Patent ID: 7099643

Claim:
A calibration circuit for a phase locked loop for selecting the frequency of a voltage controlled oscillator (VCO), the calibration circuit comprising: a frequency divider module coupled to receive a local oscillation signal from the VCO and a reference signal, the frequency divider module producing a divided local oscillation and a divided reference signal, wherein the local oscillation signal and the reference signal are divided by different values to produce a divided oscillation signal substantially equal to the divided reference signal; a period-to-voltage conversion module coupled to receive the divided local oscillation and the divided reference signal, the period-to-voltage module to convert the divided local oscillation and the divided reference signal to a threshold voltage signal and a reference voltage signal, respectively; a comparator module coupled to receive the threshold and reference voltage signals, the comparator module for comparing the threshold and reference voltage signals and for producing a frequency adjustment signal; and a logic module coupled to receive the frequency adjustment signal, the logic module for producing a frequency compensation signal responsive to the frequency adjustment signal.