Thermal model of transducer for thermal protection and resistance estimation

1. A method for determining a direct current impedance of a transducer, comprising:

in response to a driving signal applied to the transducer:

estimating an electrically-measured direct current impedance based on an electrical model of the transducer;

estimating an electrically-measured coil temperature based on the electrically-measured direct current impedance; and

setting one or more state variables of the thermal model based on the electrically-measured coil temperature;

receiving an input signal indicative of an electrical power consumed by the transducer; and

calculating, by a thermal model of the transducer, the direct current impedance based on the electrical power.

2. The method of claim 1 , wherein calculating the direct current impedance comprises:

generating, by the thermal model of the transducer, a coil temperature associated with the transducer; and

calculating the direct current impedance based on the coil temperature.

3. The method of claim 1 , wherein calculating the direct current impedance comprises calculating the direct current impedance directly from the electrical power, without an intermediate calculation of a coil temperature associated with the transducer.

4. The method of claim 1 , further comprising mixing the direct current impedance with an estimated impedance value derived from an electrical model of the direct current impedance.

5. The method of claim 1 , further comprising controlling a load power delivered to the transducer based on at least one of the coil temperature and another temperature generated by the thermal model.

6. The method of claim 5 , wherein controlling the load power comprises determining a gain to be applied to the driving signal for driving the transducer based on at least one of the coil temperature and another temperature generated by the thermal model.

7. The method of claim 5 , wherein controlling the load power comprises clipping to the driving signal for driving the transducer.

8. The method of claim 1 , wherein the thermal model is implemented with a Kalman filter.

9. The method of claim 1 , wherein the thermal model is implemented with an infinite impulse response filter.

10. The method of claim 1 , wherein the transducer is a haptic transducer.

11. The method of claim 1 , wherein the transducer is an audio speaker.

12. The method of claim 1 , further comprising in the absence of the driving signal including a haptic event, driving a pilot tone to the transducer at regular intervals to set an ambient temperature as one of the one or more state variables.

13. The method of claim 1 , further comprising:

halting updates to the one or more state variables between haptic events within the driving signal; and

prior to driving the transducer with the driving signal comprising a haptic event, updating the one or more state variables based on a time elapsed since a previous haptic event.

14. A system comprising:

an input for receiving an input signal indicative of an electrical power consumed by the transducer; and

a control system for monitoring operation of the transducer and configured to determine a direct current impedance of a transducer by:

estimating an electrically-measured direct current impedance based on an electrical model of the transducer;

estimating an electrically-measured coil temperature based on the electrically-measured direct current impedance;

setting one or more state variables of the thermal model based on the electrically-measured coil temperature; and

calculating, by a thermal model of the transducer implemented by the control system, the direct current impedance based on the electrical power.

15. The system of claim 14 , wherein calculating the direct current impedance comprises:

generating, by the thermal model of the transducer, a coil temperature associated with the transducer; and

calculating the direct current impedance based on the coil temperature.

16. The system of claim 14 , wherein calculating the direct current impedance comprises calculating the direct current impedance directly from the electrical power, without an intermediate calculation of a coil temperature associated with the transducer.

17. The system of claim 14 , wherein the thermal model is configured to mix the direct current impedance with an estimated impedance value derived from an electrical model of the direct current impedance.

18. The system of claim 14 , wherein the control system is further configured to control a load power delivered to the transducer based on at least one of the coil temperature and another temperature generated by the thermal model.

19. The system of claim 18 , wherein controlling the load power comprises determining a gain to be applied to a driving signal for driving the transducer based on at least one of the coil temperature and another temperature generated by the thermal model.

20. The system of claim 18 , wherein controlling the load power comprises clipping to a driving signal for driving the transducer.

21. The system of claim 14 , wherein the thermal model is implemented with a Kalman filter.

22. The system of claim 14 , wherein the thermal model is implemented with an infinite impulse response filter.

23. The system of claim 14 , wherein the transducer is a haptic transducer.

24. The system of claim 14 , wherein the transducer is an audio speaker.

25. The system of claim 14 , wherein the control system is further configured to, in the absence of the driving signal including a haptic event, cause a driver to drive a pilot tone to the transducer at regular intervals to set an ambient temperature as one of the one or more state variables.

26. The system of claim 14 , wherein the control system is further configured to:

halt updates to the one or more state variables between haptic events within the driving signal; and

prior to driving the transducer with the driving signal comprising a haptic event, update the one or more state variables based on a time elapsed since a previous haptic event.