Best Practices to Quantify Linearity Performance of GaN HEMTs for Power Amplifier Applications

In this paper, we discuss the limitations of using conventional linearity metrics (i.e., OIP3 and OP1dB) to evaluate the linearity performance of GaN HEMTs for power amplifier (PA) applications. Unlike Silicon and other traditional III-V devices, GaN HEMTs suffer from soft compression, making the use of conventional metrics "unfair" when compared to other transistor technologies. Through simulation-based evaluation of two different commercial GaN devices, we provide insight on best practices and limitations on quantifying the linearity of GaN HEMTs using various linearity performance metrics. We propose using communication standard-based metrics such as adjacent channel power ratio (ACPR) and error vector magnitude (EVM) to account for realistic device performance at the circuit and system level. Using Keysight ADS Verification Test Bench (VTB), we show that a device with 1.3 dB higher OIP3 results in 1.17% and 1.1 dB worse EVM and ACPR, respectively, under backed-off conditions, when compared to a device with lower OIP3.