Patent ID: 7982552

Claim:
An automatic frequency calibration apparatus for a phase-locked loop based frequency synthesizer, the apparatus comprising: a frequency-to-digital converter configured to count directly a frequency of a VCO output signal from a VCO and convert the frequency of the VCO output signal into a first digital value; a target value setting section configured to output a second digital value corresponding to a target frequency; and a finite state machine configured to calibrate the frequency of the VCO output signal by using a difference of the first digital value and the second digital value, wherein the frequency-to-digital converter includes: a frequency divider configured to divide the frequency of the VCO output signal with a given dividing ratio, convert the divided signals into multiple phase signals having multiple phases, and output the multiple phase signals; at least one counter configured to count at least one of the multiple phase signals; and an adder configured to add the counted results by the at least one counter.