Erik Steen Pedersen

RF CMOS Varactors for 2 GHz Applications

CMOS varactors are important components for the integration of tunable RF filters and VCOs. This paper presents a performance evaluation and comparison of three different types of CMOS varactors based on measurements. The tested varactor types are: (i) p+-to-n-well junction, (ii) standard mode nMOS, and (iii) accumulation mode nMOS. The performance of each varactor type with respect to capacitance ratio and quality factor Q is evaluated at 2 GHz. Further, it is shown how these varactor types must be configured in LC-tank circuits for optimum performance. Finally, the three varactor types are compared and it is concluded that the Standard Mode nMOS type seems to the best choice for RF applications.