Method for maintaining the white colour point in a field-sequential LCD over time

• US 20060071900A1
• Filed: 10/05/2004
• Published: 04/06/2006
• Est. Priority Date: 10/05/2004
• Status: Active Grant

• Current Assignee: Malikie Innovations Limited (Key Patent Innovations Limited)
• Original Assignee: Blackberry Limited
• Inventors: Mailloux, Jerry, Lowles, Robert, Robinson, James, Drader, Marc
• Granted Patent: US 7,714,829 B2
• Time in Patent Office: Days
• US Class Current: 345/102
• CPC Class Codes: G09G 2320/0242 Compensation of deficiencies in the appearance of colours
• 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 3/3413 Details of control of colour illumination sources

Abstract

A field sequential liquid crystal display maintains its white colour point through compensation values to at least one colour light emitting diode that illuminates the display. The compensation values may be impedances to control the current or pulsing of the current source according to a pulse width modulation technique. A degradation curve may be used to calculate extrapolate the theoretical forward voltage of the light emitting diode. Additional complexity arises from the need for calculating uptime for multiple light emitting diodes of different colours. Brightness levels may also be factored in.

Claims

1. A method for maintaining a colour point on a display, comprising:

determining a first value corresponding to on time for a light source of a first colour;

comparing the first value against a first threshold; and

if the first value exceeds the first threshold, setting a second value for the light source to compensate for aging.

2. The method of claim 1, further comprising comparing the first value against a second threshold.

3. The method of claim 1, further comprising comparing the first value against a second threshold if the first value exceeds the first threshold.

4. The method of claim 3, further comprising, if the first value exceeds the second threshold, then setting a second compensation value for the light source.

5. The method of claim 4, further comprising, if the first value exceeds the second threshold, then setting a third compensation value for the light source.

6. The method of claim 5, wherein the light source is a light emitting diode for illuminating a field sequential colour liquid crystal display.

7. The method of claim 1, wherein the first value corresponds to the total time the light source has been turned on.

8. The method of claim 1, wherein the first value corresponds to a function of turn on time and intensity of the light source when turned on.

9. The method of claim 8, wherein the function is a summation of the product of turn on time interval and intensity of the light source during the turn on time interval.

10. The method of claim 1, wherein the second value is an impedance element switched in series with the light source between power and ground.

11. The method of claim 1, wherein the second value is an impedance element switched in a parallel relationship with the light source.

12. The method of claim 1, wherein the second value is a first impedance element switched in series with the light source between power and ground and a second impedance element switched in a parallel relationship with the light source.

13. The method of claim 1, wherein the compensation for aging is accomplished through a pulse width modulation technique.

14. A field sequential liquid crystal display that compensates for white colour point drift over time, comprising:

a liquid crystal display; and

a first light emitting diode for illuminating the liquid crystal display, the white colour point drift of the liquid crystal display being compensated through compensation applied to the first light emitting diode.

15. The field sequential liquid crystal display of claim 14, wherein the liquid crystal display is a field sequential liquid crystal display.

16. The field sequential liquid crystal display of claim 15, further comprising second and third light emitting diodes.

17. The field sequential liquid crystal display of claim 16, wherein at least one of the second and third light emitting diodes is compensated to compensate for the white colour point drift of the liquid crystal display.

18. The field sequential liquid crystal display of claim 16, wherein the first light emitting diode is red.

19. The field sequential liquid crystal display of claim 16, wherein the first light emitting diode is green.

20. The field sequential liquid crystal display of claim 16, wherein the first light emitting diode is blue.

21. The field sequential liquid crystal display of claim 16, wherein the liquid crystal display is used in a wireless handheld communications device.