Increased feedback due to package mounting

The affects of a discontinuity in the ground plane created by a difference in package and PCB thickness is examined. The overall circuit affects for a packaged transistor, in which its thickness is different than the PCB thickness, were simulated with commercially available electromagnetic 2D and 3D CAD tools. It was determined from the simulation results, that the discontinuity creates an inductive feedback path around the package that affects circuit performance. The affect of the ground step discontinuity and its associated strong dependency of the source inductance on FET device's common source gain have been highlighted.