Patent Publication Number: US-RE48614-E

Title: Dynamic adjustment of received signal threshold in an active stylus

Description:
RELATED APPLICATION 
     This application claims the benefit, under 35 U.S.C. §119(e), of U.S. Provisional Patent Application No. 61/553,114, filed 28 Oct. 2011, which is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     This disclosure generally relates to touch-position sensors. 
     BACKGROUND 
     A touch sensor may detect the presence and location of a touch or the proximity of an object (such as a user&#39;s finger or a stylus) within a touch-sensitive area of the touch sensor overlaid on a display screen, for example. In a touch-sensitive-display application, the touch sensor may enable a user to interact directly with what is displayed on the screen, rather than indirectly with a mouse or touch pad. A touch sensor may be attached to or provided as part of a desktop computer, laptop computer, tablet computer, personal digital assistant (PDA), smartphone, satellite navigation device, portable media player, portable game console, kiosk computer, point-of-sale device, or other suitable device. A control panel on a household or other appliance may include a touch sensor. There are a number of different types of touch sensors, such as, for example, resistive touch screens, surface acoustic wave touch screens, and capacitive touch screens. Herein, reference to a touch sensor may encompass a touch screen, and vice versa, where appropriate. When an object touches or comes within proximity of the surface of the capacitive touch screen, a change in capacitance may occur within the touch screen at the location of the touch or proximity. A touch-sensor controller may process the change in capacitance to determine its position on the touch screen. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an example touch sensor. 
         FIG. 2  illustrates an example active stylus exterior. 
         FIG. 3  illustrates an example active stylus interior. 
         FIG. 4  illustrates an example active stylus with touch sensor device. 
         FIG. 5  illustrates an example controller in an active stylus. 
         FIG. 6  illustrates an example method for adjusting a received signal threshold in an active stylus. 
         FIG. 7  illustrates an example method for filtering a signal received by an active stylus. 
         FIG. 8  illustrates an example filter in an active stylus. 
         FIG. 9  illustrates an example method for filtering a signal received by an active stylus. 
         FIG. 10  illustrates an example filter in an active stylus. 
         FIG. 11  illustrates an example method for filtering a signal received by an active stylus. 
         FIG. 12  illustrates an example filter in an active stylus. 
         FIG. 13  illustrates an example method for filtering a signal received by an active stylus. 
         FIG. 14  illustrates an example method for transmitting a signal from an active stylus to a device. 
     
    
    
     DESCRIPTION OF EXAMPLE EMBODIMENTS 
       FIG. 1  illustrates an example touch sensor  10  with an example touch-sensor controller  12 . Touch sensor  10  and touch-sensor controller  12  may detect the presence and location of a touch or the proximity of an object within a touch-sensitive area of touch sensor  10 . Herein, reference to a touch sensor may encompass both the touch sensor and its touch-sensor controller, where appropriate. Similarly, reference to a touch-sensor controller may encompass both the touch-sensor controller and its touch sensor, where appropriate. Touch sensor  10  may include one or more touch-sensitive areas, where appropriate. Touch sensor  10  may include an array of drive and sense electrodes (or an array of electrodes of a single type) disposed on one or more substrates, which may be made of a dielectric material. Herein, reference to a touch sensor may encompass both the electrodes of the touch sensor and the substrate(s) that they are disposed on, where appropriate. Alternatively, where appropriate, reference to a touch sensor may encompass the electrodes of the touch sensor, but not the substrate(s) that they are disposed on. 
     An electrode (whether a ground electrode, guard electrode, drive electrode, or sense electrode) may be an area of conductive material forming a shape, such as for example a disc, square, rectangle, thin line, other suitable shape, or suitable combination of these. One or more cuts in one or more layers of conductive material may (at least in part) create the shape of an electrode, and the area of the shape may (at least in part) be bounded by those cuts. In particular embodiments, the conductive material of an electrode may occupy approximately 100% of the area of its shape. As an example and not by way of limitation, an electrode may be made of indium tin oxide (ITO) and the ITO of the electrode may occupy approximately 100% of the area of its shape (sometimes referred to as a 100% fill), where appropriate. In particular embodiments, the conductive material of an electrode may occupy substantially less than 100% of the area of its shape. As an example and not by way of limitation, an electrode may be made of fine lines of metal or other conductive material (FLM), such as for example copper, silver, or a copper- or silver-based material, and the fine lines of conductive material may occupy approximately 5% of the area of its shape in a hatched, mesh, or other suitable pattern. Herein, reference to FLM encompasses such material, where appropriate. Although this disclosure describes or illustrates particular electrodes made of particular conductive material forming particular shapes with particular fill percentages having particular patterns, this disclosure contemplates any suitable electrodes made of any suitable conductive material forming any suitable shapes with any suitable fill percentages having any suitable patterns. 
     Where appropriate, the shapes of the electrodes (or other elements) of a touch sensor may constitute in whole or in part one or more macro-features of the touch sensor. One or more characteristics of the implementation of those shapes (such as, for example, the conductive materials, fills, or patterns within the shapes) may constitute in whole or in part one or more micro-features of the touch sensor. One or more macro-features of a touch sensor may determine one or more characteristics of its functionality, and one or more micro-features of the touch sensor may determine one or more optical features of the touch sensor, such as transmittance, refraction, or reflection. 
     A mechanical stack may contain the substrate (or multiple substrates) and the conductive material forming the drive or sense electrodes of touch sensor  10 . As an example and not by way of limitation, the mechanical stack may include a first layer of optically clear adhesive (OCA) beneath a cover panel. The cover panel may be clear and made of a resilient material suitable for repeated touching, such as for example glass, polycarbonate, or poly(methyl methacrylate) (PMMA). This disclosure contemplates any suitable cover panel made of any suitable material. The first layer of OCA may be disposed between the cover panel and the substrate with the conductive material forming the drive or sense electrodes. The mechanical stack may also include a second layer of OCA and a dielectric layer (which may be made of PET or another suitable material, similar to the substrate with the conductive material forming the drive or sense electrodes). As an alternative, where appropriate, a thin coating of a dielectric material may be applied instead of the second layer of OCA and the dielectric layer. The second layer of OCA may be disposed between the substrate with the conductive material making up the drive or sense electrodes and the dielectric layer, and the dielectric layer may be disposed between the second layer of OCA and an air gap to a display of a device including touch sensor  10  and touch-sensor controller  12 . As an example only and not by way of limitation, the cover panel may have a thickness of approximately 1 mm; the first layer of OCA may have a thickness of approximately 0.05 mm; the substrate with the conductive material forming the drive or sense electrodes may have a thickness of approximately 0.05 mm; the second layer of OCA may have a thickness of approximately 0.05 mm; and the dielectric layer may have a thickness of approximately 0.05 mm. Although this disclosure describes a particular mechanical stack with a particular number of particular layers made of particular materials and having particular thicknesses, this disclosure contemplates any suitable mechanical stack with any suitable number of any suitable layers made of any suitable materials and having any suitable thicknesses. As an example and not by way of limitation, in particular embodiments, a layer of adhesive or dielectric may replace the dielectric layer, second layer of OCA, and air gap described above, with there being no air gap to the display. 
     One or more portions of the substrate of touch sensor  10  may be made of polyethylene terephthalate (PET) or another suitable material. This disclosure contemplates any suitable substrate with any suitable portions made of any suitable material. In particular embodiments, the drive or sense electrodes in touch sensor  10  may be made of ITO in whole or in part. In particular embodiments, the drive or sense electrodes in touch sensor  10  may be made of fine lines of metal or other conductive material. As an example and not by way of limitation, one or more portions of the conductive material may be copper or copper-based and have a thickness of approximately 5 μm or less and a width of approximately 10 μm or less. As another example, one or more portions of the conductive material may be silver or silver-based and similarly have a thickness of approximately 5 μm or less and a width of approximately 10 μm or less. This disclosure contemplates any suitable electrodes made of any suitable material. 
     Touch sensor  10  may implement a capacitive form of touch sensing. In a mutual-capacitance implementation, touch sensor  10  may include an array of drive and sense electrodes forming an array of capacitive nodes. A drive electrode and a sense electrode may form a capacitive node. The drive and sense electrodes forming the capacitive node may come near each other, but not make electrical contact with each other. Instead, the drive and sense electrodes may be capacitively coupled to each other across a space between them. A pulsed or alternating voltage applied to the drive electrode (by touch-sensor controller  12 ) may induce a charge on the sense electrode, and the amount of charge induced may be susceptible to external influence (such as a touch or the proximity of an object). When an object touches or comes within proximity of the capacitive node, a change in capacitance may occur at the capacitive node and touch-sensor controller  12  may measure the change in capacitance. By measuring changes in capacitance throughout the array, touch-sensor controller  12  may determine the position of the touch or proximity within the touch-sensitive area(s) of touch sensor  10 . 
     In a self-capacitance implementation, touch sensor  10  may include an array of electrodes of a single type that may each form a capacitive node. When an object touches or comes within proximity of the capacitive node, a change in self-capacitance may occur at the capacitive node and controller  12  may measure the change in capacitance, for example, as a change in the amount of charge needed to raise the voltage at the capacitive node by a pre-determined amount. As with a mutual-capacitance implementation, by measuring changes in capacitance throughout the array, controller  12  may determine the position of the touch or proximity within the touch-sensitive area(s) of touch sensor  10 . This disclosure contemplates any suitable form of capacitive touch sensing, where appropriate. 
     In particular embodiments, one or more drive electrodes may together form a drive line running horizontally or vertically or in any suitable orientation. Similarly, one or more sense electrodes may together form a sense line running horizontally or vertically or in any suitable orientation. In particular embodiments, drive lines may run substantially perpendicular to sense lines. Herein, reference to a drive line may encompass one or more drive electrodes making up the drive line, and vice versa, where appropriate. Similarly, reference to a sense line may encompass one or more sense electrodes making up the sense line, and vice versa, where appropriate. 
     Touch sensor  10  may have drive and sense electrodes disposed in a pattern on one side of a single substrate. In such a configuration, a pair of drive and sense electrodes capacitively coupled to each other across a space between them may form a capacitive node. For a self-capacitance implementation, electrodes of only a single type may be disposed in a pattern on a single substrate. In addition or as an alternative to having drive and sense electrodes disposed in a pattern on one side of a single substrate, touch sensor  10  may have drive electrodes disposed in a pattern on one side of a substrate and sense electrodes disposed in a pattern on another side of the substrate. Moreover, touch sensor  10  may have drive electrodes disposed in a pattern on one side of one substrate and sense electrodes disposed in a pattern on one side of another substrate. In such configurations, an intersection of a drive electrode and a sense electrode may form a capacitive node. Such an intersection may be a location where the drive electrode and the sense electrode “cross” or come nearest each other in their respective planes. The drive and sense electrodes do not make electrical contact with each other—instead they are capacitively coupled to each other across a dielectric at the intersection. Although this disclosure describes particular configurations of particular electrodes forming particular nodes, this disclosure contemplates any suitable configuration of any suitable electrodes forming any suitable nodes. Moreover, this disclosure contemplates any suitable electrodes disposed on any suitable number of any suitable substrates in any suitable patterns. 
     As described above, a change in capacitance at a capacitive node of touch sensor  10  may indicate a touch or proximity input at the position of the capacitive node. Touch-sensor controller  12  may detect and process the change in capacitance to determine the presence and location of the touch or proximity input. Touch-sensor controller  12  may then communicate information about the touch or proximity input to one or more other components (such one or more central processing units (CPUs)) of a device that includes touch sensor  10  and touch-sensor controller  12 , which may respond to the touch or proximity input by initiating a function of the device (or an application running on the device). Although this disclosure describes a particular touch-sensor controller having particular functionality with respect to a particular device and a particular touch sensor, this disclosure contemplates any suitable touch-sensor controller having any suitable functionality with respect to any suitable device and any suitable touch sensor. 
     Touch-sensor controller  12  may be one or more integrated circuits (ICs), such as for example general-purpose microprocessors, microcontrollers, programmable logic devices (PLDs) or programmable logic arrays (PLAs), application-specific ICs (ASICs). In particular embodiments, touch-sensor controller  12  comprises analog circuitry, digital logic, and digital non-volatile memory. In particular embodiments, touch-sensor controller  12  is disposed on a flexible printed circuit (FPC) bonded to the substrate of touch sensor  10 , as described below. The FPC may be active or passive, where appropriate. In particular embodiments multiple touch-sensor controllers  12  are disposed on the FPC. Touch-sensor controller  12  may include a processor unit, a drive unit, a sense unit, and a storage unit. The drive unit may supply drive signals to the drive electrodes of touch sensor  10 . The sense unit may sense charge at the capacitive nodes of touch sensor  10  and provide measurement signals to the processor unit representing capacitances at the capacitive nodes. The processor unit may control the supply of drive signals to the drive electrodes by the drive unit and process measurement signals from the sense unit to detect and process the presence and location of a touch or proximity input within the touch-sensitive area(s) of touch sensor  10 . The processor unit may also track changes in the position of a touch or proximity input within the touch-sensitive area(s) of touch sensor  10 . The storage unit may store programming for execution by the processor unit, including programming for controlling the drive unit to supply drive signals to the drive electrodes, programming for processing measurement signals from the sense unit, and other suitable programming, where appropriate. Although this disclosure describes a particular touch-sensor controller having a particular implementation with particular components, this disclosure contemplates any suitable touch-sensor controller having any suitable implementation with any suitable components. 
     Tracks  14  of conductive material disposed on the substrate of touch sensor  10  may couple the drive or sense electrodes of touch sensor  10  to connection pads  16 , also disposed on the substrate of touch sensor  10 . As described below, connection pads  16  facilitate coupling of tracks  14  to touch-sensor controller  12 . Tracks  14  may extend into or around (e.g. at the edges of) the touch-sensitive area(s) of touch sensor  10 . Particular tracks  14  may provide drive connections for coupling touch-sensor controller  12  to drive electrodes of touch sensor  10 , through which the drive unit of touch-sensor controller  12  may supply drive signals to the drive electrodes. Other tracks  14  may provide sense connections for coupling touch-sensor controller  12  to sense electrodes of touch sensor  10 , through which the sense unit of touch-sensor controller  12  may sense charge at the capacitive nodes of touch sensor  10 . Tracks  14  may be made of fine lines of metal or other conductive material. As an example and not by way of limitation, the conductive material of tracks  14  may be copper or copper-based and have a width of approximately 100 μm or less. As another example, the conductive material of tracks  14  may be silver or silver-based and have a width of approximately 100 μm or less. In particular embodiments, tracks  14  may be made of ITO in whole or in part in addition or as an alternative to fine lines of metal or other conductive material. Although this disclosure describes particular tracks made of particular materials with particular widths, this disclosure contemplates any suitable tracks made of any suitable materials with any suitable widths. In addition to tracks  14 , touch sensor  10  may include one or more ground lines terminating at a ground connector (which may be a connection pad  16 ) at an edge of the substrate of touch sensor  10  (similar to tracks  14 ). 
     Connection pads  16  may be located along one or more edges of the substrate, outside the touch-sensitive area(s) of touch sensor  10 . As described above, touch-sensor controller  12  may be on an FPC. Connection pads  16  may be made of the same material as tracks  14  and may be bonded to the FPC using an anisotropic conductive film (ACF). Connection  18  may include conductive lines on the FPC coupling touch-sensor controller  12  to connection pads  16 , in turn coupling touch-sensor controller  12  to tracks  14  and to the drive or sense electrodes of touch sensor  10 . In another embodiment, connection pads  16  may be connected to an electro-mechanical connector (such as a zero insertion force wire-to-board connector); in this embodiment, connection  18  may not need to include an FPC. This disclosure contemplates any suitable connection  18  between touch-sensor controller  12  and touch sensor  10 . 
       FIG. 2  illustrates an example exterior of an example active stylus  20 . Active stylus  20  may include one or more components, such as buttons  30  or sliders  32  and  34  integrated with an outer body  22 . These external components may provide for interaction between active stylus  20  and a user or between a device and a user. As an example and not by way of limitation, interactions may include communication between active stylus  20  and a device, enabling or altering functionality of active stylus  20  or a device, or providing feedback to or accepting input from one or more users. The device may by any suitable device, such as, for example and without limitation, a desktop computer, laptop computer, tablet computer, personal digital assistant (PDA), smartphone, satellite navigation device, portable media player, portable game console, kiosk computer, point-of-sale device, or other suitable device. Although this disclosure provides specific examples of particular components configured to provide particular interactions, this disclosure contemplates any suitable component configured to provide any suitable interaction. Active stylus  20  may have any suitable dimensions with outer body  22  made of any suitable material or combination of materials, such as, for example and without limitation, plastic or metal. In particular embodiments, exterior components (e.g.  30  or  32 ) of active stylus  20  may interact with internal components or programming of active stylus  20  or may initiate one or more interactions with one or more devices or other active styluses  20 . 
     As described above, actuating one or more particular components may initiate an interaction between active stylus  20  and a user or between the device and the user. Components of active stylus  20  may include one or more buttons  30  or one or more sliders  32  and  34 . As an example and not by way of limitation, buttons  30  or sliders  32  and  34  may be mechanical or capacitive and may function as a roller, trackball, or wheel. As another example, one or more sliders  32  or  34  may function as a vertical slider  34  aligned along a longitudinal axis, while one or more wheel sliders  32  may be aligned along the circumference of active stylus  20 . In particular embodiments, capacitive sliders  32  and  34  or buttons  30  may be implemented using one or more touch-sensitive areas. Touch-sensitive areas may have any suitable shape, dimensions, location, or be made from any suitable material. As an example and not by way of limitation, sliders  32  and  34  or buttons  30  may be implemented using areas of flexible mesh formed using lines of conductive material. As another example, sliders  32  and  34  or buttons  30  may be implemented using a FPC. 
     Active stylus  20  may have one or more components configured to provide feedback to or accepting feedback from a user, such as, for example and without limitation, tactile, visual, or audio feedback. Active stylus  20  may include one or more ridges or grooves  24  on its outer body  22 . Ridges or grooves  24  may have any suitable dimensions, have any suitable spacing between ridges or grooves, or be located at any suitable area on outer body  22  of active stylus  20 . As an example and not by way of limitation, ridges  24  may enhance a user&#39;s grip on outer body  22  of active stylus  20  or provide tactile feedback to or accept tactile input from a user. Active stylus  20  may include one or more audio components  38  capable of transmitting and receiving audio signals. As an example and not by way of limitation, audio component  38  may contain a microphone capable of recording or transmitting one or more users&#39;voices. As another example, audio component  38  may provide an auditory indication of a power status of active stylus  20 . Active stylus  20  may include one or more visual feedback components  36 , such as a light-emitting diode (LED) indicator. As an example and not by way of limitation, visual feedback component  36  may indicate a power status of active stylus  20  to the user. 
     One or more modified surface areas  40  may form one or more components on outer body  22  of active stylus  20 . Properties of modified surface areas  40  may be different than properties of the remaining surface of outer body  22 . As an example and not by way of limitation, modified surface area  40  may be modified to have a different texture, temperature, or electromagnetic characteristic relative to the surface properties of the remainder of outer body  22 . Modified surface area  40  may be capable of dynamically altering its properties, for example by using haptic interfaces or rendering techniques. A user may interact with modified surface area  40  to provide any suitable functionally. For example and not by way of limitation, dragging a finger across modified surface area  40  may initiate an interaction, such as data transfer, between active stylus  20  and a device. 
     One or more components of active stylus  20  may be configured to communicate data between active stylus  20  and the device. For example, active stylus  20  may include one or more tips  26  or nibs. Tip  26  may include one or more electrodes configured to communicate data between active stylus  20  and one or more devices or other active styluses. Tip  26  may be made of any suitable material, such as a conductive material, and have any suitable dimensions, such as, for example, a diameter of 1 mm or less at its terminal end. Active stylus  20  may include one or more ports  28  located at any suitable location on outer body  22  of active stylus  20 . Port  28  may be configured to transfer signals or information between active stylus  20  and one or more devices or power sources. Port  28  may transfer signals or information by any suitable technology, such as, for example, by universal serial bus (USB) or Ethernet connections. Although this disclosure describes and illustrates a particular configuration of particular components with particular locations, dimensions, composition and functionality, this disclosure contemplates any suitable configuration of suitable components with any suitable locations, dimensions, composition, and functionality with respect to active stylus  20 . 
       FIG. 3  illustrates an example internal components of example active stylus  20 . Active stylus  20  may include one or more internal components, such as a controller  50 , sensors  42 , memory  44 , or power source  48 . In particular embodiments, one or more internal components may be configured to provide for interaction between active stylus  20  and a user or between a device and a user. In other particular embodiments, one or more internal components, in conjunction with one or more external components described above, may be configured to provide interaction between active stylus  20  and a user or between a device and a user. As an example and not by way of limitation, interactions may include communication between active stylus  20  and a device, enabling or altering functionality of active stylus  20  or a device, or providing feedback to or accepting input from one or more users. 
     Controller  50  may be a microcontroller or any other type of processor suitable for controlling the operation of active stylus  20 . Controller  50  may be one or more ICs—such as, for example, general-purpose microprocessors, microcontrollers, PLDs, PLAs, or ASICs. Controller  50  may include a processor unit, a drive unit, a sense unit, and a storage unit. The drive unit may supply signals to electrodes of tip  26  through center shaft  41 . The drive unit may also supply signals to control or drive sensors  42  or one or more external components of active stylus  20 . The sense unit may sense signals received by electrodes of tip  26  through center shaft  41  and provide measurement signals to the processor unit representing input from a device. The sense unit may also sense signals generated by sensors  42  or one or more external components and provide measurement signals to the processor unit representing input from a user. The processor unit may control the supply of signals to the electrodes of tip  26  and process measurement signals from the sense unit to detect and process input from the device. The processor unit may also process measurement signals from sensors  42  or one or more external components. The storage unit may store programming for execution by the processor unit, including programming for controlling the drive unit to supply signals to the electrodes of tip  26 , programming for processing measurement signals from the sense unit corresponding to input from the device, programming for processing measurement signals from sensors  42  or external components to initiate a pre-determined function or gesture to be performed by active stylus  20  or the device, and other suitable programming, where appropriate. As an example and not by way of limitation, programming executed by controller  50  may electronically filter signals received from the sense unit. Although this disclosure describes a particular controller  50  having a particular implementation with particular components, this disclosure contemplates any suitable controller having any suitable implementation with any suitable components. 
     In particular embodiments, active stylus  20  may include one or more sensors  42 , such as touch sensors, gyroscopes, accelerometers, contact sensors, or any other type of sensor that detect or measure data about the environment in which active stylus  20  operates. Sensors  42  may detect and measure one or more characteristic of active stylus  20 , such as acceleration or movement, orientation, contact, pressure on outer body  22 , force on tip  26 , vibration, or any other suitable characteristic of active stylus  20 . As an example and not by way of limitation, sensors  42  may be implemented mechanically, electronically, or capacitively. As described above, data detected or measured by sensors  42  communicated to controller  50  may initiate a pre-determined function or gesture to be performed by active stylus  20  or the device. In particular embodiments, data detected or received by sensors  42  may be stored in memory  44 . Memory  44  may be any form of memory suitable for storing data in active stylus  20 . In other particular embodiments, controller  50  may access data stored in memory  44 . As an example and not by way of limitation, memory  44  may store programming for execution by the processor unit of controller  50 . As another example, data measured by sensors  42  may be processed by controller  50  and stored in memory  44 . 
     Power source  48  may be any type of stored-energy source, including electrical or chemical-energy sources, suitable for powering the operation of active stylus  20 . In particular embodiments, power source  48  may be charged by energy from a user or device. As an example and not by way of limitation, power source  48  may be a rechargeable battery that may be charged by motion induced on active stylus  20 . In other particular embodiments, power source  48  of active stylus  20  may provide power to or receive power from the device. As an example and not by way of limitation, power may be inductively transferred between power source  48  and a power source of the device. 
       FIG. 4  illustrates an example active stylus  20  with an example device  52 . Device  52  may have a display (not shown) and a touch sensor with a touch-sensitive area  54 . Device  52  display may be a liquid crystal display (LCD), a LED display, a LED-backlight LCD, or other suitable display and may be visible though a cover panel and substrate (and the drive and sense electrodes of the touch sensor disposed on it) of device  52 . Although this disclosure describes a particular device display and particular display types, this disclosure contemplates any suitable device display and any suitable display types. 
     Device  52  electronics may provide the functionality of device  52 . As example and not by way of limitation, device  52  electronics may include circuitry or other electronics for wireless communication to or from device  52 , execute programming on device  52 , generating graphical or other user interfaces (UIs) for device  52  display to display to a user, managing power to device  52  from a battery or other power source, taking still pictures, recording video, other suitable functionality, or any suitable combination of these. Although this disclosure describes particular device electronics providing particular functionality of a particular device, this disclosure contemplates any suitable device electronics providing any suitable functionality of any suitable device. 
     In particular embodiments, active stylus  20  and device  52  may be synchronized prior to communication of data between active stylus  20  and device  52 . As an example and not by way of limitation, active stylus  20  may be synchronized to device through a pre-determined bit sequence transmitted by the touch sensor of device  52 . As another example, active stylus  20  may be synchronized to device by processing the drive signal transmitted by drive electrodes of the touch sensor of device  52 . Active stylus  20  may interact or communicate with device  52  when active stylus  20  is brought in contact with or in proximity to touch-sensitive area  54  of the touch sensor of device  52 . In particular embodiments, interaction between active stylus  20  and device  52  may be capacitive or inductive. As an example and not by way of limitation, when active stylus  20  is brought in contact with or in the proximity of touch-sensitive area  54  of device  52 , signals generated by active stylus  20  may influence capacitive nodes of touch-sensitive area of device  52  or vice versa. As another example, a power source of active stylus  20  may be inductively charged through the touch sensor of device  52 , or vice versa. Although this disclosure describes particular interactions and communications between active stylus  20  and device  52 , this disclosure contemplates any suitable interactions and communications through any suitable means, such as mechanical forces, current, voltage, or electromagnetic fields. 
     In particular embodiments, measurement signal from the sensors of active stylus  20  may initiate, provide for, or terminate interactions between active stylus  20  and one or more devices  52  or one or more users, as described above. Interaction between active stylus  20  and device  52  may occur when active stylus  20  is contacting or in proximity to device  52 . As an example and not by way of limitation, a user may perform a gesture or sequence of gestures, such as shaking or inverting active stylus  20 , whilst active stylus  20  is hovering above touch-sensitive area  54  of device  52 . Active stylus may interact with device  52  based on the gesture performed with active stylus  20  to initiate a predetermined function, such as authenticating a user associated with active stylus  20  or device  52 . Although this disclosure describes particular movements providing particular types of interactions between active stylus  20  and device  52 , this disclosure contemplates any suitable movement influencing any suitable interaction in any suitable way. 
     Active stylus  20  may receive signals from external sources, including device  52 , a user, or another active stylus. Active stylus  20  may encounter noise when receiving such signals. As examples, noise may be introduced into the received signals from data quantization, limitations of position-calculation algorithms, bandwidth limitations of measurement hardware, accuracy limitations of analog front ends of devices with which active stylus  20  communicates, the physical layout of the system, sensor noise, charger noise, device noise, stylus circuitry noise, or external noise. The overall noise external to active stylus  20  may have frequency characteristics covering a wide range of the spectrum, including narrow band noise and wide band noise, as well. 
     Active stylus  20  may transmit signals based in part on the determination that it has received a signal, and not simply noise, from a signal source. As an example, active stylus  20  may determine whether it has received a signal from device  52  by comparing the received signal to a signal threshold. If the received signal satisfies the threshold requirement (e.g., meets the minimum value of this signal threshold), active stylus  20  may process the received signal, including, for example, amplifying or phase-shifting the received signal, in order to create a transmit signal to transmit back to device  52 . It may be desirable for active stylus  20  to, for example, dynamically adjust the threshold for determining that a received signal contains a signal from device  52 , or any other signal source, and not merely noise. As an example, if the signal threshold is too low, active stylus  20  may incorrectly determine that a pure noise signal is actually a signal from device  52 , proceed to process the noise signal, and incorrectly transmit a response signal. As another example, if signal threshold is too high, active stylus  20  may incorrectly determine that a signal from device  52  is purely a noise signal and fail to process the received signal and transmit a response signal. The threshold adjustment may be based on some factors and may be done dynamically. 
       FIG. 5  illustrates an example controller  50 , which may be incorporated in an active stylus (e.g., active stylus  20 ). In particular embodiments, a signal S is received by one or more electrodes capable of sensing signals in active stylus  20 . These electrodes may reside on active stylus tip  26 . In other embodiments, signal S is received by another component of active stylus  20 , including, for example, a radio frequency receiver. The signal S received by the electrodes in active stylus  20  may then be transmitted from the electrodes to controller  50 . In particular embodiments, signal S is transmitted to controller  50  via center shaft  41 . Controller  50 , as discussed above, may include, without limitation, a drive unit, a sense unit, a storage unit, and a processor unit. The components illustrated in  FIG. 5  may reside in controller  50 , and in certain embodiments may be a part of the processor unit of controller  50 . 
     In particular embodiments including the one illustrated by  FIG. 5 , received signal S may be amplified by an amplifier  100 . Amplifier  100  may be any suitable amplifier, including a digital or an analog amplifier. After the signal S is amplified, it may be filtered by a filter  200 . In some embodiments, filter  200  may be an analog filter including analog circuit components, such as one or more resistors, capacitors, or inductors. In other embodiments, filter  200  may be a digital filter, such as a finite-impulse-response (FIR) filter, or a Kalman filter implemented, for example, on a processor. Filter  200  may be any suitable filter for any type of processing of the received signal (e.g., signal S), including, for example, a filter for noise removal. Filter  200  may be, for example and without limitation, a low pass filter, a band pass filter, or a high pass filter. In particular embodiments, filter  200  may be a band pass filter whose frequency characteristics are designed to attenuate noise and amplify a signal. Filter  200  may also be used to boost signal strength of the received signal at active stylus  20 . 
     Referring to  FIG. 5 , amplified and/or filtered signal S, denoted S_filter, proceeds to control processor  300 . Control processor  300  may be a microcontroller. Control processor  300  includes comparator  310  and processor  320 . Comparator  310  may, in particular embodiments, be an analog comparator, including analog circuitry. In other embodiments, comparator  310  may be a digital comparator, and in yet other embodiments, comparator  310  may be a processor. Comparator  310  receives as input S_filter. Comparator  310  then compares S_filter to at least one signal threshold to determine whether S_filter represents noise alone or a received signal in addition to noise. As an example, if S_filter is a voltage, comparator  310  compares S_filter to a voltage threshold value V_th to determine whether S_filter is less than, equal to, or greater than V_th. In this example, if S_filter is equal to or greater than V_th, comparator  310  determines that S_filter contains a signal, and not merely noise, and outputs this determination to processor  320  via output line  330 . In particular embodiments, if S_filter meets or exceeds the signal threshold V_th, processor  320  may then output S_filter for further processing by active stylus  20 . In addition to having a signal threshold V_th, comparator  310  may also have a threshold for diagnostic purposes. As an example, comparator  310  may have a second threshold, V_diag, with a value different from V_th, and the output of a comparison of S_filter and V_diag is sent to processor  320  via output line  340 . In this example, the determination by comparator  310  whether S_filter meets or exceeds signal threshold V_th controls whether or not S_filter is processed further by active stylus  20 , and the determination whether S_filter meets or exceeds diagnostic threshold V_diag allows processor  320  to determine future values of V_th or V_diag. 
     In the example embodiment of  FIG. 5 , comparator  310  may also output additional data to processor  320 . Comparator  310  may analyze S_filter and output any type of information about S_filter to processor  320  via output line  340 . As an example, comparator  310  may calculate the signal-to-noise ratio (SNR) of S_filter and send this information to processor  320 . As another example, comparator  310  may determine the amplitude characteristics of S_filter and send this to processor  320 . As yet another example, comparator  310  may determine the frequency characteristics of S_filter, including the bandwidth of S_filter, and send this to processor  320 . As yet another example, comparator  310  may determine the phase characteristics of S_filter and send this to processor  320 . As yet another example, comparator  310  may determine whether a digital or analog signature or pattern is present or absent in S_filter and send this information to processor  320 . Output line  340  may carry one or more signals containing any type of relevant information about S_filter from comparator  310  to processor  320 . 
     As illustrated in the example embodiment of  FIG. 5 , processor  320  receives data from comparator  310  via output lines  330  and  340 . Processor  320  may adjust threshold V_th or V_diag based on the data received from comparator  310 . Additionally, processor  320  may adjust V_th or V_diag based on data received from any other components of active stylus  20 , including other parts of controller  50  (such as the sense unit, drive unit, storage unit, or processor unit), memory  44 , power source  48 , or sensors  42 . Processor  320  may send adjusted threshold values of V_th and V_diag to comparator  310  via output line  350 . Additionally, processor  320  may send other types of data to comparator  310  via output line  350  or additional output lines, including, for example, SNR cutoff values. Although  FIG. 5  illustrates a particular embodiment in which processor  320  receives data from comparator  310 , processor  320  may also receive data from or send data to any part of active stylus  20 . As an example, processor  320  may receive data regarding known characteristics (such as bandwidth, frequency, phase, amplitude, or synchronization patterns) of the signal of interest transmitted by a signal source such as device  52 . As another example, processor  320  may receive data regarding the mode in which active stylus  20  is operating (such as, for example, a hover mode). 
     In particular embodiments, processor  320  may adjust V_th so that V_th is approximately proportional to the SNR of S_filter. As an example, if the SNR of S_filter is high, as may be the case when active stylus  20  is near to a signal source like device  52 , processor  320  may adjust V_th upward, so that the new value of V_th is higher than the old value of V_th. This may allow for improved noise rejection by active stylus  20 . As another example, if the SNR of S_filter is low or if the amplitude of S_filter is low, as may be the case when active stylus  20  is far from a signal source like device  52 , processor  320  may adjust V_th downward, so that the new value of V_th is lower than the old value of V_th. This may allow for improved signal detection by active stylus  20  in low SNR or low amplitude situations. 
     In other embodiments, if processor  320  determines that comparator  310  is falsely triggering too frequently on S_filter (that is, if comparator  310  too frequently incorrectly determines that S_filter contains a signal when S_filter is purely noise), processor  320  may increase V_th to improve noise rejection. False triggering may occur more frequently in very low SNR situations where the amplitude or frequency characteristics of the noise are comparable to those of the signal. Thus, in particular embodiments, processor  320  may reduce V_th in low SNR situations until some minimum value of V_th is reached (where false triggering occurs too frequently), at which point processor  320  may increase V_th to prevent further false triggering. In other embodiments, processor  320  may reduce V_th in low SNR situations until some minimum SNR value for S_filter is reached (such as, for example, an SNR of 1), at which point processor  320  may increase V_th to prevent further false triggering. 
     In yet other embodiments, if processor  320  determines that comparator  310  is too frequently incorrectly rejecting S_filter as purely noise, processor  320  may decrease V_th to improve signal detection. Thus, in particular embodiments, processor  320  may increase V_th until some maximum value of V_th is reached (for example, where signal rejection occurs too frequently), at which point processor  320  may decrease V_th to prevent further signal rejection. 
     Processor  320  may use diagnostic threshold V_diag to determine if active stylus is operating in a low SNR range. For example, if V_th is set to 2 volts, V_diag is set to 1.5 volts, and S_filter is consistently in the range between 1.5 and 2 volts (without meeting or exceeding 2 volts), comparator  310  will reject S_filter as a noise signal. Processor  32 , however, may have data indicating that S_filter is not pure noise (based, for example, on known characteristics of the signal transmitted by device  52 ). Processor  320  may analyze the fact that S_filter meets the diagnostic threshold, V_diag, and not the signal detection threshold, V_th, and determine that active stylus  20  is operating in a low SNR range. 
     In addition to analyzing current data from comparator  310  and other data sources from active stylus  20 , processor  320  may access stored information. As an example, processor  320  may access prior data values received from comparator  310  (such as threshold comparison outputs, SNR of S_filter, or amplitude of S_filter) or other components of active stylus  20  to determine future values of V_th or V_diag. Prior data values accessed by processor  320  may, for example, be stored in processor  320  or in memory  44 . Initial or prior values for V_th or V_diag may also be accessed or stored by processor  320 . 
       FIG. 6  illustrates an example method for dynamically adjusting a signal detection threshold in active stylus  20 . The method may start at step  600 , where a signal received by active stylus  20  is accessed. With reference again to  FIG. 5 , in particular embodiments, this step may occur when control processor  300  receives S_filter from filter  200 . At step  610 , one or more characteristics of the signal are determined. In particular embodiments, this step may occur in control processor  300 , with certain characteristics determined by comparator  310  (including, for example, whether a threshold is met) and certain characteristics determined by processor  320  (including, for example, SNR). In particular embodiments, one of the characteristics determined for the signal is whether the signal satisfies the threshold requirement based on the current value of the threshold. This may be determined by comparing the signal to the current value of the threshold. At step  620 , a threshold is adjusted based on the one or more characteristics of the signal. This may result in the threshold having a new value. In particular embodiments, the steps illustrated in  FIG. 6  may be repeated any number of times (e.g., any number of iterations). For example, during a second iteration, a second signal may be received (returning back to step  600 ). One or more characteristics may be determined for the second signal at step  610 . Again, one of the characteristics determined for the second signal is whether the second signal satisfies the threshold requirement based on the current value of the threshold. Note that the current value of the threshold may have been adjusted during the previous iteration. At step  620 , the threshold may be adjusted again based on the characteristics of the second signal. 
     In particular embodiments, processor  320  adjusts signal detection threshold V_th based on data received from comparator  310  and sends adjusted V_th to comparator  310  via output line  350 . In this manner, comparator  310 , output lines  330  and  340 , processor  320 , and output line  350  form a feedback loop for controlling the one or more signal thresholds against which S_filter is compared. Particular embodiments may repeat the steps of the method of  FIG. 6 , where appropriate. Moreover, although this disclosure describes and illustrates particular steps of the method of  FIG. 6  as occurring in a particular order, this disclosure contemplates any suitable steps of the method of  FIG. 6  occurring in any suitable order. Furthermore, although this disclosure describes and illustrates particular components, devices, or systems carrying out particular steps of the method of  FIG. 6 , this disclosure contemplates any suitable combination of any suitable components, devices, or systems carrying out any suitable steps of the method of  FIG. 6 . 
       FIG. 7  illustrates an example method for filtering a signal received by active stylus  20 . The method may start at step  700 , where a signal received by active stylus  20  is accessed. With reference again to  FIG. 5 , in particular embodiments, this step may occur when filter  200  receives signal S from amplifier  100 . At step  710 , the signal S is processed by filter  200 . The output of filter  200 , S_filter, may then be further processed by controller  50  or any other component of active stylus  20 . In particular embodiments, no output S_filter is provided when certain conditions of filter  200  (for example, a threshold) are not met. Particular embodiments may repeat the steps of the method of  FIG. 7 , where appropriate. Moreover, although this disclosure describes and illustrates particular steps of the method of  FIG. 7  as occurring in a particular order, this disclosure contemplates any suitable steps of the method of  FIG. 7  occurring in any suitable order. Furthermore, although this disclosure describes and illustrates particular components, devices, or systems carrying out particular steps of the method of  FIG. 7 , this disclosure contemplates any suitable combination of any suitable components, devices, or systems carrying out any suitable steps of the method of  FIG. 7 . 
     As illustrated in the example embodiment of  FIG. 8 , active stylus  20  may have a filter  200  (or one or more filters that comprise filter  200 ) with a signal detection threshold  800 . In one embodiment, if the received signal S does not meet or exceed the minimum signal detection threshold  800 , filter  200  will not output a signal for further processing. That is, S_filter will have a value of 0 or, alternatively, will not be output by filter  200 . This allows filter  200  to reject signals that may be noise rather than a communication from, for example, device  52 . Filter  200  may have a threshold  800  that is dynamically assigned or adjusted. Additionally, filter  200  may have a threshold  800  that is based on the signal-to-noise ration (SNR) of received signal S, on the mode of operation of active stylus  20 , or any other quantity that active stylus  20  has access to. 
       FIG. 9  illustrates an example method for filtering, with a threshold, a signal received by active stylus  20 . The method may start at step  900 , where a signal received by active stylus  20  is accessed. With reference again to  FIG. 5 , in particular embodiments, this step may occur when filter  200  receives signal S from amplifier  100 . At step  910 , the signal S is processed by filter  200  having a threshold  800 . At step  920 , if received signal S meets or exceeds threshold  800 , then the output of filter  200 , S_filter, may then be further processed by controller  50  or any other component of active stylus  20 . In particular embodiments, when received signal S does not meet or exceed threshold  800 , no output from filter  200 , S_filter, is provided to controller  50  (or, in particular embodiments, a signal of value 0 is provided). Particular embodiments may repeat the steps of the method of  FIG. 9 , where appropriate. Moreover, although this disclosure describes and illustrates particular steps of the method of  FIG. 9  as occurring in a particular order, this disclosure contemplates any suitable steps of the method of  FIG. 9  occurring in any suitable order. Furthermore, although this disclosure describes and illustrates particular components, devices, or systems carrying out particular steps of the method of  FIG. 9 , this disclosure contemplates any suitable combination of any suitable components, devices, or systems carrying out any suitable steps of the method of  FIG. 9 . 
       FIG. 10  illustrates an example embodiment of active stylus  20  with a filter  200  with the characteristic of a non-linear gain. Although  FIG. 10  depicts filter  200  with threshold  1000 , filter  200  may have a non-linear gain without having threshold  1000 . As an example of a non-linear gain, when the amplitude of received signal S is above threshold  1000  but still near threshold  1000 , the gain (in particular embodiments, the ratio of S_filter to S) may be proportionally higher than when the amplitude of received signal S is more significantly above threshold  1000 . This is illustrated in  FIG. 10 , where at location  1010 , the gain of filter  200  is proportionally higher than for higher values of received signal S. The parameters of filter  200  may be adjusted in any number of ways, including, for example, having more nonlinear regions like location  1010  in the filter, to ensure that input signal S has the desired gain level applied to it depending on the value of S. This type of filter  200  may be useful in situations when active stylus  20  is in between drive lines of device  52 , causing the amplitude of the received signal S to be low. As an example, if the amplitude of the received signal S is low but active stylus  20  must still transmit with sufficient power to be properly detected by device  52 , a non-linear gain may be desirable. 
       FIG. 11  illustrates an example method for filtering, with a non-linear gain, a signal received by active stylus  20 . The method may start at step  1100 , where a signal received by active stylus  20  is accessed. With reference again to  FIG. 5 , in particular embodiments, this step may occur when filter  200  receives signal S from amplifier  100 . The signal S is processed by filter  200  having a non-linear gain, as typified by the filter output value S_filter at location  1010 . At step  1110 , a non-linear function of the received signal S may be computed (or, in particular embodiments, may be predetermined), and at step  1120 , the output of filter  200 , S_filter, may then be further processed by controller  50  or any other component of active stylus  20 . In particular embodiments, with threshold  1000 , when received signal S does not meet or exceed threshold  1000 , no output from filter  200 , S_filter, is provided to controller  50  (or, in particular embodiments, a signal of value 0 is provided). Particular embodiments may repeat the steps of the method of  FIG. 11 , where appropriate. Moreover, although this disclosure describes and illustrates particular steps of the method of  FIG. 11  as occurring in a particular order, this disclosure contemplates any suitable steps of the method of  FIG. 11  occurring in any suitable order. Furthermore, although this disclosure describes and illustrates particular components, devices, or systems carrying out particular steps of the method of  FIG. 11 , this disclosure contemplates any suitable combination of any suitable components, devices, or systems carrying out any suitable steps of the method of  FIG. 11 . 
       FIG. 12  illustrates an example embodiment of active stylus  20  with filter  200  having the characteristic of a proportional gain. Although  FIG. 12  depicts filter  200  without a threshold, filter  200  may have a proportional gain with a threshold. The value of the output of filter  200 , S_filter, is proportional to the value of the received signal S. The parameters of filter  200  may be adjusted in any number of ways, including, for example, having a higher or lower proportional gain (or ratio of S_filter to S) to ensure that input signal S has the desired proportional gain level applied to it depending on the value of S. In particular embodiments, the signal transmitted from active stylus  20  to device  52  is a function of the signal S received by active stylus. Thus, a filter  200  with a proportional gain, as illustrated in  FIG. 12 , may be useful in situations when transmitting a signal proportional to the received signal is desirable. As an example, if active stylus  20  is close to device  52 , it may be desirable for active stylus to transmit proportionally to the signal S that it receives, rather than transmitting at a high and constant energy level, in order to ensure that device  52  to be able to more accurately detect the location of active stylus  20 . 
       FIG. 13  illustrates an example method for filtering, with a proportional gain, a signal received by active stylus  20 . The method may start at step  1300 , where a signal received by active stylus  20  is accessed. With reference again to  FIG. 5 , in particular embodiments, this step may occur when filter  200  receives signal S from amplifier  100 . At step  1310 , the signal S is processed by filter  200  having a proportional gain, with filter output value S_filter being proportional to filter input S. A proportional function of the received signal S is computed (or, in particular embodiments, may be predetermined), and at step  1320 , the output of filter  200 , S_filter, may then be further processed by controller  50  or any other component of active stylus  20 . In particular embodiments, output from filter  200 , S_filter, is provided to controller  50 , and active stylus  20  may transmit a signal proportional to received signal S. Particular embodiments may repeat the steps of the method of  FIG. 13 , where appropriate. Moreover, although this disclosure describes and illustrates particular steps of the method of  FIG. 13  as occurring in a particular order, this disclosure contemplates any suitable steps of the method of  FIG. 13  occurring in any suitable order. Furthermore, although this disclosure describes and illustrates particular components, devices, or systems carrying out particular steps of the method of  FIG. 13 , this disclosure contemplates any suitable combination of any suitable components, devices, or systems carrying out any suitable steps of the method of  FIG. 13 . 
     Active stylus  20  may transmit a signal to device  52  based on the signal S that active stylus  20  received from device  52 . In particular embodiments, the signal transmitted from active stylus  20  to device  52  is a function of the signal S received by active stylus, including, for example, a function of S_filter (itself a function of received signal S).  FIG. 14  illustrates an example method for transmitting a signal from active stylus  20  to device  52  based on the signal S received by active stylus  20 . The method may start at step  1400 , where a signal received by active stylus  20  is accessed. With reference again to  FIG. 5 , in particular embodiments, this step may occur when filter  200  receives signal S from amplifier  100 . At step  1410 , received signal S is compared to first and second pre-determined thresholds. In particular embodiments, one or both of these thresholds may be a threshold (such as threshold  800  or threshold  1000 ) of filter  200 , but in other embodiments, the first or second thresholds may be independent of any thresholds of filter  200 . The first or second thresholds may be static pre-determined thresholds or dynamic pre-determined thresholds, and may be set by controller  50  or any other component of active stylus  20 . At step  1420 , a determination is made as to whether some characteristic of signal S, such as, for example, an amplitude of signal S, exceeds the first pre-determined threshold. If the amplitude of signal S does not exceed the first pre-determined threshold, then the method returns to step  1400 , where another signal received by active stylus  20  is accessed, and the method restarts. If the amplitude of signal S does exceed the first pre-determined threshold, then the method proceeds to step  1430 , where a determination is made as to whether the same characteristic of signal S, such as, for example, an amplitude of signal S, exceeds the second pre-determined threshold. If the amplitude of signal S does not exceed the second pre-determined threshold, then the method proceeds to step  1440 , where active stylus  20  transmits a signal of fixed amplitude to device  52 . In particular embodiments, the signal transmitted is a maximum-amplitude signal that may enable better performance of active stylus  20  in modes such as hover mode. If, at step  1430 , the amplitude of signal S exceeds the second predetermined threshold, then the method proceeds to step  1450 , where active stylus  20  transmits a signal that is a function of the filtered version of signal S, S_filter. In particular embodiments, the function of S_filter may be non-linear. In yet other embodiments, the function of S_filter may be a phase change of S_filter or a multiplicative gain applied S_filter. In yet other embodiments, active stylus  20  may take one action if both the first and second thresholds are exceeded, and a second action if only the first (and not the second) threshold is exceeded, including, but not limited to, transmitting different types of signals to device  52 . As another example, active stylus  20  may filter or process signal S differently based on the specific combination of thresholds exceeded. As a particular embodiment, active stylus  20  may process signal S with one function (which may be linear or nonlinear, proportional, or constant, for example) when the first threshold is exceeded, and active stylus  20  may process signal S with another function (which may also be linear or nonlinear, proportional, or constant, for example) when the second threshold is exceeded. Active stylus  20  may have more than two thresholds, and more than two types of actions that are taken based on the combination of thresholds exceeded. Particular embodiments may repeat the steps of the method of  FIG. 14 , where appropriate. Moreover, although this disclosure describes and illustrates particular steps of the method of  FIG. 14  as occurring in a particular order, this disclosure contemplates any suitable steps of the method of  FIG. 14  occurring in any suitable order. Furthermore, although this disclosure describes and illustrates particular components, devices, or systems carrying out particular steps of the method of  FIG. 14 , this disclosure contemplates any suitable combination of any suitable components, devices, or systems carrying out any suitable steps of the method of  FIG. 14 . 
     Active stylus  20  may transmit a signal to device  52  based on input from sensors  42  of active stylus  20 . As an example, and without limitation, if a pressure sensor, one type of sensor that may comprise sensors  42 , determines that active stylus  20  is touching device  52 , then active stylus  20  may transmit a signal to device  52  that is a function of the received signal S (or, in other embodiments, a function of filtered received signal S_filter). In other embodiments, active stylus  20  may transmit a signal that is a function of received signal S (or filtered received signal S_filter) based on controller  50  determining that active stylus  20  is touching device  52 . In yet other embodiments, active stylus  20  may receive data from device  52  that allows active stylus  20  to determine that active stylus  20  and device  52  are in physical contact, such that active stylus  20  transmits a signal that is a function of S or S_filter to device  52 . In particular embodiments, active stylus  20  may transmit a signal to device  52  that is one function of the signal S (or S_filter) when active stylus  20  is not touching device  52 , and active stylus  20  may transmit a signal to device  52  that is a different function of the signal S (or S_filter) when active stylus  20  is touching device  52 . 
     Any of the filters  200  described in this disclosure may be used in conjunction with any suitable components or algorithms for active stylus  20 , including, without limitation, the use of dynamic received-signal threshold adjustment or the use of dynamic electrode reconfiguration. The parameters of filter  200  may, in particular embodiments, be adjusted by controller  50  (or any other component of active stylus  20 ) based on operating characteristics of active stylus  20  or characteristics of received signal S, including SNR. In particular embodiments, either a single filter or a combination of multiple filters (e.g., of different types) may be incorporated in active stylus  20  for processing the received signal. 
     Herein, reference to a computer-readable non-transitory storage medium encompasses a semiconductor-based or other integrated circuit (IC) (such, as for example, a field-programmable gate array (FPGA) or an application-specific IC (ASIC)), a hard disk, an HDD, a hybrid hard drive (HHD), an optical disc, an optical disc drive (ODD), a magneto-optical disc, a magneto-optical drive, a floppy disk, a floppy disk drive (FDD), magnetic tape, a holographic storage medium, a solid-state drive (SSD), a RAM-drive, a SECURE DIGITAL card, a SECURE DIGITAL drive, or another suitable computer-readable non-transitory storage medium or a combination of two or more of these, where appropriate. A computer-readable non-transitory storage medium may be volatile, non-volatile, or a combination of volatile and non-volatile, where appropriate. 
     Herein, “or” is inclusive and not exclusive, unless expressly indicated otherwise or indicated otherwise by context. Therefore, herein, “A or B” means “A, B, or both,” unless expressly indicated otherwise or indicated otherwise by context. Moreover, “and” is both joint and several, unless expressly indicated otherwise or indicated otherwise by context. Therefore, herein, “A and B” means “A and B, jointly or severally,” unless expressly indicated otherwise or indicated otherwise by context. 
     This disclosure encompasses all changes, substitutions, variations, alterations, and modifications to the example embodiments herein that a person having ordinary skill in the art would comprehend. Moreover, reference in the appended claims to an apparatus or system or a component of an apparatus or system being adapted to, arranged to, capable of, configured to, enabled to, operable to, or operative to perform a particular function encompasses that apparatus, system, component, whether or not it or that particular function is activated, turned on, or unlocked, as long as that apparatus, system, or component is so adapted, arranged, capable, configured, enabled, operable, or operative.