Disk drive servo control using hybrid upsample filter
View Patent ↗A disk drive is disclosed comprising a disk comprising a plurality of servo tracks, wherein each servo track comprises a plurality of servo sectors, and an actuator for actuating a head over the disk in response to an actuator control signal. The servo sectors are read to generate a first sequence of control samples x[k] at a sample frequency corresponding to a frequency of the servo sectors. A hybrid upsample filter is used to upsample by a factor of N the first sequence of control samples x[k] to generate a second sequence of control samples y[k i ], wherein the hybrid upsample filter provides a higher phase gain than a zero-order type upsample filter at frequencies less than one kilohertz, and approximately the same attenuation as a first-order type upsample filter around the sample frequency. The actuator control signal is generated in response to the second sequence of control samples y[k i ].
1. A disk drive comprising:
a disk comprising a plurality of servo tracks, wherein each servo track comprises a plurality of servo sectors;
a head;
an actuator for actuating the head over the disk in response to an actuator control signal; and
control circuitry operable to:
read the servo sectors to generate a first sequence of control samples x[k] at a sample frequency corresponding to a frequency of the servo sectors;
use a hybrid upsample filter to upsample by a factor of N the first sequence of control samples x[k] to generate a second sequence of control samples y[k i ], wherein the hybrid upsample filter provides a higher phase gain than a zero-order type upsample filter at frequencies less than one kilohertz, and approximately the same attenuation as a first-order type upsample filter around the sample frequency; and
generate the actuator control signal in response to the second sequence of control samples y[k i ].
2. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to upsample the first sequence of control samples x[k] to generate the second sequence of control samples y[k i ] during a seek operation and during a tracking operation.
3. The disk drive as recited in claim 1 , wherein the hybrid upsample filter provides approximately the same attenuation as the first-order type upsample filter around one or more harmonics of the sample frequency.
4. The disk drive as recited in claim 1 , wherein the hybrid upsample filter comprises an upsampler and an interpolator.
5. The disk drive as recited in claim 4 , wherein the hybrid upsample filter comprises a transfer function of:
G
=
(
a
0
+
a
1
z
-
1
+
a
2
z
-
2
+
a
3
z
-
3
+
a
4
z
-
4
+
a
5
z
-
5
+
a
6
z
-
6
…
a
m
z
-
m
)
|
z
=
e
s
T
s
N
where:
1/T s represents the sample frequency; and
a 0 . . . a m are coefficients that define a m th order filter.
6. The disk drive as recited in claim 5 , wherein the coefficients a 0 . . . a m are optimized to provide the higher phase gain than the phase gain of the zero-order type upsample filter at frequencies less than one kilohertz, and approximately the same attenuation as the first-order type upsample filter around the sample frequency.
7. The disk drive as recited in claim 5 , wherein the coefficients a 0 . . . a m are the same during a seek operation and during a tracking operation thereby minimizing a transient when transitioning from a seek operation to a tracking operation.
8. The disk drive as recited in claim 5 , wherein the coefficients a 0 . . . a m are the same during a seek operation and during a tracking operation thereby minimizing a transient when transitioning from the tracking operation to the seek operation.
9. A method of operating a disk drive comprising a disk comprising a plurality of servo tracks, wherein each servo track comprises a plurality of servo sectors, and an actuator for actuating a head over the disk in response to an actuator control signal, the method comprises:
reading the servo sectors to generate a first sequence of control samples x[k] at a sample frequency corresponding to a frequency of the servo sectors;
using a hybrid upsample filter to upsample by a factor of N the first sequence of control samples x[k] to generate a second sequence of control samples y[k i ], wherein the hybrid upsample filter provides a higher phase gain than a zero-order type upsample filter at frequencies less than one kilohertz, and approximately the same attenuation as a first-order type upsample filter around the sample frequency; and
generating the actuator control signal in response to the second sequence of control samples y[k i ].
10. The method as recited in claim 9 , further comprising upsampling the first sequence of control samples x[k] to generate the second sequence of control samples y[k i ] during a seek operation and during a tracking operation.
11. The method as recited in claim 9 , wherein the hybrid upsample filter provides approximately the same attenuation as the first-order type upsample filter around one or more harmonics of the sample frequency.
12. The method as recited in claim 9 , wherein the hybrid upsample filter comprises an upsampler and an interpolator.
13. The method as recited in claim 12 , wherein the hybrid upsample filter comprises a transfer function of:
G
=
(
a
0
+
a
1
z
-
1
+
a
2
z
-
2
+
a
3
z
-
3
+
a
4
z
-
4
+
a
5
z
-
5
+
a
6
z
-
6
…
a
m
z
-
m
)
|
z
=
e
s
T
s
N
where:
1/T s represents the sample frequency; and
a 0 . . . a m are coefficients that define a m th order filter.
14. The method as recited in claim 13 , wherein the coefficients a 0 . . . a m are optimized to provide the higher phase gain than the phase gain of the zero-order type upsample filter at frequencies less than one kilohertz, and approximately the same attenuation as the first-order type upsample filter around the sample frequency.
15. The method as recited in claim 13 , wherein the coefficients a 0 . . . a m are the same during a seek operation and during a tracking operation thereby minimizing a transient when transitioning from the seek operation to the tracking operation.
16. The method as recited in claim 13 , wherein the coefficients a 0 . . . a m are the same during a seek operation and during a tracking operation thereby minimizing a transient when transitioning from the tracking operation to the seek operation.