Cross-talk measurement in array reader magnetic recording system

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 cross-talk measurement circuit connected to the first preamplifier and to the second preamplifier, operable to measure cross-talk between a first signal from the first read head and a second signal from the second read head based on the first signal and on the second signal while one of the read heads is driven and a remainder of the plurality of read heads in the array reader are not driven.

2. The apparatus of claim 1 , wherein the cross-talk measurement circuit is operable to measure a relative power of the cross-talk.

3. The apparatus of claim 2 , wherein the cross-talk measurement circuit comprises an energy calculator circuit operable to calculate an energy of the first signal, and a divider circuit operable to divide a plurality of energy calculations from the energy calculator circuit to yield a measurement of relative cross-talk energy.

4. The apparatus of claim 3 , wherein the cross-talk measurement circuit comprises an energy calculator circuit operable to calculate a first energy of the first signal when the first read head is driven and the second read head is not driven, and to calculate a second energy of the first signal when the second read head is driven and the first read head is not driven.

5. The apparatus of claim 1 , wherein the cross-talk measurement circuit is operable to characterize a cross-talk transfer function.

6. The apparatus of claim 1 , wherein the cross-talk measurement circuit comprises at least one convolution circuit operable to convolve the first signal with a time-reversed version of the data from the magnetic storage medium.

7. The apparatus of claim 1 , wherein the cross-talk measurement circuit comprises at least one inversion calculator operable to compute an inverse of a transfer function.

8. The apparatus of claim 1 , wherein the cross-talk measurement circuit comprises:

a first convolution circuit operable to convolve the first signal with a time-reversed version of the data from the magnetic storage medium;

an inversion calculator connected to the first convolution circuit operable to compute an inverse of a transfer function based on an output of the first convolution circuit;

a second convolution circuit operable to convolve the second signal with the time-reversed version of the data from the magnetic storage medium; and

a third convolution circuit operable to convolve an output of the inversion calculator with an output of the second convolution circuit to yield a cross-talk transfer function.

9. The apparatus of claim 1 , further comprising a first analog front end circuit connected to the first preamplifier and a second analog front end circuit connected to the second preamplifier, wherein the cross-talk measured by the cross-talk measurement circuit includes cross-talk between the first analog front end circuit and the second analog front end circuit.

10. The apparatus of claim 1 , further comprising a flexible transmission line between the array reader and the preamplifiers, wherein the cross-talk measured by the cross-talk measurement circuit includes cross-talk between conductors in the flexible transmission line.

11. The apparatus of claim 1 , further comprising a plurality of bias circuits operable to provide read currents to the plurality of read heads, wherein only one of the plurality of read heads at a time is biased when the cross-talk measurement circuit measures the cross-talk.

12. The apparatus of claim 1 , wherein each of the plurality of read heads comprises a write line, wherein one of the plurality of read heads at a time is driven by the corresponding write line when the cross-talk measurement circuit measures the cross-talk.

13. A method for measuring cross-talk in an array reader magnetic recording system, comprising:

driving a first read head in a plurality of read heads in an array reader while a remainder of the plurality of read heads in the array reader are not driven;

reading an analog signal from the array reader;

amplifying the analog signal;

digitizing the amplified analog signal to yield digital samples; and

calculating a cross-talk between the plurality of read heads based at least in part on the digital samples.

14. The method of claim 13 , wherein driving the first read head comprises biasing the first read head with a read current and passing the array reader over a pseudo-random bit sequence on a magnetic storage medium, wherein the remainder of the plurality of read heads in the array reader are not driven by bias currents.

15. The method of claim 13 , wherein driving the first read head comprises writing data to a write line in the first read head, wherein the remainder of the plurality of read heads in the array reader are not driven by associated write lines.

16. The method of claim 15 , wherein the array reader is positioned to prevent receiving transitioning data from a magnetic storage medium during the reading.

17. The method of claim 13 , wherein the calculating comprises:

measuring a first energy in the digital samples with the first read head being driven;

driving a second read head in the plurality of read heads while a remainder of the plurality of read heads in the array reader are not driven, including the first read head;

measuring a second energy in the digital samples with the second read head being driven; and

computing a ratio between the first energy and the second energy.

18. The method of claim 13 , wherein driving the first read head comprises reading a pseudo-random bit sequence from a magnetic storage medium, wherein reading an analog signal from the array reader comprises reading a first analog signal from the first read head and reading a second analog signal from a second read head in the plurality of read heads, wherein amplifying the analog signal comprises amplifying the first analog signal and amplifying the second analog signal, and wherein digitizing the amplified analog signal comprises digitizing the first amplified analog signal to yield first digital samples and digitizing the second amplified analog signal to yield second digital samples.

19. The method of claim 18 , wherein calculating the cross-talk comprises:

convolving the first digital samples with a time-reversed version of the pseudo-random bit sequence to yield first convolution results;

convolving the second digital samples with the time-reversed version of the pseudo-random bit sequence to yield second convolution results; and

computing an inverse transfer function based on the first convolution results; and

convolving the second convolution results with the inverse transfer function.

20. 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 cross-talk measurement circuit connected to the first preamplifier and to the second preamplifier, operable to measure cross-talk between a first signal from the first read head and a second signal from the second read head based on the first signal and on the second signal while one of the read heads is driven and a remainder of the plurality of read heads are not driven.