Stability analysis of microwave circuits

It is common knowledge that stability analysis is a critical step of RF design flow. Nowadays powerful CAD tools allow accurate simulation of the performances of microwave and RF circuits. But the prediction of instabilities giving rise to frequency divisions or spurious oscillations is still a challenge, especially for MMIC designs whose adjustment after fabrication is impossible. This paper presents a new tool for stability analysis of microwave circuits, valid for small-signal and large-signal regimes. The technique used in this tool allows to detect and determine the nature of oscillations, such as parametric oscillations in power amplifiers that can be for example function of the input drive signal. Knowledge of the type of oscillation mode facilitates the insertion of stabilization networks, with a better balance between the required oscillation avoidance and maintaining the original circuit performances. The integration of this tool in the design flow with commercial CAD tools will be presented.