| 摘要 |
PURPOSE: A frequency synthesizer is provided to maintain a relativity of K: fs=1: 20 by variably controlling the value of the current Ip out of variables determining a unity gain bandwidth K of a voltage controlled oscillator. CONSTITUTION: A frequency synthesizer comprises: a first divider for receiving a control bit determining a division value and generating a first output of a second frequency by dividing a first frequency of a reference clock by the control bit; a second divider for generating the first output of the second frequency by dividing a third frequency of an output signal by N; a phase frequency detector for detecting the phase difference between the first output and the second output, and generating a pumping-up signal and a pumping-down signal; a controller for generating a first control signal after comparing the difference between the first and second frequencies and the value of the control bit; a charge pump for generating a pumping voltage while a charge pumping operation is controlled by the pumping-up and pumping-down signals, the charge pump equipped with a current source variably controlled by the first control signal; a low pass filter for converting the pumping voltage to a direct voltage; and a voltage controlled oscillator for generating the output signal having a frequency determined by the direct voltage.
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