Preamble defect detection and mitigation

1. An apparatus comprising:

a circuit configured to:

synchronize a sampling phase for sampling a signal pattern, including:

sample a preamble field of the signal pattern to obtain sample values;

split the sample values into a plurality of groups, each group including a plurality of samples;

generate an amplitude estimate for each group;

determine an amplitude error for each group, including:

select a selected group from the plurality of groups;

determine a difference between the amplitude estimate of the selected group and a selected target value, the selected target value includes an average amplitude estimate based on amplitude estimates of multiple groups from the plurality of groups;

determine defect groups having samples corresponding to defects in the preamble field, including determining the selected group is one of the defect groups when the amplitude error of the selected group and the selected target value is greater than a threshold;

remove the defect groups from the plurality of groups; and

synchronize the sampling phase based on the plurality of groups.

2. The apparatus of claim 1 further comprising:

synchronizing the sampling phase includes:

determine a sampling phase estimate based on the plurality of groups, the sampling phase estimate based on a sampling phase at which the sample values were obtained; and

adjust the sampling phase based on the sampling phase estimate to achieve a selected sampling phase.

3. The apparatus of claim 1 comprising the circuit further configured to:

generate a sampling phase estimate for each group, the sampling phase estimate based on a sampling phase at which sample values of the group were obtained; and

synchronize the sampling phase based on the sampling phase estimates of the plurality of groups.

4. The apparatus of claim 3 comprising the circuit further configured to:

determine a combined sampling phase estimate based on sampling phase estimates of multiple groups from the plurality of groups;

determine a phase error for each group, including:

select a selected group from the multiple groups;

determine a difference between the sampling phase estimate of the selected group and the combined sampling phase estimate; and

determine the selected group is one of the defect groups when the phase error of the selected group is greater than a threshold.

5. The apparatus of claim 3 comprising the circuit further configured to:

determine an initial sampling phase estimate, corresponding to an initial sampling phase at which a first group of samples from the plurality of groups is obtained, based on the sample values;

adjust the sampling phase by an adjustment amount relative to the initial sampling phase based on the initial sampling phase estimate, including controlling a phase interpolator to modify a clock signal;

determine a current sampling phase estimate for a current group;

remove the adjustment amount corresponding to the current group from the current sampling phase estimate to obtain an updated initial sampling phase estimate, the updated initial sampling phase estimate being the sampling phase estimate for the current group; and

determine the defect groups based on the updated initial sampling phase estimate.

6. The apparatus of claim 1 further comprising:

the circuit includes a data channel of a data storage device;

the signal pattern includes a signal generated by detecting a magnetic field recorded to a magnetic data storage medium;

the preamble field includes a preamble of a sector stored to the magnetic data storage medium;

the circuit further configured to:

determine a number of groups in the defective groups determined for the preamble field; and

reallocate the sector to a new location of the magnetic data storage medium when the number of groups is greater than a second threshold.

7. A method comprising:

synchronizing a sampling phase for sampling a signal pattern, including:

sampling a preamble field of the signal pattern to obtain sample values;

splitting the sample values into a plurality of groups, each group including a plurality of samples;

generating a sampling phase estimate for each group, the sampling phase estimate based on a sampling phase at which sample values of the group were obtained;

determining a combined sampling phase estimate based on sampling phase estimates of multiple groups from the plurality of groups;

determining a phase error for each group, including:

selecting a selected group from the multiple groups;

determining a difference between the sampling phase estimate of the selected group and the combined sampling phase estimate;

determining defect groups having samples corresponding to defects in the preamble field, including determining the selected group is one of the defect groups when the phase error of the selected group is greater than a threshold;

removing the defect groups from the plurality of groups; and

synchronizing the sampling phase based on the sampling phase estimates of the plurality of groups.

8. The method of claim 7 further comprising:

synchronizing the sampling phase includes:

determining a sampling phase estimate based on the plurality of groups, the sampling phase estimate based on a sampling phase at which the sample values were obtained; and

adjusting the sampling phase based on the sampling phase estimate to achieve a selected sampling phase.

9. The method of claim 7 further comprising:

determining a set of groups from the multiple groups having phase errors greater than the threshold; and

determining at least one defect group from the set of groups, the at least one defect group including a selected number of groups with largest phase errors among the set of groups.

10. The method of claim 7 further comprising:

determining an initial sampling phase estimate, corresponding to an initial sampling phase at which a first group of samples from the plurality of groups is obtained, based on the sample values;

adjusting the sampling phase by an adjustment amount relative to the initial sampling phase based on the initial sampling phase estimate, including controlling a phase interpolator to modify a clock signal;

determining a current sampling phase estimate for a current group;

removing the adjustment amount corresponding to the current group from the current sampling phase estimate to obtain an updated initial sampling phase estimate; and

determine the defect groups based on the updated initial sampling phase estimate.

11. The method of claim 7 further comprising:

generating an amplitude estimate for each group;

determining an amplitude error for each group, including:

select a selected group from the plurality of groups;

determine a difference between the amplitude estimate of the selected group and a selected target value; and

determining the selected group is one of the defect groups when the amplitude error of the selected group is greater than a second threshold.

12. The method of claim 11 further comprising:

determining multiple groups from the plurality of groups having amplitude errors greater than the second threshold; and

determining the selected group is one of the defect groups based on the selected group having the highest amplitude error from the multiple groups.

13. An apparatus comprising:

a clock signal generator configured to generate clock pulses;

an analog-to-digital converter configured to sample a signal at a sampling phase controlled by the clock pulses to obtain sample values;

a preamble error detection module configured to:

split preamble sample values into a plurality of groups, the preamble sample values including sample values sampled from a preamble field of the signal, each group including a plurality of samples;

generate a sampling phase estimate for each group, the sampling phase estimate based on the sampling phase at which sample values of the group were obtained;

determine a combined sampling phase estimate based on sampling phase estimates of multiple groups from the plurality of groups;

determine defect groups having sample values corresponding to defects in the preamble field, including:

determine a phase error for each group, including:

select a selected group from the multiple groups;

determine a difference between the sampling phase estimate of the selected group and the combined sampling phase estimate;

determine the selected group is one of the defect groups when the phase error of the selected group is greater than a threshold;

remove the defect groups from the plurality of groups; and

synchronize the sampling phase to the signal based on the combined sampling phase estimate of the plurality of groups to achieve a selected sampling phase.

14. The apparatus of claim 13 further comprising:

a phase interpolator configured to:

modify the clock pulses to adjust the sampling phase;

receive an initial sampling phase estimate based on the sample values;

adjust the sampling phase by an adjustment amount relative to an initial sampling phase based on the initial sampling phase estimate; and

the preamble error detection module further configured to:

generate the sampling phase estimate for each group, including removing the adjustment amount to obtain the sampling phase estimate relative to the initial sampling phase.

15. The apparatus of claim 13 further comprising each group of the plurality of groups includes consecutively-obtained samples.

16. The apparatus of claim 1 further comprising each group of the plurality of groups includes consecutively-obtained samples.

17. The method of claim 7 further comprising each group of the plurality of groups includes consecutively-obtained samples.