Multimode TRL and LRL calibrated measurements of differential devices

A multimode TRL (MTRL) calibration technique is discussed to characterize broadband differential devices. This algorithm has the advantage of using ground-signal-signal-ground (G-S-S-G) probes in the measurements without the frequency limitations of some other 4-port algorithms due to the coupling between the signal lines. Calibration standards and the issues associated with them are described. Practical issues of the underlying theory, such as assigning the calculated eigenvalues to the correct mode and to the propagation direction, have also been addressed and one case-specific solution is suggested. Also an MTRL algorithm has been adopted to avoid some of the difficulties of calibration structures with MTRL. Odd mode test results of differential active circuits with MTRL using G-S-S-G probes are shown to be consistent with the two port test results of the same devices using S-G probes.