Viterbi decoder of partial response maximum likelihood channel

A Viterbi decoder of a partial response maximum likelihood channel, a partial response maximum likelihood system in an optical disc system having an analog/digital converter, which receives an analog signal and outputs a digital signal to said Viterbi decoder, said Viterbi decoder comprising:

• an adaptive level Viterbi decoding unit, according to a signal level, operating said received digital signal to obtain a decision bit and a survivor metrics value, and output said decision bit and said survivor metrics value;
• a signal level mapping algorithm, used to receive a delay signal and a path-confirm information, wherein said delay signal and said path-confirm information are operated with judging and statistic, so as to obtain said signal level, which can be output by said signal level mapping algorithm;
• a received signal delay chain, used to receive said digital signal, said digital signal being delayed to obtain said delay signal, which can be output by said received signal delay chain;
• a hard decoder, used to receive said digital signal, performing quantization, comparison, and determining path, so as to obtain said decision bit and said path-confirm information, wherein said hard decoder can output said decision bit and said path-confirm information;
• a mode selection algorithm, used to receive said decision bit and said survivor metrics value output from said adaptive level Viterbi decoding unit, and said decision bit from said hard decoder, wherein after calculation and comparison, a selection signal is obtained and can be output by said mode selection algorithm;
• and
• a first multiplexer, used to receive said selection signal, which is used to determine one of said decision bits from said adaptive level Viterbi decoding unit and said hard decoder.