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Adaptive characterization of write-precompensation circuits

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Adaptive characterization of write-precompensation circuits - Magnetics,null IEEE Transactions on IEEE TRANSACTIONS ON MAGNETICS, VOL. 39, NO. 4, JULY 2003 2109 Adaptive Characterization of Write-Precompensation Circuits Jan W. M. Bergmans, Senior Member, IEEE Abstract—Write-precompensation circuits are widely used in digital magnetic recording systems to counteract nonlinearities in the recording process. They act to shift transitions in the binary write signal in nonlinear dependence on neighboring bits. This paper develops a general and accurate technique for assessing the quality of these circuits. The technique permits joint assessment of the actual transition shifts introduced by the circuits and of data-dependent, periodic, and random jitter of the transitions. The action of a phase-locked loop (PLL) can be mimicked so as to characterize only the harmful portion of the jitter, namely the portion that is left behind by the PLL. Experimental results for a fifth-order write-precompensation circuit illustrate the merits of the technique. Index Terms—Adaptive filtering, digital storage, jitter, nonlin- earities, write precompensation. I. INTRODUCTION AT HIGH data rates and information densities, recordeddata patterns in digital magnetic recording systems can exhibit severe nonlinearities. Key causes for these nonlinearities are bandwidth limitations of the write path and demagnetizing fields in the recording medium [1]. Write-precompensation schemes are widely used to counteract these nonlinearities [2]–[5]. They act to shift the transitions of the binary write signal in nonlinear dependence on neighboring bits. This is generally done with mixed-signal electronic circuits. These circuits are programmable so as to be able to tailor the shifts to the conditions at hand. Performance of the recording system is quite sensitive to the accuracy of precompensation and to the jitter of the transitions. Broadly speaking, three types of jitter can be distinguished: • data-dependent jitter

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