Cirrus Logic Inc.

Jay Neil Livingston

David E Reed

Marvin L Vis

William G Bliss

Control circuitry for a disk drive system that has improved data detection by using log likelihood values and erasure pointers. The control circuitry is comprised of a log likelihood modification system and a decoder. The log likelihood modification system receives log likelihood values that represent data and erasure pointers. The erasure pointers point to at least one of the log likelihood values that has been corrupted in some manner. The log likelihood modification system sets the log likelihood values, that the erasure pointer points to, to an error value to generate modified log likelihood values. The log likelihood modification system transfers the modified log likelihood values to the decoder. The decoder processes the modified log likelihood values based on code constraints to generate estimated log likelihood values. The decoder then decodes the data from the estimated log likelihood values.

Data detection in a disk drive system using erasure pointers

Data storage system circuitry comprises randomizer circuitry and grading circuitry. The randomizer circuitry concurrently generates multiple randomized versions of user data. The grading circuitry selects one of the multiple randomized versions of the user data for data storage. Decoding circuitry decodes the selected one of the multiple randomized versions of the user data. In some examples of the invention, the grading circuitry selects the one of the multiple randomized versions of the user data based on zero run characteristics of the multiple randomized versions of the user data. In some examples of the invention, the user data is not encoded with a run length limit algorithm.

Data randomization in a data storage system

In a sampled amplitude read channel for disk storage systems, a post processor is employed to correct errors in a preliminary sequence caused by the dominant error events of a trellis sequence detector. By correlating a sample error sequence with the dominant error events, error filters compute a Euclidean distance error metric between the samples sequence selected by the trellis sequence detector and the sample sequence that would have been selected if an error event did not occur. The minimum error metric is assigned to the symbols in the preliminary sequence that differ from the symbol sequence that would have been generated if the error event did not occur. After processing a predetermined number of the symbols in the preliminary sequence, the error metrics assigned, to the symbols are used to detect and correct error events in the preliminary sequence.

Sampled amplitude read channel employing a trellis sequence detector and a post processor for generating error metrics used to correct errors made by the trellis sequence detector

Erroneous column(s) in the matrix of data obtained from a transmission channel are first determined on the basis of column parity violation. An error instance in the matrix is next ascertained by matching the erroneous column(s) with an error event characteristic of the transmission channel. A candidate error row is then located in the matrix with respect to the error instance. Lastly, positions in the matrix specified by an intersection of the candidate error row and the erroneous column(s) of the error instance are corrected. Data reliability values assigned to positions of the matrix are used to determine the candidate error row. In particular, with respect to the erroneous column(s) of the error instance, and for each of plural rows of the matrix, factors (e.g., squares) of the reliability values assigned to positions of the matrix are summed to determine a least reliable row as the candidate error row. The operation of the invention is preferably preceded by a row error detection/correction operation which corrects single bit and tri-bit row errors in the matrix.

Error correction using reliability values for data matrix

Data storage system circuitry comprises randomizer circuitry and run-length control circuitry. The randomizer circuitry generates randomized user data. The run-length control circuitry grades the randomized user data to determine if the randomized user data requires run-length encoding. The run-length control circuitry applies the run-length encoding to the randomized user data if the randomized user data requires run-length encoding. The run-length control circuitry may encode decoding information and error correction information for the decoding information into the randomized user data. The run-length encoding may comprise de-randomization or RLL encoding. If de-randomization is used, RLL encoding may be eliminated altogether for the randomized user data.

Data encoding to provide run-length control in a data storage system

A sampled amplitude read channel is disclosed for disk storage systems comprising a encoder/decoder for implementing a high rate channel code that codes out specific minimum distance error events of a trellis sequence detector by enforcing a particular code constraint. The trellis sequence detector comprises a state machine matched to the code constraint which effectively removes the corresponding minimum distance errors from the detected output sequence. Additionally, the channel code encodes redundancy bits into the write data for implementing an error detection code. The redundancy bits are processed during a read operation to generate an error syndrome used to detect and correct other dominant error events, such as the NRZ (&plus;) and (&plus;&minus;&plus;) error events. In this manner, the most likely error events of the trellis sequence detector are either coded out by the channel code constraint, or detected and corrected using the error syndrome. As a result, the present invention provides a significant distance enhancing performance gain over the prior art without decreasing the system's code rate, thereby providing a substantial increase in linear bit density and overall storage capacity.

Sampled amplitude read channel employing a trellis sequence detector matched to a channel code constraint and a post processor for correcting errors in the detected binary sequence using the signal samples and an error syndrome

In an encoding method which utilizes plural codebooks, certain bits of a user data input sequence are considered as branch selection bit(s) which determine (1) how the remainder of the input sequence is to be divided into plural subsequences and (2) which codebooks are addressed using the plural subsequences in order to generate corresponding plural output sequences. The plural output sequences are then concatentated together to form a codeword. The method reduces the size of the codebooks that otherwise would be employed for the particular code involved in the encoding method. The encoding of the present invention is particularly suitable for a Quadbit Modulo 2 (QM2) code.

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Superior, CO, United States of America

Jay Neil Livingston