Monte-Carlo stability analysis of microwave amplifiers

Pole-zero identification is being increasingly used as a method to analyze the stability of microwave circuits. However, in its current form, the stability analysis through pole-zero identification relies on a quality assessment that is based on visual inspection. This implies a manual approach that limits in practice the handling of a large amount of data as in the case of a yield or sensitivity analysis. Here, an automated methodology based on pole-zero identification is applied to the stability evaluation in the context of a Monte-Carlo analysis. The methodology is based on an algorithm that prevents the adverse effects due to undermodeling and overmodeling on the stability criteria. The approach is illustrated through its application to two in-home built amplifier prototypes: a medium power band L FET amplifier exhibiting a low frequency oscillation and a SiGe HBT reconfigurable amplifier for Wifi/Wimax applications that shows an undesired frequency division for some particular input drive conditions.