Fault tolerant sync mark detector enabled relative to a frequency of an acquisition preamble for sampled amplitude recording

摘要

A sampled amplitude read channel reads data from a magnetic medium by detecting digital data from a sequence of discrete time sample values generated by sampling an analog read signal from a read head positioned over the magnetic medium. The digital data comprises a preamble field followed by a sync mark followed by a data field. Timing recovery in the read channel synchronizes to a phase and frequency of the preamble field and a sync detector detects the sync mark in order to frame operation of an RLL decoder for decoding the detected data field. To decrease the probability of early misdetection, the sync mark is chosen to have minimum correlation with shifted versions of the sync mark concatenated with the preamble field. To further increase the fault tolerance, the sync mark detector is enabled by timing recovery relative to the end of the preamble field. A state machine in timing recovery generates expected sample values used to acquire the preamble field, and a current state of the state machine indicates when the preamble ends relative to a predetermined clock interval. In this manner, the search for an appropriate sync mark need only look for minimum correlation during shifts at the predetermined clock interval, thereby increasing the fault tolerant characteristic of the sync mark.