KR102407490B1 - Light Emitting Display Device and Driving Method thereof - Google Patents

Abstract

The present invention provides an electroluminescent display device including a sub-pixel having a light emitting diode that emits light and a driving transistor that provides a driving current for the operation of the light emitting diode. In the driving transistor, an electric field in a first direction is formed during the first period, and an electric field in a second direction opposite to the first direction is formed during the second period.

Description

Electroluminescent display device and driving method thereof

The present invention relates to an electroluminescent display device and a driving method thereof.

As information technology develops, the market for display devices, which is a connection medium between users and information, is growing. Accordingly, the use of various types of display devices such as an electroluminescent display device, a liquid crystal display device, and a plasma display device is increasing.

The display device includes a display panel including a plurality of sub-pixels, a driving unit for driving the display panel, and a power supply unit for supplying power to the display panel. The driver includes a scan driver that supplies a scan signal (or a gate signal) to the display panel and a data driver that supplies a data signal to the display panel.

In the electroluminescent display device, when a scan signal and a data signal are supplied to the sub-pixels, the light emitting diodes of the selected sub-pixels emit light, so that an image can be displayed. The light emitting diode is implemented based on an organic material or is implemented based on an inorganic material.

The electroluminescent display device performs a compensation operation for compensating for sub-pixels of a display panel and an image display operation for displaying an image on the display panel. Sensing of a threshold voltage for compensating the driving transistor in the sub-pixel is performed during the compensation operation period.

In order to sense the threshold voltage of the driving transistor, it is necessary to add compensation circuits related to compensation inside the sub-pixel. However, the compensation method proposed in the prior art may cause variations in the driving transistor as well as an afterimage defect on the display panel, so improvement is required.

The present invention for solving the problems of the above-mentioned background technology is to keep the display quality constant even when deterioration occurs due to the lapse of time, and to solve the increase in the density of electrodes so that a sub-pixel layout suitable for high-resolution application is possible.

As a means of solving the above problems, the present invention provides an electroluminescent display device including a sub-pixel having a light emitting diode that emits light and a driving transistor that provides a driving current for the operation of the light emitting diode. In the driving transistor, an electric field in a first direction is formed during the first period, and an electric field in a second direction opposite to the first direction is formed during the second period.

The first period may be a period in which the light emitting diode emits light, and the second period may be a period in which the threshold voltage of the driving transistor is sensed.

An electric field may be formed in a direction from the source to the drain of the driving transistor during the first period, and an electric field may be formed in a direction from the drain to the source of the driving transistor during the second period.

The driving transistor may receive an electric field alternating in the first direction and the second direction from the source electrode and the drain electrode during one frame.

In the sub-pixel, as the first transistor connected to the source electrode of the driving transistor and the second transistor connected to the drain electrode of the driving transistor are simultaneously turned on, the electric field alternates in the first direction and the second direction at the source electrode and the drain electrode for one frame can take

The sub-pixel includes the driving transistor having a gate electrode connected to a first node, a first electrode connected to a second node, and a second electrode connected to a third node, and one end connected to a first power line and the other end connected to the first node The connected capacitor, the organic light emitting diode having the cathode electrode connected to the second power line, the gate electrode connected to the Nth scan line, the first electrode connected to the first node, and the second electrode connected to the second node A transistor, a gate electrode connected to an Nth scan line, a first electrode connected to a data line, and a second transistor connected to a third node with a second electrode, a gate electrode connected to an Nth emission control line, and a first power source A third transistor with a first electrode connected to the line and a second electrode connected to a second node, a gate electrode connected to an Nth emission control line, a first electrode connected to the third node, and an anode electrode of the organic light emitting diode A fourth transistor to which the second electrode is connected, a fifth transistor to which a gate electrode is connected to an N-1th scan line, a first electrode is connected to an initialization voltage line, and a second electrode is connected to a first node, and an Nth scan line and a sixth transistor connected to the gate electrode, the first electrode connected to the initialization voltage line, and the second electrode connected to the anode electrode of the organic light emitting diode.

In another aspect, the present invention provides a method of driving an electroluminescent display device including a sub-pixel having a light emitting diode that emits light and a driving transistor that provides a driving current for the operation of the light emitting diode. An electric field in a first direction is formed in the driving transistor during the first period, and an electric field in a second direction opposite to the first direction is formed in the driving transistor during the second period.

The first period may be a period in which the light emitting diode emits light, and the second period may be a period in which the threshold voltage of the driving transistor is sensed.

An electric field may be formed in a direction from the source to the drain of the driving transistor during the first period, and an electric field may be formed in a direction from the drain to the source of the driving transistor during the second period.

The driving transistor may receive an electric field alternating in the first direction and the second direction from the source electrode and the drain electrode during one frame.

According to the present invention, the level of occurrence of an afterimage on the display panel can be reduced by using a compensation method capable of alleviating the fluctuation of the driving transistor even when deterioration occurs due to the lapse of time, thereby maintaining the display quality constant. In addition, the present invention has the effect of resolving the increase in the density of electrodes to enable a sub-pixel layout suitable for high-resolution application.

1 is a schematic block diagram of an organic light emitting display device;
2 is a cross-sectional view of a display panel;
3 is a schematic circuit configuration diagram of a sub-pixel;
4 is an exemplary diagram of a circuit configuration of a sub-pixel according to an experimental example;
5 to 7 are diagrams showing a driving state of a circuit according to an operation for each section of the experimental example shown in FIG. 4;
8 is a driving waveform diagram for driving a sub-pixel according to the experimental example shown in FIG. 4;
9 is a simulation waveform diagram illustrating a voltage change for each electrode of a driving transistor according to an operation for each section of an experimental example;
10 is an exemplary diagram of a circuit configuration of a sub-pixel according to an embodiment;
11 to 13 are diagrams illustrating a driving state of a circuit according to an operation for each section according to the embodiment shown in FIG. 10;
FIG. 14 is a driving waveform diagram for driving a sub-pixel according to the embodiment shown in FIG. 10;
15 is a simulation waveform diagram illustrating a voltage change for each electrode of a driving transistor according to an operation for each section according to the embodiment;
16 is a voltage/current value comparison waveform diagram of an organic light emitting diode for comparing driving characteristics between an experimental example and an embodiment;
17 is a waveform diagram for comparing threshold voltage sensing values of a driving transistor for comparing driving characteristics between an experimental example and an embodiment;
18 is a waveform diagram for comparing luminance changes according to a threshold voltage deviation for comparing driving characteristics between an experimental example and an embodiment;
19 and 20 are diagrams for explaining the biggest difference between the experimental example and the embodiment.

Hereinafter, specific details for carrying out the present invention will be described with reference to the accompanying drawings.

The electroluminescent display device described below may be implemented as a TV, an image player, a personal computer (PC), a home theater, a smart phone, a virtual reality device (VR), and the like. In addition, as an electroluminescent display device to be described below, an organic light emitting display device implemented based on an organic light emitting diode (light emitting device) will be described as an example. However, the electroluminescent display device to be described below may be implemented based on an inorganic light emitting diode.

The thin film transistor of the electroluminescent display device to be described below may be named as a source electrode and a drain electrode or a drain electrode and a source electrode depending on the type except for the gate electrode. To avoid limitation, the first electrode and the second electrode explained as

1 is a schematic block diagram of an organic light emitting display device, FIG. 2 is a cross-sectional view of a display panel, and FIG. 3 is a schematic circuit configuration diagram of a sub-pixel.

As shown in FIG. 1 , the organic light emitting display device includes an image processing unit 110 , a timing control unit 120 , a data driving unit 130 , a scan driving unit 140 , a display panel 150 , and a power supply unit 160 . Included.

The image processing unit 110 outputs a data enable signal DE along with the data signal DATA supplied from the outside. The image processing unit 110 may output one or more of a vertical synchronization signal, a horizontal synchronization signal, and a clock signal in addition to the data enable signal DE, but these signals are omitted for convenience of description.

The timing controller 120 receives the data signal DATA from the image processing unit 110 as well as a driving signal including a data enable signal DE or a vertical synchronization signal, a horizontal synchronization signal, and a clock signal. The timing controller 120 includes a gate timing control signal GDC for controlling the operation timing of the scan driver 140 and a data timing control signal DDC for controlling the operation timing of the data driver 130 based on the driving signal. to output

The data driver 130 samples and latches the data signal DATA supplied from the timing controller 120 in response to the data timing control signal DDC supplied from the timing controller 120 , converts it into a gamma reference voltage, and outputs it . The data driver 130 outputs the data signal DATA through the data lines DL1 to DLn. The data driver 130 may be formed in the form of an integrated circuit (IC).

The scan driver 140 outputs a scan signal in response to the gate timing control signal GDC supplied from the timing controller 120 . The scan driver 140 outputs a scan signal through the scan lines GL1 to GLm. The scan driver 140 is formed in the form of an integrated circuit (IC) or is formed in the display panel 150 in the form of a gate in panel.

The power supply unit 160 outputs a high potential voltage, a low potential voltage, and the like. The high potential voltage and low potential voltage output from the power supply unit 160 are supplied to the display panel 150 . The high potential voltage is supplied to the display panel 150 through the first power line EVDD, and the low potential voltage is supplied to the display panel 150 through the second power line EVSS.

The display panel 150 displays an image corresponding to the data signal DATA and the scan signal supplied from the data driver 130 and the scan driver 140 , and the power supplied from the power supply unit 160 . The display panel 150 includes sub-pixels SP that operate to display an image.

2 , the display panel 150 includes a first substrate (or thin film transistor substrate) 150a, a display area AA, a non-display area NA, and a second substrate (or a protective substrate, a protective film). ) (150b) and the like. The display area AA is an area for displaying an image, and the non-display area NA is an area for not displaying an image. The display area AA includes pixels P for displaying an image. The display area AA is sealed by the second substrate 150b since it is vulnerable to moisture or oxygen. The first substrate 150a may be selected from glass or a flexible material, and the second substrate 150b may be selected from a composite film in which an organic film and an inorganic film are alternated or the same material as the first substrate 150a.

A pixel (P) consists of red (R), blue (B) and green (G) sub-pixels, or red (R), white (W), blue (B) and green (G) sub-pixels. can be done The sub-pixels may have one or more different emission areas according to emission characteristics. Therefore, the arrangement order of the sub-pixels may be variously changed depending on the light emitting area as well as the configuration (or structure) of the light emitting material or the compensation circuit.

As shown in FIG. 3 , the N-th sub-pixel SP includes a pixel circuit PC, a driving transistor DT, and an organic light emitting diode (OLED). The driving transistor DT generates a driving current in response to the operation of the pixel circuit PC. The organic light emitting diode OLED emits light in response to a driving current generated from the driving transistor DT.

When the device included in the N-th sub-pixel SP is driven for a long period of time, the threshold voltage moves, and deterioration occurs. The threshold voltage of the driving transistor DT among the elements included in the N-th sub-pixel SP moves in a negative or positive direction according to the characteristics of the applied voltage. For this reason, compensation circuits for compensating for device deterioration are included in the pixel circuit PC. The N-th sub-pixel SP may be configured in various forms including a pixel circuit PC and a driving transistor DT, such as a 3T (Transistor) 1C (Capacitor) structure, 3T2C, 4T2C, 5T1C, 6T2C, 7T1C, and the like.

The N-th sub-pixel SP is connected to the data line DL1 , the scan line GL1 , the first power line EVDD, and the second power line EVSS. Since compensation circuits are included in the N-th sub-pixel SP, the scan line GL1 includes an N-th scan line Scan[n-1], an N-th scan line Scan[n-1] and A plurality of N-th emission control lines EM[n] may be included. The N-th scan line (Scan[n-1]) is defined as a scan line to which a scan signal for operating the N-th sub-pixel SP is supplied, whereas the N-1th scan line (Scan[n-1]) may be defined as a scan line to which a scan signal for operating an N-1 th sub-pixel positioned at the front end of the N-th sub-pixel SP is supplied. However, the number of scan lines may vary depending on the configuration of the pixel circuit PC and compensation circuits.

When an organic light emitting display is implemented based on a pixel circuit PC having a compensation circuit such as the N-th sub-pixel SP, a compensation operation for compensating the sub-pixels of the display panel and an image are displayed on the display panel To perform an image display operation, etc. Sensing of a threshold voltage for compensating the driving transistor in the sub-pixel is performed during the compensation operation period.

As described above, in order to sense the threshold voltage of the driving transistor, it is necessary to add compensation circuits related to compensation inside the sub-pixel. However, the compensation method proposed in the prior art may cause variations in the driving transistor as well as an afterimage defect on the display panel, so improvement is required.

Hereinafter, a 7T1C-based sub-pixel is set as an experimental example, and an embodiment for improving it will be described. Incidentally, in the following description, all transistors are implemented as a P-type in which a scan signal of logic low is turned on as an example, but the present invention is not limited thereto.

<Experimental example>

4 is an exemplary diagram of a circuit configuration of a sub-pixel according to an experimental example, FIGS. 5 to 7 are diagrams showing a driving state of a circuit according to an operation for each section of the experimental example shown in FIG. 4, and FIG. 8 is shown in FIG. It is a driving waveform diagram for driving the sub-pixels according to the experimental example, and FIG. 9 is a simulation waveform diagram showing the voltage change for each electrode of the driving transistor according to the operation for each section of the experimental example.

As shown in Fig. 4, the sub-pixel according to the experimental example includes a first transistor T1, a second transistor T2, a third transistor T3, a fourth transistor T4, a fifth transistor T5, It includes a sixth transistor T6, a driving transistor DT, a capacitor Cst, and an organic light emitting diode (OLED). That is, the sub-pixel according to the experimental example has a 7T1C structure. In FIG. 4 , “Coled” refers to a parasitic capacitor present in an organic light emitting diode (OLED).

The driving transistor DT has a gate electrode connected to a first node N1, a first electrode connected to a second node DRS (source node), and a second electrode connected to a third node DRD (drain node). connected The capacitor Cst has one end connected to the first power line EVDD and the other end connected to the first node N1. The organic light emitting diode OLED has an anode electrode connected to the second electrode of the fourth transistor T4 and a cathode electrode connected to the second power line EVSS.

The first transistor T1 has a gate electrode connected to the N-th scan line SCAN[N], a first electrode connected to a first node N1, and a second electrode connected to a third node DRD. The second transistor T2 has a gate electrode connected to the N-th scan line SCAN[N], a first electrode connected to the data line DL1, and a second electrode connected to the second node DRS. The third transistor T3 has a gate electrode connected to the Nth emission control line EM[n], a first electrode connected to the first power line EVDD, and a second electrode connected to the second node DRS. do.

The fourth transistor T4 has a gate electrode connected to the Nth emission control line EM[n], a first electrode connected to the third node DRD, and a second electrode connected to the anode electrode of the organic light emitting diode OLED. this is connected The fifth transistor T5 has a gate electrode connected to the N-1th scan line SCAN[N-1], a first electrode connected to an initialization voltage line VINI, and a second electrode connected to the first node N1. this is connected The sixth transistor T6 has a gate electrode connected to the Nth scan line SCAN[N], a first electrode connected to an initialization voltage line VINI, and a second electrode connected to the anode electrode of the organic light emitting diode OLED. connected

5 to 7 and 8 , the sub-pixels according to the experimental example operate in the order of an initialization period T1, a threshold voltage sensing period T2, a sustain period T3, and an emission period T4. do. The voltage change for each electrode (voltage change for each node) of the driving transistor during the initialization period T1 , the threshold voltage sensing period T2 , the sustain period T3 , and the light emission period T4 is shown in FIG. 9 . In FIG. 9 , DRS is the voltage of the source electrode of the driving transistor DT, DRD is the voltage of the drain electrode of the driving transistor DT, and DRG is the voltage of the gate electrode of the driving transistor DT.

During the initialization period T1, the N-1th scan signal Scan[n-1] of logic low, the Nth scan line SCAN[N], A logic high N-th scan signal Scan[n] is transmitted, and a logic-high N-th emission control signal Em[n] is transmitted to the N-th emission control line EM[n].

During the initialization period T1, the first transistor T1, the second transistor T2, the third transistor T3, the fourth transistor T4, the sixth transistor T6, and the driving transistor DT are turned off. state, but the fifth transistor T5 has a turned-on state.

During the initialization period T1, the fifth transistor T5 is turned on in response to the N-1 th scan signal Scan[n-1] transmitted through the N-1 th scan line SCAN[N-1]. do. When the fifth transistor T5 is turned on, the initialization voltage Vini transmitted through the initialization voltage line VINI is applied to the first node N1 . The capacitor Cst is initialized (or residual charges are discharged) by the initialization voltage Vini applied to the first node N1.

During the threshold voltage sensing period T2, the N-1th scan signal Scan[n-1] of logic high and the Nth scan line SCAN[N-1] ]) of a logic low N-th scan signal Scan[n], and a logic-high N-th emission control signal Em[n] is transmitted to the N-th emission control line EM[n].

During the threshold voltage sensing period T2, the third transistor T3, the fourth transistor T4, and the fifth transistor T5 have a turned-off state, but the first transistor T1, the second transistor T2, and the 6 transistor T6 has a turned-on state.

During the threshold voltage sensing period T2, the first transistor T1 is turned on in response to the N-th scan signal Scan[n] transmitted through the N-th scan line SCAN[N]. When the first transistor T1 is turned on, the drain electrode and the gate electrode of the driving transistor DT are connected to the diode connection state. Accordingly, the threshold voltage Vth of the driving transistor DT is sensed and sampled. An operation for sensing and sampling the threshold voltage Vth of the driving transistor DT is defined as a compensation operation.

During the threshold voltage sensing period T2, the second transistor T2 is turned on in response to the N-th scan signal Scan[n] transmitted through the N-th scan line SCAN[N]. When the second transistor T2 is turned on, the data voltage transferred through the data line DL1 passes through the source electrode of the driving transistor DT and then through the drain electrode and is applied to the other end of the capacitor Cst. By the turn-on operation of the second transistor T2 and the diode connection operation of the driving transistor DT, the capacitor Cst starts to be charged with the data voltage Vdata+Vth reflecting the threshold voltage variation of the driving transistor DT.

In the driving transistor DT, threshold voltage sensing and sampling are performed by the turn-on operation of the first transistor T1 connected to the third node DRD, and at the same time, the second transistor T2 connected to the second node DRS is turned on. A path for storing the data voltage is formed by the operation. In this case, the path for storing the data voltage is in the order of the second node DRS, the third node DRD, and the first node N1 of the driving transistor DT.

During the threshold voltage sensing period T2, the sixth transistor T6 is turned on in response to the N-th scan signal Scan[n] transmitted through the N-th scan line SCAN[N]. When the sixth transistor T6 is turned on, the initialization voltage Vini transmitted through the initialization voltage line VINI is applied to the anode electrode of the organic light emitting diode OLED. Accordingly, the organic light emitting diode (OLED) is initialized.

During the sustain period T3, the N-1th scan signal Scan[n-1] of logic high and the Nth scan line SCAN[N] are provided on the N-1th scan line SCAN[N-1]. A logic high N-th scan signal Scan[n] is transmitted, and a logic-high N-th emission control signal Em[n] is transmitted to the N-th emission control line EM[n].

During the holding period T3, the first transistor T1, the second transistor T2, the third transistor T3, the fourth transistor T4, the fifth transistor T5, the sixth transistor T6, and driving The transistor DT has a turned off state. During the sustain period T3 , the capacitor Cst is charged with the data voltage Vdata+Vth in which the threshold voltage variation of the driving transistor DT is reflected, and the charged voltage value is maintained.

During the light emission period T4, the N-1th scan signal Scan[n-1] of logic high and the Nth scan line SCAN[N] are connected to the N-1th scan line SCAN[N-1]. A logic-high N-th scan signal Scan[n] is transmitted, and a logic-low N-th emission control signal Em[n] is transmitted to the N-th emission control line EM[n].

During the light emission period T4, the first transistor T1, the second transistor T2, the fifth transistor T5, and the sixth transistor T6 have a turned-off state, but the third transistor T3 and the fourth transistor T6 (T4) and the driving transistor DT have a turned-on state.

During the emission period T4, the third and fourth transistors T3 and T4 are turned on in response to the N-th emission control signal Em[n] transmitted through the N-th emission control line EM[n]. . The driving transistor DT is turned on in response to the data voltage stored in the capacitor Cst, and generates a driving current based on the first power voltage Vdd transmitted through the first power line EVDD. As a result, the organic light emitting diode OLED receives the driving current generated from the driving transistor DT to emit light. An operation in which the organic light emitting diode (OLED) emits light is defined as an image display operation on the display panel.

The sub-pixel according to the experimental example may perform the compensation operation and the image display operation as described above. However, it was found that the sub-pixel according to the experimental example may cause defects such as an afterimage on the display panel without considering characteristics that may occur during driving of the display panel. In addition, it has been found that the sub-pixel according to the experimental example may cause an increase in the density of electrodes made of the semiconductor layer and the source/drain layer, and as a result, it may be difficult to layout the sub-pixel for high-resolution application. The problem of the sub-pixel according to the experimental example is hereinafter with reference to FIG. 19 .

As a result of studying the sub-pixels according to the experimental example, the reason why the above problem occurs is the configuration (connection relationship) and operation characteristics of the first and second transistors T1 and T2 located around the driving transistor DT. It is confirmed that this is because the embodiment improves it as follows.

<Example>

10 is an exemplary diagram of a circuit configuration of a sub-pixel according to an embodiment, FIGS. 11 to 13 are diagrams showing a driving state of a circuit according to an operation for each section of the embodiment shown in FIG. 10, and FIG. 14 is shown in FIG. It is a driving waveform diagram for driving a sub-pixel according to an embodiment of the present invention, and FIG. 15 is a simulation waveform diagram illustrating a voltage change for each electrode of the driving transistor according to an operation for each section of the embodiment.

10, the sub-pixel according to the embodiment includes a first transistor T1, a second transistor T2, a third transistor T3, a fourth transistor T4, a fifth transistor T5, It includes a sixth transistor T6, a driving transistor DT, a capacitor Cst, and an organic light emitting diode (OLED). That is, the sub-pixel according to the experimental example has a 7T1C structure. In FIG. 10 , “Coled” refers to a parasitic capacitor present in an organic light emitting diode (OLED).

The driving transistor DT has a gate electrode connected to a first node N1, a first electrode connected to a second node DRS (source node), and a second electrode connected to a third node DRD (drain node). connected The capacitor Cst has one end connected to the first power line EVDD and the other end connected to the first node N1. The organic light emitting diode OLED has an anode electrode connected to the second electrode of the fourth transistor T4 and a cathode electrode connected to the second power line EVSS.

The first transistor T1 has a gate electrode connected to the N-th scan line SCAN[N], a first electrode connected to a first node N1, and a second electrode connected to the second node DRS. The second transistor T2 has a gate electrode connected to the N-th scan line SCAN[N], a first electrode connected to the data line DL1, and a second electrode connected to the third node DRD. The third transistor T3 has a gate electrode connected to the Nth emission control line EM[n], a first electrode connected to the first power line EVDD, and a second electrode connected to the second node DRS. do.

The fourth transistor T4 has a gate electrode connected to the Nth emission control line EM[n], a first electrode connected to the third node DRD, and a second electrode connected to the anode electrode of the organic light emitting diode OLED. this is connected The fifth transistor T5 has a gate electrode connected to the N-1th scan line SCAN[N-1], a first electrode connected to an initialization voltage line VINI, and a second electrode connected to the first node N1. this is connected The sixth transistor T6 has a gate electrode connected to the Nth scan line SCAN[N], a first electrode connected to an initialization voltage line VINI, and a second electrode connected to the anode electrode of the organic light emitting diode OLED. connected

11 to 13 and 14 , the sub-pixel according to the embodiment operates in the order of an initialization period T1, a threshold voltage sensing period T2, a sustain period T3, and an emission period T4. do. A voltage change (voltage change for each node) of the driving transistor for each electrode during the initialization period T1 , the threshold voltage sensing period T2 , the sustain period T3 , and the light emission period T4 is shown in FIG. 15 . In FIG. 15 , DRS is the voltage of the source electrode of the driving transistor DT, DRD is the voltage of the drain electrode of the driving transistor DT, and DRG is the voltage of the gate electrode of the driving transistor DT.

During the initialization period T1, the N-1th scan signal Scan[n-1] of logic low, the Nth scan line SCAN[N], A logic high N-th scan signal Scan[n] is transmitted, and a logic-high N-th emission control signal Em[n] is transmitted to the N-th emission control line EM[n].

During the initialization period T1, the first transistor T1, the second transistor T2, the third transistor T3, the fourth transistor T4, the sixth transistor T6, and the driving transistor DT are turned off. state, but the fifth transistor T5 has a turned-on state.

During the initialization period T1, the fifth transistor T5 is turned on in response to the N-1 th scan signal Scan[n-1] transmitted through the N-1 th scan line SCAN[N-1]. do. When the fifth transistor T5 is turned on, the initialization voltage Vini transmitted through the initialization voltage line VINI is applied to the first node N1 . The capacitor Cst is initialized (or residual charges are discharged) by the initialization voltage Vini applied to the first node N1.

During the threshold voltage sensing period T2, the N-1th scan signal Scan[n-1] of logic high and the Nth scan line SCAN[N-1] ]) of a logic low N-th scan signal Scan[n], and a logic-high N-th emission control signal Em[n] is transmitted to the N-th emission control line EM[n].

During the threshold voltage sensing period T2, the third transistor T3, the fourth transistor T4, and the fifth transistor T5 have a turned-off state, but the first transistor T1, the second transistor T2, and the 6 transistor T6 has a turned-on state.

During the threshold voltage sensing period T2, the first transistor T1 is turned on in response to the N-th scan signal Scan[n] transmitted through the N-th scan line SCAN[N]. When the first transistor T1 is turned on, the drain electrode and the gate electrode of the driving transistor DT are connected to the diode connection state. Accordingly, the threshold voltage Vth of the driving transistor DT is sensed and sampled. An operation for sensing and sampling the threshold voltage Vth of the driving transistor DT is defined as a compensation operation.

During the threshold voltage sensing period T2, the second transistor T2 is turned on in response to the N-th scan signal Scan[n] transmitted through the N-th scan line SCAN[N]. When the second transistor T2 is turned on, the data voltage transferred through the data line DL1 passes through the drain electrode of the driving transistor DT and then through the source electrode and then is applied to the other end of the capacitor Cst. By the turn-on operation of the second transistor T2 and the diode connection operation of the driving transistor DT, the capacitor Cst starts to be charged with the data voltage Vdata+Vth reflecting the threshold voltage variation of the driving transistor DT.

In the driving transistor DT, threshold voltage sensing and sampling are performed by the turn-on operation of the first transistor T1 connected to the second node DRS, and at the same time, the second transistor T2 connected to the third node DRD is turned on. A path for storing the data voltage is formed by the operation. In this case, the path for storing the data voltage is in the order of the third node DRD, the second node DRS, and the first node N1 of the driving transistor DT.

During the threshold voltage sensing period T2, the sixth transistor T6 is turned on in response to the N-th scan signal Scan[n] transmitted through the N-th scan line SCAN[N]. When the sixth transistor T6 is turned on, the initialization voltage Vini transmitted through the initialization voltage line VINI is applied to the anode electrode of the organic light emitting diode OLED. Accordingly, the organic light emitting diode (OLED) is initialized.

During the sustain period T3, the N-1th scan signal Scan[n-1] of logic high and the Nth scan line SCAN[N] are provided on the N-1th scan line SCAN[N-1]. A logic high N-th scan signal Scan[n] is transmitted, and a logic-high N-th emission control signal Em[n] is transmitted to the N-th emission control line EM[n].

During the holding period T3, the first transistor T1, the second transistor T2, the third transistor T3, the fourth transistor T4, the fifth transistor T5, the sixth transistor T6, and driving The transistor DT has a turned off state. During the sustain period T3 , the capacitor Cst is charged with the data voltage Vdata+Vth in which the threshold voltage variation of the driving transistor DT is reflected, and the charged voltage value is maintained.

During the light emission period T4, the N-1th scan signal Scan[n-1] of logic high and the Nth scan line SCAN[N] are connected to the N-1th scan line SCAN[N-1]. A logic-high N-th scan signal Scan[n] is transmitted, and a logic-low N-th emission control signal Em[n] is transmitted to the N-th emission control line EM[n].

During the light emission period T4, the first transistor T1, the second transistor T2, the fifth transistor T5, and the sixth transistor T6 have a turned-off state, but the third transistor T3 and the fourth transistor T6 (T4) and the driving transistor DT have a turned-on state.

During the emission period T4, the third and fourth transistors T3 and T4 are turned on in response to the N-th emission control signal Em[n] transmitted through the N-th emission control line EM[n]. . The driving transistor DT is turned on in response to the data voltage stored in the capacitor Cst, and generates a driving current based on the first power voltage Vdd transmitted through the first power line EVDD. As a result, the organic light emitting diode OLED receives the driving current generated from the driving transistor DT to emit light. An operation in which the organic light emitting diode (OLED) emits light is defined as an image display operation on the display panel.

The sub-pixel according to the embodiment may perform the compensation operation and the image display operation as described above. It was found that the sub-pixel according to the embodiment can improve defects such as an afterimage on the display panel in consideration of characteristics that may occur when the display panel is driven. Improvements of the sub-pixels according to the embodiment will be hereinafter with reference to FIGS. 16 to 18 and 20 .

In the sub-pixel according to the embodiment, the positions of the first transistor T1 and the second transistor T2 are swapped in consideration of the circuit configuration and operation characteristics, and the data line DL1 and the first power line ( EVDD) provides a structure that can be arranged separately. According to the embodiment, it is possible to optimize the layout in a limited space while separately disposing the data line DL1 and the first power line EVDD. It was found that the sub-pixel according to the embodiment can solve the increase in the density of electrodes comprising the semiconductor layer and the source-drain layer, and as a result, it is also possible to solve the difficulty of sub-pixel layout for high-resolution application.

16 is a voltage/current value comparison waveform diagram of an organic light emitting diode for comparing driving characteristics between Experimental Example and Example, and FIG. 17 is a threshold voltage sensing value of a driving transistor for comparing driving characteristics between Experimental Example and Example. It is a comparative waveform diagram, and FIG. 18 is a waveform diagram for comparing the luminance change according to the threshold voltage deviation for comparing driving characteristics between the experimental example and the embodiment, and FIGS. 19 and 20 are to explain the biggest difference between the experimental example and the embodiment drawings for

In FIG. 16 , Vdata(V) is a data voltage applied to a display panel manufactured based on Experimental Examples and Examples, and Ioled is a driving current of the organic light emitting diode based on the data voltage described above. As can be seen from FIG. 16 , the driving ability of the organic light emitting diode according to the applied data voltage was almost similar to the experimental example and the example.

In FIG. 17 , Vdata(V) is a data voltage applied to a display panel manufactured based on the experimental examples and embodiments, and the Vth sensing voltage (V) is the threshold voltage sensing of the driving transistor based on the data voltage described above. is the value As can be seen from FIG. 17 , the threshold voltage compensation capability of the driving transistor according to the applied data voltage was almost similar to the experimental example and the example, or the example was found to be somewhat superior.

In FIG. 18 , ΔVth voltage (V) is the threshold voltage deviation of the driving transistor, and ΔIoled is the driving current deviation of the organic light emitting diode according to the threshold voltage deviation of the driving transistor. As can be seen from FIG. 18 , the threshold voltage sensitivity of the driving transistor was lower in the Example than in the Experimental Example. That is, the embodiment means that the luminance change according to the threshold voltage deviation of the driving transistor occurs less than the experimental example. Therefore, the embodiment has a robust characteristic to the threshold voltage deviation of the driving transistor compared to the experimental example.

19 is a view for explaining the results of forming an experimental example on a first substrate made of polyimide (PI) and evaluating driving characteristics and compensation characteristics. 20 is a view for explaining the result of forming the embodiment on a first substrate made of polyimide (PI) and evaluating driving characteristics and compensation characteristics.

In the driving transistor of the experimental example, an electric field (E-Field) is formed only on one side as shown in FIG. 19 during all sections, such as the light emission section and the threshold voltage sensing section. That is, in the driving transistor, an electric field in a single direction is applied to the source electrode and the drain electrode during one frame, and an electric field in a single direction is applied in all frames.

As such, in the experimental example, as a unidirectional electric field is continuously formed (the electric field is formed only in the source to drain direction of the driving transistor), polarization (problem due to charge accumulation) occurs in the first substrate made of polyimide. . In addition, in the experimental example, it was found that an afterimage may appear on the display panel due to variations in the driving characteristics of the driving transistor due to the influence of polarization.

In the driving transistor of the embodiment, an electric field (E-Field) is formed in the first direction (source to drain direction of the driving transistor) during the light emission period as shown in FIG. An electric field (D-Field) is formed in the second direction (drain to source direction of the driving transistor). That is, in the driving transistor, an electric field alternating in the first direction and the second direction is applied from the source electrode and the drain electrode during one frame, and an electric field alternating in both directions is applied in all frames.

As described above, in the embodiment, as an electric field is formed in the first direction and in the second direction opposite to the first direction (the electric field is formed in the source-drain direction and the drain-to-source direction of the driving transistor), the first substrate made of polyimide material It has been shown to suppress the polarization that may occur in In addition, it was found that the variation in driving characteristics of the driving transistor is alleviated by the influence of the polarization suppression, thereby reducing the level of afterimages on the display panel. That is, even if the elements of the display panel deteriorate due to the lapse of time, the ability to keep the display quality constant is improved.

As described above, according to the present invention, the level of occurrence of an afterimage on the display panel can be reduced by using a compensation method capable of alleviating fluctuations in the driving transistor even when deterioration occurs due to the lapse of time, thereby maintaining the display quality constant. In addition, the present invention has the effect of resolving the increase in the density of electrodes to enable a sub-pixel layout suitable for high-resolution application.

Although the embodiments of the present invention have been described above with reference to the accompanying drawings, the technical configuration of the present invention can be changed to other specific forms by those skilled in the art to which the present invention pertains without changing the technical spirit or essential features of the present invention. It will be appreciated that this may be practiced. Therefore, it should be understood that the embodiments described above are illustrative in all respects and not restrictive. In addition, the scope of the present invention is indicated by the following claims rather than the above detailed description. In addition, all changes or modifications derived from the meaning and scope of the claims and their equivalents should be construed as being included in the scope of the present invention.

T1: Initialization period T2: Threshold voltage sensing period
T3: holding period T4: light emission period
T1: first transistor T2: second transistor
T3: third transistor T4: fourth transistor
T5: fifth transistor T6: sixth transistor
DT: driving transistor Cst: capacitor
OLED: organic light emitting diode

Claims (13)

A sub-pixel comprising: a light emitting diode that emits light; and a driving transistor that provides a driving current for the operation of the light emitting diode;
In the driving transistor, an electric field in a first direction is formed during a first period, and an electric field in a second direction opposite to the first direction is formed during a second period,
The sub-pixel is
a first transistor connected to the source electrode of the driving transistor;
As the second transistor connected to the drain electrode of the driving transistor is simultaneously turned on, an electric field alternating in the first direction and the second direction is applied to the source electrode and the drain electrode for one frame. According to claim 1,
The first section is a section in which the light emitting diode emits light,
The second section is a section for sensing a threshold voltage of the driving transistor. 3. The method of claim 2,
During the first period, an electric field is formed in a direction from the source to the drain of the driving transistor,
An electric field is formed in a direction from a drain to a source of the driving transistor during the second period. According to claim 1,
The driving transistor is
An electric field alternating in the first direction and the second direction is applied to the source electrode and the drain electrode during one frame. delete According to claim 1,
The sub-pixel is
the driving transistor having a gate electrode connected to a first node, a first electrode connected to a second node, and a second electrode connected to a third node;
a capacitor having one end connected to the first power line and the other end connected to the first node;
the light emitting diode having a cathode electrode connected to a second power line;
a first transistor having a gate electrode connected to the Nth scan line, a first electrode connected to the first node, and a second electrode connected to the second node;
a second transistor having a gate electrode connected to the Nth scan line, a first electrode connected to a data line, and a second electrode connected to the third node;
a third transistor having a gate electrode connected to the Nth emission control line, a first electrode connected to the first power line, and a second electrode connected to the second node;
a fourth transistor having a gate electrode connected to the Nth emission control line, a first electrode connected to the third node, and a second electrode connected to an anode electrode of the light emitting diode;
a fifth transistor having a gate electrode connected to an N-1th scan line, a first electrode connected to an initialization voltage line, and a second electrode connected to the first node;
and a sixth transistor having a gate electrode connected to the Nth scan line, a first electrode connected to the initialization voltage line, and a second electrode connected to an anode electrode of the light emitting diode. A driving method of an electroluminescent display device comprising: a light emitting diode that emits light; and a sub-pixel having a driving transistor that provides a driving current for the operation of the light emitting diode;
forming an electric field in a first direction in the driving transistor during a first period; and
Forming an electric field in a second direction opposite to the first direction in the driving transistor during a second period,
In the forming of the electric field in the second direction, the first transistor connected to the source electrode of the driving transistor and the second transistor connected to the drain electrode of the driving transistor are simultaneously turned on to form an electric field in the second direction A method of driving a light emitting display device. 8. The method of claim 7,
The first section is a section in which the light emitting diode emits light,
The second section is a section for sensing a threshold voltage of the driving transistor. 8. The method of claim 7,
During the first period, an electric field is formed in a direction from the source to the drain of the driving transistor,
During the second period, an electric field is formed in a direction from a drain to a source of the driving transistor. 8. The method of claim 7,
The driving transistor is
A method of driving an electroluminescent display device in which an electric field alternating in the first direction and the second direction is applied to the source electrode and the drain electrode during one frame. A sub-pixel comprising: a light emitting diode that emits light; and a driving transistor that provides a driving current for the operation of the light emitting diode;
In the driving transistor, an electric field in a first direction is formed during a first period, and an electric field in a second direction opposite to the first direction is formed during a second period,
The sub-pixel is
the driving transistor having a gate electrode connected to a first node, a first electrode connected to a second node, and a second electrode connected to a third node;
A capacitor having one end connected to the first power line and the other end connected to the first node;
the light emitting diode having a cathode electrode connected to a second power line;
a first transistor having a gate electrode connected to the Nth scan line, a first electrode connected to the first node, and a second electrode connected to the second node;
a second transistor having a gate electrode connected to the Nth scan line, a first electrode connected to a data line, and a second electrode connected to the third node;
a third transistor having a gate electrode connected to the Nth emission control line, a first electrode connected to the first power line, and a second electrode connected to the second node;
a fourth transistor having a gate electrode connected to the Nth emission control line, a first electrode connected to the third node, and a second electrode connected to the anode electrode of the light emitting diode;
a fifth transistor having a gate electrode connected to an N-1th scan line, a first electrode connected to an initialization voltage line, and a second electrode connected to the first node;
and a sixth transistor having a gate electrode connected to the Nth scan line, a first electrode connected to the initialization voltage line, and a second electrode connected to an anode electrode of the light emitting diode. a driving transistor having a gate electrode connected to a first node, a first electrode connected to a second node, and a second electrode connected to a third node;
A capacitor having one end connected to the first power line and the other end connected to the first node;
a light emitting diode having a cathode electrode connected to the second power line;
a first transistor having a gate electrode connected to the Nth scan line, a first electrode connected to the first node, and a second electrode connected to the second node, and
a second transistor having a gate electrode connected to the N-th scan line, a first electrode connected to a data line, and a second electrode connected to the third node,
In the driving transistor, an electric field in a first direction is formed during a first period and an electric field in a second direction opposite to the first direction is formed during a second period. 13. The method of claim 12,
a third transistor having a gate electrode connected to the Nth emission control line, a first electrode connected to the first power line, and a second electrode connected to the second node;
a fourth transistor having a gate electrode connected to the Nth emission control line, a first electrode connected to the third node, and a second electrode connected to the anode electrode of the light emitting diode;
a fifth transistor having a gate electrode connected to an N-1th scan line, a first electrode connected to an initialization voltage line, and a second electrode connected to the first node;
and a sixth transistor having a gate electrode connected to the Nth scan line, a first electrode connected to the initialization voltage line, and a second electrode connected to an anode electrode of the light emitting diode.

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