PATENT DOCUMENT

Publication Number: US-10728969-B2
Application Number: US-201916353896-A
Country: US
Kind Code: B2

Title: Split driver backlightsystems and methods

Abstract:
Aspects of the subject technology relate to control circuitry for light-emitting diodes. The control circuitry may operate a light-emitting diode using a multi-peak pulse-width-modulation signal. The control circuitry may include a multi-stage driver having a relatively larger driver stage for providing a direct current through a light-emitting diode and a relatively smaller driver stage configured to cooperate with a pulse-width-modulation controller to pulse-width-modulate a current through the light-emitting diode.

Claims:
What is claimed is: 
     
       1. An electronic device having a display with a backlight, the backlight comprising:
 a light-emitting diode; and 
 a backlight driver having:
 a first driver stage coupled to the light-emitting diode and having:
 a pulse-width modulation controller to provide pulse-width-modulation control of a first current through the light-emitting diode; and 
 a first linear current controller; and 
 
 a second driver stage coupled to the light-emitting diode and having a second linear current controller to provide a second current through the light-emitting diode. 
 
 
     
     
       2. The electronic device of  claim 1 , wherein the first linear current controller comprises:
 a first current control transistor coupled to the light-emitting diode; and 
 a first digital-to-analog converter having an output terminal coupled, via a switch, to a gate terminal of the first current control transistor. 
 
     
     
       3. The electronic device of  claim 2 , wherein the pulse-width modulation controller is configured to operate the switch to provide pulse-width-modulation control of the first current through the light-emitting diode and the first current control transistor. 
     
     
       4. The electronic device of  claim 3 , wherein the second linear current controller comprises:
 a second current control transistor having a first source/drain terminal coupled to the light-emitting diode, a second source/drain terminal coupled to a ground voltage via an additional resistor, and a gate terminal; and 
 a second digital-to-analog converter having an output terminal coupled to the gate terminal of the second current control transistor. 
 
     
     
       5. The electronic device of  claim 4 , wherein the first linear current controller further comprise an amplifier coupled between the switch and the gate terminal of the first current control transistor. 
     
     
       6. The electronic device of  claim 5 , wherein the second linear current controller further comprise an additional amplifier coupled between the second digital-to-analog converter and the gate terminal of the second current control transistor. 
     
     
       7. The electronic device of  claim 4 , further comprising:
 a first current digital-to-analog converter coupled to the first digital-to-analog converter; and 
 a second current digital-to-analog converter coupled to the second digital-to-analog converter. 
 
     
     
       8. The electronic device of  claim 7 , wherein the pulse-width modulation (PWM) controller performs PWM control at lower currents below a transition point and linear current control of the second driver stage is provided at higher currents above the transition point with the transition point between PWM control and linear control is both trimmable and scalable. 
     
     
       9. An electronic device having a display, the display comprising:
 a backlight unit, comprising:
 a light-emitting diode; 
 direct current control circuitry; and 
 pulse-width-modulation current control circuitry to modulate a first peak current provided by the direct current control circuitry through the light-emitting diode and to modulate a second peak current provided by the direct current control circuitry through the light-emitting diode to provide tunable multiple peak currents to control and reduce headroom voltage of the light-emitting diode, wherein the first peak current is larger than the second peak current. 
 
 
     
     
       10. The electronic device of  claim 9 , wherein the direct current control circuitry comprises:
 a current control transistor coupled in series between the light-emitting diode and a ground voltage; and 
 a digital-to-analog converter coupled to a gate terminal of the current control transistor. 
 
     
     
       11. The electronic device of  claim 10 , wherein the pulse-width-modulation current control circuitry comprises a switch coupled between the light-emitting diode and the current control transistor, the switch operable based on a pulse-width-modulation signal from a pulse-width-modulation controller. 
     
     
       12. The electronic device of  claim 11 , wherein the digital-to-analog converter is operable to provide the first peak current and the second peak current using the current control transistor, and wherein, in some modes of operation, the second peak current is unmodulated by the pulse-width-modulation current control circuitry. 
     
     
       13. The electronic device of  claim 11 , wherein the digital-to-analog converter is operable to provide the first peak current using the current control transistor and wherein the direct current control circuitry further comprises an additional digital-to-analog converter operable to provide the second peak current using an additional current control transistor. 
     
     
       14. The electronic device of  claim 13 , wherein the pulse-width-modulation current control circuitry further comprises an additional switch coupled between the light-emitting diode and the additional current control transistor. 
     
     
       15. A method of operating an electronic device, comprising:
 operating at least one light-emitting diode with a pulse-width-modulation controller using a first pulse-width-modulation duty cycle and a first peak current; and 
 operating the at least one light-emitting diode with the pulse-width-modulation controller using a second pulse-width-modulation duty cycle and a second peak current, wherein the first and second peak currents are different and tunable to control and reduce headroom voltage of the at least one light-emitting diode. 
 
     
     
       16. The method of  claim 15 , wherein the first peak current is larger than the second peak current. 
     
     
       17. The method of  claim 15 , wherein operating at least one light-emitting diode using the first pulse-width-modulation duty cycle and the first peak current comprises providing the first peak current using a digital-to-analog converter and providing the first pulse-width-modulation duty cycle with a pulse-width-modulation controller. 
     
     
       18. The method of  claim 17 , wherein operating at least one light-emitting diode using the second pulse-width-modulation duty cycle and the second peak current comprises providing the second peak current using the digital-to-analog converter and providing the second pulse-width-modulation duty cycle with the pulse-width-modulation controller. 
     
     
       19. The method of  claim 17 , wherein operating at least one light-emitting diode using the second pulse-width-modulation duty cycle and the second peak current comprises providing the second peak current using an additional digital-to-analog converter and providing the second pulse-width-modulation duty cycle with an additional pulse-width-modulation controller. 
     
     
       20. A method of operating an electronic device, comprising:
 operating a light-emitting diode with a first driver circuit having a first linear current controller that provides a constant current to the light-emitting diode; and 
 operating the light-emitting diode with a second driver circuit having a pulse-width modulation controller that provides a modulated current to the light-emitting diode. 
 
     
     
       21. The method of  claim 20 , wherein the first driver circuit comprises a first digital-to-analog converter coupled to a first current control transistor for the light-emitting diode. 
     
     
       22. The method of  claim 21 , wherein the second driver circuit comprises a second digital-to-analog converter coupled to a second current control transistor for the light-emitting diode. 
     
     
       23. The method of  claim 22 , wherein operating the light-emitting diode using the second driver circuit that provides the modulated current to the light-emitting diode comprises modulating a current from the second digital-to-analog converter using a switch coupled between the second digital-to-analog converter and the second current control transistor. 
     
     
       24. The method of  claim 22 , wherein the first digital-to-analog converter is an N-bit digital-to-analog converter, wherein the second digital-to-analog converter is an M-bit digital-to-analog converter, and wherein N is greater than M.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of U.S. patent application Ser. No. 15/784,943, entitled “SPLIT DRIVER BACKLIGHT SYSTEMS AND METHOD,” filed on Oct. 16, 2017, which claims the benefit of U.S. Provisional Patent Application Ser. No. 62/546,456, entitled “SPLIT DRIVER BACKLIGHT SYSTEMS AND METHOD,” filed on Aug. 16, 2017, both of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present description relates generally to electronic devices with displays, and more particularly, but not exclusively, to electronic devices with displays having backlights. 
     BACKGROUND 
     Electronic devices such as computers, media players, cellular telephones, set-top boxes, and other electronic equipment are often provided with displays for displaying visual information. Displays such as organic light-emitting diode (OLED) displays and liquid crystal displays (LCDs) typically include an array of display pixels arranged in pixel rows and pixel columns. Liquid crystal displays commonly include a backlight unit and a liquid crystal display unit with individually controllable liquid crystal display pixels. 
     The backlight unit commonly includes one or more light-emitting diodes (LEDs) that generate light that exits the backlight toward the liquid crystal display unit. The liquid crystal display pixels are individually operable to control passage of light from the backlight unit through that pixel to display content such as text, images, video, or other content on the display. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Certain features of the subject technology are set forth in the appended claims. However, for purpose of explanation, several embodiments of the subject technology are set forth in the following figures. 
         FIG. 1  illustrates a perspective view of an example electronic device having a display in accordance with various aspects of the subject technology. 
         FIG. 2  illustrates a block diagram of a side view of an electronic device display having a backlight unit in accordance with various aspects of the subject technology. 
         FIG. 3  illustrates a schematic diagram of light-emitting diode (LED) driver circuitry for direct and pulse-width-modulation (PWM) current control in accordance with various aspects of the subject technology. 
         FIG. 4  illustrates a brightness control scheme for direct and PWM light-emitting diode (LED) currents in accordance with various aspects of the subject technology. 
         FIG. 5  illustrates a brightness control scheme for multi-peak PWM light-emitting diode (LED) currents in accordance with various aspects of the subject technology. 
         FIG. 6  illustrates LED headroom voltages generated using direct and PWM light-emitting diode (LED) currents in accordance with various aspects of the subject technology. 
         FIG. 7  illustrates LED headroom voltages generated using direct and multi-peak PWM light-emitting diode (LED) currents in accordance with various aspects of the subject technology. 
         FIG. 8  illustrates a schematic diagram of light-emitting diode (LED) driver circuitry having multiple drivers each for providing direct and pulse-width-modulation (PWM) current control in accordance with various aspects of the subject technology. 
         FIG. 9  illustrates a schematic diagram of light-emitting diode (LED) driver circuitry having a first driver for providing direct LED current control and a second driver for providing pulse-width-modulation (PWM) LED current control in accordance with various aspects of the subject technology. 
         FIG. 10  illustrates a schematic diagram of light-emitting diode (LED) driver circuitry having current scaling circuitry for each of a first driver for providing direct LED current control and a second driver for providing pulse-width-modulation (PWM) LED current control in accordance with various aspects of the subject technology. 
         FIG. 11  illustrates a brightness control scheme for direct and PWM light-emitting diode (LED) currents with a trimmalbe and scalable knee point in accordance with various aspects of the subject technology. 
         FIG. 12  is a flow chart of illustrative operations that may be performed for multi-peak PWM LED current control in accordance with various aspects of the subject technology. 
         FIG. 13  is a flow chart of illustrative operations that may be performed for dual driver LED current control in accordance with various aspects of the subject technology. 
     
    
    
     DETAILED DESCRIPTION 
     The detailed description set forth below is intended as a description of various configurations of the subject technology and is not intended to represent the only configurations in which the subject technology may be practiced. The appended drawings are incorporated herein and constitute a part of the detailed description. The detailed description includes specific details for the purpose of providing a thorough understanding of the subject technology. However, it will be clear and apparent to those skilled in the art that the subject technology is not limited to the specific details set forth herein and may be practiced without these specific details. In some instances, well-known structures and components are shown in block diagram form in order to avoid obscuring the concepts of the subject technology. 
     The subject disclosure provides electronic devices such as cellular telephones, media players, tablet computers, laptop computers, set-top boxes, smart watches, wireless access points, and other electronic equipment that include light-emitting diode arrays such as in backlight units of displays. Displays are used to present visual information and status data and/or may be used to gather user input data. A display includes an array of display pixels. Each display pixel may include one or more colored subpixels for displaying color images. 
     Each display pixel may include a layer of liquid crystals disposed between a pair of electrodes operable to control the orientation of the liquid crystals. Controlling the orientation of the liquid crystals controls the polarization of backlight from a backlight unit of the display. This polarization control, in combination with polarizers on opposing sides of the liquid crystal layer, allows light passing into the pixel to be manipulated to selectively block the light or allow the light to pass through the pixel. 
     The backlight unit includes one or more light-emitting diodes (LEDs) such as one or more strings and/or arrays of light-emitting diodes that generate the backlight for the display. In various configurations, strings of light-emitting diodes may be arranged along one or more edges of a light guide plate that distributes backlight generated by the strings to the LCD unit, or may be arranged to form a two-dimensional array of LEDs. 
     Although examples discussed herein describe LEDs included in display backlights, it should be appreciated that the LED control circuitry and methods described herein can be applied to LEDs implemented in other devices or portions of a device (e.g., in a backlit keyboard or a flash device). 
     Mixed mode dimming of LEDs is sometimes performed for LEDs that receive a common supply voltage, by individually controlling the current through one or more LEDs using multiple current control modes. Mixed-mode dimming includes directly controlling the current through one or more LEDs for LED currents above a knee point and controlling the current below the knee point using pulse-width modulation (PWM) of the current with a fixed peak current. The fixed peak current is equal to the knee point current, which is also the minimum of the directly controlled current. 
     For example mixed-mode dimming can be used for local dimming of display backlights to enhance the displayed content on the display (e.g., to enhance the brightness of bright regions of the displayed content by increasing backlight brightness and to provide darker dark regions of the displayed content by reducing backlight brightness in those regions). 
     Mixed mode dimming can be provided by an LED driver that includes a direct current supply (e.g., a digital-to-analog converter that operates a current-control transistor) and a PWM switch. However, providing mixed-mode dimming using a single DAC and a single PWM switch can have disadvantages in terms of power loss, current accuracy, susceptibility to noise, and driver area. 
     In accordance with various aspects of the subject disclosure, mixed mode dimming of LEDs includes PWM dimming using multiple peak currents (e.g., by varying a PWM duty cycle with each of two or more peak currents, modified using PWM on pulses). PWM dimming using multiple peak currents may help reduce headroom voltages at the end of one or more LED strings (e.g., the voltage at a location between a last LED in a series-coupled string of LEDs and current control circuitry for that string), which can reduce power consumption by the device. 
     In accordance with various aspects of the subject disclosure, mixed mode dimming of LEDs is provided using multiple drivers (e.g., a dual driver circuit having a relatively smaller driver stage for PWM dimming and a relatively larger driver stage for providing direct current control). A dual driver circuit for LEDs as described herein can provide a selectable and/or trimmable direct-to-PWM transition current and/or other advantages as discussed in further detail hereinafter. 
     An illustrative electronic device having light-emitting diodes is shown in  FIG. 1 . In the example of  FIG. 1 , device  100  has been implemented using a housing that is sufficiently small to be portable and carried by a user (e.g., device  100  of  FIG. 1  may be a handheld electronic device such as a tablet computer or a cellular telephone). As shown in  FIG. 1 , device  100  may include a display such as display  110  mounted on the front of housing  106 . Display  110  may be substantially filled with active display pixels or may have an active portion and an inactive portion. Display  110  may have openings (e.g., openings in the inactive or active portions of display  110 ) such as an opening to accommodate button  104  and/or other openings such as an opening to accommodate a speaker, a light source, or a camera. 
     Display  110  may be a touch screen that incorporates capacitive touch electrodes or other touch sensor components or may be a display that is not touch-sensitive. Display  110  may include display pixels formed from light-emitting diodes (LEDs), organic light-emitting diodes (OLEDs), plasma cells, electrophoretic display elements, electrowetting display elements, liquid crystal display (LCD) components, or other suitable display pixel structures. Arrangements in which display  110  is formed using LCD pixels and LED backlights are sometimes described herein as an example. This is, however, merely illustrative. In various implementations, any suitable type of display technology may be used in forming display  110  if desired. 
     Housing  106 , which may sometimes be referred to as a case, may be formed of plastic, glass, ceramics, fiber composites, metal (e.g., stainless steel, aluminum, etc.), other suitable materials, or a combination of any two or more of these materials. 
     The configuration of electronic device  100  of  FIG. 1  is merely illustrative. In other implementations, electronic device  100  may be a computer such as a computer that is integrated into a display such as a computer monitor, a laptop computer, a somewhat smaller portable device such as a wrist-watch device, a pendant device, or other wearable or miniature device, a media player, a gaming device, a navigation device, a computer monitor, a television, or other electronic equipment. 
     For example, in some implementations, housing  106  may be formed using a unibody configuration in which some or all of housing  106  is machined or molded as a single structure or may be formed using multiple structures (e.g., an internal frame structure, one or more structures that form exterior housing surfaces, etc.). Although housing  106  of  FIG. 1  is shown as a single structure, housing  106  may have multiple parts. For example, housing  106  may have upper portion and lower portion coupled to the upper portion using a hinge that allows the upper portion to rotate about a rotational axis relative to the lower portion. A keyboard such as a QWERTY keyboard and a touch pad may be mounted in the lower housing portion, in some implementations. An LED backlight array may also be provided for the keyboard and/or other illuminated portions of device  100 . 
     In some implementations, electronic device  100  may be provided in the form of a computer integrated into a computer monitor. Display  110  may be mounted on a front surface of housing  106  and a stand may be provided to support housing (e.g., on a desktop). 
       FIG. 2  is a schematic diagram of display  110  in which the display is provided with a liquid crystal display unit  204  and a backlight unit  202 . As shown in  FIG. 2 , backlight unit  202  generates backlight  208  and emits backlight  208  in the direction of liquid crystal display unit  204 . Liquid crystal display unit  204  selectively allows some or all of the backlight  208  to pass through the liquid crystal display pixels therein to generate display light  210  visible to a user. Backlight unit  202  includes one or more subsections  206 . 
     In some implementations, subsections  206  may be elongated subsections that extend horizontally or vertically across some or all of display  110  (e.g., in an edge-lit configuration for backlight unit  202 ). In other implementations, subsections  206  may be square or other rectilinear subsections (e.g., subarrays of a two-dimensional LED array backlight). Accordingly, subsections  206  may be defined by one or more strings and/or arrays of LEDs disposed in that subsection. Subsections  206  may be controlled individually for local dimming of backlight  208 . 
     Although backlight unit  202  is shown implemented with a liquid crystal display unit, it should be appreciated that a backlight unit such as backlight unit  202  may be implemented in a backlit keyboard, or to illuminate a flash device or otherwise provide illumination for an electronic device. 
       FIG. 3  shows a schematic diagram of exemplary LED circuitry such as backlight circuitry for display  110 . For example, LED circuitry  300  of  FIG. 3  may be implemented in backlight unit  202  or other LED lighting devices. In the example of  FIG. 3 , circuitry  300  includes at least one LED  302  (e.g., an LED in a string of series-coupled LEDs) and an associated driver  301  for controlling the brightness of the LED. 
     In the example of  FIG. 3 , LED circuitry  300  includes switch  304 , transistor  306 , and resistor  308  coupled in series between LED  302  and a ground voltage. Switch  304  is operated by PWM driver  301 . Transistor  306  is operated by controlling a gate voltage for the transistor with a selectable voltage reference  312  such as a digital-to-analog converter (DAC) coupled to the gate terminal. As shown in  FIG. 3 , an operational amplifier  314  may be coupled between DAC  312  and the gate terminal of transistor  306  to provide feedback control of the current through transistor  306 . A first input terminal of amplifier  314  receives an output of DAC  312  and a second input terminal of amplifier  314  receives a residual voltage for comparison, by amplifier  314  to the input voltage from DAC  312 . The output of amplifier  314  includes an output terminal coupled to the gate terminal of transistor  306 . In the example of  FIG. 3 , the feedback voltage is a residual voltage at a location between transistor  306  and resistor  308 . 
     Driver  301  converts input brightness information to current levels to drive LEDs  302  (e.g., implemented in LED strings). LED current is controlled either using linear scaling of the current using DAC  312  to operate current control transistor  306  or by PWM control using PWM driver  310  at a fixed peak current to operate switch  304  such that average current through LED  302  is controlled by adjusting the duty cycle of a fixed frequency PWM waveform.  FIG. 4  shows an example plot  400  of LED current ILED vs. LED brightness in which an LED is controlled using a PWM current  402  at low currents (e.g., currents below a knee point or switch (SW) point) and using linearly scaled current  404  at relatively high current (e.g., at currents above the knee point). PWM brightness control can help avoid color shifts at low LED current levels. 
     However, operating LED  302  using the currents illustrated in  FIG. 4  with a single LED driver  301  as shown in  FIG. 3  can have disadvantages, if care is not taken. For example, the headroom voltage at the end of one or more LED strings (e.g., at a location between the last LED  302  in the string and current control circuitry such as switch  304  and/or transistor  306  for that string) can be high causing unwanted power dissipation. As another example, in some scenarios, 12 bits of PWM resolution is desired which can lead to PWM duty cycles equal to approximately 0.025% (e.g., with an approximately 10 ns pulse width for a PWM frequency of 25 kHz). This can lead to relatively narrow pulses to achieve high resolution, which can become distorted in time. 
     In accordance with some aspects of the subject disclosure, multi-peak PWM control of LED  302  can be performed, which can help reduce headroom voltage and power dissipation.  FIG. 5  shows an example plot  500  of PWM-controlled LED currents  502  and  504  each having a different peak current (e.g., respective peak currents of approximately 6.25 milliamps (mA) and 33 mA). As indicated in  FIG. 5 , the two peak currents may be tunable to control the headroom voltage of the LED device. 
       FIG. 6  shows example headroom voltages for three strings  602  of LEDs  604  of an LED device  600 , operated with mixed mode dimming as shown in  FIG. 3 . In each string  602 , one or more LEDs  604  are coupled in series between a supply voltage Vout and a current controller  606  (e.g., driver  301  of  FIG. 3 ). Illustrative LED currents and resulting string voltages  610  and headroom voltages  608  are shown. In the example of  FIG. 6 , direct controlled LED currents of 40 mA and 20 mA result in string voltages  610  of 6.1 Volts (V) and 5.7 V and headroom voltages of 0.7 V and 1.1 V. A PWM current  612  of 7.5 mA results in string voltage of 5.4 V and a residual voltage of 1.4 V. 
     As shown in  FIG. 7 , if the middle string  602  is instead operated with a 20 mA PWM current  700  generated by a 40 mA peak current with a 50% PWM duty cycle, the headroom voltage on that string is reduced to 0.7 V. As illustrated by  FIGS. 6 and 7 , operating LEDs using multi-peak PWM currents as in the example of  FIG. 4 , can facilitate the use of reduced headroom voltages which can reduce the overall power consumption of an LED device. 
     The multi peak PWM control can be applied by changing the output of DAC  312  of  FIG. 3  to raise and/or lower the fixed peak current, or can be provided by an LED driver circuit with multiple drivers.  FIG. 8  shows an example of exemplary LED circuitry such as backlight circuitry for display  110  that includes multiple drivers. For example, LED circuitry  800  of  FIG. 8  may be implemented in backlight unit  202  or other LED lighting devices. In the example of  FIG. 8 , circuitry  800  includes at least one LED  802  (e.g., an LED in a string of series-coupled LEDs) and associated drivers  801  and  821  (sometimes referred to as driver stages of an overall driver for LED  802 ), coupled in parallel between LED  802  and the ground voltage, for controlling the brightness of the LED. 
     In the example of  FIG. 8 , driver  801  includes switch  804 , transistor  806 , and resistor  808  coupled in series between LED  802  and the ground voltage. Switch  804  is operated by PWM driver  810 . Transistor  806  is operated by controlling a gate voltage for the transistor with a digital-to-analog converter (DAC)  812  coupled to the gate terminal. As shown in  FIG. 8 , an operational amplifier  814  may be coupled between DAC  812  and the gate terminal of transistor  806  to provide feedback control of the current through transistor  806 . A first input terminal of amplifier  814  receives an output of DAC  812  and a second input terminal of amplifier  814  receives a residual voltage for comparison, by amplifier  814  to the input voltage from DAC  812 . The output of amplifier  814  includes an output terminal coupled to the gate terminal of transistor  806 . 
     In the example of  FIG. 8 , driver  831  includes switch  834 , transistor  836 , and resistor  838  coupled in series between LED  802  and the ground voltage. Switch  834  is operated by PWM driver  830 . Transistor  836  is operated by controlling a gate voltage for the transistor with a digital-to-analog converter (DAC)  832  coupled to the gate terminal. As shown in  FIG. 8 , an operational amplifier  844  may be coupled between DAC  832  and the gate terminal of transistor  836  to provide feedback control of the current through transistor  836 . A first input terminal of amplifier  844  receives an output of DAC  832  and a second input terminal of amplifier  844  receives a residual voltage for comparison, by amplifier  844  to the input voltage from DAC  832 . The output of amplifier  844  includes an output terminal coupled to the gate terminal of transistor  836 . 
     Drivers  801  and/or  821  convert input brightness information to current levels to drive LEDs  802  (e.g., implemented in LED strings). When using driver  801  alone, LED current is controlled by linearly modifying the current from DAC  812  or by setting a fixed peak current using DAC  812  to operate current control transistor  806  and by reducing the average current through LED  802  by PWM control using PWM driver  810  to operate switch  804 . When using driver  821  alone, LED current is controlled by linearly modifying the current from DAC  832 , or by setting a fixed peak current using DAC  832  to operate current control transistor  836  and by reducing the average current through LED  802  by PWM control using PWM driver  830  to operate switch  834 . 
     Driver  801  may be used when driver  821  is decoupled from LED  802  (e.g., with switch  834 ). Driver  821  may be used when driver  801  is decoupled from LED  802  (e.g., with switch  804 ). For example, one of drivers  801  and  821  may be a relatively larger than the other of drivers  801  and  821 . For very low brightness, only the small driver may be operational to provide high resolution with lower distortion. In some scenarios, drivers  801  and  802  may both be operated to deliver LED current (e.g., for high brightness operations). In some scenarios, driver  801  and  821  may co-operate to provide multi-peak PWM control as described above in connection with  FIG. 5 . 
     For example, for a first LED brightness, DAC  812  can provide a first peak current (e.g., an adjustable peak current of about 5-10 mA) which can be reduced, on average, by PWM controller  810  to a first average current corresponding to the first LED brightness. For a second LED brightness, DAC  832  can provide a second peak current (e.g., an adjustable peak current of about 30-40 mA) which can be reduced, on average, by PWM controller  830  to a second average current corresponding to the second LED brightness. 
     In other scenarios, high resolution PWM dimming of LED  802  can be performed by inter-modulating the PWM control of drivers  801  and  821 . In other scenarios, mixed mode dimming of LED  802  can be performed by using the smaller one of drivers  801  and  821  for PWM dimming and the larger of drivers  801  and  821  for the linear current control. In accordance with some aspects, mixed mode dimming of LEDs may be provided by a dual driver LED control circuit in which only one of the drivers is PWM controllable. 
       FIG. 9  shows an example of LED circuitry such as backlight circuitry for display  110  that includes multiple drivers in which only one of the drivers is PWM controllable. In the example of  FIG. 9 , LED circuitry  900  includes a first driver  921  and a second driver  901  coupled in parallel between LED  902  and a ground voltage. 
     Driver  921  may be operated to provide PWM controlled current through LED  902  by operation of switch  944  by PWM controller  930  to selectively couple and decouple DAC  932  (e.g., an 8 bit DAC) from a first input terminal of operational amplifier  934 . As shown, a second input terminal of operational amplifier  934  receives a feedback voltage for comparison to the PWM controlled voltage from DAC  932 . The output terminal of amplifier  934  is coupled to the gate terminal of transistor  936  for controlling current through LED  902 . PWM controller  930  may provide dithering (e.g., PWM controller may be a 14 bit controller that provides 10 bits PWM resolution and 4 bits dithering). The peak value of the current in the PWM cycle generated by driver  921  may be trimmed using DAC  932 . DAC  932  may provide, for example, a peak current of 5-10 mA (e.g., 6.25 mA plus 20 percent). 
     Driver  901  may be operated to provide linear current control for higher LED currents through LED  902  (e.g., direct currents of up to between 30 mA and 40 mA, such as a 33.75 mA current). DAC  912  (e.g., a 10 bit DAC) selects the output current of linear driver  901 . As shown, the output of DAC  912  can be provided to a first input terminal of an operational amplifier  914  that has an output terminal coupled to the gate terminal of transistor  904  (coupled in series between LED  902  and resistor  906 ). A second input terminal of amplifier  914  receives a feedback voltage from a location between transistor  904  and resistor  906 . 
     In order to provide additional control of drivers  901  and  921 , current DACs (IDACs) such as IDACs  1000  and  1010  may be coupled, respectively to DACs  932  and  912  as shown in  FIG. 10 . In the configuration of  FIG. 10 , the transition point between PWM control by driver  921  and linear control by driver  901  may be selectable using IDAC  1000  (e.g., selectively coupling a current source  1002  to DAC  932  using switches  1004 ). In the configuration of  FIG. 10 , trimming of the transition point between PWM control by driver  921  and linear control by driver  901  may be performed using trim values  1008  for DAC  932 . In the configuration of  FIG. 10 , analog control of the current through LED  902  can be performed using only DAC  912 . In the configuration of  FIG. 10 , display-wide dimming of backlight unit  202  may be performed using IDAC  1010  (e.g., by selectively coupling a current source  1012  to DAC  912  using switches  1014 ). In various implementations, IDACs  1000  and  1010  may be coupled one or more drivers of one or more LEDs provide local or global transition point selection and/or global dimming for a display. 
     LED circuitry as shown in  FIG. 10  provides mixed mode current control, as shown by the current plot  400  of  FIG. 11 , in which PWM control is performed at low currents by driver  921 , linear current control is provided at higher currents by driver  901 , and the switch (SW) or transition point between PWM control and linear control is both trimmable (e.g., by +20%/−44%) and scalable. LED circuitry as shown in  FIG. 9  and  FIG. 10 , as examples, can provide reduced power loss, better accuracy, better noise immunity, and a smaller driver area (e.g., for a 10 bit composite DAC/PWM driver relative to a 14 bit single DAC/PWM driver). 
       FIG. 12  depicts a flow diagram of an example process for multi-peak PWM control of LED current in accordance with various aspects of the subject technology. For explanatory purposes, the example process of  FIG. 12  is described herein with reference to the components of  FIGS. 3 and 8-10 . Further for explanatory purposes, the blocks of the example process of  FIG. 12  are described herein as occurring in series, or linearly. However, multiple blocks of the example process of  FIG. 12  may occur in parallel. In addition, the blocks of the example process of  FIG. 12  need not be performed in the order shown and/or one or more of the blocks of the example process of  FIG. 12  need not be performed. 
     In the depicted example flow diagram, at block  1200 , at least one light-emitting diode is operated using a first pulse-width-modulation duty cycle and a first peak current. For example, the first PWM duty cycle and the first peak current may correspond to the duty cycles and/or peak current of PWM current  502  of  FIG. 5 . 
     At block  1202 , the at least one light-emitting diode is operated using a second pulse-width-modulation duty cycle and a second peak current, where the first and second pulse-width-modulation duty cycles and/or the first and second peak currents are different. For example, the second PWM duty cycle and the second peak current may correspond to the duty cycles and/or peak current of PWM current  504  of  FIG. 5 . 
       FIG. 13  depicts a flow diagram of an example process for multi-peak PWM control of LED current in accordance with various aspects of the subject technology. For explanatory purposes, the example process of  FIG. 13  is described herein with reference to the components of  FIGS. 8-10 . Further for explanatory purposes, the blocks of the example process of  FIG. 13  are described herein as occurring in series, or linearly. However, multiple blocks of the example process of  FIG. 13  may occur in parallel. In addition, the blocks of the example process of  FIG. 13  need not be performed in the order shown and/or one or more of the blocks of the example process of  FIG. 13  need not be performed. 
     In the depicted example flow diagram, at block  1300 , at least one light-emitting diode is operated using a first driver circuit (e.g., driver  901  of  FIG. 9  or  FIG. 10 ) that provides a constant current to the at least one light-emitting diode. 
     At block  1302 , the at least one light-emitting diode is operated using a second driver circuit (e.g., driver  921  of  FIG. 9  or  FIG. 10 ) that provides a modulated (e.g., PWM) current to the at least one light emitting diode. 
     In accordance with various aspects of the subject disclosure, an electronic device having a display with a backlight is provided, the backlight including a light-emitting diode and a backlight driver. The backlight driver includes a first driver stage coupled to the light-emitting diode and having a pulse-width modulation controller and a first linear current controller. The backlight driver also includes a second driver stage coupled to the light-emitting diode and having a second linear current controller. 
     In accordance with other aspects of the subject disclosure, an electronic device having a display is provided, the display including a backlight unit that includes a light-emitting diode, direct current control circuitry, and pulse-width-modulation current control circuitry to modulate a first current provided by the direct current control circuitry through the light-emitting diode and to modulate a second current provided by the direct current control circuitry through the light-emitting diode. The first current is larger than the second current. 
     In accordance with other aspects of the subject disclosure, a method is provided that includes operating at least one light-emitting diode using a first pulse-width-modulation duty cycle and a first peak current and operating the at least one light-emitting diode using a second pulse-width-modulation duty cycle and a second peak current. The first and second peak currents are different. 
     In accordance with other aspects of the subject disclosure, a method is provided that includes operating at least one light-emitting diode using a first driver circuit that provides a constant current to the at least one light-emitting diode and operating the at least one light-emitting diode using a second driver circuit that provides a modulated current to the at least one light-emitting diode. 
     Various functions described above can be implemented in digital electronic circuitry, in computer software, firmware or hardware. The techniques can be implemented using one or more computer program products. Programmable processors and computers can be included in or packaged as mobile devices. The processes and logic flows can be performed by one or more programmable processors and by one or more programmable logic circuitry. General and special purpose computing devices and storage devices can be interconnected through communication networks. 
     Some implementations include electronic components, such as microprocessors, storage and memory that store computer program instructions in a machine-readable or computer-readable medium (alternatively referred to as computer-readable storage media, machine-readable media, or machine-readable storage media). Some examples of such computer-readable media include RAM, ROM, read-only compact discs (CD-ROM), recordable compact discs (CD-R), rewritable compact discs (CD-RW), read-only digital versatile discs (e.g., DVD-ROM, dual-layer DVD-ROM), a variety of recordable/rewritable DVDs (e.g., DVD-RAM, DVD-RW, DVD+RW, etc.), flash memory (e.g., SD cards, mini-SD cards, micro-SD cards, etc.), magnetic and/or solid state hard drives, ultra density optical discs, any other optical or magnetic media, and floppy disks. The computer-readable media can store a computer program that is executable by at least one processing unit and includes sets of instructions for performing various operations. Examples of computer programs or computer code include machine code, such as is produced by a compiler, and files including higher-level code that are executed by a computer, an electronic component, or a microprocessor using an interpreter. 
     While the above discussion primarily refers to microprocessor or multi-core processors that execute software, some implementations are performed by one or more integrated circuits, such as application specific integrated circuits (ASICs) or field programmable gate arrays (FPGAs). In some implementations, such integrated circuits execute instructions that are stored on the circuit itself. 
     As used in this specification and any claims of this application, the terms “computer”, “processor”, and “memory” all refer to electronic or other technological devices. These terms exclude people or groups of people. For the purposes of the specification, the terms “display” or “displaying” means displaying on an electronic device. As used in this specification and any claims of this application, the terms “computer readable medium” and “computer readable media” are entirely restricted to tangible, physical objects that store information in a form that is readable by a computer. These terms exclude any wireless signals, wired download signals, and any other ephemeral signals. 
     To provide for interaction with a user, implementations of the subject matter described in this specification can be implemented on a computer having a display device as described herein for displaying information to the user and a keyboard and a pointing device, such as a mouse or a trackball, by which the user can provide input to the computer. Other kinds of devices can be used to provide for interaction with a user as well; for example, feedback provided to the user can be any form of sensory feedback, such as visual feedback, auditory feedback, or tactile feedback; and input from the user can be received in any form, including acoustic, speech, or tactile input. 
     Many of the above-described features and applications are implemented as software processes that are specified as a set of instructions recorded on a computer readable storage medium (also referred to as computer readable medium). When these instructions are executed by one or more processing unit(s) (e.g., one or more processors, cores of processors, or other processing units), they cause the processing unit(s) to perform the actions indicated in the instructions. Examples of computer readable media include, but are not limited to, CD-ROMs, flash drives, RAM chips, hard drives, EPROMs, etc. The computer readable media does not include carrier waves and electronic signals passing wirelessly or over wired connections. 
     In this specification, the term “software” is meant to include firmware residing in read-only memory or applications stored in magnetic storage, which can be read into memory for processing by a processor. Also, in some implementations, multiple software aspects of the subject disclosure can be implemented as sub-parts of a larger program while remaining distinct software aspects of the subject disclosure. In some implementations, multiple software aspects can also be implemented as separate programs. Finally, any combination of separate programs that together implement a software aspect described here is within the scope of the subject disclosure. In some implementations, the software programs, when installed to operate on one or more electronic systems, define one or more specific machine implementations that execute and perform the operations of the software programs. 
     A computer program (also known as a program, software, software application, script, or code) can be written in any form of programming language, including compiled or interpreted languages, declarative or procedural languages, and it can be deployed in any form, including as a stand alone program or as a module, component, subroutine, object, or other unit suitable for use in a computing environment. A computer program may, but need not, correspond to a file in a file system. A program can be stored in a portion of a file that holds other programs or data (e.g., one or more scripts stored in a markup language document), in a single file dedicated to the program in question, or in multiple coordinated files (e.g., files that store one or more modules, sub programs, or portions of code). A computer program can be deployed to be executed on one computer or on multiple computers that are located at one site or distributed across multiple sites and interconnected by a communication network. 
     It is understood that any specific order or hierarchy of blocks in the processes disclosed is an illustration of example approaches. Based upon design preferences, it is understood that the specific order or hierarchy of blocks in the processes may be rearranged, or that all illustrated blocks be performed. Some of the blocks may be performed simultaneously. For example, in certain circumstances, multitasking and parallel processing may be advantageous. Moreover, the separation of various system components in the embodiments described above should not be understood as requiring such separation in all embodiments, and it should be understood that the described program components and systems can generally be integrated together in a single software product or packaged into multiple software products. 
     The previous description is provided to enable any person skilled in the art to practice the various aspects described herein. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects. Thus, the claims are not intended to be limited to the aspects shown herein, but are to be accorded the full scope consistent with the language claims, wherein reference to an element in the singular is not intended to mean “one and only one” unless specifically so stated, but rather “one or more.” Unless specifically stated otherwise, the term “some” refers to one or more. Pronouns in the masculine (e.g., his) include the feminine and neuter gender (e.g., her and its) and vice versa. Headings and subheadings, if any, are used for convenience only and do not limit the subject disclosure. 
     The predicate words “configured to”, “operable to”, and “programmed to” do not imply any particular tangible or intangible modification of a subject, but, rather, are intended to be used interchangeably. For example, a processor configured to monitor and control an operation or a component may also mean the processor being programmed to monitor and control the operation or the processor being operable to monitor and control the operation. Likewise, a processor configured to execute code can be construed as a processor programmed to execute code or operable to execute code 
     A phrase such as an “aspect” does not imply that such aspect is essential to the subject technology or that such aspect applies to all configurations of the subject technology. A disclosure relating to an aspect may apply to all configurations, or one or more configurations. A phrase such as an aspect may refer to one or more aspects and vice versa. A phrase such as a “configuration” does not imply that such configuration is essential to the subject technology or that such configuration applies to all configurations of the subject technology. A disclosure relating to a configuration may apply to all configurations, or one or more configurations. A phrase such as a configuration may refer to one or more configurations and vice versa. 
     The word “example” is used herein to mean “serving as an example or illustration.” Any aspect or design described herein as “example” is not necessarily to be construed as preferred or advantageous over other aspects or design 
     All structural and functional equivalents to the elements of the various aspects described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. No claim element is to be construed under the provisions of 35 U.S.C. § 112, sixth paragraph, unless the element is expressly recited using the phrase “means for” or, in the case of a method claim, the element is recited using the phrase “step for.” Furthermore, to the extent that the term “include,” “have,” or the like is used in the description or the claims, such term is intended to be inclusive in a manner similar to the term “comprise” as “comprise” is interpreted when employed as a transitional word in a claim.

Metadata:
Filing Date: 20190314
Publication Date: 20200728
Grant Date: 20200728
Priority Date: 20170816
Inventors: NAVABI-SHIRAZI, MOHAMMAD J.
ASCORRA, ALEJANDRO LARA
HUSSAIN, ASIF
RYOO, JI YEOUL
CHEN, JINGDONG
QI, JUN
PANDYA, MANISHA P.
XIE, Yanhui
Assignee: APPLE INC
CPC Classifications: [{"code": "G09G3/3406", "inventive": true, "first": true, "tree": "[]"}, {"code": "H05B45/3725", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05B45/10", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133601", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05B45/46", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05B45/3725", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G3/3406", "inventive": true, "first": true, "tree": "[]"}, {"code": "G09G2320/0633", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/064", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05B45/395", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G2330/021", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/064", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05B45/395", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G2330/021", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/0633", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05B45/46", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133528", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/134309", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05B45/10", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/1336", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/3406", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/1336", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/0633", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2330/021", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05B45/46", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F2001/133601", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/064", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133528", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05B45/395", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/134309", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05B45/37", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05B45/10", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 65360216