Disk drive calibrating laser power for heat assisted magnetic recording based on quality metric and track width
View Patent ↗A disk drive is disclosed comprising a head actuated over a disk, wherein the head comprises a laser operable to heat the disk while writing data to the disk. A laser power of the laser is initialized, and a test pattern is written to the disk. The test pattern is read from the disk to generate a read signal, and a quality metric and a track width of the test pattern is measured based on the read signal. The laser power is adjusted and the process is repeated until at least one of the quality metric substantially matches a target value and the track width substantially matches a track width threshold.
1. A disk drive comprising:
a disk;
a head actuated over the disk, wherein the head comprises a laser operable to heat the disk while writing data to the disk; and
control circuitry operable to:
a) initialize a laser power of the laser;
b) write a test pattern to the disk;
c) read the test pattern from the disk to generate a read signal;
d) measure a quality metric of the read signal;
e) measure a track width of the test pattern based on the read signal;
f) adjust the laser power and repeat elements (b) through (f) until the track width substantially matches a track width threshold; and
g) terminate the repeating in element (f) when the quality metric of the read signal substantially matches a target value.
2. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to adjust the laser power at element (f) by increasing the laser power.
3. The disk drive as recited in claim 1 , wherein the quality metric comprises an amplitude of the read signal.
4. The disk drive as recited in claim 3 , wherein the quality metric comprises a setting for a variable gain amplifier.
5. The disk drive as recited in claim 3 , wherein the quality metric substantially matches the target value when a derivative of the amplitude of the read signal falls below a target threshold.
6. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to decrease the laser power after element (f) when the track width exceeds the track width threshold.
7. The disk drive as recited in claim 1 , wherein the control circuitry is operable to measure the track width by scanning the head across the test pattern to generate an amplitude profile of the read signal.
8. The disk drive as recited in claim 7 , wherein the quality metric corresponds to a maximum in the amplitude profile of the read signal.
9. The disk drive as recited in claim 7 , wherein:
the head comprises a write element radially offset from a read element; and
the control circuitry is further operable to measure the radial offset based on the amplitude profile.
10. The disk drive as recited in claim 9 , wherein the radial offset is based on a maximum in the amplitude profile of the read signal.
11. A method of operating a disk drive comprising a head actuated over a disk, wherein the head comprises a laser operable to heat the disk while writing data to the disk, the method comprising:
a) initializing a laser power of the laser;
b) writing a test pattern to the disk;
c) reading the test pattern from the disk to generate a read signal;
d) measuring a quality metric of the read signal;
e) measuring a track width of the test pattern based on the read signal;
f) adjusting the laser power and repeating elements (b) through (f) until the track width substantially matches a track width threshold; and
g) terminating the repeating in element (f) when the quality metric of the read signal substantially matches a target value.
12. The method as recited in claim 11 , further comprising adjusting the laser power at element (f) by increasing the laser power.
13. The method as recited in claim 11 , wherein the quality metric comprises an amplitude of the read signal.
14. The method as recited in claim 13 , wherein the quality metric comprises a setting for a variable gain amplifier.
15. The method as recited in claim 13 , wherein the quality metric substantially matches the target value when a derivative of the amplitude of the read signal falls below a target threshold.
16. The method as recited in claim 11 , further comprising decreasing the laser power after element (f) when the track width exceeds the track width threshold.
17. The method as recited in claim 11 , further comprising measuring the track width by scanning the head across the test pattern to generate an amplitude profile of the read signal.
18. The method as recited in claim 17 , wherein the quality metric corresponds to a maximum in the amplitude profile of the read signal.
19. The method as recited in claim 17 , wherein:
the head comprises a write element radially offset from a read element; and
the method further comprises measuring the radial offset based on the amplitude profile.
20. The method as recited in claim 19 , wherein the radial offset is based on a maximum in the amplitude profile of the read signal.