A Scalable Large-Signal Multiharmonic Model of AlGaN/GaN HEMTs and Its Application in C-Band High Power Amplifier MMIC
A scalable electrothermal large-signal AlGaN/GaN HEMTs model for both fundamental and multiharmonics is presented based on the modified Angelov model. To obtain accurate scalability of the electrothermal model, a simple empirical expression is proposed for the geometric and power-dissipation-dependent nonlinear thermal resistance <inline-formula> <tex-math notation="LaTeX">$R_{{\mathrm {th}}}$ </tex-math></inline-formula>. Only one additional parameter with linear scaling rule is needed in the drain-source current (<inline-formula> <tex-math notation="LaTeX">$I_{{\mathrm {ds}}}$ </tex-math></inline-formula>) model for a scalable large-signal multiharmonic model. The proposed model has been validated by different AlGaN/GaN HEMTs characterized by on-wafer measurements. It shows that the presented scalable model can well predict the dc <inline-formula> <tex-math notation="LaTeX">$I$ </tex-math></inline-formula>–<inline-formula> <tex-math notation="LaTeX">$V$ </tex-math></inline-formula>, pulsed <inline-formula> <tex-math notation="LaTeX">$I$ </tex-math></inline-formula>–<inline-formula> <tex-math notation="LaTeX">$V$ </tex-math></inline-formula>, scattering (S) parameters, and large-signal performance up to third harmonic. Furthermore, to further validation, a C-band power amplifier is designed. The amplifier is realized using the second-harmonic tuned approach to enhance the efficiency. Measurement results show that the GaN high power amplifier (HPA) microwave monolithic integrated circuit (MMIC) exhibits more than 40% power-added efficiency and 60-W output power (<inline-formula> <tex-math notation="LaTeX">$P_{{\mathrm {out}}}$ </tex-math></inline-formula>) with associated gain of 25 dB in 5–6 GHz measured at 28-V drain voltage and pulse signal with 100-<inline-formula> <tex-math notation="LaTeX">$\mu \text{s}$ </tex-math></inline-formula> pulsewidth and 10% duty cycle. The area of the chip is 3.2 mm <inline-formula> <tex-math notation="LaTeX">$\times5.3$ </tex-math></inline-formula> mm (16.96 mm<sup>2</sup>). These results show that the proposed model will be useful for high-efficiency HPA MMIC design.