Patent ID: 7830766

Claim:
A data reproduction apparatus for reproducing recorded data from an optical disk by using a PRML method, the recorded data of the optical disk being recorded in recording marks arranged with a pitch less than a diffraction limit, the data reproduction apparatus comprising: an optical head including a light source, an optical system having an objective lens for condensing light emitted from the light source to the optical disk, and a photodetector for receiving light reflected from the optical disk; a signal generation circuit for generating an RF signal from a signal output from the photodetector; a waveform equalizer for equalizing a waveform of the RF signal to a waveform having a predetermined partial response characteristic of the PRML method; a pattern compensation memory for storing a plurality of compensation values corresponding to bit patterns of the recording marks; a path memory for storing past determination results corresponding to a plurality of states according to the PRML method; and a branch metric calculator for calculating likelihood of the equalized RF signal by using one of the plural compensation values in accordance with the past determination results stored in the path memory; and wherein said path memory is arranged to output a provisional decision result to said pattern compensation memory, such that the provisional decision result is used in the calculation of a branch metric by the branch metric calculator.