Granted Patent B1

US 8,300,338 · App. 12/895,115 · Granted Oct 30, 2012

Abstract

Claims (47)

1. A disk drive comprising:

a first disk surface;

a first head actuated over the first disk surface; and

control circuitry operable to:

generate a first fly height measurement for the first head over the first disk surface by measuring a first metric;

generate a second fly height measurement for the first head over the first disk surface by measuring a second metric different from the first metric; and

verify the first fly height measurement by detecting a positive correlation in the first and second fly height measurements.

2. The disk drive as recited in claim 1 , wherein the first metric comprises an overwrite metric.

3. The disk drive as recited in claim 2 , wherein the control circuitry is further operable to:

write a first pattern to a track on the first disk surface at a first frequency;

read the track and measure a first read signal amplitude;

write a second pattern to the track at a second frequency;

read the track to and measure a second read signal amplitude; and

generate the first metric in response to the first and second read signal amplitudes.

4. The disk drive as recited in claim 3 , wherein the second metric comprises a harmonic ratio metric.

5. The disk drive as recited in claim 4 , wherein the control circuitry is further operable to:

write data to the track;

read the track to generate a read signal;

measure a first amplitude of the read signal at a first harmonic;

measure a second amplitude of the read signal at a second harmonic; and

generate the second metric in response to the first and second amplitudes.

6. The disk drive as recited in claim 3 , wherein the second metric comprises a setting for a variable gain amplifier operable to amplify a read signal emanating from the first head while reading data from the track.

7. The disk drive as recited in claim 1 , further comprising a second disk surface and a second head actuated over the second disk surface, wherein the control circuitry is further operable to:

generate a third fly height measurement for the second head over the second disk surface opposite the first disk surface by measuring a third metric different from the first metric; and

verify the first fly height measurement by detecting a negative correlation in the first and third fly height measurements.

8. A method of operating a disk drive comprising a first disk surface and a first head actuated over the first disk surface, the method comprising:

generating a first fly height measurement for the first head over the first disk surface by measuring a first metric;

generating a second fly height measurement for the first head over the first disk surface by measuring a second metric different from the first metric; and

verifying the first fly height measurement by detecting a positive correlation in the first and second fly height measurements.

9. The method as recited in claim 8 , wherein the first metric comprises an overwrite metric.

10. The method as recited in claim 9 , further comprising:

writing a first pattern to a track on the first disk surface at a first frequency;

reading the track and measuring a first read signal amplitude;

writing a second pattern to the track at a second frequency;

reading the track to and measuring a second read signal amplitude; and

generating the first metric in response to the first and second read signal amplitudes.

11. The method as recited in claim 10 , wherein the second metric comprises a harmonic ratio metric.

12. The method as recited in claim 11 , further comprising:

writing data to the track;

reading the track to generate a read signal;

measuring a first amplitude of the read signal at a first harmonic;

measuring a second amplitude of the read signal at a second harmonic; and

generating the second metric in response to the first and second amplitudes.

13. The method as recited in claim 10 , wherein the second metric comprises a setting for a variable gain amplifier operable to amplify a read signal emanating from the first head while reading data from the track.

14. The method as recited in claim 8 , further comprising a second disk surface and a second head actuated over the second disk surface, further comprising:

generating a third fly height measurement for the second head over the second disk surface opposite the first disk surface by measuring a third metric different from the first metric; and

verifying the first fly height measurement by detecting a negative correlation in the first and third fly height measurements.

Assignments (7)