Anti-biased RF MEMS varactor topology for 20–25 dB linearity enhancement

A new topology for significantly improving the linearity of RF MEMS varactors is reported in this paper. A single MEMS varactor subject to a low frequency noise and/or modulating signal is the main structure under consideration. The key idea is to separate the single varactor into two varactors in parallel, which are anti-biased. This leads to out-of-phase vibration of the two beams under the influence of the low-frequency noise and/or modulating signal, which eventually leads to a nearly constant capacitance value of the entire topology. The effectiveness of the new method is demonstrated by both measured results from fabricated RF MEMS varactors and simulated results using a large-signal model of MEMS varactor in Agilent´s Advanced Design System (ADS). Both experimental and simulated results indicate an improvement of 20-25 dB compared to the conventional design when the varactors are biased close to their pull-in voltage and the low-frequency signal is close to their self-resonant frequency. This underlines the potential of the proposed topology in high-power RF MEMS circuits.