Emission control in aged active matrix OLED display using voltage ratio or current ratio with temperature compensation

• US 8,077,123 B2
• Filed: 03/18/2008
• Issued: 12/13/2011
• Est. Priority Date: 03/20/2007
• Status: Expired due to Fees

• Current Assignee: Siliconfile Technologies Incorporated (SK Hynix Inc.)
• Original Assignee: Leadin Technology Co., Ltd.
• Inventors: Naugler, Walter Edward Jr.
• Primary Examiner(s): Lao, Lun-Yi
• Assistant Examiner(s): Abebe, Sosina
• Application Number:
  US12/050,700
• Publication Number:
  US 20080231558A1
• Time in Patent Office: 1,365 Days
• Field of Search: 345 76- 83, 315/169.3
• US Class Current: 345/76
• CPC Class Codes: G09G 2320/0276 for the purpose of adaptation to the characteristics of a display device, i.e. gamma correction
• CPC Class Codes: G09G 2320/029 by monitoring one or more pixels in the display panel, e.g. by monitoring a fixed reference pixel
• CPC Class Codes: G09G 2320/041 Temperature compensation
• CPC Class Codes: G09G 2320/043 Preventing or counteracting the effects of ageing
• CPC Class Codes: G09G 2320/045 Compensation of drifts in the characteristics of light emitting or modulating elements
• CPC Class Codes: G09G 3/2003 Display of colours specific for liquid crystal displays G09G3/3607
• CPC Class Codes: G09G 3/3233 with pixel circuitry controlling the current through the light-emitting element

Abstract

Compensation needed to be made for reduced light efficiency in aged sub-pixels of an active matrix organic light-emitting diode (OLED) display are determined using a current ratio or a voltage ratio pertaining to an aged sub-pixel relative to un-aged, reference sub-pixels. When the current through the sub-pixels or the voltage across the sub-pixels are measured to determine the age of the sub-pixels, correction is made to the measured current or voltage to account for variations in the ambient temperature in which the OLED display is placed.

Claims

1. A method of determining compensation needed for reduced light efficiency in aged sub-pixels of an active matrix organic light-emitting diode (OLED) display, the method comprising:

applying a predetermined voltage across one or more of reference sub-pixels that are not aged and determining a first current through said one or more of the reference sub-pixels;

determining a current difference between the first current and a reference current, the reference current corresponding to current of said one or more of the reference sub-pixels with the predetermined voltage applied to said one or more of the reference sub-pixels at an initial timing, and the current difference being indicative of the change in current of said one or more of the reference sub-pixels due to change in ambient temperature in which the active matrix OLED display is placed;

applying the predetermined voltage across an aged sub-pixel and determining a second current through said aged sub-pixel;

subtracting the current difference from the second current to obtain a third current, the third correct corresponding to the second current with correction for the change in ambient temperature;

determining an age of the aged sub-pixel based on the third current relative to the reference current;

selecting one of a plurality of age curve look-up tables to use for correction of digital numbers indicative of desired brightness in said aged sub-pixel based upon the determined age of said aged sub-pixel, each of the plurality of age curve look-up tables corresponding to a different age of the aged sub-pixel and mapping the digital numbers to said corrections to be made to the digital numbers for the corresponding age of the aged sub-pixel and one or more of the aged sub-pixels of the OLED display being assigned to use said one of the age curve look-up tables for correction of the digital numbers.

2. The method of claim 1, wherein the active matrix OLED display includes a plurality of sections of sub-pixels, the sections including at least a first section including the aged sub-pixels and a second section including the reference sub-pixels that are not aged, and determining the first current includes measuring the first current through two or more of the reference sub-pixels and averaging the measured first current.

3. The method of claim 1, wherein each of the sub-pixels of the active matrix OLED display includes a thin film transistor configured to drive an OLED of the sub-pixel, and current through the aged sub-pixel or the reference sub-pixel is measured with the thin film transistor biased in linear mode.

4. The method of claim 1, wherein the age of said aged sub-pixel is determined based on a current ratio of the third current to the reference current, the current ratio being less than one and being smaller as the sub-pixels have longer effective age.

5. The method of claim 1, wherein the age of said aged sub-pixel is determined based on a difference between the third current and the reference current.

6. A method of determining compensation needed for reduced light efficiency in aged sub-pixels of an active matrix organic light-emitting diode (OLED) display, the method comprising:

forcing a predetermined current through one or more of reference sub-pixels that are not aged and determining a first voltage across said one or more of the reference sub-pixels;

determining a voltage difference between the first voltage and a reference voltage, the reference voltage corresponding to voltage across said one or more of the reference sub-pixels with the predetermined current flow through said one or more of the reference sub-pixels at an initial timing, and the voltage difference being indicative of the change in voltage across said one or more of the reference sub-pixels due to change in ambient temperature in which the active matrix OLED display is placed;

forcing the predetermined current through an aged sub-pixel and determining a second voltage across said aged sub-pixel;

subtracting the voltage difference from the second voltage to obtain a third voltage, the third voltage corresponding to the second voltage with correction for the change in ambient temperature;

determining an age of the aged sub-pixel based on the third voltage relative to the reference voltage;

selecting one of a plurality of age curve look-up tables to use for correction of digital numbers indicative of desired brightness in said aged sub-pixel based upon the determined age of said aged sub-pixel, each of the plurality of age curve look-up tables corresponding to a different age of the aged sub-pixel and mapping the digital numbers to said corrections to be made to the digital numbers for the corresponding age of the aged sub-pixel and one or more of the aged sub-pixels of the OLED display being assigned to use said one of the age curve look-up tables for correction of the digital numbers.

7. The method of claim 6, wherein the active matrix OLED display includes a plurality of sections of sub-pixels, the sections including at least a first section including the aged sub-pixels and a second section including the reference sub-pixels that are not aged, and determining the first voltage includes measuring the first voltage across two or more of the reference sub-pixels and averaging the measured first voltage.

8. The method of claim 6, wherein each of the sub-pixels of the active matrix OLED display includes a thin film transistor configured to drive an OLED of the sub-pixel, and voltage across the aged sub-pixel or the reference sub-pixel is measured with the thin film transistor biased in linear mode.

9. The method of claim 6, wherein the age of said aged sub-pixel is determined based on a voltage ratio of the third voltage to the reference voltage current, the voltage ratio being greater than one and being greater as the sub-pixels have longer effective age.

10. The method of claim 6, wherein the age of said aged sub-pixel is determined based on a difference between the third voltage and the reference voltage.

11. An active matrix organic light-emitting diode (OLED) display comprising:

a plurality of OLED elements arranged in a plurality of rows and a plurality of columns, each of the OLED elements corresponding to a sub-pixel of the OLED display; and

an active matrix drive circuit configured to drive current through the OLED elements, the active matrix drive circuit including;

a plurality of age curve look-up tables each corresponding to a different age of aged sub-pixels of the OLED display and mapping digital numbers to corrections to be made to the digital numbers for the corresponding age of the aged sub-pixel, one or more of the aged sub-pixels of the OLED display being assigned to use said one of the age curve look-up tables for correction of the digital numbers; and

a calibration circuit configured to;

apply a predetermined voltage across one or more of reference sub-pixels that are not aged and determine a first current through said one or more of the reference sub-pixels;

determine a current difference between the first current and a reference current, the reference current corresponding to current of said one or more of the reference sub-pixels with the predetermined voltage applied to said one or more of the reference sub-pixels at an initial timing, and the current difference indicative of the change in current of said one or more of the reference sub-pixels due to change in ambient temperature in which the active matrix OLED display is placed;

apply the predetermined voltage across an aged sub-pixel and determining a second current through said aged sub-pixel;

subtract the current difference from the second current to obtain a third current, the third correct corresponding to the second current with correction for the change in ambient temperature;

determine an age of the aged sub-pixel based on the third current relative to the reference current; and

select one of said plurality of age curve look-up tables to use for correction of digital numbers indicative of desired brightness in said aged sub-pixel based upon the determined age of said aged sub-pixel.

12. The active matrix OLED display of claim 11, wherein each of the sub-pixels of the active matrix OLED display include a thin film transistor configured to drive an OLED of the sub-pixel, and current through the aged sub-pixel or the reference sub-pixel is measured with the thin film transistor biased in linear mode.

13. The active matrix OLED display of claim 11, wherein the age of said aged sub-pixel is determined based on a current ratio of the third current to the reference current, the current ratio being less than one and being smaller as the sub-pixels have longer effective age.

14. The active matrix OLED display of claim 11, wherein the age of said aged sub-pixel is determined based on a difference between the third current and the reference current.

15. An active matrix organic light-emitting diode (OLED) display comprising:

a plurality of OLED elements arranged in a plurality of rows and a plurality of columns, each of the OLED elements corresponding to a sub-pixel of the OLED display; and

an active matrix drive circuit configured to drive current through the OLED elements, the active matrix drive circuit including;

a plurality of age curve look-up tables each corresponding to a different age of aged sub-pixels of the OLED display and mapping digital numbers to corrections to be made to the digital numbers for the corresponding age of the aged sub-pixel, one or more of the aged sub-pixels of the OLED display being assigned to use said one of the age curve look-up tables for correction of the digital numbers; and

a calibration circuit configured to;

force a predetermined current through one or more of reference sub-pixels that are not aged and determine a first voltage across said one or more of the reference sub-pixels;

determine a voltage difference between the first voltage and a reference voltage, the reference voltage corresponding to voltage across said one or more of the reference sub-pixels with the predetermined current flow through said one or more of the reference sub-pixels at an initial timing, and the voltage difference indicative of the change in voltage across said one or more of the reference sub-pixels due to change in ambient temperature in which the active matrix OLED display is placed;

force the predetermined current through an aged sub-pixel and determine a second voltage across said aged sub-pixel;

subtract the voltage difference from the second voltage to obtain a third voltage, the third voltage corresponding to the second voltage with correction for the change in ambient temperature;

determine an age of the aged sub-pixel based on the third voltage relative to the reference voltage; and

select one of a plurality of age curve look-up tables to use for correction of digital numbers indicative of desired brightness in said aged sub-pixel based upon the determined age of said aged sub-pixel.

16. The active matrix OLED display of claim 15, wherein each of the sub-pixels of the active matrix OLED display includes a thin film transistor configured to drive an OLED of the sub-pixel, and voltage across the aged sub-pixel or the reference sub-pixel is measured with the thin film transistor biased in linear mode.

17. The active matrix OLED display of claim 15, wherein the age of said aged sub-pixel is determined based on a voltage ratio of the third voltage to the reference voltage, the voltage ratio being greater than one and being greater as the sub-pixels have longer effective age.

18. The active matrix OLED display of claim 15, wherein the age of said aged sub-pixel is determined based on a difference between the third voltage and the reference voltage.