Design, implementation and performance evaluation of an MDFE read channel

A 100 Mb/s (1,7) MDFE (multi-level decision feedback equalization) read channel has been designed, prototyped, and tested on a spinstand. It is made up of an analog forward equalizer consisting of two biquads, a comparator, a feedback equalizer consisting of 6 taps plus an analog exponential decay circuit, timing/gain/dc-offset control circuits, an analog PLL and VCO, and VGA. An analytical technique has been developed for equalizer design. It incorporates certain key constraints for reducing hardware complexity as well as error propagation. The measured bit-error-rate and off-track performance demonstrate the robustness of the equalizer over a broad range of user densities. The experimental results confirm that MDFE is a viable signal detection technique for achieving high density and high data rate magnetic recording.