Electrothermal analysis of nonlinear microwave circuits containing thermally coupled active devices

The paper discusses a novel harmonic-balance (HB) technique for the electrothermal analysis of microwave integrated circuits containing temperature-dependent nonlinear devices. All the thermal couplings among active devices are rigorously taken into account. The heat flow among the hot spots of the chip surface (e.g., the FET gates) is described in terms of a thermal conductance matrix. The latter is evaluated by a 3-D layout-oriented numerical analysis based on an electrostatic analogy. The storage of thermal energy inside the chip is described in terms of the chip enthalpy, so that thermal transient effects may be taken into account. The resulting thermal equations are coupled to the electrical equations of the circuit through the state-dependent dissipated powers in the active devices. The whole problem is formulated in the frequency domain as a nonlinear set of coupled electro thermal HB equations which are simultaneously solved by a Newton iteration.