PATENT DOCUMENT

Publication Number: US-8743062-B2
Application Number: US-96037110-A
Country: US
Kind Code: B2

Title: Noise reduction for touch controller

Abstract:
A touch controller having noise reduction circuitry is disclosed. The touch controller can include a transmit section for generating stimulation signals to drive a touch display to sense a touch or hover event. The touch controller can also include a receive section for processing touch signals from the touch display indicative of the touch or hover event. The touch controller can reduce noise introduced into the stimulation signals and propagated through the touch display into the touch signals, thereby interfering with touch and hover sensing. To reduce the noise, the transmit section&#39;s noise reduction circuitry can isolate and subtract some or all of the noise from the stimulation signals. In addition or alternatively, the receive section&#39;s noise reduction circuitry can isolate and subtract some or all of the noise from the touch signals.

Claims:
What is claimed is: 
     
       1. A touch controller comprising:
 a transmit section configured to reduce noise, the transmit section including
 a digital-to-analog converter (DAC) configured to output a first stimulation signal and a second stimulation signal, the stimulation signals including the noise, and 
 multiple output buffers, a first output buffer configured to convert the noise to first differential noise and output the first stimulation signal with the first differential noise to a touch sensor panel, and a second output buffer configured to convert the noise to second differential noise and output the second stimulation signal with the second differential noise to the touch sensor panel; and 
 
 a receive section configured to receive a touch signal generated from the first and second stimulation signals, the received touch signal having the first and second differential noise canceled therefrom. 
 
     
     
       2. The touch controller of  claim 1 , wherein the received touch signal comprises a first touch signal generated from the first stimulation signal with the first differential noise and a second touch signal generated from the second stimulation signal with the second differential noise, the first and second touch signals being coupled together to cancel out the first and second differential noise. 
     
     
       3. The touch controller of  claim 1 , wherein the first output buffer receives the first stimulation signal as a first input and the second stimulation signal as a second input so as to convert the noise in the first and second stimulation signals into the first differential noise, and the second output buffer receives the second stimulation signal as a first input and the first stimulation signal as a second input so as to convert the noise in the first and second stimulation signals into the second differential noise. 
     
     
       4. The touch controller of  claim 3 , wherein the first output buffer receives a bias voltage coupled with the second stimulation signal as the second input to the first output buffer, and the second output buffer receives a bias voltage coupled with the first stimulation signal as the second input to the second output buffer. 
     
     
       5. The touch controller of  claim 4 , wherein the bias voltage is coupled with the first stimulation signal through one or more voltage dividers. 
     
     
       6. The touch controller of  claim 4 , wherein the bias voltage is coupled with the second stimulation signal through one or more voltage dividers. 
     
     
       7. The touch controller of  claim 4 , wherein the bias voltage introduces a second noise into the first and second stimulation signals. 
     
     
       8. The touch controller of  claim 7 , wherein the second noise is canceled out by using the bias voltage as a reference. 
     
     
       9. The touch controller of  claim 1 , wherein the first and second stimulation signals have opposite phases, one having a positive phase and the other having a negative phase. 
     
     
       10. The touch controller of  claim 1 , wherein the converter induces the noise in the stimulation signals. 
     
     
       11. The touch controller of  claim 1 , wherein the noise comprises common mode noise. 
     
     
       12. The touch controller of  claim 1 , wherein the transmit section further comprises:
 multiple DAC buffers, a first DAC buffer configured to transmit the first stimulation signal with the noise for generating a first touch signal and a second DAC buffer configured to transmit the second stimulation signal with the noise for generating a second touch signal. 
 
     
     
       13. A touch sensitive device comprising:
 a touch sensor panel; and 
 a touch controller comprising:
 a transmit section configured to reduce noise, the transmit section including
 a digital-to-analog converter (DAC) configured to output a first stimulation signal and a second stimulation signal, the stimulation signals including the noise, and 
 multiple output buffers, a first output buffer configured to convert the noise to first differential noise and output the first stimulation signal with the first differential noise to the touch sensor panel, and a second output buffer configured to convert the noise to second differential noise and output the second stimulation signal with the second differential noise to the touch sensor panel; and 
 
 a receive section configured to receive a touch signal generated from the first and second stimulation signals, the received touch signal having the first and second differential noise canceled therefrom. 
 
 
     
     
       14. The touch sensitive device of  claim 13 , wherein the received touch signal comprises a first touch signal generated from the first stimulation signal with the first differential noise and a second touch signal generated from the second stimulation signal with the second differential noise, the first and second touch signals being coupled together to cancel out the first and second differential noise. 
     
     
       15. The touch sensitive device of  claim 13 , wherein the first output buffer receives the first stimulation signal as a first input and the second stimulation signal as a second input so as to convert the noise in the first and second stimulation signals into the first differential noise, and the second output buffer receives the second stimulation signal as a first input and the first stimulation signal as a second input so as to convert the noise in the first and second stimulation signals into the second differential noise. 
     
     
       16. The touch sensitive device of  claim 15 , wherein the first output buffer receives a bias voltage coupled with the second stimulation signal as the second input to the first output buffer, and the second output buffer receives a bias voltage coupled with the first stimulation signal as the second input to the second output buffer. 
     
     
       17. The touch sensitive device of  claim 16 , wherein the bias voltage is coupled with the first stimulation signal through one or more voltage dividers. 
     
     
       18. The touch sensitive device of  claim 16 , wherein the bias voltage is coupled with the second stimulation signal through one or more voltage dividers. 
     
     
       19. The touch sensitive device of  claim 16 , wherein the bias voltage introduces a second noise into the first and second stimulation signals. 
     
     
       20. The touch sensitive device of  claim 19 , wherein the second noise is canceled out by using the bias voltage as a reference. 
     
     
       21. The touch sensitive device of  claim 13 , wherein the first and second stimulation signals have opposite phases, one having a positive phase and the other having a negative phase. 
     
     
       22. The touch sensitive device of  claim 13 , wherein the converter induces the noise in the stimulation signals. 
     
     
       23. The touch sensitive device of  claim 13 , wherein the noise comprises common mode noise. 
     
     
       24. The touch sensitive device of  claim 13 , wherein the transmit section further comprises:
 multiple DAC buffers, a first DAC buffer configured to transmit the first stimulation signal with the noise for generating a first touch signal and a second DAC buffer configured to transmit the second stimulation signal with the noise for generating a second touch signal.

Description:
FIELD 
     This relates generally to touch controllers in touch sensitive devices and more particularly, to noise reduction for touch controllers in touch sensitive devices. 
     BACKGROUND 
     Many types of input devices are available for performing operations in a computing system, such as buttons or keys, mice, trackballs, touch sensor panels, joysticks, touch pads, touch screens, and the like. Touch sensitive devices, and touch screens, in particular, are becoming increasingly popular because of their ease and versatility of operation as well as their declining price. Touch sensitive devices 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 substantially cover at least a portion of the viewable area of the display device. Touch sensitive devices can generally allow a user to perform various functions by touching or hovering over the touch sensor panel using one or more fingers, a stylus or other object at a location often dictated by a user interface (UI) including virtual buttons, keys, bars, displays, and other elements, being displayed by the display device. In general, touch sensitive devices can recognize a touch event and the position of the touch event on the touch sensor panel or a hover event and the position of the hover event on the touch sensor panel, and the computing system can then interpret the touch or hover event in accordance with the display appearing at the time of the event, and thereafter can perform one or more operations based on the event. 
     The ability to recognize and interpret the touch or hover event can be compromised by noise introduced into the touch sensitive device by various components. However, it can be challenging to substantially reduce or eliminate the noise so that the touch sensitive device can perform touch and hover operations effectively and efficiently. 
     SUMMARY 
     This relates to a touch sensitive device having a touch controller with noise reduction circuitry. The touch controller can include a transmit section for generating stimulation signals to drive a touch display to sense a touch or hover event. The touch controller can also include a receive section for processing touch signals from the touch display indicative of the touch or hover event. Noise can be introduced into the stimulation signals and propagated through the touch sensitive device components into the touch signals, thereby interfering with touch and hover sensing. To reduce the noise, the touch controller can operate noise reduction circuitry in the transmit section, the receive section, or both. In one example, the transmit section&#39;s noise reduction circuitry can isolate and subtract noise from the stimulation signals. In another example, the receive section&#39;s noise reduction circuitry can isolate and subtract noise from the touch signals. In still another example, the transmit section&#39;s noise reduction circuitry can isolate and subtract some noise from the stimulation signals, while the receive section&#39;s noise reduction circuitry can isolate and subtract remaining noise from the touch signals. In addition to a touch display, the touch controller can be similarly used with a touch sensor panel. Noise reduction circuitry can advantageously improve touch and hover sensing in the touch sensitive device by providing clearer, more accurate touch and hover events for processing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an exemplary touch sensitive device having a touch controller with noise reduction circuitry according to various embodiments. 
         FIG. 2  illustrates an exemplary method of reducing noise in a touch sensitive device, such as in  FIG. 1 , according to various embodiments. 
         FIG. 3  illustrates an exemplary touch controller having a transmit section with noise reduction circuitry according to various embodiments. 
         FIG. 4  illustrates an exemplary method of reducing noise in a touch controller, such as in  FIG. 3 , according to various embodiments. 
         FIG. 5  illustrates another exemplary touch controller having a transmit section with noise reduction circuitry according to various embodiments. 
         FIG. 6  illustrates an exemplary method of reducing noise in a touch controller, such as in  FIG. 5 , according to various embodiments. 
         FIG. 7  illustrates an exemplary touch controller having transmit and receive sections with noise reduction circuitry according to various embodiments. 
         FIG. 8  illustrates an exemplary method of reducing noise in a touch controller, such as in  FIG. 7 , according to various embodiments. 
         FIG. 9  illustrates another exemplary touch controller having transmit and receive sections with noise reduction circuitry according to various embodiments. 
         FIG. 10  illustrates an exemplary method of reducing noise in a touch controller, such as in  FIG. 9 , according to various embodiments. 
         FIG. 11  illustrates an exemplary touch controller having a receive section with noise reduction circuitry according to various embodiments. 
         FIG. 12  illustrates an exemplary method of reducing noise in a touch controller, such as in  FIG. 11 , according to various embodiments. 
         FIG. 13  illustrates another exemplary touch controller having a transmit section with noise reduction circuitry according to various embodiments. 
         FIG. 14  illustrates an exemplary method of reducing noise in a touch controller, such as in  FIG. 13 , according to various embodiments. 
         FIG. 15  illustrates an exemplary computing system having a touch controller with noise reduction circuitry according to various embodiments. 
         FIG. 16  illustrates an exemplary mobile telephone having a touch sensitive device with noise reduction circuitry according to various embodiments. 
         FIG. 17  illustrates an exemplary digital media player having a touch sensitive device with noise reduction circuitry according to various embodiments. 
         FIG. 18  illustrates an exemplary personal computer having a touch sensitive device with noise reduction circuitry 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 a touch sensitive device having a touch controller with noise reduction circuitry. The touch controller can include a transmit section for generating stimulation signals to drive a touch display to sense a touch or hover event. The touch controller can also include a receive section for processing touch signals from the touch display indicative of the touch or hover event. Noise, e.g., correlated or common mode noise, can be introduced into the stimulation signals and propagated through the touch sensitive device components into the touch signals, thereby interfering with touch and hover sensing. To reduce the noise, the touch controller can operate noise reduction circuitry in the transmit section, the receive section, or both. In some embodiments, the transmit section&#39;s noise reduction circuitry can isolate and subtract noise from the stimulation signals. In some embodiments, the receive section&#39;s noise reduction circuitry can isolate and subtract noise from the touch signals. In some embodiments, the transmit section&#39;s noise reduction circuitry can isolate and subtract some noise from the stimulation signals, while the receive section&#39;s noise reduction circuitry to isolate and subtract remaining noise from the touch signals. Noise reduction circuitry can advantageously improve touch and hover sensing in the touch sensitive device by providing clearer, more accurate touch and hover events for processing. 
     Although various embodiments describe the touch controller being used with a touch display, it is to be understood that the touch controller can also be used in the same or a similar manner with a touch sensor panel (i.e., without a display) and any other touch sensitive device according to various embodiments. 
       FIG. 1  illustrates an exemplary touch sensitive device having a touch controller with noise reduction circuitry according to various embodiments. In the example of  FIG. 1 , touch sensitive device  100  can include touch display  124  for displaying image and/or graphics data on circuitry, e.g., pixels, during display mode and for sensing a touching and/or hovering object by circuitry, e.g., pixels, during touch mode. The touch display  124  can include active area  134  having pixels for displaying the data and sensing the object touch and/or hover. The touch display  124  can also include gate driver  138  for driving the active area  134  with gate signals  136  during the display and touch modes to facilitate the displaying and sensing. The touch sensitive device  100  can also include touch controller  106  for controlling the touch display  124  during the touch mode. The touch controller  106  can include transmit section  114  for driving the touch display  124  via stimulation signals  116  to sense the object touch and/or hover. The touch controller  106  can also include receive section  107  for receiving and processing touch signals  103  from the touch display  124  indicative of the sensed touch and/or hover. The touch sensitive device  100  can further include display controller  142  for controlling the touch display  124  during the display mode. The display controller  142  can supply voltage signals  133  and timing signals  135  to the gate driver  138  to cause the gate driver to drive the touch display  124  via the gate signals  136  during the display mode and to remain static during the touch mode. The display controller  142  can also transmit pixel control signals  141  via source drivers (not shown) to the active area  134  to facilitate the displaying of data at the touch display  124 . The transmit section  114  and/or the receive section  107  of the touch controller  106  can include noise reduction circuitry, according to various embodiments, to reduce noise present in the stimulation signals  116  and the touch signals  103 , thereby improving touch and hover sensing. Examples of the noise reduction circuitry will be described in more detail below. 
     It is to be understood that the touch sensitive device of  FIG. 1  is not limited to the components and configuration shown, but can include other and/or additional components and configurations according to various embodiments. For example, the touch controller and the display controller can be integrated into a single controller. Or the gate driver can be separate from the touch display. Or the gate driver and the display controller can be omitted in devices that do not require data displaying, e.g., track-pads. 
       FIG. 2  illustrates an exemplary method of reducing noise for a touch controller in a touch sensitive device according to various embodiments. In the example of  FIG. 2 , a component in a transmit section of a touch controller can generate a stimulation signal for driving a touch display ( 210 ). The component can inadvertently induce noise in the generated signal. The stimulation signal with the noise can be transmitted to downstream components in the transmit section for further processing before driving the touch display ( 220 ). The downstream components can also induce noise in the processed signal ( 230 ). Since the noise source is a single upstream component, the noise induced by and/or propagating through the downstream components can be additive and therefore appear as correlated noise or common mode noise on the processed signal across multiple drive inputs (or ports) to the touch display. The correlated noise can subsequently be reduced in the transmit section of the touch controller, in a receive section of the touch controller, or in both, as will be described in more detail below, to improve touch and hover sensing ( 240 ). In the transmit section, the noise can be reduced in the stimulation signal. In the receive section, the noise can be reduced in a touch signal generated from the stimulation signal and transmitted to the receive section from the touch display. The stimulation signal with reduced noise can then drive the touch display and the touch signal with reduced noise can then be used to perform some operation of the touch sensitive device ( 250 ). 
       FIG. 3  illustrates an exemplary transmit section of a touch controller having noise reduction circuitry according to various embodiments. In the example of  FIG. 3 , transmit section  300  can generate stimulation signals for driving a touch display (not shown). The transmit section  300  can include digital-to-analog converter (DAC)  312  for generating stimulation signals to drive the touch display. The DAC  312  can output a positive stimulation signal Vp 1  and a negative stimulation signal Vn 1 , each signal having induced noise. The transmit section  300  can also include DAC buffers  322 ,  324  to receive the respective stimulation signals Vp 1 , Vn 1  from the DAC  312 . The DAC buffers  322 ,  324  can have input impedances Zin 1  and feedback impedances Zfb 1 . In some embodiments, the DAC buffers  322 ,  324  can amplify the stimulation signals Vp 1 , Vn 1  to an effective level to drive the touch display, where the gain of the DAC buffers can be (1+Zfb 1 /Zin 1 ). As a consequence, the induced noise in the stimulation signals Vp 1 , Vn 1  can also be amplified. The DAC buffers  322 ,  324  can also induce additional noise into the stimulation signals Vp 1 , Vn 1  to form correlated noise or common mode noise in the stimulation signals Vp 2 , Vn 2  outputted from the buffers. 
     The transmit section  300  can include voltage divider  332 , with characteristic impedance Zdiv, to receive the stimulation signals Vp 2 , Vn 2  from the buffers  322 ,  324  and to isolate the correlated noise Vnz therefrom. The center tap of the voltage divider  332  can be connected via impedance Zref to a second bias voltage Vbias 2  and also to the non-inverting input of the output buffers. Because the stimulation signals Vp 2 , Vn 2  are closely matched, they can cancel each other out in the voltage divider  332 , leaving the correlated noise Vnz as an output from the divider. The transmit section  300  can also include output buffers  342 ,  344  to receive the respective stimulation signals Vp 2 , Vn 2  from the DAC buffers  322 ,  324  and the isolated noise Vnz from the voltage divider  332 . The output buffers  342 ,  344  can have input impedances Zin 2  and feedback impedance Zfb 2 . Assuming Zfb 2 /Zin 2 =Zref/Zdiv, the voltage at the output of the output buffer  342  can be as follows. 
                       Vp   ⁢           ⁢   3     =         (     Vob_ref   -     Vp   ⁢           ⁢   2       )     *     (       Zfb   ⁢           ⁢   2       Zin   ⁢           ⁢   2       )       +     Vbias   ⁢           ⁢   2         ,           (   1   )               
where Vp 3 =the positive stimulation signal output from the output buffer  342 , Vob_ref=the voltage at the center of the voltage divider  332 , Vp 2 =the positive stimulation signal output from the DAC buffer  322 , Zfb 2 =the feedback impedance of the output buffer  342 , Zin 2 =the input impedance of the output buffer  342 , and Vbias 2 =the bias voltage inputted to the output buffer  342 . Similarly, the voltage at the output of the output buffer  344  can be as follows.
 
                       Vn   ⁢           ⁢   3     =         (     Vob_ref   -     Vn   ⁢           ⁢   2       )     *     (       Zfb   ⁢           ⁢   2       Zin   ⁢           ⁢   2       )       +     Vbias   ⁢           ⁢   2         ,           (   2   )               
where Vn 3 =the negative stimulation signal output from the output buffer  344 , Vn 2 =the negative stimulation signal output from the DAC buffer  324 , Zfb 2 =the feedback impedance of the output buffer  344 , Zin 2 =the input impedance of the output buffer  344 , and Vbias 2 =the bias voltage inputted to the output buffer  344 .
 
     The output buffers  342 ,  344  can operate as differential buffers to subtract the isolated noise Vnz from the stimulation signals Vp 2 , Vn 2  and to refer the output buffer dynamic signal to a second bias voltage level Vbias 2 . An array of the output buffers  342 ,  344  can then output the respective stimulation signals Vp 3 , Vn 3  with substantially reduced noise to the touch display for touch and hover sensing. 
     In an example, the stimulation signals Vp 1 , Vn 1  outputted from the DAC  312  can contribute voltage noise densities ENZ_DACP and ENZ_DACN, respectively. As a result, each DAC buffer  322 ,  324  can have input referred voltage noise densities ENZ_DBUF and each output buffer  342 ,  344  can have input referred voltage noise densities ENZ_OB. For simplicity, in this example, it is assumed that the various passive feedback and input impedances Zin 1 , Zin 2 , Zfb 1 , Zfb 2  and bias references Vbias 1 , Vbias 2  are noise free or have negligible noise. 
     Without noise compensation, the total correlated output noise density of the positive stimulation signal Vp 3  due to the DAC induced output noise density of the positive stimulation signal Vp 1  alone could be as follows.
 
 ENZ   —   Vp 3 =G   —   DBUF*G   —   OB*ENZ   —   DACP,   (3)
 
where ENZ_Vp 3 =the total correlated output noise density of the stimulation signal Vp 3 , G_DBUF=the gain of the DAC buffer  322 , G_OB=the gain of the output buffer  342 , and ENZ_DACP=the voltage noise density contributed by the DAC  312  in the stimulation signal Vp 1 . Similarly, without noise compensation, the total correlated output noise density of the negative stimulation signal Vn 3  due to the DAC induced noise density of the negative stimulation signal Vn 1  alone could be as follows.
 
 ENZ   —   Vn 3 =G   —   DBUF*G   —   OB*ENZ   —   DACN,   (4)
 
where ENZ_Vn 3 =the total correlated output noise density of the stimulation signal Vn 3 , G_DBUF=the gain of the DAC buffer  324 , G_OB=the gain of the output buffer  344 , and ENZ_DACN=the voltage noise density contributed by the DAC  312  in the stimulation signal Vn 1 .
 
     It should be understood that a correlated noise component in the stimulation signals Vp 3 , Vn 3 , as the noise component distributed to the drive ports of a touch display, can be additive in nature, such that the noise component can be n times higher across the drive ports than it would have been at the output of a single output buffer, where n=the number of drive ports. In contrast, an uncorrelated noise component in the stimulation signals Vp 3 , Vn 3 , can be scaled by the square root of the total number of drive lines (of a touch display) driven by the stimulation signals, such that the uncorrelated noise component can be √{square root over (n)} times lower than the correlated noise component. 
     By using noise compensation, according to various embodiments, the dominant correlated noise component can be substantially reduced or eliminated, as described in the following example. 
     The voltage noise density at the output of the DAC buffer  322  can be as follows.
 
 ENZ   —   Vp 2 =G   —   DBUF*ENZ   —   DACP,   (5)
 
where ENZ_Vp 2 =the voltage noise density of the stimulation signal Vp 2 , G_DBUF=the gain of the DAC buffer  322 , and ENZ_DACP=the voltage noise density contributed by the DAC  312  in the stimulation signal Vp 1 . Here, the voltage noise density contributed by the DAC  312  can be scaled by the gain of the DAC buffer  322  to provide the voltage noise density at the output of the DAC buffer. Similarly, the voltage noise density at the output of the DAC buffer  324  can be as follows.
 
 ENZ   —   Vn 2 =G   —   DBUF*ENZ   —   DACN,   (6)
 
where ENZ_Vn 2 =the voltage noise density of the stimulation signal Vn 2 , G_DBUF=the gain of the DAC buffer  324 , and ENZ_DACN=the voltage noise density contributed by the DAC  312  in the stimulation signal Vn 1 . Here, the voltage noise density contributed by the DAC  312  can be scaled by the gain of the DAC buffer  324  to provide the voltage noise density at the output of the DAC buffer.
 
     The center tap Vob_ref of the voltage divider  332  can see half of the noise densities ENZ_Vn 2 , ENZ_Vp 2 , represented as follows.
 
 Vob   —   ref =(½  ENZ   —   Vn 2,½  ENZ   —   Vp 2),  (7)
 
where the comma separating the components is a notation used herein to identify individual noise contributors and to separate correlated and non-correlated noise components.
 
     Therefore, with noise compensation, the total correlated output noise density of the positive stimulation signal Vp 3  due to the DAC induced output noise density of the positive stimulation signal Vp 1  can be as follows. 
                       ENZ_Vp   ⁢           ⁢   3     =       (     Vob_ref   -     ENZ_Vp   ⁢           ⁢   2       )     *     (       Zfb   ⁢           ⁢   2       Zin   ⁢           ⁢   2       )         ,           (   8   )               
where ENZ_Vp 3 =the total correlated output noise density of the stimulation signal Vp 3  outputted by the output buffer  342 , Vob_ref=the voltage at the center of the voltage divider  332 , ENZ_Vp 2 =the voltage noise density of the stimulation signal Vp 2 , Zfb 2 =the feedback impedance of the output buffer  342 , and Zin 2 =the input impedance of the output buffer  342 . Compared to the noise density without noise compensation, as in Equation (3), the noise density with noise compensation, as in Equation (8), can be substantially lower.
 
     Similarly, with noise compensation, the total correlated output noise density of the negative stimulation signal Vn 3  due to the DAC induced output noise density of the negative stimulation signal Vn 1  can be as follows. 
                       ENZ_Vn   ⁢           ⁢   3     =       (     Vob_ref   -     ENZ_Vn   ⁢           ⁢   2       )     *     (       Zfb   ⁢           ⁢   2       Zin   ⁢           ⁢   2       )         ,           (   9   )               
where ENZ_Vn 3 =the total correlated output noise density of the stimulation signal Vn 3  outputted by the output buffer  344 , ENZ_Vn 2 =the voltage noise density of the stimulation signal Vp 2 , Zfb 2 =the feedback impedance of the output buffer  344 , and Zin 2 =the input impedance of the output buffer  344 . Compared to the noise density without noise compensation, as in Equation (4), the noise density with noise compensation, as in Equation (9), can be substantially lower.
 
     Due to half of a touch display being driven with the positive stimulation signal Vp 3  and the other half being driven with the negative stimulation signal Vn 3 , the total correlated noise component ENZ_SAO at the output of a touch controller&#39;s receive section&#39;s sense amplifier (from touch signals received from a touch display and then processed) can be as follows. 
                     ENZ_SAO   =       (       (     NSTM_P   *   ENZ_Vp   ⁢           ⁢   3     )     +     (     NSTM_N   *   ENZ_Vn   ⁢           ⁢   3     )       )     *     (     Csig   Cfb     )         ,           (   10   )               
where Csig=the touch signal capacitance, Cfb=the feedback capacitance of the sense amplifier, NSTM_P=the number of ports driven with the positive stimulation signal Vp 3 , NSTM_N=the number of ports driven with the negative stimulation signal Vn 3 , ENZ_Vp 3 =the total correlated output noise density of the stimulation signal Vp 3  outputted by the output buffer  342 , and ENZ_Vn 3 =the total correlated output noise density of the stimulation signal Vn 3  outputted by the output buffer  344 .
 
     Written another way, Equation (10) becomes 
                   ENZ_SAO   =       (     NSTM_P   +   NSTM_N     )     *     (     Csig   Cfb     )     *   G_OB   *     (         -   G_DBUF     *   ENZ_DACP     ,       1   2     ⁢   G_DBUF   *   ENZ_DACP     ,       1   2     ⁢   G_DBUF   *   ENZ_DACN     ,       -   G_DBUF     *   ENZ_DACN     ,       1   2     ⁢   G_DBUF   *   ENZ_DACP     ,       1   2     ⁢   G_DBUF   *   ENZ_DACN       )               (   11   )               
where the noise components expressed in the parentheses can be subdivided into two uncorrelated terms, each being zero, as follows.
 
     
       
         
           
             
               
                 
                   
                     ( 
                     
                       
                         
                           
                             
                               ENZ_DACP 
                               * 
                               
                                 ( 
                                 
                                   
                                     
                                       1 
                                       2 
                                     
                                     ⁢ 
                                     G_DBUF 
                                   
                                   + 
                                   
                                     
                                       1 
                                       2 
                                     
                                     ⁢ 
                                     G_DBUF 
                                   
                                   - 
                                   G_DBUF 
                                 
                                 ) 
                               
                             
                             , 
                           
                         
                       
                       
                         
                           
                             ENZ_DACN 
                             * 
                             
                               ( 
                               
                                 
                                   
                                     1 
                                     2 
                                   
                                   ⁢ 
                                   G_DBUF 
                                 
                                 + 
                                 
                                   
                                     1 
                                     2 
                                   
                                   ⁢ 
                                   G_DBUF 
                                 
                                 - 
                                 G_DBUF 
                               
                               ) 
                             
                           
                         
                       
                     
                     ) 
                   
                   = 
                   
                     
                       ( 
                       
                         0 
                         , 
                         0 
                       
                       ) 
                     
                     = 
                     0. 
                   
                 
               
               
                 
                   ( 
                   12 
                   ) 
                 
               
             
           
         
       
     
     Accordingly, this noise reduction scheme according to various embodiments can reduce noise by subtracting half of the correlated noise in the stimulation signals at the output buffers  342 ,  344 , and then converting the remaining correlated noise from single ended to differential noise, which can then be canceled in the touch controller&#39;s receive section. The conversion from single ended to differential noise can be accomplished by cross coupling the isolated noise Vnz at point Vob_ref between output buffers of opposite polarity. 
     The example of  FIG. 3  illustrates transmit section components for outputting two stimulation signals to drive a touch display. However, it is to be understood that additional similar components can be used to generate and output more than two stimulation signals according to the needs of the touch display. 
       FIG. 4  illustrates an exemplary method of reducing noise in a touch controller of a touch sensitive device according to various embodiments. This method can be applied to the touch controller of  FIG. 3 , for example. In the example of  FIG. 4 , a positive stimulation signal Vp 1  and a negative stimulation signal Vn 1  with noise can be generated, for example, by a DAC ( 410 ). The noise can come from the component generating the stimulation signals and/or from downstream components processing the stimulation signals. In some embodiments, the noise can be correlated or common mode. The noise can be isolated from the stimulation signals Vp 1 , Vn 1 , for example, by a voltage divider ( 420 ). The isolated noise can then be subtracted from the stimulation signals Vp 2 , Vn 2 , for example, by a differential output buffer ( 430 ). The resulting stimulation signals Vp 3 , Vn 3  can be outputted with substantially reduced noise ( 440 ). 
       FIG. 5  illustrates another exemplary transmit section of a touch controller having noise reduction circuitry according to various embodiments. The transmit section of  FIG. 5  is similar to that of  FIG. 3  with the addition of a second voltage divider between the DAC and DAC buffers. In the example of  FIG. 5 , transmit section  500  can include DAC  512  to generate a positive stimulation signal Vp 1  and a negative stimulation signal Vn 1 , each signal having induced noise. The transmit section  500  can also include first voltage divider  534  to receive the stimulation signals Vp 1 , Vn 1  from the DAC  512  and to isolate the induced noise Vnz 1  therefrom. The transmit section  500  can include DAC buffers  522 ,  524  to receive the respective stimulation signals Vp 1 , Vn 1  from the DAC  312  and the isolated noise Vnz 1  from the voltage divider  534 . The DAC buffers  522 ,  524  can have feedback impedances Zfb 1  and input impedances Zin 1 . The buffers  522 ,  524  can operate as differential buffers to subtract the isolated noise Vnz 1  from the stimulation signals Vp 1 , Vn 1 . Here, common mode voltage at the output of the DAC buffers  522 ,  524  can advantageously be independent on the common mode voltage of the DAC  512 . As such, a separate bias voltage input for the DAC buffers  522 ,  524  can be omitted (as opposed to the separate bias voltage input Vbias 1  in  FIG. 3 ). 
     The buffers  522 ,  524  can then output the respective stimulation signals Vp 2 , Vn 2  with the noise from the DAC  512  substantially reduced. However, the buffers  522 ,  524  can also induce noise in the stimulation signals Vp 2 , Vn 2 , which can be isolated and reduced as described in  FIG. 3 . That is, in the example of  FIG. 5 , the transmit section  500  can include second voltage divider  532  to isolate noise Vnz 2  from the stimulation signals Vp 2 , Vn 2  outputted by the DAC buffers  522 ,  524 . The transmit section  500  can also include output buffers  542 ,  544  to receive the respective stimulation signals Vp 2 , Vn 2  from the DAC buffers  522 ,  524  and the isolated noise Vnz 2  from the second voltage divider  532 . The output buffers  542 ,  544  can have input impedances Zin 2  and feedback impedances Zfb 2 . The output buffers  542 ,  544  can operate as differential buffers to subtract the isolated noise Vnz 2  from the stimulation signals Vp 2 , Vn 2 . An array of output buffers  542 ,  544  can then output respective stimulation signals Vp 3 , Vn 3  with substantially reduced noise to the touch display for touch and hover sensing. 
     The example of  FIG. 5  illustrates transmit section components for outputting two stimulation signals to drive a touch display. However, it is to be understood that additional similar components can be used to generate and output more than two stimulation signals according to the needs of the touch display. 
       FIG. 6  illustrates another exemplary method of reducing noise in a touch controller of a touch sensitive device according to various embodiments. This method can be applied to the touch controller of  FIG. 5 , for example. In the example of  FIG. 6 , a positive stimulation signal Vp and a negative stimulation signal Vn with noise can be generated, for example, by a DAC ( 610 ). The noise can come from the component generating the stimulation signals. In some embodiments, the noise can be correlated or common mode. The noise can be isolated from the stimulation signals Vp, Vn, for example, by a voltage divider ( 620 ). The isolated noise can then be subtracted from the stimulation signals Vp, Vn, for example, by a DAC buffer ( 630 ). Further noise, either added or remaining, can be isolated from the stimulation signals Vp, Vn, for example, by another voltage divider ( 640 ). The additional noise can be residual noise from the component generating the stimulation signals and/or induced noise from downstream components processing the stimulation signals. In some embodiments, the noise can be correlated or common mode. The further isolated noise can be subtracted from the stimulation signals Vp, Vn, for example, by a differential output buffer ( 650 ). The resulting stimulation signals Vp, Vn can be outputted with substantially reduced noise ( 660 ). 
       FIG. 7  illustrates an exemplary transmit section and receive section of a touch controller having noise reduction circuitry according to various embodiments. In the example of  FIG. 7 , transmit section  700  can generate stimulation signals for driving touch display  730  and receive section  750  can process touch signals generated from the stimulation signals at the touch display. The transmit section  700  can include digital-to-analog converter (DAC)  712  for generating stimulation signals to drive the touch display  730 . The DAC  712  can output a positive stimulation signal Vp 1  having induced noise. The transmit section  700  can also include first DAC buffer  722  to receive the stimulation signal Vp 1  from the DAC  712 . The DAC buffer  722  can have feedback impedances Zfb 1  and Zin 1 . In some embodiments, the DAC buffer  722  can amplify the stimulation signal Vp 1  to an effective level to drive the touch display and/or facilitate noise reduction. The gain of the DAC buffer  722  can be (1+Zfb 1 /Zin 1 ). As a consequence of amplifying the stimulation signal Vp 1  by the gain, the induced noise in the stimulation signal can also be amplified. The first DAC buffer  722  can also induce additional noise into the stimulation signal Vp 1  to form correlated noise or common mode noise in the stimulation signal Vp 2  outputted from the buffer. 
     The first DAC buffer  722  can output the stimulation signal Vp 2  to first output buffer  742  and to the second DAC buffer  724  in the transmit section  700 . The second DAC buffer  724 , which can be configured as an inverter, can invert the stimulation signal Vp 2  into a negative stimulation signal Vn 2  having inverted induced noise. The DAC buffer  724  can also induce additional noise into the signal Vn 2 . The DAC buffer  724  can have an input impedance Zin 2  and feedback impedance Zfb 2 , where the gain of the second DAC buffer  724  can be −Zfb 2 /Zin 2 . In some embodiments, the second DAC buffer  724  can invert and amplify the stimulation signal Vp 2  to an effective level to drive the touch display and/or facilitate noise reduction. As a consequence of amplifying and inverting the stimulation signal Vp 2 , the induced noise in the stimulation signal can also be amplified. The gain (or amplification) of the DAC buffers  722 ,  724  can be set based on the touch display drive requirements and/or the noise reduction needs. In some embodiments, the gain of the first DAC buffer  722  can be larger than the gain of the second DAC buffer  724  to facilitate noise reduction. For example, the gain in the first DAC buffer can be 4, while the gain in the second DAC buffer can be 1. In some embodiments, the second DAC buffer  724  can induce additional noise into the stimulation signal Vp 2 . However, due to the different gains in the DAC buffers  722 ,  724 , the induced noise from the second DAC buffer  724  can be negligible compared to that from the first DAC buffer  722 . 
     The second DAC buffer  724  can output the negative stimulation signal Vn 2  to second output buffer  744  in the transmit section. The output buffers  742 ,  744  can output the respective stimulation signals Vp 3 , Vn 3  with induced noise to the touch display  730 . The output buffers  742 ,  744  can have input impedances Zin 3  and feedback impedances Zfb 3 . The first output buffer  722  can output the induced noise from the DAC  712  and the first DAC buffer  722  in the positive stimulation signal Vp 3 . The second output buffer  724  can output the induced noise, inverted, from the DAC  712  and the first DAC buffer  722  in the negative stimulation signal Vn 3 . 
     Receive section  750  can include sense amplifier  762  for receiving and processing touch signals generated at the touch display  730 . The sense amplifier  762  can include a feedback capacitor Cfb. The touch display  730  can be driven by the stimulation signals Vp 3 , Vn 3  from the transmit section&#39;s output buffers  742 ,  744  to generate touch signals indicative of a touch or hover at the display. An array of NSTM_P output buffers  742  can couple into NSTM_P signal capacitors Csig in the touch display  730  generating signal charge NSTM_P*Csig*Vp 3  into the inverting input node of the sense amplifier  762 , where NSTM_P=the number of output buffers  742  outputting a positive stimulation signal Vp 3 . Similarly, an array of NSTM_N output buffers  744  can couple into NSTM_N signal capacitors Csig in the display  730  generating signal charge NSTM_N*Csig*Vn 3  into the inverting input node of the sense amplifier  762 , where NSTM_N=the number of output buffers  744  outputting a negative stimulation signal Vn 3 . Since Vp 3 =−Vn 3 , the effective charge Qsig_in into the sense amplifier  762  can be zero, in the absence of a touch or hover at the display  730 , and can be non-zero if one of the Csig capacitors in the display is modulated by Csig_sns, i.e., a change in sense capacitance due to a touch or hover at the display. 
     In an example, the DAC  712  can have an output voltage noise density ENZ_DAC. The first DAC buffer  722  can have an input referred noise density ENZ_DBUF 1 . The second DAC buffer  724  can have an input referred noise density ENZ_DBUF 2 . The output buffers  742 ,  744  can have a noise density ENZ_OB. For simplicity, in this example, it is assumed that the various passive feedback and input impedances Zin 1 , Zin 2 , Zin 3 , Zfb 1 , Zfb 2 , Zfb 3 , and bias reference Vbias are noise free or have negligible noise. Accordingly, the total correlated output noise density of the stimulation signal Vp 3  outputted by the output buffer  742  can be as follows.
 
 ENZ   —   Vp 3 =G   —   DBUF 1 *G   —   OB*ENZ   —   DAC,   (13)
 
where ENZ_Vp 3 =the total correlated output noise density of the stimulation signal Vp 3 , G_DBUF 1 =the gain of the first DAC buffer  722 , G_OB=the gain of the output buffer  742 , and ENZ_DAC=the voltage noise density contributed by the DAC  712  in the stimulation signal Vp 1 .
 
     The total correlated output noise density of the negative stimulation signal Vn 3  due to the DAC induced noise density of the negative stimulation signal Vn 1  can be as follows. 
                       ENZ_Vn   ⁢           ⁢   3     =     (             G_OB   *     (     1   +     G_DBUF   ⁢           ⁢   2       )     *   ENZ_DAC     ,               G_OB   *   G_DBUF   ⁢           ⁢   2   *   ENZ_DBUF   ⁢           ⁢   2           )       ,           (   14   )               
where ENZ_Vn 3 =the total correlated output noise density of the stimulation signal Vn 3 , G_DBUF 2 =the gain of the second DAC buffer  724 , G_OB=the gain of the output buffer  744 , ENZ_DAC=the voltage noise density contributed by the DAC  712  in the stimulation signal Vp 1 , and ENZ_DBUF 2 =the voltage noise density contributed by the DAC buffer  724  in the stimulation signal Vn 2 .
 
     As described above regarding Equation (10), due to half of the touch display  730  being driven with the positive stimulation signal Vp 3  and the other half being driven with the negative stimulation signal Vn 3 , the total correlated noise component ENZ_SAO at the output of the sense amplifier  762  in the receive section  750  can be as follows. 
                     ENZ_SAO   =       (       (     NSTM_P   *   ENZ_Vp   ⁢           ⁢   3     )     +     (     NSTM_N   *   ENZ_Vn   ⁢           ⁢   3     )       )     *     (     Csig   Cfb     )         ,           (   15   )               
where Csig=the touch signal capacitance, Cfb=the feedback capacitance of the sense amplifier  762 , NSTM_P=the number of ports driven with the positive stimulation signal Vp 3 , NSTM_N=the number of ports driven with the negative stimulation signal, ENZ_Vp 3 =the total correlated output noise density of the stimulation signal Vp 3  outputted by the output buffer  742 , and ENZ_Vn 3 =the total correlated output noise density of the stimulation signal Vn 3  outputted by the output buffer  744 .
 
     Suppose that the gains of the DAC buffers  722 ,  724  are opposite, e.g., G_DBUF 1 =−G_DBUF 2 =1, and the gain of the output buffers  724 ,  744  are G_OB=−1. Substituting Equations (13) and (14) and the gains into Equation (15) can result in the following. 
                     ENZ_SAO   =       (     NSTM_P   +   NSTM_N     )     *     (     Csig   Cfb     )     *     (       ENZ_DAC   -   ENZ_DAC     ,     ENZ_DBUF   ⁢           ⁢   2       )         ,           (   16   )               
where the DAC induced correlated noise component ENZ_DAC can cancel out because of the inversion in the second DAC buffer  724  of the positive stimulation signal Vp 2  (and the induced noise) into the negative stimulation signal Vn 2  (and the induced noise), leaving the correlated noise induced by the second DAC buffer in the negative stimulation signal Vn 2  to be additive across the drive ports at the touch display  730  and subsequently at the output of the sense amplifier  762  as follows.
 
                     ENZ_SAO   =       (       -   NSTM_N     *   ENZ_DBUF   ⁢           ⁢   2     )     *     (     Csig   Cfb     )         ,           (   17   )               
where this remaining noise component can be small enough to be negligible is some instances.
 
     The example of  FIG. 7  illustrates transmit section components for outputting two stimulation signals Vp 3 , Vn 3  to drive a touch display and receive section components for outputting one touch signal Vo to perform operations at a touch sensitive device. However, it is to be understood that additional similar components can be used to generate and output more than two stimulation signals and one touch signal according to the needs of the touch display. 
     Though  FIG. 7  illustrates the DAC generating a positive stimulation signal Vp that is later inverted to a negative stimulation signal Vn, it is to be understood that the DAC could alternatively generate a negative stimulation signal Vn that is later inverted to a positive stimulation signal Vp for noise reduction. 
       FIG. 8  illustrates an exemplary method of reducing noise in a touch controller of a touch sensitive device according to various embodiments. This method can be applied to the touch controller of  FIG. 7 , for example. In the example of  FIG. 8 , a positive stimulation signal Vp with noise can be generated, for example, by a DAC ( 810 ). The noise can come from the component generating the stimulation signal and/or from downstream components processing the stimulation signal. In some embodiments, the noise can be correlated or common mode. The positive stimulation signal Vp can be outputted for driving generation of a touch signal, for example, by a touch display ( 820 ). The stimulation signal Vp can also be inverted to a negative stimulation signal Vn with inverted noise ( 830 ). The stimulation signal Vn can be outputted for driving generation of a touch signal, for example, by the touch display ( 840 ). The touch signals can be generated from the stimulation signals Vp, Vn, where the noise is passed to the generated signals ( 850 ). The touch signals can be coupled together for processing, for example, by a sense amplifier ( 860 ). Because one touch signal having inverted noise is coupled to another touch signal having non-inverted noise, the noise can cancel out ( 870 ). The resulting coupled signal can be outputted with substantially reduced noise ( 880 ). 
       FIG. 9  illustrates another exemplary transmit section and receive section of a touch controller having noise reduction circuitry according to various embodiments. The receive section in  FIG. 9  is the same as that in  FIG. 7 . The transmit section in  FIG. 9  is similar to that in  FIG. 7  with the addition of a voltage divider to isolate inverter-induced noise. In the example of  FIG. 9 , transmit section  900  can include DAC  912  for generating stimulation signals to drive the touch display  930 . The DAC  912  can output a positive stimulation signal Vp 1  having induced noise. The transmit section  900  can also include first DAC buffer  922  to receive the stimulation signal Vp 1  from the DAC  912 . The DAC buffer  922  can include feedback impedances Zin 1  and Zfb 1  and can have a gain of (1+Zfb 1 /Zin 1 ). In some embodiments, the DAC buffer  922  can amplify the stimulation signal Vp 1  to an effective level to drive the touch display and/or facilitate noise reduction. As a consequence of amplifying the stimulation signal Vp 1 , the induced noise in the stimulation signal can also be amplified. The first DAC buffer  922  can also induce additional noise into the stimulation signal Vp 1  to form correlated noise or common mode noise in the stimulation signal Vp 2  outputted from the buffer. The first DAC buffer  922  can output the stimulation signal Vp 2  to first output buffer  942  and to second DAC buffer in the transmit section  900 . The first output buffer  942  can include a input impedance Zin 3  and feedback impedance Zfb 3  and can have a gain. 
     The transmit section  900  can include second DAC buffer  924  which can be configured as an inverter. The DAC buffer  924  can include an input impedance Zin 2  and a feedback impedance Zfb 2 . In some embodiments, the second DAC buffer  924  can amplify and invert the stimulation signal Vp 2  to an effective level to drive the touch display and/or facilitate noise reduction. As a consequence of amplifying and inverting the stimulation signal Vp 2 , the induced noise in the stimulation signal can also be amplified. The gain (or amount of amplification) of the DAC buffers  922 ,  924  can be the same or different based on the touch display drive requirements and/or the noise reduction needs. 
     The transmit section  900  can also include voltage divider  932  to receive the positive stimulation signal Vp 2  from the first DAC buffer  922  and the negative stimulation signal Vn 2  from the second DAC buffer  924  and isolate the noise induced by the second DAC buffer. Because the stimulation signals Vp 2 , Vn 2  with their DAC-induced noise are closely matched, they can cancel each other out, leaving the inverter-induced noise Vnz as an output from the voltage divider  932 . The transmit section  900  can include second output buffer  944  to receive the negative stimulation signal Vn 2  from the second DAC buffer  924  and the isolated noise Vnz from the voltage divider  932 . The second output buffer  944  can include an input impedance Zin 3  and a feedback impedance Zfb 3 . The second output buffer  944  can operate as a differential buffer to subtract the isolated inverter-induced noise Vnz from the stimulation signal Vn 2 , leaving the DAC-induced noise therein. The output buffers  942 ,  944  can output the respective stimulation signals Vp 3 , Vn 3  with DAC-induced noise to the touch display  930 . 
     Receive section  950  can include sense amplifier  962  for receiving and processing touch signals generated at the touch display  930 . The sense amplifier  962  can include a feedback capacitor Cfb. The touch display  930  can be driven by the stimulation signals Vp 3 , Vn 3  from the transmit section&#39;s output buffers  942 ,  944  to generate touch signals indicative of a touch or hover at the display. As described with respect to  FIG. 7 , here the touch signals can have inverted and non-inverted DAC-induced noise passed from their respective stimulation signals Vp 3 , Vn 3 . An array of NSTM_P output buffers  942  can couple into NSTM_P signal capacitors Csig in the touch display  930  generating signal charge NSTM_P*Csig*Vp 3  into the inverting input node of the sense amplifier  962 , where NSTM_P=the number of output buffers  942  outputting a positive stimulation signal Vp 3 . Similarly, an array of NSTM_N output buffers  944  can couple into NSTM_N signal capacitors Csig in the display  930  generating signal charge NSTM_N*Csig*Vn 3  into the inverting input node of the sense amplifier  962 , where NSTM_N=the number of output buffers  944  outputting a negative stimulation signal Vn 3 . Since Vp 3 =−Vn 3 , the effective charge Qsig_in into the sense amplifier  962  can be zero, in the absence of a touch or hover at the display  930 , and can be non-zero if one of the Csig capacitors in the display is modulated by Csig_sns, i.e., a change in sense capacitance due to a touch or hover at the display. When the touch signals are coupled together as input to the sense amplifier  962 , the DAC-induced noise can cancel out as described previously. The sense amplifier  962  can then output touch signal Vo with substantially reduced noise for touch and hover sensing. 
     Here, as in  FIG. 7 , the DAC-induced noise can be canceled out. Additionally, the second DAC buffer-induced noise (as illustrated in Equation (17)) can also be substantially reduced or eliminated using the voltage divider  932  as described previously. In an example, the voltage divider  932  having impedances Zdiv 1  and Zdiv 2  can isolate the noise component Vnz of the second DAC buffer  924 . Suppose the second DAC buffer  924  has an input referred noise density ENZ_DBUF 2  and a gain G_DBUF 2 =Zfb 2 /Zin 2 =−1. The output noise density of the second DAC buffer  924  can be the product of the non-inverting gain of the buffer and the input referred noise. That is, 
                       ENZ_Vn   ⁢           ⁢   2     =       ENZ_DBUF   ⁢           ⁢   2   *     (     1   +       Zfb   ⁢           ⁢   2       Zin   ⁢           ⁢   2         )       =     2   *   ENZ_DBUF   ⁢           ⁢   2         ,           (   18   )               
where ENZ_Vn 2 =the output noise density at the second DAC buffer  924 , Zfb 2 =the feedback impedance of the second DAC buffer, and Zin 2 =the input impedance of the second DAC buffer. The stimulation signal Vn 3  can see the inverted output noise density as follows.
 
 ENZ   —   Vn 3 —   N=− 2 *ENZ   —   DBUF 2,  (19)
 
where ENZ_Vn 3 _N=the inverted output noise density at the second output buffer  944 .
 
     The voltage divider  932  can cancel out the signal components of the stimulation signals Vp 2 , Vn 2 , but isolate half of the second DAC buffer output voltage noise density ENZ_Vn 2  because the impedances Zdiv 1 =Zdiv 2 . In other words, the center tap of the voltage divider  924  can have a noise component ENZ_DBUF 2 , which can be passed on to the non-inverting input of the second output buffer  944  and gained up by the non-inverting noise gain of the output buffer. Assuming that the gain of the second output buffer  944  is −1, i.e., the second output buffer impedances Zfb 3 =Zin 3 , the non-inverting noise gain of the second output buffer can be as follows. 
                       G_OB   ⁢   _NI     =       1   +       Zfb   ⁢           ⁢   3       Zin   ⁢           ⁢   3         =   2       ,           (   20   )               
where G_OB_NI=the non-inverting noise gain of the second output buffer  944 .
 
     The output noise density due to the isolated noise density component from the voltage divider  932  can be as follow.
 
 ENZ   —   Vn 3 —   P=G   —   OB   —   NI*ENZ   —   DBUF 2=2 *ENZ   —   DBUF 2,  (21)
 
where ENZ_Vn 3 _P=the output noise density from the voltage divider  932  at the second output buffer  944 .
 
     Accordingly, the total voltage noise density at the output of the second output buffer  944  due to the noise introduced by the second DAC buffer  924  can be canceled at the output buffer because the non-inverting input to the output buffer can be the inverted output noise density ENZ_Vn 3 _N, as in Equation (19), and the inverting input to the output buffer can be the output noise density ENZ_Vn 3 _P, as in Equation (21), such that when combined in the output buffer, ENZ_Vn 3 _N+ENZ_Vn 3 _P=0. 
     The example of  FIG. 9  illustrates transmit section components for outputting two stimulation signals Vp 3 , Vn 3  to drive a touch display and receive section components for outputting one touch signal Vo to perform operations at a touch sensitive device. However, it is to be understood that additional similar components can be used to generate and output more than two stimulation signals and one touch signal according to the needs of the touch display. 
     Though  FIG. 9  illustrates the DAC generating a positive stimulation signal Vp that is later inverted to a negative stimulation signal Vn from which noise is isolated, it is to be understood that the DAC could alternatively generate a negative stimulation signal Vn that is later inverted to a positive stimulation signal Vp from which the noise is isolated for noise reduction. 
       FIG. 10  illustrates another exemplary method of reducing noise in a touch controller of a touch sensitive device according to various embodiments. This method can be applied to the touch controller of  FIG. 9 , for example. In the example of  FIG. 10 , a positive stimulation signal Vp with noise can be generated, for example, by a DAC ( 1010 ). The noise can come from the component generating the stimulation signal and/or from downstream components processing the stimulation signal. In some embodiments, the noise can be correlated or common mode. The positive stimulation signal Vp can be outputted for driving generation of a touch signal, for example, by a touch display ( 1020 ). The stimulation signal Vp can also be inverted to a negative stimulation signal Vn with inverted noise ( 1030 ). Additional noise that was introduced into the negative stimulation signal Vn when inverted can be isolated from the signal. ( 1040 ). The isolated noise can then be subtracted from the stimulation signal Vn, for example, by a differential output buffer ( 1050 ). The stimulation signal Vn can be outputted for driving generation of a touch signal, for example, by the touch display ( 1060 ). The touch signals can be generated from the stimulation signals Vp, Vn, where the noise and inverted noise is passed to the generated signals ( 1070 ). The touch signals can be coupled together for processing, for example, by a sense amplifier ( 1080 ). Because one touch signal having inverted noise is coupled to another touch signal having non-inverted noise, the noise can cancel out ( 1090 ). The resulting coupled signal can be outputted with substantially reduced noise ( 1095 ). 
       FIG. 11  illustrates an exemplary receive section of a touch controller having noise reduction circuitry according to various embodiments. In the example of  FIG. 11 , receive section  1150  can include sense amplifier  1162  for receiving and processing touch signals from touch display  1130 . The sense amplifier  1162  can have a feedback capacitor Cfb. As described previously, the touch display  1130  can be driven with stimulation signals Vp 3 , Vn 3  from respective output buffers  1142 ,  1144  of touch controller transmit section  1100  to generate the respective touch signals Csig,p, Csig,n. An array of NSTM_P output buffers  1142  can couple into NSTM_P signal capacitors Csig in the touch display  1130  generating signal charge NSTM_P*Csig*Vp 3 , where NSTM_P=the number of output buffers  1142  outputting a positive stimulation signal Vp 3 . Similarly, an array of NSTM_N output buffers  1144  can couple into NSTM_N signal capacitors Csig in the display  1130  generating signal charge NSTM_N*Csig*Vn 3 , where NSTM_N=the number of output buffers  1144  outputting a negative stimulation signal Vn 3 . The signals can couple for effective chart Qsig_tot_n=NSTM_N*Csig into the inverting input node of the sense amplifier  1162 . Since Vp 3 =−Vn 3 , the effective charge Qsig_in into the sense amplifier  1162  can be zero, in the absence of a touch or hover at the display  1130 , and can be non-zero if one of the Csig capacitors in the display is modulated by Csig_sns, i.e., a change in sense capacitance due to a touch or hover at the display. 
     Gate driver  1138  of the touch display  1138  can powered by gate signal Vg from display controller  1110  which can form a parasitic capacitance Cg with the inverting input of the sense amplifier  1162 , thereby introducing noise Vgnz into the inverting input of the sense amplifier. The resulting output noise from the sense amplifier  1162  can be as follows.
 
 Vgnz   —   sao   —   n=G   —   SA   —   NI*Vgnz,   (22)
 
where Vgnz_sao_n=the output noise from the sense amplifier  1162 , and G_SA_NI=the inverting gain (−Cg/Cfb) of the sense amplifier.
 
     To reduce the output noise, the sense amplifier  1162  can operate as a differential amplifier to subtract an input based on the gate signal Vg from the touch signal input. For this, the gate signal Vg can be AC coupled into the non-inverting input of the sense amplifier  1162  via capacitor Cvb 1  relative to Vbias. The cut-off frequency of the high pass filter formed by capacitors Cvb 1 , Cvb 2  and resistor Rvb can be chosen well below the lowest stimulus frequency (for example, ten times lower) to prevent attenuation of the noise Vgnz in the stimulus frequency range. Tunable capacitor Cvb 2  can form a capacitive divider with capacitor Cvb 1  and can be used to adjust the noise level Vg_div to be applied to the non-inverting input of the sense amplifier  1162 . The ratio between the capacitors Cvb 1  and Cvb 2  can be adjusted so as to accomplish optimum noise cancellation and/or reduction at the output of the sense amplifier  1162 . 
     The noise Vgnz induced into the non-inverting input of the sense amplifier  1162  can be gained up by the non-inverting noise gain of the sense amplifier as follows. 
                       Vgnz_sao   ⁢   _p     =     Vgnz   *   α   *     (     1   +     Csi   Cfb       )         ,           (   23   )               
where Vgnz_sao_p=the noise at the non-inverting input of the sense amplifier  1162 , α=a noise scale factor adjustable by capacitor Cvb 2 , Csi=the total stray capacitance (not shown) at the input of the sense amplifier, and Cfb=the feedback capacitor of the sense amplifier.
 
     In order to cancel Vgnz, the noise at the non-inverting input, Vgnz_sao_p, of the sense amplifier  1162  and the noise at the inverting input, Vgnz_sao_n, can be the same, such that Vgnz_sao_p+Vgnz_sao_n=0. Substituting this condition into Equation (23) can result in the following. 
     
       
         
           
             
               
                 
                   
                     
                       
                         - 
                         Vgnz 
                       
                       * 
                       
                         ( 
                         
                           Cg 
                           Cfb 
                         
                         ) 
                       
                     
                     + 
                     
                       Vgnz 
                       * 
                       α 
                       * 
                       
                         ( 
                         
                           1 
                           + 
                           
                             Csi 
                             Cfb 
                           
                         
                         ) 
                       
                     
                   
                   = 
                   0. 
                 
               
               
                 
                   ( 
                   24 
                   ) 
                 
               
             
           
         
       
     
     After further simplification and re-arrangement of Equation (24), the optimum noise scale factor for which the Vgnz noise component can be canceled can be found as follows. 
     
       
         
           
             
               
                 
                   α 
                   = 
                   
                     
                       Cg 
                       
                         Cfb 
                         + 
                         Csi 
                       
                     
                     . 
                   
                 
               
               
                 
                   ( 
                   25 
                   ) 
                 
               
             
           
         
       
     
     Accordingly, the tunable capacitor Cvb 2  can be adjusted until the optimum noise scale factor is reached, thereby allowing the sense amplifier  1162  to cancel out the induced noise Vgnz. The sense amplifier  1162  can then output touch signal Vo with substantially reduced noise for touch and hover sensing. 
     The example of  FIG. 11  illustrates receive section components for outputting one touch signal to perform operations at a touch sensitive device. However, it is to be understood that additional similar components can be used to generate and output more than one touch signal according to the needs of the touch display. 
       FIG. 12  illustrates an exemplary method of reducing noise in a touch controller of a touch sensitive device according to various embodiments. This method can be applied to the touch controller of  FIG. 11 , for example. In the example of  FIG. 12 , a touch signal can be generated, for example, by a touch display ( 1210 ). Noise can be introduced into the touch signal at a component, for example, a sense amplifier, that receives the touch signal for processing. The noise can come from a power supply to the touch display, for example. A signal from the touch signal noise source can also be inputted to the component to operate the component as a differential circuit ( 1220 ). The noise signal can be subtracted from the touch signal ( 1230 ). The resulting touch signal can be outputted with substantially reduced noise ( 1240 ). 
     Prior to or during operation of the touch sensitive device, device components, e.g., tunable capacitors, can be adjusted to an optimum noise scale factor at which the sense amplifier can optimally subtract out the noise from the touch signal as described above. 
       FIG. 13  illustrates an exemplary transmit section of a touch controller having noise reduction circuitry according to various embodiments. In the example of  FIG. 13 , transmit section  1300  can generate stimulation signals for driving touch display  1330 . The transmit section  1300  can include digital-to-analog converter (DAC)  1312  for generating stimulation signals to drive the touch display  1330 . The DAC  1312  can output a positive stimulation signal Vp 1  and a negative stimulation signal Vn 1 , each signal having induced noise. The transmit section  1300  can also include DAC buffers  1322 ,  1324  to receive the respective stimulation signals Vp 1 , Vn 1  (or Ip 1 , In 1  in a current mode DAC) from the DAC  1312 . The DAC buffers  1322 ,  1324  can have feedback impedances Zfb 1  and Zin 1 . In some embodiments, the DAC buffers  1322 ,  1324  can amplify the stimulation signals Vp 1 , Vn 1  to an effective level to drive the touch display. As a consequence, the induced noise in the stimulation signals Vp 1 , Vn 1  can also be amplified. 
     The transmit section  1300  can also include output buffers  1342 ,  1344  to receive the respective stimulation signals Vp 2 , Vn 2  from the DAC buffers  1322 ,  1324  as one input and the other respective stimulation signals Vn 2 , Vp 2  from the buffers as the other input. For example, the output buffer  1342  can receive the positive stimulation signal Vp 2  from the DAC buffer  1322  as one input and the negative stimulation signal Vn 2  from the DAC buffer  1324  as the other input. Similarly, the output buffer  1344  can receive the negative stimulation signal Vn 2  from the DAC buffer  1324  as one input and the positive stimulation signal Vp 2  from the DAC buffer  1322  as the other input. The output buffers  1342 ,  1344  can have input impedances Zin 2  and feedback impedances Zfb 2 . The output buffers  1342 ,  1344  can convert noise inputted with the stimulation signals Vp 2 , Vn 2  into differential noise. In some embodiments, the noise to be converted can be correlated or common mode noise. In some embodiments, the noise to be converted can also include other types of noise. The stimulation signals Vn 2 , Vp 2  in the other input can be coupled to a bias voltage Vbias into the DAC buffers  1322 ,  1324  through voltage dividers Zdiv 1  and Zdiv 2 . The output buffers  1342 ,  1344  can then output the respective stimulation signals Vp 3 , Vn 3  with the differential noise to the touch display  1330  to generate touch signals, Csig,p, Csig,n. The generated touch signals can be coupled together to cancel out the differential noise, resulting in touch signals with substantially reduced noise. 
     In an example, the stimulation signal Vp 1  can have a voltage noise density ENZ_DACP and the stimulation signal Vp 2  can have a voltage noise density ENZ_DACN. For simplicity, in this example, it is assumed that the various passive feedback and input impedances Zin 1 , Zin 2 , Zdiv 1 , Zdiv 2 , Zfb 1 , Zfb 2 , and bias reference Vbias are noise free or have negligible noise. The voltage noise density at DAC buffer  1322  can be as follows.
 
 ENZ   —   Vp 2 =G   —   DBUF*ENZ   —   DACP,   (26)
 
where ENZ_Vp 2 =the voltage noise density of the stimulation signal Vp 2 , G_DBUF=the gain of the DAC buffer  1322 , and ENZ_DACP=the voltage noise density contributed by the DAC  1312  in the stimulation signal Vp 1 . Similarly, the voltage noise density at DAC buffer  1324  can be as follows.
 
 ENZ   —   Vn 2 =G   —   DBUF*ENZ   —   DACN,   (27)
 
where ENZ_Vn 2 =the voltage noise density of the stimulation signal Vn 2 , G_DBUF=the gain of the DAC buffer  1324 , and ENZ_DACN=the voltage noise density contributed by the DAC  1312  in the stimulation signal Vn 1 .
 
     Assuming Zfb 2 /Zin 2 =Zdiv 2 /Zdiv 1 , the voltage at the output of the output buffer  1342  can be as follows. 
                       Vp   ⁢           ⁢   3     =       (       Vn   ⁢           ⁢   2     -     Vp   ⁢           ⁢   2       )     *     (       Zfb   ⁢           ⁢   2       Zin   ⁢           ⁢   2       )         ,           (   28   )               
where Vp 3 =the positive stimulation signal output from the output buffer  1342 , Vn 2 =the negative stimulation signal output from the DAC buffer  1324 , Vp 2 =the positive stimulation signal output from the DAC buffer  1322 , Zfb 2 =the feedback impedance of the output buffers  1342 ,  1344 , and Zin 2 =the input impedance of the output buffers. Similarly, the voltage at the output of the output buffer  1344  can be as follows.
 
                       Vn   ⁢           ⁢   3     =       (       Vp   ⁢           ⁢   2     -     Vn   ⁢           ⁢   2       )     *     (       Zfb   ⁢           ⁢   2       Zin   ⁢           ⁢   2       )         ,           (   29   )               
where Vn 3 =the negative stimulation signal output from the output buffer  1344 .
 
     The resulting voltage noise density at the output of the output buffer  1342  can be as follows. 
                       ENZ_Vp   ⁢           ⁢   3     =     G_DBUF   *     (     ENZ_DACN   -   ENZ_DACP     )     *     (       Zfb   ⁢           ⁢   2       Zin   ⁢           ⁢   2       )         ,           (   30   )               
where ENZ_Vp 3 =the voltage noise density of the stimulation signal Vp 3  outputted by the output buffer  1342 , G_DBUF=the gain of the DAC buffer  1322 , ENZ_DACP=the voltage noise density contributed by the DAC  1312  in the stimulation signal Vp 1 , ENZ_DACN=the voltage noise density contributed by the DAC  1312  in the stimulation signal Vn 1 , Zfb 2 =the feedback impedance of the output buffer  1342 , and Zin 2 =the input impedance of the output buffer  1342 . Similarly, the resulting voltage noise density at the output of the output buffer  1344  can be as follows.
 
                       ENZ_Vn   ⁢           ⁢   3     =     G_DBUF   *     (     ENZ_DΛCP   -   ENZ_DΛCN     )     *     (       Zfb   ⁢           ⁢   2       Zin   ⁢           ⁢   2       )         ,           (   31   )               
where ENZ_Vn 3 =the voltage noise density of the stimulation signal Vn 3  outputted by the output buffer  1344 , G_DBUF=the gain of the DAC buffer  1324 , Zfb 2 =the feedback impedance of the output buffer  1344 , and Zin 2 =the input impedance of the output buffer  1344 .
 
     For the case where equal numbers of positive and negative stimulation signals Vp 3 , Vn 3  drive the touch display  1330  to generate touch signals, Csig,p, Csig,n, the noise can be canceled out when the touch signals are coupled as follows. 
                     ENZ_TOT   =       G_DBUF   *     (       ENZ_DACP   -   ENZ_DACN     ,     ENZ_DACN   -   ENZ_DACP       )     *     (       Zfb   ⁢           ⁢   2       Zin   ⁢           ⁢   2       )       =       G_DBUF   *     (     0   ,   0     )     *     (       Zfb   ⁢           ⁢   2       Zin   ⁢           ⁢   2       )       =   0         ,           (   32   )               
where ENZ_TOT=the voltage noise density in the coupled touch signals at the touch display  1330 .
 
     The example of  FIG. 13  illustrates transmit section components for outputting two stimulation signals to drive a touch display. However, it is to be understood that additional similar components can be used to generate and output more than two stimulation signals according to the needs of the touch display. 
       FIG. 14  illustrates an exemplary method of reducing noise in a touch controller of a touch sensitive device according to various embodiments. This method can be applied to the touch controller of  FIG. 13 , for example. In the example of  FIG. 14 , a positive stimulation signal Vp 1  and a negative stimulation signal Vn 1  with noise can be generated, for example, by a DAC ( 1410 ). The noise can come from the component generating the stimulation signals and/or from downstream components processing the stimulation signals. In some embodiments, the noise can be correlated or common mode. The noise can be converted to differential noise, for example, by output buffers ( 1420 ). The resulting stimulation signals Vp 3 , Vn 3  can be outputted with differential noise to a touch display for generating touch signals indicative of a touch or hover at the display ( 1430 ). The touch signals can be coupled together, thereby canceling out the differential noise ( 1440 ). The resulting touch signal output Vo can be outputted with substantially reduced noise ( 1450 ). 
     In additional to correlated or common mode noise introduced into the stimulation signals Vp, Vn, noise can be introduced in the bias voltage Vbias. The noise in the bias voltage Vbias can be canceled out by measuring the output Vo with respect to the bias voltage source. 
       FIG. 15  illustrates an exemplary computing system that can include a touch controller having noise reduction circuitry according to various embodiments. In the example of  FIG. 15 , computing system  1500  can include touch controller  1506 . The touch controller  1506  can be a single application specific integrated circuit (ASIC) that can include one or more processor subsystems  1502 , which can include one or more main processors, such as ARM968 processors or other processors with similar functionality and capabilities. However, in other embodiments, the processor functionality can be implemented instead by dedicated logic, such as a state machine. The processor subsystems  1502  can also include peripherals (not shown) such as random access memory (RAM) or other types of memory or storage, watchdog timers and the like. The touch controller  1506  can also include receive section  1507  for receiving signals, such as touch signals  1503  of one or more sense channels (not shown), other signals from other sensors such as sensor  1511 , etc. The touch controller  1506  can also include demodulation section  1509  such as a multistage vector demodulation engine, display scan logic  1510 , and transmit section  1514  for transmitting stimulation signals  1516  to touch display  1524  to drive the display. The scan logic  1510  can access RAM  1512 , autonomously read data from the sense channels, and provide control for the sense channels. In addition, the scan logic  1510  can control the transmit section  1514  to generate the stimulation signals  1516  at various frequencies and phases that can be selectively applied to rows of the touch display  1524 . 
     The touch controller  1506  can also include charge pump  1515 , which can be used to generate the supply voltage for the transmit section  1514 . The stimulation signals  1516  can have amplitudes higher than the maximum voltage by cascading two charge store devices, e.g., capacitors, together to form the charge pump  1515 . Therefore, the stimulus voltage can be higher (e.g., 6V) than the voltage level a single capacitor can handle (e.g., 3.6 V). Although  FIG. 15  shows the charge pump  1515  separate from the transmit section  1514 , the charge pump can be part of the transmit section. 
     Computing system  1500  can include display controller  1542 . The display controller  1542  can be a single application specific integrated circuit (ASIC) that can include one or more processor subsystems (not shown), which can include one or more main processors, such as ARM968 processors or other processors with similar functionality and capabilities. However, in other embodiments, the processor functionality can be implemented instead by dedicated logic, such as a state machine. The processor subsystems can also include peripherals such as random access memory (RAM) or other types of memory or storage, watchdog timers and the like. The display controller  1542  can control the touch display  1524  during the display mode. The display controller  142  can supply voltage signals  1533  and timing signals  1535  to the gate driver  1538  to cause the gate driver to drive the touch display  1524  via the gate signals  1536  during the display mode and to remain static during the touch mode. The display controller  1542  can also transmit pixel control signals  1541  via source drivers (not shown) to the active area  1534  to facilitate the displaying of data at the touch display  1524 . 
     Computing system  1500  can include host processor  1528  for receiving outputs from the processor subsystems  1502  and performing actions based on the outputs that can include, but are not limited to, moving an object such as a cursor or pointer, scrolling or panning, adjusting control settings, opening a file or document, viewing a menu, making a selection, executing instructions, operating a peripheral device coupled to the host device, answering a telephone call, placing a telephone call, terminating a telephone call, changing the volume or audio settings, storing information related to telephone communications such as addresses, frequently dialed numbers, received calls, missed calls, logging onto a computer or a computer network, permitting authorized individuals access to restricted areas of the computer or computer network, loading a user profile associated with a user&#39;s preferred arrangement of the computer desktop, permitting access to web content, launching a particular program, encrypting or decoding a message, and/or the like. The host processor  1528  can also perform additional functions that may not be related to touch processing. 
     Touch display  1524  can include active area  1534  having touch sensing circuitry that can include a capacitive sensing medium having drive lines and sense lines. It should be noted that the term “lines” can sometimes be used herein to mean simply conductive pathways, as one skilled in the art can readily understand, and is not limited to structures that can be strictly linear, but can include pathways that change direction, and can include pathways of different size, shape, materials, etc. Drive lines can be driven by stimulation signals  1516  and resulting touch signals  1503  generated in sense lines can be transmitted to receive section  1507  in touch controller  1506 . In this way, drive lines and sense lines can be part of the touch sensing circuitry that can interact to form capacitive sensing nodes, which can be thought of as touch picture elements (touch pixels), such as touch pixels  1526 . This way of understanding can be particularly useful when touch display  1524  can be viewed as capturing an “image” of touch. In other words, after touch controller  1506  has determined whether a touch has been detected at each touch pixel in the touch display, the pattern of touch pixels in the touch display at which a touch occurred can be thought of as an “image” of touch (e.g. a pattern of fingers touching the touch display). 
     The touch display  1524  can also include gate driver  1538 , which can receive the voltage signals  1533  and the timing signals  1535  and generate gate signals  1536  for driving the active area  1534  of the touch display  1524  to display data during the display mode and to sense a touch or hover during the touch mode. 
     Note that one or more of the functions described above, can be performed, for example, by firmware stored in memory (e.g., one of the peripherals) and executed by the processor subsystem  1502 , or stored in the program storage  1532  and executed by the host processor  1528 . The firmware can also be stored and/or transported within any 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 “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 computer readable storage medium can include, but is not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus or device, a portable computer diskette (magnetic), a random access memory (RAM) (magnetic), a read-only memory (ROM) (magnetic), an erasable programmable read-only memory (EPROM) (magnetic), a portable optical disc such a CD, CD-R, CD-RW, DVD, DVD-R, or DVD-RW, or flash memory such as compact flash cards, secured digital cards, USB memory devices, memory sticks, and the like. 
     The firmware can also be propagated within any transport medium for use by or in connection with an instruction execution system, apparatus, or device, such as a computer-based system, processor-containing system, or other system that can fetch the instructions from the instruction execution system, apparatus, or device and execute the instructions. In the context of this document, a “transport medium” can be any medium that can communicate, propagate or transport the program for use by or in connection with the instruction execution system, apparatus, or device. The transport readable medium can include, but is not limited to, an electronic, magnetic, optical, electromagnetic or infrared wired or wireless propagation medium. 
     It is to be understood that the touch display, as described in  FIG. 15 , can sense touch and hover according to various embodiments. In addition, the touch display described herein can be either single- or multi-touch and hover. 
       FIG. 16  illustrates an exemplary mobile telephone  1640  that can include touch sensitive device  1644  and other computing system blocks that can include a touch controller with noise reduction circuitry according to various embodiments. 
       FIG. 17  illustrates an exemplary digital media player  1750  that can include touch sensitive device  1754  and other computing system blocks that can include a touch controller with noise reduction circuitry according to various embodiments. 
       FIG. 18  illustrates an exemplary personal computer  1860  that can include touch sensitive device  1864  and other computing system blocks that can include a touch controller with noise reduction circuitry according to various embodiments. 
     The mobile telephone, media player, and personal computer of  FIGS. 16 through 18  can have improved touch and hover sensing with a touch controller having noise reduction circuitry 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: 20101203
Publication Date: 20140603
Grant Date: 20140603
Priority Date: 20101203
Inventors: KRAH CHRISTOPH HORST
MOTAMED ALI
Assignee: APPLE INC
CPC Classifications: [{"code": "G06F3/04182", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F3/044", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0418", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F3/044", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 46161776