, β is set as the minimum value that can extend the display life of the organic EL element. With respect to the wiring resistance values of the scanning electrode wiring and the data electrode wiring when = 0.1 (or β ′ = 0.1), specific numerical values are calculated with reference to FIG. The range of β is preferably 0.1 ≦ β ≦ 10, more preferably 0.1 ≦ β ≦ 9.0, and further preferably 0.1 ≦ β ≦ 5.0. This is more preferable as described above. Here, a case where the lower limit value of β (or β ′) is 0.1 will be described as an example.

<2.3 Calculation of wiring resistance>
FIG. 10 is a diagram showing the relationship between the light emission voltage of one organic EL element used in this display device, its internal resistance value, and the flowing current value. As shown in FIG. 10, the vertical axis on the left side of the figure indicates the internal resistance value of the organic EL element, the vertical axis on the right side indicates the current value flowing through the organic EL element, and the horizontal axis indicates the light emission voltage of the organic EL element. Show. The solid line indicates the relationship between the light emission voltage of the organic EL element and its internal resistance value, and the dotted line indicates the relationship between the light emission voltage of the organic EL element and the flowing current value.

  Here, the current value I flowing through the organic EL element is set so that the light emission voltage of one organic EL element used in the display device is 10.9 [V]. At this time, referring to FIG. 10, the internal resistance value of the organic EL element is 13170 [Ω], and the current value I is 0.000828 [A]. Further, since the power supply voltage Vdd is 12V, the remaining 1.1 [V] voltage obtained by subtracting the light emission voltage is applied to the scan electrode wiring and the data electrode wiring. Therefore, when the total wiring resistance value (Rs + Rd) of the scanning electrode wiring and the data electrode wiring when β = 0.1 that significantly increases the display life of the organic EL element appears, it is 1329 [Ω].

  Here, the total resistance value of the scan electrode and the data electrode is set to approximately 0 [Ω]. However, when the total resistance value is considerably larger than 0 [Ω], the above total is obtained by subtracting the total resistance value. A wiring resistance value can be calculated.

  Since the maximum number of organic EL elements connected to one scan electrode is 96, the maximum current value flowing through one scan electrode is 0.0795 [A], which is 96 times the current value I. As described above, the total resistance value Relall, which is the combined resistance of all the internal resistances in the organic EL elements connected in parallel, and the combined resistance value of the wiring resistances of the data electrodes and the scanning electrodes. The total wiring resistance value Rall varies depending on the number X of data electrodes contributing to light emission.

Here, when X = 96, the internal resistance value Rel of the organic EL element is 13170 [Ω]. Therefore, when these are substituted into the above equation (6), the electro-optic element total resistance value Rellall is expressed by the following equation (31). ) Can be calculated as follows.
Relall = 13170/96
= 137.2 [Ω] (31)

Further, when the resistance value Rs of the scanning electrode wiring connected to the scanning electrode is set to 0 [Ω], if this is substituted into the above equation (7), the wiring total resistance value Rall is calculated as the following equation (32). Can do.
Rall = 0 + 1329/96
= 13.8 [Ω] (32)

  Thus, under the above conditions, regardless of X, the emission voltage of the organic EL element that emits light is 10.9 [V], and the voltage value applied to the scan electrode wiring and the data electrode wiring is 1.1 [V]. Therefore, it can be seen that the resistance ratio β (or resistance ratio β ′) between the insertion resistance value Rr and the resistance value Rel at the time of light emission of the electro-optic element is also 0.1 and does not change.

Next, when the resistance value Rs of the scan electrode wiring connected to the scan electrode is larger than 0 [Ω], the current value changes according to the number of data electrodes contributing to light emission, and thus the peak luminance is generated as described above. Just as you did. Therefore, the total wiring resistance value (Rs + Rd) of the scanning electrode wiring and the data electrode wiring is set to 1329 [Ω] as described above so that β = 0.1 when X = 1, and further Rs = 10 [Ω], Rd = 1319 [Ω]. Then, when X = 96 so as to increase the number of light emitting organic EL elements, if these are substituted into the above equation (7), the total wiring resistance value Rall can be calculated as in the following equation (33). .
Rall = 10 + 1319/96
= 23.8 [Ω] (33)

  At this time, if 10.9 V is applied to the organic EL element that emits light, a current of 0.0795 [A] flows through the wiring resistance having the total wiring resistance value of 23.8 [Ω]. The voltage value is 1.9 [V], and the sum of these voltage values exceeds 12 [V] which is the power supply voltage Vdd. Accordingly, when the voltage value applied to the organic EL element is calculated again, when X = 96 (that is, when all the organic EL elements connected to one scanning electrode emit light), the current flowing through the wiring resistance is one organic The voltage applied to the wiring resistance is equal to the total current value Iall multiplied by 23.8 [Ω], which is equal to the total current value Iall that is 96 times the current value flowing through the EL element. The sum of the voltage applied to the wiring resistance and the voltage value Vrel applied to the organic EL element is 12 [V]. It can be seen that the voltage value Vrel applied to the organic EL element satisfying these relationships is 10.54 [V] with reference to FIG. Therefore, the voltage value applied to the wiring resistance is 1.46 [V], and β at this time is a ratio of these voltages, and can be calculated as 0.14.

  Referring to FIG. 10, the current value that flows when one organic EL element emits light (when X = 1) is the same as when all 96 organic EL elements connected to one scan electrode emit light (X It can be seen that the current value is 1.29 times that of the current flowing in (= 96). As described above, since it is known that the current flowing through the organic EL element and the light emission luminance are in a substantially proportional relationship, the peak luminance ratio is 1.29 times. Thus, it is preferable that the peak luminance rate is larger than 1 in order to make the display on the display device more vivid. When there are few organic EL elements that emit light, the organic EL element having the peak luminance makes the display more vivid. . However, as the peak luminance ratio increases, the deterioration rate of the element increases and the display life is shortened. Therefore, in consideration of such a suitable balance between the beauty of display and the length of display life, the peak luminance ratio is approximately It can be said that it is preferable to set the value from 1.2 to 2.0. In this way, setting the peak luminance ratio within a predetermined range by providing the scanning electrode wiring with a resistance value larger than 0 while extending the display life of the organic EL element by adjusting the wiring resistance value in this way It can be said that this is a matter that should be taken into consideration when determining each wiring resistance value in the apparatus.

  Here, the total resistance value of the scan electrode and the data electrode is set to approximately 0 [Ω]. However, when the total resistance value is considerably larger than 0 [Ω], the organic EL connected to the scan electrode or the data electrode is used. Since the luminance of the element may vary, it is preferable that the total wiring resistance value (Rs + Rd) is appropriately set according to the wiring resistance as described above. As a method for appropriately setting the wiring resistance, it is conceivable to adjust the sheet resistance value, the wiring length, and the wiring width (or wiring depth) of each wiring as described above. For example, if the length of this wiring is 3000 μm and the wiring width is 10 μm, the sheet resistance value of the data electrode wiring is 4.4 [Ω / □] from the above equation (24), and the sheet resistance value of the scanning electrode wiring is 0.03 [Ω / □].

<3. Effect>
As described above, the display device of this embodiment does not insert a resistance element in series with respect to each organic EL element, but from a power source connected to a scan electrode or a data electrode for flowing a current to the organic EL element. Β or β ′ is adjusted by appropriately adjusting any one or more of the resistance of the wiring, typically the sheet resistance value of the wiring, the length of the wiring, and the width of the wiring, and the range of β 0.1 ≦ β ≦ 10 (or the range of β ′ is 0.1 ≦ β ′ ≦ 10), more preferably 0.1 ≦ β ≦ 9.0 (or the range of β ′ is 0.1 ≦ β ′ ≦ 9.0), and even more preferably by setting the range of β to 0.1 ≦ β ≦ 5.0 (or the range of β ′ to 0.1 ≦ β ′ ≦ 5.0), With a simple configuration, it is possible to extend the display life by compensating the luminance deterioration with time of the electro-optic element.

  Further, the display device of the present embodiment has a configuration in which the scan electrodes corresponding to the odd rows and the scan electrodes corresponding to the even rows among the scan electrodes SL1 to SL64 are connected to the scan electrode wirings corresponding to the left and right alternately. While mitigating variations in luminance of the organic EL elements in the left-right direction of the screen, it is possible to extend the display life by compensating for the time-dependent luminance deterioration of the electro-optic elements with a simple configuration.

  Further, the scanning electrode wirings connected to the scanning electrodes at closer positions are bent to the left and right so that all the scanning electrode wirings Ls1 to Ls64 have the same wiring length. Scanning connected to the scanning electrode SL64 which is configured to have a wiring shape, or the wiring width of the scanning electrode wiring Ls1 connected to the scanning electrode SL1 arranged at the uppermost position in the drawing is the largest. The wiring of all the scanning electrode wirings Ls1 to Ls64 is adjusted by appropriately adjusting the configuration in which the wiring width of the electrode wiring Ls64 is minimized and the wiring depth of each scanning electrode wiring (the film thickness of the wiring in the direction perpendicular to the display surface). Make the resistances approximately the same. Thus, while eliminating or reducing the luminance variation of each organic EL element in the vertical direction, it is possible to extend the display life by compensating the luminance deterioration with time of the electro-optic element with a simple configuration.

<4. Modification>
<4.1 Main modification>
The constant voltage power supply 400 provided in the display device in the above embodiment is configured to output the power supply voltage Vdd (12 [V]) regardless of the driving load. As described above, such a constant voltage power supply is pulsed. As described above with reference to FIG. 7, the same effect of extending the display life can be obtained even if the power supply is replaced. Therefore, the display device according to this main modification is provided with a pulse power supply that outputs a pulse voltage of 12 [V] instead of the constant voltage power supply 400 of the above embodiment. Since other components are the same as those in the above embodiment, the description thereof is omitted.

  Since this pulse power supply can control the average current density, the internal temperature of the organic EL element can be kept lower than the constant voltage power supply. The organic EL element is known to have a display life that is abruptly shortened when its internal temperature rises. Further, as shown in Non-Patent Document 1, the organic EL element depends on the magnitude of the time average current density. It is also known that the display lifetime is determined.

Here, the light emission voltage of the organic EL element is Vel, the current density is Ael [mA / cm ² ], the duty number for driving the pulse power supply is Y (Y is a natural number), and these ratios are γ (= When Ael / Y), the power density P [W / cm ² ] can be expressed as the following equation (34).
P = γ / 1000 * Vel (34)

In general, when the power density P is 0.1 [W / cm ² ] or less, the temperature rise of the organic EL element can be suppressed to about several degrees. Therefore, the above equation (34) is used to suppress the temperature increase. Substituting P = 0.1 or less into can be expressed as in the following equation (35).
0.1 ≧ γ / 1000 * Vel (35)

  As described above, the light emission voltage of the organic EL element is preferably 2 [V] to 20 [V]. Therefore, when Vel = 2 to 20 is substituted into the above equation (35), the preferable range of γ is Vel. Depending on the value, the value is 50 to 5. Further, as described above, since the light emission voltage of the organic EL element is more preferably 2 [V] to 18.2 [V], it is more preferable to substitute Vel = 2 to 18.2 into the above equation (35). The range of γ is a value from 50 to 5.5 depending on Vel. Further, as described above, since the light emission voltage of the organic EL element is more preferably from 2 [V] to 10.9 [V], it is more preferable to substitute Vel = 2 to 10.9 into the above equation (35). The range of γ is a value from 50 to 9.2 depending on Vel.

  Next, in the display device according to the main modification example, the light emission voltage of the organic EL element that has the effect of extending the display life in relation to the increase in the internal temperature will be specifically examined with reference to FIG.

FIG. 11 is a diagram showing the relationship between the current density and the light emission voltage of the organic EL element having the characteristics shown in FIG. Here, when the duty factor of the pulse power source is 64, which is used relatively, and the emission voltage is 10.9 [V], the current density of the organic EL element for suppressing the temperature rise is given by the above equation (35). When calculated more, it must be 587 [mA / cm ² ] or less. However, referring to FIG. 11, since the actual current density is 2874 [mA / cm ² ], there is an effect of extending the display life similar to the display device in the above embodiment, but in this case, the inside of the organic EL element The display life is shortened due to the temperature rise.

Therefore, since the current density of the organic EL element for suppressing the temperature increase calculated from the above equation (35) is 587 [mA / cm ² ] or less, the temperature increase can be suppressed with reference to FIG. When the emission voltage of the organic EL element is obtained, it is found that it is approximately 9.1 V or less. Therefore, in this display device using a pulse power supply, the light emission voltage of the organic EL element may be 10.9 V in order to obtain the same display life extension effect as the display device using the constant voltage power supply described above. In order to obtain the effect of extending the display life by suppressing the increase in the internal temperature of the organic EL element, the light emission voltage is preferably 9.1 V or less. In this case, the voltage applied to the wiring resistance is 2.9 V or more. Therefore, it can be said that it is more preferable to adjust the wiring resistance value so that such a voltage is applied.

  From the above examination results, in order to obtain an effect of extending the display life by suppressing the increase in the internal temperature of the organic EL element when the duty number of the pulse power supply is 64, the light emission voltage of the organic EL element is 2 [ Since V] to 9.1 [V] is even more preferable, if Vel = 2 to 9.1 is substituted into the above equation (35), a more preferable range of γ is from 50 to 11 depending on Vel. Value.

<4.2 Other Modifications>
In the above-described embodiment, the wiring resistances of the scan electrode wiring and the data electrode wiring are appropriately adjusted. Instead of adjusting these wiring resistances, a known resistor or resistance substance is inserted. A resistance value corresponding to the wiring resistance value may be given.

  In the above embodiment, among the scan electrodes SL1 to SL64, the scan electrodes corresponding to the odd rows and the scan electrodes corresponding to the even rows are connected to the scan electrode wirings corresponding to the left and right alternately, but the data electrodes DL1 to DL96 are used. Of these, the data electrode corresponding to the odd-numbered column and the data electrode corresponding to the even-numbered column may be connected to the data electrode wiring corresponding to the top and bottom alternately. In this case, the organic EL elements farthest from the constant voltage power source 400 can be arranged so as to alternately be the upper end or the lower end for each column. With this configuration, the luminance variations of the organic EL elements in the vertical direction of the display screen are averaged as a result, thereby reducing the luminance variations.

  In the above embodiment, the scanning electrode wirings Ls1 to Ls64 have the same wiring length. For example, the scanning electrode wiring connected to the scanning electrode at a closer position is bent to the left and right, thereby passing a longer detour. Although the wiring shape is as described above, all the data electrode wirings Ld1 to Ld96 may be configured to have the same wiring length. In the above embodiment, the scanning electrode wiring Ls1 connected to the scanning electrode SL1 arranged at the uppermost position in the drawing has the largest wiring width, and the scanning electrode connected to the scanning electrode SL64 arranged at the lowermost position in the drawing. The wiring resistance of all the scanning electrode wirings Ls1 to Ls64 is adjusted by appropriately adjusting the configuration in which the wiring width of the wiring Ls64 is minimized and the wiring depth of each scanning electrode wiring (the film thickness of the wiring in the direction perpendicular to the display surface). Are substantially the same, but the wiring resistances of the data electrode wirings Ld1 to Ld96 may be substantially the same with the same configuration. By these things, the brightness dispersion | variation of each organic EL element in the left-right direction of a figure can be eliminated or reduced.

  Since the present invention can be applied regardless of the shape and size of the light-emitting element, even if the shape of the light-emitting element such as a power meter portion, a numerical portion, or a clock in an automobile speedometer is different, for example, the scanning electrode line Has a constant voltage circuit that supplies or cuts off the current to the light emitting element at a predetermined timing according to the image signal in a state where it is always in a selected state, that is, a predetermined low voltage or ground voltage. A display device configuration in which the range is 0.1 to 10, more preferably β is in the range 0.1 to 9.0, and even more preferably β is in the range 0.1 to 5.0. It is sufficient if there are various display devices such as a segment system, and the same effect as that of the above embodiment is achieved.

FIG. 3 is a circuit diagram illustrating an electro-optical element when a single light is emitted for explaining the principle of a display device according to an embodiment of the present invention. In order to explain the principle of the display device according to the embodiment, it is a circuit diagram showing these elements when a resistance element is inserted in series with the electro-optic element. FIG. 5 is a diagram showing an equivalent circuit diagram when one scan electrode is selected in a simple matrix display device using a constant voltage control method in order to explain the principle of the display device according to the embodiment. It is a figure which shows the equivalent circuit by which 220 organic EL elements were connected in parallel with respect to direct-current constant voltage power supply, in order to demonstrate the principle of the display apparatus which concerns on the said one Embodiment. FIG. 5 is a diagram showing the time-dependent change in the normalized light emission luminance of the organic EL element shown in FIG. 4 in order to explain the principle of the display device according to the one embodiment. It is a figure which shows the equivalent circuit which connected the organic EL element and insertion resistance in series with respect to the pulse power supply in order to demonstrate the principle of the display apparatus which concerns on the said one Embodiment. FIG. 7 is a diagram showing a time-dependent change in the emission luminance of the organic EL element shown in FIG. 6 in order to explain the principle of the display device according to the embodiment. It is a figure which shows simply the whole structure of the display apparatus which concerns on one Embodiment of this invention. It is a top view which shows simply the wiring structure of the display panel in the said one Embodiment. It is a figure which shows the relationship between the light emission voltage of one organic EL element used for the display apparatus which concerns on the said one embodiment, its internal resistance value, and the electric current value which flows. It is a figure which shows the relationship between the current density and light emission voltage about the organic EL element which has the characteristic shown by FIG. 10 in the said one Embodiment. It is a figure which shows the fall of the light emission luminance with time passage of the organic EL element by the constant voltage type control system and the constant current type control system in the conventional example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Organic EL element 100 ... Display panel 101 ... Odd scan electrode connector 102 ... Data electrode connector 103 ... Even scan electrode connector 200 ... Scan electrode drive circuit 300 ... Data electrode drive circuit 400 ... Constant voltage power supply SL1-SL64 ... Scan electrode DL1 To DL96 ... data electrodes Ls1 to Ls64 ... scanning electrode wiring Ld1 to Ld96 ... data electrode wiring Rd ... wiring resistance value of data electrode Rs ... wiring resistance value of scanning electrode Rel ... internal resistance value during emission of electro-optic element Rr ... insertion Resistance value Vel: Voltage value applied to electro-optic element Vr: Voltage value applied to insertion resistance element (insertion resistance value Rr) Vdd: Power supply voltage

Claims (24)

A first and a second electrode; an electro-optical element that is arranged at an intersection of the first and second electrodes and emits light when a current is applied; and a constant voltage that supplies a current to be supplied to the electro-optical element A display device comprising: a power source; first switch means for selectively grounding the first electrode; and second switch means for selectively applying a voltage from the constant voltage power source to the second electrode. Because
The first resistance value Rs from the electro-optical element that emits light until it is grounded via the first switch means and the constant-voltage power source that is connected from the electro-optical element that emits light via the second switch means The second resistance value Rd up to is the ratio of the sum of the first resistance value Rs and the second resistance value Rd to the resistance value Rel at the time of light emission of the electro-optic element β (= (Rs + Rd) / Rel ), The display device is set to satisfy 0.1 ≦ β ≦ 10.   The display device according to claim 1, wherein the first resistance value Rs and the second resistance value Rd are set to satisfy 0.1 ≦ β ≦ 9.0.   The display device according to claim 2, wherein the first resistance value Rs and the second resistance value Rd are set to satisfy 0.1 ≦ β ≦ 5.0.   The first electrode is formed of a metal layer composed of Cr alone, a laminated structure of Cr and Ta, a laminated structure of Cr and ITO, or a laminated structure of Cr, Ta, and ITO. The display device according to claim 1.   The display device according to claim 1, wherein the second electrode is made of ITO. A first wiring that connects the first electrode and the first switch means; and a second wiring that connects the second electrode and the second switch means;
By setting at least one of a wiring length, a wiring width, and a wiring sheet resistance value in at least one of the first and second wirings to a predetermined value, the first resistance value Rs and the second resistance value are set. The display device according to claim 1, wherein a resistance value Rd is set. A plurality of the first and second wirings are provided,
7. The display device according to claim 6, wherein at least one of the first and second wirings has substantially the same wiring resistance in the plurality of wirings because the wiring lengths in the plurality of wirings are substantially equal. . A plurality of the first and second wirings are provided,
7. The wiring resistance of the plurality of wirings is substantially the same by setting a wiring width of at least one of the first and second wirings according to a wiring length of the plurality of wirings. The display device described in 1. A plurality of the first and second wirings are provided,
The wiring resistance of the plurality of wirings is substantially the same as at least one of the first and second wirings, wherein a wiring depth is determined according to a wiring length of the plurality of wirings. 6. The display device according to 6. A first electrode that is a plurality of parallel electrodes extending in a predetermined direction; a second electrode that is a plurality of parallel electrodes extending in a direction orthogonal to the first electrode; and the first and second electrodes A plurality of electro-optic elements arranged in a matrix corresponding to the intersections of the electrodes, forming a plurality of pixels, a constant voltage power source for supplying a current to be passed to the electro-optic elements, and the first electrode Comprising: first switch means for selectively grounding each other for a predetermined period; and second switch means for selectively applying a voltage from the constant voltage power source to the second electrode,
When the number of the second electrodes to which the voltage from the constant voltage power source is selectively applied by the second switch means within the predetermined period is X, all the electro-optical elements that emit light are A first resistance value Rs until grounded via one switch means and a third resistance until all light-emitting electro-optic elements are connected to the constant voltage power source via the second switch means The value (Rd / X) is a ratio of the sum of the first resistance value Rs and the third resistance value (Rd / X) to the total resistance value Reall of all the light-emitting electro-optic elements, β ′ (= ( Rs + Rd / X) / Relall), the display device is set to satisfy 0.1 ≦ β ′ ≦ 10.   The display according to claim 10, wherein the first resistance value Rs and the third resistance value (Rd / X) are set to satisfy 0.1 ≦ β ′ ≦ 9.0. apparatus.   The display according to claim 11, wherein the first resistance value Rs and the third resistance value (Rd / X) are set to satisfy 0.1 ≦ β ′ ≦ 5.0. apparatus.   The first electrode is formed of a metal layer composed of Cr alone, a laminated structure of Cr and Ta, a laminated structure of Cr and ITO, or a laminated structure of Cr, Ta, and ITO. The display device according to claim 10.   The display device according to claim 10, wherein the second electrode is made of ITO. A first wiring that connects the first electrode and the first switch means; and a second wiring that connects the second electrode and the second switch means;
By setting at least one of a wiring length, a wiring width, and a wiring sheet resistance value in at least one of the first and second wirings to a predetermined value, the first resistance value Rs and the third resistance value are set. The display device according to claim 10, wherein a resistance value (Rd / X) is set.   At least one of the first electrode and the second electrode is connected to a corresponding first or second wiring at an end which is a different side between two electrodes adjacent in parallel. The display device according to claim 15. A plurality of the first and second wirings are provided,
16. The display device according to claim 15, wherein at least one of the first and second wirings has substantially the same wiring resistance in the plurality of wirings because the wiring lengths in the plurality of wirings are substantially equal. . A plurality of the first and second wirings are provided,
16. At least one of the first and second wirings has a wiring width determined according to a wiring length in the plurality of wirings, whereby wiring resistances in the plurality of wirings are substantially the same. The display device described in 1. A plurality of the first and second wirings are provided,
The wiring resistance of the plurality of wirings is substantially the same as at least one of the first and second wirings, wherein a wiring depth is determined according to a wiring length of the plurality of wirings. 15. The display device according to 15. The constant voltage power supply is a pulse power supply,
When the light emission voltage of the electro-optical element is set to 2 [V] to 20 [V], the current density Ael [mA / mA flowing through the electro-optical element with respect to the duty number Y (Y is a natural number) for driving the pulse power source. 11. The display device according to claim 1, wherein a ratio γ (= Ael / Y) of cm ² ] is set within a range of 50 to 5. 11.   21. The ratio γ is determined within a range of 50 to 5.5 when a light emission voltage of the electro-optical element is 2 [V] to 18.2 [V]. Display device.   The display according to claim 21, wherein when the light emission voltage of the electro-optic element is 2 [V] to 9.1 [V], the ratio [gamma] is set within a range of 50 to 11. apparatus.   11. The display device according to claim 1, wherein the electro-optic element is gradation-controlled with a binary value so as to be in a light emitting state or a non-light emitting state.   The display device according to claim 1, wherein the electro-optic element is an organic electroluminescence element.

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