Harmonic sensor phase error detection for data storage devices
Example systems, data storage devices, and methods for using a harmonic sensor in the read channel of a data storage device to determine phase error are described. The data storage device includes a storage medium with data tracks and a head that can be positioned for reading and writing those tracks. A tone pattern may be written to a data track and a read signal from the tone pattern may subsequently be processed through the harmonic sensor to acquire amplitude data corresponding differences between a target frequency of the tone pattern and a read frequency from the read signal. The amplitude data may be processed to determine phase error values that correspond to an operating condition during writing, such as mode hops and/or down track thermal gradients related to operation of a laser during heat assisted magnetic recording.
1. A data storage device, comprising:
a non-volatile storage medium;
a head actuated over the non-volatile storage medium; and
control circuitry configured to:
write, using the head, a tone pattern to at least one track on the non-volatile storage medium;
acquire, using a harmonic sensor in a read channel configured to receive a read signal from the head, amplitude data from the tone pattern and corresponding to differences between a target frequency of the tone pattern and a read frequency from the read signal;
determine, based on the amplitude data, a plurality of phase error values; and
determine, based on the plurality of phase error values, an operating condition during the write.
2. The data storage device of claim 1 , wherein:
the head comprises a laser configured to heat the non-volatile storage medium while writing data to the non-volatile storage medium; and
the operating condition corresponds to an operating characteristic of the laser.
3. The data storage device of claim 2 , wherein:
the operating condition comprises at least one mode hop of the laser;
the control circuitry is further configured to:
configure an acquisition window of the harmonic sensor corresponding to a sector portion of the at least one track; and
configure a set of acquisition frequencies of the harmonic sensor corresponding to a plurality of data points proximate the target frequency of the tone pattern; and
determining the operating condition comprises detecting the at least one mode hop based on a comparison of amplitude data values at the set of acquisition frequencies to determine the plurality of phase error values.
4. The data storage device of claim 3 , wherein detecting the at least one mode hop comprises:
determining, using the set of acquisition frequencies, at least three data points for a target peak;
determining a relationship among the at least three data points to determine a phase error value; and
comparing the phase error value to a mode hop threshold to determine that the at least one mode hop has been detected.
5. The data storage device of claim 4 , wherein determining the operating condition further comprises calculating an average frequency error to quantify a size of the at least one mode hop.
6. The data storage device of claim 3 , wherein:
the non-volatile storage medium comprises a rotating disk;
the at least one track comprises a plurality of sector portions along a length of the at least one track; and
acquiring the amplitude data comprises sampling frequency error for the set of acquisition frequencies at the plurality of sector portions for at least one revolution of the rotating disk.
7. The data storage device of claim 3 , wherein the control circuitry is further configured to, during field operation of the data storage device:
band erase, prior to writing the tone pattern, the at least one track;
adjust, responsive to detecting the at least one mode hop and based on at least one parameter corresponding to the at least one mode hop, at least one operating parameter selected from:
a first laser current parameter selected to reduce mode hops;
a second laser current parameter selected to compensate for changing write widths based on a size of the at least one mode hop;
an adjacent track interference weighting parameter based on the size of the at least one mode hop; and
a risk parameter correlating the size of the at least one mode hop to degradation of the head; and
write, to the non-volatile storage medium, user data using the adjusted at least one operating parameter.
8. The data storage device of claim 2 , wherein:
the operating condition comprises a down track thermal gradient value correlating changes in laser power to changes in position of written data;
the control circuitry is further configured to:
configure an acquisition window of the harmonic sensor corresponding to a sector portion of the at least one track;
determine a range of laser current values used during writing the tone pattern in the sector portion; and
configure a set of acquisition frequencies of the harmonic sensor corresponding to positions of changes in laser current value across the range of laser current values; and
determining the operating condition comprises using the plurality of phase error values to calculate phase shift relative to the changes in laser power to determine corresponding set of down track thermal gradient values.
9. The data storage device of claim 8 , wherein the control circuitry is further configured to:
determine a baseline set of down track thermal gradient values;
compare, during field operation of the data storage device, the corresponding set of down track thermal gradient values to the baseline set of down track thermal gradient values to generate at least one thermal gradient change value;
adjust, responsive to the at least one thermal gradient change value meeting a change threshold, at least one operating parameter selected from:
a laser current parameter selected to adjust down track thermal gradient based on the at least one thermal gradient change value;
an adjacent track interference weighting parameter based on a correlation between down track thermal gradient values and a write width parameter;
a risk parameter correlating the at least one thermal gradient change to degradation of the head;
a smear removal threshold for initiating a smear removal operation based on low down track thermal gradient values; and
a thermal fly height control parameter to adjust head-media spacing based on the at least one thermal gradient change; and
write, to the non-volatile storage medium, user data using the adjusted at least one operating parameter.
10. The data storage device of claim 2 , wherein the control circuitry is further configured to set, prior to field operation of the data storage device and based on the plurality of phase error values, at least one parameter selected from:
a squeeze margin parameter for determining track format based on at least one mode hop measurement;
a squeeze margin parameter for determining track format based on at least one down track thermal gradient measurement;
a head failure parameter based on at least one mode hop measurement meeting at least one failure threshold;
a head failure parameter based on at least one down track thermal gradient measurement meeting at least one failure threshold;
a laser current parameter based on mode hop measurements to reduce mode hops during write operations;
a write current parameter based on mode hop measurements to reduce mode hops during write operations;
a write quality parameter based on mode hop measurements to qualify data sectors; and
a risk parameter based on changes in at least one down track thermal gradient measurement over a test time.
11. A method comprising:
writing, using a head actuated over a non-volatile storage medium of a data storage device, a tone pattern to at least one track on the non-volatile storage medium;
acquiring, using a harmonic sensor in a read channel configured to receive a read signal from the head, amplitude data from the tone pattern and corresponding to differences between a target frequency of the tone pattern and a read frequency from the read signal;
determining, based on the amplitude data, a plurality of phase error values; and
determining, based on the plurality of phase error values, an operating condition during the writing.
12. The method of claim 11 , further comprising:
heating, using a laser in the head, the non-volatile storage medium while writing data to the non-volatile storage medium, wherein the operating condition corresponds to an operating characteristic of the laser.
13. The method of claim 12 , further comprising:
configuring an acquisition window of the harmonic sensor corresponding to a sector portion of the at least one track;
configuring a set of acquisition frequencies of the harmonic sensor corresponding to a plurality of data points proximate the target frequency of the tone pattern; and
detecting, based on a comparison of amplitude data values at the set of acquisition frequencies to determine the plurality of phase error values, at least one mode hop of the laser, wherein the operating condition comprises the at least one mode hop of the laser.
14. The method of claim 13 , wherein detecting the at least one mode hop comprises:
determining, using the set of acquisition frequencies, at least three data points for a target peak;
determining a relationship among the at least three data points to determine a phase error value; and
comparing the phase error value to a mode hop threshold to determine that the at least one mode hop has been detected.
15. The method of claim 14 , wherein determining the operating condition further comprises calculating an average frequency error to quantify a size of the at least one mode hop.
16. The method of claim 13 , wherein:
the non-volatile storage medium comprises a rotating disk;
the at least one track comprises a plurality of sector portions along a length of the at least one track; and
acquiring the amplitude data comprises sampling frequency error for the set of acquisition frequencies at the plurality of sector portions for at least one revolution of the rotating disk.
17. The method of claim 13 , further comprising, during field operation of the data storage device:
band erasing, prior to writing the tone pattern, the at least one track;
adjusting, responsive to detecting the at least one mode hop and based on at least one parameter corresponding to the at least one mode hop, at least one operating parameter selected from:
a first laser current parameter selected to reduce mode hops;
a second laser current parameter selected to compensate for changing write widths based on a size of the at least one mode hop;
an adjacent track interference weighting parameter based on the size of the at least one mode hop; and
a risk parameter correlating the size of the at least one mode hop to degradation of the head; and
writing, to the non-volatile storage medium, user data using the adjusted at least one operating parameter.
18. The method of claim 12 , further comprising:
configuring an acquisition window of the harmonic sensor corresponding to a sector portion of the at least one track;
determining a range of laser current values used during writing the tone pattern in the sector portion;
configuring a set of acquisition frequencies of the harmonic sensor corresponding to positions of changes in laser current value across the range of laser current values; and
determining, using the plurality of phase error values to calculate phase shift relative to the changes in laser power, a corresponding set of down track thermal gradient values, wherein the operating condition comprises the set of down track thermal gradient values correlating changes in laser power to changes in width and position of written data.
19. The method of claim 18 , further comprising:
determining a baseline set of down track thermal gradient values;
comparing, during field operation of the data storage device, the corresponding set of down track thermal gradient values to the baseline set of down track thermal gradient values to generate at least one thermal gradient change value;
adjusting, responsive to the at least one thermal gradient change value meeting a change threshold, at least one operating parameter selected from:
a laser current parameter selected to adjust down track thermal gradient based on the at least one thermal gradient change value;
an adjacent track interference weighting parameter based on a correlation between down track thermal gradient values and a write width parameter;
a risk parameter correlating the at least one thermal gradient change to degradation of the head;
a smear removal threshold for initiating a smear removal operation based on low down track thermal gradient values; and
a thermal fly height control parameter to adjust head-media spacing based on the at least one thermal gradient change; and
writing, to the non-volatile storage medium, user data using the adjusted at least one operating parameter.
20. A data storage device comprising:
a non-volatile storage medium comprising a plurality of data tracks;
a head actuated over the non-volatile storage medium, wherein the head comprises a laser configured to heat the non-volatile storage medium while writing data to the non-volatile storage medium;
means for writing, using the head, a tone pattern to at least one track on the non-volatile storage medium;
means for acquiring, using a harmonic sensor in a read channel configured to receive a read signal from the head, amplitude data from the tone pattern and corresponding to differences between a target frequency of the tone pattern and a read frequency from the read signal;
means for determining, based on the amplitude data, a plurality of phase error values; and
means for determining, based on the plurality of phase error values, an operating condition of the laser during the writing.