Measurement technique for increasing the linearity by optimising the source: impedance of RF power amplifiers

Out-of-band source impedances have a significant impact on the linearity of RF power stages. The source-pull measurement technique presented in this paper shows that linearity improvements up to 8 dB for a CE BJT stage can be achieved by providing optimum source impedance at the envelope frequency. If predistorters are used, the memory effects caused by the stage and predistorter can be partially cancelled by providing optimum source impedances at different envelope frequencies. As a result, the cancellation performance of the predistorter will be significantly improved.