Adaptive characterization of write-precompensation circuits

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.