KR101182237B1 - Light emitting display - Google Patents

Abstract

The light emitting display device includes a plurality of data lines for transmitting a data signal, a plurality of first scanning lines for transmitting a first selection signal, and a plurality of pixels defined by the data lines and the first scanning lines and each having a pixel circuit. The pixel of includes a plurality of first pixels emitting light of a first color and a plurality of second pixels emitting light of a second color. The pixel circuit includes a light emitting device that emits light in response to an applied current, a first switching device that transmits a data signal from a data line in response to a first selection signal from a scanning line, and a driving current for emitting the light emitting device. A transistor connected to the diode while the data signal is transmitted from the first switching element, a first storage element storing a first voltage corresponding to the data signal from the first switching element, and a first scan line and a control electrode of the transistor. A second storage connected between the second storage device and the second storage device to change the first voltage of the first storage device to a second voltage through coupling with the first storage device when the first selection signal changes from the first level to the second level. And a capacitance ratio of the first storage element and the second storage element of the pixel circuit formed in the first pixel to the pixel circuit formed in the second pixel. It is different from quantity ratio.

OLED, light emitting display device, pixel circuit

Description

Light emitting display device {LIGHT EMITTING DISPLAY}

 1 is a diagram schematically illustrating a configuration of an organic light emitting display device according to an exemplary embodiment of the present invention.

2 is an equivalent circuit diagram of a pixel circuit according to an exemplary embodiment of the present invention.

3 is a view showing a signal waveform applied to the recovery circuit.

The present invention relates to a light emitting display device, and more particularly, to an organic light emitting display device using light emission of an organic material.

In general, an organic light emitting display device is a display device using an organic light emitting device using light emission of an organic material. An N ㅧ M organic light emitting cells arranged in a matrix form are driven by voltage driving or current driving to display an image. The organic light emitting cell has a diode characteristic and is also referred to as an organic light emitting diode (hereinafter, referred to as an organic light emitting diode) and has a structure of an anode, an organic thin film, and a cathode electrode layer.

Such an organic light emitting device has a different light emission efficiency depending on the color to be displayed. In general, the light emitting efficiency of the organic light emitting device that displays green is the highest, and next, the light emitting efficiency of red and blue is the highest. Hereinafter, green, red, and blue are denoted by G, R, and B, respectively. Since the light emission efficiency varies depending on the colors R, G, and B to be displayed, the gray scales displayed by the light emitting elements of the respective colors are different even if the data voltages applied to the pixel circuits are the same. In addition, since the luminous efficiency is different for each color (R, G, B), the data voltage swing range per gray for each color causes a difference in color. Therefore, when the color coordinates are matched in full white, the gamma gray scales are different for green (G), red (R), and blue (B), and the color coordinates may be different because the swing range of the data voltage is different for each RGB at the halftone level. have.

SUMMARY OF THE INVENTION The present invention has been made in an effort to provide a light emitting display device capable of reducing a difference in swing range caused by color.

A light emitting display device according to the present invention includes a plurality of data lines for transmitting a data signal, a plurality of first scanning lines for transmitting a first selection signal, and a plurality of pixel circuits defined by the data lines and the first scanning lines, respectively. And a plurality of pixels, the plurality of pixels including a plurality of first pixels emitting light of a first color and a plurality of second pixels emitting light of a second color. The pixel circuit may include a light emitting device that emits light in response to an applied current, a first switching device that transmits a data signal from the data line in response to a first selection signal from the scan line, and emits the light emitting device. A transistor for diode driving while the data signal is transmitted from the first switching element, a first storage element for storing a first voltage corresponding to the data signal from the first switching element, and A connection between the first scan line and a control electrode of the transistor, and when the first selection signal changes from a first level to a second level, coupling of the first storage element to the first storage element; A second storage element for converting a first voltage to a second voltage, wherein the pixel circuit is formed in the first pixel; The capacitance ratio of the first storage element and the second storage element is different from the capacitance ratio of the pixel circuit formed in the second pixel.

A light emitting display device according to another aspect of the present invention includes a plurality of data lines for transmitting a data signal, a plurality of first scanning lines for transmitting a selection signal, and a plurality of pixels defined by the data lines and the first scanning lines. It includes a plurality of connected pixel circuits. The pixel circuit may include a first switching device having a first electrode connected to the data line, a control electrode connected to the first scan line, and a first electrode connected to a second electrode of the first switching device. A second switching element electrically connected to a first electrode of the first power supply, a second switching element connected between a control electrode and a second electrode of the transistor, and a control electrode connected to a first scan line, and the first power supply A first reservoir connected to the one electrode, and a second reservoir connected to the control electrode of the transistor, and a second reservoir connected between the control electrode of the transistor and the first scan line. The first and second pixel circuit groups have different capacity ratios of the reservoir and the second reservoir.

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. In the drawings, parts irrelevant to the description are omitted in order to clearly describe the present invention. Like reference numerals designate like parts throughout the specification.

Throughout the specification, when a part is "connected" to another part, this includes not only the "directly connected" but also the "electrically connected" between other elements in between. Also, when a part is referred to as "including " an element, it does not exclude other elements unless specifically stated otherwise.

Hereinafter, an organic light emitting diode display and a pixel circuit, which is an embodiment of the display device of the present invention, will be described in detail with reference to the accompanying drawings.

1 is a view schematically illustrating an organic light emitting display device according to an exemplary embodiment of the present invention.

As shown in FIG. 1, the organic light emitting diode display according to the exemplary embodiment includes a display unit 100, a scan driver 200, a data driver 300, and a light emitting signal driver 400.

The display unit 100 includes a plurality of data lines D1 -Dm extending in the column direction, a plurality of scanning lines S1 -Sn extending in the row direction, a plurality of emission control lines E1 -En, and a plurality of pixels. The pixel circuit 110 is formed in each pixel. The data lines D1 -Dm transmit a data signal representing an image signal to the pixel circuit 110, and the scan lines S1 -Sn transfer a selection signal to the pixel circuit 110.

Meanwhile, in order to implement color display, each pixel uniquely displays one color of the primary colors or each pixel alternately displays the primary colors with time, so that a desired color is recognized by a spatial or temporal sum of these primary colors. Examples of primary colors include red (R), green (G), and blue (B). In this case, when colors are displayed by a time sum, R, G, and B colors are alternately displayed in one pixel to realize one color. In the case of displaying colors by spatial sum, one color is implemented by three pixels of the R pixel, the G pixel, and the B pixel, so that each pixel is referred to as a subpixel and three subpixels are referred to as one pixel. In addition, in the case of displaying colors in a spatial sum, R pixels, G pixels, and B pixels may be alternately arranged in a row direction or a column direction, or three pixels may be arranged at positions corresponding to three vertices of a triangle. .

The scan driver 200 sequentially generates and applies selection signals to the scan lines S1 -Sn, and when defining terms relating to the scan lines, the scan line to which the current selection signal is to be transmitted is referred to as a "current scan line". The scanning line which transmitted the selection signal immediately before the selection signal is transmitted is referred to as the "previous scanning line".

The data driver 300 generates and applies a data voltage corresponding to the image signal to the data lines D1 -Dm.

The light emission control driver 400 sequentially applies a light emission control signal for controlling light emission of the organic light emitting diode to the light emission control lines E1 to En.

The scan driver 200, the data driver 300, and / or the light emission control driver 400 may be electrically connected to the display panel 100, or may be attached to the display panel 100 and electrically connected to the tape carrier package. Tape carrier package, TCP) may be mounted in the form of a chip. Alternatively, the display panel 100 may be mounted in a flexible printed circuit (FPC) or a film that is adhered to and electrically connected to the display panel 100 in the form of a chip. Alternatively, the scan driver 200, the data driver 300, and / or the light emission control driver 400 may be directly mounted on the glass substrate of the display panel, or the scan line, data line, emission control line, and thin film transistor may be mounted on the glass substrate. It may be replaced by a drive circuit formed of the same layers as or directly mounted.

2 is an equivalent circuit diagram illustrating a pixel circuit 110 according to a first embodiment of the present invention.

As shown in FIG. 2, the pixel circuit 110 includes five transistors M1-M6, two capacitors C1 and C2, and an organic light emitting diode OLED. The six transistors M1-M6 use a p-channel metal oxide semiconductor (PMOS) transistor. These transistors M1-M6 have two electrodes and a gate electrode forming a source electrode and a drain electrode. An organic light emitting diode (OLED) has a diode characteristic and is called an organic light emitting diode, and generally has a structure of an anode electrode, an organic thin film, and a cathode electrode.

The transistor M1 is a driving transistor for driving the organic light emitting diode OLED. The transistor M1 is connected between the power supply for supplying the voltage VDD and the organic light emitting diode OLED, and is applied to the gate by the voltage applied to the gate. The current flowing through the OLED is controlled through the OLED. The transistor M4 is connected between a power supply for supplying the voltage VDD and a power supply for supplying the initial voltage Vinit, and when the transistor M4 is turned on in response to a selection signal from the immediately preceding scan line Sn-1, The initial voltage Vinit is transferred to the gate of the transistor M1. The transistor M2 has a source and a drain connected to the gate and the drain of the transistor M1, respectively, and diode-connects the transistor M1 in response to a selection signal from the current scan line Sn. The transistor M3 has a source and a drain connected to the data line and the source of the transistor M1, respectively, and applies the data voltage VDATA to the source electrode of the transistor M1 in response to a selection signal from the current scan line Sn. To pass. The transistor M5 connects a power supply for supplying the transistor M1 and the voltage VDD in response to an emission control signal of the emission control line En. The transistor M6 is connected between the transistor M1 and the organic light emitting element OLED, and flows through the transistor M1 to the organic light emitting element OLED in response to a light emission control signal from the light emission control line En. Transfer current. The capacitor C1 is connected between the transistor M4 and a power supply for supplying the voltage VDD. When the transistor M4 is turned on, the capacitor C1 is charged with a voltage VDD-Vinit corresponding to the difference between the voltage VDD and the initial voltage Vinit, and the gate electrode and the voltage VDD of the transistor M1 are charged. Maintain constant voltage between power supply. One capacitor is currently connected to the scan line Sn and the other electrode is connected to the gate electrode of the transistor M1. The capacitor C2 keeps the voltage difference between the selection signal from the current scan line Sn and the gate of the transistor M1 constant. The organic light emitting diode OLED is connected between the drain of the transistor M6 and the power supply VSS. In the pixel circuit 110 according to the exemplary embodiment of the present invention, the voltage level of the power supply VDD has a level higher than that of the power supply VSS.

Next, the operation of the pixel circuit 110 will be described with reference to FIG. 3. 3 is a diagram illustrating a signal waveform applied to the recovery circuit 110.

First, during the period D1, when the selection signal from the previous scan line Sn-1 is applied with a low level (enable level) scan voltage, the transistor M4 is turned on so that one end of the capacitor C1 is initialized. Initialized by Vinit, the voltage VDD-Vinit corresponding to the difference between the power supply voltage VDD and the initial voltage Vinit is charged.

Next, during the period D2, the selection signal from the current scan line Sn becomes a low level (enable level Vlow), and the transistors M2 and M3 are turned on. When the transistor M2 is turned on, the transistor M1 is diode-connected in the forward direction by the initial voltage Vinit applied to the gate of the transistor M1. The data voltage VDATA is transferred to the source electrode of the transistor M1 through the turned-on transistor M3. Then, the voltage difference between the gate and the source of the diode-connected transistor M1 changes until the threshold voltage VTH of the transistor M1 is applied, and the voltage VDATA + VTH is applied to the gate electrode of the transistor M1. Accordingly, voltages VDATA + VTH and Vlow are applied to both ends of the capacitor C2, and the voltages VDATA + VTH -Vlow are charged to the capacitor C2.

Next, in the period D3, the selection signal from the current scanning line Sn becomes a high level (disable level, Vhigh), and the emission control signal from the emission control line E _n is a low level (enable level). , Vlow turns on the transistors M5 and M6 in response to the emission control signal. Then, in the period D2, the drain electrode and the source electrode of the transistor M1 are changed to the source electrode and the drain electrode, respectively, in the period D3. The voltage VDD is applied to the source electrode of the transistor M1, and the voltage VDATA + VTH applied during the period D2 to the gate electrode becomes the high level Vhigh as the selection signal from the current scan line Sn is high. Fluctuations occur.

When the selection signal from the current scan line Sn goes from the low level Vlow to the high level Vhigh, the voltage at the contact point of the capacitor C2 and the current scan line Sn increases by the level rising width ΔV _S of the selection signal. . Therefore, due to the coupling of the capacitors C1 and C2, the gate voltage V _G of the transistor M1 increases with respect to the voltage in the period D2, and the increase amount ΔV _G is expressed by Equation 1 below.

Since the gate voltage V _{G of the} transistor M1 has increased by ΔV _G , the current I _OLED flowing through the transistor M1 is expressed by Equation 2 below. That is, the magnitude of the gate-source voltage V _GS of the transistor M1 varies as the gate voltage V _{G of the} transistor M1 varies, and the magnitude of the drain current I _OLED of the transistor M1 also changes. It fluctuates accordingly. In the pixel circuit 110 according to the exemplary embodiment of the present invention, since the gate voltage of the transistor M1 is increased, the magnitude of the voltage V _GS decreases and the magnitude of the drain current I _OLED of the transistor M1 also decreases. .

In addition, in Equation 2, if the difference between the voltage VDATA and the voltage VDD is replaced with the voltage ΔV, and the above Equation 1 is substituted into ΔV _G , Equation 3 is obtained. If the ratio of the capacitor C1 to the capacitor C2 is defined as α (= C2 / C1), the equation (3) is summarized as in equation (4).

,

,

In Equation 4, ΔV _S is a voltage (Vhigh-Vlow) corresponding to the difference between the high level voltage and the low level voltage of the selection signal currently transmitted to the scan line Sn, and thus has a constant value and is transmitted to each pixel circuit of RGB. If the data voltages to be equal are the same, the voltage [Delta] V also has a constant value. Therefore, the current flowing through the organic light emitting diode OLED of each of the RGB pixel circuits is determined according to the ratio α of the organic light emitting diode OLED of each of the RGB pixel circuits.

Therefore, the capacitance of two capacitors included in the pixel circuit corresponding to each RGB in order to prevent the gradation and the swing range of the data voltage are different when the same data voltage is applied to the organic light emitting device for each RGB. The ratio α of the value can be adjusted.

Specifically, assume that the luminous efficiency is 0.25, 0.3, and 0.2 for the red (R), green (G), and blue (B) pixels, respectively, ΔV _S is 3V, and the voltage ΔV is 5V. In order for each RGB pixel to have the same data voltage swing range, the same gray level should be displayed for the same data voltage. For this purpose, the current I _OLED of the pixel circuit corresponding to each RGB pixel should have the same value. In order for the current I _OLED of the pixel circuit corresponding to each RGB pixel to have the same value, an appropriate ratio value in the pixel circuit corresponding to each RGB pixel can be obtained using Equation 4.

When the ratio is calculated based on the above-described assumptions, the ratio α is 1 in the pixel circuit corresponding to the red (R) pixel, and the ratio α is 1.42 in the pixel circuit corresponding to the green (G) pixel. In the pixel circuit corresponding to the blue (B) pixel, a value of the ratio α may be about 0.618.

As described above, in the pixel circuit according to the embodiment of the present invention, the value of the highest ratio in the pixel circuit corresponding to the green pixel having the highest luminous efficiency and the value of the lowest ratio in the pixel circuit corresponding to the lowest blue pixel And the ratio in the pixel circuit corresponding to the red pixel can be set to the intermediate value thereof.

In the exemplary embodiment of the present invention, a pixel circuit using six transistors and two capacitors has been described, but the present invention can be applied to all pixel circuits including two or more capacitors.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, It belongs to the scope of right.

According to the present invention, it is possible to reduce the difference in the swing range of the data voltage caused by the light emission efficiency depending on the color, and to express the same gray level for the same data voltage.

Claims (16)

A plurality of data lines for transmitting a data signal, a plurality of first scanning lines for transmitting a first selection signal, and a plurality of pixels defined by the data lines and the first scanning lines and having pixel circuits, respectively; A pixel includes a plurality of first pixels that emit light of a first color and a plurality of second pixels that emit light of a second color. The pixel circuit, A light emitting device for emitting light in response to the applied current, A first switching element transferring a data signal from the data line in response to a first selection signal from the first scan line; A transistor for supplying a driving current for emitting the light emitting element and diode-connected while the data signal is transmitted from the first switching element; A first storage element for storing a first voltage corresponding to the data signal from the first switching element, The first storage device is coupled between the first scan line and the control electrode of the transistor, and is coupled to the first storage device when the first selection signal is changed from a first level to a second level. A second storage element for changing a first voltage of the second voltage to a second voltage; And a capacitance ratio of the first storage element and the second storage element of the pixel circuit formed in the first pixel is different from the capacitance ratio of the pixel circuit formed in the second pixel. The method of claim 1, The first storage device is connected between the first electrode and the control electrode of the transistor. 3. The method of claim 2, And a second switching element connected between the first electrode and the control electrode of the transistor and diode-connecting the transistor in response to the first selection signal. The method of claim 3, Each of the plurality of pixels further includes a plurality of second scan lines that transmit a control signal. The pixel circuit, And a third switching element configured to transfer the driving current output from the transistor by the second voltage to the light emitting element in response to the control signal. 5. The method of claim 4, The pixel circuit, And a fourth switching element transferring a third voltage to the first electrode of the transistor in response to the control signal. The method of claim 5, Each of the plurality of pixels includes a plurality of third scan lines that transmit a second selection signal. The pixel circuit, And a fifth switching device configured to transfer a fourth voltage to one end of a first storage device connected to the control electrode of the transistor in response to the second selection signal. The method of claim 6, Wherein the first selection signal is shifted by a first period than the second selection signal. The method according to any one of claims 1 to 7, The second level is higher than the first level, and the second voltage is smaller than the first voltage. 9. The method of claim 8, The first and second storage elements are capacitors, and the capacitance ratio is a value obtained by dividing the capacitance of the second storage element by the capacitance of the first storage element according to the first and second pixels. The capacitance ratio varies according to two pixels, and as the ratio increases, the second voltage decreases. 10. The method of claim 9, The capacity ratio is, The light emitting display device when the currents transmitted to the light emitting elements of each of the first and second pixels are the same, the capacitance ratio corresponding to the pixel having the higher luminous efficiency is larger than the capacitance ratio of the pixel having the smaller luminous efficiency. A plurality of data lines for transmitting a data signal, a plurality of first scanning lines for transmitting a selection signal, and a plurality of pixel circuits connected to each of the plurality of pixels defined by the data lines and the first scanning line. In The pixel circuit, A first switching element having a first electrode connected to the data line and a control electrode connected to the first scan line; A transistor having a first electrode connected to a second electrode of the first switching element and having a second electrode electrically connected to a first power source; A second switching element connected between the control electrode and the second electrode of the transistor and having a control electrode connected to a first scan line; A first reservoir having one electrode connected to the first power source and another electrode connected to the control electrode of the transistor; and A light emitting display including a first and second plurality of pixel circuit groups including a second reservoir connected between a control electrode of the transistor and the first scan line, and having different capacitance ratios of the first reservoir and the second reservoir; Device. 12. The method of claim 11, A plurality of second scanning lines for transmitting a control signal, The pixel circuit, A third switching element having a first electrode connected to the first electrode of the transistor and a control electrode connected to the second scan line, and A light emitting display device further includes a fourth switching element having a first electrode connected to the first power supply, a second electrode connected to a second electrode of the transistor, and a control electrode connected to the second scan line. . The method of claim 12, A plurality of third scan lines through which the selection signal immediately before the selection signal is transmitted; The pixel circuit, A light emitting display device further includes a fifth switching element having a first electrode connected to the other electrode of the first reservoir, a control electrode connected to the third scan line, and a second electrode connected to a second power source. . 14. The method of claim 13, And a voltage level of the second power supply is lower than the first power supply voltage level. The method according to any one of claims 11 to 14, And the first and second pixel circuit groups respectively correspond to a plurality of pixels displaying first and second colors of the plurality of pixels. 16. The method of claim 15, The first and second storage elements are capacitors, and the capacitance ratio is a ratio obtained by dividing the capacitance of the second reservoir by the capacitance of the first reservoir.

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