On the Load-Pull Effect in MMIC Oscillator Measurements

Abstract

Low phase-noise MMIC oscillators are key components for microwave and mm-wave systems. As a consequence, phase-noise measurements of these circuits have become a subject of growing interest and importance. This paper demonstrates that MMIC oscillator circuits with their relatively low Q factors are prone to specific measurement errors. Caused by a load-pull effect, the measurement system can become part of the oscillator, which yields phase-noise data significantly below reality. Special care has to be taken in order to avoid such phenomena.

Analysis of Output Loading Effects in Autonomous Circuits

“…Among the possible undesired effects is the frequency pulling, or oscillation-frequency variations due to reflections from the load [16]- [19]. Some previous works on frequency pulling focus on the experimental characterization of this phenomenon, such as [18]- [19], or propose a linear open-loop simulation [20] of the oscillator transmission amplitude and phase, under variations of the load reflection coefficient.…”

“…Among the possible undesired effects is the frequency pulling, or oscillation-frequency variations due to reflections from the load [16]- [19]. Some previous works on frequency pulling focus on the experimental characterization of this phenomenon, such as [18]- [19], or propose a linear open-loop simulation [20] of the oscillator transmission amplitude and phase, under variations of the load reflection coefficient. Analytical studies, such as those in [16], [21]- [22], are very insightful, but assume a small variation of the output load, so that the oscillator total admittance or impedance function can be linearized with respect to this load.…”