Impact of Matching Networks on the Impedance Settling Time in High Frequency Power Amplifiers

This paper presents a study on the settling time of the impedance loading the high frequency transistors in power amplifiers. Depending on the matching network type and complexity, the impedance can take significant time for settling. This will affect the ability of the power amplifier to respond to fast changing modulation signals or fast, short RF pulses, hence becoming a limiting factor for emerging wireless systems, alongside other effects such as bias networks and thermal response. The study is based on fitting the frequency domain response with a rational function, allowing the application of a sinewave stimulus starting at t =0 for evaluating the transient behavior. The results show that the settling time is not easily relatable to parameters usually considered such as the group delay, hence suggesting that full understanding of these effects will need deeper studies.