Backlight module for displays

1. An apparatus comprising:

a backlight module comprising:

a light-emitting unit comprising a plurality of light-emitting diodes; and

a controller, for receiving a first control signal and generating a second control signal to digitally control an average luminance of the light-emitting unit, the controller causes the second control signal to have a first frequency if a duty cycle of the first control signal is larger than a threshold value, and causes the second control signal to have a second frequency if the duty cycle of the first control signal is less than the threshold value, wherein the frequency of the first control signal is predetermined, the first frequency is equal to the frequency of the first control signal ,and the second frequency is larger than the first frequency;

wherein the second control signal leads all of the light-emitting diodes of the light-emitting unit to simultaneously provide all pixels of a liquid crystal display panel the average luminance.

2. The apparatus of claim 1 in which the first threshold value is between 15% to 25%.

3. The apparatus of claim 1 in which the first frequency is between 180 Hz to 220 Hz.

4. The apparatus of claim 3 in which the second frequency is between 9 KHz to 11 KHz.

5. The apparatus of claim 1 in which the average luminance of the light-emitting unit varies according to the duty cycle of the second control signal.

6. The apparatus of claim 1 in which the light-emitting unit further comprises a current regulator to regulate currents that pass the light-emitting diodes.

7. The apparatus of claim 6 in which the second control signal controls the current regulator in regulating the currents.

8. An apparatus comprising:

a light source comprising:

a light-emitting unit comprising a plurality of light-emitting diodes; and

a controller to receive, for receiving a first control signal and generating a second control signal to digitally control an average luminance of the light-emitting unit, the controller causes the second control signal to have a first frequency if a duty cycle of the first control signal is larger than a threshold value, and causes the second control signal to have a second frequency if the duty cycle of the first control signal is less than the threshold value, wherein the frequency of the first control signal is predetermined, the first frequency is equal to the frequency of the first control signal ,and the second frequency is larger than the first frequency; and

a reflective display device that is illuminated by the light source;

wherein the second control signal leads all of the light-emitting diodes of the light-emitting unit to simultaneously provide all pixels of a liquid crystal display panel the average luminance.

9. A method for digitally driving a backlight module comprising a light-emitting unit, the light-emitting unit comprises a plurality of light-emitting diodes, the method comprises:

receiving a first control signal;

determining whether a duty cycle of the first control signal is larger than or equal to a first threshold value, wherein the frequency of the first control signal is predetermined;

outputting a second control signal having a first frequency to the light-emitting unit if the duty cycle of the first control signal is larger than or equal to the first threshold value, the first frequency is equal to the frequency of the first control signal; and

outputting a second control signal having a second frequency to the light-emitting unit if the duty cycle of the first control signal is smaller than the first threshold value, the second frequency is larger than the first frequency;

wherein the second control signal leads all of the light-emitting diodes of the light-emitting unit to simultaneously provide all pixels of a liquid crystal display panel the average luminance.

10. The method of claim 9 in which the first threshold value is between 15% to 25%.

11. The method of claim 9 in which the first frequency is between 180 Hz to 220 Hz.

12. The method of claim 9 in which the second frequency is between 9 KHz to 11 KHz.

13. The method of claim 9 , further comprising, if the duty cycle of the first control signal is smaller than the first threshold value, determining whether the duty cycle of the first control signal is larger than or equal to a second threshold value that is smaller than the first threshold value,

outputting the second control signal having the second frequency to the light-emitting unit if the duty cycle of the first control signal is larger than or equal to the second threshold value, and

outputting the second control signal having a third frequency to the light-emitting unit if the duty cycle of the first control signal is less than the second threshold value.

14. A liquid crystal display, comprising:

a liquid crystal display panel having a plurality of pixels;

a light-emitting unit comprising a plurality of light-emitting diodes; and

a frequency controller, for receiving a first control signal and generating a second control signal that is sent to the light-emitting unit to digitally control an average luminance of the light-emitting unit, the second control signal alternating between high and low levels and having a first frequency if a duty cycle of the first control signal is greater than or equal to a threshold value, the second control signal having a second frequency if the duty cycle of the first control signal is less than the threshold value, the light-emitting unit emitting light according to a frequency and duty cycle that correspond to the frequency and duty cycle of the second control signal;

wherein the frequency of the first control signal is predetermined, the first frequency is equal to the frequency of the first control signal ,and the second frequency is larger than the first frequency, and the second control signal leads all of the light-emitting diodes of the light-emitting unit to simultaneously provide all pixels of the liquid crystal display panel the average luminance.