Data storage device using branch metric from adjacent track to compensate for inter-track interference

• US 9,025,267 B1
• Filed: 06/09/2014
• Issued: 05/05/2015
• Est. Priority Date: 06/09/2014
• Status: Active Grant

• Current Assignee: JP Morgan Chase Bank, N.A. (JP Morgan Chase & Co)
• Original Assignee: Western Digital Technologies Incorporated (Western Digital Corporation)
• Inventors: Wang, Alvin J., Dahandeh, Shafa
• Primary Examiner(s): ALUNKAL, THOMAS D
• Application Number:
  US14/299,309
• Time in Patent Office: 330 Days
• Field of Search: 360/63, 360/39, 360/55, 360/64, 360/246.6, 360/53
• US Class Current: 360/39
• CPC Class Codes: G11B 20/10296 using the Viterbi algorithm
• CPC Class Codes: G11B 20/10379 based on soft decisions, e.g. confidence values, probability estimates, likelihoods values or path metrics of a statistical decoding algorithm
• CPC Class Codes: G11B 20/1833 by adding special lists or symbols to the coded information G11B20/1806, G11B20/1866 take precedence
• CPC Class Codes: G11B 2020/1859 wherein a trellis is used for decoding the error correcting code
• CPC Class Codes: G11B 2020/1863 wherein the Viterbi algorithm is used for decoding the error correcting code
• CPC Class Codes: G11B 5/012 Recording on, or reproducing or erasing from, magnetic disks G11B17/00, G11B19/00 take precedence
• CPC Class Codes: G11B 5/02 Recording, reproducing, or erasing methods; Read, write or erase circuits therefor
• CPC Class Codes: G11B 5/09 Digital recording

Abstract

A data storage device is disclosed comprising a disk comprising a plurality of data tracks, and a head comprising a first read element and a second read element. A first data track is read using the first read element to generate a first read signal, and the first read signal is sampled to generate first signal samples. A first branch metric is generated in a first trellis sequence detector when detecting a first data sequence based on one of the first signal samples. A second data track adjacent the first data track is read using the second read element to generate a second read signal, and the second read signal is sampled to generate second signal samples. A second branch metric is generated in a second trellis sequence detector when detecting a second data sequence based on one of the second signal samples and the first branch metric.

Claims

1. A data storage device comprising:

a disk comprising a plurality of data tracks;

a head actuated over the disk, the head comprising a plurality of read elements including a first read element and a second read element; and

control circuitry configured to;

read a first data track using the first read element to generate a first read signal;

sample the first read signal to generate first signal samples;

generate a first branch metric in a first trellis sequence detector when detecting a first data sequence based on one of the first signal samples;

read a second data track adjacent the first data track using the second read element to generate a second read signal;

sample the second read signal to generate second signal samples; and

when detecting a second data sequence, generate a second branch metric in a second trellis sequence detector based on one of the second signal samples and the first branch metric.

2. The data storage device as recited in claim 1, wherein the control circuitry is further operable to generate the second branch metric based on:

BM₂=∥

y₂(k)−

d₂−

α

d₁∥

²

where;

d₁ represents a first expected sample corresponding to a first branch selected by the first trellis sequence detector based on the first branch metric when detecting the first data sequence;

α

is a scalar;

y₂(k) represents one of the second signal samples;

d₂ represents a second expected sample corresponding to a second branch of the second trellis sequence detector; and

BM₂ represents the second branch metric.

3. The data storage device as recited in claim 1, wherein the first trellis sequence detector is configured to generate the first branch metric when detecting the first data sequence based on one of the first signal samples and the second branch metric.

4. The data storage device as recited in claim 3, wherein the first trellis sequence detector is configured to generate the first branch metric when detecting the first data sequence based on a second expected sample corresponding to a second branch selected by the second trellis sequence detector based on the second branch metric when detecting the second data sequence.

5. The data storage device as recited in claim 3, wherein the control circuitry is further configured to iterate the generating the first branch metric and the second branch metric at least twice.

6. The data storage device as recited in claim 1, wherein the head comprises a third read element and the control circuitry is further configured to:

read a third data track using the third read element to generate a third read signal;

sample the third read signal to generate third signal samples;

generate a third branch metric in a third trellis sequence detector when detecting a third data sequence based on one of the third signal samples; and

generate the second branch metric in the second trellis sequence detector when detecting the second data sequence based on one of the second signal samples, the first branch metric, and the third branch metric.

7. The data storage device as recited in claim 6, wherein the second trellis sequence detector is configured to generate the second branch metric when detecting the second data sequence based on a third expected sample corresponding to a third branch selected by the third trellis sequence detector based on the third branch metric when detecting the third data sequence.

8. A method of operating a data storage device, the method comprising:

reading a first data track on a disk using a first read element of a head to generate a first read signal;

sampling the first read signal to generate first signal samples;

generating a first branch metric in a first trellis sequence detector when detecting a first data sequence based on one of the first signal samples;

reading a second data track adjacent the first data track using a second read element of the head to generate a second read signal;

sampling the second read signal to generate second signal samples; and

when detecting a second data sequence, generating a second branch metric in a second trellis sequence detector based on one of the second signal samples and the first branch metric.

9. The method as recited in claim 8, further comprising generating the second branch metric based on:

BM₂=∥

y₂(k)−

d₂−

α

d₁∥

²

where;

d₁ represents a first expected sample corresponding to a first branch selected by the first trellis sequence detector based on the first branch metric when detecting the first data sequence;

α

is a scalar;

y₂(k) represents one of the second signal samples;

d₂ represents a second expected sample corresponding to a second branch of the second trellis sequence detector; and

BM₂ represents the second branch metric.

10. The method as recited in claim 8, further comprising the first trellis sequence detector generating the first branch metric when detecting the first data sequence based on one of the first signal samples and the second branch metric.

11. The method as recited in claim 10, further comprising the first trellis sequence detector generating the first branch metric when detecting the first data sequence based on a second expected sample corresponding to a second branch selected by the second trellis sequence detector based on the second branch metric when detecting the second data sequence.

12. The method as recited in claim 10, further comprising iterating the generating the first branch metric and the second branch metric at least twice.

13. The method as recited in claim 8, further comprising:

reading a third data track using a third read element of the head to generate a third read signal;

sampling the third read signal to generate third signal samples;

generating a third branch metric in a third trellis sequence detector when detecting a third data sequence based on one of the third signal samples; and

generating the second branch metric in the second trellis sequence detector when detecting the second data sequence based on one of the second signal samples, the first branch metric, and the third branch metric.

14. The method as recited in claim 13, further comprising the second trellis sequence detector generating the second branch metric when detecting the second data sequence based on a third expected sample corresponding to a third branch selected by the third trellis sequence detector based on the third branch metric when detecting the third data sequence.