Optical disk reproducing apparatus

Abstract

An optical disk reproducing apparatus is provided which is capable of supporting even a situation in which a reproduction signal characteristic is changed due to a factor other than recording density of an optical disk by using PRML of different constrained length and capable of improving reading accuracy. The optical disk reproducing apparatus includes a PRML circuit of a first constrained length (for example, 4) and a PRML circuit of a second constrained length (for example, 5). Equalization error values obtained during calculation of equalization learning in respective circuits are compared with each other in a determination circuit. Switching control of a switch is performed so that an output of one of the PRML circuits having a smaller equalization error value is selected.

1 . An optical disk reproducing apparatus comprising:
 a pickup configured to irradiate laser light to an optical disk and to convert reflected light thereof to an electric signal;   an analog front end configured to perform an analog processing to the electric signal outputted from the pickup;   a digitalization circuit configured to digitalize an analog signal outputted from the analog front end and to output a multi-level signal;   a first PRML processing circuit of a PRML method with a constrained length of m; and   a second PRML processing circuit of the PRML method with a constrained length of n   wherein the first PRML processing circuit includes:   a first equalization circuit configured to equalize the multi-level signal with a target signal of the PRML method with the constrained length of m;   a first reference-value generation circuit configured to generate a first target signal of the PRML method with the constrained length of m from a first equalization signal outputted from the first equalization circuit and a first binarization signal comprised of a maximum-likelihood decoded output;   a first adaptive learning circuit configured to determine a parameter of the first equalization circuit from the first equalization signal and the first target signal; and   a first maximum-likelihood decoding circuit configured to obtain the first binarization signal from the first target signal and the first equalization signal based on the PRML method with the constrained length of m,   wherein the second PRML processing circuit includes:   a second equalization circuit configured to equalize the multi-level signal with a target signal of the PRML method with the constrained length of n;   a second reference-value generation circuit configured to generate a second target signal of the PRML method with the constrained length of n from a second equalization signal outputted from the second equalization circuit and a second binarization signal comprised of a maximum-likelihood decoded output;   a second adaptive learning circuit configured to determine a parameter of the second equalization circuit from the second equalization signal and the second target signal; and   a second maximum-likelihood decoding circuit configured to obtain the second binarization signal from the second target signal and the second equalization signal based on the PRML method with the constrained length of n, and   wherein the optical disk reproducing apparatus includes:   a switch configured to select and output one of an output of the first maximum-likelihood decoding circuit and an output of the second maximum-likelihood decoding circuit;   a decoder configured to perform a decode-processing to an output of the switch and to output a reproduction data signal;   a circuit configured to perform one of obtaining and determination of information about a type and a reproduction speed of the optical disk reproduced or to be reproduced; and   a determination circuit configured to perform switching control of the switch between the output of the first maximum-likelihood decoding circuit and the output of the second maximum-likelihood decoding circuit based on the information about the type and the reproduction speed of the optical disk.   
     
     
         2 . The optical disk reproducing apparatus according to  claim 1 ,
 wherein the determination circuit is configured to perform control so that the output of the second maximum-likelihood decoding circuit is selected only when the type and the reproduction speed of the optical disk configure a predetermined combination.