Methods and apparatus for focus control in an imaging system

1. An autofocus apparatus, comprising:

a temperature-sensitive component;

wherein the temperature-sensitive component comprises at least one of: a lens, a lens barrel, a driving magnet, a spring, a substrate, a sensing magnet, a position sensor, and an image sensor;

a temperature sensor adjacent to the temperature-sensitive component and configured to:

measure an ambient temperature around the temperature-sensitive component; and

generate temperature data; and

a correction circuit coupled to the temperature sensor and configured to:

receive the temperature data;

compute a relative temperature according to a base temperature and the ambient temperature;

model a degree of focus of the autofocus apparatus; and

compute a corrected target position.

2. The autofocus apparatus according to claim 1 , wherein the correction circuit is further configured to compute a thermal response of the temperature-sensitive component according to the relative temperature and a thermal time constant of the temperature-sensitive component.

3. The autofocus apparatus according to claim 2 , wherein the correction circuit is further configured to compute a position shift value according to the thermal response of the temperature-sensitive component.

4. The autofocus apparatus according to claim 3 , wherein the correction circuit utilizes the position shift value and a target position to compute the corrected target position.

5. The autofocus apparatus according to claim 1 , wherein the correction circuit:

computes a change in the effective focal length of the lens according to a thermal response of the lens; and

computes a change in length of the lens barrel according to a thermal response of the lens barrel.

6. The autofocus apparatus according to claim 1 , further comprising a position sensor configured to detect an actual position of the lens module, wherein the correction circuit further utilizes the actual position to compute the corrected target position.

7. A method of operating an autofocus apparatus having a temperature-sensitive component, comprising:

measuring an ambient temperature of the temperature-sensitive component;

wherein the temperature-sensitive component comprises at least one of: a lens, a lens barrel, a driving magnet, a spring, a substrate, a sensing magnet, a position sensor, and an image sensor;

computing a relative temperature according to a base temperature and the measured ambient temperature;

computing a thermal response of the temperature-sensitive component comprising:

computing a first thermal response of the lens according to the relative temperature; and

computing a second thermal response of the lens barrel according to the relative temperature; and

computing a corrected target position according to the computed thermal response.

8. The method according to claim 7 , further comprising, computing:

a target position of the lens;

a position shift value based on the first and second thermal responses; and

a corrected target position based on the computed position shift value and computed the target position.

9. The method according to claim 7 , further comprising:

computing the change in the effective focal length of the lens according to a thermal response of the lens; and

computing the change in length of the lens barrel according to a thermal response of the lens barrel.

10. An imaging system, comprising:

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

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

an image sensor;

a lens module positioned adjacent to the image sensor, comprising:

a lens coupled to a lens barrel; and

a control circuit responsive to the image signal processor and configured to generate a drive signal for moving the lens module, comprising:

a temperature sensor positioned adjacent to the lens module and configured to:

measure an ambient temperature of the lens module; and

generate temperature data; and

a correction circuit coupled to the temperature sensor and configured to:

receive the generated temperature data; and

compute a corrected target position utilizing:

 the generated temperature data;

 the target position signal;

 a thermal response of the lens; and

 a thermal response of the lens barrel.

11. The imaging system according to claim 10 , wherein the correction circuit is further configured to compute a relative temperature according to a base temperature and the ambient temperature.

12. The imaging system according to claim 10 , wherein the correction circuit is further configured to:

compute a change in an effective focal length of the lens;

compute a thermal expansion of the lens barrel; and

compute a position shift value according to the change in the effective focal length of the lens and the thermal expansion of the lens barrel.

13. The imaging system according to claim 12 , wherein:

the change in effective focal length of the lens is based on a temperature characteristic coefficient; and

the change in length of the lens barrel is based on a linear expansion coefficient.

14. The imaging system according to claim 13 , wherein the correction circuit utilizes the position shift value and the target position signal to compute the corrected target position.

15. The imaging system according to claim 10 , wherein:

the thermal response of the lens is based on the ambient temperature and a thermal time constant of the lens; and

the thermal response of the lens barrel is based on the ambient temperature and a thermal time constant of the lens barrel.