Data storage device measuring radial offset between read element and write element

1. A data storage device comprising:

a disk comprising a plurality of tracks;

a head actuated over the disk, the head comprising a read element radially offset from a write element; and

control circuitry configured to:

write a first pattern to a single track;

read the first pattern from the single track to generate a first read signal;

generate a first quality metric based on the first read signal;

write a second pattern to the single track, wherein the second pattern is different from the first pattern;

read the second pattern from the single track to generate a second read signal;

generate a second quality metric based on the second read signal; and

measure the radial offset of the read element and write element based on the first and second quality metrics.

2. The data storage device as recited in claim 1 , wherein the control circuitry is further configured to overwrite at least part of the first pattern with at least part of the second pattern.

3. The data storage device as recited in claim 2 , wherein the control circuitry is further configured to:

write the first pattern to the single track during a first revolution of the disk;

read the first pattern from the single track during a second revolution of the disk;

write the second pattern to the single track during a third revolution of the disk; and

read the second pattern from the single track during a fourth revolution of the disk.

4. The data storage device as recited in claim 1 , wherein the control circuitry is further configured to:

write the first pattern to a first part of the single track; and

write the second pattern to a second part of the single track.

5. The data storage device as recited in claim 4 , wherein the control circuitry is further configured to write the first pattern and the second pattern to the single track during a first revolution of the disk.

6. The data storage device as recited in claim 5 , wherein the control circuitry is further configured to read the first pattern and the second pattern from the single track during a second revolution of the disk.

7. The data storage device as recited in claim 1 , wherein the first pattern comprises a DC pattern and the second pattern comprises a periodic pattern.

8. The data storage device as recited in claim 1 , wherein the first pattern comprises a first periodic pattern having a first frequency and the second pattern comprises a second periodic pattern having a second frequency different from the first frequency.

9. The data storage device as recited in claim 1 , wherein:

the first quality metric comprises a first setting for a variable gain amplifier; and

the second quality metric comprises a second setting for the variable gain amplifier.

10. The data storage device as recited in claim 1 , wherein the control circuitry is further configured to measure the radial offset of the read element and write element based on a difference between the first quality metric and the second quality metric.

11. The data storage device as recited in claim 1 , wherein the control circuitry is further configured to:

read at least one track adjacent the single track to generate a third read signal;

generate a third quality metric based on the third read signal; and

measure the radial offset of the read element and write element based on the first, second, and third quality metrics.

12. A data storage device comprising:

a disk comprising a plurality of tracks;

a head actuated over the disk, the head comprising a read element radially offset from a write element; and

control circuitry configured to:

write a first pattern to a target track;

read the first pattern from the target track to generate a first read signal;

generate a first quality metric based on the first read signal;

write a second pattern to the target track, wherein the second pattern is different from the first pattern;

read the second pattern from the target track to generate a second read signal;

generate a second quality metric based on the second read signal;

generate a third quality metric based on the first quality metric and the second quality metric; and

measure the radial offset of the read element and write element based on the third quality metric.

13. The data storage device as recited in claim 12 , wherein the control circuitry is further configured to overwrite at least part of the first pattern with at least part of the second pattern.

14. The data storage device as recited in claim 13 , wherein the control circuitry is further configured to:

write the first pattern to the target track during a first revolution of the disk;

read the first pattern from the target track during a second revolution of the disk;

write the second pattern to the target track during a third revolution of the disk; and

read the second pattern from the target track during a fourth revolution of the disk.

15. The data storage device as recited in claim 14 , wherein the control circuitry is further configured to:

write the first pattern to a first part of the target track; and

write the second pattern to a second part of the target track.

16. The data storage device as recited in claim 15 , wherein the control circuitry is further configured to write the first pattern and the second pattern to the target track during a first revolution of the disk.

17. The data storage device as recited in claim 16 , wherein the control circuitry is further configured to read the first pattern and the second pattern from the target track during a second revolution of the disk.

18. The data storage device as recited in claim 12 , wherein the first pattern comprises a DC pattern and the second pattern comprises a periodic pattern.

19. The data storage device as recited in claim 12 , wherein the first pattern comprises a first periodic pattern having a first frequency and the second pattern comprises a second periodic pattern having a second frequency different from the first frequency.

20. The data storage device as recited in claim 12 , wherein:

the first quality metric comprises a first setting for a variable gain amplifier; and

the second quality metric comprises a second setting for the variable gain amplifier.

21. The data storage device as recited in claim 20 , wherein the control circuitry is further configured to generate the third quality metric based on a difference between the first quality metric and the second quality metric.

22. A method of operating a data storage device, the method comprising:

using a head to write a first pattern to a single track on a disk;

using the head to read the first pattern from the single track to generate a first read signal;

generating a first quality metric based on the first read signal;

using the head to write a second pattern to the single track, wherein the second pattern is different from the first pattern;

using the head to read the second pattern from the single track to generate a second read signal;

generating a second quality metric based on the second read signal; and

measuring a radial offset of a read element and a write element of the head based on the first and second quality metrics.

23. The method as recited in claim 22 , further comprising:

writing the first pattern to a first part of the single track; and

writing the second pattern to a second part of the single track.

24. The method as recited in claim 23 , further comprising writing the first pattern and the second pattern to the single track during a first revolution of the disk.

25. The method as recited in claim 24 , further comprising reading the first pattern and the second pattern from the single track during a second revolution of the disk.

26. A method of operating a data storage device, the method comprising:

using a head to write a first pattern to a target track on a disk;

using the head to read the first pattern from the target track to generate a first read signal;

generating a first quality metric based on the first read signal;

using the head to write a second pattern to the target track, wherein the second pattern is different from the first pattern;

using the head to read the second pattern from the target track to generate a second read signal;

generating a second quality metric based on the second read signal;

generating a third quality metric based on the first quality metric and the second quality metric; and

measuring the radial offset of a read element and a write element of the head based on the third quality metric.

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

writing the first pattern to a first part of the target track; and

writing the second pattern to a second part of the target track.

28. The method as recited in claim 27 , further comprising writing the first pattern and the second pattern to the target track during a first revolution of the disk.

29. The method as recited in claim 28 , further comprising reading the first pattern and the second pattern from the target track during a second revolution of the disk.