Accurate Multi-Port De-Embedding of Crosstalk-Affected Fixtures for High Speed Devices

The paper investigates how much the crosstalk within the fixtures for multi-port device measurements affect the de-embedded results. Usually such type of fixtures are designed to minimize the crosstalk among the lines or the differential pairs, thus the de-embedded can be performed by applying iteratively the well-known 4-port de-embedding process based on the S-to-T and T-to-S parameter conversion. However such process ignores the crosstalk among the lines within the fixtures; in the case that the coupling is not negligible or it is ignored, especially for devices working at very high frequency (tens of GHz), the simple 4-port de-embedding leads to errors in the extraction DUT S-parameters. The multiport de-embedding algorithm reviewed in this paper, instead, is able to take this coupling into account, independently on the amount of crosstalk within the fixtures. The de-embedding based on multiport S-to-T parameters conversion (and vice-versa) always provides perfectly de-embedded DUT parameters, as highlighted by a realistic exampled based on a multipin connector for PAM4-based 112 Gbps applications.