New Low-Frequency Dispersion Model for AlGaN/GaN HEMTs Using Integral Transform and State Description

A new concept for the low-frequency dispersion aspect of large-signal modeling of microwave III-V field-effect transistors is presented. The approach circumvents the integrability problem between the small-signal transconductance GmRF and the output conductance G_dsRF by means of an integral formulation and simultaneously yields a proper description of the drain channel current in the small- and large-signal regime. In the theoretical description of the approach and in an extraction example of an AlGaN/GaN HEMT, it is shown that three independent 2-D nonlinear quantities determine the intrinsic drain channel current (GmRF, G_dsRF, and dc current). The concept is transferred to the modeling of the nonlinear charge control, where the integrability problem between the large-signal charge functions and the small-signal intrinsic capacitance matrix (C_gs, C_gd, and C_ds) is addressed consistently under consideration of the charge control delays. For the large-signal modeling under pulsed-dc/RF excitation, the dc continuous wave (dc-CW) modeling approach is combined with the state-modeling concept using a superposition formula for drain current and charges, respectively. The new model is implemented in ADS using a 12- and 14-port symbolically defined device for both the dc-CW and pulsed-RF case, respectively. The model has been verified by comparison to measured CW and pulsed-RF load-pull and waveform data at 10-GHz fundamental frequency.