Influence of novel MOS varactors on the performance of a fully integrated UMTS VCO in standard 0.25-μm CMOS technology

A novel MOS varactor design is compared to standard MOS varactors and its influence on the tuning range, phase noise, and pushing of a CMOS voltage-controlled oscillator (VCO) for UMTS is presented. Three fully integrated CMOS VCOs have been fabricated in standard 0.25-μm technology, two with different versions of a novel device, and one with a conventional nMOSFET as the tuning element. All of the fully integrated VCOs fulfill UNITS tuning and phase noise specifications with a power consumption of only 7.5 mW at a 2.5-V power supply. The new varactors outperform the nMOSFET by increasing the frequency tuning from ±7% to ±11% or ±13%, while the measured phase noise of all three VCOs is -117 dBc/Hz at a 1 MHz offset from a 4-GHz carrier