An oscillator (30) supplies a high frequency signal (S) to a frequency divider (31). A phase comparator (32) produces a signal measuring phase difference between the divided frequency signal (QA) and a reference signal. A low-pass filter (34) controls the oscillator on the basis of the measurement signal....http://www.google.com/patents/US7668278?utm_source=gb-gplus-sharePatent US7668278 - Phase-locked loop
