Variable frequency chevron in printed media reference pattern to improve servo demodulation
View Patent ↗Reference patterns in accordance with the present invention can include variable frequency chevrons incorporated into a reference pattern on a printed media surface to improve servo demodulation. In an embodiment, the reference pattern can include one or more servo wedges having a preamble including digital information at a first frequency relative to the head when the rotatable medium is rotated at a spin speed. The servo wedges further include at least one field having a first set of a plurality of phase-bursts forming a positive chevron angle relative to the preamble and a second set of a plurality of phase-bursts forming a negative chevron angle relative to the preamble, wherein a frequency of the at least one field relative to the head when the rotatable medium is rotated at the spin speed varies between a first end of the media surface and a second end.
1. A rotatable disk for use in a data storage device, the rotatable disk comprising:
an inner diameter;
an outer diameter;
a servo wedge disposed between the inner diameter and the outer diameter, the servo wedge including:
a first end,
a second end,
a preamble field extending from the first end to the second end; and
a servo-burst field extending from the first end to the second end and having a set of servo-bursts forming a chevron angle relative to the preamble field;
wherein a burst-frequency of the set of servo-bursts varies between the first end and the second end.
2. The rotatable disk of claim 1 , wherein:
the set of servo-bursts is a first set of servo-bursts;
the servo-burst field further includes a second set of servo-bursts; and
a burst-frequency of one or both of the first and second sets of servo-bursts varies between the first end and the second end.
3. The rotatable disk of claim 2 , wherein:
the burst-frequency of the first and second sets of servo-bursts between the first end and a transition region is a first frequency;
the burst-frequency of the first and second sets of servo-bursts between the transition region and the second end is a second frequency;
the transition region is between the first end and the second end; and
the transition region includes one of the first and second sets of servo-bursts at the first frequency, and the other of the first and second sets of servo-bursts at the second frequency.
4. The rotatable disk of claim 3 , wherein the second frequency is higher than the first frequency.
5. The rotatable disk of claim 3 , wherein the burst-frequency of digital information within the preamble field is the first frequency.
6. The rotatable disk of claim 2 , further comprising:
a transition region between the first end and the second end;
wherein:
between the first end and the transition region, the burst-frequency one of the first and second sets of servo-bursts is a first frequency and the burst-frequency of the other of the first and second sets of servo-bursts is a second frequency;
between the transition region and the second end, the burst-frequency one of the first and second sets of servo-bursts is a first frequency and the burst-frequency of the other of the first and second sets of servo-bursts is a second frequency;
the transition region includes both of the first and second sets of servo-bursts at one of the first frequency the second frequency.
7. The rotatable disk of claim 1 , wherein a frequency across the preamble field is substantially the same from the first end to the second end.
8. A system to self-servo write one or more disks in a hard disk drive, the system comprising:
a housing;
a spindle rotatably connected with the housing;
a reference disk associated with the spindle and including an inner diameter, an outer diameter, and a servo wedge disposed between the inner diameter and the outer diameter having:
a first end,
a second end,
a preamble field extending from the first end to the second end;
a servo-burst field extending from the first end to the second end and having a set of servo-bursts forming a chevron angle relative to the preamble field,
wherein a burst-frequency of the set of servo-bursts varies between the first end and the second end
a read/write head adapted to communicate with the reference disk; and
a circuit to convert a signal of the servo wedge read by the read/write head so that the signal does not vary between the first end and the second end.
9. The system of claim 8 , wherein:
the set of servo-bursts is a first set of servo-bursts;
the servo-burst field further includes a second set of servo-bursts; and
a burst-frequency of one or both of the first and second sets of servo-bursts varies between the first end and the second end.
10. The system of claim 9 , wherein:
the burst-frequency of the first and second sets of servo-bursts between the first end and a transition region is a first frequency;
the burst-frequency of the first and second sets of servo-bursts between the transition region and the second end is a second frequency; and
the transition region is between the first end and the second end; and
the transition region includes one of the first and second sets of servo-bursts at the first frequency, and the other of the first and second sets of servo-bursts at the second frequency.
11. The system of claim 10 , wherein the frequency of digital information within the preamble field is the first frequency.
12. The system of claim 10 , wherein the transition region includes one of the first and second sets of servo-bursts at the first frequency, and the other of the first and second sets of servo-bursts at the second frequency.
13. The system of claim 10 , wherein the second frequency is higher than the first frequency.
14. The system of claim 8 , wherein the circuit comprises:
an interpolator circuit;
one or more filters; and
a down sampler.
15. The system of claim 14 , wherein the one or more filters is a low-pass bi-quad filter.
16. The system of claim 8 , wherein the circuit comprises:
a de-multiplexor;
a first signal processor including one or more filters and a downsampler; and
a second signal processor including one or more filter and a downsampler;
wherein the first signal processor processes at a first frequency; and
wherein the second signal processor processes at a second frequency.
17. The system of claim 16 , wherein the one or more filters is a low-pass bi-quad filter.
18. The system of claim 8 , wherein a frequency across the preamble field is substantially the same from the first end to the second end.
19. A method to determine a position of a head over a disk having an inner diameter and an outer diameter in a hard disk drive, the method comprising:
providing a reference pattern disposed between the inner diameter and the outer diameter, the reference pattern including a first end, a second end, and a servo wedge extending from the first end to the second end having a preamble field including digital information arranged circumferentially across the preamble field at a first frequency, and a servo-burst field including a set of servo-bursts arranged across the servo-burst field circumferentially at the first frequency from the first end to a transition region of the disk and arranged at a second frequency from a transition region to the second end;
rotating the disk;
positioning the head over the reference pattern;
sampling the digital information from the preamble field with the head;
obtaining a preamble signal from the digital information samples from the preamble field;
filtering the preamble signal;
sampling the set of servo-bursts of the servo-burst field with the head;
obtaining a servo-burst signal based on the first set of servo-burst samples from the servo-burst field;
wherein:
when the head is positioned between the first end and the transition region, the servo-burst signal is the set of servo-burst samples; and
when the head is positioned between the transition region and the outer second end, the servo-burst signal is obtained by:
converting the set of servo-burst samples from the second frequency to a third frequency,
filtering the servo-burst samples, and
converting the filtered set of servo-burst samples from the third frequency to the first frequency; and
filtering the servo-burst signal.