Write equalization in high-linear-density magnetic recording

For many years, equalization has been used on the read side of a magnetic-recording channel to obtain a desired signal shape at the detector. Compensation on the write side has, for the most part, been limited to moving transition locations to offset read-signal peak shifts. This paper presents a new method of equalization on the write side through the addition of pulses at strategic locations on the write waveform. The resulting write current continues to be a two-level signal, so ac bias is not required. A linear transfer function can be derived for these write equalizers. This enables the recording-channel designer to partition the equalization more optimally between the write and read sides. The principal benefit of write equalization is that the read-flux-amplitude differences between high and low densities are significantly reduced. This permits maximum use of the linear operating region of the magnetoresistive read head. By providing high-frequency boosts on the write side, write equalization can reduce high-frequency noises at the read detector. Test results of channel linearity, as well as read signal waveshapes, are presented.