Disk drive employing velocity insensitive servo burst pattern

1. A disk drive comprising:

a disk comprising a plurality of servo sectors that define a plurality of servo tracks, wherein the servo sectors comprise a plurality of servo bursts including:

a first servo burst;

a second servo burst following the first servo burst and offset radially in a first direction by approximately one half of a servo track from the first servo burst;

a third servo burst following the second servo burst and offset radially in the first direction by approximately one full servo track from the second servo burst; and

a fourth servo burst following the third servo burst and offset radially in a second direction opposite the first direction by approximately one half of a servo track from the third servo burst;

a head actuated over the disk; and

control circuitry operable to:

position the head over a servo track;

read at least two of the servo bursts;

generate a numerator in response to: (i) the first and fourth servo bursts, (ii) the second and third servo bursts, or (iii) the first, second, third, and fourth servo bursts;

generate a denominator in response to a difference between two of the servo bursts;

generate a position error signal (PES) in response to a ratio of the numerator and the denominator; and

position the head over the disk in response to the PES.

2. The disk drive as recited in claim 1 , wherein an accuracy of the PES is substantially insensitive to a radial velocity of the head.

3. The disk drive as recited in claim 1 , wherein the control circuitry is operable to select the servo bursts for generating the numerator and the denominator based on a boundary condition for the head.

4. The disk drive as recited in claim 3 , wherein the control circuitry is operable to generate the PES in response to at least one of:

D

-

C

⁢

_

B

-

A

;

and

B

-

A

_

D

-

C

depending on the boundary condition for the head, where:

C is the first servo burst;

A is the second servo burst;

B is the third servo burst; and

D is the fourth servo burst.

5. The disk drive as recited in claim 3 , wherein the control circuitry is operable to generate the PES in response to at least one of:

B

+

D

-

A

-

C

D

-

C

;

B

+

D

-

A

-

C

A

-

B

;

A

+

D

-

B

-

C

A

-

B

;

A

+

D

-

B

-

C

C

-

D

;

A

+

C

-

B

-

D

C

-

D

;

A

+

C

-

B

-

D

B

-

A

;

B

+

C

-

A

-

D

B

-

A

;

and

⁢

B

+

C

-

A

-

D

D

-

C

depending on the boundary condition for the head, where:

C is the first servo burst;

A is the second servo burst;

B is the third servo burst; and

D is the fourth servo burst.

6. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to:

generate repeatable runout (RRO) compensation values representing a repeatable runout of the servo tracks; and

subtract the RRO compensation values from the PES thereby causing a radial velocity of the head relative to a servo track during a tracking operation.

7. A method of operating a disk drive comprising:

a head actuated over a disk comprising a plurality of servo sectors that define a plurality of servo tracks, wherein the servo sectors comprise a plurality of servo bursts including:

a first servo burst;

a second servo burst following the first servo burst and offset radially in a first direction by approximately one half of a servo track from the first servo burst;

a third servo burst following the second servo burst and offset radially in the first direction by approximately one full servo track from the second servo burst; and

a fourth servo burst following the third servo burst and offset radially in a second direction opposite the first direction by approximately one half of a servo track from the third servo burst;

the method comprising:

positioning the head over a servo track;

reading at least two of the servo bursts;

generating a numerator in response to: (i) the first and fourth servo bursts, (ii) the second and third servo bursts, or (iii) the first, second, third, and fourth servo bursts;

generating a denominator in response to a difference between two of the servo bursts;

generating a position error signal (PES) in response to a ratio of the numerator and the denominator; and

positioning the head over the disk in response to the PES.

8. The method as recited in claim 7 , wherein an accuracy of the PES is substantially insensitive to a radial velocity of the head.

9. The method as recited in claim 7 , further comprising selecting the servo bursts for generating the numerator and the denominator based on a boundary condition for the head.

10. The method as recited in claim 9 , further comprising generating the PES in response to at least one of:

D

-

C

⁢

_

B

-

A

;

and

B

-

A

_

D

-

C

depending on the boundary condition for the head, where:

C is the first servo burst;

A is the second servo burst;

B is the third servo burst; and

D is the fourth servo burst.

11. The method as recited in claim 9 , further comprising generating the PES in response to at least one of:

B

+

D

-

A

-

C

D

-

C

;

B

+

D

-

A

-

C

A

-

B

;

A

+

D

-

B

-

C

A

-

B

;

A

+

D

-

B

-

C

C

-

D

;

A

+

C

-

B

-

D

C

-

D

;

A

+

C

-

B

-

D

B

-

A

;

B

+

C

-

A

-

D

B

-

A

;

and

⁢

B

+

C

-

A

-

D

D

-

C

depending on a boundary condition for the head, where:

C is the first servo burst;

A is the second servo burst;

B is the third servo burst; and

D is the fourth servo burst.

12. The method as recited in claim 7 , further comprising:

generating repeatable runout (RRO) compensation values representing a repeatable runout of the servo tracks; and

subtracting the RRO compensation values from the PES thereby causing a radial velocity of the head relative to a servo track during a tracking operation.

13. A disk drive comprising:

a disk comprising a plurality of servo sectors that define a plurality of servo tracks, wherein the servo sectors comprise a plurality of servo bursts including:

a first servo burst;

a second servo burst following the first servo burst and offset radially in a first direction by approximately one half of a servo track from the first servo burst;

a third servo burst following the second servo burst and offset radially in the first direction by approximately one full servo track from the second servo burst; and

a fourth servo burst following the third servo burst and offset radially in a second direction opposite the first direction by approximately one half of a servo track from the third servo burst;

a head actuated over the disk; and

control circuitry operable to:

position the head over a servo track;

read at least two of the servo bursts;

generate a numerator in response to at least two of the servo bursts;

generate a denominator in response to the difference between the first and fourth servo bursts or the difference between the second and third servo bursts;

generate a position error signal (PES) in response to a ratio of the numerator and the denominator; and

position the head over the disk in response to the PES.

14. The disk drive as recited in claim 13 , wherein an accuracy of the PES is substantially insensitive to a radial velocity of the head.

15. The disk drive as recited in claim 13 , wherein the control circuitry is operable to select the servo bursts for generating the numerator and the denominator based on a boundary condition for the head.

16. The disk drive as recited in claim 13 , wherein the control circuitry is further operable to:

generate repeatable runout (RRO) compensation values representing a repeatable runout of the servo tracks; and

subtract the RRO compensation values from the PES thereby causing a radial velocity of the head relative to a servo track during a tracking operation.

17. A method of operating a disk drive comprising:

a head actuated over a disk comprising a plurality of servo sectors that define a plurality of servo tracks, wherein the servo sectors comprise a plurality of servo bursts including:

a first servo burst;

a second servo burst following the first servo burst and offset radially in a first direction by approximately one half of a servo track from the first servo burst;

a third servo burst following the second servo burst and offset radially in the first direction by approximately one full servo track from the second servo burst; and

a fourth servo burst following the third servo burst and offset radially in a second direction opposite the first direction by approximately one half of a servo track from the third servo burst;

the method comprising:

positioning the head over a servo track;

reading at least two of the servo bursts;

generating a numerator in response to at least two of the servo bursts;

generating a denominator in response to the difference between the first and fourth servo bursts, or the difference between the second and third servo bursts;

generating a position error signal (PES) in response to a ratio of the numerator and the denominator; and

positioning the head over the disk in response to the PES.

18. The method as recited in claim 17 , wherein an accuracy of the PES is substantially insensitive to a radial velocity of the head.

19. The method as recited in claim 17 , further comprising selecting the servo bursts for generating the numerator and the denominator based on a boundary condition for the head.

20. The method as recited in claim 17 , further comprising:

generating repeatable runout (RRO) compensation values representing a repeatable runout of the servo tracks; and

subtracting the RRO compensation values from the PES thereby causing a radial velocity of the head relative to a servo track during a tracking operation.