Chroma compensated backlit display

• US 20050259439A1
• Filed: 05/24/2004
• Published: 11/24/2005
• Est. Priority Date: 05/24/2004
• Status: Active Grant

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: Davey, Dennis M., Ronning, Eric D., Cull, Brian D.
• Granted Patent: US 7,339,332 B2
• Time in Patent Office: Days
• US Class Current: 362/612
• CPC Class Codes: G02F 1/133603 with LEDs
• CPC Class Codes: G02F 1/133606 including a specially adapted diffusing, scattering or light controlling members
• CPC Class Codes: G09G 2320/043 Preventing or counteracting the effects of ageing
• CPC Class Codes: G09G 2320/0606 Manual adjustment
• CPC Class Codes: G09G 2320/0626 for control of overall brightness
• 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

Methods and apparatus are provided for a backlit display with variable luminance and chrominance. The apparatus comprises i groups of LEDs of different colors and one or more sensors optically coupled to the LEDs. The combined light produced by the LEDs is directed to a transmissive liquid crystal display, preferably through a diffusing layer. The sensors monitor the output S_i of each group of LEDs. S_i for each group of LEDs is multiplied by a chrominance determining parameter K_i to obtain K_i*S_i which is then compared to a commanded luminance signal L_C to obtain L_C−K_i*S_i, which difference is used to adjust the drive current to each group of LEDs to achieve L_C with the desired chrominance set by K_i. By changing K_i and L_C the chrominance and luminescence of the display may be varied and aging effects compensated.

Claims

1. An electro-optical apparatus, comprising:

a first group of LEDs configured to emit light of a first color, a second group of LEDs configured to emit light of a second color, and a third group of LEDs configured to emit light of a third color;

one or more sensors optically coupled to the LEDs and configured to measure quantities S₁, S₂ and S₃ proportional to the intensities of light emitted from the first, second, and third groups of LEDs respectively;

electronic circuitry coupled to the one or more sensors and the groups of LEDs for receiving S₁, S₂ and S₃, K₁, K₂, and K₃, and L_C, and determining

D₁=L_C−

K₁*S₁,
D₂=L_C−

K₂*S₂, and
D₃=L_C−

K₃*S₃,

where D₁, D₂, and D₃ determine current drive levels for the first, second, and third group of LEDs respectively, L_C is a commanded luminance signal determining overall luminance produced by the LEDs and K₁, K₂, and K₃ are chrominance parameters for determining the relative light output from the first, second, and third group of LEDs respectively.

2. The apparatus of claim 1 further comprising an LCD region receiving combined light output of the first, second and third groups of LEDs.

3. The apparatus of claim 2 further comprising an optical diffuser located between the LEDs and the LCD region.

4. The apparatus of claim 1 wherein the LEDs of each group are series coupled.

5. The apparatus of claim 1 wherein the one or more sensors comprise first, second and third sensors receiving combined light from the first, second and third groups of LEDs, and each of the sensors has thereon a different color filter selective to light from one of the first, second and third groups of LEDs, so as to produce S₁, S₂ and S₃.

6. The apparatus of claim 1 wherein the one or more sensors comprise a first sensor coupled to an LED only of the first group for providing S₁ and a second sensor coupled to an LED only of the second group for providing S₂ and a third sensor coupled to an LED only of the third group for providing S₃.

7. A backlit display comprising:

a backlight configured to produce producing light from multiple LEDs;

a transmissive LCD layer optically coupled to the backlight and adapted to selectively transmit and block the light produced by the backlight; and

one or more sensors optically coupled to the backlight and configured to monitor the light produced by the backlight.

8. The display of claim 7 further comprising one or more difference amplifiers whose inputs are coupled to the one or more sensors and whose outputs are coupled to the LEDs

9. The display of claim 7 further comprising a comparator for comparing a signal derived from the one or more sensors to a luminance command signal L_C and adjusting current supplied to the LEDs to achieve luminance corresponding to L_C.

10. The display of claim 7 wherein the multiple LEDs comprise a first group of LEDs of a first color and a second group of LEDs of a second color, and wherein the one or more sensors comprise a first sensor measuring light intensity S₁ produced by the first group of LEDs and a second sensor measuring light intensity S₂ produced by the second group of LEDs.

11. The display of claim 10 further comprising an electronic circuit coupled to the sensors and the LEDs for providing K₁*S₁ and K₂*S₂ where K₁ and K₂ are parameters input to the electronic circuit for adjusting the color of the light from the backlight by varying the relative output of the first and second groups of LEDs.

12. The display of claim 11 further comprising one or more comparators for comparing K₁*S₁ or K₂*S₂ or both to a luminance command signal L_C and adjusting current supplied to the first and second groups of LEDs to achieve an overall luminance from both groups of LEDs corresponding to the L_C.

13. A method for operating a backlit display with variable luminance and chrominance using i groups of LEDs of different colors and one or more sensors optically coupled to the LEDs and electrically coupled through a feedback controller and current drivers to the LEDs, comprising:

obtaining from the one or more sensors values S_i proportional to the intensity of light emitted by each group of LEDs;

determining K_i*S_i for each group of LEDs where K_i is a chrominance adjustment parameter for each group of LEDs;

comparing K_i*S_i to a luminance command signal L_C where L_C determines the overall luminance; and

adjusting current drive to each group of LEDs so that L_C−

K_i*S_i˜

0.

14. The method of claim 13 wherein the adjusting step comprises:

(a) adjusting the current drive to each group of LEDs depending upon the sign of the difference L_C−

K_i*S_i;

(b) obtaining a new value of S_i;

(c) determining if L_C−

K_i*S_i;

˜

0 and if YES (TRUE) fixing the drive current for each group of LEDs and if NO (FALSE) repeating steps (a)-(c) until the determining if L_C−

K_i*S_i;

˜

0 step is true.

15. The method of claim 13 wherein the determining step comprises:

(a) determining whether a current value of K_i corresponds to a desired chrominance; and

(b) if YES (TRUE) using the current value of K_i to determine K_i*S_i; and

(c) if NO (FALSE) adjusting K_i to correspond to the desired chrominance; and

(d) then determining K₁*S_i.

16. An electro-optical apparatus, comprising:

a first group of LEDs adapted to emit light of a first color and intensity, a second group of LEDs adapted to emit light of a second color and intensity, and a third group of LEDs adapted to emit light of a third color and intensity;

one or more sensors optically coupled to the LEDs and configured to sense the light intensities emitted from the first, second, and third groups of LEDs, respectively, and supply intensity signals representative thereof;

a controller coupled to receive the intensity signals, a plurality of chrominance parameters, and a commanded luminance signal and operable, in response thereto, to determine drive current magnitudes for the first, second, and third groups of LEDs.

17. A method for operating a backlit display with variable luminance and chrominance using a plurality of groups of LEDs each configured to receive a current drive signal and, in response thereto, to emit light of different colors and intensities, the method comprising the steps of:

determining values proportional to the light intensities emitted by each group of LEDs;

determining a chrominance adjustment parameter for each group of LEDs;

combining the intensity values and the chrominance adjustment values to obtain feedback values;

comparing the feedback values to a luminance command value; and

adjusting the current drive signals to each group of LEDs based on the comparison of the feedback values and the luminance command value.