International Business Machines Corporation

Nec Electronics Corporation

Hemant K Thapar

Razmik Karabed

Paul H Siegel

Shih-Ming Shih

James Wilson Rae

Lisa Fredrickson

Kwok Wah Yeung

Roger William Wood

Gerhard P Fettweis

Lyle J Fredrickson

Apparatus and Methods are disclosed for adaptively optimizing an ER filter in a readback system of a storage device, such as a disk drive. A sample value is read from the storage device and an error measure is calculated between the sample value and an ideal value. Pole parameters and zeros of the ER filter are modified to minimize the ER filter. The apparatus and methods disclosed can function with customer data to adaptively optimize the ER filter in real time during normal operation of the storage device. Furthermore, temperature compensation circuits are disclosed to compensate for temperature dependencies in the ER filter.

Method for optimizing an equalization and receive filter

A less complex maximum likelihood detector can be implemented in a partial response maximum likelihood (PRML) system without degrading system performance by saturating y values from a gain control loop to a smaller range before the y values are supplied to the maximum likelihood detector. A quantity 'D' of a maximum likelihood detector operating in accordance with a partial response scheme has a particular relationship with respect to the maximum (ymax) of the y input values processed by the maximum likelihood detector. In some embodiments, y values from a gain control loop are saturated from a first larger range (defined by ymaxreal) to a second smaller range (defined by a value SAT) which is at least as great as the ymax of the ideal input signal (ymaxideal) for the partial response scheme. The saturated y values are provided to the maximum likelihood detector. The D of the maximum likelihood detector (given the partial response scheme and the smaller range of y values) is in a different 'two to the power of an integer range' than the D would have been given the same partial response scheme but the larger range of y values.

PRML system with reduced complexity maximum likelihood detector

A method and means for detecting spectral null sequences of a spectrally-constrained code at the output of a noisy communications channel by tracking the spectral content of said sequences with a Viterbi detector using an N stage trellis and mapping each spectral null sequence to a unique path of acyclic successive states and edges through said trellis by selectively outsplitting counterpart states at preselected times modulo N in said trellis such that no pair of unique paths support the same spectral null sequence.

Method and means for generating and detecting spectrally constrained

Apparatus and method for transmitting spectral null sequences of a spectrally-constrained code over a partial response channel. A Viterbi detector receives the sequences from the channel and has a time-varying detector trellis structure derived from a running-digital-sum (RDS) trellis structure that requires each one of a set of quasicatastrophic sequences to be generated only from a trellis state corresponding to a respective preselected unique RDS value.

Matched spectral null codes with partitioned systolic trellis structures

Maximum likelihood detection of a trellis code using a Viterbi detector constructed from a time-varying trellis structure that is associated with a partial response channel and consists of connected trellises with periodically repeated patterns of nodes and subtrellises of said trellises. Each subtrellis has nodes representing a current state of the channel and value of a predetermined tracked attribute. A survivor metric and a survivor sequence from a node at the end of one subtrellis are reassigned to a node at the beginning of an adjacent subtrellis having a different value of the tracked attribute for increasing minimum distance properties, reducing error event length and improving code constraints for timing and gain control. The one subtrellis and adjacent subtrellis may be within a single trellis or in adjacent trellises.

Permuted trellis codes for input restricted partial response channels

A Viterbi decoder having a recursive processor modified to process each node in a trellis of a partial response coded signal to shift the branch metric additions over the node to effectuate compare, select, add operation order on the predecessor survivor metrics terminating in that node, to compare the metrics of the predecessor sequences terminating in the node, to select a survivor sequence, and to add the shifted branch metrics to the metric of the selected survivor sequence.

Method and means for detecting partial response waveforms using a

A method and apparatus for detecting spectral null sequences of a spectrally-constrained code on a noisy communications channel. From a Viterbi detector with a trellis structure comprising a plurality of states and edges, predetermined ones of the states and edges in the trellis structure are deleted at preselected times modulo N, such as times .phi. modulo N and/or at intermediate times m modulo N, where m=.phi., thereby to create a time-varying trellis structure for limiting the maximum length of dominant error events. The deleted edges are generally those edges which would have entered or emanated from the deleted states if they were not deleted. The trellis structure may be a so-called systolic structure, in which case the spectral null sequences are preferably DC-free or Nyquist free.

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San Jose, CA, United States of America

Hemant K Thapar