About the Oscillator Basics and Low-Noise Techniques for Microwave Oscillators and VCOs

Microwave oscillator design is based on the principle of generating a negative resistance to compensate for the losses of the resonator. Several circuit combinations, including oneand two-port oscillators, are possible. In this discussion, we will first evaluate the conditions of oscillation for the Colpitts and Clapp-Gouriet oscillator. We will then evaluate a 19-GHz SiGe-based oscillator by assuming values, backed up by available S parameters and dc I-V curves, that we assigned to the nonlinear BFP520 model. So far it has been difficult to obtain complete documentation on modeling for the SiGe transistors, but our approximation appears to be justified. Next, we will evaluate a ceramic-resonator-based oscillator and show its performance. Going up to higher frequencies, we will introduce a 47-GHz lumped-resonator oscillator and a VCO at the same frequency that uses GaAsFETs as varactors. In all cases, we will give a thorough treatment of the circuits and their performance.