Multi-Tone Measurement System With the State-of-the-Art Active if and Rf Load-Pull Capability

Abstract

This paper reports a re¯ned multi-tone waveform measurement system for the robust characterization and optimization of nonlinear microwave devices when driven by broadband multitone stimuli. This enhanced system has the ability to present speci¯c, constant broadband impedances, not only at baseband (IF) frequencies, but also at RF frequencies, particularly, around the carrier and signi¯cant harmonics. This functionality is key in studying the e®ects of out-of-band impedance termination on both short and long-term electrical memory e®ects. Achieving such comprehensive impedance control across wide modulation bandwidths is also critical in allowing the \emulation" of emerging power ampli¯er modes and architectures, and the subsequent waveform characterization of devices operating in these complex and often dynamic impedance environments. Initially, the baseband load-pull capabilities of the enhanced measurement system are experimentally demonstrated through the measurement of adjacent channel power (ACP) behavior of a class AB biased 10 W GaN HEMT, in response to a varying baseband load. Complete baseband and RF impedance control is then demonstrated through the emulation and analysis of a modulated Class-J impedance environment, which interestingly highlights the presence of separate optimum baseband impedance conditions necessary for the suppression of individual IM products.