PATENT DOCUMENT

Publication Number: US-10277119-B2
Application Number: US-201715798193-A
Country: US
Kind Code: B2

Title: Charge pump having AC and DC outputs for touch panel bootstrapping and substrate biasing

Abstract:
A charge pump that can be configured to operate in a first mode and a second mode is disclosed. The charge pump can comprise a charging capacitor coupled to a first node and configured to transfer a first DC voltage to the first node. The charge pump can also comprise a first output node and a second output node coupled to the first node. During the first mode, the first output node can be configured to output a second DC voltage based on the first DC voltage, and the second output node can be configured to output a third DC voltage based on the first DC voltage. During the second mode, the first output node can be configured to output the second DC voltage, and the second output node can be configured to output an AC voltage, the AC voltage being offset by the third DC voltage.

Claims:
The invention claimed is: 
     
       1. Charge pump circuitry configured to operate in a first mode and a second mode, the charge pump circuitry comprising:
 a first switch formed in a first well in a substrate, wherein the first switch is coupled to a first output node of the charge pump circuitry; and 
 a second switch formed in a second well in the substrate, wherein the second switch is coupled to a second output node of the charge pump circuitry, and the first well is disposed within the second well, 
 wherein:
 the first output node is configured to output a first voltage to a touch-sensitive device, 
 the second output node is configured to output a second voltage to the touch-sensitive device, different than the first voltage, 
 during the first mode, the first output node is configured to output a first DC voltage, and the second output node is configured to output a second DC voltage, and 
 during the second mode, the first output node is configured to output a first AC voltage, and the second output node is configured to output a second AC voltage. 
 
 
     
     
       2. The charge pump circuitry of  claim 1 , wherein the touch-sensitive device comprises a touch screen, and the first output node and the second output node are configured to be coupled to respective gate lines of display pixels included in the touch screen. 
     
     
       3. The charge pump circuitry of  claim 1 , wherein the first voltage is a low voltage, and the second voltage is a high voltage. 
     
     
       4. The charge pump circuitry of  claim 1 , wherein the first switch and the first output node are part of a first charge pump, and the second switch and the second output node are part of a second charge pump, different than the first charge pump. 
     
     
       5. The charge pump circuitry of  claim 1 , wherein the first well is biased by the first output node, and the second well is biased by the second output node. 
     
     
       6. The charge pump circuitry of  claim 1 , wherein the first well is a first type of well, and the second well is a second type of well, different than the first type of well. 
     
     
       7. The charge pump circuitry of  claim 6 , wherein the first type of well is a p-type well, and the second type of well is an n-type well. 
     
     
       8. The charge pump circuitry of  claim 1 , wherein the substrate is biased by a DC output node of the charge pump circuitry. 
     
     
       9. A method of fabricating charge pump circuitry, comprising:
 forming a first switch in a first well in a substrate, wherein the first switch is coupled to a first output node of the charge pump circuitry; and 
 forming a second switch in a second well in the substrate, wherein the second switch is coupled to a second output node of the charge pump circuitry, and the first well is disposed within the second well, 
 wherein:
 the first output node is configured to output a first voltage to a touch-sensitive device, 
 the second output node is configured to output a second voltage to the touch-sensitive device, different than the first voltage, 
 during a first mode, the first output node is configured to output a first DC voltage, and the second output node is configured to output a second DC voltage, and 
 during a second mode, the first output node is configured to output a first AC voltage, and the second output node is configured to output a second AC voltage. 
 
 
     
     
       10. A method of operating charge pump circuitry configured to operate in a first mode and a second mode, the method comprising:
 outputting, at a first output node of the charge pump circuitry, a first voltage to a touch-sensitive device, wherein the charge pump circuitry comprises a first switch formed in a first well in a substrate, and the first switch is coupled to the first output node of the charge pump circuitry; 
 outputting, at a second output node of the charge pump circuitry, a second voltage to the touch-sensitive device, different than the first voltage, wherein the charge pump circuitry comprises a second switch formed in a second well in the substrate, the second switch is coupled to the second output node of the charge pump circuitry, and the first well is disposed within the second well; 
 during the first mode:
 outputting, at the first output node, a first DC voltage; and 
 outputting, at the second output node, a second DC voltage; and 
 
 during the second mode:
 outputting, at the first output node, a first AC voltage; and 
 outputting, at the second output node, a second AC voltage. 
 
 
     
     
       11. The method of  claim 10 , wherein the touch-sensitive device comprises a touch screen, the method further comprises coupling the first output node and the second output node to respective gate lines of display pixels included in the touch screen. 
     
     
       12. The method of  claim 10 , wherein the first voltage is a low voltage, and the second voltage is a high voltage. 
     
     
       13. The method of  claim 10 , wherein the first switch and the first output node are part of a first charge pump, and the second switch and the second output node are part of a second charge pump, different than the first charge pump. 
     
     
       14. The method of  claim 10 , further comprising:
 biasing the first well with the first output node, and 
 biasing the second well with the second output node. 
 
     
     
       15. The method of  claim 10 , wherein the first well is a first type of well, and the second well is a second type of well, different than the first type of well. 
     
     
       16. The method of  claim 15 , wherein the first type of well is a p-type well, and the second type of well is an n-type well. 
     
     
       17. The method of  claim 10 , further comprising biasing the substrate with a DC output node of the charge pump circuitry.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation/divisional of U.S. patent application Ser. No. 15/043,405, filed Feb. 12, 2016, now U.S. Pat. No. 9,806,608 B2, which claims priority to U.S. Provisional Application No. 62/116,178, filed Feb. 13, 2015, which is hereby incorporated by reference in its entirety for all purposes. 
    
    
     FIELD OF THE DISCLOSURE 
     This relates generally to touch sensor panels, and more particularly, to a charge pump for a touch sensor panel or touch screen that has AC and DC outputs that can be used for bootstrapping the touch sensor panel or touch screen, and biasing a driver IC substrate. 
     BACKGROUND OF THE DISCLOSURE 
     Many types of input devices are presently available for performing operations in a computing system, such as buttons or keys, mice, trackballs, joysticks, touch sensor panels, touch screens and the like. Touch screens, in particular, are becoming increasingly popular because of their ease and versatility of operation as well as their declining price. Touch screens can include a touch sensor panel, which can be a clear panel with a touch-sensitive surface, and a display device such as a liquid crystal display (LCD) that can be positioned partially or fully behind the panel so that the touch-sensitive surface can cover at least a portion of the viewable area of the display device. Touch screens can allow a user to perform various functions by touching the touch sensor panel using a finger, stylus or other object at a location often dictated by a user interface (UI) being displayed by the display device. In general, touch screens can recognize a touch and the position of the touch on the touch sensor panel, and the computing system can then interpret the touch in accordance with the display appearing at the time of the touch, and thereafter can perform one or more actions based on the touch. In the case of some touch sensing systems, a physical touch on the display is not needed to detect a touch. For example, in some capacitive-type touch sensing systems, fringing electrical fields used to detect touch can extend beyond the surface of the display, and objects approaching near the surface may be detected near the surface without actually touching the surface. 
     Capacitive touch sensor panels can be formed by a matrix of substantially transparent or non-transparent conductive plates made of materials such as Indium Tin Oxide (ITO). It is due in part to their substantial transparency that capacitive touch sensor panels can be overlaid on a display to form a touch screen, as described above. Some touch screens can be formed by at least partially integrating touch sensing circuitry into a display pixel stackup (i.e., the stacked material layers forming the display pixels). 
     SUMMARY OF THE DISCLOSURE 
     Some capacitive touch sensor panels can be formed by a matrix of substantially transparent or non-transparent conductive plates made of materials such as Indium Tin Oxide (ITO), and some touch screens can be formed by at least partially integrating touch sensing circuitry into a display pixel stackup (i.e., the stacked material layers forming the display pixels). In some examples, one or more components (e.g., a gate line) of the display pixel stackups can be biased by a charge pump on a driver integrated circuit (IC). The charge pump can also provide a bias voltage to a driver IC substrate (i.e., a substrate on which the driver IC can be formed). In some examples, the one or more components of the display pixel stackups may require AC biasing, whereas the driver IC substrate may require DC biasing—in such examples, AC biasing of the driver IC substrate may cause various components on the driver IC to malfunction. The examples of the disclosure are directed to various charge pump configurations that can provide AC or DC biasing of the one or more components of the display pixel stackups, depending on an operational mode of the touch screen, while concurrently providing DC biasing of the driver IC substrate. In some examples, this can be accomplished by providing a charge pump that has separate AC and DC output nodes. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A-1C  illustrate an example mobile telephone, an example media player, and an example portable computing device that each include an exemplary touch screen according to examples of the disclosure. 
         FIG. 2  is a block diagram of an example computing system that illustrates one implementation of an example self-capacitance touch screen according to examples of the disclosure. 
         FIG. 3  illustrates an exemplary touch sensor circuit corresponding to a self-capacitance touch node electrode and sensing circuit according to examples of the disclosure. 
         FIG. 4  illustrates an example configuration in which common electrodes can form portions of the touch sensing circuitry of a touch sensing system according to examples of the disclosure. 
         FIG. 5  illustrates a partial circuit diagram of some of the touch sensing circuitry within a display pixel of an example touch screen according to examples of the disclosure. 
         FIG. 6  illustrates an example electrical circuit corresponding to a self-capacitance touch node electrode, a sensing circuit and a driver integrated circuit (IC) according to examples of the disclosure. 
         FIG. 7  illustrates a cross section of a driver IC substrate, and a biasing scheme via which a charge pump can bias the driver IC substrate according to examples of the disclosure. 
         FIGS. 8A-8B  illustrate exemplary operation and structure of a charge pump with a single output node according to examples of the disclosure. 
         FIGS. 9A-9B  illustrate exemplary operation and structure of a charge pump with two output nodes according to examples of the disclosure. 
         FIG. 9C  illustrates exemplary operation and structure of another charge pump with two output nodes according to examples of the disclosure. 
         FIG. 10  illustrates a switch, which can correspond to a switch in the charge pump of  FIG. 9B , formed in a P-type well of a driver IC substrate according to examples of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description of examples, reference is made to the accompanying drawings that form a part hereof, and in which it is shown by way of illustration specific examples that can be practiced. It is to be understood that other examples can be used and structural changes can be made without departing from the scope of the disclosed examples. 
     Some capacitive touch sensor panels can be formed by a matrix of substantially transparent or non-transparent conductive plates made of materials such as Indium Tin Oxide (ITO), and some touch screens can be formed by at least partially integrating touch sensing circuitry into a display pixel stackup (i.e., the stacked material layers forming the display pixels). In some examples, one or more components (e.g., a gate line) of the display pixel stackups can be biased by a charge pump on a driver integrated circuit (IC). The charge pump can also provide a bias voltage to a driver IC substrate (i.e., a substrate on which the driver IC can be formed). In some examples, the one or more components of the display pixel stackups may require AC biasing, whereas the driver IC substrate may require DC biasing—in such examples, AC biasing of the driver IC substrate may cause various components on the driver IC to malfunction. The examples of the disclosure are directed to various charge pump configurations that can provide AC or DC biasing of the one or more components of the display pixel stackups, depending on an operational mode of the touch screen, while concurrently providing DC biasing of the driver IC substrate. In some examples, this can be accomplished by providing a charge pump that has separate AC and DC output nodes. 
       FIGS. 1A-1C  show example systems in which a touch screen according to examples of the disclosure may be implemented.  FIG. 1A  illustrates an example mobile telephone  136  that includes a touch screen  124 .  FIG. 1B  illustrates an example digital media player  140  that includes a touch screen  126 .  FIG. 1C  illustrates an example portable computing device  144  that includes a touch screen  128 . Touch screens  124 ,  126 , and  128  can be based on self-capacitance. A self-capacitance based touch system can include a matrix of small, individual plates of conductive material that can be referred to as touch node electrodes (as described below with reference to touch screen  220  in  FIG. 2 ). For example, a touch screen can include a plurality of individual touch node electrodes, each touch node electrode identifying or representing a unique location on the touch screen at which touch or proximity (i.e., a touch or proximity event) is to be sensed, and each touch node electrode being electrically isolated from the other touch node electrodes in the touch screen/panel. Such a touch screen can be referred to as a pixelated self-capacitance touch screen, though it is understood that in some examples, the touch node electrodes on the touch screen can be used to perform scans other than self-capacitance scans on the touch screen (e.g., mutual capacitance scans). During operation, a touch node electrode can be stimulated with an AC waveform, and the self-capacitance to ground of the touch node electrode can be measured. As an object approaches the touch node electrode, the self-capacitance to ground of the touch node electrode can change. This change in the self-capacitance of the touch node electrode can be detected and measured by the touch sensing system to determine the positions of multiple objects when they touch, or come in proximity to, the touch screen. In some examples, the electrodes of a self-capacitance based touch system can be formed from rows and columns of conductive material, and changes in the self-capacitance to ground of the rows and columns can be detected, similar to above. In some examples, a touch screen can be multi-touch, single touch, projection scan, full-imaging multi-touch, capacitive touch, etc. 
       FIG. 2  is a block diagram of an example computing system  200  that illustrates one implementation of an example self-capacitance touch screen  220  according to examples of the disclosure. Computing system  200  can be included in, for example, mobile telephone  136 , digital media player  140 , portable computing device  144 , or any mobile or non-mobile computing device that includes a touch screen, including a wearable device. Computing system  200  can include a touch sensing system including one or more touch processors  202 , peripherals  204 , a touch controller  206 , and touch sensing circuitry (described in more detail below). Peripherals  204  can include, but are not limited to, random access memory (RAM) or other types of memory or storage, watchdog timers and the like. Touch controller  206  can include, but is not limited to, one or more sense channels  208  and channel scan logic  210 . Channel scan logic  210  can access RAM  212 , autonomously read data from sense channels  208  and provide control for the sense channels. In addition, channel scan logic  210  can control sense channels  208  to generate stimulation signals at various frequencies and phases that can be selectively applied to the touch nodes of touch screen  220 , as described in more detail below. In some examples, touch controller  206 , touch processor  202  and peripherals  204  can be integrated into a single application specific integrated circuit (ASIC), and in some examples can be integrated with touch screen  220  itself. 
     Touch screen  220  can include touch sensing circuitry that can include a capacitive sensing medium having a plurality of electrically isolated touch node electrodes  222  (e.g., a pixelated self-capacitance touch screen). Touch node electrodes  222  can be coupled to sense channels  208  in touch controller  206 , can be driven by stimulation signals from the sense channels through drive/sense interface  225 , and can be sensed by the sense channels through the drive/sense interface as well, as described above. Labeling the conductive plates used to detect touch (i.e., touch node electrodes  222 ) as “touch node” electrodes can be particularly useful when touch screen  220  is viewed as capturing an “image” of touch (e.g., a “touch image”). In other words, after touch controller  206  has determined an amount of touch detected at each touch node electrode  222  in touch screen  220 , the pattern of touch node electrodes in the touch screen at which a touch occurred can be thought of as a touch image (e.g., a pattern of fingers touching the touch screen). 
     Computing system  200  can also include a host processor  228  for receiving outputs from touch processor  202  and performing actions based on the outputs. For example, host processor  228  can be connected to program storage  232  and a display controller, such as an LCD driver  234 . The LCD driver  234  can provide voltages on select (e.g., gate) lines to each pixel transistor and can provide data signals along data lines to these same transistors to control the pixel display image as described in more detail below. Host processor  228  can use LCD driver  234  to generate a display image on touch screen  220 , such as a display image of a user interface (UI), and can use touch processor  202  and touch controller  206  to detect a touch on or near touch screen  220 . The touch input can be used by computer programs stored in program storage  232  to perform actions that can include, but are not limited to, moving an object such as a cursor or pointer, scrolling or panning, adjusting control settings, opening a file or document, viewing a menu, making a selection, executing instructions, operating a peripheral device connected to the host device, answering a telephone call, placing a telephone call, terminating a telephone call, changing the volume or audio settings, storing information related to telephone communications such as addresses, frequently dialed numbers, received calls, missed calls, logging onto a computer or a computer network, permitting authorized individuals access to restricted areas of the computer or computer network, loading a user profile associated with a user&#39;s preferred arrangement of the computer desktop, permitting access to web content, launching a particular program, encrypting or decoding a message, and/or the like. Host processor  228  can also perform additional functions that may not be related to touch processing. 
     Note that one or more of the functions described herein, including the configuration of switches, can be performed by firmware stored in memory (e.g., one of the peripherals  204  in  FIG. 2 ) and executed by touch processor  202 , or stored in program storage  232  and executed by host processor  228 . The firmware can also be stored and/or transported within any non-transitory computer-readable storage medium for use by or in connection with an instruction execution system, apparatus, or device, such as a computer-based system, processor-containing system, or other system that can fetch the instructions from the instruction execution system, apparatus, or device and execute the instructions. In the context of this document, a “non-transitory computer-readable storage medium” can be any medium (excluding signals) that can contain or store the program for use by or in connection with the instruction execution system, apparatus, or device. The computer-readable storage medium can include, but is not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus or device, a portable computer diskette (magnetic), a random access memory (RAM) (magnetic), a read-only memory (ROM) (magnetic), an erasable programmable read-only memory (EPROM) (magnetic), a portable optical disc such a CD, CD-R, CD-RW, DVD, DVD-R, or DVD-RW, or flash memory such as compact flash cards, secured digital cards, USB memory devices, memory sticks, and the like. 
     The firmware can also be propagated within any transport medium for use by or in connection with an instruction execution system, apparatus, or device, such as a computer-based system, processor-containing system, or other system that can fetch the instructions from the instruction execution system, apparatus, or device and execute the instructions. In the context of this document, a “transport medium” can be any medium that can communicate, propagate or transport the program for use by or in connection with the instruction execution system, apparatus, or device. The transport medium can include, but is not limited to, an electronic, magnetic, optical, electromagnetic or infrared wired or wireless propagation medium. 
       FIG. 3  illustrates an exemplary touch sensor circuit  300  corresponding to a self-capacitance touch node electrode  302  and sensing circuit  314  according to examples of the disclosure. Touch node electrode  302  can correspond to touch node electrode  222 . Touch node electrode  302  can have an inherent self-capacitance to ground associated with it, and also an additional self-capacitance to ground that is formed when an object, such as finger  305 , is in proximity to or touching the electrode. The total self-capacitance to ground of touch node electrode  302  can be illustrated as capacitance  304 . Touch node electrode  302  can be coupled to sensing circuit  314 . Sensing circuit  314  can include an operational amplifier  308 , feedback resistor  312  and feedback capacitor  310 , although other configurations can be employed. For example, feedback resistor  312  can be replaced by a switched capacitor resistor in order to minimize a parasitic capacitance effect that may be caused by a variable feedback resistor. Touch node electrode  302  can be coupled to the inverting input (−) of operational amplifier  308 . An AC voltage source  306  (Vac) can be coupled to the non-inverting input (+) of operational amplifier  308 . Touch sensor circuit  300  can be configured to sense changes in the total self-capacitance  304  of the touch node electrode  302  induced by a finger or object either touching or in proximity to the touch sensor panel. Output  320  can be used by a processor to determine the presence of a proximity or touch event, or the output can be inputted into a discrete logic network to determine the presence of a proximity or touch event. 
     Referring back to  FIG. 2 , in some examples, touch screen  220  can be an integrated touch screen in which touch sensing circuit elements of the touch sensing system can be integrated into the display pixel stackups of a display. The circuit elements in touch screen  220  can include, for example, elements that can exist in LCD or other displays, such as one or more pixel transistors (e.g., thin film transistors (TFTs)), gate lines, data lines, pixel electrodes and common electrodes. In a given display pixel, a voltage between a pixel electrode and a common electrode can control a luminance of the display pixel. The voltage on the pixel electrode can be supplied by a data line through a pixel transistor, which can be controlled by a gate line. It is noted that circuit elements are not limited to whole circuit components, such as a whole capacitor, a whole transistor, etc., but can include portions of circuitry, such as only one of the two plates of a parallel plate capacitor.  FIG. 4  illustrates an example configuration in which common electrodes  402  can form portions of the touch sensing circuitry of a touch sensing system—in some examples of this disclosure, the common electrodes can form touch node electrodes used to detect a touch image on touch screen  400 , as described above. Each common electrode  402  can include a plurality of display pixels  401 , and each display pixel  401  can include a portion of a common electrode  402 , which can be a circuit element of the display system circuitry in the display pixel stackup (i.e., the stacked material layers forming the display pixels) of the display pixels of some types of LCDs or other displays—in other words, the common electrodes can operate as part of the display system to display a display image on touch screen  400 . 
     In the example shown in  FIG. 4 , each common electrode  402  can serve as a multi-function circuit element that can operate as display circuitry of the display system of touch screen  400  and can also operate as touch sensing circuitry of the touch sensing system. Specifically, each common electrode  402  can operate as a common electrode of the display circuitry of the touch screen  400  (e.g., during a display phase), as described above, and can also operate as a touch node electrode of the touch sensing circuitry of the touch screen (e.g., during a touch sensing phase). Other circuit elements of touch screen  400  can also form part of the touch sensing circuitry. More specifically, in some examples, during the touch sensing phase, a gate line can be connected to a power supply, such as a charge pump, that can apply a voltage to maintain TFTs in display pixels included in a common electrode  402  in an “off” state. Stimulation signals can be applied to the common electrode  402 . Changes in the total self-capacitance of the common electrode  402  can be sensed through one or more operational amplifiers, as previously discussed. The changes in the total self-capacitance of the common electrode  402  can depend on the proximity of an object, such as finger  305 , to the common electrode. In this way, the measured changes in total self-capacitance of the common electrode  402  can provide an indication of touch on or near the touch screen. 
     In general, each of the touch sensing circuit elements may be either a multi-function circuit element that can form part of the touch sensing circuitry and can perform one or more other functions, such as forming part of the display circuitry, or may be a single-function circuit element that can operate as touch sensing circuitry only. Similarly, each of the display circuit elements may be either a multi-function circuit element that can operate as display circuitry and perform one or more other functions, such as operating as touch sensing circuitry, or may be a single-function circuit element that can operate as display circuitry only. Therefore, in some examples, some of the circuit elements in the display pixel stackups can be multi-function circuit elements and other circuit elements may be single-function circuit elements. In other examples, all of the circuit elements of the display pixel stackups may be single-function circuit elements. 
     In addition, although examples herein may describe the display circuitry as operating during a display phase, and describe the touch sensing circuitry as operating during a touch sensing phase, it should be understood that a display phase and a touch sensing phase may be operated at the same time, e.g., partially or completely overlapping, or the display phase and touch sensing phase may operate at different times. Also, although examples herein describe certain circuit elements as being multi-function and other circuit elements as being single-function, it should be understood that the circuit elements are not limited to the particular functionality in other examples. In other words, a circuit element that is described in one example herein as a single-function circuit element may be configured as a multi-function circuit element in other examples, and vice versa. 
     The common electrodes  402  (i.e., touch node electrodes) and display pixels  401  of  FIG. 4  are shown as rectangular or square regions on touch screen  400 . However, it is understood that the common electrodes  402  and display pixels  401  are not limited to the shapes, orientations, and positions shown, but can include any suitable configurations according to examples of the disclosure. 
       FIG. 5  illustrates a partial circuit diagram  500  of some of the touch sensing circuitry within display pixel  501  of an example touch screen according to examples of the disclosure. For the sake of clarity, only one display pixel  501  structure is shown. However, it is understood that other display pixels of the touch screen can include the same or similar circuitry as described below for display pixel  501 . Thus, the following description of the operation of display pixel  501  can be considered a description of the operation of the touch screen, in general. 
     Display pixel  501  can include display TFT  507 , gate line  511 , data line  513 , pixel electrode  515 , and common electrode  517 . Common electrode  517  can correspond to any one of touch node electrodes  222  in  FIG. 2 , touch node electrode  302  in  FIG. 3  and/or common electrodes  402  in  FIG. 4 . Gate line  511  can supply one or more voltages to the gate terminal of display TFT  507  to control the operational state of the TFT (e.g., “on” or “off”), and data line  513  can supply one or more voltages for setting the voltage on pixel electrode  515 . In some examples, gate line  511  can be shared by more than one display pixel (i.e., the gate line can be connected to the gate terminal of more than one display TFT), though a single display pixel is shown for simplicity. Storage capacitance  519  can exist between common electrode  517  and pixel electrode  515 , and can store a charge—set by the voltage difference between data line  513  and common electrode  517 —for controlling a luminance of display pixel  501 . In some examples, offset capacitance  521  (or “parasitic capacitance”) can exist between the drain terminal of display TFT  507  and the gate terminal of the TFT. Offset capacitance  521  can vary based on the voltage difference between gate line  511  and pixel electrode  515 , and can include capacitances such as the gate-to-drain capacitance of TFT  507  and/or other capacitances resulting from the layout of various components of the touch screen. Operational amplifier  508  can be configured to sense changes in the total self-capacitance of common electrode  517 , as described above, to determine the presence of a proximity or touch event at the common electrode. Although display pixel  501  has been described as including a single display TFT (i.e., TFT  507 ), in some examples, the display pixel may include more than a single TFT. For example, display pixel  501  can include two TFTs connected in series, both gate terminals of which can be connected to gate line  511 . The operation of such display pixels can be substantially the same as the operation of display pixel  501  in  FIG. 5 . For ease of description, the examples of the disclosure will be described with reference to the display pixel configuration of  FIG. 5 , although it is understood that the scope of the disclosure is not so limited. 
     During a touch sensing phase of the touch screen, gate line  511  can supply a voltage to the gate of display TFT  507  for turning “off” the TFT. Operational amplifier  508  can sense changes in the total self-capacitance of common electrode  517 . As described above, this total self-capacitance can include a touch capacitance  504  due to an object, such as finger  505 , being in proximity to or touching common electrode  517 , as well as other capacitances that may be seen at the common electrode. In some examples, the total self-capacitance seen at common electrode  517  can include storage capacitance  519  in series with offset capacitance  521 . In some examples, storage capacitance  519  can be much larger than offset capacitance  521 , and can thus dominate the non-touch-related total capacitance seen at common electrode  517 . As such, the total self-capacitance seen at common electrode  517  can be approximately a combination of touch capacitance  504  and offset capacitance  521 . 
     Ignoring touch capacitance  504 , the gain of operational amplifier  508  in the configuration illustrated in  FIG. 5  can be expressed as:
 
 A =1 +C   gp   /C   fb   (1)
 
where A can represent the gain of the operational amplifier, C fb , can correspond to feedback capacitance  510 , and C gp  can correspond to offset capacitance  521 . In some examples, offset capacitance  521  can be on the order of nanofarads (˜1 nF, in some examples), and feedback capacitance  510  can be on the order of picofarads (˜10 pF, in some examples). In such cases, the gain of operational amplifier  508  due only to offset capacitance  521  can be approximately 101. In other words, an input voltage of 1V provided by AC voltage source  506  at the non-inverting input of operational amplifier  508  can result in an output voltage of 101V at the output of the operational amplifier. With such a large offset due simply to offset capacitance  521 , it can be difficult to detect changes in the output voltage of operational amplifier  508  resulting from changes in touch capacitance  504 , and thus it can be difficult to detect touch and/or proximity events on the touch screen. Additionally, the dynamic range of sensing circuit  514  can be significantly reduced due to offset capacitance  521 , and in some examples may render the sensing circuit inoperable.
 
       FIG. 6  illustrates an example electrical circuit  600  corresponding to self-capacitance touch node electrode  617 , sensing circuit  614  and driver integrated circuit (IC)  640  according to examples of the disclosure. Electrical circuit  600  can be a simplified version of circuit diagram  500  in  FIG. 5 . For example, touch node electrode  617  can correspond to common electrode  517  in  FIG. 5 , sensing circuit  614  can correspond to sensing circuit  514  in  FIG. 5 , and gate line  611  can correspond to gate line  511  in  FIG. 5 . Circuit  600  can additionally include driver IC  640 , which can be coupled to gate line  611 . Offset capacitance  621 , as before, can exist between touch node electrode  617  and gate line  611 . In some examples, driver IC  640  can include charge pump  630 , which can be formed on or in a driver IC substrate, as will be described in more detail later. During a non-touch sensing phase of the touch screen (e.g., during a display phase), charge pump  630  can output a direct current (DC) voltage via output line  631  to gate line  611  to facilitate proper touch screen operation (e.g., to turn on or off pixel TFT  507  in  FIG. 5 ), as described previously in this disclosure. During a touch sensing phase of the touch screen, in some examples, charge pump  630  can output an alternating current (AC) voltage—in some examples, offset by the same or a different DC voltage as outputted during the non-touch sensing phase of the touch screen—via output line  631  to gate line  611 . This driving of gate line  611  with an AC voltage can be referred to as “bootstrapping.” In some cases, the AC voltage outputted by output line  631  to gate line  611  can be substantially the same as an AC voltage provided by AC voltage source  606  to operational amplifier  608 . Because of the operational characteristics of operational amplifier  608 , the voltage at common electrode  617  can also be substantially the same as the voltage provided by AC voltage source  606 . Thus, the voltage and/or changes in the voltage on common electrode  617  and gate line  611  can be substantially the same, and therefore the voltage and/or changes in the voltage across offset capacitance  621  can be substantially eliminated; as such, the current flow into the offset capacitance can also be virtually eliminated. As a result, the effect of offset capacitance  621  on the total self-capacitance seen at touch node electrode  617  can be substantially reduced. In this way, changes in touch capacitance  604 , and the effect of the touch capacitance on the output voltage of operational amplifier  608 , can be more readily detected, and thus touch and/or proximity events can be more easily sensed. Thus, it can be beneficial for charge pump  630  to output the DC voltage to gate line  611  during a non-touch sensing phase of the touch screen, and output the AC voltage (in some examples, offset by a DC voltage) to the gate line  611  during a touch sensing phase of the touch screen. In some examples, charge pump  630  and AC voltage source  606  can be combined or can be located on the same driver IC  640 . 
     In some examples, charge pump  630  can, in addition to outputting DC or AC voltages to gate line  611 , bias the driver IC substrate on which it is formed via output line  632 . Such biasing can ensure that various semiconductor junctions in the substrate (e.g., P-N junctions) function properly during touch screen operation, as will be discussed below. It should be noted that charge pump  630  is illustrated as having two output lines—output lines  631  and  632 —in some examples, those two output lines can be coupled to the same output node in the charge pump; in other words, the two output lines can both output the same output voltage.  FIG. 7  illustrates cross section  700  of driver IC substrate  702 , and a biasing scheme via which charge pump  630  can bias the driver IC substrate according to examples of the disclosure. As described previously, charge pump  630  can be formed on driver IC substrate  702 . In some examples, driver IC substrate  702  can include P-type substrate (PSUB)  708 . A deep N-type well (NWELL)  706  can be formed within PSUB  708 , and a P-type well (PWELL)  704  can be formed within NWELL  706 . PSUB  708 , NWELL  706  and PWELL  704  can provide various semiconductor environments in which various components (e.g., transistors) of charge pump  630  can operate. However, these P-type and N-type wells can create a parasitic PNP bipolar junction, illustrated by parasitic bipolar junction transistor (BJT)  710 . It can be beneficial to prevent parasitic BJT  710  from unintentionally turning on, which can be accomplished by biasing PWELL  704 , NWELL  706  and PSUB  708  at appropriate voltages. For example, in the configuration illustrated in  FIG. 7 , node  714  can be coupled to PWELL  704 , node  720  can be coupled to NWELL  706  and node  718  can be coupled to PSUB  708 . Node  714  (and thus PWELL  704 ) can be coupled to DC voltage source  712 . DC voltage source  712  can be a negative rail voltage of the driver IC, and can have a voltage of −5.7V, for example. Node  720  (and thus NWELL  706 ) can be coupled to ground (i.e., 0V). Node  718  (and thus PSUB  708 ) can be coupled to line  732 , which can correspond to output line  632  from charge pump  630  in  FIG. 6 . In other words, charge pump  630  can bias PSUB  708  via node  718 . In some examples, PSUB  708  can be biased at −7V. Thus, in a steady state, all of the P-N junctions between PWELL  704 , NWELL  706  and PSUB  708  can be reverse biased, and parasitic BJT  710  can remain off. It is understood that the voltages provided above and throughout this disclosure are exemplary only, and that different voltages can be utilized in accordance with the examples of this disclosure. 
     In some examples, the voltage at output line  632  of charge pump  630  in  FIG. 6  (and thus the voltage at node  718 ) may take a non-zero amount of time to ramp from 0V (e.g., when the charge pump is inactive or off) to −7V. During this ramping time, parasitic BJT  710  can contribute to lateral latch up (i.e., the inadvertent creation of a low-impedance path between, for example, power supply nodes) in driver IC substrate  702 . To prevent latch up, Schottky diode  716 —in some examples, external to driver IC substrate  702 —can be inserted between nodes  714  and  718 , as illustrated. Schottky diode  716  can ensure that the voltage at node  718  is not greater than (i.e., more positive than) the voltage at node  714  by more than a turn-on voltage of the Schottky diode. As such, Schottky diode  716  can maintain the voltage at node  718  (and thus at PSUB  708 ) at an acceptable level until charge pump  630  ramps to its final voltage, which in some examples can be −7V. Once charge pump  630  and node  718  ramp to −7V, PWELL  704 , NWELL  706  and PSUB  708  can be biased appropriately, and the driver IC can function properly. 
     As described previously, charge pump  630  in  FIG. 6  can bias driver IC substrate  702 . Further, during certain periods of time (e.g., during a touch sensing phase of the touch screen), charge pump  630  can output an AC voltage rather than a DC voltage. This can mean that node  718  can be biased at an AC voltage during certain periods of touch screen operation. In some examples, an AC voltage at node  718  can cause Schottky diode  716  to become forward biased and to turn on, which can cause a large amount of current to flow through the Schottky diode, wasting power and possibly causing damage to the driver IC and other components of the touch screen. For example, if node  714  is biased at −5.7V, and node  718  is biased at a DC voltage of −7V with a 3V peak-to-peak AC signal, the voltage at node  718  can reach as high as −5.5V. With −5.7V at node  714  and −5.5V at node  718 , Schottky diode  716  can become forward biased, and a large amount of current can flow through the Schottky diode. This can be undesirable. It can, therefore, be beneficial to bias node  718  with a DC voltage (e.g., −7V) during all time periods of touch screen operation, even when gate line  611  is biased at an AC voltage (e.g., −7V with 3V peak-to-peak AC voltage) during the touch sensing phase of the touch screen. A charge pump with a single output node may not be able to provide such operation. 
       FIGS. 8A-8B  illustrate exemplary operation and structure of charge pump  850  with single output node  830  according to examples of the disclosure. Specifically,  FIG. 8A  illustrates exemplary operation and structure of charge pump  850  in a non-touch sensing mode of the charge pump (e.g., corresponding to the display phase of the touch screen), and  FIG. 8B  illustrates exemplary operation and structure of the charge pump in a touch sensing mode of the charge pump (e.g., corresponding to the touch sensing phase of the touch screen). As illustrated in  FIG. 8A , charge pump  830  can include charging capacitor  836 , positive voltage input  833 , first negative voltage input  834 , second negative voltage input  835 , output capacitor  837 , output line  831  and output line  832 . Output lines  831  and  832 , and output capacitor  837 , can all be coupled to output node  830 , as illustrated. Output lines  831  and  832  can correspond to output lines  631  and  632  in  FIG. 6 . During charge pump  850  operation, a positive voltage, AVDDH, can be supplied to positive voltage input  833 , and a negative voltage, AVDDN, can be supplied to negative voltage inputs  834  and  835 . In some examples, AVDDH can be +5.7V and AVDDN can be −5.7V, which can also be the voltage supplied by voltage source  712  to node  714  in  FIG. 7 . Switch  801  can be coupled between positive voltage input  833  and terminal A of charging capacitor  836 . Switch  802  can be coupled between first negative voltage input  834  and terminal B of charging capacitor  836 . Switch  803  can be coupled between second negative voltage input  835  and terminal A of charging capacitor  836 . Switch  804  can be coupled between output node  830  and terminal B of charging capacitor  836 . 
     In order to provide a voltage at output node  830 , charge pump  850  can alternate between a first stage of operation and a second stage of operation. During the first stage of operation, switches  801  and  802  can be closed, and switches  803  and  804  can be open. Terminal A of charging capacitor  836  can be charged by voltage AVDDH, while terminal B of the charging capacitor can be charged by voltage AVDDN, thus establishing a voltage across the charging capacitor of substantially the voltage difference between AVDDH and AVDDN—in some examples, this voltage difference can be +11.4V (+5.7V-(−5.7V)). During the second stage of operation, switches  801  and  802  can be opened, and switches  803  and  804  can be closed. Voltage AVDDN can be applied to terminal A of charging capacitor  836  via second negative voltage input  835 , thus transferring (or “pumping”) charge from the charging capacitor to output capacitor  837 . Output capacitor  837  can store the charge, which can create a voltage at output node  830  that can depend on the capacitance of the output capacitor. In some examples, the voltage at output node  830  can depend on a ratio of the capacitance of charging capacitor  836  to the capacitance of output capacitor  837 . Output lines  831  and  832  can output the voltage at output node  830  to gate line  611  in  FIG. 6  and to driver IC substrate  702  in  FIG. 7 , as previously described. The timing of alternating between the first and second stages of operation can be such that capacitors  836  and  837  can be appropriately charged and discharged so as to create a substantially steady DC voltage at output node  830 , which can be outputted by both output lines  831  and  832  during the non-touch sensing phase of charge pump  850 . In some examples, switches  801 ,  802 ,  803  and  804  can be controlled by one clock signal; in some examples, switches  801  and  802  can be controlled by a first clock signal, and switches  803  and  804  can be controlled by a second clock signal. The above clock signals can be provided by a touch controller (e.g., touch controller  206 ). 
       FIG. 8B  illustrates exemplary operation and structure of charge pump  850  in a touch sensing mode of the charge pump according to examples of the disclosure. During the touch sensing mode, charge pump  850  can operate substantially the same as during the non-touch sensing mode to charge or maintain the voltage at output node  830  at the proper DC voltage (e.g., −7V). However, instead of terminal C of output capacitor  837  being grounded (as in  FIG. 8A ), terminal C of the output capacitor can be coupled to AC voltage source  840  (e.g., a buffer or other circuitry that can provide an AC signal to its output). AC voltage source  840  can, through output capacitor  837 , modulate the voltage at output node  830  in accordance with the peak-to-peak voltage provided by the AC voltage source. That is to say that output capacitor  837  can provide the DC component of the voltage at output node  830 , and AC voltage source  840  can provide the AC component of the voltage at the output node. For example, output capacitor  837  can be charged to provide −7V at output node  830 , and AC voltage source  840  can modulate that voltage with a 3V peak-to-peak signal, thus providing a 3V peak-to-peak AC voltage on output lines  831  and  832  having a DC offset of −7V. Output line  831  can output the AC voltage on output node  830  to, for example, gate line  611 , as illustrated in  FIG. 6 . In some examples, terminal C of output capacitor  837  can be coupled to a switch (e.g., any type of switching circuitry) that can selectively couple terminal C of the output capacitor to ground or to AC voltage source  840 . For example, during the non-touch sensing mode of charge pump  850 , the switch can couple terminal C of output capacitor  837  to ground (as illustrated in  FIG. 8A ), and during the touch sensing mode of the charge pump, the switch can couple terminal C of the output capacitor to AC voltage source  840  (as illustrated in  FIG. 8B ). In some examples, the state of this switch can be controlled by a touch controller (e.g., touch controller  206  in  FIG. 2 ). It is noted that while terminal C of output capacitor  837  is illustrated as being grounded in  FIG. 8A , in some examples, terminal C of the output capacitor can be coupled to another reference voltage (e.g., +/−1V, +/−2V, etc.). 
     As explained with respect to  FIG. 6 , it can be beneficial to provide an AC voltage to gate line  611  via output line  631  during a touch sensing mode of charge pump  630  in order to “bootstrap” the touch screen. However, as explained with respect to  FIG. 7 , it can be problematic to bias driver IC substrate  702 , via output line  632 , at that AC voltage. Charge pump  850  of  FIGS. 8A and 8B  has only one output node (output node  830 ), and thus cannot concurrently output an AC voltage to gate line  611  (for “bootstrapping”) and a DC voltage to driver IC substrate  702  (for driver IC substrate biasing). 
       FIGS. 9A-9B  illustrate exemplary operation and structure of charge pump  950  with two output nodes  930   a  and  930   b  according to examples of the disclosure. While two output nodes  930   a  and  930   b  are illustrated, additional output nodes can be implemented in accordance with and in an analogous manner to that described below.  FIG. 9A  illustrates exemplary operation and structure of charge pump  950  in a non-touch sensing mode of the charge pump (e.g., corresponding to the display phase of the touch screen), and  FIG. 9B  illustrates exemplary operation and structure of the charge pump in a touch sensing mode of the charge pump (e.g., corresponding to the touch sensing phase of the touch screen). Referring to  FIG. 9A , the configuration of charge pump  950  can be substantially the same as the configuration of charge pump  850  in  FIG. 8A , except that charge pump  950  can additionally include switch  905  and output capacitor  938 , as illustrated. Switch  905  can be coupled between terminal B of charging capacitor  936  and output node  930   b , and output capacitor  938  can be coupled to output node  930   b . Output capacitor  937  can provide an output voltage at output node  930   a , which can be outputted by output line  931 , and output capacitor  938  can provide an output voltage at output node  930   b , which can be outputted by output line  932 . 
     The operation of charge pump  950  can be substantially the same as that of charge pump  850  in  FIG. 8A . Switch  905  can operate with substantially the same timing and substantially the same behavior as switches  903  and  904  (which can correspond to switches  803  and  804  in  FIG. 8A ). In some examples, switches  901 ,  902 ,  903 ,  904  and  905  can be controlled by one clock signal; in some examples, switches  901  and  902  can be controlled by a first clock signal, and switches  903 ,  904  and  905  can be controlled by a second clock signal. In some examples, switches  904  and  905  can be controlled by different clock signals. The above clock signals can be provided by a touch controller (e.g., touch controller  206 ). 
     Operating in the manner described with respect to  FIG. 8A , not only can output capacitor  937  be charged to a particular voltage, but so can output capacitor  938 . In this way, charge pump  950  can have two output nodes  930   a  and  930   b  from which voltages can be outputted via output lines  931  and  932 , respectively. The voltages at output nodes  930   a  and  930   b  can depend on ratios of the capacitance of charging capacitor  936  to the capacitances of output capacitors  937  and  938 , respectively. In some examples, output capacitors  937  and  938  can have substantially the same capacitances, in which case the voltages at output nodes  930   a  and  930   b  can be substantially the same. In some examples, output capacitors  937  and  938  can have substantially different capacitances, in which case the voltages at output nodes  930   a  and  930   b  can be substantially different. During a non-touch sensing mode of charge pump  950 , the charge pump can charge output nodes  930   a  and  930   b  to respective DC voltages—output line  931  can output the DC voltage on output node  930   a  to, for example, gate line  611 , as illustrated in  FIG. 6 , and output line  932  can output the DC voltage on output node  930   b  to, for example, PSUB  708 , as illustrated in  FIG. 7 . 
       FIG. 9B  illustrates exemplary operation and structure of charge pump  950  during a touch sensing mode of the charge pump according to examples of the disclosure. During the touch sensing mode, charge pump  950  can operate substantially the same as during the non-touch sensing mode to charge or maintain the voltages at output nodes  930   a  and  930   b  at the proper DC voltages (e.g., −7V). However, instead of terminal C of output capacitor  937  being grounded (as in  FIG. 9A ), terminal C of the output capacitor can be coupled to AC voltage source  940  (e.g., a buffer or other circuitry that can provide an AC signal to its output). AC voltage source  940  can, through output capacitor  937 , modulate the voltage at output node  930   a  in accordance with the peak-to-peak voltage provided by the AC voltage source. That is to say that output capacitor  937  can provide the DC component of the voltage at output node  930   a , and AC voltage source  940  can provide the AC component of the voltage at output node  930   a . For example, output capacitor  937  can be charged to provide −7V at output node  930   a , and AC voltage source  940  can modulate that voltage with a 3V peak-to-peak signal, thus providing a 3V peak-to-peak AC voltage on output line  931  having a DC offset of −7V. Output line  931  can output the AC voltage on output node  930   a  to, for example, gate line  611 , as illustrated in  FIG. 6 . Similar to as described with reference to  FIGS. 8A-8B , in some examples, terminal C of output capacitor  937  can be coupled to a switch (e.g., any type of switching circuitry) that can selectively couple terminal C of the output capacitor to ground or to AC voltage source  940 . For example, during the non-touch sensing mode of charge pump  950 , the switch can couple terminal C of output capacitor  937  to ground (as illustrated in  FIG. 9A ), and during the touch sensing mode of the charge pump, the switch can couple terminal C of the output capacitor to AC voltage source  940  (as illustrated in  FIG. 9B ). In some examples, the state of this switch can be controlled by a touch controller (e.g., touch controller  206  in  FIG. 2 ). It is noted that while output capacitors  937  and  938  are illustrated as being grounded in  FIG. 9A , in some examples, the output capacitors can be coupled to other reference voltages (e.g., +/−1V, +/−2V, etc.). 
     While output node  930   a  and output line  931  can provide an AC voltage output from charge pump  950 , output node  930   b  and output line  932  can continue to provide a DC voltage output from the charge pump, even during the touch sensing mode of the charge pump. This can be due to the fact that output capacitor  938  can remain grounded in the touch sensing mode of charge pump  950 , and can function in substantially the same manner as it does in the non-touch sensing mode of the charge pump (illustrated in  FIG. 9A ). In this way, output line  932  can output a DC voltage to, for example, PSUB  708 , as illustrated in  FIG. 7 , even while output line  931  outputs an AC voltage to, for example, gate line  611 , as illustrated in  FIG. 6 . In some examples, output line  931  can also output an AC voltage to, for example, operational amplifier  308 ,  508  and/or  608 . 
       FIG. 9C  illustrates exemplary operation and structure of another charge pump  951  with two output nodes  930   a  and  930   b  according to examples of the disclosure. Like charge pump  950  in  FIGS. 9A-9B , charge pump  951  in  FIG. 9C  can have two output nodes  930   a  and  930   b  coupled to output lines  931  and  932 , respectively. Similar to above, during a non-touch sensing mode of charge pump  951 , output lines  931  and  932  can output respective DC voltages; during a touch sensing mode of the charge pump, output line  931  can output an AC voltage, and output line  932  can output a DC voltage. However, instead of output capacitors  937  and  938  being coupled in parallel to terminal B of charging capacitor  936  (as in  FIGS. 9A-9B ), output capacitors  937  and  938  can be coupled in series to terminal B of the charging capacitor, as illustrated in  FIG. 9C . Switch  906  in  FIG. 9C  can operate in substantially the same manner and with substantially the same timing as switch  905  in  FIGS. 9A-9B . Thus, the operation of charge pump  951  can be substantially the same as the operation of charge pump  950  in  FIGS. 9A-9B  in charging output capacitors  937  and  938  to respective DC voltages. As described previously with respect to  FIG. 9B , the voltage at output node  930   a  (and thus output line  931 ) can be modulated during the touch sensing mode of charge pump  951  by AC voltage source  940 —that is to say that switch  907  can couple terminal C of output capacitor  937  to the AC voltage source during the touch sensing mode of the charge pump. During the non-touch sensing mode of charge pump  951 , switch  907  can couple terminal C of output capacitor  937  to ground, and output node  930   a  can output a DC voltage via output line  931 . Output node  930   b  can output a DC voltage via output line  932  during both the touch sensing and non-touch sensing modes of charge pump  951 , as described previously. Switches  901 ,  902 ,  903 ,  904 ,  906  and  907  can be controlled by a touch controller (e.g., touch controller  206 ). Other details relating to the operation and structure of charge pump  951 , and the various voltages outputted by the charge pump, can be as described above with respect to charge pump  950  in  FIGS. 9A-9B , and will be omitted here for brevity. 
     Thus, as described above, charge pump  950  of  FIGS. 9A and 9B , and charge pump  951  of  FIG. 9C , can supply a DC voltage to gate line  611  in  FIG. 6  during a non-touch sensing mode of the charge pumps, and an AC voltage to the gate line during a touch sensing mode of the charge pumps. Concurrently, charge pumps  950  and  951  can supply a DC voltage to PSUB  708  in  FIG. 7  during both the non-touch sensing and the touch sensing modes of the charge pumps. Thus, turn-on of Schottky diode  716  in  FIG. 7  can be avoided. 
     As described previously, the charge pump of the disclosure can be formed in the driver IC substrate. Thus, one or more of switches  901 ,  902 ,  903 ,  904 ,  905 ,  906  and  907  can be implemented by transistors that can be formed in PWELL  704 , NWELL  706  and/or PSUB  708  of driver IC substrate  702  in  FIG. 7 .  FIG. 10  illustrates switch  1010 , which can correspond to switch  904  from  FIG. 9B , formed in PWELL  1004  according to examples of the disclosure. In some examples, switch  1010  can be implemented by transistor  1011 . Transistor  1011  can be an nMOSFET (n-type metal-oxide-semiconductor field-effect transistor), the drain of which can be coupled to node  1030   a —node  1030   a  can also be coupled to PWELL  1004 . Node  1030   a  can correspond to node  930   a  in  FIG. 9B . As discussed with reference to  FIG. 9B , during the touch sensing mode of charge pump  950 , the voltage at node  930   a  (and thus at  1030   a ) can include a DC component (represented by DC voltage source  1037 ) and an AC component (represented by AC voltage source  1040 ). Therefore, the voltage at PWELL  1004  can include the DC component and the AC component—in some examples, these can be −7V and 3V peak-to-peak, respectively. The voltage at PWELL  1004  can, therefore, range from −5.5V to −8.5V. 
     PSUB  1008  can be biased by the charge pump at a DC voltage, as described previously. Specifically, PSUB  1008  can be coupled to line  1032 , which can correspond to output line  932  in  FIG. 9B . In some examples, the voltage on line  1032  can be a DC voltage, such as −7V. Therefore, the voltage at PSUB  1008  can be −7V. 
     In some examples, the driver IC of the disclosure can include multiple charge pumps: charge pump  630  (as described with reference to  FIGS. 8-9 ) that can output relatively low voltages (e.g., negative voltages), and a second charge pump that can output relatively high voltages (e.g., positive voltages). For example, charge pump  630  can output voltages in the range of −7V (AC and/or DC), whereas the second charge pump on the driver IC can output voltages in the range of +11V (AC and/or DC). These relatively high voltages can be utilized by the touch screen when high voltages are needed for touch screen operation—for example, to turn on pixel TFT  507  in  FIG. 5 . The second charge pump can operate analogously to charge pump  630 , except that the switches of the second charge pump can be implemented with pMOSFETs (p-type MOSFETs) instead of nMOSFETs due to the relatively high voltages that the second charge pump can produce. Switch  1012  in  FIG. 10 , implemented by pMOSFET  1013 , can correspond to such a switch in the second charge pump. The source of transistor  1013  can be coupled to node  1060   a —node  1060   a  can also be coupled to NWELL  1006 . Node  1060   a  can correspond to an AC signal output node in the second charge pump (analogous to node  1030   a  with respect to charge pump  630 ). During the touch sensing mode of the second charge pump, the voltage at the AC signal output node in the second charge pump (and thus at  1060   a ) can include a DC component (represented by DC voltage source  1067 ) and an AC component (represented by AC voltage source  1070 ). Therefore, the voltage at NWELL  1006  can include the DC component and the AC component—in some examples, these can be +11V and 3V peak-to-peak, respectively. The voltage at NWELL  1006  can, therefore, range from +9.5V to +12.5V. 
     In summary, the voltage at PWELL  1004  can range from −5.5V to −8.5V, the voltage at NWELL  1006  can range from +9.5V to +12.5V, and the voltage at PSUB  1008  can be −7V. Therefore, all of the P-N junctions in driver IC substrate  1002  can remain reverse biased, and the components formed in the driver IC substrate can function properly. As such, the multiple-output node charge pumps of the disclosure can function on a single driver IC substrate. It is understood that the voltages provided above and throughout this disclosure are exemplary only, and that different voltages can be utilized in accordance with the examples of this disclosure. 
     Thus, the examples of the disclosure provide a charge pump configuration that has AC and DC outputs that can be used for concurrently “bootstrapping” the touch screen of the disclosure and biasing the driver IC substrate of the disclosure. 
     Therefore, according to the above, some examples of the disclosure are directed to a charge pump configured to operate in a first mode and a second mode, the charge pump comprising: a charging capacitor coupled to a first node and configured to transfer a first direct current (DC) voltage to the first node; a first output node coupled to the first node; and a second output node coupled to the first node, wherein: during the first mode, the first output node is configured to output a second DC voltage based on the first DC voltage, and the second output node is configured to output a third DC voltage based on the first DC voltage, and during the second mode, the first output node is configured to output the second DC voltage based on the first DC voltage, and the second output node is configured to output an alternating current (AC) voltage, the AC voltage being offset by the third DC voltage. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the first output node is coupled to the first node via a first switch, and the second output node is coupled to the first node via a second switch. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the first switch and the second switch are controlled by a single clock signal. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the first switch and the second switch are controlled by different clock signals. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the second DC voltage and the third DC voltage are the same. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the charge pump further comprises: a first holding capacitor having a first terminal and a second terminal, the first terminal coupled to the first output node; and a second holding capacitor having a third terminal and a fourth terminal, the third terminal coupled to the second output node, wherein the second DC voltage is further based on the first holding capacitor, and the third DC voltage is further based on the second holding capacitor. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the first holding capacitor and the second holding capacitor have substantially the same capacitance. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the second terminal of the first holding capacitor is coupled to a first reference DC voltage, and the fourth terminal of the second holding capacitor is coupled to: a second reference DC voltage during the first mode, and an AC voltage source during the second mode. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the first reference DC voltage and the second reference DC voltage are ground voltages. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the charge pump further comprises: switching circuitry coupled between: the fourth terminal of the second holding capacitor, and the second reference DC voltage and the AC voltage source, wherein during the first mode, the switching circuitry is configured to couple the fourth terminal of the second holding capacitor to the second reference DC voltage, and during the second mode, the switching circuitry is configured to couple the fourth terminal of the second holding capacitor to the AC voltage source. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the first output node is configured to be coupled to a substrate on which the charge pump is formed. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the second output node is configured to be coupled to the touch screen. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the second output node is configured to be coupled to a gate line of a display pixel included in the touch screen. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the second output node is further configured to be coupled to sense circuitry, the sense circuitry configured to sense touch at the display pixel. 
     Some examples of the disclosure are directed to a charge pump configured to operate in a first mode and a second mode, the charge pump comprising: means for transferring a first direct current (DC) voltage to a first node; means for coupling a first output node to the first node; and means for coupling a second output node to the first node, wherein: during the first mode, the first output node is configured to output a second DC voltage based on the first DC voltage, and the second output node is configured to output a third DC voltage based on the first DC voltage, and during the second mode, the first output node is configured to output the second DC voltage based on the first DC voltage, and the second output node is configured to output an alternating current (AC) voltage, the AC voltage being offset by the third DC voltage. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the charge pump further comprises: means for coupling a first terminal of a first holding capacitor to the first output node, the first holding capacitor having the first terminal and a second terminal; means for coupling a third terminal of a second holding capacitor to the second output node, the second holding capacitor having the third terminal and a fourth terminal, wherein the second DC voltage is further based on the first holding capacitor, and the third DC voltage is further based on the second holding capacitor. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the second terminal of the first holding capacitor is coupled to a first reference DC voltage, and the fourth terminal of the second holding capacitor is coupled to: a second reference DC voltage during the first mode, and an AC voltage source during the second mode. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the charge pump further comprises: means for: during the first mode, coupling the fourth terminal of the second holding capacitor to the second reference DC voltage, and during the second mode, coupling the fourth terminal of the second holding capacitor to the AC voltage source. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the charge pump further comprises: means for coupling the first output node to a substrate on which the charge pump is formed. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the charge pump further comprises: means for coupling the second output node to a gate line of a display pixel included in a touch screen. 
     Some examples of the disclosure are directed to a method of operating a charge pump in a first mode and a second mode, the method comprising: transferring a first direct current (DC) voltage to a first node; coupling a first output node to the first node; and coupling a second output node to the first node, wherein: during the first mode, the first output node is configured to output a second DC voltage based on the first DC voltage, and the second output node is configured to output a third DC voltage based on the first DC voltage, and during the second mode, the first output node is configured to output the second DC voltage based on the first DC voltage, and the second output node is configured to output an alternating current (AC) voltage, the AC voltage being offset by the third DC voltage. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the method further comprises: coupling a first terminal of a first holding capacitor to the first output node, the first holding capacitor having the first terminal and a second terminal; coupling a third terminal of a second holding capacitor to the second output node, the second holding capacitor having the third terminal and a fourth terminal, wherein the second DC voltage is further based on the first holding capacitor, and the third DC voltage is further based on the second holding capacitor. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the method further comprises: coupling the second terminal of the first holding capacitor to a first reference DC voltage; during the first mode, coupling the fourth terminal of the second holding capacitor to a second reference DC voltage; and during the second mode, coupling the fourth terminal of the second holding capacitor to an AC voltage source. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the method further comprises: coupling the first output node to a substrate on which the charge pump is formed. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the method further comprises: coupling the second output node to a gate line of a display pixel included in a touch screen. 
     Although examples of this disclosure have been fully described with reference to the accompanying drawings, it is to be noted that various changes and modifications will become apparent to those skilled in the art. Such changes and modifications are to be understood as being included within the scope of examples of this disclosure as defined by the appended claims.

Metadata:
Filing Date: 20171030
Publication Date: 20190430
Grant Date: 20190430
Priority Date: 20150213
Inventors: YAO, WEIJUN
STRONKS, David A.
BAE, HOPIL
BRAHMA, KINGSUK
YAO, WEI HSIN
BI, YAFEI
LI, YINGXUAN
Assignee: APPLE INC
CPC Classifications: [{"code": "G06F1/3262", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0416", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/044", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0412", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/041", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02M3/07", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01L23/642", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0443", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/04166", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02M3/07", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L23/642", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/3262", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/04166", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F1/3262", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/044", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0412", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/041", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 55646844