RF Power Insensitive Varactors

In this letter, the influence of the RF voltage swing on the effective capacitance of continuously tunable capacitive devices, e.g., varactors, is investigated. Using Volterra series, equations are derived that describe the change in effective capacitance versus RF voltage, which are in agreement with simulations and have been verified by measurements. Comparing conventional and IM3 compensated varactor configurations, significant differences are found for their capacitance variation versus power. It is found that an anti-series configuration of two varactors with exponential C(V_R) behavior and proper center-tap termination outperforms all other known varactor configurations and shows a maximum capacitance variation below 0.1% compared to 10% for conventional varactor elements using identical excitation.