Disk drive adapting target values of a sequence detector relative to bit error rate of the sequence detector
View Patent ↗A disk drive is disclosed comprising a disk and a head actuated radially over the disk, wherein the head generates a read signal. A sampling device samples the read signal to generate a sequence of read signal samples when reading a training data sequence recorded on the disk, and an equalizer comprising a plurality of coefficients equalizes the read signal samples to generate a sequence of equalized samples. A sequence detector detects an estimated data sequence from the equalized samples, wherein the sequence detector operates according to a target response comprising a plurality of target values. Control circuitry adapts the target values by computing error values in response to a difference between expected samples and the equalized samples, computing a gradient in response to a correlation of the training data sequence with the error values, and adjusting at least one of the target values in response to the gradient.
1. A disk drive comprising:
a disk;
a head actuated radially over the disk, the head operable to generate a read signal when reading a training data sequence recorded on the disk;
a sampling device operable to sample the read signal to generate a sequence of read signal samples;
an equalizer comprising a plurality of coefficients, the equalizer operable to equalize the read signal samples to generate a sequence of equalized samples;
a sequence detector for detecting an estimated data sequence from the equalized samples, wherein the sequence detector operates according to a target response comprising a plurality of target values; and
control circuitry operable to adapt the target values by:
computing error values in response to a difference between expected samples and the equalized samples;
computing a gradient in response to a correlation of the training data sequence with the error values; and
adjusting at least one of the target values in response to the gradient,
wherein the control circuitry is operable to compute the gradient in response to an error event of the sequence detector convolved with the target values of the target response.
2. The disk drive as recited in claim 1 , wherein the control circuitry is operable to compute the gradient by scaling the correlation with at least one of the target values of the target response.
3. The disk drive as recited in claim 1 , wherein the error event comprises a ‘+’ error event.
4. The disk drive as recited in claim 1 , wherein the control circuitry is operable to compute the gradient by minimizing:
e y i T R z e y y
where:
e y i represents the error event convolved with the target values of the target response; and
R z is a noise correlation matrix.
5. The disk drive as recited in claim 1 , wherein the control circuitry is operable to compute the gradient according to:
Δ
gn
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k
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n
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V
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1
g
i
e
k
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i
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g
i
g
j
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k
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a
k
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j
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where:
a k is a predetermined data sequence;
the target response comprises V target values g 0 -g V-1 ;
e k are the error values; and
Δ gn is a gradient for the g n target value.
6. The disk drive as recited in claim 5 , wherein the control circuitry does not adjust at least one of the target values.
7. The disk drive as recited in claim 6 , wherein the control circuitry does not adjust the first target value g 0 .
8. A method of operating a disk drive, the disk drive comprising a disk, a head actuated radially over the disk, the head operable to generate a read signal when reading a training data sequence recorded on the disk, a sampling device operable to sample the read signal to generate a sequence of read signal samples, an equalizer comprising a plurality of coefficients, the equalizer operable to equalize the read signal samples to generate a sequence of equalized samples, a sequence detector for detecting an estimated data sequence from the equalized samples, wherein the sequence detector operates according to a target response comprising a plurality of target values, the method comprising:
computing error values in response to a difference between expected samples and the equalized samples;
computing a gradient in response to a correlation of the training data sequence with the error values; and
adjusting at least one of the target values in response to the gradient, wherein:
the gradient is computed in response to an error event of the sequence detector convolved with the target values of the target response.
9. The method as recited in claim 8 , wherein the gradient is computed by scaling the correlation with at least one of the target values of the target response.
10. The method as recited in claim 8 , wherein the error event comprises a ‘+’ error event.
11. The method as recited in claim 8 , wherein the gradient is computed by minimizing:
e y i T R z e y i
where:
e y i represents the error event convolved with the target values of the target response; and
R z is a noise correlation matrix.
12. The method as recited in claim 8 , wherein the gradient is computed according to:
Δ
gn
=
e
k
-
n
∑
i
=
0
V
-
1
g
i
e
k
-
i
-
∑
i
=
0
V
-
1
∑
j
=
0
V
-
1
g
i
g
j
e
k
-
i
a
k
-
j
-
n
where:
a k is a predetermined data sequence;
the target response comprises V target values g 0 -g V-1 ;
e k are the error values; and
Δ gn is a gradient for the g n target value.
13. The method as recited in claim 12 , wherein at least one of the target values is not adjusted.
14. The method as recited in claim 13 , wherein the first target value g 0 is not adjusted.