Decision feedback equalization implementation of partial-response signaling in a magnetic recording channel
First Claim
1. A method for recovering symbols from a magnetic recording medium, the method comprising the steps of:
- producing a readback signal from the magnetic recording medium, the readback signal representing a sequence of the symbols during a sequence of timing intervals, the sequence of symbols including symbols that are adjacent in that they are represented by the readback signal during consecutive timing intervals, and are subject to inter-symbol interference;
sampling the readback signal to produce a sequence of samples {xn } having amplitudes representing the readback signal during corresponding sample intervals n=1 through N;
processing the sequence of samples {xn } with a feedforward and feedback arrangement to produce a sequence of equalized samples {yn } that sequentially represent the symbols with substantially less inter-symbol interference between adjacent symbols, the processing step including;
a. filtering the sequence of samples {xn } with an asymmetrical feed-forward filter to produce a sequence of feed-forward equalized samples {wn }, the asymmetrical feed-forward filter having a response that is asymmetrically balanced to cause preferential reduction of precursor inter-symbol interference between adjacent symbols represented by the samples yn ;
b. producing a sequence of detected symbols from the sequence of equalized samples {yn } such that each detected symbol corresponds to a successive timing interval;
c. filtering the sequence of detected symbols with an asymmetrical feedback filter to produce a sequence of equalization feedback values {en } such that each detected symbol affects a group of the immediately succeeding equalization feedback values substantially more than any equalization feedback value defined subsequent to the group, the asymmetrical feedback filter having a response that is asymmetrically balanced to cause preferential reduction of postcursor inter-symbol interference between adjacent symbols represented by the samples yn ; and
d. sequentially subtracting the equalization feedback values en from the feed-forward equalized samples wn to produce the sequence of equalized samples yn ; and
processing the sequence of equalized samples {yn } with a maximum-likelihood sequence detector to recover sequences of the symbols recovered from the magnetic recording medium.
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Abstract
A partial-response maximum-likelihood (PRML) sequence detector with decision feedback equalization (DFE) for a disk drive read channel. The symbol recovery method for a disk drive read channel produces a sequence of samples Xn of a magnetic readback signal with amplitudes representing the readback signal during corresponding sample intervals n=1-N. A DFE circuit generates a sequence of equalized samples yn and includes a feed-forward filter that removes precursor ISI from the sequence of sample signals xn to produce a sequence of feed-forward equalized samples wn, detection logic that translates the sequence of equalized samples yn into a sequence of detected symbols yn, and a feedback filter that filters the sequence of detected symbols yn to produce a sequence of equalization feedback values en to offset postcursor ISI remaining in the sequence of feed-forward equalized samples wn. A combinational circuit receives the feed-forward equalized samples wn and the feedback values en and combines a sample wk with an equalization feedback value ek to produce an equalized sample yk for each sample interval k in the range of k=1-N. A PRML sequence detector, such as a Viterbi detector, is used with the DFE circuit to recover a user data symbol ak for sample interval k corresponding to the equalized sample yk in response to the sequence of equalized samples yn. The detected symbols yn used in the feedback path are generated using separate detectors, which allows for feedback with a delay of only one sample interval.
134 Citations
42 Claims
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1. A method for recovering symbols from a magnetic recording medium, the method comprising the steps of:
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producing a readback signal from the magnetic recording medium, the readback signal representing a sequence of the symbols during a sequence of timing intervals, the sequence of symbols including symbols that are adjacent in that they are represented by the readback signal during consecutive timing intervals, and are subject to inter-symbol interference; sampling the readback signal to produce a sequence of samples {xn } having amplitudes representing the readback signal during corresponding sample intervals n=1 through N; processing the sequence of samples {xn } with a feedforward and feedback arrangement to produce a sequence of equalized samples {yn } that sequentially represent the symbols with substantially less inter-symbol interference between adjacent symbols, the processing step including; a. filtering the sequence of samples {xn } with an asymmetrical feed-forward filter to produce a sequence of feed-forward equalized samples {wn }, the asymmetrical feed-forward filter having a response that is asymmetrically balanced to cause preferential reduction of precursor inter-symbol interference between adjacent symbols represented by the samples yn ; b. producing a sequence of detected symbols from the sequence of equalized samples {yn } such that each detected symbol corresponds to a successive timing interval; c. filtering the sequence of detected symbols with an asymmetrical feedback filter to produce a sequence of equalization feedback values {en } such that each detected symbol affects a group of the immediately succeeding equalization feedback values substantially more than any equalization feedback value defined subsequent to the group, the asymmetrical feedback filter having a response that is asymmetrically balanced to cause preferential reduction of postcursor inter-symbol interference between adjacent symbols represented by the samples yn ; and d. sequentially subtracting the equalization feedback values en from the feed-forward equalized samples wn to produce the sequence of equalized samples yn ; and processing the sequence of equalized samples {yn } with a maximum-likelihood sequence detector to recover sequences of the symbols recovered from the magnetic recording medium. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
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16. A disk drive comprising:
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a magnetic recording disk; a readback circuit, coupled with the magnetic recording disk, that produces a readback signal from the magnetic recording disk, the readback signal representing a sequence of symbols during a sequence of timing intervals, the sequence of symbols including symbols that are adjacent in that they are represented by the readback signal during consecutive timing intervals, and are subject to inter-symbol interference; the readback circuit sampling the readback signal to produce a sequence of samples {xn } having amplitudes representing the readback signal during corresponding sample intervals n=1 through N; a decision feedback equalization circuit for processing the sequence of samples {xn } with a feedforward and feedback arrangement to produce a sequence of equalized samples {yn } that sequentially represent the symbols with substantially less inter-symbol interference between adjacent symbols, the decision feedback equalization circuit including; a. an asymmetrical feed-forward filter for filtering the sequence of samples {xn } to produce a sequence of feed-forward equalized samples {wn }, the asymmetrical feed-forward filter having a response that is asymmetrically balanced to cause preferential reduction of precursor inter-symbol interference between adjacent symbols represented by the samples yn ; b. symbol detection means for producing a sequence of detected symbols from the sequence of equalized samples {yn } such that each detected symbol corresponds to a successive timing interval; c. an asymmetrical feedback filter for filtering the sequence of detected symbols to produce a sequence of equalization feedback values {en } such that each detected symbol affects a group of the immediately succeeding equalization feedback values substantially more than any equalization feedback value defined subsequent to the group, the asymmetrical feedback filter having a response that is asymmetrically balanced to cause preferential reduction of postcursor inter-symbol interference between adjacent symbols represented by the samples yn ; and d. means for sequentially subtracting the equalization feedback values en from the feed-forward equalized samples wn to produce the sequence of equalized samples yn ; and a maximum-likelihood sequence detector coupled to the decision feedback equalization circuit that recovers a symbol an corresponding to the equalized sample yn in response to the sequence of equalized samples {yn }. - View Dependent Claims (17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29)
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30. A read channel for recovering symbols from a data channel read from a magnetic recording disk, comprising:
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a decision feedback equalization circuit for processing a sequence of sample signals {xn } having amplitudes representing the data channel during corresponding sample intervals n=1 through N, and which produces a sequence of equalized samples {yn }, the decision feedback equalization circuit including; a. an asymmetrical feed-forward filter for filtering the sequence of samples {xn } to produce a sequence of feed-forward equalized samples {wn }, the asymmetrical feed-forward filter having a response that is asymmetrically balanced to cause preferential reduction of precursor inter-symbol interference between adjacent symbols represented by the samples yn ; b. symbol detection means for producing a sequence of detected symbols from the sequence of equalized samples {yn } such that each detected symbol corresponds to a successive timing interval; c. an asymmetrical feedback filter for filtering the sequence of detected symbols to produce a sequence of equalization feedback values {en } such that each detected symbol affects a group of the immediately succeeding equalization feedback values substantially more than any equalization feedback value defined subsequent to the group, the asymmetrical feedback filter having a response that is asymmetrically balanced to cause preferential reduction of postcursor inter-symbol interference between adjacent symbols represented by the samples yn ; and d. means for sequentially subtracting the equalization feedback values en from the feed-forward equalized samples wn to produce the sequence of equalized samples yn ; and a maximum-likelihood sequence detector coupled to the decision feedback equalization circuit that recovers a symbol an corresponding to the equalized sample yn, in response to the sequence of equalized samples {yn }. - View Dependent Claims (31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42)
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Specification