Methods and apparatus for driving a transducer
Embodiments described herein relate to methods and apparatus for driving a haptic transducer with a driving signal. The method comprises estimating, based on a current through the haptic transducer and a terminal voltage across the haptic transducer, a back electromotive force, EMF, voltage representative of a velocity of a mass in the haptic transducer; comparing a phase of a voltage signal derived from the terminal voltage with a phase of the estimated back EMF voltage; and based on the comparison, adjusting a frequency or a phase of an output signal, wherein the driving signal is derived from the output signal, such that a frequency of the driving signal converges to a resonant frequency of the haptic transducer.
1. A method for driving a haptic transducer with a driving signal, the method comprising:
estimating, based on a current through the haptic transducer and a terminal voltage across the haptic transducer, a back electromotive force, EMF, voltage representative of a velocity of a mass in the haptic transducer;
comparing a phase of a voltage signal derived from the terminal voltage with a phase of the estimated back EMF voltage; and
based on the comparison, adjusting a frequency or a phase of an output signal, wherein the driving signal is derived from the output signal, such that a frequency of the driving signal converges to a resonant frequency of the haptic transducer.
2. The method of claim 1 wherein the step of adjusting comprises utilizing a phase locked loop to converge the frequency of the output signal to the resonance frequency of the estimated back EMF voltage.
3. The method of claim 2 wherein, the step of adjusting comprises adjusting the frequency of the output signal around a quiescent or a center frequency by:
setting an initial value of the quiescent or center frequency to be a predetermined value associated with the haptic transducer, and
adapting the quiescent or center frequency according to a smoothed instantaneous frequency of the driving signal.
4. The method of claim 3 wherein the adaptive quiescent or center frequency is bounded to be within a predetermined frequency range that represents an expected range of the resonant frequency of the haptic transducer.
5. The method of claim 1 further comprising:
sensing the terminal voltage; and
delaying the terminal voltage to generate the voltage signal.
6. The method of claim 1 further comprising:
shaping a waveform of the output signal to control a shape of the driving signal for driving the haptic transducer.
7. The method of claim 1 further comprising:
adding a low frequency pilot tone to the output signal, such that the driving signal comprises the low frequency pilot tone.
8. A resonant frequency tracker for driving a haptic transducer with a driving signal, the resonance-frequency tracker comprising:
a back electromotive force, EMF, modelling module configured to estimate, based on a current through the haptic transducer and a terminal voltage across the haptic transducer, a back-EMF voltage representative of a velocity of a mass in the haptic transducer; and
a controller configured to:
receive a voltage signal derived from the terminal voltage;
compare a phase of the voltage signal with a phase of the estimated back EMF voltage, and
based on the comparison, adjust a frequency or a phase of an output signal output by the controller, wherein the driving signal is derived from the output of the controller, such that a frequency of the driving signal converges to a resonant frequency of the haptic transducer.
9. The resonant frequency tracker of claim 8 wherein the controller comprises a phase locked loop, PLL, module configured to converge the frequency of the output signal to the resonance frequency of the estimated back EMF voltage.
10. The resonant frequency tracker of claim 9 wherein the PLL module is configured to determine the frequency of the driving signal.
11. The resonant frequency tracker of claim 9 wherein the PLL module adjusts the frequency of the output of the controller around a quiescent or a center frequency, wherein the PLL module is configured to:
set an initial value of the quiescent or center frequency to be a predetermined value associated with the haptic transducer, and
adapt the quiescent or center frequency according to a smoothed instantaneous frequency of the driving signal.
12. The resonant frequency tracker of claim 11 wherein the adaptive quiescent or center frequency is bounded to be within a predetermined frequency range that represents an expected range of the resonant frequency of the haptic transducer.
13. The resonant frequency tracker of claim 8 , further comprising:
a terminal voltage sensing block configured to sense the terminal voltage; and
a compensator module coupled and configured to delay the terminal voltage to generate the voltage signal.
14. The resonant frequency tracker of claim 8 , further comprising a nonlinear device coupled to receive the output signal, wherein the nonlinear device shapes a waveform of the output signal to control a shape of the driving signal for driving the haptic transducer.
15. The resonant frequency tracker of claim 8 , further comprising:
a pilot tone generator coupled to the output of the controller, wherein the pilot tone generator adds a low frequency pilot tone to the output signal such that the driving signal comprises the low frequency pilot tone.
16. The resonant frequency tracker of claim 8 further comprising:
a first band-pass filter configured to filter the estimated back EMF and to input the filtered estimated back EMF into the controller.
17. The resonant frequency tracker of claim 16 further comprising:
a second band-pass filter configured to filter the terminal voltage or a delayed terminal voltage, to generate the voltage signal, wherein the second band-pass filter matches the first band-pass filter.
18. An electronic apparatus comprising:
a haptic transducer; and
a resonant frequency tracker comprising:
a back electromotive force, EMF, modelling module configured to estimate, based on a current through the haptic transducer and a terminal voltage across the haptic transducer, a back-EMF voltage representative of a velocity of a mass in the haptic transducer; and
a controller configured to:
receive a voltage signal derived from the terminal voltage;
compare a phase of the voltage signal with a phase of the estimated back EMF voltage, and
based on the comparison, adjust a frequency or a phase of an output signal output by the controller, wherein the driving signal is derived from the output of the controller, such that a frequency of the driving signal converges to a resonant frequency of the haptic transducer.
19. An electronic apparatus as claimed in claim 18 wherein said electronic apparatus is at least one among: a portable device; a battery power device; a computing device; a communications device; a gaming device; a mobile telephone; a personal media player; a laptop, tablet or notebook computing device.