Digital PLL circuit

摘要

A digital PLL circuit recovers a clock signal from an analog baseband signal. The PLL circuit has a phase comparator. The phase comparator provides a loop filter with a control value for a period of the recovered clock signal after a determination is made. If the determination is that the baseband signal has crossed a transition level, the control value corresponds to a time difference between a sampling point and a transition-level crossing point of the baseband signal. If the determination is that the baseband signal has not crossed the transition level, the control value is 0. The PLL circuit shortens a lockup time and provides stable operation even if the baseband signal involves an offset.