Systems and methods for controlling brightness of an avionics display

• US 20030214242A1
• Filed: 05/14/2002
• Published: 11/20/2003
• Est. Priority Date: 05/14/2002
• Status: Active Grant

• Current Assignee: Garmin AT, Inc. (Garmin Limited)
• Original Assignee: Garmin AT, Inc. (Garmin Limited)
• Inventors: Berg-johansen, Roar
• Granted Patent: US 6,841,947 B2
• Time in Patent Office: Days
• US Class Current: 315/169.3
• 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 2320/0626 for control of overall brightness
• CPC Class Codes: G09G 2320/0633 by amplitude modulation of the brightness of the illumination source
• CPC Class Codes: G09G 2320/064 by time modulation of the brightness of the illumination source
• CPC Class Codes: G09G 2360/144 the light being ambient light
• CPC Class Codes: G09G 2360/145 the light originating from the display screen
• CPC Class Codes: G09G 3/14 Semiconductor devices, e.g. diodes
• CPC Class Codes: G09G 3/32 semiconductive, e.g. using light-emitting diodes [LED]
• CPC Class Codes: G09G 3/3406 Control of illumination source illumination devices structurally associated with liquid crystal cells G02F1/1336
• CPC Class Codes: H05B 45/12 using optical feedback
• CPC Class Codes: H05B 45/18 using temperature feedback

Abstract

The present invention provides for systems and methods for dimming a LED matrix functioning as a backlight to an avionics display. A system according to an embodiment of the present invention comprises a processor for receiving inputs of ambient lighting and temperature, as well as light generated by the LED matrix. The processor provides modulated pulse wave signals (square waves) to two control circuits for controlling the LED matrix in two modes. At low dimming levels, the processor modulates the duty cycle of a first square wave for affecting the light level and maintains a minimal duty cycle of a second square wave. Once the highest light level is obtained by increasing the duty cycle of the first square wave, the processor then modulates a second square wave by increasing its duty cycle. The duty cycle of the second square wave is modified by a circuit to produce a voltage level which is provided as an input to control light level of the LED matrix. As the duty cycle of the second signal is increased, so is the voltage level provided to the LED matrix and the light generated by the LED matrix.

Claims

1. A system for controlling the brightness of an avionics display, comprising:

a LED matrix comprising a plurality of light emitting diodes operatively connected to receive a pulse width modulated control signal and a current control voltage signal;

a sensor operatively connected with a processor, wherein said sensor detects light emitted by said LED matrix and generates in response thereto an input signal;

a processor that receives said input signal and provides a first output digital signal and a second output digital signal based at least in part on said input signal;

a pulse width modulator circuit, wherein said pulse width modulator circuit receives said first output digital signal and generates said pulse width modulated control signal of a given duty cycle related to said first output digital signal; and

a current control circuit, wherein said current control circuit receives said second output digital signal and generates said current control voltage signal related to said second output digital signal.

2. The system of claim 1 wherein said processor further receives a second input signal indicative of ambient light levels relative to said avionics display, and wherein said first output digital signal and said second output digital signal are based at least in part on said second input signal.

3. The system of claim 2 wherein said processor further receives a third input signal indicative of temperature levels relative to said avionics display, and wherein said first output digital signal and said second output digital signal are based at least in part on said third input signal.

4. The system of claim 1 wherein said pulse width modulator circuit comprises a resistor and a capacitor that operate to slow rise and fall times associated with said pulse width modulated control signal.

5. The system of claim 1 wherein said pulse width modulator control signal is of a frequency minimizing interference with a vertical synchronous refresh frequency of said avionics display.

6. The system of claim 1 wherein said first output digital signal is a pulse width modulated signal and said second output digital signal is a pulse width modulated signal.

7. A method of controlling the brightness of an avionics display comprising a plurality of LEDs operating in an aircraft cockpit, the method comprising:

detecting light generated by at least one of said plurality of LEDs;

determining a pulse width modulated wave control signal having a given duty cycle and a current control voltage signal having a given voltage level to control at least partially light generated by said plurality of LEDs; and

adjusting one or both of said duty cycle of said pulse width modulated wave and said voltage level of said current control voltage signal based on light generated from said one of said plurality of LEDs.

8. The method according to claim 7 wherein adjusting is based at least in part on backlight ambient temperature level.

9. The method according to claim 7 wherein adjusting said duty cycle or said current control voltage level is based on at least in part on ambient light level.

10. An apparatus for controlling the brightness of an LED matrix providing backlight to an avionics display operating in an aircraft cockpit, comprising:

a processor that receives an input signal that provides a first output digital signal, and a second output digital signal;

a pulse width modulator controller that receives said first output digital signal and provides a pulse width modulated control signal wherein said pulse width modulated control signal is of a fixed periodic frequency and having a duty cycle related to said first output digital signal;

a current controller that receives said second output digital signal and provides a current control voltage signal related to said LED matrix;

a sensor for detecting light levels and generating said input signal in response thereto.

11. The apparatus of claim 10 wherein said processor means receives a second input signal, wherein said second input signal is related to ambient light conditions of the aircraft cockpit.

12. The apparatus of claim 10 wherein said processor means receives a third input signal, wherein said third input signal is related to a temperature of said LED matrix.

13. The apparatus of claim 10 wherein said pulse width modulated control signal is of a frequency minimizing interference with the vertical synchronous refresh rate of said display.

14. An apparatus for controlling the brightness of an LED matrix, comprising:

an LED matrix that receives a brightness control signal and comprises a plurality of light-emitting-diodes arranged in a planar array affixed to a substrate with a first side and a second side where substantially all of the LEDs are affixed to said first side of said substrate and the remaining LEDs are affixed to said second side of said substrate;

a sensor that detects light generated by said LEDs to said second side of said substrate and generates an input signal; and

a control unit that receives said input signal and provides said brightness control signal based on at least in part on said input signal.

15. The apparatus of claim 14 wherein the control unit provides a brightness control signal comprising a pulse width modulated signal.

16. The apparatus of claim 14 wherein the control unit provides a brightness control signal having a DC voltage level.