An adaptive DFE for storage channels suffering from nonlinear ISI [magnetic recording]

The authors explore the magnetic recording channel in some detail and describe some of the characteristics of the channel that point to the random access memory decision feedback equalizer (RAM-DFE) as a suitable detection method. The structure and adaptation of the RAM-DFE are described. The RAM-DFE with the signed-LMS (least mean square) algorithm and the constrained step size (μ=2^-n) is shown to be well suited to the magnetic storage application. Not only does RAM-DFE outperform the conventional DFE under many circumstances, but it is also more conducive to a high-speed digital implementation, making the RAM-DFE appropriate for the higher data rates (linear densities) that its improved performance facilitates. Preliminary investigations indicate that the RAM-DFE can be implemented in 1.6-μm CMOS on a single VLSI chip (about 50000 transistors) with a sampling (data) rate of 54 MHz