Power Amplifier Efficiency Enhancement Using Adaptive Load Transformation

An adaptive load transformation technique utilizing switched coupled lines as impedance transformers is proposed to improve the back-off efficiency of power amplifiers. This transformer technique is capable of presenting nearly any desired real impedance value at the input while simultaneously handling high powers. The load impedance can be switched between a defined minimum and maximum value by switched coupled lines. Therefore application in high power amplifiers is possible. The transformer is explained in detail and measurement results for impedance transformation and insertion loss are presented. Finally measurement results for application in a PA are also given.