COMBINED CIRCUIT COMPOSED OF DIGITAL PHASE COMPARATOR WITH ZERO-DEBT BAND AND MINIMUM OFFSET AND CHARGE PUMP

摘要

PURPOSE: To eliminate the phase comparison dead band of a digital phase locked loop(PLL) by resetting a comparator through the function of a charge pump having both the functions of charging and discharging. CONSTITUTION: High-speed charging/discharging operation is performed inside a charge pump 15, a means for detecting the time when simultaneously executing both the functions of charging and discharging is provided, and the charge pump 15 is connected to a power source, the injection current source of a low- pass filter(LPF) and voltage controlled oscillator(VCO) coupling to be used for the PLL. Besides, since a digital phase detector 11 has a reset terminal for responding to the simultaneous charging/discharging operation of the charge pump 15, two kinds of charge pump operation appear before resetting is generated, and any delay element is not required. When increasing the frequency of a VCO, the up output of a phase comparator is made superior and the charge pump 15 injects a current into the LPF. When decreasing the frequency of the VCO, the down output of the phase comparator is made dominant, and the charge pump pulls a current out of the LPF. Thus, the dead band is removed.