Readback channel equalization in digital magnetic recording

In order to attain high transfer rates and/or high recording density in digital magnetic recording, a new equalization technique has been developed. It is applicable to a readbacak channel employing a widely used inductive type head and suppresses head resonance noise and high band pre-amplifier noise. The essentials of the equalization are to tune the damping coefficient of parallel resonance at the head-to-pre-amplifier interface less than the conventional value of1/√2, and then, to equalize it to1/sqrt{2}in a later step using a simple equalizer. When combined with pulse slimming by cosine equalization, intersymbol interference is reduced and signal-to-noise ratio is simultaneously improved. This technique was effectively applied to high transfer rate magnetic disk drives and attained a more than doubled signal detection margin at a transfer rate of 2MB/s in NRZI code.