LOOP FILTER AND FREQUENCY SYNTHESIZER USING THE SAME

摘要

PURPOSE: A loop filter and a frequency synthesizer using the same are provided to obtain stability corresponding to large current change by freely changing a current change ratio which determines a bandwidth of the loop filter. CONSTITUTION: A reference oscillator(100) controls frequency disturbance according to temperature change in a crystal oscillator. A phase-frequency detector(200) transmits an error signal to a current pump(300) by comparing a phase and frequency of a reference signal and an oscillation signal. The current pump provides a specific amount of electric charges to a loop filter(400) according to the error signal or absorbs the electric charges. The loop filter applies a voltage generated by charged/discharged currents to a frequency control input of a voltage controlled oscillator(500). The voltage controlled oscillator outputs an oscillation signal having a frequency corresponding to the voltage of the charged/discharged loop filter. A frequency divider(600) divides the oscillation signal into 1/10 times.