(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2013/0264973 A1
`Garg et al.
`(43) Pub. Date:
`Oct. 10, 2013
`
`US 20130264973A1
`
`(75)
`
`(54) METHOD AND APPARATUS TO DRIVE A
`LINEAR RESONANT ACTUATORATTS
`RESONANT FREQUENCY
`Inventors: Mayank Garg, Richardson, TX (US);
`David Hernandez-Garduno, Dallas, TX
`(US); Brandon J. Beckham, Dallas, TX
`(US); David J. Baldwin, Allen, TX
`(US); Brett E. Forejt, Garland, TX (US)
`Assignee: Texas Instruments Incorporated,
`Dallas, TX (US)
`Appl. No.: 13/443,741
`Filed:
`Apr. 10, 2012
`
`(73)
`
`(21)
`(22)
`
`(52) U.S. Cl.
`USPC .......................................................... 318/130
`
`ABSTRACT
`(57)
`A method for driving a Linear Resonant Actuator (LRA) is
`provided. During a first off interval, the back-emf of the LRA
`is measured. During a first off interval, a timer is started when
`the back-emf reaches a predetermined threshold, and after a
`predetermined delay has lapsed following the back-emf
`reaching the predetermined threshold during the first off
`interval, the LRA is driven over a drive interval having a
`length and drive strength. A second off interval is entered
`following the drive interval, and during the second off inter
`val, the back-emf of the LRA is measured. During the second
`off interval, the timer is stopped when the back-emf reaches
`the predetermined threshold. The value from the timer that
`corresponds to the duration between the back-emf reaching
`the predetermined threshold during the first off interval and
`the back-emf reaching the predetermined threshold during
`the second off interval determines the length.
`
`Publication Classification
`
`(51)
`
`Int. C.
`HO2K33/00
`
`(2006.01)
`
`Operational
`Mode
`407
`
`
`
`
`
`
`
`Zero
`Crossing?
`4.08
`
`
`
`
`
`Set Ential Drive
`Duration
`402
`
`Initialization
`Mode
`40
`
`
`
`
`
`
`
`
`
`
`
`
`
`Start Timer
`40
`
`Initial Drive
`406
`
`Update the Drive
`Duration
`420
`
`Stop Timer
`418
`
`
`
`Subtract
`Back-EMF value
`44
`
`
`
`
`
`
`
`
`
`Zero
`Crossing?
`46
`
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`Patent Application Publication
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`US 2013/0264973 A1
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`Oct. 10, 2013
`
`METHOD AND APPARATUS TO DRIVE A
`LINEAR RESONANT ACTUATORATITS
`RESONANT FREQUENCY
`
`0007 Some examples of conventional systems are: U.S.
`Pat. No. 7,843,277; and U.S. Patent Pre-Grant Publ. No.
`2010/O153845.
`
`TECHNICAL FIELD
`0001. The invention relates generally to a motor driver
`and, more particularly, to a motor driver that is configured to
`drive a Linear Resonant Actuator (LRA) substantially at its
`resonant frequency.
`
`BACKGROUND
`0002 An LRA is a common-place motor used in a variety
`of applications (including haptics or force-feedback applica
`tions). Generally, an LRA has a mass that is secured to a
`spring, and the mass is moved by use of a coil that is located
`in proximity to the mass. As a result of their construction,
`LRAS have a resonant frequency, and, at this resonant fre
`quency, the LRA can be driven efficiently. However, the effi
`ciency falls off sharply as the drive frequency moves away
`from the resonant frequency of the LRA. For example (as
`shown in FIG. 1), the vibrational strength is decreased by
`25% if the drive frequency is +2.5 Hz from the resonant
`frequency (i.e., 175 Hz). Moreover, the resonant frequency of
`an LRA is not constant; there can be a frequency shift that can
`be caused by a number of environmental factors (such as
`mechanical wear, temperature, and LRA orientation or posi
`tion). As a result this frequency shift, driving an LRA at a
`substantially constant drive frequency would result in poor
`efficiency.
`0003. One conventional method that has been employed in
`an attempt to combat some of the issues associated with
`driving an LRA can be seen in FIG. 2. For this method, a drive
`interval with a predetermined or pre-defined length is
`employed. Typically, the LRA is driven over this drive inter
`val. Following the drive interval the driver is shut-off or
`placed in a high impedance state to allow the back electro
`motive force (back-emf) to be monitored during a “monitor
`interval.” Once the back-emfreaches a predetermined thresh
`old (in what can be referred to as a “Zero-crossing), a mea
`surement of the back-emf is made after a delay interval, which
`is subtracted from the input signal. The LRA is then driven
`over the drive interval having the predetermined length.
`0004. A problem with the method is that, when the drive
`period is divided into its four quadrants T to T. (as shown in
`FIG. 3), the LRA is only driven during the quadrants T and
`T. This means that the LRA has a drive period that is less than
`one-quarter of its resonant period during quadrants T and T
`and has about one-quarter of its resonant period during quad
`rants T and T. The total drive period is, thus, less than the
`resonant period, resulting in a drive frequency that is greater
`than the resonant frequency.
`0005. Another problem with this method relates to braking
`Typically, again is applied to the back-emf value (measured
`after the delay interval) and subtracted from the input signal
`to obtain the output drive amplitude. If the gain is large, the
`drive amplitude tends to be smaller for the same input, so it is
`undesirable to have a large gain. However, if the gain is Small,
`braking is weaker and more ineffective because, at the time of
`braking, the input signal is Zero and the output amplitude is
`negative.
`0006. Therefore, there is a need for a method and/or appa
`ratus for driving an LRA with improved performance.
`
`SUMMARY
`0008. An embodiment of the present invention, accord
`ingly, provides an apparatus. The apparatus comprises an
`input circuit that is configured to receive an input signal; a
`signal generator that is coupled to the input circuit and that is
`configured to output a drive signal that is based at least in part
`on the input signal, wherein the drive signal includes a plu
`rality of positive drive intervals, a plurality of negative driver
`intervals, and a plurality of off intervals; and a driver that is
`coupled to the signal generator and the input circuit, that is
`configured to drive a linear resonant actuator (LRA), and that
`is configured to receive the drive signal, wherein the input
`circuit is configured to measure the back electromotive force
`(back-emf) of the LRA during the plurality of off periods of
`the drive signal, and wherein the signal generator adjusts the
`duration of at least one of the positive and negative intervals
`based at least in part on the measured back-emfso as to drive
`the LRA Substantially at its resonant frequency.
`0009. In accordance with an embodiment of the present
`invention, the apparatus has an operational mode and an
`initialization mode, wherein each period of drive signal dur
`ing the operational mode includes at least one positive drive
`interval or at least one negative drive interval between two
`consecutive off intervals, and wherein the measurement cir
`cuit is configured to determine whether the back-emf has
`reached a predetermined threshold in each of the two con
`secutive off intervals, and the controller is configured to mea
`sure the duration between the back-emf reaching the prede
`termined threshold for the two consecutive off intervals.
`0010. In accordance with an embodiment of the present
`invention, the signal generator further comprises: an analog
`to-digital converter (ADC) that is coupled to the input circuit;
`and a controller that is coupled between the ADC and the
`driver.
`0011. In accordance with an embodiment of the present
`invention, the measurement circuit further comprises: a sense
`amplifier that is coupled to the driver; and a multiplexer that
`is coupled to the sense amplifier, the ADC, and the controller,
`wherein the multiplexer is configured to receive the input
`signal, and wherein the controller is configured to control the
`multiplexer.
`0012. In accordance with an embodiment of the present
`invention, the driver is a class AB driver.
`0013. In accordance with an embodiment of the present
`invention, the driver is a class D driver having: a gate drive
`circuit that is coupled to the controller; and an H-bridge that
`is coupled to the gate drive circuit and the sense amplifier.
`0014. In accordance with an embodiment of the present
`invention, the ADC receives a Supply Voltage as a reference
`Voltage.
`0015. In accordance with an embodiment of the present
`invention, the multiplexer receives a Supply Voltage as an
`input, and wherein the controller further comprises: a logic
`circuit that is coupled to the ADC; and a compensator that is
`coupled between the logic circuit and the gate drive circuit.
`0016. In accordance with an embodiment of the present
`invention, a method is provided. The method comprises dur
`ing a first off interval, measuring the back-emf of an LRA;
`during a first off interval, starting a timer when the back-emf
`reaches a predetermined threshold; after a predetermined
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`delay has lapsed following the back-emf reaching the prede
`termined threshold during the first off interval, driving the
`LRA over a drive interval having a length with a drive
`strength, wherein the drive strength is based at least in part on
`an input signal and the back-emf entering a second off inter
`val following the drive interval; during the second off interval,
`measuring the back-emf of the LRA; during the second off
`interval, stopping the timer when the back-emf reaches the
`predetermined threshold; and setting a value from the timer
`that corresponds to duration between the back-emf reaching
`the predetermined threshold during the first off interval and
`the back-emf reaching the predetermined threshold during
`the second off interval minus a delay period as the length of
`the drive interval.
`0017. In accordance with an embodiment of the present
`invention, the predetermined threshold further comprises a
`first predetermined threshold, and wherein the drive interval
`further comprises a first drive interval, and wherein the
`method further comprises the step of performing initializa
`tion by: retrieving the length; determining whether the back
`emf magnitude of the LRA is less than a second predeter
`mined threshold; and if the back-emf magnitude is less than
`the second predetermined threshold, driving the LRA over a
`second drive interval of one-half of the length.
`0018. In accordance with an embodiment of the present
`invention, the first off interval further comprises a first delay
`interval following the time when the back-emf reaches the
`predetermined threshold, and wherein the second off interval
`further comprises a second delay interval following the time
`when the back-emf reaches the predetermined threshold.
`0019. In accordance with an embodiment of the present
`invention, the first and second delay intervals are about 200
`LS.
`0020. In accordance with an embodiment of the present
`invention, an apparatus is provided. The apparatus comprises
`a touch panel; a touchpanel controller that is coupled to touch
`panel, wherein the touch panel includes an interface; an LRA;
`and a haptics driver having an operational mode and an ini
`tialization mode, wherein the haptics driver includes: an input
`circuit that is coupled to receive an input signal from the
`interface; a signal generator that is coupled to the input circuit
`and that is configured to output a drive signal that is based at
`least in part on the input signal, wherein the drive signal
`includes a plurality of positive drive intervals, a plurality of
`negative drive intervals, and a plurality of off intervals; and an
`LRA driver that is coupled to the signal generator, the input
`circuit, and the LRA, wherein the LRA driver is configured to
`receive the drive signal from the signal generator, and
`wherein the input circuit is configured to measure the back
`emf of the LRA during the plurality of off periods of the drive
`signal, and wherein each period of drive signal during the
`operational mode includes at least one positive drive interval
`or at least one negative drive interval between two consecu
`tive off intervals, and wherein the measurement circuit is
`configured to determine whether the back-emf has reached a
`predetermined threshold in each of the two consecutive off
`intervals, and the controller is configured to measure the
`duration between the back-emf reaching the predetermined
`threshold for the two consecutive off intervals, and wherein
`the signal generator adjusts the duration of at least one of the
`positive and negative intervals based at least in part on the
`duration between the back-emf reaching the predetermined
`threshold for the two consecutive off intervals so as to drive
`the LRA Substantially at its resonant frequency.
`
`0021. In accordance with an embodiment of the present
`invention, the ADC further comprises a first ADC, and
`wherein the interface further comprises a first interface, and
`wherein the touch panel controller further comprises: a sec
`ond interface that is coupled to the touchpanel; a second ADC
`that is coupled to the second interface; and a pre-processing
`circuit that is coupled to ADC and the first interface.
`0022. In accordance with an embodiment of the present
`invention, the apparatus further comprises a host processor
`that is coupled to the second interface.
`0023. In accordance with an embodiment of the present
`invention, the LRA driver further comprises a class AB driver.
`0024. In accordance with an embodiment of the present
`invention, the LRA driver further comprises: a gate drive
`circuit that is coupled to the controller; and an H-bridge that
`is coupled between the gate drive circuit and the LRA.
`0025. In accordance with an embodiment of the present
`invention, the haptics driver further comprises a filter that is
`coupled between the second interface and the multiplexer.
`0026. The foregoing has outlined rather broadly the fea
`tures and technical advantages of the present invention in
`order that the detailed description of the invention that fol
`lows may be better understood. Additional features and
`advantages of the invention will be described hereinafter
`which form the subject of the claims of the invention. It
`should be appreciated by those skilled in the art that the
`conception and the specific embodiment disclosed may be
`readily utilized as a basis for modifying or designing other
`structures for carrying out the same purposes of the present
`invention. It should also be realized by those skilled in the art
`that such equivalent constructions do not depart from the
`spirit and scope of the invention as set forth in the appended
`claims.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`0027. For a more complete understanding of the present
`invention, and the advantages thereof, reference is now made
`to the following descriptions taken in conjunction with the
`accompanying drawings, in which:
`0028 FIG. 1 is a diagram depicting an example of the
`general operation of an LRA;
`0029 FIGS. 2 and 3 are diagrams of an example of a
`conventional driving method for an LRA;
`0030 FIG. 4 is a diagram of an example of a system in
`accordance with the present invention;
`0031
`FIG. 5 is a diagram of an example of the touch panel
`controller of FIG. 4;
`0032 FIG. 6 is a diagram of an example of a system in
`accordance with the present invention;
`0033 FIGS. 7 and 8 are diagrams of examples of the
`haptics drivers of FIGS. 4-6; and
`0034 FIGS. 9-11 are diagrams depicting examples of the
`general operation of the haptics drivers of FIGS. 4-8.
`
`DETAILED DESCRIPTION
`0035 Refer now to the drawings wherein depicted ele
`ments are, for the sake of clarity, not necessarily shown to
`scale and wherein like or similar elements are designated by
`the same reference numeral through the several views.
`0036 Turning to FIGS. 4-6, examples of systems 100-1
`and 100-2 in accordance with the present invention can be
`seen. These systems 100-1 and 100-2 can, for example, be
`mobile phones, tablet computers, or other such devices hav
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`ing a touch panel 102. Typically, in these systems 100-1 and
`100-2, there is a host process 104 (which can, for example, be
`an applications processor and/or baseband processor) and a
`LRA110 (which can provide haptics effects like touchbutton
`effects that can vary based on amplitude and duration of an
`applied drive signal). The difference between systems 100-1
`and 100-2, however, generally lies between the touch panel
`controllers 106-1 and 106-2. Each of the touch panel control
`lers 106-1 and 106-2 include a touch panel interface 202
`(which allows for measurements of the touch panel 102 to be
`made), an analog-to-digital converter (ADC) 204 (which can,
`for example, be a Successive approximation register or SAR
`ADC or a sigma-delta ADC), a pre-processor 206, a clock
`210, and a host interface 208. With controller 106-1, the
`haptics driver 108 (which drives the LRA 110) is included
`(i.e., as part of the same integrated circuit or IC), and with
`controller 106-2, the haptics driver 108 is separate from con
`troller 106-2 (i.e., different IC). Other combinations (where
`portions of the haptics driver 108 are included with the con
`troller 106) may also be used.
`0037. The haptics driver 108 (which is labeled 108-A for
`FIG. 7) is able to drive the LRA 110 (so as to have different
`haptics effects) based on an input signal from the host inter
`face 208. Usually, this input signal from host interface 208 is
`filtered by filter 302 and applied to the input circuit 310-A
`(which generally comprises multiplexer 313-A and sense
`amplifier 312). The multiplexer 313-A is also generally con
`trolled by the controller 306-A of signal generator 311-A, but,
`when set to apply the filtered input signal, the ADC 304
`(which receives a reference signal REF and may, for example,
`be a SARADC) is able to generate a digital representation of
`the filtered input signal for the controller 306-A that generates
`a drive signal for driver 308-A (which can, for example, be a
`class AB driver or a class D driver). The sense amplifier 312
`(which is coupled to the driver 308-A) is then able to perform
`back-emfmeasurements so as to allow the controller 306-A to
`adjust the drive signal to substantially drive the LRA110 at its
`resonant frequency.
`0038. When a class D driver is employed as driver 308-A
`or 308-B (as shown in FIG. 8), several configurations can be
`employed. When employed as a class D driver, drivers 308-A
`and 308-B would employ a gate drive circuit 318 and
`H-bridge 320 (as shown in FIG. 8). In one configuration, the
`reference voltage REF for ADC 304 can be seen to the supply
`Voltage VDD, and, in an alternative configuration (shown in
`FIG. 8), multiplexer 313-B can receive the supply voltage
`VDD as an input, while the reference voltage REF is gener
`ally constant. With this alternative configuration, the control
`ler 306-B would include logic 314 and a compensator 316
`(which would use the information gathered from a measure
`ment of the supply voltage VDD to provide adequate com
`pensation to the drive signal).
`0039. In operation (as shown in FIGS. 9-11), the controller
`306-A or 306-B (hereinafter 306) employs a drive signal that
`substantially matches the resonant frequency of the LRA110.
`To do this, the controller 306 centers or aligns the positive and
`negative intervals of the drive signal with the back-emfso that
`the LRA is driven in each quadrant T to T. (as shown in FIG.
`9), and the controller 306 uses an initialization mode 401 and
`an operational mode 407 (as shown in FIGS. 10 and 11).
`During the initialization mode 401, the controller 306
`retrieves a saved drive interval T,
`having a duration or
`length from memory (which can be included as part of the
`controller 306) in step 402. During a monitoring interval,
`
`where the multiplexer 313-A or 313-B (hereinafter 313) is set
`to provide a back-emf measurement from sense amplifier 312
`to ADC 304, the controller 306 determines whether the back
`emfmagnitude of LRA 110 is less than a predetermined value
`k. If the back-emf is less than value k, the LRA 110 is pre
`sumed to be “stopped,” and the LRA is initially driven for
`drive interval T- (which is typically one-half of interval
`T,) in step 406. The controller 306 can then enter the
`operational mode 407 in step 408. When entering the opera
`tional mode 407, the driver 308-A or 308-B (hereinafter 308)
`is set to an off or high impedance state during an off interval.
`During this off interval, multiplexer 313 is set so that control
`ler 306 is able to receive the back-emf from sense amplifier
`312 to determine whether the back-emf has reached a zero
`crossing (i.e., reached a predetermined threshold) in step 408.
`Once the Zero-crossing has occurred, a timer (which can be
`part of controller 306) is started at time TC1 in step 410, and,
`after a delay interval D1 in step 412, the measured back-emf
`value is measured and Subtracted from the input signal (which
`is measured by virtue of setting multiplexer 313 to provide the
`input signal to ADC 304) in order for a proper or desired
`amplitude to be achieved. The LRA 110 is then driven in step
`415 over drive interval T. Once the interval T,
`has
`lapsed, the controller enters a subsequent off intervalso that
`the timer can be stopped at time TC2 when the back-emf
`reaches the threshold in step 418. In step 420, the duration or
`time period between the Zero-crossings in the two consecu
`tive off intervals less or minus a delay period (which is typi
`cally twice the delay interval D1) can be set as the drive
`duration or the length of the drive interval. Then, in starting
`again at step 410, the LRA 110 is driven after the delay
`interval D1. This drive duration can then be continually
`adjusted for each positive or negative drive interval (i.e.,
`between times TC2 and TC3).
`0040. One other feature that is implemented in controller
`306 is an improved braking and acceleration ability. Typi
`cally, in step 414, the controller 306 applies a gain to the
`back-emf before subtracting it from the input signal. With
`conventional techniques, the gain was usually fixed, but with
`haptics driver 108, the controller 306 can adjust the gain
`applied to the back-emf depending on whether braking or
`acceleration is employed or may be needed.
`0041 Having thus described the present invention by ref
`erence to certain of its preferred embodiments, it is noted that
`the embodiments disclosed are illustrative rather than limit
`ing in nature and that a wide range of variations, modifica
`tions, changes, and Substitutions are contemplated in the fore
`going disclosure and, in some instances, some features of the
`present invention may be employed without a corresponding
`use of the other features. Accordingly, it is appropriate that the
`appended claims be construed broadly and in a manner con
`sistent with the scope of the invention.
`1. An apparatus comprising:
`an input circuit that is configured to receive an input signal;
`a signal generator that is coupled to the input circuit and
`that is configured to output a drive signal that is based at
`least in part on the input signal, wherein the drive signal
`includes a plurality of positive drive intervals, a plurality
`of negative drive intervals, and a plurality of off inter
`vals; and
`a driver that is coupled to the signal generator and the input
`circuit, that is configured to drive a linear resonant actua
`tor (LRA), and that is configured to receive the drive
`signal, wherein the input circuit is configured to measure
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`the back electromotive force (back-emf) of the LRA
`during the plurality of off periods of the drive signal, and
`wherein the signal generator adjusts the duration of at
`least one of the positive and negative intervals based at
`least in part on the measured back-emfso as to drive the
`LRA Substantially at its resonant frequency.
`2. The apparatus of claim 1, wherein the apparatus has an
`operational mode and an initialization mode, wherein each
`period of drive signal during the operational mode includes at
`least one positive drive interval or at least one negative drive
`interval between two consecutive off intervals, and wherein
`the measurement circuit is configured to determine whether
`the back-emf has reached a predetermined threshold in each
`of the two consecutive off intervals, and the controller is
`configured to measure the duration between the back-emf
`reaching the predetermined threshold for the two consecutive
`off intervals.
`3. The apparatus of claim 2, wherein the signal generator
`further comprises:
`an analog-to-digital converter (ADC) that is coupled to the
`input circuit; and
`a controller that is coupled between the ADC and the driver.
`4. The apparatus of claim 3, wherein the measurement
`circuit further comprises:
`a sense amplifier that is coupled to the driver, and
`a multiplexer that is coupled to the sense amplifier, the
`ADC, and the controller, wherein the multiplexer is con
`figured to receive the input signal, and wherein the con
`troller is configured to control the multiplexer.
`5. The apparatus of claim 4, wherein the driver is a class AB
`driver.
`6. The apparatus of claim 4, wherein the driver is a class D
`driver having:
`a gate drive circuit that is coupled to the controller, and
`an H-bridge that is coupled to the gate drive circuit and the
`sense amplifier.
`7. The apparatus of claim 6, wherein the ADC receives a
`Supply Voltage as a reference Voltage.
`8. The apparatus of claim 6, wherein the multiplexer
`receives a Supply Voltage as an input, and wherein the con
`troller further comprises:
`a logic circuit that is coupled to the ADC; and
`a compensator that is coupled between the logic circuit and
`the gate drive circuit.
`9. A method comprising:
`during a first off interval, measuring the back-emf of an
`LRA;
`during a first off interval, starting a timer when the back
`emf reaches a predetermined threshold;
`after a predetermined delay has lapsed following the back
`emf reaching the predetermined threshold during the
`first off interval, driving the LRA over a drive interval
`having a length with a drive strength, wherein the drive
`strength is based at least in part on an input signal and the
`back-emf
`entering a second off interval following the drive interval:
`during the second off interval, measuring the back-emf of
`the LRA;
`during the second off interval, stopping the timer when the
`back-emf reaches the predetermined threshold; and
`setting a value from the timer that corresponds to the dura
`tion between the back-emf reaching the predetermined
`threshold during the first off interval and the back-emf
`
`reaching the predetermined threshold during the second
`off interval minus a delay period as the length of the
`drive interval.
`10. The method of claim 9, wherein the predetermined
`threshold further comprises a first predetermined threshold,
`and wherein the drive interval further comprises a first drive
`interval, and wherein the method further comprises the step of
`performing initialization by:
`retrieving the length;
`determining whether the back-emf magnitude of the LRA
`is less than a second predetermined threshold; and
`if the back-emf magnitude is less than the second prede
`termined threshold, driving the LRA over a second drive
`interval of one-half of the length.
`11. The method of claim 10, wherein the first off interval
`further comprises a first delay interval following the time
`when the back-emfreaches the predetermined threshold, and
`wherein the second off interval further comprises a second
`delay interval following the time when the back-emf reaches
`the predetermined threshold.
`12. The method of claim 11, wherein the first and second
`delay intervals are about 200 us.
`13. An apparatus comprising:
`a touch panel;
`a touch panel controller that is coupled to a touch panel,
`wherein the touch panel includes an interface;
`an LRA; and
`a haptics driver having an operational mode and an initial
`ization mode, wherein the haptics driver includes:
`an input circuit that is coupled to receive an input signal
`from the interface;
`a signal generator that is coupled to the input circuit and
`that is configured to output a drive signal that is based
`at least in part on the input signal, wherein the drive
`signal includes a plurality of positive drive intervals, a
`plurality of negative drive intervals, and a plurality of
`off intervals; and
`a LRA driver that is coupled to the signal generator, the
`input circuit, and the LRA, wherein the LRA driver is
`configured to receive the drive signal from the signal
`generator, and wherein the input circuit is configured
`to measure the back-emf of the LRA during the plu
`rality of off periods of the drive signal, and wherein
`each period of drive signal during the operational
`mode includes at least one positive drive interval or at
`least one negative drive interval between two con
`secutive off intervals, and wherein the measurement
`circuit is configured to determine whether the back
`emf has reached a predetermined threshold in each of
`the two consecutive off intervals, and the controller is
`configured to measure the duration between the back
`emf reaching the predetermined threshold for the two
`consecutive off intervals, and wherein the signal gen
`erator adjusts the duration of at least one of the posi
`tive and negative intervals based at least in part on the
`duration between the back-emfreaching the predeter
`mined threshold for the two consecutive off intervals
`so as to drive the LRA substantially at its resonant
`frequency.
`14. The apparatus of claim 13, wherein the signal generator
`further comprises:
`an ADC that is coupled to the input circuit; and
`a controller that is coupled between the ADC and the LRA
`driver.
`
`IPR2022-00058
`Apple EX1012 Page 15
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`US 2013/0264973 A1
`
`Oct. 10, 2013
`
`15. The apparatus of claim 14, wherein the measurement
`circuit further comprises:
`a sense amplifier that is coupled to the LRA driver; and
`a multiplexer that is coupled to the sense amplifier, the
`ADC, and the controller, wherein the multiplexer is con
`figured to receive the input signal, and wherein the con
`troller is configured to control the multiplexer.
`16. The apparatus of claim 15, wherein the ADC further
`comprises a first ADC, and wherein the interface further
`comprises a first interface, and wherein the touch panel con
`troller further comprises:
`a second interface that is coupled to the touch panel;
`a second ADC that is coupled to the second interface; and
`a pre-processing circuit that is coupled to ADC and the first
`interface.
`17. The apparatus of claim 16, wherein the apparatus fur
`ther comprises a host proce