PRML sampled data channel synchronous servo detector

A synchronous servo data detection subsystem for a partial response, maximum likelihood sampled data channel for a hard disk drive including a rotating data disk storage surface defining a multiplicity of concentric data tracks and a plurality of radially extending servo sectors, each servo sector including a servo synchronization field followed by a synchronous servo address mark field defining a unique recording pattern, followed by fields providing the coarse and fine head position information, a data head adjacent to the data storage surface for reading and writing data signals from and to the storage surface, a voice coil actuator structure for positioning the data transducer head at each selected data track, a head position servo loop for controlling movement of the actuator structure, the sampled data channel connected to receive, synchronously sample and decode into digital data the analog signals read by the head during the data reading operations, the synchronous servo data detection subsystem being operative as the data head passes over a said servo sector for sampling and detecting the synchronously recorded coarse and fine head position information and for supplying the detected servo information to the head position servo loop, and comprising:

• timing loop means for synchronizing the sampled data channel to the servo synchronization field to provide synchronous samples from the servo sector,
• a synchronous servo address mark pattern detector connected to an output of the sampled data channel for detecting the unique recording pattern and for thereupon generating a servo address mark found signal,
• a synchronous coarse head position information detector connected to an output of the sampled data channel responsive to the address mark found signal for detecting and accumulating coarse bits comprising the coarse head position information, and
• a synchronous fine head position detector connected to the sampled data channel for detecting the fine head position information.

An embedded servo sector pattern for use in a disk drive including a disk rotating at a constant angular velocity, a data transducer head positioned by a servo loop relative to concentric data tracks arranged in a plurality of concentric data zones defined on a surface of the rotating disk, each zone having a data transfer rate adapted to disk radius, and a partial-response, maximum likelihood data channel connected to the data transducer head, the pattern comprising:

• a series of circumferentially spaced apart, radial boundaries marking beginning of a series of embedded servo sectors, each servo sector within each concentric track including:
• a preamble pattern comprising a predetermined number of 1/4T magnet patterns recorded at a highest synchronous data transfer rate available within each said zone,
• a servo address mark magnet pattern following the preamble pattern,
• a plural-bit Gray coded track identification magnet pattern, and
• wherein the preamble pattern, the servo address mark pattern and the Gray coded track identification field are detected synchronously during a data reading operation by a maximum likelihood detector of the partial-response, maximum-likelihood data channel during playback from the disk.

A method for synchronously decoding head positioning servo information recorded within embedded servo sectors of a hard disk drive including a rotating data storage disk, a data transducer head positionable at concentric data tracks formed on a storage surface of the disk by a head position servo loop, and a synchronous digital data channel connected to the data transducer head for providing plural synchronous digital data samples of each analog magnetic flux transition read from a data storage surface, each embedded servo sector defining a series of circumferentially spaced apart, radial boundaries marking beginning of a series of embedded servo sectors, each servo sector within each concentric track including:

• a preamble pattern comprising a predetermined number of 1/4T magnet patterns recorded at a highest synchronous data transfer rate available within each said zone,
• a servo address mark magnet pattern following the preamble pattern,
• a plural-bit Gray coded track identification magnet interleave pattern, the method for synchronously decoding the head positioning servo information comprising the steps of:
• detecting arrival of each embedded servo sector at the data transducer head,
• synchronizing a timing loop to the preamble pattern to provide a sample clock,
• controlling timing and phase of an analog to digital conversion means with the sample clock for sampling magnetic flux transitions read from the embedded servo sector being read to provide synchronous digital data samples,
• passing the synchronous digital data samples through a digital finite impulse response filter to provide conditioned digital data samples,
• decoding within a synchronous interleave maximum likelihood decoder the conditioned digital data samples into coded data groups,
• decoding the coded data groups with a post coder into a stream of binary servo data,
• detecting the servo address mark magnet pattern within the stream of binary servo data with a synchronous servo address mark detector to provide a servo sector clocking signal,
• resetting a timing means with the servo sector clocking signal, for marking in time the location of the Gray coded track identification magnet interleave pattern, and
• decoding the Gray coded track identification magnet interleave pattern within the stream of binary servo data with an interleave Gray code decoder to provide the coarse head positioning information to the head position servo loop for positioning the head.