Mitigation of laser power variation induced phase shift in heat assisted magnetic recording systems
View Patent ↗A system for compensating for heat induced transient phase shift in a heat assisted magnetic recording system. A heat assisted magnetic data recording system includes a near field thermal transducer that locally heats the media during writing. The thermal transducer, when activated, results in a change in size of a magnetic transition written to the magnetic media. This change in size of the thermal transition results in a transient phase shift of the data recorded on the magnetic media. The system includes circuitry for predetermining an anticipated amount of transient phase shift and adjusting a subsequent read signal to compensate for the known transient phase shift, thereby eliminating signal errors resulting from the transient phase shift.
1. A magnetic data recording system, comprising:
a magnetic media;
an actuator;
a slider connected with the actuator for movement adjacent to a surface of the magnetic media;
a magnetic head formed on the slider, the magnetic head including a read element and a write element; and
circuitry configured to determine an anticipated transient phase shift and use the anticipated transient phase shift to compensate for a current transient phase shift;
wherein the magnetic data recording system is a heat assisted magnetic recording system and wherein the write element of the magnetic head further comprises a near field thermal transducer; and
wherein the transient phase shift results from heating of the near field thermal transducer.
2. A magnetic data recording system, comprising:
a magnetic media;
an actuator;
a slider connected with the actuator for movement adjacent to a surface of the magnetic media;
a magnetic head formed on the slider, the magnetic head including a read element and a write element; and
circuitry configured to determine an anticipated transient phase shift and use the anticipated transient phase shift to compensate for a current transient phase shift;
wherein the compensating for the current transient phase shift comprises adjusting a clock frequency.
3. The magnetic data recording system as in claim 1 wherein the circuitry comprises a phase lock loop.
4. The magnetic data recording system as in claim 1 , wherein the circuitry is further configured to adjust a write signal to compensate for the current transient phase shift.
5. The magnetic data recording system as in claim 1 , wherein the circuitry comprises:
a memory for storing the anticipated transient phase shift; and
a phase shifter for retrieving the anticipated transient phase shift from the memory and adjusting a phase of a write signal to compensate for the anticipated transient phase shift.
6. A method for compensating for heat induced transient phase shift in a magnetic data recording system, comprising:
determining an anticipated transient phase shift from at least one previous read pass;
storing the anticipated transient phase shift;
performing a subsequent data write to generate a data signal, the data signal having a current transient phase shift; and
compensating for the current transient phase shift based on the stored anticipated transient phase shift;
wherein the anticipated transient phase shift and current transient phase shift both result from thermal heating.
7. The method as in claim 6 , wherein the compensating for the current transient phase shift comprises adjusting a sample clock phase.
8. The method as in claim 6 , wherein the compensating for the current transient phase shift comprises adjusting a clock frequency.
9. The method as in claim 6 , wherein the method is embodied in circuitry residing in a magnetic data recording system.
10. The method as in claim 6 , wherein the method is embodied in circuitry of a heat assisted magnetic recording system and wherein the anticipated transient phase shift and current transient phase shift result from heating from a near field thermal transducer formed within a magnetic write element of the magnetic data recording system.
11. A method for compensating for heat induced transient phase shift in a magnetic data recording system, comprising:
determining an anticipated transient phase shift from at least one previous read pass;
storing the anticipated transient phase shift;
performing a subsequent data write to generate a data signal, the data signal having a current transient phase shift; and
compensating for the current transient phase shift based on the stored anticipated transient phase shift;
wherein the determination of the anticipated transient phase shift comprises: reading signals from multiple previous read passes;
calculating a transient phase shift for each of the multiple previous read passes; and
calculating an average transient phase shift from each of the transient phase shifts of the multiple previous read passes.
12. The method as in claim 6 , wherein the compensating for the current transient phase shift further comprises adjusting a phase of a write signal.
13. The method as in claim 6 , wherein the compensating for the current transient phase shift further comprises retrieving the anticipated transient phase shift, and adjusting a phase of a current write signal based on the retrieved anticipated transient phase shift.
14. The method as in claim 13 , wherein the phase of the transient phase shift is adjusted in a manner opposite to the anticipated transient phase shift.