Experimental study of reader nonlinearity in perpendicular recording using pseudorandom sequences

The reader nonlinearity is characterized using the pseudorandom sequence method. A simple model is developed and simulated waveforms are used to substantiate the physical interpretation of the echo pulse that corresponds to the reader nonlinearity. It is shown that the measured reader saturation effect increases relatively with the linear density when the linear density is not extremely high. Depending on the extent of the reader saturation, the measurement of nonlinear transition shift (NLTS) can move from positive to negative even though the intrinsic NLTS is positive in perpendicular recording. The optimal write precompensation is dependent on both NLTS and reader saturation. It is also shown that as the linear density goes higher, the amplitude exhibits more asymmetry due to the intrinsic reader asymmetry and the reader asymmetry can change sign.