Patent Publication Number: US-2013249870-A1

Title: Dual mode active stylus for writing both on a capacitive touchscreen and paper

Description:
FIELD OF THE DISCLOSURE 
     The present disclosure relates generally to writing instruments for an electronic device having a touch-sensitive interface and more particularly to a writing stylus for writing both on an electronic device, including a capacitive touch-sensitive interface, and traditional paper. 
     BACKGROUND 
     Today&#39;s users of mobile wireless communication devices and electronic signage boards that employ touchscreens as displays are required to use at least two writing instruments when the touchscreen interface has a capacitive sensing design, for example. One instrument is for writing on the touchscreen itself (e.g., a stylus), another is for writing off of the touchscreen (e.g., a pen or pencil), specifically on paper type products, such as note pads, composition books, daily planners, and tablets, for example. This dual necessity causes most users to remember to have both writing instruments in their possession during the day so that they are well-equipped for meetings, for example 
     Additionally, one or more embodiments may be useful in electronic devices that include a touch-sensitive interface, but may not be a communication device akin to a mobile wireless communication device. Therefore, the realized benefits of what&#39;s being proposed is not specifically limited to mobile wireless communication, and instead includes one or more electronic devices with touch-sensitive interfaces. 
     Capacitive touch-sensitive devices generally work by emitting a periodic waveform, such as a square wave or sine wave. When an object, like a user&#39;s finger, for example, comes in close proximity with the surface of the touch sensitive, the object disturbs electric field lines between the periodic waveform generator and receptor electrodes. A sensing circuit can detect this distortion as user input. 
     One solution has been utilizing a stylus with a thick tip for writing on a display with a capacitive touchscreen. These types of passive solutions (i.e., those that are devoid of any circuitry) require thick tips that are sized to mimic the capacitance effect of a human finger. However, the thick tip makes it difficult for a writer to determine his written strokes and/or other device interface requirements (e.g., screen selections, tracking for games, etc.) during the writing exercise, because of the density of lines resulting from the thick tipped passive stylus are larger on an order of magnitude. Consequently, selection of icons on a smaller display screen of a smartphone, for example, may be less than accurate. 
     Another solution can employ an active stylus (i.e., a stylus incorporating circuitry) in other applications different from capacitive sensing, such as acoustic, thermal, optical, or resistive applications. However, each of these applications are uniquely distinct from the capacitive sensing approach. Notably, capacitive approaches have significant advantages that manufacturers have come to appreciate, including spatial needs within mobile communication devices and less complexity in electronic chipsets than acoustic or thermal, for example. Capacitive touchscreens have become the desirable choice for manufacturers of devices inclusive of any touch-sensitive interfaces. Accordingly, there is a need for a dual-mode active stylus that enables a user to be able to write on a capacitive touchscreen and paper with a single instrument. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The accompanying figures, where like reference numerals refer to identical or functionally similar elements throughout the separate views, together with the detailed description below, are incorporated in and form part of the specification, and serve to further illustrate embodiments of concepts that include the claimed invention, and explain various principles and advantages of those embodiments. 
         FIG. 1  exemplarily illustrates a dual mode active stylus in accordance with one or more embodiments. 
         FIG. 2  exemplarily illustrates an ink cartridge incorporated within the dual mode active stylus. 
         FIG. 3  exemplarily illustrates internal electronics in the dual mode active stylus. 
         FIG. 4  exemplarily illustrates a close up view of the writing tip portion of the dual mode active stylus. 
         FIG. 5  exemplarily illustrates segmented portions of the body of the retractable writing tip for the dual mode active stylus. 
         FIG. 6  exemplarily illustrates internal mechanisms for retractable writing tip for the dual mode active stylus. 
         FIG. 7  exemplarily illustrates external body for retractable writing tip for the dual mode active stylus. 
         FIG. 8  exemplarily illustrates ballpoint pen functions combined in a stylus tip for the dual mode active stylus. 
         FIG. 9  exemplarily illustrates one active stylus interacting with an electronic device having a touch-sensitive interface. 
         FIG. 10  exemplarily illustrates one active stylus configured to interact with a touch-sensitive interface. 
         FIG. 11  exemplarily illustrates a schematic block diagram of one active circuit suitable for use in a stylus. 
         FIG. 12  illustrates a stimulus received by a touch-sensitive device from a stylus that does not include an active circuit. 
         FIG. 13  illustrates a stimulus received by a touch-sensitive device from an active stylus comprised of electronic circuitry. 
         FIG. 14  illustrates two types of active styluses capable of coupling capacitively with a stylus user. 
         FIG. 15  illustrates the ability of a user to transfer from a paper writing surface to a touch-sensitive writing surface using one embodiment of the active stylus. 
         FIG. 16  illustrates the ability of a user to transfer from a paper writing surface to a touch-sensitive writing surface using another embodiment of the active stylus. 
     
    
    
     Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention. 
     The dual mode active stylus components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein. 
     DETAILED DESCRIPTION 
     An active stylus writing apparatus for writing on a capacitive touchscreen and paper is disclosed herein. The active stylus writing apparatus (hereinafter, “active stylus”) can include a conductive carrier that is coupled on a first end of the active stylus and that is also coupled and/or connected to internal circuitry for providing an active electrically charged capacitive field to simulate a human touch upon the capacitive touchscreen. The active stylus can also include a removable compound end cap, comprising at least two segments in one embodiment, for example, including a conductive segment. The removable compound end cap is configured to electrically couple to the conductive carrier when the end cap covers the conductive carrier on the first end of the active stylus. The compound end cap is conductive in at least one segment, such as at the cap tip; while the body of the end cap is non-conductive. 
     The active stylus disclosed herein offers several advantages. A clear advantage is that one writing instrument is useful for writing on touchscreen and paper. Therefore, there is no need to carry two writing instruments for users of a mobile communication device or of electronic office-type signage boards. The writing tip of the active stylus is smaller than the thick tip employed in passive style writing instruments for capacitive touchscreens, as well as for any other touch interfaces. As such, accuracy of selections of screen icons is greater and a user can easily discern their own writing strokes. Additionally, an active stylus may function without the need for direct contact to the touch screen corresponding to the tuning of the capacitive touch-sensitive interface; thereby, allowing sensing of gestures and depth sensing capabilities. 
     Embodiments of the present invention provide an active stylus configured for interaction with a touch-sensitive interface such as interface employing a capacitive touch sensor. The term “active” is used herein to refer to circuit components within the stylus that are powered by an electrical energy source, such as a battery or other power supply. Examples of active components include integrated circuits, operational amplifiers, comparators, buffers, inverters, and the like. This contrasts with “passive” components that do not require an energy source, examples of which include capacitors, resistors, inductors, and transmission lines. 
     The active styluses described herein include an active circuit and one or more electrodes. For example, a center electrode and a shroud electrode, disposed concentrically about the center electrode, are operable with an active circuit to “inject” charge into sensors disposed within a touch-sensitive display or interface. The injection of charge works to increase, or in some complementary embodiments decrease, the effective capacitance presented to a capacitively-enabled touch-sensitive device. 
     The electrodes of styluses described herein are configured to inject charge through a Miller capacitance created between the electrodes and the touch-sensitive device. Miller capacitance can be undesirable in some active circuits, in that it can compromise gain. However, when used in accordance with embodiments of the present invention, it works to increase (or in complementary embodiments decrease) the capacitive coupling between the stylus and the touch-sensitive display. It however needs to be noted that the art disclosed will work with other capacitive stylus approaches; i.e., not only w/ Miller effect based ones. 
       FIG. 1  exemplarily illustrates a dual mode active stylus  100 . The dual mode active stylus  100  can be used to write on capacitive touchscreens that are deployed in mobile communication device displays. Mobile communication devices can include, for example, smartphones, tablet computing devices, and electronic reading devices, referred to as e-readers. Other electronic devices that employ capacitive touchscreens, for example, electronic office-type signage boards or any other touch interface that can receive input information via a stylus will benefit from the active stylus  100 . Active stylus  100  includes a conductive carrier coupled on a first end of the active stylus writing apparatus, and also coupled to internal circuitry for providing an active electrically charged capacitive field to simulate a human touch upon the capacitive touchscreen. The conductive carrier may be configured to retain ink, pencil lead, light, or be formed by lead, for example. Another exemplary device may be a pointer combined with a capacitive stylus that is incapable of functioning as a writing device. The conductive carrier may be formed of metal or semi-conductive material. 
     Active stylus  100  includes a removable end cap  110  for protecting a ball point writing tip  120 , which is mechanically and electrically coupled to active stylus  100 . Removable end cap  110  also is equipped with a compound writing tip on the closed end of the cap (also referred to herein interchangeably as “compound writing cap tip” and “cap tip”). The compound writing cap tip is conductive and functional for writing on capacitive touchscreen surfaces. The cap tip may have many shapes, not only the depicted one. For example, the cap tip can employ a conventional bullet type shape. 
     Removable end cap  110  provides protection for the ball point writing tip  120  when removable cap  110  covers the ball point writing tip and is adjoined to active stylus  100 . Removable end cap  110  is segmented into at least two sections, a non-conductive section  112  and a conductive section  113 . Non-conductive section  112  isolates a ground connection corresponding to the user&#39;s position relative to Earth (i.e., user&#39;s ground) from conductive section  113 . Conductive section  113  enables the capacitive touch screen interaction and writing function of the active stylus  100  upon the capacitive touch screen. The conductive section  113  provides an active electrically charged capacitive field to simulate a human touch upon the capacitive touchscreen. The conductive section may be made of elastomer, plastic, metal, or a combination thereof. The capacitive touchscreen is protected from scratches or other unwanted marks that may be attributed to the ball point pen writing tip  120  of the active stylus  100 . Specifically, the removable cap  110  also protects the capacitive touchscreen from ink and metal shavings dispersed by ball point writing tip  120 . 
     One embodiment may employ an end cap tightness notification means including one or more of the following: an audible click, a color change, and gel expansion within the removable end cap. The compound cap tip  114  may be in direct contact w/ the writing tip  120 , or alternatively, in proximity of the writing tip  120 ; in which case electrical charge is transferred via capacitance. The compound cap tip  114  may be formed of many shapes, including the conventional bullet type shape as already noted. The compound cap tip  114  can be coated with or comprised of metallic particles to enhance conductivity. 
       FIG. 2  illustrates an internal view of ball point writing tip  120  within active stylus  100 . Ball point writing tip  120  is comprised of an elongated ink cartridge  125  of a predetermined diameter for residing within active stylus  100  along with a printed circuit board (PCB)  130  for active stylus  100 . One embodiment uses an ink cartridge having a writing tip of less than 2.5 millimeters. Design choices for length and diameter of the elongated ink cartridge  125  are many. Additionally, the size of PCB  130  can be varied as well to accommodate elongated ink cartridge  125  within the housing of active stylus  100 . PCB  130  is directly connected to the ink cartridge to provide a necessary electrical charge; however, there may be configurations where the electrical charge could be transferred by other means, such as a capacitive means. 
       FIG. 3  exemplarily illustrates additional internal components for active stylus  100 . Active stylus  100  can include within its housing an ink cartridge  125  having a ball point writing tip  120 ; a PCB  130  having control electronics and circuitry for enabling active stylus  100  to interact with a capacitive touchscreen; and a power supply  140 , which can be a battery, a solar panel, nano-electronics, a micro-electro mechanical grating system, or a piezoelectric element, for example. 
       FIG. 4  exemplarily illustrates one end of active stylus  100  having a stylus housing  150  in a capped mode  405 , wherein the removable cap  110  is providing protection to ball point pen writing tip  120 . The ball point pen writing tip  120  resides firmly within removable cap  110 . Removable cap  110  includes a conductive section  113  on the closed end of the removable cap to enable capacitive touchscreen writing and interaction.  FIG. 4  also shows the same end of active stylus  100  in an uncapped mode  410 , wherein the ball point writing tip  120  is uncovered and lacks the protection of removable cap  110 . The internal circuitry in the conductive carrier is selectably controllable by covering the first end of the conductive carrier with the removable end cap. 
       FIG. 5  exemplarily illustrates another embodiment for active stylus  100 . For example, active stylus  100  may include an electrically non-conductive body  510  or housing coupled to an electrically conductive tip  520  that holds an electrically conductive ink cartridge or lead  530 ; wherein the ink cartridge or lead  530  is capable of protruding from the end of the tip  520  of active stylus  100 ; and the end of the active stylus  100  is equipped or formed to function as a writing tip  520 . Internal to active stylus  100  is a power supply  140  on the far end of the active stylus  100  in relation to the tip of the active stylus  100 . The power supply may be coupled directly or indirectly to an electronics circuitry  130 . There exists a coupling from the ink cartridge to a conductive tip  520  for enabling capacitive touchscreen writing/interaction. An electro-conductive elastomer, plastic, metal, or their combination may be used for the conductive tip  520  to cause electrical coupling between the conductive carrier  1440  (further shown in  FIG. 14 ) of the active stylus and the conductive tip  520 . The conductive tip  520  can be coated with or comprised of metallic particles to enhance conductivity. 
       FIG. 6  exemplarily illustrates internal mechanisms for retractable writing tip for another embodiment of the dual mode active stylus. Active stylus  100  may include a retractable writing tip  120  comprised of a paper writing tool, such as an ink cartridge or pencil lead cartridge. Any well-known means of retracting the cartridges can be employed to form a retractable conductive carrier, for example a touch sensor, push-push mechanism, rotational mechanism, and other typical approaches for retractable ink cartridges. The same means of retracting or deploying the ink or pencil lead cartridges may be used to control the power circuitry of the active stylus  100 , i.e., turning the active stylus  100  off or on. 
       FIG. 7  exemplarily illustrates views of the external body for retractable writing tip for the dual mode active stylus  100 . In this embodiment, the body or housing of the active stylus  100  performs the function of interacting with a capacitive touchscreen by utilizing a touch sensor (not shown) near one end of the active stylus  100 . 
     Another embodiment of the dual mode active stylus  100  utilizes the writing tip  120  of an ink cartridge  125 , for example, as also a stylus tip for the capacitive touchscreen. Writing tip  120  directly touches the capacitive touchscreen when an internal touch sensor is activated. Special ink formulations may be used to provide ink that does not leave any undesirable marks on the capacitive touchscreen. In this embodiment, there is no need for a removable cap  110  or for the ball point writing tip  120  to retract. 
       FIG. 9  exemplarily illustrates the stylus of  FIG. 1  being used with an electronic device  900  that includes a touch-sensitive interface  910 . The illustrative touch-sensitive user interface  910  is a capacitive touch-sensitive user interface, although other technologies are contemplated and may be used. Capacitive touch-sensitive devices include a plurality of capacitive sensors, e.g., electrodes, which are disposed along a substrate. Each capacitive sensor is configured, in conjunction with associated control circuitry, to detect an object in close proximity with-or touching-the surface of the electronic device  900  by establishing electric field lines between pairs of capacitive sensors and then detecting perturbations or changes of those field lines. The electric field lines can be established in accordance with a periodic waveform, such as a square wave, sine wave, triangle wave, or other periodic waveform that is emitted by one sensor and detected by another. The capacitive sensors can be formed, for example, by disposing indium tin oxide patterned as electrodes on the substrate. Indium tin oxide is useful for such systems, because it is transparent and conductive. Further, it is capable of being deposited in thin layers by way of a printing process. The capacitive sensors may also be deposited on the substrate by electron beam evaporation, physical vapor deposition, or other various sputter deposition techniques. 
     A user  920  provides an electrical return path between the stylus  100  and the electronic device  900  as follows: Both the stylus  100  and electronic device  900  are capacitively coupled to the user  920  through the user&#39;s hands  922 ,  924 . The user  920  is also capacitively coupled to earth ground. This capacitive return to earth ground provides a reference point from which the compound tip  114  can inject charge into the touch-sensitive interface  910 . The compound tip  114  may be inclusive of the end cap  110  shown in  FIG. 1  or may be a part of the cartridge  125  as shown in  FIG. 8 . While a user  920  is shown holding the stylus  100  in  FIG. 9 , this need not be the case for the stylus  100  to work. Said differently, the stylus  100  also works when the electronic device  900  is somewhere other than in the user&#39;s hand  924 . For example, if the electronic device  900  were sitting on a non-conductive surface such as a wooden table rather than in the user&#39;s hand  924 , even though there is no direct return path to earth ground through the user&#39;s hand  204  and body in this instance, the wooden table and surrounding environment would still provide sufficient coupling to earth ground for the stylus  100  to work. 
     In the configuration shown in  FIG. 9 , the compound tip  114  “sniffs” electric field variations emitted from the touch-sensitive interface  910 . The active circuit of the stylus  100  applies gain, which in one embodiment is inverting and amplifying, and injects charge into the touch-sensitive interface  910  to alter the capacitance formed between the touch-sensitive interface  910  and the compound tip  114 . An advantage offered by the stylus  100  is that the electronic device  900  need not be configured with special software or application specific hardware components to detect the stylus&#39;s compound tip  114 . The Miller capacitance formed between the compound tip  114  and the touch-sensitive interface  910  works to increase the capacitive coupling between a signal source embedded within the electronic device  900  and the dynamic node of the compound tip  114 . 
     In one embodiment, the stylus  100  is configured with an energy harvesting circuit  105 . Since the power required to run the active circuit is relatively small, in a stylus having advanced power management the energy harvesting circuit  105  can be configured to draw power from the received electric field variations by way of capacitive coupling circuitry. In another embodiment, where the stylus includes a power supply  140 , such as a battery (exemplarily shown in  FIG. 3 ), the energy harvesting circuit  105  can be configured to periodically charge the battery, thereby extending its operable life. Alternate methods of harvesting energy may use a mechanical strain component or a heat sensor configured to absorb heat from the user&#39;s hand  922 , for example. In yet another embodiment, the stylus  100  can be configured with a micro-USB connector for harvesting power. 
     In one or more embodiments, the compound tip  114  is configured with a sensor, such as an optical sensor, mechanical sensor, or switch. In one embodiment in which the compound tip  114  may employ a center electrode, the sensor can be configured to detect the center electrode that comes directly in contact with, or very close to, the touch-sensitive interface  910 . In one or more embodiments, the sensor can be used to actuate the active circuit when the sensor detects that the center electrode is close to or directly in contact with the touch-sensitive interface  910 . Further, the sensor can be used to deactivate the active circuit when, or after, the stylus  100  is removed from the electronic device  900 . 
     In yet another embodiment, the stylus  100  includes a communication circuit  107  configured for communicating with a corresponding communication circuit disposed within the electronic device  900 . Examples of suitable communication circuits include Bluetooth, infrared, magnetic field modulation, acoustic, and Wi-Fi circuits. 
     The ability for the stylus  100  to communicate with the electronic device  900  enables the stylus  100  to obtain real-time phase information for scanning purposes. Rather than this information being detected by the compound tip  114 , it can be obtained from the communication circuit  107 . Where the communication circuit  107  is included, the communication circuit  107  provides dual-mode functionality in that one function of the stylus  100  can be initiated with charge injection from the compound tip  114 , while another is initiated by the communication circuit  107 . 
       FIG. 10  exemplarily illustrates a sectional view of one embodiment of the stylus  100  interacting with one embodiment of touch-sensitive interface  910 . The touch-sensitive interface  910  includes a touch-sensitive surface  1031 . A signal generator  1032  generates a periodic waveform  1007 , which can be a square wave, sine wave, triangle wave, or other periodic waveform. The periodic waveform  1007  establishes an electric field between the signal generator  1032  and an array  1033  of receive electrodes. Circuits  1034  and  1035  represent the capacitive coupling to earth ground provided by the user&#39;s hands ( 922 ,  924 ) in  FIG. 9 . 
     When the compound tip  114  of the stylus  100  is brought into close proximity with the touch-sensitive surface  1031 , a Miller capacitance  1036  is formed between the compound tip  114  and the touch-sensitive interface  910 . The center electrode  101 , which works here as a receive electrode, detects the electric field variations  1007 . The active circuit  103  then applies gain to the detected field variations and injects  1037  charge into the touch sensitive interface  910  by varying a potential of the end cap  110  or alternatively the concentrically aligned shroud electrode  102 , which works here as a transmit electrode. In one embodiment, the injection of charge occurs synchronously with the electric field variations detected by the receive electrode of the compound tip  114 . 
     In the illustrative embodiment of  FIG. 10 , the periodic waveform  1007  comprises positive transitions  1038  and negative transitions  1039  that establish electric field variations between the signal generator  1032  and the array  1033  of receive electrodes. The active circuit  103  can be configured to respond to these transitions in a variety of ways. For example, the active circuit  103  can be configured to inject  1037  charge only on a predetermined sequence of transitions. In one embodiment, the active circuit  103  is configured to inject  1037  charge only on the positive transitions  1038 . In another embodiment, the active circuit  103  is configured to inject  1037  charge only negative transitions  1039 . In another embodiment, the active circuit  103  is configured to inject  1037  charge only on every other positive transition  1038 . 
     Different responses to the electric field variations  1007  can be used to modify the charge injection  1037  so that the stylus  100  responds to some events while ignoring others. For instance, one implementation might inject negative charge after detecting a rising edge, and then inject negative charge after detecting the immediately following falling edge. Upon the next pair of rising and falling edges occurring, the compound tip  114  could be configured not to inject charge. In this way, the touch-sensitive interface  910  can distinguish the stylus  100  form a user&#39;s finger. 
     In one embodiment, the stylus  100  is configured with an optional force sensor  1050 . By changing the impedance of the electrical pathway between the active circuit  103  and either one or both of the center electrode  101  and shroud electrode  102  in response to force, it is possible to change the magnitude of the capacitive coupling by a corresponding amount. 
     In the illustrative embodiment of  FIG. 10 , the force sensor  1050  is shown as a mechanical force sensor, such as a spring, disposed between the center electrode  101  and the stylus body  104 . The force sensor  1050  can be used to activate the active circuit  103  when the center electrode  101  is in contact with the touch-sensitive interface surface  331 . In another embodiment, the active circuit can use output information from the force sensor  1050  to alter the magnitude of the injected charge as a function of forces detected by the force sensor  1050 . Accordingly, a user may be able to draw darker lines, for example, by applying more pressure. 
     It will be clear to those of ordinary skill in the art having the benefit of this disclosure that other sensors could be used with, or substituted for, the force sensor  1050 . Examples of these sensors include a switch, communication circuit, nano sensing technology, micro-electro mechanical systems, or an optical sensor. Additionally, piezoresitive elements may be disposed between the stylus body  104  and the center electrode  101 . In any of these embodiments, the force sensor  1050  enables the stylus  100  to deliver a varying capacitance based upon detected, applied force. This capability is well suited for applications such as signature recognition, in which user-applied force is a measurable biometric. 
     In one embodiment, the stylus  100  is configured to deliver a slant detection indication to the touch-sensitive interface  910 . This best illustrated by way of example. As shown in  FIG. 10 , the stylus  100  extends from the touch-sensitive surface  1031  at a downward angle. At the same time, the shroud electrode  102  has a conical shape. When the active circuit  103  injects  1037  charge, the lower side of the shroud electrode  102  is closer to the touch-sensitive surface  1031  than the upper side. Consequently, the charge  1040  injected by the lower side is greater than the charge  1041  injected by the upper side. The array  1033  of sensor electrodes with the touch-sensitive interface  910  can be configured to interpret this as a slant detection indication, and can use this information in manipulation of objects presented on the touch-sensitive interface  910 . The conical shape of the shroud electrode  102  ensures that the slant detection indication is linearly increasing as the stylus  100  is further inclined. 
       FIG. 11  exemplarily illustrates a schematic block diagram of one illustrative active circuit  103  configured in accordance with one or more embodiments of the invention. As shown in  FIG. 11 , the active circuit  103  comprises a buffer  1141  powered by a voltage source  1142 . The buffer  1141  has an input  1143  that is coupled to the center electrode  101 . An output  1144  of the buffer  1141  is coupled to the shroud electrode  102 . In the illustrative embodiment of  FIG. 11 , the gain of the buffer  1141  is negative such that rising edges detected by the center electrode  101  corresponds to negative charge injection by the shroud electrode  102 . 
     A voltage divider  1145  is coupled across the voltage source  1142 , with a central node  1146  of the voltage divider  1145  coupled to the input  1143  of the buffer  1141 . In one embodiment, the voltage divider  1145  is configured such that the potential established at the central node  1146  is set at a transition-threshold level of the buffer  1141 . This transition-threshold level is the voltage at which the output  1144  toggles from an active high state to an active low state or vice-versa. In one embodiment, the output  1144  of the buffer  1141  is coupled to the stylus body  104 . In this embodiment, circuit  1134  represents the coupling of the stylus body  104  to earth ground by way of the user&#39;s hand. 
     Referring again to  FIG. 10 , when the center electrode  101  detects a rising (positive) edge  1038  or a falling edge  1039  from the touch-sensitive interface  910 , the buffer  1141  toggles and changes the potential of the shroud electrode  102 . In the configuration of  FIG. 11 , negative charge is injected into the touch-sensitive interface  910  when a rising (or positive-going) edge is detected by the center electrode  101 . Likewise, a positive charge is injected into the touch-sensitive interface  910  when a falling (or negative-going) edge is detected by the center electrode  101 . This “bang-bang” action on rising and falling edges enhances the capacitive coupling between the compound tip  114  and the touch-sensitive interface  910 . 
       FIGS. 12 and 13  illustrate the charge detected by a stylus that does not include an active circuit coming into contact with a touch-sensitive interface, and a stylus configured in accordance with one or more embodiments disclose herein, respectively. In each figure, horizontal axes  1202 ,  1203  and  1302 ,  1303  represent the planar surface area of a touch-sensitive surface, while the vertical axes  1204 ,  1304  represent the magnitude of detection signals along that planar surface area. 
     Most prior art styluses either require advanced hardware and software in both the stylus and receiver, or are simply mechanical devices having no active circuitry.  FIG. 12  shows a charge detection peak  1201  of the latter, i.e., a fine-tipped stylus having no active circuit. Passive devices provide small touch signals, similar to that shown in  FIG. 12 . The actual signal delivered will change minutely based upon the width of the stylus tip. 
     By sharp contrast, the charge detection peak  1301  of embodiments disclosed herein is shown in  FIG. 13 . As shown, it is orders of magnitude higher than those presented by passive prior art styluses. Further, the compound tip of embodiments of the present invention can configured as a finer point, such as with a 2.5 millimeter center electrode or end cap writing tip, thereby closely resembling a ballpoint pen. 
       FIG. 14  illustrates two different type of styluses  100 . One stylus may be capped. The second stylus is retractable. However, both styluses  100  include a conductive section  1440  that enables the stylus to be capacitively responsive (i.e., “coupled”) to the body of a stylus user as the user engages with the stylus during writing. Notably, not all sections of stylus  100  need to be fully conductive, especially with strong tuning capabilities. Additional sections of stylus  100  were previously described above and include a non-conductive section  510 , a conductive tip  520  (for either coupling to an ink cartridge or a touch-sensitive interface or a stylus user&#39;s body during writing), and a conductive ink or lead cartridge  530 . 
       FIG. 15  illustrates the ability of a user to transfer from one writing surface such as a pad of paper to a second writing surface having a touch-sensitive interface while using a single writing instrument. The active stylus shown is a retractable type embodiment, wherein to write on paper the ballpoint pen tip as a part of an ink cartridge is exposed. The ink cartridges can be multi-colored. To write on or engage with or interact with a touch-sensitive interface on an electronic device, the user retracts the exposed ballpoint pen writing tip and instead uses the electrically conductive writing tip surrounding the ballpoint pen tip and that includes an opening for the ballpoint pen tip to enter and exit during upon control to retract pen or not. Control for retraction of ballpoint pen tip may be mechanical, optical, or electrical. 
       FIG. 16  illustrates the ability of a user to transfer from one writing surface such as a pad of paper to a second writing surface having a touch-sensitive interface while using a single writing instrument. The active stylus shown employs a removable end cap type embodiment, wherein to write on paper, the ballpoint pen tip as a part of an ink cartridge is exposed once the protective pen cap is removed from the end of the writing tip. The ink cartridges can be multi-colored. To use this embodiment to engage or interact with a touch-sensitive interface, a user places the protective end cap over the ballpoint pen writing tip and uses the protective end cap to write characters. 
     One embodiment of an active stylus enables a method for configuring the active stylus to write on paper and also an electronic touch-sensitive interface. The method includes detecting an electric field variation associated with a conductive carrier that is configured to retain ink or pencil lead in a cartridge; and applying a gain, with a circuit that is internal to the active stylus, to a signal corresponding to the electric field variation. The method also includes injecting charge from the internal circuit of the active stylus to the cartridge; and coupling the cartridge to a conductive segment of a removable compound end cap. 
     Another embodiment of an active stylus enables a method for configuring the active stylus to write both on paper and an electronic touch-sensitive interface, wherein the method includes detecting an electric field variation with a conductive carrier that is configured to retain a pen or pencil lead in an electrically conductive cartridge and applying a gain, with a circuit that is internal to the active stylus, to a signal corresponding to the electric field variation. The method also includes injecting charge from the internal circuit of the active stylus to the electrically conductive cartridge; and coupling the electrically conductive cartridge to a conductive tip of the pen or pencil lead. 
     The various embodiments described herein offer numerous advantages over prior art solutions. For instance, “gloved hand” operation is generally not supported by most touch-sensitive interfaces. The various styluses described herein permit gloved-hand operation. Additionally, while shown illustratively herein as a stylus, embodiments of the invention could also be configured as thimbles suitable for user wear under a glove, for incorporation into one or more fingertips of a glove, or other configurations. In any configuration, embodiments described herein increase capacitive coupling—even when the user is wearing gloves—so that the touch-sensitive interface can detect touches of the stylus. 
     Additionally, embodiments of the present invention provide stylus interaction that appears, to the touch-sensitive interface, as a “finger-touch.” In so doing, the styluses described herein can be used in conjunction with fingers to perform multi-finger gesture operations. 
     The several novel and inventive protective removable cap and retractable pen/pencil embodiments described above for an active stylus substantially differ from conventional protective caps for passive styluses. One difference can be in the material selection. Another difference can be in the ink cartridge proximity to the cap and writing tips or nubs of the stylus. For example, the protective cap for a passive stylus needs to be fully conductive, so that the stylus couples to the user&#39;s body. In addition, the protective cap tip typically needs to be comprised of conductive compliant material (such as elastomer) to be “visible” to a touch-sensitive interface, like a touchscreen, when pressure is applied (that is the tip gets compressed to create a larger contact area upon the surface of the touch-sensitive interface). The conductive areas of the passive stylus are connected to transfer the signal from the user&#39;s body to the touch screen. Alternatively, if the tip is made of solid material, it may require a large flat area for contacting the surface of the touch-sensitive interface. In addition, there is no concern about proximity between the ink cartridge and the protective cover cap tip or its other sections. All interface signals are conducted via the protective cap. 
     In sharp contrast, the protective cap for active stylus, as described above, preferably includes at least one section of the cap to be nonconductive and one other section of the cap (the writing tip) to be conductive. While the protective cap writing tip can be made of elastomer, it need not be as well. The nonconductive section of the protective cap electrically isolates the conductive body section of the stylus from the conductive cap writing tip when the protective cap is attached to the active stylus. This enables a capacitive return to earth ground with the user capacitively coupled to earth ground and the stylus body during a writing exercise. In addition, the active stylus includes detection of proximity of the ink cartridge to the cap writing tip to further enable capacitive coupling between ink cartridge and the cap writing tip. 
     Similarly, conventional design for passive stylus with retractable ink cartridges requires a conductive body section to be directly connected to the body&#39;s tip. This tip also needs to be made of conductive compliant material (e.g., elastomer) to be “visible” to the touchscreen upon pressing of the tip to the touchscreen surface. In addition, there is no concern over the proximity between the ink cartridge and the pen&#39;s tip. 
     In sharp contrast, the active stylus with retractable ink cartridge, as exemplarily described above, further includes isolating the pen&#39;s tip from the stylus&#39; conductive body section by placing a non-conductive section in between the conductive body section and the conductive pen tip. Additionally, the active stylus includes detection of proximity of the ink cartridge to the pen writing tip to further enable capacitive coupling between ink cartridge and the pen writing tip of the retractable embodiment. 
     In the foregoing specification, specific embodiments have been described. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the invention as set forth in the claims below. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of present teachings. 
     The benefits, advantages, solutions to problems, and any element(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential features or elements of any or all the claims. The invention is defined solely by the appended claims including any amendments made during the pendency of this application and all equivalents of those claims as issued. 
     Moreover in this document, relational terms such as first and second, top and bottom, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. The terms “comprises,” “comprising,” “has”, “having,” “includes”, “including,” “contains”, “containing” or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises, has, includes, contains a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by “comprises . . . a”, “has . . . a”, “includes . . . a”, “contains . . . a” does not, without more constraints, preclude the existence of additional identical elements in the process, method, article, or apparatus that comprises, has, includes, contains the element. The terms “a” and “an” are defined as one or more unless explicitly stated otherwise herein. The terms “substantially”, “essentially”, “approximately”, “about” or any other version thereof, are defined as being close to as understood by one of ordinary skill in the art, and in one non-limiting embodiment the term is defined to be within 10%, in another embodiment within 5%, in another embodiment within 1% and in another embodiment within 0.5%. The term “coupled” as used herein is defined as connected, although not necessarily directly and not necessarily mechanically. A device or structure that is “configured” in a certain way is configured in at least that way, but may also be configured in ways that are not listed. 
     It will be appreciated that some embodiments may be comprised of one or more generic or specialized processors (or “processing devices”) such as microprocessors, digital signal processors, customized processors and field programmable gate arrays (FPGAs) and unique stored program instructions (including both software and firmware) that control the one or more processors to implement, in conjunction with certain non-processor circuits, some, most, or all of the functions of the method and/or apparatus described herein. Alternatively, some or all functions could be implemented by a state machine that has no stored program instructions, or in one or more application specific integrated circuits (ASICs), in which each function or some combinations of certain of the functions are implemented as custom logic. Of course, a combination of the two approaches could be used. 
     Moreover, an embodiment can be implemented as a computer-readable storage medium having computer readable code stored thereon for programming a computer (e.g., comprising a processor) to perform a method as described and claimed herein. Likewise, computer-readable storage medium can comprise a non-transitory machine readable storage device, having stored thereon a computer program that include a plurality of code sections for performing operations, steps or a set of instructions. 
     Examples of such computer-readable storage mediums include, but are not limited to, a hard disk, a CD-ROM, an optical storage device, a magnetic storage device, a ROM (Read Only Memory), a PROM (Programmable Read Only Memory), an EPROM (Erasable Programmable Read Only Memory), an EEPROM (Electrically Erasable Programmable Read Only Memory) and a Flash memory. Further, it is expected that one of ordinary skill, notwithstanding possibly significant effort and many design choices motivated by, for example, available time, current technology, and economic considerations, when guided by the concepts and principles disclosed herein will be readily capable of generating such software instructions and programs and ICs with minimal experimentation. 
     The Abstract of the Disclosure is provided to allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. In addition, in the foregoing Detailed Description, it can be seen that various features are grouped together in various embodiments for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed embodiments require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter lies in less than all features of a single disclosed embodiment. Thus the following claims are hereby incorporated into the Detailed Description, with each claim standing on its own as a separately claimed subject matter.