Disk drive calibrating VCM notch filter by increasing the width and/or the depth of the notch
A disk drive is disclosed comprising a disk, a head, a voice coil motor (VCM) for actuating the head over the disk, and control circuitry comprising a notch filter for generating a VCM control signal, wherein a notch of the notch filter comprises a frequency, a width, and a depth. The notch filter is calibrated by initializing at least one of the width and the depth of the notch, measuring a quality metric of the notch filter, and increasing at least one of the width and the depth of the notch until the quality metric indicates good performance.
1. A disk drive comprising:
a disk;
a head;
a voice coil motor (VCM) for actuating the head over the disk; and
control circuitry comprising a notch filter for generating a VCM control signal, wherein a notch of the notch filter comprises a frequency, a width, and a depth, the control circuitry further operable to calibrate the notch filter by:
initialize the width of the notch to a first width setting and measure a quality metric of the notch filter;
when the quality metric indicates poor performance, sweep the depth of the notch over a range of settings for the first width setting;
when the depth of the notch filter reaches a last setting and the quality metric continues to indicate poor performance, increase the width of the notch to a second width setting and re-measure the quality metric of the notch filter; and
when the quality metric continues to indicate poor performance, sweep the depth of the notch over the range of settings for the second width setting.
2. The disk drive as recited in claim 1 , wherein a transfer function of the notch filter comprises:
A
0
+
(
A
1
+
C
1
(
f
-
f
0
)
)
z
-
1
+
A
2
z
-
2
B
0
+
(
B
1
+
D
1
(
f
-
f
0
)
)
z
-
1
+
B
2
z
-
2
where f is the frequency of the notch, f 0 is a linearized center frequency, and A 0 , A 1 , A 2 , B 0 , B 1 , B 2 , C 1 and D 1 are coefficients.
3. The disk drive as recited in claim 2 , wherein A 0 , A 1 , A 2 , B 0 , B 1 , B 2 , C 1 and D 1 are adjusted to increase at least one of the width and the depth of the notch.
4. The disk drive as recited in claim 1 , wherein when the quality metric indicates poor performance, the control circuitry is further operable to adjust the frequency of the notch.
5. The disk drive as recited in claim 4 , wherein the control circuitry is further operable to adjust the frequency of the notch in response to a measured temperature.
6. The disk drive as recited in claim 1 , wherein the quality metric is measured relative to a peak in an error rejection curve.
7. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to adjust the frequency of the notch relative to a peak in an error rejection curve.
8. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to:
initialize the width of the notch to a first width setting;
initialize the depth of the notch to a first depth setting; and
when the quality metric indicates poor performance, increase the width and the depth of the notch.
9. The disk drive as recited in claim 8 , wherein the control circuitry is further operable to adjust the frequency of the notch for each width and depth setting so that the adjusted frequency substantially matches a peak in an error rejection curve.
10. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to adjust the frequency of the notch for each depth setting so that the adjusted frequency substantially matches a peak in an error rejection curve.
11. The disk drive as recited in claim 1 , the control circuitry is further operable to:
measure a first quality metric at a first radial location and measure a second quality metric at a second radial location; and
select the quality metric indicating the poorest performance to calibrate the notch filter.
12. A method of operating a disk drive, the disk drive comprising
a disk, a head, a voice coil motor (VCM) for actuating the head over the disk, and
a notch filter for generating a VCM control signal, wherein a notch of the notch filter comprises a frequency, a width, and a depth, the method comprising:
initializing the width of the notch to a first width setting and measuring a quality metric of the notch filter;
when the quality metric indicates poor performance, sweeping the depth of the notch over a range of settings for the first width setting;
when the depth of the notch filter reaches a last setting and the quality metric continues to indicate poor performance, increasing the width of the notch to a second width setting and re-measuring the quality metric of the notch filter; and
when the quality metric continues to indicate poor performance, sweeping the depth of the notch over the range of settings for the second width setting.
13. The method as recited in claim 12 , wherein a transfer function of the notch filter comprises:
A
0
+
(
A
1
+
C
1
(
f
-
f
0
)
)
z
-
1
+
A
2
z
-
2
B
0
+
(
B
1
+
D
1
(
f
-
f
0
)
)
z
-
1
+
B
2
z
-
2
where f is the frequency of the notch, f 0 is a linearized center frequency, and A 0 , A 1 , A 2 , B 0 , B 1 , B 2 , C 1 and D 1 are coefficients.
14. The method as recited in claim 13 , further comprising adjusting A 0 , A 1 , A 2 , B 0 , B 1 , B 2 , C 1 and D 1 to increase at least one of the width and the depth of the notch.
15. The method as recited in claim 12 , wherein when the quality metric indicates poor performance, further comprising adjusting the frequency of the notch.
16. The method as recited in claim 15 , further comprising adjusting the frequency of the notch in response to a measured temperature.
17. The method as recited in claim 12 , wherein the quality metric is measured relative to a peak in an error rejection curve.
18. The method as recited in claim 12 , further comprising adjusting the frequency of the notch relative to a peak in an error rejection curve.
19. The method as recited in claim 12 , further comprising:
initializing the width of the notch to a first width setting;
initializing the depth of the notch to a first depth setting; and
when the quality metric indicates poor performance, increasing the width and the depth of the notch.
20. The method as recited in claim 19 , further comprising adjusting the frequency of the notch for each width and depth setting so that the adjusted frequency substantially matches a peak in an error rejection curve.
21. The method as recited in claim 12 , further comprising adjusting the frequency of the notch for each depth setting so that the adjusted frequency substantially matches a peak in an error rejection curve.
22. The method as recited in claim 12 , further comprising:
measuring a first quality metric at a first radial location and measuring a second quality metric at a second radial location; and
selecting the quality metric indicating the poorest performance to calibrate the notch filter.
23. A disk drive comprising:
a disk;
a head;
a voice coil motor (VCM) for actuating the head over the disk; and
control circuitry comprising a notch filter for generating a VCM control signal, wherein a notch of the notch filter comprises a frequency, a width, and a depth, the control circuitry further operable to calibrate the notch filter by:
initialize at least one of the width and the depth of the notch;
measure a quality metric of the notch filter; and
increase at least one of the width and the depth of the notch until the quality metric indicates good performance,
wherein a transfer function of the notch filter comprises:
A
0
+
(
A
1
+
C
1
(
f
-
f
0
)
)
z
-
1
+
A
2
z
-
2
B
0
+
(
B
1
+
D
1
(
f
-
f
0
)
)
z
-
1
+
B
2
z
-
2
where f is the frequency of the notch, f 0 is a linearized center frequency, and A 0 , A 1 , A 2 , B 0 , B 1 , B 2 , C 1 and D 1 are coefficients.
24. A disk drive comprising:
a disk;
a head;
a voice coil motor (VCM) for actuating the head over the disk; and
control circuitry comprising a notch filter for generating a VCM control signal, wherein a notch of the notch filter comprises a frequency, a width, and a depth, the control circuitry further operable to calibrate the notch filter by:
initialize at least one of the width and the depth of the notch;
measure a quality metric of the notch filter;
increase at least one of the width and the depth of the notch until the quality metric indicates good performance;
measure a first quality metric at a first radial location and measure a second quality metric at a second radial location; and
select the quality metric indicating the poorest performance to calibrate the notch filter.