Contrast control for a backlit LCD

• US 5,818,553 A
• Filed: 10/06/1997
• Issued: 10/06/1998
• Est. Priority Date: 04/10/1995
• Status: Expired due to Fees

• Current Assignee: Norand Corporation (Baker Hughes Company)
• Original Assignee: Norand Corporation (Baker Hughes Company)
• Inventors: Koenck, Steven E., Keehn, William Henry II
• Primary Examiner(s): Sikes, William L.
• Assistant Examiner(s): MALINOWSKI, WALTER J
• Application Number:
  US08/944,720
• Time in Patent Office: 365 Days
• Field of Search: 359/48, 359/72, 359/84, 359/85, 250/201.1, 250/205, 250/214 AL, 349/116, 349/199, 349/61, 349/62, 349/63, 349/64, 349/65, 349/66, 349/67, 349/68, 349/69, 349/70, 349/71, 349/16, 349/85, 349/104, 345/102, 345/207, 345/147
• US Class Current: 349/61
• CPC Class Codes: G02F 1/13318 Circuits comprising a photodetector
• CPC Class Codes: G09G 2320/0626 for control of overall brightness
• CPC Class Codes: G09G 2320/066 for control of contrast
• CPC Class Codes: G09G 2360/144 the light being ambient light
• CPC Class Codes: G09G 3/3406 Control of illumination source illumination devices structurally associated with liquid crystal cells G02F1/1336
• CPC Class Codes: G09G 3/36 using liquid crystals

Abstract

A contrast controller for a liquid-crystal display maximizes the display contrast by using a light sensor to detect ambient light levels and light blocked by the LCD panel. The display contrast is maximized by maximizing the difference between the ambient and blocked light levels. Further contrast maximization is accomplished through variable control of the LCD backlight in accordance with sensed light levels.

Claims

1. A contrast controller for a liquid-crystal display, comprising:

(a) at least one light sensor for detecting varying levels of light impinging thereupon and producing a varying electrical output related to the varying levels of light;

(b) a sensor pixel positioned between the impinging light and said at least one light sensor for controlling the light impinged upon said at least one light sensor proportional to the amount of light transmitted through the liquid-crystal display, wherein the impinging light includes light from a backlighting device of the liquid-crystal display; and

(c) contrast maximizing means responsive to the varying electrical output of said at least one light sensor for maximizing the contrast of the liquid-crystal display.

2. The contrast controller of claim 1 wherein said sensor pixel is a pixel of said liquid-crystal display.

3. The contrast controller of claim 1 wherein said sensor pixel is electrically driven by the drive circuitry of the liquid-crystal display.

4. The contrast controller of claim 1 wherein said sensor pixel is electrically driven at a rate equivalent to the average drive rate of the liquid-crystal display.

8. An apparatus as claimed in claim 1, wherein said sensor pixel is a pixel of the liquid-crystal display.

9. An apparatus as claimed in claim 1, wherein said sensor pixel is driven by said driver circuit.

5. A method for controlling the contrast of a liquid-crystal display comprising:

(a) detecting the level of light incident upon the liquid-crystal display including light produced by a backlighting device of the liquid-crystal display;

(b) detecting the level of light transmitted through the liquid-crystal display; and

(c) adjusting the contrast of the liquid-crystal display until a maximum difference between the incident light level and the transmitted light level is reached.

6. The method according to claim 5 further including the step of adjusting the backlighting level of the liquid-crystal display until a maximum difference between the incident light level and the transmitted light level is reached.

7. An apparatus for controlling the contrast of a liquid-crystal display, comprising:

a driver circuit for electrically driving the liquid-crystal display;

a sensor pixel being electrically connected to said driver circuit;

a first light sensor being disposed relative to the liquid-crystal display to detect ambient light directly impinging thereupon including light produced by a backlighting device of the liquid-crystal display, said first light sensor providing an output proportional to the ambient light; and

a second light sensor being disposed relative to said sensor pixel to detect light transmitted therethrough, said second light sensor providing an output proportional light transmitted through said sensor pixel wherein said driver circuit adjusts the contrast according the outputs from said first and said second light sensors.

10. An apparatus as claimed in claim 7, wherein said sensor pixel is driven at a rate equivalent to the average drive rate of the liquid-crystal display.

11. An apparatus as claimed in claim 7, wherein the contrast of the liquid-crystal display is controlled by maximizing the difference between the outputs of said first and said second light sensors.

12. An apparatus as claimed in claim 7, wherein the contrast of the liquid-crystal display is maximized as a function of the difference of the outputs of said first and said second light sensors.