KR20220095467A - Display device - Google Patents

Abstract

According to an embodiment of the present invention, a display device includes: a substrate on which a plurality of sub-pixels including a plurality of light emitting devices are disposed; and an initialization transistor connected to an anode of each of a plurality of light emitting devices, wherein as the luminance of light emitted from the plurality of light emitting devices increases, initialization voltage transmitted to the anode through the initialization transistor may increase. Therefore, by varying the initialization voltage of the anode according to the luminance of light emitted from the light emitting device, it is possible to stably display all from black images to high grayscale images.

Description

display device {DISPLAY DEVICE}

The present invention relates to a display device, and more particularly, to a display device capable of stably displaying images of various grayscales when driven at a high speed.

Display devices used in computer monitors, TVs, and mobile phones include organic light emitting displays (OLEDs) that emit light by themselves, and liquid crystal displays (LCDs) that require a separate light source. have.

Display devices are being applied to personal portable devices as well as computer monitors and TVs, and research on a display device having a reduced volume and weight while having a large display area is in progress.

Meanwhile, the display device may use a positive gamma grayscale method or an inverse gamma grayscale method as a method of expressing various grayscales. The positive gamma gradation method is a method in which a data voltage is proportional to a gray level, and the inverse gamma gray level method is a method in which a voltage level and a gray level are inversely proportional.

SUMMARY OF THE INVENTION An object of the present invention is to provide a display device capable of stably expressing various gray scales when driving at a high speed in a display device using an inverse gamma gray scale method.

Another object of the present invention is to provide a display device capable of easily charging the voltage of an anode of a light emitting device when driving at a high speed in a display device using an inverse gamma grayscale method.

Another object of the present invention is to provide a display device capable of easily displaying a high luminance or low luminance image by varying a voltage for initializing a light emitting element according to the luminance of a displayed image.

The problems of the present invention are not limited to the problems mentioned above, and other problems not mentioned will be clearly understood by those skilled in the art from the following description.

In order to solve the above problems, a display device according to an embodiment of the present invention includes a substrate on which a plurality of sub-pixels including a plurality of light emitting devices are disposed, and an initialization transistor connected to an anode of each of the plurality of light emitting devices. In addition, as the luminance of light emitted from the plurality of light emitting devices increases, the initialization voltage transmitted to the anode through the initialization transistor may increase. Accordingly, by varying the initialization voltage of the anode according to the luminance of light emitted from the light emitting device, it is possible to stably display everything from a black image to a high grayscale image.

In order to solve the above problems, a display device according to another embodiment of the present invention provides a plurality of sub-pixels on a substrate, a plurality of sub-pixels, a plurality of sub-pixels, and a plurality of cathodes connected to low-potential power lines. a light emitting device, an initialization transistor connected to an anode of each of the plurality of light emitting devices to initialize the voltage of the anode to an initialization voltage, and a plurality of data lines transmitting data voltages to the plurality of sub-pixels; The initialization voltage may decrease and the data voltage may increase as the image displayed by the display has a low grayscale, and the initialization voltage may increase and the data voltage may decrease as the image displayed by the high grayscale increases. Therefore, by varying the initialization voltage of the anode according to the gray level of the displayed image, the high gray level image is displayed by easily increasing the voltage of the anode to the target voltage within a limited time in the high gray level image, and the high gray level image is displayed in the black image. By configuring the voltage to be at least lower than the threshold voltage of the light emitting device, it is possible to minimize the phenomenon in which the light emitting device emits light in the black image.

Details of other embodiments are included in the detailed description and drawings.

According to the present invention, an image of various gray levels can be displayed by varying the initialization voltage of the anode according to the gray level of the image displayed on the display device.

The present invention initializes the voltage of the anode to a relatively high voltage when displaying a high-gradation image, so that the voltage of the anode can be easily charged and increased to the target voltage within a limited time, thereby stably displaying the high-gradation image. .

According to the present invention, when the black image is displayed, the problem that the black image is not displayed can be minimized by setting the initialization voltage of the anode to at least a voltage lower than the threshold voltage of the light emitting device, so that the light emitting device emits light.

According to the present invention, a separate IC or circuit structure for changing the initialization voltage can be simplified by outputting the initialization voltage that is changed according to the grayscale of the image to be displayed using the data voltage.

The present invention can simplify the structure of the pixel circuit by inverting the data voltage in the inverse gamma grayscale method and using it as an initialization voltage for initializing the anode.

According to the present invention, the initialization voltage of the anode can be easily varied by controlling the discharge rate of the parasitic capacitor of the light emitting device according to the gray level of the image to be displayed.

The effect according to the present invention is not limited by the contents exemplified above, and more various effects are included in the present invention.

1 is a schematic configuration diagram of a display device according to an exemplary embodiment of the present invention.
2 is a circuit diagram of a pixel circuit of a display device according to an exemplary embodiment.
3 is a timing diagram illustrating waveforms of signals input to a pixel circuit of a display device according to an exemplary embodiment.
4 is a waveform diagram illustrating a voltage of an anode of a light emitting device of a display device according to an exemplary embodiment of the present invention.
5 is a waveform diagram illustrating a voltage of an anode of a light emitting device of a display device according to a comparative example.
6 is a circuit diagram of a pixel circuit of a display device according to another exemplary embodiment of the present invention.
7 is a diagram for describing a discharge current of a display device according to another exemplary embodiment of the present invention.
8 is a circuit diagram of a pixel circuit of a display device according to another exemplary embodiment of the present invention.
9 is a diagram for explaining a discharge current of a display device according to another exemplary embodiment of the present invention.

Advantages and features of the present invention, and a method of achieving them will become apparent with reference to the embodiments described below in detail in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but will be implemented in a variety of different shapes, only these embodiments allow the disclosure of the present invention to be complete, and common knowledge in the technical field to which the present invention pertains It is provided to fully inform those who have the scope of the invention, and the present invention is only defined by the scope of the claims.

The shapes, areas, ratios, angles, numbers, etc. disclosed in the drawings for explaining the embodiments of the present invention are illustrative and the present invention is not limited to the illustrated matters. Like reference numerals refer to like elements throughout. In addition, in describing the present invention, if it is determined that a detailed description of a related known technology may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted. When 'includes', 'have', 'consists of', etc. mentioned in the present invention are used, other parts may be added unless 'only' is used. When a component is expressed in the singular, cases including the plural are included unless otherwise explicitly stated.

In interpreting the components, it is construed as including an error range even if there is no separate explicit description.

In the case of a description of the positional relationship, for example, when the positional relationship of two parts is described as 'on', 'on', 'on', 'beside', etc., 'right' Alternatively, one or more other parts may be positioned between two parts unless 'directly' is used.

Reference to a device or layer “on” another device or layer includes any intervening layer or other device directly on or in the middle of the other device or layer.

Also, although the first, second, etc. are used to describe various components, these components are not limited by these terms. These terms are only used to distinguish one component from another. Accordingly, the first component mentioned below may be the second component within the spirit of the present invention.

Like reference numerals refer to like elements throughout.

The area and thickness of each component shown in the drawings are illustrated for convenience of description, and the present invention is not necessarily limited to the area and thickness of the illustrated component.

Each feature of the various embodiments of the present invention can be partially or wholly combined or combined with each other, technically various interlocking and driving are possible, and each of the embodiments may be independently implemented with respect to each other or implemented together in a related relationship. may be

Hereinafter, various embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a schematic configuration diagram of a display device according to an exemplary embodiment of the present invention. In FIG. 1 , only the display panel PN, the gate driver GD, the data driver DD, and the timing controller TC are illustrated among various components of the display device 100 for convenience of explanation.

Referring to FIG. 1 , the display device 100 includes a display panel PN including a plurality of sub-pixels SP, a gate driver GD and a data driver DD supplying various signals to the display panel PN. , and a timing controller TC controlling the gate driver GD and the data driver DD.

The timing controller TC aligns the image data RGB input from the outside and supplies it to the data driver DD. The timing controller TC generates a gate control signal GCS and a data control signal DCS using an externally input synchronization signal SYNC, for example, a dot clock signal, a data enable signal, and a horizontal/vertical synchronization signal. can create In addition, the timing controller TC supplies the generated gate control signal GCS and the data control signal DCS to the gate driver GD and the data driver DD, respectively, to control the gate driver GD and the data driver DD. can be controlled

The gate driver GD supplies the plurality of scan signals SCAN to the plurality of scan lines SL according to the plurality of gate control signals GCS provided from the timing controller TC. Although one gate driver GD is illustrated as being spaced apart from one side of the display panel PN in FIG. 1 , the number and arrangement of the gate drivers GD is not limited thereto.

The data driver DD converts the image data RGB input from the timing controller TC into the data voltage Vdata by using the reference gamma voltage according to the plurality of data control signals DCS provided from the timing controller TC. do. In addition, the data driver DD may supply the converted data voltage Vdata to the plurality of data lines DL.

The display panel PN is configured to display an image to a user and includes a plurality of sub-pixels SP. In the display panel PN, the plurality of scan lines SL and the plurality of data lines DL cross each other, and each of the plurality of sub-pixels SP is connected to the scan line SL and the data line DL. In addition, although not shown in the drawings, each of the plurality of sub-pixels SP may be connected to a high potential power line, a low potential power line, an initialization signal line, a light emission control line, and the like.

The plurality of sub-pixels SP is a minimum unit constituting a screen, and each of the plurality of sub-pixels SP includes a light emitting device and a pixel circuit for driving the plurality of sub-pixels. The plurality of light emitting devices may be defined differently depending on the type of the display panel PN. For example, when the display panel PN is an organic light emitting display panel, the light emitting device may be an organic light emitting device including an anode, an organic layer, and a cathode. In addition, a quantum dot light-emitting diode (QLED) including a quantum dot (QD) may be further used as the light emitting device. Hereinafter, it is assumed that the light emitting device is an organic light emitting device including an anode and a cathode, but the type of the light emitting device is not limited thereto.

The pixel circuit is a circuit for controlling the driving of the light emitting element. The pixel circuit may include, for example, a plurality of transistors and capacitors, but is not limited thereto.

Hereinafter, the plurality of sub-pixels SP will be described in more detail with reference to FIGS. 2 and 3 .

2 is a circuit diagram of a pixel circuit of a display device according to an exemplary embodiment. 3 is a timing diagram illustrating waveforms of signals input to a pixel circuit of a display device according to an exemplary embodiment.

Referring to FIG. 2 , a light emitting device OLED and a pixel circuit for driving the light emitting device OLED are disposed in each of the plurality of sub-pixels SP.

The pixel circuit may include a plurality of transistors and a storage capacitor Cst. For example, the pixel circuit includes a first transistor T1 , a second transistor T2 , a third transistor T3 , a fourth transistor T4 , a fifth transistor T5 , a sixth transistor T6 , and a driver. It may have a 7T1C structure including a transistor DT and one storage capacitor Cst. However, the number of transistors and capacitors included in the pixel circuit may be variously configured, but is not limited thereto.

Meanwhile, the plurality of transistors may be N-type transistors or P-type transistors. In the N-type transistor, since carriers are electrons, electrons may flow from the source electrode to the drain electrode, and current may flow from the drain electrode to the source electrode. In the P-type transistor, since carriers are holes, holes may flow from the source electrode to the drain electrode, and current may flow from the source electrode to the drain electrode. For example, one transistor of the plurality of transistors may be an N-type transistor, and the other transistor of the plurality of transistors may be a P-type transistor. Hereinafter, it is assumed that the plurality of transistors are P-type transistors, but the present invention is not limited thereto.

The driving transistor DT is a transistor that controls a driving current applied to the light emitting device OLED. In the driving transistor DT, a first electrode is connected to a first node N1 , a gate electrode is connected to a second node N2 , and a second electrode is connected to a third node N3 . The first node N1 is a node to which the high potential power voltage VDD or the data voltage Vdata is transmitted, and the driving transistor DT is connected to the high potential power supply line or data line DL through the first node N1. can be electrically connected to The second node N2 is a node between the storage capacitor Cst and the first initialization line, and the driving transistor DT is turned on or turned on based on the voltage transferred to the second node N2 . can be turned off. The third node N3 is a node between the driving transistor DT and the light emitting device OLED, and a driving current may be transferred to the anode of the light emitting device OLED through the third node N3.

The first transistor T1 selectively connects the data line DL and the first node N1 according to a voltage applied to the gate electrode. The first transistor T1 may have a gate electrode connected to the N-th scan line SL, and may be turned on or off by the N-th scan signal SCAN(N). When the first transistor T1 is turned on, it may electrically connect the first node N1 and the data line DL.

The second transistor T2 selectively connects the high potential power line and the first node N1 according to the voltage applied to the gate electrode. The second transistor T2 may have a gate electrode connected to the light emission control line and may be turned on or off by the light emission control signal EM applied to the light emission control line. When the second transistor T2 is turned on, it may electrically connect the first node N1 and the high potential power line.

A third transistor T3 is connected between the second node N2 and the third node N3 . The third transistor T3 may be connected between the gate electrode and the second electrode of the driving transistor DT. The third transistor T3 has a gate electrode connected to the N-th scan line SL, and may be turned on or off by the N-th scan signal SCAN(N). The turned-on third transistor T3 may diode-connect the driving transistor DT by shorting the gate electrode and the second electrode of the driving transistor DT.

If the driving transistor DT is diode-connected by the third transistor T3, a current may flow from the first electrode to the second electrode of the driving transistor DT, and the voltage at the second node N2 is can continue to rise. In this case, the voltage of the second node N2 connected to the gate electrode of the driving transistor DT rises to a value obtained by subtracting the threshold voltage of the driving transistor DT from the data voltage Vdata, and thus the threshold voltage of the driving transistor DT can be sampled. Accordingly, the third transistor T3 may allow a voltage obtained by compensating the threshold voltage of the driving transistor DT to the data voltage Vdata to be applied to the driving transistor DT.

A fourth transistor T4 is disposed between the first initialization line and the second node N2 . The fourth transistor T4 is turned on by the N-1 th scan signal SCAN(N-1) applied to the N-1 th scan line SL to connect the first initialization line and the second node N2. It can be electrically connected. The fourth transistor T4 transfers the first initialization voltage Vini1 to the gate electrode of the driving transistor DT and the second node N2 to change the voltage of the gate electrode of the driving transistor DT to the first initialization voltage ( Vini1) can be initialized.

A fifth transistor T5 is disposed between the driving transistor DT and the light emitting device OLED. The fifth transistor T5 may be turned on by the emission control signal EM of the emission control line to transmit a driving current to the light emitting device OLED. By adjusting the turn-on timing of the fifth transistor T5 , the light emission timing of the light emitting device OLED may be controlled.

A sixth transistor T6 is disposed between the anode of the light emitting device OLED and the second initialization line. The sixth transistor T6 is turned on by the N-th scan signal SCAN(N) applied to the N-th scan line SL to change the voltage of the anode of the light emitting device OLED to the second initialization voltage Vini2 . can be initialized with In this case, the sixth transistor T6 that initializes the voltage of the anode to the second initialization voltage Vini2 may be referred to as an initialization transistor.

A storage capacitor Cst is disposed between the high potential power line and the second node N2 . The storage capacitor Cst may store a constant voltage to constantly maintain the voltage of the gate electrode of the driving transistor DT during the light emission period.

The light emitting device OLED has an anode connected to the fifth transistor T5 and a cathode connected to a low potential power line. The light emitting device OLED may emit light by receiving a driving current controlled by the driving transistor DT.

Meanwhile, the pixel circuit may be driven by dividing it into an initialization period (initial), a sampling and data writing period (Sampling & Writing), and an emission period (Emission) during one frame.

Referring to FIG. 3 , the voltage of the gate electrode of the driving transistor DT may be initialized during the initialization period.

First, a low-level N-1 th scan signal SCAN(N-1) may be applied to the N-1 th scan line SL during the initialization period. When the N-1 th scan signal SCAN(N-1) of the low level is applied, the fourth transistor T4 is turned on to change the voltage of the gate electrode of the driving transistor DT to the first initialization voltage Vini1 ) can be initialized.

Next, the N-th scan signal SCAN(N) of a low level may be applied to the N-th scan line SL in the sampling and data writing period. In this case, the first transistor T1 , the third transistor T3 , and the sixth transistor T6 having the gate electrode connected to the N-th scan line SL may be turned on.

As the first transistor T1 is turned on, the data voltage Vdata may be supplied to the first node N1 and the first electrode of the driving transistor DT. At this time, as described above, as the third transistor T3 is turned on, the voltage of the second node N2 may rise to a value obtained by subtracting the threshold voltage of the driving transistor DT from the data voltage Vdata, and the driving transistor A voltage in which the threshold voltage of the driving transistor DT is compensated may be applied to the data voltage Vdata to the gate electrode of DT.

In addition, when the sixth transistor T6 is turned on, the second initialization voltage Vini2 may be transferred to the anode of the light emitting device OLED, and the voltage of the anode may be initialized to the second initialization voltage Vini2.

Finally, the low-level emission control signal EM is applied during the emission period to turn on the second transistor T2 and the fifth transistor T5 . The second transistor T2 is turned on to supply the high potential power voltage VDD to the driving transistor DT, and the fifth transistor T5 is turned on to transmit a driving current from the driving transistor DT to the light emitting device ( OLED). Accordingly, during the light emission period, the light emitting device OLED may receive a driving current to emit light.

On the other hand, when the second initialization voltage Vini2 for initializing the anode voltage of the light emitting device OLED is fixed to a predetermined level, it is difficult to display either a high grayscale image or a low grayscale image. For example, when the second initialization voltage Vini2 is fixed to a low voltage similar to the low potential power supply voltage VSS, the time required to increase the anode voltage to the target voltage required to display a high-brightness image is insufficient. Therefore, it may be difficult to display a high-brightness image. If, in order to solve this problem, the second initialization voltage Vini2 is increased to give a large difference from the low potential power voltage VSS, the second initialization voltage Vini2 is the light emitting device even though a high-brightness image is easily displayed. As the light emitting device (OLED) emits light because it has a value greater than the threshold voltage of the OLED, it may be difficult to display a black image.

Accordingly, in the display device 100 according to an embodiment of the present invention, the voltage of the anode may be initialized by varying the second initialization voltage Vini2 according to the grayscale of the image to be displayed.

Hereinafter, a method of easily realizing both high grayscale and low grayscale images by varying the second initialization voltage Vini2 will be described in detail with reference to FIGS. 4 and 5 .

4 is a waveform diagram illustrating a voltage of an anode of a light emitting device of a display device according to an exemplary embodiment of the present invention. 5 is a waveform diagram illustrating a voltage of an anode of a light emitting device of a display device according to a comparative example. In the display device 100 according to the embodiment of the present invention, the second initialization voltage Vini2 and the anode voltage are variable, and in the display device according to the comparative example, the second initialization voltage Vini2, that is, the anode voltage is variable. fixed at a certain level.

Referring to FIG. 4 , the second initialization voltage Vini2 applied to the anode may vary as the luminance of the light emitted from the light emitting device OLED varies according to the gray level of the image to be displayed.

First, when displaying a high grayscale image, it may be assumed that an anode voltage, which is a target for emitting light of high luminance from the light emitting device OLED, is the first anode voltage V_anode1 . In this case, in order to increase from the second initialization voltage Vini2_1 that is the initial voltage of the anode to the first anode voltage V_anode1 for a limited time, it may be advantageous for the second initialization voltage Vini2_1 to have a high value. As the second initialization voltage Vini2_1 has a higher value, the time required to rise from the second initialization voltage Vini2_1 to the first anode voltage V_anode1 may be reduced. Therefore, the higher the grayscale image, the higher the second initialization voltage Vini2_1 is configured to reduce the voltage difference between the target anode voltage and the second initialization voltage Vini2_1, and the second initialization voltage Vini2_1 and the low potential power supply The voltage difference D1 between the voltages VSS may increase.

Next, when a low grayscale image is displayed, it may be assumed that an anode voltage, which is a target for emitting light of low luminance from the light emitting device OLED, is the second anode voltage V_anode2 . In this case, even when the second initialization voltage Vini2_2 is configured as a voltage lower than the second initialization voltage Vini2_1 in the high grayscale image, the voltage of the anode may sufficiently rise to the second anode voltage V_anode2 for a limited time. . Accordingly, the second initialization voltage Vini2_2 may decrease from the high grayscale to the low grayscale image, and the voltage difference D2 between the second initialization voltage Vini2_2 and the low potential power voltage VSS may also decrease. .

Subsequently, when a black image is displayed, it may be assumed that an anode voltage, which is a target so that light is not emitted from the light emitting device OLED, is a third anode voltage V_anode3 . If the third anode voltage V_anode3 is higher than the threshold voltage Vth_OLED of the light emitting device OLED, the light emitting device OLED emits light and thus black cannot be displayed, so the third anode voltage V_anode3 is the light emitting device OLED ) may be lower than the threshold voltage Vth_OLED. In this case, by configuring the second initialization voltage Vini2_3 to be a lower voltage, it is possible to prevent the voltage of the anode from rising above the threshold voltage Vth_OLED. When a black image is displayed, the second initialization voltage Vini2_3 may be configured as the lowest voltage, and the voltage difference D3 between the second initialization voltage Vini2_3 and the low potential power voltage VSS may also be the smallest. have.

In summary, the second initialization voltage Vini2 of the anode may be proportional to the gray level of the image to be displayed, that is, the luminance of the light emitting device OLED. The second initialization voltage Vini2_1 may be a relatively high voltage in the high grayscale image requiring high luminance light, and the second initialization voltage Vini2_2, Vini2_3 in the low grayscale image or black image that does not require low luminance light or light. ) may be a relatively low voltage.

Meanwhile, in the display device according to the comparative example, since the second initialization voltage is fixed, it may be difficult to display a high grayscale image or a black image.

Specifically, referring to FIG. 5 , when the second initialization voltage Vini2_4 , which is the initial voltage of the anode, is fixed to a lower voltage, the voltage of the anode is the first target at the second initialization voltage Vini2_4 for a limited time. It may be difficult to rise to the anode voltage (V_anode1). That is, when the voltage difference D4 between the second initialization voltage Vini2_4 and the low-potential power supply voltage VSS is small, the voltage of the anode increases from the second initialization voltage Vini2_4 to the first anode voltage V_anode1 for a limited time. It can be difficult to climb. When the display device is driven at a high speed, since the time for which the voltage of the anode of the light emitting device OLED rises is limited, it may be difficult to charge the anode with sufficient voltage. Therefore, it may be difficult to display a high grayscale image according to the voltage level of the second initialization voltage Vini2_4 .

However, when the second initialization voltage Vini2_5 is fixed to a higher voltage to display a high grayscale image, it may be difficult to display a black image. For example, when the second initialization voltage Vini2_5 is increased, the initial voltage of the anode and the second initialization voltage Vini2_5 may be higher than the threshold voltage Vth_OLED of the light emitting device OLED. . When the voltage difference D5 between the second initialization voltage Vini2_5 and the low-potential power supply voltage VSS is large, the initial anode voltage is higher than or similar to the threshold voltage Vth_OLED of the light emitting device OLED may occur. When the second initialization voltage Vini2_5 is higher than the threshold voltage Vth_OLED of the light emitting device OLED, if the voltage of the anode is not discharged to a voltage below the threshold voltage Vth_OLED, the light emitting device OLED emits light and a black image cannot be displayed Therefore, when the second initialization voltages Vini2_4 and Vini2_5 are fixed to specific voltages as in the display device according to the comparative example, it may be difficult to display a high grayscale image or to display a black image.

Accordingly, in the display device 100 according to an embodiment of the present invention, the voltage of the anode can be easily controlled by varying the second initialization voltage Vini2 according to the grayscale of the displayed image. Specifically, when displaying a high grayscale image, the anode voltage can be easily increased to a target high voltage within a limited time by setting the second initialization voltage Vini2, that is, the initial voltage of the anode to a higher voltage. have. When displaying a low grayscale image, by setting the second initialization voltage Vini2, which is the initial voltage of the anode, to a lower voltage, the anode voltage can be easily increased to a target low voltage within a limited time. In addition, when a black image is displayed, the initial voltage of the anode, which is the second initialization voltage Vini2, is set to at least a voltage lower than the threshold voltage Vth_OLED, so that the initial voltage of the anode can be configured to be less than or equal to the threshold voltage Vth_OLED. and a black image can be easily displayed.

On the other hand, the display device 100 according to an embodiment of the present invention may output the second initialization voltage Vini2 that is changed according to the gray level by using another voltage applied to the existing pixel circuit. For example, the display device 100 according to an embodiment of the present invention may output the second initialization voltage Vini2 varying according to the gray level using the data voltage Vdata according to the inverse gamma gray level method.

Specifically, the display device 100 according to an embodiment of the present invention may operate in an inverse gamma grayscale scheme. In the inverse gamma grayscale method, the magnitude and luminance of the data voltage Vdata are inversely proportional to each other. As the data voltage Vdata increases, the luminance may decrease, and as the data voltage Vdata decreases, the luminance may increase. The inverse gamma grayscale method is configured to apply a data voltage Vdata in a voltage range lower than the voltage of the gate electrode of the driving transistor DT to the first electrode of the driving transistor DT. In this case, as the data voltage Vdata increases, the voltage Vgs between the gate electrode and the first electrode of the driving transistor DT decreases, so that the driving current and luminance may decrease. Therefore, in the inverse gamma grayscale method, as the data voltage Vdata increases, the luminance of the display device 100 may decrease.

On the other hand, as described above, the second initialization voltage Vini2 is configured to have a higher voltage as the image of the high grayscale is higher, so it is advantageous to have a large voltage difference from the low potential power voltage VSS. It is advantageous that the voltage difference between the low potential power supply voltage (VSS) and the voltage difference is small because it is composed of a low voltage. Therefore, as the display device 100 displays a high-luminance image, the second initialization voltage Vini2 may increase.

In this case, in the inverse gamma grayscale method, the data voltage Vdata may be configured as a low positive voltage for a high grayscale image, and may be configured as a high positive voltage for a low grayscale image. In addition, if the polarity of the data voltage Vdata is inverted, the negative data voltage -Vdata in the high grayscale image may have a higher value than the negative data voltage -Vdata in the low grayscale image. For example, the data voltage Vdata may be configured as 2V to display a high grayscale image, and the data voltage Vdata may be configured as a higher 6V to display a low grayscale image. And if the polarity of the data voltage Vdata is inverted, the negative data voltage (-Vdata) becomes -2V in the high grayscale, and the negative data voltage (-Vdata) in the low grayscale becomes -6V, and becomes negative in the high grayscale. The data voltage -Vdata may have a greater value than the negative data voltage -Vdata in the low grayscale.

Accordingly, when the negative data voltage (-Vdata) is used as the second initialization voltage Vini2, the second initialization voltage Vini2 in the high grayscale image is changed to a voltage higher than the second initialization voltage Vini2 in the low grayscale image. configurable. For example, when displaying a high grayscale image, if the data voltage Vdata is configured to be 2V, the second initialization voltage Vini2 may be configured to be -2V. Conversely, when a low grayscale image or a black image is displayed, if the data voltage Vdata is increased to 6V, the second initialization voltage Vini2 is decreased to -6V, so that the voltage of the anode may be lower than at least the threshold voltage Vth_OLED. .

Meanwhile, the second initialization voltage Vini2 may be supplied in various ways. For example, the inverter IV is connected between the data line DL and the second initialization line that applies the second initialization voltage Vini2 to convert the negative data voltage -Vdata into the second initialization voltage Vini2. may be applied, or the second initialization voltage Vini2 may be applied using a DC-DC converter. For example, the driver including the timing controller TC and the data driver DD may generate the second initialization voltage Vini2 based on the grayscale of the image to be displayed and then output it to the second initialization wire. have. In this case, the second initialization voltage Vini2 may be generated using a look-up table in which information on the second initialization voltage Vini2 according to the gray level of the image is stored or another voltage applied to the existing pixel circuit. Accordingly, a method of applying the second initialization voltage Vini2 may be configured in various ways, but is not limited thereto.

In the present specification, it has been described that the second initialization voltage Vini2 is varied using the data voltage Vdata, but the second initialization voltage Vini2 may be varied using another voltage instead of the data voltage Vdata. It is not limited thereto.

In addition, although it has been described in this specification that the pixel circuit has a 7T1C structure, a pixel circuit including a configuration that uses an inverse gamma method and initializes the anode voltage, for example, a circuit such as an 8T1C structure, may be used. not limited

In the display device 100 according to an embodiment of the present invention, a high grayscale image, a low grayscale image, and a black image are stabilized by varying the second initialization voltage Vini2 for initializing the voltage of the anode according to the grayscale of the image to be displayed. can be displayed as After the voltage of the anode is initialized to the second initialization voltage Vini2 before the light emission period, the voltage of the anode is increased to a target voltage to display images of various grayscales. In this case, in a situation in which the voltage of the anode needs to be increased to a specific voltage in order to display a high grayscale image within a limited time, it may be advantageous to set the second initialization voltage Vini2 to be closer to the specific voltage. Conversely, in order to display a black image, the second initialization voltage Vini2, which is the initial voltage of the anode, is configured to be at least below the threshold voltage Vth_OLED of the light emitting device OLED so that the light emitting device OLED does not emit light in the black image. can Accordingly, the display device 100 according to an embodiment of the present invention may stably display images of various grayscales by varying the second initialization voltage Vini2 of the anode according to the grayscale of the image to be displayed.

In the display device 100 according to an embodiment of the present invention, a driving IC or data for varying the second initialization voltage Vini2 and applying the second initialization voltage Vini2 by using the data voltage Vdata to vary the second initialization voltage Vini2. The structure of the driver DD and the like can be simplified. Specifically, the display device 100 according to an embodiment of the present invention may be driven in an inverse gamma grayscale scheme in which the data voltage Vdata and luminance are inversely proportional to each other. In this case, the data voltage Vdata may be formed as a relatively low positive voltage in the high grayscale image, and the data voltage Vdata may be formed as a relatively high positive voltage in the low grayscale image. In this case, the negative data voltage -Vdata in which the data voltage Vdata is inverted may be used as the second initialization voltage Vini2. For example, when the data voltage Vdata is 2V in the high-luminance image, the second initialization voltage Vini2 may be -2V. In the low-luminance image, when the data voltage Vdata is 6V, the second initialization voltage Vini2 is It can be -6V. In addition, in order to display the high-luminance image, the second initialization voltage Vini2 is configured as a voltage with a large voltage difference from the low-potential power supply voltage VSS, and in the low-luminance image, the second initialization voltage Vini2 is the low-potential power supply voltage VSS. ) and the voltage difference may be small. That is, the second initialization voltage Vini2 in the high luminance image should have a greater value than the second initialization voltage Vini2 in the low luminance image. And when the data voltage Vdata is inverted to a negative data voltage (-Vdata) and used as the second initialization voltage Vini2, the second initialization is performed in a high-luminance image than -6V, which is the second initialization voltage Vini2, in a low-luminance image. The voltage Vini2 has a larger value of -2V. Accordingly, in the display device 100 according to an embodiment of the present invention, the data voltage Vdata used in the inverse gamma grayscale method is inverted and used as the second initialization voltage Vini2, so that the second initialization voltage ( Vini2) may be varied, and a structure of a separate driving IC or data driver DD for generating the second initialization voltage Vini2 may be simplified.

6 is a circuit diagram of a pixel circuit of a display device according to another exemplary embodiment of the present invention. 7 is a diagram for describing a discharge current of a display device according to another exemplary embodiment of the present invention. Compared to the display device 100 of FIGS. 1 to 4 , the display device 600 of FIGS. 6 and 7 varies the second initialization voltage Vini2 transferred to the anode using the seventh transistor T7. Except for , since other configurations are substantially the same, a redundant description will be omitted.

Referring to FIG. 6 , a seventh transistor T7 is disposed between the sixth transistor T6 and the cathode of the light emitting device OLED. Charges of the parasitic capacitor COLED of the light emitting device OLED may be discharged through the seventh transistor T7 . The seventh transistor T7 and the sixth transistor T6 may discharge the parasitic capacitor COLED across the light emitting device OLED to vary the voltage of the anode to various second initialization voltages Vini2 .

The gate electrode of the seventh transistor T7 is connected to the data line DL with the inverter IV interposed therebetween. The positive data voltage Vdata from the data line DL passes through the inverter IV and may be converted into a negative data voltage -Vdata, and the negative data voltage -Vdata is transferred to the seventh transistor T7. can be applied to the gate electrode of At this time, the discharge rate of the parasitic capacitor COLED of the light emitting device OLED through the seventh transistor T7 is determined according to the magnitude of the negative data voltage -Vdata applied to the gate electrode of the seventh transistor T7. and a second initialization voltage Vini2 that is an initial voltage of the anode may be determined.

Referring to FIG. 7 together, a discharge current Idc may flow from the parasitic capacitor COLED through the seventh transistor T7. In this case, the discharge current Idc flowing through the seventh transistor T7 may be controlled according to the magnitude of the negative data voltage -Vdata applied to the gate electrode of the seventh transistor T7 . In this case, the seventh transistor T7 connected to the sixth transistor T6 referred to as an initialization transistor to control the discharge current Idc may be referred to as a discharge control transistor.

For example, it may be assumed that the data voltage Vdata is 2V in the high grayscale image and the data voltage Vdata is 6V in the low grayscale image. In this case, the negative data voltage (-Vdata) in the high grayscale image is -2V, and the negative data voltage (-Vdata) in the low grayscale image is -6V. In this case, the discharge current Idc may flow more when -6V is applied than when -2V is applied to the seventh transistor T7 .

Therefore, in the high grayscale image, when -2V is applied to the gate electrode of the seventh transistor T7 and a relatively small discharge current Idc flows, the anode voltage is initialized to the relatively high second initialization voltage Vini2. can Conversely, when -6V is applied to the gate electrode of the seventh transistor T7 and a relatively large discharge current Idc flows in the low grayscale image, the anode voltage is initialized to the relatively low second initialization voltage Vini2. can Accordingly, by increasing the discharge current Idc flowing through the seventh transistor T7 in the low grayscale image than the discharge current Idc flowing through the seventh transistor T7 in the high grayscale image, the voltage of the anode in the low grayscale image can be initialized to a relatively low voltage.

Accordingly, in the display device 600 according to another embodiment of the present invention, the seventh transistor T7 is turned on or turned off by the negative data voltage (-Vdata) and connects the anode and the cathode of the light emitting device OLED. ) to initialize the voltage of the anode to various second initialization voltages Vini2. Specifically, the seventh transistor T7 is connected between the parasitic capacitor COLED of the light emitting device OLED and the low potential power voltage VSS, and when turned on, discharges the charge of the parasitic capacitor COLED. . At this time, the inverter IV converts the data voltage Vdata to a negative data voltage -Vdata, and then applies it to the gate electrode of the seventh transistor T7 to turn on or turn on the seventh transistor T7. can be turned off The magnitude of the discharge current Idc flowing through the seventh transistor T7 may be determined according to the magnitude of the negative data voltage -Vdata applied to the gate electrode of the seventh transistor T7, and the second initialization of the anode The voltage Vini2 may also vary. Since the data voltage Vdata varies according to the high gray level or the low gray level, the discharge current Idc flowing through the seventh transistor T7 may also vary. For example, in a high grayscale image, the second initialization voltage Vini2 of the anode can be controlled to a relatively high voltage by reducing the size of the discharge current Idc, and in a low grayscale image, the size of the discharge current Idc can be decreased. By increasing it, the second initialization voltage Vini2 of the anode may be controlled to a relatively low voltage. Accordingly, in the display device 600 according to another embodiment of the present invention, the magnitude of the discharge current Idc flowing when the parasitic capacitor COLED of the light emitting element OLED is discharged is controlled according to the negative data voltage -Vdata. By arranging the seventh transistor T7, the second initialization voltage Vini2 of the anode may be varied to various voltages. Therefore, it is possible to stably display a high-brightness image by charging the voltage of the anode to the target voltage within a limited time, and the second initialization voltage Vini2, which is the initial voltage of the anode, increases the threshold voltage Vth_OLED of the light emitting device OLED. The black image can be easily displayed by not exceeding it.

8 is a circuit diagram of a pixel circuit of a display device according to another exemplary embodiment. 9 is a diagram for explaining a discharge current of a display device according to another exemplary embodiment of the present invention. Compared to the display device 600 of FIGS. 6 and 7 , the display device 800 of FIGS. 8 and 9 has substantially the same configuration except that it further includes a reference voltage line, and thus a redundant description thereof will be omitted.

8 and 9 together, the seventh transistor T7 is connected between the anode and the reference voltage line. If a turn-on voltage is applied to the gate electrode of the seventh transistor T7, the discharge current Idc flows from the anode of the light emitting device OLED to the reference voltage line through the seventh transistor T7, and the light emitting device The parasitic capacitor COLED of the OLED may be discharged.

In this case, the voltage Vds between the first electrode and the second electrode of the seventh transistor T7 may be controlled according to the reference voltage Vref of the reference voltage line. The discharge current Idc flowing through the seventh transistor T7 may be determined by the voltage Vgs between the gate electrode and the first electrode and the voltage Vds between the first electrode and the second electrode. In this case, as the voltage Vds between the first electrode and the second electrode increases, the discharge current Idc may also increase. For example, in order to display a low grayscale image, the reference voltage Vref is configured to be lower than the low potential power voltage VSS through the voltage Vds between the first electrode and the second electrode and the seventh transistor T7. The flowing discharge current Idc may be increased, and the second initialization voltage Vini2, which is an initial voltage of the anode, may also be set to a low value. Conversely, the voltage Vds and the discharge current Idc between the first electrode and the second electrode can be reduced by configuring the reference voltage Vref to be higher than the low-potential power supply voltage VSS in order to display a high grayscale image. , the second initialization voltage Vini2, which is the initial voltage of the anode, may also be set to a high value.

Accordingly, in the display device 800 according to another embodiment of the present invention, the seventh transistor T7 connected to the anode of the light emitting element OLED is connected to the reference voltage line, and the discharge flowing through the seventh transistor T7 is connected. The magnitude of the current Idc may be controlled, and the second initialization voltage Vini2, which is the initial voltage of the anode, may be variously varied according to the grayscale of the displayed image. A discharge current Idc may flow through the sixth transistor T6 and the seventh transistor T7 connected to the parasitic capacitor COLED of the light emitting device OLED to discharge the parasitic capacitor COLED, and accordingly, the anode A second initialization voltage Vini2 that is an initial voltage may be determined. In this case, the discharge current Idc may be controlled according to the voltage Vgs between the gate electrode and the first electrode of the seventh transistor T7 and the voltage Vds between the first electrode and the second electrode. In this case, the voltage Vds between the first electrode and the second electrode of the seventh transistor T7 may be controlled by controlling the reference voltage Vref of the reference voltage line connected to the seventh transistor T7, and discharge The magnitude of the current Idc may be determined. If the discharge current Idc is increased by controlling the voltage Vds between the first electrode and the second electrode, the parasitic capacitor COLED is discharged in a relatively large amount so that the second initialization voltage Vini2 is relatively low. voltage can be determined. Conversely, when the discharge current Idc is reduced by controlling the voltage Vds between the first electrode and the second electrode, the parasitic capacitor COLED is discharged relatively little and the second initialization voltage Vini2 is relatively high. can be determined as Accordingly, in the display device 800 according to another embodiment of the present invention, the voltage Vds between the first electrode and the second electrode and the resulting discharge current Idc by connecting the seventh transistor T7 to the reference voltage line ) can be controlled, and the second initialization voltage Vini2, which is the initial voltage of the anode, can be variously varied according to the grayscale of the image to be displayed.

Display devices according to embodiments of the present invention may be described as follows.

A display device according to an embodiment of the present invention includes a substrate on which a plurality of sub-pixels including a plurality of light emitting devices are disposed, and an initialization transistor connected to an anode of each of the plurality of light emitting devices, and light is emitted from the plurality of light emitting devices As the luminance of the used light increases, the initialization voltage transmitted to the anode through the initialization transistor may increase.

According to another feature of the present invention, it further includes a low-potential power wiring supplying a low-potential power supply voltage to the cathodes of each of the plurality of light-emitting devices, and as the light emitted from the plurality of light-emitting devices has a higher luminance, the initialization voltage and the low-potential power supply The voltage difference between the voltages may increase.

According to another feature of the present invention, as the luminance of the light emitted from the plurality of light emitting devices is lower, the voltage difference between the initialization voltage and the low potential power supply voltage may decrease.

According to another feature of the present invention, the device further includes a plurality of data lines supplying a data voltage to each of the plurality of sub-pixels, and the luminance of light emitted from the plurality of light emitting devices may be inversely proportional to the data voltage.

According to another feature of the present invention, the device may further include an initialization line connected to the first electrode of the initialization transistor, and the first voltage applied to the first electrode through the initialization line may be lower than the data voltage.

According to another feature of the present invention, the absolute value of the first voltage and the data voltage may be the same.

According to another feature of the present invention, the display device may further include a discharge control transistor connected to the initialization transistor, and an inverter connected between the gate electrode of the discharge control transistor and each of the plurality of data lines.

According to another feature of the present invention, in the discharge control transistor, a first electrode may be connected to a low-potential power line, and a second electrode may be connected to an initialization transistor.

According to another feature of the present invention, a reference voltage line connected to the first electrode of the discharge control transistor may be further included.

A display device according to another embodiment of the present invention includes a substrate on which a plurality of sub-pixels are defined, a plurality of light-emitting devices disposed on the plurality of sub-pixels and including a cathode connected to a low-potential power line, and each of the plurality of light-emitting devices an initialization transistor connected to the anode to initialize the voltage of the anode to the initialization voltage, and a plurality of data lines transmitting data voltages to the plurality of sub-pixels, wherein the image displayed by the plurality of sub-pixels is initialized as the grayscale is lower The voltage may decrease, the data voltage may increase, and the initialization voltage may increase and the data voltage may decrease as the image has a higher grayscale.

According to another feature of the present invention, when the image is a black image, the initialization voltage may be a voltage lower than the threshold voltages of at least the plurality of light emitting devices.

According to another feature of the present invention, the method may further include an initialization line connected to the first electrode of the initialization transistor, and an absolute value of the first voltage transmitted from the initialization line to the first electrode may be the same as an absolute value of the data voltage.

According to another feature of the present invention, the display device may further include a discharge control transistor connected to the first electrode of the initialization transistor, and an inverter connected between the gate electrode of the discharge control transistor and each of the plurality of data lines.

According to another feature of the present invention, one of the first electrode and the second electrode of the discharge control transistor may be connected to the cathodes of the plurality of light emitting devices, and the other may be connected to the first electrode of the initialization transistor.

According to still another feature of the present invention, it further includes a reference voltage line connected to one of the first electrode and the second electrode of the discharge control transistor, wherein the reference voltage of the reference voltage line is lower than the low potential power supply voltage of the low potential power line. It can be voltage.

Although the embodiments of the present invention have been described in more detail with reference to the accompanying drawings, the present invention is not necessarily limited to these embodiments, and various modifications may be made within the scope without departing from the technical spirit of the present invention. . Therefore, the embodiments disclosed in the present invention are not intended to limit the technical spirit of the present invention, but to explain, and the scope of the technical spirit of the present invention is not limited by these embodiments. Therefore, it should be understood that the embodiments described above are illustrative in all respects and not restrictive. The protection scope of the present invention should be construed by the following claims, and all technical ideas within the scope equivalent thereto should be construed as being included in the scope of the present invention.

100, 600, 800: display device
PN: display panel
GD: gate driver
DD: data driver
TC: Timing Controller
SP: sub pixel
SL: scan wiring
DL: data wiring
RGB: image data
SYNC: Sync signal
GCS: gate control signal
DCS: data control signal
DT: driving transistor
T1: first transistor
T2: second transistor
T3: third transistor
T4: fourth transistor
T5: fifth transistor
T6: sixth transistor
T7: 7th transistor
Cst: storage capacitor
COLED: Parasitic Capacitors
OLED: light emitting element
IV: inverter
N1: first node
N2: second node
N3: third node
SCAN: scan signal
SCAN(N): Nth scan signal
SCAN(N-1): N-1th scan signal
Vdata: data voltage
VDD: high potential supply voltage
VSS: Low-potential supply voltage
Vini1: first initialization voltage
Vini2: second initialization voltage
EM: light emission control signal
Idc: discharge current
Vref: reference voltage
V_anode1: first anode voltage
V_anode2: second anode voltage
V_anode3: third anode voltage
V_anode4: fourth anode voltage
V_anode5: fifth anode voltage
Vth_OLED: Threshold voltage of the light emitting device
D1, D2, D3, D4, D5: voltage difference between the second initialization voltage and the low-potential power supply voltage

Claims (15)

a substrate on which a plurality of sub-pixels including a plurality of light emitting devices are disposed; and
Including an initialization transistor connected to the anode of each of the plurality of light emitting devices,
The initialization voltage transmitted to the anode through the initialization transistor increases as the luminance of the light emitted from the plurality of light emitting devices increases. According to claim 1,
Further comprising a low potential power supply wiring for supplying a low potential power supply voltage to the cathode of each of the plurality of light emitting devices,
A voltage difference between the initialization voltage and the low-potential power supply voltage increases as the light emitted from the plurality of light emitting devices has a higher luminance. 3. The method of claim 2,
A voltage difference between the initialization voltage and the low potential power supply voltage decreases as the light emitted from the plurality of light emitting devices has a lower luminance. 3. The method of claim 2,
a plurality of data lines supplying data voltages to each of the plurality of sub-pixels;
and a luminance of light emitted from the plurality of light emitting devices is inversely proportional to the data voltage. 5. The method of claim 4,
Further comprising an initialization wire connected to the first electrode of the initialization transistor,
The first voltage applied to the first electrode through the initialization line is a voltage lower than the data voltage. 6. The method of claim 5,
and the first voltage and the data voltage have the same absolute value. 5. The method of claim 4,
a discharge control transistor connected to the initialization transistor; and
and an inverter connected between the gate electrode of the discharge control transistor and each of the plurality of data lines. 8. The method of claim 7,
In the discharge control transistor, a first electrode is connected to a low potential power line, and a second electrode is connected to the initialization transistor. 8. The method of claim 7,
and a reference voltage line connected to the first electrode of the discharge control transistor. a substrate on which a plurality of sub-pixels are defined;
a plurality of light emitting devices disposed in the plurality of sub-pixels and including a cathode connected to a low potential power line;
an initialization transistor connected to an anode of each of the plurality of light emitting devices to initialize a voltage of the anode to an initialization voltage; and
a plurality of data lines for transferring data voltages to the plurality of sub-pixels;
As the image displayed by the plurality of sub-pixels has a lower gray scale, the initialization voltage decreases and the data voltage increases,
The initialization voltage increases and the data voltage decreases as the image has a higher grayscale. 11. The method of claim 10,
When the image is a black image, the initialization voltage is at least a voltage lower than a threshold voltage of the plurality of light emitting devices. 11. The method of claim 10,
Further comprising an initialization line connected to the first electrode of the initialization transistor,
and an absolute value of the first voltage transmitted from the initialization line to the first electrode is the same as an absolute value of the data voltage. 11. The method of claim 10,
a discharge control transistor connected to a first electrode of the initialization transistor; and
and an inverter connected between the gate electrode of the discharge control transistor and each of the plurality of data lines. 14. The method of claim 13,
one of the first and second electrodes of the discharge control transistor is connected to the cathodes of the plurality of light emitting devices, and the other is connected to the first electrode of the initialization transistor. 14. The method of claim 13,
Further comprising a reference voltage line connected to one of the first electrode and the second electrode of the discharge control transistor,
The reference voltage of the reference voltage line is a voltage lower than a low potential power voltage of the low potential power line.

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