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Frame synchronization for viterbi detector    
United States Patent6493162   
Link to this pagehttp://www.wikipatents.com/6493162.html
Inventor(s)Fredrickson; Lisa (Seattle, WA)
AbstractA method and apparatus for synchronizing a Viterbi detector to data frames corresponding to code words read from of a medium is provided. A timing pattern and a synchronization pattern is provided, the detector is synchronized to the synchronization pattern based upon the timing pattern, the detector is further synchronized to the data frame based upon the synchronization pattern



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Drawing from US Patent 6493162
Frame synchronization for viterbi detector - US Patent 6493162 Drawing
Frame synchronization for viterbi detector
Inventor     Fredrickson; Lisa (Seattle, WA)
Owner/Assignee     Seagate Technology LLC (Scotts Valley, CA)
Patent assignment
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Publication Date     December 10, 2002
Application Number     09/205,871
PAIR File History     Application Data   Transaction History
Image File Wrapper   Patent Term   Fees
Litigation
Filing Date     December 4, 1998
US Classification     360/51 360/46 375/341
Int'l Classification     G11B  005/09
Examiner     Holder; Regina N.
Assistant Examiner    
Attorney/Law Firm     Westman, Champlin & Kelly, P.A.
Address
Parent Case     REFERENCE TO RELATED APPLICATION The present application claims priority from provisional application serial No. 60/067,673 filed on Dec. 5, 1997.
Priority Data    
USPTO Field of Search     360/46 360/51 375/262 375/265 375/341
Patent Tags     frame synchronization viterbi detector
   
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 Technical Review Submit all comments and votes
 Claims Submit all comments and votes
 


What is claimed is:

1. A method of synchronizing a Viterbi detector to data frames corresponding to code words read from a medium, the method comprising steps of:

(a) providing a timing pattern;

(b) providing a synchronization pattern in the timing pattern having a plurality of features;

(c) synchronizing the Viterbi detector to the synchronization pattern based upon the timing pattern; and

(d) synchronizing the Viterbi detector to the data frame based upon based upon identification of the plurality of features in the synchronization pattern.

2. The method of claim 1 including a time varying trellis in the Viterbi detector.

3. The method of claim 2 wherein the synchronizing step (d) comprises synchronizing the time varying trellis to the data frames based upon the synchronization pattern.

4. The method of claim 1 wherein the timing pattern comprises a sequence of alternating bit pairs, each bit pair comprising two bits of the same value.

5. The method of claim 1 wherein the Viterbi detector comprises a radix-4 Viterbi detector.

6. The method of claim 1 wherein the synchronizing step (c) comprises detecting polarity of the timing pattern.

7. The method of claim 6 wherein synchronizing to the timing pattern further comprises inserting a temporary offset in the timing pattern to align the detector with the bit pairs.

8. The method of claim 6 wherein synchronizing to the timing pattern further comprises determining the phase of the timing pattern.

9. The method of claim 8 wherein the timing pattern has four possible phases.

10. The method of claim 8 wherein synchronizing to the synchronization pattern comprises biasing the Viterbi detector based upon the phase of the timing pattern.

11. The method of claim 1 implemented in a disc storage system.

12. The method of claim 1 wherein the identification of the features is a function of an XOR.

13. The method of claim 1 wherein the synchronization pattern includes four distinguishing features.

14. The method of claim 1 wherein the features are separated by at least two bits.

15. The method of claim 14 wherein the at least two bits directly correspond to the timing pattern.

16. The method of claim 1 wherein the synchronization pattern is at least 30 bits.

17. An apparatus for synchronizing a Viterbi detector to a time varying data code read from a medium, comprising:

timing pattern synchronization circuitry adapted to determine a phase of a timing pattern in the data code;

synchronization signal detection circuitry operatively coupled to the timing pattern synchronization circuitry, adapted to identify a synchronization contained in the timing pattern signal containing a plurality of features in the data code based upon the phase of the timing pattern; and

data frame synchronization circuitry operatively coupled to the detection circuitry, adapted to synchronize the Viterbi detector to a data frame of the data code based upon identification of the plurality of features in the synchronization signal.

18. The apparatus of claim 17 wherein the Viterbi detector includes a time varying trellis.

19. The apparatus of claim 18 wherein the time varying trellis is synchronized to data frames by the data frame synchronization circuitry.

20. The apparatus of claim 17 wherein the timing pattern comprises a sequence of alternating bit pairs, each bit pair comprising two bits of the same value.

21. The apparatus of claim 17 wherein the Viterbi detector comprises a radix-4 Viterbi detector.

22. The apparatus of claim 17 wherein the synchronization signal detection circuitry detects polarity of the timing pattern.

23. The apparatus of claim 17 wherein synchronization signal detection circuitry further detects phase of the timing pattern.

24. The apparatus of claim 17 implemented in a disc storage system.

25. The apparatus of claim 17 wherein the data frame synchronization circuitry includes an XOR and the identification is a function of the XOR.

26. The apparatus of claim 17 wherein the synchronization signal includes four distinguishing features.

27. The apparatus of claim 26 wherein the features are separated by at least two bits.

28. The apparatus of claim 17 wherein the synchronization signal is at least 30 bits.

29. An apparatus for synchronizing a Viterbi detector to a time varying data code read from a medium, comprising:

means for determining a phase of a timing pattern in the data code;

means for identifying a synchronization signal in the timing pattern; and

means for synchronizing the Viterbi detector to a data frame of the data code.
 Description Submit all comments and votes
 


FIELD OF THE INVENTION

The present invention relates generally to information storage systems and, more particularly, to detection of data retrieved from storage in such systems

BACKGROUND OF THE INVENTION

Digital data magnetic recording, or storage and retrieval, systems store digital data by recording same in a moving magnetic media layer using a storage, or "write", electrical current-to-magnetic field transducer, or "head", positioned immediately adjacent thereto. The data is stored or written to the magnetic media by switching the direction of flow in an otherwise substantially constant magnitude write current that is established in coil windings in the write transducer in accordance with the data. Each write current direction transition results in a reversal of the magnetization direction, in that portion of the magnetic media just then passing by the transducer during this directional switching of the current flow, with respect to the magnetization direction in that media induced by the previous in the opposite direction. In one recording scheme, often termed non-return-to-zero inverted (NRZI), each magnetization direction reversal occurring over a short portion of the magnetic media moving past the transducer represents a binary number system digit "1", and the lack of any such reversals in that portion represents a binary digit "0".

Recovery of such recorded digital data is accomplished through positioning a retrieval, or "read" magnetic field-to-voltage transducer, (which may be the same as the storage transducer if both of these transducers rely on inductive coupling between the media fields and the transducer) or "head", is positioned to have the magnetic media, containing previously stored data, pass thereby. Such passing by of the media adjacent to the transducer permits the flux accompanying the magnetization reversal regions in that media either to induce a corresponding voltage pulse in forming an analog output read signal for that retrieval transducer or, alternatively, change a transducer circuit parameter to thereby provide such an output signal voltage pulse. In the coding scheme described above, each such voltage pulse in the read transducer output signal due to the reversal of magnetization directions between adjacent media portions is taken to represent a binary digit "1", and the absence of such a pulse in corresponding media portions is taken to represent a binary digit "0".

Digital data magnetic recording systems have used peak detection methods for the detection of such voltage pulses in the retrieved analog signal as the basis for digitizing this signal. Such methods are based on determining which peaks in that signal exceed a selected threshold to determine that a binary digit "1" related pulse occurred in the retrieved signal, and also use the times between those voltage pulses to reconstruct the timing information used in the preceding recording operation in which the data were stored in the magnetic media as described above. The analog retrieved signal is provided to a phase-locked loop forming a controlled oscillator, or a phase-locked oscillator or synchronizer, which produces an output timing signal, or "clock" signal, from the positions of the detected peaks in this analog retrieved signals Absolute time is not used in operating the data retrieval system portion since the speed of the magnetic media varies over time during both the storage operation and the retrieval operation to result in nonuniform time intervals, or nonuniform multiples thereof, occurring between the voltage pulses in the analog retrieved signal.

There is always a desire in magnetic recording systems to devote less of the magnetic media along a track therein to the storage of a bit to thereby permit increasing the density of the bits stored. The use of peak detection places a limit on the density of bits along a track because increasing that density beyond some point will lead to too much intersymbol interference which in turn leads to errors in the recovery of data using such peak detection methods. Because of this limit, recent increases in bit density along a track in a magnetic media have come with the acceptance of a controlled, or known, amount of intersymbol interference which, since known, allows detection of the pulses involved despite this interference. The read transducer analog output signal generated from the binary bits or symbols stored in the magnetic media is sampled with the resulting samples being converted to digital data, and the samples are taken at a rate which leads to more than one sample per pulse rather than the single sample per pulse which would be sufficient for peak detection if sampling was used therewith. Since each individual sample reflects only part of the pulse response, this process used in a system results in referring to such a system as a partial response system.

A digital data magnetic recording system typically comprises a bandpass data retrieval channel in that it is unable to transmit very low frequencies, and in that it has an upper frequency beyond which its transmission