Linearity Performance of Derivative Superposition in GaN HEMTs: A Device-to-Circuit Perspective

Abstract

A significant disconnect exists between the linearity metrics used by device and circuit engineers, degrading the maximum achievable performance in gallium nitride (GaN) technology. A detailed linearity analysis is performed using both device and circuit metrics on GaN devices that employ derivative superposition (DS) to evaluate the amplifier performance under modulated conditions of four different device variants. The limitations of conventional linearity metrics used at the device level, such as the output third-order intercept point ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text {OI}\text {P}_{{3}}$ </tex-math></inline-formula> ) and output 1-dB compression point ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text {OP}_{{1} \text {dB}}$ </tex-math></inline-formula> ), are examined and compared with communication standard-based metrics, such as the adjacent channel power ratio (ACPR) and error vector magnitude (EVM) to provide best practices for quantifying power amplifier (PA) linearity. It is found that employing more devices in the context of DS primarily improves the input-bias range of the device and not the peak amplifier performance under modulation. Ultimately, this work provides device engineers with a circuit-level perspective on linearity to help design transistors with enhanced RF performance for practical real-world deployment.