Frequency synthesizer using a wide-band voltage controlled oscillator and a fast adaptive frequency calibration method

摘要

A frequency synthesizer is provided. The frequency synthesizer includes an adaptive frequency calibration circuit and a phase locked loop (PLL). The frequency synthesizer performs in a frequency lock mode and in a phase lock mode. In the frequency lock mode, the adaptive frequency calibration circuit compares the frequency of an input signal with the frequency of an output signal of a voltage controlled oscillator of the PLL and outputs control bits as a result of the comparison. The voltage controlled oscillator has a plurality of operating characteristic curves and selects a curve from among the plurality of operating characteristic curves in response to the control bits. In the phase lock mode, the PLL controls an output phase of the voltage controlled oscillator based on a tuning voltage from the selected operating characteristic curve.