Analysis of linearity degradation in multi-stage RF MEMS circuits

This paper reports for the first time on RF nonlinearity analysis of complex multi-device RF MEMS circuits. The nonlinearity analysis is done for the two most commonly-used RF MEMS tuneable-circuit concepts, i.e. digital MEMS varactor banks and MEMS switched capacitor banks. In addition, the nonlinearity of a novel MEMS tuneable capacitor concept by the authors, based on a MEMS actuator with discrete tuning steps, is discussed. This paper presents closed-form analytical formulas for the IIP3 (nonlinearity) of the three MEMS multi-device circuit concepts, and an analysis of the nonlinearity based on measured device parameters (capacitance, gap), of the different concepts. Finally, this paper also investigates the effect of scaling of the circuit complexity, i.e. the degradation of the overall circuit linearity depending on the number of stages/bits of the MEMS-tuning circuit.