The Role of Active Device in Power Amplifier Design

Power amplifier designers know the importance of having a good model or characterization data of an active device to achieve the proper performance of the PA design. Less well known is how to optimize or synthesize the behavior of the active device into the design itself for optimal performance and trade off of goals such as linearity, bandwidth, efficiency, power and gain. Knowledge of behaviors such as bifurcations (hysteresis) during drive-ups, AM to AM and AM to PM, harmonic generation and short-term memory effects can be leveraged to improve the end performance of the amplifier. Different technologies have different characteristic behaviors, for example, the large-signal behavior of GaN has a greater consistency of the nonlinear output capacitance of the device. A knowledge of the characteristics of the particular active device is crucial to obtaining the best performance from the device. An example of how to take advantage of the nonlinear behavior of the device to gain the best performance in applications such as supply, load or phase modulation, switchmode or simple Class AB will be presented.