PATENT DOCUMENT

Publication Number: US-10062334-B2
Application Number: US-201213665616-A
Country: US
Kind Code: B2

Title: Backlight dimming control for a display utilizing quantum dots

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:
What is claimed is: 
     
       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.

Description:
FIELD 
     This relates generally to backlight dimming control and, more specifically, backlight dimming control for a display utilizing quantum dots (QDs). 
     BACKGROUND 
     Display screens of various types of technologies, such as liquid crystal displays (LCDs), organic light emitting diode (OLED) displays, etc., can be used as screens or displays for a wide variety of electronic devices, including such consumer electronics as televisions, computers, and handheld devices (e.g., mobile telephones, tablet computers, audio and video players, gaming systems, and so forth). LCD devices, for example, typically provide a flat display in a relatively thin package that is suitable for use in a variety of electronic goods. In addition, LCD devices typically use less power than comparable display technologies, making them suitable for use in battery-powered devices or in other contexts where it is desirable to minimize power usage. 
     Liquid crystal displays generally include a backlight that provides visible light to a liquid crystal layer, which takes the light from the backlight and controls the brightness and color at each individual pixel in the display in order to render a desired image. 
     The backlight often contains light emitting diodes that are coated with a phosphor, such as Yttrium Aluminum Garnet (YAG), in order to produce a white light, which the liquid crystal layer then uses to render desired colors for the display. In other backlight devices, the phosphor can be replaced with quantum dots that are configured to emit light at various wavelengths. One metric that can be used to judge the quality of a display is the uniformity of color generated by the display over varying levels of brightness. In some displays, the current used to drive the display can be increased or decreased based on the desired display brightness. However, in quantum dot displays, a change in driving current can result in a shift in the wavelength or color of the light produced by the display. Another metric that can be used to judge the quality of a display is the power efficiency of the display. Thus, it can be desirable to have an energy efficient display that experiences reduced shift in wavelength over various drive current levels. 
     SUMMARY 
     This relates to quantum dot backlights for use in displays (e.g., LED, OLED displays, and the like) and processes for controlling the dimming of quantum dot backlights. The backlight can include a blue LED configured to emit blue light through a sheet of quantum dots. The quantum dots can be configured to emit red and green light in response to the light emitted from the blue LED. Thus, the red and green light emitted from the quantum dots can be mixed with the light from a blue LED that is passed through the quantum dot sheet to form white light. To control the relative luminance, or light intensity, the backlight can be controlled through the use of current dimming (e.g., increasing or decreasing a forward current through the LED) to adjust the brightness of an LED in a backlight 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. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  illustrates an exemplary display screen stack-up according to some disclosed examples. 
         FIG. 1B  illustrates exemplary layers of an LCD display screen stack-up according to some disclosed examples. 
         FIG. 2  illustrates an exemplary backlight, according to some disclosed examples. 
         FIG. 3  illustrates another exemplary backlight, according to some disclosed examples. 
         FIG. 4  illustrates an exemplary graph showing a relationship between relative light intensity and forward current of an LED according to some disclosed examples. 
         FIG. 5  illustrates an exemplary graph showing a relationship between dominant wavelength shift and forward current of an LED according to some disclosed examples. 
         FIG. 6  illustrates an exemplary process for increasing a relative light intensity of a backlight according to examples of the present disclosure. 
         FIG. 7  illustrates an exemplary process for decreasing a relative light intensity of a backlight according to examples of the present disclosure. 
         FIGS. 8A and 8B  illustrate exemplary graphs showing example drive currents and duty cycles that may be used according to the processes of  FIGS. 6 and 7 . 
         FIG. 9  is a block diagram of an example computing system that illustrates one implementation of an example display with backlight dimming control integrated with a touch screen according to examples of the present disclosure. 
         FIG. 10A  illustrates an example mobile telephone that includes a display screen according to some disclosed examples. 
         FIG. 10B  illustrates an example digital media player that includes a display screen according to some disclosed examples. 
         FIG. 10C  illustrates an example personal computer that includes a display screen according to some disclosed examples. 
         FIG. 10D  illustrates an example tablet computing device that includes a display screen according to some disclosed examples. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description of the disclosure and examples, reference is made to the accompanying drawings in which it is shown by way of illustration specific examples that can be practiced. It is to be understood that other examples can be practiced and structural changes can be made without departing from the scope of the disclosure. 
     This relates to quantum dot backlights for use in displays (e.g., LED, OLED displays, and the like) and processes for controlling the dimming of quantum dot backlights. The backlight can include a blue LED configured to emit blue light through a sheet of quantum dots. The quantum dots can be configured to emit red and green light in response to the light emitted from the blue LED. Thus, the red and green light emitted from the quantum dots can be mixed with the light from a blue LED that is passed through the quantum dot sheet to form white light. To control the relative luminance, or light intensity, the backlight can be controlled through the use of current dimming (e.g., increasing or decreasing a forward current through the LED) to adjust the brightness of an LED in a backlight 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. 
     Although examples disclosed herein may be described and illustrated herein in terms of displays that utilize side emitting LEDs, it should be understood that the examples are not so limited, but are additionally applicable to top emitting LEDs or bottom emitting LEDs. Furthermore, although examples may described in terms of displays, it should be understood that the examples are not so limited, but are additionally applicable to displays that are integrated with touch screens which can accept touch inputs from a user or object, such as a stylus. 
       FIG. 1A  illustrates an exemplary display screen stack-up in which a backlight controlled using backlight dimming controls according to various examples can be used. Display screen  100  can be any type of display, such as an LCD, OLED display, or the like, and can include series of layers  102  that can be bonded together to constitute the display.  FIG. 1B  illustrates one exemplary type of display in which a backlight (e.g., a quantum dot backlight) according to various examples can be used. Specifically,  FIG. 1B  illustrates exemplary layers of an LCD display screen stack-up according to some disclosed examples. Stack  100  can include backlight  104  for providing white light that can be directed towards the aperture of the stack-up. As will be discussed below, the backlight can supply the rest of the display stack-up with light that can be oriented in particular orientation based on the needs of the rest of the stack-up. In order to control the brightness of the light, the white light produced by the backlight  104  can be fed into a polarizer  106  that can impart polarity to the light. The polarized light coming out of polarizer  106  can be fed through bottom glass  108  into a liquid crystal layer  112  that can be sandwiched between an Indium Tin Oxide (ITO) layer  114  and a Thin Film Transistor (TFT) layer  110 . TFT substrate layer  110  can contain the electrical components necessary to create the electric field, in conjunction with ITO layer  114  that can drive the liquid crystal layer  112 . More specifically, TFT substrate  110  can include various different layers that can include display elements, such as data lines, gate lines, TFTs, common and pixel electrodes, etc. These components can help create a controlled electric field that can orient liquid crystals located in liquid crystal layer  112  into a particular orientation, based on the desired color to be displayed at any particular pixel. The orientation of a liquid crystal element in liquid crystal layer  112  can alter the orientation of the polarized light that is passed through it from backlight  104 . The altered light from liquid crystal layer  112  can then be passed through color filter layer  116 . Color filter layer  116  can contain a polarizer. The polarizer in color filter layer  116  can interact with the polarized light coming from liquid crystal layer  112 , whose orientation can be altered depending on the electric field applied across the liquid crystal layer. The amount of light allowed to pass through color filter layer  116  into top glass  118  can be determined by the orientation of the light as determined by the orientation of the liquid crystal layer  112 . By polarizing the white light coming out of back light  104 , changing the orientation of the light in liquid crystal layer  112 , and then passing the light through a polarizer in color filter layer  116 , the brightness of light can be controlled on a per pixel basis. Color filter layer  116  also can contain a plurality of color filters that can change the light passed through it into red, green and blue. By controlling the brightness and color of light on a per pixel basis, a desired image can be rendered on the display. Additionally, as discussed in greater detail below with respect to  FIGS. 5-9 , the amount of light generated by the backlight can also be adjusted to control the overall brightness and color of the entire display. 
     In some examples, a quantum dot backlight can be used for backlight  104 . Quantum dots are tiny, nanocrystal phosphors that can be about 2-10 nm in size. They can be distinguished from bulk semiconductor material (used to fabricate LEDs) not only in size, but also by their energy levels. The energy levels in bulk material can be so close together that the levels are essentially continuous; however, quantum dots can contain only two discrete energy bands that can be occupied by the electrons. The valence band can be located below the bandgap and the conduction band can be located above the bandgap. When an electron in the valence band is imparted with sufficient energy to surmount the bandgap, it can become excited and jump to the conduction band. The electron will then want to return to its lowest energy state, and in doing so, can release energy in the form of electromagnetic radiation. The electron can fall back down to the valence band, emitting a photon with wavelength corresponding to the wavelength of radiation or the bandgap energy. For quantum dots, their small size leads to quantum confinement, where the energy levels can become discrete and quantized with finite separation. When the quantum dots are excited, the electromagnetic radiation corresponding to the wavelength can be released in the form of light. The main difference relative to bulk material is that the discrete energy levels for the QDs can allow for precise tunability of the emitted photon. For quantum dots, the energy levels can be finely tuned based on the size of the dot, which in turn can lead to tuning the wavelength of the emitted photon. This tunability can allow the QDs the ability to emit nearly any frequency of light, a quality that bulk semiconductor material, and hence a stand-alone, standard light-emitting diode (LED) lacks. The quantum dots can be tuned to emit colors at more precise wavelengths relative to YAG phosphors with narrower spectral emission and a smaller full width at half maximum (FWHM) bandwidth. The heightened spectral precision of quantum dots can allow the color filter in color filter layer  116  to be narrowed, thus improving both the color quality and color gamut of the display. Quantum dots can be formed on a sheet that is placed within the display, so that it can be exposed to the light produced by an LED. 
       FIG. 2  illustrates one exemplary quantum dot backlight  200  that can be used in stack  100 . Backlight  200  can include plurality of elements that can be arranged so as to provide white light to the rest of display stack-up  100 . Backlight  200  can contain light emitting diode (LED)  202 , which can act as the primary light source for the entire display stack-up  100 . As pictured, LED  202  can be a side emitting LED. The light generated by LED  202  can irradiate quantum dot sheet  204  that can produce a light of a particular color or colors when excited by light source, such as an LED. Quantum dot sheet  204  can include individual quantum dots arranged in groups, such that each group can contain, for example, 3 quantum dots, one red, one green and one blue, such that the light generated by each group when mixed together can produce white light. In other examples, a blue LED can be used to excite the quantum dots, obviating the need for a quantum dot that emits blue light, and thus the group of quantum dots may contain only a red and green quantum dot. Thus, the red and green light emitted from the quantum dots can be mixed with the light from a blue LED that is passed through the quantum dot sheet to form white light. Quantum dot sheet  204  can be excited by light generated by LED  202 . In some examples, LED  202  can be operable to generate ultra violet (UV) light. The light generated by LED  202  can provide the energy required to excite the quantum dots so that they emit photons of light at precisely tuned wavelengths. The wavelengths can be tuned by adjusting the size of the quantum dots. When the light generated by LED  202  excites the quantum dots in sheet  204 , each quantum dot can release light. An excited quantum dot may release isotropic light. In other words, the light emitted from a quantum dot will be emitted uniformly in all directions from the quantum dot. 
     The light emitted from quantum dot sheet  204  can be fed into light guide  208 , which in conjunction with reflective plate  206  can work to turn the light being emitted from the side emitting LED  202  into the LCD module. The light that is emitted upwards toward the LCD module  216  can first enter prism sheet  210 , which can act to turn the light further, so that it can enter the LCD module perpendicular to its bottom plane. The light that passes through prism sheet  210  can also be fed into a diffuser  212 . Diffuser  212  can act to mix the red, green and blue light emitted from quantum dot sheet  204  in order to create white light. The mixed light from diffuser  212  can then be fed into a second prism sheet  214  that can again turn the direction of the light, so that it can enter the LCD module  216  perpendicularly. 
       FIG. 3  illustrates another exemplary quantum dot backlight  300  that can be used in stack  100 . In this example, the quantum dot sheet  322  can be moved away from LED  302 , and can be placed between diffuser  312  and prism sheet  314 . While the quantum dot sheet  322  is illustrated in  FIG. 3  as being placed between diffuser sheet  312  and prism sheet  314 , in other examples prism sheet  310 , diffuser sheet  312 , quantum dot sheet  322  and prism sheet  314  can be arranged in other combinations or orders. Placing the quantum dot sheet  322  proximal to the diffuser and prism sheets can be advantageous in that the quantum dot sheet  322  is positioned further away from LED  322  and thus can be less susceptible to the effects of heat generated by the LED. 
     To control the brightness of a display, the brightness of the light generated by a backlight LED, such as LED  202  or  302 , can be adjusted. For example,  FIG. 4  illustrates an exemplary graph showing a relationship between relative light intensity and forward current passing through an LED. Thus, to reduce the light intensity of the LED, and thus the intensity of light generated by a backlight, the drive current sent through the LED can be reduced. The drive current can be generated by drive circuitry known to those of ordinary skill in the art and can be controlled by a drive circuitry controller. However, when using a blue LED as LED  202  or  302 , a change in forward current can undesirably cause a shift in wavelength of the light emitted by the LED. For example,  FIG. 5  illustrates an exemplary graph showing a relationship between dominant wavelength shift and forward current of a blue LED. The dominant wavelength (e.g., color) of the emitted light can change as a function of forward current. In some examples, the amount of wavelength shift can be more pronounced at lower current levels. Thus, while drive current can be changed to adjust the brightness of a blue LED within a backlight, the change in drive current can result in a change in the color of the light emitted by the backlight, resulting in an undesired change in color of a display in which the backlight is used. 
       FIGS. 6 and 7  illustrate exemplary processes  600  and  700  for controlling the brightening and dimming of an LED, such as a blue LED, thereby adjusting the brightness of a quantum dot backlight (e.g., backlight  200 ,  300 , or other backlight). Generally, process  600  and  700  can include the use of current dimming to adjust the brightness of the LED of the backlight at high 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 luminance settings to reduce the amount of wavelength shift experienced by the LED. To illustrate,  FIG. 8A  shows an exemplary graph depicting the relationship between a relative luminance (e.g., with a relative luminance value of 0 corresponding to an off state of the LED and a relative luminance value of 1 corresponding to a maximum brightness of the LED) of the LED and the relative values of the duty cycle  803  and drive current  801  e.g., with a relative value of 0 corresponding to a 0% duty cycle and zero drive current and a relative value of 1 corresponding to a 100% duty cycle and a maximum drive current). As shown in  FIG. 8A , the drive current can have a constant, or at least substantially constant (e.g., within 1%, 2%, 3%, 4%, 5%, or 10%), minimum current value  807  (e.g., 0.5) from zero relative luminance to a threshold luminance value  805  (e.g., 0.5). To adjust the luminance of the LED between relative luminance values of zero and the threshold value  805 , the duty cycle  803  can be changed to generate the desired luminance. However, between the threshold luminance value  805  and a luminance value of 1, the duty cycle can have a constant, or at least substantially constant (e.g., within 1%, 2%, 3%, 4%, 5%, or 10%), value (e.g., 1). To adjust the luminance of the LED between the threshold luminance value  805  and a luminance value of 1, the drive current can be changed to generate the desired luminance.  FIG. 8B  illustrates a graph showing the relationship between relative forward current values through the LED and the relative luminance of the LED. It should be appreciated that the current values shown between 0 relative luminance and threshold luminance value  805  do not reflect actual current values, and instead represent relative duty cycle ratios. 
     In the examples shown in  FIGS. 8A and 8B , the threshold luminance value  805  has been selected to be 0.5, meaning that a switch between pulse width modulation and current dimming can occur at half the maximum luminance of the LED. At luminance values below threshold luminance value  805 , duty cycle  803  ranges from 0 to 1 (e.g., 0% to 100% duty cycle) between luminance values of 0 and the threshold luminance value  805  of 0.5. Additionally, at luminance values below threshold luminance value  805 , drive current  801  can have a constant, or at least substantially constant, minimum current value  807  of 0.5 (representing half of the maximum drive current). At luminance values greater than the threshold luminance value  805 , duty cycle  803  can be set to its maximum value of 1 (corresponding to a 100% duty cycle). Additionally, at luminance values greater than the threshold luminance value  805 , the drive current  801  can range from the minimum current value  807  of 0.5 to a maximum relative value of 1. 
     While specific current dimming and pulse width modulation dimming parameters are shown in  FIGS. 8A and 8B , it should be appreciated by one of ordinary skill that these values can be adjusted based on specific components used and desired operational characteristics of the backlight. For example, minimum current value  807  can be selected such that the dominant wave length shift between the minimum current value  807  and the maximum relative current value is less than a desired amount (e.g., as shown in  FIG. 5 ). Additionally, the threshold relative luminance value  805  can be selected based on the selected minimum current value  807  and a desired efficiency of the backlight. For example, current dimming can be more efficient for light generation than pulse width modulation. Thus, to increase efficiency, the threshold relative luminance value  805  and minimum current value  807  can be reduced. Conversely, to improve color uniformity, the threshold relative luminance value  805  and minimum current value  807  can be increased. Given the contents of the present disclosure, one of ordinary skill can select current dimming and pulse width modulation dimming parameters based on the specific components used and desired operational characteristics of the backlight. 
     Referring back to  FIG. 6 , an exemplary process  600  for increasing the luminance of an LED within a quantum dot backlight based on the mixed-mode dimming shown in  FIGS. 8A and 8B  is provided. At block  601 , an LED (e.g., a blue LED), such as LED  202  or  302 , of a backlight, such as backlight  200  or  300 , can be driven with a drive current at a duty cycle value. For example, an LED can be driven with a duty cycle value and a drive current value shown in  FIG. 8A . At block  603 , it can be determined if the relative luminance corresponding to the drive current and duty cycle used at block  601  is less than a threshold relative luminance value. If the luminance value is less than the threshold relative luminance value, the process can proceed to block  605 . At block  605 , the duty cycle of the drive current can be increased to increase the luminance of the LED. For example, as shown in  FIG. 8A , if the luminance value is less than the threshold luminance value  805 , the duty cycle can be increased while maintaining a constant, or at least substantially constant, drive current. The process may then return to block  603  where the blocks of process  600  can be repeated until obtaining a desired luminance. 
     If, however, it is determined at block  603  that the current luminance value is not less than the threshold luminance value, the process can proceed to block  607 . At block  607 , the drive current can be increased to increase the luminance of the LED. For example, as shown in  FIG. 8A , if the luminance value is not less than the threshold luminance value  805 , the drive current can be increased while maintaining a constant, or at least substantially constant, duty cycle. The process may then return to block  603  where the blocks of process  600  can be repeated until obtaining a desired luminance. 
     Similarly,  FIG. 7  illustrates an exemplary process  700  for decreasing the luminance of an LED of a quantum dot backlight. At block  701 , an LED of the backlight can be driven with a drive current at a duty cycle. For example, the LED can be driven with a duty cycle value and current value shown in  FIG. 8A . At block  703 , it can be determined if the relative luminance corresponding to the drive current and duty cycle used at block  701  is greater than or equal to a threshold relative luminance value. If the luminance value is greater than or equal to the threshold relative luminance value, the process can proceed to block  705 . At block  705 , the drive current can be decreased to decrease the luminance of the LED. For example, as shown in  FIG. 8A , if the luminance value is greater than or equal to the threshold luminance value  805 , the drive current can be decreased while maintaining a constant, or at least substantially constant, duty cycle. The process may then return to block  703  where the blocks of process  700  can be repeated until obtaining a desired luminance. 
     If, however, it is determined at block  703  that the current luminance value is not greater than or equal to the threshold luminance value, the process can proceed to block  707 . At block  707 , the duty cycle can be decreased to decrease the luminance of the LED. For example, as shown in  FIG. 8A , if the luminance value is not greater than or equal to the threshold luminance value  805 , the duty cycle can be decreased while maintaining a constant, or at least substantially constant, drive current. The process may then return to block  703  where the blocks of process  700  can be repeated until obtaining a desired luminance. 
     While processes  600  and  700  are shown in separate figures, it should be appreciated that both processes can be used to brighten or dim an LED within a backlight, thereby adjusting the brightness of the backlight. 
       FIG. 9  is a block diagram of an example computing system  900  that illustrates one implementation of an example display with the backlight utilizing quantum dots described above integrated with a touch screen  920  according to examples of the disclosure. Computing system  900  could be included in, for example, a mobile telephone, digital media player, personal computer, or any mobile or non-mobile computing device that includes a touch screen. Computing system  900  can include a touch sensing system including one or more touch processors  902 , peripherals  904 , a touch controller  906 , and touch sensing circuitry. Peripherals  904  can include, but are not limited to, random access memory (RAM) or other types of memory or storage, watchdog timers and the like. Touch controller  906  can include, but is not limited to, one or more sense channels  908 , channel scan logic  910 , and driver logic  914 . Channel scan logic  910  can access RAM  912 , autonomously read data from the sense channels and provide control for the sense channels. In addition, channel scan logic  910  can control driver logic  914  to generate stimulation signals  916  at various frequencies and phases that can be selectively applied to drive regions of the touch sensing circuitry of touch screen  920 , as described in more detail below. In some examples, touch controller  906 , touch processor  902  and peripherals  904  can be integrated into a single application specific integrated circuit (ASIC). 
     Computing system  900  can also include a host processor  928  for receiving outputs from touch processor  902  and performing actions based on the outputs. For example, host processor  928  can be connected to program storage  932  and a display controller, such as an LCD driver  934 . Host processor  928  can use LCD driver  934  to generate an image on touch screen  920 , such as an image of a user interface (UI), and can use touch processor  902  and touch controller  906  to detect a touch on or near touch screen  920 , such a touch input to the displayed UI. The touch input can be used by computer programs stored in program storage  932  to perform actions that can include, but are not limited to, moving an object such as a cursor or pointer, scrolling or panning, adjusting control settings, opening a file or document, viewing a menu, making a selection, executing instructions, operating a peripheral device connected to the host device, answering a telephone call, placing a telephone call, terminating a telephone call, changing the volume or audio settings, storing information related to telephone communications such as addresses, frequently dialed numbers, received calls, missed calls, logging onto a computer or a computer network, permitting authorized individuals access to restricted areas of the computer or computer network, loading a user profile associated with a user&#39;s preferred arrangement of the computer desktop, permitting access to web content, launching a particular program, encrypting or decoding a message, and/or the like. Host processor  928  can also perform additional functions that may not be related to touch processing. For example, host processor  928  can control the drive current output by LCD driver  934 , as described above. 
     Integrated display and touch screen  920  can include touch sensing circuitry that can include a capacitive sensing medium having a plurality of drive lines  922  and a plurality of sense lines  923 . It should be noted that the term “lines” is sometimes used herein to mean simply conductive pathways, as one skilled in the art will readily understand, and is not limited to elements that are strictly linear, but includes pathways that change direction, and includes pathways of different size, shape, materials, etc. Drive lines  922  can be driven by stimulation signals  916  from driver logic  914  through a drive interface  924 , and resulting sense signals  917  generated in sense lines  923  can be transmitted through a sense interface  925  to sense channels  908  (also referred to as an event detection and demodulation circuit) in touch controller  906 . In this way, drive lines and sense lines can be part of the touch sensing circuitry that can interact to form capacitive sensing nodes, which can also be referred to as touch regions, such as touch regions  926  and  927 . This way of understanding can be particularly useful when touch screen  920  is viewed as capturing an “image” of touch. In other words, after touch controller  906  has determined whether a touch has been detected at each touch region in the touch screen, the pattern of touch region in the touch screen at which a touch occurred can be thought of as an “image” of touch (e.g. a pattern of fingers touching the touch screen). 
     In some examples, touch screen  920  can be an integrated touch screen in which touch sensing circuit elements of the touch sensing system can be integrated into the display pixels stackups of a display. 
     The firmware can also be propagated within any transport medium for use by or in connection with an instruction execution system, apparatus, or device, such as a computer-based system, processor-containing system, or other system that can fetch the instructions from the instruction execution system, apparatus, or device and execute the instructions. In the context of this document, a “transport medium” can be any medium that can communicate, propagate or transport the program for use by or in connection with the instruction execution system, apparatus, or device. The transport readable medium can include, but is not limited to, an electronic, magnetic, optical, electromagnetic or infrared wired or wireless propagation medium. 
       FIGS. 10A-10D  show example systems in which backlights and display screens (which can be part of touch screens) according to examples of the disclosure may be implemented.  FIG. 10A  illustrates an example mobile telephone  1036  that includes a display screen  1024 .  FIG. 10B  illustrates an example digital media player  1040  that includes a display screen  1026 .  FIG. 10C  illustrates an example personal computer  1044  that includes a display screen  1028 .  FIG. 10D  illustrates an example tablet computing device  1048  that includes a display screen  1030 . Display screens  1024 ,  1026 ,  1028  and  1030  can include numerous layers that are stacked on top of each other and bonded together to form the display. 
     Although the disclosure and examples have been fully described with reference to the accompanying drawings, it is to be noted that various changes and modifications will become apparent to those skilled in the art. Such changes and modifications are to be understood as being included within the scope of the disclosure and examples as defined by the appended claims.

Metadata:
Filing Date: 20121031
Publication Date: 20180828
Grant Date: 20180828
Priority Date: 20120731
Inventors: YOU, CHENHUA
DROLET, JEAN-JACQUES P.
Assignee: APPLE INC
CPC Classifications: [{"code": "G09G2320/045", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2330/021", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/3413", "inventive": true, "first": true, "tree": "[]"}, {"code": "G09G2320/064", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/0242", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/3413", "inventive": true, "first": true, "tree": "[]"}, {"code": "G09G2320/045", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2330/021", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/0242", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/064", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 50025046