A data-dependent equalizer for an optical storage channel

Although information storage devices have increasingly faster data transfer rates and higher storage capacities at a lower cost, equalizing such devices often causes serious noise enhancement. Therefore, this work presents a novel equalization method capable of reducing serious noise enhancement and also combating the intersymbol interference (ISI) effects. The equivalent channel which combines the storage channel response and the power spectral density of the recorded run-length-limited (RLL) sequences is equalized to a desired response with cutoff frequency Ωc, where the determination of Ωc compromises noise enhancement and ISI. Two quantified values, SNRo(Ωc) and RISI(Ωc), related to noise enhancement and ISI respectively are derived to explicitly determine Ωc. In addition, the type II filter is demonstrated to be best suited for implementing the proposed equalizer. The readback signal from a digital versatile disk (DVD) is obtained and simulated. Simulation results indicate that the noise enhancement of the proposed equalization method is significantly reduced over that of the conventional one.