Transistor S parameter measurement: 2-port to 3-port transforms

In 2-port s parameter measurements on active devices, residual common-electrode impedance can cause serious errors, particularly in the common-emitter configuration. Transforms have already been given for the elimination of this impedance prior to transformation to the corresponding 3-port parameters for checking the sum-to-unity property. It is shown that, by combining the two sets of transforms, it is possible to convert directly from the measured 2-port parameters, including the effect of common-electrode impedance, to 3-port parameters. The necessary circuit conditions that must be satisfied in the use of the transforms are re-emphasised.