Accurate calculation of MEMS varactor based VCO phase noise using multitone-FM Analysis

MEMS varactors monolithically integrated into the metal stack of a modern semiconductor process are an attractive alternative to FET gate channel or bipolar transistor varactors for continuous VCO frequency tuning. Due to their mechanical properties MEMS varactors add significantly to the total VCO phase noise if exposed to thermal noise or vibrations. The phase noise contribution of a MEMS varactor can be calculated applying multitone-FM analysis. This paper compares the calculated and measured phase noise of a VCO with continuous frequency tuning using a MEMS varactor and verifies the high accuracy of the phase noise prediction provided by multitone-FM Analysis.