Comparison of CMOS VCOs for UMTS tuned by standard and novel varactors in standard 0.25 µm technology

The influence of a novel MOS varactor design on tuning range and phase noise of a VCO in standard 0.25µm CMOS technology is presented. Three VCOs for integrated UMTS transceivers with two novel devices and one standard NMOSFET as tuning elements have been fabricated and measured. The novel varactors outperform the conventional NMOSFET varactor as tuning element. They offer an increase of frequency tuning range from ±7% (conventional NMOSFETs) to at least ±11%. All of the fully integrated VCOs fulfill the UMTS phase noise and tuning range requirements while consuming only 3mA at a 2.5V power supply. Figure of merits are better than -180.3dBc/Hz at a 1MHz offset from 4GHz carrier frequency.