Data storage device calibrating laser write power for heat assisted magnetic recording

• US 9,117,479 B1
• Filed: 09/24/2014
• Issued: 08/25/2015
• Est. Priority Date: 09/24/2014
• 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: Moser, Andreas, Madison, Michael R.
• Primary Examiner(s): Young, Wayne
• Assistant Examiner(s): Butcher, Brian
• Application Number:
  US14/494,710
• Time in Patent Office: 335 Days
• Field of Search: None
• US Class Current: 1/1
• CPC Class Codes: G11B 11/10504 Recording for shaping of magnetic domains G11B11/10528, for compensation of shift G11B11/1053
• CPC Class Codes: G11B 2005/0021 Thermally assisted recording using an auxiliary energy source for heating the recording layer locally to assist the magnetization reversal
• 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 5/40 Protective measures on heads, e.g. against excessive temperature G11B5/31 takes precedence; protection against wear G11B5/255 ; protective structure of the head: see under structures, e.g. G11B5/3106
• CPC Class Codes: G11B 5/455 Arrangements for functional testing of heads; Measuring arrangements for heads
• CPC Class Codes: G11B 5/5534 Initialisation, calibration, e.g. cylinder "set-up"
• CPC Class Codes: G11B 7/1267 Power calibration

Abstract

A data storage device is disclosed comprising a head actuated over a disk, wherein the head comprises a laser configured to heat the disk during write operations. A first test pattern written at a first laser power is read to generate a first track width metric and a first peak amplitude. A second test pattern written at second laser power is read to generate a second track width metric and a second peak amplitude. The first track width metric, the first peak amplitude, the second track width metric, and the second peak amplitude are processed to estimate a coefficient C of an error function. An operating write power for the laser is calibrated based on the estimated coefficient C of the error function.

Claims

1. A data storage device comprising:

a disk;

a head actuated over the disk, wherein the head comprises a laser configured to heat the disk while writing data to the disk; and

control circuitry configured to;

apply a first write power to the laser and write a first test pattern to the disk;

read the first test pattern while the head crosses over a width of the first test pattern to generate a first read signal;

generate a first track width metric based on the first read signal;

generate a first peak amplitude based on the first read signal;

apply a second write power to the laser and write a second test pattern to the disk;

read the second test pattern while the head crosses over a width of the second test pattern to generate a second read signal;

generate a second track width metric based on the second read signal;

generate a second peak amplitude based on the second read signal;

process the first track width metric, the first peak amplitude, the second track width metric, and the second peak amplitude to estimate a coefficient C of an error function (erf);

PeakAmplitude=Amax*erf(TrackWidthMetric/C)

where A max represents a maximum peak amplitude; and

calibrate an operating write power for the laser based on the estimated coefficient C of the error function.

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

move the head at a substantially constant velocity radially over the disk while writing the first test pattern; and

maintain the head at a substantially constant radial location while reading the first test pattern to generate the first read signal.

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

maintain the head at a substantially constant radial location while writing the first test pattern; and

move the head at a substantially constant velocity radially over the disk while reading the first test pattern to generate the first read signal.

4. The data storage device as recited in claim 1, wherein the control circuitry is further configured to generate the first track width metric based on a product of the first peak amplitude and a full width at half maximum (FWHM) of a pulse represented by the first read signal.

5. The data storage device as recited in claim 1, wherein the control circuitry is further configured to generate the first track width metric by integrating the first read signal.

6. The data storage device as recited in claim 1, wherein the control circuitry is further configured to calibrate the operating write power by processing the first write power, the first track width metric, the second write power, and the second track width metric to generate a power function representing a relationship between the laser power to the track width metric.

7. The data storage device as recited in claim 6, wherein the control circuitry is further configured to calibrate the operating write power by:

generating a first target track width metric based on a target value for the ratio;

TrackWidthMetric/C; and

generating a third write power for the laser based on the power function and the first target track width metric.

8. The data storage device as recited in claim 7, wherein the control circuitry is further configured to:

apply the third write power to the laser and write a third test pattern to the disk;

read the third test pattern while the head crosses over a width of the third test pattern to generate a third read signal;

generate a third track width metric based on the third read signal; and

update the coefficient C of the error function based on the third track width metric.

9. The data storage device as recited in claim 8, wherein the control circuitry is further configured to calibrate the operating write power by:

using the updated coefficient C to generate a second target track width metric based on the target value for the ratio;

TrackWidthMetric/C; and

generating a fourth write power for the laser based on the power function and the second target track width metric.

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

applying a first write power to a laser of a head and writing a first test pattern to a disk;

reading the first test pattern while the head crosses over a width of the first test pattern to generate a first read signal;

generating a first track width metric based on the first read signal;

generating a first peak amplitude based on the first read signal;

applying a second write power to the laser and writing a second test pattern to the disk;

reading the second test pattern while the head crosses over a width of the second test pattern to generate a second read signal;

generating a second track width metric based on the second read signal;

generating a second peak amplitude based on the second read signal;

processing the first track width metric, the first peak amplitude, the second track width metric, and the second peak amplitude to estimate a coefficient C of an error function (erf);

PeakAmplitude=Amax*erf(TrackWidthMetric/C)

where A max represents a maximum peak amplitude; and

calibrating an operating write power for the laser based on the estimated coefficient C of the error function.

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

moving the head at a substantially constant velocity radially over the disk while writing the first test pattern; and

maintaining the head at a substantially constant radial location while reading the first test pattern to generate the first read signal.

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

maintaining the head at a substantially constant radial location while writing the first test pattern; and

moving the head at a substantially constant velocity radially over the disk while reading the first test pattern to generate the first read signal.

13. The method as recited in claim 10, further comprising generating the first track width metric based on a product of the first peak amplitude and a full width at half maximum (FWHM) of a pulse represented by the first read signal.

14. The method as recited in claim 10, further comprising generating the first track width metric by integrating the first read signal.

15. The method as recited in claim 10, further comprising calibrating the operating write power by processing the first write power, the first track width metric, the second write power, and the second track width metric to generate a power function representing a relationship between the laser power to the track width metric.

16. The method as recited in claim 15, further comprising calibrating the operating write power by:

generating a first target track width metric based on a target value for the ratio;

TrackWidthMetric/C; and

generating a third write power for the laser based on the power function and the first target track width metric.

17. The method as recited in claim 16, further comprising:

applying the third write power to the laser and write a third test pattern to the disk;

reading the third test pattern while the head crosses over a width of the third test pattern to generate a third read signal;

generating a third track width metric based on the third read signal; and

updating the coefficient C of the error function based on the third track width metric.

18. The method as recited in claim 17, further comprising calibrating the operating write power by:

using the updated coefficient C to generate a second target track width metric based on the target value for the ratio;

TrackWidthMetric/C; and

generating a fourth write power for the laser based on the power function and the second target track width metric.