Modeling ground signal probe invasiveness and its effect on extracted inductor Q

The invasive nature of the ground-signal wafer probe is modeled and its effect on extracted inductor Q is investigated. Data is presented demonstrating that the extracted Q of surface mount (SMT) inductors is lower when measured with ground-signal (GS) versus ground-signal-ground (GSG) coaxial wafer probes. We believe that the degradation in Q is caused by a quasi-TEM mode that effectively adds resistive loss to the inductor. A simple circuit model is proposed which accounts for the interaction of this mode with the inductor.