A MEMS low-IF IQ-mixer in Metal MUMPS : modelling and simulation

Abstract

This study presents a MEMS proof-of-concept in integrating RF mixing and filtering to obtain in-phase and quadrature signals ready for ADC. Electrostatic actuation is used to achieve mixing of the RF and local oscillator (LO) signals. A solution is presented whereby even harmonics arising from the nonlinear nature of this interaction are attenuated. This relaxes mechanical filtering design constraints within the same structure. Sensing of the resulting displacements is achieved using a differential setup. The nonlinear differential equations that model the whole process of actuation, filtering and sensing are used to develop a methodical design procedure by analysing the frequency shifting and/or filtering characteristics at the actuation and sensing. This optimises the gain at the required output frequency: the low-IF. Numerical simulations with different QAM signals are performed with RF and LO signals at 17 volts RMS, a footprint of around 40,000 pm 2 and resulting output voltage levels of 0.18 volts RMS for the in-phase and quadrature signals.