Linearity characteristics study of millimeter-wave GaN power amplifier

In this paper, a digital waveform system for evaluating the linearity characteristics of millimeter-wave GaN HEMT devices and MMICs is described. It is capable of generating and analyzing a wide range of waveforms. The linearity performance of a sample Ka-band one-stage GaN/SiC MMIC power amplifier is characterized to demonstrate the capabilities of the system. Performance metrics associated with different waveforms are measured. These include AM/AM and AM/PM for single-tone, intermodulation-product-to-carrier-ratio for two-tone, EVM and ACPR for digitally modulated waveforms. The dependence of these metrics on drain bias current is studied. This digital waveform system and its associated test methodology will help MMIC designers to assess device linearity characteristics to improve MMIC PA design with optimized power, efficiency and linearity.