A digital Phase Locked Loop (PLL) comprises a Voltage Controlled Oscillator (VCO) and a phase detector. The output of the VCO is coupled to a first input of the phase detector whose output is coupled to the input of the VCO by way of a low-pass filter. A second input of the phase detector is coupled...http://www.google.com.hk/patents/US5349613?utm_source=gb-gplus-share專利 US5349613 - Digital phase locked loop, and digital oscillator arranged to be used in the digital phase locked loop
