A system for recovering a clock signal from a data signal is described. The
system uses an oscillator adapted to generate an oscillator output signal,
a first detecting circuit for obtaining a coarse frequency-lock condition
between the data signal and a recovered clock signal, a second detecting
circuit for obtaining a phase-locked condition between the data signal and
the recovered clock signal, a lock-detecting circuit responsive to the
first detecting circuit for detecting an out-of-lock condition between the
data signal and the recovered clock signal, and a control circuit
responsive to the lock-detecting circuits and adapted to control the
oscillator to generate an oscillator output signal on the basis of the
first detecting circuit during an out-of-lock condition, and otherwise to
generate the oscillator output signal on the basis of the second detecting
circuit. The advantages include a much wider pull-in range for frequency
acquisition, and an accurate and robust measure of a quality of received
data.
