A metal-oxide-semiconductor varactor

CMOS technology scaling opens up the possibility of designing variable capa citors based on a metal oxide semiconductor structure with improved tuning range and quality factor. This is due to an increase in the oxide capacitan ce and a reduction in the parasitic resistance. A prototype metal-oxide-sem iconductor (MOS) variable capacitor of 3.1 pF nominal value has been realiz ed in a 0.35-mu m standard CMOS process. A factor two capacitance change ha s been achieved for a 2-V variation of the controlling voltage. The varacto r Q ranges from 17 to 35, at 1.8 GHz.