Characterizing a varactor contribution to the residual distortion of load-modulated PAs

In this paper, a technique for extracting the Taylor series expansion coefficients of a varactor reactive nonlinearity is presented. A single diode and a dual-device antiseries (back-to-back cathode) combination have been characterized, aimed to accurately control their contribution to the residual intermodulation distortion (IMD) appearing in load-modulated power amplifiers (PAs). A test set-up for dynamically measuring the harmonic content has been implemented, able to be extended to the evaluation of load-based envelope tracking transmitters.