Transistor S parameter measurement: corrections for 2-port common-electrode impedance and the corresponding 2-port to 3-port transforms

In 2-port transmission-parameter measurements on active devices, a residual common-electrode impedance can cause serious errors, particularly in the common-emitter configuration. Transforms are given which enable the true S parameters to be derived in terms of the measured parameters and the common-electrode impedance. It is shown that the inverses of these transforms can be used to derive the 3-port S parameters in terms of measured 2-port values. It is also shown that a unique relationship exists between the 2-port driving-point s parameters in the three configurations, which can be used as a partial check on system accuracy without the need for transformation to 3-port parameters.