KR101560417B1 - Organic Light Emitting Diode Display And Driving Method Thereof - Google Patents

Abstract

The present invention relates to an organic light emitting diode (OLED) display device and a driving method thereof that can reduce image sticking due to deterioration of an organic light emitting diode.

The organic light emitting diode display device includes an organic light emitting diode (OLED), a driving TFT for controlling a driving current flowing through the organic light emitting diode, and a plurality of data lines A display panel including a plurality of pixels each having a source follower TFT connected between the organic light emitting diodes; A memory for storing sensing data; A timing controller for determining a compensation value for compensating for a deterioration deviation of the organic light emitting diode based on the sensing data, and for modulating input digital video data with reference to the compensation value; And a data driving circuit for converting the anode voltage of the organic light emitting diode sensed through the source follower TFT during the compensation driving into the sensing data, converting the modulated digital video data to a data voltage, Respectively.

Description

[0001] The present invention relates to an organic light emitting diode (OLED) display device,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic light emitting diode display, and more particularly, to an organic light emitting diode (OLED) display device and a driving method thereof that can reduce image sticking due to deterioration of an organic light emitting diode.

2. Description of the Related Art In recent years, an organic light emitting diode display device that has been spotlighted as a display device has advantages of high response speed, high luminous efficiency, high brightness, and a wide viewing angle by using a self-luminous element that emits light by itself.

The organic light emitting diode display device has an organic light emitting diode as shown in FIG. The organic light emitting diode has organic compound layers (HIL, HTL, EML, ETL, EIL) formed between the anode electrode and the cathode electrode.

The organic compound layer includes a hole injection layer (HIL), a hole transport layer (HTL), an emission layer (EML), an electron transport layer (ETL), and an electron injection layer EIL). When a driving voltage is applied to the anode electrode and the cathode electrode, holes passing through the HTL and electrons passing through the ETL are transferred to the EML to form excitons, Thereby generating visible light.

The organic light emitting diode display device arranges the pixels including the organic light emitting diode in a matrix form and controls the brightness of the pixels selected by the scan pulse according to the gray level of the video data.

2 shows one pixel equivalently in an organic light emitting diode display. 2, the pixel of the active matrix type organic light emitting diode display device includes an organic light emitting diode OLED, a data line DL and a gate line GL intersecting with each other, a switch TFT SW, a driving TFT DT ), And a storage capacitor (Cst). The switch TFT (SW) and the drive TFT (DT) are implemented as a P-type MOS-FET.

The switch TFT SW is turned on in response to a scan pulse from the gate line GL, thereby making the current path between the source electrode and the drain electrode conductive. The switch TFT SW applies a data voltage from the data line DL to the gate electrode of the drive TFT DT and the storage capacitor Cst during the turn-on period. The driving TFT DT controls the current flowing in the organic light emitting diode OLED according to the difference voltage Vgs between its gate electrode and the source electrode. The storage capacitor Cst keeps the gate potential of the driving TFT DT constant for one frame. The organic light emitting diode OLED has a structure as shown in FIG. 1 and is connected between the drain electrode of the driving TFT DT and the low potential voltage source VSS.

Generally, the non-uniformity of luminance between pixels in an organic light emitting diode display device is caused by various causes, for example, electric characteristic deviation of a driving TFT, variation of a high potential driving voltage according to a display position, and deterioration of an organic light emitting diode. Particularly, the deterioration of the organic light emitting diode occurs because the deterioration rate of the organic light emitting diode varies for each pixel for a long period of time. When this deteriorates, an image sticking phenomenon occurs and the image quality deteriorates as a result.

In order to compensate for the deterioration of the organic light emitting diode, an external compensation technique and an internal compensation technique are known.

The external compensation technique places a current source outside the pixel, applies a constant current to the organic light emitting diode through the current source, measures a voltage corresponding thereto, and compensates for the deterioration of the organic light emitting diode. However, since this technique requires a current to flow through the data line between the current source and the organic light emitting diode to charge the parasitic capacitor of the data line, it is possible to sense the anode voltage of the organic light emitting diode so that the sensing speed is very slow and the sensing time is long Loses. As a result, it is difficult to sense the anode voltage of the organic light emitting diode at the time between adjacent frames, or when the display device is turned on / off.

The internal compensation technique connects a coupling capacitor between the anode of the organic light emitting diode and the gate of the driving TFT to automatically reflect the degree of deterioration of the organic light emitting diode to the current flowing through the organic light emitting diode. However, this technique changes the magnitude of the current according to the turn-on voltage of the organic light emitting diode due to the current equation of the driving TFT, so that it is difficult to accurately compensate and requires a complicated pixel structure. It is not necessary to compensate for the deterioration deviation of the organic light emitting diode in real time while complicating the pixel structure because the degradation speed of the organic light emitting diode is slow.

Accordingly, it is an object of the present invention to provide an organic light emitting diode display device and a method of driving the same, which can improve the accuracy of compensation for the deterioration of an organic light emitting diode and reduce the time required for compensation.

According to an aspect of the present invention, there is provided an organic light emitting diode (OLED) display device including a plurality of gate lines and a plurality of data lines, the OLED display including a plurality of organic light emitting diodes A display panel including a plurality of pixels each having a driving TFT for controlling a driving current flowing therethrough and a source follower TFT connected between the data line and the organic light emitting diode; A memory for storing sensing data; A timing controller for determining a compensation value for compensating for a deterioration deviation of the organic light emitting diode based on the sensing data, and for modulating input digital video data with reference to the compensation value; And a data driving circuit for converting the anode voltage of the organic light emitting diode sensed through the source follower TFT during the compensation driving into the sensing data, converting the modulated digital video data to a data voltage, Respectively.

Wherein the sensing data includes first sensing data and second data; The data driving circuit converts a first sensing voltage, which is an anode voltage of the organic light emitting diode sensed first through the source follower TFT, into the first sensing data, Converting a second sensing voltage, which is an anode voltage of the diode, into the second sensing data; The timing controller determines the compensation value based on the difference between the first and second sensing data.

Wherein the data driving circuit comprises: an ADC for converting the first and second sensing voltages into the first and second sensing data; A plurality of DACs for converting the modulated digital video data into a data voltage; And first and second sensing voltages, which are connected in a one-to-one manner to the data line and the DAC and are commonly connected to the ADC and apply a reference current to the data line and the pixel and are fed back through the data line, And a plurality of sensing & output units for supplying data voltages from the DAC to the data lines.

The sensing & output unit includes: an OP-AMP having a first input, a second input, and an output coupled selectively to the ADC and the data line; A reference current source for generating the reference current; A first switch for switching between the first input terminal and the DAC; A second switch for switching between the output terminal and the data line; A third switch for switching between the reference current source and the data line; A fourth switch for switching between the first input terminal and the data line; And a fifth switch for switching between the output terminal and the ADC.

The gate line unit includes a scan pulse supply line to which a scan pulse is applied, an emission pulse supply line to which an emission pulse is applied, and a sensing pulse supply line to which a sensing pulse is applied.

The pixel includes a driving TFT connected between a high potential source and the organic light emitting diode and controlling an amount of current flowing to the organic light emitting diode according to a voltage applied between the high potential source and the first node; A source follower TFT connected between the data line and the organic light emitting diode and adapted to follow its source voltage to an anode voltage of the organic light emitting diode applied to its gate electrode; A first switch TFT connected between the first node and the drive TFT, the first switch TFT being switched in response to the scan pulse; A second switch TFT connected between the data line and a second node, the second switch TFT being switched in response to the scan pulse; A third switch TFT connected between the reference voltage source and the second node, the third switch TFT being switched in response to the emission pulse; A fourth switch TFT connected between the driving TFT and the organic light emitting diode and being switched in response to the emission pulse; And a fifth switch TFT connected between the data line and the source follower TFT and switched in response to the sensing pulse.

Wherein the compensating drive comprises: a first period for applying a programming data voltage to the pixel; A second period for precharging the data line with a precharge data voltage; A third period for supplying the reference current to the source follower TFT by charging the data line with the reference current; And a fourth period for sensing the first and second sensing voltages through the source follower TFT.

The data driving circuit further comprises a sixth switch for selectively connecting the driving TFT to a high potential voltage source and a ground voltage source; The first sensing voltage is sensed while the driving TFT is connected to the base voltage source during the fourth period; And the second sensing voltage is sensed while the driving TFT is connected to the high potential voltage source during the fourth period.

The first sensing voltage is sensed while the fourth switch TFT is turned off during the fourth period; During the fourth period, the second sensing voltage is sensed while the fourth switch TFT is turned on.

A method of driving an organic light emitting diode display device including a plurality of pixels each having an organic light emitting diode and connected to a data line according to an embodiment of the present invention includes the steps of driving a source follower TFT connected between the data line and the organic light emitting diode (A) converting an anode voltage of the sensed organic light emitting diode into sensing data; (B) determining a compensation value for compensating for a deterioration deviation of the organic light emitting diode based on the sensing data, and modulating input digital video data with reference to the compensation value; And a step (C) of converting the modulated digital video data into a data voltage and supplying the data voltage to the pixel.

The organic light emitting diode display device and the driving method thereof according to the present invention are characterized in that the anode voltage of the organic light emitting diode is sensed twice using the source follower TFT and the sensed result value The compensation of the deterioration of the organic light emitting diode can be compensated for, so that the accuracy of the compensation can be greatly increased. In addition, since the data line is pre-charged with the pre-charge voltage prior to sensing, the time required for compensation can be greatly reduced.

Hereinafter, preferred embodiments of the present invention will be described with reference to FIGS. 3 to 16B.

FIG. 3 is a block diagram showing an organic light emitting diode display device according to an embodiment of the present invention, and FIG. 4 shows an internal structure of a timing controller and a data driving circuit.

3 and 4, an OLED display according to an exemplary embodiment of the present invention includes a display panel 10 on which pixels P are formed, a data driving circuit 12 for driving the data lines 14, A timing controller 11 for controlling the driving timings of the data driving circuit 12 and the gate driving circuit 13 and a timing controller 11 for controlling the driving timing of the data driving circuit 12 and the gate driving circuit 13, 16).

In the display panel 10, m (m is a positive integer) data lines 14 and n (n is a positive integer) gate line portions 15 are intersected with each other, and m × n pixels (P) are arranged in a matrix form. The gate line unit 15 includes a scan pulse supply line 15a, an emission pulse supply line 15b, and a sensing pulse supply line 15c. Each pixel P is connected to the data driving circuit 12 through the data line 14 and to the gate driving circuit 13 through the gate line portion 15. [ Each pixel P is commonly supplied with a high potential driving voltage Vdd, a ground voltage Gnd, and a reference voltage Vref. The high potential driving voltage Vdd is generated by the high potential voltage source, the ground potential Gnd is generated by the base voltage source, and the reference voltage Vref is generated by the reference voltage source. The reference voltage Vref is set to a voltage level between the base low voltage Gnd and the high potential driving voltage Vdd, preferably lower than the threshold voltage of the organic light emitting diode. Each pixel P includes an organic light emitting diode, a driving TFT, a source follower TFT, and a plurality of switch TFTs.

The timing controller 11 includes a data processing circuit 111 and a control signal generating circuit 112.

The data processing circuit 111 generates programming data (Data_PG) and precharge data (Data_PC) for compensation driving and supplies them to the data driving circuit 12. The programming data (Data_PG) means data previously programmed so that the driving current flowing to the organic light emitting diode (OLED) of the pixels (P) during the compensation driving becomes constant. The precharge data Data_PC means data predetermined to shorten the charge settling time for the data line 14 in the compensation driving. The data processing circuit 111 refers to the sensing data SD1 and SD2 stored in the memory 16 to determine a compensation value for compensating for the deterioration of the organic light emitting diode for each pixel, Modulates the digital video data (RGB) input from the input device (not shown) to generate digital modulated data R'G'B '. Then, the data processing circuit 111 supplies the digital modulated data (R'G'B ') to the data driving circuit 12 for normal driving.

The control signal generating circuit 112 generates a control signal based on the timing signals such as the vertical synchronization signal Vsync, the horizontal synchronization signal Hsync, the dot clock signal DCLK, and the data enable signal DE input from the system board A data control signal DDC and switch control signals? 1 to? 3 for controlling the operation timing of the data driving circuit 12 and a gate control signal GDC for controlling the operation timing of the gate driving circuit 13, .

The data driving circuit 12 converts the programming data Data_PG to the programming data voltage and the precharge data Data_PC to the precharge data voltage under the control of the timing controller 11 during the compensation driving, Supply. Subsequently, the first sensing voltage SD1 fed back from each pixel P is converted into a second sensing data SD2, and the second sensing voltage SD2 fed back from each pixel P is converted into a second sensing data SD2. And supplies the first and second sensing data SD1 and SD2 to the memory 16. [ The data driving circuit 12 converts the digital modulated data R'G'B 'into a video data voltage (hereinafter, referred to as a data voltage) under the control of the timing controller 11 during normal driving, . To this end, the data driving circuit 12 includes an analog-to-digital converter (ADC) 121, a plurality of digital-to-analog converters (DAC) 122, And a sensing &

The sensing and outputting sections 123 are connected to the data lines 14 in a one-to-one manner and are operated in response to the switch control signals? 1 to? 3 from the timing controller 11, And supplies the reference voltage Iref to the data line P and outputs the first and second sensing voltages fed back through the data line 14 to the ADC 121 and the data voltage from the DAC 122 to the data line 14. [ (14).

The ADC 121 is commonly connected to the sensing & The ADC 121 converts the first and second sensing voltages from the respective sensing and output sections 123 into first and second sensing data SD1 and SD2, respectively. The ADC 121 may be implemented by a known Pipe-Line type, SAR type, Single-Slope type, or the like.

The DACs 122 are connected to the sensing and outputting units 123 on a one-to-one basis, respectively, and convert digital modulated data R'G'B 'input under the control of the timing controller 11 into data voltages.

The gate driver circuit 13 includes a shift register and a level shifter and generates a scan pulse SCAN, a sensing pulse SEN and an emission pulse EM under the control of the timing controller 11. [ The scan pulse SCAN is applied to the scan pulse supply line 15a and the emission pulse EM is applied to the emission pulse supply line 15b and the sensing pulse SEN is supplied to the sensing pulse supply line 15c . The shift register array constituting the gate drive circuit 13 can be formed directly on the display panel 10 by a GIP (Gate In Panel) method.

The memory 16 stores at least one or more lookup tables and stores first and second sensing data SD1 and SD2 for each pixel P input from the data driving circuit 12. [

5 shows the sensing & output unit 123 of FIG. 4 in detail.

Referring to FIG. 5, the sensing and output unit 123 includes an operational amplifier (hereinafter referred to as "OP-AMP"), a reference current source IREF, and a plurality of switches SW1 to SW5. The switches SW1 to SW5 may be implemented as N-type MOSFETs.

OP-AMP has a first input terminal (+), a second input terminal (-), and an output terminal. The OP-AMP functions as an output buffer between the DAC 122 and the data line 14 or between the data line 14 and the ADC 121 by way of the switching action of the switches SW1 to SW5, .

The reference current source IREF generates a reference current Iref to charge the data line 14 and flows the reference current Iref to the source follower TFT of the pixel P. [

The first switch SW1 is connected between the first input terminal (+) of the OP-AMP and the DAC 122, and is switched in response to the first switch control signal? 1. The second switch SW2 is connected between the output terminal of the OP-AMP and the data line 14 and is switched in response to the first switch control signal? 1. The third switch SW3 is connected between the reference current source IREF and the data line 14 and is switched in response to the second switch control signal? 2. The fourth switch SW4 is connected between the first input terminal (+) of the OP-AMP and the data line 14, and is switched in response to the second switch control signal? 2. The fifth switch SW5 is connected between the output terminal of the OP-AMP and the ADC 121, and is switched in response to the third switch control signal? 3.

Fig. 6 shows the pixel P shown in Fig. 3 in detail.

6, the pixel P includes an organic light emitting diode (OLED), a driving TFT DT, a source follower TFT (SFT), a plurality of switch TFTs ST1 to ST5, and a storage capacitor Cst do. The driver TFT (DT), the source follower TFT (SFT), and the switch TFTs (ST1 to ST5) may be implemented as a P-type MOSFET.

The organic light emitting diode OLED has an anode electrode connected to the third node N3 and a cathode electrode connected to the ground voltage source GND. The organic light emitting diode OLED emits light by a current flowing between the high potential source VDD and the ground voltage source GND.

The driving TFT DT is connected between the high potential voltage source VDD and the third node N3 and has a source-gate voltage of its own, that is, a voltage applied between the high potential source VDD and the first node N1 The amount of current flowing through the organic light emitting diode OLED is controlled.

The source follower TFT (SFT) has a gate electrode connected to the third node N3, a source electrode connected to the data line 14 through the fifth switch TFT ST5, and a drain electrode connected to the reference voltage source VREF Respectively. In the source follower TFT (SFT), when the reference current flows from the source electrode to the drain electrode, the potential of the source electrode follows the potential of the gate electrode. 7, the voltage Vsf applied to the source electrode of the source follower TFT SFT is the voltage across the gate electrode of the source follower TFT SFT, that is, the anode voltage Vanode of the organic light emitting diode OLED, And has a linear proportional relationship. The anode voltage (Vanode) of the organic light emitting diode OLED is lower than the leakage current of the fifth switch TFT SW because the data line 14 and the third node N3 are electrically insulated by the source follower TFT (SFT) It is not affected. Accordingly, when the source follower TFT (SFT) is used, the anode voltage (Vanode) of the organic light emitting diode (OLED) can be accurately sensed.

The first switch TFT ST1 is connected between the first node N1 and the driver TFT DT and is switched in response to the scan pulse SCAN from the scan pulse supply line 15a. The second switch TFT ST2 is connected between the data line 14 and the second node N2 and is switched in response to the scan pulse SCAN from the scan pulse supply line 15a. The third switch TFT ST3 is connected between the reference voltage source VREF and the second node N2 and is switched in response to the emission pulse EM from the emission pulse supply line 15b. The fourth switch TFT (ST4) is connected between the driver TFT (DT) and the third node (N3) and is switched in response to the emission pulse EM from the emission pulse supply line 15b. The fifth switch TFT (ST5) is connected between the data line 14 and the source electrode of the source follower TFT (SFT), and is switched in response to the sensing pulse SEN from the sensing pulse supply line 15c.

The storage capacitor Cst is connected between the first node N1 and the second node N2.

Such organic light emitting diode display devices are largely operated by compensation driving and normal driving. The normal driving designates driving for realizing a display image in a state where the deterioration deviation of the organic light emitting diode is compensated through data modulation. The compensation driving is a drive for sensing the anode voltage of the organic light emitting diode OLED in order to determine the degree of deterioration of the organic light emitting diode OLED. In order to improve the accuracy of sensing, the anode voltage of the organic light emitting diode OLED (P). The compensation drive may be performed for at least one frame synchronized with the on timing of the drive power supply, or for all the pixels P during at least one frame in synchronism with the off timing of the drive power supply. In addition, the compensation driving can be performed for the pixels P for one horizontal line per blank period between adjacent frames in the course of normal driving.

Hereinafter, the circuit operation in the compensation driving and the circuit operation in the normal driving will be sequentially described. One example of the compensating drive can be proposed in Figs. 8 to 11, and another example of the compensating driving can be proposed in Figs. 12 to 14. Fig. The normal driving can be proposed through Figs. 15 to 16B.

FIG. 8 is a waveform diagram of control signals applied for the compensation driving according to the first embodiment, and FIGS. 9A to 9E sequentially show the operation states of the display device at the time of the compensation operation.

8, the compensation driving includes a first period CT1 for applying a programming data voltage Vdata_PG to the pixel P so that a driving current flowing through the organic light emitting diode OLED is kept constant, A third period CT2 for charging the data line 14 with the reference current Iref and a reference current Iref flowing through the source follower TFT SFT during a second period CT2 for precharging the data line 14 with Vdata_PC, (CT4) in which the anode voltage of the organic light emitting diode (OLED) is sensed twice through the source follower TFT (CT3) and the source follower TFT (SFT), and first and second sensing voltages of different levels are generated .

8 and 9A, during the first period CT1, the first switch control signal? 1 is generated at the turn-on level, and the first and second switches SW1 and SW2 in the data driving circuit 12 Turn on. The second and third switch control signals? 2 and? 3 are generated at the turn-off level to turn off the third to fifth switches SW3 to SW5 in the data driving circuit 12. The scan pulse SCAN is generated at the low logic level L during the first period CT1 to turn on the first and second switch TFTs ST1 and ST2 of the pixel P. [ And the emission pulse EM and the sensing pulse SEN are generated at the high logic level H to turn off the third to fifth switch TFTs ST3 to ST5 of the pixel P. [

As a result, the programming data voltage Vdata_PG supplied from the DAC 122 is applied to the second node N2 of the pixel P, and the first node N1 of the pixel P is supplied with the programming data voltage Vdata_PG The voltage X1 obtained by subtracting the threshold voltage of the driving TFT DT from the high-potential driving voltage is applied by the diode connection.

8 and 9B, the switch control signals? 1,? 2 and? 3 during the second period CT2 are maintained at the same level as the first period CT1 so that the first and second switches SW1, SW2 are continuously turned on and the third to fifth switches SW3 to SW5 are continuously turned off. The scan pulse SCAN is inverted to the high logic level H to turn off the first and second switch TFTs ST1 and ST2 during the second period CT2 and the emission pulse EM is turned to the low logic level L to turn on the third and fourth switch TFTs ST3 and ST4 and the sensing pulse SEN is held at the high logic level H to turn off the fifth switch TFT ST5 .

As a result, the data line 14 is precharged to the precharge data voltage Vdata_PC supplied from the DAC 122, and the potential of the second node N2 is switched from the programming data voltage Vdata_PG to the reference voltage Vref . The potential variation of the second node N2 is directly reflected to the first node N1 by the boosting effect of the storage capacitor Cst. The potential of the first node N1 is set to the voltage X2 at the voltage X1. On the other hand, the precharge data voltage Vdata_PC may be supplied by an external power source connected to the data line 14 via a switch, instead of being supplied from the DAC 122. [

Referring to FIGS. 8 and 9C, during the third period CT3, the first switch control signal? 1 is inverted to the turn-off level to turn off the first and second switches SW1 and SW2, The control signal? 2 is inverted to the turn-on level to turn on the third and fourth switches SW3 and SW4. Then, the third switch control signal? 3 is maintained at the turn-off level to turn off the fifth switch SW5. During the third period CT3, the scan pulse SCAN is maintained at the high logic level H to turn off the first and second switch TFTs ST1 and ST2, and the emission pulse EM is turned to the low logic The third and fourth switch TFTs ST3 and ST4 are kept turned on and the sensing pulse SEN is inverted to the low logic level L to turn the fifth switch TFT ST5 Turn on.

As a result, the parasitic capacitors of the data line 14 are charged by the reference current Iref supplied from the reference current source IREF. At this time, since the parasitic capacitors of the data line 14 are precharged with the precharge data voltage Vdata_PC during the second period CT2, the charge settling time becomes very short even if the low reference current Iref is applied . When the charging to the data line 14 is completed, the reference current Iref flows through the source follower TFT (SFT) of the pixel P.

8 and 9D, during the fourth period CT4, the first and second switch control signals phi 1 and phi 2 are maintained the same as the third period CT3, and the first and second switches SW1 , SW2, and the third and fourth switches SW3, SW4 are continuously turned on. Then, the third switch control signal? 3 is inverted to the turn-on level to turn on the fifth switch SW5. During this fourth period CT4, the fifth switch SW5 of the sensing & output units 123 of Fig. 4 responds to the third switch control signals? 3 (1) to? 3 (m) And are sequentially turned on. During the fourth period CT4, the scan pulse SCAN is maintained at the high logic level H to turn off the first and second switch TFTs ST1 and ST2, and the emission pulse EM is turned to the low logic The third and fourth switch TFTs ST3 and ST4 are kept turned on and the sensing pulse SEN is held at the low logic level L to continue the fifth switch TFT ST5 And turn on.

As a result, the reference current Iref continues to flow through the source follower TFT (SFT) of the pixel P. [ At this time, when the base voltage source (GND) is connected to the driving TFT (DT) through a switching operation or the like as shown in Fig. 10, the voltage applied to the third node N3 is lowered to the base voltage. The sixth switch SW6 in Fig. 10 may be formed in the data driving circuit 12. Fig. The voltage of the third node N3, that is, the anode voltage of the organic light emitting diode OLED, is read out as the first sensing voltage Vout1 together with the voltage drop due to the parasitic components as shown in Equation 1 below. The first sensing voltage Vout1 is converted to the first sensing data SD1 through the ADC 121. [

In the formula (1), "Vsg" represents the source-gate voltage of the source follower TFT (SFT), and Iref ( _Rst5 + R _DL ) represents the voltage drop amount by the fifth switch TFT Respectively.

8 and 9E, in a state in which the reference current Iref continues to flow through the source follower TFT (SFT) of the pixel P during the fourth period CT4, When the high potential source VDD is connected to the driving TFT DT and the driving current Ioled flowing through the organic light emitting diode OLED is maximized through the third node N3, Is read out as the second sensing voltage Vout2 together with the voltage drop due to the parasitic components as shown in the following equation (2): " (2) " The second sensing voltage Vout2 is converted to the second sensing data SD2 through the ADC 121. [

In order to remove the voltage drop due to the parasitic components, the first sensing voltage Vout1 should be subtracted from the second sensing voltage Vout2 as shown in Equation 3 below.

The calculation of the equation (3) is performed in the data processing circuit 111 of the timing controller 11. [ The data processing circuit 111 removes the influence of the parasitic components by subtracting the first sensing data SD1 from the second sensing data SD2. The data processing circuit 111 judges that the degree of deterioration of the organic light emitting diode OLED is getting worse as the calculated value becomes larger (Vanode ---> Vanode ') as shown in FIG. 11 and the deterioration of the organic light emitting diode OLED Thereby increasing the compensation value for compensation.

FIG. 12 is a waveform diagram of control signals applied for the compensation driving according to the second embodiment, and FIGS. 13A to 13E sequentially show the operation states of the display device at the time of the compensation operation.

12, the compensation driving includes a first period DT1 for applying the programming data voltage Vdata_PG to the pixel P so that the driving current flowing through the organic light emitting diode OLED is kept constant, A second period DT2 in which the data line 14 is precharged with the reference current Iref and the reference current Iref is supplied to the source follower TFT SFT by charging the data line 14 with the reference current Iref, A fourth period DT4 in which the anode voltage of the organic light emitting diode OLED is sensed twice through the source follower TFT SFT and the first and second sensing voltages of different levels are generated .

Referring to Figs. 13A to 13C together with Fig. 12, the first period DT1 to the third period DT3 in the compensating driving according to the second embodiment correspond to the first Is substantially the same as the period (CT1) to the third period (CT3). 13A to 13C are denoted by the same reference numerals as those in Figs. 9A to 9C, respectively, and a detailed description thereof will be omitted.

12 and 13D, during the fourth period DT4, the first and second switch control signals? 1 and? 2 are maintained at the same level as the third period DT3, so that the first and second switches SW1, and SW2 are turned off, and the third and fourth switches SW3 and SW4 are continuously turned on. Then, the third switch control signal? 3 is inverted to the turn-on level to turn on the fifth switch SW5. During this fourth period DT4, the fifth switch SW5 of the sensing & output units 123 of Fig. 4 is turned on to turn on the third switch control signals phi 3 (1) to phi 3 (m) And turns on sequentially in response. During the fourth period DT4, the scan pulse SCAN is maintained at the high logic level H to turn off the first and second switch TFTs ST1 and ST2, The third and fourth switch TFTs ST3 and ST4 are turned off and the sensing pulse SEN is held at the low logic level L so that the fifth switch TFT ST5 continues to be turned Turn on.

As a result, the reference current Iref continues to flow through the source follower TFT (SFT) of the pixel P, and the voltage applied to the third node N3 flows through the organic And is lowered to the threshold voltage of the light emitting diode OLED. The voltage of the third node N3, that is, the anode voltage of the organic light emitting diode OLED, is read as the first sensing voltage Vout1 together with the voltage drop due to the parasitic components as shown in Equation (4) below. The first sensing voltage Vout1 is converted to the first sensing data SD1 through the ADC 121. [

In the formula (1), "Vsg" represents the source-gate voltage of the source follower TFT (SFT), and Iref ( _Rst5 + R _DL ) represents the voltage drop amount by the fifth switch TFT Quot; Vtho "represents the threshold voltage of the organic light emitting diode (OLED), respectively.

12 and 13E, in a state in which the reference current Iref continues to flow through the source follower TFT (SFT) of the pixel P during the fourth period DT4, When the TFT ST4 is turned on and the driving current Ioled flowing through the organic light emitting diode OLED is maximized, the voltage of the third node N3, that is, the anode voltage Vanode of the organic light emitting diode OLED, The second sensing voltage Vout2 is read together with the voltage drop due to the parasitic components as shown in Equation (2). The second sensing voltage Vout2 is converted to the second sensing data SD2 through the ADC 121. [

In order to remove the voltage drop due to the parasitic components, the first sensing voltage Vout1 should be subtracted from the second sensing voltage Vout2 as shown in Equation 6 below.

The above calculation is performed in the data processing circuit 111 of the timing controller 11. [ The data processing circuit 111 removes the influence of the parasitic components by subtracting the first sensing data SD1 from the second sensing data SD2. The data processing circuit 111 determines that the degree of deterioration of the organic light emitting diode (OLED) is getting worse as the calculation value becomes larger ((Vanode-Vtho) ---> (Vanode'-Vtho ')) Thereby increasing the compensation value for compensating the deterioration of the organic light emitting diode (OLED).

FIG. 15 is a waveform diagram of control signals applied for normal driving, and FIGS. 16A and 16B sequentially show operation states of the display device at the time of normal driving. The normal driving progresses in a first period ET1 for compensating the driving TFT deterioration deviation and the high potential driving voltage deviation and in a second period ET2 for light emission.

15 and 16A, during the first period ET1, the first switch control signal? 1 is generated at the turn-on level, and the first and second switches SW1 and SW2 in the data driving circuit 12 Turn on. The second and third switch control signals? 2 and? 3 are generated at the turn-off level to turn off the third to fifth switches SW3 to SW5 in the data driving circuit 12. During the first period ET1, the scan pulse SCAN is generated at the low logic level L to turn on the first and second switch TFTs ST1 and ST2 of the pixel P, Is generated at a high logic level (H) to turn off the third and fourth switch TFTs (ST3 and ST4) of the pixel P and the sensing pulse SEN is generated at the high logic level (H) ) Of the fifth switch TFT (ST5).

As a result, the data voltage Vdata supplied from the DAC 122 is applied to the second node N2 of the pixel P, and the first node N1 of the pixel P is supplied with a voltage An intermediate compensation value (Vdd-Vth) obtained by subtracting the threshold voltage of the driving TFT (DT) from the high-potential driving voltage by a connection (Diode-Connection) is applied. The storage capacitor Cst holds the potential of the first node N1 at the intermediate compensation value Vdd-Vth and the potential at the second node N2 at the data voltage Vdata. Here, a compensation value for eliminating the deterioration of the organic light emitting diode (OLED) is reflected in the data voltage (Vdata).

16 and 17B, during the second period DT2, the first to third switch control signals? 1 to? 3 are maintained at the same level as the first period DT1, so that the first and second switches SW1 and SW2 are continuously turned on and the third to fifth switches SW3 to SW5 are continuously turned off. The scan pulse SCAN is inverted to the high logic level H to turn off the first and second switch TFTs ST1 and ST2 during the second period DT2 and the emission pulse EM is turned to the low logic level L and the third and fourth switch TFTs ST3 and ST4 are turned on and the sensing pulse SEN is maintained at the high logic level H to turn on the fifth switch TFT ST5 of the pixel P And then turns off continuously.

As a result, the reference voltage Vref is applied to the second node N2 of the pixel P and the potential of the second node N2 changes from the data voltage Vdata to the reference voltage Vref. The potential variation (Vdata-Vref) of the second node N2 is directly reflected to the first node N1 by the boosting effect of the storage capacitor Cst. The potential of the first node N1 is set to the final compensation value {(Vdd-Vth) - (Vdata-Vref)} obtained by subtracting the potential variation (Vdata-Vref) of the second node from the intermediate compensation value (Vdd-Vth) . At this time, the driving current Ioled flowing through the organic light emitting diode OLED is expressed by the following equation (3).

In Equation 7, "k" represents a constant determined by mobility, parasitic capacitance, and channel size, and "Vsg" represents a source-gate voltage of the driving TFT DT.

The driving current Ioled according to the present invention depends on the data voltage Vdata and the reference voltage Vref that can be controlled by the user and can be controlled by the threshold voltage of the driving TFT DT Vth and the high-level driving voltage Vdd applied to the driving TFT DT. This means that the deviation between the deterioration deviation of the driving TFT DT and the high potential driving voltage Vdd is internally compensated.

As described above, in the organic light emitting diode display device and the driving method thereof according to the present invention, the anode voltage of the organic light emitting diode is sensed twice using the source follower TFT, and the deterioration of the organic light emitting diode The accuracy of the compensation can be greatly increased. In addition, since the data line is pre-charged with the pre-charge voltage prior to sensing, the time required for compensation can be greatly reduced.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit of the 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 defined by the claims.

1 is a view showing the principle of light emission of a general organic light emitting diode display device.

FIG. 2 is an equivalent view of one pixel in a conventional 2T1C structure organic light emitting diode display. FIG.

3 is a view illustrating an organic light emitting diode display device according to an embodiment of the present invention.

FIG. 4 is a diagram showing an internal configuration of the data driving circuit and the timing controller of FIG. 3. FIG.

5 is a detailed view of the sensing &

FIG. 6 is a view showing the pixel of FIG. 3;

7 is a view showing input / output characteristics of a source follower TFT.

8 is a diagram showing waveforms of control signals applied for compensating driving according to the first embodiment;

9A to 9E are diagrams sequentially showing operation states of a display device at the time of a compensation operation.

10 is a view showing an example in which a high potential voltage source and a ground voltage source are selectively connected to a driving TFT;

11 is a view showing an example in which the calculated value changes according to the degree of deterioration of the organic light emitting diode.

12 is a view showing waveforms of control signals applied for compensation driving according to the second embodiment;

13A to 13E are diagrams sequentially showing operation states of a display device at the time of a compensation operation.

14 is a view showing another example in which the calculated value is changed according to the degree of deterioration of the organic light emitting diode.

15 shows waveforms of control signals applied for normal driving;

16A and 16B are diagrams sequentially showing the operation states of the display device at the time of normal driving;

Description of the Related Art

10: Display panel 11: Timing controller

12: data driving circuit 13: gate driving circuit

14: Data line 15: Gate line part

16: memory 111: data processing circuit

121: ADC 122: DAC

123: sensing & output section

Claims (12)

A plurality of gate lines and a plurality of data lines arranged in a matrix form at intersections of the plurality of gate lines and the plurality of data lines, the organic light emitting diodes, the driving TFTs controlling the driving current flowing through the organic light emitting diodes, A display panel including a plurality of pixels each having a source follower TFT having a source electrode connected to the data line through a fifth switch TFT, and a drain electrode connected to a reference voltage source; A memory for storing sensing data; A timing controller for determining a compensation value for compensating for a deterioration deviation of the organic light emitting diode based on the sensing data, and for modulating input digital video data with reference to the compensation value; And A data driving circuit for converting the anode voltage of the organic light emitting diode sensed through the source follower TFT during the compensation driving into the sensing data and for converting the modulated digital video data into a data voltage during normal driving, And an organic light emitting diode (OLED) display device. The method according to claim 1, Wherein the sensing data includes first sensing data and second sensing data; The data driving circuit converts a first sensing voltage, which is an anode voltage of the organic light emitting diode sensed first through the source follower TFT, into the first sensing data when a base voltage source is connected to a source electrode of the driving TFT Converts a second sensing voltage, which is an anode voltage of the organic light emitting diode sensed through the source follower TFT, to the second sensing data when a high potential source is connected to the source electrode of the driving TFT; Wherein the timing controller determines the compensation value based on the difference between the first and second sensing data. 3. The method of claim 2, The data driving circuit includes: An ADC converting the first and second sensing voltages into the first and second sensing data; A plurality of DACs for converting the modulated digital video data into a data voltage; And One of the first and second sensing voltages is connected to the data line and the DAC and is commonly connected to the ADC and applies the reference current to the data line and the pixel and supplies the first and second sensing voltages fed back through the data line to the ADC And a plurality of sensing & output units for supplying data voltages from the DAC to the data lines. The method of claim 3, The sensing & An OP-AMP having a first input, a second input, and an output connected selectively to the ADC and the data line; A reference current source for generating the reference current; A first switch for switching between the first input terminal and the DAC; A second switch for switching between the output terminal and the data line; A third switch for switching between the reference current source and the data line; A fourth switch for switching between the first input terminal and the data line; And And a fifth switch for switching between the output terminal and the ADC. 5. The method of claim 4, Wherein the gate line unit comprises a scan pulse supply line to which a scan pulse is applied, an emission pulse supply line to which an emission pulse is applied, and a sensing pulse supply line to which a sensing pulse is applied. 6. The method of claim 5, The pixel includes: A driving TFT connected between the high potential source and the organic light emitting diode and adjusting an amount of current flowing to the organic light emitting diode according to a voltage between the high potential source and the first node; A source follower TFT connected between the data line and the organic light emitting diode and adapted to follow its source voltage to an anode voltage of the organic light emitting diode applied to its gate electrode; A first switch TFT connected between the first node and the drive TFT, the first switch TFT being switched in response to the scan pulse; A second switch TFT connected between the data line and a second node, the second switch TFT being switched in response to the scan pulse; A third switch TFT connected between the reference voltage source and the second node, the third switch TFT being switched in response to the emission pulse; A fourth switch TFT connected between the driving TFT and the organic light emitting diode and being switched in response to the emission pulse; And And the fifth switch TFT connected between the data line and the source follower TFT and being switched in response to the sensing pulse. The method according to claim 6, Wherein the compensation drive comprises: A first period for applying a programming data voltage to the pixel; A second period for precharging the data line with a precharge data voltage; A third period for supplying the reference current to the source follower TFT by charging the data line with the reference current; And And a fourth period for sensing the first and second sensing voltages through the source follower TFT. 8. The method of claim 7, The data driving circuit further comprises a sixth switch for selectively connecting the driving TFT to a high potential voltage source and a ground voltage source; The first sensing voltage is sensed while the driving TFT is connected to the base voltage source during the fourth period; And the second sensing voltage is sensed while the driving TFT is connected to the high potential voltage source during the fourth period. 8. The method of claim 7, The first sensing voltage is sensed while the fourth switch TFT is turned off during the fourth period; And the second sensing voltage is sensed while the fourth switch TFT is turned on during the fourth period. A method of driving an organic light emitting diode display device including a plurality of pixels each having an organic light emitting diode and connected to a data line, A gate electrode connected to an anode electrode of the organic light emitting diode, a source electrode connected to the data line through a fifth switch TFT, and a drain electrode connected to a reference voltage source, (A) converting the anode voltage of the diode into sensing data; (B) determining a compensation value for compensating for a deterioration deviation of the organic light emitting diode based on the sensing data, and modulating input digital video data with reference to the compensation value; And And converting the modulated digital video data into a data voltage and supplying the converted data voltage to the pixel (C). 11. The method of claim 10, Wherein the sensing data includes first sensing data and second sensing data; In the step (A), when the base voltage source is connected to the source electrode of the driving TFT, the first sensing voltage, which is the anode voltage of the organic light emitting diode sensed first through the source follower TFT, is converted into the first sensing data Converts a second sensing voltage, which is an anode voltage of the organic light emitting diode sensed through the source follower TFT, to the second sensing data when a high potential source is connected to the source electrode of the driving TFT; Wherein the step (B) determines the compensation value based on the difference between the first and second sensing data. 12. The method of claim 11, The step (A) A first step of applying a programming data voltage to the pixel; A second step of precharging the data line with a precharge data voltage; A third step of supplying the reference current to the source follower TFT by charging the data line with a reference current; And And a fourth step of sensing the first and second sensing voltages through the source follower TFT.

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