Data storage device detecting media defects by writing opposite polarity test pattern
View Patent ↗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.
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.