A Volterra-Based Procedure for Multi-Port and Multi-Zone GaN FET Amplifier CAD Simulation

This paper reports a systematic method for the computer-aided-design (CAD) simulation of GaN FET power amplifiers (PAs). The core of the proposal is a Volterra-based behavioral model (BM) with multi-spectral and multi-node capabilities, which black-box structure is formally derived from a circuit-level representation of the PA and accounts for both short and long-term memory effects. Starting with the equivalent circuit of a typical FET device with thermal power feedback, the structures of the kernels for the gate, drain and thermal nodes are developed and are shown to be dependent on the frequency response of the PA terminating impedances and thermal filter. The model has been applied to simulate the nonlinear response of a typical PA circuit, showing the ability of the proposed model to provide an accurate prediction of multi-spectral, multi-node characteristics, including AM/AM-AM/PM conversion, spectral regrowth, intermodulation, and temperature rise, under diverse input signal waveforms and bandwidths. These results have been successfully compared with commercial CAD tools based on harmonic balance or envelope simulation.