Method and drive means for color correction in an organic electroluminescent device

• US 7,145,529 B2
• Filed: 08/22/2002
• Issued: 12/05/2006
• Est. Priority Date: 08/23/2001
• Status: Active Grant

• Current Assignee: Beijing Xiaomi Mobile Software Co., Ltd. (Xiaomi Corp.)
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Liedenbaum, Coen Theodorus Hubertus Fransiscus, Vulto, Simone Irene Elisabeth
• Primary Examiner(s): Hjerpe, Richard
• Assistant Examiner(s): Said, Mansour M.
• Application Number:
  US10/487,207
• Publication Number:
  US 20040239595A1
• Time in Patent Office: 1,566 Days
• Field of Search: 345 74- 78, 345/60, 345/80, 345 82- 84, 345/204, 345/206, 345/291
• US Class Current: 345/76
• CPC Class Codes: G09G 2320/0285 using tables for spatial correction of display data
• 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 2320/0666 for control of colour parameters, e.g. colour temperature
• CPC Class Codes: G09G 2320/0693 Calibration of display systems
• CPC Class Codes: G09G 3/14 Semiconductor devices, e.g. diodes
• CPC Class Codes: G09G 3/3208 organic, e.g. using organic light-emitting diodes [OLED]

Abstract

This invention relates to a method for color correction in an organic electroluminescent device (1), having at least one pixel (6), comprising an electro-luminescent material layer (5), which is sandwiched between a first and a second electrode (2, 3), and constituting at least a first and a second light-emitting element (6R,6G), wherein said method comprises the steps of: inputting a data signal (S) comprising information to be displayed by said light-emitting elements (6R,6G), generating, in a correction means (10), a correction factor for each light-emitting element (6R, 6G), said correction factor being based on a relationship between a color point wavelength shift (Δλ) and a measured shift in one of a voltage across at least one of said light-emitting elements (6R,6G) at a predetermined current (I_s) and a current through at least one of said light-emitting elements (6R,6G), at a predetermined voltage (V_s), applying said correction factor on said data signal (S), and supplying the corrected data signal (S) to the light-emitting elements (6R, 6G).

The invention also relates to a drive means implementing the above-described method.

Claims

1. A method for color correction in an organic electroluminescent device (1) having at least one pixel (6) comprising an electroluminescent material layer (5), which is sandwiched between a first and a second electrode (2, 3), the pixel constituting a first and a second light-emitting element (6R, 6G), wherein said method comprises the steps of:

inputting a data signal (S) comprising information to be displayed by said light-emitting elements (6R, 6G),

generating a correction factor for each light-emitting element (6R, 6G), said correction factors being based on;

(i) a measured shift in a voltage (V) across a light-emitting element (6R, 6G) at a predetermined current (I_s) through said light-emitting element, and a relation between the measured shift in the voltage and a color point wavelength shift Δ

λ

of said light-emitting element, or

(ii) a measured shift in a current (I) through a light-emitting element (6R, 6G) at a predetermined voltage (V_s) across said light-emitting element, and a relation between the measured shift in the current and a color point wavelength shift Δ

λ

of said light-emitting element,

applying said correction factor to said data signal (S); and

supplying the corrected data signal (S) to the light-emitting elements (6R, 6G).

2. A method as claimed in claim 1, wherein said correction means (10) comprise a look-up table containing pre-measured information regarding the relation between the voltage applied across a light-emitting element (6R or 6G), or current applied through said light-emitting element (6R or 6G), and the wavelength shift Δ

λ

of said light-emitting element.

3. A method as claimed in claim 1, further comprising the steps of feeding, with predetermined time intervals, one of said light-emitting elements (6R;

6G) with the predetermined current (I_s),

measuring the voltage (V) over the light-emitting element (6R;

6G) as the predetermined current (I_s) is fed through the light-emitting element (6R;

6G),

calculating a voltage shift Δ

V between said measured voltage (V) and a previous voltage (V₀) for the predetermined current (I_s), and

outputting a correction factor corresponding to a wavelength shift Δ

λ

of said light-emitting element (6R;

6G), based on said voltage shift Δ

V.

4. A method as claimed in claim 3, wherein the wavelength shift Δ

λ

for a light-emitting element (6R;

6G) is calculated by;

Δ

λ

=k·

Δ

V,

where k is a correction coefficient and wherein k is pre-stored for each light-emitting element (6R;

6G) or for each type of light-emitting element.

5. A method as claimed in claim 3, wherein said previous voltage V₀ is an initial voltage across said light-emitting element (6R;

6G), measured during manufacture of the device (1).

6. A method as claimed in claim 3, wherein said previous voltage V₀ is a voltage across said light-emitting element (6R;

6G), measured previously during the drive of the device.

7. A method as claimed in claim 1, comprising the steps of feeding, with predetermined time intervals, one of said light-emitting elements (6R;

6G) with a predetermined voltage (V_s),

measuring the current (I) through said light-emitting element (6R;

6G) as the predetermined voltage (V_s) is applied across the light-emitting element (6R;

6G),

calculating a current shift Δ

I between said measured current (I) and a previous current I_O,

outputting a correction factor corresponding to a wavelength shift Δ

λ

of said light-emitting element (6R;

6G), based on said current shift Δ

I.

8. A method as claimed in claim 7, wherein the wavelength shift Δ

λ

for said light-emitting element (6R;

6G)is calculated by;

Δ

λ

=k·

Δ

I

where k is a correction factor and wherein k is pre-stored in said correction means (10) for each light-emitting element (6R;

6G) or for each type of light-emitting element.

9. A method as claimed in claim 1, wherein said electroluminescent material layer (5) comprises a polymer light-emitting material, an organic light-emitting material, or a mixture of a polymer and an organic light-emitting material.

10. A method as claimed in claim 1, wherein said correction factor is arranged to provide a substantially constant total color point for the pixel, based on the light output from each of said light-emitting elements (6R, 6G).

11. A drive means (7) for an organic electroluminescent device (1), comprising a layer (5) of electroluminescent material which is sandwiched between a first and a second electrode pattern (2, 3), wherein said patterns define at least one pixel (6), comprising at least a first and a second light-emitting element (6R, 6G), said drive means (7) being connected to said electrodes (2, 3) and arranged to apply a current (I) through said electroluminescent material in order to achieve light emission from said material, said drive means (7) comprising:

an input connection (8) for inputting a data signal (S), comprising information to be displayed by each of said light-emitting elements (6R, 6G),

a correction means (10) for applying a correction factor to said data signal (S), said correction factor being based on a relationship between a color point wavelength shift and a measured shift in one of a voltage (V) across at least one of said light-emitting elements (6R, 6G) and a current (I) through this light-emitting elements (6R, 6G), and

an output means (9) for outputting said color-corrected data signal to said light-emitting elements (6R, 6G).