Synchronous detection of wide bi-phase coded servo information for disk drive

#The present invention relates to apparatus and methods for storing, detecting, and synchronously detecting servo information stored on disk drive media, and in particular to apparatus and methods useful within partial response, maximum likelihood detection channels and magnetic disk media.

#By reading servo information recorded within data tracks on a disk surface, a disk drive head positioner servo system is able to estimate data transducer head position. The recorded servo information typically includes track (i.e. cylinder and head) addresses and servo bursts. Each circumferential data track on a disk surface has a unique track address, which is recorded in servo sectors embedded in the track, and servo burst patterns frequently repeat every two or more tracks. When a disk drive is seeking to a radial track location, the track addresses are used as coarse positioning information to approximately estimate the position of the read head and the servo bursts are used as fine positioning information to position the head precisely on the desired radial location.

#At seek time while reading track addresses, the head may be positioned between two adjacent tracks. In this situation, the head may receive a superposition of signals from both tracks. One solution to this ambiguity is to encode the track addresses into Gray-coded addresses so that the encoded addresses of any two adjacent tracks differ from each other by only in a single bit position. With this solution, when the head is reading between two tracks, the ambiguity after decoding the address is one track, and an error of one track can be resolved during seek settle time, by reference to the servo burst or fine-position pattern.

#In the Drawings:

#FIG. 1 is a block diagram of a disk drive read channel providing PR4 and EPR4 targets.

#FIG. 2 is a schematic diagram of a recording surface of a disk in the disk drive.

#Turning to FIG. 1, a disk drive 10 incorporates a programmable and adaptive PR4,ML read channel. The disk drive 10 may be one of a variety of embodiments, such as that disclosed in commonly assigned U.S. Pat. No. 5,341,249 to Abbott et al., entitled: "Disk Drive Using PRML Class IV Sampling Data Detection with Digital Adaptive Equalization", the disclosure thereof being incorporated herein by reference. (This patent is the parent of the Abbott et al. U.S. Pat. No. 5,345,342, referenced hereinabove.)

#The drive 10 includes at least one data storage disk 16. As is conventional, a data transducer head 26, for example, a magneto-resistive head, is associated in a "flying" relationship over a storage surface of each disk 16. The head 26 is positioned relative to selected ones of a multiplicity of concentric data storage tracks 71 defined on each storage surface of the rotating disk 16, see FIG. 2.

#Embedded servo patterns are written in a conventional servo writing process during drive manufacturing on selected data storage surfaces of the disk 16, see FIG. 2, for example, in accordance with the methods described in a commonly assigned U.S. Pat. No. 5,170,299, the disclosure of which is incorporated here by this reference. Alternatively, the drive 10 may self-write some or all of its servo patterns during a post-assembly servo writing process.