KR102706727B1 - Display and driving method thereof - Google Patents

Abstract

A display device and a driving method thereof are disclosed. The display device includes a pixel circuit including a light-emitting element and a driving element for driving the light-emitting element, and connected to a data line, a sensing line, and a gate line; a comparator which compares a sensing data voltage with a feedback voltage input from a driving element of the pixel circuit through the sensing line in a sensing step to generate an output voltage that changes by a difference between the sensing data voltage and the feedback voltage, and which operates as a buffer in a driving step to supply the pixel data voltage to the data line; and a data providing unit which supplies the sensing data voltage to the comparator in the sensing step and stores compensation data obtained from the output voltage of the comparator in a memory, and modulates pixel data of an input image with the compensation data in the driving step to generate the pixel data voltage and supplies the pixel data voltage to the comparator.

Description

DISPLAY AND DRIVING METHOD THEREOF

The present invention relates to a display device capable of compensating for changes in electrical characteristics of a driving element.

An active matrix type organic light emitting display device includes an organic light emitting diode (hereinafter referred to as "OLED") that emits light by itself, and has the advantages of a fast response speed, high luminous efficiency, high brightness, and large viewing angle.

An organic light-emitting diode, which is a self-luminous element, includes an anode electrode, a cathode electrode, and an organic compound layer (HIL, HTL, EML, ETL, EIL) formed between them. The organic compound layer is composed of a hole injection layer (HIL), a hole transport layer (HTL), an emission layer (EML), an electron transport layer (ETL), and an electron injection layer (EIL). When a driving voltage is applied to the anode and the cathode electrode, holes passing through the hole transport layer (HTL) and electrons passing through the electron transport layer (ETL) move to the emission layer (EML) to form excitons, and as a result, the emission layer (EML) emits visible light.

Each pixel of an organic light-emitting display device includes a driving element (thin film transistor) to control the driving current flowing to the organic light-emitting diode. It is desirable that the electrical characteristics of the driving element, such as threshold voltage and mobility, be designed to be the same for all pixels, but in reality, the electrical characteristics of the driving element for each pixel are non-uniform due to process conditions, driving environments, etc. For this reason, the driving current according to the same data voltage varies for each pixel, resulting in a luminance deviation between pixels. To solve this problem, a picture quality compensation technology is known that senses characteristic parameters (threshold voltage, mobility) of the driving element from each pixel and appropriately compensates input data based on the sensing results to reduce luminance unevenness.

There are two types of image quality compensation technology: external compensation and internal compensation. The external compensation method directly obtains the sensing voltage after operating the driving element, converts it into digital data, and compensates the image data using the compensation value determined accordingly. The external compensation method not only requires an analog-to-digital converter to convert the sensing voltage into digital data, but also has the disadvantage of not being able to compensate in real time.

The internal compensation method compensates by using the driving current passing through the driving element regardless of the size of the threshold voltage of the driving element, and real-time compensation is possible. However, in order to apply the internal compensation method, a large number of transistors are required in the pixel, so the circuit becomes complicated and the aperture ratio decreases, which is a disadvantage.

The present invention provides an organic light-emitting display device capable of compensating for changes in electrical characteristics of a driving element using a simplified sensing and compensation circuit.

The tasks of the present invention are not limited to the tasks mentioned above, and other tasks not mentioned will be clearly understood by those skilled in the art from the description below.

The display device of the present invention includes a light-emitting element, a driving element for driving the light-emitting element, and a pixel circuit connected to a data line, a sensing line, and a gate line; a comparator for comparing a sensing data voltage with a feedback voltage input from a driving element of the pixel circuit through the sensing line in a sensing step to generate an output voltage that changes by a difference between the sensing data voltage and the feedback voltage, and for operating as a buffer in a driving step to supply the pixel data voltage to the data line; and a data providing unit for supplying the sensing data voltage to the comparator in the sensing step and storing compensation data obtained from the output voltage of the comparator in a memory, and for modulating pixel data of an input image with the compensation data in the driving step to generate the pixel data voltage and supplying the pixel data voltage to the comparator.

The driving method of the display device includes: a step of comparing a sensing data voltage with a feedback voltage input from a driving element of the pixel circuit through the sensing line in a sensing step, and generating an output voltage of the comparator that changes by a difference between the sensing data voltage and the feedback voltage; a step of supplying the sensing data voltage to the comparator in the sensing step and storing compensation data obtained from the output voltage of the comparator in a memory; a step of modulating pixel data of an input image with the compensation data in a driving step to generate the pixel data voltage and supplying the pixel data voltage to the comparator; and a step of supplying the pixel data voltage to the data line in the driving step, by which the comparator operates as a buffer.

The present invention can compensate for changes in the electrical characteristics of a driving element by sensing the electrical characteristics of the driving element in real time when the light-emitting element of the pixel circuit is not driven and updating compensation data stored in a memory.

The present invention can temporally separate the sensing step and the driving step by using switch elements added within the drive IC.

The present invention compensates for changes in the electrical characteristics of a driving element over time by compensating for a pixel data voltage applied to a gate of a driving element using the results of sensing changes in the electrical characteristics of the driving element in a sensing step after shipment of a display device, thereby compensating for changes in the driving element over time.

The effects of the present invention are not limited to the effects mentioned above, and other effects not mentioned will be clearly understood by those skilled in the art from the description of the claims.

Figure 1 is a block diagram showing a display device according to an embodiment of the present invention.
Figure 2 is a circuit diagram showing a pixel circuit and a compensation unit.
Figure 3 is a circuit diagram showing the operation of the pixel circuit and compensation unit.
Figures 4 to 9 are circuit diagrams showing other examples of compensation units.
Figure 10 is a waveform diagram showing a method of driving a display device according to an embodiment of the present invention.
Figure 11 is a diagram showing data voltage for sensing.
Figure 12 is a diagram showing pixel data voltage.
Figure 13 is a circuit diagram showing a sensing step of a display device according to an embodiment of the present invention.
Figure 14 is a circuit diagram showing a driving step of a display device according to an embodiment of the present invention.

The advantages and features of the present invention, and the methods for achieving them, will become clearer with reference to the embodiments described in detail below together with the accompanying drawings. The present invention is not limited to the embodiments disclosed below, but may be implemented in various different forms, and the embodiments are provided only to make the disclosure of the present invention complete and to fully inform those skilled in the art of the scope of the invention, and the present invention is defined only by the scope of the claims.

The shapes, sizes, ratios, angles, numbers, etc. disclosed in the drawings for explaining embodiments of the present invention are exemplary, and the present invention is not limited to the matters illustrated in the drawings. The same reference numerals throughout the specification refer to substantially the same components. In addition, in explaining the present invention, if it is determined that a detailed description of a related known technology may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted.

In the present invention, when the terms “comprises,” “includes,” “has,” and “consists of,” are used, other parts may be added unless “only” is used. When a component is expressed in the singular, it may be interpreted as plural unless there is a specifically explicit description.

When interpreting a component, it is interpreted as including the error range even if there is no separate explicit description.

When describing a positional relationship, for example, when a positional relationship is described between two components as 'on', 'above', 'below', 'next to', etc., one or more other components may intervene between those components where 'directly' or 'directly' is not used.

Although the first, second, etc. may be used to distinguish the components, the functions or structures of these components are not limited by the ordinal numbers or component names preceding the components. Since the patent claims are written based on essential components, the ordinal numbers preceding the component names in the patent claims and the ordinal numbers preceding the component names in the embodiments may not match.

The following embodiments may be partially or wholly combined or combined with each other, and may be technically capable of various interconnections and operations. Each embodiment may be implemented independently of each other, or may be implemented together in a related relationship.

The pixel circuit, gate driver, etc. of the present invention may include transistors. The transistors may be implemented as an oxide thin film transistor (TFT) including an oxide semiconductor, an LTPS TFT including low temperature poly silicon (LTPS), etc. Each of the transistors may be implemented as a transistor having a p-channel MOSFET (metal-oxide-semiconductor field effect transistor) or an n-channel MOSFET structure.

A transistor is a three-electrode device that includes a gate, a source, and a drain. The source is the electrode that supplies carriers to the transistor. In a transistor, carriers start to flow from the source. The drain is the electrode through which carriers leave the transistor. In a transistor, the flow of carriers flows from the source to the drain. In the case of an n-channel transistor, since the carriers are electrons, the source voltage is lower than the drain voltage so that electrons can flow from the source to the drain. In an n-channel transistor, the direction of current flows from the drain to the source. In the case of a p-channel transistor (PMOS), since the carriers are holes, the source voltage is higher than the drain voltage so that holes can flow from the source to the drain. In a p-channel transistor, since holes flow from the source to the drain, current flows from the source to the drain. It should be noted that the source and drain of a transistor are not fixed. For example, the source and drain can change depending on the applied voltage. Therefore, the invention is not limited by the source and drain of the transistor. In the following description, the source and drain of the transistor are referred to as the first and second electrodes.

Below, an example is described in which the transistors of the pixel circuit are implemented as p-channel transistors, but the present invention is not limited thereto.

The gate signal transitions between a gate on voltage and a gate off voltage. The gate on voltage is set to a voltage higher than the threshold voltage of the transistor, and the gate off voltage is set to a voltage lower than the threshold voltage of the transistor. The transistor is turned on in response to the gate on voltage, while it is turned off in response to the gate off voltage. For an n-channel transistor, the gate on voltage can be a gate high voltage (VGH), and the gate off voltage can be a gate low voltage (VGL). For a p-channel transistor, the gate on voltage can be a gate low voltage (VGL), and the gate off voltage can be a gate high voltage (VGH).

The gate-on voltage and gate-off voltage that control the transistors within the drive IC can be logic voltages of 3.3 V and 0 V, which are lower than the voltage difference between the gate high voltage (VGH) and the gate low voltage (VGL).

Referring to FIG. 1, a display device according to an embodiment of the present invention comprises a display panel (100) in which pixels (P) are arranged in a matrix form, a data driver (400) connected to data lines (DL1 to DLn, where n is a natural number) and sensing lines (SL1 to SLn), a gate driver (300) connected to gate lines (GL1 to GLm, where m is a natural number), and a timing controller (200) for controlling the driving timing of the data driver (400) and the gate driver (300).

The screen of the display panel (100) includes a pixel array on which an image is displayed. The pixel array includes data lines (DL1 to DLn) and sensing lines (SL1 to SLn), gate lines (GL1 to GLm) intersecting the data lines (DL1 to DLn) and sensing lines (S1 to Sn), and pixels (P) arranged in a matrix form defined by these signal lines (DL1 to DLn, SL1 to SLn, GL1 to GLm).

When the resolution of the pixel array is n*m, the pixel array (AA) includes n pixel columns (Column) and m pixel lines (HL1 to HLm) intersecting the pixel columns. The pixel columns include pixels arranged along the y-axis direction. The pixel lines include pixels arranged along the x-axis direction. One horizontal period (1H) is the time obtained by dividing one frame period by the number of m pixel lines (L1 to Lm). Pixel data is written to the pixels of one pixel line in one horizontal period (1H).

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

The pixel circuit may include a light-emitting element, a plurality of transistors, and a capacitor, as shown in FIG. 2. The light-emitting element may be implemented as an OLED. Hereinafter, a pixel may be interpreted as a sub-pixel.

Each of the sub-pixels is connected to a pair of data lines and sensing lines, and a gate line. The gate lines can be divided into a first gate line to which a scan signal is applied, and a second gate line to which an emission control signal (hereinafter, referred to as an “EM signal”) is applied. In FIGS. 2 to 14, 21 and 22 represent a pair of data lines (21) and sensing lines (22) applied to one sub-pixel.

Touch sensors may be arranged on the display panel (100) to implement a touch screen. Touch input may be sensed using separate touch sensors or may be sensed through pixels. The touch sensors may be implemented as in-cell type touch sensors that are arranged on the screen of the display panel as an on-cell type or an add on type or built into a pixel array.

The timing controller (200) receives pixel data of an input image from the host system (20) and a timing signal synchronized therewith. The pixel data of the input image received by the timing controller (200) is a digital signal. The timing controller (130) transmits the pixel data to the data driving unit (400). The timing signal may include a vertical synchronization signal (Vsync), a horizontal synchronization signal (Hsync), a clock signal (DCLK), and a data enable signal (DE). Since the vertical period and the horizontal period can be known by counting the data enable signal (DE), the vertical synchronization signal (Vsync) and the horizontal synchronization signal (Hsync) may be omitted. The data enable signal (DE) has a cycle of 1 horizontal period (1H).

The timing controller (200) generates a data timing control signal for controlling the data driving unit (400) and a gate timing control signal for controlling the gate driving unit (300) based on a timing signal received from the host system (20), thereby controlling the operation timing of the data driving unit (400) and the gate driving unit (300).

The data driving unit (400) converts pixel data of an input image received as a digital signal from the timing controller (200) for each frame into an analog gamma compensation voltage and outputs a voltage (data voltage) of a data signal. The data driving unit (400) supplies the data voltage (Vdata) to the data lines (DL1 to DLn). The data voltage (Vdata) is applied to the gate of the driving element (DT) through the comparator (501) of the compensation unit (500) and the first switch element (T1), as illustrated in FIG. 2.

The data driving unit (400) may include a compensation unit (500) as shown in Fig. 2. A data voltage (Vdata) is output using a digital-to-analog converter (hereinafter referred to as “DAC”) that converts a digital signal into an analog gamma compensation voltage and supplied to the compensation unit (500) as shown in Fig. 2.

The data driving unit (110) senses changes in the electrical characteristics of the driving elements of the pixels (P) using a compensation unit (500) as shown in Fig. 2 and compensates the data voltage (Vdata) by the amount of the change in electrical characteristics. Here, the electrical characteristics of the driving element include the threshold voltage and mobility of the driving element.

The gate driver (300) receives a gate timing control signal from a level shifter (not shown), generates a gate signal, and supplies the gate signal to the gate lines (GL1 to GLm). The gate signal applied to the gate lines (GL1 to GLn) turns on the switch elements of the sub-pixels to sequentially select the pixel lines (HL1 to HLn) into which pixel data is written. The gate signal may be generated as a pulse signal that transitions between a gate high voltage (VGH) and a gate low voltage (VGL). The gate signal may include a scan signal (SCAN) and an EM signal as illustrated in FIG. 2.

The level shifter converts the voltage of the gate timing control signal received from the timing controller (200). For example, the level shifter converts the high logic voltage of the input signal received as a digital signal voltage level into a gate high voltage (VGH), and converts the low logic voltage of the input signal into a gate low voltage (VGL).

The host system (20) may be any one of a TV system, a set-top box system, a navigation system, a computer system, a home theater system, a mobile system, and a wearable system. In mobile devices and wearable devices, a data drive unit (400), a timing controller (200), a level shifter, etc. may be integrated into one drive IC (DIC).

Figure 2 is a circuit diagram showing a pixel circuit and a compensation unit (500).

Referring to FIG. 2, a pixel circuit (P) is formed on a display panel (PNL). A compensation unit (500) may be formed on a drive IC (DIC).

The pixel circuit may include an OLED, a driving element (DT), a capacitor (Cst), and switching elements (T1, T2). The driving element (DT) and the switching elements (T1, T2) may be implemented as p-channel transistors.

The OLED includes an organic compound layer formed between an anode and a cathode. The organic compound layer may include, but is not limited to, a hole injection layer (HIL), a hole transport layer (HTL), an emission layer (EML), an electron transport layer (ETL), and an electron injection layer (EIL). The anode of the OLED is connected to a driving element (DT) and a second switching element (T2) through a second node (N2). A low-potential power supply voltage (ELVSS) is applied to the cathode of the OLED. The driving element (DT) supplies current to the light emitting element (EL) according to the source-gate voltage (Vsg) to drive the OLED. The OLED emits light with current flowing by the source-gate voltage (Vsg) of the driving element (DT). The current path of the OLED is switched by the third switching element (T3).

The driving element (DT) includes a gate connected to a first node (N1), a first electrode to which a pixel driving voltage (ELVDD) is applied, and a second electrode connected to a second node (N2). A capacitor (Cst) charges the source-gate voltage (Vsg) of the driving element (DT).

The first switching element (T1) connects the data line (21) to the gate of the driving element (DT) in response to the scan signal (SCAN). The first switching element (T1) includes a gate connected to the scan line (31), a first electrode connected to the output terminal of the comparator (501), and a second electrode connected to the first node (N1).

The second switching element (T2) connects the drain of the driving element (DT) to the sensing line (22) in response to the scan signal (SCAN). The second switching element (T2) includes a gate connected to the scan line (31), a first electrode connected to the second node (N2), and a second electrode connected to the sensing line (22).

The third switching element (T3) connects the drain of the driving element (DT) to the anode of the OLED in response to the EM signal (EM). The third switching element (T3) includes a gate connected to the second gate line (32), a first electrode connected to the second node (N2), and a second electrode connected to the anode of the OLED.

The compensation unit (500) performs a programming process of writing pixel data into pixels (P) and an operation of compensating for a threshold voltage deviation of a driving element (DT). The compensation unit (500) receives a sensing voltage (Vsen) of a second node (N2) in which a change in the electrical characteristics of the driving element (DT) is reflected as a feedback input and compares it with a data voltage (Vdata). The compensation unit (500) adjusts an output voltage (Vout) applied to the first node (N1) until the sensing voltage (Vsen) and the data voltage (Vdata) become the same level. The sensing voltage (Vsen) is equal to the drain voltage of the driving element (DT) when the OLED of the pixel circuit is turned off.

The compensation unit (500) includes a comparator (501), a data providing unit (510) connected to the inverting input terminal (-) of the comparator (501), and a pull-down circuit unit (550) connected to the non-inverting input terminal (+) of the comparator (501). The compensation unit (500) may be built into a single drive IC together with the data driving unit (400), but is not limited thereto.

A comparator (501) compares a drain voltage of a driving element (DT) with a data voltage (Vdata) and applies an output voltage to a gate of the driving element (DT), thereby compensating for a change in the electrical characteristics of the driving element (DT) by the gate voltage of the driving element (DT). The comparator (501) operates as a comparator and compensates for the electrical characteristics of the driving element (DT) in real time. The electrical characteristics of the driving element (DT) reflect the threshold voltage and mobility of the driving element (DT).

The comparator (501) can be implemented as an operational amplifier (op-amp) having an inverting input terminal (-) and a non-inverting input terminal (+). The comparator (501) includes an inverting input terminal (-) connected to a data providing unit (510), a non-inverting input terminal (+) connected to a pull-down circuit unit (550), and an output terminal connected to a first electrode of a first switching element (T1).

The output voltage (Vout) is controlled by comparing the data voltage (Vdata) applied to the inverting input terminal (-) of the comparator (501) with the sensing voltage (Vsen) applied to the non-inverting input terminal (+). The sensing voltage (Vsen) is equal to the second node voltage, that is, the second electrode (or drain) voltage of the driving element (DT). Therefore, the sensing voltage (Vsen) is a feedback voltage input to the comparator (501) from the driving element (DT) through the sensing line (22).

The comparator (501) compares the voltages of the inverting input terminal (-) and the non-inverting input terminal (+), and lowers the output voltage (Vout) when the voltage of the inverting input terminal (-) is greater than the voltage of the non-inverting input terminal (+). The comparator (501) increases the output voltage (Vout) when the voltage of the inverting input terminal (-) is less than the voltage of the non-inverting input terminal (+).

The data providing unit (510) supplies the data voltage (Vdata) of pixel data to the inverting input terminal (-) of the comparator (501). The data providing unit (510) may include one or more resistors for adjusting the size of the data voltage (Vdata). In addition, the data providing unit (510) may further include a memory, an analog-to-digital converter (hereinafter, referred to as “ADC”), an operation unit, a data voltage generation unit, etc., as illustrated in FIGS. 13 and 14.

The pull-down circuit (550) is connected to the voltage detection node (VN) and the non-inverting input terminal (+) of the comparator (501). The pull-down circuit (550) discharges the current of the second node (N2) and the voltage detection node (VN) when the first and second switch elements (T1, T2) are turned on, thereby pulling down the voltage of the second node (N2), i.e., the drain voltage of the driving element (DT).

The sensing voltage (Vsen) applied to the non-inverting input terminal (+) of the comparator (501) is appropriately lowered by the pull-down circuit (550). If the pull-down circuit (550) is not present, the voltage of the voltage detection node (VN) becomes excessively high, causing the output voltage (Vout) of the comparator (501) to become high, and as a result, the driving element (DT) is turned off.

Figure 3 is a circuit diagram showing the operation of the pixel circuit and compensation unit (500).

Referring to Fig. 3, in the sensing and data writing step, the third switch element (T3) is maintained in the off state. The first and second switch elements (T1, T2) are turned on in response to the gate-on voltage of the scan signal (SCAN) in the sensing and data writing step. At this time, the output voltage (Vout) of the comparator (501) is applied to the first node (N1), that is, the gate of the driving element (DT). The output voltage (Vout) of the comparator (501) is programmed with the data voltage (Vdata). Therefore, the gate voltage of the driving element (DT) is a voltage that reflects the data voltage.

When the voltage of the first node (N1) increases, the driving element (DT) is turned on and a current (Isd) flows through the channel of the driving element (DT). The current (Isd) flows through the second node (N2), the second switching element (T2) and the pull-down circuit (550), and the sensing voltage (Vsen) is applied to the non-inverting input terminal (+) of the comparator (501). The sensing voltage (Vsen) is a voltage that reflects the threshold voltage and mobility of the driving element (DT) when the driving element (DT) is turned on. Therefore, the electrical characteristics of the driving element (DT) are detected in the sensing and data writing stages. The comparator (501) compares the sensing voltage (Vsen) and the data voltage, compensates for the change in the electrical characteristics of the driving element (DT) by the data voltage, and applies the compensated data voltage to the gate of the driving element (DT).

Due to the characteristics of the comparator (501), when the inverting input voltage is greater than the non-inverting input voltage, the output voltage (Vout) of the comparator (501) decreases, so that the gate voltage of the driving element (DT) decreases. Here, the inverting input voltage is the voltage of the inverting input terminal (-) of the comparator (501), and the non-inverting input voltage is the voltage of the non-inverting input terminal (+) of the comparator (501). When the gate voltage of the driving element (DT) decreases, the amount of current flowing through the channel of the driving element (DT) increases, so that the second electrode voltage of the driving element (D2), i.e., the drain voltage, increases.

When the gate voltage of the driving element (DT) decreases, the source-gate voltage (Vsg) of the driving element (DT) increases, so that the amount of current of the driving element (DT) increases, and as a result, the drain voltage of the driving element (DT) increases. When the drain voltage of the driving element (DT) increases, the sensing voltage (Vsen) increases. When the positive input voltages of the comparator (501) become the same, the potential difference disappears, so that the gate voltage of the driving element (DT) does not change but becomes constant.

Due to the characteristics of the comparator (501), when the inverting input voltage is lower than the non-inverting input voltage, the output voltage (Vout) of the comparator (501) increases, so the gate voltage of the driving element (DT) increases.

When the gate voltage of the driving element (DT) increases, the source-gate voltage (Vsg) of the driving element (DT) decreases, so that the amount of current of the driving element (DT) decreases, and as a result, the drain voltage of the driving element (DT) decreases. When the drain voltage of the driving element (DT) decreases, the sensing voltage (Vsen) decreases. When the positive input voltages of the comparator (501) become the same, the potential difference disappears, so that the gate voltage of the driving element (DT) does not change but becomes constant.

In the emission stage, the EM signal (EM) is inverted to the gate-on voltage. At this time, current can flow through the OLED and emit light.

Therefore, the present invention can compensate for changes in the electrical characteristics of a driving element (DT) in real time without a separate compensation algorithm.

The pull-down circuit (550) can be implemented with a resistor, a diode, or a combination thereof depending on the characteristics of the display panel.

Figures 4 to 9 are circuit diagrams showing other examples of compensation units and pixel circuits.

Referring to FIG. 4, the data providing unit (510) may include a first resistor (R1). The first resistor (R1) determines the size of the data voltage.

Referring to FIG. 5, the data providing unit (510) includes a first resistor (R1) and a second resistor (R2). The first resistor (R1) and the second resistor (R2) form a voltage dividing circuit that divides the data voltage (Vdata). The size of the data voltage (Vdata) is determined according to the ratio of the first resistor (R1) and the second resistor (R2).

Referring to FIG. 6, the pull-down circuit unit (550) may be configured as a circuit having a predetermined impedance. The pull-down circuit unit (550) may include a voltage detection node (VN) and a diode (DI) connected to an input terminal of a low-potential power supply voltage (ELVSS). When the voltage of the voltage detection node (VN) is higher than the threshold voltage of the diode (DI), the diode (DI) is turned on and the voltage of the voltage detection node (VN) is discharged. Therefore, when the diode (DI) is turned on, the drain voltage of the driving element (DT) is lowered. It is preferable that the diode (DI) be designed to have the same characteristics as those of an organic light-emitting diode (OLED).

In the sensing and data writing stage, the current (Idiode) flows to the low-potential power supply voltage (ELVSS) through the pull-down circuit (550). The sum of the voltage (Vds) between the drain and source of the driving element (DT) and the voltage difference across the diode (DI) is equal to the difference between the pixel driving voltage (ELVDD) and the low-potential power supply voltage (ELVSS). Therefore, in the sensing and data writing stage, the voltage (Vds) between the drain and source of the driving element (DT) is Vds=ELVDD-Vb, which is obtained by subtracting the voltage difference between the voltage detection node (VN) and the low-potential power supply voltage (ELVSS) from the pixel driving voltage (ELVDD). Here, Vb is the voltage of the voltage detection node (VN).

In the emission stage, current flows to the OLED through the driving element (DT) and the third switching element (T3). Therefore, the voltage (Vds) between the drain and source of the driving element (DT) in the emission stage is Vds = ELVDD - Vc, which is the pixel driving voltage (ELVDD) minus the anode voltage of the OLED. Here, Vc is the anode voltage of the OLED.

The voltage (Vds) between the drain and source of the driving element (DT) varies depending on the current flowing through the diode (DI) or the organic light-emitting diode (OLED) of the pull-down circuit (550). That is, if the driving characteristics of the diode (DI) are different from the driving characteristics of the OLED of the pixel (P), the voltage (Vds) between the drain and source of the driving element (DT) may vary during the sensing and data writing stage and the light emitting stage.

Since the driving element (DT) operates in the saturation region, there is little change in the current flowing through the channel of the driving element (DT) regardless of the drain-source voltage (Vds), but it may be somewhat affected when the current amount is small. Therefore, it is desirable that the driving characteristics of the diode (DI) be set to be the same as the driving characteristics of the organic light-emitting diode (OLED).

Referring to FIG. 7, the pull-down circuit (550) may include a resistor (R3) connected between the voltage detection node (VN) and the input terminal of the low-potential power supply voltage (ELVSS).

At low gray levels, the voltage of the voltage detection node (VN) may be lower than the threshold voltage of the diode (DI) because the current of the voltage detection node (VN) is low. In this case, the voltage of the voltage detection node (VN) may not be pulled down because the diode (DI) is not turned on. In this case, the voltage of the voltage detection node (VN) is not pulled down at low gray levels. The resistor (R3) can pull down the voltage of the voltage detection node (VN) even if the current of the voltage detection node (VN) is low at low gray levels.

When the pull-down circuit part (550) is formed of a third resistor (R3), the gamma characteristic of the data voltage in the data providing part (510) may vary. The size of the data voltage (Vdata) is set in consideration of the voltage-current characteristic of the OLED. The OLED has a nonlinear characteristic in which the amount of current change decreases in proportion to the voltage in a high voltage region. The size of the data voltage (Vdata) is set in consideration of the voltage-current characteristic of the OLED.

Referring to FIG. 8, the pull-down circuit (550) may include a diode (DI) and a resistor (R3) connected in parallel between a voltage detection node (VN) and an input terminal of a low-potential power supply voltage (ELVSS).

The diode (DI) is turned on when the voltage of the voltage detection node (VN) rises above its threshold voltage, thereby discharging the voltage of the voltage detection node (VN). The resistor (R3) discharges the voltage detection node (VN) at a low-gray, low-current level at which the diode (DI) does not turn on.

Referring to FIG. 9, the pixel circuit may further include a fourth switching element (T4).

The fourth switching element (T4) includes a gate connected to the scan line (31), a first electrode to which an initialization voltage (Vinit) is applied, and a second electrode connected to the anode of the OLED. The fourth switching element (T4) is turned on according to the gate-on voltage of the scan signal (SCAN) to initialize the anode voltage of the OLED to the initialization voltage (Vinit).

Fig. 10 is a waveform diagram showing a method of driving a display device according to an embodiment of the present invention. Fig. 11 is a diagram showing a data voltage for sensing. Fig. 12 is a diagram showing a pixel data voltage.

Referring to FIGS. 10 and 11, a method of driving a display device includes a sensing step (Ts) of sensing an electrical characteristic of a driving element (DT) in each of sub-pixels and storing the sensing in a memory, and a driving step (Tdrv) of compensating a data voltage by the electrical characteristic of the driving element (DT).

The sensing step (Ts) senses the electrical characteristics of the driving element (DT) for each grayscale in each sub-pixel and stores them in memory. The electrical characteristics of the driving element (DT) can be sensed for each grayscale, but can be sensed for N grayscales (N is a natural number greater than or equal to 2 and lower than the total number of grayscales).

The electrical characteristics of the driving element (DT) can be sensed in real time at three gradations including a lower gradation, an intermediate gradation, and an upper gradation. The lower gradation can be a gradation value of 0 (zero) or a black gradation value at which the luminance of the pixel is minimum. The upper gradation can be a gradation value of 255 in 8-bit pixel data or a white gradation value at which the luminance of the pixel is maximum. The intermediate gradation is a gradation value between the lower gradation and the upper gradation. The intermediate gradation can be a gradation value of 30 as in the examples of FIGS. 11 and 12, but is not limited thereto.

For the remaining gradations that are not sensed in real time, the electrical characteristic values of the driving element (DT) can be estimated from values calculated by the interpolation operation method.

In order to sense the electrical characteristics of the driving elements (DT) in all sub-pixels in the sensing step (Ts), the pulse of the scan signal (SCAN) is sequentially supplied to the scan lines (31) while shifting by one pixel line in synchronization with the sensing data voltage (Vdata) as shown in Fig. 11. The pulse of the scan signal (SCAN) is generated as a gate-on voltage (ON) to turn on the first and second switching elements (T1, T2) of the pixel circuit as shown in Fig. 13.

The sensing signal (SENSE) is generated as a gate-on voltage (ON) in the sensing stage (Ts) to turn on the sensing switch elements (T01, T04, T05, T06) as illustrated in Fig. 10.

When the compensation unit (500) is built into the drive IC, the gate off voltage (OFF) of the sensing signal (SENSE) may be a lower voltage than the gate off voltage (OFF) of the scan signal (SCAN) because it is a digital logic voltage within the drive IC.

In the sensing stage (Ts), the driving signal (DRV) maintains the gate-off voltage (OFF). Therefore, the buffer driving switch elements (T02, T03) controlled by the driving signal (DRV) are in the OFF state in the sensing stage (Ts).

In the sensing step (Ts), the EM signal (EM) is generated as a gate-off voltage (OFF) so that the OLED of the pixel circuit is turned off. Since the third switch element (T3) is turned off according to the gate-off voltage (OFF) of the EM signal (EM) in the sensing step (Ts), the OLED is turned off, so no current flows through the OLED.

The sensing data voltage (Vdata) is applied to the inverting input terminal (-) of the comparator (501). The sensing data voltage (Vdata) is a data voltage for sensing the electrical characteristics of the driving element (DT) for each grayscale. The sensing data voltage (Vdata) may be set to a reverse gamma characteristic slope that increases as the grayscale value increases, as illustrated in Fig. 11, in order to sense the electrical characteristics of the driving element (DT) under the same condition as when current flows through the OLED in the driving stage (Tdrv). In the curve of the sensing data voltage (Vdata), the slope between the lower grayscale and the middle grayscale is higher than the slope between the middle grayscale and the upper grayscale.

The sensing data voltage (Vdata) is a voltage for sensing the electrical characteristics of the driving element (DT) for each grayscale by sensing the anode voltage of the OLED. The pixel data voltage (Vdata) is compensated for the electrical characteristics of the driving element (DT) obtained based on the sensing results for each grayscale and applied to the gate of the driving element (DT) in the driving stage (Tdrv). The pixel data voltage (Vdata) is a voltage for setting the source-gate voltage (Vsg) of the driving element (DT) in the driving stage (Tdrv) in which pixel data is written to the pixels (P). Therefore, as illustrated in FIGS. 11 and 12, the voltage ranges of the sensing data voltage (Vdata) and the pixel data voltage (Vdata) may be different.

In the driving stage (Tdrv), the pulse of the scan signal (SCAN) is sequentially supplied to the scan lines (31) while shifting one pixel line at a time in synchronization with the pixel voltage. The pulse of the scan signal (SCAN) is generated as a gate-on voltage (ON) to turn on the first and second switch elements (T1, T2) of the pixel circuit as illustrated in Fig. 14.

The sensing signal (SENSE) is generated as a gate-off voltage (ON) in the driving stage (Tdrv). Therefore, as shown in Fig. 14, the sensing switch elements (T01, T04, T05, T06) controlled by the sensing signal (SENSE) are in the OFF state.

The driving signal (DRV) is generated as a gate-on voltage (ON) in the driving stage (Tdrv). Therefore, the switch elements (T02, T03) for driving the buffer are turned on in the driving stage (Tdrv) as illustrated in Fig. 14 to operate the comparator (501) as a buffer. When the switch elements (T02, T03) are turned on, the pixel data voltage (Vdata) is applied to the non-inverting input terminal (+) of the comparator (501), and the inverting input terminal (-) and the output terminal of the comparator (501) are connected to operate as a buffer including a voltage follower.

In the driving stage (Tdrv), the EM signal (EM) is generated as a gate-on voltage (ON) to allow current to flow in the OLED of the pixel circuit. The third switch element (T3) of the pixel circuit controlled by the EM signal (EM) is turned on in the driving stage (Tdrv) to form a current path between the driving element (DT) and the second node.

The pixel data voltage (Vdata) generated in the driving stage (Tdrv) is applied to the non-inverting input terminal (+) of the comparator (501). As illustrated in Fig. 12, the pixel data voltage (Vdata) lowers the gate voltage of the driving element (DT) as the grayscale of the pixel data increases, thereby increasing the amount of current flowing into the OLED. As illustrated in Fig. 12, the pixel data voltage (Vdata) decreases as the grayscale value increases. In the curve of the pixel data voltage (Vdata), the slope between the lower grayscale and the middle grayscale is higher than the slope between the middle grayscale and the upper grayscale.

Figures 13 and 14 illustrate in detail a compensation unit according to an embodiment of the present invention. Figure 13 is a circuit diagram showing a sensing step of a display device according to an embodiment of the present invention. Figure 14 is a circuit diagram showing a driving step of a display device according to an embodiment of the present invention.

Referring to FIGS. 13 and 14, the compensation unit (500) includes a comparator (501), a data providing unit (510) connected to the inverting input terminal (-) and the non-inverting input terminal (+) of the comparator (501) through switch elements (T01, T02), and a pull-down circuit unit (550) connected to the non-inverting input terminal (+) of the comparator (501) through a switch element (T05). The compensation unit (500) may be built into a single drive IC together with the data driving unit (400), but is not limited thereto.

The comparator (501) compares the sensing data voltage (Vdata) illustrated in FIG. 11 with the feedback voltage input from the driving element (DT) of the pixel circuit through the sensing line (22) in the sensing step (Ts) and generates an output voltage that changes by the difference between the sensing data voltage (Vdata) and the feedback voltage. The comparator (501) supplies the pixel data voltage (Vdata) illustrated in FIG. 12 to the data line (21) in the driving step (Tdrv).

The data providing unit (510) supplies a sensing data voltage (Vdata) as shown in FIG. 11 to the comparator (501) in the sensing step (Ts). The sensing data voltage (Vdata) is input to the inverting input terminal (-) of the comparator (501). The data providing unit (510) measures the output voltage of the comparator (501) in the sensing step (Ts) and stores the obtained compensation data in the memory (122). The data providing unit (510) modulates pixel data into compensation data in the driving step (Tdrv) to generate a pixel data voltage (Vdata) as shown in FIG. 12. The pixel data voltage modulated into the compensation data is input to the inverting input terminal (-) of the comparator (501). Accordingly, the data providing unit (510) supplies the sensing data voltage (Vdata) to the comparator (501) in the sensing step (Ts) and stores compensation data obtained from the output voltage of the comparator (501) in the memory (122), modulates the pixel data of the input image with the compensation data in the driving step (Tdrv) to generate a pixel data voltage (Vdata), and supplies this pixel data voltage (Vdata) to the comparator (501).

The data providing unit (510) includes an ADC (121), a memory (122), an operation unit (123), and a data voltage generating unit (125 to 128).

The ADC (121) converts the output voltage of the comparator (501) into a digital signal, compensation data, in the sensing stage (Ts) and supplies it to the memory (122). The output voltage of the comparator (501) is a data voltage applied to the gate of the driving element (DT) through the data line (21) and the first switch element (T1) after the electrical characteristics of the driving element (DT) are compensated.

In the sensing step (Ts), the electrical characteristics of the driving element (DT) can be sensed at all grayscales, but as described above, the electrical characteristics of the driving element (DT) can be sensed at N grayscales. In this case, the digital values of the output voltage of the comparator (501) at N grayscales, for example, three grayscales including a lower grayscale, a middle grayscale, and an upper grayscale, can be stored in the memory (122).

The initial data stored in the memory (122) is a digital value of the output voltage of the comparator (501) for each gray level measured in the sensing step (Ts) performed before the product shipment of the display device. Therefore, the initial data of the memory (122) is the initial electrical characteristic value of the driving element (DT) in each pixel.

After the display device is shipped, the electrical characteristics of the driving element (DT) deteriorate over time due to the driving time of the pixels and the accumulation of stress. The sensing step (Ts) can be performed when an image is not displayed after the display device is shipped. For example, when a user touches the home button of a mobile device to switch the display panel (100) to standby mode, the sensing step (Ts) is performed so that the electrical characteristic changes of the driving element (DT) due to the change over time can be sensed in real time. In the sensing step (Ts), since the third switch element (T3) is in the off state, the OLED of the pixels (P) is turned off, so that the lowest brightness, that is, black gradation, is displayed.

As the electrical characteristics of the driving element (DT) deteriorate while the user uses the mobile device, the sensing data voltage (Vdata) is compensated and output as the output voltage of the comparator (501). The output voltage of the comparator (501) is converted into compensation data by the ADC (121) and input into the memory (122). The compensation data stored in the memory (122) is updated at each sensing step (Ts) by compensating for the electrical characteristics of the driving element (DT) that change over time.

The calculation unit (123) can perform an interpolation operation based on the sensing values of the N grayscale to estimate the electrical characteristics of the driving element (DT) in the remaining grayscales other than the N grayscale, thereby generating compensation data of the remaining grayscales other than the compensation data obtained as a real-time sensing result. The sensing values of the N grayscales are compensation data obtained from the output voltage of the comparator (501) measured in each of the N grayscales, for example, three grayscales.

The calculation unit (123) can calculate compensation data for tones between the upper tones and the middle tones by using the compensation data obtained from the upper tones and the middle tones through an interpolation method. The calculation unit (123) can calculate compensation data for tones between the lower tones and the middle tones through an interpolation method by using the compensation data obtained from the middle tones and the lower tones.

The operation unit (123) can modulate pixel data into compensation data in the entire grayscale based on the compensation data read from the memory (122) and the interpolation operation result. The operation unit (123) is enabled in the driving stage (Tdrv) as shown in Fig. 14, modulates pixel data (DATAdrv) into compensation data input from the memory (122), and supplies it to the DAC (125).

The data voltage generator (125 to 128) and the ADC (125) convert sensing data into sensing data voltage (Vdata) in the sensing stage (Ts). The data voltage generator (125 to 128) and the ADC (125) convert pixel data modulated into compensation data into pixel data voltage (Vdata) in the driving stage (Tdrv).

The data voltage generator (125 to 128) includes a first gamma reference voltage generator (126), a second gamma reference voltage generator (127), a grayscale voltage generator (128), and a DAC (125).

The first gamma reference voltage generator (126) is enabled in the sensing step (Ts) as shown in Fig. 13 to generate an upper reference voltage and a lower reference voltage that define the OLED anode voltage range of the pixel circuit. The upper reference voltage and the lower reference voltage output from the first gamma reference voltage generator (126) correspond to the highest voltage of 4 V and the lowest voltage of -2 V of the sensing data voltage (Vdata) as shown in Fig. 11. The first gamma reference voltage (126) is disabled in the driving step (Tdrv) as shown in Fig. 14 to not generate an output voltage.

The second gamma reference voltage generator (127) is enabled in the driving stage (Tdrv) as shown in Fig. 14 to generate an upper reference voltage and a lower reference voltage that define the gate voltage range of the driving element (DT) of the pixel circuit. The upper reference voltage and the lower reference voltage output from the second gamma reference voltage generator (127) correspond to the highest voltage of 3 V and the lowest voltage of 0 V of the pixel data voltage (Vdata) as shown in Fig. 12. The second gamma reference voltage (127) is disabled in the sensing stage (Ts) as shown in Fig. 13 to not generate an output voltage.

The first and second gamma reference voltage generators (126, 127) can be implemented as a programmable gamma voltage generator circuit whose output voltage can be varied according to the register setting value.

The grayscale voltage generator (128) divides the upper reference voltage and the lower reference voltage input from the first gamma reference voltage generator (126) or the second gamma reference voltage generator (127) using a voltage division circuit. The grayscale voltage generator (128) divides the upper reference voltage generated from the first gamma reference voltage generator (126) in the sensing step (Ts) to generate a gamma compensation voltage for each grayscale of the sensing data (DATAs). The grayscale voltage generator (128) divides the upper reference voltage generated from the second gamma reference voltage generator (127) in the driving step (Tdrv) to generate a gamma compensation voltage for each grayscale of the pixel data (DATAdrv). The grayscale voltage generator (128) can be implemented as a programmable gamma voltage generator circuit whose output voltage can be varied according to a register setting value.

The DAC (125) converts sensing data (DATAs) or pixel data (DATAdrv) input as a digital signal into a gamma compensation voltage for each grayscale input from a grayscale voltage generator (128) to generate a sensing data voltage (Vdata) as in Fig. 11 or a pixel data voltage (Vdata) as in Fig. 12. The DAC (125) converts sensing data (DATAs) into a gamma compensation voltage for each grayscale input from a grayscale voltage generator (128) in a sensing step (Ts) to output a sensing data voltage (Vdata) as in Fig. 11. The DAC (125) converts pixel data (DATAdrv) into a gamma compensation voltage for each grayscale input from a grayscale voltage generator (128) in a driving step (Tdrv) to output a pixel data voltage (Vdata) as in Fig. 12.

When the sensing data voltage (Vdata) is obtained as a real-time sensing result from the entire grayscale, the sensing data (DATAs) are generated with different values from each grayscale of the entire grayscale. When the sensing data voltage (Vdata) is obtained as a real-time sensing result from N grayscales, for example, three grayscales, the sensing data (DATAs) are generated with only three grayscale data. The sensing data (DATAs) can be generated from the timing controller (200) regardless of the pixel data of the input image and input to the data driving unit (400).

Pixel data (DATAdrv) is pixel data of an input image input to the timing controller (200). Therefore, pixel data (DATAdrv) has different values for each grayscale in the overall grayscale.

Pixel data (DATAdrv) is converted into compensation data compensated for the electrical characteristics of the driving element (DT) by the operation unit (123) and input to the DAC (125).

The sensing switch elements (T01, T04, T05, T06) are turned on according to the gate-on voltage (ON) of the sensing signal (SENSE). The sensing switch elements (T01, T04, T05, T06) are turned on in the sensing step (Ts) as shown in Fig. 13, and are turned off in the driving step (Tdrv) as shown in Fig. 14.

The sensing switch elements (T01, T04, T05, T06) include a first sensing switch element (T01) connected between the output node of the DAC (125) and the inverting input terminal (-) of the comparator (501), a second sensing switch element (T05) connected between the non-inverting input terminal (+) of the comparator (501) and the voltage detection node (VN), a third sensing switch element (T04) connected between the output terminal of the comparator (501) and the ADC (121) of the compensation unit (510), and a fourth sensing switch element (T06) connected between the voltage detection node (VN) and the sensing line (22).

The first sensing switch element (T01) connects the output node of the DAC (125) to the inverting input terminal (-) of the comparator (501) in response to the sensing signal (SENSE) in the sensing step (Ts). The first sensing switch element (T01) includes a gate to which the sensing signal (SENSE) is applied, a first electrode connected to the output node of the DAC (125), and a second electrode connected to the inverting input terminal (-) of the comparator (501).

The second sensing switch element (T05) connects the non-inverting input terminal (+) of the comparator (501) to the voltage detection node (VN) in response to the sensing signal (SENSE) in the sensing step (Ts). The second sensing switch element (T05) includes a gate to which the sensing signal (SENSE) is applied, a first electrode connected to the non-inverting input terminal (+) of the comparator (501), and a second electrode connected to the voltage detection node (VN).

The third sensing switch element (T04) connects the output terminal of the comparator (501) and the data line (21) to the input node of the ADC (121) in response to the sensing signal (SENSE) in the sensing step (Ts). The third sensing switch element (T04) includes a gate to which the sensing signal (SENSE) is applied, a first electrode connected to the output terminal of the comparator (501) and the data line (21), and a second electrode connected between the input node of the ADC (121) of the compensation unit (510).

The fourth sensing switch element (T06) connects the voltage detection node (VN) to the sensing line (22) in response to the sensing signal (SENSE) in the sensing step (Ts). The fourth sensing switch element (T06) includes a gate to which the sensing signal (SENSE) is applied, a first electrode connected to the voltage detection node (VN), and a second electrode connected to the sensing line (22).

The switch elements (T02, T03) for driving the buffer are turned on according to the gate-on voltage (ON) of the driving signal (DRV). The switch elements (T02, T03) for driving the buffer are turned on in the driving stage (Tdrv) as shown in Fig. 14, and are turned off in the sensing stage (Ts) as shown in Fig. 13.

The buffer driving switch elements (T02, T03) include a first buffer driving switch element (T02) connected between the output node of the DAC (125) and the non-inverting input terminal (+) of the comparator (501), and a second buffer driving switch element (T03) connected between the inverting input terminal (-) of the comparator (501) and the output terminal of the comparator (501). The comparator (501) operates as a buffer when the buffer driving switch elements (T02, T03) are turned on in the driving stage (Tdrv).

The first buffer driving switch element (T02) connects the output node of the DAC (125) to the non-inverting input terminal (+) of the comparator (501) in response to the driving signal (DRV) in the driving stage (Tdrv). The first buffer driving switch element (T02) includes a gate to which the driving signal (DRV) is applied, a first electrode connected to the output node of the DAC (125), and a second electrode connected to the non-inverting input terminal (+) of the comparator (501).

The second buffer driving switch element (T03) connects the inverting input terminal (-) of the comparator (501) to the output terminal of the comparator (501) and the data line (21) in response to the driving signal (DRV) in the driving stage (Tdrv).

The second buffer driving switch element (T03) includes a gate to which a driving signal (DRV) is applied, a first electrode connected to the inverting input terminal (-) of the comparator (501), and a second electrode connected to the output terminal of the comparator (501) and the data line (21).

The above-described embodiments may be applied alone or in combination. The display device of the present invention and its driving method can be explained by the following embodiments.

The display device includes a pixel circuit including a light-emitting element and a driving element that drives the light-emitting element, and is connected to a data line, a sensing line, and a gate line; a comparator that compares a sensing data voltage with a feedback voltage input from a driving element of the pixel circuit through the sensing line in a sensing step to generate an output voltage that changes by a difference between the sensing data voltage and the feedback voltage, and operates as a buffer in a driving step to supply the pixel data voltage to the data line; and a data providing unit that supplies the sensing data voltage to the comparator in the sensing step and stores compensation data obtained from the output voltage of the comparator in a memory, and modulates pixel data of an input image with the compensation data in the driving step to generate the pixel data voltage and supplies the pixel data voltage to the comparator.

The above display device further includes a pull-down circuit section that pulls down the feedback voltage in the sensing step and supplies it to the comparator.

The above comparator includes an operational amplifier including an inverting input terminal to which the sensing data voltage and the pixel data voltage are supplied in the sensing step, a non-inverting input terminal to which a feedback voltage is input in the sensing step, and an output terminal connected to the data line.

The above pull-down circuit includes at least one of a resistor and a diode. In the sensing step, one side of the resistor and the anode of the diode are connected to the non-inverting input terminal of the comparator. A low-potential power supply voltage is applied to the other side of the resistor and the cathode of the diode.

The data providing unit includes: an analog-to-digital converter which converts an output voltage of the comparator into digital data in the sensing step and outputs the compensation data; a memory in which the compensation data is stored; a calculation unit which modulates the pixel data with the compensation data; a data voltage generation unit which generates a gamma compensation voltage for each grayscale of the sensing data in the sensing step and a gamma compensation voltage for each grayscale of the pixel data in the driving step; and a digital-to-analog converter which converts the sensing data into the gamma compensation voltage for each grayscale of the sensing data in the sensing step and supplies the sensing data voltage to the comparator and converts the pixel data modulated with the compensation data into the gamma compensation voltage for each grayscale of the compensation data in the driving step and supplies the pixel data voltage to the comparator.

The above data voltage generator includes a first gamma reference voltage generator which generates a first upper reference voltage and a first lower reference voltage which define an anode voltage range of the light-emitting element in the sensing step; a second gamma reference voltage generator which generates a second upper reference voltage and a second lower reference voltage which define a gate voltage range of the driving element in the driving step; and a grayscale voltage generator which generates a gamma compensation voltage for each grayscale of the sensing data by dividing the first upper reference voltage in the sensing step, and generates a gamma compensation voltage for each grayscale of the pixel data by dividing the second upper reference voltage from the second gamma reference voltage generator in the driving step.

The above sensing data voltage and the above pixel voltage have different voltage ranges.

The sensing data has three gradation values including an upper gradation, an intermediate gradation, and a lower gradation. The compensation data stored in the memory includes output voltage values of the comparator measured at the upper gradation, the intermediate gradation, and the lower gradation of the sensing data. The calculation unit calculates compensation data of gradations between the upper gradation and the intermediate gradation by an interpolation method using the compensation data obtained at the upper gradation and the intermediate gradation. The calculation unit calculates compensation data of gradations between the lower gradation and the intermediate gradation by the interpolation method using the compensation data obtained at the intermediate gradation and the lower gradation.

The driving element includes a gate connected to a first node, a first electrode to which a pixel driving voltage is applied, and a second electrode connected to a second node. The pixel circuit further includes a first switching element connecting the data line to the first node in response to a scan signal in each of the sensing step and the driving step; a second switching element connecting the second node to the sensing line in response to a scan signal in each of the sensing step and the driving step; a third switching element connecting the second node to the light-emitting element in response to a light-emitting control signal in the driving step; and a capacitor connected between the first node and the second node.

The display device further includes a first sensing switch element which connects an output node of the digital-to-analog converter to an inverting input terminal of the comparator in response to a sensing signal in the sensing step; a second sensing switch element which connects a non-inverting input terminal of the comparator to a voltage detection node in response to the sensing signal in the sensing step; a third sensing switch element which connects an output terminal of the comparator and the data line to an input node of an analog-to-digital converter in response to the sensing signal in the sensing step; and a fourth sensing switch element which connects the voltage detection node to the sensing line in response to the sensing signal in the sensing step.

The display device further includes a first buffer driving switch element that connects an output node of the digital-to-analog converter to a non-inverting input terminal of the comparator in response to a driving signal in the driving step; and a second buffer driving switch element that connects an inverting input terminal of the comparator to an output terminal of the comparator and the data line in response to the driving signal in the driving step.

The driving method of the display device includes: a step of comparing a sensing data voltage with a feedback voltage input from a driving element of the pixel circuit through the sensing line in a sensing step using a comparator, and generating an output voltage of the comparator that changes by a difference between the sensing data voltage and the feedback voltage; a step of supplying the sensing data voltage to the comparator in the sensing step and storing compensation data obtained from the output voltage of the comparator in a memory; a step of modulating pixel data of an input image with the compensation data in a driving step to generate the pixel data voltage and supplying the pixel data voltage to the comparator; and a step of supplying the pixel data voltage to the data line in the driving step by having the comparator operate as a buffer.

The driving method of the above display device further includes a step of pulling down the feedback voltage in the sensing step by using a pull-down circuit connected to the non-inverting input terminal of the comparator.

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

100: Display panel 121: ADC
122: Memory 123: Operation Unit
125: DAC 126: 1st gamma reference voltage generator
127: Second gamma reference voltage generator 128: Grayscale voltage generator
200: Timing controller 300: Gate driver
400: Gate driver 500: Compensation unit
501: Comparator 510: Data Provider
550: Pull-down circuit DRV: Drive signal SCAN: Scan signal
SENSE: Sensing signal T01, T04, T05, T06: Switch element for sensing
T02, T03: Switch element for driving buffer DT: Driving element of pixel circuit
T1, T2, T3, T4: Switch elements of pixel circuit Cst: Capacitor of pixel circuit

Claims (13)

A pixel circuit including a light-emitting element, a driving element that drives the light-emitting element, a first switching element that connects a data line to a gate of the driving element in response to a scan signal supplied from a gate line, and a second switching element that connects a sensing line to a first electrode of the driving element in response to the scan signal;
A comparator comprising an inverting input terminal into which a sensing data voltage is input, a non-inverting input terminal into which a feedback voltage of the driving element sensed through the sensing line is input, and an output terminal connected to the first electrode of the first switching element, wherein the comparator compares the sensing data voltage with the feedback voltage in a sensing step to generate an output voltage that changes by the difference between the sensing data voltage and the feedback voltage, and operates as a buffer in a driving step to supply a pixel data voltage to the data line; and
A display device including a data providing unit that stores compensation data obtained from the output voltage of the comparator in the sensing step in a memory, modulates pixel data of an input image with the compensation data in the driving step to generate the pixel data voltage, and supplies the pixel data voltage to the comparator. In the first paragraph,
A display device further comprising a pull-down circuit section for pulling down the feedback voltage and supplying it to the comparator in the sensing step. In the second paragraph,
The output terminal of the above comparator is a display device connected to the first electrode of the first switch element through the data line. In the third paragraph,
The above pull-down circuit part,
Containing at least one of a resistor and a diode,
In the above sensing step, one side of the resistor and the anode of the diode are connected to the non-inverting input terminal of the comparator,
A display device in which a low-potential power supply voltage is applied to the other side of the above resistor and the cathode of the above diode. In the third paragraph,
The above data provider is,
An analog-to-digital converter that converts the output voltage of the comparator into digital data in the sensing step and outputs the compensation data;
Memory in which the above compensation data is stored;
A computational unit that modulates the above pixel data into the above compensation data;
A data voltage generation unit that generates a gamma compensation voltage for each grayscale of the sensing data in the sensing step and generates a gamma compensation voltage for each grayscale of the pixel data in the driving step; and
A display device including a digital-to-analog converter which converts sensing data into a gamma compensation voltage for each grayscale in the sensing step and supplies the voltage to the comparator, and converts pixel data modulated by the compensation data into a gamma compensation voltage for each grayscale of the compensation data in the driving step and supplies the pixel data voltage to the comparator. In paragraph 5,
The above data voltage generating unit is,
A first gamma reference voltage generator which generates a first upper reference voltage and a first lower reference voltage defining an anode voltage range of the light-emitting element in the sensing step;
A second gamma reference voltage generator that generates a second upper reference voltage and a second lower reference voltage that define a gate voltage range of the driving element in the driving step; and
A display device including a grayscale voltage generating unit that generates a gamma compensation voltage for each grayscale of the sensing data by dividing the first upper reference voltage in the sensing step, and generates a gamma compensation voltage for each grayscale of the pixel data by dividing the second upper reference voltage from the second gamma reference voltage generating unit in the driving step. In any one of claims 1 to 4,
A display device in which the sensing data voltage and the pixel data voltage have different voltage ranges. In paragraph 5,
The above sensing data has three grayscale values including upper grayscale, middle grayscale, and lower grayscale.
The compensation data stored in the above memory includes the output voltage values of the comparator measured at the upper grayscale, the middle grayscale, and the lower grayscale of the sensing data,
The above operation unit,
Using the compensation data obtained from the upper grayscale and the intermediate grayscale, compensation data for grayscales between the upper grayscale and the intermediate grayscale is calculated using an interpolation method,
A display device that uses compensation data obtained from the intermediate tone and the lower tone to produce compensation data for tone levels between the lower tone and the intermediate tone using the interpolation method. In paragraph 5,
The above driving element
It includes a gate connected to a first node, a first electrode to which a pixel driving voltage is applied, and a second electrode connected to a second node,
The above pixel circuit,
A first switching element connecting the data line to the first node in response to a scan signal in each of the sensing step and the driving step;
A second switching element connecting the second node to the sensing line in response to a scan signal in each of the sensing step and the driving step;
a third switching element connecting the second node to the light-emitting element in response to a light-emitting control signal in the driving step; and
A display device further comprising a capacitor connected between the first node and the second node. In paragraph 5,
A first sensing switch element that connects an output node of the digital-to-analog converter to an inverting input terminal of the comparator in response to a sensing signal in the sensing step;
A second sensing switch element that connects the non-inverting input terminal of the comparator to a voltage detection node in response to the sensing signal in the sensing step;
A third sensing switch element that connects the output terminal of the comparator and the data line to the input node of an analog-to-digital converter in response to the sensing signal in the sensing step; and
A display device further comprising a fourth sensing switch element that connects the voltage detection node to the sensing line in response to the sensing signal in the sensing step. In Article 10,
A first buffer driving switch element that connects the output node of the digital-to-analog converter to the non-inverting input terminal of the comparator in response to a driving signal in the driving step; and
A display device further comprising a second buffer driving switch element that connects the inverting input terminal of the comparator to the output terminal of the comparator and the data line in response to the driving signal in the driving step. A method for driving a display device including a pixel circuit including a light-emitting element, a driving element for driving the light-emitting element, a first switching element for connecting a data line to a gate of the driving element in response to a scan signal supplied from a gate line, and a second switching element for connecting a sensing line to a first electrode of the driving element in response to the scan signal,
A step of comparing the sensing data voltage and the feedback voltage in a sensing step by using a comparator including an inverting input terminal into which a sensing data voltage is input, a non-inverting input terminal into which a feedback voltage of the driving element sensed through the sensing line is input, and an output terminal connected to the first electrode of the first switch element, and generating an output voltage of the comparator that changes by the amount of the difference between the sensing data voltage and the feedback voltage;
A step of storing compensation data obtained from the output voltage of the comparator in the sensing step into a memory;
A step of modulating pixel data of an input image with the compensation data in the driving step to generate a pixel data voltage and supplying the pixel data voltage to the comparator; and
A driving method for a display device, comprising a step in which the comparator operates as a buffer in the driving step and the pixel data voltage is supplied to the data line. In Article 12,
A method for driving a display device further comprising a step of pulling down the feedback voltage in the sensing step using a pull-down circuit connected to the non-inverting input terminal of the comparator.