Display device and driving method thereof

Abstract

A display device includes: pixels connected to scan lines, control lines, data lines, and sensing lines; a scan driving unit supplying a scan signal to the scan line and supplying a control signal to the control line; a data driving unit supplying one of an image data signal and a sensing data signal to the data lines; a sensing unit sensing a characteristic based on a sensing current supplied through the sensing line during a sensing period; and a power supply unit supplying a voltage of the first power to the pixels. The sensing period includes: a first sensing period during which a first sensing current is extracted based on a first sensing data signal corresponding to the first gradation; and a second sensing period during which a second sensing current is extracted based on a second sensing data signal corresponding to the second gradation, in which a voltage of the first power supplied during the first sensing period is different from a voltage of the first power supplied during the second sensing period.

Description

[0001] This application is a divisional application of the invention patent application "Display device and driving method thereof" with application date of June 12, 2020 and application number 202080033324.9. Technical Field

[0002] Various embodiments of the present disclosure generally relate to a display device and a method of driving the display device, and more particularly to a display device to which an external compensation scheme is applied and a method of driving the display device. Background Art

[0003] A self-emissive display device uses pixels connected to a plurality of scan lines and data lines to display images. To this end, each pixel has a light emitting element and a driving transistor.

[0004] The driving transistor controls the amount of current supplied to the light emitting element in response to a data signal supplied from a corresponding data line. The light emitting element generates light having a predetermined brightness according to the amount of current supplied from the driving transistor.

[0005] In order for the display device to display an image with uniform image quality, the driving transistor included in each pixel should supply substantially the same current to the light emitting element according to the data signal. However, the driving transistor included in each pixel has its inherent characteristic value in which there may be deviation.

[0006] In an example, the threshold voltage and mobility of the driving transistor may be set differently in each pixel, or may change due to degradation caused by use thereof, and thus a brightness difference between images may occur. Summary of the invention

[0007] Technical issues An object of the present disclosure is to provide a display device which changes a voltage of a first power to be supplied to a pixel depending on a grayscale of a data signal during a sensing period.

[0008] Another object of the present disclosure is to provide a method for driving a display device.

[0009] However, the objects of the present disclosure are not limited to the aforementioned objects and may be expanded in various forms without departing from the spirit and scope of the present disclosure.

[0010] Technical Solution In order to achieve the purpose of the present disclosure, the display device according to the embodiment of the present disclosure can be driven so that the period of the display device is divided into a display period and a sensing period, an image is displayed during the display period, and the characteristics of the driving transistor included in each pixel are sensed during the sensing period. The display device may include: a pixel connected to a scan line, a control line, a data line, and a sensing line; a scan driver configured to supply a scan signal to the scan line and a control signal to the control line; a data driver configured to supply one of an image data signal and a sensing data signal to the data line; a sensing circuit configured to sense the characteristics based on a sensing current supplied through the sensing line during the sensing period; and a power supply configured to supply a voltage of a first power to the pixel. The sensing period may include a first sensing period and a second sensing period, during which a first sensing current is extracted based on a first sensing data signal corresponding to a first grayscale, and during which a second sensing current is extracted based on a second sensing data signal corresponding to a second grayscale, and the voltage of the first power supplied during the first sensing period may be different from the voltage of the first power supplied during the second sensing period.

[0011] According to an embodiment, the first sensing period and the second sensing period may be performed sequentially.

[0012] According to an embodiment, the power supply may be configured to output the first power having the first sensing voltage according to the first gray scale during the first sensing period.

[0013] According to an embodiment, the power supply may be configured to output the first power having a second sensing voltage according to a second grayscale during the second sensing period, the second sensing voltage being different from the first sensing voltage.

[0014] According to an embodiment, the power supply may be configured to output the first power having a display voltage for image display during the display period.

[0015] According to an embodiment, the display voltage may be equal to one of the first sensing voltage and the second sensing voltage.

[0016] According to an embodiment, the difference between the first sensing voltage and the second sensing voltage may be a result obtained by reflecting a difference between channel length modulation effects of a driving transistor depending on a difference between a first grayscale and a second grayscale.

[0017] According to an embodiment, the difference between the first sensing voltage and the second sensing voltage may be proportional to a difference between a gate-source voltage of the driving transistor depending on the first sensing data signal and a gate-source voltage of the driving transistor depending on the second sensing data signal.

[0018] According to an embodiment, the data driver may be configured to supply a first sensing data signal to the pixel during a first sensing period, and to supply a second sensing data signal to the pixel during a second sensing period.

[0019] According to an embodiment, the sensing circuit may be configured to simultaneously calculate a mobility characteristic and a threshold voltage characteristic of the driving transistor based on the first sensing period and the second sensing period.

[0020] According to an embodiment, the sensing circuit may include: an analog-to-digital converter configured to convert a first sensing current and a second sensing current into first sensing data and second sensing data both having a digital format; and a compensator configured to calculate a mobility characteristic and a threshold voltage characteristic of a driving transistor by performing operations on the first sensing data and the second sensing data, and configured to determine a compensation value for image data based on the mobility characteristic and the threshold voltage characteristic.

[0021] According to an embodiment, the sensing circuit may further include: a memory configured to store at least one of the first sensing data and the second sensing data.

[0022] According to an embodiment, among pixels, a pixel located on an i-th horizontal line (where i is a natural number) may include: a light emitting element; a first transistor configured to control a current flowing from a first power into a second node according to a voltage of a first node, the first transistor corresponding to a driving transistor; a second transistor connected between the first node and one of the data lines, the second transistor including a gate electrode connected to an i-th scanning line; a third transistor connected between the second node and a j-th sensing line (where j is a natural number), the third transistor including a gate electrode connected to an i-th control line; and a storage capacitor connected between the first node and the second node.

[0023] According to an embodiment, the control signal supplied during each of the first sensing period and the second sensing period may have a length greater than that of the control signal supplied during the display period.

[0024] According to an embodiment, during each of the first sensing period and the second sensing period, a portion of a control signal supplied to the i th control line may overlap with a scan signal supplied to the i th scan line, and a time for supplying the control signal is longer than a time for supplying the scan signal.

[0025] According to an embodiment, when the second transistor and the third transistor are turned on, the reference voltage can be supplied to the second node through the jth sensing line, and when the second transistor is turned off in the on state of the third transistor, one of the first sensing current and the second sensing current can be supplied to the sensing circuit through the jth sensing line.

[0026] To achieve the purpose of the present disclosure, a method for driving a display device according to an embodiment of the present disclosure may include: supplying a first sensing data signal corresponding to a first grayscale, a first power having a first sensing voltage, and a reference voltage to a pixel during a first sensing period; sensing a first sensing current generated based on the first sensing voltage from a pixel during the first sensing period; supplying a second sensing data signal corresponding to a second grayscale, a first power having a second sensing voltage, and a reference voltage to a pixel during a second sensing period; sensing a second sensing current generated based on the second sensing voltage from a pixel during a second sensing period; and calculating a characteristic of a driving transistor of a pixel using the first sensing current and the second sensing current. The first sensing data signal and the second sensing data signal may be different from each other, and the first sensing voltage and the second sensing voltage may be different from each other.

[0027] According to an embodiment, the mobility characteristic and the threshold voltage characteristic of the driving transistor may be simultaneously calculated based on the first sensing period and the second sensing period.

[0028] According to an embodiment, the first sensing data signal may be greater than the second sensing data signal, and the first sensing voltage may be greater than the second sensing voltage.

[0029] According to an embodiment, the method may further include compensating the input image data based on the calculated characteristics of the driving transistor.

[0030] Beneficial Effects According to the display device and the method for driving the display device of the embodiment of the present disclosure, the voltage level of the first power supplied to the drain electrode of the driving transistor can be changed based on the grayscale value for current sensing during the external compensation driving. Therefore, the channel length modulation effect of the driving transistor is reflected in the image data compensation, so that the compensation error can be greatly reduced and the image quality can be improved.

[0031] However, the advantages of the present disclosure are not limited to the aforementioned advantages and may be extended in various forms without departing from the spirit and scope of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 is a block diagram illustrating a display device according to an embodiment of the present disclosure.

[0033] Figure 2 It is shown Figure 1 FIG. 1 is a diagram of an example of a pixel and a sensing circuit included in a display device of FIG.

[0034] Figure 3 It is shown Figure 1 A timing diagram of an example of the operation of a display device.

[0035] Figure 4 It is shown Figure 1 FIG. 1 is a timing diagram of an example of operation of a display device during a sensing period.

[0036] Figure 5 is used to explain the Figure 2 Diagram of the channel length modulation effect occurring in the first transistor in a pixel.

[0037] Figure 6 is a diagram for explaining an example in which the voltage of the first power is adjusted by reflecting the channel length modulation effect.

[0038] Figure 7 It is shown Figure 1 A block diagram of an example of a compensator included in a sensing circuit of a display device.

[0039] Figure 8a is a graph schematically showing an error rate of external compensation based on conventional 2-point current sensing, and Figure 8b is a graph schematically illustrating an error rate of an external compensation scheme according to an embodiment of the present disclosure.

[0040] Fig. 9 is a flowchart illustrating a method of driving a display device according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0041] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. Throughout the accompanying drawings, the same reference numerals are used to represent the same or similar components, and repeated descriptions thereof will be omitted.

[0042] Figure 1 is a block diagram illustrating a display device according to an embodiment of the present disclosure.

[0043] Reference Figure 1 , the display device 1000 may include a pixel part 100 , a scan driver 200 , a data driver 300 , a sensing circuit 400 , a power supply 500 , and a timing controller 600 .

[0044] The display device 1000 may be a flat display device, a flexible display device, a curved display device, a foldable display device, or a bendable display device. In addition, the display device may be applied to a transparent display device, a head-mounted display device, a wearable display device, etc. In addition, the display device 1000 may be applied to various electronic devices such as a smart phone, a tablet computer, a smart tablet computer, a television (TV), and a monitor.

[0045] In addition, the display device 1000 may be implemented as an organic light emitting display device, a liquid crystal display device, etc. However, this configuration is only an example, and the configuration of the display device 1000 is not limited thereto. For example, the display device 1000 may be a self-emitting display device including an inorganic light emitting element.

[0046] In an embodiment, the display device 1000 may be driven while a period of the display device 1000 is divided into a display period during which an image is displayed and a sensing period during which characteristics of a driving transistor included in each pixel PX are sensed.

[0047] The pixel part 100 may include pixels PX disposed to be coupled to data lines DL1 to DLm (where m is a natural number), scan lines SL1 to SLn (where n is a natural number), control lines CL1 to CLn, and sensing lines SSL1 to SSLm. Voltages of the first power VDD and the second power VSS may be supplied from the outside to the pixels PX.

[0048] In addition, despite Figure 1 For example, one or more control lines, scan lines, emission control lines, sensing lines, etc. may be additionally formed in the pixel portion 100 according to the circuit structure of each pixel PX.

[0049] In an embodiment, the transistor included in each pixel PX may be an N-type oxide thin film transistor (TFT). For example, such an oxide TFT may be a low temperature polycrystalline oxide (LTPO) TFT. However, this is only an example, and the N-type transistor is not limited thereto. For example, the active pattern (semiconductor layer) included in each transistor may include an inorganic semiconductor (e.g., amorphous silicon or polycrystalline silicon), an organic semiconductor, etc. In addition, at least one of the transistors included in the display device 1000 may be replaced with a P-type transistor.

[0050] The timing controller 600 may generate a data drive control signal DCS, a scan drive control signal SCS, and a power drive control signal PCS in response to an externally supplied synchronization signal. The data drive control signal DCS generated by the timing controller 600 may be supplied to the data driver 300, the scan drive control signal SCS may be supplied to the scan driver 200, and the power drive control signal PCS may be supplied to the power supply 500.

[0051] In addition, the timing controller 600 may supply the compensated image data CDATA to the data driver 300 based on the externally supplied input image data IDATA.

[0052] The data drive control signal DCS may include a source start signal and a clock signal. The source start signal may control the time point at which the sampling of the data starts. The clock signal may be used to control the sampling operation.

[0053] The scan drive control signal SCS may include a scan start signal, a control start signal and a clock signal. The scan start signal may control the timing of the scan signal. The control start signal may control the timing of the control signal. The clock signal may be used to offset the scan start signal and / or the control start signal.

[0054] The power driving control signal PCS may control supply of voltages of the first power VDD and the second power VSS and levels of the voltages.

[0055] The timing controller 600 may also control the operation of the sensing circuit 400. For example, the timing controller 600 may control the timing of supplying the reference voltage to the pixel PX through the sensing lines SSL1 to SSLm and / or the timing of sensing the current generated in the pixel PX through the sensing lines SSL1 to SSLm.

[0056] The scan driver 200 may receive the scan driving control signal SCS from the timing controller 600. The scan driver 200, having received the scan driving control signal SCS, may supply the scan signals to the scan lines SL1 to SLn, and may supply the control signals to the control lines CL1 to CLn.

[0057] For example, the scan driver 200 may sequentially supply scan signals to the scan lines SL1 to SLn. When the scan signals are sequentially supplied to the scan lines SL1 to SLn, the pixels PX may be selected on a horizontal line basis. To this end, each scan signal may be set to a gate-on voltage (e.g., a logic high level) so that a transistor included in a corresponding pixel PX is turned on.

[0058] Similarly, the scan driver 200 may sequentially supply control signals to the control lines CL1 to CLn. The control signals may be used to sense (or extract) a driving current flowing through a pixel (i.e., a current flowing through a driving transistor). The timing and waveform of supplying the scan signals and the control signals may be differently set depending on the display period and the sensing period.

[0059] In addition, despite Figure 1 , a single scan driver 200 is shown as outputting both scan signals and control signals, but the present disclosure is not limited thereto. For example, the scan driver 200 may include a first scan driver that supplies scan signals to the pixel portion 100 and a second scan driver that supplies control signals to the pixel portion 100.

[0060] The data driver 300 may receive a data driving control signal DCS from the timing controller 600. The data driver 300 may supply a data signal for detecting pixel characteristics (e.g., a sensing data signal) to the pixel portion 100 during a sensing period. The data driver 300 may supply a data signal for displaying an image to the pixel portion 100 based on the compensated image data CDATA during a display period.

[0061] The sensing circuit 400 may generate a compensation value for compensating a characteristic value of the pixel PX based on a sensing value (i.e., a sensing current) provided from the sensing lines SSL1 to SSLm. For example, the sensing circuit 400 may detect and compensate for a change in a threshold voltage of a driving transistor included in each pixel PX, a change in mobility of the driving transistor, and a change in characteristics of a light emitting element.

[0062] In an embodiment, the sensing circuit 400 may detect a first sensing current IS1 corresponding to a first grayscale during a first sensing period, and may detect a second sensing current IS2 corresponding to a second grayscale during a second sensing period. Here, the first grayscale may be a first test grayscale for current sensing, and the second grayscale may be a second test grayscale different from the first grayscale.

[0063] The sensing circuit 400 can use the operation of the first sensing current IS1 and the second sensing current IS2 to simultaneously calculate the threshold voltage characteristic and the mobility characteristic of each pixel PX, and can compensate the image data of the corresponding pixel PX based on the calculated characteristics. The compensation scheme of performing external compensation on the pixel PX using the sensing current corresponding to two grayscales according to an embodiment of the present disclosure can be defined as a 2-point current sensing scheme.

[0064] In an embodiment, the sensing circuit 400 may supply a predetermined reference voltage to the pixel PX through the sensing lines SSL1 to SSLm, and receive a current or voltage extracted from the pixel PX during a sensing period. The extracted current or voltage may correspond to a sensing value, and the sensing circuit 400 may detect a change in the characteristics of the driving transistor based on the sensing value. The sensing circuit 400 may calculate a compensation value for compensating the input image data IDATA based on the detected characteristic change. The compensation value may be provided to the timing controller 600 or the data driver 300.

[0065] During a display period, the sensing circuit 400 may supply a predetermined reference voltage for displaying an image to the pixel part 100 through the sensing lines SSL1 to SSLm.

[0066] Despite Figure 1, the sensing circuit 400 is shown as a component separate from the timing controller 600, but at least some of the components of the sensing circuit 400 may be included in the timing controller 600. For example, the sensing circuit 400 and the timing controller 600 may be formed in a single driver integrated circuit (IC). In addition, the data driver 300 may also be included in the timing controller 600. Therefore, at least some of the sensing circuit 400, the data driver 300, and the timing controller 600 may be formed in a single driver IC.

[0067] The power supply 500 may supply a voltage of the first power VDD and a voltage of the second power VSS to the pixel portion 100 in response to the power driving control signal PCS. In an embodiment, the first power VDD may be used to determine a drain voltage of the driving transistor, and the second power VSS may be used to determine a cathode voltage of the light emitting element.

[0068] In an embodiment, the power supply 500 may change the voltage of the first power VDD supplied to the pixel PX during the sensing period. For example, the power supply 500 may change the voltage of the first power VDD so that the channel length modulation effect of the driving transistor is reflected in the operation of sensing the characteristics of the driving transistor and the compensation operation for the driving transistor.

[0069] Next, a compensation scheme in which the channel length modulation effect is reflected will be described in detail.

[0070] Figure 2 It is shown Figure 1 FIG. 1 is a diagram of an example of a pixel and a sensing circuit included in a display device of FIG.

[0071] exist Figure 2 In the figure, for convenience of description, pixels located on an i-th horizontal line and connected to a j-th data line DLj are shown.

[0072] Reference Figure 2 , the pixel PXij may include a light emitting element LD, a first transistor T1 (ie, a driving transistor), a second transistor T2 , a third transistor T3 , and a storage capacitor Cst.

[0073] A first electrode (anode electrode or cathode electrode) of the light emitting element LD is connected to the second node N2, and a second electrode (cathode electrode or anode electrode) of the light emitting element LD is connected to a source of a second power VSS. The light emitting element LD can generate light with a predetermined brightness according to the amount of current supplied from the first transistor T1.

[0074] A first electrode of the first transistor T1 may be connected to a source of first power VDD, and a second electrode thereof may be connected to a first electrode of the light emitting element LD. A gate electrode of the first transistor T1 may be connected to a first node N1. The first transistor T1 controls the amount of current flowing into the light emitting element LD according to a voltage of the first node N1.

[0075] A first electrode of the second transistor T2 may be connected to the data line DLj, and a second electrode thereof may be connected to the first node N1. A gate electrode of the second transistor T2 may be connected to the scan line SLi. When a scan signal is supplied through the scan line SLi, the second transistor T2 may be turned on, and then a data signal may be transmitted from the data line DLj to the first node N1.

[0076] The third transistor T3 may be connected between the sensing line SSLj and the second electrode (ie, the second node N2) of the first transistor T1. The gate electrode of the third transistor T3 may be connected to the control line CLi. When a control signal is supplied through the control line CLi, the third transistor T3 may be turned on, and then the sensing line SSLj and the second node N2 (ie, the second electrode of the first transistor T1) may be electrically coupled to each other.

[0077] In an embodiment, when the third transistor T3 is turned on, the reference voltage may be supplied to the second node N2 . In another embodiment, when the third transistor T3 is turned on, the current generated in the first transistor T1 may be supplied to the sensing circuit 400 .

[0078] The storage capacitor Cst may be connected between the first node N1 and the second node N2. The storage capacitor Cst may store a voltage corresponding to a voltage difference between the first node N1 and the second node N2.

[0079] In addition, in the embodiment of the present disclosure, the circuit structure of the pixel PXij is not affected by Figure 2 For example, the light emitting element LD may be disposed between the source of the first power VDD and the first electrode of the first transistor T1.

[0080] In addition, a parasitic capacitor Cpara may be formed between the gate electrode (ie, the first node N1 ) and the drain electrode of the first transistor T1 .

[0081] In an embodiment, the sensing circuit 400 connected to the sensing line SSLj may include a first switch SW1 , a second switch SW2 , an analog-to-digital converter (ADC) 420 , a compensator 440 , and a memory 460 .

[0082] The first switch SW1 and the second switch SW2 may be turned on alternately. When the first switch SW1 is turned on, the reference voltage Vref may be supplied to the second node. Therefore, the voltage of the second node N2 (ie, the source voltage of the first transistor T1) may be initialized to the reference voltage Vref.

[0083] When the second switch SW2 is turned on, the sensing current of the pixel PXij may flow into the sensing circuit 400 .

[0084] The analog-to-digital converter (ADC) 420 may sense a voltage from a sensing current of the sensing line SSLj, convert the value of the sensing voltage into a digital value, and output the digital value as sensing data. In an embodiment, the output sensing data may be stored in the memory 460. For example, the first sensing current IS1 in the first sensing period may be converted into the first sensing data, and the second sensing current IS2 in the second sensing period may be converted into the second sensing data.

[0085] The compensator 440 may perform an operation on the first sensing data and the second sensing data and then may simultaneously calculate the mobility characteristic and the threshold voltage characteristic of the first transistor T1. The compensator 440 may determine the compensation value COMV for the input image data IDATA based on the mobility characteristic and the threshold voltage characteristic.

[0086] The memory 460 may store at least one of the first sensing data and the second sensing data. In an embodiment, the memory 460 may further include a lookup table required for image data compensation, etc.

[0087] In addition, despite Figure 2 , the transistors T1 to T3 are shown as NMOS transistors, but the present disclosure is not limited thereto. For example, at least one of the transistors T1 to T3 may be implemented as a PMOS transistor.

[0088] Figure 3 It is shown Figure 1 A timing diagram of an example of the operation of a display device.

[0089] Reference Figures 1 to 3 , the display device 1000 may be driven such that a period of the display device 1000 is divided into a display period DP during which an image is displayed and a sensing period SP during which a characteristic of the first transistor T1 included in each pixel PX is sensed.

[0090] In an embodiment, during the sensing period SP, image data may be compensated based on the sensed characteristic information.

[0091] During the display period DP, the first switch SW1 may be turned on, and the second switch SW2 may be set to an off state. Thus, the reference voltage Vref as a constant voltage may be supplied to the sensing lines SSL1 to SSLm.

[0092] During the display period DP, the scan driver 200 may sequentially supply scan signals to the scan lines SL1 to SLn. Also, during the display period DP, the scan driver 200 may sequentially supply control signals to the control lines CL1 to CLn.

[0093] For the i-th horizontal line, the scan signal and the control signal may be supplied substantially at the same time. Therefore, the second transistor T2 and the third transistor T3 may be turned on or off at the same time.

[0094] When the second transistor T2 is turned on, a data signal DS corresponding to image data may be supplied to the first node N1. When the third transistor T3 is turned on, a reference voltage Vref may be supplied to the second node N2. Therefore, the storage capacitor Cst may store a voltage corresponding to a voltage difference between the data signal DS and the reference voltage Vref.

[0095] Here, since the reference voltage Vref is set to a constant voltage, the voltage stored in the storage capacitor Cst may be stably determined by the data signal DS.

[0096] When supply of the scan signal and the control signal to the i-th scan line SLi and the i-th control line CLi is stopped, the second transistor T2 and the third transistor T3 may be turned off.

[0097] Thereafter, the first transistor T1 may control the amount of current (driving current) supplied to the light emitting element LD according to the voltage stored in the storage capacitor Cst. Therefore, the light emitting element LD may emit light having brightness corresponding to the driving current of the first transistor T1.

[0098] In an embodiment, during the display period DP, the power supply 500 may output the first power VDD having the display voltage DIS_V. The first power VDD may be output in the form of a constant voltage during the display period DP. The display voltage DIS_V may have a typical voltage level to be applied for image display. In addition, the display voltage DIS_V may have a constant voltage level regardless of the grayscale of the image and the size (voltage level) of the data signal.

[0099] In an embodiment, during the sensing period SP, the scan driver 200 may sequentially supply scan signals to the scan lines SL1 to SLn. Also, during the display period DP, the scan driver 200 may sequentially supply control signals to the control lines CL1 to CLn.

[0100] In an embodiment, the length of the control signal supplied during the sensing period SP may be longer than the length of the control signal supplied during the display period DP. In addition, during the sensing period SP, a portion of the control signal supplied to the i-th control line CLi may overlap with the scan signal supplied to the i-th scan line SLi. The length of the control signal may be greater than the length of the scan signal. For example, the control signal supplied to the i-th control line CLi starts to be supplied simultaneously with the scan signal supplied to the i-th scan line SLi, and may be supplied for a time longer than the time the scan signal is supplied.

[0101] When the scan signal and the control signal are supplied at the same time, the second transistor T2 and the third transistor T3 are turned on. Here, the first switch SW1 is in an on state. When the second transistor T2 is turned on, a sensing data signal SGV (or data voltage) for sensing may be supplied to the first node N1. While the sensing data signal is supplied, the reference voltage Vref may be supplied to the second node N2 by the turn-on operation of the third transistor T3. Therefore, the storage capacitor Cst may store a voltage corresponding to the voltage difference between the sensing data signal SGV and the reference voltage Vref.

[0102] Thereafter, when the supply of the scan signal stops, the second transistor T2 may be turned off. When the second transistor T2 is turned off, the first node N1 may float. Therefore, the voltage of the second node N2 increases, and a sensing current is generated through the first transistor T1. When the voltage increases, the sensing current flows through the sensing line SSLj, and the sensing capacitor Cse may be charged. The speed of the voltage increase may vary with the current capability of the first transistor T1 (i.e., its mobility).

[0103] In addition, due to the parasitic capacitor Cpara, a voltage distribution occurs between the storage capacitor Cst and the parasitic capacitor Cpara, and the gate-source voltage of the first transistor T1 may be unintentionally changed. Therefore, during the compensation operation, compensation for the voltage drop attributable to the parasitic capacitor Cpara may also be performed.

[0104] After the voltage has increased for a preset time, the second switch SW2 may be turned on, and thus the sensing line SSLj may be connected to the analog-to-digital converter 420 of the sensing circuit 400. Therefore, the analog-to-digital converter 420 may generate a digital code corresponding to the voltage charged in the sensing capacitor Cse (ie, the voltage corresponding to the sensing current).

[0105] In an embodiment, during the sensing period SP, the power supply 500 may output the first power VDD having the sensing voltage SEN_V to calculate the characteristic.

[0106] In the display device 1000 to which the 2-point current sensing scheme is applied, channel length modulation occurs depending on the magnitude of the gate voltage of the first transistor T1, and thus the value of the actual sensing current may have a different error rate depending on the grayscale. Therefore, an error in sensing data occurs, and a large degradation compensation error may occur particularly in a low grayscale region. In order to overcome this compensation error, the voltage level of the first power VDD may be changed during the sensing period SP so that the channel length modulation effect is reflected in the compensation operation.

[0107] Therefore, the compensation error occurring in the external compensation scheme can be greatly reduced, the compensation efficiency can be maximized, and the image quality can be improved.

[0108] According to an embodiment, the sensing period SP may be performed at least once before the display device 1000 is shipped. In this case, initial characteristic information of the first transistor T1 may be stored before the display device 1000 is shipped, and the input image data IDATA may be compensated using the characteristic information, so the pixel part 100 may display an image with uniform image quality.

[0109] In addition, even when the display device 1000 is actually used, the sensing period SP may be performed at intervals of a predetermined period. For example, the sensing period SP may be arranged in a portion of the time during which the display device 1000 is turned on and / or off. Then, even if the characteristics of the first transistor T1 in each of the pixels PX change according to the use of the display device, the characteristic information may be updated in real time, which may then be reflected in the generation of the data signal. However, this is only an example, and the sensing period SP may be inserted between predetermined display periods DP. Therefore, the pixel portion 100 may continuously display an image with uniform image quality.

[0110] Figure 4 It is shown Figure 1 FIG. 1 is a timing diagram of an example of operation of a display device during a sensing period.

[0111] Reference Figures 2 to 4 , the sensing period SP may include a first sensing period SP1 and a second sensing period SP2.

[0112] The current sensing schemes in the first sensing period SP1 and the second sensing period SP2 may be substantially identical to each other.

[0113] During the first sensing period SP1 , a first sensing data signal GV1 corresponding to a first grayscale may be supplied to the data line DLj. Here, the power supply 500 may supply the first power VDD as a first sensing voltage V1 corresponding to the first grayscale to the pixel part 100 .

[0114] A first sensing current IS1 may be generated and extracted based on the first sensing data signal GV1 and the first sensing voltage V1.

[0115] During the second sensing period SP2, a second sensing data signal GV2 corresponding to the second grayscale may be supplied to the data line DLj. Here, the power supply 500 may supply the first power VDD as the second sensing voltage V2 corresponding to the second grayscale to the pixel part 100.

[0116] A second sensing current IS2 may be generated and extracted based on the second sensing data signal GV2 and the second sensing voltage V2.

[0117] In addition, the first grayscale and the second grayscale may be experimentally set values. That is, the first grayscale and the second grayscale may be set to grayscale values ​​that can minimize the errors of the mobility characteristics and the threshold voltage characteristics. For example, when the pixel PX emits within a range of grayscale values ​​varying from 0 to 255, the first grayscale may be a grayscale value of 224, and the second grayscale may be a grayscale value of 128. However, these values ​​are only examples, and the first grayscale and the second grayscale are not limited thereto.

[0118] In an embodiment, the difference dVDD between the first sensing voltage V1 and the second sensing voltage V2 may be a result obtained by reflecting the difference between the channel length modulation effect of the first transistor T1 caused by the difference between the first grayscale and the second grayscale. For example, the difference dVDD may be proportional to the difference between the gate-source voltage of the first transistor T1 depending on the first sensing data signal GV1 and the gate-source voltage of the first transistor T1 depending on the second sensing data signal GV2.

[0119] For example, when the first sensing data signal GV1 is greater than the second sensing data signal GV2 , the first sensing voltage V1 may be greater than the second sensing voltage V2 .

[0120] Therefore, a sensing error caused by a channel length modulation effect may be eliminated or minimized, and thus a degradation compensation error may be removed.

[0121] Figure 5 is used to explain the Figure 2 A diagram of the channel length modulation effect occurring in the first transistor in a pixel of FIG. 1 , and Figure 6 is a diagram for explaining an example in which the voltage of the first power is adjusted in consideration of the channel length modulation effect.

[0122] Reference Figure 2 , Figure 4 , Figure 5 and Figure 6, when the drain-source voltage Vds of the first transistor T1 becomes equal to the difference between the gate-source voltage Vgs of the first transistor T1 and the threshold voltage Vth (ie, Vds=Vgs-Vth), the first transistor T1 may operate in a saturation state.

[0123] In addition, if Figure 6 As shown in , it is generally assumed that the driving current Id (ie, the drain-source current Ids of the first transistor T1 ) is constant regardless of the drain-source voltage Vds in a saturation state.

[0124] Therefore, the driving current Id (or drain current) in the saturation state can be determined as a value that is different depending on the size of the gate voltage Vg of the first transistor T1. For example, when the first sensing data signal GV1 corresponding to the first grayscale GR1 is supplied to the gate electrode of the first transistor T1, the first driving current I1 theoretically flows in the saturation state. When the second sensing data signal GV2 corresponding to the second grayscale GR2 is supplied to the gate electrode of the first transistor T1, the second driving current I2 theoretically flows in the saturation state.

[0125] However, in reality, the effective channel length L of the first transistor T1 can be operated as if it is modulated (changed) depending on the drain voltage Vd (i.e., the drain-source voltage Vds). That is, when the drain-source voltage Vds increases, the depletion region increases, resulting in a decrease in the effective channel length L. When the effective channel length L is shortened, the moving distance of the carriers is shortened, and thus the drive current Id increases. This is called a channel length modulation effect.

[0126] This channel length modulation effect affects the driving current Id as shown in the following [Equation 1].

[0127] [Equation 1] Id=1 / 2β(Vgs-Vth) 2 (1+λVds) Here, Id represents a driving current, β represents a variable including mobility characteristics, Vgs represents a gate-source voltage, Vth represents a threshold voltage, and λVds represents a ratio of an effective channel length variation Lx to an effective channel length L (ie, Lx / L).

[0128] Therefore, when the voltage of the first power VDD is supplied as the display voltage DIS_V which is a sufficiently high voltage, as shown in FIG. Figure 6 As shown in , the first drive current I1 and the second drive current I2 can be increased from theoretical values.

[0129] In addition, since the saturated drain-source voltage Vds changes depending on the magnitude of the gate voltage Vg, the effective channel length variation Lx depending on the gate voltage Vg changes for the same drain-source voltage Vds. Therefore, when the display voltage DIS_V of the first power VDD is supplied as the drain voltage Vd, the error of the first drive current I1 with respect to the theoretical value (e.g., the first error E1) may be different from the error of the second drive current I2 with respect to the theoretical value (e.g., the second error E2). For example, the first error E1, which more reflects the channel length modulation effect, may be larger than the second error E2.

[0130] Therefore, in the 2-point current sensing scheme in which the channel length modulation effect is not reflected in the external compensation of the pixel PX, a compensation error inevitably occurs.

[0131] The display device 1000 according to an embodiment of the present disclosure reflects the first error E1 and the second error E2 in current sensing. That is, in order to offset the channel length modulation effect in which the driving current Id rises, the voltage of the first power VDD as the drain voltage Vd can be set differently depending on the first grayscale GR1 and the second grayscale GR2 for sensing.

[0132] The drain voltage Vd may be adjusted so that the first drive current I1 and the second drive current I2 are output as values ​​corresponding to the saturation state curve SC depending on the gate voltage Vg. That is, the voltage of the first power VDD for detecting the first drive current I1 may be determined as the first sensing voltage V1, and the voltage of the first power VDD for detecting the second drive current I2 may be determined as the second sensing voltage V2. For example, Figure 6 As shown in , the first sensing voltage V1 and the second sensing voltage V2 may be determined based on a first point PT1 and a second point PT2 corresponding to a saturation state curve SC.

[0133] Here, since only the difference between the first error E1 and the second error E2 needs to be removed, the voltage difference dVDD between the first sensing voltage V1 and the second sensing voltage V2 can be determined based on the gate voltage Vg in the saturation state. That is, the difference dVDD between the first sensing voltage V1 and the second sensing voltage V2 can be a result obtained by reflecting the difference between the channel length modulation effects of the first transistor T1 depending on the difference between the first grayscale GR1 and the second grayscale GR2. In an embodiment, the relationship between the first sensing voltage V1 and the second sensing voltage V2 can be expressed by the following [Equation 2]: [Equation 2] V2=V1-(Vgs 1 -Vgs 2 ) Here, Vgs 1may be a gate-source voltage Vgs corresponding to the first grayscale GR1, and Vgs 2 The gate-source voltage Vgs corresponding to the second grayscale GR2 may be a gate-source voltage Vgs. Since the source voltage Vs is a constant voltage, the voltage difference dVDD between the first sensing voltage V1 and the second sensing voltage V2 may be determined depending on the change in the gate voltage Vg. That is, the difference dVDD between the first sensing voltage V1 and the second sensing voltage V2 may be the same as the gate-source voltage Vgs of the first transistor T1 corresponding to the first sensing data signal GV1. 1 and the gate-source voltage Vgs of the first transistor T1 corresponding to the second sensing data signal GV2 2 is proportional to the difference between them.

[0134] For example, when the first sensing data signal GV1 is 3 V corresponding to the gray value 196, the second sensing data signal GV2 is 2.5 V corresponding to the gray value 128, and the first sensing voltage V1 is 10 V, the second sensing voltage V2 may be set to 9.5 V. However, this is only an example, and the first sensing voltage V1 may be equal to the display voltage DIS_V. Here, the second sensing voltage V2 may be smaller than the first sensing voltage V1.

[0135] As described above, when the external compensation driving is performed, the first power VDD having the first sensing voltage V1 may be supplied during the first sensing period SP1, and the first power VDD having the second sensing voltage V2 may be supplied during the second sensing period SP2. Therefore, the channel length modulation effect is reflected in the image data compensation, so that the compensation error can be greatly reduced and the image quality can be improved.

[0136] Figure 7 It is shown Figure 1 A block diagram of an example of a compensator included in a sensing circuit of a display device.

[0137] Reference Figures 1 to 7 , the compensator 440 may include a lookup table (LUT) 442 , a first calculator 444 , and a second calculator 446 .

[0138] The compensator 440 may perform an operation on the first sensing data ID1 and the second sensing data ID2 and then may calculate the mobility characteristic and the threshold voltage characteristic of the first transistor T1. The compensator 440 may determine the compensation value COMV for the input image data IDATA based on the calculated mobility characteristic and the threshold voltage characteristic.

[0139] During image display and sensing, the source voltage Vs is fixed to the reference voltage Vref, and thus degradation of the first transistor T1 may be compensated by adjusting the gate voltage of the first transistor T1 for a predetermined grayscale.

[0140] That is, the compensation value COMV may be a value for adjusting a data signal corresponding to a predetermined grayscale (ie, a voltage supplied to the gate electrode of the first transistor T1 ).

[0141] The lookup table 442 may output a first gate-source voltage Vgs_dis corresponding to the input image data IDATA. For example, the lookup table 442 may include a digital-to-analog converter (DAC). In addition, whenever the image data is compensated, the lookup table may be updated using the relationship between the new input image data IDATA and the first gate-source voltage Vgs_dis.

[0142] The first calculator 444 may calculate a gain G and an offset OS for compensating the first gate-source voltage Vgs_dis based on the first sensing data ID1 and the second sensing data ID2. The first sensing data ID1 may correspond to the first sensing current IS1, and the second sensing data ID2 may correspond to the second sensing current IS2.

[0143] The first calculator 444 may calculate the gain G including the mobility characteristic and the offset OS including the threshold voltage characteristic based on the above [Equation 1]. In [Equation 1], the driving current Id may be the first sensing current IS1 or the second sensing current IS2, the gate-source voltage Vgs may be a constant depending on the first sensing data signal GV1 or the second sensing data signal GV2, (1+λVds) may be a value compensated by the voltage level of the first power VDD, and β and Vth may be variables. Therefore, the first calculator 444 may calculate β and Vth based on the first sensing current IS1 and the second sensing current IS2 by calculation of two simultaneous equations. The gain G may include the mobility characteristic β and may be multiplied by the first gate-source voltage Vgs_dis. The offset OS may include the threshold voltage (Vth) characteristic and may be added to the first gate-source voltage Vgs_dis. That is, the first calculator 444 may simultaneously calculate the mobility characteristic β and the threshold voltage (Vth) characteristic of the first transistor T1 using the first sensing data ID1 and the second sensing data ID2.

[0144] The second calculator 446 may calculate a compensation value COMV for compensating the first gate-source voltage Vgs_dis. In an embodiment, the second calculator 446 may multiply the gain G by the first gate-source voltage Vgs_dis, and may add the offset OS to the result value. Therefore, a compensation value COMV for a piece of input image data IDATA corresponding to one pixel PX may be calculated. The compensation value COMV may correspond to a voltage obtained by newly updating the first gate-source voltage Vgs_dis. The input image data IDATA may be compensated based on the compensation value COMV to correspond to the voltage of the newly updated data signal.

[0145] In this manner, the mobility characteristic β and the threshold voltage (Vth) characteristic of the first transistor T1 may be simultaneously calculated based on the first sensing data ID1 and the second sensing data ID2 sensed using the 2-point current sensing scheme, and then the image data may be compensated.

[0146] Figure 8a is a graph schematically showing an error rate of external compensation based on conventional 2-point current sensing, and Figure 8b is a graph schematically illustrating an error rate of an external compensation scheme according to an embodiment of the present disclosure.

[0147] Reference Figure 8a and Figure 8b , the error rate of the external compensation scheme based on the driving current sensing for the first grayscale and the second grayscale may change with the value of the first grayscale and the value of the second grayscale.

[0148] Figure 8a and Figure 8b An error rate of displaying a grayscale value in a state in which the source voltage of the first transistor T1 is initialized to 1.5 V is shown. The sign of G255, G224, or G192 may indicate a first grayscale and a second grayscale set for 2-point current sensing.

[0149] like Figure 8a As shown in , the error rate of external compensation based on conventional 2-point current sensing may increase in the direction away from the measured grayscale (ie, the first grayscale and the second grayscale). For example, when the first grayscale and the second grayscale may have a grayscale value of 255 (G255) and a grayscale value of 128 (G128), the error rate is greater in the low grayscale region farther away from the first grayscale and the second grayscale than in the high grayscale region. Therefore, the compensation capability in the low grayscale region may deteriorate, and brightness deviations such as stains may be perceived. The reason for this is that the difference (error) between the driving currents occurring for each grayscale due to the channel length modulation effect is not reflected in the compensation.

[0150] The display device 1000 according to an embodiment of the present disclosure can reflect the error attributable to the channel length modulation effect in the 2-point current sensing. That is, during the first sensing period in which the current sensing for the first grayscale is performed, the first power (eg, Figure 1 VDD) may have a first sensing voltage, and during a second sensing period in which current sensing for a second grayscale is performed, the first power (eg, Figure 1 During the first sensing period and during the second sensing period, different voltages are supplied to the first transistor (eg, Figure 2The error attributable to the channel length modulation effect can be removed or minimized.

[0151] Therefore, if Figure 8b As shown in , the error rate of external compensation based on 2-point current sensing can be greatly improved. Therefore, the degradation compensation efficiency and image quality of pixels and display devices can be improved.

[0152] Fig. 9 is a flowchart illustrating a method of driving a display device according to an embodiment of the present disclosure.

[0153] Reference Fig. 9 , the method for driving a display device may include: step S100, supplying a first sensing data signal corresponding to a first grayscale (or a first test grayscale), a first power having a first sensing voltage, and a reference voltage to each pixel during a first sensing period; step S200, sensing a first sensing current generated based on the first sensing voltage from the pixel during the first sensing period; step S300, supplying a second sensing data signal corresponding to a second grayscale (or a second test grayscale), a first power having a second sensing voltage, and a reference voltage to the pixel during a second sensing period; and step S400, sensing a second sensing current generated based on the second sensing voltage from the pixel. In addition, the method for driving a display device may further include: step S500, calculating a driving transistor of the pixel (e.g., Figure 2 Characteristics of the first transistor T1).

[0154] In an embodiment, the first grayscale and the second grayscale may be different grayscales, and thus the first sensing data signal and the second sensing data signal may have different voltage levels. For example, when the first sensing data signal is larger than the second sensing data signal, the first sensing voltage may be set to a value larger than the second sensing voltage. Therefore, the first sensing current and the second sensing current may have sensing values ​​from which errors attributable to the channel length modulation effect of the driving transistor are removed.

[0155] In addition, the mobility characteristic and the threshold voltage characteristic of the driving transistor can be calculated simultaneously during the first sensing period and the second sensing period. Unlike a conventional external compensation sensing scheme in which the operation of sensing the mobility characteristic and the operation of sensing the threshold voltage characteristic are different from each other, the method of driving a display device according to the present disclosure can use two sensing currents sensed during the first sensing period and the second sensing period to simultaneously calculate the mobility characteristic and the threshold voltage characteristic. Therefore, the sensing time can be shortened, and the accuracy of real-time sensing can be improved.

[0156] In an embodiment, the method of driving a display device may further include: step S600 of compensating input image data based on the calculated characteristic of the driving transistor.

[0157] Because the above has been referred to Figures 1 to 8b The method of driving the display device is described in detail, so a repeated description thereof will be omitted.

[0158] As described above, the display device and the method for driving the display device according to the embodiment of the present disclosure can change the voltage level of the first power supplied to the drain electrode of the driving transistor according to the grayscale value for current sensing during the external compensation driving. Therefore, the channel length modulation effect of the driving transistor is reflected in the image data compensation, so that the compensation error can be greatly reduced and the image quality can be improved.

[0159] Although the embodiments of the present disclosure have been described, it will be understood by those skilled in the art that the present disclosure can be modified and changed in various forms without departing from the spirit and scope of the present disclosure as claimed in the appended claims.

Claims

1. A display device, comprising: A pixel comprising: a light emitting element; a first transistor configured to control the amount of current flowing into the light emitting element; and a second transistor connected between the first transistor and a sensing line; a power supply that supplies power of different voltages to a drain electrode of the first transistor during a sensing period; and a sensing circuit that senses a sensing current supplied through the sensing line during the sensing period, The sensing period includes a first sensing period and a second sensing period. During the first sensing period, the sensing circuit senses a first sensing current among the sensing currents based on a first sensing data signal corresponding to a first grayscale. During the second sensing period, the sensing circuit senses a second sensing current among the sensing currents based on a second sensing data signal corresponding to a second grayscale. wherein a voltage of power supplied to the drain electrode of the first transistor during the first sensing period is a first sensing voltage, and Herein, a voltage of power supplied to the drain electrode of the first transistor during the second sensing period is a second sensing voltage different from the first sensing voltage.

2. The display device according to claim 1, wherein: The second grayscale is different from the first grayscale.

3. The display device according to claim 1, wherein: The sensing circuit simultaneously calculates a mobility characteristic and a threshold voltage characteristic of the first transistor by using the first sensing current and the second sensing current.

4. The display device according to claim 1, wherein: The first sensing period and the second sensing period are performed sequentially.

5. The display device according to claim 1, wherein: The difference between the first sensing voltage and the second sensing voltage is a result obtained by reflecting a difference between channel length modulation effects of the first transistor depending on a difference between the first grayscale and the second grayscale.

6. The display device according to claim 5, wherein: The difference between the first sensing voltage and the second sensing voltage is proportional to a difference between a gate-source voltage of the first transistor corresponding to the first sensing data signal and a gate-source voltage of the first transistor corresponding to the second sensing data signal.

7. The display device according to claim 1, wherein: The pixel also includes: a third transistor connected between the first transistor and the data line, and Wherein, the display device further includes: A data driver supplies the first sensing data signal to the data line during the first sensing period and supplies the second sensing data signal to the data line during the second sensing period.

8. The display device according to claim 1, wherein: The sensing circuit comprises: an analog-to-digital converter, converting the first sensing current and the second sensing current into first sensing data and second sensing data both having digital formats; and A compensator calculates a mobility characteristic and a threshold voltage characteristic of the first transistor by performing an operation on the first sensing data and the second sensing data, and determines a compensation value for image data based on the mobility characteristic and the threshold voltage characteristic.

9. The display device according to claim 8, wherein: The sensing circuit further comprises: A memory stores at least one of the first sensing data and the second sensing data.

10. A method for driving a display device, the method comprising: supplying a first sensing data signal corresponding to a first grayscale and power having a first sensing voltage to a pixel during a first sensing period; sensing a first sensing current generated based on the first sensing voltage from the pixel during the first sensing period; supplying a second sensing data signal corresponding to a second grayscale and power having a second sensing voltage to the pixel during a second sensing period; sensing a second sensing current generated based on the second sensing voltage from the pixel during the second sensing period; as well as calculating a characteristic of a first transistor of the pixel using the first sensing current and the second sensing current, wherein the first sensing data signal and the second sensing data signal are different from each other, wherein a voltage of power supplied to a drain electrode of the first transistor during the first sensing period is the first sensing voltage, and Herein, a voltage of power supplied to the drain electrode of the first transistor during the second sensing period is the second sensing voltage different from the first sensing voltage.

11. The method according to claim 10, wherein: A mobility characteristic and a threshold voltage characteristic among the characteristics of the first transistor are simultaneously calculated based on the first sensing current and the second sensing current.

12. The method according to claim 10, further comprising: Input image data is compensated based on the calculated characteristic of the first transistor.

13. The method according to claim 10, wherein: applying a reference voltage to the pixel during the first sensing period, and Wherein, the reference voltage is applied to the pixel during the second sensing period.

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