SNA5000A time domain, TDR, and distance measurements

Here is the log mag and delay of Sdd11 (a balanced differential config) for a circuit that we need to characterize in the time domain:

Those are essentially the standard VNA measurements.

We can also use the math transform into the time domain.

In this setup, there is about 3 feet of cabling to my board and then a USB cable off of that in the analysis path that is also about 3 feet long. So the main discontinuity is at ~1.83 meters where the cable ends: 

You can zoom in and see data in mm or different lengths to view different portions of the board’s response:

Higher frequency analyzers may improve the time and distance resolution for small details. Markers show the distance in nsec and mm.

You can set this up as Impulse, step, or band pass depending on your time domain needs:

You can go into TDR mode and set It up for a specific topology as well. Here we are using 2 ports to make differential reflection measurements.

There is a deskew procedure in this wizard as well.

And here is the full TDR mode, shown here with data and memory on the left for comparison with or without the 2nd cable attached. Solid, repeatable data and good detail on impedance changes with markers showing distance from the port.

The left graph in this view uses impedance as the Y-axis as a different way to view changes in the circuit over distance.

VNAs like the SNA5000A have options including TDA and TDR that add complete options for time domain analysis of boards and paths. Siglent also offers single ended and differential TDR probes that may be useful for this type of analysis. 

You can learn more about these options in our TDR solution page: https://siglentna.com/time-domain-analysis-of-rf-systems/

For more details on TDR for transmissions using eye diagram and jitter analysis on the VNA platform, view the related article below.