Application of multimode TRL technique for accurate balun characterization and estimation of its impact on measurement of differential devices

Direct characterization of differential components requires multiport equipment, which is not always available. Thus, it is a common practice to attach balanced-unbalanced (balun) circuits to convert between single-ended and differential signals and perform the measurement using a lower cost two-port vector network analyzer (VNA) or a spectrum analyzer. However, removing the impact of baluns is a challenge. The Insertion Loss technique is commonly applied for two-port measurements of active differential devices to remove the impact of the baluns. In this work we apply the multimode TRL technique for accurate characterization of balun´s S-parameters. We apply the obtained characteristics to provide insight into the impact of balun´s and device under test (DUT) properties on the de-embedding accuracy when the Insertion Loss method is used to characterize active differential devices. The error estimation approach has been verified for a differential Low-Noise Amplifier (LNA) at 24 GHz realized in SiGe:C technology. S-parameters of the LNA have been measured directly using a four-port VNA and compared with those obtained from a two-port measurement implementing the Insertion Loss de-embedding technique.