Disk drive demodulating a spiral track by finding a maximum correlation between a spiral track crossing signal and a time-shifted nominal spiral track crossing signal
View Patent ↗A disk drive is disclosed comprising a disk including a plurality of spiral tracks, wherein each spiral track comprises a high frequency signal interrupted by a sync mark at a sync mark interval, and a head actuated over the disk. The spiral tracks are demodulated by reading a spiral track to generate a spiral track crossing signal g(x n ), where x n is a time in a demodulation window, and determining a position error signal (PES) by determining a time-shift L that maximizes a correlation between g(x n ) and a function that estimates a nominal spiral track crossing signal having the time-shift of L.
1. A disk drive comprising:
a disk comprising a plurality of spiral tracks, wherein each spiral track comprises a high frequency signal interrupted by a sync mark at a sync mark interval;
a head actuated over the disk; and
control circuitry operable to demodulate the spiral tracks by:
using the head to read a spiral track to generate a spiral track crossing signal g(x n ), where x n is a time in a demodulation window; and
determining a position error signal (PES) by determining a time-shift L that maximizes a correlation between g(x n ) and a function that estimates a nominal spiral track crossing signal having the time-shift of L.
2. The disk drive as recited in claim 1 , wherein the function that estimates the nominal spiral track crossing signal comprises f(x n -x 0 ) and the control circuitry is further operable to use the equation
S
(
L
)
=
∑
n
=
1
N
(
g
(
x
n
)
-
f
(
x
n
-
x
0
+
L
)
)
2
to determine the PES.
3. The disk drive as recited in claim 2 , wherein x 0 is a time that corresponds to a peak in the nominal spiral track crossing signal.
4. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to use the PES to maintain the head along a servo track while writing product servo sectors along the servo track.
5. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to generate the spiral track crossing signal g(x n ) by integrating a read signal between the sync marks, wherein each sample of the spiral track crossing signal g(x n ) represents the integration of the read signal between the sync marks.
6. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to generate the function by reading a plurality of the spiral tracks.
7. The disk drive as recited in claim 6 , wherein the control circuitry is further operable to generate the function by integrating a read signal representing a spiral track crossing to generate an integrated signal, and servoing the head in response to the integrated signal.
8. The disk drive as recited in claim 6 , wherein the control circuitry is further operable to generate the function by sampling a read signal representing a spiral track crossing and curve fitting the function to the read signal samples.
9. The disk drive as recited in claim 6 , wherein the control circuitry is further operable to generate the function by:
processing a sampled read signal representing a spiral track crossing to generate a servo signal;
servoing the head in response to the servo signal;
shifting the read signal samples relative to the servo signal; and
curve fitting the function to the shifted read signal samples.
10. The disk drive as recited in claim 1 , wherein the function comprises a Gaussian function.
11. The disk drive as recited in claim 10 , wherein the Gaussian function comprises:
1
σ
2
π
e
(
x
n
+
L
)
2
2
σ
2
where the time-shift L is a mean and σ is a standard deviation.
12. A method of operating a disk drive, the disk drive comprising a disk comprising a plurality of spiral tracks, wherein each spiral track comprises a high frequency signal interrupted by a sync mark at a sync mark interval, and a head actuated over the disk, the method comprising:
using the head to read a spiral track to generate a spiral track crossing signal g(x n ), where x n is a time in a demodulation window; and
determining a position error signal (PES) by determining a time-shift L that maximizes a correlation between g(x n ) and a function that estimates a nominal spiral track crossing signal having the time-shift of L.
13. The method as recited in claim 12 , wherein the function that estimates the nominal spiral track crossing signal comprises f(x n -x 0 ) and determining the PES uses the equation
S
(
L
)
=
∑
n
=
1
N
(
g
(
x
n
)
-
f
(
x
n
-
x
0
+
L
)
)
2
.
14. The method as recited in claim 13 , wherein x 0 is a time that corresponds to a peak in the nominal spiral track crossing signal.
15. The method as recited in claim 12 , further comprising using the PES to maintain the head along a servo track while writing product servo sectors along the servo track.
16. The method as recited in claim 12 , wherein the spiral track crossing signal g(x n ) is generated by integrating a read signal between the sync marks, wherein each sample of the spiral track crossing signal g(x n ) represents the integration of the read signal between the sync marks.
17. The method as recited in claim 12 , wherein the function is generated by reading a plurality of the spiral tracks.
18. The method as recited in claim 17 , wherein the function is generated by integrating a read signal representing a spiral track crossing to generate an integrated signal, and servoing the head in response to the integrated signal.
19. The method as recited in claim 17 , wherein the function is further generated by sampling a read signal representing a spiral track crossing and curve fitting the function to the read signal samples.
20. The method as recited in claim 17 , wherein the function is further generated by:
processing a sampled read signal representing a spiral track crossing to generate a servo signal;
servoing the head in response to the servo signal;
shifting the read signal samples relative to the servo signal; and
curve fitting the function to the shifted read signal samples.
21. The method as recited in claim 12 , wherein the function comprises a Gaussian function.
22. The method as recited in claim 21 , wherein the Gaussian function comprises:
1
σ
2
π
e
(
x
n
+
L
)
2
2
σ
2
where the time-shift L is a mean and σ is a standard deviation.
23. A disk drive comprising:
a disk comprising a plurality of spiral tracks, wherein each spiral track comprises a high frequency signal interrupted by a sync mark at a sync mark interval;
a head actuated over the disk; and
a means for using the head to read a spiral track to generate a spiral track crossing signal g(x n ), where x n is a time in a demodulation window; and
a means for determining a position error signal (PES) by determining a time-shift L that maximizes a correlation between g(x n ) and a function that estimates a nominal spiral track crossing signal having the time-shift of L.