PATENT DOCUMENT

Publication Number: US-10175830-B2
Application Number: US-201514870815-A
Country: US
Kind Code: B2

Title: Systems and methods for pre-charging a display panel

Abstract:
A method for pre-charging a display panel may include simultaneously charging the display panel that displays image data and receives one or more touch inputs via a first voltage source and a capacitor that provides a first voltage to the display panel via a second voltage source. The first voltage is associated with receiving the one or more touch inputs, and the display panel and the capacitor are simultaneously charged for a first amount of time. The method may then include charging the display panel via the capacitor after the first amount of time for a second amount of time and charging the display panel via the second voltage source after the second amount of time for a third amount of time.

Claims:
What is claimed is: 
     
       1. A display driver circuit, comprising:
 a first switch configured to couple a first voltage source in series with a display panel, wherein the display panel is configured to receive a first voltage via the first voltage source, and wherein the display panel is configured to display image data and receive one or more touch inputs; 
 a second switch configured to couple a second voltage source in series with a capacitor; 
 a third switch configured to couple the capacitor in series with the display panel, wherein the capacitor is configured to provide a second voltage to the display panel; and 
 a fourth switch configured to couple the second voltage source in series with the display panel, wherein the second voltage source is configured to provide the second voltage to the display panel, and wherein the capacitor is configured to enable the display panel to settle to the second voltage more quickly as compared to if the display panel were charged via the second voltage source without using the capacitor. 
 
     
     
       2. The display driver circuit of  claim 1 , wherein the first voltage source is configured to enable the display panel to display the image data, and wherein the second voltage source is configured to enable the display panel to receive the one or more touch inputs. 
     
     
       3. The display driver circuit of  claim 1 , wherein the first switch and the second switch are configured to open and close at the same time. 
     
     
       4. The display driver circuit of  claim 1 , comprising a processor configured to:
 close the first switch and the second switch for a first amount of time thereby charging the display panel via the first voltage source and charging the capacitor via the second voltage source; 
 close the third switch for a second amount of time thereby charging the display panel via the capacitor; and 
 close the fourth switch for a third amount of time thereby charging the display panel via the second voltage source. 
 
     
     
       5. The display driver circuit of  claim 4 , wherein the processor is configured to open the first switch and the second switch when the third switch is closed. 
     
     
       6. The display driver circuit of  claim 4 , wherein the processor is configured to open the third switch when the fourth switch is closed. 
     
     
       7. The display driver circuit of  claim 1 , comprising an operational amplifier configured to output a touch voltage based on an input voltage provided via the second voltage source. 
     
     
       8. The display driver circuit of  claim 7 , comprising a resistor directly coupled between the second switch and the operational amplifier. 
     
     
       9. The display driver circuit of  claim 4 , wherein the display panel is configured to charge from a first voltage value after the first amount of time to a second voltage value after the third amount of time. 
     
     
       10. The display driver of  claim 9 , wherein a voltage of the display panel is configured to settle to the second voltage time during the second amount of time and the third amount of time. 
     
     
       11. The display driver of  claim 10 , wherein the second amount of time and the third amount of time is approximately 5 μs. 
     
     
       12. A system comprising:
 a display panel configured to display image data and receive one or more touch inputs; 
 a capacitor configured to provide a first voltage to the display panel; 
 a first switch configured to couple the capacitor in series with the display panel; 
 a second switch configured to couple a voltage source in series with the display panel; and 
 a processor configured to:
 charge the display panel via the capacitor and the first switch for a first amount of time, wherein the first amount of time is less than approximately 1 μs; and 
 charge the display panel via the voltage source and the second switch for a second amount of time. 
 
 
     
     
       13. The system of  claim 12 , wherein the display panel is configured to receive one or more touch inputs during the first amount of time and the second amount of time. 
     
     
       14. The system of  claim 12 , comprising a third switch configured to couple the capacitor in series with the voltage source. 
     
     
       15. The system of  claim 14 , wherein the processor is configured to:
 close the third switch when the first switch is open thereby charging the capacitor via the voltage source; and 
 simultaneously open the third switch and close the first switch thereby charging the display panel via the capacitor. 
 
     
     
       16. The system of  claim 15 , wherein the processor is configured to simultaneously open the first switch and close the second switch thereby charging the display panel via the voltage source. 
     
     
       17. An electronic device, comprising:
 a display panel configured to display image data and receive one or more touch inputs; 
 a first voltage source configured to output a first voltage associated with displaying the image data via the display panel; 
 a second voltage source configured to output a second voltage associated with receiving one or more touch inputs via the display panel; 
 a capacitor configured to provide a third voltage to the display panel; 
 a plurality of switches configured to couple the first voltage source, the second voltage source, the capacitor, or any combination thereof to the display panel; and 
 a processor configured to:
 cause the display panel to charge via the first voltage source and a first switch of the plurality of switches; 
 cause the display panel to charge via the capacitor and a second switch of the plurality of switches after the display panel is charged via the first switch; and 
 cause the display panel to charge via the second voltage source and a third switch of the plurality of switches after the display panel is charged via the second switch, wherein the capacitor is configured to enable the display panel to settle to the third voltage more quickly as compared to if the display panel were charged via the second voltage source and the third switch. 
 
 
     
     
       18. The electronic device of  claim 17 , wherein the processor is configured to disconnect the first voltage source from the display panel via the first switch when the display panel is charging via the capacitor and the second switch. 
     
     
       19. The electronic device of  claim 17 , wherein the processor is configured to disconnect the capacitor from the display panel via the second switch when the display panel is charging via the second voltage source and the third switch. 
     
     
       20. A method, comprising:
 simultaneously charging a display panel comprising a plurality of pixels configured to display image data, wherein the display panel is configured to receive one or more touch inputs via a first voltage source and a capacitor configured to provide a first voltage to at least one of the plurality of pixels in the display panel via a second voltage source, wherein the first voltage is associated with receiving the one or more touch inputs, and wherein the display panel and the capacitor are simultaneously charged for a first amount of time; 
 charging the display panel via the capacitor after the first amount of time for a second amount of time; and 
 charging the display panel via the second voltage source after the second amount of time for a third amount of time. 
 
     
     
       21. The method of  claim 20 , comprising:
 determining whether a difference between a second voltage of the display panel and a third voltage of the capacitor is greater than a threshold; and 
 charging the capacitor via a plurality of switches when the difference is greater than the threshold. 
 
     
     
       22. The method of  claim 20 , comprising:
 determining whether a difference between a second voltage of the display panel and a third voltage of the capacitor is greater than a threshold; and 
 charging the display panel via the capacitor and a plurality of switches when the difference is greater than the threshold. 
 
     
     
       23. A system comprising:
 a display panel comprising a plurality of pixels configured to display image data, wherein the display panel is configured to receive one or more touch inputs; 
 a capacitor configured to provide a first voltage to at least one of the plurality of pixels in the display panel, wherein the capacitor is coupled in series with a first voltage source; 
 a first plurality of switches configured to couple the capacitor in series with the first voltage source; 
 a second plurality of switches configured to couple the capacitor in series with the display panel; 
 a first switch configured to couple the first voltage source in series with the capacitor; 
 a second switch configured to couple the capacitor in series with the display panel; and 
 an operational amplifier configured to: 
 receive a difference between a first voltage of the display panel and a second voltage of the capacitor; 
 charge the capacitor via the first switch when the difference is below the threshold; 
 charge the capacitor via the first plurality of switches when the difference is above the threshold; 
 charge the display panel via the capacitor and the second plurality of switches when the threshold is above the threshold after the capacitor is charged for a first amount of time; and 
 charge the display panel via the first voltage source and the second switch for a second amount of time after the first amount of time. 
 
     
     
       24. The system of  claim 23 , wherein the first plurality of switches and the second plurality of switches comprise a plurality of metal-oxide-semiconductor field-effect transistors (MOSFETs). 
     
     
       25. The system of  claim 23 , wherein the operational amplifier comprises the first plurality of switches, the second plurality of switches, the first switch, and the second switch. 
     
     
       26. The system of  claim 23 , wherein the first plurality of switches and the second plurality of switches each comprises at least sixteen switches. 
     
     
       27. The system of  claim 23 , comprising a comparator circuit configured to determine the difference between the first voltage and the second voltage. 
     
     
       28. A system comprising:
 a display panel configured to display image data and receive one or more touch inputs; 
 a capacitor configured to provide a first voltage to the display panel, wherein the capacitor is coupled in series with a first voltage source configured to output a first voltage; 
 a first switch configured to couple the capacitor in series with the first voltage source; 
 a second switch configured to couple the capacitor in series with ground; 
 a multiplexer configured to couple the capacitor in series with the display panel, wherein the multiplexer is a 4:1 multiplexer; and 
 an operational amplifier configured to:
 receive a second voltage from a second voltage source, wherein the first voltage is greater than the second voltage; 
 charge the capacitor via the first switch and the first voltage source; 
 charge the display panel via the capacitor and the multiplexer after the capacitor is charged for a first amount of time; and 
 charge the display panel via the second voltage source for a second amount of time after the first amount of time. 
 
 
     
     
       29. The system of  claim 28 , wherein an output of the capacitor is coupled in series with an inverted input of the operational amplifier. 
     
     
       30. The system of  claim 28 , wherein a third voltage source configured to output a third voltage that corresponds to a display period of the display panel is coupled in series with the multiplexer. 
     
     
       31. The system of  claim 28 , wherein the capacitor is configured to enable the display panel to settle to the second voltage more quickly as compared to when the display panel is charged via the second voltage source without using the capacitor. 
     
     
       32. The system of  claim 28 , comprising a buffer circuit, wherein buffer circuit comprises the capacitor, the multiplexer, the operational amplifier, the first switch, and the second switch, and wherein an impedance of the buffer circuit is configured to decrease a noise output to the display panel.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is related to U.S. Patent Application Ser. No. 62/111,077, and is hereby incorporated by reference in its entirety. 
     BACKGROUND 
     The present disclosure relates generally to pre-charging a display panel and, more specifically, to pre-charging a display panel for display periods and touch periods. 
     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. 
     Various types of electronic devices include display panels to display image data and receive touch inputs from a user, such that the user may interact with the electronic device. Generally, to display image data and receive touch inputs, the display panel may alternate between a display period when the image data is displayed and a touch period when touch inputs are detected. During the display period, the display panel (e.g., capacitance) may be pre-charged to a first voltage that enables the display panel to display the image data. In the same manner, during the touch period, the display panel may be pre-charged to a second voltage that enables the display panel to detect touch inputs. The first and second voltages may be different values. To effectively display image data and receive touch inputs at the same time, the display panel may alternate between the display period and touch period at a rapid rate (e.g., 60 Hz). That is, the display panel may pre-charge to the first voltage for displaying the image data for a first amount of time and pre-charge to the second voltage for receiving touch inputs for a second amount of time, such that two amounts of time occur quickly enough that a user (e.g., human) would not detect the change between the display period and the touch period. 
     To enhance the ability of the display panel to detect touch inputs, the display panel may switch between the display period and the touch period more frequently. However, various challenges may arise when increasing the frequency in which an electronic device switches between the display period and the touch period. 
     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. 
     The present disclosure generally relates to pre-charging a display panel (e.g., capacitance) with two voltages, such that the display panel may effectively display image and receive touch inputs. More specifically, the present disclosure relates to pre-charging the display panel to a display voltage via a display voltage source (VCOM_D) and pre-charging the display panel to a touch voltage via multiple stage process that limits the current output to the display panel while making the transition from the display voltage to the touch voltage within a certain amount of time (e.g., 5 μs). In certain embodiments, an electronic device may use a display panel as a display and as an interface to receive touch inputs via touch-sensing circuitry within the display panel. To simultaneously display image data and detect touches, the display panel may frequently alternate between a display period mode (e.g., when a frame of image data is rendered on an active display region of the display panel) and touch period mode (e.g., when the active display region detects touch inputs). The display period and touch period modes for the display panel may be characterized by two different sets of voltages applied to the active display region of the display panel via two voltage sources (e.g., high and low, display voltage source and touch voltage source). 
     During the display period, the active display region may receive a display voltage (VCOM_D) from the display voltage source such that the active display region may be capable of displaying the image data. During the touch period, the active display region may receive a touch voltage (VCOM_T) from the touch voltage source such that the active display region may be capable of detecting touch inputs. In one embodiment, the touch voltage (VCOM_T) may be provided to the display panel via a bypass capacitor (Cb) that may be coupled to the touch voltage source. The bypass capacitor (Cb) may limit the amount of current provided to the display panel and control the amount of time for the voltage in the display panel to settle to the touch voltage (VCOM_T). When the display panel is operating in the display period mode, the display panel may receive the display voltage (VCOM_D) via the display voltage source. At the same time, the bypass capacitor (Cb) may be charged via the touch voltage source. When transitioning from the display voltage to the touch voltage, a first switch that couples the display voltage source to the display panel and a second switch that couples the touch voltage to the bypass capacitor (Cb) may be opened while a third switch that couples the bypass capacitor (Cb) to the display panel may be closed. 
     Initially, since the display panel is connected to just the bypass capacitor (Cb), the amount of current output to the display panel may be limited by a resistor in series with the bypass capacitor (Cb). Moreover, the size of the bypass capacitor (Cb) may be selected to limit the amount of current output to the display panel. In addition, by initially charging the display panel via the bypass capacitor (Cb) alone, the pre-charge settle time for the display panel or the time that the voltage received by display panel via the bypass capacitor (Cb) may settle within a certain amount of time. Although the pre-charge settle time for the display panel may be within a desired amount of time, the display panel may not be charged to the touch voltage (VCOM_T) within the same amount of time. As such, after the third switch has been closed for a first amount of time (e.g., 1 μs), the third switch may open while a fourth switch in series with the touch voltage source and the display panel may be closed until the voltage of the display panel is charged to the touch voltage (VCOM_T). After reaching the touch voltage (VCOM_T), the fourth switch may be opened and the first and third switches may be closed again, such that the display panel may receive the display voltage (VCOM_D) from the display voltage source and the bypass capacitor (Cb) may be charged via the touch voltage source. This process may be continuously repeated, thereby enabling the display panel to simultaneously display image data and detect touch inputs. 
     By charging the display panel to the touch voltage (VCOM_T) using the bypass capacitor (Cb) and the touch voltage source during two different stages, the display panel may effectively switch between the display voltage (VCOM_D) to the touch voltage (VCOM_T) while limiting an amount of current provided to the display panel and decreasing the amount of time for the touch voltage to settle in the display panel. As a result, the display panel may alternate between the display period and the touch period more frequently (e.g., 120 Hz), thereby improving the ability of the display panel to detect touches and display better quality image data. 
     Various refinements of the features noted above may exist in relation to various aspects of the present disclosure. Further features may also be incorporated in these various aspects as well. These refinements and additional features may exist individually or in any combination. For instance, various features discussed below in relation to one or more of the illustrated embodiments may be incorporated into any of the above-described aspects of the present disclosure alone or in any combination. The brief summary presented above is intended only to familiarize the reader with certain aspects and contexts of embodiments of the present disclosure without limitation to the claimed subject matter. 
    
    
     
       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 simplified block diagram of components of an electronic device that may depict image data on a display, in accordance with embodiments described herein; 
         FIG. 2  is a perspective view of the electronic device of  FIG. 1  in the form of a notebook computing device, in accordance with embodiments described herein; 
         FIG. 3  is a front view of the electronic device of  FIG. 1  in the form of a desktop computing device, in accordance with embodiments described herein; 
         FIG. 4  is a front view of the electronic device of  FIG. 1  in the form of a handheld portable electronic device, in accordance with embodiments described herein; 
         FIG. 5  is a front view of the electronic device of  FIG. 1  in the form of a tablet computing device, in accordance with embodiments described herein; 
         FIG. 6  is an example circuit diagram of a display driver integrated circuit (IC) in the display of the electronic device of  FIG. 1 , in accordance with an embodiment; 
         FIG. 7  is another example circuit diagram of a display driver integrated circuit (IC) in the display of  FIG. 5 , in accordance with an embodiment; 
         FIG. 8  illustrates timing and voltage chart for switches and capacitor voltages of the example circuit diagram of  FIG. 7 ; 
         FIG. 9  illustrates another timing and voltage chart for switches and capacitor voltages of the example circuit diagram of  FIG. 7 ; 
         FIG. 10  illustrates a flow chart of a method for alternating between a display period and a touch period in a display panel of  FIG. 1 ; 
         FIG. 11  is an example circuit diagram of a display driver integrated circuit (IC) that may pre-charge the display panel in the display of  FIG. 5  more efficiently than the example circuit of  FIG. 7 , in accordance with an embodiment; and 
         FIG. 12  is an example circuit diagram of components within an operational amplifier in the example circuit of  FIG. 11 , in accordance with an embodiment; 
         FIG. 13  is an example circuit diagram of a display driver integrated circuit (IC) that may pre-charge the display panel in the display of  FIG. 5  with an improved noise level as compared to the example circuit of  FIG. 12 , in accordance with an embodiment; 
         FIG. 14  illustrates a timing and voltage chart for the switches and MUX related to the operation of the circuit  240  of  FIG. 13 . 
     
    
    
     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. 
     The present disclosure is directed to systems and methods for pre-charging a display panel of an electronic device. More specifically, the present disclosure is related to systems and methods for charging a display panel (e.g., capacitance) between a display voltage (VCOM_D) and a touch voltage (VCOM_T) using two stages to limit the current output to the display panel and the amount of time for the display panel voltage to settle to the touch voltage (VCOM_T). Additional details with regard to how the display panel is charged from the display voltage (VCOM_D) to the touch voltage (VCOM_T) via the two stages will be discussed below with reference to  FIGS. 1-9 . 
     By way of introduction,  FIG. 1  is a block diagram illustrating an example of an electronic device  10  that may include the gate driver and column driver circuitry mentioned above. The electronic device  10  may be any suitable electronic device, such as a laptop or desktop computer, a mobile phone, a digital media player, television, or the like. By way of example, the electronic device  10  may be a portable electronic device, such as a model of an iPod® or iPhone®, available from Apple Inc. of Cupertino, Calif. The electronic device  10  may be a desktop or notebook computer, such as a model of a MacBook®, MacBook® Pro, MacBook Air®, iMac®, Mac® Mini, or Mac Pro®, available from Apple Inc. In other embodiments, electronic device  10  may be a model of an electronic device from another manufacturer. 
     As shown in  FIG. 1 , the electronic device  10  may include various components. The functional blocks shown in  FIG. 1  may represent hardware elements (including circuitry), software elements (including code stored on a computer-readable medium) or a combination of both hardware and software elements. In the example of  FIG. 1 , the electronic device  10  includes input/output (I/O) ports  12 , input structures  14 , one or more processors  16 , a memory  18 , nonvolatile storage  20 , networking device  22 , power source  24 , display  26 , and one or more imaging devices  28 . It should be appreciated, however, that the components illustrated in  FIG. 1  are provided only as an example. Other embodiments of the electronic device  10  may include more or fewer components. To provide one example, some embodiments of the electronic device  10  may not include the imaging device(s)  28 . 
     Before continuing further, it should be noted that the system block diagram of the device  10  shown in  FIG. 1  is intended to be a high-level control diagram depicting various components that may be included in such a device  10 . That is, the connection 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 . Indeed, as discussed below, the depicted processor(s)  16  may, in some embodiments, include multiple processors, such as a main processor (e.g., CPU), and dedicated image and/or video processors. In such embodiments, the processing of image data may be primarily handled by these dedicated processors, thus effectively offloading such tasks from a main processor (CPU). 
     Considering each of the components of  FIG. 1 , the I/O ports  12  may represent ports to connect to a variety of devices, such as a power source, an audio output device, or other electronic devices. The input structures  14  may enable user input to the electronic device, and may include hardware keys, a touch-sensitive element of the display  26 , and/or a microphone. 
     The processor(s)  16  may control the general operation of the device  10 . For instance, the processor(s)  16  may execute an operating system, programs, user and application interfaces, and other functions of the electronic device  10 . The processor(s)  16  may include one or more microprocessors and/or application-specific microprocessors (ASICs), or a combination of such processing components. For example, the processor(s)  16  may include one or more instruction set (e.g., RISC) processors, as well as graphics processors (GPU), video processors, audio processors and/or related chip sets. As may be appreciated, the processor(s)  16  may be coupled to one or more data buses for transferring data and instructions between various components of the device  10 . In certain embodiments, the processor(s)  16  may provide the processing capability to execute an imaging applications on the electronic device  10 , such as Photo Booth®, Aperture®, iPhoto®, Preview®, iMovie®, or Final Cut Pro® available from Apple Inc., or the “Camera” and/or “Photo” applications provided by Apple Inc. and available on some models of the iPhone®, iPod®, and iPad®. 
     A computer-readable medium, such as the memory  18  or the nonvolatile storage  20 , may store the instructions or data to be processed by the processor(s)  16 . The memory  18  may include any suitable memory device, such as random access memory (RAM) or read only memory (ROM). The nonvolatile storage  20  may include flash memory, a hard drive, or any other optical, magnetic, and/or solid-state storage media. The memory  18  and/or the nonvolatile storage  20  may store firmware, data files, image data, software programs and applications, and so forth. 
     The network device  22  may be a network controller or a network interface card (NIC), and may enable network communication over a local area network (LAN) (e.g., Wi-Fi), a personal area network (e.g., Bluetooth), and/or a wide area network (WAN) (e.g., a 3G or 4G data network). The power source  24  of the device  10  may include a Li-ion battery and/or a power supply unit (PSU) to draw power from an electrical outlet or an alternating-current (AC) power supply. 
     The display  26  may display various images generated by device  10 , such as a GUI for an operating system or image data (including still images and video data). The display  26  may be any suitable type of display, such as a liquid crystal display (LCD), plasma display, or an organic light emitting diode (OLED) display, for example. Additionally, as mentioned above, the display  26  may include a touch-sensitive element that may represent an input structure  14  of the electronic device  10 . The imaging device(s)  28  of the electronic device  10  may represent a digital camera that may acquire both still images and video. Each imaging device  28  may include a lens and an image sensor capture and convert light into electrical signals. 
     In certain embodiments, the display  26  may include a display driver integrated circuit (IC)  30  and a display panel  32 . The display driver IC  30  may be separate or integral to the display  26 . The display driver IC  30  may include circuit components to provide the display panel  32  with voltages to enable the display panel  32  to depict image data and receive touch inputs. 
     With the foregoing in mind, the electronic device  10  may take any number of suitable forms. Some examples of these possible forms appear in  FIGS. 2-5 . Turning to  FIG. 2 , a notebook computer  40  may include a housing  42 , the display  26 , the I/O ports  12 , and the input structures  14 . The input structures  14  may include a keyboard and a touchpad mouse that are integrated with the housing  42 . Additionally, the input structure  14  may include various other buttons and/or switches which may be used to interact with the computer  40 , such as to power on or start the computer, to operate a GUI or an application running on the computer  40 , as well as adjust various other aspects relating to operation of the computer  40  (e.g., sound volume, display brightness, etc.). The computer  40  may also include various I/O ports  12  that provide for connectivity to additional devices, as discussed above, such as a FireWire® or USB port, a high definition multimedia interface (HDMI) port, or any other type of port that is suitable for connecting to an external device. Additionally, the computer  40  may include network connectivity (e.g., network device  24 ), memory (e.g., memory  18 ), and storage capabilities (e.g., storage device  20 ), as described above with respect to  FIG. 1 . 
     The notebook computer  40  may include an integrated imaging device  28  (e.g., a camera). In other embodiments, the notebook computer  40  may use an external camera (e.g., an external USB camera or a “webcam”) connected to one or more of the I/O ports  12  instead of or in addition to the integrated imaging device  28 . In certain embodiments, the depicted notebook computer  40  may be a model of a MacBook®, MacBook® Pro, MacBook Air®, or PowerBook® available from Apple Inc. In other embodiments, the computer  40  may be portable tablet computing device, such as a model of an iPad® from Apple Inc. 
       FIG. 3  shows the electronic device  10  in the form of a desktop computer  50 . The desktop computer  50  may include a number of features that may be generally similar to those provided by the notebook computer  40  shown in  FIG. 4 , but may have a generally larger overall form factor. As shown, the desktop computer  50  may be housed in an enclosure  42  that includes the display  26 , as well as various other components discussed above with regard to the block diagram shown in  FIG. 1 . Further, the desktop computer  50  may include an external keyboard and mouse (input structures  14 ) that may be coupled to the computer  50  via one or more I/O ports  12  (e.g., USB) or may communicate with the computer  50  wirelessly (e.g., RF, Bluetooth, etc.). The desktop computer  50  also includes an imaging device  28 , which may be an integrated or external camera, as discussed above. In certain embodiments, the depicted desktop computer  50  may be a model of an iMac®, Mac® mini, or Mac Pro®, available from Apple Inc. 
     The electronic device  10  may also take the form of portable handheld device  60  or  70 , as shown in  FIGS. 4 and 5 . By way of example, the handheld device  60  or  70  may be a model of an iPod® or iPhone® available from Apple Inc. The handheld device  60  or  70  includes an enclosure  42 , which may function to protect the interior components from physical damage and to shield them from electromagnetic interference. The enclosure  42  also includes various user input structures  14  through which a user may interface with the handheld device  60  or  70 . Each input structure  14  may control various device functions when pressed or actuated. As shown in  FIGS. 4 and 5 , the handheld device  60  or  70  may also include various I/O ports  12 . For instance, the depicted I/O ports  12  may include a proprietary connection port for transmitting and receiving data files or for charging a power source  24 . Further, the I/O ports  12  may also be used to output voltage, current, and power to other connected devices. 
     The display  26  may display images generated by the handheld device  60  or  70 . For example, the display  26  may display system indicators that may indicate device power status, signal strength, external device connections, and so forth. The display  26  may also display a GUI  52  that allows a user to interact with the device  60  or  70 , as discussed above with reference to  FIG. 3 . The GUI  52  may include graphical elements, such as the icons, which may correspond to various applications that may be opened or executed upon detecting a user selection of a respective icon. 
     With the foregoing in mind,  FIG. 6  illustrates an example circuit  80  that may be part of the display driver  30  described above. The circuit  80  may be employed to provide a display voltage (VCOM_D) (e.g., −2.5 V) and a touch voltage (VCOM_T) (e.g., 2.5 V) to the display panel  32  (capacitance C panel ). In one embodiment, the display voltage (VCOM_D) may be provided to the display panel  32  via a display voltage source  82 , a switch  84 , and a resistor  86 . That is, the switch  84  may be closed and the display voltage source  82  may provide a voltage to the resistor  86  via the switch  84 , such that the display panel  32  may receive the display voltage (VCOM_D). It should be noted that the switch  84  and other switches mentioned herein may include any type of device that connects two nodes of an electrical circuit together. As such, the switch  84  may include a transistor, a metal-oxide-semiconductor field-effect transistor (MOSFET), and the like. 
     In addition to the display voltage source  82 , the circuit  80  may include a touch voltage source  92 , which may provide a voltage to an operational amplifier (op-amp)  94 . In one embodiment, the op-amp  94  may be a unity op-amp that may output the same voltage provided to it. The voltage output by the op-amp  94  may be provided to a resistor  96 , which may be coupled to a bypass capacitor (C b )  98 . Since the touch voltage source  92  is coupled to the bypass capacitor  98  via the op-amp  94  and the resistor  96 , the bypass capacitor  98  may remain charged to a touch voltage (VCOM_T) via the touch voltage source  92 . 
     In one embodiment, when the display panel  32  switches from a display period to a touch period, the switch  84  may open and a switch  100  coupled between the bypass capacitor  98  and the display panel  32  may close. As such, the touch voltage (VCOM_T) may be provided to the display panel  32  via the bypass capacitor  98 , the switch  100 , and a resistor  102 . In certain embodiments, the resistor  96  and the bypass capacitor  98  may be sized such that the current output via the op-amp  94  may be limited to some value (e.g., 50 mA) to meet the current specifications of the display panel  32 . Additionally, the resistor  96  and the bypass capacitor  98  may be sized such that a settling time (t settle ) or a time in which the display panel  32  may receive the touch voltage (VCOM_T) and settle to within a certain range (e.g., 50 mV) of the touch voltage (VCOM_T) value may be within some amount of time (e.g., 5 μs). 
     In order to limit the output current (I out ) and settling time (t settle ) to certain values, the sizes of the resistor  96  and the bypass capacitor  98  within the circuit  80  may become relatively large with respect to the electronic device  10  where space is a limited commodity. Moreover, it may prove to be challenging to identify a certain combination of a capacitance of the bypass capacitor  98  and the resistance of the resistor  96 . That is, as the capacitance of the bypass capacitor  98  decreases, the resulting output current (I out ) increases and the settling time (t settle ) decreases. In the same manner, as the resistance of the resistor  96  decreases, the resulting output current (I out ) increases and the settling time (t settle ) decreases. As such, there is a direct contention between the output current (I out ) and the settling time (t settle ) based on the sizes of the resistor  96  and the bypass capacitor  98 . 
     With this in mind,  FIG. 7  illustrates a circuit  110  that may be employed within the display driver IC  30  and used to provide the display voltage (VCOM_D) and the touch voltage (VCOM_T) while limiting the output current (I out ) and settling time (t settle ) and minimizing the sizes of the bypass capacitor  98  and the resistor  96 . Referring now to  FIG. 7 , the circuit  110  may include similar components as described above with reference to the circuit  80  of  FIG. 6 . For instance, the circuit  110  may include the display voltage source  82 , the switch  84  and the resistor  86  coupled in series with each other to provide the display voltage (VDCOM_D) to the display panel  32 . 
     Like the circuit  80 , the circuit  110  may also include the touch voltage source  92 , the op-amp  94 , the resistor  96  and the bypass capacitor  98 . However, unlike the circuit  80 , the circuit  110  may include a switch  112  coupled between the resistor  96  and the bypass capacitor  98 . In addition to the switch  112 , the circuit  110  may include a resistor  114  and a switch  116  coupled between the display panel  32  and the output of the op-amp  94 . In this way, the display panel  32  may be charged to the touch voltage (VCOM_T) via two distinct charging paths  118  and  120 . That is, if the switch  100  is closed while the switch  116  is open, the display panel  32  may receive the touch voltage (VCOM_T) via the bypass capacitor  98  and charging path  118 . However, if the switch  100  is open and the switch  116  is closed, the display panel  32  may receive the touch voltage (VCOM_T) directly from the output of the op-amp  94  via charging path  120 . 
     In one embodiment, the display driver IC  30  may include logic or a processor that may control the operation of each of the switches depicted in the circuit  110 . Keeping this in mind, the display driver IC  30  may close the switches  84  and  112  while keeping the switches  100  and  116  open during the display period. As such, the display panel  32  may receive the display voltage (VCOM_D) similar as performed by the circuit  80 . 
     When transitioning from the display period to the touch period, the display driver IC  30  may close the switch  100  and simultaneously open the switch  84  and the switch  96 . At this time, the display panel  32  may begin charging to the touch voltage (VCOM_T) via the stored energy of the bypass capacitor  98 . After a certain amount of time passes (e.g., 1 μs), the display panel  32  may be within a certain range (e.g., 50 mV) of the touch voltage (VCOM_T). At this time, the display driver IC  30  may open the switch  100  and close the  116  to enable the display panel  32  to completely charge to the touch voltage (VCOM_T). Since the voltage at the display panel  32  is within a certain range of the touch voltage (VCOM_T) when the switch  116  closes, the voltage difference between the output of the op-amp and the voltage of the display panel is smaller as compared to before the switch  100  was closed and the display panel was charged at the display voltage (VCOM_D). As a result, the output current (I out2 ) through the resistor  114  may be significantly lower as compared to if the switch  116  was closed when the display panel was charged to the display voltage (VCOM_D) instead of the switch  100 . 
     For example, assuming that the display panel  32  charges to −2.5 V during the display period and +2.5 V during the touch period, if the switch  116  is closed instead of the switch  100  and the resistance of the of the resistor  114  is 10Ω, the output current (Iout2) across the charging path  120  would be as follows:
 
Δ V/R =(−2.5V−2.5V)/10Ω=−5V/10Ω=500 mA  (1)
 
     However, if the switch  100  closes before the switch  116  as described above, and the voltage of the display panel  32  settles to within 50 mV of the touch voltage (2.5V) before the switch  100  opens again, when the switch  116  closes, the output current (Iout2) across the charging path  120 , as calculated above, would be as follows:
 
Δ V/R =(2.45V−2.5V)/10Ω=−0.05V/10Ω=5 mA  (2)
 
     As shown in Equation 2, the output current (I out2 ) is significantly lower by using the bypass capacitor  98  to initially charge the display panel  32 . As a result, smaller capacitor and resistor values may be used in the circuit  110  as compared to the circuit  80  to maintain a certain output current and settling time. 
     Moreover, since the display panel  32  is initially charged via the bypass capacitor  98  when the bypass capacitor  98  is not connected to the op-amp  94 , the output current to the display panel  32  is limited by the size of the capacitor  98  and the time in which the capacitor  98  is coupled to the display panel  32 . Furthermore, since the resistor  96  is not coupled to the display panel  32  at any time, the output current (I out ) from the op-amp  94  is limited to charge the bypass capacitor  98 . As such, the likelihood of a relatively high output current (I out ) conducting across the resistor  96  due to the large voltage difference between the display voltage (e.g., −2.5V) and the touch voltage (e.g., 2.5V) output via the op-amp  94  is eliminated because the resistor  96  will not be electrically coupled to the display panel  32 , as per the operation of the circuit  110 . As a result, the size of the resistor  96  may also be minimized. 
     With the foregoing in mind,  FIG. 8  illustrates a timing and voltage chart  130  that indicates how the switches of the circuit  110  may operate and how the voltages of the bypass capacitor  98  and the display panel  32  may react. Referring now to  FIG. 8 ,  IFP  (interframe pause) signal  132  may correspond to a signal used to control the operation of the switch  84  and the switch  112 . That is, when the  IFP  signal is high, the switches  84  and  112  may be closed, and when the  IFP  signal is low, the switches  84  and  112  may be open. The  IFP  signal  132  may mirror the IFP signal  134 , which may correspond to a synchronization signal that may be used to indicate when the display panel  32  may be switching between display periods and touch periods. IFP signal  136  may correspond to a signal used to control the operation of the switch  100  and IFP signal  138  may correspond to a signal used to control the operation of the switch  116 . 
     As shown in  FIG. 8 , before time T 1 , the  IFP  signal  132  may be high and the switches  84  and  112  may be closed. As such, the display panel  32  may be charged to the display voltage (VCOM_D) (voltage signal  142 ) via the display voltage source  82 . In the same manner, the bypass capacitor  98  may be charging to the touch voltage (VCOM_T) (voltage signal  144 ) via the op-amp  94 . 
     At time T 1 , the  IFP  signal  132  may go low, thereby causing the switches  84  and  112  to open. As such, the display voltage source  82  and the resistor  96  may be effectively removed from the circuit  110 . Also at time T 1 , the IFP signal  136  may go high causing the switch  100  to close. Here, the display panel  32  may begin discharging the display voltage (VCOM_D) and charging to the touch voltage (VCOM_T) using the charge of the bypass capacitor  98 . As such, at time T 1 , the voltage signal  142  of the display panel  32  may increase rapidly due to the charged bypass capacitor  98  being coupled to the display panel  32 . At the same time, the voltage signal  144  of the bypass capacitor  98  may decrease rapidly as it is being discharged to charge the display panel  32 . 
     In one embodiment, the IFP signal  136  may remain high for a certain amount of time (e.g., 1 μs) to enable the display panel to charge to within a range of the touch voltage (VCOM_T), as described above. Alternatively, care may be taken to ensure that the IFP signal  136  may remains high until the bypass capacitor  98  has fully discharged or just before it has fully discharged to ensure that the voltage of the display panel  32  continues to move toward the touch voltage (VCOM_T). 
     At time T 2 , the IFP signal  136  may return to low while the IFP signal  138  moves from low to high. As a result, the switch  100  may open at the same time that the switch  116  closes. When the switch  100  opens, the bypass capacitor  98  is disconnected from the display panel  32 . At the same time, when the switch  116  closes, the output of the op-amp  94  and the resistor  114  is coupled to the display panel  32 . As a result, the voltage signal  142  of the display panel  32  continues to increase until it reaches the touch voltage (VCOM_T). In one embodiment, the switch  116  may be closed for a certain amount of time (e.g., 4 μs) until the voltage at the display panel  32  settles at the touch voltage (VCOM_T) at time T 3 . As such, the settling time (t settle ) may correspond to the time between time T 1  and time T 3 . 
     The timing signals described in  FIG. 8  may continuously repeat to enable the electronic device  10  to simultaneously display image data and detect touch inputs. As electronic devices operate using higher refresh rates and shorter times between display periods and touch periods, it may be useful to limit the settling time (t settle ) such that the display panel  32  may display image data more clearly and detect touch inputs more accurately. 
     With the foregoing in mind,  FIG. 9  illustrates a timing and voltage chart  150  that indicates how the switches of the circuit  110  may operate and how the voltages of the bypass capacitor  98  and the display panel  32  may react. For example, time synchronization signal  152  may be a periodic signal that specifies when the display panel  32  may be in a display period and a touch period. The touch period may begin when the signal  136  becomes high at T 1 , as described above with regard to  FIG. 8 . As such, the voltage signal  142  of the display panel  32  may increase from the display voltage (VCOM_D) to the touch voltage (VCOM_T) via the bypass capacitor  98  at T 1 . 
     At time T 2 , the bypass capacitor  98  may be disconnected from the display panel  32  and the touch voltage source  92  may be connected to the display panel  32 . As such, the voltage signal  142  may continue to increase to the touch voltage (VCOM_T) and remain at the touch voltage (VCOM_T) until the touch period is completed at time T 4 . 
     In one embodiment, after the voltage signal  142  has settled at time T 3 , the display panel  32  may begin to receive a voltage signal  154  as a sine wave, which may be used to detect the touch inputs. It should be noted that the voltage signal  154  is not depicted at the same scale as the voltage signal  142  associated with the display panel  32 . Instead, voltage signal  154  is provided in  FIG. 9  to illustrate how the display panel  32  may begin to receive a sine voltage signal for detecting touch inputs after the display panel  32  has been pre-charged using the circuit  110  described above or using the method described below with reference to  FIG. 10 . 
     With the foregoing in mind,  FIG. 10  illustrates a flow chart of a method  160  that may be employed by the display driver IC  30  for alternating between a display period and a touch period for the display panel  32 . In certain embodiments, the display driver IC  30  may perform the method  160  using components of the circuit  110  described above or other equivalent component or circuit arrangements. 
     Referring now to  FIG. 10 , at block  162 , the display driver IC  30  may charge the display panel  32  using the display voltage source  82  while simultaneously charging the bypass capacitor  98  using the touch voltage source  92  for a first amount of time. The first amount of time may correspond to a display period in which the display panel  32  may display image data. 
     After the first amount of time expires, at block  164 , the display driver IC  30  may stop charging the display panel  32  and the bypass capacitor  98  and begin charging the display panel  32  using the stored energy of the bypass capacitor  98 . Here, the display driver IC  30  may charge the display panel  32  using the bypass capacitor  98  for a second amount of time, such that the display panel  32  may charge to within a range of a desired voltage value. In certain embodiments, the size of the bypass capacitor  98  may be determined based on how quickly the stored energy of the bypass capacitor  98  may charge the display panel  32  to within the range of the desired voltage value. In addition, the size of the bypass capacitor  98  may be determined based on a current limit or desired current amount that the display panel  32  may be designed to receive. 
     After charging the display panel  32  via the bypass capacitor  98  for the second amount of time, the display driver IC  30  may stop charging the display panel  32  via the bypass capacitor  98  and begin charging the display panel  32  via the touch voltage source  92  for a third amount of time. During this third amount of time, the voltage of the display panel  32  may reach the desired voltage value. However, since the bypass capacitor  98  previously charged the display panel  30  to within a range of the desired voltage value, the output current (I out2 ) provided via the op-amp  94  may be significantly lower as compared to if the bypass capacitor  98  was not used to previously charge the display panel  30 . 
     After the display panel  32  is charged via the touch voltage source  92  for a third amount of time, the display driver  30  may repeat the method  160 . By continuously repeating the method  160 , the electronic device  10  that includes the display  26  may be capable of displaying image data using a faster refresh rate. Moreover, by providing synchronization signals to the display panel  32  more frequently, the display driver IC  30  may better detect touch inputs that may be received via the display panel  32 . 
     In certain embodiments, it may be desirable to pre-charge the bypass capacitor  98  and the display panel  32  more quickly, as compared to the manner in which the circuit  110  may pre-charge the bypass capacitor  98  and the display panel  32 . With this in mind,  FIG. 11  illustrates a circuit  180  that may pre-charge the bypass capacitor  98  and the display panel  32  more quickly than the circuit  110  using a fast mode of operation. 
     Generally, the circuit  180  operates under the same principles of the embodiments described above. That is, the bypass capacitor  98  may be charged while the display panel  32  is charged to the display voltage (VCOM_D) via the display voltage source  82  and the switch  84 , and the display panel  32  may initially be charged to the touch voltage (VCOM_T) via the bypass capacitor  98  and then via the touch voltage source  92 . However, in lieu of some of the circuit components included in the circuit  110 , the circuit  180  may include operational amplifier  182  (op-amp  182 ), which may control how the display panel  32  is charged via the charging path  118  or the charging path  120 . Components of the op-amp  182  will be described in more detail with reference to  FIG. 12 . 
     In addition to the op-amp  182 , the circuit  180  may include a comparator component  184 . The comparator component  184  may receive inputs that correspond to a voltage of the display panel  32  and a voltage of the bypass capacitor  98 . In one embodiment, the comparator component  184  may determine a difference between the voltage of the display panel  32  and the bypass capacitor  98  after the display voltage source  82  is disconnected from the display panel  32 . If the difference between the two voltages is greater than some threshold, the op-amp  182  may use internal circuit components (e.g., switches) to charge the bypass capacitor  98  or the display panel  32  using a fast mode of operation. 
     With the foregoing in mind,  FIG. 12  illustrates a circuit diagram  192  of components within the op-amp  182  of the circuit  180 . As shown in  FIG. 12 , the op-amp  182  may include additional op-amps  192  and  194 , MOSFETs  196 ,  198 ,  200 , and  202 . The op-amps  192  and  194  may provide gate voltages to the gates of the MOSFETs  196 ,  198 ,  200 , and  202 . In one embodiment, the op-amps  192  and  194  may control the operation of the MOSFETs  196 ,  198 ,  200 , and  202  based on the output of the comparator component  184 . For example, when the difference between the voltage of the bypass capacitor  98  and the voltage of the display panel  32  is below the threshold, and the display panel  32  is in display mode, the op-amps  192  and  194  may provide a gate voltage to the MOSFET  196  while not providing a gate voltage to the MOSFET  198 , respectively, thereby charging the bypass capacitor  98  via the touch source voltage  92  and the MOSFET  196 . 
     With this in mind, when the difference between the voltage of the bypass capacitor  98  and the voltage of the display panel  32  is below the threshold, and the display panel  32  is in display mode, the op-amps  192  and  194  may provide a gate voltage to the MOSFET  196  while not providing a gate voltage to the MOSFET  198 , respectively, and closing a switch  204 , thereby providing a gate voltage to the MOSFET  200 . The MOSFET  200  may include a number (e.g., 16) of switches in parallel coupled between the touch source voltage  92  and the bypass capacitor  98 . As such, the MOSFET  200  may charge the bypass capacitor  98  a number (e.g., 16) of times faster per unit of time, as compared to a single MOSFET. 
     In the same manner, when the difference is above the threshold and the display panel  32  is operating in a touch mode, the op-amps  192  and  194  may provide not provide a gate voltage to the MOSFET  196  and provide a gate voltage to the MOSFET  198 , respectively, and open the switch  204  and close a switch  206 , thereby providing a gate voltage to the MOSFET  202 . As a result, the bypass capacitor  98  may be coupled to the display panel  32  via the charging path  118 . The MOSFET  202  may be similar to the MOSFET  200  in that the MOSFET  202  may include a number (e.g., 16) of switches in parallel coupled between the bypass capacitor  98  and the display panel  32 . As such, the MOSFET  202  may charge the display panel  32  a number (e.g., 16) of times faster per unit of time, as compared to a single MOSFET. 
     After the bypass capacitor  98  has been discharged or after a certain amount of time passes, the switch  206  may open and the op-amps  192  and  194  may provide gate voltages to the MOSFETs  196  and  198 , thereby charging the display panel  32  via the charging path  120 . In one embodiment, the switch  206  may open after the display panel  32  has been charged to within a certain range (e.g., 50 mV) of a desired voltage level. 
     By using the circuit  180  and the circuit components of the circuit  190  described above, the bypass capacitor  98  and the display panel  32  may be charged more quickly to ensure that the display panel  32  is pre-charged quickly. As a result, faster refresh rates for displaying image data and detecting touch inputs may be capable by the display panel  32 . It should be noted that although the circuit  190  has been described as including MOSFETs, switches, and op-amps, other circuit components may be used in place of these components to perform similar operations. 
     In another embodiment, a circuit may pre-charge the display panel  32  using a fast mode similar to that described above with reference to  FIG. 12 , while providing low noise and low power consumption characteristics during the touch period relative to the circuit  180  described above. With this in mind,  FIG. 13  illustrates a circuit diagram  240  of components of a buffer circuit  242 . As shown in  FIG. 13 , the buffer circuit  242  may include an op-amp  244  in addition to the MOSFETs  198  and  202  and the switches  204  and  206 , as described above. The buffer circuit  242  may also include MOSFETs  246  and  248 , which may include inverted inputs at their respective gates. 
     The circuit  240  may also include a high voltage source  250  that outputs a high voltage value (AVDDH). The high voltage source  250  may be coupled to the source sides of the MOSFETs  246  and  248 . The voltage value (AVDDH) provided by the high voltage source  250  may be a positive voltage supply greater than the voltage (VCOM_T) provided by the touch voltage source  92 . The source sides of the MOSFETs  198  and  202  may be coupled to ground and the charging path  120  may be coupled to an inverted input of the op-amp  244 . 
     Additionally, the circuit  240  may also include a 4-to-1 multiplexer (MUX)  252 . The MUX  252  may receive inputs from the display voltage source  82  and from an output of the buffer circuit  242 . The MUX  252  may also receive sense and drive inputs as part of the four input of the MUX  252 . The sense and drive inputs may be signals supplied by a touch subsystem that enables the display panel  32  to detect the touch inputs. 
     The MUX  252  may also receive a control input (VCOM_CTRL). The control input may cause the MUX  252  to switch between providing the output of the buffer circuit  242  and the sense and drive signals after the display panel  32  has been pre-charged to the touch voltage (VCOM_T).  FIG. 14  illustrates a timing and voltage chart for the switches and MUX related to the operation of the circuit  240  of  FIG. 13 . 
     Referring now to the timing and voltage chart  260  of  FIG. 14 , a time synchronization signal  262  may indicate when the display panel  32  is operating in a touch period and a display period. A fast settle signal  264  may be used to operate the switches  204  and  206  of the buffer circuit  242 . As such, when the fast settle signal  264  is high, the coupled to the high voltage source  250  or ground depending on the gate signals provided to the MOSFET  248  and  202 . 
     A first voltage signal (VCOM 0 )  266  and a second voltage signal  268  (VCOM 1 ) may correspond to voltage signals provided to the display panel  32  via the MUX  252  during the pre-charge phase and after the pre-charge phase, respectively. In one embodiment, the control signal provided to the MUX  252  may control which of the first voltage signal  266  and the second voltage signal  268  is provided to the display panel  32 . By charging the display panel  32  using the circuit  240  of  FIG. 13 , the display panel  32  may charge more quickly relative to the circuit  110  while providing lower noise and power consumption characteristics during the touch period of the display panel  32 . 
     With the foregoing in mind, by charging the display panel  32  more quickly, the time available to the display panel  32  for detecting touch inputs becomes greater, which effectively enables longer touch integration and thus lower touch signal-to-noise ratios and lower noise during the touch phase when maintaining a signal-to-noise ratio above a certain threshold. Referring to the timing and voltage chart  260 , upon rising edge of signals  262  and  1264 , the display panel  32  is connected to the output of the bypass capacitor  98 , while the switches  204  and  206  are closed. As such, MOSFETs  246  and  248 , and similarly MOSFETS  198  and  202 , are connected in parallel, thereby lowering an effective output impedance of the buffer circuit  242  by enabling fast charging of the display panel  32  at the expense of higher noise as the bandwidth of the buffer circuit  242  is increased while the power consumption of the buffer circuit  242  also increases. 
     The falling edge of the fast settle signal  264  concludes the pre-charge phase causing MOFET  248  and the switch  206  to be disconnected from the output stage of the buffer circuit  242  in preparation of entering the touch period. At this time, the impedance at the output of the buffer circuit  242  is increased, thereby causing a decrease of the bandwidth of the buffer circuit  242 . As a result, the output noise of the buffer circuit  242  may decrease while also reducing an amount of current consumption by the buffer circuit  242 . 
     During the pre-charge phase, the MUX  252  may output the voltage signal  266  based on the control signal. That is, the MUX  252  may output the voltage (VCOM_T) provided by the bypass capacitor  98  to the display panel  32 . After, the pre-charge period or after the display panel  32  has charged to the touch voltage (VCOM_T), the control signal may specify to the MUX  252  to provide the voltage signal  268  at time T 3 . As such, the voltage signal  268  may correspond to a touch drive signal that enables the display panel  32  to receive touch inputs. 
     Referring again to  FIG. 14 , parameter VDELTA_TD between times T 2  and T 3  specifies a voltage difference between the touch voltage (VCOM_T) and a touch common mode voltage. Nominally, those two voltages may be the same or substantially similar but may differ due to tolerances in the display  32 . In any case, with respect to the voltage signal  268 , a touch controller of the display  32  may take over a common electrode of the display panel  32  by connecting a drive signal (e.g., voltage signal  268 ) to the respective VCOM electrode of the display panel  32  after the pre-charge phase or when the display panel  32  settles from the touch voltage (VCOM_T) to the touch common mode voltage. At the same time, the voltage signal  266  may keep the touch voltage (VCOM_T) connected to the VCOM electrode of the display panel  32  via the charging path  120  throughout the touch period. 
     It should be noted that the buffer circuit  242  is used to pre-charge the display panel  32  from a display voltage (VCOM_D) to a touch voltage (VCOM_T). Discharging the display panel  32  from the touch voltage (VCOM_T) to the display voltage (VCOM_D) may be handled by a similar but separate buffer circuit having a similar configuration but different voltage levels. That is, a negative supply may be used in place of the high voltage source  250 , such that the negative supply may be below the display voltage (VCOM_D) level (e.g., −2.5V). This buffer circuit would thus connect the display voltage (VCOM_D) to the 4:1 MUX mentioned above after the touch phase is complete upon falling edge of the signal  262  at time T 4   
     In certain embodiments, a plurality of MUXs  252  may be present in the display  32  such that there may be one MUX  252  per touch sensor. As a result, the display panel  32  may receive less noise signals during the touch phase, such that noise from touch sensors connected to the touch voltage source  92  may not be misinterpreted as touch inputs. By employing the circuits described above, the display panel  32  effectively enables longer touch integration and thus lower touch signal-to-noise ratios and lower noise during the touch phase when maintaining a signal-to-noise ratio above a certain threshold 
     Although the above disclosure has been described with regard to enabling the display panel  32  to switch from the display period to the touch period, it should be noted that the systems and methods described herein may also be used in the same manner to assist the display panel  32  to pre-charge to the display voltage (VCOM_D) at the end of the touch period. In this case, the circuit components of  FIGS. 7, 11, 12, and 13  may operate in a mirror arrangement. That is, the display voltage source  82  and the touch voltage source  92  may be switched with each other, such that the bypass capacitor  98  may be used to initially charge the display panel  32  to the display voltage (VCOM_D). As such, the display panel  32  may efficiently switch between display mode and touch mode to display image data and receive touch inputs more effectively. 
     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: 20150930
Publication Date: 20190108
Grant Date: 20190108
Priority Date: 20150930
Inventors: SYED, TAIF A.
BRAHMA, KINGSUK
KRAH, CHRISTOPH H.
Assignee: APPLE INC
CPC Classifications: [{"code": "G06F3/0412", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F2203/04101", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F3/044", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F3/04184", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/044", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F2203/04101", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F3/0412", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/044", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F3/0412", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F2203/04101", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 58407157