Calculating impedance spectrum

[GlenS]

Hi,

I'm trying to take an impedance spectrum of a semiconductor.  I'm using a PCIe-6221 DAQ and a function generator.  I've written a VI which causes the function generator perform a frequency sweep and then records the AC signal.  My problem is that I now need to extract the spectrum from the AC signal.  I really just need to get (time, voltage) data points from the maxima of the sine sweep and then join them (see attached diagram, sorry for poor drawing quality).  I'm completely stuck for an efficient way to do this however.  I've been reading the impedance spectrum posts but can't find any reference to this specifc problem.

[Margaret F.]

Hi,

Thank you for posting to the NI Forums! A suggestion would be to find the difference between your highest peak and your lowest. You could do this using something like the Array Max & Min function. You could then decide that you want to find every peak that is for instance greater than 50% of that difference. Say the difference is 4.8, so 50% is 2.4. You could search through the data for anything above 2.4 and have the loop end when the signal drops below 2.4 thereby leaving you 1 "hump" of data. You could then search this data for a max value. 

You would then have to pick up where you left off and go to the next "hump" in the next iteration of the loop.

Just to let you know, there is an express vi in the Sound and Vibration Toolkit called  Peak Search which actaully does this for you. Hope this helps!

[GlenS]

Hi Margaret,

Thanks for the suggestion.  The solution is actually just to Fourier Transform the data.  I can't believe it took me two days to work that out.  Thanks for the help though.  🙂

Glen