TRANSFER CHARACTERISTIC OF IM3 RELATIVE PHASE FOR A GAAS-FET AMPLIFIER

The transfer characteristic of relative phase of the third-order inter modulation distortion (IM3) of a GaAs FET amplifier is measured and an alyzed. The measurement system and method are also described. For driv es in the weakly nonlinear region, the measured relative phase of IM3 is equal to that of the carrier and is in agreement with the analysis results using Volterra-series representation. For drives in the satura tion region, the measured relative phase of IM3 versus the input power moves drastically compared with that of the carrier and is in agreeme nt with numerical analysis using discrete Fourier transform. Compariso n between measured and analytical results shows the drastic move of IM 3 relative phase is caused by the generation of IM3 due to AM-PM conve rsion. The measured results and the measurement method are useful for the design and adjustment of predistortion-type linearizers for GaAs F ET high-power amplifiers.