Adaptive equalization in a sub-sampled read channel for a disk storage system

A method for reading data recorded on a disk storage medium at a predetermined baud rate by detecting the recorded data from discrete-time sample values generated by sampling an analog read signal from a read head positioned over the disk storage medium, comprising the steps of:

• (a) substantially bandlimiting a signal spectrum of the analog read signal to less than 90% of a bandwidth of a target partial response;
• (b) asynchronously sampling the analog read signal at less than 90% of the baud rate to generate the discrete-time sample values;
• (c) adaptively equalizing the asynchronous sample values according to the target partial response to generate equalized sample values;
• and
• (d) detecting the recorded data from the equalized sample values.

A sampled amplitude read channel for reading data recorded on a disk storage medium at a predetermined baud rate by detecting the recorded data from discrete-time sample values generated by sampling an analog read signal from a read head positioned over the disk storage medium, comprising:

• (a) a sampling device for asynchronously sampling the analog read signal at less than 90% of the baud rate to generate the discrete-time sample values;
• (b) an adaptive equalizer, responsive to the discrete-time sample values, for generating equalized sample values according to a target partial response;
• (c) interpolated timing recovery for up-sampling the equalized sample values to generate synchronous sample values substantially synchronized to the baud rate;
• and
• (d) a discrete-time sequence detector for detecting the recorded data from the synchronous sample values.

A sampled amplitude read channel for reading data recorded on a disk storage medium at a predetermine baud rate by detecting the recorded data from discrete-time sample values generated by sampling an analog read signal from a read head positioned over the disk storage medium, comprising:

• (a) a sampling device for sampling the analog read signal to generate the discrete-time sample values;
• (b) a timing recovery circuit for extracting timing information from the discrete-time sample values;
• (c) an adaptive equalizer, responsive to the discrete-time sample values, for generating equalized sample values according to a target partial response;
• (d) a sample value estimator, responsive to the equalized sample values, for generating estimated ideal sample values corresponding to the target partial response;
• (e) a sample error generator, responsive to the discrete-time sample values and the estimated ideal sample values, for generating a sample error value;
• (f) a sample error adjuster for adjusting the sample error value according to a predetermined criteria to thereby generate an adjusted error value;
• (g) a coefficient updating circuit for updating coefficients of the adaptive equalizer in response to the adjusted error value;
• and
• (h) a discrete-time sequence detector for detecting the recorded data from the equalized sample values.