Partial Response Maximum Likelihood (PRML)

PRML is currently the industry standard high performance channel, replacing the classic peak detector. The readback signal is equalized so to a class IV partial response as shown to the right so that the samples are {1,0,-1}. Because only these three samples are signficant, the corresponding maximum likelihood detector implemented with the Viterbi algorithm requires only four states (below). Because the second sample in the response is zero, it is possible to operate two two-state Viterbi detectors in an interleaved manner. This arrangement, which is used in commercial products, provides for higher operating speeds because each of the two detectors needs only to operate at half the sample rate.

For more information, see

• R, Cideciyan, F. Dolivo, R. Hermann, W.Hirt and W. Schott, "A PRML system for digital magnetic recording," IEEE J. Sel. Areas Commun., vol. 10, no. 1, pp. 38-56, Jan. 1992.
  
  
• K. D. Fisher, W. L. Abbot, J. L. Sonntag and R. Nesin, "PRML detection boosts hard-disk drive capacity," IEEE Spectrum, vol. 33, no. 11, pp. 70-76, Nov. 1996.

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Last modified Mar 2007