Dynamic magnetic information storage or retrieval – General processing of a digital signal – Head amplifier circuit
Patent
1997-10-29
2000-09-05
Faber, Alan T.
Dynamic magnetic information storage or retrieval
General processing of a digital signal
Head amplifier circuit
360 49, 360 65, 360 53, G11B 509
Patent
active
06115198&
ABSTRACT:
A partial response class-IV (PR4) sampled amplitude read channel is disclosed for detecting user data and embedded servo data. The detected servo data is encoded using a novel servo code capable of accurately decoding detected codewords representing servo track address during seek operations, even when the recording head flies between two adjacent tracks, and capable of correcting errors in the detected codedwords caused by noise in the read signal, such as inter-symbol interference. In one embodiment, the servo code corrects certain minimum distance error events, such as a bit shift error event, associated with a trellis type sequence detector. To achieve the equivalent effect of a conventional Gray code, the codewords are arranged such that adjacent track addresses differ by a number of bits relative to the minimum distance error events corrected. In this manner, when the recording head spans two adjacent tracks during a seek operation, the ambiguity in the detected codeword will be resolved in favor of one of the adjacent track addresses. To further increase performance, the servo data PR4 sample values are converted into an EPR4 response and detected with a sliding threshold detector. This modification provides the same performance gain as a PR4 sequence detector matched to a d=1 constraint, but at less cost. One of the PR4 sliding threshold detectors for detecting user data can be advantageously shared to detect the servo data-the only additional hardware required is a 1+D filter for converting the PR4 samples of the servo data to EPR4 samples.
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Bliss William G.
Reed David E.
Cirrus Logic Inc.
Faber Alan T.
Sheerin Howard H.
Shifrin Dan
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