PATENT DOCUMENT

Publication Number: US-9818367-B2
Application Number: US-201514660619-A
Country: US
Kind Code: B2

Title: Content-driven slew rate control for display driver

Abstract:
Devices and methods related to liquid crystal displays (LCDs) are provided. For example, such an electronic device may include an LCD with a slew rate control unit that adjusts a slew rate for source drivers of the LCD. The slew rate may be adjusted differently for each source driver and for each frame of data signal delivered by the source driver. Individually adjusting the slew rate of the source driver enables the LCD to respond to or reduce noise within the LCD that may otherwise contribute to flickering or other unwanted display events.

Claims:
What is claimed is: 
     
       1. An electronic device comprising:
 a display having a plurality of pixels arranged in a grid comprising rows and columns; 
 a plurality of source drivers each configured to drive one or more columns or rows of pixels with a data signal; 
 a slew rate control unit configured to incrementally adjust a slew rate of the data signal delivered by the source drivers in the plurality of source drivers during operation of the electronic device to reduce flickering of the display. 
 
     
     
       2. The electronic device of  claim 1 , comprising sensors configured to detect noise within the electronic device and deliver a signal indicative of the noise to the slew rate control unit. 
     
     
       3. The electronic device of  claim 1 , wherein each source driver in the plurality of source drivers may independently adjust the slew rate of the data signal. 
     
     
       4. The electronic device of  claim 1 , comprising a line buffer configured to compare a first frame of the data signal to a second frame of the data signal and output a signal indicative of a likelihood of noise caused by a data signal within the liquid crystal display. 
     
     
       5. A method for adjusting a slew rate in a liquid crystal display, comprising:
 receiving, at a slew rate control unit, a first signal voltage of image data for a first source driver, wherein the first source driver is configured to drive a first column of pixels of the liquid crystal display or a first row of pixels in the liquid crystal display; 
 receiving, at the slew rate control unit, a noise signal from the liquid crystal display; 
 determining disturbance levels and recovery times corresponding to each of a first plurality of slew rates of the first signal voltage for the first source driver, wherein:
 the disturbance levels comprise voltage levels of voltage disturbances of one or more common electrodes of the liquid crystal display; 
 the recovery times comprise lengths of time that the one or more common electrodes are undisturbed by the voltage disturbances; and 
 the disturbance levels and the recovery times are based on the first signal voltage and the noise signal; 
 
 determining a first set of slew rates from the first plurality of slew rates that correspond to the recovery times that are less than a first cutoff recovery time; and 
 selecting the slew rate from the first set of slew rates that corresponds to the least disturbance level to send to the first source driver. 
 
     
     
       6. The method of  claim 5 , comprising
 receiving, at the slew rate control unit, a second signal voltage of image data for a second source driver, wherein the second source driver is configured to drive a second column of pixels of the liquid crystal display or a second row of pixels in the liquid crystal display; 
 determining disturbance levels and recovery times corresponding to each of a second plurality of slew rates of the second signal voltage for the second source driver, wherein the disturbance levels and recovery times are based on the second signal voltage and the noise signal; 
 determining a second set of slew rates from the second plurality of slew rates that correspond to the recovery times that are less than a second cutoff recovery time; 
 selecting a second slew rate from the second set of slew rates that corresponds to the least disturbance level to send to the second source driver. 
 
     
     
       7. The method of  claim 5 , comprising receiving a second frame of image data for the first source driver and determining a second slew rate for the first source driver that is different from the slew rate. 
     
     
       8. The method of  claim 7 , wherein the second frame of image data comprises image data for a second pixel in the first column of pixels. 
     
     
       9. The method of  claim 5 , wherein determining the slew rate comprises selecting one of 8 different possible slew rates. 
     
     
       10. The method of  claim 5 , wherein selecting the slew rate comprises setting the first cutoff for at least one recovery time of the recovery times. 
     
     
       11. The method of  claim 5 , wherein selecting the slew rate comprises selecting, from a remainder of possible slew rates, the slew rate from the plurality of slew rates that minimizes disturbance level. 
     
     
       12. The method of  claim 5 , wherein the noise signal comprises touch sensor noise, wireless signal noise, noise from a common voltage layer, or any combination thereof. 
     
     
       13. A source driver integrated circuit (IC), comprising:
 one or more tangible, machine-readable media comprising processor-executable instructions to:
 receive, at a slew rate control unit, a second signal voltage of image data for a second source driver, wherein the second source driver is configured to drive a second column of pixels of the liquid crystal display or a second row of pixels in the liquid crystal display; 
 determine disturbance levels and recovery times corresponding to each of a plurality of slew rates of the second signal voltage for the second source driver, wherein:
 the disturbance levels comprise voltage levels of voltage disturbances of one or more common electrodes of the liquid crystal display; 
 the recovery times comprise lengths of time that the one or more common electrodes are undisturbed by the voltage disturbances; and 
 the disturbance levels and the recovery times are based on the second signal voltage and a noise signal; 
 
 determine a set of slew rates of the plurality of slew rates that correspond to the disturbance levels that are less than a cutoff disturbance level; and 
 select a slew rate from the set of slew rates that corresponds to the greatest recovery time to send to the second source driver. 
 
 
     
     
       14. An electronic device comprising:
 one or more input structures; 
 a storage structure encoding one or more executable routines; 
 a processor capable of interfacing with the input structures and the storage structure; and 
 a display device configured to display an output of the processor, wherein the display device comprises:
 a liquid crystal display (LCD) panel comprising a plurality of pixels arranged in rows and columns, wherein each of the plurality of pixels comprises a thin-film-transistor (TFT), a pixel electrode, and a common electrode, wherein each column of pixels corresponds to a source line of the LCD panel, and wherein each row of pixels corresponds to a gate line of the LCD panel; 
 a gate driver circuit configured to provide a gate activation signal to gate lines of the LCD panel; 
 a source driver integrated circuit (IC) configured to send a data signal to source lines of the LCD panel, comprising:
 a slew rate control unit configured to receive image data from the processor and output a first slew rate signal by:
 determining a set of slew rate signals of a plurality of slew rate signals that each comprise a disturbance level that is less than a cutoff disturbance level, wherein each disturbance level comprises a voltage level of voltage disturbances of at least one common electrode of the LCD panel; and 
 selecting the first slew rate signal from the set of slew rate signals that comprises the greatest amount of recovery time, wherein the recovery time comprise a length of time that the at least one common electrode is undisturbed by the voltage disturbances of the at least one common electrode; 
 
 a first source driver configured to drive a first data line at a data signal, wherein the data line alternates between the data signal voltage and a minimum voltage, and the rate at which the first source driver alternates between the data signal voltage and the minimum voltage is controlled by a first slew rate signal from the slew rate control unit. 
 
 
 
     
     
       15. The electronic device of  claim 14 , wherein the source driver IC comprises a second source driver configured to drive a second data line at the data signal, wherein the data line alternates between the data signal voltage and a second minimum voltage, and the rate at which the second source driver alternates between the data signal voltage and the second minimum voltage is controlled by a second slew rate signal from the slew rate control unit, and the second slew rate signal is different than the first slew rate signal. 
     
     
       16. The electronic device of  claim 14 , comprising sensors configured to detect system noise within the electronic device, wherein the first slew rate signal is based on an amount of detected system noise. 
     
     
       17. The electronic device of  claim 16 , wherein system noise includes noise from the one or more input structures. 
     
     
       18. The electronic device of  claim 14 , wherein the first slew rate signal comprises a first value at a first time, and a second value at a second time. 
     
     
       19. The electronic device of  claim 14 , wherein the slew rate control unit is configured to receive a settling signal from the gate lines, the thin-film-transistor (TFT), the pixel electrode, the common electrode, or any combination thereof, indicative of stray capacitive voltages, wherein the first slew rate signal depends on the settling signal. 
     
     
       20. The electronic device of  claim 14 , wherein the first slew rate signal is selected from at least 8 possible slew rate signals.

Description:
BACKGROUND 
     The present disclosure relates generally to liquid crystal display (LCD) panels and, more particularly, to display drivers for LCD panels that adjust source driver slew rates based on content to be displayed. 
     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. 
     Display panels are commonly used as part of an electronic device to provide visual information from the device. One type of display is a liquid crystal display (LCD), which may include a grid of rows and columns of thin-film-transistors (TFTs) arranged in a layer adjacent to liquid crystal material. The TFTs may control one or more image pixels for each image displayed on the device. The LCD may selectively modulate the amount and color of light passing through each of the pixels by a varying an electric field associated with each respective pixel to control the orientation of the liquid crystals. By controlling the amount of light that may be emitted from each pixel, the LCD may cause a viewable image to be displayed. 
     During operation of an LCD, the gate of a TFT associated with a pixel may be switched on upon receiving a gate activation signal provided by a gate driver circuit. When the TFT is switched on, a data voltage applied to the source of the TFT may be stored as a charge in a pixel electrode coupled to the TFT. By way of example, the TFTs within the pixel array may be switched on sequentially one row at a time, and image data corresponding to a selected row may be sent to the pixels of the selected row when it is activated. When the source of the TFT transitions from a minimum voltage to the data voltage, rise and fall transition time properties (e.g., slew rate) of source signal may influence and affect channel charge distribution behavior of the TFT. For instance, when a TFT is switched from an on state to an off state, charge remaining in the channel of the transistor is redistributed between a corresponding pixel electrode and source line. This redistribution may be called coupling, and in some instances may affect the voltages throughout the circuitry of the LCD panel. Coupling may also change or affect the amount of light emitted by the pixels, which can cause inconsistencies in color and luminance over the entire LCD 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 devices and methods related to liquid crystal displays (LCDs). For example, such an electronic device may include an LCD with a slew rate control unit that controls a slew rate for individual source drivers of each data line in the LCD. The slew rate may be adjusted based on frame to frame data voltage movement to minimize the alternating current coupling effect. The slew rate may also be adjusted in response to feedback from sensors that detect system noise and/or from the data signals being delivered to the LCD. Rather than adjusting the slew rate of the entire LCD during manufacture, the LCD may achieve better picture quality, lower noise levels, and brighter light luminance by adjusting the slew rate dynamically during operation of the LCD. The slew rate may be adjusted globally for the entire LCD, or may be adjusted for each individual source driver based on the current line charge and forthcoming data signals. 
    
    
     
       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 exemplary components of an electronic device, in accordance with aspects of the present disclosure; 
         FIG. 2  is a front view of a handheld electronic device in accordance with aspects of the present disclosure; 
         FIG. 3  is a view of a computer in accordance with aspects of the present disclosure; 
         FIG. 4  is a circuit diagram of switching and display circuitry of LCD pixels, in accordance with aspects of the present disclosure; 
         FIG. 5  is a schematic diagram of the LCD panel and the slew rate control unit; 
         FIG. 6  is a diagram of voltages delivered by the source drivers and experienced by the pixels of the LCD panel; and 
         FIG. 7  is a flow chart of the method practiced by the slew rate control unit to control the slew rate within the LCD panel. 
     
    
    
     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. 
     When introducing elements of various embodiments of the present disclosure, the articles “a,” “an,” and “the” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. The embodiments discussed below are intended to be examples that are illustrative in nature and should not be construed to mean that the specific embodiments described herein are necessarily preferential in nature. Additionally, it should be understood that references to “one embodiment,” “an embodiment,” “some embodiments,” and the like are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the disclosed features. 
     Present embodiments relate to a liquid crystal display (LCD) panel. In particular, the development, production, and/or use of such a LCD panel may include adjusting the slew rate of a data signal within the LCD panel to reduce display noise. More specifically, the embodiments discussed herein relate to adjusting the slew rate on a line-by-line or frame-by-frame basis. The slew rate may be adjusted between a number of possible settings to balance the noise and recovery time of the data lines within the LCD panel. Several factors may influence the noise and recovery time of the data lines. Primarily, the data signal may produce noise on a data line, particularly when the data signal includes significant change in voltage (i.e., bright pixel intensity to dark pixel intensity, or vice versa). Additionally, display noise may be generated from a number of sources, including signals from the LCD panel itself, or external sources such as touch sensors or wireless/radio signals. 
     As explained in detail below, the present embodiments include slew adjustment circuitry to adjust the slew rate for each of the source drivers for each data line, which may thus individually adjust the slew rate for each of the data lines. It is believed that these embodiments enable a LCD panel that is responsive to system noise and emits a more consistent high-quality picture. 
     With the foregoing points in mind,  FIG. 1  provides a block diagram illustrating an example of an electronic device  10  that may include logic configured to control the slew rate of source driver signals sent to a display  12 , such as a liquid crystal display (LCD), in accordance with aspects of the present disclosure. The electronic device  10  may be any type of electronic device, such as a laptop or desktop computer, a mobile phone, a digital media player, or the like, that includes the display  12 . The various functional blocks depicted in  FIG. 1  may include hardware elements (including circuitry), software elements (including computer code stored on computer-readable media, such as a hard drive or system memory), or a combination of both hardware and software elements. It should be noted that  FIG. 1  is merely one example of a particular implementation and is merely intended to illustrate the types of components that may be present in the electronic device  10 . For example, in the illustrated embodiment, these components may include the display  12  referenced above, as well as input/output (I/O) ports  14 , input structures  16 , one or more processors  18 , memory device(s)  20 , non-volatile storage  22 , network interface(s)  24  (e.g., wireless and/or physically connected networks), and power source  26 . 
     Before continuing, it should be understood that the system block diagram of the electronic device  10  shown in  FIG. 1  is intended to represent a high-level control diagram. That is, the illustrated connective lines between each individual component shown in  FIG. 1  may not necessarily represent paths or directions through which data flows or is transmitted between various components of the device  10 , but is merely intended to show that the processor(s)  18  may interface and/or communicate either directly or indirectly with each component of the device  10 . Additionally, the blocks represented in the block diagram may not represent relative locations of the components. Each of the components represented by the blocks may be integrally formed together which can cause the signals to each of the various components to influence each other in ways that cannot be predicted during manufacture of the device  10 . 
     The display  12  may be used to display various images generated by the electronic device  10 . In the illustrated embodiment, the display  12  may be a liquid crystal display (LCD), such as an LCD that employs fringe-field switching (FFS), in-plane switching (IPS) or other techniques use in operating such LCD devices. The display  12  may be a color display utilizing a plurality of color channels for generating color images. By way of example, the display  12  may utilize a red, green, and blue color channel. As discussed further below, the display  12  in the form of an LCD may include a panel having an array of thin-film transistors (TFTs) representative of image pixels, and may also include slew rate control circuitry that is configured to select a desired slew rate for gate activation signals supplied to the TFTs to reduce the effects of voltage kickback and coupling (which may cause visual artifacts, such as flicker, to occur), and thus improve overall image quality. Further, in other embodiments, the display  12  may also be a display that uses plasma or organic light emitting diode (OLED) technologies. In one embodiment, the display may be a high-resolution LCD display having 300 or more pixels per inch, such as a Retina Display®, available from Apple Inc. Moreover, in some embodiments, the display  12  may be provided in conjunction with a touch-sensitive element, such as a touch screen, that may function as one of the input structures  16  for the electronic device  10 . For instance, the touch screen may sense inputs based on contact with a user&#39;s finger or with a stylus. As hinted at above, the input structures  16 , particularly those touch-based input structures  16  that are integrally formed with the display  12 , can cause coupling of signals that affect signals to the display  12 . 
     The processor(s)  18  may control the general operation of the device  10 . For instance, the processor(s)  18  may provide the processing capability to execute an operating system, programs, user and application interfaces, and any other functions of the electronic device  10 . The processor(s)  18  may include one or more microprocessors, such as one or more “general-purpose” microprocessors, one or more special-purpose microprocessors and/or application-specific microprocessors (ASICs), or a combination of such processing components. For example, the processor(s)  18  may include one or more processors based upon x86 or RISC instruction set architectures, as well as dedicated graphics processors (GPU), image signal processors, video processors, audio processors and/or related chip sets. By way of example only, the processor(s)  18  may, in one embodiment, include a model of a system-on-a-chip (SoC) processor, such an A4 processor, available from Apple Inc. As should be appreciated, the processor(s)  18  may be coupled to one or more data buses for transferring data and instructions between various components of the device  10 . 
     The instructions or data to be processed by the processor(s)  18  may be stored in a computer-readable medium, such as a memory device  20 . The memory device  20  may be provided as volatile memory, such as random access memory (RAM), or as non-volatile memory, such as read-only memory (ROM), or as a combination of RAM and ROM devices. The memory  20  may store a variety of information and may be used for various purposes. For example, the memory  18  may store firmware for the device  10 , such as a basic input/output system (BIOS), an operating system, various programs, applications, or any other routines that may be executed on the device  10 , including user interface functions, processor functions, and so forth. The memory  20  may additionally be used for buffering or caching during operation of the device  10 . 
     In addition to memory  20 , the device  10  may further include a non-volatile storage  22  for persistent storage of data and/or instructions. The non-volatile storage  20  may include flash memory, a hard drive, or any other optical, magnetic, and/or solid-state storage media, or some combination thereof. Thus, although depicted as a single device in  FIG. 1  for purposes of clarity, the non-volatile storage  22  may include a combination of one or more of such storage devices operating in conjunction with the processor(s)  18 . The non-volatile storage  22  may be used to store firmware, data files, image data, software programs and applications, and any other suitable data. For instance, the non-volatile storage  22  may store image and/or video data that may be displayed and/or played back on the display device  12  for viewing by a user. Further, the RF circuitry  26  may enable the device  10  to connect to a network, such as a local area network, a wireless network (e.g., an 802.11x network or Bluetooth network), or a mobile network (EDGE, 3G, 4G, LTE, etc.), and to communicate with other devices over the network. 
       FIG. 2  illustrates an embodiment of the electronic device  10  in the form of a computer  30 . The computer  30  may include computers that are generally portable (such as laptop, notebook, tablet, and handheld computers), as well as computers that are generally used in one place (such as conventional desktop computers, workstations and/or servers). The depicted computer  30  includes a housing or enclosure  32 , the display  12  (e.g., LCD or other suitable display), I/O ports  14 , and input structures  16 . By way of example, certain embodiments of the computer  30  may include a model of a MacBook®, MacBook Pro®, MacBook Air®, iMac®, Mac Mini®, or Mac Pro®, all available from Apple Inc. 
     The display  12  may be integrated with the computer  30  (e.g., the display of a laptop computer) or may be a standalone display that interfaces with the computer  30  through one of the I/O ports  14 , such as via a DisplayPort, DVI, High-Definition Multimedia Interface (HDMI), or analog (D-sub) interface. For instance, in certain embodiments, such a standalone display  12  may be a model of an Apple Cinema Display®, available from Apple Inc. As will be discussed in further detail below, the display  12  in the form of the LCD may include logic for controlling the slew rate of data signals supplied by source drivers for to a TFT array of the LCD  34  in a manner that helps to reduce the occurrence of visual display artifacts, such as flicker, resulting from the effects of coupling and interference from system noise that may be present in the computer  30 . 
       FIG. 3  depicts the electronic device  10  in the form of a portable handheld electronic device  40 , which may be a model of an iPod® or iPhone® available from Apple Inc. The handheld device  40  includes an enclosure  42 , which may protect the interior components from physical damage and may also allow certain frequencies of electromagnetic radiation, such as wireless networking and/or telecommunication signals, to pass through to wireless communication circuitry (e.g., network interfaces  24 ), which may be disposed within the enclosure  42 . As shown, the enclosure  42  also includes various user input structures  16  through which a user may interface with the device  10 . For instance, each input structure  14  may be configured to control one or more device functions when pressed or actuated. 
     The device  40  also includes various I/O ports  14 . For example, a connection port  14  (e.g., a 30-pin dock-connector available from Apple Inc. or a lightning dock-connector available from Apple Inc.) for transmitting and receiving data and for charging the power source  26 , which may include one or more removable, rechargeable, and/or replaceable batteries. The I/O ports  14  may also include an audio connection port  14  for connecting the device  40  to an audio output device (e.g., headphones or speakers). 
     The display  12  may display various images generated by the handheld device  40 . For example, the display  12  may display a graphical user interface (GUI)  44  that allows a user to interact with the device  40 . In the presently illustrated embodiment, the displayed screen image of the GUI  44  may represent a home-screen of an operating system running on the device  40 , which may be a version of the Mac OS® or iOS® (previously iPhone OS®) operating systems, both available from Apple Inc. The GUI  44  may include various graphical elements, such as icons  46 , corresponding to various applications that may be executed upon user selection (e.g., receiving a user input corresponding to the selection of a particular icon  46 ). 
     As noted briefly above, the display  12  represented in the embodiments of  FIGS. 1-3  may be a liquid crystal display (LCD).  FIG. 4  represents a circuit diagram of such a display  12 , in accordance with an embodiment. As shown, the display  12  may include an LCD display panel  50  including unit pixels  52  disposed in a pixel array or matrix. In such an array, each unit pixel  52  may be defined by the intersection of rows and columns, represented here by the illustrated gate lines  54  (also referred to as “scanning lines”) and source lines  56  (also referred to as “data lines”), respectively. Only six unit pixels  52   a - 42   f  are shown for purposes of simplicity. However, it should be understood that in an actual implementation, each source line  56  and gate line  54  may include thousands or more of such unit pixels  52 . 
     As shown in the present embodiment, each unit pixel  52  includes a thin film transistor (TFT)  58  for switching a data signal stored on a respective pixel electrode  60 . In the depicted embodiment, a source  62  of each TFT  58  may be electrically connected to a source line  56  and a gate  64  of each TFT  58  may be electrically connected to a gate line  54 . A drain  66  of each TFT  58  may be electrically connected to a respective pixel electrode  60 . Each TFT  58  serves as a switching element that 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  64  of the TFT  58 . 
     When activated, the TFT  58  may store the image signals received via a respective source line  56  as a charge upon its corresponding pixel electrode  60 . The image signals stored by the pixel electrode  60  may be used to generate an electrical field between the respective pixel electrode  60  and a common electrode  65 . The electrical field between the respective pixel electrode  60  and the common electrode may alter the polarity of a liquid crystal layer above the unit pixel  52 . The electrical field may align liquid crystals molecules within the liquid crystal layer to modulate light transmission. As the electrical field changes, the amount of light may increase or decrease. In general, light may pass through the unit pixel  52  at an intensity corresponding to the applied voltage (e.g., from a corresponding source line  56 ). As will be discussed below, however, lingering charges within the panel  50 , stray charges from elsewhere within the device  10 , and/or external electrical signals may influence the unit pixel  52  which can disrupt the applied voltage. 
     The display  12  also may include a source driver integrated circuit (IC)  68 , which may include a chip, such as a processor or ASIC, that controls the display panel  50  by receiving image data  70  from the processor(s)  12  and sending corresponding image signals to the unit pixels  52  of the panel  50 . The source driver IC  68  also may couple to a gate driver IC  72  that may activate or deactivate rows of unit pixels  52  via the gate lines  54 . As such, the source driver IC  68  may send timing information, shown here by reference number  74 , to gate driver IC  72  to facilitate activation/deactivation of individual rows of pixels  52 . In other embodiments, timing information may be provided to the gate driver IC  72  in some other manner. 
     In operation, the source driver IC  68  receives the image data  70  from the processor(s)  12  or a separate display controller and, based on the received data, outputs signals to control the pixels  52 . For instance, to display image data  70 , the source driver IC  68  may adjust the voltage of the pixel electrodes  50  one row at a time. To access an individual row of pixels  52 , the gate driver IC  72  may send an activation signal (e.g., an activation voltage) to the TFTs  48  associated with the row of pixels  52 , rendering the TFTs  48  of the addressed row conductive. The source driver IC  68  may transmit certain data signals to the unit pixels  52  of the addressed row via respective source lines  56 . Thereafter, the gate driver IC  72  may deactivate the TFTs  48  in the addressed row by applying a deactivation signal (e.g., a lower voltage than the activation voltage, such as ground), thereby impeding the pixels  52  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  52  in the panel  50  to reproduce image data  70  as a viewable image on the display  12 . 
     The source driver IC  68  shown in  FIG. 4  may be include a slew rate control unit  82  in a manner depicted in  FIG. 5 . As described above, the source driver IC  68  receives the image data  70  to deliver to the panel  50 . The image data  70  may come from the processor(s)  18 , or may come from other sources. The source driver IC  68  includes source drivers  76  that deliver the image data  70  to one or more of the source lines  56 . Specifically, the source drivers  76  may deliver the image data  70  to 1, 2, 3, 4, or more source lines  56 . Each source driver  76  (S 1 , S 2 , S 3 , Sy, Sz, wherein there are “Z” total source drivers  76 ) receives a data signal  70  (D 1 , D 2 , D 3 , Dy, Dz, again, a total of “Z” data signals  70  for the source drivers  76 ) that is specific to that source driver  76 . Each source driver  76  individually adjusts the slew rate (i.e., the rate at which the signal on the source line  56  reaches the image data voltage) for the particular data signal (e.g., D 1 , D 2 , D 3 , Dy, Dz) that the source driver  76  receives. The source drivers  76  adjust the slew rate based on a slew rate signal  80  from a slew rate control unit  82 . For example, if the first source driver  76  S 1  receives a high slew rate signal  80  from the slew rate control unit  82 , then the source driver  76  S 1  will adjust the data signal so that it quickly reaches the data voltage. Alternatively, if the first source driver  76  S 1  receives a low slew rate signal  80  from the slew rate control unit  82 , then the source driver  76  S 1  will adjust the data signal to reach the data voltage more gradually. This is shown in detail in  FIG. 7 . 
     To adjust the slew rate signal  80 , the slew rate control unit  82  performs digital signal processing based on the image data  70 , adjusted image data  83 , and/or other signals or noise within the device  10 . The update frequency of the slew rate adjustment may be limited to the frequency at which the source driver  76  updates the data signal  70  on the data line  56 . Additionally, when the voltage difference between sequential frames is large, the slew rate may change significantly in response. In certain embodiments, the step size of these slew rate signals  80  is filtered to prevent flickering and/or other odd effects. In certain embodiments, the slew rate control unit  82  may receive the image data  70  (e.g., D 1 , D 2 , D 3  . . . Dy, Dz) for each source driver  76  (e.g., S 1 , S 2 , S 3  . . . Sy, Sz) to compare one data signal (e.g., D 1 ) to a second data signal (e.g., D 2 ). In other embodiments, the slew rate control unit  82  may receive adjusted image data  83  (e.g., ΔD 1  . . . ΔDz) that has been adjusted by a comparator  84  with a delayed image data signal from a line buffer  85 . The line buffer  85  receives the image data  70  for each source driver  76  and holds the image data  70  for one frame or one line (i.e., until the gate driver IC  72  deactivates one gate line  54  and activates the next). The comparator  84  then compares the previous image data  70  (e.g., D 1   previous ) to the current image data  70  (e.g., D 1   current ) for each source driver  76  (i.e., D 1   previous  . . . Dz previous  compared respectively to D 1   current  . . . Dz current ) to determine the adjusted image data  83  (e.g., ΔD 1  . . . ΔDz). The slew rate control unit  82  uses the adjusted image data  83  in part to select the slew rate signal  80  to deliver to the source drivers  76 . 
     Also illustrated in the diagram of  FIG. 5  are signals that the source driver IC  68  may receive from the device  10  and the panel  50 . As explained below, the source driver IC  68  may adjust the slew rate of the source drivers  76  based on a settling signal  86  from the panel  50  and system noise  88  from the device  10 . Each of the settling signal  86  and the system noise  88  may include analog signals converted to digital signals so that the source driver IC  68  may determine a degree to which the settling signal  86  and the system noise  88  may be affecting the image within the pixel  52 . The settling signal  86  may include timing information indicative of how the pixels are disturbed and how soon the pixels recover from noise that may be generated when the data signal or other signals are applied within the display  50 . 
     To determine the slew rate for each source driver  76 , the slew rate control unit  82  may employ a method  100  illustrated in  FIG. 6 . The method  100  starts when the source driver IC  68  receives  102  the image data  70 . The image data  70  may be received directly by the source drivers  76 , and may also be received by the slew rate control unit  82 , the line buffer  85 , or any combination thereof. The image data  70  is received as frames of images for the panel  50 . The frames of the image data  70  may, for a given time period, remain consistent from one frame to the next. In other instances, such as when the device is playing a video, the frames of the image data  70  may include images that change significantly in the amount of luminance from one frame to the next. In such circumstances, the fast changing of the signal from the source drivers  76  may increase the potential for noise within the panel  50 . In other circumstances, the image data  70  from the same source driver (e.g., D 1  data for S 1  source driver) may vary from one gate line  54  to the next. These circumstances have the potential to cause noise in the display  50  and/or prolong the recovery time of the pixel which can cause inefficiency in the display  50 . The line buffer  85  may be programmed to recognize the potential for noise and indicate to the slew rate control unit  82  to adjust the slew rate accordingly. 
     As part of the method  100  performed by the source driver IC  68 , the source driver IC  68  also receives  104  noise from the device  10  and/or feedback from the display panel  50 . For example, the slew rate control unit  82  may receive a settling signal  86  that indicates the noise or condition of the pixels  52  within the panel  50 . The settling signal  86  may include voltage information from common electrodes  65  in the panel  50  which may indicate that settling has not occurred in one or more pixels  52  or columns/rows of pixels  52 . In particular, the common electrode  65  for one or more pixels  52  may have disturbance due to the capacitance within circuitry of the pixels  52 . The settling signal  86  may also represent capacitance voltages on the gate lines  54  that could cause flickering or other unwanted display event. Additionally, the settling signal  86  may include a disturbance voltage on the data line, gate line, or other circuit component as shown and discussed with regard to  FIG. 7 . 
     The slew rate control unit  82  may also receive signals indicative of system noise  88  that may influence the operation of the panel  50 . For example, wireless signals (e.g., external noise: cellular signals, near-field communication signals, wireless charging, wireless local internet signals, Bluetooth, power line interference, etc.), touch signals, clock coupling noise, general operation of the processor(s)  18 , charging of the power source  26 , etc. may impact the interaction of the circuitry of the display  12  and/or the panel  50 . The slew rate control unit  82  may receive indications for levels of noise that are present in the device  10  from sensors, or the slew rate control unit  82  may infer an amount of noise based on signal levels. 
     Once the source drive IC  68  receives  104  the noise, a noise level and recovery time is determined  106  based on the image data and the noise. The slew rate is then selected  108  to balance the level of noise and the recovery time of the pixels  52  in the display  50 . An example of the relationship between slew rate, noise, and recovery time is illustrated in the graph  110  of  FIG. 7 . The graph  110  includes three examples of the voltage  112  that one of the source drivers  76  may deliver to the source line  56 . Each example alternates between a signal voltage  114  and a minimum voltage  115 . The abscissa of the graph  110  is time, though the relative distances for which the rising, falling, and maintaining of the voltage  112  in the illustrated embodiment showed not be limiting for other embodiments. The graph  110  shows the relationship of the signal voltage  112  to a disturbance voltage  117  of the common electrode  65 . A slew rate of a first data signal  116  has a “high” slew rate such that the first data signal  116  reaches the signal voltage  114  in a short amount of time. A high slew rate corresponds to high peak disturbance  118  of the common electrode  65 . In some instances, high disturbance of the common electrode  65  may be less desirable, as disturbances in the common electrode  65  may cause inaccurate color in the display  12 . A high slew rate, first slew rate  116 , however, also includes disturbance of the common electrode  65  that does not last very long. That is, the total time from a signal start  118  through a peak disturbance  120  to significant drop off in disturbance  117  is short. The length of time in which the common electrode  65  is undisturbed is known as the recovery time, and under some circumstances the recovery time may be used by the device  10  to handle other non-display related operations (e.g., touch sensing). As a contrasting example, if a second slew rate for a second data signal  122  is low, a corresponding peak disturbance  120  is also low, but the common electrode  65  experiences disturbance for a longer duration (i.e., less recovery time). A third slew rate for a third data signal  124  in  FIG. 7  shows that a slew rate between the first slew rate of the first data signal  116  and the second slew rate of the second data signal  120  also experiences a peak disturbance  120  and a recovery time that is between the peak disturbance  120  and the recovery time of the first data signal  116  and the second data signal  122 . While  FIG. 7  illustrates three difference slew rates, the source driver IC  68  may include capabilities for any suitable number of slew rates (e.g., 4, 5, 6, 7, 8, or more different slew rates) at which the source drivers  76  may deliver the signal to the source lines  56 . For example, the source driver IC  68  may have three-bit slew rate adjustment capability to select between 8 different slew rates (i.e., LLL to HHH). The corresponding peak disturbances  120  of the common electrode  65  may be stored as a lookup table within the slew rate control unit  82  for any given signal voltage  114  and received noise level. 
     Returning to the method  100  introduced above, from the discussion of  FIG. 7 , it may be more clear what evaluation the slew rate control unit  82  considers when selecting  108  the slew rate to send to the source driver  76 . For example, the slew rate control unit  82  determines  106 , based on the signal voltage  114  and the noise it receives, that a slew rate will correspond to a certain disturbance and/or a certain recovery time. When selecting the slew rate, the slew rate control unit  82  may include a cutoff for recovery time. Any slew rate with a recovery time that is longer than the cutoff recovery time will not be considered a valid option. Of the remaining possible slew rates, the slew rate control unit  82  may select the slew rate that corresponds to the least amount of disturbance  120 . As mentioned above, the slew rate control unit  82  may filter the selected slew rate such that the slew rate does not jump significantly, which can cause flickering. For example, if a source driver  76  is currently set at a slew rate of 1 and the slew rate control unit  82  determines that a slew rate of 7 or 8 is desirable, then the slew rate may be filtered first to slew rate 3 or 4 for a second frame, and then 7 or 8 for the subsequent frame afterward. In addition to a cutoff for recovery time, a cutoff for maximum disturbance level  117  may be selected with options to maximize recovery time. The slew rate may be selected either digitally or through analog circuits. For example, the slew rate control unit  82  may includes a look-up table that associates certain noise levels to certain slew rates, while also having some dependence on current slew rate. In certain other embodiments, analog circuits in the source driver IC  68  may amplify noise to set the bias of the line buffer  85 , so that the slew rate control unit  82  may adjust the slew rate. 
     As should be understood, the various techniques described above and relating to slew rate control of a signal are provided herein by way of example. Accordingly, it should be understood that the present disclosure should not be construed as being limited to only the examples provided above. Further, it should be appreciated that the slew rate control disclosed herein techniques may be implemented in any suitable manner, including hardware (suitably configured circuitry), software (e.g., via a computer program including executable code stored on one or more tangible computer readable medium), or via using a combination of both hardware and software elements. 
     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: 20150317
Publication Date: 20171114
Grant Date: 20171114
Priority Date: 20150317
Inventors: LIN HUNG SHENG
WANG CHAOHAO
SACCHETTO PAOLO
Assignee: APPLE INC
CPC Classifications: [{"code": "G09G2330/06", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2310/0289", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/3688", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G2320/029", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2310/027", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/029", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/3648", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G3/3696", "inventive": true, "first": true, "tree": "[]"}, {"code": "G09G2330/06", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2310/027", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/3688", "inventive": true, "first": true, "tree": "[]"}, {"code": "G09G3/3648", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G2330/08", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/0209", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/0209", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2310/0291", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2310/0291", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/029", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/0209", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/3648", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G3/3688", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G2310/0289", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2330/06", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/3696", "inventive": true, "first": true, "tree": "[]"}, {"code": "G09G2310/027", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2330/08", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2310/0291", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 56925186