Products > Test Equipment
Affordable <200MHz PDN analysis / impedance measurement hardware?
inevitableavoidance:
--- Quote ---If you have space for UFL connectors, placing them in the design is a great way to probe power rails. Just place the vias right into the footprint, when you solder these manually it doesn't matter.
--- End quote ---
I love this idea - possibly also for PDN impedance measurements but mainly for supply ripple measurements. For the supply ripple measurements one could easily incorporate a DC blocking resistor and a 50R series termination resistor as well to make accurately probing them ridiculously easy. Definitely going to try this on a future project.
tszaboo:
--- Quote from: inevitableavoidance on November 28, 2024, 03:19:00 pm ---
--- Quote ---If you have space for UFL connectors, placing them in the design is a great way to probe power rails. Just place the vias right into the footprint, when you solder these manually it doesn't matter.
--- End quote ---
I love this idea - possibly also for PDN impedance measurements but mainly for supply ripple measurements. For the supply ripple measurements one could easily incorporate a DC blocking resistor and a 50R series termination resistor as well to make accurately probing them ridiculously easy. Definitely going to try this on a future project.
--- End quote ---
For ripple measurements, there are a few ways I was experimenting with. 2.54mm headers work of course, and it's a low effort solution. It's often there in many designs already. The UFL connectors work great. If you place a 1KOhm resistor in series with it, keep your 50 Ohm rules, you can create a makeshift 1:21 probe if you terminate it into the 50 Ohm of the oscilloscope. Depending on your application this 1KOhm load could be acceptable. I actually developed a power rail probe called PRP1 to cancel out the DC, and to provide the standard 50KOhm loading. I send those with a UFL-SMA cable with the intention to allow this probing method.
(shameless self promotion:) https://www.eevblog.com/forum/testgear/prp1-low-cost-2ghz-power-rail-probe/
joeqsmith:
--- Quote from: tszaboo on November 28, 2024, 02:13:49 pm ---The CMRR of these transformers on the low end is impacted by the physical size limitations. They are also fairly expensive, or time consuming to build and characterize. Compared to that an amplifier is easy (or it requires different skills).
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A few benefits to using a transformer are the wide frequency range they can operate over, they are well behaved (no resonances) and they are robust. The 3dB point for the transformer on the right is about 100Hz. Far below what these low cost VNAs can currently measure.
--- Quote ---In the manual, I show measuring my standards using my old HP network analyzer at 2.5kHz. The 0.1 ohm standard had 2.74% error without the common mode transformer. With it, 0.54%. I could repeat this at higher frequencies but it will only get worse. I could also attempt it with my H4 with / without transformer. I doubt it would meet your requirements with a direct connection.
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https://www.eevblog.com/forum/testgear/affordable-lt200mhz-pdn-analysis-hardware/msg5711731/#msg5711731
We were fortunate that Brian (Copper Mountain Tech) took the time to characterize and provide us with the S-parameters for a production transformer. Having that level of detail certainly helped speed up the design. I use that word loosely as it was more a lot of trial and error... :-DD So, yes, wasted time. Cost wise, I think the connectors were the highest priced components. Then the cores, box, coax, Kapton tape, hardware, labels.
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Attached is taken from Solver's user manual. Showing errors for all four test resistors being measured with and without the transformer. The 100uOhm shunt has an S21 of almost 100dB into the muck. My old HP can not even measure down this far. Even a noise free, solid-state approach wouldn't seem to gain me much.
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Old data prior to modifying the standards was shown (now crossed out). Showing the final results with and without transformer after mods, from the manual... :palm: Didn't member it being that bad...
joeqsmith:
Paper written by local member. Note how the powered and unpowered circuits diverge again above 20MHz.
https://www.signalintegrityjournal.com/blogs/8-for-good-measure/post/1344-using-a-vna-for-power-plane-impedance-analysis
joeqsmith:
A short clip from Copper Mountain Technologies presentation with Steve Sandler, after viewer asks about their common mode transformer design.
--- Quote ---Mom drowned all the dumb kids
--- End quote ---
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