Display apparatus

A display device which includes a substrate having a pixel unit that receiving first and second voltages is disclosed. In one aspect, the first and second power lines are coupled to the first and second voltages, and are supplied to the pixel unit via first and second power pads. In some aspects, the first and second power pads are alternately disposed while being spaced apart from each other in at least a portion of the peripheral area, and the second power pads are disposed in the space between the respective first power pads.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to and the benefit of Korean Patent Application No. 10-2012-0108568, filed on Sep. 28, 2012, in the Korean Intellectual Property Office, the entire content of which is incorporated herein by reference. Any and all applications for which a foreign or domestic priority claim is identified in the Application Data Sheet as filed with the present application are hereby incorporated by reference under 37 CFR 1.57.

BACKGROUND

The present disclosure relates to a flat panel display, specifically, to a display driven by varying voltage levels.

2. Description of the Related Technology

Organic light emitting display devices display images using organic light emitting diodes (OLEDs) that emit light through recombination of electrons and holes. Since the OLED display device has a fast response speed and is driven with low power consumption, if it has been identified as a next-generation display.

Generally, the OLED display device includes a pixel unit having a matrix of pixels, driving circuits for supplying driving signals to the pixel unit, and a power supply circuit for supplying pixel power to the pixel unit.

When a scan signal is supplied to each pixel, the pixel is synchronized with a gate signal so as to emit light with luminance corresponding to a data signal.

However, in the OLED display device, the emission luminance of the pixels is influenced by the applied voltage level. That is, the voltage applied to a pixel, or pixel power, becomes a factor in the resulting emission luminance of the pixels, in addition to the data signal.

Therefore, the same voltage should be applied to each pixel so as to display images having uniform image quality.

However, pixel power is a DC voltage determined by the difference between a power supply voltage having a high voltage level and a ground voltage having a low voltage level. While passing through a power line, a voltage drop (IR drop) occurs in the power voltage, and a voltage rise (IR rise) occurs in the ground voltage.

In the case where the voltage drop and the voltage rise overlap with each other, the luminance inequality of the display panel increases, and white spots may be locally produced.

Particularly, as the display panel of the display device becomes large in size, the length of the power line is lengthened, and therefore, the difference in luminance between the pixels may be increased according to distances from power pads for receiving pixel power supplied from the power supply circuit.

SUMMARY

Embodiments described herein provide a display device for reducing luminance inequality.

Various embodiments reduce luminance inequality. One aspect relates to a display device, comprising a substrate having a pixel unit configured to display an image powered by a first voltage and second voltage, wherein the first and second voltages are different; a peripheral area at the outside of the pixel unit; first power lines through which the first voltage is supplied to the pixel unit; second power lines through which the second voltage is supplied to the pixel unit; and first power pads electrically coupled to the first power lines configured to provide the first voltage to the first power lines; and second power pads electrically coupled to the second power lines configured to provide the second voltage to the second power lines; wherein the first and second power pads are alternately disposed in at least a portion of the peripheral area, the first power pads being spaced apart from each other, and the second power pads being disposed in the space between the first power pads.

In some embodiments, the first and second power pads are spaced apart from each other at a constant interval.

In some embodiments, the first and second power pads are arranged along at least two sides of the substrate.

In some embodiments, the first and second power pads are arranged along opposite sides of the substrate such that at least one of the first power pads is aligned opposite another of the first power pads.

In some embodiments, the first and second power pads are arranged on opposite sides of the substrate such that at least one of the first power pads is aligned opposite one of the second power pads.

In some embodiments, the first and second power lines are disposed substantially parallel to each other, the first and second power lines forming a pair.

In some embodiments, the first and second power pads have equivalent dimensions.

In some embodiments, the first voltage is a high voltage relative to the second voltage and the second power is a low voltage relative to the first voltage.

In some embodiments, the pixel unit comprises pixels which each comprise an organic light emitting diode.

DETAILED DESCRIPTION

Hereinafter, some exemplary embodiments according of a display device will be described with reference to the accompanying drawings. Here, when a first element is described as being coupled to a second element, the first element may be not only directly coupled to the second element but may also be indirectly coupled to the second element via a third element. Further, some of the elements that are not essential to the complete understanding of the invention are omitted for clarity. Also, like reference numerals refer to like elements throughout.

FIG. 1is a block diagram illustrating the structure of a display device according to an embodiment of the present invention.

Referring toFIG. 1, the display device1000includes a pixel unit100having a plurality of pixels P11to Pnm coupled to gate lines S1to Sn and data lines D1to Dm, a data driver110that outputs a data voltage corresponding to an input image to each pixel P11to Pnm through the data lines D1to Dm, a gate driver120that outputs scan signals to each pixel P11to Pnm through the gate lines S1to Sn, and a timing controller130that generates control signals and outputs the generated control signals to the data driver110and the gate driver120.

The gate driver120may perform an operation of outputting an emission control signal to a plurality of emission control lines (not shown) connected to the plurality of pixels, as well as the scan signals.

The pixel unit100has the pixels P11to Pnm positioned at intersection portions of the gate lines S1to Sn and the data lines D1to Dm. The pixels P11to Pnm may be arranged in an n×m matrix as shown inFIG. 1.

Each of the pixels P11to Pnm includes a light emitting device, and receives a first power ELVDD as a high power voltage and a second power ELVSS as a low power voltage, which are supplied from the outside of the pixel unit100, which power the light emitting device (organic light emitting diode).

Each pixel P11to Pnm allows the light emitting device to emit light with luminance corresponding to a data voltage by supplying driving current or voltage to the light emitting device.

Each pixel P11to Pnm controls the amount of current supplied to the light emitting device, corresponding to the data voltage provided through the data lines D1to Dm, and the light emitting device emits light with luminance corresponding to the data voltage.

The timing controller130receives an input image signal and an input control signal for controlling display of the input image signal from an external graphic controller (not shown). The timing controller130generates an input image data DATA, a source start pulse SSP, a source shift clock SSC, a source output enable SOE, etc. from the input image signal and the input control signal, and provides them to the data driver110.

The timing controller130generates a gate driving clock CPV, a start pulse STV, etc., and outputs them to the gate driver120.

FIG. 2is a circuit diagram illustrating the structure of an embodiment of a pixel shown inFIG. 1.

The organic light emitting display device depicted inFIG. 2is exemplary, and should not be construed as limiting pixel unit100provided in display device1000shown inFIG. 1.

Referring toFIG. 2, the pixel Pij according to this embodiment includes an OLED as a light emitting device, and a pixel circuit101.

The OLED receives driving current IOLEDinput from the pixel circuit101so as to emit light. The luminance of the light emitted from the OLED is changed depending on the amplitude of the driving current IOLED.

The pixel circuit101includes a capacitor C1, a driving transistor M1and a switching transistor M2.

The driving transistor M1includes a first terminal D to which a first power ELVDD is supplied, a second terminal S coupled to an anode of the OLED, and a gate terminal coupled to a second terminal of the switching transistor M2.

The anode of the OLED is coupled to the second terminal S of the driving transistor M1, and a cathode of the OLED is coupled to a second power ELVSS.

The switching transistor M2includes a first terminal coupled to a data line Dj, a second terminal coupled to the gate terminal of the driving transistor M1, and a gate terminal coupled to a scan line S1.

The capacitor C1is coupled between the gate terminal and the first terminal D of the driving transistor M1.

If a scan signal having a gate-on level is applied to the switching transistor M2through the scan line Si, a data voltage supplied from data line Dj is applied to the gate terminal of the driving transistor M1and a first terminal of the capacitor C1through the switching transistor M2. While a data voltage is applied through the data line Dj, a voltage level corresponding to the data voltage is charged in the capacitor C1.

The driving transistor M1generates driving current IOLEDaccording to the voltage level of the data voltage and outputs the generated driving current IOLEDto the OLED.

The OLED receives the driving current IOLEDinput from the pixel circuit101, so as to emit light with luminance corresponding to the data voltage.

FIG. 3is a plan view illustrating the structure of first and second power pads which provide power to the pixel unit ofFIG. 1.FIG. 4is a graph illustrating voltage levels of the first and second powers at points A, B and C shown inFIG. 3.

Referring toFIG. 3, first and second power lines20and30and first and second power pads25and35are formed on a substrate10. Although not shown in this figure, the data and gate drivers110and120described above may also be mounted on the substrate10.

The substrate10is implemented as a transparent insulating substrate. The substrate10has the pixel unit100for displaying an image and a peripheral area (SA) at the outside of the pixel unit100.

The pixel unit100may be disposed in a central portion of the substrate10. The first and second powers ELVDD and ELVSS that are static voltage DC powers having voltage levels different from one another are supplied to the pixel unit100.

In this embodiment, the first power ELVDD is a high power voltage having a high voltage level, and the second power ELVSS is a low power voltage having a low voltage level. For example, the first power ELVDD may have a positive voltage level of 15V, and the second power ELVSS may have a negative voltage level of −5V or a ground voltage level of 0V.

The first power lines20and the second power lines30supply the respective first and second powers ELVDD and ELVSS to the pixel unit100. The first and second power lines20and30are disposed in parallel with each other while forming a pair.

Although not shown in detail in this figure, the first and second power lines20and30are extended into the pixel unit100so as to form a network, and may supply the first power ELVDD and the second power ELVSS to each pixel P11to Pnm. Alternatively, the first and second power lines20and30may be respectively coupled to conductive layers formed to overlap with the pixel unit100. In this case, the conductive layers may be electrically coupled to the respective pixels P11to Pnm through contact holes so as to supply power

The first and second power lines20and30may be formed of a transparent conductive material or low-resistive metal such as molybdenum (Mo), silver (Ag), titanium (Ti), aluminum (Al) or copper (Cu), or may be formed into a stacked structure of the metals.

The first power pads25are electrically coupled to the first power lines20so as to provide the first power ELVDD applied from the outside, and the second power pads35are electrically coupled to the second power lines30so as to provide the second power ELVSS applied from the outside.

Here, the first power ELVDD may include sub-powers having different voltage levels, which are respectively supplied to red, green and blue pixels. The second power pads25may also include a plurality of sub-power pads (not shown) corresponding to the respective sub-powers.

The first and second power pads25and35are alternately disposed while being spaced apart from each other in at least a portion of the peripheral area SA.

As one embodiment, the first and second power pads25and35may be arranged along one side11of the substrate10and the other side12opposite to the one side11of the substrate10. Here, the first and second power pads25and35arranged along the one side11and the first and second power pads25and35arranged along the other side12may be arranged symmetrical to each other.

The first and second power pads25and35may have the same area. The first and second power pads25and35may be formed of the same material in the same layer as the first and second power lines20and30.

As another embodiment, the first and second power pads25and35may be formed in a region protruded outward from the one side11of the substrate10.

A pad portion of a driving circuit board (not shown) that supplies the first power ELVDD and the second power ELVSS is electrically coupled to the first and second power pads25and35. For the purpose of the coupling, an anisotropic conductive film may be interposed between the pad portion of the driving circuit board and the first and second power pads25and35.

As described above, the power for driving the pixel unit100is a DC power determined by the difference between the first power ELVDD and the second power ELVSS. While the power for driving the pixel unit100passes through the first and second power lines20and30, a voltage drop (IR drop) occurs in the first power ELVDD having a high voltage level, and a voltage rise (IR rise) occurs in the second power ELVSS having a low voltage level.

However, since a power voltage pad and a ground voltage pad are disposed adjacent to each other while forming a pair, like connection lines, in the related art display device, the voltage drop and voltage rise overlaps with each other in a region between the pads, and therefore, the luminance inequality of the display panel increases. Accordingly, white spots may be locally produced.

According to this embodiment, the second power pads35are disposed in central regions between the respective first power pads25, so that it is possible to prevent the phenomenon that the voltage drop and voltage rise overlap with each other and to minimize the luminance inequality of the display panel, thereby improving image quality.

Specifically, the first and second power pads25and35are alternately disposed along the one side11of the substrate10, and are preferably spaced apart from each other at a constant interval so as not to be adjacent to each other or to be biased to any one side.

The distribution of voltage levels of the first and second powers ELVDD and ELVSS at the points A, B and C ofFIG. 3will be described with reference toFIG. 4.

The voltage drop of the first power ELVDD does not occur at the points A and B at which the first power pads25are positioned, but the voltage rise of the second power ELVSS occurs due to a spacing distance from the second power pads35. Therefore, A voltage Va, obtained by subtracting a voltage increment Vr from the first voltage level V1of the first power ELVDD, becomes a significant voltage level at the point A.

Here, the spacing distances of the points A and B from the point C at which the second power ELVSS is input are identical to each other, and hence the voltage increments Vr of the points A and B are identical to each other. As a result, the A voltage Va and the B voltage Vb are identical to each other.

The voltage rise of the second power ELVSS does not occur at the point C, where the second power pad35is positioned, but the voltage drop of the first power ELVDD occurs due to a spacing distance from the first power pads25. Therefore, C voltage Vc, obtained by subtracting a voltage decrement Vd from the first voltage level V1of the first power ELVDD, becomes a significant voltage level at the point C.

Here, the point C is the middle between the points A and B, and hence the line resistances of the power lines at the three points are identical to one another when being viewed from each point. Since the line resistances at the three points are identical to each other, the voltage decrement Vd at the point C is identical to the voltage increment Vr at the points A and B. As a result, the C voltage Vc, the A voltage Va and the B voltage Vb are identical to one another.

The points A, B and C are set based on any one point on the first and second power pads25and35, but the first and second power lines20and30extended from the first and second power pads25and35are extended in equal proportion at an equal ratio. Therefore, the voltage levels at the points A, B and C show a similar voltage-level distribution in the inside of the pixel unit100, as well as the first and second power lines20and30.

Although it has been described in this embodiment that the second power pads35are disposed in the central regions between the respective first power pads25, this is relative, and has the substantially same structure and effect as the first power pads25are disposed in the central regions between the respective power pads35.

As described above, the first and second power pads25and35are spaced apart from each other at a uniform interval so as not to be adjacent to each other or to be biased to any one side, so that the difference in voltage between the first and second power pads25and35can be equally distributed. Further, the difference between voltages supplied to the pixel unit100is equalized, so that it is possible to improve luminance inequality.

FIG. 5is a plan view illustrating the structure of first and second power pads according to another embodiment of the present invention. In this embodiment, components having the same reference numerals as those in the aforementioned embodiment may refer to the aforementioned descriptions, and therefore, their descriptions will be omitted to avoid redundancy.

Referring toFIG. 5, in the power pads according to this embodiment, first and second power pads25aand35aarranged along a first side11of the substrate10and first and second power pads25band35barranged along a second side12of the substrate10may be arranged to be across from each other.

The voltage level at a specific point on the substrate10is distorted in proportion to line resistance of the first and second power lines20and30, and the line resistance is determined according to spacing distances from the first and second power pads25band35b, to which the respective first and second powers ELVDD and ELVSS are supplied. Thus, the first and second power pads25band35bare distributed as equally as possible, so that it is possible to maximize uniformity of the line resistance.

In this embodiment, the first and second power pads25aand35aare disposed to be across from each other based on the width of the substrate10as well as the length direction of the substrate10, so that it is possible to simultaneously improve the equality of the voltage level distribution in the length direction of the substrate10and the equality of the voltage level distribution in the width direction of the substrate10.