Cable Shield Resistance Issue in a 2-port Impedance Measurement

Updated: Mar 3

November 15, 2021

Steve Sandler

For this extreme measurement example, I selected a simple problem that has been widely published by myself and many others, including past DesignCon papers. The solution is well understood, providing a simple example to illustrate the process.

Figure 1 An example of the very large error created by the cable shield resistance in the traditional 2-port Shunt-Through measurement setup.

The shield resistance error is often much larger than the device we are measuring, as is the case in Figure 1, showing a 500% error. There are three possible solutions to this measurement issue. One possible solution is to calibrate out the error. While this may work, the calibration does not correct the sensitivity, so very small changes in contact resistance of the probes or shield resistance, for example, will result in large measurement errors.

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