Load-pull measurement comparison of a LDMOS device with two-tone and digitally modulated stimuli

A large-signal fully automated load-pull system for characterization of adjacent channel power for wideband code-division multiple-access (WCDMA) based wireless communication systems, with varying peak-to-average ratios (PAR) is described. Load-pull measurements are used to determine optimum load impedances for power gain and adjacent channel power ratio (ACPR) in an LDMOS stimulated with WCDMA sources with five different PAR values. The results are compared to load-pull measurements of gain and third-order intermodulated products, based on a two-tone source signal. The results indicate that the optimum match impedance changes depending on whether a two-tone or a digitally modulated source is used as a stimulus. Furthermore, it is shown that the optimum load impedance for power gain and ACPR is also dependant on the PAR of a digitally modulated signal. It is shown, that the change in the optimum load match for the different types of signals is significant enough to warrant further investigation.