Phase noise performance comparison between LIGA-MEMS and on-chip CMOS capacitors for a VCO application

An integrated voltage-controlled oscillator using TSMC 0.18 mum CMOS technology is presented to demonstrate and compare the phase noise performance between the VCO using a new type of MEMS variable capacitor and that using conventional CMOS varactor, which is built on-chip together with the CMOS VCO. A representative MEMS variable capacitor, fabricated using the LIGA process, has a nominal capacitance of 1.05 pF and exhibits a Q factor of 40.9 at 2.7 GHz. The simulation results show that with this LIGA-MEMS capacitor, a 4.3 dB of phase noise improvement at 300 kHz offset from the carrier is achieved when the VCO operates at 2.7 GHz