Display Drive Systems

• US 20100026725A1
• Filed: 08/30/2007
• Published: 02/04/2010
• Est. Priority Date: 08/31/2006
• Status: Active Grant

• Current Assignee: Cambridge Display Technology Limited (Sumitomo Chemical Company Limited)
• Original Assignee: Cambridge Display Technology Limited (Sumitomo Chemical Company Limited)
• Inventors: Smith, Euan
• Granted Patent: US 8,427,512 B2
• Time in Patent Office: Days
• US Class Current: 345/690
• CPC Class Codes: G09G 2300/0842 forming a memory circuit, e.g. a dynamic memory with one capacitor
• 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 2320/043 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 2320/048 using evaluation of the usage time
• CPC Class Codes: G09G 3/3216 using a passive matrix
• CPC Class Codes: G09G 3/3233 with pixel circuitry controlling the current through the light-emitting element
• CPC Class Codes: G09G 3/3241 the current through the light-emitting element being set using a data current provided by the data driver, e.g. by using a two-transistor current mirror

Abstract

This invention generally relates to methods, apparatus and computer program code for improved OLED (organic light emitting diode) display drive systems, in particular to compensate for burn-in.

A method of compensating an OLED display device for burn-in of pixels of the OLED display, the method comprising: measuring a first voltage drop across at least one test pixel of the display; measuring a second voltage drop across at least one other pixel of the display; determining, from said first and second voltages and a from value (V₁) representing a drive voltage increase for a loss in efficiency of said display due to burn-in, an estimated reduction in efficiency of said display due to burn-in; and compensating a drive to said display using said estimated efficiency reduction.

Claims

1. A method of compensating an OLED display device for burn-in of pixels of the OLED display, the method comprising:

measuring a first voltage drop across at least one test pixel of the display;

measuring a second voltage drop across at least one other pixel of the display;

determining, from said first and second voltages and a from value (V₁) representing a drive voltage increase for a loss in efficiency of said display due to burn-in, an estimated reduction in efficiency of said display due to burn-in; and

compensating a drive to said display using said estimated efficiency reduction.

2. A method as claimed in claim 1 wherein said value (V₁) representing said loss in efficiency of said display comprises a stored value representing an increase in a pixel drive voltage needed to compensate for a defined level of efficiency reduction, and wherein said determining comprises determining said reduction in efficiency using a relationship dependent on said defined level of efficiency reduction.

3. A method as claimed in claim 1 wherein said measuring of said first and second voltage drops is performed at switch-on of said display.

4. A method as claimed in claim 1, wherein said compensating comprises increasing a drive current to a pixel of said display by a factor dependent upon an inverse of said estimated efficiency reduction.

5. A method as claimed in claim 1 comprising measuring said second voltage drop for a plurality of pixels of said display and calculating an average from said measured second voltage drops for use in said determining of said efficiency reduction.

6. A method as claimed in claim 1 comprising measuring said second voltage drop for a plurality of pixels of said display, wherein said determining of said efficiency reduction comprises determining a plurality of efficiency reduction values for said plurality of pixels, and wherein said compensating uses respective ones of said efficiency values for compensating a drive for respective ones of said plurality of pixels.

7. A method as claimed in claim 1 wherein said test pixel comprises a pixel of the display which is not used for displaying information.

8. A method as claimed in claim 1 wherein said test pixel comprises a pixel in a region of said display used for displaying information.

9. A method as claimed in claim 8 wherein said test pixel is selected from the 20% of pixels of said display having least aging.

10. A method as claimed in claim 9 wherein said test pixel comprises a substantially least aged pixel of said display.

11. A method as claimed in claim 8 further comprising measuring a time for which said test pixel is on at greater than threshold drive level;

and wherein said determining of said estimated efficiency reduction comprises compensating for temperature using said measured on-time.

12. A method as claimed in claim 1 comprising measuring said first voltage drop for a plurality of pixels of said display and calculating an average from said measured first voltage drops for use in said determining of said efficiency reduction.

13. A method as claimed in claim 1 comprising measuring said first voltage drop for a plurality of pixels of said display, wherein said determining of said efficiency reduction comprises determining a plurality of efficiency reduction values for said plurality of pixels, and wherein said compensating uses respective ones of said efficiency values for compensating pixel drives to different respective regions of said display.

15. A carrier carrying processor control code for implementing the method of claim 1.

18. An active matrix OLED display pixel driver circuit for use with the method of claim 1, said pixel driver circuit including a transistor having an input connection coupled to an OLED device of the pixel for measuring a voltage across said OLED device, an output coupled to a first electrode line of said display and a control connection coupled to a second electrode line of said display.

19. An active matrix OLED display pixel driver circuit as claimed in claim 18 wherein for a pixel driver circuit in a row or column of said display said second electrode line comprises a power supply line of an adjacent row or column of said display.

20. An active matrix OLED display pixel driver circuit as claimed in claim 19 wherein said second electrode line comprises a positive supply line and wherein said transistor is controlled on by pulling said control connection low.

23. An active matrix OLED display pixel driver circuit as claimed in claim 18 wherein for a pixel driver circuit in a row or column of said display said second electrode line comprises a power supply line of an adjacent row or column of said display.

24. An active matrix OLED display pixel driver circuit as claimed in claim 23 wherein said second electrode line comprises a positive supply line and wherein said transistor is controlled on by pulling said control connection low.

14. A method of controlling a drive to a pixel of an OLED display, the method comprising determining a drive voltage, V, for said pixel using:

$V=V_0+\frac{1}{1-\mathrm{\alpha <br><br>}}<br><br>V_1<br><br>\left(1-\frac{\mathrm{\eta <br><br>}}{{\mathrm{\eta <br><br>}}_0}\right)$

where V₀ and η

₀ are a voltage drive to said pixel at a test drive current and a luminance efficiency of said pixel at said test drive current at an initial time; and

V₁ is an end of life voltage increase in said voltage drive for said test drive current; and

wherein said end of life is defined as a point at which an efficiency, η

, of said pixel has fallen to a of an initial efficiency value (η

₀) at said initial time.

21. A carrier carrying processor control code for implementing the method of claim 14.

22. An active matrix OLED display pixel driver circuit for use with the display driver of claim 14, said pixel driver circuit including a transistor having an input connection coupled to an OLED device of the pixel for measuring a voltage across said OLED device, an output coupled to a first electrode line of said display and a control connection coupled to a second electrode line of said display.

16. An OLED display driver, the display driver comprising:

an input for measuring a first voltage drop across at least one test pixel of the display;

an input for measuring a second voltage drop across at least one other pixel of the display;

a store storing a value (V₁) representing a drive voltage increase for a loss in efficiency of said display;

a system for determining an estimated reduction in efficiency of said display from said first and second voltages and said value (V₁) representing said drive voltage increase for a loss in efficiency of said display; and

a system for compensating a drive to said display using said estimated efficiency reduction.

17. A combination of the OLED display driver of claim 16 and an active matrix OLED display, wherein said active matrix OLED display is configured for measuring a voltage across an OLED device of a pixel of said display.