Electroluminescence display and driving method thereof

Abstract

In an embodiment of the present invention, an electroluminescent display device may include: a display panel having a plurality of pixels connected to a data line and a gate line, having a light-emitting element and a driving TFT that controls a driving current flowing through the light-emitting element; a panel driving unit connected to the data line and the gate line; and a timing control unit that controls the operation of the panel driving unit to drive the light-emitting element by dividing it into a light-emitting period during which the light-emitting element emits light and a non-light-emitting period during which light emission is stopped, inputs a data voltage through the data line during the non-light-emitting period, and controls the light-emitting elements to which the data voltage is applied during the light-emitting period to emit light simultaneously.

Description

Technology Field

[0001] The present invention relates to an electroluminescent display device having a driving element that drives pixels. Background Technology

[0002] Electroluminescent display devices are broadly classified into inorganic light-emitting display devices and organic light-emitting display devices depending on the material of the light-emitting layer. Among these, active matrix type organic light-emitting display devices include self-emitting organic light-emitting diodes (OLEDs).

[0003] An organic light-emitting display arranges pixels, each containing an OLED, in a matrix form and controls the brightness of the pixels according to the grayscale of the image data. Each pixel basically includes a driving TFT (Thin Film Transistor) that controls the driving current flowing to the OLED according to the gate-source voltage, and one or more switch TFTs for programming the gate-source voltage of the driving TFT.

[0004] Organic light-emitting displays are being applied in various fields due to their advantages, such as being suitable for thinning, having low power consumption, fast response speed, high luminous efficiency, brightness, and viewing angle.

[0005] Accordingly, research is continuing to improve the performance of organic light-emitting display devices, such as image quality. The problem to be solved

[0006] The present invention aims to provide an electroluminescent display device and a driving method thereof that can reproduce uniform brightness across the entire display panel by improving the brightness deviation occurring in each display panel area when applying Black Data Insertion (BDI) technology, which inserts an emission off section within one frame to improve the image quality of the display device. means of solving the problem

[0007] As a means for solving the above-described problem, an electroluminescent display device according to an embodiment of the present invention may include: a display panel having a plurality of pixels connected to a data line and a gate line, having a light-emitting element and a driving TFT that controls a driving current flowing through the light-emitting element; a panel driving unit connected to the data line and the gate line; and a timing control unit that controls the operation of the panel driving unit to drive the light-emitting element by dividing it into a light-emitting period in which the light-emitting element emits light and a non-light-emitting period in which light emission is stopped, inputs a data voltage through the data line during the non-light-emitting period, and controls the light-emitting elements to which the data voltage is applied during the light-emitting period to emit light simultaneously.

[0008] The above timing control unit can implement Back Data Insertion (BDI) operation by controlling the display of an image during the light emission period and the display of a black image during the non-light emission period.

[0009] The timing control unit can sequentially input the data voltage to all pixel lines of the display panel during the non-luminous period and control all pixel lines to emit light simultaneously during the luminous period.

[0010] The timing control unit can divide the horizontal pixel lines of the display panel into a plurality of blocks, sequentially input the data voltage in units of divided blocks, and control simultaneous emission in units of blocks.

[0011] The timing control unit above can compensate the data voltage based on the change in low potential voltage due to the light emission of the light-emitting elements.

[0012] The panel driving unit may include: a data driving unit that supplies the data voltage to the data line; and a gate driving unit that sequentially outputs a switch signal for inputting the data voltage and simultaneously outputs a light emission signal to pixels to which the data voltage is applied.

[0013] As a means for solving the above-described problem, an electroluminescent display device according to another embodiment of the present invention comprises: a display panel in which data lines and gate lines intersect and a plurality of pixels are arranged; a data driving unit that supplies a data voltage to the data lines; and a gate driving unit that sequentially outputs a switch signal for inputting the data voltage and simultaneously outputs a light emission signal to the pixels to which the data voltage is applied, wherein each of the pixels comprises: a light-emitting element in which an anode electrode is connected to a high potential driving voltage; a driving transistor connected between the cathode electrode of the light-emitting element and a low potential driving voltage to control the driving current of the light-emitting element according to the voltage difference between the gate and the source; a switching transistor that connects the data line and a first node according to the switch signal; a light-emitting transistor that connects the first node and a second node according to the light emission signal; and a first capacitor connected to the first node to charge the data voltage input to the data lines. and may include a second capacitor connected to the second node and the source node of the driving transistor, which charges the data voltage charged in the first capacitor to the gate-source voltage of the driving transistor upon input of the light emission signal.

[0014] The first capacitor above can charge the data voltage while the light-emitting element is off.

[0015] When the switching transistor is turned on, the light-emitting transistor remains in an off state so that the data voltage is charged in the first capacitor, and when the light-emitting transistor is turned on, the switching transistor remains in an off state so that the data voltage charged in the first capacitor can be charged in the first capacitor.

[0016] The above driving transistor can control the magnitude of the driving current applied to the light-emitting element according to the magnitude of the data voltage charged in the second capacitor, with the drain electrode connected to the cathode electrode of the light-emitting element, the source electrode connected to the low potential driving voltage, and the gate electrode connected to the second node.

[0017] As a means for solving the above-described problem, an electroluminescent display device according to another embodiment of the present invention may include: a light-emitting element having an anode electrode connected to a high potential driving voltage; a driving transistor connected between the cathode electrode of the light-emitting element and a low potential driving voltage to control the driving current of the light-emitting element according to the voltage difference between the gate and the source; a switching transistor connecting a data line and a first node according to a switch signal; a first capacitor connected to the first node to charge a data voltage input to the data line; a light-emitting transistor connecting the first node and a second node according to a light-emitting signal; and a second capacitor connected to the second node and the source node of the driving transistor.

[0018] The first capacitor above can charge the data voltage while the light-emitting element is off.

[0019] The second capacitor can charge the data voltage charged in the first capacitor into the gate-source voltage of the driving transistor when the light-emitting signal is input.

[0020] When the switching transistor is turned on, the light-emitting transistor remains in an off state so that the data voltage is charged in the first capacitor, and when the light-emitting transistor is turned on, the switching transistor remains in an off state so that the data voltage charged in the first capacitor can be charged in the first capacitor.

[0021] The driving period for emitting light of the light-emitting element includes a first to a fourth period, and in the first period, the switching transistor is turned on and the light-emitting transistor is turned off so that the data voltage is charged in the first capacitor, in the second period, the switching transistor and the light-emitting transistor are turned off so that the data voltage is maintained in the first capacitor, in the third period, the switching transistor is turned off and the light-emitting transistor is turned on so that the data voltage is charged in the second capacitor, and in the fourth period, the driving transistor is turned on according to the data voltage charged in the second capacitor so that a driving power supply can be applied to the light-emitting element. Effects of the invention

[0022] The electroluminescent display device of the present invention writes image data for each line during the emission off period when black data is displayed, and when the image data writing is completed, emits pixels of all lines simultaneously, thereby ensuring that all lines have the same duty cycle and preventing brightness deviation. Brief explanation of the drawing

[0023] FIG. 1 is a control block diagram of an electroluminescent display device according to an embodiment of the present invention. FIG. 2 is a drawing for explaining a driving method of an electroluminescent display device according to an embodiment of the present invention. FIG. 3 is a circuit diagram of one pixel for implementing the driving technology according to the present invention. Figure 4 is a waveform of the signal supplied to the pixel of Figure 3. FIGS. 5 to 8 are drawings for explaining a method of driving a pixel. FIG. 9 is a drawing for explaining a driving method of an electroluminescent display device according to a first embodiment of the present invention. FIG. 10 is a drawing for explaining a driving method of an electroluminescent display device according to a second embodiment of the present invention. FIGS. 11 to 13 are drawings for explaining a method for compensating for EVSS rising during driving of an electroluminescent display device according to a second embodiment. Specific details for implementing the invention

[0024] The advantages and features of this specification and the methods for achieving them will become clear by referring to the embodiments described below in detail together with the accompanying drawings. However, this specification is not limited to the embodiments disclosed below but may be implemented in various different forms; these embodiments are provided merely to ensure that the disclosure of this specification is complete and to fully inform those skilled in the art of the scope of the invention, and this specification is defined only by the scope of the claims.

[0025] Shapes, sizes, ratios, angles, numbers, etc. disclosed in the drawings for describing the embodiments of this specification are exemplary and are not limited to the details illustrated in this specification. Throughout the specification, the same reference numerals refer to the same components. Where terms such as "comprising," "having," or "consisting of" are used in this specification, other parts may be added unless "only" is used. Where a component is expressed in the singular, it includes cases where it includes the plural unless specifically stated otherwise.

[0026] In interpreting the components, they are interpreted to include a margin of error even in the absence of a separate explicit statement.

[0027] In the case of describing a positional relationship, for example, when the positional relationship between two parts is described using expressions such as 'on top of,' 'above,' 'below,' or 'next to,' one or more other parts may be located between the two parts unless 'immediately' or 'directly' is used.

[0028] "First," "second," etc., may be used to describe various components, but these components are not limited by these terms. These terms are used merely to distinguish one component from another. Accordingly, the first component mentioned below may be the second component within the technical scope of this specification.

[0029] In the electroluminescent display device of the present invention, the pixel circuit includes a driving element and a switching element. The driving element and the switching element can be implemented as one or more transistors among n-type transistors (NMOS) and p-type transistors (PMOS). On the display panel, the transistor can be implemented as a thin film transistor (TFT). The transistor can be implemented as an oxide transistor having an oxide semiconductor pattern or as an LTPS transistor having a low-temperature polysilicon (LTPS) semiconductor pattern. The transistor is a three-electrode device including a gate, a source, and a drain. The source is the electrode that supplies carriers to the transistor. Within the transistor, carriers begin to flow from the source. The drain is the electrode from which carriers exit the transistor. The flow of carriers in the transistor flows from the source to the drain. In the case of an n-type transistor (NMOS), since the carriers are electrons, the source voltage has a lower voltage than the drain voltage to allow electrons to flow from the source to the drain. In an n-type transistor (NMOS), the direction of current flows from the drain to the source. In the case of a p-type transistor (PMOS), since the carrier is a hole, the source voltage is higher than the drain voltage so that holes can flow from the source to the drain. In a p-type transistor (PMOS), since holes flow from the source to the drain, current flows from the source to the drain. It should be noted that the source and drain of the transistor are not fixed. For example, the source and drain can change depending on the applied voltage. Therefore, the invention is not limited by the source and drain of the transistor. In the following description, the source and drain of the transistor will be referred to as the first and second electrodes.

[0030] The gate signal of a transistor used as a switching element swings between the gate-on voltage and the gate-off voltage. The gate-on voltage is set to a voltage higher than the transistor's threshold voltage, and the gate-off voltage is set to a voltage lower than the transistor's threshold voltage. The transistor turns on in response to the gate-on voltage, while it turns off in response to the gate-off voltage. In the case of an n-type transistor (NMOS), the gate-on voltage can be the gate-high voltage (VGH), and the gate-off voltage can be the gate-low voltage (VGL). In the case of a p-type transistor (PMOS), the gate-on voltage can be the gate-low voltage (VGL), and the gate-off voltage can be the gate-high voltage (VGH).

[0031] Hereinafter, various embodiments of the present invention will be described in detail with reference to the attached drawings. In the following embodiments, the electroluminescent display device is described primarily as an organic light-emitting display device including an organic light-emitting material. The technical concept of the present invention is not limited to organic light-emitting display devices and can be applied to inorganic light-emitting display devices including inorganic light-emitting materials.

[0032] Throughout the specification, the same reference numerals refer to substantially the same components. In the following description, if it is determined that a detailed description of a known function or configuration related to this specification could unnecessarily obscure the essence of this specification, such detailed description is omitted.

[0033] FIG. 1 is a schematic block diagram of a display device according to an embodiment of the present invention.

[0034] Referring to FIG. 1, the display device includes a display panel (10) including a plurality of pixels, a panel driving unit including a data driving unit (12) and a gate driving unit (13) for driving the panel, and a timing control unit (11) for controlling the operation of the panel driving unit.

[0035] A plurality of data lines (14) and a plurality of gate lines (15A, 15B) intersect in the display panel (10), and pixels (SP) are arranged in a matrix form at each intersection area to form a pixel array. The pixel array is provided with a plurality of horizontal pixel lines (HL1 ~ HLn), and a horizontal pixel line (HL) includes a plurality of pixels (SP) arranged adjacent to each other along the horizontal direction.

[0036] The gate lines (15A, 15B) may include first gate lines (15A) to which a switch signal is applied and second gate lines (15B) to which an EM signal is applied. Each pixel (SP) may be connected to any one of the data lines (14), any one of the first gate lines (15A), and any one of the second gate lines (15B).

[0037] Each pixel (SP) may include a light-emitting element (hereinafter OLED) and switch elements such as a driving TFT and a switching TFT for driving it. Such a pixel (SP) receives a high-potential driving voltage (EVDD) and a low-potential driving voltage (EVSS) from a power block (not shown). The OLED included in the pixel (SP) includes an anode electrode and a cathode electrode, and an organic compound layer formed between them. The organic compound layer consists of a hole injection layer (HIL), a hole transport layer (HTL), an emission layer (EML), an electron transport layer (ETL), and an electron injection layer (EIL). When a power supply voltage is applied to the anode electrode and the cathode electrode, holes passing through the hole transport layer (HTL) and electrons passing through the electron transport layer (ETL) move to the light-emitting layer (EML) to form excitons, and as a result, the light-emitting layer (EML) generates visible light. The TFTs constituting the pixel (SP) can be implemented as p-type, n-type, or hybrid types. In addition, the semiconductor layer of the TFTs constituting the pixel (SP) may include amorphous silicon, polysilicon, or oxide.

[0038] The timing control unit (11) can receive timing signals, such as input image data (DATA) and a data enable signal (Data Enable, DE), from the outside. Based on the timing signals received from the outside, the timing control unit (11) can generate various control signals (DDC, GDC) required for the driving operation of the data driving unit (12) and the gate driving unit (13). The timing control unit (11) converts the input image data (DATA) received from the outside to match the data signal format used by the data driving unit (12) and outputs the converted image data (DATA).

[0039] The data driving unit (11) converts image data (DATA) in a digital data format into a data voltage according to the data timing control signal (DDC) and supplies it to the data lines (14).

[0040] The gate driving unit (13) generates a scan signal in response to a gate timing control signal (GDC) supplied from the timing control unit (11) and supplies it to the first gate lines (15A), and generates an EM signal and supplies it to the second gate lines (15B).

[0041] The timing control unit (11) can control the timing of image data being written to the horizontal pixel lines (HL1 ~ HLn) of the display panel (10) and the timing of light emission using timing control signals (GDC, DDC). The timing control unit (11) can implement BDI driving by dividing the operation into a light emission period during which the pixel (SP) emits light and a non-light emission period during which light emission is stopped. The timing control unit (11) can input a data voltage through the data line during the non-light emission period and control the pixels (SP) to which the data voltage is applied during the light emission period to emit light simultaneously.

[0042] The data writing timing and light emission timing controlled by the timing control unit (11) are explained with reference to FIG. 2.

[0043] FIG. 2 is a drawing for explaining a driving method of an electroluminescent display device according to an embodiment of the present invention.

[0044] Referring to FIG. 2, the timing control unit (11) can perform a Black Data Insertion (BDI) drive that inserts black data within one frame. BDI means inserting an emission off section within one frame to mitigate TFT afterimage characteristics and improve video quality, such as motion blur.

[0045] The timing control unit (11) controls the data driving unit (12) and the gate driving unit (13) during the period (Black) when a black screen is displayed on the display panel (10) to sequentially write image data to the horizontal pixel line (HL).

[0046] When data entry is completed, the timing control unit (11) can control the horizontal pixel lines (HL1 to HLn) for which data entry is completed to emit light simultaneously. During the emission period, the OLED emits light according to the image data entered in each pixel so that image data can be realized.

[0047] The timing control unit (11) can control the horizontal pixel lines (HL1 to HLn) of the entire display panel (10) to emit light simultaneously, or it is also possible to divide the n horizontal pixel lines into multiple blocks and control them to emit light simultaneously in each block unit. In this way, when the horizontal pixel lines (HL1 to HLn) emit light simultaneously, they all have the same emission duty, so the brightness deviation can be minimized.

[0048] FIG. 3 shows a pixel configuration for implementing the driving technology according to the present invention.

[0049] Referring to FIG. 3, a pixel according to the present invention may include an OLED, a driving TFT (Thin Film Transistor) (DT), a switching TFT (ST), a light-emitting TFT (EM), a first capacitor (C1), and a second capacitor (C2). The driving TFT (DT), the switching TFT (ST), and the light-emitting TFT (EM) each have a gate electrode, a drain electrode, and a source electrode. The first electrode may be the drain electrode and the second electrode may be the source electrode. The driving TFT (DT), the switching TFT (ST), and the light-emitting TFT (EM) may be implemented as a p-type, an n-type, or a hybrid type. In the following description, the case where the TFTs are implemented as an n-type will be exemplified.

[0050] An OLED includes an anode electrode and a cathode electrode. The anode electrode of the OLED is connected to a high potential driving voltage (EVDD), and the cathode electrode is connected to the drain node of a driving TFT (DT). The luminous brightness of the OLED can be controlled according to the magnitude of the driving current input to the anode electrode.

[0051] The gate electrode of the driving TFT (DT) is connected to the first node (N1), the drain electrode is connected to the cathode electrode of the OLED, and the source electrode is connected to the low potential driving voltage (EVSS). The driving TFT (DT) controls the amount of current flowing through the organic light-emitting diode (OLED) according to the difference voltage (Vgs) between the gate voltage applied to the gate electrode and the source voltage applied to the source electrode.

[0052] One electrode of the light-emitting TFT (ET) is connected to the first node (N1), and the other electrode is connected to the second node (N2), and a light-emitting signal (EM) is received through the gate electrode. When the light-emitting signal (EM) is input to the ON level, the light-emitting TFT (ET) is turned on to connect the first node (N1) and the second node (N2).

[0053] One electrode of the switch TFT (ST) is connected to the data line (16), and the other electrode is connected to the first node (N1), and the switch signal (SW) is received as input through the gate electrode. When the switch signal (SW) is input to the ON level, the switch TFT (ST) is turned on to connect the data line (16) and the first node (N1). The switch TFT (ST) is turned on by the switch signal (SW) and can transmit the data voltage (VDATA) supplied to the data line (16) to the first node (N1).

[0054] One electrode of the first capacitor (C1) is connected to the first node (N1), and the other electrode is connected to the low potential driving voltage (EVSS). Accordingly, when the switch TFT (ST) is turned on and the data line (16) and the first node (N1) are connected, the data voltage (VDATA) input through the data line (16) can be charged to the first capacitor (C1) connected to the first node (N1).

[0055] One electrode of the second capacitor (C2) is connected to the second node (N2), which is the gate node of the driving TFT (DT), and the other electrode is connected to the third node (N3), which is the source node of the driving TFT (DT). Accordingly, when the light-emitting TFT (ET) is turned on, the first node (N1) and the second node (N2) are connected, and the voltage of the first node (N1) is reflected in the second node (N2). The second capacitor (C2) can reflect the voltage applied to the second node (N2) as the gate-source voltage (Vgs) of the driving TFT (DT).

[0056] As described above, the pixel according to the present invention is composed of three TFTs (DT, ST, ET) and two capacitors (C1, C2) and has a structure connected to one data line (16) without a separate reference line (Vref).

[0057] Figure 4 is a waveform of the signal supplied to the pixel of Figure 3.

[0058] Referring to FIG. 4, the method for driving a pixel according to an embodiment of the present invention may include first to fourth periods (T1 to T4).

[0059] The data voltage (VDATA) is applied as a high-level data power source (DATA_H) having a high-level potential during the first and second periods (T1 to T2), and as a low-level data power source (VDATA_L) having a low-level potential during the third and fourth periods (T3 to T4).

[0060] The light emission signal (EM) is applied to the ON level during the third period (T3). Accordingly, the light-emitting TFT (ET) receiving the light emission signal (EM) is turned on during the third period (T3) to connect the first node (N1) and the second node (N2).

[0061] The switch signal (SW) is applied to the ON level during the first period (T1), then applied to the OFF level during the second and third periods (T2 to T3), and then applied to the ON level again during the fourth period (T4). Accordingly, the switch TFT (ST) receiving the switch signal (SW) is turned on during the first period (T1) to transmit the high-level data power (VDATA_H) input to the data line (16) to the first node (N1), is turned off during the second and third periods (T2 to T3), and is turned on again during the fourth period (T4) to transmit the low-level data power (VDATA_L) to the first node (N1).

[0062] Due to the above driving waveform, image data (VDATA) is written to the first capacitor (C1) during the first period (T1), the written image data (VDATA) is held during the second period (T2), and the image data (VDATA) stored in the first capacitor (C1) is transferred to the second capacitor (C2) during the third period (T3), so that the OLED can emit light during the fourth period (T4).

[0063] The operation of the pixel in each period is explained in detail with reference to FIGS. 5 to 8.

[0064] Figure 5 is a diagram illustrating the operation of a pixel during the first period (T1).

[0065] Referring to FIG. 5, during the first period (T1), a high-level data power supply (VDATA_H) is applied to the data line (16), the switch signal (SW) is applied at the ON level, and the light-emitting signal (EM) is applied at the OFF level. Accordingly, during the first period (T1), the switch TFT (ST) is turned on by receiving the ON-level switch signal (SW), and the light-emitting TFT (ET) is kept in an OFF state by receiving the OFF-level light-emitting signal (EM).

[0066] As the switch TFT (ST) is turned on, the data line (16) and the first node (N1) are connected. Accordingly, the high-level data power (VDATA_H) input to the data line (16) is transmitted to the first node (N1).

[0067] Since the light-emitting TFT (ET) is in an off state, the first node (N1) and the second node (N2) are disconnected. Accordingly, the high-level data power (VDATA_H) applied to the first node (N1) is charged to the first capacitor (C1) connected to the first node (N1), and the potential of the first node (N1) rises to the potential of the high-level data power (VDATA_H).

[0068] During the first period (T1), high-level data power (VDATA_H) is supplied sequentially to all horizontal pixel lines (HL1 ~ HLn) so that data can be written to each pixel.

[0069] Figure 6 is a diagram illustrating the operation of a pixel during the second period (T2).

[0070] Referring to FIG. 6, during the second period (T2), a high-level data power supply (VDATA_H) is applied to the data line (16), the switch signal (SW) is applied at an off level, and the light-emitting signal (EM) is applied at an off level. Accordingly, during the second period (T2), the switch TFT (ST) is turned off by receiving the off-level switch signal (SW), and the light-emitting TFT (ET) is also turned off by receiving the off-level light-emitting signal (EM).

[0071] As the switch TFT (ST) is turned off, the data line (16) and the first node (N1) remain disconnected. Since the light-emitting TFT (ET) is also turned off, the first capacitor (C1) connected to the first node (N1) remains charged with a high-level data power supply (VDATA_H).

[0072] The display device of the present invention controls the horizontal pixel lines (HL1 to HLn) to emit light simultaneously after data writing is completed, so data writing for each horizontal pixel line proceeds during the second period (T2). Therefore, the length of the second period (T2) can be longer for pixels in which data is written earlier, so the length of the second period (T2) can vary depending on the horizontal line to which the pixel belongs.

[0073] Figure 7 is a diagram illustrating the operation of a pixel in the third period (T3).

[0074] Referring to FIG. 7, during the third period (T3), a low-level data power supply (VDATA_L) is applied to the data line (16), the switch signal (SW) is applied at an off level, and the light emission signal (EM) is applied at an on level. Accordingly, during the third period (T3), the switch TFT (ST) is turned off by receiving the off-level switch signal (SW), and the light emission TFT (ET) is turned on by receiving the on-level light emission signal (EM).

[0075] As the switch TFT (ST) is turned off, the data line (16) and the first node (N1) remain disconnected. The light-emitting TFT (ET) is turned on, and the first node (N1) and the second node (N2) are connected. Accordingly, the potential of the first node (N1) is reflected in the second node (N2), and the second capacitor (C2) is charged with a high-level data power supply (VDATA_H). Accordingly, the potential of the second node (N2) rises to the potential of the high-level data power supply (VDATA_H).

[0076] FIG. 8 is a diagram illustrating the operation of a pixel in the fourth period (T4).

[0077] Referring to FIG. 8, during the fourth period (T4), a low-level data power supply (VDATA_L) is applied to the data line (16), the switch signal (SW) is applied at the ON level, and the light emission signal (EM) is applied at the OFF level. Accordingly, during the fourth period (T4), the switch TFT (ST) is turned on by receiving the ON-level switch signal (SW), and the light emission TFT (ET) is turned off by receiving the OFF-level light emission signal (EM).

[0078] As the switch TFT (ST) is turned on, the data line (16) and the first node (N1) are connected. Accordingly, the low-level data power (VDATA_L) input to the data line (16) is transmitted to the first node (N1). Therefore, the potential of the first node (N1) gradually decreases from the potential of the high-level data power (VDATA_H) to the potential of the low-level data power (VDATA_L).

[0079] As the light-emitting TFT (ET) is turned off, the connection between the first node (N1) and the second node (N2) is disconnected.

[0080] The driving TFT (DT) is turned on by the potential of the high-level data power supply (VDATA_H) charged in the second capacitor (C2) connected between the second node (N2), which is the gate node, and the third node (N3), which is the source node. When the driving TFT (DT) is turned on, a current path is created that connects from the high-potential driving voltage (EVDD) through the OLED and the driving TFT (DT) to the low-potential driving voltage (EVSS), causing the OLED to emit light. Since the amount of current flowing through the driving TFT (DT) is controlled according to the gate-source voltage (Vgs) of the driving TFT (DT), the magnitude of the driving current input to the OLED can be adjusted according to the potential of the high-level data power supply (VDATA_H) charged in the second capacitor (C2), and as a result, the luminous brightness of the OLED can be adjusted.

[0081] FIG. 9 is a drawing for explaining a driving method of an electroluminescent display device according to a first embodiment of the present invention.

[0082] Referring to FIG. 9, the electroluminescent display device according to the first embodiment performs BDI (Black Data Insertion) driving, and includes a period (Black) during which the OLED remains off and a black screen is displayed, and a period (Emission) during which the OLED emits light and displays image data.

[0083] During the period when the black screen is displayed (Black), switch signals are sequentially input to the horizontal pixel lines of the display panel to write image data (VDATA). Once data writing to all horizontal pixel lines is complete, the OLEDs of all horizontal pixel lines emit light to display the image data.

[0084] For this operation, the gate driver (13) sequentially inputs switch signals (SW) to all horizontal pixel lines during the period (Black) when a black screen is displayed. If the display panel has n horizontal pixel lines (HL1 to HLn), the gate driver (13) sequentially inputs n switch signals (SW1 to SWn) to the corresponding horizontal pixel lines (HL1 to HLn). The data driver (12) sequentially supplies image data (VDATA) to each horizontal pixel line (HL1 to HLn) in accordance with the operation of the gate driver (13).

[0085] When data is written to n horizontal pixel lines (HL1 to HLn), a light emission signal (EM) is simultaneously input to n horizontal pixel lines (HL1 to HLn). Accordingly, the OLEDs of all horizontal pixel lines emit light simultaneously, and image data is displayed.

[0086] In conventional driving methods, horizontal pixel lines (HL1 ~ HLn) emit light sequentially, so an EVSS rising phenomenon may occur in which the potential of the low-potential driving voltage (EVSS) rises as the OLED emits light. Accordingly, conventional driving methods required compensating for image data (VDATA) by taking into account EVSS rising. On the other hand, the electroluminescent display device according to the first embodiment of the present invention can eliminate the effect of EVSS rising because it writes image data (VDATA) during the period when a black screen is displayed (Black), that is, when all OLEDs are turned off. In addition, since the OLEDs of all horizontal pixel lines emit light simultaneously and the light emission duty is the same, it is possible to prevent the perception of brightness deviation caused by differences in light emission duty for each line.

[0087] FIG. 10 is a drawing for explaining a driving method of an electroluminescent display device according to a second embodiment of the present invention.

[0088] Referring to FIG. 10, the electroluminescent display device according to the second embodiment performs Black Data Insertion (BDI) driving, and divides the entire horizontal pixel lines (HL1 to HLn) into a plurality of blocks (B1 to Bm) to control image data (VDATA) writing and emission operations on a block-by-block basis.

[0089] In each block, image data (VDATA) is sequentially written during the period when a black screen is displayed (Black), and when the data writing for a corresponding block is completed, the horizontal pixel lines of that block emit light simultaneously to display the image data. When the image data (VDATA) writing for the previous block is completed, data writing for the next block begins, and the image data writing for the next block can proceed while the black screen is displayed during the previous block's light-emitting period. In this way, each block (B1~Bm) can display one frame by sequentially performing data writing and light-emitting operations.

[0090] The driving method of the electroluminescent display device according to the second embodiment can extend the emission time compared to the driving method of the first embodiment. On the other hand, since data writing for the next blocks proceeds while the previous block is in the emission operation, an EVSS rising phenomenon may occur. Accordingly, it was necessary to compensate the image data (VDATA) in consideration of the EVSS rising.

[0091] FIGS. 11 to 13 are drawings for explaining a method of compensating for EVSS fluctuation values ​​when driving an electroluminescent display device.

[0092] Figure 11 is a graph showing the result of simulating the fluctuation phenomenon of EVSS that occurs when video data is input.

[0093] The simulation graph of Fig. 11 illustrates the results of simulating changes in EVSS values ​​when a data driver is located at the top and supplies image data in a display device with vertical numbers 0 to 2101.

[0094] According to the simulation graph, when the display panel is driven, the EVSS increases and is measured to be 2.5V or higher between Vertical number 500 and 1000, 2.0V between Vertical number 1000 and 1500, 1.5V near Vertical number 1500, and 1.0V between Vertical number 1500 and 2000, gradually decreasing so that the EVSS is measured to be about 0.5V near Vertical number=2000, where the video data is supplied last.

[0095] In other words, it can be confirmed that the greater the distance from the data driver, the greater the increase in EVSS. When the EVSS value increases, the brightness decreases even when data of the same grayscale is input. The simulation result of Fig. 11 shows the current (I) flowing through the OLED based on 1 pixel (1 PXL). PXL Assuming the current is 1.4uA and the resistance is 0.77, the simulation of EVSS values ​​per horizontal pixel line confirms that there is a difference of approximately 2.4V between the EVSS of the top and bottom. In such cases where EVSS differs, there can be a difference of about 87% in brightness between the top and bottom of the panel at the same grayscale level. To improve this brightness non-uniformity, the data voltage can be compensated by reflecting the variation in EVSS.

[0096] FIG. 12 is a diagram illustrating the calculation timing for compensating for fluctuations in EVSS, and FIG. 13 is an equivalent circuit diagram of one vertical line of a display panel.

[0097] Referring to FIGS. 12 and 13, EVSS voltages for each position are stored at the end of the first frame (Frame-End) to compensate for EVSS fluctuations. If the display panel includes n horizontal pixel lines (HL1 to HLn), n voltage values ​​can be stored in one vertical line.

[0098] Afterwards, when writing data for the next second frame (Frame-Writing), the EVSS fluctuation voltage is calculated using the EVSS voltages stored at the time the previous frame ends. Afterwards, the voltage of the image data can be compensated by reflecting the EVSS fluctuation voltage. FIG. 13 is an equivalent circuit diagram of one vertical line of a display panel, which is a display panel having a first horizontal pixel line (HL1) to an nth horizontal pixel line (HLn), and as shown in FIG. 13, data is input in the order from the first horizontal pixel line (HL1) to the nth horizontal pixel line (HLn), and the OLED emits light in the same order.

[0099] In this embodiment, the data driver supplying the data voltage is located at a position adjacent to the nth horizontal pixel line (HLn), that is, at the bottom in the drawing. The resistors (R) on the vertical lines represent the resistance due to the pixel, and the current (I1~I n ) represents the current applied to each pixel. The direction of the current arrow indicates the flow of current when the OLED emits light.

[0100] Assuming that the current of a pixel flows from the first horizontal pixel line (HL1) toward the nth horizontal pixel line (HLn), the voltage of each pixel can be calculated as the product of the resistance and current of the corresponding pixel (V=IR).

[0101] V1 to Vn, which are EVSS voltages of each pixel line at the frame-end, can be calculated using the following calculation method. Here, the frame-end is the point in time when the first horizontal pixel line (HL1) finishes emitting light and the nth horizontal pixel line (HLn) starts emitting light, as shown in FIG. 12.

[0102] EVSS voltage at the end of the frame (Frame-End)

[0103]

[0104] Here, .... Therefore, this implies that IS1 = I1, IS2 = I1 + I2, and IS3 = I1 + I2 + I3. The voltage at point V1 is the sum of the voltage at point V2 and the voltage calculated by multiplying I1 by the resistance (I1*R). That is, V1 can have the value V2 = V2 + IS1*R. In the same way, the voltage at point V2 is the sum of the voltage at point V3 and the voltage calculated by multiplying the current "I1 + I2" by the resistance. That is, V2 can have the value V3 + IS2*R. Here, since V1 = V2 + IS1*R and V2 = V3 + IS2*R, V1 can be expressed as V3 + (IS1 + IS2)*R. In the same way, if we substitute V3 with V4 in the equation for calculating V1, and finally substitute Vn with ISn*R, then V1 = It can be represented as such. Through the above calculation method, the voltage at the end of the frame can be calculated.

[0105] Afterwards, when writing data for the next frame, the EVSS voltage fluctuation is calculated using the EVSS voltage calculated at the end of the previous frame (Frame-End), and the data voltage to be written is compensated by reflecting the calculated EVSS fluctuation. Here, for the area driving the black screen, the current of the black driving area is replaced with 0 and stored.

[0106] The EVSS fluctuation voltage during the frame-writing interval for frame driving can be calculated using the following calculation method. In the calculation formula, the prime (') symbol indicates the value calculated from the previous frame.

[0107] <EVSS Fluctuation Voltage in Frame-Writing Interval>

[0108]

[0109] As shown in FIG. 12, at the end of the previous frame (Frame-End), the first horizontal pixel line (HL1) completes emitting light, and the data for the next frame is written. Therefore, since there is no change in voltage of the first horizontal pixel line (HL1) from the time the V1 voltage is calculated until the data for the next frame is written, V1 is calculated as V1 = V1'.

[0110] V2 of the second horizontal pixel line (HL2) is calculated by reflecting the change in the current of the first horizontal pixel line (HL1) compared to the frame end time. The current change is calculated by subtracting the current IS1' that flowed in the first line in the previous frame from the current IS1 that is applied to the first line in the current frame, and V2 in the current frame can be calculated by multiplying this by the resistance R*(n-1) that extends to the data driving unit.

[0111] The EVSS value calculated in this way is reflected in the data voltage for data writing to calculate a compensated data voltage, and by inputting the compensated data voltage, the target brightness can be obtained even if the EVSS fluctuates.

[0112] The above calculation and compensation process of the EVSS compensation voltage may be carried out under the control of the timing control unit (11) along with compensation functions such as driving TFT compensation and OLED compensation, but is not limited thereto.

[0113] As explained above, in order to compensate for EVSS fluctuations, the EVSS fluctuation value of the corresponding line is calculated before data is written, and then the EVSS fluctuation value is reflected in the data voltage to supply the compensated data voltage. Since the above-described method for compensating for EVSS fluctuations involves writing and emitting data in units of one horizontal line, the EVSS fluctuation value is calculated based on one horizontal line, and compensation is performed accordingly. Based on this principle, as in the second embodiment of the present invention, the entire horizontal pixel lines (HL1 ~ HLn) are divided into multiple blocks (B1 ~ Bm), image data (VDATA) is written in units of blocks, and when data writing is completed, the horizontal pixel lines of the corresponding blocks emit light simultaneously. In this case, EVSS calculations can be performed at every timing of light emission in units of blocks. For example, when data writing of the previous block is completed and light emission begins, the EVSS fluctuation value of the next block is calculated to compensate the data voltage, and then the compensated data voltage can be written.

[0114] As described above, the driving method of the electroluminescent display device according to the first embodiment of the present invention writes image data (VDATA) during the period (Black) when the OLED is maintained in an off state and a black screen is displayed, and when the data writing is completed, the OLEDs of all horizontal pixel lines emit light simultaneously to display the image data. Since the image data (VDATA) is written when all OLEDs are in an off state, the effect of EVSS rising can be eliminated, and since the OLEDs of all horizontal pixel lines emit light simultaneously and the light emission duty is the same, it is possible to prevent the perception of brightness deviation due to differences in light emission duty for each line.

[0115] The driving method of an electroluminescent display device according to the second embodiment of the present invention can divide the entire horizontal pixel lines (HL1 to HLn) into a plurality of blocks (B1 to Bm) and control the recording of image data (VDATA) and emission operation on a block-by-block basis. Since the recording of data and emission operation proceed on a block-by-block basis (B1 to Bm) to display one frame, the driving method of an electroluminescent display device according to the second embodiment can extend the emission time compared to the driving method of the first embodiment.

[0116] The pixel circuit of the present invention for implementing the driving method of the first and second embodiments of the present invention is composed of three TFTs (DT, ST, ET) and two capacitors (C1, C2) and may have a structure connected to one data line (16) without a separate reference line (Vref). The pixel circuit of the present invention may store an image data voltage in the first capacitor (C1) during the period (Black) when a black screen is displayed, and transmit the image data voltage to the second capacitor (C2) which controls the gate source voltage of the driving TFT when a light emission signal (EM) is input.

[0117] From the above description, those skilled in the art will understand that various changes and modifications are possible within the scope of the technical concept of this specification. Accordingly, the technical scope of this specification should not be limited to the contents described in the detailed description of the specification, but should be determined by the claims. Explanation of the symbols

[0118] 10: Display panel 11: Timing control unit 12: Data driver 13: Gate driver

Claims

Claim 1 An electroluminescent display device comprising: a light-emitting element, a driving TFT that controls a driving current flowing through the light-emitting element, and a first capacitor, and a plurality of pixels connected to a gate line and a data line connected to the gate electrode of the driving TFT through a first node; a panel driving unit connected to the data line and the gate line; and a timing control unit that controls the operation of the panel driving unit to drive the light-emitting element by dividing it into a light-emitting period during which the light-emitting element emits light and a non-light-emitting period during which light-emitting is stopped, inputs a data voltage through the data line during the non-light-emitting period, and controls the light-emitting elements to which the data voltage is applied to emit light simultaneously during the light-emitting period, wherein the first capacitor is connected to the first node to charge the data voltage according to a first data power input through the data line during the non-light-emitting period and discharges the data voltage according to a second data power during the light-emitting period. Claim 2 In claim 1, the timing control unit controls to display an image during the light emission period and to display a black image during the non-light emission period, thereby implementing Back Data Insertion (BDI) driving in an electroluminescent display device. Claim 3 In claim 1, the timing control unit sequentially inputs the data voltage to all pixel lines of the display panel during the non-luminous period and controls all pixel lines to emit light simultaneously during the luminous period, thereby forming an electroluminous display device. Claim 4 In claim 1, the timing control unit divides the horizontal pixel lines of the display panel into a plurality of blocks, sequentially inputs the data voltage in units of divided blocks, and controls the simultaneous emission of light in units of blocks, thereby forming an electroluminescent display device. Claim 5 In paragraph 4, the timing control unit is an electroluminescent display device that compensates the data voltage based on a change in low potential voltage according to the light emission of the light-emitting elements. Claim 6 The electroluminescent display device according to claim 1, wherein the panel driving unit comprises: a data driving unit that supplies the data voltage to the data line; and a gate driving unit that sequentially outputs a switch signal for inputting the data voltage and simultaneously outputs a light emission signal to pixels to which the data voltage is applied. Claim 7 A display panel having data lines and gate lines intersecting and a plurality of pixels arranged therein; a data driving unit supplying a first data power source for charging a data voltage and a second data power source for discharging the data voltage to the data lines; and a gate driving unit outputting a switch signal for inputting the first data power source or the second data power source and simultaneously outputting a light-emitting signal to pixels to which the data voltage is applied, wherein each of the pixels comprises: a light-emitting element with an anode electrode connected to a high-potential driving voltage; a driving transistor connected between the cathode electrode of the light-emitting element and a low-potential driving voltage to control the driving current of the light-emitting element according to the voltage difference between the gate and the source; a switching transistor connecting the data line and a first node according to the switch signal; a light-emitting transistor connecting the first node and a second node according to the light-emitting signal; and a first capacitor connected to the first node to charge the data voltage input to the data line. The electroluminescent display device comprises: a second capacitor connected to the second node and the source node of the driving transistor, which charges the data voltage charged in the first capacitor to the gate-source voltage of the driving transistor upon input of the light-emitting signal; wherein the first capacitor charges the data voltage by the first data power input to the data line while the light-emitting element is off, and discharges the data voltage by the second data power input to the data line while the light-emitting element is on. Claim 8 In claim 7, the gate driving unit supplies the first data power to the first capacitor by sequentially supplying the switch signal to the gate lines while the light-emitting element is off, and supplies the second data power to the first capacitor by simultaneously supplying the switch signal to the gate lines while the light-emitting element is on. Claim 9 An electroluminescent display device according to claim 7, wherein the driving period for emitting light of the light-emitting element includes a first to a fourth period, wherein in the first period the switching transistor is turned on and the light-emitting transistor is turned off so that the data voltage is charged in the first capacitor, in the second period the switching transistor and the light-emitting transistor are turned off so that the data voltage is maintained in the first capacitor, in the third period the switching transistor is turned off and the light-emitting transistor is turned on so that the data voltage is charged in the second capacitor, and in the fourth period the driving transistor is turned on according to the data voltage charged in the second capacitor to apply a driving power supply to the light-emitting element, and the switching transistor is turned on to discharge the data voltage charged in the first capacitor. Claim 10 In claim 7, the driving transistor is an electroluminescent display device in which the drain electrode is connected to the cathode electrode of the light-emitting element, the source electrode is connected to the low-potential driving voltage, and the gate electrode is connected to the second node to control the magnitude of the driving current applied to the light-emitting element according to the magnitude of the data voltage charged in the second capacitor. Claim 11 An electroluminescent display device comprising: a light-emitting element with an anode electrode connected to a high potential driving voltage; a driving transistor connected between the cathode electrode of the light-emitting element and a low potential driving voltage to control the driving current of the light-emitting element according to the voltage difference between the gate and the source; a switching transistor connecting a data line and a first node according to a switch signal; a first capacitor connected to the first node to charge a data voltage according to a first data power source input to the data line and discharge the data voltage according to a second data power source; a light-emitting transistor connecting the first node and a second node according to a light-emitting signal; and a second capacitor connected to the second node and the source node of the driving transistor. Claim 12 In claim 11, the first capacitor charges the data voltage while the light-emitting element is off and discharges the data voltage while the light-emitting element is on. Claim 13 In claim 11, the second capacitor is an electroluminescent display device that charges the data voltage charged in the first capacitor into the gate-source voltage of the driving transistor upon input of the light-emitting signal. Claim 14 An electroluminescent display device according to claim 11, wherein when the switching transistor is turned on, the light-emitting transistor maintains an off state so that the data voltage is charged or discharged in the first capacitor, and when the light-emitting transistor is turned on, the switching transistor maintains an off state so that the data voltage charged in the first capacitor is charged in the second capacitor. Claim 15 An electroluminescent display device according to claim 11, wherein the driving period for emitting light of the light-emitting element includes a first to a fourth period, wherein in the first period the switching transistor is turned on and the light-emitting transistor is turned off so that the data voltage is charged in the first capacitor, in the second period the switching transistor and the light-emitting transistor are turned off so that the data voltage is maintained in the first capacitor, in the third period the switching transistor is turned off and the light-emitting transistor is turned on so that the data voltage is charged in the second capacitor, and in the fourth period the driving transistor is turned on according to the data voltage charged in the second capacitor to apply a driving power supply to the light-emitting element, and the switching transistor is turned on to discharge the data voltage charged in the first capacitor.

Images