Resonance driver for determining a resonant frequency of a haptic device
This document discusses, among other things, apparatus and methods for controlling a haptic transducer. In an example, a haptic controller can include an active termination driver having a configurable output impedance. The active termination driver can be configured to drive a haptic transducer and to process back electro-magnetic force (EMF) of the haptic transducer to provide motion feedback of the haptic transducer. In an example, the haptic controller can include a processor to provide a command signal to the active termination driver and to determine a resonant frequency of the haptic device using the motion feedback of the haptic transducer.
1. A haptic controller comprising:
an active termination driver having a configurable output impedance, the active termination driver configured to drive a haptic transducer and to process back electro-magnetic force (EMF) of the haptic transducer to provide motion feedback of the haptic transducer;
a processor to provide a command signal to the active termination driver and to determine a resonant frequency of the haptic device using the motion feedback of the haptic transducer;
a peak detector configured to detect at least one of a minimum peak or a maximum peak of the back EMF: and
a zero-crossing detector configured to provide timing information to the processor relative to the back EMF crossing a voltage value approximately halfway between the minimum peak and the maximum peak of the back EMF.
2. The haptic controller of claim 1 , wherein the active termination driver includes an active element configured to provide the configurable output impedance.
3. The haptic controller of claim 2 , wherein the active element includes a negative impedance converter.
4. The haptic controller of claim 3 , wherein the negative pedance converter is configured to provide an amplified voltage indicative of the back EMF.
5. The haptic controller of claim 4 , wherein the negative impedance converter is configured to receive a digital output from the processor and to provide a negative impedance based on the digital output.
6. The haptic controller of claim 1 , wherein the processor is configured to adjust a braking rate of the haptic transducer using a negative impedance converter.
7. A method comprising:
receiving a command signal at an active termination driver from a processor; driving a haptic transducer using the active termination driver and the command signal;
processing back EMF of the haptic transducer using the active termination driver to provide motion feedback of the haptic transducer; and
determining a resonant frequency of the haptic transducer using the motion feedback of the haptic transducer;
wherein the determining a resonant frequency of the haptic transducer includes detecting a period of the resonant frequency using the motion feedback of the haptic transducer; and
wherein the detecting a period includes;
detecting a maximum peak of the back EMF using a peak detector;
detecting a minimum peak of the back EMF using the peak detector; and
detecting two sequential crossings of the back EMF of a value halfway between the minimum peak and the maximum peak using a zero-crossing detector.
8. The method of claim 7 , wherein processing the back EMF includes amplifying the back EMF of the haptic transducer to provide the motion feedback using a negative impedance converter.
9. The method of claim 8 , including braking resonant otion of the haptic transducer using the negative impedance converter.
10. The method of claim 9 , wherein braking the resonant motion includes receiving a impedance information from the processor at the negative impedance converter; and
adjusting a negative impedance of the negative impedance converter using the impedance information.
11. The method of claim 10 , wherein the impedance information includes digital impedance information.
12. The method of claim 7 , wherein detecting a period includes driving an output of the active termination driver to predetermined value; and
detecting two sequential zero crossings of the back EMF using a zero-crossing detector.
13. A system comprising:
a resonant haptic transducer; and
haptic controller configured to couple to the resonant haptic transducer, the haptic controller including:
an active termination driver configured to drive a haptic transducer and to process back electro-magnetic force (EMF) to provide motion feedback of the haptic transducer;
a processor to provide a command signal to the active termination driver and to determine a resonant frequency of the haptic device using the motion feedback of the haptic transducer
a peak detector configured to detect at least one of a minimum peak or a maximum peak of the back EMF; and
a zero-crossing detector configured to provide timing information to the processor relative to the back EMF crossing a voltage value approximately halfway between the minimum peak and the maximum peak of the back EMF.
14. The haptic controller of claim 13 , wherein the active termination driver includes a negative impedance converter.
15. The haptic controller of claim 14 , wherein the negative impedance converter is configured to provide an amplified voltage indicative of the back EMF.
16. The haptic controller of claim 14 , wherein the negative impedance converter is configured to receive a digital output from the processor and to provide a negative impedance based on a value of the digital output.
17. Wreviously Presented) The haptic controller of claim 13 , wherein the processor is configured to adjust a braking rate of the haptic transducer using a negative impedance converter.