When self-consistency makes a difference

Compound semiconductor power RF and microwave device modeling requires, in many cases, the use of self- consistent electrothermal equivalent circuits. The slow thermal dynamics and the thermal nonlinearity should be accurately included in the model; otherwise, some response features subtly related to the detailed frequency behavior of the slow thermal dynamics would be inaccurately reproduced or completely distorted. Two examples have been shown, concerning current collapse in HBTs and modeling of IMPs in GaN HEMTs. Accurate thermal modeling can be made compatible with circuit-oriented CAD tools through a proper choice of system-level approximation; in the discussion presented it exploited a Wiener approach, but of course the strategy should be tailored to the specific problem under consideration.