Characterization and spectral equalization for hight-density disk recording

For a 3350 type head/disk interface, the amplitude spectrum of an experimental characteristic pulse deviates slightly from the idealized Lorentzian distribution in the signal bandwidth; but the phase spectrum of the experimental pulse is quite distorted from the desired linear phase, causing the widely observed asymmetrical time-domain waveform. A quantitative characterization and comparison are presented and individual transfer functions for ideal linear equalization are proposed. To remove the intersymbol interference, i.e., the linear portion of the distortion, from the playback signal of a high-density system, several cosine-power-law spectral candidates, with minimized noise enhancement and the capability of restoring amplitude loss and timing error, are explored. A unified relationship for the entire family of cosine-power-law spectral shapes and their bandwidth tradeoffs are identified, allowing for optimum read equalization at a tolerable signal-to-noise penalty. This is a useful tool for exploring practical density limitations of any given head/disk interface.