Disk drive selecting target response based on identified response
View Patent ↗A disk drive is disclosed comprising a head actuated over a disk. A test pattern is written to the disk and read from the disk to generate a read signal. The read signal is sampled to generate signal samples, the signal samples are filtered with an equalizer filter to generate a first output, and the test pattern is filtered with a target filter to generate a second output. An error signal is generated based on a difference between the first output and the second output. Coefficients of the target filter are adapted in response to the error signal, and after adapting the coefficients of the target filter, a sequence detector is configured based on the coefficients of the target filter.
1. A disk drive comprising:
a disk;
a head actuated over the disk; and
control circuitry operable to:
write a test pattern to the disk;
read the test pattern from the disk to generate a read signal;
sample the read signal to generate signal samples;
filter the signal samples with an equalizer filter to generate a first output;
filter the test pattern with a target filter to generate a second output;
generate an error signal based on a difference between the first output and the second output;
adapt coefficients of the target filter in response to the error signal;
after adapting the coefficients of the target filter, configure a sequence detector based on the coefficients of the target filter; and
adapt the coefficients of the target filter in order to minimize the error signal by minimizing:
∂
∂
h
^
i
∑
n
(
x
[
n
]
-
x
^
[
n
]
)
2
where:
ĥ i represents the coefficients of the target filter;
x[n] represents the first output; and
{circumflex over (x)}[n] represents the second output.
2. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to adapt coefficients of the equalizer filter in response to the error signal prior to adapting the coefficients of the target filter.
3. The disk drive as recited in claim 2 , wherein the control circuitry is further operable to adapt coefficients of the equalizer filter in response to the error signal after adapting the coefficients of the target filter.
4. The disk drive as recited in claim 1 , wherein the equalizer filter comprises a finite impulse response (FIR) filter.
5. The disk drive as recited in claim 1 , wherein the coefficients of the target filter are adapted according to a Wiener filter solution.
6. The disk drive as recited in claim 1 , wherein the coefficients of the target filter are adapted according to a least mean squares (LMS) solution.
7. The disk drive as recited in claim 6 , wherein the control circuitry is further operable to adapt the coefficients of the target filter according to:
ĥ i [n+ 1 ]=ĥ i [n]+ 2μ( e[n ])( s[n−i ])
where:
e[n] represents the error signal;
s[n−i] represents the test pattern; and
μ is a step size.
8. The disk drive as recited in claim 1 , wherein the sequence detector comprises a trellis sequence detector.
9. The disk drive as recited in claim 8 , wherein the sequence detector comprises a Viterbi sequence detector.
10. A method of operating a disk drive, the disk drive comprising a head actuated over a disk, the method comprising:
writing a test pattern to the disk;
reading the test pattern from the disk to generate a read signal;
sampling the read signal to generate signal samples;
filtering the signal samples with an equalizer filter to generate a first output;
filtering the test pattern with a target filter to generate a second output;
generating an error signal based on a difference between the first output and the second output;
adapting coefficients of the target filter in response to the error signal;
after adapting the coefficients of the target filter, configuring a sequence detector based on the coefficients of the target filter; and
adapting the coefficients of the target filter in order to minimize the error signal by minimizing:
∂
∂
h
^
i
∑
n
(
x
[
n
]
-
x
^
[
n
]
)
2
where:
ĥ i represents the coefficients of the target filter;
x[n] represents the first output; and
{circumflex over (x)}[n] represents the second output.
11. The method as recited in claim 10 , further comprising adapting coefficients of the equalizer filter in response to the error signal prior to adapting the coefficients of the target filter.
12. The method as recited in claim 11 , further comprising adapting coefficients of the equalizer filter in response to the error signal after adapting the coefficients of the target filter.
13. The method as recited in claim 10 , wherein the equalizer filter comprises a finite impulse response (FIR) filter.
14. The method as recited in claim 10 , wherein the coefficients of the target filter are adapted according to a Wiener filter solution.
15. The method as recited in claim 10 , wherein the coefficients of the target filter are adapted according to a least mean squares (LMS) solution.
16. The method as recited in claim 15 , further comprising adapting the coefficients of the target filter according to:
ĥ i [n+ 1 ]=ĥ i [n]+ 2μ( e[n ])( s[n−i ])
where:
e[n] represents the error signal;
s[n−i] represents the test pattern; and
μ is a step size.
17. The method as recited in claim 10 , wherein the sequence detector comprises a trellis sequence detector.
18. The method as recited in claim 17 , wherein the sequence detector comprises a Viterbi sequence detector.