A 1.9 GHz micromachined-based low-phase-noise CMOS VCO

Low-phase-noise microwave oscillators require capacitors and inductors with high Q-factors, since the phase noise of an oscillator is inversely proportional to the Q-factor of the resonant circuit. Often the frequency of oscillations must be electronically tunable, and hence, at least one of these reactive elements must be tunable. In practice, it is difficult to realize a high-quality electronically tunable inductor, and an electronically tunable capacitor is generally used. The CMOS inverter VCO takes advantage of the large voltage swing property of the micromachined tunable capacitor. The cross-coupled CMOS inverters realize the negative resistance and form the core of the oscillator.