deembedding

Deembedding is a process used in high-frequency and RF testing to remove the influence of test fixtures, probes, and interconnects from measured electrical characteristics in order to reveal the intrinsic behavior of a device under test (DUT). By correcting for parasitic elements such as pad capacitances, probe inductances, and connector mismatches, deembedding places the reference planes at the actual device terminals, enabling repeatable and comparable measurements across different setups and test campaigns.

The practice relies on calibration techniques that characterize the non-DUT contributions, using a set of known standards. The most common methods are SOLT (short-open-load-thru), TRL (thru-reflect-line), and LRM (line-reflect-match). SOLT uses open, short, and matched load standards together with a through connection to model the fixture’s effect, while TRL uses a through, a reflect standard, and a line of known length. LRM employs a line and a reflect standard to extract the fixture parasitics. Each method has applicability depending on the transmission medium (for example coax, microstrip, or waveguide) and the available standards. Deembedding can be performed in the frequency domain on S-parameters or in the time domain for time-g-domain analyses.

The procedure typically involves performing a calibration with the standards, measuring the DUT, and then applying a computed deembedding model to shift the reference planes to the device terminals. Limitations include reliance on accurate standards and linear, time-invariant behavior; residual errors can remain if the standards are imperfect or if the DUT deviates from the model assumptions, such as in highly lossy or nonlinear cases. Deembedding is widely used in semiconductor testing, RF circuit design, and high-speed interconnect characterization.