Large-signal FET simulation using time domain and harmonic balance methods

Lumped-element circuit models, modified to include RF voltage-dependent elements may be used to describe the large-signal performance of a MESFET. Several solution methods exist for the analysis of amplifier circuits incorporating the large-signal device model. The paper reports the results of a comparative study of three solution methods: harmonic balance, modified SPICE and time domain methods. A simple amplifier, with 50 ¿¿ generator and load impedances is used to show the importance of the nonlinear gate-source capacitance and avalanche breakdown in predicting harmonic generation in the MESFET. An amplifier, with cascaded transmission-line input and output matching sections, illustrates the effect on the large-signal analysis, of using the three alternative solution methods with their associated descriptions of the distributed external microwave circuits. It is concluded that, for this application, the harmonic balance method is faster and more accurate than the other solution methods.