PATENT DOCUMENT

Publication Number: US-9176604-B2
Application Number: US-201213560953-A
Country: US
Kind Code: B2

Title: Stylus device

Abstract:
Styluses capable of generating stylus stimulation signals and touch sensitive devices capable of receiving stylus stimulation signals are disclosed. In one example, a stylus can receive a stimulation signal from a touch sensor of a touch sensitive device and generate a stylus stimulation signal by changing an amplitude or frequency of the received stimulation signal. The stylus can transmit the stylus stimulation signal back into the touch sensor of the touch sensitive device. The touch sensor can generate a touch signal based on the device&#39;s own stimulation signals and the stylus stimulation signal. The touch sensitive device can process the touch signal to determine a location of the stylus on the touch sensor. The stylus can include a force sensor to detect an amount of force applied to a tip of the stylus. The stylus stimulation signal can be modulated based on the force detected by the force sensor.

Claims:
What is claimed is: 
     
       1. A stylus comprising:
 a stylus tip capable of receiving a stimulation signal from a touch sensitive device and further capable of transmitting a stylus stimulation signal to the touch sensitive device; 
 a force sensor circuit capable of detecting a force applied to the stylus tip; 
 an amplification circuit coupled to receive the stimulation signal from the stylus tip, the amplification circuit comprising a processor and an amplifier, the processor coupled to receive an output signal from the amplifier and capable of generating a gain signal, wherein the amplification circuit is capable of modulating the received stimulation signal to generate the stylus stimulation signal based on the gain signal and the force detected by the force sensor circuit; and 
 a mixer circuit coupled to receive the gain signal and an output from the force sensor circuit and capable of controlling the amount of amplification applied to the received stimulation signal based on the output from the force sensor circuit and the gain signal. 
 
     
     
       2. The stylus of  claim 1 , wherein a phase and a frequency of the stylus stimulation signal are at least substantially equal to a phase and a frequency of the stimulation signal from the touch sensitive device. 
     
     
       3. The stylus of  claim 1 , wherein the amplification circuit comprises a regenerative or super regenerative amplifier, and wherein a quench rate of the super regenerative amplifier is synchronous to at least a portion of the received stimulation signal and a gain of the super regenerative amplifier is based on the received stimulation signal. 
     
     
       4. The stylus of  claim 1 , wherein the amplification circuit further comprises a plurality of capacitive elements switchably coupled between an input and an output of the amplifier and the gain signal selectively couples one or more of the plurality of capacitive elements to modulate an amplitude of the received stimulation signal. 
     
     
       5. The stylus of  claim 1 , wherein the amplification circuit further comprises a plurality of capacitive elements switchably coupled between an input and an output of the amplifier and the force sensor circuit is capable of adjusting the capacitance of one or more of the plurality of capacitive elements based on the amount of force applied to the stylus tip. 
     
     
       6. A method comprising:
 receiving a stimulation signal from a touch-sensitive device; 
 generating a stylus stimulation signal based on the received stimulation signal and a force detected by a force sensor, wherein generating the stylus stimulation signal comprises
 generating a gain vector using a processor receiving an amplified version of the received stimulation signal, 
 modulating an amplitude of the received stimulation signal based at least in part on the output of a mixer circuit, wherein the mixer is coupled to receive the gain vector and an output from the force sensor; and 
 
 transmitting the generated stylus stimulation signal to the touch-sensitive device. 
 
     
     
       7. The method of  claim 6 , wherein generating the stylus stimulation signal further comprises selectively coupling one or more capacitive elements between the input and output of an amplifier based on the gain vector to modulate the amplitude of the received stimulation signal. 
     
     
       8. The method of  claim 6 , wherein generating the stylus stimulation signal comprises modulating the amplitude of the received stimulation signal using a regenerative amplifier.

Description:
FIELD 
     This relates generally to touch sensitive devices and, more specifically, to styluses for use with touch sensitive devices. 
     BACKGROUND 
     Touch sensitive devices have become popular as input devices to computing systems due to their ease and versatility of operation as well as their declining price. A touch sensitive device can include a touch sensor panel, which can be a clear panel with a touch sensitive surface, and a display device, such as a liquid crystal display (LCD), that can be positioned partially or fully behind the panel or integrated with the panel so that the touch sensitive surface can cover at least a portion of the viewable area of the display device. The touch sensitive device can allow a user to perform various functions by touching the touch sensor panel using a finger, stylus or other object at a location often dictated by a user interface (UI) being displayed by the display device. In general, the touch sensitive device can recognize a touch event and the position of the touch event on the touch sensor panel, and the computing system can then interpret the touch event in accordance with the display appearing at the time of the touch event, and thereafter can perform one or more actions based on the touch event. 
     As touch sensing technology continues to improve, touch sensitive devices are increasingly being used to compose and mark-up electronic documents. In particular, styluses have become popular input devices as they emulate the feel of traditional writing instruments. However, while touch sensing technology has greatly improved over the past few years, little has been done to improve the stylus itself. Most conventional styluses simply include a bulky tip made of a material capable of interacting with the touch sensitive device. As a result, conventional styluses lack the precision and control of traditional writing instruments. 
     SUMMARY 
     Styluses capable of receiving stimulation and force signals and generating stylus stimulation signals, and touch sensitive devices capable of receiving stylus stimulation signals are disclosed. In one example, a stylus can receive a stimulation signal from a touch sensor of a touch sensitive device and generate a stylus stimulation signal by changing an amplitude or frequency of the received stimulation signal. The stylus can transmit the stylus stimulation signal back into the touch sensor of the touch sensitive device. The touch sensor can generate a touch signal based on the device&#39;s own stimulation signals and the stylus stimulation signal. The touch sensitive device can process the touch signal to determine a location of the stylus on the touch sensor. The stylus can include a force sensor to detect an amount of force applied to a tip of the stylus. The stylus stimulation signal can be modulated based on the force detected by the force sensor. 
     In one example, a touch sensor of a touch sensitive device can generate a touch signal based on the device&#39;s own stimulation signals and the stylus stimulation signal. The touch sensitive device can process the touch signal to determine that a stylus has been detected, a location of the stylus on the touch sensor, and an amount of pressure applied by the stylus to the touch sensitive device. The determinations can be made based on properties of the touch signal caused by the stylus stimulation signal. 
     Processes for generating and processing stylus stimulation signals are also disclosed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an exemplary touch sensor that can be used with a touch sensitive device according to various embodiments. 
         FIG. 2  illustrates a block diagram of an exemplary stylus according to various embodiments. 
         FIG. 3  illustrates a system block diagram showing the interaction between a touch sensitive device and an exemplary stylus according to various embodiments. 
         FIG. 4  illustrates a system block diagram showing the interaction between another touch sensitive device and an exemplary stylus according to various embodiments. 
         FIG. 5  illustrates an exemplary touch and stylus combo matrix according to various embodiments. 
         FIG. 6  illustrates exemplary stylus stimulus vectors according to various embodiments. 
         FIG. 7  illustrates an exemplary touch/stylus combo system according to various embodiments. 
         FIG. 8  illustrates a system block diagram showing the interaction between a touch sensitive device and another exemplary stylus according to various embodiments. 
         FIG. 9  illustrates an exemplary process for generating a stylus stimulation signal according to various embodiments. 
         FIG. 10  illustrates an exemplary process for processing a stylus stimulation signal according to various embodiments. 
         FIG. 11  illustrates an exemplary system for generating or processing a stylus stimulation signal according to various embodiments. 
         FIG. 12  illustrates an exemplary personal device that includes a touch sensor according to various embodiments. 
         FIG. 13  illustrates another exemplary personal device that includes a touch sensor according to various embodiments. 
         FIG. 14  illustrates a symbolic illustration of one or more capacitive elements coupled between the input and output of an amplifier according to various embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description of example embodiments, reference is made to the accompanying drawings in which it is shown by way of illustration specific embodiments that can be practiced. It is to be understood that other embodiments can be used and structural changes can be made without departing from the scope of the various embodiments. 
     This relates to styluses capable of receiving stimulation and force signals and generating stylus stimulation signals and touch sensitive devices capable of receiving stylus stimulation signals. In one example, a stylus can receive a stimulation signal from a touch sensor of a touch sensitive device and generate a stylus stimulation signal by changing an amplitude or frequency of the received stimulation signal. The stylus can transmit the stylus stimulation signal back into the touch sensor of the touch sensitive device. The touch sensor can generate a touch signal based on the device&#39;s own stimulation signals and the stylus stimulation signal. The touch sensitive device can process the touch signal to determine a location of the stylus on the touch sensor. The stylus can include a force sensor to detect an amount of force applied to a tip of the stylus. The stylus stimulation signal can be modulated based on the force detected by the force sensor. A touch sensor of a touch sensitive device can generate a touch signal based on the device&#39;s own stimulation signals and the stylus stimulation signal. The touch sensitive device can process the touch signal to determine that a stylus has been detected, a location of the stylus on the touch sensor, and an amount of pressure applied by the stylus to the touch sensitive device. The determinations can be made based on properties of the touch signal caused by the stylus stimulation signal. Processes for generating and processing stylus stimulation signals are also disclosed. 
       FIG. 1  illustrates touch sensor  100  that can be used to detect touch events on a touch sensitive device, such as a mobile phone, tablet, touchpad, portable computer, portable media player, or the like. Touch sensor  100  can include an array of touch regions or nodes  105  that can be formed at the crossing points between rows of drive lines  101  (D 0 -D 3 ) and columns of sense lines  103  (S 0 -S 4 ). Each touch region  105  can have an associated mutual capacitance Csig  111  formed between the crossing drive lines  101  and sense lines  103  when the drive lines are stimulated. The drive lines  101  can be stimulated by stimulation signals  107  provided by drive circuitry (not shown) and can include an alternating current (AC) waveform. The sense lines  103  can transmit touch signals  109  indicative of a touch at the touch sensor  100  to sense circuitry (not shown), which can include a sense amplifier for each sense line, or a fewer number of sense amplifiers that can be multiplexed to connect to a larger number of sense lines. 
     To sense a touch at the touch sensor  100 , drive lines  101  can be stimulated by the stimulation signals  107  to capacitively couple with the crossing sense lines  103 , thereby forming a capacitive path for coupling charge from the drive lines  101  to the sense lines  103 . The crossing sense lines  103  can output touch signals  109 , representing the coupled charge or current. When an object, such as a stylus, finger, etc., touches the touch sensor  100 , the object can cause the capacitance Csig  111  to reduce by an amount ΔCsig at the touch location. This capacitance change ΔCsig can be caused by charge or current from the stimulated drive line  101  being shunted through the touching object to ground rather than being coupled to the crossing sense line  103  at the touch location. The touch signals  109  representative of the capacitance change ΔCsig can be transmitted by the sense lines  103  to the sense circuitry for processing. The touch signals  109  can indicate the touch region where the touch occurred and the amount of touch that occurred at that touch region location. 
     While the embodiment shown in  FIG. 1  includes four drive lines  101  and five sense lines  103 , it should be appreciated that touch sensor  100  can include any number of drive lines  101  and any number of sense lines  103  to form the desired number and pattern of touch regions  105 . Additionally, while the drive lines  101  and sense lines  103  are shown in  FIG. 1  in a crossing configuration, it should be appreciated that other configurations are also possible to form the desired touch region pattern. While  FIG. 1  illustrates mutual capacitance touch sensing, other touch sensing technologies may also be used in conjunction with embodiments of the disclosure, such as self-capacitance touch sensing, resistive touch sensing, projection scan touch sensing, and the like. Furthermore, while various embodiments describe a sensed touch, it should be appreciated that the touch sensor  100  can also sense a hovering object and generate hover signals therefrom. 
       FIG. 2  illustrates a block diagram of an exemplary stylus  200  that can be used with a touch sensitive device, such as a mobile phone, touchpad, portable computer, or the like. Stylus  200  can generally include tip  201 , ring  203 , body  207 , and stylus stimulation signal circuitry  205  located within body  207 . As will be described in greater detail below, stylus stimulation signal circuitry  205  can be used to generate a stimulation signal that can be transmitted to a touch sensitive device through tip  201 . Tip  201  can include a material capable of transmitting the stylus stimulation signal from stylus stimulation signal circuitry  205  to the touch sensitive device, such as a flexible conductor, a metal, a conductor wrapped by a non-conductor, a non-conductor coated with a metal, a transparent conducting material (e.g., indium tin oxide (ITO)) or a transparent non-conductive material (e.g., glass) coated with a transparent (e.g., ITO) (if the tip is also used for projection purposes) or opaque material, or the like. In some examples, tip  201  can have a diameter of 1 mm or less. Tip  201  can be coupled to body  207  by ring  203 . Ring  203  can include a conductive material, such as a flexible conductor, a metal, a conductor wrapped by a non-conductor, a non-conductor coated with a metal, a transparent conducting material (e.g., ITO) or a transparent non-conductive material (e.g., glass) coated with a transparent (e.g., ITO if the tip is used for projection purposes) or opaque material, or the like. Ring  203  can serve other purposes, such as providing an alternative means for transmitting the stylus stimulation signal from the stylus to the touch sensitive device by serving as an antenna for a wireless module (e.g., RFID, Bluetooth, WI-FI, or the like). Similarly, tip  201  can also be used to sense the touch signal from the touch sensitive device. Both tip  201  and ring  203  can be segmented and each segment can be independently controlled according to the description above. 
     In some examples, stylus  200  can be a modular stylus, such as that described in U.S. patent application Ser. No. 13/560,960, entitled “Modular Stylus Device”. 
       FIG. 3  illustrates a functional block diagram of an exemplary system  300  showing the interaction between stylus  301 , touch sensor  321 , and touch circuitry  341 . In this embodiment, a stimulation signal from touch sensor  321  can be detected at a location where the tip of stylus  301  contacts or is near touch sensor  321  (e.g., where the tip contacts or hovers above a screen of a touch sensitive device). A modified stimulation signal can then be transmitted back into touch sensor  321  at the same frequency in phase or at an arbitrary phase (including quadrature) at the same location. The modified stimulation signal can be transmitted back into touch sensor  321  through the tip and/or ring of stylus  301 . It should be appreciated that  FIG. 3  is a functional block diagram and that the actual components used to implement the various portions of system  300  can vary and one of ordinary skill, given the functional diagram, can select known circuit elements to implement the system. 
     Stylus  301  is one example of stylus  200  that can be used as an input device to a touch sensitive device having a touch sensor similar or identical to touch sensor  100 . Stylus  301  can be configured to generate a stylus stimulation signal having a greater magnitude than that generated by the touch sensitive device. Thus, when stylus  301  is used with a touch sensitive device, stylus  301  can cause the touch sensitive device to measure a “negative” touch. In other words, the charge detected at the stylus&#39; touch location can be greater than the amount of charge detected when no touch is present. This is different than non-stylus touch events, which typically cause the charge detected at the touch location to decrease. 
     Stylus  301  can include amplifier  305  coupled to receive a stimulation signal (e.g., a stimulation signal similar or identical to stimulation signal  107 ) generated by an associated touch sensitive device and transmit a stylus stimulation signal to the associated touch sensitive device. The associated touch sensitive device can include a touch sensitive device in contact with, or in close proximity to, the tip of stylus  301 . Stylus  301  can receive the stimulation signal through the touch sensor (e.g., touch sensor  321 ) of the touch sensitive device. Amplifier  305  can be configured to receive and amplify the stimulation signal by an amount based at least in part on a force detected by force sensor  309  and a gain vector generated by processor  307 . In some examples, amplifier  305  can be configured to amplify the received stimulation signal by an amount representing an increase of capacitance by 0.1 pF or more, depending on the particular configuration. However, it should be appreciated that other amplifications can be used depending on the system design. 
     Stylus  301  can further include force sensor  309  to detect an amount of force applied to the tip of stylus  301 . Force sensor  309  can include any type of force sensor, such as a capacitive pressure sensor, semiconductor strain gauge, or the like. The amount of force detected by force sensor  309  can be used by amplifier  305  to determine the amount of amplification to be applied to the stimulation signal received from the associated touch sensitive device. In this way, the magnitude of the amplified stimulation signal generated by amplifier  305  can be adjusted based on how hard the stylus tip is applied to the surface of the associated touch sensitive device. This allows stylus  301  to convey information associated with the location of its tip on the surface of the touch sensitive device as well as the amount of force being applied to the surface of the touch sensitive device. In response, the touch sensitive device can interpret the location and force information as two different inputs. For example, in a drawing application, a brush stroke can be displayed on the screen of the touch sensitive device corresponding to a location of the tip of stylus  301  and with a width corresponding to the amount of force being applied to the touch sensitive device by the tip of stylus  301 . 
     Stylus  301  can further include processor  307  coupled to receive an amplified stimulation signal from amplifier  305 . Processor  307  can be configured to generate a signal representative of a gain vector that can be used to modulate the amplified output of amplifier  305 . The processor can monitor the stimulation signal received from the touch sensor  321  in order to synchronize the gain vector with the received stimulation sequence. The gain vector signal can be transmitted to mixer  306  where it, along with the output of force sensor  309 , can be used to control the amount of amplification applied to the stimulation signal from touch sensor  321 . The amplified and modulated stimulation signal can be transmitted back into touch sensor  321  as the stylus stimulation signal. 
     It should be appreciated that amplifier  305  can be configured to amplify the received stimulation signal based on the amount of force detected by force sensor  309  and the gain vector of processor  307  in many ways. In one example, amplifier  305  can include a regenerative amplifier operable to amplify the received stimulation signal using a feedback loop between the amplifier output and the amplifier input.  FIG. 14  illustrates a symbolic illustration of one or more capacitive elements  1401  coupled between the input and output of an amplifier  305 . The received stimulation signal can be added at the amplifier input in phase. The amplified stimulation signal can be transmitted to touch sensor  321 , thereby increasing the signal charge locally between drive and sense (negative pixel) as opposed to reducing it in the presence of a touch. In this example, force sensor  309  can control one or more capacitive elements  1401  coupled between the input and output of amplifier  305 . Switches can also be coupled to the capacitive elements to selectively couple the capacitive elements between the input and output of amplifier  305 . The one or more capacitive elements  1401  can be configured such that the capacitance of each of the one or more capacitive elements is inversely related to the amount of force applied to the tip of stylus  301 . Thus, as the force against the tip of stylus  300  increases, the capacitance of the one or more capacitive elements  1401  of force sensor  309  decreases, thereby increasing the overall gain of amplifier  305 . Conversely, as the force against the tip of stylus  300  decreases, the capacitance of the one or more capacitive elements  1401  of force sensor  309  increases, thereby decreasing the overall gain of amplifier  305 . In this example, processor  307  can be configured to cause amplifier  305  to modulate the stimulation signal using a gain vector by selectively coupling one of the one or more capacitive elements  1401  (each having a different capacitance value) between the input and output of amplifier  305  based on the gain vector. Processor  307  can accomplish this by selectively opening and closing the switches coupled to each capacitive element. In this way, the gain caused by each of the capacitive elements  1401  can be changed by adjusting the pressure applied to the tip of stylus  301  while processor  307  can modulate the amplified signal by selecting between each of the capacitive elements having different capacitance values. 
     In some examples, amplifier  305  can be configured to yield a loop gain of less than one to prevent oscillation. In other alternative examples, amplifier  305  can include a super regenerative amplifier, comprised of an amplifier with a loop gain of greater than 1 and a quench signal generator having a quench rate based on the received stimulation signal from touch sensor  321 . In these examples, the quench signal generator can apply a quench signal that can cause the gain of the regenerative amplifier to drop substantially below the gain needed for the regenerative amplifier to sustain oscillation, causing the regenerative amplifier to repeatedly go into oscillation at the beginning of each scan step. In yet other examples, amplifier  305  can add the received stimulation signal at the amplifier input in a different phase (including quadrature). 
     System  300  can further include touch sensor  321  of a touch sensitive device. Touch sensor  321  can include a touch sensor similar or identical to touch sensor  100 , described above. As shown in  FIG. 3 , touch sensor  321  can include a drive line  329  coupled to receive a stimulation signal similar or identical to stimulation signal  107  from touch circuitry  341  and a sense line  331  capacitively coupled to drive line  329  and coupled to transmit a touch signal similar or identical to touch signal  109  to touch circuitry  341 . It should be appreciated that touch sensor  321  is shown with only one drive line and one sense line for illustrative purposes only and that touch sensor  321  can actually include any number of drive lines and any number of sense lines. 
     A mutual capacitance Csig  327  can be formed between the crossing drive line  329  and sense line  331  when the drive line is stimulated. Similarly, a mutual capacitance Cts  323  and Ctd  325  can be formed between the tip of stylus  301  and sense line  331  and drive line  329 , respectively, when the stylus stimulation signal is generated. As mentioned above, if the tip of stylus  301  is placed near or at the crossing point between drive line  329  and sense line  331 , stylus  301  can receive the stimulation signal transmitted on drive line  329  via the capacitive path formed between the stylus tip and drive line  329 , amplify the received stimulation signal using amplifier  305 , force sensor  309 , and processor  307 , and transmit an amplified stimulation signal in the form of a stylus stimulation signal back into touch sensor  321  via the capacitive path formed between the stylus tip and sense line  331 . Thus, the touch signal generated by sense line  331  can include charges coupled from both drive line  329  and stylus  301 . As a result, the amount of charge detected by sense line  331  can increase when the tip of stylus  301  is placed on or above the crossing point between drive line  329  and sense line  331 . This increase in charge can be used by the touch sensitive device to distinguish a stylus touch event from a non-stylus touch event because, as mentioned above, non-stylus touch events typically cause capacitance Csig  327  to decrease due to charge or current from the stimulated drive line  329  being shunted through the non-stylus object to ground rather than being coupled to the crossing sense line  331  at the touch location. Moreover, the touch sensitive device can determine the location of the stylus touch event because the same stimulation signal being driven on drive line  329  is being amplified and transmitted back into the touch sensor at the crossing point between drive line  329  and sense line  331 . 
     System  300  can further include touch circuitry  341  included in or associated with the touch sensitive device. Touch circuitry  341  can include multi-stim matrix  343  stored in a computer-readable storage medium. Multi-stim matrix  343  can include a matrix containing stimulation phase information for stimulation signals that can be simultaneously applied to the drive lines of touch sensor  321 , such as that described in U.S. patent Ser. No. 12/208,329, entitled “Multiple Stimulation Phase Determination.” Specifically, each row of the matrix can represent a single step among multiple steps needed to compute values for generating an image of touch, each column of the matrix can represent a drive line of touch sensor panel  321  to be stimulated, and each cell of the matrix can represent the phase of a stimulation signal to be applied to a particular drive line in a particular step. In one example, multi-stim matrix  343  can include an additional row and column to support the stylus stimulation signal from stylus  301 . Specifically, the additional column can represent a drive line that is not driven, or a drive line that does not actually exist on touch sensor panel  321 . The purpose of the additional column is to detect the stylus stimulation signal. Touch circuitry  341  can further include inverse multi-stim matrix  353  stored in a computer-readable storage medium. Inverse multi-stim matrix  353  can include a matrix representing an inverse of multi-stim matrix  343  for decoding a touch signal received from a sense line of touch sensor  321  to generate a touch image representing a touch detected by touch sensor  321 . These matrices will be described in greater detail below with respect to  FIGS. 4-7 . 
     Referring back to  FIG. 3 , touch circuitry  341  can further include transmitter channel  345  coupled to transmit a stimulation signal to drive line  329  of touch sensor  321 . Transmitter channel  345  can be configured to generate a stimulation signal similar or identical to stimulation signal  107  to be applied to drive line  329  based on the phase information contained in multi-stim matrix  343 . In some examples, the stimulation signal can have a frequency between 80-120 KHz (e.g., 90, 100, or 110 KHz) and an amplitude between 3-5V (e.g., 4V). In other examples, the stimulation signal can have a frequency between 100 KHz to 1 MHz or higher (e.g., between 100-300 KHz or 100-500 KHz). Although not shown, touch circuitry  341  can include one transmitter channel for each drive line of touch sensor  321 . 
     Touch circuitry  341  can further include receiver circuitry  347  coupled to receive a touch signal from sense line  331  of touch sensor  321 . Receiver circuitry  347  can include amplifiers, filters, and/or analog to digital converters that one of ordinary skill in the art can select to appropriately process the touch signal received from sense line  331 . Although not shown, touch circuitry  341  can include additional receiver circuitry for each sense line of touch sensor  321 . 
     Touch circuitry  341  can further include in-phase (I-phase) demodulation circuitry  349  configured to demodulate the touch signal received from receiver circuitry  347 . I-phase demodulation circuitry  347  can include a demodulation mixer and a demodulation integrator to extract the I-phase component of the touch signal output by sense line  331 . Although not shown, touch circuitry  341  can include additional I-phase demodulation circuitry for each sense line of touch sensor  321 . In some examples, transmitter channel  345 , receiver circuitry  347 , and I-phase demodulation circuitry  349  can include circuitry similar or identical to that described in U.S. patent application Ser. No. 11/818,345, which is incorporated by reference herein in its entirety as if put forth in full below. 
     Touch circuitry  341  can further include multi-stim decode circuitry  351  configured to decode the I-phase component of the touch signal received from I-phase demodulation circuitry  341 . Multi-stim decode circuitry  351  can include a mixer coupled to multiply the I-phase component of the touch signal received from I-phase demodulation circuitry  341  with inverse multi-stim matrix  353 . Multi-stim decode circuitry  351  can further include an integrator coupled to receive the output of the mixer and to output touch image  355  representing a touch detected by sense line  331  of touch sensor  321 . Although not shown, touch circuitry  341  can include additional multi-stim decode circuitry for each sense line of touch sensor  3211 . 
       FIG. 4  illustrates a functional block diagram of another exemplary system  400  showing the interaction between stylus  401 , touch sensor  421 , and touch circuitry  441 . In this embodiment, similar to that shown in  FIG. 3 , stylus  401  can receive a stimulation signal from touch sensor  421  at a location where the tip of stylus  401  contacts or is near touch sensor  421  (e.g., where the tip contacts or hovers above a screen of a touch sensitive device). A modified stimulation signal can then be transmitted back into touch sensor  421  at the same frequency in phase or at an arbitrary phase (including quadrature) at the same location. The modified stimulation signal can be transmitted back into touch sensor  421  through the tip and/or ring of stylus  401 . It should be appreciated that  FIG. 4  is a functional block diagram and that the actual components used to implement the various portions of system  400  can vary and one of ordinary skill, given the functional diagram, can select known circuit elements to implement the system. 
     System  400  can include stylus  401 , amplifier  405 , processor  407 , mixer  406 , force sensor  409 , touch sensor  421 , Cts  423 , Ctd  425 , Csig  427 , drive line  429 , sense line  431 , multi-stim matrix  443 , transmitter channel  445 , receiver circuitry  447 , and inverse matrix  453  similar or identical to stylus  301 , amplifier  305 , processor  307 , mixer  306 , force sensor  309 , touch sensor  321 , Cts  323 , Ctd  325 , Csig  327 , drive line  329 , sense line  331 , multi-stim matrix  343 , transmitter channel  345 , receiver circuitry  347 , and inverse matrix  353 , respectively. However, touch circuitry  441  can include two demodulation paths. The first demodulation path can include stylus demodulation circuitry  449  and multi-stim decode circuitry  451  for demodulating the touch signal received from receiver circuitry  447  at a first touch phase to generate stylus image  456 . The second demodulation path can include touch demodulation circuitry  457  and multi-stim decode circuitry  459  for demodulating the touch signal received from receiver circuitry  447  at a second stylus phase to generate touch image  455 , Including a phase shift between the touch and stylus signals further helps to distinguish the touch and stylus signals in addition to the latter having a positive phase. In some examples, the difference between the first and second phases can be 90 degrees. In other examples, the phase difference between the first and second phases can have a different value. 
       FIG. 5  illustrates an exemplary touch and stylus stimulus combo matrix that can be used in systems  300  or  400 . In this embodiment, a touch stimulus matrix may be extended by M columns and M rows to form the modified touch and stylus stimulus combo matrix. The first N columns may be used for touch stimulus and the M columns may be used for stylus magnitude. Each column vector can correspond to a different channel. In order for the stimulus matrix to be invertible, the matrix should be a square matrix and therefore can be extended by M rows.  FIG. 6  illustrates M exemplary stylus stimulus vectors. Each stylus stimulus vector represents a copy of one of the M column vectors from the touch and stylus stimulus combo matrix shown in  FIG. 5 . Using the touch and stylus stimulus combo matrix, the system can support a total of N styluses. 
       FIG. 7  illustrates a simplified view of a touch/stylus combo system that utilizes separate channels to encode stylus magnitude. The touch and stylus stimulus combo matrix is extended by N columns and N rows, where N is the number of stylus or devices for which to encode magnitude information. In this example, the touch controller can drive the M drive lines for which touch and stylus location need to be resolved. M touch pixels can be modulated along the M touch pixels along a sense line by touch and up to N stylus devices. The N stylus devices may potentially modulate different touch pixels along a sense line. Each stylus device can have its own stylus stimulus vector, which represents a copy of one of the M column vectors from the touch and stylus stimulus combo matrix. The stylus can modulate the gain of the amplifier (e.g., amplifier  305  or  405 ) as a function of the stylus stimulus vector or can add its own stimulus signal directly to a given touch pixel (e.g., through the stylus ring). The stimuli from the N styluses can be synchronized in the stylus device by the respective stylus device monitoring the stimulus signal at a given touch panel location and then synchronizing its own stimulus with the received stimulus signal at that touch panel location. For example, synchronization can occur at the first scan step, representing the first row vector in the touch and stylus stimulus combo matrix. In some embodiments, all elements in the first row vector may be 1 (i.e., all M stimulus signals can be driven in positive phase), if the touch and stylus stimulus combo matrix is a hadamard matrix. The stylus device can use this first step to synchronize its own stimulus. The composite signal at the sense line can be vector demodulated with a decode matrix, which represents the inverse of the touch and stylus stimulus combo matrix. The touch and stylus locations can be stored in the touch and stylus result vector, which is comprised of M entries containing M elements indicating the location/magnitude of touch and styluses and N dedicated stylus magnitudes. 
     In some examples, some or all of the functional blocks of touch circuitry  341  or  441  can be implemented by ASIC processor, ARM processor, other electrical components, or combinations thereof. 
       FIG. 8  illustrates a functional block diagram of another exemplary system  800  showing the interaction between stylus  801 , touch sensor  821 , and touch circuitry  841 . It should be appreciated that  FIG. 8  is a functional diagram and that the actual components used to implement the various portions of system  800  can vary and one of ordinary skill, given the functional diagram, can select known circuit elements to implement the system 
     Stylus  801  is one example of stylus  200  that can be used as an input device to a touch sensitive device having a touch sensor similar or identical to touch sensor  100 . Stylus  801  can be configured to generate a stylus stimulation signal having a frequency that is different than a frequency of a stimulation signal generated by the touch sensitive device. In some examples, the stylus stimulation frequency can be between 40-60 KHz (e.g., about 50 Khz) greater than or less than the frequency of a stimulation signal from a touch sensor. Thus, when stylus  801  is used with a touch sensitive device, stylus  801  can cause the touch sensitive device to generate a touch signal containing signals having two or more different frequencies. 
     Stylus  801  can optionally include sense amplifier  805  coupled to receive a stimulation signal (e.g., a stimulation signal similar or identical to stimulation signal  107 ) generated by an associated touch sensitive device and transmit a stylus stimulation signal to the associated touch sensitive device. The associated touch sensitive device can include a touch sensitive device in contact with, or in close proximity to, the tip of stylus  801 . Sense amplifier  805  can be used to amplify the received stimulation signal to a level sufficient to be used by stylus  801  to generate a stylus stimulation signal, which is described in greater detail below. However, if the strength of the received stimulation signal is sufficiently high, sense amplifier  805  can be omitted from stylus  801 . 
     Stylus  801  can further include force sensor  809  for detecting the amount of force applied to the tip of stylus  801 . Force sensor  809  can be similar or identical to force sensor  309 , described above. For example, force sensor  809  can include any type of force sensor, such as a capacitive pressure sensor, semiconductor strain gauge, or the like, operable to detect the amount of force applied to the tip of stylus  801 . The amount of force detected by force sensor  809  can be used to modulate an oscillating signal generated by oscillator  813 . In this way, the magnitude of the oscillating signal generated by oscillator  813  can be adjusted based on how hard the stylus tip is applied to the surface of the associated touch sensitive device. As described above, this allows stylus  801  to convey information associated with the location of its tip on the surface of the touch sensitive device as well as the amount of force being applied to the surface of the touch sensitive device. 
     Stylus  801  can further include comparator  811  coupled to receive the output of force sensor  809  and a threshold voltage Vth. Comparator  811  can be configured to compare the output of force sensor  809  to the threshold voltage Vth and output a force detection signal based on the comparison. For example, the force detection signal can be driven high (or low, depending on the circuit design) when the output of force sensor  809  is greater than threshold voltage Vth and can be drive low (or high, depending on the circuit design) when the output of force sensor  809  is less than threshold voltage Vth. 
     Stylus  801  can further include processor  803  coupled to receive the force detection signal output by comparator  811 . Processor  803  can be configured to generate a power control signal based on the received force detection signal. For example, if the force detection signal is at a level indicating that the force detected by force sensor  809  is greater than a threshold amount (represented by threshold voltage Vth), processor  803  can drive the power control signal to a high level (or low, depending on the circuit design) to cause oscillator  813  to generate a signal. The force detection signal and the power control signal can be used to control the power state of some or all components within stylus  801  to improve battery life. For example, if the force is below the set force threshold, the device can be in an idle state and the device can remain in a low power state, thereby conserving battery power. When the force is above the force detection threshold, the device can transitions into an active mode. This way battery power can be conserved when the stylus is not actively being used. 
     Stylus  801  can further include oscillator  813  configured to generate an oscillating signal having frequency F off . Oscillator  813  can include any type of oscillator, such as a tuned LC oscillator (e.g, a colpitts-oscillator), crystal oscillator, MEMS based oscillator, voltage controlled oscillator, RC oscillator, ring oscillator, or the like. In one example, oscillator  813  can be configured to generate a sinusoidal signal having an amplitude between 8-12V (e.g., 9, 10, or 11V) and a frequency F off  between 80-120 KHz (e.g., 90, 100, or 110 KHz). In other examples, the stimulation signal can have a frequency between 100 KHz to 1 MHz or higher (e.g., between 100-300 KHz or 100-500 KHz). The signal generated by oscillator  813  can have the same phase as the stimulation signal received from touch sensor  821 . 
     Stylus  801  can further include mixer  807  coupled to receive the output of force sensor  809 , the signal having frequency F off  output by oscillator  813 , and the amplified stimulation signal from sense amplifier  805 . Mixer  807  can be configured to modulate the amplitude of the signal having frequency F off  output by oscillator  813  by an amount corresponding to the force detected by force sensor  809  to generate a modulated oscillating signal. Mixer  807  can be further configured to mix the modulated oscillating signal with the amplified signal received from sense amplifier  805  to generate a stylus stimulation signal. The resultant composite stimulation signal can have a frequency equal to the frequency of the stimulation signal received from touch sensor  821  plus or minus the offset frequency F off  amplitude modulated by the force signal. 
     Stylus  801  can further include transmission amplifier  815  coupled to receive the stylus stimulation signal output by mixer  807 . Amplifier  815  can be configured to amplify the composite stimulation signal by an amount sufficient to be received by touch sensor  821 . 
     System  800  can further include touch sensor  821  of a touch sensitive device. Touch sensor  821  can include a touch sensor similar or identical to touch sensor  100 , described above. As shown in  FIG. 8 , touch sensor  821  can include a drive line  829  coupled to receive a stimulation signal similar or identical to stimulation signal  107  from touch circuitry  841  and a sense line  831  capacitively coupled to drive line  829  and coupled to transmit a touch signal similar or identical to touch signal  109  to touch circuitry  841 . It should be appreciated that touch sensor  821  is shown with only one drive line and one sense line for illustrative purposes only and that touch sensor  821  can actually include any number of drive lines and any number of sense lines. 
     A mutual capacitance Csig  827  can be formed between the crossing drive line  829  and sense line  831  when the drive line is stimulated. Similarly, a mutual capacitance Cts  823  and Ctd  825  can be formed between the tip of stylus  801  and sense line  831  and drive line  829 , respectively, when the stylus stimulation signal is generated. A mutual capacitance Crs  833  and Crd  835  can also be formed between the ring of stylus  801  and sense line  831  and drive line  829 , respectively, when the composite stylus stimulation signal is generated. As mentioned above, if the tip of stylus  801  is placed at the crossing point between drive line  829  and sense line  831 , stylus  801  can receive the stimulation signal transmitted on drive line  829  via the capacitive path formed between the stylus tip and drive line  829 , amplify the received stimulation signal using sense amplifier  805 , mix the amplified stimulation signal with a modulated oscillating signal generated by modulating a signal having frequency F off  by an amount corresponding to a force detected by force sensor  809 , and transmit the stylus stimulation signal back into touch sensor  821  via the capacitive path formed between the stylus ring and sense line  831 . Thus, the touch signal generated by sense line  831  can include charge coupled from both drive line  829  and stylus  801 . 
     System  800  can further include touch circuitry  841  included in or associated with the touch sensitive device. Touch circuitry  841  can be similar to touch circuitry  341 , described above, except that touch demodulation circuitry  849  and multi-stim decode circuitry  851  can be configured to demodulate the touch component of the signal output by receiver circuitry  847  and post the result in a touch image memory  855 . Touch circuitry  841  can further include stylus demodulation circuitry  857  and multi-stim decode circuitry  859  to demodulate the stylus component of the signal output by receiver circuitry  847  and post the result to stylus image memory  861 . In the illustrated example, stylus demodulation can occur at FSTM+/−FOFF, since the received signal on the stylus device can be FSTM and modulated with FOFF to generate the stylus signal. The touch demodulation can be performed at FSTM. Multi-stim matrix  843 , transmitter channel  845 , receiver circuitry  847 , and inverse matrix  853  can be similar or identical to multi-stim matrix  343 , transmitter channel  345 , receiver circuitry  347 , and inverse matrix  353  of touch circuitry  341 , respectively. However, multi-stim matrix  843  and inverse matrix  853  may not include an extra row and step like that contained in multi-stim matrix  343  and inverse matrix  353 . The differences between touch circuitry  341  and touch circuitry  841  will now be described in more detail. 
     Touch circuitry  841  can include separate demodulation and decode circuitry for handling stylus touch events and non-stylus touch events. Specifically, touch circuitry  841  can include touch demodulation circuitry  849  and multi-stim decode circuitry  851  to process non-stylus touch events and can include stylus demodulation circuitry  857  and multi-stim decode circuitry  859  to process stylus touch events. 
     Touch demodulation circuitry  849  can be configured to demodulate the portion of the touch signal received from receiver circuitry  847  having a frequency corresponding to the frequency of the stimulation signal generated by transmitter channel  845 . Touch demodulation circuitry  849  can include a demodulation mixer and a demodulation integrator to extract the touch component of the signal output by sense line  831  having the frequency corresponding to the frequency of the stimulation signal generated by transmitter channel  845 . 
     Multi-stim decode circuitry  851  can be configured to decode the touch component of the signal received from touch demodulation circuitry  849 . Multi-stim decode circuitry  851  can include a mixer coupled to multiply the touch component of the signal received from touch demodulation circuitry  849  with inverse multi-stim matrix  853 . Multi-stim decode circuitry  851  can further include an integrator coupled to receive the output of the mixer and to post the result in a touch image memory  855 , representing a non-stylus touch detected by sense line  831  of touch sensor  821 . 
     Stylus demodulation circuitry  857  can be configured to demodulate the portion of the touch signal received from receiver circuitry  847  having a frequency corresponding to the frequency of the stimulation signal generated by transmitter channel  845  plus or minus the offset frequency F off . Stylus demodulation circuitry  857  can include a demodulation mixer and a demodulation integrator to extract the stylus component of the signal output by sense line  831  having the frequency corresponding to the frequency of the stimulation signal generated by transmitter channel  845  plus or minus the offset frequency F off . 
     Multi-stim decode circuitry  859  can be configured to decode the stylus component of the signal received from stylus demodulation circuitry  857 . Multi-stim decode circuitry  859  can include a mixer coupled to multiply the stylus component of the touch signal received from stylus demodulation circuitry  857  with inverse multi-stim matrix  853 . Multi-stim decode circuitry  859  can further include an integrator coupled to receive the output of the mixer and to post the result in a touch image memory  861 , representing a stylus touch detected by sense line  831  of touch sensor  821 . 
     In some examples, the functional blocks of touch circuitry  841  can be implemented by ASIC processor, ARM processor, other electrical components, or combinations thereof. 
     While system  800  is shown and described above as using one signal having an offset frequency F off , it should be appreciated that any number of these signals can be used. For example, stylus  801  can include any number of additional oscillators to generate additional signals to be modulated by an amount corresponding to the force detected by force sensor  809 . These additional signals can have varying frequencies and can each be mixed with the amplified stimulation signal received from sense amplifier  805  (or non-amplified stimulation signal received from touch sensor  821  if no sense amplifier  805  is used) to generate the stylus stimulation signal. In this example, touch circuitry  841  can also include additional circuitry to process the additional signals generated by stylus  801 . For example, touch circuitry can include additional I-phase demodulations circuits and multi-stim decoder circuits for each additional signal to be demodulated. 
       FIG. 9  illustrates an exemplary process  900  for generating and transmitting a stylus stimulation signal. At block  901 , a stimulation signal can be received by a stylus from a touch sensitive device. The stimulation signal can be received by capacitively coupling a portion of the stylus to the touch sensitive device. In one example, a stimulation signal similar or identical to stimulation signal  107  can be generated by a touch sensitive device similar or identical to those shown in  FIGS. 3 ,  4 , and  8 . The stimulation signal can be generated by a transmitter channel similar or identical to transmitter channels  345 ,  445 , or  845  using a multi-stim matrix similar or identical to multi-stim matrix  343 ,  443 , or  843 . The stimulation signal can be sent through a drive line similar or identical to drive lines  329 ,  429 , or  829  of a touch sensor similar or identical to touch sensors  321 ,  421 , or  821 . A stylus similar or identical to stylus  200 ,  301 ,  401 , or  801  having a tip similar or identical to tip  201  can receive the stimulation signal via a capacitive path formed between the drive line and the tip of the stylus when the stylus tip is placed on or near the touch sensitive surface of the touch sensitive device. 
     At block  903 , a stylus stimulation signal can be generated by changing a characteristic of the received stimulation signal. For example, one or more of a frequency or amplitude of the received stimulation signal can be changed to generate the stylus stimulation signal. 
     In one example, an amplifier similar or identical to amplifier  305  or  405  including a regenerative amplifier can be used to amplify the received stimulation signal. The amplification can be based on an amount of force detected by a force sensor similar or identical to force sensor  309  or  409  and a gain vector generated by processor similar or identical to processor  307  or  407 . The force sensor can detect the amount of force being applied to the tip of the stylus. In this way, the magnitude of the stylus stimulation signal can be varied by adjusting the amount of force being applied between the stylus tip and the surface of the touch sensitive device. 
     In another example, an oscillator and mixer similar or identical to oscillator  813  and mixer  807  can be used to change a frequency of the received stimulation signal. In this example, the oscillator can be configured to generate an oscillating signal (e.g., a sinusoidal signal) having a frequency that is different from that of the received stimulation signal. In some examples, the oscillator can be configured to turn on in response to a sufficient force being applied to the tip of the stylus as detected by a force sensor similar or identical to force sensor  809 . The stylus signal generated by the oscillator can modulated at a mixer similar or identical to mixer  807  by an output of the force sensor such that the amplitude of the amplitude modulated stylus stimulation signal corresponds to an amount of force detected by the force sensor. The amplitude modulated oscillating signal can be mixed with the received stimulation signal by a mixer similar or identical to mixer  807  to generate a stylus stimulation signal. In some examples, prior to mixing with the amplitude modulated stylus stimulation signal, the received stimulation signal can be amplified using an amplifier to increase the signal strength to a desirable amount. For example, an amplifier similar or identical to sense amplifier  805  can be used to amplify the received stimulation signal. 
     At block  905 , the stylus stimulation signal can be transmitted to the touch sensitive device. For example, the stylus stimulation signal generated at block  903  can be transmitted to the touch sensitive device via a capacitive path formed between the stylus device and the touch sensor of the device. 
     In one example, an amplitude-modulated stylus stimulation signal generated by a stylus similar or identical to stylus  301  or  401  can be transmitted to a touch sensor similar or identical to touch sensor  321  or  421  of a touch sensitive device via a capacitive path formed between the stylus device and the touch sensor of the device. 
     In another example, a frequency-shifted composite stylus stimulation signal generated by a stylus similar or identical to stylus  801  can be transmitted to a touch sensor similar or identical to touch sensor  821  of a touch sensitive device via a capacitive path formed between the stylus device and the touch sensor of the device. The frequency-shifted composite stylus stimulation signal can be amplified prior to transmission using a transmission amplifier similar or identical to transmission amplifier  815 . 
       FIG. 10  illustrates an exemplary process  1000  for receiving and processing a touch signal having a stylus stimulation signal. At block  1001 , a stimulation signal can be generated by a touch sensitive device. The stimulation signal can be transmitted to drive lines of a touch sensor. In one example, a stimulation signal similar or identical to stimulation signal  107  can be generated by a touch sensitive device similar or identical to those shown in  FIGS. 3 ,  4 , and  8 . The stimulation signal can be generated by a transmitter channel similar or identical to transmitter channels  345 ,  445 , or  845  using a multi-stim matrix similar or identical to multi-stim matrices  343 ,  443 , or  843 . The stimulation signal can be sent through a drive line similar or identical to drive lines  329 ,  429 , or  829  of a touch sensor similar or identical to touch sensors  321 ,  421 , or  821 . 
     At block  1003 , a touch signal having a stylus stimulation signal can be received by the touch sensitive device. The touch signal can represent a detected touch event on a touch sensitive surface of the touch sensitive device. In one example, a touch signal similar or identical to touch signal  109  can be received from a sense line similar or identical to sense line  331 ,  431 , or  831  of a touch sensor similar or identical to touch sensor  321 ,  421 , or  821 . The touch signal can contain a stylus stimulation signal generated by a stylus similar or identical to stylus  301 ,  401 , or  801 . The stylus stimulation signal can be an amplitude-modulated and/or frequency-shifted version of the stimulation signal. 
     At block  1005 , the received sense signal can be processed. For example, the received sense signal can be filtered, converted from an analog to a digital signal, amplified, or combinations thereof. The signal can further be demodulated and decoded to generate a touch image representing a touch event detected by the touch sensor. In one example, a receiver circuitry similar or identical to receiver circuitry  347 ,  447 , or  847  can be used to filter, convert the signal from an analog to a digital signal, amplify, or combinations thereof, the received sense signal. 
     In one example, the signal output by the receiver circuitry, such as receiver circuitry  347 , can be sent through demodulation circuitry similar or identical to demodulation circuitry  349  to extract the I-phase component of the touch signal. The demodulated signal can be transmitted to decode circuitry similar or identical to multi-stim decode circuitry  351  to generate a touch image similar or identical to touch image  355 . In another example, the signal output by the receiver circuitry, such as receiver circuitry  447 , can be sent through demodulation circuitry similar or identical to touch demodulation circuitry  457  and stylus demodulation circuitry  449  to extract the touch and stylus components of the touch signal. The demodulated signals can be transmitted to decode circuitry similar or identical to multi-stim decode circuitry  451  and  459  to generate a stylus image similar or identical to stylus image  456  and a touch image similar or identical to touch image  455 . 
     In another example, the signal output by receiver circuitry, such as receiver circuitry  847 , can be sent through two or more sets of demodulation circuitry similar or identical to touch and stylus demodulation circuitry  849  and  857  to extract the touch and stylus components of the touch signal. The touch demodulation circuitry  849  can be configured to demodulate the signal output by the receiver circuitry at a frequency corresponding to the frequency of the signal transmitted at block  1001 . The stylus demodulation circuitry  857  can be configured to demodulate the signal output by the receiver circuitry at the frequency corresponding to the frequency of the signal transmitted at block  1001  plus or minus an offset frequency corresponding to a frequency of an oscillating signal generated by the stylus device. If the stylus is configured to generate more than one oscillating signal, additional demodulation circuits can be used to demodulate the signal output by the receiver circuitry at frequencies corresponding to the frequency of the signal transmitted at block  1001  plus or minus offset frequencies corresponding to frequencies of the additional oscillating signals. The demodulated signal can be transmitted to decode circuitry similar or identical to multi-stim decode circuitry  851  or  859 . Additional decode circuitry can be included if additional demodulation circuits are used. The multi-stim decode circuitry can be used to generate touch images similar or identical to touch and stylus images  855  and  861 . 
     Using styluses  301 ,  401 , and  801  or processes  900  or  1000 , a stylus device can be used to input both positional data and pressure into a touch sensitive device. These inputs can be used to improve a user experience in various applications. For example, in a drawing application, a user can use the stylus as a paintbrush, with the stylus&#39; motion and pressure being detected by the touch sensitive device. As the user increases the pressure of the stylus against the touch sensitive device, the thickness of the brushstrokes can be increased. As the user reduces the pressure of the stylus against the touch sensitive device, the thickness of the brushstrokes can similarly decrease. In another example, when drawing with a line rather than a brush, the line thickness can change as a function of pressure. Similarly, when using the stylus as an eraser, the eraser width can vary as a function of pressure. 
     One or more of the functions relating to the generation or processing of a stylus stimulation signal described above can be performed by a system similar or identical to system  1100  shown in  FIG. 11 . System  1100  can include instructions stored in a non-transitory computer readable storage medium, such as memory  1103  or storage device  1101 , and executed by processor  1105 . The instructions can also be stored and/or transported within any non-transitory computer readable storage medium for use by or in connection with an instruction execution system, apparatus, or device, such as a computer-based system, processor-containing system, or other system that can fetch the instructions from the instruction execution system, apparatus, or device and execute the instructions. In the context of this document, a “non-transitory computer readable storage medium” can be any medium that can contain or store the program for use by or in connection with the instruction execution system, apparatus, or device. The non-transitory computer readable storage medium can include, but is not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus or device, a portable computer diskette (magnetic), a random access memory (RAM) (magnetic), a read-only memory (ROM) (magnetic), an erasable programmable read-only memory (EPROM) (magnetic), a portable optical disc such a CD, CD-R, CD-RW, DVD, DVD-R, or DVD-RW, or flash memory such as compact flash cards, secured digital cards, USB memory devices, memory sticks, and the like. 
     The instructions can also be propagated within any transport medium for use by or in connection with an instruction execution system, apparatus, or device, such as a computer-based system, processor-containing system, or other system that can fetch the instructions from the instruction execution system, apparatus, or device and execute the instructions. In the context of this document, a “transport medium” can be any medium that can communicate, propagate or transport the program for use by or in connection with the instruction execution system, apparatus, or device. The transport medium can include, but is not limited to, an electronic, magnetic, optical, electromagnetic or infrared wired or wireless propagation medium. 
     The system  1100  shown in  FIG. 11  can be used in either the stylus to generate a stylus stimulation signal as described above with respect to  FIGS. 3 ,  4 ,  8 , and  9 , or the touch sensitive device to receive and process a touch signal as described above with respect to  FIGS. 3 ,  4 ,  8 , and  10 . 
     It is to be understood that the system is not limited to the components and configuration of  FIG. 11 , but can include other or additional components in multiple configurations according to various embodiments. Additionally, the components of system  1100  can be included within a single device, or can be distributed between multiple devices. 
       FIG. 12  illustrates an exemplary personal device  1200 , such as a tablet, that can be used with a stylus according to various embodiments. 
       FIG. 13  illustrates another exemplary personal device  1300 , such as a mobile phone, that can be used with a stylus according to various embodiments. 
     Although embodiments have been fully described with reference to the accompanying drawings, it is to be noted that various changes and modifications will become apparent to those skilled in the art. Such changes and modifications are to be understood as being included within the scope of the various embodiments as defined by the appended claims.

Metadata:
Filing Date: 20120727
Publication Date: 20151103
Grant Date: 20151103
Priority Date: 20120727
Inventors: KRAH CHRISTOPH HORST
YOUSEFPOR MARDUKE
WHITE KEVIN J.
GRUNTHANER MARTIN PAUL
Assignee: APPLE INC
CPC Classifications: [{"code": "G06F3/044", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/033", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/03545", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F3/041", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/04162", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0442", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0447", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0446", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/033", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/03545", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F3/033", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/03545", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F3/0446", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/041", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 48703919