Multimode TRL calibration method for the deembedding of differential devices

The differential RF output and input pins of our RF chips are connected to the outside world through a balun (balanced to unbalanced converter). In order to design such a passive balun, it is necessary to first measure the differential and common-mode S-parameters (scattering parameters) at the pins of the chip. These S-parameters are measured using a NWA (Network Analyzer).

With such a relatively large NWA it is physically impossible to directly connect the NWA to the pins of the chip. Therefore, RF cables and PCB (Printed Circuit Board) traces connect the NWA to the pins of the chip. This requires a so-called ‘’calibration’ procedure to correct the measurement data for the influence of the RF cables and PCB traces. With single-ended pins, the procedure is quite straight forward (SOLT or TRL calibration). With differential pins it is not, because the traces on the PCB are close to each other and therefore couple with each other. We cannot consider them as two separate single-ended pins anymore. Because of the coupling, we need a ‘multimode’ calibration, which takes into account the differential-mode and common-mode S-parameters as well as the mixed-mode S-parameters.

The task for the student is to develop a multimode calibration method and implement it as an easy to use software tool.

This project is split up into several parts:

  • start with the well-known 2-port single-ended TRL (Thru Reflect Line) calibration
  • expand the 2-port single-ended TRL calibration into a 2-port multimode calibration
  • measure teststructures on a PCB for the verification of both calibration procedures
  • implement both calibration procedures as an easy to use software tool

Supervisor:             Peter Baltus
Project duration:     9 months