Finding touchdown frequency for a head in a disk drive

1. A disk drive comprising:

a disk;

a head actuated over the disk

a touchdown sensor for generating a sensor signal; and

control circuitry operable to:

filter the sensor signal using at least three bandpass filters to generate at least three filtered signals; and

decrease the fly height of the head until one of the filtered signals indicates the head has contacted the disk,

wherein:

the bandpass filters collectively span a frequency range; and

the control circuitry is operable to adjust a center frequency of at least one of the bandpass filters in order to substantially center the frequency range about a frequency defined by the filtered signal that indicates the head has contacted the disk.

2. The disk drive as recited in claim 1 , wherein the touchdown sensor is integrated with the head.

3. The disk drive as recited in claim 1 , wherein the touchdown sensor comprises a microactuator for actuating the head over the disk.

4. The disk drive as recited in claim 1 , wherein:

the head is coupled to a distal end of an actuator arm; and

the touchdown sensor is mounted on the actuator arm.

5. The disk drive as recited in claim 1 , wherein:

the filtered signals are wired-ORed to generate a composite signal; and

the control circuitry is operable to detect when the head contacts the disk by comparing the composite signal to a threshold.

6. The disk drive as recited in claim 5 , wherein the control circuitry is operable to adjust the threshold.

7. The disk drive as recited in claim 1 , wherein the control circuitry is operable to detect when the head contacts the disk by comparing each filtered signal to a respective threshold.

8. The disk drive as recited in claim 7 , wherein at least two of the respective thresholds are different.

9. The disk drive as recited in claim 8 , wherein the control circuitry is operable to adjust at least one of the respective thresholds.

10. The disk drive as recited in claim 1 , wherein the control circuitry is operable to:

measure a noise level of at least one of the bandpass filters; and

adjust a threshold for detecting the head has contacted the disk in response to the noise level.

11. The disk drive as recited in claim 1 , wherein the control circuitry is operable to adjust a gain of at least one of the bandpass filters.

12. The disk drive as recited in claim 1 , wherein the control circuitry is operable to adjust a center frequency of at least one of the bandpass filters.

13. The disk drive as recited in claim 12 , wherein the control circuitry is operable to adjust the center frequency of at least one of the bandpass filters until one of the filtered signals indicates the head has contacted the disk.

14. The disk drive as recited in claim 13 , wherein the control circuitry is operable to estimate an environmental condition in response to the sensor signal that indicates the head has contacted the disk.

15. The disk drive as recited in claim 12 , wherein the control circuitry is operable to adjust the center frequency of at least one of the bandpass filters in response to the filtered signal that indicates the head has contacted the disk.

16. The disk drive as recited in claim 12 , wherein:

the disk drive comprises an environmental sensor; and

the control circuitry is operable to adjust the center frequency of at least one of the bandpass filters in response to the environmental sensor.

17. A method of calibrating a touchdown in a disk drive, the disk drive comprising a head actuated over a disk, and a touchdown sensor for generating a sensor signal, the method comprising:

filtering the sensor signal using at least three bandpass filters to generate at least three filtered signals; and

decreasing the fly height of the head until one of the filtered signals indicates the head has contacted the disk,

wherein:

the bandpass filters collectively span a frequency range; and

further comprising adjusting a center frequency of at least one of the bandpass filters in order to substantially center the frequency range about a frequency defined by the filtered signal that indicates the head has contacted the disk.

18. The method as recited in claim 17 , wherein the touchdown sensor is integrated with the head.

19. The method as recited in claim 17 , wherein the touchdown sensor comprises a microactuator for actuating the head over the disk.

20. The method as recited in claim 17 , wherein:

the head is coupled to a distal end of an actuator arm; and

the touchdown sensor is mounted on the actuator arm.

21. The method as recited in claim 17 , wherein:

the filtered signals are wired-ORed to generate a composite signal; and

the method further comprises detecting when the head contacts the disk by comparing the composite signal to a threshold.

22. The method as recited in claim 21 , further comprising adjusting the threshold.

23. The method as recited in claim 17 , further comprising detecting when the head contacts the disk by comparing each filtered signal to a respective threshold.

24. The method as recited in claim 23 , wherein at least two of the respective thresholds are different.

25. The method as recited in claim 24 , further comprising adjusting at least one of the respective thresholds.

26. The method as recited in claim 17 , further comprising:

measuring a noise level of at least one of the bandpass filters; and

adjusting a threshold for detecting the head has contacted the disk in response to the noise level.

27. The method as recited in claim 17 , further comprising adjusting a gain of at least one of the bandpass filters.

28. The method as recited in claim 17 , further comprising adjusting a center frequency of at least one of the bandpass filters.

29. The method as recited in claim 28 , further comprising adjusting the center frequency of at least one of the bandpass filters until one of the filtered signals indicates the head has contacted the disk.

30. The method as recited in claim 29 , further comprising estimating an environmental condition in response to the sensor signal that indicates the head has contacted the disk.

31. The method as recited in claim 28 , further comprising adjusting the center frequency of at least one of the bandpass filters in response to the filtered signal that indicates the head has contacted the disk.

32. The method as recited in claim 28 , further comprising adjusting the center frequency of at least one of the bandpass filters in response to an environmental sensor.

33. The method as recited in claim 17 , further comprising setting an ambient temperature of the disk drive to a nominal value.

34. A disk drive comprising:

a disk;

a head actuated over the disk

a touchdown sensor for generating a sensor signal; and

control circuitry operable to:

filter the sensor signal using at least three bandpass filters to generate at least three filtered signals; and

decrease the fly height of the head until one of the filtered signals indicates the head has contacted the disk,

wherein:

the disk drive comprises an environmental sensor; and

the control circuitry is operable to adjust a center frequency of at least one of the bandpass filters in response to the environmental sensor.

35. A method of calibrating a touchdown in a disk drive, the disk drive comprising a head actuated over a disk, and a touchdown sensor for generating a sensor signal, the method comprising:

filtering the sensor signal using at least three bandpass filters to generate at least three filtered signals;

decreasing the fly height of the head until one of the filtered signals indicates the head has contacted the disk; and

adjusting a center frequency of at least one of the bandpass filters in response to an environmental sensor.

36. A disk drive comprising:

a disk;

a head actuated over the disk

a touchdown sensor for generating a sensor signal; and

control circuitry operable to:

filter the sensor signal using at least three bandpass filters to generate at least three filtered signals;

decrease the fly height of the head until one of the filtered signals indicates the head has contacted the disk; and

estimate an environmental condition in response to the sensor signal that indicates the head has contacted the disk.

37. The disk drive as recited in claim 36 , wherein the environmental condition comprises an ambient temperature.

38. A method of calibrating a touchdown in a disk drive, the disk drive comprising a head actuated over a disk, and a touchdown sensor for generating a sensor signal, the method comprising:

filtering the sensor signal using at least three bandpass filters to generate at least three filtered signals;

decreasing the fly height of the head until one of the filtered signals indicates the head has contacted the disk; and

estimating an environmental condition in response to the sensor signal that indicates the head has contacted the disk.

39. The method as recited in claim 38 , wherein the environmental condition comprises an ambient temperature.