PATENT DOCUMENT

Publication Number: US-11997777-B2
Application Number: US-202017031570-A
Country: US
Kind Code: B2

Title: Electrostatic discharge robust design for input device

Abstract:
An electrostatic discharge (ESD) robust design for an input device such as a stylus is disclosed. The input device can include one or more components, such as one or more Schottky diodes, that can be damaged by ESD events. To reduce the likelihood of damage to sensitive components, the parasitic capacitance between sensitive conductive paths and reference ground paths of the input device that could otherwise provide electrostatic discharge paths can be reduced (arranging current limiting resistance at specific locations among sensitive components, creating physical separation between sensitive conductive paths and reference ground paths), shielding can be added to shield the sensitive electronics from ESD pulses, and high dielectric breakdown material can be added to prevent ESD pulse entry or exit of not otherwise protected circuit parts.

Claims:
What is claimed is: 
     
       1. An input device for providing input, comprising:
 a housing; 
 a tip electrode disposed at a tip end of the housing and configured for providing input to a proximate surface; 
 a handle electrode coupled to the housing; 
 a plurality of diodes and a current limiting resistance network in a series connection between the tip electrode and the handle electrode, wherein the plurality of diodes includes a first diode and a second diode, the tip electrode is electrically coupled to an anode terminal of the first diode, and a cathode terminal of the second diode is electrically coupled to the handle electrode; 
 wherein at least one of the plurality of diodes is located between the current limiting resistance network and the handle electrode; 
 a shield electrode electrically coupled to the handle electrode and substantially surrounding at least a portion of the series connection of the plurality of diodes and the current limiting resistance network, the shield electrode terminating at a shield end located closest to the tip electrode; and 
 a first pad directly connected to the current limiting resistance network and electrically coupled between the current limiting resistance network and the tip electrode, 
 wherein a location of the first pad and the current limiting resistance network within the series connection with respect to the handle electrode is selected to produce a total parasitic capacitance between the first pad and the shield and handle electrodes of less than 147 femtofarads. 
 
     
     
       2. The input device of  claim 1 , wherein the series connection includes first, second, third and fourth component positions from the tip electrode to the handle electrode, and wherein the current limiting resistance network is located in the third component position. 
     
     
       3. The input device of  claim 1 , wherein the current limiting resistance network comprises first and second resistors connected in series, connected in parallel with third and fourth resistors connected in series. 
     
     
       4. The input device of  claim 1 , further comprising one or more resistors connected in series with each other and connected in parallel with at least the plurality of diodes. 
     
     
       5. The input device of  claim 1 , further comprising one or more voltage suppression diodes connected in series with each other and connected in parallel with at least the plurality of diodes and the current limiting resistance network. 
     
     
       6. The input device of  claim 1 , further comprising:
 a first pad directly connected to the current limiting resistance network and electrically coupled between the current limiting resistance network and the tip electrode; 
 wherein a location of the first pad and the current limiting resistance network within the series connection is selected to produce an overlap of the shield electrode between first pad and the shield end of between 1.6-2.6 mm. 
 
     
     
       7. The input device of  claim 1 , further comprising:
 a circuit board; 
 at least one pad for the current limiting resistance network formed on the circuit board; and 
 at least one routing trace of the handle electrode formed on the circuit board; 
 wherein at least a portion of the at least one routing trace of the handle electrode is formed along a first edge of the circuit board to reduce capacitive coupling between the handle electrode and the at least one pad. 
 
     
     
       8. The input device of  claim 7 , wherein the at least one pad is formed along a second edge of the circuit board opposite the first edge to further reduce capacitive coupling between the handle electrode and the at least one pad. 
     
     
       9. The input device of  claim 1 , wherein the shield is located on an outside surface of the housing. 
     
     
       10. An input device for providing input, comprising:
 a housing; 
 a tip electrode disposed at a tip end of the housing and configured for providing input to a proximate surface; 
 a handle electrode coupled to the housing; 
 a plurality of diodes and a current limiting resistance network in a series connection between the tip electrode and the handle electrode, wherein the plurality of diodes includes a first diode, a second diode, and a third diode; 
 a high dielectric breakdown strength material coupled to the housing and substantially surrounding at least a portion of the series connection of the plurality of diodes and the current limiting resistance network; 
 a shield electrode electrically coupled to the handle electrode and substantially surrounding at least a portion of the series connection of the plurality of diodes and the current limiting resistance network, the shield electrode terminating at a shield end located closest to the tip electrode; and 
 a first pad connected directly to the current limiting resistance network and electrically coupled between the current limiting resistance network and the tip electrode, 
 wherein the shield electrode is configured to produce a distance between the first pad and the shield of at least 2 mm. 
 
     
     
       11. The input device of  claim 10 , wherein the high dielectric breakdown strength material substantially covers an entirety of at least a front portion of the input device. 
     
     
       12. The input device of  claim 10 , wherein the high dielectric breakdown strength material substantially surrounds the series connection between the tip electrode and the shield end of the shield electrode. 
     
     
       13. The input device of  claim 10 , further comprising a low dielectric breakdown strength material covering the high dielectric breakdown strength material at least at a front portion of the input device. 
     
     
       14. The input device of  claim 10 , wherein at least one diode is located between the current limiting resistance network and the handle electrode. 
     
     
       15. The input device of  claim 10 , wherein the series connection includes first, second, third and fourth component positions from the tip electrode to the handle electrode, and wherein the current limiting resistance network is located in the third component position. 
     
     
       16. The input device of  claim 10 , wherein the current limiting resistance network comprises first and second resistors connected in series, connected in parallel with third and fourth resistors connected in series. 
     
     
       17. The input device of  claim 10 , further comprising one or more resistors connected in series with each other and connected in parallel with at least the plurality of diodes. 
     
     
       18. The input device of  claim 10 , further comprising one or more voltage suppression diodes connected in series with each other and connected in parallel with at least the plurality of diodes and the current limiting resistance network.

Description:
FIELD 
     This relates to an input device such as a stylus for providing input to a touch-sensitive surface, and more particularly, to an electrostatic discharge robust design for the input device. 
     BACKGROUND 
     Many types of input devices are presently available for performing operations in a computing system, such as buttons or keys, mice, trackballs, joysticks, touch panels, touch screens and the like. Touch screens, in particular, are popular because of their ease and versatility of operation as well as their declining price. Touch screens can include a touch panel, which can be a clear panel with a touch-sensitive surface, and a display device such as a liquid crystal display (LCD), light emitting diode (LED) display or organic light emitting diode (OLED) display 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 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 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 some examples, touch panels can be included in other input devices that are separate from any display screen, such as trackpads. 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. 
     As mentioned above, a stylus is one type of input device that can provide touch input. In some examples, a stylus can be an active stylus that includes a power supply and generates a stylus signal that can be detected by a touch-sensitive surface of the electronic device. The electronic device can detect an active stylus by detecting the stylus signal, which can capacitively couple to one or more touch electrodes of the touch-sensitive surface. In other examples, a stylus can be a passive stylus that does not include a power supply. The passive stylus can include one or more conductive components that can capacitively couple to an electrode of the touch screen to produce or modify a received signal that is thereafter sensed by the electronic device. For example, a passive stylus may reduce the capacitive coupling between a drive line and a sense line of the touch-sensitive surface by also being capacitively coupled to the drive and sense lines, thereby modifying the signal sensed by the sense line, thus enabling the electronic device to detect the stylus. 
     SUMMARY 
     This relates to an input device such as a stylus for providing input to a touch-sensitive surface, and more particularly, to an electrostatic discharge (ESD) robust design for the input device. In some examples, the input device can include one or more components, such as one or more diodes, that can be damaged by ESD events. To reduce the likelihood of damage to sensitive components, some examples of the disclosure reduce the parasitic capacitance between sensitive conductive paths and reference ground paths of the input device that could otherwise provide ESD paths to earth ground. In some examples, parasitic capacitance can be reduced by adding shielding, arranging current limiting resistance at specific locations among sensitive components, creating physical separation between sensitive conductive paths and reference ground paths, or adding high dielectric breakdown material. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS.  1 A- 1 E  illustrate example systems that can receive input from ESD-robust input devices according to examples of the disclosure. 
         FIG.  2    illustrates an example computing system including a touch screen that can receive input from ESD-robust input devices according to examples of the disclosure. 
         FIG.  3    illustrates an exemplary stylus and exemplary electronic device according to some examples of the disclosure. 
         FIG.  4    illustrates an exemplary stylus according to some examples of the disclosure. 
         FIG.  5    illustrates a schematic diagram of front tip stylus circuitry according to some examples of the disclosure. 
         FIG.  6 A  illustrates a schematic diagram of front tip stylus circuitry with a current limiting resistance network according to some examples of the disclosure. 
         FIG.  6 B  illustrates a schematic diagram of front tip stylus circuitry with a current limiting resistance network in a different location as compared to  FIG.  6 A  according to some examples of the disclosure. 
         FIG.  7 A  illustrates a schematic diagram of front tip stylus circuitry with transient voltage suppression diodes according to some examples of the disclosure. 
         FIG.  7 B  illustrates a schematic diagram of front tip stylus circuitry with another transient voltage suppression diode and current limiting resistance network configuration according to some examples of the disclosure. 
         FIG.  8 A  illustrates a schematic diagram of front tip stylus circuitry and a shield electrode according to some examples of the disclosure. 
         FIG.  8 B  illustrates a schematic diagram of front tip stylus circuitry and a shield electrode with a different placement of a current limiting resistance network as compared to  FIG.  8 A  according to some examples of the disclosure. 
         FIG.  9    illustrates a cross-sectional view of a portion of a stylus including front tip stylus circuitry and a shield electrode according to some examples of the disclosure. 
         FIG.  10    illustrates a schematic diagram of front tip stylus circuitry and a shield electrode with yet another current limiting resistance network placement according to some examples of the disclosure. 
         FIG.  11 A  illustrates a layout of current limiting resistor pads, a portion of a handle electrode net, and other routing traces on a circuit board according to some examples of the disclosure. 
         FIG.  11 B  illustrates a layout of current limiting resistor pads, revised routing of a portion of a handle electrode net, and other routing traces on a circuit board according to some examples of the disclosure. 
         FIG.  11 C  illustrates a revised layout of current limiting resistor pads, revised routing of a portion of a handle electrode net, and other routing traces on a circuit board according to some examples of the disclosure. 
         FIG.  12 A  illustrates a cross-sectional view of a portion of a stylus including front tip stylus circuitry and a shield electrode according to some examples of the disclosure. 
         FIG.  12 B  illustrates a cross-sectional view of a portion of a stylus including front tip stylus circuitry and a different shield electrode structure as compared to  FIG.  12 A  according to some examples of the disclosure. 
         FIG.  13 A  illustrates a cross-sectional view of a portion of a stylus including front tip stylus circuitry and a discharge path outside of a shield electrode according to some examples of the disclosure. 
         FIG.  13 B  illustrates a cross-sectional view of a portion of a stylus including front tip stylus circuitry employing high dielectric breakdown strength material according to some examples of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description of examples, reference is made to the accompanying drawings which 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. 
     Examples of the disclosure relate to a handheld input device such as a stylus for providing input to a touch-sensitive surface, and more particularly, to an electrostatic discharge (ESD) robust design for the input device. In some examples, the input device can include one or more components, such as one or more diodes, that can be damaged by ESD events. To reduce the likelihood of damage to sensitive components, some examples of the disclosure reduce the parasitic capacitance between sensitive conductive paths and reference ground paths of the input device that could otherwise provide ESD paths to earth ground. In some examples, parasitic capacitance can be reduced by adding shielding, arranging current limiting resistance at specific locations among sensitive components, creating physical separation between sensitive conductive paths and reference ground paths, or adding high dielectric breakdown material. 
       FIGS.  1 A- 1 E  illustrate example systems that can receive input from an ESD-robust handheld input device according to examples of the disclosure.  FIG.  1 A  illustrates an example mobile telephone  136  that includes a touch screen  124  that can receive input from an ESD-robust input device according to examples of the disclosure.  FIG.  1 B  illustrates an example digital media player  140  that includes a touch screen  126  that can receive input from an ESD-robust input device according to examples of the disclosure.  FIG.  1 C  illustrates an example personal computer  144  that includes a touch screen  128  that can receive input from an ESD-robust input device according to examples of the disclosure.  FIG.  1 D  illustrates an example tablet computing device  148  that includes a touch screen  130  that can receive input from an ESD-robust input device according to examples of the disclosure.  FIG.  1 E  illustrates an example wearable device  150  attachable to a user using a strap  152  and including a touch screen  132  that can receive input from an ESD-robust input device according to examples of the disclosure. It is understood that other devices can also receive input from an ESD-robust input device as well. 
     In some examples, touch screens  124 ,  126 ,  128 ,  130  and  132  can be based on self-capacitance. A self-capacitance based touch system can include a matrix of small, individual plates of conductive material or groups of individual plates of conductive material forming larger conductive regions that can be referred to as touch electrodes or as touch node electrodes. For example, a touch screen can include a plurality of touch electrodes, each touch electrode identifying or representing a unique location (e.g., a touch node) on the touch screen at which touch or proximity 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 alternating current (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 (e.g., increase). 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 touch node 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. 
     In some examples, touch screens  124 ,  126 ,  128 ,  130  and  132  can be based on mutual capacitance. A mutual capacitance based touch system can include electrodes arranged as drive and sense lines that may cross over each other on different layers (in a double-sided configuration), or may be adjacent to each other on the same layer. The crossing or adjacent locations can form touch nodes. During operation, the drive line can be stimulated with an AC waveform and the mutual capacitance of the touch node can be measured. As an object approaches the touch node, the mutual capacitance of the touch node can change (e.g., decrease). This change in the mutual capacitance of the touch node 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. As described herein, in some examples, a mutual capacitance based touch system can form touch nodes from a matrix of small, individual plates of conductive material. 
     In some examples, touch screens  124 ,  126 ,  128 ,  130  and  132  can be based on mutual capacitance and/or self-capacitance. The electrodes can be arrange as a matrix of small, individual plates of conductive material or as drive lines and sense lines, or in another pattern. The electrodes can be configurable for mutual capacitance or self-capacitance sensing or a combination of mutual and self-capacitance sensing. For example, in one mode of operation electrodes can be configured to sense mutual capacitance between electrodes and in a different mode of operation electrodes can be configured to sense self-capacitance of electrodes. In some examples, some of the electrodes can be configured to sense mutual capacitance therebetween and some of the electrodes can be configured to sense self-capacitance thereof. 
     In some examples, touch screens  124 ,  126 ,  128 ,  130 , and  132  can sense an active input device such as an active stylus. The active input device can produce a device signal that can capacitively couple to the touch electrodes of touch screen  124 ,  126 ,  128 ,  130 , and  132  to be sensed by sense circuitry coupled to the touch electrodes. In some examples, a touch screen including touch node electrodes can determine the location of the stylus by determining which touch node electrodes detect the stylus signal. In other examples, touch screens  124 ,  126 ,  128 ,  130 , and  132  can sense a passive input device such as a passive stylus that does not include a power supply. The passive stylus can include one or more conductive components that can capacitively couple to an electrode of the touch screen to produce or modify a received signal that is thereafter sensed by the electronic device. For example, a passive stylus may reduce the capacitive coupling between a drive line and a sense line of the touch-sensitive surface by also being capacitively coupled to the drive and sense lines, thereby modifying the signal sensed by the sense line, thus enabling the electronic device to detect the stylus. In some examples, a touch screen including row electrodes and column electrodes can determine the location of the stylus along the rows and along the columns to determine the location of the stylus on the touch screen. Touch screens can be configured to detect both passive conductive objects (e.g., fingers, passive styluses) and active styluses. 
       FIG.  2    illustrates an example computing system including a touch screen that can receive input from an ESD-robust handheld input device according to examples of the disclosure. Computing system  200  can be included in, for example, a mobile phone, tablet, touchpad, portable or desktop computer, portable media player, wearable device or any mobile or non-mobile computing device that includes a touch screen. Although the example of  FIG.  2    illustrates a touch screen, in other examples computing system  200  can be included in an electronic device employing a touch sensor panel. 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  (e.g., including one or more of sensing circuit  314 ), channel scan logic  210  and driver logic  214 . Channel scan logic  210  can access RAM  212 , autonomously read data from the sense channels and provide control for the sense channels. In addition, channel scan logic  210  can control driver logic  214  to generate stimulation signals  216  at various frequencies and/or phases that can be selectively applied to drive regions of the touch sensing circuitry 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. 
     It should be apparent that the architecture shown in  FIG.  2    is only one example architecture of computing system  200 , and that the system could have more or fewer components than shown, or a different configuration of components. The various components shown in  FIG.  2    can be implemented in hardware, software, firmware or any combination thereof, including one or more signal processing and/or application specific integrated circuits. 
     Computing system  200  can 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/driver  234  (e.g., a Liquid-Crystal Display (LCD) driver). It is understood that although some examples of the disclosure may described with reference to LCD displays, the scope of the disclosure is not so limited and can extend to other types of displays, such as Light-Emitting Diode (LED) displays, including Organic LED (OLED), Active-Matrix Organic LED (AMOLED) and Passive-Matrix Organic LED (PMOLED) displays. Display 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. 
     Host processor  228  can use display 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 , such as a touch input to the displayed UI. 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 multi-frequency stylus scans, can be performed by firmware stored in memory (e.g., one of the peripherals  204  in  FIG.  2   ) and executed by touch processor  202  and/or touch controller  206 , 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. In some examples, RAM  212  or program storage  232  (or both) can be a non-transitory computer readable storage medium. One or both of RAM  212  and program storage  232  can have stored therein instructions, which when executed by touch processor  202  or host processor  228  or both, can cause the device including computing system  200  to perform one or more functions and methods of one or more examples of this disclosure. 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. 
     Touch screen  220  can be used to derive touch information at multiple discrete locations of the touch screen, referred to herein as touch nodes. Touch screen  220  can include touch sensing circuitry that can include a capacitive sensing medium having a plurality of drive lines  222  and a plurality of sense lines  223 . It should be noted that the term “lines” is sometimes used herein to mean simply conductive pathways, as one skilled in the art will readily understand, and is not limited to elements that are strictly linear, but includes pathways that change direction, and includes pathways of different size, shape, materials, etc. Drive lines  222  can be driven by stimulation signals  216  from driver logic  214  through a drive interface  224 , and resulting sense signals  217  generated in sense lines  223  can be transmitted through a sense interface  225  to sense channels  208  in touch controller  206 . In this way, drive lines and sense lines can be part of the touch sensing circuitry that can interact to form capacitive touch nodes, which can be thought of as touch picture elements (touch pixels) and referred to herein as touch nodes, such as touch nodes  226  and  227 . This way of understanding can be particularly useful when touch screen  220  is viewed as capturing an “image” of touch (“touch image”). In other words, after touch controller  206  has determined whether a touch has been detected at each touch nodes in the touch screen, the pattern of touch nodes in the touch screen at which a touch occurred can be thought of as an “image” of touch (e.g., a pattern of fingers touching the touch screen). As used herein, an electrical component “coupled to” or “connected to” another electrical component encompasses a direct or indirect connection providing electrical path for communication or operation between the coupled components. Thus, for example, drive lines  222  may be directly connected to driver logic  214  or indirectly connected to driver logic  214  via drive interface  224  and sense lines  223  may be directly connected to sense channels  208  or indirectly connected to sense channels  208  via sense interface  225 . In either case an electrical path for driving and/or sensing the touch nodes can be provided. 
     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 stack-ups of a display. The circuit elements in touch screen  220  can include, for example, elements that can exist in LCD or other displays (LED display, OLED display, etc.), 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.  3    illustrates an exemplary system including a handheld input device  320  and an electronic device  300  according to some examples of the disclosure. A handheld input device  320  (e.g., a stylus, marking tool, smart pen, smart brush, wand, chisel, user-manipulated electronic input device, or any other suitable accessory, such as a glove) may be configured to provide input to electronic device  300  (e.g., a tablet computer, laptop computer, desktop computer, and the like) when the handheld input device  320  is proximate to (in contact with, or in proximity to) a surface of the electronic device. (Although the term “stylus” is primarily used hereinbelow for convenience, it should be understood that any reference to the term “stylus” is inclusive of other handheld input devices such as those listed above.) A system user may manipulate the orientation and position of stylus  320  relative to a surface of a touch-sensitive display or panel of electronic device  300  to convey information to electronic device  300 , such as, but not limited to, writing, sketching, scrolling, gaming, selecting user interface elements, moving user interface elements, and so on. In some examples, the surface of the touch-sensitive display of electronic device  300  may be a multi-touch display screen. However, in some examples, the surface of the touch-sensitive display of electronic device  300  may be a non-display surface of the touch-sensitive display, such as, but not limited to, a trackpad or drawing tablet. The touch-sensitive surface may be a foldable or flexible panel or display. Electronic device  300  may be used to capture free-form user input from stylus  320 . For example, the user can slide, move, draw, or drag a tip of stylus  320  across the surface of the touch-sensitive display of electronic device  300 , which, in response, may render a graphical object (e.g., a line) using a display positioned below the surface of the touch-sensitive display. In such an example, the rendered graphical object may follow or otherwise correspond to the path of stylus  320  across the surface of the touch-sensitive display of electronic device  300 . The thickness and/or shape and/or intensity and/or any other suitable rendered characteristic of the rendered graphical object may vary based, at least in part, on one, some, or each of various characteristics, including, but not limited to, a force or speed with which the user moves stylus  320  across the surface of the touch-sensitive display, an angle of stylus  320  relative to the surface of the touch-sensitive display (e.g., the inclination of stylus  320  relative to a plane of the surface of the touch-sensitive display, a writing angle of stylus  320  relative to a horizontal writing line traversing the surface of the touch-sensitive display, etc.), a variable setting of a variable input component of stylus  320 , which one of multiple tips of stylus  320  is interacting with the surface of the touch-sensitive display, a variable setting of an application running on electronic device  300  (e.g., a virtual drawing space application), and/or a combination thereof. 
     Electronic device  300  may be any portable, mobile, or hand-held electronic device configured to interact with stylus  320  for changing any suitable characteristic(s) of device  300  (e.g., any suitable graphical object input tool characteristics that may be utilized to render a graphical object) in response to manipulation of stylus  320  across a surface of the touch-sensitive display of electronic device  300 . Alternatively, electronic device  300  may not be portable at all, but may instead be generally stationary. Electronic device  300  can include, but is not limited to, a media player, video player, still image player, game player, other media player, music recorder, movie or video camera or recorder, still camera, other media recorder, radio, medical equipment, domestic appliance, transportation vehicle instrument, musical instrument, calculator, cellular telephone, other wireless communication device, personal digital assistant, remote control, pager, computer (e.g., a desktop, laptop, tablet, server, etc.), merchant accessory (e.g., signature pad (e.g., as may be used in a check-out line of a merchant store during payment processing)), monitor, television, stereo equipment, set up box, set-top box, wearable device (e.g., watch, clothing, etc.), boom box, modem, router, printer, and combinations thereof. Electronic device  300  may include one or more components described above with reference to  FIG.  2    (e.g., electronic device  300  can be the same as electronic device  200 ). 
     In the example of  FIG.  3   , a user can manipulate the orientation and position of stylus  320  relative to surface of the touch-sensitive display input component (e.g., a particular input component) of electronic device  300  in order to convey information to electronic device  300 . Electronic device  300  may be configured to perform or coordinate multiple operations such as, but not limited to, locating stylus  320 , estimating the angular position of stylus  320 , estimating the magnitude of force by stylus  320  to surface of the touch-sensitive display, determining a variable setting of a variable input component of stylus  320 , determining a variable setting of an application running on electronic device  300  (e.g., a virtual drawing space application), and/or a combination thereof. The electronic device  300  can perform these and other operations at the same time or at different times. 
     As shown in  FIG.  3   , the user can grip a barrel or handle or body portion  322  of stylus  320  extending between a front tip portion  315  of stylus  320  and a rear tip portion  324  of stylus  320 . The user may interact with the electronic device  300  by sliding a tip portion, such as tip portion  315 , of stylus  320  across surface of the touch-sensitive display of electronic device  300 . As shown in  FIG.  3   , for example, device  300  can be a tablet computing device. It should be understood that many other electronic devices (with or without displays positioned below a stylus surface of the touch-sensitive display), such as any of the electronic device described above with reference to  FIGS.  1 A- 1 E , can be used to detect stylus  320 . For example, the electronic device can be implemented as a peripheral input device, a trackpad, a drawing tablet, and the like. 
     In some examples, stylus  320  may have a general form of a writing instrument, such as a pen or a pencil-like structure with a cylindrical body  322  with two ends, such as a first end terminated at front portion  315  and a second end terminated at rear portion  324 . One or more of portions  315  and  324  can be removable, affixed to body  322 , or an integral part of body  322 . In some examples, other input devices with different form factors are possible. 
     The stylus  320  can include one or more input or output components, which can be located at one or more of portions  315 - 324  of stylus  320 . These components can include a button, a dial, a slide, a force pad, a touch pad, audio component, haptic component and the like. As one example, at least a portion of a simple mechanical switch or button input component that may be manipulated by the user for adjusting a variable setting of stylus  320  can be located at aperture  316 . In some examples, stylus  320  can operate in a first mode when such an input component is manipulated in a first way and in a second mode when such an input component is manipulated in a second way. 
     Rear portion  324  of stylus  320  may provide a cosmetic end to body  322 . Rear portion  324  may be formed integrally with body  322 . In some examples, rear portion  324  may be formed similarly to front portion  315 . For example, rear portion  324  may provide another tip feature for interacting with a surface of the touch-sensitive display of device  300  (e.g., stylus  320  may be flipped over by the user to drag portion  324  across surface of the touch-sensitive display of electronic device  300  rather than portion  315 , which may enable different interactions with device  300 ). In some examples, rear portion  324  may include a switch or button or any other input component that may be manipulated by the user for adjusting a setting of stylus  320 . 
     Tip portion  315  of stylus  320  may be configured to contact or nearly contact surface of the touch-sensitive display of device  300 , allowing the user to use the stylus  320  to interact with the device  300 . In some examples, tip  315  can include a tapered end or point, similar to a pen, which can enable the user to more precisely control stylus  320  and provide a familiar form factor. In some examples, tip  315  may be blunt or rounded, may take the form of a rotatable or fixed ball, or may have another shape. Tip  315  can include a material that can be softer than a material of the surface of the touch-sensitive display. For example, tip  315  can include a silicone, a rubber, a fluoro-elastomer, a plastic, a nylon, conductive or dielectric foam, a brass or metal ball with a polymer coating or dielectric coating (e.g., a thin coating with a high dielectric constant) or any other suitable coating, or any other suitable material or combination of materials that does not cause damage to the surface of the touch-sensitive display or layers applied to surface of the touch-sensitive display when the stylus  320  is in use. 
     A stylus may not include a power supply (e.g., battery or wired powered supply), and therefore may not be operative to generate any stylus electric field independently (e.g., without being stimulated by an external stimulus). Instead, a stylus may be provided with limited stylus I/O circuitry that may be operative to be stimulated by an external stimulus, such as a device stimulus that may be generated by device I/O circuitry of device I/O interface  311   a  of electronic device  300  (e.g., a touch-sensitive display). The device stimulus may be operative to stimulate the stylus I/O circuitry when located proximate to device I/O interface  311   a . The stimulation of the stylus I/O circuitry may be operative to generate a suitable stylus electric field that may then be detected by device  300  for estimating the location of the stylus. The stylus electric field that may be distinguishable by device  300  from an electric field that may be provided by a user&#39;s direct contact with device I/O interface  311   a.    
     For example,  FIG.  4    illustrates an exemplary stylus  400  according to some examples of the disclosure. In some examples, stylus  400  may include stylus I/O circuitry  411   a . Stylus I/O circuitry  411   a  may operate in response to external stimulus, such as a drive signal generated by an electronic device (e.g., electronic device  136 ,  140 ,  144 ,  148 ,  150 ,  200 , or  300 ). As shown by  FIG.  4   , for example, stylus  400  may include body portion  417   a  extending between a front tip portion  415   a  and a rear tip portion (not shown), where body portion  417   a  may be configured to be held by user to interact with an electronic device. 
     In some examples, body stylus circuitry  427   a  may be electrically coupled to front tip stylus circuitry  426   a  and/or to rear tip stylus circuitry (not shown). Body stylus circuitry  427   a  may be any suitable circuitry that may be operative to be electrically coupled (e.g., capacitively coupled) to a user holding stylus  400  about at least a portion of body portion  417   a . As shown in  FIG.  4   , for example, body stylus circuitry  427   a  may include conductive material extending along at least a portion of a length of body portion  417   a  of stylus  400 , which may be insulated by any suitable insulation  428   a . In some examples, body stylus circuitry  427   a  may include a conductive (e.g., copper) tape along a portion of body  417   a , where such tape may be positioned under any suitable insulation, such as a finger pad of any suitable material. The stylus can include any suitable housing  410   a , such as a plastic housing. In some examples, the housing  410   a  can include insulation  428   a . In some examples, at least a portion of body stylus circuitry  427   a  may be at least partially exposed via housing  410   a  and/or insulation  428   a , thereby enabling direct contact by a user. 
     In some examples, stylus I/O circuitry  411   a  can include a front tip interface component  421   a  that can be included in front tip portion  415   a  of the stylus  400 . In some examples, front tip interface component  421   a  can include one or more of, silicone, rubber, fluoro-elastomer, plastic, nylon, conductive or dielectric foam, metal (e.g., brass with a dielectric or polymer coating (e.g., a thin coating with a high dielectric constant)), or any other suitable material or combination of materials. The conductive material of front tip interface component  412   a  may be referred to herein as a tip electrode. By using such materials for the front tip interface, contact and movement of front tip interface component  421   a  across surface of the touch-sensitive display of electronic device  300  should not damage surface of the touch-sensitive display or layers applied to surface of the touch-sensitive display. In some examples, front tip interface component  421   a  can be removably attached to body  417   a , such as via threadings/screws, detents and/or recesses, interference-fit or snap-fit, magnetic attraction, and the like. 
     Front tip stylus circuitry  426   a  may be positioned between and electrically coupled to front tip interface component  421   a  and body stylus circuitry  427   a . Front tip stylus circuitry  426   a  can provide a non-linear load between body stylus circuitry  427   a  and front tip interface component  421   a . In some examples, the front tip interface component  421   a  of stylus  400  may be stimulated by a signal that can be generated by device I/O circuitry of device I/O interface  311   a  of electronic device  300 . For example, front tip stylus circuitry  426   a  may include any suitable non-linear electrical circuitry  423   a  that may be electrically coupled (e.g., in series) between front tip interface component  421   a  and body stylus circuitry  427   a . For example, the non-linear circuitry  423   a  of stylus  400  can include at least one diode  422   a , such as a Schottky diode. As shown in  FIG.  4   , an anode A of diode  422   a  may be electrically coupled to body stylus circuitry  427   a  and a cathode C of diode  422   a  may be electrically coupled to front tip interface component  421   a . It should be understood, however, that it is possible to orient the diode  422   a  in the opposite way (e.g., connecting the anode A to the front tip interface component  421   a ). In some examples, the stylus  400  can include any suitable number (e.g., one or two or three or four or more) of diodes  422   a . The diodes can be coupled together in series (e.g., a cathode of one diode may be coupled to an anode of a next diode) or in parallel. 
     Device I/O circuitry of I/O interface  311   a  of an electronic device  300  may provide a drive signal that can stimulate front tip interface component  421   a  of stylus  400  when it is proximate to or touching the surface of the touch-sensitive display of I/O interface  311   a . In some examples, the drive signal can be capacitively coupled to the front tip interface component  421   a  of the stylus  400 . A non-linear response from the stylus  400  can be transmitted via front tip interface component  421   a  to one or more sense electrodes of the electronic device  300 , enabling the electronic device  300  to detect and locate the stylus  400 . 
     In some examples, circuitry  426   a  may also include (e.g., in parallel with non-linear electrical circuitry  423   a ) any suitable resistance circuitry  425   a  (e.g., at least one resistor  424   a ). Resistor  424   a  can control reverse leakage current of non-linear electrical circuitry  423   a  and/or prevent direct current (“DC”) positive voltage build up at the diode by, for example, draining off any DC while maintaining non-linearity of circuitry  426   a . The resistance of resistor  424   a  may be selected in any suitable manner, such as by using a model of the panel, including its stimulation voltage and capacitance to the tip, and a model of the non-linear device. As an example, when using one or more Schottky diodes for non-linear electrical circuitry  423   a , the resistance of resistor  424   a  can be in the range of 1-30 MΩ. In some examples, the resistance of resistor  424   a  can be in the range of 5-15 MΩ. In some examples, the resistance of resister  424   a  can be in the range of 4-6 MΩ. 
     In some examples, non-linear electrical circuitry  423   a , may modulate and rectify a voltage on front tip interface component  421   a  and may provide a load (e.g., a capacitance of front tip interface component  421   a ) and resistance circuitry  425   a , such as resistor  424   a , and may be used to discharge the capacitance and/or to prevent capacitance from charging up. In some examples, a high performance and/or low capacitance and/or low voltage Schottky diode (e.g., on an insulating substrate) may be used. As another example, a diode may be made of any suitable material(s), including, but not limited to gallium arsenide and/or titanium nitride, which may have a large reverse leakage, but such leakage may be appropriately managed by resistance circuitry  425   a . In some embodiments, a diode can be configured to have a current-voltage characteristic (e.g., an I-V curve) with certain properties, including, but not limited to, one with an abrupt or substantially abrupt non-linearity at a predetermined voltage and one that may maintain that voltage by balancing forward and reverse characteristics. In some examples, the materials of the diode can be selected to achieve desired performance characteristics. 
       FIG.  5    illustrates a schematic diagram of front tip stylus circuitry  500  according to some examples of the disclosure. As discussed above, front tip stylus circuitry  500  can include a plurality of diodes  502  such as Schottky diodes in first, second and third component positions (as viewed from left to right) connected in series, and can include resistance circuitry such as a plurality of resistors  504  in first, second and third component positions connected in series. The plurality of series diodes  502  can be in parallel with the plurality of series resistors  504 . This circuit configuration can generate harmonics (e.g., 2 nd  harmonics) of a stimulation signal received from a proximate electronic device, which can then be detected by the electronic device. However, unlike the front tip stylus circuitry of  FIG.  4   , in the example of  FIG.  5    the diodes are oriented with their anodes to the left (toward tip electrode  506 ) and cathodes to the right (toward handle electrode  508 ). For example, the anode of the diode in the first component position is connected to tip electrode  506  disposed at a tip end of the stylus, while the cathode of the diode in the third component position is connected to handle electrode  508 . Handle electrode  508  can be coupled to, or otherwise formed within, a housing of the stylus and can serve as a reference ground for the stylus, and in some examples can extend along most of the length of the stylus. In some examples, handle electrode  508  can be covered by a material such as a low or high dielectric breakdown strength material. Handle electrode  508  can be capacitively coupled to a user&#39;s hand through the material. In some examples, handle electrode  508  can be directly coupled to a user&#39;s hand (e.g., via direct contact by a user to an exposed portion of handle electrode  508 ). Resistors  504  can be “bleed” resistors that can control the reverse leakage current of diodes  502  and prevent a DC voltage buildup at the diodes by draining off any DC voltage while maintaining the nonlinearity of the diodes. 
       FIG.  6 A  illustrates a schematic diagram of front tip stylus circuitry  600  with a current limiting resistance (CLR) network  610  according to some examples of the disclosure. As mentioned above, some sensitive components, such as diodes  502  of  FIG.  5   , can be damaged or destroyed if they are part of an electrostatic discharge path. To limit this damage, CLR network  610  can be placed in series with diodes  602  in the sensitive component path. The example of  FIG.  6 A  shows only two Schottky diodes  602  in first and second component positions and CLR  610  in the third component position, connected in series and also connected in parallel with three bleed resistors  604 , but in other examples more or fewer diodes and resistors may be employed. Although  FIG.  6 A  illustrates only a single resistor for CLR  610 , it should be understood that the representation of the CLR in  FIG.  6 A  is only symbolic, and that the CLR can be formed of a single resistor, or multiple resistors or resistive elements in various circuit network configurations. For example, a network of four resistors (two in series, connected in parallel with another two in series) can be employed to provide robustness and redundancy in view of possible damage or degradation due to ESD passing through the network. 
       FIG.  6 B  illustrates a schematic diagram of front tip stylus circuitry  600  with CLR network  610  in a different location according to some examples of the disclosure. In the example of  FIG.  6 B , three Schottky diodes  602  in first, second and third component positions are connected in parallel with bleed resistors  604 , and CLR  610  is connected in series with the parallel configuration, though more or fewer diodes and resistors may be employed. 
       FIG.  7 A  illustrates a schematic diagram of front tip stylus circuitry  700  with transient voltage suppression (TVS) diodes  712  according to some examples of the disclosure. In the example of  FIG.  7 A , a plurality of bidirectional TVS diodes  712  can be connected in parallel with the circuit of  FIG.  6 B . Although only three TVS diodes  712  are shown in  FIG.  7 A , more or fewer diodes may be employed. TVS diodes  712  can shunt excess current when an induced voltage (such as from an ESD event) exceeds the avalanche breakdown potential of the TVS diodes, effectively clamping the voltage to the breakdown voltage. TVS diodes  712  can provide a least impedance path for ESD events, so that current entering from tip electrode  706  passes through the TVS diodes instead of Schottky diodes  702 , thereby protecting the Schottky diodes. In operation, CLR  710  can protect Schottky diodes  702  until TVS diodes  712  reach their breakdown voltages and start conducting. 
       FIG.  7 B  illustrates a schematic diagram of front tip stylus circuitry  700  with another TVS diode  712  and CLR network  710  configuration according to some examples of the disclosure. In the example of  FIG.  7 B , CLR  710  is configured as a network of four resistors (two in series, connected in parallel with another two in series), and six TVS diodes  712  are employed. As with the preceding figures, more or fewer Schottky diodes, CLR resistors, bleed resistors and TVS diodes may also be employed. 
     The human body can accumulate charge and create ESD, but the resistance of the human body can control the frequency content of ESD current and can limit ESD events to relatively low frequencies. Because of these frequency limitations, the values and characteristics of the components in front tip stylus circuitry  700  of  FIGS.  7 A and  7 B  can be selected to protect against ESD events caused by a user. However, high-frequency ESD events can also be generated. For example, when metallic objects and insulative objects such as plastic comingle and rub against each other (such as in a backpack, purse or pocket), the insulative objects can cause a buildup of charge on the metallic objects. If these metallic objects come into contact (or close proximity) to the tip electrode of a stylus, high frequency ESD events (e.g., in a range of approximately 3 GHz-6 GHz) can be generated (as compared to lower frequency ESD events (e.g., up to around 1 GHz) that can be generated from the human body). These high frequency ESD events can have characteristics such as frequency, voltage, duration, and rise/fall times that depend on factors such as the electron affinity of the materials, temperature and humidity. Non-linear circuits such as the previously discussed Schottky diodes can be particularly susceptible to these high frequency ESD events. 
       FIG.  8 A  illustrates a schematic diagram of front tip stylus circuitry  800  and shield electrode  814  according to some examples of the disclosure. In the example of  FIG.  8 A , the circuit of  FIG.  7 B  can be substantially surrounded by shield electrode  814 , which is electrically connected to handle electrode  808  and can serve as the reference ground for the stylus. Although not evident in  FIG.  8 A , shield electrode  814  can substantially surround at least a portion of front tip stylus circuitry  800  on all sides but one (e.g., the shield electrode can be generally cylindrical in shape, or have other shapes that substantially surround at least a portion of the front tip stylus circuitry), with some or all of the side of the shield electrode facing tip electrode  806  being open to allow the tip electrode, circuit board and other components in the front tip stylus circuitry to enter the shielded area within the shield electrode. Because shield electrode  814  covers some or all of front tip stylus circuitry  800 , it can protect the circuitry from ESD sources outside the stylus. 
     However, shield electrode  814  can also create undesirable ESD paths. For example,  FIG.  8 A  illustrates parasitic capacitance  816  that can form between the left node or pad P of CLR  810  (from the perspective of  FIG.  8 A ) and shield electrode  814  due to the proximity of pad P to the shield electrode. Parasitic capacitance  818  can also form between pad P of CLR  810  and the handle electrode  808 . (Parasitic capacitances are illustrated with dashed lines herein.) Each of these parasitic capacitances can provide discharge paths for high frequency ESD pulses from tip electrode  806  that can bypass CLR  810  and its protection, resulting in possible damage to Schottky diodes  802 . Therefore, it can be desirable to modify the circuit of  FIG.  8 A  in a way that increases the likelihood that the high frequency current passes through CLR  810  and gets attenuated enough so that it does not cause permanent damage to Schottky diodes  802 . Note that although parasitic capacitances  816  and  818  are specifically described herein and illustrated in  FIG.  8 A , it should be understood that other parasitic capacitances can form between other circuit nodes and components and shield electrode  814 , although these are not shown in  FIG.  8 A  or the following figures in order to simplify the figures. 
       FIG.  8 B  illustrates a schematic diagram of front tip stylus circuitry  800  and shield electrode  814  with a different placement of CLR  810  according to some examples of the disclosure. In the example of  FIG.  8 B , CLR  810  is located in the third component position instead of the fourth component position, while third Schottky diode  802  is located in the fourth component position instead of the third component position. Although  FIG.  8 B  shows CLR  810  as a single resistor, in other examples the four resistor network of  FIG.  8 A  or other resistive element configurations can also be employed. In some examples, the distance from pad P to tip electrode  806  can be between 7.5 to 10 mm, which increases the distance from pad P to handle electrode  808 . During lower frequency ESD events, such as from the human body, the operation of Schottky diodes  802  and CLR  810  can remain essentially the same, despite the change in locations of the CLR and the third Schottky diode. That is, Schottky diodes  802  can effectively short-circuit during the lower-frequency ESD event, but can be protected by CLR  810 , resulting in a voltage rise across the CLR. As a result, most of the current can flow through TVS diodes  812  and not through Schottky diodes  802 . 
     Because CLR  810  is moved to the left in  FIG.  8 B , there is a greater distance between pad P of CLR  810  to handle electrode  808  as compared to  FIG.  8 A , and therefore a lower parasitic capacitance  818  can form between pad P and the handle electrode. Because of this lower parasitic capacitance, there can be a reduced chance that high frequency ESD pulses from tip electrode  806  will bypass CLR  810  and discharge across parasitic capacitance  818  to the handle electrode, causing damage to the Schottky diodes  802 . Conversely, there can be an increased chance that high frequency ESD pulses from tip electrode  806  will pass through CLR  810  and sufficiently attenuate current flow so that it does not cause permanent damage to the Schottky diodes. 
       FIG.  9    illustrates a cross-sectional view of a portion of a stylus including front tip stylus circuitry  900  and shield electrode  914  according to some examples of the disclosure. Shield  914  extends along a portion of the stylus, terminating at shield end  930  located closest to tip electrode  906 . Note that Schottky diodes  902 , bleed resistors  904 , CLR  910  and TVS diodes  912  are illustrated symbolically on printed circuit board (PCB)  936  (e.g., with the bleed resistors  904  and TVS diodes  912  on a bottom side of PCB  936  and Schottky diodes  902  and CLR  910  on the top side of PCB  936 ). As discussed above, a parasitic capacitance can form between the left node or pad P of CLR  910  and shield electrode  914 , based on the amount of overlap of the shield electrode and the components and traces in the sensitive component path. If the overlap (and therefore the parasitic capacitive coupling) between the sensitive component path and shield electrode  914  is large enough, the impedance of the parasitic capacitive coupling between pad P and shield electrode  914  can be low enough relative to the impedance of the CLR  910  that ESD current can discharge to the shield electrode rather than through the CLR as intended. 
     Moving CLR  910  towards tip electrode  906  can also reduce the overlap of the sensitive component path and shield electrode  914  and decrease the parasitic capacitive coupling between the sensitive components and the shield electrode. In the example of  FIG.  9   , CLR  910  is located in the third component position while the third Schottky diode  902  is located in the fourth component position, which is the same order as in  FIG.  8 B .  FIG.  9    illustrates an example overlap of L 1  (e.g., 2.6 mm) between pad P and shield end  930 , which was selected based on a desired maximum parasitic capacitance of 150 femtoFarads (fF), and a distance between pad P and tip electrode  906  of L 2 . However, it should be understood that in other examples and for other desired parasitic capacitances, L 1  and L 2  can be different distances. In some examples, L 1  can be between 1.6-2.6 mm to optimize overall performance and ESD robustness. In other examples, L 1  can be less than 1.6 mm to provide acceptable parasitic capacitance for ESD purposes, but with reduced overall performance. This further reduction in parasitic capacitance due to reduced shield electrode overlap can reduce the chance that high frequency ESD pulses from tip electrode  906  will bypass CLR  910  and discharge to shield electrode  914 , causing damage to Schottky diodes  902 . Conversely, there can be an increased chance that high frequency ESD pulses from tip electrode  906  will pass through CLR  910  and sufficiently attenuate current flow so that it does not cause permanent damage to Schottky diodes  902 . 
     In examples where the total parasitic capacitance between pad P and the shield and handle electrodes (which are electrically connected together and represent system ground) can have a requirement such as less than 147 fF, moving CLR  910  to the third component position can cause a reduction in the parasitic capacitance between pad P and the handle electrode (not shown in  FIG.  9   ) from approximately 120 fF to approximately 13 fF, and a reduction of the parasitic capacitance between pad P and the shield electrode  914  from approximately 256 fF to approximately 134 fF. The total parasitic capacitance can therefore be reduced from approximately 376 fF to approximately 147 fF. In some examples, the parasitic capacitance can be within a range of 100 fF-150 fF to reduce the parasitic capacitance as much as possible without affecting other parameters. Moving CLR  910  to the third component position can also change the total impedance between pad P and the shield and handle electrodes at 1 GHz (representative of ESD from a human body) from 423 ohms to 1008 ohms, and can change the total impedance between pad P and the shield and handle electrodes at 6 GHz (representative of ESD from plastic-charged metallic objects) from 70 ohms to 180 ohms. Peak ESD current passing through Schottky diodes  902  can be reduced from about 6 amps to about 4 amps. In both instances, the higher impedance can discourage ESD events from discharging to the shield and handle electrodes instead of through CLR  910 . 
       FIG.  10    illustrates a schematic diagram of front tip stylus circuitry  1000  and shield electrode  1014  with yet another CLR  1010  placement according to some examples of the disclosure. In the example of  FIG.  10   , CLR  1010  is located in the second component position instead of the third component position (from left to right) as in  FIG.  8 B , while the second and third Schottky diodes  1002  are located in the third and fourth component positions, respectively. Although  FIG.  10    shows CLR  1010  as a single resistor, in other examples the four resistor network of  FIG.  8 A  or other resistive element configurations can also be employed. In some examples, the distance L 2  from pad P to tip electrode  1006  can be about 6 mm, which increases the distance from pad P to the handle electrode  1008  even more as compared to  FIG.  8 B . In other examples, L 2  can be about 5-6 mm to optimize overall performance and ESD robustness, and can even be smaller than 5 mm to provide acceptable parasitic capacitance for ESD purposes, but with reduced overall performance. During lower frequency ESD events, such as from the human body, the operation of Schottky diodes  1002  and CLR  1010  can remain essentially the same, despite the change in locations of the CLR and the Schottky diodes. That is, Schottky diodes  1002  can effectively short-circuit during the lower-frequency ESD event, but can be protected by CLR  1010 , resulting in a voltage rise across the CLR. As a result, most of the current can flow through TVS diodes  1012  and not through Schottky diodes  1002 . 
     Because CLR  1010  is moved further to the left in  FIG.  10   , there is a greater distance between pad P of CLR  1010  to handle electrode  1008  as compared to  FIG.  8 B , and therefore a lower parasitic capacitance  1018  can form between pad P and the handle electrode. Because of this lower parasitic capacitance, there can be a reduced chance that high frequency ESD pulses from tip electrode  1006  will bypass CLR  1010  and discharge across parasitic capacitance  1018  to the handle electrode, causing damage to Schottky diodes  1002 . Conversely, there can be an increased chance that high frequency ESD pulses from tip electrode  1006  will pass through CLR  1010  and sufficiently attenuate current flow so that it does not cause permanent damage to Schottky diodes  1002 . 
     In some examples, CLR  1010  can be located in the first component position (from left to right), while the first, second and third Schottky diodes  1002  can be located in the second, third and fourth component positions, respectively. In these examples, CLR  1010  can be a single resistor, the four resistor network of  FIG.  8 A , or other resistive element configurations. In some examples, the distance from pad P to tip electrode  1006  can be about 3.6 mm, which increases the distance from pad P to the handle electrode even more as compared to  FIG.  10   . In other examples, this distance can be about 1.8-3.6 mm based on the mechanical limitations of the circuit board design. This configuration can provide similar decreases in parasitic capacitance between pad P and handle electrode  1008 , and can provide a similar advantage of increasing the likelihood that ESD current flows through CLR  1010  rather than discharging to shield electrode  1014  and bypassing CLR  1010 . 
     Although the previous discussion and associated figures primarily describe and depict the front tip stylus circuitry only schematically as being located between the handle electrode and the tip electrode, without physical detail, in various product design examples the front tip stylus circuitry can be formed on one or more layers of a circuit board that may also include routing traces of a handle electrode net. The handle electrode net traces, in particular, which act as a reference ground for the stylus, can be routed in close proximity to sensitive components of the front tip stylus circuitry and can create parasitic capacitive coupling with those components, creating electrostatic discharge paths that bypass the CLR and put sensitive components such as Schottky diodes at risk. 
       FIG.  11 A  illustrates a layout of current limiting resistor pads, a portion of a handle electrode net, and other routing traces on circuit board  1132  according to some examples of the disclosure. In the example of  FIG.  11 A , two representative CLRs  1110  are shown symbolically, installed on pads. Handle electrode  1108  is electrically connected to trace  1120  of a larger handle electrode net. Because of the close proximity of trace  1120  to pad P, parasitic capacitance  1116  can form between pad P and trace  1120 . Parasitic capacitance  1116  can provide a discharge path for high frequency ESD pulses from the tip electrode that bypass CLRs  1110  and their protection, resulting in possible damage to the Schottky diodes (not shown in  FIG.  11   ). 
       FIG.  11 B  illustrates a layout of current limiting resistor pads, revised routing of a portion of a handle electrode net, and other routing traces on a circuit board according to some examples of the disclosure. In the example of  FIG.  11 B , trace  1120 , which is part of the larger handle electrode net, is routed to be farther away from the sensitive component pads, including pad P, as compared to  FIG.  11 A  (whose trace routing is shown in dashed lines in  FIG.  11 B  for comparison; see arrows). In some examples, trace  1120  can be routed to an edge of circuit board  1132  on which it is formed. Because of the greater distance between trace  1120  and pad P as compared to  FIG.  11 A , a smaller parasitic capacitance  1116  can be formed between pad P and trace  1120  as compared to  FIG.  11 A . In some examples, approximately a 45% reduction in parasitic capacitance can be achieved. The smaller parasitic capacitance  1116  can make it less likely that high frequency ESD pulses from the tip electrode will discharge to handle electrode  1108  via trace  1120  and bypass CLRs  1110  and their protection, resulting in a decreased chance of damage to the Schottky diodes. 
       FIG.  11 C  illustrates a revised layout of current limiting resistor pads, revised routing of a portion of a handle electrode net, and other routing traces on a circuit board according to some examples of the disclosure. In the example of  FIG.  11 C , the pads for CLRs  1110 , including pad P, are laid out to be farther away from trace  1120  as compared to  FIGS.  11 A-B  (whose pad layout is shown in dashed lines in  FIG.  11 C  for comparison; see arrows). In some examples, the pads can be routed to an edge of circuit board  1132  on which it is formed. Because of the greater distance between trace  1120  and pad P as compared to  FIG.  11 B , a smaller parasitic capacitance  1116  can be formed between pad P and trace  1120  as compared to  FIG.  11 B . The smaller parasitic capacitance  1116  can make it less likely that high frequency ESD pulses from the tip electrode will discharge to handle electrode  1108  via trace  1120  and bypass CLRs  1110  and their protection, resulting in a decreased chance of damage to the Schottky diodes. In other examples not shown in  FIG.  11 C , trace  1120  can remain as shown in  FIG.  11 A , while the pads can be laid out to be farther away from the trace as shown in  FIG.  11 C . 
     As discussed above with respect to  FIG.  9   , a parasitic capacitance can form between the left node or pad P of the CLR (or other sensitive components or conductive areas) and the shield electrode, based on the amount of overlap of the shield electrode and the components and traces in the sensitive component path. If the overlap (and therefore the parasitic capacitive coupling) between the sensitive component path and the shield electrode is large enough, the impedance of the parasitic capacitive coupling path between pad P and the shield electrode can be low enough relative to the impedance of the CLR that electrostatic current can discharge to the shield electrode rather than through the CLR as intended, reducing or eliminating the effectiveness of the CLR and subjecting sensitive components such as the Schottky diodes to potential damage or destruction. However, increased parasitic capacitance between the shield electrode and a sensitive component or area, such as pad P, can occur for reasons other than increased shield electrode overlap. In some examples, close proximity of the shield electrode to sensitive components or areas such as pad P can also cause increased parasitic capacitance. 
       FIG.  12 A  illustrates a cross-sectional view of a portion of a stylus including front tip stylus circuitry  1200  and shield electrode  1214  according to some examples of the disclosure. Note that Schottky diodes  1202 , bleed resistors  1204 , CLR  1210  and TVS diodes  1212  are illustrated symbolically on PCB  1236 . Although the example of  FIG.  12 A  illustrates CLR  1210  (represented symbolically by a pair of blocks on each side of a circuit board) located in the fourth component position (along the top of the circuit board), it should be understood that CLR  1210  can alternatively be located in the third, second or first component positions. In the example of  FIG.  12 A , the diameter of shield electrode  1214  results in a distance D 1  between pad P and the shield electrode. If distance D 1  is small enough, the parasitic capacitance between pad P and shield electrode  1214  can be large enough to create a discharge path to the shield electrode rather than through CLR  1210 , as discussed above. 
       FIG.  12 B  illustrates a cross-sectional view of a portion of a stylus including front tip stylus circuitry  1200  and a different shield electrode structure  1214  according to some examples of the disclosure. Note that Schottky diodes  1202 , bleed resistors  1204 , CLR  1210  and TVS diodes  1212  are illustrated symbolically on PCB  1236 . Although the example of  FIG.  12 B  illustrates CLR  1210  (represented symbolically by a pair of blocks on each side of a circuit board) located in the fourth component position (along the top of the circuit board), it should be understood that CLR  1210  can alternatively be located in the third, second or first component positions. In the example of  FIG.  12 B , shield electrode  1214  is located on an outside surface of the stylus housing, although in other examples the shield electrode can be located within the body of the stylus, but farther away from pad P than shown in  FIG.  12 A . The diameter of shield electrode  1214  results in a distance D 2  between pad P and the shield electrode. In the examples of  FIGS.  12 A and  12 B , D 2  is greater than D 1 . If distance D 2  is large enough, the parasitic capacitance between pad P and shield electrode  1214  can be small enough to not create a discharge path to the shield electrode. As a result, current from an ESD event is more likely to flow through the CLR, protecting the sensitive components. 
     In some examples of the disclosure, the location of shield electrode  1214  can be selected such that D 2  is at least 2 mm or in a range of 2-4 mm. In other examples, the location of shield electrode  1214  can be selected such that the diameter of the shield electrode (when the shield electrode is cylindrical) is about 2.6 mm, which can produce a total parasitic capacitance between pad P and the shield electrode of about 147 fF. In other examples, the diameter can be about 3 mm for a total parasitic capacitance of about 138 fF, or about 3.4 mm for a total parasitic capacitance of about 130 fF, or about 3.8 mm for a total parasitic capacitance of about 114 fF. 
       FIG.  13 A  illustrates a cross-sectional view of a portion of a stylus including front tip stylus circuitry  1300  and discharge path  1324  outside of shield electrode  1314  according to some examples of the disclosure. Note that the example of  FIG.  13 A  presents an inverted view (with Schottky diodes  1302  on the bottom of a circuit board and TVS diodes  1312  on the top of the circuit board) as compared with previous figures. Schottky diodes  1302 , bleed resistors  1304 , CLR  1310  and TVS diodes  1312  are illustrated symbolically. Although the example of  FIG.  13 A  illustrates CLR  1310  (represented symbolically by a single block on one side of the circuit board) located in the third component position (along the bottom of the circuit board), it should be understood that CLR  1310  can alternatively be located in the fourth, second or first component positions. In the example of  FIG.  13 A , at least a front portion of the stylus is covered with a low dielectric breakdown strength material  1328  such as a thermoplastic elastomer (e.g., polyether block amide). When some ESD events occur, a low impedance path from tip electrode  1306  to the handle electrode (not shown in  FIG.  13 A ) through TVS diodes  1312  can form, allowing the current to bypass critical components such as Schottky diodes  1302  and reducing the chance of damage to them. 
     However, in some instances when ESD pulse  1322  enters tip electrode  1306 , it can exit the stylus at location  1324  through low dielectric breakdown strength material  1328  prior to passing within shield electrode  1314 , and can discharge to an external object such as a conductive table. If ESD pulse  1322  passes through any sensitive components such as Schottky diode  1302  before exiting at location  1324  (bypassing CLRs or TVS diodes), those sensitive components can be damaged or destroyed. 
       FIG.  13 B  illustrates a cross-sectional view of a portion of a stylus including front tip stylus circuitry  1300  employing high dielectric breakdown strength material  1326  according to some examples of the disclosure. Although the example of  FIG.  13 B  illustrates CLR  1310  (represented symbolically by a single block on one side of a circuit board) located in the third component position (along the bottom of the circuit board), it should be understood that CLR  1310  can alternatively be located in the fourth, second or first component positions. In the example of  FIG.  13 B , at least a front portion of the stylus, located in an area without shield electrode  1314  (i.e., the area between tip electrode  1306  and the start of shield electrode  1314 ) is covered with high dielectric breakdown strength material  1326  such as Polyamide 11. High dielectric breakdown strength material  1326  can substantially surround all or at least a portion of the front tip stylus circuitry  1300  (e.g., high dielectric breakdown strength material  1326  can be generally cylindrical in shape, or have other shapes that substantially surround at least a portion of the front tip stylus circuitry), and can additionally cover other areas of the stylus, as shown in  FIG.  13 B . In other examples not shown in  FIG.  13 B , only the area between tip electrode  1306  and the start of shield electrode  1314  can be covered with high dielectric breakdown strength material  1326 . In some examples, the dielectric breakdown strength of high dielectric breakdown strength material  1326  can be at least 800 volts/mil. If high dielectric breakdown strength material  1326  is the outward-facing material intended to contact a surface, a material that is soft, durable, thin, and having a sufficiently high dielectric breakdown strength can be used. 
     In the example of  FIG.  13 B , at least a tip portion of high dielectric strength material  1326  is covered with low dielectric breakdown strength material  1328  such as a thermoplastic elastomer (e.g., polyether block amide). In some examples (not shown in  FIG.  13 B ), low dielectric breakdown strength material  1328  is absent, and the front portion of the stylus is covered only with high dielectric breakdown strength material  1326 . In other examples (not shown in  FIG.  13 B ), shield electrode  1314  can be absent, and instead high dielectric breakdown strength material  1326  can extend over areas of the front tip stylus circuitry that would otherwise have been covered by the shield electrode, and act as a replacement for the shield electrode. 
     When ESD pulse  1322  occurs, high dielectric breakdown strength material  1326  can prevent the pulse from discharging to an external object (see “X”  1334 ), and instead the current can follow a low impedance path from tip electrode  1306  to the handle electrode (not shown in  FIG.  13 A ) through TVS diodes  1312 , bypassing critical components such as Schottky diodes  1302  and reducing the chance of damage to them. The effectiveness of high dielectric breakdown strength material  1326  can depend on its total breakdown strength, which is a function of its thickness and its breakdown strength per unit distance. For example, if an ESD pulse having a peak current of 15 kV is to be expected, a material with a total dielectric breakdown strength greater than 15 kV can be chosen. The breakdown strength in volts/mm can determine the needed thickness of the material. 
     Although various examples of CLR placement, shield electrode placement and size, placement and routing of component pads and traces, and high dielectric breakdown strength materials may be described above in different paragraphs and shown in different figures for convenience of explanation, it should be understood that different permutations and combinations of these features are contemplated in different examples of the disclosure. 
     Therefore, according to the above, some examples of the disclosure are directed to an input device for providing input, comprising a housing, a tip electrode disposed at a tip end of the housing and configured for providing input to a proximate surface, a handle electrode coupled to the housing, and a plurality of diodes and a current limiting resistance network in a series connection between the tip electrode and the handle electrode, wherein at least one of the plurality of diodes is located between the current limiting resistance network and the handle electrode. As an alternative to or in addition to one more of the examples disclosed above, in some examples the series connection includes first, second, third and fourth component positions from the tip electrode to the handle electrode, and wherein the current limiting resistance network is located in the third component position. As an alternative to or in addition to one more of the examples disclosed above, in some examples the current limiting resistance network comprises first and second resistors connected in series, connected in parallel with third and fourth resistors connected in series. As an alternative to or in addition to one more of the examples disclosed above, in some examples the input device further comprises one or more resistors connected in series with each other and connected in parallel with at least the plurality of diodes. As an alternative to or in addition to one more of the examples disclosed above, in some examples the input device further comprises one or more voltage suppression diodes connected in series with each other and connected in parallel with at least the plurality of diodes and the current limiting resistance network. As an alternative to or in addition to one more of the examples disclosed above, in some examples the input device further comprises a shield electrode electrically coupled to the handle electrode and substantially surrounding at least a portion of the series connection of the plurality of diodes and the current limiting resistance network, the shield electrode terminating at a shield end located closest to the tip electrode. As an alternative to or in addition to one more of the examples disclosed above, in some examples the input device further comprises a first pad directly connected to the current limiting resistance network and electrically coupled between the current limiting resistance network and the tip electrode, wherein a location of the first pad and the current limiting resistance network within the series connection with respect to the handle electrode is selected to produce a total parasitic capacitance between the first pad and the shield and handle electrodes of less than 147 femtofarads. As an alternative to or in addition to one more of the examples disclosed above, in some examples the input device further comprises a first pad directly connected to the current limiting resistance network and electrically coupled between the current limiting resistance network and the tip electrode, wherein a location of the first pad and the current limiting resistance network within the series connection is selected to produce an overlap of the shield electrode between first pad and the shield end of between 1.6-2.6 mm. As an alternative to or in addition to one more of the examples disclosed above, in some examples the input device further comprises a circuit board, at least one pad for the current limiting resistance network formed on the circuit board, and at least one routing trace of the handle electrode formed on the circuit board, wherein at least a portion of the at least one routing trace of the handle electrode is formed along a first edge of the circuit board to reduce capacitive coupling between the handle electrode and the at least one pad. As an alternative to or in addition to one more of the examples disclosed above, in some examples the at least one pad is formed along a second edge of the circuit board opposite the first edge to further reduce capacitive coupling between the handle electrode and the at least one pad. As an alternative to or in addition to one more of the examples disclosed above, in some examples the input device further comprises a first pad connected directly to the current limiting resistance network and electrically coupled between the current limiting resistance network and the tip electrode, wherein the shield is configured to produce a distance between the first pad and the shield of at least 2 mm. As an alternative to or in addition to one more of the examples disclosed above, in some examples the shield is located on an outside surface of the housing. 
     Some examples of the disclosure are directed to an input device for providing input, comprising a housing, a tip electrode disposed at a tip end of the housing and configured for providing input to a proximate surface, a handle electrode coupled to the housing, a plurality of diodes and a current limiting resistance network in a series connection between the tip electrode and the handle electrode, and a high dielectric breakdown strength material coupled to the housing and substantially surrounding at least a portion of the series connection of the plurality of diodes and the current limiting resistance network. As an alternative to or in addition to one more of the examples disclosed above, in some examples the high dielectric breakdown strength material substantially covers an entirety of at least a front portion of the input device. As an alternative to or in addition to one more of the examples disclosed above, in some examples the input device further comprises a shield electrode coupled to the handle electrode and substantially surrounding at least a portion of the series connection of the plurality of diodes and the current limiting resistance network, the shield electrode terminating at a shield end located closest to the tip electrode. As an alternative to or in addition to one more of the examples disclosed above, in some examples the high dielectric breakdown strength material substantially surrounds the series connection between the tip electrode and the shield end of the shield electrode. As an alternative to or in addition to one more of the examples disclosed above, in some examples the input device further comprises a low dielectric breakdown strength material covering the high dielectric breakdown strength material at least at a front portion of the input device. As an alternative to or in addition to one more of the examples disclosed above, in some examples at least one diode is located between the current limiting resistance network and the handle electrode. As an alternative to or in addition to one more of the examples disclosed above, in some examples the series connection includes first, second, third and fourth component positions from the tip electrode to the handle electrode, and wherein the current limiting resistance network is located in the third component position. As an alternative to or in addition to one more of the examples disclosed above, in some examples the current limiting resistance network comprises first and second resistors connected in series, connected in parallel with third and fourth resistors connected in series. As an alternative to or in addition to one more of the examples disclosed above, in some examples the input device further comprises one or more resistors connected in series with each other and connected in parallel with at least the plurality of diodes. As an alternative to or in addition to one more of the examples disclosed above, in some examples the input device further comprises one or more voltage suppression diodes connected in series with each other and connected in parallel with at least the plurality of diodes and the current limiting resistance network. 
     Although the disclosed examples 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 the disclosed examples as defined by the appended claims.

Metadata:
Filing Date: 20200924
Publication Date: 20240528
Grant Date: 20240528
Priority Date: 20200924
Inventors: BECHSTEIN, DANIEL JACOB BENJAMIN
KHORRAMI, Mohammadali
AYANOOR-VITIKKATE, VIPIN
MARSHALL, BLAKE R.
WANG, ZHIBIN
CAO, YING
LIU, ROBERT UBO
SMITH, JOHN STEPHEN
Assignee: APPLE INC
CPC Classifications: [{"code": "H05F3/00", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F3/03545", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0442", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F3/0446", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F3/03545", "inventive": true, "first": true, "tree": "[]"}, {"code": "H05F3/00", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F2203/0384", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F3/0446", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F3/0442", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F3/0442", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F3/0446", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F3/03545", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 80741181