Micromachined RF voltage-controlled oscillator with phase noise characterization

An RF voltage-controlled oscillator (VCO) is implemented employing an on-chip, high-Q micromachined variable capacitor and three-dimensional (3D) coil inductor. The micromachined variable capacitor achieves a 15% tuning range with a nominal 2 pF capacitance and a Q value above 60 at 1 GHz. The 3D inductor minimizes the substrate loss and achieves a Q of 16 at 1 GHz. Both passive components are fabricated on silicon substrates and thus amenable to monolithic integration with standard IC processes. The prototype VCO exhibits a phase noise of -136 dBc/Hz at 3 MHz offset frequency from the carrier, suitable for various wireless communication applications, in particular GSM. The VCO is tunable from 855 MHz to 863 MHz under 3V, limited by the test setup. The micromachined VCO exhibits an additional phase noise caused by mechanical-thermal vibration of the suspended plate, which can potentially be dominant within the low offset frequency. This noise source can be suppressed by placing the oscillator in a vacuum environment.