A Simplified Model for Signals in the Magnetic Recording Channel and a Method for Characterization

The magnetic recording channel is characterized by the behavior of the readback signals and by the interference and noise that is inevitably present. Here we focus on just the signal behavior. The signals are deterministic by definition, but are subject to linear and nonlinear distortions. We propose a simplified model that includes the mechanisms that cause nonlinear distortion during writing and during reading. The writing process is modeled as a simple transition-shift proportional to the linear sum of effects from prior NRZ bits. The reading process is modeled as a simple memoryless polynomial transfer function. The 'extracted dipulse' is a technique widely used in magnetic recording to characterize both the linear and the various nonlinear components in the readback signal. However, it is not straightforward to map the results back to any simple channel model. The distortion mechanisms act upon an initially linear channel response but the distortions affect the subsequent measurement of that linear response. An iterative approach is presented here where initial estimates of the channel response and nonlinearities are corrected and gradually refined using the known effects of the nonlinear mechanisms on the linear response. This approach is validated on some synthetic waveforms and then tested on several real magnetic recording components and is shown to reasonably capture the channel behavior.