Experimental Characterization of Power Transistors for Linearity Optimization

In this paper, different techniques are combined in a unique characterization system dedicated for power transistor linearity improvement. Successive optimizations are performed using source-pull/load-pull techniques at the fundamental and base-band frequencies associated with an instantaneous memoryless base-band predistortion procedure. Measurement results performed at 1.575 GHz on a MESFET power transistor biased in class AB for a QPSK modulated signal, show that fundamental frequency source-pull measurements lead to an ACPR variation equal to 3 dB. Moreover, the influence of base-band impedance on ACPR and EVM is found to be 15 dB and 4.5 points, respectively. Finally, instantaneous memoryless base-band predistortion improves ACPR and EVM values by 5 dB and 1 point, respectively.