Patent ID: 7054403

Claim:
A phase lock circuit (phase-locked loop circuit) having a signal path to which a phase comparator, a loop filter and a voltage control oscillator (voltage-controlled oscillator) are connected in series, said phase comparator being adapted to compare the phase of an input signal V IN with the phase in the output signal of said voltage control oscillator and to output its result of comparison, said loop filter being adapted to receive the output signal of said phase comparator and to output a Direct Current (DC) voltage; said voltage control oscillator being adapted to control the output oscillation frequency depending on the DC output voltage of said loop filter, said phase lock circuit further comprising voltage tracking circuit for adding, to the voltage of said signal path, a signal causing the average voltage in the output voltage of said phase comparator to coincide with a predetermined reference voltage, whereby said voltage tracking circuit can enlarge the lock range in said phase lock circuit wherein said voltage tracking circuit comprises reference voltage generator means for generating a voltage within the output voltage range of said phase comparator, a differential amplifier for outputting a voltage proportional to a difference between the output voltage of said phase comparator and the output voltage of said reference voltage generator means, a filter for converting the output of said differential amplifier into DC voltage, and adder means for adding the output of said filter to the output voltage of said phase comparator and for outputting the result to said loop filter.