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Perpendicular recording is an alternative to longitudinal recording that shows promise in mitigating the super-paramagnetic limit. This channel passes DC and thus presents challenges to the read channel design. Compounding the problem, the MR head signal is susceptible to thermal asperities which manifest as low-frequency disturbances. We compare the performance of a DC-coupled PRML channel architecture which uses a non-DC-free target with a first-order DC loop to remove low-frequency disturbances to that of an alternate architecture that uses a DC-free target. We show through analysis and simulation results that the former architecture degrades with increasing latency of the DC loop and performs worse than the DC-free target for large latencies. In addition, the detection performance with DC-free target can be improved by the use of a block code with single parity bit.

Nonlinear transition shift (NLTS) and partial erasure (PE) are two channel nonlinearities that degrade bit-error-rate (BER) performance of detectors at high den sities. In this paper, we compare BER performances of par tial response maximum-likelihood (PRML) detectors de veloped for (0, k) run-length-limited (RLL) coded channels with multi-level DFE (MDFE) family detectors at different levels of nonlinearity. Bit-by-bit simulations indicate that the MDFE family detectors are relatively robust to NLTS and PE compared to the PRML detectors. Results also show that the M3DFE detector, an advanced detector in the MDFE family, outperforms the other detectors at high densities under ,channel nonlinearities. Index Terms--Chan'nel nonlinearity, MDFE, PRML . Lor n1zian channel PE: 10% at PW50/2.5 User Denaty . Fig. 5. Constant BER curves with 10% PE at PW50/2.5