Servo data recovery circuit for disk drive having digital embedded sector servo

In a disk drive including:

• a base, a storage disk rotating relative to the base at a predetermined angular velocity and defining a multiplicity of concentric data tracks, each track for storing user data, and a plurality of radially aligned, embedded servo sectors interrupting the data tracks and containing a plurality of servo information fields comprising a servo sync field, a servo address mark field, a binary track number field and plural track centerline correction burst fields, a data transducer head for reading data from the tracks and servo information fields, and for writing data to the tracks, and an electromechanical head positioner means within a head positioner servo loop for controlling the position of the data transducer head during track seeking operations during which the head is moved from a departure track to a destination track, and during track following operations during which the head is maintained in alignment with a selected data track being followed, the head positioner servo loop including:
• a servo field decoder including an internal servo timer means and connected to the data transducer head for detecting and decoding said servo sync field, said servo address mark field and said binary track number field, for controlling timing of sampling of signals read from said plural centerline correction burst fields in said servo sector, and for resetting said internal servo timer means upon detection of the said address mark pattern,
• sample and hold means connected to the data transducer head and controlled by the servo field decoder for sampling and holding amplitudes of the signals read from said centerline correction burst fields,
• analog to digital conversion means connected to the sample and hold means for converting held amplitudes into digital head position values, and
• programmed digital processor means connected to the servo field pattern decoder and to the analog to digital conversion means,
• the servo field pattern decoder comprising a master state machine and a plurality of slave state machines connected to the master state machine and including:
• internal clock generator means connected to the internal servo timer means for generating a reference clock signal at a nominal servo sector information data rate,
• raw data synchronizer means responsive to the reference clock signal for receiving and framing raw servo data pulses read by the data transducer head within periods of the reference clock signal into clock-aligned asynchronous digital servo data in which flux transitions become data aligned with the reference clock within plus or minus one clock interval of the nominal servo sector information data rate,
• a sync field and servo address mark field slave state machine activated by the master state machine and connected to the internal clock generator means and to the raw data synchronizer means for detecting a plurality of predetermined first digital servo data patterns comprising the sync field and for detecting a plurality of predetermined second digital servo data patterns comprising at least an initial portion of the servo address mark field from the clock-aligned asynchronous digital servo data and for signaling detection of said first and second patterns to the master state machine,
• a data reader slave state machine activated by the master state machine and connected to the internal clock generator means and to the raw data synchronizer means for detecting from the clock-aligned asynchronous digital servo data third digital servo data patterns comprising track number bits of the track number field and for sending each of the detected track number bits to the master state machine,
• the servo timer means including a servo sector timer for timing recurrence of each servo sector as timed from detection of a servo address mark in a preceding servo sector, and a delay timer for timing delays associated with arrival and duration of at least one of said servo information fields, and
• the master state machine being responsive to said servo sector timer means to locate the beginning of each servo sector for activating said sync field and servo address mark field pattern slave state machine, and for subsequently activating said data reader slave state machine upon detection of the plurality of predetermined first and second digital servo data patterns, and being responsive to said delay timer for marking in time said centerline correction burst fields within said servo sector and for controlling the sample and hold means, and for detecting a servo address mark from patterns detected by said sync field and servo address mark field pattern and the data reader slave state machine and for thereupon resetting said servo sector timer means and for accumulating each track number bit of said track number detected by said data reader slave state machine in a track number register and for providing the track number accumulated in the track number register to said programmed digital processor means,
• the programmed digital processor means including calculation means for calculating head position control values from the track number and from the digital head position value, and
• digital to analog conversion means connected to the programmed digital processor means for putting out the head position control values as analog driving signals to said electromechanical head positioner means.