Disk drive decoding binary sequence from phases of servo bursts
View Patent ↗A disk drive is disclosed comprising a disk including a plurality of servo tracks defined by a plurality of servo sectors, wherein each servo sector comprises a plurality of servo bursts, and each servo burst comprises at least one of four phases. A first two of the phases are orthogonal, and a second two of the phases are orthogonal. As a head is actuated over the disk a servo sector is read to generate a read signal. The read signal is processed to demodulate the servo bursts into a position error signal (PES) representing an offset of the head from a target radial location on the disk, and the read signal is also processed to decode at least two of the phases of the servo bursts into a binary sequence.
1. A disk drive comprising:
a disk comprising a plurality of servo tracks defined by a plurality of servo sectors, wherein
each servo sector comprises a plurality of servo bursts; and
each servo burst comprises at least one of four phases, wherein a first two of the phases are orthogonal, and a second two of the phases are orthogonal;
a head actuated over the disk; and
control circuitry operable to:
read a servo sector to generate a read signal;
process the read signal to demodulate the servo bursts into a position error signal (PES) representing an offset of the head from a target radial location on the disk; and
process the read signal to decode at least two of the phases of the servo bursts into a binary sequence.
2. The disk drive as recited in claim 1 , wherein:
the first two of the four phases represent a first binary value; and
the second two of the four phases represents a second binary value.
3. The disk drive as recited in claim 1 , wherein the servo bursts comprise a quadrature servo pattern.
4. The disk drive as recited in claim 1 , wherein the servo bursts comprise an orthogonal phase servo pattern.
5. The disk drive as recited in claim 4 , wherein each servo burst comprises one of four phases selected from the group consisting of 0 degrees, 90 degrees, 180 degrees, and 270 degrees.
6. The disk drive as recited in claim 5 , wherein:
a first servo track comprises a first servo burst comprising 0 degrees phase and an adjacent servo track comprises a second servo burst comprising 90 degrees phase; and
the first servo track comprises a third servo burst comprising 180 degrees phase and the adjacent servo track comprises a fourth servo burst comprising 270 degrees phase.
7. The disk drive as recited in claim 1 , wherein:
each servo burst comprises a plurality of burst cycles; and
a plurality of burst cycles of a servo burst represents a binary value of the binary sequence.
8. The disk drive as recited in claim 7 , wherein:
each burst cycle comprises one of the four phases;
a first two of the four phases represent a first binary value of the binary sequence; and
a second two of the four phases represents a second binary value of the binary sequence.
9. The disk drive as recited in claim 1 , wherein:
each servo burst comprises a plurality of burst cycles; and
a single burst cycle of a servo burst represents a binary value of the binary sequence.
10. The disk drive as recited in claim 9 , wherein:
a first two of the four phases represent a first binary value of the binary sequence; and
a second two of the four phases represents a second binary value of the binary sequence.
11. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to decode the phases by:
computing a sine component of the servo bursts; and
computing a cosine component of the servo bursts.
12. The disk drive as recited in claim 11 , wherein the control circuitry is further operable to decode the phases by evaluating a sign of the sine component and a sign of the cosine component.
13. The disk drive as recited in claim 1 , wherein the phases of the servo bursts are decoded into a Gray codeword representing at least part of a servo track address.
14. A method of operating a disk drive, the disk drive comprising a disk comprising a plurality of servo tracks defined by a plurality of servo sectors, wherein
each servo sector comprises a plurality of servo bursts; and
each servo burst comprises at least one of four phases, wherein a first two of the phases are orthogonal, and a second two of the phases are orthogonal;
and a head actuated over the disk, the method comprising:
reading a servo sector to generate a read signal;
processing the read signal to demodulate the servo bursts into a position error signal (PES) representing an offset of the head from a target radial location on the disk; and
processing the read signal to decode at least two of the phases of the servo bursts into a binary sequence.
15. The method as recited in claim 14 , wherein:
the first two of the four phases represent a first binary value; and
the second two of the four phases represents a second binary value.
16. The method as recited in claim 14 , wherein the servo bursts comprise a quadrature servo pattern.
17. The method as recited in claim 14 , wherein the servo bursts comprise an orthogonal phase servo pattern.
18. The method as recited in claim 17 , wherein each servo burst comprises one of four phases selected from the group consisting of 0 degrees, 90 degrees, 180 degrees, and 270 degrees.
19. The method as recited in claim 18 , wherein:
a first servo track comprises a first servo burst comprising 0 degrees phase and an adjacent servo track comprises a second servo burst comprising 90 degrees phase; and
the first servo track comprises a third servo burst comprising 180 degrees phase and the adjacent servo track comprises a fourth servo burst comprising 270 degrees phase.
20. The method as recited in claim 14 , wherein:
each servo burst comprises a plurality of burst cycles; and
a plurality of burst cycles of a servo burst represents a binary value of the binary sequence.
21. The method as recited in claim 20 , wherein:
each burst cycle comprises one of the four phases;
a first two of the four phases represent a first binary value of the binary sequence; and
a second two of the four phases represents a second binary value of the binary sequence.
22. The method as recited in claim 14 , wherein:
each servo burst comprises a plurality of burst cycles; and
a single burst cycle of a servo burst represents a binary value of the binary sequence.
23. The method as recited in claim 22 , wherein:
a first two of the four phases represent a first binary value of the binary sequence; and
a second two of the four phases represents a second binary value of the binary sequence.
24. The method as recited in claim 14 , wherein decoding the phases comprises:
computing a sine component of the servo bursts; and
computing a cosine component of the servo bursts.
25. The method as recited in claim 24 , wherein decoding the phases comprises evaluating a sign of the sine component and a sign of the cosine component.
26. The method as recited in claim 14 , wherein the phases of the servo bursts are decoded into a Gray codeword representing at least part of a servo track address.