Minimization of baseband electrical memory effects in GaN HEMTs using active IF load-pull

This paper presents a rigorous way to quantify the role played by higher baseband impedances in determining baseband electrical memory effects observed in power transistors under two-carrier excitation. These effects typically appear not only as asymmetrical distortion terms in the frequency domain, but also more reliably as a recognizeable hysteresis or looping in the dynamic transfer characteristics extracted from measured input voltage and output current envelopes of a power device. Investigations have been carried out using a commercially available 10W GaN HEMT device characterised at 2GHz within a high-power modulated wavefor measurement system. Active IF loadpull has been employed to present specific baseband impedance environments, allowing the sensitivity of IMD symmetry to baseband impedance variations to be investigated.