Characterization Technique to Reveal Critical Resonances in Non-linear RF Circuits

Abstract

The presence of critical resonances can significantly impact the stable and robust operation of microwave amplifiers, leading to spurious oscillations in the worst case. In this work, a technique based on noise measurements performed with a spectrum analyzer is presented to experimentally characterize these resonances. Broadband white noise is injected into the input of the circuit, so the critical resonances are clearly revealed above the noise floor of the measuring instrument, without the need of exigent settings and far from the bifurcation point. In addition to detecting potentially risky resonances, the actual position of the critical poles on the pole-zero map can be estimated from these noise measurements by applying pole-zero identification techniques. The noise injection technique has been tested in two nonlinear prototypes in microstrip technology: an analog frequency divider and an L -band amplifier.