Electroluminescent display device

Abstract

An electroluminescent display device according to an embodiment of the disclosure includes a display panel including a plurality of pixels each having a light emitting element and a drive TFT for controlling a drive current flowing through the light emitting element and connected to a data line and a gate line, a panel driver connected to the data line and the gate line, and a timing controller configured to control an operation of the panel driver such that the operation is divided into a light emitting period in which the light emitting element emits light and a non-light emitting period in which the light emitting element stops emitting light, and perform control such that a data voltage is input through the data line during the non-light emitting period, and the light emitting element to which the data voltage is applied emits light at the same time during the light emitting period.

Description

Technical Field

[0001] This disclosure relates to an electroluminescent display device including driving elements for driving pixels. Background Technology

[0002] Based on the material of the light-emitting layer, electroluminescent display devices are broadly classified into inorganic light-emitting display devices and organic light-emitting display devices. Among them, active-matrix organic light-emitting display devices include organic light-emitting diodes (hereinafter referred to as "OLEDs") that emit light spontaneously.

[0003] Organic light-emitting display devices include OLEDs and pixels arranged in a matrix, and the brightness of the pixels is adjusted according to the gray levels of image data. Each pixel essentially includes a driving thin-film transistor (TFT) that controls the driving current flowing through the OLED according to the gate-source voltage, and one or more switching TFTs for programming the gate-source voltage of the driving TFT.

[0004] Organic light-emitting diode (OLED) displays have advantages such as thinness, low power consumption, high response speed, high luminous efficiency, high brightness, and wide viewing angle, and therefore have been applied in various fields.

[0005] Therefore, research continues to improve the performance of organic light-emitting display devices, such as image quality. Summary of the Invention

[0006] One object of this disclosure is to provide an electroluminescent display device and a driving method thereof, which can reproduce uniform brightness throughout the entire area of ​​the display panel by preventing or reducing the generation of brightness deviations in the display panel area when applying black data insertion (BDI) technology that inserts a light-off period within a frame to improve the picture quality of the display device.

[0007] To achieve these objectives and other advantages and in accordance with the purposes of this disclosure, as implemented and broadly described herein, an electroluminescent display device includes: a display panel comprising a plurality of pixels, each pixel having a light-emitting element and a driving TFT for controlling a driving current flowing through the light-emitting element and connected to a data line and a gating line; a panel driver connected to the data line and the gating line; and a timing controller configured to operate the panel driver such that the operation is divided into a light-emitting period in which the light-emitting element emits light and a non-light-emitting period in which the light-emitting element stops emitting light, and to perform control such that during the non-light-emitting period, a data voltage is input through the data line, and during the light-emitting period, the light-emitting element to which the data voltage is applied emits light simultaneously.

[0008] The timing controller can perform black data insertion (BDI) operations by executing controls to display an image during the luminous period and a black image during the non-luminous period.

[0009] The timing controller can perform control so that during non-light-emitting periods, data voltages are sequentially input to all pixel lines of the display panel, and during light-emitting periods, all pixel lines emit light simultaneously.

[0010] The timing controller can divide the horizontal pixel rows of the display panel into multiple blocks and execute control so that data voltage is input sequentially in the divided blocks and the horizontal pixel rows illuminate simultaneously in blocks.

[0011] The timing controller can compensate for the data voltage based on the change in the light emission of the light-emitting element when the voltage level is low.

[0012] The panel driver may include: a data driver configured to provide a data voltage to a data line; and a gating driver configured to sequentially output a switching signal for inputting the data voltage and simultaneously output an emitting signal to the pixel to which the data voltage is applied.

[0013] In another aspect of this disclosure, an electroluminescent display device includes: a display panel, wherein data lines and gate lines intersect and a plurality of pixels are disposed thereon; a data driver configured to provide a data voltage to the data lines; and a gate driver configured to sequentially output a switching signal for inputting the data voltage and simultaneously output a light-emitting signal to the pixels to which the data voltage is applied, wherein each pixel includes: a light-emitting element having an anode to which a high-level driving voltage is applied; a driving transistor connected between the cathode of the light-emitting element and a low-level 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 configured to connect a corresponding data line and a first node according to a corresponding switching signal; a light-emitting transistor configured to connect a first node and a second node according to the light-emitting signal; a first capacitor connected to the first node to be charged using the data voltage applied to the data lines; and a second capacitor connected to the second node and the source node of the driving transistor to be charged using the data voltage charged into the first capacitor as the gate-source voltage of the driving transistor when the light-emitting signal is input.

[0014] The first capacitor can be charged using the data voltage when the light-emitting element is turned off.

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

[0016] In the driving transistor, the drain electrode can be connected to the cathode of the light-emitting element, the source electrode can be provided with a low-level driving voltage, and the gate electrode can be connected to a 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 into the second capacitor.

[0017] In another aspect of this disclosure, an electroluminescent display device includes: a light-emitting element having an anode to which a high-level driving voltage is applied; a driving transistor connected between a cathode of the light-emitting element and a low-level driving voltage to control the driving current of the light-emitting element according to a voltage difference between a gate and a source; a switching transistor configured to connect a data line and a first node according to a switching signal; a first capacitor connected to the first node to be charged using a data voltage input to the data line; a light-emitting transistor configured to connect 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 can be charged using the data voltage when the light-emitting element is turned off.

[0019] When an input light-emitting signal is received, the second capacitor can be charged using the data voltage charged into the first capacitor as the gate-source voltage of the driving transistor.

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

[0021] The driving period for the light emission of the light-emitting element may include a first period to a fourth period. In the first period, the switching transistor can be turned on and the light-emitting transistor can be turned off so that the data voltage is charged into the first capacitor. In the second period, the switching transistor and the light-emitting transistor can be turned off so that the data voltage is held in the first capacitor. In the third period, the switching transistor can be turned off and the light-emitting transistor can be turned on so that the data voltage is charged into the second capacitor. In the fourth period, the driving transistor can be turned on according to the data voltage charged into the second capacitor to apply driving power to the light-emitting element.

[0022] The electroluminescent display device disclosed herein can prevent or reduce brightness deviation by writing image data for each row during the light-off period when displaying black data and making the pixels of all rows light up simultaneously when the image data writing is completed, so that all rows have the same duty cycle. Attached Figure Description

[0023] Figure 1This is a control block diagram of an electroluminescent display device according to an embodiment of the present disclosure.

[0024] Figure 2 This is a diagram illustrating a method for driving an electroluminescent display device according to an embodiment of the present disclosure.

[0025] Figure 3 It is a circuit diagram for implementing the driving technology according to this disclosure for a pixel.

[0026] Figure 4 It is provided to Figure 3 The waveform of the signal of the pixel.

[0027] Figures 5 to 8 This is a diagram used to describe the method of driving pixels.

[0028] Figure 9 This is a diagram illustrating a method for driving an electroluminescent display device according to a first embodiment of the present disclosure.

[0029] Figure 10 This is a diagram illustrating a method for driving an electroluminescent display device according to a second embodiment of the present disclosure.

[0030] Figures 11 to 13 This is a diagram illustrating the EVSS rise compensation method during operation of the electroluminescent display device according to the second embodiment. Detailed Implementation

[0031] The advantages and features of this disclosure, and the ways in which they are obtained, will become apparent from the following detailed description of the embodiments, taken in conjunction with the accompanying drawings. However, this disclosure is not limited to the embodiments disclosed below and can be implemented in many different forms. Rather, these exemplary embodiments are provided so that this disclosure will be thorough and complete and will fully convey the scope to those skilled in the art. Therefore, the scope of this disclosure should be defined by the claims.

[0032] The shapes, dimensions, scales, angles, quantities, etc., shown in the accompanying drawings to describe various embodiments of this disclosure are given by way of example only, and therefore, this disclosure is not limited to the examples shown in the drawings. Throughout the specification, identical or very similar elements are designated by the same reference numerals. In this specification, when the terms "comprising," "including," etc., are used, other elements may be added unless the term "only" is used. Unless the context clearly indicates otherwise, elements described in the singular are intended to include multiple elements.

[0033] In interpreting the constituent elements included in the various embodiments of this disclosure, even without an explicit description thereof, these constituent elements are to be interpreted as including a range of tolerances.

[0034] In the description of various embodiments of this disclosure, when describing positional relationships, for example, when using terms such as "on," "above," "below," "next to," etc. to describe the positional relationship between two components, one or more other components may be located between the two components unless the terms "direct" or "close" are used.

[0035] In the description of the various embodiments of this disclosure, although terms such as "first" and "second" may be used to describe various elements, these terms are only used to distinguish the same or similar elements from one another. Therefore, in this specification, unless otherwise mentioned, an element modified by "first" may be the same as an element modified by "second" within the scope of the technology of this disclosure.

[0036] In the electroluminescent display device of this disclosure, the pixel circuit includes driving elements and switching elements. The driving elements and switching elements can be implemented as at least one of an n-type transistor (NMOS) and a p-type transistor (PMOS). The transistor can be implemented as a thin-film transistor (TFT) in the display panel. The transistor can be implemented as an oxide transistor with an oxide semiconductor pattern or an LTPS transistor with a low-temperature polycrystalline silicon (LTPS) semiconductor pattern. The transistor is a three-electrode device including a gate, a source, and a drain. The source is the electrode that provides charge carriers to the transistor. In the transistor, charge carriers begin to flow out from the source. The drain is the electrode through which charge carriers leave the transistor. In the transistor, charge carriers flow from the source to the drain. In the case of an n-type transistor (NMOS), the source voltage is lower than the drain voltage, allowing electrons to flow from the source to the drain, since the charge carriers are electrons. In an n-type transistor (NMOS), current flows from the drain to the source. In the case of a p-type transistor (PMOS), the source voltage is higher than the drain voltage, allowing holes to flow from the source to the drain because the charge carriers are holes. In a p-type transistor (PMOS), current flows from the source to the drain because holes flow from the source to the drain. It should be noted that the source and drain of a transistor are not fixed. For example, the source and drain can change depending on the applied voltage. Therefore, this disclosure is not limited to the source and drain of a transistor. In the following description, the source and drain of the transistor will be referred to as the first electrode and the second electrode.

[0037] The gate signal of a transistor used as a switching element oscillates between a gate on-state voltage and a gate off-state voltage. The gate on-state voltage is set to a voltage higher than the transistor's threshold voltage, and the gate off-state voltage is set to a voltage lower than the transistor's threshold voltage. The transistor turns on in response to the gate on-state voltage and turns off in response to the gate off-state voltage. In the case of an n-type transistor (NMOS), the gate on-state voltage can be a gate high voltage (VGH), and the gate off-state voltage can be a gate low voltage (VGL). In the case of a p-type transistor (PMOS), the gate on-state voltage can be a gate low voltage (VGL), and the gate off-state voltage can be a gate high voltage (VGH).

[0038] In the following description, various embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In these embodiments, electroluminescent displays will be described primarily with respect to organic light-emitting displays that include organic light-emitting materials. The technical spirit of the present disclosure is not limited to organic light-emitting display devices, but can be applied to inorganic light-emitting display devices that include inorganic light-emitting materials.

[0039] Throughout this specification, similar reference numerals denote substantially equivalent elements. In the following description, detailed descriptions of known functions or configurations relevant to this specification will be omitted where it is determined that such detailed descriptions might unnecessarily obscure the subject matter.

[0040] Figure 1 This is a schematic block diagram of a display device according to an embodiment of the present disclosure.

[0041] Reference Figure 1 The display device includes: a display panel 10, which includes a plurality of pixels; a panel driver, which includes a data driver 12 and a gating driver 13 for driving the display panel; and a timing controller 11 for controlling the operation of the panel driver.

[0042] In the display panel 10, multiple data lines 14 intersect with multiple gate lines 15A and 15B, and pixels SP are arranged in a matrix at the intersections to form a pixel array. Multiple horizontal pixel rows HL1 to HLn are arranged in the pixel array, and a horizontal pixel row HL includes multiple pixels SP arranged adjacent to each other in the horizontal direction.

[0043] Gating lines 15A and 15B may include a first gating line 15A with an applied switch signal and a second gating line 15B with an applied EM signal. Each pixel SP may be connected to any data line 14, any first gating line 15A, and any second gating line 15B.

[0044] Each pixel SP may include a light-emitting element (hereinafter referred to as an OLED) and switching elements such as driving TFTs and switching TFTs for driving the OLED. The pixel SP receives a high-level driving voltage EVDD and a low-level driving voltage EVSS from a power block (not shown). The OLED included in the pixel SP includes an anode, a cathode, and an organic compound layer formed therebetween. The organic compound layer includes a hole injection layer (HIL), a hole transport layer (HTL), an emissive layer (EML), an electron transport layer (ETL), and an electron injection layer (EIL). When a power supply voltage is applied to the anode and cathode, holes passing through the hole transport layer (HTL) and electrons passing through the electron transport layer (ETL) move to the emissive layer (EML) and form excitons, and as a result, the emissive layer (EML) generates visible light. The TFTs constituting the pixel SP may be implemented as p-type, n-type, or a hybrid type. Furthermore, the semiconductor layer constituting the TFTs of the pixel SP may include amorphous silicon, polycrystalline silicon, or oxide.

[0045] The timing controller 11 can receive input image data DATA and timing signals such as the data enable signal DE from an external source. The timing controller 11 can generate various control signals DDC and GDC required to drive the operation of the data driver 12 and the gating driver 13 based on the externally input timing signals. The timing controller 11 converts the externally input image data DATA to match the data signal format used in the data driver 12 and outputs the converted image data DATA.

[0046] The data driver 12 converts the digital data format image data DATA into data voltage according to the data timing control signal DDC and provides it to the data line 14.

[0047] The gating driver 13 generates a scan signal in response to the gating timing control signal GDC provided from the timing controller 11, provides the scan signal to the first gating line 15A, generates an EM signal, and provides the EM signal to the second gating line 15B.

[0048] The timing controller 11 can use timing control signals GDC and DDC to control the timing of writing image data into the horizontal pixel rows HL1 to HLn of the display panel 10 and the timing of illumination. The timing controller 11 can perform black data insertion (BDI) operation by operating during the illumination period when the pixel SP is illuminating and during the non-illumination period when it is not illuminating. The timing controller 11 can input a data voltage through the data line during the non-illumination period and control the pixel SP with the applied data voltage during the illumination period so that the pixel SP illuminates simultaneously.

[0049] Reference Figure 2 The data writing timing and light emission timing are described by the timing controller 11.

[0050] Figure 2 This is a diagram illustrating a method for driving an electroluminescent display device according to an embodiment of the present disclosure.

[0051] Reference Figure 2 The timing controller 11 can perform a black data insertion (BDI) operation to insert black data into a frame. BDI refers to inserting a period of light-off within a frame to mitigate TFT image retention characteristics and improve video quality such as motion blur.

[0052] The timing controller 11 controls the data driver 12 and the strobe driver 13 to sequentially write image data to the horizontal pixel line HL (data write) during the period when the black screen is displayed on the display panel 10 (black).

[0053] When the data writing is complete, the timing controller 11 can control the horizontal pixel rows HL1 to HLn that have been written with image data to emit light simultaneously. During the light emission period, the OLED emits light according to the image data written to each pixel to realize the image data.

[0054] The timing controller 11 can control all horizontal pixel rows HL1 to HLn of the display panel 10 to emit light simultaneously, or divide the n horizontal pixel rows into multiple blocks and control the horizontal pixel rows in each block to emit light simultaneously. As described above, when horizontal pixel rows HL1 to HLn emit light simultaneously, they all have the same emission duty cycle, thus minimizing brightness deviation.

[0055] Figure 3 A configuration for implementing the driving technology according to this disclosure is shown.

[0056] Reference Figure 3 According to this disclosure, the pixel may include an OLED, a driving thin-film transistor (TFT) DT, a switching TFT ST, a light-emitting TFT ET, a first capacitor C1, and a second capacitor C2. The driving TFT DT, the switching TFT ST, and the light-emitting TFT ET 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 ET can be implemented as p-type, n-type, or a hybrid type. In the following description, the case of implementing the TFT as n-type will be illustrated by example.

[0057] An OLED consists of an anode and a cathode. The anode of the OLED is supplied with a high-level drive voltage EVDD, and the cathode is connected to the drain node of the driving TFT DT. The luminous intensity of the OLED can be adjusted according to the amount of drive current input to the anode.

[0058] The gate electrode of the driving TFT DT is connected to the second node N2, the drain electrode is connected to the cathode of the OLED, and the source electrode is provided with a low-level driving voltage EVSS. The driving TFT DT controls the amount of current flowing through the organic light-emitting diode OLED based on the voltage difference Vgs between the gate voltage applied to the gate electrode and the source voltage applied to the source electrode.

[0059] One electrode of the light-emitting TFT ET is connected to a first node N1, and its other electrode is connected to a second node N2. A light-emitting signal EM is input to its gate electrode. The light-emitting TFT ET is turned on when the light-emitting signal EM is input at a conduction level to connect the first node N1 and the second node N2.

[0060] One electrode of the switch TFT ST is connected to data line 16, and its other electrode is connected to the first node N1. A switch signal SW is input to its gate electrode. When the switch signal SW is input at an ON level, the switch TFT ST is turned on to connect data line 16 and the first node N1. The switch TFT ST can be turned on by the switch signal SW to send the data voltage VDATA supplied to data line 16 to the first node N1.

[0061] One electrode of the first capacitor C1 is connected to the first node N1, and its other electrode is supplied with a low-level drive voltage EVSS. Therefore, when the switch TFT ST is turned on and thus the data line 16 is connected to the first node N1, the data voltage VDATA input through the data line 16 can be charged into the first capacitor C1 connected to the first node N1.

[0062] One electrode of the second capacitor C2 is connected to the second node N2, which serves as the gate node of the driving TFT DT, and its other electrode is connected to the third node N3, which serves as the source node of the driving TFT DT. Therefore, when the light-emitting TFT ET is turned on, the first node N1 and the second node N2 are connected, and thus 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.

[0063] As described above, the pixel according to this disclosure may include three TFTs DT, ST and ET, and two capacitors C1 and C2, and is connected to a data line 16 without a separate reference line Vref.

[0064] Figure 4 It is provided to Figure 3 The waveform of the signal of the pixel.

[0065] Reference Figure 4 The pixel driving method according to the implementation method may include a first time period t1 to a fourth time period t4.

[0066] The data voltage VDATA is applied as a high-level data voltage DATA_H with a high potential during the first time period t1 and the second time period t2, and as a low-level data voltage VDATA_L with a low potential during the third time period t3 and the fourth time period t4.

[0067] During the third time period t3, a light emission signal EM is applied at the on level. Therefore, the light emission TFTET that receives the light emission signal EM is turned on during the third time period t3 to connect the first node N1 and the second node N2.

[0068] The switching signal SW is applied at an on level during the first time period t1, at an off level during the second time period t2 and the third time period t3, and at an on level during the fourth time period t4. Therefore, the switch TFT ST receiving the switching signal SW is turned on during the first time period t1 to transmit the high-level data voltage VDATA_H input to data line 16 to the first node N1, turned off during the second time period t2 and the third time period t3, and then turned on during the fourth time period t4 to transmit the low-level data voltage VDATA_L to the first node N1.

[0069] According to the aforementioned driving waveform, image data VDATA is written into the first capacitor C1 in the first time period t1, the written image data VDATA is held in the second time period t2, and the image data VDATA stored in the first capacitor C1 is transferred to the second capacitor C2 in the third time period, so the OLED can emit light in the fourth time period t4.

[0070] Reference Figures 5 to 8 Describe in detail the operations performed on pixels in each time period.

[0071] Figure 5 It is a graph used to describe the operation of pixels in the first time period t1.

[0072] Reference Figure 5 During the first time period t1, a high-level data voltage VDATA_H is applied to data line 16, a switch signal SW is applied at the on level, and an emission signal EM is applied at the off level. Therefore, during the first time period t1, the switch TFT ST is turned on by receiving the on-level switch signal SW, and the emission TFT ET receives the off-level emission signal EM and remains in the off state.

[0073] With the TFT ST switch turned on, data line 16 is connected to the first node N1. Therefore, the high-level data voltage VDATA_H input to data line 16 is transmitted to the first node N1.

[0074] Since the light-emitting TFT ET is in the off state, the connection between the first node N1 and the second node N2 is canceled. Therefore, the high-level data voltage VDATA_H applied to the first node N1 is charged into the first capacitor C1 connected to the first node N1, thus increasing the potential of the first node N1 to the high-level data voltage VDATA_H.

[0075] During the first time period t1, the high-level data voltage VDATA_H can be sequentially provided to all horizontal pixel rows HL1 to HLn, so that data can be written to each pixel.

[0076] Figure 6 This is a graph used to describe the operation of pixels in the second time period t2.

[0077] Reference Figure 6 During the second time period t2, a high-level data voltage VDATA_H is applied to data line 16, the switch signal SW is applied at the cutoff level, and the light emission signal EM is applied at the cutoff level. Therefore, during the second time period t2, the switch TFT ST is turned off by receiving the cutoff-level switch signal SW, and the light emission TFT ET is also turned off by receiving the cutoff-level light emission signal EM.

[0078] With the TFT ST switched off, data line 16 and the first node N1 remain disconnected. Since the light-emitting TFT ET is also switched off, the first capacitor C1 connected to the first node N1 is charged with a high-level data voltage VDATA_H.

[0079] Because the display device of this disclosure performs control such that pixels emit light simultaneously when data writing in horizontal pixel rows HL1 to HLn is completed, data writing to each horizontal pixel row is performed during the second time period t2. Therefore, for pixels that have data written earlier, the duration of the second time period t2 can be longer, and thus the duration of the second time period t2 can vary depending on the horizontal pixel row to which the pixel belongs.

[0080] Figure 7 It is a graph used to describe the operation of pixels in the third time period t3.

[0081] Reference Figure 7 During the third time period t3, a low-level data voltage VDATA_L is applied to data line 16, the switch signal SW is applied at the off level, and the light emission signal EM is applied at the on level. Therefore, during the third time period t3, the switch TFTST 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.

[0082] With the TFT ST switched off, data line 16 and the first node N1 remain disconnected. The TFT ET is turned on, thus connecting the first node N1 and the second node N2. Therefore, the potential of the first node N1 is also reflected in the second node N2, and the high-level data voltage VDATA_H is charged into the second capacitor C2. Consequently, the potential of the second node N2 increases to the high-level data voltage VDATA_H.

[0083] Figure 8 It is a graph used to describe the operation of pixels in the fourth time period t4.

[0084] Reference Figure 8 During the fourth time period t4, a low-level data voltage VDATA_L is applied to 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. Therefore, during the fourth time period t4, the switch TFTST 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.

[0085] With the TFT ST switch turned on, data line 16 is connected to the first node N1. Therefore, the low-level data voltage VDATA_L input through data line 16 is transmitted to the first node N1. Consequently, the potential of the first node N1 gradually decreases from the high-level data voltage VDATA_H to the low-level data voltage VDATA_L.

[0086] As the light-emitting TFT ET is turned off, the connection between the first node N1 and the second node N2 is canceled.

[0087] The driving TFT DT is turned on by charging a high-level data voltage VDATA_H into a second capacitor C2 connected between the second node N2 (used as the gate node) and the third node N3 (used as the source node). When the driving TFT DT is turned on, a current path is generated through the OLED and the driving TFT DT from the high-level driving voltage EVDD to the low-level driving voltage EVSS, thus 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 amount of driving current input to the OLED can be controlled according to the high-level data voltage VDATA_H charged into the second capacitor C2, thereby adjusting the OLED's brightness.

[0088] Figure 9 This is a diagram illustrating a method for driving an electroluminescent display device according to a first embodiment of the present disclosure.

[0089] Reference Figure 9According to the first embodiment, the electroluminescent display device performs BDI operation, which includes a period of time when the OLED is kept in a closed state to display a black screen (black) and a period of time when the OLED emits light to display an image (emitting light).

[0090] During the period when a black screen is displayed (black), switching signals are sequentially input to the horizontal pixel rows of the display panel, thus writing image data VDATA. Once the data writing is complete in all horizontal pixel rows, the OLEDs in all horizontal pixel rows illuminate to display the image data.

[0091] For this operation, the gating driver 13 sequentially inputs the switch signal SW to all horizontal pixel rows during the period when a black screen is displayed (black). When the display panel has n horizontal pixel rows HL1 to HLn, the gating driver 13 sequentially inputs n switch signals SW1 to SWn to the horizontal pixel rows HL1 to HLn. The data driver 12 provides image data VDATA sequentially to the horizontal pixel rows HL1 to HLn according to the operation of the gating driver 13.

[0092] When data writing to n horizontal pixel rows HL1 to HLn is completed, the emission signal EM is simultaneously input to the n horizontal pixel rows HL1 to HLn. Therefore, the OLEDs of all horizontal pixel rows emit light simultaneously to display image data.

[0093] In conventional driving methods, horizontal pixel rows HL1 to HLn emit light sequentially, resulting in an EVSS rise phenomenon where the potential of the low-level driving voltage EVSS rises simultaneously with the OLED emission. Therefore, considering the EVSS rise in conventional driving methods, image data VDATA needs to be compensated. On the other hand, in the electroluminescent display device according to the first embodiment of this disclosure, since the image data VDATA is written during the period when a black screen is displayed (black) (that is, all OLEDs are off), the effect of the EVSS rise can be eliminated. Furthermore, since the OLEDs of all horizontal pixel rows emit light simultaneously and therefore have the same emission duty cycle, it is possible to prevent or reduce the detection of brightness deviations due to differences in emission duty cycles between pixel rows.

[0094] Figure 10 This is a view used to describe a method for driving an electroluminescent display device according to a second embodiment of the present disclosure.

[0095] Reference Figure 10 According to the second embodiment, the electroluminescent display device can perform a black data insertion (BDI) operation, wherein all horizontal pixel rows HL1 to HLn are divided into multiple blocks B1 to Bm and the image data VDATA writing and light emission operation are controlled in blocks.

[0096] In each block, image data VDATA is written sequentially during the blackout period, and the horizontal pixel rows of the corresponding block are simultaneously illuminated to display the image data upon completion of the data writing to the corresponding block. When the writing of image data VDATA to the previous block is complete, the writing of data to the next block can begin and can be performed simultaneously with the blackout period of the previous block. In this way, data writing and illumination operations can be performed sequentially in each of blocks B1 to Bm to display one frame.

[0097] Compared to the driving method of the first embodiment, the method for driving an electroluminescent display device according to the second embodiment can extend the light-emitting time. On the other hand, since data writing to the next block is performed while the previous block is in a light-emitting state, an EVSS rise phenomenon occurs. Therefore, considering the EVSS rise, it is necessary to compensate for the image data VDATA.

[0098] Figures 11 to 13 This is a diagram used to describe a method for compensating for changes in EVSS values ​​when driving an electroluminescent display device.

[0099] Figure 11 This is a graph showing the simulation results of the EVSS changes that occur when input image data is used.

[0100] Figure 11 The simulation graph shows the results of changes in the simulated EVSS values ​​when the data driver is located on top of the display devices vertically numbered 0 to 2101 and provides image data.

[0101] According to the simulation charts, when the display panel is driven, the EVSS rises, measuring 2.5V or higher in the vertical range of 500 to 1000, 2.0V in the vertical range of 1000 to 1500, 1.5V near the vertical range of 1500, gradually decreasing to 1.0V in the vertical range of 1500 to 2000, and measuring approximately 0.5V near the vertical range of 2000 where image data is finally provided.

[0102] In other words, it can be determined that the greater the distance from the data driver, the higher the EVSS increases. If the EVSS value increases, the brightness will decrease even if the same grayscale data is input. Figure 11 The simulation results show the current I flowing through one pixel of the OLED. PXLThe simulation results show the EVSS values ​​for each horizontal pixel row under the assumptions of 1.4μA and a resistance of 0.77Ω. The simulation results determine that there is approximately a 2.4V difference between the upper and lower EVSS values. When this EVSS difference exists, there can be approximately an 87% difference in brightness between the upper and lower parts of the display panel at the same grayscale level. To improve this brightness non-uniformity, the data voltage can be compensated to reflect the EVSS variation.

[0103] Figure 12 It is a graph used to describe the operation time for compensating for changes in EVSS, and Figure 13 This is the equivalent circuit diagram of a vertical line on the display panel.

[0104] Reference Figure 12 and Figure 13 The EVSS at each location is stored at the end of the first frame (Frame-End) to compensate for EVSS variations. When the display panel includes n horizontal pixel rows HL1 to HLn, n voltage values ​​can be stored in a vertical line.

[0105] Subsequently, during frame-writing (the process of writing data to drive the next frame), the EVSS change is calculated using the EVSS voltage stored at the end of the previous frame. The voltage of the image data can then be compensated for by reflecting this EVSS change. Figure 13 This is an equivalent circuit diagram of a vertical line of a display panel. The display panel includes a first horizontal pixel row HL1 to an nth horizontal pixel row HLn, data is input in the order of the first horizontal pixel row HL1 to the nth horizontal pixel row HLn, and the OLED emits light in the same order.

[0106] In this embodiment, the data driver providing the data voltage is located adjacent to the nth horizontal pixel row HLn, i.e., at the bottom of the figure. The resistor R on the vertical line represents the pixel's resistance, and the currents I1 to I... n This is the current applied to the pixel. The arrow indicating the direction of the current indicates the current flow when the OLED emits light.

[0107] Assuming that the current of a pixel flows from the first horizontal pixel row HL1 to the nth horizontal pixel row HLn, the voltage of each pixel can be calculated as the product of the resistance and current of the corresponding pixel (V = IR).

[0108] The EVSS voltages V1 to Vn of the pixel row at the frame end time point (frame-end) can be calculated using the following method. Here, the frame end time point (frame-end) is the time point at which illumination ends in the first horizontal pixel row HL1 and begins in the nth horizontal pixel row HLn, as shown below. Figure 12 As shown.

[0109] <EVSS voltage at the end of frame>

[0110]

[0111] here, (j = vertical number). Therefore, IS1 = I1, IS2 = I1 + I2, IS3 = I1 + I2 + I3. The voltage at point V1 is the sum of the voltage at point V2 and the voltage I1*R obtained by multiplying I1 by the resistance. That is, V1 = V2 + IS1*R. Similarly, the voltage at point V2 is the sum of the voltage at point V3 and the voltage obtained by multiplying I1 + I2 by the resistance. That is, V2 = V3 + IS2*R. Here, since V1 = V2 + IS1*R and V2 = V3 + IS2*R, it can be expressed as V1 = V3 + (IS1 + IS2)*R. If V3 in the formula used to calculate V1 is substituted into V4 in the same way and finally Vn is replaced with ISN*R, then V1 can be expressed as Using the above calculation method, the voltage at the end of the frame can be calculated.

[0112] Subsequently, when writing data for the next frame, the EVSS change is calculated using the EVSS voltage calculated at the end of the previous frame (frame-end), and the voltage of the data to be written is compensated by reflecting the calculated EVSS change. Here, for areas of black screen, the current is replaced with 0 and stored.

[0113] During the frame-write period used to drive the frame, the EVSS change can be calculated using the following method. The apostrophe (') in the calculation formula indicates the value calculated in the previous frame.

[0114] <EVSS changes during frame-write period>

[0115]

[0116] like Figure 12 As shown, the emission in the first horizontal pixel row HL1 is completed at the end of the previous frame (frame-end), so the data for the next frame is written. Therefore, since the voltage of the first horizontal pixel row HL1 does not change after the voltage V1 is calculated until the data for the next frame is written, V1 = V1' is calculated.

[0117] The voltage V2 of the second horizontal pixel row HL2 is calculated by reflecting the current change of the first horizontal pixel row HL1, since the current of the first horizontal pixel row HL1 has changed at the end of the frame (frame-end). The current change is calculated by subtracting the current IS1' flowing through the first row in the previous frame from the current IS1 to be applied to the first row in the current frame, and V2 in the current frame can be calculated by multiplying the current change by the resistor R*(n-1) leading to the data driver.

[0118] By incorporating the EVSS value calculated as described above into the data voltage used for data writing to calculate the compensated data voltage and writing the compensated data voltage, the target brightness can be obtained even if the EVSS changes.

[0119] The above-mentioned calculation and compensation of EVSS can be performed under the control of the timing controller 11 along with compensation functions such as driving TFT compensation and OLED compensation, but is not limited thereto.

[0120] As described above, to compensate for EVSS variations, the EVSS variation value for the corresponding row is calculated before data is written, and then a data voltage is provided that is compensated by reflecting the EVSS variation value. Since data is written and emitted in units of one horizontal pixel row, the EVSS variation value is calculated based on one horizontal pixel row and compensation is performed accordingly. In this way, when all horizontal pixel rows HL1 to HLn are divided into multiple blocks B1 to Bm, image data VDATA is written in blocks, and the horizontal pixel rows of the corresponding blocks emit light simultaneously when data writing is completed. As in the second embodiment of this disclosure, EVSS can be calculated at each emission timing point in blocks. For example, when the data writing of the current block is completed and emission begins, the EVSS variation value of the next block can be calculated to compensate for the data voltage, and then the compensated data voltage can be written.

[0121] As described above, in the method for driving an electroluminescent display device according to the first embodiment of this disclosure, image data VDATA is written during a period when a black screen is displayed (black) while the OLED remains in an off state, and when the data writing is complete, all OLEDs in all horizontal pixel rows emit light simultaneously to display the image data. Since image data VDATA is written while all OLEDs are off, the effect of rising EVSS can be eliminated. Because all OLEDs in all horizontal pixel rows emit light simultaneously and therefore have the same emission duty cycle, brightness deviations due to differences in emission duty cycles between rows can be prevented or reduced from being detected.

[0122] In the method for driving an electroluminescent display device according to the second embodiment of this disclosure, by dividing all horizontal pixel rows HL1 to HLn into multiple blocks B1 to Bm, the operation of writing image data VDATA and the emission operation can be controlled on a block-by-block basis. Since the data writing and emission operations are performed on a block-by-block basis to display one frame, the method for driving an electroluminescent display according to the second embodiment can extend the emission time compared to the driving method of the first embodiment.

[0123] The pixel circuit of this disclosure, used to implement the driving methods of the first and second embodiments, may include three TFTs DT, ST, and ET, and two capacitors C1 and C2, and may be connected to a data line 16 without a separate reference line Vref. In the pixel circuit of this disclosure, image data voltage can be stored in the first capacitor C1 during the period when a black image is displayed (black), and when an input light emission signal EM is received, the image data voltage can be transferred to the second capacitor C2, which controls the gate-source voltage of the driving TFT.

[0124] Those skilled in the art will recognize that various modifications and variations can be made to this disclosure without departing from the spirit or scope thereof. Therefore, this disclosure should not be limited to the specific embodiments described herein, but should be accorded the widest scope consistent with the principles and novel features disclosed herein.

[0125] This application claims the benefit of Korean Patent Application No. 10-2021-0187457, filed on December 24, 2021, which is incorporated herein by reference as if fully set forth herein.

Claims

1. An electroluminescent display device, the electroluminescent display device comprising: The display panel includes a plurality of pixels, each pixel having a light-emitting element and a driving TFT for controlling the driving current flowing through the light-emitting element and connected to a data line and a gate line. Each of the plurality of pixels also includes a switching transistor connected between the data line and a first node and a first capacitor connected to the first node. A panel driver, the panel driver being connected to the data line and the strobe line; as well as A timing controller is configured to control the operation of the panel driver such that the operation is divided into an emitting period when the light-emitting elements emit light and a non-emitting period when they stop emitting light, and to perform control such that during the non-emitting period, a data voltage is input to the plurality of pixels through the data line, and during the emitting period, the light-emitting elements to which the data voltage is applied emit light simultaneously. During the light-emitting period, a low voltage on the data line is input to the plurality of pixels through the data line, causing the data voltage charged in the first capacitor to be discharged.

2. The electroluminescent display device according to claim 1, wherein, The timing controller performs a black data insertion (BDI) operation by executing control to display an image during the luminous period and a black image during the non-luminous period.

3. The electroluminescent display device according to claim 2, wherein, During the non-light-emitting period, the data voltage is sequentially written to the plurality of pixels, and the light-emitting element is turned off to display the black image.

4. The electroluminescent display device according to claim 1, wherein, The timing controller performs control such that during the non-light-emitting period, the data voltage is sequentially input to all pixel rows of the display panel, and during the light-emitting period, all pixel rows emit light simultaneously.

5. The electroluminescent display device according to claim 1, wherein, The timing controller divides the horizontal pixel rows of the display panel into multiple blocks and executes control to input the data voltage sequentially in units of the divided blocks, and the horizontal pixel rows emit light simultaneously in units of blocks.

6. The electroluminescent display device according to claim 5, wherein, The timing controller compensates for the data voltage based on changes in the light emission of the light-emitting element using a low-level voltage.

7. The electroluminescent display device according to claim 1, wherein, The panel driver includes: A data driver configured to provide the data voltage to the data line; and A gating driver is configured to sequentially output a switching signal for inputting the data voltage and simultaneously output a light emission signal to the pixel to which the data voltage is applied.

8. An electroluminescent display device, the electroluminescent display device comprising: A display panel in which data lines and gate lines intersect and multiple pixels are provided; A data driver configured to provide a data voltage to the data line; as well as A gating driver, configured to sequentially output switching signals for inputting the data voltage and simultaneously output light emission signals to pixels to which the data voltage is applied. Each of the pixels includes: A light-emitting element having an anode to which a high-level driving voltage is applied; A driving transistor is connected between the cathode of the light-emitting element and a low-level 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, the switching transistor being configured to connect a corresponding data line and a first node according to a corresponding switching signal; A light-emitting transistor, the light-emitting transistor being configured to connect the first node and the second node according to the light-emitting signal; A first capacitor, connected to the first node, is charged using the data voltage applied to the data line and discharged based on the low voltage of the data line when the light-emitting transistor is off; and A second capacitor is connected to the second node and the source node of the driving transistor to be charged using the data voltage charged into the first capacitor as the gate-source voltage of the driving transistor when the light-emitting signal is input.

9. The electroluminescent display device according to claim 8, wherein, The first capacitor is charged using the data voltage when the light-emitting element is turned off.

10. The electroluminescent display device according to claim 8, wherein, When the switching transistor is turned on, the light-emitting transistor remains off so that the data voltage is charged into the first capacitor, and when the light-emitting transistor is turned on, the switching transistor remains off so that the data voltage charged into the first capacitor is charged into the second capacitor.

11. The electroluminescent display device according to claim 8, wherein, In the driving transistor, the drain electrode is connected to the cathode of the light-emitting element, the source electrode is provided with the low-level 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 into the second capacitor.

12. An electroluminescent display device, the electroluminescent display device comprising: A light-emitting element having an anode to which a high-level driving voltage is applied; A driving transistor is connected between the cathode of the light-emitting element and a low-level 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, the switching transistor being configured to connect a data line and a first node according to a switching signal; A first capacitor is connected to the first node to be charged using the data voltage input to the data line and to be discharged based on the low voltage of the data line when the light-emitting transistor is turned off. A light-emitting transistor, the light-emitting transistor being configured to connect the first node and the second node according to a light-emitting signal; as well as A second capacitor is connected to the second node and the source node of the driving transistor.

13. The electroluminescent display device according to claim 12, wherein, The first capacitor is charged using the data voltage when the light-emitting element is turned off.

14. The electroluminescent display device according to claim 12, wherein, When the light-emitting signal is input, the second capacitor is charged using the data voltage charged into the first capacitor as the gate-source voltage of the driving transistor.

15. The electroluminescent display device according to claim 12, wherein, When the switching transistor is turned on, the light-emitting transistor remains off so that the data voltage is charged into the first capacitor, and when the light-emitting transistor is turned on, the switching transistor remains off so that the data voltage charged into the first capacitor is charged into the second capacitor.

16. The electroluminescent display device according to claim 12, wherein, The driving periods for the light-emitting element include a first period, a second period, a third period, and a fourth period. During the first time period, the switching transistor is turned on and the light-emitting transistor is turned off, so that the data voltage is charged into the first capacitor. During the second time period, the switching transistor and the light-emitting transistor are turned off so that the data voltage is maintained in the first capacitor. During the third time period, the switching transistor is turned off and the light-emitting transistor is turned on so that the data voltage is charged into the second capacitor, and During the fourth time period, the driving transistor is turned on according to the data voltage charged into the second capacitor to apply driving power to the light-emitting element.

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