KR102478991B1 - Electroluminescence display and driving method thereof - Google Patents

Abstract

The present invention relates to an electroluminescent display device and a method for driving the same, wherein a screen is divided into two or more local regions in which a black offset voltage is independently determined, and the black offset voltage is calculated by calculating the threshold voltage characteristic of a driving element for each local region and the local region. The black offset voltage may be optimized for the entire screen by determining for each local region based on at least one of the luminance characteristics for each region.

Description

Electroluminescence display device and its driving method {ELECTROLUMINESCENCE DISPLAY AND DRIVING METHOD THEREOF}

The present invention relates to an electroluminescent display device to which a black offset voltage can be differently applied depending on a position on a screen.

The electroluminescent display device is roughly divided into an inorganic light emitting display device and an organic light emitting display device according to the material of the light emitting layer. An active matrix type organic light emitting display includes an organic light emitting diode (OLED) that emits light by itself, and has a fast response speed, high luminous efficiency, luminance, and viewing angle. There are advantages.

The pixels of the organic light emitting display device include an OLED and a driving element that drives the OLED by supplying a current to the OLED according to a voltage between a gate and a source. An OLED of an organic light emitting display device includes an anode, a cathode, and an organic compound layer formed between the electrodes. The organic compound layer includes 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 current flows through the OLED, 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) emits visible light. .

The driving element may be implemented as a TFT having a metal oxide semiconductor field effect transistor (MOSFET) structure. The electrical characteristics of the driving element should be uniform among all pixels, but there may be differences between the pixels due to process variation and element characteristic variation, and may change according to the lapse of display driving time. In order to compensate for the variation in electrical characteristics of the driving element, an internal compensation method and an external compensation method may be applied to the electroluminescent display. The internal compensation method samples the gate-source voltage (Vgs) of the driving device, which varies according to the electrical characteristics of the driving device, and compensates for the data voltage by the gate-source voltage. The external compensation method senses the voltage of a pixel that changes according to the electrical characteristics of the driving element, and modulates data of an input image in an external circuit based on the sensed voltage, thereby compensating for deviations in electrical characteristics of the driving element between pixels.

As the display driving time increases, gate bias stress of the driving element may be accumulated so that the threshold voltage of the driving element may be shifted to a negative polarity voltage. A shift in the threshold voltage of the driving element may cause image quality deterioration such as afterimages.

When the threshold voltage of the driving device is sensed and the threshold voltage is shifted, the shift of the threshold voltage may be delayed by adjusting a black offset voltage. The black offset voltage may adjust a voltage between a gate and a source of a driving element without increasing the luminance of a pixel in a black gradation.

The black offset adjustment method adjusts the black offset voltage equally across the entire screen without considering that the gate bias stress of the driving element may vary depending on the position on the screen. For this reason, when the black offset voltage is adjusted according to the position on the screen, the negative polarity stress of the driving element increases and the luminance of the pixel in the black gradation may increase.

Accordingly, the present invention provides an electroluminescent display device and a method of driving the same to optimize a black offset voltage over the entire screen.

The electroluminescent display device of the present invention includes a display panel in which data lines and gate lines cross each other on a screen and sub-pixels including driving elements for driving light emitting elements are arranged, and a black offset set to a voltage without an increase in luminance of a black gray level. and a data driver that outputs voltage to the data lines.

The screen is divided into two or more local regions in which the black offset voltage is independently determined.

The black offset voltage is determined for each local area based on at least one of a threshold voltage characteristic of a driving device for each local area and a luminance characteristic for each local area.

The driving method of the electroluminescent display includes dividing a screen into two or more local regions in which a black offset voltage is independently determined, and the black offset voltage is selected from among a threshold voltage characteristic of a driving element for each local region and a luminance characteristic for each local region. The step of determining for each of the local regions based on at least one, and the step of supplying a data voltage including the black offset voltage to the data lines.

According to the present invention, a screen is divided into two or more local areas, and a block offset voltage is determined in each local area based on at least one of a threshold voltage characteristic of a driving element for each local area and a luminance characteristic for each local area. voltage can be optimized.

As a result, the present invention can improve picture quality and lifespan by reducing the negative polarity stress of driving elements on the entire screen of the electroluminescent display.

1 is a block diagram showing an electroluminescent display device according to an exemplary embodiment of the present invention.
2 is a circuit diagram showing an external compensation circuit connected to a pixel circuit.
3 is a diagram illustrating an example in which a screen of a display panel is divided into a plurality of local areas.
4 is a diagram showing a power-on sequence, a display driving period, and a power-off sequence.
5 is a diagram showing an active period and a vertical blank period in detail.
6 is a diagram illustrating an example of a failure management index for a threshold voltage of a driving element.
7 is a diagram showing in detail a voltage setting for each section of a data voltage.
8 is a diagram showing an example of a black offset voltage for each local area.
9 is a flowchart illustrating a driving method of an electroluminescent display device according to an exemplary embodiment of the present invention.
10 is a diagram illustrating an example of varying a black offset voltage for each local region according to time based on a result of sensing a threshold voltage of a driving element in real time.
11 and 12 are diagrams illustrating a black offset voltage that varies according to a luminance distribution of a screen.

Advantages and features of the present invention, and methods of achieving them, will become clear with reference to the detailed description of the following embodiments taken in conjunction with the accompanying drawings. The present invention is not limited to the embodiments disclosed below, but will be implemented in a variety of different forms, only the embodiments will make the disclosure of the present invention complete, and those of ordinary skill in the art to which the present invention belongs It is provided to fully inform the scope of the invention, the invention is defined only by the scope of the claims.

Since the shape, size, ratio, angle, number, etc. disclosed in the drawings for explaining the embodiments of the present invention are exemplary, the present invention is not limited to those shown in the drawings. Like reference numbers designate substantially like elements throughout the specification. In addition, in describing the present invention, if it is determined that a detailed description of related known technologies may unnecessarily obscure the subject matter of the present invention, the detailed description will be omitted.

When "comprises", "includes", "has", "consists of", etc. mentioned in this specification is used, other parts may be added unless '~ only' is used. When a component is expressed in the singular, it may be interpreted in the plural unless specifically stated otherwise.

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

In the case of a description of a positional relationship, for example, when a positional relationship between two components is described as 'on ~', 'on top of ~', 'on the bottom of ~', 'next to', etc., ' One or more other components may be interposed between those components where 'immediately' or 'directly' is not used.

Although first, second, etc. may be used to distinguish the components, the function or structure of these components is not limited to the ordinal number or component name attached to the front of the component.

The following embodiments may be partially or wholly combined or combined with each other, and technically various interlocking and driving operations are possible. Each of the embodiments may be implemented independently of each other or together in an association relationship.

In the electroluminescent display device of the present invention, the pixel circuit includes a driving element and a switch element. The driving element and the switch element may be implemented with one or more of n-channel transistors (NMOS) and p-channel transistors (PMOS). The transistor may be implemented as an oxide transistor having an oxide semiconductor pattern or an LTPS transistor having a low temperature poly-silicon (LTPS) semiconductor pattern. A transistor is a three-electrode device including a gate, a source, and a drain. The transistor may be implemented as a TFT (Thin Film Transistor) on the display panel 100 . The source is an electrode that supplies a carrier to the transistor. Within a transistor, carriers start flowing from the source. The drain is an electrode through which carriers exit from the TFT. The flow of carriers in a transistor flows from the source to the drain. In the case of an n-channel transistor (NMOS), since carriers are electrons, the source voltage has a voltage lower than the drain voltage so that electrons can flow from the source to the drain. In an n-channel transistor (NMOS), the direction of current flows from the drain to the source. In the case of a p-channel 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-channel transistor (PMOS), current flows from the source to the drain because holes flow from the source to the drain. Accordingly, it should be noted that the source and drain of the transistor are not fixed because the source and drain can change depending on the applied voltage. In the following description, the source and drain of the transistor will be referred to as first and second electrodes.

A gate signal of a TFT used as a switch element swings between a gate on voltage and a gate off voltage. The gate-on voltage is set to a voltage higher than the threshold voltage of the TFT, and the gate-off voltage is set to a voltage lower than the threshold voltage of the TFT. A TFT is turned on in response to a gate-on voltage, while it is turned off in response to a gate-off voltage. In the case of NMOS, the gate-on voltage may be a gate high voltage (VGH), and the gate-off voltage may be a gate low voltage (VGL). In the case of PMOS, the gate-on voltage may be the gate low voltage (VGL), and the gate-off voltage may be the gate high voltage (VGH).

Hereinafter, various embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following embodiments, an organic light emitting display device including an organic light emitting material will be mainly described for the electroluminescent display device, but is not limited thereto.

The electroluminescent display device of the present invention operates in a normal driving mode for displaying an input image on the screen and a sensing mode for sensing electrical characteristics of pixels. In the normal driving mode, the display panel driving circuit writes pixel data into the pixels in every active period of every frame period during the display driving period. In the sensing mode, electrical characteristics of the driving element are sensed in each of the sub-pixels, and pixel data of an input image is modulated with a compensation value reflecting the sensing result, thereby compensating for a change in electrical characteristics of the driving element.

1 is a block diagram showing an electroluminescent display device according to an exemplary embodiment of the present invention. 2 is a circuit diagram showing an external compensation circuit connected to a pixel circuit.

Referring to FIGS. 1 and 2 , an electroluminescent display device according to an exemplary embodiment of the present invention includes a display panel 100 and a display panel driving circuit.

The screen of the display panel 100 includes an active area AA displaying an input image. A pixel array is disposed in the active area AA. The pixel array includes a plurality of data lines 102, a plurality of gate lines 104 crossing the data lines 102, and a plurality of sensing lines 103, and pixels arranged in a matrix form. .

Each of the pixels may be divided into a red sub-pixel, a green sub-pixel, and a blue sub-pixel for color implementation. Each of the pixels may further include a white sub-pixel. Each of the subpixels 101 includes a pixel circuit.

Touch sensors may be disposed on the display panel 100 . A touch input may be sensed using separate touch sensors or sensed through pixels. Touch sensors are implemented as on-cell type or add-on type touch sensors disposed on the screen of a display panel or embedded in a pixel array. can

The display panel driving circuits 110 , 112 , and 120 include a data driver 110 and a gate driver 120 . A demultiplexer 112 may be disposed between the data driver 110 and the data lines 102 . The demultiplexer 112 may be omitted.

The display panel driving circuits 110, 112, and 120 write data of an input image into the pixels of the display panel 100 under the control of a timing controller (TCON) 130 in the normal driving mode and input the data to the screen. display the video The display panel driving circuits 110, 112, and 120 may further include a touch sensor driver for driving the touch sensors. The touch sensor driver is omitted in FIG. 1 . In a mobile device or a wearable device, the data driver 110, the timing controller 130, and a power circuit (not shown) may be integrated into one integrated circuit.

The power circuit generates power necessary for driving the timing controller 130, the display panel driving circuits 110, 112, and 120, and the display panel 100 when an input voltage is supplied from a host system (not shown). For example, the power supply circuit outputs a gamma reference voltage, a gate high voltage (VGH), a gate low voltage (VGL), and the like. The gamma reference voltage is divided into voltages for each gray level, converted into a gamma compensation voltage, and supplied to a digital to analog converter (hereinafter referred to as “DAC”) of the data driver 110 . The power circuit may be implemented with a power IC including a charge pump, a regulator, a buck converter, a boost converter, and the like.

The data driver 110 converts digital data of an input image received from the timing controller 130 in each frame period into a gamma compensation voltage using a DAC and outputs a data voltage Vdata. The data voltage Vdata is applied to the pixels through the demultiplexer 112 and the data line 102 . According to the present invention, the black offset voltage of the data voltage Vdata output from the data driver 110 is varied for each of two or more local regions divided on the screen.

The demultiplexer 112 is disposed between the data driver 110 and the data lines 102 using a plurality of switch elements to distribute the data voltage Vdata output from the data driver 110 to the data lines 102. do. Since one channel of the data driver 110 is time-divisionally connected to a plurality of data lines by the demultiplexer 112, the number of data lines 102 may be reduced.

The gate driver 120 may be implemented as a gate in panel (GIP) circuit formed directly on a bezel area of the display panel 100 together with a TFT array in the active area AA. The gate driver 120 outputs gate signals to the gate lines 104 under the control of the timing controller 130 . The gate driver 120 may sequentially supply the gate signals to the gate lines 104 by shifting the gate signals using a shift register. The gate signal may include a scan signal SCAN and a sensing signal SENSE, but is not limited thereto.

The timing controller 130 receives digital video data (DATA) of an input image and a timing signal synchronized therewith from the host system. The timing signal includes a vertical synchronizing signal Vsync, a horizontal synchronizing signal Hsync, a clock signal DCLK, and a data enable signal DE. The host system may be any one of a television (TV) system, a set top box, a navigation system, a personal computer (PC), a home theater system, a mobile device, and a wearable device.

The timing controller 130 may adjust the frame rate to a frequency higher than the input frame frequency. For example, the timing controller 130 multiplies the input frame frequency by i to determine the operation timing of the display panel drivers 110, 112, and 120 at a frame frequency of frame frequency × i (i is a positive integer greater than 0) Hz. can control. The frame frequency is 60 Hz in the National Television Standards Committee (NTSC) method and 50 Hz in the Phase-Alternating Line (PAL) method. The timing controller 130 may lower the frame frequency to a frequency between 1 Hz and 30 Hz in order to lower the refresh rate of pixels in the low power consumption driving mode.

The timing controller 130 generates data timing control signals for controlling operation timings of the display panel driving circuits 110, 112, and 120 based on the timing signals Vsync, Hsync, and DE received from the host system. The voltage level of the gate timing control signal output from the timing controller 130 is converted into a gate high voltage (VGH) and a gate low voltage (VGL) through a level shifter (not shown) and supplied to the gate driver 120 It can be. The level shifter converts a low level voltage of the gate timing control signal into a gate low voltage (VGL) and converts a high level voltage of the gate timing control signal into a gate high voltage (VGH). .

As shown in FIG. 2 , the external compensation circuit includes a sensing line 103 connected to the pixel circuit, a sensing unit 111, and a compensating unit 131 receiving sensing data (digital data) from the sensing unit 111. . The DAC and sensing unit 111 of the data driver 110 may be integrated into an integrated circuit (IC) of the data driver 110 . The compensator 131 may be built into the timing controller 130 .

The external compensation circuit initializes the source voltage of the sensing line 103 and the driving element DT, that is, the voltage of the second node n2, with a reference voltage, and then senses the source voltage of the driving element DT to drive the driving element ( DT) can be sensed. Electrical characteristics of the driving element DT capable of sensing include a threshold voltage (Vth) and mobility (μ). The sensing unit 111 samples the voltage on the sensing line 103 in the sensing mode, converts it into digital data through an analog to digital converter (hereinafter referred to as “ADC”), and outputs sensing data.

The sensing unit 111 may include an ADC and switch elements M3 and M4. The switch element M3 supplies a predetermined reference voltage Vref to the sensing line 103 to initialize the source voltage of the driving element DT to the reference voltage Vref. The switch element M4 is turned on after the switch element M3 is turned off to supply the source voltage of the driving element DT to the ADC. The ADC converts the analog sensing voltage on the sensing line 103 into digital data and transmits it to the compensator 131 . Initial values of the threshold voltage (Vth) and mobility (μ) of the driving element in each of the subpixels are stored in the compensator 131 . The compensator 131 compares the sensing data for each sub-pixel received from the ADC with an initial value to sense a change in electrical characteristics of the driving element, and determines a compensation value reflecting the sensing result. The compensation unit 131 adds or multiplies the pixel data (digital data) of the input image by the compensation value to modulate the pixel data. The pixel data modulated by the sensing unit 111 is transmitted to the data driver 110 through the timing controller 13, converted into a data voltage Vdata, and supplied to the data line 102. Compensation unit 131 may be installed in timing controller 130 .

The compensator 131 can reduce the stress of the driving element by increasing the black offset value in the black gradation of the pixel data. Black gradation is the lowest gradation of pixel data. In 8-bit pixel data, the black gradation is 00000000 ₂ . The black offset value is a digital value defining a black offset voltage without an increase in luminance of a black gray level. The black offset value is added to the pixel data within a range in which the luminance of the black gray level is not increased. The black offset value may vary according to a Vth defect management index (hereinafter referred to as “Vth_LSL”) determined based on the threshold voltage of the driving element DT sensed in real time in a power-off sequence and/or a luminance distribution. The black offset value is added to the pixel data and transmitted to the data driver 110 . In the data voltage Vdata, the block offset voltage is the voltage of the black offset value added to the pixel data, and the grayscale voltage is the voltage of the grayscale value of the pixel data.

As in the example of FIG. 2 , the pixel circuit includes an OLED, a driving element DT connected to the OLED, a plurality of switch elements M1 and M2, and a capacitor Cst. The driving element and the switch element may be implemented as a TFT having an n-type transistor (NMOS) or a p-type transistor (PMOS) structure. It should be noted that the pixel circuit is not limited to FIG. 2 .

The OLED emits light with current generated according to the gate-source voltage Vgs of the driving element DT, which varies according to the data voltage Vdata. An OLED includes an organic compound layer formed between an anode and a cathode. The organic compound layer may include, but is not limited to, 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). The anode of the OLED is connected to the driving element DT through the second node n2, and the cathode of the OLED is connected to the VSS electrode to which the low potential power supply voltage VSS is applied. In FIG. 2, “Coled” is a parasitic capacitance of OLED.

The first switch element M1 is turned on according to the scan signal SCAN and supplies the data voltage Vdata to the gate of the driving element DT connected to the first node n1. The first switch element M1 includes a gate connected to the first gate line 1041 to which the scan signal SCAN is applied, a first electrode connected to the data line 102, and a second electrode connected to the first node n1. includes

The second switch element M2 is turned on according to the sensing signal SENSE and supplies the reference voltage Vref to the second node n2. The second switch element M2 includes a gate connected to the second gate line 1042 to which the sensing signal SENSE is applied, a first electrode connected to the sensing line 103 to which the reference voltage Vref is applied, and a second node. and a second electrode connected to (n2).

The driving element DT supplies current to the OLED according to its gate-source voltage Vgs. The driving element DT includes a gate connected to the first node n1, a first electrode to which the pixel driving voltage VDD is supplied, and a second electrode connected to the anode of the OLED through the second node n2.

The capacitor Cst is connected between the first node n1 and the second node n2. The voltage of the capacitor Cst is Vgs of the driving element DT.

In the electroluminescent display device of the present invention, in the sensing mode, the screen of the display panel 100 is divided into two or more local areas BL11 to BL44 as shown in FIG. By sensing, the black offset voltages Vblack1 to Vblack16 are increased for each local area within a range in which the luminance of the black gray level does not rise. The Vth of the driving element DT for each local area is a representative value of Vth of the driving elements existing in the local area. The Vth of the driving elements DT for each local area may be obtained as Vth_LSL determined based on the sensing result of the driving elements in the power-off sequence.

In the black grayscale, the gate voltage of the driving element DT is less than or equal to the source voltage. Since the voltage difference between the gate voltage of the driving element DT and the source voltage of the driving element DT to which the reference voltage Vref is applied is reduced when the gate voltage of the driving element is increased in the black gradation, the black offset voltage is applied to the driving element ( DT) Vgs can be reduced. Accordingly, when the black offset voltage of the data voltage Vdata is appropriately increased in the black grayscale, the Vgs of the driving element DT is reduced, thereby reducing the stress of the driving element DT.

4 is a diagram showing a power ON sequence, a display driving period, and a power OFF sequence. FIG. 5 is a diagram showing an active period and a vertical blank period in detail.

Referring to FIGS. 4 and 5 , the sensing mode is divided into before product shipment and after product shipment. Before product shipment, the threshold voltage of the driving element DT is sensed in each sub-pixel through a sensing path connected to the pixels, and then the threshold voltage deviation is compensated for in all sub-pixels based on the sensing result. Also, the mobility of the driving element DT is sensed in each of the sub-pixels to compensate for the mobility deviation. In the sensing mode, the compensation value is updated based on the result of sensing the mobility μ and the threshold voltage Vth of the driving element DT.

The power-on sequence (ON) starts when the power of the electroluminescent display is turned on and an input voltage is generated from the host system. In the power-on sequence (0N), the driving voltage of the display panel driving circuit and the display panel 100 is generated, and the timing controller 130 and the display panel driving circuits 110, 112, and 120 are initialized.

The mobility of the driving element DT is sensed in the vertical blank interval (VB) of the power-on sequence (0N) and the display driving period, and the selected mobility compensation value is updated according to the sensing value.

During the display driving period, pixel data written to pixels is modulated with a compensation value for each active period (AT) of each frame period, and an image is displayed on the screen.

The power-off sequence (OFF) starts after the power-off signal of the electroluminescent display is received. In the power-off sequence (OFF), the threshold voltage (Vth) of each of the sub-pixels is sensed during a delay time during which the display panel driving circuit and the external compensation circuit are additionally driven. In the power-off sequence (OFF), the threshold voltage (Vth) of the driving element (DT) is sensed in sub-pixels of the entire screen, and Vth_LSL is determined for each local area (BL11 to BL44) based on the sensing result.

In the power-off sequence (OFF), black offset voltages Vblack1 to Vblack16 optimized for each local area are determined according to Vth_LSL obtained for each local area (BL11 to BL44). The black offset voltage may be set to a voltage lower than Vth_LSL in each local region so that the luminance of a subpixel does not increase in a black grayscale.

An active interval (AT) is a time during which data of one frame is written to all pixels on the screen. The vertical blank period VB is a blank period in which pixel data of the input image is not received between the active period AT of the N−1th frame period and the active period AT of the Nth frame period. During the vertical blank period (VB), the timing controller 130 does not receive the next frame data (N-th frame data).

The vertical synchronization signal Vsync defines one frame period. The horizontal synchronization signal (Hsync) defines one horizontal period (Horizontal time). The data enable signal DE defines a valid data period including pixel data to be displayed on the screen.

The data enable signal DE is synchronized with valid data to be displayed on the pixel array of the display panel 100 . One pulse period of the data enable signal DE corresponds to one horizontal period, and a high logic period of the data enable signal DE indicates data input timing of one pixel line. One horizontal period is a time required to write data to pixels of one pixel line in the display panel 100 .

The timing controller 130 receives the data enable signal DE and data of the input image during the vertical active period AT. There is no data enable signal DE and data of the input image in the vertical blank period VB. During the active period AT, one frame of data to be written in all pixels is received by the timing controller 130 . One frame period is the sum of the active period (AT) and the vertical blank period (VB).

As can be seen from the data enable signal DE, input data is not received by the display device during the vertical blank period VB. The vertical blank period VB includes a vertical sync time (VS), a vertical front porch (FP), and a vertical back porch (BP).

6 is a diagram showing an example of Vth_LSL.

Referring to FIG. 6 , Vth_LSL may be used as one of the defect management indicators of the display panel 100 . For example, It can be determined as a Vth value that satisfies 4.5σ. Vth_LSL may be determined based on 4.5σ, but is not limited thereto. For example, a representative value of the threshold voltage of the driving element DL for each local area may be determined by using another index representing the threshold voltage Vth of the driving element DL.

7 is a diagram showing in detail voltage settings for each section of the data voltage output from the data driver 110 .

Referring to FIG. 7 , the data voltage Vdata may include a first compensation period lower than the grayscale expression range and a second compensation period higher than the grayscale expression range.

The first compensation period includes a black offset range that is a variable range of the black offset voltage (HCT), a negative polarity compensation voltage margin range (NBTiS Margin), and an initial Vth compensation range. The initial Vth compensation range is a compensation voltage margin set to compensate for the threshold voltage of the driving element DT before shipment.

The negative polarity compensation voltage margin range (NBTiS Margin) is set as a voltage range between the black offset range and the grayscale expression range, and includes the above-described Vth_LSL compensation range for each local area. When the threshold voltage Vth of the driving element shifts to a negative polarity, the data voltage Vdata is reduced within the compensation voltage margin range NBTiS Margin, so that the shift in the threshold voltage of the driving element DT can be compensated for.

The second compensation period of the data voltage Vdata includes a mobility compensation range, an elapsed Vth compensation range, and an OLED afterimage compensation range. The mobility compensation range is a voltage margin set to compensate for a difference in mobility of driving elements measured in real time during a power-on sequence and a display driving period. The elapsed Vth compensation range is set to compensate for a change in the threshold voltage when the threshold voltage of the driving element DT shifts to a positive polarity voltage due to the positive stress of the driving element, which increases as the driving time of the pixels increases. is the voltage margin. OLED afterimage compensation range is a voltage margin for compensating for afterimage caused by parasitic capacitance of OLED. According to the present invention, black grayscale voltages of pixel data for each local region of a screen are adjusted within a black offset range. Accordingly, it should be noted that the second compensation period of the data voltage Vdata is not essential in the present invention.

8 is a diagram showing an example of a black offset voltage for each local area.

Referring to FIG. 8 , during a power-off sequence, threshold voltages Vth of driving elements DT are sensed through an external compensation circuit on the entire screen of the display panel. The compensator 131 calculates threshold voltage distributions 81 and 82 of the driving elements DT by dividing them into preset local regions.

Due to differences in driving histories of pixels and physical characteristics of driving elements, the amount of change in the threshold voltage of driving elements may vary depending on the position of the screen. As a result, the threshold voltage distributions 81 and 82 for each local area are different. Since the threshold voltage representative value of the driving device, that is, Vth_LSL is calculated based on the threshold voltage distributions 81 and 82, Vth_LSL in the threshold voltage distributions 81 and 82 for each local area is different for each local area. In the example of FIG. 8 , the first threshold voltage distribution 81 and the second threshold voltage distribution 82 assume threshold voltage distributions obtained in local areas at different positions on the screen. When the threshold voltage distributions 81 and 82 are different for each local area, Vth_LSL (LSL1 and LSL2) are different for each local area. The black offset voltages (Vblack1, Vblack2) should be set smaller than Vth_LSL so that the luminance of sub-pixels does not increase in the black gradation, and the stress of the driving elements should be reduced on the entire screen by reducing Vgs of the driving elements independently for each local region. Therefore, if the threshold voltage distributions 81 and 82 are different for each local region, the optimal black offset voltages Vblack1 and Vblack2 for each local region that can reduce the Vgs of the driving element for each local region in the black gradation are different values for each local region is determined by

9 is a flowchart illustrating a driving method of an electroluminescent display device according to an exemplary embodiment of the present invention.

Referring to FIG. 9 , when the power switch of the electroluminescent display device is turned on (Power ON), pixel data of an input image is received in the electroluminescence display device through a power-on sequence, and a normal driving mode is executed to display the input image. Pixel data is displayed on the screen of the display panel 100 (S01 to S04). The mobility of the driving element DT is sensed in real time in the vertical blank period VB in every frame period, and pixel data is modulated based on the sensing result to compensate for the mobility of the driving element DT (S05). .

When the power switch of the electroluminescent display device is turned off, a power off signal is generated and a power off sequence starts (S06). During a preset delay time in the power-off sequence, the display panel driving circuit and the external compensation circuit are driven so that the threshold voltages Vth of the driving elements DT are sensed on the entire screen (S07). The compensator 131 calculates the threshold voltage distributions 81 and 82 for each local region based on the threshold voltage sensing results of the driving elements DT, and uses the threshold voltage distributions 81 and 82 to determine a predetermined defect management acceptance criterion. The indicated threshold voltage value is determined as Vth_LSL (LSL1, LSL2) (S08).

The voltage levels of the black offset voltages Vblack1 and Vblack2 are determined in proportion to Vth_LSL (LSL1 and LSL2) for each local area (S09). The compensator 131 determines the black offset voltages Vblack1 and Vblack2 as maximum values within a range smaller than Vth_LSL (LSL1, LSL2) for each local area. When the black offset voltages Vblack1 and Vblack2 are increased, since Vgs of the driving element DT is reduced in the black grayscale, stress of the driving element DT is reduced and life span of the driving element DT can be extended. If the black offset voltages (Vblack1, Vblack2) rise above Vth_LSL (LSL1, LSL2), the luminance of the sub-pixel in the black grayscale may increase, so the black offset voltages (Vblack1, Vblack2) must be smaller than Vth_LSL (LSL1, LSL2). . The black offset voltages Vblack1 and Vblack2 optimized for each local area are stored in the memory of the compensator 131 and applied as the black offset of the data voltage Vdata when the electroluminescent display is turned on again.

After the optimal black offset voltages (Vblack1, Vblack2) for each local area are determined, the input voltage of the electroluminescent display is cut off so that the display panel driving circuit and compensation circuit do not operate (S10).

The present invention varies black offset voltages (Vblack1, Vblack2) in each local area based on the threshold voltage sensing result of the driving element obtained for each local area divided on the screen, and as shown in FIGS. 11 and 12, the screen The black offset voltage may be varied for each local area based on the luminance distribution of the image.

When the use period of the EL display device becomes longer, the threshold voltage of the driving element DT may be shifted due to the deterioration of the driving element DT. The external compensation circuit of the present invention senses the threshold voltage (Vth) of the driving element in real time, and based on the threshold voltage distribution (81, 82) for each local area obtained as a result of the real-time sensing, the optimal black offset voltage (Vblack1, Vblack1, 82) for each local area. Vblack2) may be changed to update black offset voltage information in real time.

The negative polarity stress of the transistor is greatly affected by luminance. When a driving element DT in a local area with high luminance and a driving element DT in a local area with relatively low luminance have the same driving history, the driving element DT in a local area with high luminance is negatively stressed. receive more

The gate signals SCAN and SENSE may have different gate waveforms according to the position of the screen according to the RC delay of the gate line 104 on the screen, as shown in the examples of FIGS. 11 and 12 . 11 shows gate signal waveforms 111a and 111b in the form of a general square wave. 12 is an example in which the gate high voltage VGH is adjusted low at the falling edges of the gate signal waveforms 112a and 112b. 11 and 12 , since the RC delay of the gate line 104 increases as the distance from the gate driver 120 increases, the delay of the gate signal waveform 112b increases.

The luminance of a subpixel may vary according to the waveforms of the gate signals SCAN and SENSE. In the case of the example of FIG. 11 , when pixel data of the same middle gray level is written to all pixels on the screen, the luminance of the middle portion of the screen may be higher than that of the edge portion. In this case, the driving elements of the middle local area receive more negative stress than the driving elements of the edge local area.

In the case of the example of FIG. 12 , when pixel data of the same middle gray level is written to all pixels on the screen, the luminance of the edge portion of the screen may be higher than that of the middle portion. In this case, the driving elements located in the edge local area with relatively high luminance receive more negative polarity stress than the driving elements in the central local area of the screen.

According to the present invention, the voltage level of the black offset voltage Vblak is determined in proportion to the luminance in the luminance distribution of the screen to reduce negative polarity stress of driving elements present in a local region where the luminance is relatively high. In the example of FIG. 11 , the black offset voltage of the central local area having relatively high luminance is set higher than that of the edge local area. In the example of FIG. 12 , the black offset voltage of the edge local area is set higher than that of the central local area.

According to the present invention, black offset voltages Vblak may be differently set between local regions based on a luminance profile of a previously photographed screen. In addition, according to another embodiment of the present invention, the black offset voltage of a local region having relatively high luminance may be higher than that of other local regions by analyzing the luminance distribution of the input image every frame. In this case, the black offset voltage Vblack may be updated in each of the local regions in every frame period.

Through the above description, those skilled in the art will understand that various changes and modifications are possible without departing from the spirit of the present invention. Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification, but should be determined by the claims.

100: display panel 110: data driving unit
120: gate driver 130: timing controller
131: compensation unit BL11 to BL44: local area
DT: drive element M1~M4: switch element

Claims (13)

a display panel in which data lines and gate lines intersect on a screen and sub-pixels including driving elements that respectively drive light emitting elements are disposed;
a data driver that receives pixel data including black offset values and outputs black offset voltages to the data lines;
a sensing unit configured to sense a threshold voltage of the driving element in each of the sub-pixels; and
The data driving unit determines the black offset value based on at least one of a threshold voltage characteristic of a driving element for each local region of the screen and a luminance characteristic for each local region of the screen and adds the black offset value to the pixel data of the input image Equipped with a compensation unit for supplying
The screen is divided into two or more local regions to which the black offset voltage is independently applied;
The compensation unit calculates the distribution of the threshold voltages of the driving elements obtained in the sub-pixels of the entire screen for each local area, and the threshold voltage distribution of the driving elements obtained for each local area of the screen is a threshold indicated by the defect management index. Determine a voltage value as a representative value of the threshold voltage of the driving element obtained for each local region;
The output voltage of the data driver includes a grayscale expression range, a compensation voltage margin range lower than the grayscale expression range, and a black offset range lower than the compensation voltage margin range;
The black offset voltage is adjusted within the black offset range;
The compensation voltage margin range includes a compensation range of the defect management index. delete delete According to claim 1,
A data voltage output from the data driver is applied to a gate of the driving element and a predetermined reference voltage is supplied to a source of the driving element;
An electroluminescence display device in which a black gradation data voltage is equal to or lower than the reference voltage. According to claim 1 or 4,
In each of the local regions, the black offset value is determined as a value smaller than a representative value of the threshold voltage of the driving element obtained for each local region;
If the representative threshold voltage of the driving element is different between the local areas, the black offset value is different between the local areas. delete a display panel in which data lines and gate lines intersect on a screen and sub-pixels including driving elements that respectively drive light emitting elements are disposed;
a data driver that receives pixel data including black offset values and outputs black offset voltages to the data lines;
a sensing unit configured to sense a threshold voltage of the driving element in each of the sub-pixels; and
a compensator for determining the black offset value based on at least one of a threshold voltage characteristic of a driving element for each local area and a luminance characteristic for each local area, adding the black offset value to the pixel data of an input image, and supplying the black offset value to the data driver; do,
The screen is divided into two or more local regions to which the black offset voltage is independently applied;
The output voltage of the data driver includes a grayscale expression range, a compensation voltage margin range lower than the grayscale expression range, and a black offset range lower than the compensation voltage margin range;
The black offset voltage is adjusted within the black offset range;
The electroluminescent display device of claim 1 , wherein the black offset voltage of a local area having relatively higher luminance than other local areas is higher than the black offset voltage of another local area. a display panel in which data lines and gate lines intersect on a screen and sub-pixels including driving elements that respectively drive light emitting elements are disposed;
a data driver that receives pixel data including black offset values and outputs black offset voltages to the data lines;
a sensing unit configured to sense a threshold voltage of the driving element in each of the sub-pixels; and
a compensator for determining the black offset value based on at least one of a threshold voltage characteristic of a driving element for each local area and a luminance characteristic for each local area, adding the black offset value to the pixel data of an input image, and supplying the black offset value to the data driver; do,
The screen is divided into two or more local regions to which the black offset voltage is independently applied;
The output voltage of the data driver includes a grayscale expression range, a compensation voltage margin range lower than the grayscale expression range, and a black offset range lower than the compensation voltage margin range;
The black offset voltage is adjusted within the black offset range;
An electroluminescent display according to an analysis result of an input image, wherein the black offset voltage of a local area where an image with high luminance is displayed is higher than that of another local area. A driving method of an electroluminescent display device comprising a display panel on a screen in which data lines and gate lines intersect and sub-pixels including driving elements for driving light emitting elements are arranged, and a data driver for driving the data lines ,
dividing the screen into two or more local areas;
sensing a threshold voltage of a driving element in each of the sub-pixels for each local region of the screen;
The distribution of the threshold voltages of the driving elements obtained from the sub-pixels of the entire screen is calculated for each local area, and the threshold voltage value indicated by the defect management index is calculated from the distribution of the threshold voltages of the driving elements obtained for each local area. determining a representative value of the threshold voltage of the driving element obtained for each local region of ;
determining a black offset value based on at least one of a threshold voltage characteristic of a driving element for each local region and a luminance characteristic for each local region, adding the black offset value to pixel data of an input image, and supplying the black offset value to the data driver; and
and outputting, by the data driver, a black offset voltage to the data lines by receiving pixel data including the black offset value;
The output voltage of the data driver includes a grayscale expression range, a compensation voltage margin range lower than the grayscale expression range, and a black offset range lower than the compensation voltage margin range;
The black offset voltage is adjusted within the black offset range;
The compensation voltage margin range includes a compensation range of the defect management index. According to claim 9,
and determining the black offset voltage as a voltage smaller than the representative threshold voltage in each of the local regions. According to claim 9,
The step of determining the black offset voltage as a voltage smaller than the representative threshold voltage in each of the local regions,
The driving method of the electroluminescent display device determining the black offset voltage as a maximum voltage within a range smaller than the threshold voltage representative value in each of the local regions. A driving method of an electroluminescent display device comprising a display panel on a screen in which data lines and gate lines intersect and sub-pixels including driving elements for driving light emitting elements are arranged, and a data driver for driving the data lines ,
dividing the screen into two or more local areas and defining a local area of the screen based on a luminance distribution of the screen;
sensing a threshold voltage of a driving element in each of the sub-pixels for each local region of the screen;
determining a black offset value based on at least one of a threshold voltage characteristic of a driving element for each local region and a luminance characteristic for each local region, adding the black offset value to pixel data of an input image, and supplying the black offset value to the data driver;
increasing a black offset voltage in a local area having higher luminance than in other local areas; and
and outputting, by the data driver, a black offset voltage to the data lines by receiving pixel data including the black offset value;
The output voltage of the data driver includes a grayscale expression range, a compensation voltage margin range lower than the grayscale expression range, and a black offset range lower than the compensation voltage margin range;
A method of driving an electroluminescent display device in which the black offset voltage is adjusted within the black offset range. A driving method of an electroluminescent display device comprising a display panel on a screen in which data lines and gate lines intersect and sub-pixels including driving elements for driving light emitting elements are arranged, and a data driver for driving the data lines ,
analyzing the luminance distribution of the input image;
dividing the screen into two or more local areas and defining a local area of the screen based on a luminance distribution of the screen;
sensing a threshold voltage of a driving element in each of the sub-pixels for each local region of the screen;
determining a black offset value based on at least one of a threshold voltage characteristic of a driving element for each local region and a luminance characteristic for each local region, adding the black offset value to pixel data of an input image, and supplying the black offset value to the data driver;
increasing a black offset voltage of a local area where a relatively high luminance portion of the input image is displayed compared to other local areas; and
and outputting, by the data driver, a black offset voltage to the data lines by receiving pixel data including the black offset value;
The output voltage of the data driver includes a grayscale expression range, a compensation voltage margin range lower than the grayscale expression range, and a black offset range lower than the compensation voltage margin range;
A method of driving an electroluminescent display device in which the black offset voltage is adjusted within the black offset range.

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