ORGANIC LIGHT EMITTING DISPLAY AND METHOD OF DRIVING THE SAME

• US 20090027377A1
• Filed: 05/06/2008
• Published: 01/29/2009
• Est. Priority Date: 07/27/2007
• Status: Active Grant

• Current Assignee: Samsung Display Company Limited (Samsung Electronics Co. Ltd.)
• Original Assignee: Samsung Display Company Limited (Samsung Electronics Co. Ltd.)
• Inventors: Kwon, Oh-Kyong
• Granted Patent: US 8,274,503 B2
• Time in Patent Office: Days
• US Class Current: 345/214
• CPC Class Codes: G09G 2300/0819 used for counteracting undesired variations, e.g. feedback or autozeroing
• CPC Class Codes: G09G 2300/0842 forming a memory circuit, e.g. a dynamic memory with one capacitor
• CPC Class Codes: G09G 2320/0295 by monitoring each display pixel
• CPC Class Codes: G09G 2320/043 Preventing or counteracting the effects of ageing
• CPC Class Codes: G09G 3/3233 with pixel circuitry controlling the current through the light-emitting element
• CPC Class Codes: G09G 3/3291 in which the data driver supplies a variable data voltage for setting the current through, or the voltage across, the light-emitting elements

Abstract

An organic light emitting display includes: a sensing unit for extracting degradation information of an organic light emitting diode included in each of the pixels, and for transferring a first digital value and a second digital value corresponding to the extracted degradation information to a data driver; the data driver for generating data signals corresponding to second data supplied from a timing controller during a normal driving period; a first analog-digital converter for converting the voltage corresponding to the first digital value to a fourth digital value, and for converting the voltage corresponding to the second digital value to a fifth digital value; and the timing controller for storing the fourth digital value and the fifth digital value, and for changing first data supplied from an exterior in accordance with the fourth digital value and the fifth digital value to generate the second data.

Claims

1. An organic light emitting display comprising:

pixels at crossing regions of data lines, scan lines, feedback lines, control lines, and emission control lines, each of the pixels comprising an organic light emitting diode;

a scan driver for driving the scan lines and the emission control lines;

a control line driver for driving the control lines;

a sensing unit for supplying an electric current to the feedback lines during a sensing period to extract degradation information of the organic light emitting diode, and for outputting a first digital value and a second digital value corresponding to the extracted degradation information of the organic light emitting diode;

a data driver for supplying voltages corresponding to the first digital value and the second digital value to the pixels during the sensing period, and for generating data signals corresponding to second data during a normal driving period;

a first analog-digital converter for receiving and converting the voltage corresponding to the first digital value to a fourth digital value, and for receiving and converting the voltage corresponding to the second digital value to a fifth digital value; and

a timing controller for storing the fourth digital value and the fifth digital value, and for changing externally supplied first data in accordance with the fourth digital value and the fifth digital value to generate the second data.

2. The organic light emitting display as claimed in claim 1, wherein the data driver comprises:

a shift register unit comprising a plurality of shift registers configured to sequentially generate sampling signals;

a sampling latch unit comprising a plurality of sampling latches configured to sequentially store the second data corresponding to the sampling signals;

a holding latch unit comprising a plurality of holding latches configured to temporarily store the second data stored in the sampling latch unit;

a signal generator comprising a plurality of digital-analog converters configured to generate the data signal utilizing the second data stored in the holing latch unit; and

a buffer unit comprising a plurality of buffers configured to transfer the data signal to the data lines.

3. The organic light emitting display as claimed in claim 2, wherein the sensing unit comprises:

a plurality of current sources coupled to the feedback lines for supplying the electric current;

a second analog-digital converter coupled to the feedback lines for converting a voltage applied to the organic light emitting diode in a pixel among the plurality of pixels to a third digital value when the electric current is supplied; and

a look-up table for supplying the first digital value and the second digital value corresponding to the third digital value to a digital-analog converter coupled to the pixel among the plurality of digital-analog converters with an interval between the first digital value and the second digital value.

4. The organic light emitting display as claimed in claim 3, wherein a current value of each of the current source is between approximately 50 nA and approximately 50 μ

A.

5. The organic light emitting display as claimed in claim 3, wherein the first digital value and the second digital value have different voltage information.

6. The organic light emitting display as claimed in claim 5, wherein the first digital value comprises voltage information to be applied to an anode electrode of the organic light emitting diode to express luminance of a maximum gradation regardless of the degradation information of the organic light emitting diode.

7. The organic light emitting display as claimed in claim 5, wherein the second digital value comprises first voltage information or second voltage information, the first voltage information for generating one fourth luminance of luminance corresponding to the first digital value by the organic light emitting diode, and the second voltage information for generating luminance of a minimum gradation by the organic light emitting diode.

8. The organic light emitting display as claimed in claim 3, wherein the sensing unit comprises:

a fifth transistor between each of the current sources and each of the feedback lines, and being turned on during a first period of the sensing period;

a sixth transistor between the second analog-digital converter and each of the feedback lines, and being turned on during the first period of the sensing period; and

a seventh transistor between the look-up table and the digital-analog converter, and being turned on during a second period of the sensing period.

9. The organic light emitting display as claimed in claim 3, wherein the digital-analog converter sequentially converts the first digital value and the second digital value to analog voltages, and supplies the analog voltages to a buffer coupled to the specific pixel, during a second period of the sensing period.

10. The organic light emitting display as claimed in claim 9, wherein the buffer comprises an operational amplifier, and polarities of a first input terminal and a second input terminal of the operational amplifier are inverted.

11. The organic light emitting display as claimed in claim 10, further comprising:

an eighth transistor between the first input terminal of the operational amplifier and the digital-analog converter, and turned on during the second period of the sensing period;

a ninth transistor between the second input terminal of the operational amplifier and a corresponding feedback line among the feedback lines, and turned on during the second period of the sensing period; and

a tenth transistor between the second input terminal and an output terminal of the operational amplifier, and being turned on during the normal driving period.

12. The organic light emitting display as claimed in claim 9, wherein an output terminal voltage of the buffer is controlled so that a voltage of the second input terminal is increased to have the same value as the analog voltages corresponding to the first and second digital values when the analog voltages are inputted to the first input terminal during the second period of the sensing period.

13. The organic light emitting display as claimed in claim 12, wherein the first analog-digital converter converts a voltage applied to a gate electrode of a drive transistor in the pixel to the fourth digital value corresponding to the first digital value, and converts the voltage applied to the gate electrode of the drive transistor to the fifth digital value corresponding to the second digital value.

14. The organic light emitting display as claimed in claim 13, wherein the timing controller comprises:

a memory for storing the fourth digital value and the fifth digital value; and

a calculator for changing the externally supplied first data in accordance with the fourth and fifth digital values to generate the second data.

15. The organic light emitting display as claimed in claim 14, wherein the fourth and fifth digital values of all of the plurality of pixels are stored in the memory.

16. The organic light emitting display as claimed in claim 14, wherein the calculator is configured to extract the fourth digital value and the fifth digital value corresponding to the pixel from the memory when the first data to be supplied to the pixel is inputted, and changes the first data to generate the second data so that a degradation of the organic light emitting diode of the pixel, and a threshold voltage and mobility of the drive transistor in the pixel are compensated.

17. The organic light emitting display as claimed in claim 16, wherein the calculator is configured to extract the fourth and fifth digital values from the memory when the first data to be supplied to the pixel is inputted thereto, to subtract the fourth digital value from the fifth digital value to extract mobility information and degradation compensation information of the drive transistor of the pixel, multiply the fifth digital value by two, subtract the fourth digital value from the multiplied result, and subtract a digital value of a first power source from the subtraction result to thereby extract threshold voltage information of the drive transistor.

18. The organic light emitting display as claimed in claim 17, wherein the calculator is configured to multiply the mobility information and the degradation compensation information of the drive transistor by bit information of the first data, add the threshold voltage of the drive transistor to the multiplied result, and subtract the digital value of the first power source from the addition result, thereby generating the second data.

19. The organic light emitting display as claimed in claim 17, wherein each of the pixels further comprises:

a first transistor coupled to a corresponding scan line among the scan lines and a corresponding data line among the data lines, and configured to be turned on when a scan signal is supplied to the corresponding scan line;

a storage capacitor to be charged with a voltage corresponding to the data signal, wherein the drive transistor is configured to supply a current corresponding to the voltage stored in the storage capacitor from the first power source to a second power source through the organic light emitting diode;

a third transistor between the drive transistor and the organic light emitting diode, and configured to be turned off when an emission control signal is supplied the emission control lines; and

a fourth transistor between a corresponding feedback line among the feedback lines and an anode electrode of the organic light emitting diode, and configured to be turned on when a second control signal is supplied to the emission control lines.

20. The organic light emitting display as claimed in claim 19, wherein the fourth transistor is turned on during the sensing period, and the first transistor is turned off during a first period of the sensing period.

21. A method of driving an organic light emitting display, comprising:

supplying an electric current from a current source to an organic light emitting diode of a pixel;

converting a voltage applied to the organic light emitting diode to a third digital value corresponding to the electric current and applying the third digital value to a look-up table;

sequentially converting a first digital value and a second digital value corresponding to the third digital value from the look-up table to analog voltages, and transferring the analog voltages to the pixel;

converting a voltage applied to a gate electrode of a drive transistor of the pixel to a fourth digital value corresponding to the first digital value, and converting a voltage applied to the gate electrode of the driver transistor to a fifth digital value corresponding to the second digital value, and storing the fourth and fifth digital values; and

extracting the fourth and fifth digital values from the memory when first data to be supplied to the pixel is inputted, and generating second data to compensate for degradation of the organic light emitting diode, and a mobility and a threshold voltage of the drive transistor.

22. The method as claimed in claim 21, wherein a current value of the current source is between approximately 50 nA and approximately 50 μ

A.

23. The method as claimed in claim 21, wherein the first digital value is set to compensate for degradation of the organic light emitting diode corresponding to the third digital value.

24. The method as claimed in claim 23, wherein the first digital value comprises voltage information, which is applied to an anode electrode of the organic light emitting diode to express luminance of a maximum gradation regardless of the degradation of the organic light emitting diode.

25. The method as claimed in claim 23, wherein the second digital value comprises voltage information different from that of the first digital value.

26. The method as claimed in claim 25, wherein the second digital value comprises voltage information to generate one fourth luminance of luminance corresponding to the first digital value or to generate luminance of a minimum gradation by the organic light emitting diode.