Waveform measurement technique and its applications to optimum loading studies on power FETs

Microwave waveform measurement techniques on power transistors and power amplifiers are reviewed. Techniques of both low-impedance technique in a load-pull system and high-impedance internal node probing, including calibration approaches are presented. Applications of the low-impedance waveform technique are demonstrated in finding the optimum harmonic loads of power PHEMTs to achieve best power added efficiency (PAE). Measured versus simulated results show very good agreement and therefore verify the measurement technique. It has been shown that as high as 83% power added efficiency can be achieved under the inverse-F harmonic loading condition. Also the good agreement of high-impedance probing on a GSM power amplifier with simulated results validates the internal-node probing technique.