Backlight variation compensated display

• US 20070120806A1
• Filed: 11/28/2005
• Published: 05/31/2007
• Est. Priority Date: 11/28/2005
• Status: Active Grant

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: Haim, Victoria, Schmidt, John, Haim, Elias
• Granted Patent: US 9,093,041 B2
• Time in Patent Office: Days
• US Class Current: 345/102
• CPC Class Codes: G09G 2320/0247 Flicker reduction other than flicker reduction circuits used for single beam cathode-ray tubes
• CPC Class Codes: G09G 2320/0257 Reduction of after-image effects
• CPC Class Codes: G09G 2320/0606 Manual adjustment
• CPC Class Codes: G09G 2320/0626 for control of overall brightness
• CPC Class Codes: G09G 2360/145 the light originating from the display screen
• CPC Class Codes: G09G 3/3406 Control of illumination source illumination devices structurally associated with liquid crystal cells G02F1/1336
• CPC Class Codes: G09G 3/3648 using an active matrix G09G3/367 - G09G3/3696 take precedence
• CPC Class Codes: G09G 3/3655 Details of drivers for counter electrodes, e.g. common electrodes for pixel capacitors or supplementary storage capacitors

Abstract

Methods and apparatus are provided for compensating a liquid crystal display for changes in brightness level. The apparatus comprises a variable brightness back-light optically coupled to a display panel whose properties depend upon back-light brightness. An electrical circuit measures back-light brightness and/or display flicker and sends this information to a controller. The controller automatically determines a display panel compensation signal based on back-light brightness and/or display flicker, and sends this compensation signal to the display panel to optimize the display panel properties for the commanded or observed back-light brightness level or flicker level so as to, for example, minimize display panel flicker and/or ghost image retention. Such automatic compensation is especially useful for head-up displays that must accommodate large variations in display brightness, e.g., from starlight to full sun, and/or for large, bright projection displays adapted to operate in different ambient light conditions where back-light brightness variation is desirable.

Claims

1. A liquid crystal display having compensation for varying brightness levels, comprising:

a dimmable back-light adapted to provide varying brightness levels;

a display panel, optically coupled to the back-light for receiving illumination therefrom, and whose properties depend upon the varying back-light brightness levels and having a first input for receiving a compensating signal;

an electrical circuit for receiving back-light brightness level information;

a non-volatile memory for storing values of an optimum display panel compensating signal as a function of back-light brightness levels; and

a controller coupled to the memory, the electrical circuit and the display panel, for retrieving from the memory the optimum display panel compensating signal corresponding to the back-light brightness level received from the electrical circuit, and transmitting such optimum display panel compensating signal to the first input.

2. The display of claim 1, wherein output of the dimmable back-light can be varied over a dimming range of approximately 2 to 1 or greater.

3. The display of claim 1, wherein output of the dimmable back-light can be varied over a dimming range of up to at least 50,000 to 1.

4. The display of claim 1, wherein the display panel further comprises thin film transistors that are photosensitive.

5. The display of claim 1, wherein the first input of the display panel is coupled to a common terminal of the display panel adapted to receive a common voltage.

6. The display of claim 1, wherein the dimmable back-light comprises light emitting diodes.

7. The display of claim 1, wherein the electrical circuit comprises a back-light lamp driver and the back-light brightness information is proportional to a light producing drive signal provided to the back-light by the back-light lamp driver.

8. The display of claim 1, wherein the electrical circuit comprises a photodetector in a light path of the back-light.

9. A method for compensating a liquid crystal display for varying display brightness level, comprising:

reading a commanded or actual brightness value;

determining a display compensating signal value corresponding to the read brightness value; and

automatically applying the compensating signal level to the display.

10. The method of claim 9, wherein the determining step comprises, retrieving from a look-up table, a compensating signal corresponding to the read brightness value.

11. The method of claim 9, wherein the applying step comprises, sending a value proportional to the compensating signal to a common electrode of the display.

12. The method of claim 9, wherein the reading step comprises, measuring an actual brightness value of a back-light optically coupled to the display.

13. A liquid crystal display having compensation for varying brightness levels, comprising:

a dimmable back-light adapted to provide varying back-light brightness levels;

a display panel, optically coupled to the back-light for receiving illumination therefrom, and whose flicker properties depend upon the varying back-light brightness level, and having a first input for receiving a compensating signal;

an electrical circuit for receiving a real time flicker level of the display panel; and

a controller coupled to the electrical circuit and the display panel, adapted to receive from the electrical circuit a signal related to the display flicker level and determine based thereon a display panel compensating signal corresponding to the observed flicker level and transmit such display panel compensating signal to the first input.

14. The display of claim 13, wherein the electrical circuit comprises a sensor optically coupled to the display panel and electrically coupled to the controller, and adapted to measure the real-time flicker level of the display panel and provide such information to the controller.

15. The display of claim 14, wherein the sensor is integrated with the display panel.

16. A method for compensating a liquid crystal display for varying display brightness level, comprising:

measuring the real time display flicker;

determining a display compensating signal value corresponding to the measured display flicker; and

automatically applying the compensating signal value to the display to reduce said flicker.

17. The method of claim 16, wherein the liquid crystal display has an input for receiving a common electrode voltage and the compensating signal is applied to said input.

18. The method of claim 16, wherein the compensating signal is applied to Gamma voltages of the display, effectively changing V_COM.

19. The method of claim 16, further comprising prior to the determining step, evaluating whether the real time display flicker obtained in the measuring step has changed.

20. The method of claim 16, further comprising prior to the measuring step, illuminating the display with light obtained from an LED back-light source.