An Unequally Spaced Multi-Tone Load-Pull Characterization Technique for Simultaneous Linearity and Efficiency Assessment of RF Power Devices

This paper presents an innovative experimental method for microwave power devices linearity characterization, based on a carefully designed multi-tone signal. Measurements working deeper into the understanding of in-band (IB) signal-to-noise characterization of nonlinear devices are presented. The test signal used in this paper is based on an unequally spaced multi-tone (USMT) signal, which is a tailored stimulus signal with flexible statistics. Its originality stands in its inherent property of allowing signal and intermodulation (IM) distortion separation to facilitate the derivation of the IB signal-to-noise ratio or linearity degradation, without assuming any specific modulation format. For the first time, this paper reports measurements with small \Delta _{f} frequency arrangement using an USMT signal to investigate low frequencies (LFs) parasitic effect on the current and the linearity. Furthermore, this test bench allows to analyze together LF phenomena ("trapping effect", memory effect, etc.) and high-frequency phenomena under large-signal condition with a telecom like signal. Smith chart load-pull linearity contours under wideband USMT test signals are reported for the first time. This provides a new tool to check system-level design specifications and to optimize radio frequency (RF) power amplifier structures with modulated signals. The measurements were performed using a GaN high-electron-mobility transistors (HEMT) 3-W transistor.