A clock recovery circuit capable of fast and accurate clock phase locking
even in the presence of frequency shift and noise. The input signal
includes, in order, a preamble with an alternating bit sequence pattern,
a unique word and data. A detection unit detects zero crossings and
measures the time interval therebetween. A 1-interval judgment unit
judges whether an interval signal is within a predetermined range, and a
2-interval judgment unit sums two adjacent interval signals and judges
whether the 2-interval signal is within a predetermined range. A control
unit controls a zero-crossing signal based on the judgment result and
outputs a valid zero-crossing signal if judged in the affirmative. A
switching unit switches between outputting the zero-crossing signal and
the valid zero-crossing signal as valid phase error information based on
a frame reception signal input from a frame detection unit. A clock
generation unit uses the valid phase error information in generating a
symbol clock.