Methods and apparatus for actuator control

1. A control circuit, capable of operating an actuator, having a drive circuit and a signal generator responsive to a target position, comprising:

a digital signal processing circuit coupled to:

an input of the signal generator; and

an output of the drive circuit; and

configured to:

measure waveform characteristics of a back electromotive force (EMF) induced by the actuator; and

compute a countermeasure value according to the back EMF; and

a selector circuit coupled to the signal generator and the drive circuit, wherein the selector circuit is configured to selectively couple one of a first output terminal and a second output terminal of the drive circuit to the digital signal processing circuit according to the target position;

wherein the drive circuit is configured to operate the actuator according to the countermeasure value.

2. The control circuit according to claim 1 , wherein the digital signal processing circuit comprises:

a digital filter comprising:

a low pass filter; and

a high pass filter;

a waveform characteristic circuit configured to compute at least one of a resonance period and a peak-to-peak value of the back EMF; and

a DC computation circuit configured to compute a DC component of the back EMF.

3. The control circuit according to claim 2 , wherein the digital signal processing circuit is further configured to:

compute a trigger time value according to the resonance period; and

count a trigger time period that ends at the trigger time value.

4. The control circuit according to claim 3 , wherein:

the waveform characteristic circuit is configured to detect:

a maximum peak value; and

a minimum peak value; and

the trigger time period begins at one of the detected maximum peak value and the minimum peak value.

5. The control circuit according to claim 3 , wherein the digital signal processing circuit is further configured to generate an activation signal at the end of a trigger time period.

6. The control circuit according to claim 5 , wherein the drive circuit applies a current, in response to the computed countermeasure value, to the actuator at the end of the trigger time period.

7. The control circuit according to claim 1 , wherein the digital signal processing circuit further computes:

a resonance period of the back EMF; and

a trigger time period according to the resonance period, wherein the trigger time period begins at one of: a maximum peak and a minimum peak of the back EMF.

8. The control circuit according to claim 1 , further comprising:

an amplifier circuit coupled between an output of the selector circuit and an input of the digital signal processing circuit, comprising:

a first terminal; and

a second terminal;

wherein the output of the selector circuit is coupled to the first terminal; and

a digital to analog converter comprising:

an input terminal; and

an output terminal;

wherein the input terminal is coupled to the digital signal processing circuit and the output terminal is coupled to the second terminal of the amplifier circuit.

9. The control circuit according to claim 1 , wherein the countermeasure value is computed according to a peak-to-peak value of the back EMF.

10. A method for controlling an actuator, comprising:

selectively coupling one of a plurality of drive circuit output terminals having a back electromotive force (EMF) to a digital signal processing circuit;

computing a peak-to-peak value of the back EMF;

computing a countermeasure value according to the computed peak-to-peak value;

computing a trigger time value; and

applying a current to the actuator that corresponds to the countermeasure value at the trigger time value.

11. The method for controlling an actuator according to claim 10 , wherein the output terminal is selected according to a direction and magnitude of a current through the actuator.

12. The method for controlling an actuator according to claim 10 , further comprising:

computing a resonance period of the back EMF; and

computing a DC component of the back EMF.

13. The method for controlling an actuator according to claim 12 , wherein the trigger time value is computed according to the resonance period.

14. The method for controlling an actuator according to claim 10 , further comprising:

counting a trigger time period that ends at the trigger time value; and

generating an activation signal at the end of the trigger time period.

15. The method for controlling an actuator according to claim 14 , wherein the trigger time period begins at one of: a detected maximum peak value and a detected minimum peak value.

16. An imaging system capable of performing autofocus with an actuator, comprising:

an image signal processor;

a camera module coupled to the image signal processor, comprising:

an image sensor coupled to the image signal processor, wherein the image sensor transmits image data to the image signal processor; and

a control circuit coupled to the image signal processor and configured to receive a target position from the image signal processor, wherein the control circuit comprises:

a signal generator configured to transmit an output signal at an output terminal; wherein the output signal represents the target position at a first time and a countermeasure value at a second time;

a drive circuit, coupled to the signal generator and the actuator, comprising:

a first output terminal; and

a second output terminal;

wherein the drive circuit receives the output signal and is configured to apply a drive signal to the actuator in response to the output signal;

a selector circuit coupled to:

the output terminal of the signal generator;

the first output terminal; and

the second output terminal;

wherein the selector circuit is configured to select one of the first output terminal and the second output terminal in response to the target position; and

a digital signal processing circuit coupled to the selector circuit and configured to:

compute a peak-to-peak value of a back EMF induced by the actuator;

compute the countermeasure value according to the peak-to-peak value; and

compute a DC component of the back EMF.

17. The imaging system according to claim 16 , wherein the digital signal processing circuit further computes:

a resonance period of the back EMF; and

a trigger value according to the resonance period.

18. The imaging system according to claim 16 , further comprising:

an amplifier circuit coupled between an output of the selector circuit and an input of the digital signal processing circuit, comprising:

a first terminal; and

a second terminal;

wherein the output of the selector circuit is coupled to the first terminal; and

a digital to analog converter comprising:

an input terminal; and

an output terminal;

wherein the input terminal is coupled to the digital signal processing circuit and the output terminal is coupled to the second terminal of the amplifier circuit.

19. The imaging system according to claim 16 , wherein the digital signal processing circuit is further configured to generate an activation signal at the end of a trigger time period.

20. The imaging system according to claim 19 , wherein the driver circuit applies a current corresponding to the countermeasure value at the end of the trigger time period.