Data storage device demodulating servo burst by computing slope of intermediate integration points
A data storage device is disclosed comprising a head actuated over a disk surface comprising tracks defined by servo sectors, wherein each servo sector comprises at least one servo burst comprising a periodic pattern. The servo burst of one of the servo sectors is read to generate a read signal, and M intermediate integration points y N i are computed according to: y N i = ∑ k = 0 N i r ( k T s ) · sin ( ω k T s ) ; i = 0 , 1 , … , M - 1 where r(kT s ) represents a sample point of the read signal, T s represents a sample interval between the sample points, and ω represents a frequency of the periodic pattern in the servo burst.
1. A data storage device comprising:
a disk surface comprising tracks defined by servo sectors, wherein each servo sector comprises at least one servo burst comprising a periodic pattern;
a head actuated over the disk surface; and
control circuitry configured to:
read the servo burst of one of the servo sectors to generate a read signal; and
compute M intermediate integration points y N i according to:
y
N
i
=
∑
k
=
0
N
i
r
(
k
T
s
)
·
sin
(
ω
k
T
s
)
;
i
=
0
,
1
,
…
,
M
-
1
where:
r(kT s ) represents a sample point of the read signal;
T s represents a sample interval between the sample points; and
ω represents a frequency of the periodic pattern in the servo burst.
2. The data storage device as recited in claim 1 , wherein the control circuitry is further configured to compute a slope α of the intermediate integration points according to:
α
=
∑
i
=
0
M
-
1
x
N
i
y
N
i
∑
i
=
0
M
-
1
x
N
i
2
where X N i represents a timestamp in the sample points of the read signal.
3. The data storage device as recited in claim 2 , wherein the control circuitry is further configured to compute an amplitude of a fundamental frequency
1
T
of the read signal based on:
2
N
c
T
·
α
·
x
M
-
1
where:
N c represents a number of cycles in the periodic pattern of the servo burst; and
T equals 2π/ω.
4. The data storage device as recited in claim 2 , wherein the control circuitry is further configured to compute a plurality of local slopes α j of the intermediate integration points according to:
α
j
=
∑
i
=
0
j
N
m
-
1
x
N
i
y
N
i
∑
i
=
0
j
N
m
-
1
x
N
i
2
;
j
=
1
,
2
,
…
,
N
c
where:
N c represents a number of cycles in the periodic pattern of the servo burst; and
each period comprises N m intermediate sample points of the read signal.
5. The data storage device as recited in claim 4 , wherein the control circuitry is further configured to detect a defect in the servo burst based on the plurality of local slopes α j .
6. The data storage device as recited in claim 5 , wherein the control circuitry is further configured to detect a defect in the servo burst based on α j ·N m .
7. The data storage device as recited in claim 6 , wherein the control circuitry is further configured to detect a defect in the servo burst based on:
α
j
·
N
m
-
(
y
N
M
j
+
1
-
y
N
M
j
)
y
N
M
j
+
1
-
y
N
M
j
>
β
where β represents a threshold.
8. The data storage device as recited in claim 4 , wherein the control circuitry is further configured to compute a local slope S p,q according to:
S
p
,
q
=
∑
i
=
(
p
-
1
)
N
m
qN
m
-
1
x
N
i
y
N
i
∑
i
=
(
p
-
1
)
N
m
qN
m
-
1
x
N
i
2
;
1
≤
p
≤
q
≤
N
c
where p represents a beginning of the p th cycle, and q represents an ending of the q th cycle.
9. The data storage device as recited in claim 8 , wherein the control circuitry is further configured to detect a defect in the servo burst based on:
α
j
-
S
j
+
1
,
j
+
1
S
j
+
1
,
j
+
1
>
β
where β represents a threshold.
10. The data storage device as recited in claim 8 , wherein the control circuitry is further configured to detect a first type of defect in the servo burst when the defect is detected in a first cycle of the periodic pattern.
11. The data storage device as recited in claim 10 , wherein the control circuitry is further configured to detect a second type of defect in the servo burst when the defect is detected in one of the cycles of the periodic pattern after the first cycle.
12. A method of operating a data storage device, the method comprising:
reading a periodic pattern in a servo burst of a servo sector on a disk surface to generate a read signal; and
computing M intermediate integration points y N i according to:
y
N
i
=
∑
k
=
0
N
i
r
(
kT
s
)
·
sin
(
ω
kT
s
)
;
i
=
0
,
1
,
…
,
M
-
1
where:
r(kT s ) represents a sample point of the read signal;
T s represents a sample interval between the sample points; and
ω represents a frequency of the periodic pattern in the servo burst.
13. The method as recited in claim 12 , further comprising computing a slope LX of the intermediate integration points according to:
α
=
∑
i
=
0
M
-
1
x
N
i
y
N
i
∑
i
=
0
M
-
1
x
N
i
2
where X N i represents a timestamp in the sample points of the read signal.
14. The method as recited in claim 13 , further comprising computing an amplitude of a fundamental frequency
1
T
of the read signal based on:
2
N
c
T
·
α
·
x
M
-
1
where:
N c represents a number of cycles in the periodic pattern of the servo burst; and
T equals 2π/ω.
15. The method as recited in claim 13 , further comprising computing a plurality of local slopes α j of the intermediate integration points according to:
α
j
=
∑
i
=
0
j
N
m
-
1
x
N
i
y
N
i
∑
i
=
0
J
N
m
-
1
x
N
i
2
;
j
=
1
,
2
,
…
,
N
c
where:
N c represents a number of cycles in the periodic pattern of the servo burst; and
each period comprises N m intermediate sample points of the read signal.
16. The method as recited in claim 15 , further comprising detecting a defect in the servo burst based on the plurality of local slopes α j .
17. The method as recited in claim 16 , further comprising detecting a defect in the servo burst based on α j ·N m .
18. The method as recited in claim 17 , further comprising detecting a defect in the servo burst based on:
α
j
·
N
m
-
(
y
N
M
j
+
1
-
y
N
M
j
)
y
N
M
j
+
1
-
y
N
M
j
>
β
where β represents a threshold.
19. The method as recited in claim 15 , further comprising computing a local slope S p,q according to:
S
p
,
q
=
∑
i
=
(
p
-
1
)
N
m
q
N
m
-
1
x
N
i
y
N
i
∑
i
=
(
p
-
1
)
N
m
q
N
m
-
1
x
N
i
2
;
1
≤
p
≤
q
≤
N
c
where p represents a beginning of the p th cycle, and q represents an ending of the q th cycle.
20. The method as recited in claim 19 , further comprising detecting a defect in the servo burst based on:
α
j
-
S
j
+
1
,
j
+
1
S
j
+
1
,
j
+
1
>
β
where β represents a threshold.
21. The method as recited in claim 19 , further comprising detecting a first type of defect in the servo burst when the defect is detected in a first cycle of the periodic pattern.
22. The method as recited in claim 21 , further comprising detecting a second type of defect in the servo burst when the defect is detected in one of the cycles of the periodic pattern after the first cycle.