Time measurements of amplitude and bit shift in thin metallic media

Improved models for media noise are a prerequisite for the design of recording Channels that utilize an increased fraction of the information capacity (linear bit density) available to a given head/disk interface. Noise measurement techniques using power spectral density or RMS noise power inherently assume that all noise sources are stationary and, thus, cannot accurately predict the time-varying statistics of a non-stationary noise process. Studies have indicated that noise in metallic thin-film media is localized in the transition regions; hence, it is not a stationary process. Therefore, we have chosen to characterize media noise by direct time measurement of the readback voltage. In this paper we model thin metallic media noise by assuming that the magnetic transitions experience random variations in both position and width. A time measurement technique was employed to estimate the second order statistics of width and position of isolated readback pulses in 3 different samples of metallic thin-film media. The RMS noise estimated from the model and time measurements of the sample statistics accurately predicts the RMS noise measured by a spectrum analyzer, supporting the validity of the proposed model.