Display drive systems

• US 8,427,512 B2
• Filed: 08/30/2007
• Issued: 04/23/2013
• Est. Priority Date: 08/31/2006
• Status: Expired due to Fees

• Current Assignee: Cambridge Display Technology Limited (Sumitomo Chemical Company Limited)
• Original Assignee: Cambridge Display Technology Limited (Sumitomo Chemical Company Limited)
• Inventors: Smith, Euan
• Primary Examiner(s): Dharia, Prabodh M
• Application Number:
  US12/439,162
• Publication Number:
  US 20100026725A1
• Time in Patent Office: 2,063 Days
• Field of Search: 345 76- 98, 345204-214, 345/690, 313/500, 257/10, 257/E27.133, 257/E51.018, 257/98, 257/565
• 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 controlling a drive to a pixel of an OLED display having a test pixel and display pixels, the method comprising determining a drive current for the pixel to be controlled by first calculating a value of η

/η

₀ using;

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

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

4. A method as claimed in claim 1 comprising measuring V_now^other for a plurality of pixels of said display and calculating an average from said measured plurality of voltage drops for use in said determining of the value of η

/η

₀.

5. A method as claimed in claim 1 comprising measuring V_now^other for a plurality of pixels of said display, wherein said controlling comprises determining respective values for η

₀/η

for said plurality of pixels, and using the respective ones of said values η

₀/η

for compensating a drive for respective ones of said plurality of pixels.

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

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

8. A method as claimed in claim 7 wherein said test pixel is selected from the 20% of pixels of said display having least aging.

9. A method as claimed in claim 8 wherein said test pixel comprises a substantially least aged pixel of said display.

10. A method as claimed in claim 7 further comprising measuring a time for which said test pixel is on at greater than threshold drive level;

and wherein said determining of said value η

₀/η

comprises compensating for temperature using said measured on-time.

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

12. An active matrix OLED display having a test pixel and display pixels, the display comprising:

a display controller configured to determine a drive current for a pixel of an OLED display, the pixel to be controlled by first calculating a value of η

/η

₀ using;

13. An active matrix OLED display as claimed in claim 12 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.

14. An active matrix OLED display as claimed in claim 13 wherein said second electrode line comprises a positive supply line and wherein said transistor is controlled on by pulling said control connection low.