Read channel issues in perpendicular magnetic recording

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.