Backlight dimming control for a display utilizing quantum dots

• US 10,062,334 B2
• Filed: 10/31/2012
• Issued: 08/28/2018
• Est. Priority Date: 07/31/2012
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: You, Chenhua, Drolet, Jean-Jacques P.
• Primary Examiner(s): Lu, William
• Application Number:
  US13/665,616
• Publication Number:
  US 20140035960A1
• Time in Patent Office: 2,127 Days
• CPC Class Codes: G09G 2320/0242 Compensation of deficiencies in the appearance of colours
• CPC Class Codes: G09G 2320/045 Compensation of drifts in the characteristics of light emitting or modulating elements
• CPC Class Codes: G09G 2320/064 by time modulation of the brightness of the illumination source
• CPC Class Codes: G09G 2330/021 Power management, e.g. power saving
• CPC Class Codes: G09G 3/3413 Details of control of colour illumination sources

Abstract

Quantum dot backlights for use in displays and processes for controlling the dimming of quantum dot backlights are provided. The backlight can include an LED (e.g., a blue LED) configured to emit a light through a sheet of quantum dots. The quantum dots can be configured to emit colored light (e.g., red and green light) in response to the light emitted from the LED. To control the relative luminance of the LED, the backlight can be controlled through the use of current dimming to adjust the brightness of the LED at high relative luminance settings to increase the light output efficiency and can include the use of pulse width modulation to adjust the brightness of the LED at low relative luminance settings to reduce the amount of wavelength shift experienced by the LED.

Claims

1. A method for forming white light within a display backlight, the method comprising:

driving a LED with a drive current, the drive current comprising a duty cycle value and a drive current value, wherein the drive current causes the LED to emit a light comprising a magnitude of luminance;

directing the emitted light to a first prism sheet;

turning the emitted light towards a diffuser sheet using the first prism sheet;

mixing the turned light using the diffuser sheet;

directing the mixed light to a quantum dot sheet, the quantum dot sheet comprising quantum dots configured to emit red and green light in response to the turned light;

mixing the emitted red and green light with a blue light to form the white light;

directing the white light to a second prism sheet;

turning the white light towards the display module using the second prism sheet; and

reducing a wavelength shift of at least one of the red, green, and blue lights by;

varying the duty cycle value and maintaining the drive current value in accordance with a determination that the magnitude of luminance is less than a pre-determined magnitude of luminance threshold, and

varying the drive current value and maintaining the duty cycle value in accordance with a determination that the magnitude of luminance is greater than or equal to the pre-determined magnitude of luminance threshold.

2. The method of claim 1, wherein the emitted light is blue light, and the quantum dot sheet is configured to transmit the blue light through the quantum dot sheet.

3. The method of claim 1, wherein the pre-determined magnitude of threshold is equal to 50 percent.

4. The method of claim 1, wherein varying the duty cycle value includes linearly varying the duty cycle value with the magnitude of luminance.

5. The method of claim 1, wherein varying the drive current value includes linearly varying the drive current value with the magnitude of luminance.

6. A backlight comprising:

a light emitting diode (LED);

a quantum dot sheet;

a first prism sheet located between the LED and the quantum dot sheet;

a diffuser sheet located between the first prism sheet and the quantum dot sheet;

a second prism sheet located on a side of the quantum sheet opposite the diffuser sheet;

driver circuitry operable to output a drive current to the LED, the drive current comprising a duty cycle value and a drive current value, wherein the drive current causes the LED to emit a light having a magnitude of luminance; and

a controller operable to;

control the driver circuitry to reduce a wavelength shift of the LED by varying the duty cycle value and maintaining the drive current value in accordance with a determination that the magnitude of luminance of the LED is less than a pre-determined magnitude of luminance threshold, and

control the driver circuitry to vary the drive current value and maintain the duty cycle value in accordance with a determination that the magnitude of luminance of the LED is greater than or equal to the pre-determined magnitude of luminance threshold.

7. The backlight of claim 6, wherein the LED comprises a blue LED.

8. The backlight of claim 7, wherein the quantum dot sheet comprises:

a first plurality of quantum dots operable to emit a red light in response to a blue light emitted from the blue LED; and

a second plurality of quantum dots operable to emit a green light in response to the blue light emitted from the blue LED.

9. The backlight of claim 6, wherein varying the duty cycle value in accordance with a determination that the magnitude of luminance of the LED is less than the pre-determined magnitude of luminance threshold includes increasing the magnitude of luminance by linearly increasing the duty cycle value, and

varying the drive current value in accordance with a determination that the magnitude of luminance of the LED is greater than or equal to the magnitude of luminance threshold includes increasing the magnitude of luminance by linearly increasing the drive current value.

10. A display comprising:

a liquid crystal display module;

a backlight operable to emit a light directed towards the liquid crystal display module, wherein the backlight comprises;

a light emitting diode (LED);

a quantum dot sheet;

a first prism sheet located between the LED and the quantum dot sheet;

a diffuser sheet located between the first prism sheet and the quantum dot sheet;

a second prism sheet located on a side of the quantum sheet opposite the diffuser sheet;

driver circuitry operable to output a drive current to the LED, the drive current comprising a duty cycle value and a drive current value, wherein the drive current causes the LED to emit a light having a magnitude of luminance; and

a controller operable to;

control the driver circuitry to reduce a wavelength shift of the LED by varying the duty cycle value and maintaining the drive current value in accordance with a determination that the magnitude of luminance of the LED is less than a pre-determined magnitude of luminance threshold, and

control the driver circuitry to vary the drive current value and maintain the duty cycle value in accordance with a determination that the magnitude of luminance is greater than or equal to the pre-determined magnitude of luminance threshold.

11. The display of claim 10, wherein the backlight is operable to emit a white light directed towards the liquid crystal display module.

12. The display of claim 10, wherein the display is integrated within a mobile phone, media player, personal computer, or tablet computer.

13. The display of claim 10, wherein the controller is operable to linearly increase only one of the duty cycle value and the drive current value at a time.

14. A method for controlling a brightness of a light emitting diode (LED) within a quantum dot display backlight, the method comprising:

driving the LED with a drive current, the drive current comprising a duty cycle value and a drive current value, wherein the drive current causes the LED to emit a light comprising a magnitude of luminance, wherein;

the duty cycle value has one or more first duty cycle values and one or more second duty cycle values greater than the one or more first duty cycle values, wherein a wavelength shift of the display backlight is reduced by setting the duty cycle value to the one or more first duty cycle values in accordance with a determination that the magnitude of luminance is less than a pre-determined magnitude of luminance threshold, and

the drive current value has one or more first drive current values and one or more second drive current values greater than the one or more first drive current values, wherein an output efficiency of the LED is increased by setting the drive current value to the one or more second drive current values in accordance with a determination that the magnitude of luminance is greater than or equal to the pre-determined magnitude of luminance threshold;

directing the emitted light to a first prism sheet;

turning the emitted light towards a diffuser sheet using the first prism sheet;

mixing the turned light using the diffuser sheet;

directing the mixed light to a quantum dot sheet, the quantum dot sheet comprising quantum dots configured to emit red and green light in response to the turned light;

mixing the emitted red and green light with a blue light to form a white light;

directing the white light to a second prism sheet; and

turning the white light towards a display module using the second prism sheet.

15. The method of claim 14, wherein the one or more first duty cycle values includes a plurality of duty cycle values that varies linearly with the magnitude of luminance.

16. The method of claim 14, wherein the one or more second drive current values includes a plurality drive current values that varies linearly with the magnitude of luminance.

17. The method of claim 14, wherein the one or more second duty cycle values includes 100%.

18. The method of claim 14, wherein the first drive current value is equal to half a maximum value of the drive current value.

19. The method of claim 14, wherein the pre-determined magnitude of luminance threshold is equal to half a maximum value of the LED luminance.