Viterbi detector architecture for high speed optical storage

We describe the architecture of a Viterbi detector in a partial response maximum likelihood (PRML) system of high speed optical storage. In the high speed optical system (CDROM 30× or DVD ROM/RAM 4.5×), the analog signal from an optical pick-up is far from an ideal response. We have regarded it as an intersymbol interference (ISI) and solve this problem with the PRML system including a Viterbi detector. Eight-to-fourteen modulation (EFM) and EFM+ code used in the DVD or CDROM, have a run length limited (RLL) characteristic, and its trellis diagram is different from the ordinary one. Several states and branches can be deleted. The Viterbi detector is designed for a 5 bit A/D converter up to a 120 MHz clock speed. A register exchange structure and a special overflow control logic are used for a high speed continuous input data stream.