Extension of Thru de-embedding technique for asymmetrical and differential devices

Accurate radiofrequency (RF) characterisation of on-chip or on-board devices often requires de-embedding to account for parallel and serial parasitics associated with bonding pads and interconnects. It is usually performed by well-known techniques such as Open-Short, Pad-Open-Short or Thru. However, these approaches or alternative techniques employing more standards assume a specific lumped-element model of bonding structures. This reduces de-embedding accuracy at higher frequencies. The Thru de-embedding technique is analysed in this paper and it is shown that under certain conditions de-embedding can be performed without modelling of the internal structure of the thru standard. The possibility to obtain the parameters of an error network by using a single test structure reduces significantly the costs of manufacturing standards and saves the measurement time. Further, an extension of the Thru technique is introduced. It is shown that at the expense of one more measurement, it is possible to characterise the system without additional assumptions. The presented method can be applied, for example, for de-embedding of fixtures with different connectors on either side. Additionally, the extension of Thru technique for de-embedding of differential devices is proposed. The paper verifies the extension for asymmetrical structures by simulation performed using Sonnet electromagnetic field solver in the frequency range 1-40-GHz. Finally, the extension for differential devices is verified by measurement in the frequency range 1-20-GHz and comparison of the results with Open-Short de-embedding technique.