Clock recovery apparatus

A clock recovery apparatus for recovering a clock signal used to reproduce digital data from an incoming signal, said apparatus comprising:

• an oscillation device operable to receive a control signal, and generate, as an oscillation clock signal, a clock signal having a frequency based on the control signal;
• a sampling device operable to sample the incoming signal with a timing of the oscillation clock signal, and output a sampled value of the incoming signal;
• a phase error detection device operable to detect, based on the sampled value, a phase error between the oscillation clock signal and an ideal clock signal used to reproduce the digital data;
• a quality judgement device operable to judge a quality of the sampled incoming signal by referring to the sampled value, said quality judgement device comprising:
• a temporary judgement device operable to estimate the digital data based on the sampled value for output as a temporary judgement result;
• a reference value generation device operable to generate a reference value based on the temporary judgement result;
• and
• a calculation device operable to calculate a difference between the sampled value and the reference value, wherein the quality is judged according to the difference;
• a frequency error detection device operable to detect a difference between a frequency of the oscillation clock signal and a given reference frequency as a frequency error;
• a phase-frequency error detection device operable to output a phase-frequency error signal based on the phase error, the quality judged by said quality judgement device, and the frequency error, wherein, as the phase-frequency error signal, a given first error value, which is in accordance with a sign of the frequency error, is outputted when an absolute value of the frequency error is larger than a given threshold value, the phase error is outputted when the quality is good and when the absolute value of the frequency error is equal to or smaller than the given threshold value, and a given second error value which is in accordance with a sign of the phase error as detected when the quality changes from good to bad is outputted at least for a given duration of time right after the quality changes from good to bad;
• and
• a filter device operable to smooth the phase-frequency error signal for output to said oscillation device as the control signal,
• wherein the oscillation clock signal is outputted as the clock signal used to reproduce the digital data.