A Simple Method to Identify Parametric Oscillations in Power Amplifiers Using Harmonic Balance Solvers

A qualitative method to verify the presence of parametric oscillations at f_0/2 in power amplifiers (PAs) is presented and validated. It relies on the simultaneous application of fundamental and subharmonic tones to trigger possible parametric oscillations and can be implemented in any commercial harmonic balance solver without requiring any external software that may be expensive or however not available to the designer. Wide applicability is guaranteed by the fact that this method does not require access to any internal node of the circuit. In fact, the amplifier is handled as a black-box where only the input and output ports are accessible. The stability check is first demonstrated on a simplified case study and then validated on a real K-band integrated PA, where it correctly reproduces with simulations the parametric oscillations observed by measurements. On the redesigned amplifier, the proposed test predicted the absence of oscillations, which has been confirmed by the experimental characterization.