| This thesis proposes a comprehensive design approach, based on the use of load-pull data and suitable for designing a Doherty amplifier. This technique will be used to realize a Doherty power amplifier in L-band. This amplifier will then be linearized by making use of the baseband digital predistortion technique.; At first, transistors were characterized using load-pull measurements to extract their output power and drain current as a function of output impedance, input power and bias voltage. This information was synthesized to build a table-based nonlinear model of the transistor within simulation software environment (Advanced Design System from Agilent Technologies). This model was used to design and realize two nonlinear power amplifiers: one operating in class B and the second one in class C. Measurement results confirmed the model accuracy for designing power amplifiers operating in nonlinear conditions.; Load-pull measurement results reveal useful information on the transistor behavior and on the optimal matching technique that lead to the active load-pulling effect. This information, coupled with the previously developed nonlinear model, were used to design a Doherty power amplifier. This amplifier was then built, and showed a good agreement between simulation and measurement results. Its linearity was improved by tuning the biasing point, of both carrier and peaking amplifier to minimize the introduced distortion. (Abstract shortened by UMI.)... |
