Impeadance measurments / OSL calibration algorithm - Page 1
Forum section: electronics / rf-microwave

author: sixtimesseven
author_rank: Frequent Contributor
timestamp: December 13, 2018, 12:51:31 pm
content: HiI'm working on a script for the HP3577 to make accurate impeadance measurments over frequency according to this document:http://literature.cdn.keysight.com/litweb/pdf/5990-5902EN.pdfIn particular, I recreated the setup from page 29 (shunt-thru), with the instrument set to HighZ inputs on R and A (same as R and T as laid out in the Keysight document above).The measurements I get from my python script seem are fairly accurate without cal, however, I would like to do open / short / load calibration as the document states.QuoteI found some information on the calibration methods used when doing vna s-parameter measurements. But I could not find anything specific to impedance measurements. So I would love to be pointed to a reference to read up on the topic.So far I came up with this. In the ideal case the measurements should be:If the DUT is open: Vt ~ Vr ~Usource (because the input impedance of R and T >> Ri and >> 50Ohms)If the DUT is short: Vt = 0 and Vr = Usource * Ri / (50+Ri)If the DUT is loaded with Rload: Vt = Usource * Rload / (Rload + Ri + 50) and VR = Usource * (Ri + Rload) / (Ri + Rload + 50)This looks like some sort of optimization problem to me...(?)In addition I would first have to measure the Ri(f) and Rload(f) of course to get rid of that error as well. However the Usource might still vary and introduce an error.As I said, any sources or documents or other inputs would be appreciated.Thanks a lot!EDIT:- Apparently it is called OSL calibration- The usual spelling mistakesUPDATE:- Following papers on the topic are rather helpful:http://www.hpl.hp.com/hpjournal/94oct/oct94a12.pdfhttp://kripton2035.free.fr/Resources/Impedance%20Measurement%20Basic.pdf

author: sixtimesseven
author_rank: Frequent Contributor
timestamp: December 13, 2018, 11:50:57 pm
content: Well seems I was to quick to pose this question. Found this nice document after a lot more googling:http://www.hpl.hp.com/hpjournal/94oct/oct94a12.pdf... If I just had known for what to search for...Anyway, my code attached. Seems to givereasonablesomewhat believable resultsNow I have to measure my Load impedance and maybe build a second capacitive load as described in the document above. And I have to go over the code again some more - This is still wip and I'm also very tiered so use with care.All the relevant code I used so far is attached.Current code GitHub:https://github.com/sixtemesseven/visa-instruments

author: bson
author_rank: Unknown
timestamp: December 14, 2018, 12:45:36 am
content: Why not use the full OSL cal built in to the 3577? That's what I do...

author: sixtimesseven
author_rank: Frequent Contributor
timestamp: December 14, 2018, 07:41:15 am
content: Quote from: bson on December 14, 2018, 12:45:36 amSeveral reasons really:I like to have to have a script which I can run and document measurements without having to setup the instrument manually every time.Correct me if I'm wrong but I do not see how to input corrected impermanence over frequency values for the OLS standardsPossibility to implement other measurement schemes than implemented by HP originally