Granted Patent B1

US 8,279,550 · App. 13/397,376 · Granted Oct 2, 2012

Abstract

Claims (41)

1. A disk drive, comprising:

a disk;

a head for writing data to the disk;

a first touchdown sensor;

a second touchdown sensor; and

control circuitry comprising a first current source coupled to the first touchdown sensor and a second current source coupled to the second touchdown sensor, the control circuitry operable to:

determine a common mode voltage between the first touchdown sensor and the second touchdown sensor;

adjust the first current source and the second current source until the common mode voltage exceeds a first threshold;

determine a differential voltage between the first touchdown sensor and the second touchdown sensor;

adjust the first current source and the second current source until the differential voltage exceeds a second threshold; and

detect a touchdown event based on the differential voltage exceeding a third threshold.

2. The disk drive of claim 1 , wherein the head comprises the first touchdown sensor, the second touchdown sensor, and a thermal actuator.

3. The disk drive of claim 2 , wherein the control circuitry is further operable to adjust a thermal actuator power level.

4. The disk drive of claim 3 , wherein the control circuitry is further operable to store the thermal actuator power level associated with the touchdown event.

5. The disk drive of claim 3 , wherein the third threshold is a slope value and the control circuitry is further operable to determine a slope of the differential voltage as a function of the adjustment of the thermal actuator power level.

6. The disk drive of claim 5 , wherein the control circuitry is further operable to measure a running average of the slope of the differential voltage.

7. The disk drive of claim 1 , wherein the first threshold comprises a range of 0.5 volts to 2 volts.

8. The disk drive of claim 1 , wherein the second threshold comprises a differential voltage of zero volts.

9. The disk drive of claim 1 , wherein adjusting the first current source and the second current source until the differential voltage exceeds a second threshold comprises adjusting until the differential voltage is approximately equal to zero volts plus or minus X volts, where X is a tolerance value.

10. The disk drive of claim 1 , wherein the third threshold comprises a differential voltage that is 1% greater than a previous differential voltage.

11. The disk drive of claim 1 , wherein a first voltage level of the first touchdown sensor and a second voltage level of the second touchdown sensor correspond to a first temperature and a second temperature, respectively, and the measured differential voltage corresponds to a temperature differential between the first touchdown sensor and the second touchdown sensor.

12. The disk drive of claim 1 , wherein the control circuitry is further operable to adjust the first current source to provide a first bias current and adjust the second current source to provide a second bias current.

13. The disk drive of claim 1 , wherein the control circuitry comprises a differential amplifier.

14. The disk drive of claim 13 , wherein control circuitry comprises a common mode amplifier.

15. The disk drive of claim 14 , wherein the control circuitry further comprises an analog to digital converter coupled to the differential amplifier and the common mode amplifier.

16. The disk drive of claim 1 , wherein the first touchdown sensor is a thermistor.

17. The disk drive of claim 2 , wherein a power dissipated in the first touchdown sensor is approximately less than or equal to 10% of a nominal power dissipated by the thermal actuator.

18. A method of detecting a touchdown event between a head and a media in a disk drive comprising:

determining a common mode voltage between a first touchdown sensor and a second touchdown sensor;

adjusting a first current source and a second current source until the common mode voltage exceeds a first threshold;

determining a differential voltage between the first touchdown sensor and the second touchdown sensor;

adjusting the first current source and the second current source until the differential voltage exceeds a second threshold; and

detecting the touchdown event based on the differential voltage exceeding a third threshold.

19. The method of claim 18 , wherein the head comprises the first touchdown sensor, the second touchdown sensor, and a thermal actuator.

20. The method of claim 19 , further comprising adjusting a thermal actuator power level.

21. The method of claim 20 , further comprising storing the thermal actuator power level.

22. The method of claim 20 , further comprising determining a slope of the differential voltage as a function of the adjustment of the thermal actuator power level, wherein the third threshold is a slope value.

23. The method of claim 22 , further comprising measuring a running average of the slope of the differential voltage.

24. The method of claim 18 , wherein a first voltage level of the first touchdown sensor and a second voltage level of the second touchdown sensor correspond to a first temperature and a second temperature, respectively, and the measured differential voltage corresponds to a temperature differential between the first touchdown sensor and the second touchdown sensor.

25. The method of claim 18 , further comprising adjusting the first current source to provide a first bias current and adjusting the second current source to provide a second bias current.

26. The method of claim 18 , wherein the first touchdown sensor is a thermistor.

Assignments (7)