Fly height sensor control circuit
View Patent ↗A disk drive is disclosed 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.
1. A disk drive comprising:
a disk;
a head for writing data to the disk;
a touchdown sensor; and
control circuitry comprising a current source coupled to the touchdown sensor, the control circuitry operable to:
determine a voltage across the touchdown sensor;
adjust the current source to maintain the voltage across the touchdown sensor at a constant value; and
detect a touchdown event based on the voltage exceeding a threshold.
2. The disk drive of claim 1 , wherein the head comprises the touchdown sensor and a thermal actuator.
3. The disk drive of claim 2 , wherein the threshold comprises a change of slope of the voltage across the touchdown sensor.
4. The disk drive of claim 2 , wherein the control circuitry is further operable to measure a running average of a slope while adjusting a thermal actuator power level and determine when the slope changes.
5. The disk drive of claim 2 , wherein the control circuitry is further operable to record a thermal actuator power level when the voltage exceeds the threshold.
6. The disk drive of claim 1 , wherein the control circuitry is further operable to feedback the voltage to adjust the current source to maintain the voltage at the constant value.
7. The disk drive of claim 6 , wherein the control circuitry further comprises a low pass filter for determining the voltage.
8. The disk drive of claim 7 , wherein adjusting the current source comprises comparing the feedback voltage to a reference voltage.
9. The disk drive of claim 1 , wherein the voltage across the touchdown sensor corresponds to a temperature.
10. The disk drive of claim 1 , wherein the control circuitry comprises an amplifier.
11. The disk drive of claim 10 , wherein the control circuitry further comprises an analog to digital converter coupled to the amplifier.
12. The disk drive of claim 10 , wherein the control circuitry further comprises an offset null circuit coupled to the amplifier.
13. The disk drive of claim 12 , wherein the offset null circuit comprises a voltage source coupled to the amplifier.
14. The disk drive of claim 13 , wherein the voltage source is coupled to the amplifier and a low pass filter in a feedback control loop.
15. The disk drive of claim 1 , wherein the touchdown sensor is a thermistor.
16. A method of detecting a touchdown event between a head and a medium in a disk drive comprising:
determining a voltage across the touchdown sensor across the touchdown sensor;
adjusting a current source to maintain the voltage at a constant value; and
detecting the touchdown event based on the voltage exceeding a threshold.
17. The method of claim 16 , wherein the head comprises the touchdown sensor and a thermal actuator.
18. The method of claim 17 , wherein the threshold comprises a change of slope of the voltage across the touchdown sensor.
19. The method of claim 18 , further comprising measuring a running average of the slope while adjusting a thermal actuator power level.
20. The method of claim 19 , further comprising recording the thermal actuator power level when the voltage exceeds the slope.
21. The method of claim 16 , wherein the touchdown sensor is a thermistor.