Actuator driver circuit with self-resonance tracking

1. An actuator driver circuit comprising:

a driver having at least one output for coupling to at least one input of an actuator; and

calibration circuitry configured to:

detect a phase of a voltage signal at the at least one output of the driver;

detect a phase of a current signal at the at least one output of the driver;

determine a phase difference between the phase of the voltage signal and the phase of the current signal; and

adjust a frequency of an oscillating signal for the driver, based at least in part on the phase difference.

2. The actuator driver circuit of claim 1 , wherein the calibration circuitry comprises a phase detector having at least one input electrically coupled to the at least one output of the driver and configured to determine the phase difference between the phase of the voltage signal and the phase of the current signal.

3. The actuator driver circuit of claim 2 , wherein:

the calibration circuitry further comprises a voltage-averaging circuit electrically coupled between the at least one input of the phase detector and the at least one output of the driver and configured to generate an averaged voltage signal indicative of an average of the voltage signal at the at least one output of the driver; and

the phase detector is configured to determine the phase difference between the phase of the voltage signal and the phase of the current signal based in part on the averaged voltage signal.

4. The actuator driver circuit of claim 2 , wherein:

the calibration circuitry further comprises a current-averaging circuit electrically coupled between the at least one input of the phase detector and the at least one output of the driver and configured to generate an averaged current signal indicative of an average of the current signal at the at least one output of the driver; and

the phase detector is configured to determine the phase difference between the phase of the voltage signal and the phase of the current signal based in part on the averaged current signal.

5. The actuator driver circuit of claim 2 , wherein the calibration circuitry further comprises:

a first comparator electrically coupled between the at least one input of the phase detector and the at least one output of the driver and configured to generate a first signal indicative of the phase of the voltage signal; and

a second comparator electrically coupled between the at least one input of the phase detector and the at least one output of the driver and configured to generate a second signal indicative of the phase of the current signal.

6. The actuator driver circuit of claim 2 , further comprising a voltage-controlled oscillator (VCO) configured to generate an oscillating signal for the driver, wherein the calibration circuitry is configured to adjust a frequency of the oscillating signal, based at least in part on the phase difference.

7. The actuator driver circuit of claim 6 , wherein:

the calibration circuitry further comprises an integrator circuit electrically coupled between an output of the phase detector and an input of the VCO and configured to generate a control signal indicative of an integral of the phase difference; and

the calibration circuitry is configured to adjust the frequency of the oscillating signal for the driver, based at least in part on the integral of the phase difference.

8. A speaker amplifier integrated circuit comprising the actuator driver circuit of claim 1 .

9. An electronic device comprising a haptic feedback circuit having the actuator, wherein the at least one input of the actuator is electrically coupled to the at least one output of the driver of the actuator driver circuit of claim 1 .

10. The electronic device of claim 9 , wherein the actuator is a linear resonance actuator.

11. The electronic device of claim 10 , wherein the electronic device comprises at least one of a video game controller, a mobile phone, a tablet, a watch, a touchscreen, or a touchpad.

12. A method of driving an actuator with a driver, comprising:

detecting, with calibration circuitry, a phase of a voltage signal output by the driver;

detecting, with the calibration circuitry, a phase of a current signal output by the driver;

determining, with the calibration circuitry, a phase difference between the phase of the voltage signal and the phase of the current signal;

adjusting, with the calibration circuitry, a frequency of an oscillating signal for the driver, based at least in part on the phase difference; and

outputting, from the driver for driving the actuator, a driver signal having the adjusted frequency of the oscillating signal.

13. The method of claim 12 , further comprising averaging the voltage signal, wherein determining the phase difference comprises determining the phase difference between the phase of the voltage signal and the phase of the current signal based in part on the averaged voltage signal.

14. The method of claim 12 , further comprising averaging the current signal, wherein determining the phase difference comprises determining the phase difference between the phase of the voltage signal and the phase of the current signal based in part on the averaged current signal.

15. The method of claim 12 , further comprising:

generating, with a first comparator, a first signal indicative of the phase of the voltage signal; and

generating, with a second comparator, a second signal indicative of the phase of the current signal, wherein determining the phase difference comprises determining the phase difference between the phase of the voltage signal and the phase of the current signal based at least in part on the first signal and the second signal.

16. The method of claim 12 , further comprising integrating the phase difference, wherein adjusting the frequency comprises adjusting the frequency of the oscillating signal based at least in part on the integrated phase difference.

17. The method of claim 16 , wherein adjusting the frequency comprises tuning an oscillator based at least in part on the integrated phase difference.

18. An apparatus for haptic feedback, comprising:

means for driving an actuator;

means for detecting a phase of a voltage signal output by the means for driving;

means for detecting a phase of a current signal output by the means for driving;

means for determining a phase difference between the phase of the voltage signal and the phase of the current signal; and

means for adjusting a frequency of an oscillating signal for the means for driving, based at least in part on the phase difference, wherein the means for driving is configured to drive the actuator at the adjusted frequency of the oscillating signal.

19. The apparatus of claim 18 , further comprising:

means for averaging the voltage signal; and

means for averaging the current signal, wherein the means for determining the phase difference is configured to determine the phase difference between the phase of the voltage signal and the phase of the current signal based at least in part on the averaged current signal and the averaged voltage signal.

20. The apparatus of claim 18 , further comprising:

means for generating a first signal indicative of the phase of the voltage signal; and means for generating a second signal indicative of the phase of the current signal, wherein the means for determining the phase difference is configured to determine the phase difference between the phase of the voltage signal and the phase of the current signal based at least in part on the first signal and the second signal.