Methods and apparatus for actuator control

1. An actuator control circuit, comprising:

a drive circuit, coupled to the actuator and configured to supply a drive signal to the actuator; and

a feedback network connected to the drive circuit and configured to generate a feedback signal, wherein the feedback network comprises:

an induced voltage detection circuit connected to an output terminal of the drive circuit; and

a calibration circuit connected to the induced voltage detection circuit and configured to:

detect a DC offset level of the feedback signal; and

supply a code to the induced voltage detection circuit according to the detected DC offset level.

2. The actuator control circuit according to claim 1 , wherein the calibration circuit comprises:

a low pass filter; and

a logic circuit connected to an output terminal of the low pass filter.

3. The actuator control circuit according to claim 1 , wherein the feedback network further comprises an analog-to-digital converter (ADC) connected between the induced voltage detection circuit and the calibration circuit.

4. The actuator control circuit according to claim 3 , wherein the feedback network further comprises a feedback control circuit connected to an output terminal of the ADC.

5. The actuator control circuit according to claim 4 , wherein the calibration circuit is further configured to supply the code to the feedback control circuit to selectively operate the feedback control circuit.

6. The actuator control circuit according to claim 1 , further comprising a digital-to-analog converter (DAC) connected to an input terminal of the drive circuit and an input terminal of the induced voltage detection circuit.

7. The actuator control circuit according to claim 1 , wherein the induced voltage detection circuit comprises:

a replica circuit connected to an output terminal of the DAC configured to receive the code from the calibration circuit; and

a differential amplifier connected to an output terminal of the replica circuit.

8. The actuator control circuit according to claim 1 , wherein the induced voltage detection circuit is further configured to receive information relating to a direction of current though the drive circuit.

9. A method for controlling an actuator, comprising:

supplying a drive signal to the actuator;

detecting an induced voltage generated by the actuator;

generating a feedback signal according to the detected induced voltage;

detecting a DC offset level of the feedback signal;

calibrating the feedback signal, comprising:

selectively adjusting a resistance code based on the detected DC offset level; and

selectively operating a feedback control circuit based on the detected DC offset level; and

operating the actuator according to the feedback signal.

10. The method according to claim 9 , wherein selectively adjusting the resistance code comprises:

increasing the resistance code if the detected DC offset level is greater than a first threshold; and

decreasing the resistance code if the detected DC offset level is less than a second threshold.

11. The method according to claim 10 , wherein:

the first threshold is a predetermined positive value; and

the second threshold is a predetermined negative value.

12. The method according to claim 9 , wherein selectively operating the feedback control circuit comprises:

disabling the feedback control circuit prior to adjusting the resistance code; and

enabling the feedback control circuit after adjusting the resistance code.

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

an image signal processor configured to generate a position signal; and

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

an image sensor connected to the image signal processor; and

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

a drive circuit configured to supply a current to the actuator; and

a feedback network connected to the drive circuit and configured to generate a feedback signal, wherein the feedback network comprises:

an induced voltage detection circuit connected to an output terminal of the drive circuit; and

a calibration circuit connected to an output terminal of the induced voltage detection circuit and configured to:

 detect a DC offset level of the feedback signal; and

 supply a code to the induced voltage detection circuit according to the detected DC offset level;

wherein the control circuit generates a final position signal based on the position signal and the feedback signal.

14. The imaging system according to claim 13 , wherein the calibration circuit is further configured to increase the code if the detected DC offset level is greater than a predetermined positive threshold value.

15. The imaging system according to claim 13 , wherein the calibration circuit is further configured to decrease the code if the detected DC offset level is less than a predetermined negative threshold value.

16. The imaging system according to claim 13 , wherein the feedback network further comprises:

an analog-to-digital converter (ADC) connected between an output terminal of the induced voltage detection circuit and an input terminal of the calibration circuit; and

a feedback control circuit connected to a output terminal of the ADC.

17. The imaging system according to claim 16 , wherein:

the calibration circuit is further configured to supply the code to the feedback control circuit; and

the feedback control circuit is responsive to the code.

18. The imaging system according to claim 17 , wherein the feedback control circuit is disabled if the detected DC offset level is:

greater than a positive threshold value; and

less than a negative threshold value.

19. The imaging system according to claim 13 , wherein the calibration circuit comprises:

a low pass filter; and

a logic circuit connected to an output terminal of the low pass filter.