阅读说明：本技术 显示装置及其驱动方法 (Display device and driving method thereof ) 是由 黄英秀 吉村英雄 于 2020-06-12 设计创作，主要内容包括：一种显示装置包括：像素,连接到扫描线、控制线、数据线和感测线；扫描驱动单元,将扫描信号供应到扫描线,并且将控制信号供应到控制线；数据驱动单元,将图像数据信号和感测数据信号中的一者供应到数据线；感测单元,在感测时段期间基于通过感测线供应的感测电流来感测特性；以及电源单元,将第一电力的电压供应到像素。感测时段包括：第一感测时段,在第一感测时段期间,基于与第一灰度对应的第一感测数据信号提取第一感测电流；以及第二感测时段,在第二感测时段期间,基于与第二灰度对应的第二感测数据信号提取第二感测电流,其中,在第一感测时段期间供应的第一电力的电压与在第二感测时段期间供应的第一电力的电压不同。(A display device includes: pixels connected to the scan lines, the control lines, the data lines, and the sensing lines; a scan driving unit supplying a scan signal to the scan lines and a control signal to the control lines; 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 a sensing line during a sensing period; and a power supply unit supplying a voltage of the first power to the pixel. 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 a first gray scale; and a second sensing period during which a second sensing current is extracted based on a second sensing data signal corresponding to a second gray scale, wherein 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.)

1. A display device driven such that a period of the display device is divided into a display period during which an image is displayed and a sensing period during which a characteristic of a driving transistor included in each pixel is sensed, the display device comprising:

pixels connected to the scan lines, the control lines, the data lines, and the sensing lines;

a scan driver configured to supply a scan signal to the scan lines and supply a control signal to the control lines;

a data driver configured to supply one of an image data signal and a sensing data signal to the data lines;

sensing circuitry configured to sense the characteristic based on a sensing current supplied through the sense line during the sensing period; and

a power supply configured to supply a voltage of a first power to the pixel,

wherein 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 a first gray scale and a second sensing period during which a second sensing current is extracted based on a second sensing data signal corresponding to a second gray scale, and

wherein the voltage of the first power supplied during the first sensing period is different from the voltage of the first power supplied during the second sensing period.

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

3. The display device according to claim 1, wherein the power supply outputs the first power having a first sensing voltage according to the first gray scale during the first sensing period.

4. The display device according to claim 3, wherein the power supply outputs the first power having a second sensing voltage according to the second gray scale during the second sensing period, the second sensing voltage being different from the voltage of the first power.

5. The display device according to claim 4, wherein the power supply outputs the first power having a display voltage for image display during the display period.

6. The display device of claim 5, wherein the display voltage is equal to one of the first sensing voltage and the second sensing voltage.

7. The display device according to claim 4, 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 driving transistor depending on a difference between the first gray scale and the second gray scale.

8. The display device of claim 7, 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 driving transistor that depends on the first sensing data signal and a gate-source voltage of the driving transistor that depends on the second sensing data signal.

9. The display device of claim 1, wherein the data driver is configured to:

supplying the first sensing data signal to the pixel during the first sensing period, and

supplying the second sensing data signal to the pixel during the second sensing period.

10. The display device according to claim 1, wherein the sensing circuit simultaneously calculates a mobility characteristic and a threshold voltage characteristic of the driving transistor based on the first sensing period and the second sensing period.

11. The display device according to claim 10, wherein the sensing circuit comprises:

an analog-to-digital converter configured to convert the first and second sense currents into first and second sense data each having a digital format; and

a compensator configured to calculate the mobility characteristic and the threshold voltage characteristic of the driving transistor by performing an operation 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.

12. The display device of claim 11, wherein the sensing circuit further comprises:

a memory configured to store at least one of the first sensing data and the second sensing data.

13. The display device according to claim 1, wherein among the pixels, a pixel located on an ith horizontal line (where i is a natural number) includes:

a light emitting element;

a first transistor configured to control a current flowing from the first power into a second node according to a voltage of a first node, the first transistor corresponding to the 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 ith scan line;

a third transistor connected between the second node and a jth sensing line, the third transistor including a gate electrode connected to an ith control line; and

a storage capacitor connected between the first node and the second node.

14. The display device according to claim 13, wherein the control signal supplied during each of the first sensing period and the second sensing period has a length greater than a length of the control signal supplied during the display period.

15. The display device according to claim 13, wherein a part of the control signal supplied to the ith control line overlaps with the scan signal supplied to the ith scan line during each of the first and second sensing periods, the control signal being supplied for a longer time than the scan signal.

16. The display device according to claim 15, wherein:

when the second transistor and the third transistor are turned on, a reference voltage is supplied to the second node through the jth sensing line, and

when the second transistor is turned off in an on state of the third transistor, one of the first sensing current and the second sensing current is supplied to the sensing circuit through the jth sensing line.

17. A method of driving a display device, the method comprising:

supplying a first sensing data signal corresponding to a first gray scale, a first power having a first sensing voltage, and a reference voltage to the 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 gray scale, the first power having a second sensing voltage, and the reference 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; and

calculating a characteristic of a drive transistor of the pixel using the first sense current and the second sense current,

wherein the first sensing data signal and the second sensing data signal are different from each other, and

wherein the first sensing voltage and the second sensing voltage are different from each other.

18. The method of claim 17, wherein the mobility characteristic and the threshold voltage characteristic of the driving transistor are simultaneously calculated based on the first sensing period and the second sensing period.

19. The method of claim 17, wherein the first sense data signal is greater than the second sense data signal and the first sense voltage is greater than the second sense voltage.

20. The method of claim 17, further comprising:

compensating input image data based on the calculated characteristic of the driving transistor.

Technical Field

Various embodiments of the present disclosure relate generally to a display apparatus and a method of driving the same, and more particularly, to a display apparatus to which an external compensation scheme is applied and a method of driving the same.

Background

A self-emission display device displays an image using pixels connected to a plurality of scan lines and data lines. For this purpose, each pixel has a light emitting element and a driving transistor.

The driving transistor controls an 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 luminance according to the amount of current supplied from the driving transistor.

In order for the display device to display an image having uniform image quality, the driving transistors included in the respective pixels should supply substantially the same current to the light emitting elements according to the data signals. However, the driving transistors included in the respective pixels have their inherent characteristic values in which there may be a deviation.

In an example, the threshold voltage and mobility of the driving transistor may be set differently in each pixel, or may be changed due to degradation caused by its use, and thus a luminance difference between images may occur.

Disclosure of Invention

Technical problem

An object of the present disclosure is to provide a display device that changes a voltage of a first power to be supplied to a pixel depending on a gray scale of a data signal during a sensing period.

Another object of the present disclosure is to provide a method of driving a display device.

However, the object of the present disclosure is not limited to the foregoing object, and may be extended in various forms without departing from the spirit and scope of the present disclosure.

Technical scheme

In order to achieve the object of the present disclosure, a display device according to an embodiment of the present disclosure may be driven such that a period of the display device is divided into a display period during which an image is displayed and a sensing period during which a characteristic of a driving transistor included in each pixel is sensed. The display device may include: pixels connected to the scan lines, the control lines, the data lines, and the sensing lines; a scan driver configured to supply a scan signal to the scan lines and supply a control signal to the control lines; a data driver configured to supply one of an image data signal and a sensing data signal to the data lines; sensing circuitry configured to sense a characteristic based on a sensing current supplied through a sense line during a sensing period; and a power supply configured to supply a voltage of the first power to the pixel. The sensing period may include a first sensing period during which a first sensing current is extracted based on a first sensing data signal corresponding to a first gray scale, and a second sensing period during which a second sensing current is extracted based on a second sensing data signal corresponding to a second gray scale, and a voltage of the first power supplied during the first sensing period may be different from a voltage of the first power supplied during the second sensing period.

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

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.

According to an embodiment, the power supply may be configured to output the first power having the second sensing voltage according to the second gray scale during the second sensing period, the second sensing voltage being different from a voltage of the first power.

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

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

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 the driving transistor depending on a difference between the first gray scale and the second gray scale.

According to an embodiment, a 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.

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

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

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

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.

According to an embodiment, among the pixels, the pixels located on an ith horizontal line (where i is a natural number) may include: a light emitting element; a first transistor configured to control a current flowing from the first power into the second node according to a voltage of the first node, the first transistor corresponding to the 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 the ith scan line; a third transistor connected between the second node and a jth sensing line, the third transistor including a gate electrode connected to an ith control line; and a storage capacitor connected between the first node and the second node.

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

According to an embodiment, during each of the first and second sensing periods, a portion of the control signal supplied to the ith control line may overlap with the scan signal supplied to the ith scan line, the control signal being supplied for a longer time than the scan signal.

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

In order to achieve the object of the present disclosure, a method of driving a display device according to an embodiment of the present disclosure may include: supplying a first sensing data signal corresponding to a first gray scale, a first power having a first sensing voltage, and a reference voltage to the pixel during a first sensing period; sensing a first sensing current generated based on a first sensing voltage from the pixel during a first sensing period; supplying a second sensing data signal corresponding to a second gray scale, a first power having a second sensing voltage, and a reference 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 a second sensing period; and calculating a characteristic of a drive transistor of the pixel using the first sense current and the second sense current. The first and second sensing data signals may be different from each other, and the first and second sensing voltages may be different from each other.

According to the 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.

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.

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

Advantageous effects

The display device and the method of driving the display device according to the embodiment of the present disclosure may change a voltage level of the first power supplied to the drain electrode of the driving transistor based on the gray scale 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.

However, the advantages of the present disclosure are not limited to the foregoing advantages, and may be extended in various forms without departing from the spirit and scope of the present disclosure.

Drawings

Fig. 1 is a block diagram illustrating a display device according to an embodiment of the present disclosure.

Fig. 2 is a diagram illustrating an example of a pixel and a sensing circuit included in the display device of fig. 1.

Fig. 3 is a timing diagram illustrating an example of an operation of the display apparatus of fig. 1.

Fig. 4 is a timing diagram illustrating an example of an operation of the display apparatus of fig. 1 during a sensing period.

Fig. 5 is a diagram for explaining a channel length modulation effect occurring in the first transistor included in the pixel of fig. 2.

Fig. 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.

Fig. 7 is a block diagram illustrating an example of a compensator included in a sensing circuit of the display device of fig. 1.

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

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

Detailed Description

Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. Throughout the drawings, the same reference numerals are used to designate the same or similar components, and a repetitive description thereof will be omitted.

Fig. 1 is a block diagram illustrating a display device according to an embodiment of the present disclosure.

Referring to fig. 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.

The display device 1000 may be a flat panel display device, a flexible display device, a curved display device, a foldable display device, or a bendable display device. Further, the display device may be applied to a transparent display device, a head-mounted display device, a wearable display device, and the like. In addition, the display apparatus 1000 may be applied to various electronic apparatuses such as a smart phone, a tablet computer, a smart tablet computer, a Television (TV), and a monitor.

In addition, the display device 1000 may be implemented as an organic light emitting display device, a liquid crystal display device, or the like. However, this configuration is merely an example, and the configuration of the display device 1000 is not limited thereto. For example, the display device 1000 may be a self-emission display device including an inorganic light emitting element.

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 driving transistors included in the respective pixels PX are sensed.

The pixel section 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 externally supplied to the pixels PX.

In addition, although n scan lines SL1 to SLn are shown in fig. 1, the present disclosure is not limited thereto. For example, one or more control lines, scan lines, emission control lines, sensing lines, and the like may be additionally formed in the pixel section 100 according to a circuit structure of each pixel PX.

In an embodiment, the transistor included in each pixel PX may be an N-type oxide Thin Film Transistor (TFT). Such an oxide TFT may be, for example, a Low Temperature Poly Oxide (LTPO) TFT. However, this is merely 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, or the like. In addition, at least one of the transistors included in the display device 1000 may be replaced with a P-type transistor.

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

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

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

The scan driving 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.

The power driving control signal PCS may control supply of voltages of the first power VDD and the second power VSS and a level of the voltages.

The timing controller 600 may also control the operation of the sensing circuit 400. For example, the timing controller 600 may control a timing at which a reference voltage is supplied to the pixel PX through the sensing lines SSL1 through SSLm and/or a timing at which a current generated in the pixel PX is sensed through the sensing lines SSL1 through SSLm.

The scan driver 200 may receive a scan driving control signal SCS from the timing controller 600. The scan driver 200, which has 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.

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 the basis of a horizontal line. For this, each scan signal may be set to a gate-on voltage (e.g., a logic high level) so that the transistor included in the corresponding pixel PX is turned on.

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

In addition, although a single scan driver 200 is illustrated as outputting both scan signals and control signals in fig. 1, the present disclosure is not limited thereto. For example, the scan driver 200 may include a first scan driver supplying a scan signal to the pixel part 100 and a second scan driver supplying a control signal to the pixel part 100.

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 (e.g., a sensing data signal) for detecting a pixel characteristic to the pixel part 100 during the sensing period. The data driver 300 may supply a data signal for displaying an image to the pixel part 100 based on the compensated image data CDATA during the display period.

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

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

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

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 supplied to the timing controller 600 or the data driver 300.

During the 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.

Although the sensing circuit 400 is illustrated as a separate component from the timing controller 600 in fig. 1, 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. Accordingly, 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.

The power supply 500 may supply the voltage of the first power VDD and the voltage of the second power VSS to the pixel part 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.

In an embodiment, the power supply 500 may change the voltage of the first power VDD supplied to the pixels PX during the sensing period. For example, the power supply 500 may change the voltage of the first power VDD such 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.

Hereinafter, a compensation scheme in which the channel length modulation effect is reflected will be described in detail.

Fig. 2 is a diagram illustrating an example of a pixel and a sensing circuit included in the display device of fig. 1.

In fig. 2, for convenience of description, a pixel located on the ith horizontal line and connected to the jth data line DLj is shown.

Referring to fig. 2, the pixel PXij may include a light emitting element LD, a first transistor T1 (i.e., a driving transistor), a second transistor T2, a third transistor T3, and a storage capacitor Cst.

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 the second power VSS. The light emitting element LD may generate light having a predetermined brightness according to the amount of current supplied from the first transistor T1.

A first electrode of the first transistor T1 may be connected to a source of the 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 the voltage of the first node N1.

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

The third transistor T3 may be connected between the sensing line SSLj and the second electrode (i.e., 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 the 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 (i.e., the second electrode of the first transistor T1) may be electrically coupled to each other.

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

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.

In addition, in the embodiment of the present disclosure, the circuit structure of the pixel PXij is not limited by fig. 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.

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

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

The first switch SW1 and the second switch SW2 may be alternately turned on. When the first switch SW1 is turned on, the reference voltage Vref may be supplied to the second node. Accordingly, the voltage of the second node N2 (i.e., the source voltage of the first transistor T1) may be initialized to the reference voltage Vref.

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

An analog-to-digital converter (ADC)420 may sense a voltage from the sensing current of the sensing line SSLi, convert a 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 first sensing data, and the second sensing current IS2 in the second sensing period may be converted into second sensing data.

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.

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 or the like required for image data compensation.

In addition, although the transistors T1 to T3 are illustrated as NMOS transistors in fig. 2, the present disclosure is not limited thereto. For example, at least one of the transistors T1 through T3 may be implemented as a PMOS transistor.

Fig. 3 is a timing diagram illustrating an example of an operation of the display apparatus of fig. 1.

Referring to fig. 1 to 3, the display apparatus 1000 may be driven such that a period of the display apparatus 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.

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

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. Accordingly, the reference voltage Vref, which is a constant voltage, may be supplied to the sensing lines SSL1 to SSLm.

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

The scan signal and the control signal may be supplied substantially simultaneously for the ith horizontal line. Accordingly, the second transistor T2 and the third transistor T3 may be turned on or off at the same time.

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, the reference voltage Vref may be supplied to the second node N2. Accordingly, the storage capacitor Cst may store a voltage corresponding to a voltage difference between the data signal DS and the reference voltage Vref.

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

When the supply of the scan signal and the control signal to the ith scan line SLi and the ith control line CLi is stopped, the second transistor T2 and the third transistor T3 may be turned off.

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. Accordingly, the light emitting element LD may emit light having luminance corresponding to the driving current of the first transistor T1.

In an embodiment, the power supply 500 may output the first power VDD having the display voltage DIS _ V during the display period DP. 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 gray scale of an image and the size (voltage level) of a data signal.

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

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. Further, during the sensing period SP, a part of the control signal supplied to the ith control line CLi may overlap with the scan signal supplied to the ith 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 ith control line CLi starts to be supplied simultaneously with the scan signal supplied to the ith scan line SLi, and may be supplied for a time longer than the time for which the scan signal is supplied.

When the scan signal and the control signal are simultaneously supplied, 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. Accordingly, the storage capacitor Cst may store a voltage corresponding to a voltage difference between the sensing data signal SGV and the reference voltage Vref.

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

In addition, due to the parasitic capacitor Cpara, 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 of the voltage drop attributable to the parasitic capacitor Cpara may also be performed.

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. Accordingly, the analog-to-digital converter 420 may generate a digital code corresponding to the voltage charged in the sensing capacitor Cse (i.e., the voltage corresponding to the sensing current).

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.

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 different error rates depending on the gray scale. Therefore, an error of the sensing data occurs, and a large degradation compensation error occurs particularly in the low gray scale region. To overcome such a compensation error, the voltage level of the first power VDD may be changed during the sensing period SP such that the channel length modulation effect is reflected in the compensation operation.

Accordingly, a compensation error occurring in the external compensation scheme may be greatly reduced, compensation efficiency may be maximized, and image quality may be improved.

According to an embodiment, the sensing period SP may be performed at least once before the display apparatus 1000 is shipped. In this case, the 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 portion 100 may display an image with uniform image quality.

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

Fig. 4 is a timing diagram illustrating an example of an operation of the display apparatus of fig. 1 during a sensing period.

Referring to fig. 2 to 4, the sensing periods SP may include a first sensing period SP1 and a second sensing period SP 2.

The current sensing schemes in the first and second sensing periods SP1 and SP2 may be substantially the same as each other.

During the first sensing period SP1, the first sensing data signal GV1 corresponding to the first gray may be supplied to the data line DLj. Here, the power supply 500 may supply the first power VDD, which is the first sensing voltage V1 corresponding to the first gray scale, to the pixel part 100.

The first sensing current IS1 may be generated and extracted based on the first sensing data signal GV1 and the first sensing voltage V1.

During the second sensing period SP2, the second sensing data signal GV2 corresponding to the second gray scale 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 gray scale to the pixel part 100.

The second sensing current IS2 may be generated and extracted based on the second sensing data signal GV2 and the second sensing voltage V2.

In addition, the first and second gradations may be experimentally set values. That is, the first and second gradations may be set to gradation values that can minimize errors in the mobility characteristic and the threshold voltage characteristic. For example, when the pixel PX emits in a range of gray values ranging from 0 to 255, the first gray value may be the gray value 224, and the second gray value may be the gray value 128. However, these values are merely examples, and the first and second gradations are not limited thereto.

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 a channel length modulation effect of the first transistor T1 caused by a difference between the first gray and the second gray. For example, the difference dqvdd may be proportional to the difference between the gate-source voltage of the first transistor 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 GV 2.

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.

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

Fig. 5 is a diagram for explaining a channel length modulation effect occurring in the first transistor included in the pixel of fig. 2, and fig. 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.

Referring to fig. 2, 4, 5, and 6, when the drain-source voltage Vds of the first transistor T1 becomes equal to the difference between the gate-source voltage Vgs and the threshold voltage Vth of the first transistor T1 (i.e., Vds ═ Vgs-Vth), the first transistor T1 may operate in a saturation state.

In addition, as shown in fig. 6, it is generally assumed that the drive current Id is constant irrespective of the drain-source voltage Vds in the saturation state.

Accordingly, the driving current Id (or the drain current) in the saturation state may be determined to be a different value depending on the magnitude of the gate voltage Vg of the first transistor T1. For example, when the first sensing data signal GV1 corresponding to the first gray GR1 is supplied to the gate electrode of the first transistor T1, the first driving current I1 theoretically flows in a saturated state. When the second sensing data signal GV2 corresponding to the second gray level GR2 is supplied to the gate electrode of the first transistor T1, the second driving current I2 theoretically flows in a saturated state.

In practice, however, the effective channel length L of the first transistor T1 may operate 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, with the result that the effective channel length L decreases. When the effective channel length L is shortened, the moving distance of carriers is shortened, and thus the drive current Id is increased. This is known as the channel length modulation effect.

This channel length modulation effect affects the drive current Id as shown in [ equation 1] below.

[ equation 1]

Id＝1/2β(Vgs-Vth)²(1+λVds)

Here, Id denotes a drive current, β denotes a variable including mobility characteristics, Vgs denotes a gate-source voltage, Vth denotes a threshold voltage, and λ Vds denotes a ratio of an effective channel length change Lx to an effective channel length L (i.e., Lx/L).

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. 6, the first and second driving currents I1 and I2 may be increased from a theoretical value.

Further, since the saturated drain-source voltage Vds varies depending on the magnitude of the gate voltage Vg, the effective channel length variation Lx depending on the gate voltage Vg varies 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, an error of the first driving current I1 (e.g., the first error E1) with respect to a theoretical value may be different from an error of the second driving current I2 (e.g., the second error E2) with respect to the theoretical value. For example, the first error E1 in which the channel length modulation effect is more reflected may be larger than the second error E2.

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.

The display device 1000 according to the 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, which is the drain voltage Vd, may be differently set depending on the first and second gray levels GR1 and GR2 for sensing.

The drain voltage Vd may be adjusted such that the first driving current I1 and the second driving 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 driving current I1 may be determined as the first sensing voltage V1, and the voltage of the first power VDD for detecting the second driving current I2 may be determined as the second sensing voltage V2. For example, as shown in fig. 6, the first and second sensing voltages V1 and V2 may be determined based on the first and second points PT1 and PT2 corresponding to the saturation state curve SC.

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 may 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 may be a result obtained by reflecting a difference between channel length modulation effects of the first transistor T1 depending on a difference between the first gray level GR1 and the second gray level GR 2. In an embodiment, the relationship between the first sensing voltage V1 and the second sensing voltage V2 may be represented by [ equation 2] below:

[ equation 2]

V2＝V1-(Vgs₁-Vgs₂)

Here, Vgs₁May be a gate-source voltage Vgs corresponding to the first gray GR1, and Vgs₂May be a gate-source voltage Vgs corresponding to the second gray level GR 2. Since the source voltage Vs is a constant voltage, a voltage difference dVDD between the first sensing voltage V1 and the second sensing voltage V2 may be determined depending on a change in the gate voltage Vg. That is, the difference ddvdd between the first sensing voltage V1 and the second sensing voltage V2 may be equal to the gate-source voltage Vgs of the first transistor T1 corresponding to the first sensing data signal GV1₁And a gate-source voltage Vgs of the first transistor T1 corresponding to the second sensing data signal GV2₂The difference between them is proportional.

For example, when the first sensing data signal GV1 is 3V corresponding to the gray scale value 196, the second sensing data signal GV2 is 2.5V corresponding to the gray scale value 128, and the first sensing voltage V1 is 10V, the second sensing voltage V2 may be set to 9.5V. However, this is merely 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.

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 SP 2. 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.

Fig. 7 is a block diagram illustrating an example of a compensator included in a sensing circuit of the display device of fig. 1.

Referring to fig. 1 to 7, the compensator 440 may include a look-up table 442, a first calculator 444, and a second calculator 446.

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 image data IDATA based on the calculated mobility characteristic and threshold voltage characteristic.

During the image display and sensing, the source voltage Vs is fixed at the reference voltage Vref, and thus the degradation of the first transistor T1 can be compensated by adjusting the gate voltage of the first transistor T1 for a predetermined gray scale.

That is, the compensation value COMV may be a value for adjusting a data signal (i.e., a voltage supplied to the gate electrode of the first transistor T1) corresponding to a predetermined gray scale.

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). Further, the lookup table may be updated with the relationship between the new input image data IDATA and the first gate-source voltage Vgs _ dis every time the image data is compensated.

The first calculator 444 may calculate the gain G and the offset OS for compensating the first gate-source voltage Vgs _ dis based on the first sensing data ID1 and the second sensing data ID 2. 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 IS 2.

The first calculator 444 may calculate the gain G including the mobility characteristic and the offset OS including the threshold voltage characteristic based on [ equation 1] described above. 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+ λ Vds) may be a value compensated by the voltage level of the first power VDD, and β and Vth may be variables. Accordingly, the first calculator 444 may calculate β and Vth by calculation of two simultaneous equations based on the first sense current IS1 and the second sense current IS 2. The gain G may include a mobility characteristic β, and may be multiplied by a first gate-source voltage Vgs _ dis. The offset OS may include a 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 ID 2.

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 resultant value. Accordingly, the compensation value COMV for one piece of input image data IDATA corresponding to one pixel PX can 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 to correspond to the voltage of the newly updated data signal based on the compensation value COMV.

In this way, 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.

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

Referring to fig. 8a and 8b, an error rate of an external compensation scheme based on driving current sensing for the first and second grays may vary with the values of the first and second grays.

Fig. 8a and 8b illustrate an error rate of display gray scale values in a state in which the source voltage of the first transistor T1 is initialized to 1.5V. The sign of G255, G224, or G192 may indicate the first gray scale and the second gray scale set for 2-point current sensing.

As shown in fig. 8a, the error rate of external compensation based on conventional 2-point current sensing may increase in a direction away from the measured grays (i.e., the first and second grays). For example, when the first and second grays may have a grayscale value of 255(G255) and a grayscale value of 128(G128), the error rate has a larger value in a low grayscale region farther from the first and second grays than in a high grayscale region. Therefore, the compensation capability in the low gray area may be deteriorated, and a brightness deviation such as a stain may be perceived. The reason for this is that a difference (error) between the drive currents occurring for the respective grays due to the channel length modulation effect is not reflected in the compensation.

The display device 1000 according to an embodiment of the present disclosure may reflect an error attributable to a channel length modulation effect in 2-point current sensing. That is, during a first sensing period in which current sensing for a first gray scale is performed, the first power (e.g., VDD of fig. 1) may have a first sensing voltage, and during a second sensing period in which current sensing for a second gray scale is performed, the first power (e.g., VDD of fig. 1) may have a second sensing voltage. During the first sensing period and during the second sensing period, different voltages are supplied to the drain electrode of the first transistor (e.g., T1 of fig. 2), and thus errors attributable to channel length modulation effects may be removed or minimized.

Therefore, as shown in fig. 8b, the error rate of the external compensation based on the 2-point current sensing can be greatly improved. Accordingly, the degradation compensation efficiency and image quality of the pixel and the display device can be improved.

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

Referring to fig. 9, a method of driving a display device may include: step S100 of supplying a first sensing data signal corresponding to a first gray (or a first test gray), a first power having a first sensing voltage, and a reference voltage to each pixel during a first sensing period; step S200 of sensing a first sensing current generated based on a first sensing voltage from a pixel during a first sensing period; a step S300 of supplying a second sensing data signal corresponding to a second gray (or a second test gray), a first power having a second sensing voltage, and a reference voltage to the pixel during a second sensing period; and step S400 of sensing a second sensing current generated based on the second sensing voltage from the pixel. Further, the method of driving the display device may further include: in step S500, the characteristics of the driving transistor (e.g., the first transistor T1 of fig. 2) of the pixel are calculated using the first sensing current and the second sensing current.

In an embodiment, the first and second grayscales 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 greater than the second sensing data signal, the first sensing voltage may be set to a value greater than the second sensing voltage. Accordingly, the first sense current and the second sense current may have sense values from which errors attributable to channel length modulation effects of the drive transistor are removed.

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

In an embodiment, the method of driving the display device may further include: in step S600, the input image data is compensated based on the calculated characteristics of the driving transistor.

Since the method of driving the display device has been described in detail above with reference to fig. 1 to 8b, a repetitive description thereof will be omitted.

As described above, the display device and the method of driving the display device according to the embodiments of the present disclosure may change the voltage level of the first power supplied to the drain electrode of the driving transistor according to the gray scale 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.

Although the embodiments of the present disclosure have been described, those skilled in the art will appreciate that the present disclosure may be modified and changed in various forms without departing from the spirit and scope of the present disclosure as claimed in the appended claims.