Patent ID: 7154348

Claim:
A frequency synthesizer, comprising: a phase locked loop (PLL); a voltage controlled oscillator, which comprises a plurality of operating characteristic curves; and an adaptive frequency calibration circuit, which, in a frequency lock mode, receives an input signal, and an output signal of the voltage controlled oscillator, compares a frequency of the input signal with a frequency of the output signal of the voltage controlled oscillator, and outputs control bits as a result of the comparison, wherein the adaptive frequency calibration circuit comprises: a first counter, which receives the input signal and counts the frequency of the input signal; a second counter, which receives the output signal of the voltage controlled oscillator and counts the frequency of the output signal of the voltage controlled oscillator; a comparator, which receives an output signal of the first counter and an output signal of the second counter, compares the output signal of the first counter and the output signal of the second counter, and outputs a comparison signal as a result of the comparison; and a state machine, which receives the comparison signal from the comparator and outputs the control bits in response to the comparison signal, wherein the voltage controlled oscillator selects a curve from among the plurality of operating characteristic curves in the frequency lock mode in response to the control bits.