A simplified, low power 25 MHz CMOS equalizer for disk drive read channels

After an extensive study of waveforms measured on several popular disk head-medium combinations, we have found that the combination of the head and medium itself often distorts the read pulse in phase, and a simple equalizer correcting for this phase distortion yields dramatic improvements in bit error rate. This equalizer surprisingly requires only four poles and one zero in the right-half s-plane to perform as well as a conventional flat group delay filter, and its constellation seems to apply to all the packing densities and drive types we have evaluated. We describe here a 2-/spl mu/m CMOS monolithic implementation of this new equalizing filter, with a maximum pole frequency of 25 MHz and an active core power dissipation of only 40 mW from a 5 V supply, including all tuning and subsidiary circuits.