Detecting Critical Resonances in Microwave Amplifiers through Noise Simulations

The presence of critical resonances in microwave power amplifiers has a negative impact on its behavior and performance. These critical resonances are usually predicted from pole-zero stability simulations. In this paper, a different and less demanding approach for the circuit designer is proposed. It is based on performing noise simulations of the amplifier and observing the rise in the noise spectrum that happens when the system has low damping poles. Critical resonance detection is simplified since no additional probes have to be inserted in the circuit and no post-processing for pole-zero analysis is required. The technique is applied to two amplifier prototypes fabricated in microstrip hybrid technology and the results are compared with the conventional pole-zero approach.