BER evaluation in an optical disk decoder by counting a number of signals after PRML having a likelihood below a threshold.

摘要

A signal evaluation device for evaluating a decoded signal of maximum likelihood decoding includes: a differential metric circuit (9) for finding differential metrics; comparators (10,11) for judging whether a difference of differential metrics (9) exceeds a predetermined threshold; counters (12,13) for counting respective output pulses of the comparators (10,11); and a controller (14) for finding the probability of the differential metrics (9) falling at or below the predetermined threshold, based on the number of measured samples and the number of samples counted by the counters (12,13), and processing the probability by arithmetic operations so as to obtain an index of signal evaluation. With this arrangement, signal evaluation devices for evaluating a recording medium or a recording medium driving device can have a simpler structure and can perform evaluations in a plurality of PR modes.