An event-driven maximum-likelihood peak position detector for run-length-limited codes in magnetic recording

Many of the current digital magnetic recording devices use a peak position data detector, making a local decision with respect to a given data-derived clock window. As a consequence of an increased linear density with large intersymbol interference (ISI) and peak shifts, more sophisticated linear and nonlinear detection schemes will be necessary which take advantage of the correlation between the pulses. Besides equalization and decision feedback, the maximum-likelihood sequence estimation applied to pulse amplitude detection (PAM) [1] seems to give superior performance. As an alternative this paper will describe a Viterbi detector [2] working on pulse position data (PPM). This detector could be added to conventional implementations without redesigning the whole magnetic readback channel. Due to the nonlinearity of the PPM-channel and the fact that the restrictions of run-length-limited (RLL) codes [3] will be imbedded, the design and analysis will differ from known results.