Patent Publication Number: US-9851798-B2

Title: Electronic device including spaced apart hall effect sensor based haptic actuator driving and related methods

Description:
RELATED APPLICATION 
     The present application claims the priority benefit of provisional application Ser. No. 62/329,353 filed on Apr. 29, 2016, and 62/347,760 filed on Jun. 9, 2016, and is a continuation-in-part of application Ser. No. 15/096,379 filed on Apr. 12, 2016, which claims the priority benefit of provisional application Ser. No. 62/234,880 filed on Sep. 30, 2015, the entire contents of all of which are herein incorporated in their entirety by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to the field of electronics, and, more particularly, to the field of haptics. 
     BACKGROUND 
     Haptic technology is becoming a more popular way of conveying information to a user. Haptic technology, which may simply be referred to as haptics, is a tactile feedback based technology that stimulates a user&#39;s sense of touch by imparting relative amounts of force to the user. 
     A haptic device or haptic actuator is an example of a device that provides the tactile feedback to the user. In particular, the haptic device or actuator may apply relative amounts of force to a user through actuation of a mass that is part of the haptic device. Through various forms of tactile feedback, for example, generated relatively long and short bursts of force or vibrations, information may be conveyed to the user. 
     SUMMARY 
     An electronic device may include a haptic actuator that includes an actuator housing, a plurality of coils carried within the actuator housing, and a field member movable within the actuator housing responsive to the plurality of coils. The haptic actuator may also include a plurality of spaced apart Hall Effect sensors carried within the actuator housing between the plurality of coils and configured to sense a temperature of the field member. The electronic device may also include a controller coupled to the haptic actuator and configured to determine a temperature of the field member based upon the plurality of spaced apart Hall Effect sensors and driving the haptic actuator based upon the temperature. 
     The controller may be configured to determine the temperature based upon an output resistance of the plurality of spaced apart Hall Effect sensors. The controller may include a closed-loop controller, for example. 
     The controller may be configured to sense a drive current of the haptic actuator, and drive the haptic actuator based upon the drive current. The controller may be configured to determine a calibration of the haptic actuator based upon drive current and the sensed temperature of the field member, and drive the haptic actuator in a closed-loop configuration based upon the calibration of the haptic actuator and at least one reference pattern of movement of the field member, for example. 
     The at least one reference pattern of movement may include a plurality of different reference patterns of movement, each corresponding to a desired one of a plurality of different operating modes of haptic feedback, for example. Each of the plurality of different reference patterns of movement may have a different drive waveform associated therewith. 
     The electronic device may further include a flexible circuit substrate carrying the plurality of spaced apart Hall Effect sensors within the actuator housing, for example. The controller may include a closed-loop controller configured to determine the temperature of the field member and an actuator driver carried within the actuator housing and configured to drive the haptic actuator based upon the temperature. 
     The electronic device may also include a power amplifier coupled between the controller and the haptic actuator. The electronic device may also include a position sensor configured to sense a position of the field member during movement thereof, and wherein the controller may be configured to drive the haptic actuator based upon the position of the field member. 
     A related method aspect is directed to a method of controlling a haptic actuator that includes an actuator housing, a plurality of coils carried within the actuator housing, a field member movable within the actuator housing responsive to the at least one coil. The method may include using a controller coupled to the haptic actuator for determining a temperature of the field member based upon a plurality of spaced apart Hall Effect sensors carried within the actuator housing between the plurality of coils and capable of sensing a temperature of the field member and driving the haptic actuator based upon the temperature. 
     A related device aspect is directed to an electronic device that may include a haptic actuator including an actuator housing, at least one first coil carried within the actuator housing, and at least one second coil carried within the actuator housing. The haptic actuator may also include a field member movable within the actuator housing between the at least one first and second coils and responsive thereto, and a plurality of spaced apart Hall Effect sensors carried within the actuator housing between the at least one first and second coils and configured to sense motion of the field member. The electronic device may also include a controller coupled to the haptic actuator and configured to drive the haptic actuator based upon the sensed motion of the field member from the plurality of spaced apart Hall Effect sensors. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an electronic device including a haptic actuator according to an embodiment of the present invention. 
         FIG. 2  is a schematic block diagram of the electronic device of  FIG. 1 . 
         FIG. 3  is a more detailed schematic diagram of the haptic actuator of  FIG. 1 . 
         FIGS. 4 a  and 4 b    are bode diagrams of frequency versus magnitude and frequency versus phase, respectively for a haptic actuator in accordance with an embodiment. 
         FIG. 5 a    is a graph of an exemplary 250 Hz mini-tap drive waveform generated for the haptic actuator of  FIG. 3  in accordance with an embodiment. 
         FIG. 5 b    is a graph of exemplary tap momentum corresponding to the drive waveform of  FIG. 5   a.    
         FIG. 6 a    is a graph of an exemplary square mini-tap drive waveform generated for the haptic actuator of  FIG. 3  in accordance with an embodiment. 
         FIG. 6 b    is a graph of expected and observed displacement and velocity corresponding to the drive waveform of  FIG. 6   a.    
         FIG. 7 a    is a graph of an exemplary sinusoidal mini-tap drive waveform generated for the haptic actuator of  FIG. 3  in accordance with an embodiment. 
         FIG. 7 b    is a graph of expected and observed displacement and velocity corresponding to the drive waveform of  FIG. 7   a.    
         FIG. 8 a    is a graph of an exemplary resonance vibe drive waveform generated for the haptic actuator of  FIG. 3  in accordance with an embodiment. 
         FIG. 8 b    is a graph of displacement and velocity corresponding to the drive waveform of  FIG. 8   a.    
         FIG. 9  is a schematic diagram of a closed-loop controller in accordance with another embodiment. 
         FIG. 10  is a schematic diagram of a haptic actuator according to another embodiment. 
         FIG. 11  is a schematic diagram of an electronic device according to another embodiment. 
         FIG. 12  is a more detailed schematic diagram of a haptic actuator according to an embodiment. 
         FIG. 13  is a schematic diagram of an electronic device according to another embodiment. 
         FIG. 14  is a schematic diagram of a closed-loop architecture in accordance with an embodiment. 
         FIG. 15  is detailed schematic diagram of an exemplary analog front end of an electronic device in accordance with an embodiment. 
         FIG. 16  is a schematic block diagram illustrating sensor signal processing in accordance with an embodiment. 
         FIG. 17  is a graph of input resistance versus ambient temperature during temperature compensation using an electronic device in accordance with an embodiment. 
         FIG. 18  is a graph of output Hall sensor voltage versus ambient temperature during temperature compensation using an electronic device in accordance with an embodiment. 
         FIG. 19  is a graph of offset voltage versus ambient temperature during temperature compensation using an electronic device in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout, and prime notation and elements in increments of 100 are used to indicate similar elements in alternative embodiments. 
     Referring initially to  FIGS. 1 and 2 , an electronic device  20  illustratively includes a device housing  21  and a device controller  22  carried by the device housing. The electronic device  20  is illustratively a mobile wireless communications device, for example, a wearable wireless communications device, and includes a band  28  or strap for securing it to a user. The electronic device  20  may be another type of electronic device, for example, a cellular telephone, a tablet computer, a laptop computer, etc. 
     Wireless communications circuitry  25  (e.g. cellular, WLAN Bluetooth, etc.) is also carried within the device housing  21  and coupled to the device controller  22 . The wireless communications circuitry  25  cooperates with the device controller  22  to perform at least one wireless communications function, for example, for voice and/or data. In some embodiments, the electronic device  20  may not include wireless communications circuitry  25 . 
     A display  23  is also carried by the device housing  21  and is coupled to the device controller  22 . The display  23  may be a liquid crystal display (LCD), for example, or may be another type of display, as will be appreciated by those skilled in the art. 
     Finger-operated user input devices  24   a ,  24   b , illustratively in the form of a pushbutton switch and a rotary dial are also carried by the device housing  21  and is coupled to the device controller  22 . The pushbutton switch  24   a  and the rotary dial  24   b  cooperate with the device controller  22  to perform a device function in response to operation thereof. For example, a device function may include a powering on or off of the electronic device  20 , initiating communication via the wireless communications circuitry  25 , and/or performing a menu function. 
     The electronic device  20  illustratively includes a haptic actuator  40 . The haptic actuator  40  is coupled to the device controller  22  and provides haptic feedback to the user in the form of relatively long and short vibrations or “taps”, particularly when the user is wearing the electronic device  20 . The vibrations may be indicative of a message received, and the duration of the vibration may be indicative of the type of message received. Of course, the vibrations may be indicative of or convey other types of information. More particularly, the device controller  22  applies a voltage to move a moveable body or a mass  51  between first and second positions. 
     While a device controller  22  is described, it should be understood that the device controller  22  may include one or more of a processor and other circuitry to perform the functions described herein. The controller  22  may also be embodied as one or more of a field programmable gate array (FPGA), microcontroller, digital signal processor (DSP), central processing unit (CPU), or application specific integrated circuit. 
     Referring now additionally to  FIG. 3 , the haptic actuator  40  includes an actuator housing  41  and a coil  44  carried by the housing. Of course, there may be more than one coil carried by the housing  41 . 
     A field member  50  is movable within the housing  41  responsive the coil  44 . The movement of the field member  50  creates the haptic feedback, or tapping, as will be appreciated by those skilled in the art. While the movement of the field member  50  may be described as being moveable in one direction, i.e., a linear haptic actuator, it should be understood that in some embodiments, the field member may be movable in other directions, i.e., an angular haptic actuator, or may be a combination of both a linear and an angular haptic actuator. 
     The field member  50  may include one or more masses  51  and may be shaped for a particular application or operation. The field member  50  may also include one or more permanent magnets  52  cooperating with the coil  44  to provide movement of the field member. The field member  50  may also include a suspension system that may include one or more springs for maintaining the field member suspended in the housing  41 . The springs may include mechanical springs, such as, for example, coil springs, leaf springs, and flexures. The springs may also or additionally include magnetic springs that, through interaction with the permanent magnets and/or ferritic parts of the actuator housing  41 , if any, store and amplify the energy in the form of elastic/magnetic energy. In addition, the suspension system, for example, through shafts, linear/angular bearings, sliding bearings, flexures, multi-bar linkage mechanisms, and springs, may enable motion of the field member  50  in the desired direction (e.g. X axis in a linear actuator or around a certain axis in an angular actuator) while constraining motion in other degrees of freedom. The suspension system may include other and/or additional components for maintaining the suspension of the field member  50  as well as constrain movement of the field member. 
     The haptic actuator  40  also includes mechanical limit stops  45   a ,  45   b  between the housing  41  and the field member  50 . The mechanical limit stops  45   a ,  45   b  limit the movement of the field member to a desired range and/or stop the field member from crashing or banging into the housing  41 . While mechanical stops  45   a ,  45   b  are described, it will be appreciated that the mechanical stops may be part of or a portion of the housing  41 . 
     Typically, circuitry generates a sinusoidal drive waveform that drives the field member to move from an initial at-rest position. However, as will be appreciated by those skilled in the art, in a stationary or at-rest position, the field member  50  has a static friction associated with it which may cause the field member to “get stuck” despite the application of a drive voltage. A certain amount of force or voltage is thus needed to overcome this static friction force to cause the field member  50  to move. One approach to drive the field member  50  from the at-rest position is to increase the drive voltage or amplitude of the sinusoidal drive waveform. However, once the static friction force is overcome, the field member  50  typically rapidly accelerates and crashes or bangs into the mechanical limit stops  45   a ,  45   b.    
     In some applications it may be particularly desirable to not have the field member  50  hit or bang into the mechanical limit stops  45   a ,  45   b  as this may generate a corresponding “banging” noise. To reduce the amount of noise, for example, caused by the increased amplitude, the electronic device  20  may include circuitry for driving the field member  50  without contacting the mechanical limit stops  45   a ,  45   b , as will be described in further detail below. 
     To drive the field member  50  without contacting the mechanical limit stops  45   a ,  45   b , the electronic device  20  illustratively may also include a position sensor  32  that senses a position of the field member during movement thereof. The position sensor  32  may be a capacitive sensor, an optical sensor, a magnetic sensor, capacitive sensor, back EMF sensor, piezoresistive sensor, or piezoelectric sensor, for example. Of course, there may be more than one position sensor  32  and each position sensor may be a different type of sensor. The position sensor  32  may sense or output a pulse density modulated signal of the x-position of the haptic actuator  30  and may be used to close the closed loop and/or track a desired trajectory of the field member  50 , as will be appreciated by those skilled in the art. 
     A driver  33  drives the haptic actuator  30 , and senses a drive voltage and drive current for the haptic actuator. The driver  33  may sense one or both of the drive voltage and drive current for the haptic actuator  30 . In some embodiments, the driver  33  may drive the haptic actuator  30  at different frequencies, which, as will be described in further detail below, may be used to estimate the system or haptic actuator parameters. The driver  33  may be include a class D amplifier  35  and a step-up converter  36  coupled thereto for signal processing between the haptic actuator  30  and a closed-loop controller  60 . Additionally, position data, for example, X-axis position data, from the position sensor  32  may be processed by a position sensing component  36  of the driver  33 . 
     The closed-loop controller  60  cooperates with the position sensor  32  and the driver  33  to determine a calibration of the haptic actuator  30  based upon the sensed position of the field member  50  and one of more of the driving voltage and driving current. The closed-loop controller  60  includes a processor  61  and a memory  62  coupled thereto. While a processor  61  and a memory  62  coupled thereto are described, it will be appreciated by those skilled in the art that there may be more than one processor and/or memory, and which may be shared. Also functions described as being performed by the closed-loop controller  60  should be understood as being performed by the processor  61 . The memory  62  stores the calibration of the haptic actuator  30  and the reference pattern. The calibration may be determined based upon one or more of a resistance, inductance, capacitance, and a motor constant, for example. Of course, the calibration may be determined based upon other and/or additional factors. 
     The closed-loop controller  60 , particularly, the processor  61 , stores reference patterns of movement for the field member  50  in the memory  62 . The reference patterns of movement are different, with each reference pattern of movement corresponding to a desired one of different operating modes of haptic feedback. More particularly, it may be desirable to operate the haptic actuator  30  in any of a vibe (longer duration feedback) mode, a tap (short duration) mode, a mini-tap mode, and a braking mode, for example, with each of the reference patterns having a different drive waveform associated therewith. The haptic actuator  30  may be operated in any number of modes based upon a desired type of haptic feedback. 
     The closed-loop controller processor  61  also drives the haptic actuator in a closed-loop configuration based upon the calibration of the haptic actuator and at least one reference pattern of movement of the field member. Where the driver  33  drives the haptic actuator at different frequencies, the closed-loop controller  60  determines the calibration based upon a sensed impedance of the haptic actuator at the plurality of different frequencies. 
     In some embodiments, the closed-loop controller processor  61  may determine the calibration of the haptic actuator over a given time period and stored in the memory  62 . The closed-loop controller  60  may drive the haptic actuator  30  in the closed-loop configuration based upon the calibration of the haptic actuator over the given time period. In other words, the calibration of the haptic actuator  30  may be learned over the given time period. 
     The closed loop controller  60  may receive as an input, a command, instruction, and/or trigger, which would trigger the closed loop controller to generate the desired waveforms, or in other words, to drive the haptic actuator  30 , based upon the calibration and in one of the modes described above (e.g., mini-tap or a desired arbitrary waveform that may be synthesized by an upstream system processor or controller  22 ). The closed loop controller  60  may also optionally receive as an input, a desired trajectory input to “push” the closed loop controller to follow the arbitrary synthesized waveform, for example. 
     Further details of the closed-loop controller  60  will now be described. The processor  61  of the closed-loop controller  60  may operate as a state observer, which can generate a state space model based upon the dynamic model of the haptic actuator  30  or system, for example, the motor constant and/or the motor capacitance, and using a system identification protocol or an adaptive observer as will be appreciated by those skilled in the art. The state observer may include or operate based upon a linear quadratic estimation, for example, a Kalman filter. In other words, the calibration may be determined based upon a linear quadratic estimation. 
     Since it may be particularly desirable to obtain the velocity of the mass  51 , the closed-loop controller  60 , may estimate the velocity based upon the measured voltage and current, and may ignore the mechanical model of the haptic actuator  30  or system. The velocity may be used by the closed-loop controller  60  to close the closed loop and/or track a desired trajectory, as will be appreciated by those skilled in the art. 
     The actuator may be defined by: 
     
       
         
           
               
             
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     The state observer gain, L c , is set by placing the poles of the observed system (A c −L c C c ) at λ 1 , λ 2 , λ 3 . Discrete domain observer gains may be estimated as: L d =(A c   −1 (A d −I)L c . 
     The system identification of the haptic actuator  30  with respect to electrical impedance analysis will now be described. The dynamics of the haptic actuator  30  in the Laplace domain may be defined as: 
     
       
         
           
               
             
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     The electrical impedance of the haptic actuator  40  may be described as: 
     
       
         
           
             
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     As described above, the parameters of the system can be estimated by the exiting or driving the haptic actuator  40  at different frequencies and measuring the complex electrical impedance. This may be accomplished by using an I/Q mode or a fast Fourier transform (FFT), for example. For a relatively simple velocity based closed-loop controller  60 , only resistance R may be estimated on DC current such that:
 
2/ R=I (+ V )− I (− V ).
 
     The graphs  70 ,  71  in  FIGS. 4 a  and 4 b    are bode diagrams of frequency versus magnitude and frequency versus phase, respectively, of an electrical impedance analysis of the haptic actuator  40 . 
     Further details of the different reference patterns of movement, specifically each corresponding different operating modes of haptic feedback will now be described. In particular, one mode of haptic feedback referred to as “mini-tap drive control” may be described as: 
     
       
         
           
               
             
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     Another mode referred to as “sinusoidal tap” (e.g. low frequency tap mini-tap) may be described as: 
     
       
         
           
             
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     Other modes include: 
     “Resonance Vibe Drive”: 
                   {             u   ⁡     [   n   ]       =       V   max     ⁢     sgn   ⁡     (       x     .   ~       ⁡     [   n   ]       )                         x     .   ~       ⁡     [   n   ]       2     +       ω   0   2     ⁢         x   ~     ⁡     [   n   ]       2         &lt;       x   .     set_vibe   2                   u   ⁡     [   n   ]       =   0                   x     .   ~       ⁡     [   n   ]       2     +       ω   0   2     ⁢         x   ~     ⁡     [   n   ]       2         &gt;       x   .     set_vibe   2                     
“Specific Frequency Vibe Drive”:
 
                   {             u   ⁡     [   n   ]       =       V   max     ⁢     sgn   ⁡     (     sin   ⁡     (     2   ⁢   π   ⁢           ⁢     f   vibe     ⁢     T   s     ⁢   n     )       )                         x     .   ~       ⁡     [   n   ]       2     +       ω   vibe   2     ⁢         x   ~     ⁡     [   n   ]       2         &lt;       x   .     set_vibe   2                   u   ⁡     [   n   ]       =   0                   x     .   ~       ⁡     [   n   ]       2     +       ω   vibe   2     ⁢         x   ~     ⁡     [   n   ]       2         &gt;       x   .     set_vibe   2                     
“Tap Vibe Brake Control”:
 
                 u   PD     ⁡     [   n   ]       =         -   a     ⁢       x     .   ~       ⁡     [   n   ]         +     b   ⁢       x     .   ~       ⁡     [     n   -   1     ]                       {             u   ⁡     [   n   ]       =       u   PD     ⁡     [   n   ]                        u   PD     ⁡     [   n   ]            &lt;     V   max                   u   ⁡     [   n   ]       =       V   max     ⁢     sgn   ⁡     (       u   PD     ⁡     [   n   ]       )                          u   PD     ⁡     [   n   ]            &gt;     V   max                   
“Tap Drive Bang-Bang Control”:
 
                   {             u   ⁡     [   n   ]       =     V   max             0   &lt;   n   &lt;     0.5       f   Tap     ⁢     T   s                       u   ⁡     [   n   ]       =     -     V   max                 0.5       f   Tap     ⁢     T   s         &lt;   n   &lt;     1       f   Tap     ⁢     T   s                         
“Vibe Drive Bang-Bang Control”:
 
                   {             u   ⁡     [   n   ]       =       V   max     ⁢     sgn   ⁡     (       x     .   ~       ⁡     [   n   ]       )                            x       .   ~       ⁡     [   n   ]            &lt;       x   .     set_vibe                   u   ⁡     [   n   ]       =   0                    x     .   ~       ⁡     [   n   ]            &gt;       x   .     set_vibe                     
Of course, there may be other and/or additional modes as will be appreciated by those skilled in the art.
 
     A smoothing drive signal, for example, a first order low pass filter, may be applied as follows:
 
 u   F   [n]=au[n ]+(1−α) u[n− 1]
 
     Referring now to  FIGS. 5-8 , exemplary graphs illustrate simulations of the different drive waveforms, momentum, voltage, and/or displacement for several modes. Referring particularly to the graph  72  in  FIG. 5 a   , a normalized drive waveform for a “mini-tap” at 250 Hz is illustrated for the haptic actuator  40 . The graph  73  in  FIG. 5 b    illustrates the tap momentum for the “mini-tap” at 250 Hz. 
     The graph  74  in  FIG. 6 a    illustrates the drive waveform of a “square mini-tap” (at a frequency greater than 130 Hz) and the graph  75  in  FIG. 6 b    illustrates the “square mini-tap” response, with the line  76  indicating expected displacement (in mm), the line  77  indicating expected velocity (in m/s), the line  78  indicating observed displacement (in mm), and the line  79  indicating observed velocity (in m/s). 
     The graph  80  in  FIG. 7 a    illustrates the drive waveform of a “sine mini-tap” (at a frequency less than 130 Hz) and the graph  81  in  FIG. 7 b    illustrates the “sine mini-tap” response, with the line  82  indicating expected displacement (in mm), the line  83  indicating expected velocity (in m/s), the line  84  indicating observed displacement (in mm), and the line  85  indicating observed velocity (in m/s). 
     The graph  86  in  FIG. 8 a    illustrates a “resonance vibe” drive waveform. The graph  87  in  FIG. 8 b    illustrates the displacement  88  (in mm) and velocity  89  (in m/s) for the “resonance vibe” mode. 
     Referring now to the schematic diagram in  FIG. 9 , a more detailed schematic diagram of an exemplary embodiment of a closed-loop controller  60 ′ implemented as a field programmable gate array (FPGA) is illustrated. A clock generator  55 ′ having an input  57 ′ is illustratively carried by a substrate  56 ′. The memory  62 ′ is illustratively divided and includes configuration memory  63 ′ for storing configuration parameters, command buffers  64 ′ for storing commands, and registers  65 ′ for storing sensed data and/or other data. The memory  62 ′ also includes a calibration memory  66 ′ for storing data related to the calibration, for example, resistance, inductance, capacitance, and a motor constant. A button trigger input  67 ′ is coupled to the command buffers  64 ′, and a reset input  68 ′ and a status output  69 ′, i.e., command done, are coupled to the configuration memory  63 ′. A serial peripheral interface (SPI) interface  90 ′ is coupled to the registers  65 ′. 
     The command buffers  64 ′ may output the different reference patterns of movement each corresponding to a desired one of a plurality of different operating modes of haptic feedback, e.g., tap  91 ′, vibe  92 ′, and brake  93 ′. The output of each of the tap  91 ′, vibe  92 ′, and brake  93 ′ operating modes is coupled to a multiplexer  94 ′, an output of which is coupled to a filter  95 ′, for example, a first order low pass filter. Each of the tap  91 ′, vibe  92 ′, and brake  93 ′ modes has an input which may receive a 10 kHz signal and is coupled to the state observer  96 ′, which has been described above. As described above, the state observer  96 ′ receives or cooperates to receive or sense the drive current and the drive voltage. In the present embodiment, the state observer receives the sensed drive current and drive voltage from an inter-IC Sound (I 2 S) interface  97 ′. 
     The output of the filter  95 ′ is also coupled to the I 2 S interface  99 ′ (e.g. a 16-bit output), and also coupled to a pulse density modulator (PDM)  99 ′. The PDM outputs a clock signal  101 ′ at, for example, 6 MHz, and a data signal  102 ′. The I 2 S interface  99 ′ is coupled to an input of a multiplexer  103 ′. Another input of the multiplexer  103 ′ is coupled to a pass through  104 ′ which includes the calibration. The pass through  104 ′ is coupled to another I 2 S interface  105 ′ and communicates therewith at 48 kHz, for example. The pass through  104 ′ may optionally be coupled to each of the tap  91 ′, vibe  92 ′, and brake  93 ′ modes. 
     A method aspect is directed to a method of operating a haptic actuator  40  that includes an actuator housing  41  and a field member movable  50  within the housing. The method includes sensing, using a position sensor  32 , a position of the field member during movement thereof, driving, using a driver  33 , the haptic actuator  40 , and sensing, using the driver, at least one of a drive voltage and drive current for the haptic actuator. The method also includes using a closed-loop controller  60  cooperating with the position sensor  32  and driver  33  to determine a calibration of the haptic actuator based upon the sensed position of the field member and at least one of the driving voltage and driving current, store at least one reference pattern of movement for the field member, and drive the haptic actuator in a closed-loop configuration based upon the calibration of the haptic actuator and at least one reference pattern of movement of the field member. 
     Referring now to  FIG. 10 , in another embodiment, the haptic actuator  40 ″ may include a permanent magnet  52 ″ carried by the actuator housing  41 ″, and the field member  50 ″ may include one or more coils  44 ″ that cooperate with the permanent magnet. In other words, in contrast to the embodiment described above, the permanent magnet is stationary (i.e., carried by the actuator housing  41 ″) and the coils  44 ″, as part of the field member  50 ″ are moving (i.e., connected to the mass). Of course, there may be any number of coils and/or permanent magnets. 
     Referring now to  FIGS. 11 and 12  in another embodiment, an electronic device  120  illustratively includes a haptic actuator  140  that includes an actuator housing  141  and coils  144  (e.g., drive coils) carried within the actuator housing. The haptic actuator  140  also includes a field member  150  that is movable along an x-axis within the actuator housing  141  responsive to the coils  144 . The field member  150  may include one or more masses  151  and may be shaped for a particular application or operation. The field member  150  may also include one or more permanent magnets  152  cooperating with the coils  144  to provide movement of the field member. A connector  179  is carried by the actuator housing  141 . 
     The field member  150  is also susceptible to movement in y-axis and z-axis directions, for example, that may result from movement along the x-axis, as will be appreciated by those skilled in the art. The haptic actuator  140  also includes mechanical limit stops  145   a ,  145   b  between the housing  141  and the field member  150  as described above. 
     The haptic actuator  140  also includes spaced apart magnetic field sensors  159 , for example, Hall Effect sensors, carried within the actuator housing  141  between the coils  144 . More particularly, the spaced apart magnetic field sensors  159  (and the coils  144 ) may be carried by a flexible substrate  158  carried within the actuator housing  141 . Of course, other components may be carried by the flexible substrate  158  or a flexible substrate may not be included (e.g., the spaced apart magnetic field sensors being carried by the actuator housing  141 ). 
     The spaced apart magnetic field sensors  159  sense a magnetic field based upon movement of the field member  150 . The spaced apart magnetic field sensors  159  may sense the magnetic field based upon a differential output voltage from the magnetic field sensors, for example. Of course, other techniques may be used to sense the magnetic field from the spaced apart magnetic sensors  159 . 
     The electronic device  120  also includes a controller  160  coupled to the haptic actuator via a power amplifier  135 . The controller  160  may be a closed-loop controller, for example, as described in the above-embodiments and may include an actuator driver  133 , for example, which may be in the form of an integrated circuit and carried within the actuator housing  141 . The controller  160  determines z-axis movement of the field member based upon the spaced apart magnetic field sensors  159 . The controller  160 , and more particularly, the actuator driver  133 , also drives the haptic actuator  140  to dampen the z-axis movement. 
     As will be appreciated by those skilled in the art, using a single magnetic field sensor may be particularly undesirable as it may not allow for determination of x-axis or z-axis motion. Using more than one magnetic field sensor  159  advantageously allows for determination of x-axis and z-axis movement. In other words, increased accuracy may be preserved as z-axis movement may alter or change the x-axis movement. Any number of spaced apart magnetic field sensors  159  may be used. For example, using two spaced apart magnetic field sensors  159  may permit determination of z-axis movement, but with little sensitivity to rotation. With three spaced apart magnetic field sensors  159 , sensitivity to rotation may be increased. 
     In some embodiments, the controller  160  may also sense a drive current of the haptic actuator  140  and drive the haptic actuator based upon the drive current. The controller  160  drives the haptic actuator  140  to dampen the z-axis movement, as will be appreciated by those skilled in the art. It will be appreciated by those skilled in the art that portions of or all of the controller  160  may be carried within the actuator housing  141  or outside the actuator housing, for example, within a device housing. 
     Similar to the embodiments described above, the controller  160  may also determine a calibration of the haptic actuator based upon drive current and the sensed magnetic field from the spaced apart magnetic field sensors  159 , store a reference pattern of movement for the field member  150 , and drive the haptic actuator  140  in a closed-loop configuration based upon the calibration of the haptic actuator and a reference pattern of movement of the field member. For example, the controller  160  may, based upon the drive current, subtract the electromagnetic coupling (coil field) based upon the current. 
     The reference pattern of movement may include different reference patterns of movement, each corresponding to a desired one of different operating modes of haptic feedback, for example, tap, vibe, etc. Each of the reference patterns may have a different drive waveform associated therewith. 
     The controller  160 , for example, may perform a position response scaling and linearization based upon calibration data, for example. This may be particularly advantageous because the outputs of the spaced apart magnetic field sensors  159  are slightly non-linear. Thus it may be desirable to measure the non-linear response and apply the inverse to linearize the output of the magnetic sensors. The non-linear response may be measured from the sinusoid, as will be appreciated by those skilled in the art, and typically performed just prior to gain calibration. 
     The haptic actuator  140  also includes a position sensor  132  ( FIG. 11 ) for sensing a position of the field member  150  during movement thereof. The controller  160  also drives the haptic actuator  140  based upon the position of the field member  150 , to further dampen the z-axis movement. 
     A test platform for calibrating the haptic actuator  140  is now described. Some testing operations of the haptic actuator  140  include using a laser, but when positioned in a system, this technique may be undesirable as it requires openings in the actuator housing  141 . A Hall Effect sensor calibration using the spaced apart magnetic field sensors  159  may be used in addition to the laser technique. More particularly, back EMF is measured using the magnetic field sensors  159 . It should be noted that going between back EMF and position may introduce errors, so this may be undesirable. Using the magnetic field sensors  159  for calibration and measurement, for example, may enable contact free travel measurement (versus back EMF), and generally not require an opening in the actuator housing  141  (versus laser). This magnetic field sensor technique also may provide the benefits of enabling system level characterization (versus laser), troubleshooting of magnetic field sensors  159 , measuring magnetic leakage (module level and system level), and generally does not need calibration (fusion of data from the array). 
     In an exemplary test embodiment, an array of Hall Effect sensors, which may be in the form of an integrated circuit, may be used that is separate from the magnetic field sensors  159 . The array of Hall Effect sensors may be positioned adjacent an exterior side of the actuator housing  141 , for example, aligned along a length of the haptic actuator  140 . Thus, calibration may be performed by making measurements from the array of Hall Effect sensors. An analog-to-digital converter (ADC) is used to measure the sensor, which will generate as an output, dX. From dX, a pass/fail determination can be made. The array of Hall Effect sensors may be particularly advantageous relative to other techniques, as it may be less sensitive, as will be appreciated by those skilled in the art. The array of Hall Effect sensors may be carried within the device housing as part of the overall device or system. Alternatively, the array of Hall Effect sensors may also be carried outside the electronic device housing (i.e., system housing) 
     A method aspect is directed to a method of controlling a haptic actuator  140  that includes comprising an actuator housing  141 , a plurality of coils  144  carried within the actuator housing, and a field member  150  capable of being movable along an x-axis within the actuator housing responsive to the at least one coil. The field member  150  is also susceptible to movement in a z-axis direction. The method may include using a controller  160  coupled to the haptic actuator for determining z-axis movement of the field member  150  based upon a plurality of spaced apart magnetic field sensors  159  carried within the actuator housing  141  between the plurality of coils  144  and capable of sensing a magnetic field based upon movement of the field member, and driving the haptic actuator  140  to dampen the z-axis movement 
     Referring now to  FIG. 13 , in another embodiment, to dampen the z-axis movement, for example, spaced apart Hall Effect sensors  159 ′ that are carried within the actuator housing between the coils  144 ′ sense a temperature of the field member  150 ′. The controller  160 ′ determines a temperature of the field member  150 ′ based upon the Hall Effect sensors  159 ′ and drives the haptic actuator  140 ′ based upon the sensed temperature. The controller  160 ′ may determine the temperature of the field member  150 ′ based upon an output resistance of the Hall Effect sensors  159 ′. 
     Similar to the embodiment described above with respect to  FIGS. 11 and 12 , the controller  160 ′ may be a closed loop controller and may sense a drive current of the haptic actuator  140 ′ and drive the haptic actuator also based upon the sensed drive current. Removing the driving current may be a relatively straightforward operation, as that value is empirically determined through the calibration procedure. For temperature, for example, the Hall Effect sensors  159 ′ are used to determine temperature by measuring an output resistance (e.g., instead of looking at differential output voltage) at each Hall Effect sensor location. Resistance of the coils  144 ′ may also be measured. Accordingly, it may be desirable to know change of temperature of the field member  150 ′ or more particularly, the permanent magnet  152 ′. The permanent magnet  152 ′ may become increasingly hotter based upon use. Without temperature compensation, the error rate is above 15%, but with temperature compensation, this error rate can be brought down to about 5%, for example. 
     The controller  160 ′ may also determine a calibration and drive the haptic actuator  140 ′ based upon the calibration as described in detail above. Additional elements illustrated are similar to those described above with respect to the embodiment illustrated in  FIGS. 11 and 12  and need no further discussion. 
     As will be appreciated by those skilled in the art, while the controller may determine both z-axis movement of the haptic actuator and the temperature of the field member, and drive the haptic actuator based upon both the temperature and the z-axis movement. Position of the field member and the drive current may also be used as a basis to drive the haptic actuator. In other words, z-axis movement and/or temperature, position, and/or drive current may be used to drive the haptic actuator. 
     A method aspect is directed to a method of controlling a haptic actuator  140 ′ that includes an actuator housing  141 ′, a plurality of coils  144 ′ carried within the actuator housing, and a field member  150 ′ movable within the actuator housing responsive to the at least one coil. The method includes using a controller  160 ′ coupled to the haptic actuator for determining a temperature of the field member  150 ′ based upon a plurality of spaced apart Hall Effect sensors  159 ′ carried within the actuator housing  141 ′ between the plurality of coils and capable of sensing a temperature of the field member, and driving the haptic actuator  140 ′ based upon the temperature. 
     During operation, the magnetic fields from the spaced apart magnetic field sensors  159  are measured along with the fields generated by driving the haptic actuator  140 . In particular, measurements based upon opposite coils  144  or magnetic field sensors  159  may be used to separate x-axis and z-axis translation. The current, for example, the driving current, is measured by the controller  160  and any influence from the driving the spaced apart magnetic field sensors  159  is subtracted out. Generally there is no physical shielding. However, in some embodiments, there may be physical shielding. 
     Z-axis movement of the haptic actuator  140  is generally undesirable as it may decrease efficiency of operation and/or increase noise levels during operation. For example, dropping of the electronic device, and more particularly the haptic actuator  140  may cause changes in how the haptic actuator operates that cause z-axis movement. The controller  160  cooperating with the spaced apart magnetic field sensors  159 , (e.g., Hall Effect sensors), may advantageously dampen the z-axis movement. 
     While a haptic actuator  140  has been described herein, it should be understood that the haptic actuator may include other and/or additional components of the electronic device  120  much like the controller  160  may include other and/or additional circuitry carried within or outside the actuator housing  141 , as described above. Moreover, any of the embodiments described herein may be used with any one or more other embodiments. 
     Referring now to  FIG. 14 , a schematic diagram of a closed-loop architecture in accordance with an embodiment is illustrated. The electronic device  120 ″ includes a haptic actuator  140 ″ that may be in the form of a linear resonant actuator (LRA), for example, and includes a field member and permanent magnets as described above. The haptic actuator  140 ″ includes spaced apart magnetic sensors  159 ″ on or carried within the housing of the haptic actuator. 
     With respect to position measurement via magnetic field sensing, e.g. Hall Effect sensing, the magnetic field sensors or Hall Effect sensors  159 ″ each varies its output voltage based upon, for example, proportional to the sensed magnetic field and its current source. The Hall sensor (HS) analog front end (AFE)  172 ″ drives the Hall sensors  159 ″ by way of current sources followed by signal conditioning (offset correction, LPF, MUX) of its outputs followed by digitization (analog-to-digital converter (ADC)). A Hall Effect sensor processor  161 ″ estimates motions under various orientations (x, z, rotation, etc.) from the Hall sensor data and based upon the magnetic model of the haptic actuator  140 ″. The Hall Effect sensor processor  161 ″ also compensates for thermal effects, EM couplings from coils, and nonlinearities, for example. The Hall Effect sensor processor  161 ″ may also compensate for other and/or additional factors. 
     A motion controller  162 ″ controls the motion of the haptic actuator  140 ″ based upon closed-loop feedback to follow the desired motion defined by the external commands (e.g. coming from OS/third party apps supervised by the CPU) or internally stored pre-set waveforms, for example, as described above. 
     The state observer  163 ″ estimates the states of the haptic actuator  140 ″ (such as, for example, displacement, velocity, current, etc.) from the noisy sensed data (position measured by Hall sensing, I, V, etc.). A digital controller  164 ″ generates optimum drive signals (voltage and/or current) and drives the haptic actuator  140 ″ to follow the desired motion. 
     System parameters  165 ″ are stored in the memory of the motion controller  162 ″ and can be updated adaptively internally (by the controller itself using adaptive control algorithms or externally (by a CPU  166 ″ via offline calibration). These updated parameters are fed into the state observer  163 ″ (e.g. a Kalman filter) and the digital controller  164 ″ to improve performance. Applications  173 ″ provide external arbitrary waveforms to a task manager  174 ″, for example, based upon the context of the application, Internal waveforms  175 ″, for example, stored in a memory, may also be provided to the task manager  174 ″ for generation of a control signal. 
     A driver/amplifier circuit  167 ″ amplifiers the output of the digital controller  164 ″ to drive the haptic actuator  140 ″, for example, via a class DG amplifier  168 ″. The driver/amplifier circuit  167 ″ monitors and senses the electrical input (current and voltage) to the haptic actuator  140 ″ via I/V sensing circuitry  169 ″. The sensed current and voltage can be used and feed the Hall sensing processor  161 ″ and motion controller  162 ″ to estimate temperature, coil resistance, EM coupling and back electromotive force (EMF), for example. The driver/amplifier circuit  167 ″ also includes a boost converter  170 ″. 
     Further details of an embodiment of an analog front end  172 ′″ will now be described with respect to  FIG. 15 . Hall Effect sensors  159   a ′″ and  159   b ′″ sense x and y directional movement. Offset correction  176   a ′″,  176   n ′″ is provided as an input to respective amplifiers  177   a ′″,  177   b ′″. Respective programmable current sources  178   a ′″,  178   b ′″ that may include digital-to-analog converters are coupled to the Hall Effect sensors  159   a ′″,  159   b ′″. Bypass switches  179   a ′″,  179   b ′″ are coupled between inputs of the amplifiers  177   a ′″,  177   b ′″ and the Hall Effect sensors  159   a ′″,  159   b′″.    
     An anti-aliasing filter  180   a ′″,  180   b ′″ is coupled between the output of the amplifier  177   a ′″,  177   b ′″ and a programmable amplifier  181   a ′″,  181   b ′″. Each anti-aliasing filter  180   a ′″,  180   b ′″ includes a pair of switches  182   a ′″, a pair of parallel coupled resistors  183   a ′″,  183   b ′″, and a capacitor  184   a ′″,  184   b ′″ therebetween. Outputs of each programmable amplifier  181   a ′″,  181   b ′″ are provided to a multiplexor  108 ′″. A temperature sensor  185 ′″ is also provided as an input to the multiplexor  108 ′″. 
     An analog-to-digital converter (ADC)  186 ′″ is coupled to the output of the multiplexor  108 ′″. The ADC  186 ′″ may be 12-bit ADC, for example. The output of the ADC  186 ′″ is provided to a digital engine  187 ′″, and more particularly, a multiplexor  192 ′″. The digital engine  187 ′″ includes respective (for each channel) FIR low pass filters  188   a ′″,  188   b ′″ coupled to the multiplexor  192 ′″. Each FIR low pass filter  188   a ′″,  188   b ′″ includes a low pass filter circuit  189   a ′″,  189   b ′″ coupled to a decoder  190   a ′″,  190   b ′″. Each FIR low pass filter  188   a ′″,  188   b ′″ includes a bypass switch  191   a ′″,  191   b ′″. An I 2 C bus  109 ′″ (SCL, SDA), for example, operating at 1 MHz, is coupled to the digital engine  187 ′″. An average filter  110 ′″, for example, for temperature compensation (i.e., a temperature compensation channel) is also coupled to the multiplexor  192 ′″. 
     Further sensor signal processing steps will now be described with respect to  FIG. 16 . As described above, magnetic field density is provided to the Hall Effect sensor(s)  259 , which provide, as an output, a Hall Effect sensor signal to the analog front end  272 . Current from the programmable current source is provided to the Hall Effect sensor  259 . 
     With respect to offset correction, the offset is adjusted, for example, at an offset correction node  293  (e.g., a summing node) to obtain zero output at the haptic actuator neutral position. The offset correction is based upon a full dynamic range of the ADC  286 . 
     With respect to gain, the gain is adjusted at a gain adjustment node  294  (e.g. a multiplier), to maintain the signal within the dynamic range of the ADC  286  at maximum displacement of the haptic actuator. An anti-aliasing low pass filter  280 , for example, as described above, is coupled between the gain adjustment node  294  and the ADC  286 . 
     With respect to EM coupling, the response of the magnetic field sensors to the coil electromagnet is measured with a calibration procedure, which will be described in further detail below. A test may be performed using a DC current at the sub-assembly level (e.g. coil and magnetic field sensor only), or with transient current at the module level (permanent magnets respond to transients slowly because of inertia). During normal operation, subtracted coil current is multiplied by an EM coupling factor  296  from the scaled magnetic field sensor output at the EM coupling factor multiplier  295 , the output of which is provided to a summing node  297  which sums the output of the EM coupling factor multiplier and the output of the ADC  286 . This removes the electromagnet signal leaving only the permanent magnet signal. 
     With respect to haptic actuator motion, a model of magnetic field variation  298  with haptic actuator motion in different directions is used to separate motion components. For relatively small z-axis motion the H1 and H3 may be subtracted to obtain an x-axis position, and a ration of H1 and H3 may be used to infer the z-axis position, as will be appreciated by those skilled in the art. A calibrated gain 299 is output. 
     With respect to position calibration, a ratio of DAC counts to μm of motion is determined. This value is used to relate DAC output to the physical position. For gain calibration (at node  294 ), the ratio of μm of motion to the applied DC current is determined. This value is used to establish the correct control loop gain. 
     The self-calibration process will now be described. It should be noted that reference readings of the magnetic field sensors (e.g., Hall effect sensors) are relative to end stop locations of the haptic actuator and a polynomial model of the non-linear response of the haptic actuator is given by
 
 V   H   =Σa   i   x   i  
 
     For calibration, the haptic actuator is driven at resonance and slightly into the end stops. The output of the magnetic field sensors are recorded. The values sensed by the magnetic field sensors are fit to a sine wave (neglecting the clipped region) and optimized to find the terms of the polynomial. The scale is normalized to the clipping point. It should be understood by those skilled in the art that the haptic actuator can be initially calibrated, for example, in the factory, and then re-calibrated in the field. 
     Further details of temperature compensation will now be described. Initially, the temperature of the driver (permanent magnet) and/or Hall Effect sensors is read. Corrections for lines gain variation are applied. Corrections for offset with the polynomial model, as described above, are made or removed with chopping, as will be appreciated by those skilled in the art. Corrections for magnetic temperature are then made. The graphs  300 ,  301 , and  302  in  FIGS. 17-19  illustrate input resistance versus ambient temperature ( 303 ), output Hall sensor voltage versus ambient temperature (I c    304 , V c    305 ; both constant), and offset voltage versus ambient temperature (I c    306 , V c    307 ; both constant). 
     Still further, similar to the embodiments described above, and in the embodiments described in  FIGS. 11-13 , the haptic actuator may include a permanent magnet carried by the actuator housing, and the field member may include one or more coils that cooperate with the permanent magnet. In other words, the permanent magnet is stationary (i.e., carried by the actuator housing) and the coils, as part of the field member are moving (i.e., connected to the mass). Of course, there may be any number of coils and/or permanent magnets. For embodiments where the coils are moving, additional magnets, for example, that are relatively small in size, may be added to the field member (similar to a barcode) and may be monitored or tracked by one or more of the magnetic sensors. 
     Alternatively or additionally, one or more magnetic sensors may be mounted on the field member  150  and wirelessly communicate sensed data. It should also be understood that the spaced apart magnetic sensors may also be the driver magnets. In other words, the permanent magnets  152  that are part of the field member may also operate or be configured to perform the functions of the magnetic sensors  159  (i.e. there are not separate magnets for driving the field member and for sensing the movement of the field member. 
     Many modifications and other embodiments of the invention will come to the mind of one skilled in the art having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is understood that the invention is not to be limited to the specific embodiments disclosed, and that modifications and embodiments are intended to be included within the scope of the appended claims.