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…

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steve

May 08

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.

Picotest

March 6, 2023

PSRR Testing with the J2120A Line Injector

Dealing with Line Injection Issues (J2120A, J2123A)

Here is some information on the Power Supply Rejection Ratio (‘PSRR’) measurement setup using the J2120A line injector.

Depending on the load current and impedance you are trying to drive, the output of the injector may drop several volts.

In the vast majority of cases, the line injector is almost certainly working correctly. It is often the case that the test setup impacts the results and that a large voltage drop at its output is seen. We do get many questions about the J2120A and its operation.

After reading the following if you are still having issues, please let us know and we will be happy to have a call with you to discuss your particular measurement and test setup.

The J2120A is being asked to supply a certain amount of current (over frequency). If the impedance is too low, the J2120A runs…

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