Stability analysis of multistage power amplifiers using Multiple-Input Multiple-Output identification

Determining the origin and nature of the possible instabilities is key for an effective elimination of the unstable dynamics in multistage power amplifier design. In this work, a novel technique is proposed to provide a quantitative metrics that serves to locate and categorize the sensitive sections of the amplifier at which the unstable dynamics can be controlled and eliminated. The technique is based on an automatic Multiple- Input Multiple-Output (MIMO) frequency identification performed at different observation ports, followed by a residue analysis of critical poles. A three-stage amplifier exhibiting two common types of instabilities has been used to illustrate the complete approach.