Identification of nonlinear write effects using pseudorandom sequences

Nonlinear distortion causes significant degradation at high linear recording densities. Nonlinear distortion cannot generally be corrected by equalization and is thus particularly important to correctly identify and quantify. A technique is described which is easily applied, clearly separates linear from nonlinear effects, can be related to the underlying physical processes, and provides a good basis for modeling the channel. The technique involves the recording of a binary pseudorandom sequence and the capture and processing of the playback waveform. The technique is used to identify four distinct nonlinear effects and to examine their behavior as a function of flying height and record current.