Nonlinear modeling and verification of MMIC amplifiers using the waveform-balance method

An accurate nonlinear MESFET model, an amplifier large-signal simulation algorithm, and a reliable model verification approach are presented. The MESFET model is derived from S-parameter characterization of the MESFET, using a wide range of bias voltages. The model is shown to be accurate at various frequencies, bias voltages, and input power levels. The nonlinear simulation utilizes a hybrid circuit analysis algorithm, which uses both time- and frequency-domain analysis. Unlike the harmonic balance method, the solution is optimized in the time domain, where the closed-form error gradient matrix (Jacobian matrix) is calculated. This algorithm is shown to have good convergence speed. To verify the MESFET model, two MMIC single-stage power amplifiers and test patterns of their matching circuits are designed. The load and source impedances presented to the MESFETs in the amplifier circuits are accurately determined by on-wafer S-parameter measurements of the amplifier´s matching circuits. These S-parameter data are directly used in the simulation of the MMIC amplifiers. The simulation results agree well with the measurement data