Real-time instability detection for a reconfigurable power amplifier

Frequency-agile wireless transmitters require tunable power amplifiers that can reconfigure to maximize gain, efficiency, and spectral performance at changing operating frequencies and spectral output requirements. However, stability of the amplifier must be maintained through the reconfiguration process. This paper presents a method for predicting potential instability during a real-time load impedance gain optimization. For each candidate load reflection coefficient, gain is measured at each of four neighboring points, and the acceleration of the gain is calculated. When the acceleration becomes positive, the likelihood of potential instability is detected, and the optimization is terminated to achieve high gain while remaining stable. This method is demonstrated for two different devices in simulation and measurement. While initially innovated for application in reconfigurable devices, this method is also expected to be useful in maintaining stability during bench-top load-pull measurements.