New adaptive equalization method for PRML system using sequenced amplitude margin

Abstract

Partial response maximum likelihood (PRML) detection has recently been put into practical use to achieve high-density optical disk systems. In PRML detection, a reproduced signal is equalized to a known partial response. If the transfer function of the equalizer is fixed, it is not always optimum under the condition that the frequency characteristic and the signal-to-noise ratio of the readout system change due to the diversity of disks or the effect of tilt, resulting in deterioration of bit error rate (BER). Therefore, adaptive equalization methods, which adjust the transfer functions of equalizers in changing conditions, are effective. However, minimum square error (MSE) method [1], which is one of the most conventional methods, cannot obtain the best BER performance because it does not fully take into account the PRML process.