Phase comparator having two different phase comparison characteristics

摘要

A phase comparator has a switching circuit controlled by a switch signal and a phase comparing unit. The switching circuit receives a reference pulse signal having a duty ratio of 50% and a reception data signal having a duty ratio of less than 50%. One of these signals is selected by the switching circuit on the basis of control of the switch signal. The selected signal and an output signal from a voltage- controlled oscillator are supplied to the phase comparing unit. The phase comparing unit compares phases of the two signals. When the phase of the output signal from the voltage-controlled oscillator lags behind the phase of the selected reference pulse signal or reception data signal, the phase comparing unit outputs a first pulse signal, having a width corresponding to a phase difference between the two signals, for advancing the phase of the output signal from the voltage-controlled oscillator. When the phase of the output signal from the voltage- controlled oscillator leads ahead of the phase of the selected reference pulse signal or reception data signal, the phase comparator outputs a second pulse signal, having a width corresponding to a phase difference between the two signals, for delaying the phase of the output signal from the voltage-controlled oscillator.