Input Harmonic Sensitivity in High-Efficiency GaN Power Amplifiers

This paper presents the impact of input non-linearity and its dependence to output loading conditions in the design of Gallium Nitride (GaN) based Power Amplifiers (PAs). The drain efficiency variation due to the input non-linearity for any arbitrary second harmonic loading condition is presented. The theory presents generalized current waveform equations as a function of conduction angle $\pmb{(\alpha)}$ and input harmonic non-linearity $(\gamma_{2})$. Thereafter, to quantify the impact of source harmonics, a systematic methodology to evaluate the efficiency degradation is proposed. For practical validation, the active load pull (ALP) experiments are carried out using a 0.7 mm GaN die by NXP at 2.6 GHz. The drain efficiency variation as a function of second harmonic load reactance has been measured and reported at P3dB gain compression. While, class B, and class F shows 5–6% drain efficiency variation to second harmonic source pull, class $\mathbf{F}^{-1}$, and class $\hat{\mathbf{J}}/\hat{\mathbf{J}}^{\ast}$ shows immunity to the input non-linearity with only 1–2 % drain efficiency variation.