Data storage device detecting media defects by writing opposite polarity test pattern

• US 9,171,575 B1
• Filed: 06/23/2014
• Issued: 10/27/2015
• Est. Priority Date: 06/23/2014
• Status: Expired due to Fees

• Current Assignee: Western Digital Technologies Incorporated (Western Digital Corporation)
• Original Assignee: Western Digital Technologies Incorporated (Western Digital Corporation)
• Inventors: Alex, Michael, Bertero, Gerardo A., Almaqablah, Mazin
• Primary Examiner(s): Edun, Muhammad N
• Application Number:
  US14/312,431
• Time in Patent Office: 491 Days
• Field of Search: None
• US Class Current: 1/1
• CPC Class Codes: G11B 20/10009 Improvement or modification of read or write signals
• CPC Class Codes: G11B 20/182 using test patterns
• CPC Class Codes: G11B 20/1889 with discs
• CPC Class Codes: G11B 2220/2516 Hard disks
• CPC Class Codes: G11B 27/36 Monitoring, i.e. supervising the progress of recording or reproducing for digital recording G11B20/00 and s.gr.; for monitoring, testing or measuring of TV recorders of the type covered by H04N5/76 and subgroups, see H04N17/06
• 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 5/024 Erasing
• CPC Class Codes: G11B 5/59616 Synchronisation; Clocking G11B5/59622 takes precedence

Abstract

A data storage device is disclosed comprising a disk comprising a plurality of tracks, and a head actuated over the disk. A first test pattern having a first polarity is written to a target track, and the first test pattern is read to generate a first read signal. The first test pattern is overwritten with a second test pattern having a second polarity opposite the first polarity, and the second test pattern is read to generate a second read signal. A defect in the target track is detected based on the first read signal and the second read signal.

Claims

1. A data storage device comprising:

a disk comprising a plurality of tracks;

a head actuated over the disk; and

control circuitry configured to;

write a first test pattern having a first polarity to a target track;

read the first test pattern to generate a first read signal;

overwrite the first test pattern with a second test pattern having a second polarity opposite the first polarity;

read the second test pattern to generate a second read signal; and

detect a defect in the target track based on the first read signal and the second read signal.

2. The data storage device as recited in claim 1, wherein the control circuitry is further configured to:

sample the first read signal to generate first signal samples;

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

detect the defect in the target track based on the first and second signal samples.

3. The data storage device as recited in claim 2, wherein the control circuitry is further configured to detect the defect in the target track based on a moving window of the first and second signal samples.

4. The data storage device as recited in claim 2, wherein the control circuitry is further configured to detect the defect in the target track based on a correlation of the first and second signal samples.

5. The data storage device as recited in claim 4, wherein the control circuitry is further configured to detect the defect in the target track when the correlation exceeds a negative threshold.

6. The data storage device as recited in claim 1, wherein:

the first test pattern comprises a DC test pattern; and

the second test pattern comprises a DC test pattern.

7. The data storage device as recited in claim 1, wherein:

the first test pattern comprises a periodic test pattern; and

the second test pattern comprises a periodic test pattern.

8. The data storage device as recited in claim 1, wherein the defect in the target track increases a DC noise in the first and second read signal.

9. The data storage device as recited in claim 8, wherein the DC noise in the first read signal is opposite in polarity from the DC noise in the second read signal.

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

writing a first test pattern having a first polarity to a target track on a disk;

reading the first test pattern to generate a first read signal;

overwriting the first test pattern with a second test pattern having a second polarity opposite the first polarity;

reading the second test pattern to generate a second read signal; and

detecting a defect in the target track based on the first read signal and the second read signal.

11. The method as recited in claim 10, further comprising:

sampling the first read signal to generate first signal samples;

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

detecting the defect in the target track based on the first and second signal samples.

12. The method as recited in claim 11, further comprising detecting the defect in the target track based on a moving window of the first and second signal samples.

13. The method as recited in claim 11, further comprising detecting the defect in the target track based on a correlation of the first and second signal samples.

14. The method as recited in claim 13, further comprising detecting the defect in the target track when the correlation exceeds a negative threshold.

15. The method as recited in claim 10, wherein:

the first test pattern comprises a DC test pattern; and

the second test pattern comprises a DC test pattern.

16. The method as recited in claim 10, wherein:

the first test pattern comprises a periodic test pattern; and

the second test pattern comprises a periodic test pattern.

17. The method as recited in claim 10, wherein the defect in the target track increases a DC noise in the first and second read signal.

18. The method as recited in claim 17, wherein the DC noise in the first read signal is opposite in polarity from the DC noise in the second read signal.