I just got a Tek MSO58B scope with the PWR license and the Picotest PI Solution bundle to measure PDN impedance and capacitor parasitics out to 100 MHz. I have worked with VNAs in the past and understand the calibration / de-embedding process for RF systems and know that test fixtures and cables are going to introduce additional artifacts. However, the low frequency nature of this has me wanting to make sure I'm not missing something regarding the calibration. I have the J2102B in series to help minimize ground loop currents from impacting low frequency measurements, but want to make sure I'm not missing something else during the calibration process that would impact the measured data.
1. I'm assuming I should be taking SOL measurements to remove the effect of cables and test hardware? 2. I'm wondering if there is any integrated calibration incorporated into the Tek Power Integrity Software, like on the Bode 100? 3, Assuming there is no integrated calibration solution, what calculations measurements are required to remove the effect of the test setup from the actual measurements (assuming we're looking for Z21)?
Thanks,
Nick F.
Great questions! I do imagine the calibration software will eventually be added to the scope, but as of now, there isn't any. You didn't say anything about the impedance magnitude, but this sounds like it is a 2-port shunt through measurement, so I'll assume it is low impedance. In that case the only impactful error is the SHORT. So you could measure a SHORT and then subtract that from your measurements. This will mostly remove the cable and probe coupling, which appears as increased inductance.
My rule is to ALWAYS measure something you know, and of similar magnitude, before measuring something you don't know. We keep low value resistors around for that purpose. We have them from about 250uOhms up to about 100 milliOhms.
My experience with the MSO6B has been really good for this measurement, and yes, calibration will improve it, and I expect that could come in time. The MSO5B is higher noise than the MSO6B, which impacts the minimum measurable impedance, but since we can go to about 100uOhms with the MSO6B, I imagine you can do 1 milliOhm or better with the MSO5B.