Method and apparatus for removing baseline shifts in a read signal using filters

#The present invention relates to direct access storage devices (DASD) of the type using a digital or sampled recording channel. In particular, the present invention is in the field of magnetic recording technology using magneto-resistive (MR) heads and Partial Response channels and methods for compensating for shifts in recording levels due to shifts in DC levels and MR head temperature.

#Magnetic recording of both analog and digital information has been known and practiced in the art of audio reproduction and computer secondary storage. In magnetic recording, moving media such as a tape or disk platter may be coated with a ferro-magnetic oxide or metal coating. Information may be recorded with an electrically biased head which may be modulated with an information signal and which, in response, may generate a modulated flux field. Since a recording head may be in close proximity to a section of recording media, flux changes may cause ferro-magnetic particles in recording media to align accordingly. Conversely, information may be read from media by sensing alignment of flux fields representing recorded information.

#For information comprising digital data, recording heads may write and read flux reversals. Flux reversals, in conjunction with timing and coding information, may indicate presence or absence of a data bit. Methods for decoding flux reversals corresponding to recorded information and synchronizing bit recovery timing are well known in the art. In conventional head based recording, data density is based on parameters such as read head size and sensitivity. Also, retentivity--tendency of magnetic materials to retain residual magnetic flux and resist changes in flux alignment--of head materials may limit the rate at which a conventional head could sense a flux reversal and thereby limit maximum areal density readable by a head. Areal density refers to number of bits of information capable of being recorded within a linear measure of a particular magnetic recording medium.

#FIG. 1 is a block diagram of illustrating a 1-D sampled filter block disposed within an MR head read signal processing circuit of the present invention.

#FIG. 2a is a graph illustrating a normal read signal using Sync Field, Sync Bytes, and random customer data.

#FIG. 2b is a graph illustrating a normal continuous time filter output.

#The descriptions herein are by way of example only illustrating the preferred embodiment of the present invention. However, it should be appreciated that the method and apparatus of the present invention may be applied in a similar manner in other embodiments without departing from the spirit of the invention.

#FIG. 1 is a block diagram of illustrating a 1-D sampled filter block of the present invention. Rotating magnetic media 100 may comprise a magnetic disk platter with a ferro-magnetic or other metal or metal oxide coating susceptible to storing information as magnetic flux signatures. Rotating magnetic media 100 may contain such information as magnetic flux signatures. Head element 101 may comprise a magneto resistive (MR) head element or other element which may be continuously biased with a sense current and may respond to a magnetic field with a corresponding change in material property affecting resistance in linear or logarithmic proportion.

#Head element 101 may be placed in close proximity to rotating magnetic media 100 by a head support mechanism known in the art and may produce a signal which is input to preamp 102. Preamp 102 may supply a continuous sense current to head element 101 and may amplify read signal 119 generated in response to magneto-resistive action between head element 101 magnetic information encoded upon rotating magnetic media 100. Output of preamp 102 may be input to Variable Gain Amplifier, (VGA) 103. VGA 103 may output an amplified read signal to continuous time filter block 104 based on changes in gain correction signal 118 supplied to VGA 103 from gain tracking loop 113 and gain acquisition loop 114. Output of VGA 103 may be input to continuous time filter block 104 which may comprise a 7 pole, 2 zero equiripple filter for standard signal conditioning known in the art. Output of continuous time filter block 104 may be input to sampler 105 for sampling amplified read signal level and providing sample out signal 120 to sampled filter block 106, MUX 107, gain loop acquisition block 114, and timing loop acquisition block 116.