Design of CMOS analog and digital phase-locked loops based on resonant VCO

This paper deals with the comparison of the analog and digital phase-locked loops that use identical LC VCO. Both circuits were designed and simulated in CMOS AMS 0.35 μm (3.3 V) technology using full-custom technique. The centre frequency of the oscillator is about 1.1 GHz. The analog loop consists of the Gilbert multiplying phase detector and active low-pass filter while digital one is built of D flip-flop phase detector and charge pump.