Two dimensional magnetic recording system head separation estimator
An apparatus for estimating head separation in an array reader magnetic recording system includes an array reader with multiple read heads operable to read data from a magnetic storage medium, a first preamplifier connected to a first read head, a second preamplifier connected to a second read head, and a head separation estimation circuit connected to the first preamplifier and to the second preamplifier, operable to estimate an integer phase offset and a fractional phase offset between a first signal from the first read head and a second signal from the second read head.
1. An apparatus comprising:
an array reader comprising a plurality of read heads operable to read data from a magnetic storage medium;
a first preamplifier connected to a first read head in the plurality of read heads;
a second preamplifier connected to a second read head in the plurality of read heads; and
a head separation estimation circuit connected to the first preamplifier and to the second preamplifier, operable to estimate an integer phase offset and a fractional phase offset between a first signal from the first read head and a second signal from the second read head.
2. The apparatus of claim 1 , wherein the head separation estimation circuit comprises a phase start detector operable to determine a starting phase for the first signal and a starting phase for the second signal.
3. The apparatus of claim 2 , wherein the head separation estimation circuit further comprises a reader separation estimator operable to calculate a fractional phase offset between the first signal and the second signal based on a difference between the starting phase for the first signal and the starting phase for the second signal.
4. The apparatus of claim 1 , wherein the head separation estimation circuit further comprises a loop pulse estimation circuit operable to calculate a loop pulse estimation for the first signal.
5. The apparatus of claim 4 , wherein the head separation estimation circuit further comprises a second loop pulse estimation circuit operable to calculate a loop pulse estimation for the second signal by interpolating from the loop pulse estimation for the first signal by a fractional phase offset between the first signal and the second signal.
6. The apparatus of claim 1 , wherein the head separation estimation circuit comprises a sync detector operable to detect a syncmark in the first signal and in the second signal.
7. The apparatus of claim 6 , wherein the head separation estimation circuit further comprises a reader separation estimator operable to calculate an integer phase offset between the first signal and the second signal based on a difference between a syncmark location in the first signal detected by the sync detector and a syncmark location in the second signal detected by the sync detector, wherein the integer phase offset comprises a phase offset between the first signal and a second signal that has an integer multiple of a bit period.
8. The apparatus of claim 1 , further comprising a first-in first-out memory connected to the first signal and a second first-in first-out memory connected to the second signal, wherein the first-in first-out memories are operable to delay an output by an integer phase offset between the first signal and the second signal such that a phase offset between the output of the first-in first-out memory and the output of the second first-in first-out memory is less than a single bit period.
9. The apparatus of claim 1 , further comprising a timing loop connected to the first signal and to the second signal, wherein the timing loop is operable to generate a feedback signal to reduce a fractional phase difference between the first signal and the second signal.
10. The apparatus of claim 9 , wherein the timing loop comprises at least one multiplier to scale the first signal and the second signal before generating the feedback signal to reduce a fractional phase difference between the first signal and the second signal.
11. The apparatus of claim 1 , further comprising an adder circuit to combine the first signal and the second signal after an integer phase delay and a fractional phase delay between the first signal and the second signal have been removed, yielding a combined signal.
12. The apparatus of claim 11 , further comprising a data detector operable to detect values of samples in the combined signal.
13. A method for estimating head separation in a two dimensional magnetic recording system, comprising:
computing a phase start of a first signal from a first read head and a phase start of a second signal from a second read head;
calculating a fractional phase offset between the first signal and the second signal as a difference between the phase start of the first signal and the phase start of the second signal;
calibrating a first loop pulse estimate for the first signal;
interpolating the first loop pulse estimate by the fractional phase offset to yield a second loop pulse estimate for the second signal;
detecting a syncmark in the first signal and in the second signal; and
calculating an integer phase offset between the first signal and the second signal as a difference between a location of the syncmark in the first signal and in the second signal.
14. The method of claim 13 , further comprising setting a timing loop combining ratio to [1 0] for the first signal and the second signal before the interpolating.
15. The method of claim 13 , further comprising setting a timing loop combining ratio to [1/2 1/2] for the first signal and the second signal before detecting the syncmark.
16. The method of claim 15 , further comprising:
cancelling the fractional phase offset in a timing loop; and
cancelling the integer phase offset in a first-in first-out memory.
17. The method of claim 16 , further comprising:
combining the first signal and the second signal to yield a combined signal; and
applying a data detection algorithm to the combined signal to yield detected values.
18. A storage device, comprising:
a magnetic storage medium operable to store data;
a head assembly disposed in relation to the storage medium and comprising an array reader with a plurality of read heads to read and write the data on the storage medium;
a first preamplifier connected to a first read head in the plurality of read heads;
a second preamplifier connected to a second read head in the plurality of read heads; and
a head separation estimation circuit connected to the first preamplifier and to the second preamplifier, operable to estimate an integer phase offset and a fractional phase offset between a first signal from the first read head and a second signal from the second read head.
19. The storage device of claim 18 , wherein the head separation estimation circuit is operable to calculate a fractional phase offset between the first signal and the second signal based on phase start detection of the first signal and the second signal, further comprising a loop pulse estimation circuit operable to calibrate a loop pulse estimation for the first signal and to interpolate the loop pulse estimation for the first signal by the fractional phase offset to yield a second loop pulse estimation for the second signal.
20. The storage device of claim 19 , wherein the head separation estimation circuit is further operable to detect a syncmark in the first signal and in the second signal and to calculate an integer phase offset between the first signal and the second signal as a difference between a location of the syncmark in the first signal and a location of the syncmark in the second signal.