Comparison and optimization of digital read channels using actual data

Various digital equalization and detection schemes have been proposed for disk drive read channels and simulated as a Lorentzian channel [Moon and Carley, 1990]. With the design of linear recording densities greater than two channel bits per half amplitude pulsewidth (PW50), concerns over nonlinear distortions, such as partial erasure, require channel simulation with techniques other than the linear Lorentzian model. The paper describes the considerations a disk drive designer faces when optimizing the performance of digital read channels with a channel simulator that uses actual data obtained from a disk file environment. This real data channel simulator accomplishes equalization and detection in software using sampled data from a spinstand allowing the flexibility of investigating the performance of different channel schemes without having to build expensive hardware. Sample offtrack data for selected channels at various user (information) densities are shown, along with ontrack Lorentzian simulation. Goodness numbers for each channel are presented which approximately minimize bit error rate (BER) in a quick way, providing algorithms for a disk drive to check channel quality during adaptive adjustments