A Post-Processing De-Embedding Technique and Effect of TRL Measurement Using an Incorrect Fixturing

In conventional TRL (Thru-Reflection-Line) de-embedding technique, a test fixturing, which mimics the traces (called adaptor) leading to a DUT (Device Under Test), is fabricated. The TRL de-embedding procedure is performed on the test fixturing to obtain the calibration coefficients. Using the coefficients stored in the test instrument, the test instrument can thus report true characteristics (two-port s-parameter matrix, for example) of the DUT [1-4]. The TRL de-embedding technique is accurate only when the test fixturing is identical to the adaptor of the DUT in both length and configuration. However, in some situations, such as a multi-I/O DUT (for example, a switch SP4T that has one input and 4 outputs) with only ONE set of TRL de-embedding fixturing, the accuracy of the DUT measurement could be inaccurate. For example, the coupling of the adaptor on the DUT test vehicle could be artificially added to or subtracted from the DUT, if the TRL de-embedding fixtures are not identical in both length and configuration to the adaptors connected to the DUT. The reported isolation characteristic of the DUT is thus inaccurate. In this article, a post processing de-embedding technique, which employs directly electrical property of the adaptor, is proposed. The post-processing formulation was described and validated. The technique is then used to illustrate that the isolation of a DUT can be inaccurately reported if the TRL de-embedding fixturing is different from the adaptor of the DUT.