Seagate Technology Incorporated

Ke Du

Bernardo Rub

Robert D Cronch

Kenneth R Burns

Matthew Chad Burton

William C Little

Deanne Sue Grover

Dennis C Kastl

Jim R Shaver

Yujie Xu

An apparatus and method for removing baseline shift in low frequency readback signals of a disc drive, such signals characterized by peaks separated by baseline portions. The disc drive comprises a head controllably positionable adjacent tracks on a rotatable disc, a servo circuit which controls the position of the head in response to the readback signals and an adjustable filter operably connected to and serially disposed between the head and the servo circuit. When baseline shift is detected in the baseline portions of the readback signals at a predetermined margin threshold, the response characteristics of the adjustable filter are adjusted to remove the detected baseline shift from the readback signals.

Low frequency signal baseline shift compensation in a disc drive

An apparatus and method for improving error rate performance in a communication channel utilizes a dual decision feedback equalizer (DDFE) through the application of selective attenuation. An improved DDFE comprises first and second decision feedback equalizers (DFEs) operably connected in parallel to receive a series of input signals z,. The DFEs independently generate two series of decisions &acirc ;,and &acirc ;,in relation to peak magnitudes of the series of transmitted signals z,by filtering the series of decisions &acirc ;,and &acirc ;,to generate filtered outputs (a*p),and (a*p),based on previous decisions, and summing the filtered outputs (a*p),and (a*p),with the transmitted input series z,to generate two series of decision variables &atilde;,and &atilde;,, to remove effects of intersymbol interference. The improved DDFE further comprises first and second attenuation blocks, so that when a mismatch is detected between the series of decisions &acirc ;,and &acirc ;,, a selective attenuation gain less than one is introduced into each feedback filter loop. This results in a reallocation of some of the decision energy associated with the correct series of decisions to the erroneous series and helps the erroneous DFE to make correct decisions sooner, thereby improving the error rate performance of the channel.

Dual decision feedback equalizer with selective attenuation to improve channel performance

An apparatus and method are disclosed for reducing the effects of thermal asperities and other anomalous conditions on disc drive read operations. An improved data block format is provided having first and second sync fields in which sync patterns are stored, the first and second sync fields being separated by a selected distance within the data block. The sync pattern of the second sync field enables synchronization of a disc drive read channel to the user data in the data block when the read channel fails to be synchronized by the sync pattern of the first sync field. In one embodiment, control information used by the read channel to prepare for receipt of the user data is stored in a field between the first and second sync fields; in an alternative embodiment, a portion of the user data is stored between the first and second sync fields.

Redundant synchronization fields to improve disc drive read performance

An apparatus and associated method are disclosed for recovering user data from a data block in a disc drive in which user data are stored by way of a plurality of blocks on tracks of a disc, the blocks including data blocks in which the user data are stored in predefined increments. A head generates readback signals from the blocks and a read channel reconstructs the user data from the readback signals. An automatic gain control stage establishes a gain used to amplify the readback signal to a level suitable for use by the read channel. When an uncorrected read error is detected, the disc drive proceeds to read a previous block sequentially preceding the affected data block and sets the gain to a fixed value based upon the readback signals determined from the previous block. The fixed value of gain is then used to recover the user data from the affected data block.

Holding automatic gain control levels during read error recovery in a

An apparatus and method for optimizing detection thresholds used to identify addresses of tracks in a disc drive having a head and a disc upon which a plurality of tracks are defined, the tracks including track address fields in which track address information is stored. A comparator is provided which generates track address sequence signals in response to a corresponding plurality of readback signals obtained as the head is maintained in a fixed relationship to a selected track. A demodulator identifies erroneous track address sequence signals therefrom and increments a count in an accumulator for each detected, erroneous signal. A detection threshold circuit sequentially provides the comparator with a set of detection thresholds from a population of detection thresholds, each of which are used in turn by the comparator. An optimal set of thresholds is thereby selected for use by the disc drive in accordance with the relative number of erroneous track address sequence signals accumulated for each of the detection thresholds from the population.

Optimizing track address detection in a disc drive

A disc drive data recovery system for recovering data from a magnetic disc having asperities is disclosed. The data recovery system includes a magnetoresistive head for reading magnetically encoded data from the magnetic disc and providing in response a signal indicative of the magnetically encoded data. Contact between the magnetoresistive head and an asperity corrupts the signal such that the signal contains thermal asperity noise. The data recovery system includes an asperity recovery filter coupled to the magnetoresistive head for receiving the signal from the magnetoresistive head and reducing the thermal asperity noise in the signal.

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Oklahoma City, OK, United States of America

Ke Du