Playback Signal Processing System Using Improved Waveform Correction for High Density Optical Disc

Abstract

A new playback signal processing system capable of large-capacity optical disc playback of over 25GB in the same optical format as the Blu-ray Disc has been developed. Generally, as optical disc capacity increases, the read-out signal of minimum pits is markedly degraded due to inter-symbol interference (ISI) from adjacent pits, asymmetries caused by pit-form distortion, and the frequency characteristics of optical transfer function (OTF). Partial Response Maximum Likelihood (PRML) is known to effectively improve ISI and asymmetries by compensating for these factors electrically. However, in high-density optical discs greater than 25GB, bit errors frequently occur even when PRML is applied. This proposed system consists of a PRML circuit and Improved Waveform Correction circuit that control only read-out signals of minimum pits more surely. Bit error rate (BER) measurements of the playback of a 30GB optical disc showed better BER performance. The system can be realized without major changes to the current PRML system.