PATENT DOCUMENT

Publication Number: US-8988408-B2
Application Number: US-83910410-A
Country: US
Kind Code: B2

Title: Variable-bias power supply

Abstract:
A responsive, low-power display panel power supply is provided. In one embodiment, such a display panel power supply may include a regulator whose responsiveness varies depending on the bias current it consumes, and a current source that provides a variable bias current. The regulator may provide the display panel a supply voltage and a supply current based on a reference voltage and a bias current. Various events taking place in the display panel, such as toggling at COM lines, source lines, and/or gate lines may cause parasitic capacitances within the display panel to draw more or less supply current. To ensure the regulator remains suitably responsive to such changes in supply current, while reducing the total power consumed by the power supply, the current source may provide a higher bias current to the regulator at least while the supply current is changing than at certain other times.

Claims:
What is claimed is: 
     
       1. A power supply comprising:
 a regulator configured to output a supply current to a display panel based at least in part on a bias current; 
 a current source configured to provide the bias current to the regulator, wherein the bias current is configured to be at a relatively higher current at least while the amount of the supply current output by the regulator is expected to change than at other times; and 
 a predictive bias current circuitry configured to predict when the amount of the supply current is expected to change due to electrical changes expected to occur in the display panel, wherein the predictive bias current circuitry is configured to predict that the amount of supply current is expected to change:
 when capacitive coupling currents are generated in parasitic capacitors of the display panel; or 
 upon a rising edge of a clock signal edge of the clock signal; or 
 when an electronic component proximate to the display panel undertakes or is about to undertake an operation; 
 or any combination thereof. 
 
 
     
     
       2. The power supply of  claim 1 , wherein the bias current provided to the regulator by the current source is configured to be at the relatively higher current before the amount of supply current changes and to remain the relatively higher current while the amount of supply current is changing. 
     
     
       3. The power supply of  claim 1 , wherein the predictive bias current control circuitry is configured to control the current source such that the bias current is at a relatively lower current when the predictive bias current control circuitry predicts that the amount of supply current is expected to be stable than when the predictive bias current control circuitry predicts that the amount of supply current is expected to change. 
     
     
       4. The power supply of  claim 1 , wherein the predictive bias current control circuitry is configured to predict that the supply current is expected to change based at least in part on a time source shared by the display panel and the predictive bias current control circuitry. 
     
     
       5. A method comprising:
 providing a supply current and a supply voltage to a display panel using a low dropout regulator, wherein the supply current is generated based at least in part on a first bias current or a second bias current provided to the low dropout regulator; 
 predicting that the amount of supply current to the display panel is expected to change based on electrical changes expected to occur in the display panel using a bias current controller, wherein the bias current controller is configured to predict that the amount of supply current is expected to change:
 when capacitive coupling currents are generated in parasitic capacitors of the display panel; or 
 upon a rising edge of a clock signal edge of the clock signal; or 
 when an electronic component proximate to the display panel undertakes or is about to undertake an operation; 
 or any combination thereof; 
 
 providing the first bias current to the low dropout regulator using the bias current controller at least before and while the supply current to the display panel is expected to change; and 
 providing the second bias current to the low dropout regulator using the bias current controller at all other times. 
 
     
     
       6. The method of  claim 5 , wherein the first bias current is higher than the second bias current. 
     
     
       7. The method of  claim 5 , wherein the first bias current is provided to the low dropout regulator after the supply current to the display panel is expected to change. 
     
     
       8. The method of  claim 5 , wherein the supply current is provided by the low dropout regulator in a more responsive manner when the first bias current is provided to the low dropout regulator than when the second bias current is provided to the low dropout regulator. 
     
     
       9. An electronic device comprising:
 means for providing a supply current and a supply voltage to a display panel, wherein the supply current is generated based at least in part on a first bias current or a second bias current; 
 means for predicting that the amount of supply current to the display panel is expected to change based on electrical changes expected to occur in the display panel, wherein the means for predicting is configured to predict that the amount of supply current is expected to change:
 when capacitive coupling currents are generated in parasitic capacitors of the display panel; or 
 upon a rising edge of a the clock signal; or a falling edge of the clock signal; or 
 when an electronic component proximate to the display panel undertakes or is about to undertake an operation; 
 or any combination thereof; 
 
 means for providing the first bias current at least before and while the supply current to the display panel is expected to change; and 
 means for providing the second bias current at all other times. 
 
     
     
       10. The electronic device of  claim 9 , wherein the first bias current is higher than the second bias current. 
     
     
       11. The electronic device of  claim 9 , wherein the first bias current is provided after the supply current to the display panel is expected to change. 
     
     
       12. The electronic device of  claim 9 , wherein the supply current is provided in a more responsive manner when the first bias current is provided than when the second bias current is provided.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Patent Application No. 61/316,195, entitled “VARIABLE-BIAS POWER SUPPLY,” filed Mar. 22, 2010, which is incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     The present disclosure relates generally to power supplies for electronic devices and, more particularly, to power supplies for display panels. 
     This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present disclosure, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art. 
     Flat panel displays, such as liquid crystal displays (LCDs) and organic light emitting diode (OLED) displays are commonly used in a wide variety of electronic devices, including such consumer electronics as televisions, computers, and handheld devices (e.g., cellular telephones, audio and video players, gaming systems, and so forth). Such display panels typically provide a flat display in a relatively thin package that is suitable for use in a variety of electronic goods. In addition, such devices typically use less power then comparable display technologies, making them suitable for use in battery-powered devices or in other contexts where it is desirable to minimize power usage. 
     Display panel power supplies may include a low dropout (LDO) regulator that provides a supply voltage and a supply current based on a reference voltage and a bias current. The responsiveness of the regulator to changes in the amount of supply current drawn by the display panel may depend in part on the amount of bias current supplied to the regulator. In particular, the higher the bias current, the more rapidly the regulator may respond to changes in the supply current. However, the higher the bias current, the more power consumed by the power supply. 
     A variety of events undertaken by the display panel may cause the display panel to consume varying amounts of supply current at any given time. For example, toggling at COM lines, source lines, and gate lines in the display panel may produce spikes in the amount of supply current drawn by the display panel. To ensure that the display panel power supply is sufficiently responsive despite such supply current fluctuations, the LDO regulator of the display panel power supply may be provided with a relatively high bias current at all times, which may consume a relatively high amount of power. 
     Additionally, different display panels may be more likely to consume variable amounts of power. For example, a display panel manufactured by one vendor may draw more power when certain events occur (e.g., the display panel may operate in a manner that draws large swings of supply current) than a display panel manufactured by another vendor. As a result, a bias current sufficient for one display panel may not be sufficient for another display panel. 
     SUMMARY 
     A summary of certain embodiments disclosed herein is set forth below. It should be understood that these aspects are presented merely to provide the reader with a brief summary of these certain embodiments and that these aspects are not intended to limit the scope of this disclosure. Indeed, this disclosure may encompass a variety of aspects that may not be set forth below. 
     Embodiments of the present disclosure relate to responsive, low-power display panel power supplies. In one embodiment, such a display panel power supply may include a regulator whose responsiveness varies depending on the bias current it consumes, and a current source that provides a variable bias current. The regulator may provide the display panel a supply voltage and a supply current based on a reference voltage and a bias current. Various events taking place in the display panel, such as toggling at COM lines, source lines, and/or gate lines may cause parasitic capacitances within the display panel to draw more or less supply current. To ensure the regulator remains suitably responsive to such changes in supply current, while reducing the total power consumed by the power supply, the current source may provide a higher bias current to the regulator at least while the supply current is changing than at certain other times. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various aspects of this disclosure may be better understood upon reading the following detailed description and upon reference to the drawings in which: 
         FIG. 1  is a block diagram of components of an electronic device in accordance with an embodiment; 
         FIG. 2  is a front view of a handheld electronic device in accordance with an embodiment; 
         FIG. 3  is a perspective view of a notebook computer in accordance with an embodiment; 
         FIG. 4  is a circuit diagram illustrating the structure of unit pixels that may be provided in the display device of  FIG. 1  in accordance with an embodiment; 
         FIG. 5  is a circuit diagram depicting a single unit pixel in accordance with an embodiment; 
         FIG. 6  is a circuit diagram illustrating a power supply of the display in accordance with an embodiment; 
         FIG. 7  is a plot illustrating a relationship between a bias current and the responsiveness of the power supply of  FIG. 6  in accordance with an embodiment; 
         FIG. 8  is a flowchart describing an embodiment of a method for providing an optimized bias current to an electronic device; 
         FIG. 9  is a flowchart describing an embodiment of a method for varying a bias current of a display panel power supply based on a detected change in supply current; 
         FIG. 10  is a flowchart describing an embodiment of a method for varying a bias current of a display panel power supply depending on a predicted supply current change in accordance with an embodiment; 
         FIG. 11  is a circuit diagram depicting one manner of performing the method of  FIG. 10  in accordance with an embodiment; 
         FIG. 12  is a timing diagram illustrating a relationship between the bias current and system clock in the circuit depicted in  FIG. 11  in accordance with an embodiment; 
         FIG. 13  is a flowchart describing an embodiment of a method for providing a static bias current to a display panel power supply; and 
         FIG. 14  is a circuit diagram depicting one manner of performing the method of  FIG. 13  in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS 
     One or more specific embodiments will be described below. In an effort to provide a concise description of these embodiments, not all features of an actual implementation are described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure. 
     Present embodiments relate to techniques for providing a variable bias current for a display panel power supply for low-power operation. In particular, rather than provide a relatively high bias current to the display panel power supply at all times, which may ensure the display panel power supply supplies sufficient current, but which also may consume excessive power, present techniques may involve supplying a reduced bias current when certain events known to cause supply current variations are not occurring. Such events may include, for example, display panel operations and capacitive coupling internal to the display panel, which may generate current spikes across the display panel. 
     In accordance with certain embodiments, a change in the amount of supply current drawn by the display panel may be detected. In response, the bias current to the display panel power supply may be temporarily increased, which may enable the display panel power supply to be more responsive. Additionally or alternatively, the bias current provided to the display panel power supply may be varied based on when the amount of supply current drawn by the display panel is expected to fluctuate. For example, supply current may change in response to certain events occurring internal to the display panel. If such events may be predicted, the amount of supply current drawn by the display panel similarly may be predicted. By way of example, since such events may occur when electronic components in the display panel perform certain operations, and since such operations may take place in response to rising and/or falling edges of a clock signal, the supply current may spike at these times. Accordingly, the bias current may be temporarily raised to account for such current spikes around the rising and falling edges of the clock signal. 
     In some embodiments, the bias current provided to the display panel power supply may be preset based on characteristics of the display. For example, certain display panels (e.g., display panels manufactured by a first vendor) may consume supply current in a more variable manner than certain other display panels (e.g., display panels manufactured by a second vendor). Depending on such characteristics of the display panel, a programmable register associated with the display panel power supply may be programmed to define the bias current. Thereafter, a bias current controller may provide the bias current to the display panel power supply based on the information programmed in the register. 
     With the foregoing in mind,  FIG. 1  represents a block diagram of such an electronic device  10  capable of performing the techniques disclosed herein. Among other things, the electronic device  10  may include processor(s)  12 , memory  14 , nonvolatile storage  16 , a display  18  having associated display panel power supplies  76 , input structures  20 , an input/output (I/O) interface  22 , network interface(s)  24 , a power source  26 , and/or a system clock  28 . In alternative embodiments, the electronic device  10  may include more or fewer components. 
     In general, the processor(s)  12  may govern the operation of the electronic device  10 . In some embodiments, based on instructions loaded into the memory  14  from the nonvolatile storage  16 , the processor(s)  12  may control the amount of bias current provided to a power supply of the display  18 , as discussed below. In addition to these instructions, the nonvolatile storage  16  also may store a variety of data. By way of example, the nonvolatile storage  16  may include a hard disk drive and/or solid state storage, such as Flash memory. 
     The display  18  may be a flat panel display, such as a liquid crystal display (LCD) or an organic light emitting diode (OLED) display. The display panel power supplies  76  may be integral components of the display  18  or may be located elsewhere in the electronic device  10 . In general, the display panel power supplies  76  may supply power to certain components of the display  18  (e.g., COM, data, and gate lines), as discussed below. Various operations undertaken by the display  18  may draw varying amounts of supply current at certain times. In some embodiments, to ensure that the display panel power supplies  76  are sufficiently responsive to such supply current fluctuations, while reducing the amount of power consumed by the display panel power supplies  76 , the amount of bias currents provided to the display panel power supplies  76  may be varied, as discussed in greater detail below. In certain other embodiments, the bias currents supplied to the display panel power supplies  76  may be static, but may be selected based on certain supply current consumption characteristics of the display  18 . 
     A user may control the electronic device  10  using input structures  20 , which may include a touch-sensitive display  18 . The I/O ports  22  of the electronic device  10  may enable the electronic device  10  to transmit data to and receive data from other electronic devices  10  and/or various peripheral devices, such as external keyboards or mice. The network interface(s)  24  may enable personal area network (PAN) integration (e.g., Bluetooth), local area network (LAN) integration (e.g., Wi-Fi), and/or wide area network (WAN) integration (e.g., 3G). The power source  26  of the electronic device  10  may be any suitable source of power, such as a rechargeable lithium polymer (Li-poly) battery and/or alternating current (AC) power converter. By employing the presently-disclosed techniques, the electronic device  10  may reduce the amount of power consumed from the power source  26 . 
     The system clock  28  may generate a master clock signal used by the various components of the electronic device  10 . Since the various circuitry of the electronic device  10 , including the display  18 , may be operative upon a rising and/or falling edge of the master clock signal, the supply current drawn by the display  18  may spike at these times. Accordingly, as mentioned above, the display  18  may draw a changed amount of supply current upon the rising and/or falling edge of the master clock signal or any similar time source of the electronic device  10 , as discussed below. As also discussed below, the bias currents in the power supplies  76  of the display  18  may be increased and/or decreased in relation to the clock signal of the system clock  28 . The system clock  28  may be a separate component of the electronic device  10 , a component of the processor(s)  12 , or a component of any other of the various circuitry of the electronic device  10 . 
       FIG. 2  illustrates an electronic device  10  in the form of a handheld device  30 , here a cellular telephone. It should be noted that while the handheld device  30  is provided in the context of a cellular telephone, other types of handheld devices (such as media players for playing music and/or video, personal data organizers, handheld game platforms, and/or combinations of such devices) may also be suitably provided as the electronic device  10 . Further, the handheld device  30  may incorporate the functionality of one or more types of devices, such as a media player, a cellular phone, a gaming platform, a personal data organizer, and so forth. 
     For example, in the depicted embodiment, the handheld device  30  is in the form of a cellular telephone that may provide various additional functionalities (such as the ability to take pictures, record audio and/or video, listen to music, play games, and so forth). As discussed with respect to the general electronic device of  FIG. 1 , the handheld device  30  may allow a user to connect to and communicate through the Internet or through other networks, such as local or wide area networks. The handheld device  30  may also communicate with other devices using short-range connections, such as Bluetooth and near field communication (NFC). By way of example, the handheld device  30  may be a model of an iPod® or iPhone® available from Apple Inc. of Cupertino, Calif. 
     The handheld device  30  may include an enclosure  32  or body that protects the interior components from physical damage and shields them from electromagnetic interference. The enclosure  32  may be formed from any suitable material, such as plastic, metal or a composite material, and may allow certain frequencies of electromagnetic radiation to pass through to wireless communication circuitry within handheld device  30  to facilitate wireless communication. The enclosure  32  may also include user input structures  20  through which a user may interface with the device. Each user input structure  20  may be configured to help control a device function when actuated. For example, in a cellular telephone implementation, one or more input structures  20  may be configured to invoke a “home” screen or menu to be displayed, to toggle between a sleep and a wake mode, to silence a ringer for a cell phone application, to increase or decrease a volume output, and so forth. 
     The display  18  in the depicted embodiment of the handheld device  30  is an LCD panel. The display  18  may display a graphical user interface (GUI) that allows a user to interact with the handheld device  30 . Icons of the GUI may be selected via a touch screen included in the display  18 , or may be selected by one or more input structures  20 , such as a wheel or button. The handheld device  30  also may include various I/O ports  22  that allow connection of the handheld device  30  to external devices. For example, one I/O port  22  may be a port that allows the transmission and reception of data or commands between the handheld device  30  and another electronic device, such as a computer. Such an I/O port  22  may be a proprietary port from Apple Inc. or may be an open standard I/O port. Another I/O port  22  may include a headphone jack to allow a headset  34  to connect to the handheld device  30 . 
     In addition to the handheld device  30  of  FIG. 2 , the electronic device  10  may also take the form of a computer or other type of electronic device. Such a computer may include a computer that is generally portable (such as a laptop, notebook, and/or tablet computer) and/or a computer that is generally used in one place (such as a conventional desktop computer, workstation and/or servers). In certain embodiments, the electronic device  10  in the form of a computer may be a model of a MacBook®, MacBook® Pro, MacBook Air®, iMac®, Mac® mini, or Mac Pro® available from Apple Inc. In another embodiment, the electronic device  10  may be a tablet computing device, such as an iPad® available from Apple Inc. By way of example, a laptop computer  36  is illustrated in  FIG. 3  and represents an embodiment of the electronic device  10  in accordance with one embodiment of the present disclosure. Among other things, the computer  36  includes a housing  38 , a display  18 , input structures  20 , and I/O ports  22 . 
     In one embodiment, the input structures  22  (such as a keyboard and/or touchpad) may enable interaction with the computer  36 , such as to start, control, or operate a GUI or applications running on the computer  36 . For example, a keyboard and/or touchpad may allow a user to navigate a user interface or application interface displayed on the display  18 . Also as depicted, the computer  36  may also include various I/O ports  22  to allow connection of additional devices. For example, the computer  36  may include one or more I/O ports  22 , such as a USB port or other port, suitable for connecting to another electronic device, a projector, a supplemental display, and so forth. In addition, the computer  36  may include network connectivity, memory, and storage capabilities, as described with respect to  FIG. 1 . 
     As noted briefly above, the display  18  represented in the embodiments of  FIGS. 1-3  may be a liquid crystal display (LCD).  FIG. 4  represents a circuit diagram of the display  18  when the display  18  is such an LCD, in accordance with an embodiment. As shown, the display  18  may include an LCD display panel  40 . The display panel  40  may include multiple unit pixels  42  disposed in a pixel array or matrix defining multiple rows and columns of unit pixels that collectively form an image viewable region of the display  18 . In such an array, each unit pixel  42  may be defined by the intersection of rows and columns, represented here by the illustrated gate lines  44  (also referred to as “scanning lines”) and source lines  46  (also referred to as “source lines”), respectively. Each of the gate lines  44  and source lines  46  may supply a signal to the unit pixels  42  powered by a display panel power supply  76 . 
     Although only six unit pixels, referred to individually by the reference numbers  42   a - 42   f , respectively, are shown for purposes of simplicity, it should be understood that in an actual implementation, each source line  46  and gate line  44  may include hundreds or even thousands of such unit pixels  42 . By way of example, in a color display panel  40  having a display resolution of 1024×768, each source line  46 , which may define a column of the pixel array, may include 768 unit pixels, while each gate line  44 , which may define a row of the pixel array, may include 1024 groups of unit pixels, wherein each group includes a red, blue, and green pixel, thus totaling 3072 unit pixels per gate line  44 . By way of further example, the panel  40  may have a display resolution of 480×320 or, alternatively, 960×640. In the presently illustrated example, the group of unit pixels  42   a - 42   c  may represent a group of pixels having a red pixel ( 42   a ), a blue pixel ( 42   b ), and a green pixel ( 42   c ). The group of unit pixels  42   d - 42   f  may be arranged in a similar manner. With such a potentially large number of unit pixels  42  coupled to a gate line  44  or source line  46 , even slight variations in the amount of supply current drawn by individual pixels may translate into significant changes in the total supply current drawn across the gate line  44  or source line  46 . 
     As shown in the present embodiment, each unit pixel  42   a - 42   f  includes a thin film transistor (TFT)  48  for switching a respective pixel electrode  50 . In the depicted embodiment, the source  52  of each TFT  48  may be electrically connected to a source line  46 . Similarly, the gate  54  of each TFT  48  may be electrically connected to a gate line  44 . Furthermore, the drain  56  of each TFT  48  may be electrically connected to a respective pixel electrode  50 . Each TFT  48  serves as a switching element which may be activated and deactivated (e.g., turned on and off) for a predetermined period based upon the respective presence or absence of a scanning signal at the gate  54  of the TFT  48 . The act of toggling the TFT  48  may cause the amount of supply current drawn from the display panel power supplies  76  to vary. 
     When activated, the TFT  48  may store the image signals received via a respective source line  46  as a charge upon its corresponding pixel electrode  50 . The image signals stored by pixel electrode  50  may be used to generate an electrical field between the respective pixel electrode  50  and a common electrode (not shown in  FIG. 5 ). The reception of the image signal onto the pixel electrode  50  may also cause the amount of current drawn across the source line to vary, albeit temporarily. As a result of the electrical field between the respective pixel electrode  50  and the common electrode, the pixel electrode  50  and the common electrode may form a liquid crystal capacitor for a given unit pixel  42 . Thus, in an LCD panel  40 , such an electrical field may align liquid crystals molecules within a liquid crystal layer to modulate light transmission through a region of the liquid crystal layer that corresponds to the unit pixel  42 . For instance, light is typically transmitted through the unit pixel  42  at an intensity corresponding to the applied voltage (e.g., from a corresponding source line  46 ). 
     The display  18  may also include a source driver integrated circuit (source driver IC)  58 , which may include a chip, such as a processor or ASIC, that is configured to control various aspects of display  18  and panel  40 . For example, the source driver IC  58  may receive image data  60  from the processor(s)  12  and send corresponding image signals to the unit pixels  42  of the panel  40  powered by a display panel power supply  76 . The source driver IC  58  may also be coupled to a gate driver IC  62 , which may be configured to activate or deactivate rows of unit pixels  42  via the gate lines  44 . As such, the source driver IC  58  may send timing information, shown here by reference number  64 , to gate driver IC  62  to facilitate activation/deactivation of individual rows of pixels  42 . In other embodiments, timing information may be provided to the gate driver IC  62  in some other manner. While the illustrated embodiment shows only a single source driver IC  58  coupled to panel  40  for purposes of simplicity, it should be appreciated that additional embodiments may utilize multiple source driver ICs  58  for providing image signals to the pixels  42 . For example, additional embodiments may include multiple source driver ICs  58  disposed along one or more edges of the panel  40 , wherein each source driver IC  58  is configured to control a subset of the source lines  46  and/or gate lines  44 . 
     In operation, the source driver IC  58  receives image data  60  from the processor(s)  12  or a separate display controller and, based on the received data, outputs signals to control the pixels  42 . For instance, to display image data  60 , the source driver IC  58  may adjust the voltage of the pixel electrodes  50  (abbreviated in  FIG. 2  as P.E.) one row at a time. To access an individual row of pixels  42 , the gate driver IC  62  may send an activation signal to the TFTs  48  associated with the particular row of pixels  42  being addressed. This activation signal may render the TFTs  48  on the addressed row conductive. Accordingly, image data  60  corresponding to the addressed row may be transmitted from source driver IC  58  to each of the unit pixels  42  within the addressed row via respective source lines  86 . Thereafter, the gate driver IC  62  may deactivate the TFTs  48  in the addressed row, thereby impeding the pixels  42  within that row from changing state until the next time they are addressed. The above-described process may be repeated for each row of pixels  42  in the panel  40  to reproduce image data  60  as a viewable image on the display  18 . In general, these events may take place at certain points in time, namely, upon the rising edge and/or falling edge of a clock signal  66  from the system clock  28 . 
       FIG. 6  represents a circuit diagram of an embodiment of a pixel  42  in greater detail. As shown, the TFT  48  is coupled to the source line  46  (D x ) and the gate line  44  (G y ). The pixel electrode  50  and the common electrode  68  may form a liquid crystal capacitor  70 . The common electrode  68  is coupled to a common voltage line  72  that supplies the common voltage V COM . The V COM  line  72  may be formed parallel to the gate lines  44  or, in other embodiments, parallel to the source lines  46 . The voltage supplied on the V COM  line  72  may be supplied by a display panel power supply  76 , which may operate according to embodiments discussed below. 
     In the present embodiment, the pixel  42  also includes a storage capacitor  73  having a first electrode coupled to the drain  56  of the TFT  48  and a second electrode coupled to a storage electrode line that supplies a storage voltage V sT . In other embodiments, the second electrode of the storage capacitor  73  may be coupled instead to the previous gate line  44  (e.g., G y-1 ) or to ground. The storage capacitor  73  may sustain the pixel electrode voltage during holding periods (e.g., until the next time the gate line  44  (G y ) is activated by the gate driver IC  62 . Other capacitances associated with the pixel  42  may include a parasitic coupling capacitor  74  and/or a parasitic capacitor  75  between the source  52  and the gate  54  of the TFT  48 . The capacitances of the pixel  42  may cause the supply currents provided by the relevant display panel power supplies  76  to quickly and temporarily increase and/or decrease when toggling occurs at the V COM  line  72 , the source lines  46 , and/or the gate lines  44 . 
     As noted above, the currents resulting from such capacitances may cause the components of the display panel  18  to draw more or less supply current i s (t) from the display panel power supplies  76  at any given time. These current fluctuations may also depend upon on certain characteristics of the display  18  (e.g., which vendor manufactured the display  18 ). Despite such current fluctuations, the power supplies  76  of the display  18  may provide supply currents i s (t) to the components of the display  18  in a low-power, responsive manner.  FIG. 6  illustrates one such display panel power supply  76 , which includes a low dropout (LDO) regulator  78  that outputs a supply voltage V SUP  and the supply current i s (t) based on a reference voltage V R  and a bias current i a (t). The bias current i a (t) may be provided so as to lower the power consumption of the LDO regulator  78 , while permitting the LDO regulator  78  to remain responsive. 
     To this end, the display panel power supply  76  may control the bias current i a (t) (e.g., block  80 ) to provide a bias current high enough to be enable the display panel power supply  76  to be suitably responsive when the amount of supply current i s (t) drawn by the display  18  undergoes changes, while providing a bias current low enough to suitably conserve power at other times. In particular, the supply current i s (t) may represent the sum of current due to capacitive coupling i c (t), which may arise due to capacitive coupling internal to the display  18  (e.g., block  82 ), and the panel load currents (e.g., block  84 ), representing a DC panel load component I L  and a time-varying panel load component i l (t), (e.g., i s (t)=i c (t)+I L +i l (t)). When the capacitive coupling current i c (t) and/or the time-varying panel load component i l (t) change by increasing or decreasing, the bias current i a (t) may be increased to enable the LDO regulator  78  to respond more rapidly to the change in supply current i s (t) being drawn. 
     As mentioned above, the amount of bias current i a (t) provided to the regulator  78  impacts its responsiveness to the capacitive coupling currents i c (t).  FIG. 7  presents a plot  86  relating the relative response time of the regulator  78  (ordinate  87 ) and the bias current i a (t) provided to the regulator  78  (abscissa  88 ). In general, as shown by a response curve  89 , the response time of the regulator  78  may decrease as the bias current increases, to a point of diminishing returns. That is, the regulator  78  may respond to increases or decreases in supply current i s (t) more rapidly when the bias current i a (t) is relatively higher than when the bias current i a (t) is relatively lower. 
     By varying the bias current i a (t) at suitable times, the display panel power supply  76  may provide power to a component of the display  18  in a low-power but responsive manner, as illustrated by a flowchart  90  of  FIG. 8 . The embodiment of the method shown in flowchart  90  may begin when a bias current i a (t) is provided to the LDO regulator  78  (block  92 ). Depending on the capacitive coupling current i c (t) and other time-varying currents that draw power from the display panel power supply  76  (e.g., i l (t)), the bias current i a (t) may be varied (block  94 ). In general, the bias current i a (t) may be varied such that increases and/or decreases in the amount of supply current i s (t) drawn by the display  18  are accompanied by increases in bias current i a (t). As discussed below, the action taken in block  94  may involve a variety of techniques, including detecting and responding to changes in supply current i s (t) and/or predicting such changes and preemptively increasing the bias current i a (t). Thereafter, the LDO regulator  78  may respond in a suitably responsive manner by maintaining the supply voltage V SUP  despite changes in the supply current i s (t) (block  96 ). 
     As noted above, one manner of varying the bias current i a (t) may involve detecting and responding to changes in supply current i s (t). One embodiment of such a method is represented by a flowchart  100  of  FIG. 9 , which may begin by detecting a change in the amount of supply current i s (t) being drawn by a component of the display panel  18  (block  102 ). When a change in the amount of supply current i s (t) is detected, a time-varying component of the bias current i a (t) may be increased (block  104 ) to enable the LDO regulator  78  to respond in a suitably responsive manner. In some embodiments, the method of the flowchart  100  may be carried out using current-sensing circuitry, which may detect and digitize the supply current i s (t). Thereafter, the processor(s)  12  or another integrated circuit (IC) may monitor the supply current i s (t) for rapid changes, sending a signal to increase the bias current i a (t) when changes are detected and/or to lower the bias current i a (t) when the supply current i s (t) is stable. 
       FIG. 10  is a flowchart  130  presenting an additional or alternative manner of varying the bias current i a (t), which may involve predicting changes in the supply current i s (t) and preemptively increasing the bias current i a (t) as a result. The flowchart  130  may begin by predicting when a change in the amount of supply current i s (t) being drawn by the display panel  18  will occur (block  132 ). When a change in the amount of supply current i s (t) is expected, a time-varying component of the bias current i a (t) may be increased (block  134 ) to enable the LDO regulator  78  to respond in a suitably responsive manner. 
       FIG. 11  depicts a display panel power supply  76 A, which represents one embodiment of the display panel power supply  76  that is configured to carry out an embodiment of the method of  FIG. 10 . As shown in  FIG. 11 , the LDO regulator  78  may output the supply voltage V SUP  and the supply current i s (t) based on the reference voltage V R  and the bias current i a (t). As noted above, the bias current i a (t) may be represented by two components, a DC component I B  and a time-varying component i b (t), respectively modeled by the current sources  112  and  114 . The current source  114  may be a variable current source controlled by a signal BIAS CONTROL output by a predictive bias controller  138 . The predictive bias controller  138  may output the BIAS CONTROL signal to cause the bias current i a (t) to increase when the supply current i s (t) is expected to change. 
     In the depicted embodiment of the display panel power supply  76 A, the supply current i s (t) is equal to the sum of the capacitive coupling current i c (t), the DC panel load component I L  and the time-varying panel load component i i (t) (e.g., i s (t)=i c (t)+I L +i l (t)). The capacitive coupling current i c (t) is modeled as arising due to capacitive coupling in the display  18  through the resistive element  120  and the capacitive element  122 . The DC panel load component I L  and the time-varying panel load component i l (t) are respectively modeled as arising due to the current sources  124  and  126 . The predictive bias controller  138  may control the bias current i a (t) in part due to a manner in which the time-varying panel load component i l (t) may behave in relationship to a time source shared by the predictive bias controller  138  and the current source  126  (shown as a signal SHARED TIME SOURCE). A programmable register  139  may store values that define the DC component I B  and/or the maximum or minimum time-varying component i b (t) of the bias current i a (t), as discussed below with reference to  FIG. 13 . 
     The predictive bias controller  138  may predict when the supply current i s (t) is expected to change in a variety of ways. For example, the predictive bias controller  138  or the processor(s)  12  may record when changes in the supply current i s (t) have historically taken place. When conditions similar to conditions historically associated with changes in the supply current i s (t) occur (e.g., the network interface(s)  24  are expected to transmit data), the predictive bias controller  138  or the processor(s)  12  may expect that similar changes in the supply current i s (t) are likely to occur again. When such changes in the supply current i s (t) are expected by the predictive bias controller  138  or the processor(s)  12 , the predictive bias controller  138  may adjust the bias current i a (t) accordingly. 
     In certain embodiments, the predictive bias controller  138  may expect the supply current i s (t) to change based on timing associated with the system clock  28  of the electronic device. As illustrated by a timing diagram  140  of  FIG. 12 , time-varying components of the supply current i s (t) may correspond to rising and/or falling edges of the system clock  28 , and thus the predictive bias controller  138  may control the bias current i a (t) accordingly. In the timing diagram  140 , a curve  142  represents a system clock of the electronic device  10 , a curve  144  represents the supply current i s (t) drawn by the display  18 , a curve  146  represents the signal BIAS CONTROL output by the predictive bias controller  138 , and a curve  148  represents the total bias current i a (t). 
     As represented by the curves  142  and  144 , the supply current i s (t) may change most dramatically at the rising and/or falling edges of the SYSTEM CLOCK SIGNAL, as indicated by numerals  150 . Specifically, the supply current may reach a minimum or a maximum (e.g., at numeral  152 ) due to dynamic current (e.g., i c (t)+i l (t)) arising from capacitive coupling when certain events occur that are latched to the system clock. For example, toggling at the V COM  line  72 , the source lines  46 , and/or the gate lines  44  generally may take place at the rising edge and/or falling edge of the SYSTEM CLOCK signal. Such toggling may cause the parasitic capacitances  75  of the display  18  to draw additional supply current i s (t) through the lines  72 ,  46 , and  44  at these times. These dynamic current swings (e.g., spike currents) shown at numerals  150  may be based around the DC panel load current I L  (e.g., at numeral  154 ). 
     To ensure that the LDO regulator  78  is suitably responsive during the dynamic current swings (e.g., at numerals  150 ), the predictive bias controller  138  may output the BIAS CONTROL signal such that the bias current i a (t) ramps up to a relatively higher bias current (e.g., at numeral  156 ) before such dynamic current swings  150 . This relatively higher bias current  156  generally may remain in place while the dynamic current swings  150  take place. Similarly, at other times when the dynamic current swings  150  are not taking place (e.g., at numeral  154 ), the bias current i a (t) may be reduced to a relatively lower bias current (e.g., at numeral  158 ). In this manner, the variability of the bias current i a (t) may enable the LDO regulator  78  to achieve a suitable responsiveness when the supply current i s (t) is expected to change (e.g., upon rising and/or falling edges of the SYSTEM CLOCK signal), while reducing excess power consumed due to the bias current i a (t) when the supply current i s (t) is expected to remain stable. 
     In alternative embodiments, a slope  160  of the bias current i a (t) may be higher or lower, depending on the components employed in the variable current source  114 . For instance, a higher slope may be achieved using more expensive components, which may allow a shorter bias current i a (t) duty cycle. In other words, if even further reductions in power consumption are desired, a higher slope  160  may enable a shorter duty cycle at the cost of more expensive components. In some embodiments, the slope and/or the duty cycle of the bias current i a (t) may be register programmable. 
     Moreover, because certain displays  18  may have certain supply current consumption characteristics, the DC component I B  (or a maximum or minimum time-varying component i b (t)) of the bias current i a (t) may be defined in a programmable register associated with a bias current controller (e.g., the predictive bias controller  138  of  FIG. 11  or the static bias controller  182  of  FIG. 14 ) of the display panel power supply  76 . As illustrated in a flowchart  170  of  FIG. 13 , certain supply current consumption characteristics of the display  18  may be assessed, and the bias current i a (t) to be employed by the display panel power supply  76  may be ascertained (block  172 ). By way of example, vendors may test the displays  18  for various operating characteristics during or after the manufacture of the displays  18 . These characteristics may include, among other things, the variability of the amount of supply current i s (t) drawn during certain operations. In some embodiments, the DC component I B  or a maximum or minimum time-varying component i b (t) of the bias current i a (t) may be selected from among several discrete values (e.g., low, medium, or high). 
     Next, the determined bias current i a (t) value(s) may be programmed into the programmable register  139  associated with the bias current controller of the display panel power supply  76  in the electronic device  10  (block  174 ). For example, the programmable register  139  may store values associated with the DC component I B  and/or the maximum or minimum time-varying component i b (t) of the bias current i a (t). Thereafter, the bias current i a (t) provided to the regulator  78  may be defined according to the values stored in the programmable register  139  (block  176 ). 
     In certain embodiments, the bias current i a (t) provided to the regulator  78  may not change with time, but rather may be static. For example, as illustrated by a display panel power supply  76 B of  FIG. 14 , which represents another embodiment of the display panel power supply  76 , a variable current source  180  may provide a DC component I B  of the bias current i a (t), which may lack a time-varying component i b (t). The variable current source  180  may be controlled via a signal BIAS CONTROL provided by a static bias controller  182 . The static bias controller  182  may output the BIAS CONTROL signal based on a value stored in a programmable register  139  associated with the static bias controller  182 . In this manner, the DC component I B  of the bias current i a (t) may vary from one display  18  to another, without need for different electrical components to supply such different bias currents i a (t). 
     The specific embodiments described above have been shown by way of example, and it should be understood that these embodiments may be susceptible to various modifications and alternative forms. It should be further understood that the claims are not intended to be limited to the particular forms disclosed, but rather to cover all modifications, equivalents, and alternatives falling within the spirit and scope of this disclosure.

Metadata:
Filing Date: 20100719
Publication Date: 20150324
Grant Date: 20150324
Priority Date: 20100322
Inventors: LEE YONGMAN
Assignee: APPLE INC
CPC Classifications: [{"code": "G06F1/3218", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/3203", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F1/3218", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/3203", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 44646850