A simplified decision-directed threshold scheme for EPR4 channel detection

The ever-increasing quest to improve the storage density in digital magnetic recording channels has led to the adoption of some partial response signaling (PAS) polynomials as the pertinent equalization target; for instance, the class-IV PRS polynomial (PR4) and the extended class-IV PRS polynomial (EPR4). The PR4 model serves, as a compromise between storage density and hardware complexity, but the EPR4 is a better model for a very high-density recording channel; nonetheless it has a greater hardware implementation complexity. In this paper, it is shown that a decision-directed threshold approach could be applied to the EPR4 channel detection to reduce the complexity of implementation. Also, it is revealed that by using a computationally efficient threshold definition, a versatile detection scheme could be achieved for this complex, eight states, and five-level output EPR4 channel.