Multi-level decision feedback equalization for saturation recording

An impediment to the practical use of fixed-delay tree search with decision feedback (FDTS/DF) for retrieving data from hard disk drives is that four additions and one multiplications must be evaluated in one clock cycle. It is shown here that on recording channels using 2/3(1,7) run-length-limited (RLL) coding, a detector achieving the performance of FDTS/DG can be implemented with a two-tap transversal filter. The feedback loop can be rearranged so that this transversal filter no longer resides in the forward path of the feedback loop. Instead, its transfer function is incorporated into the specification of the forward and backward equalizers. This modification leads to a simpler equalizer architecture in which the slicer performs binary decisions on a multilevel signal. Implementation issues pertaining to phase detection, gain detection, DC detection and adaptive equalization using a least-mean-squared (LMS) technique are addressed. Simulation results are given