Products > Test Equipment

Affordable <200MHz PDN analysis / impedance measurement hardware?

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rhb:
I’ve reflected on this a good bit and would like to urge you as strongly as possible to attack the problem from first principles, a 4 channel DSO and a clean 50-50 square wave source.  And all that annoying algebra.  I got the crap beat out of me doing a 1st order approximation of a thermistor a few days ago.  Trivial algebra, but if you don’t practice, all skills atrophy and die.  Boy, did I ever get handed my head on a platter.  I finally sorted it, but it took hours to do what would have taken 5 minutes in HS.

It’s a significant effort, but your understanding of network analysis will expand greatly.  Based on my experience, the value of the education exceeds the price of a 4395A.

I have dozens of small bits of test gear I built when I was a grad student.  Don’t even remember what they are or how to hook them up.  Some succeeded, some failed and some succeeded but I and an EE at work failed to test it correctly and it was 30+ years before I realized I’d done it!  At that point I had a crazy high end lab and had learned a bit about impedance matching and what a *really* bad mismatch looks like.


Failure is your best friend.  It tells you what doesn’t work.

The directional bridge is the sum of a pair of sinusoids measured at different points.  If you are looking for impedance mismatch it’s handy.  As I understood the question it was directed at locating power supply impedance mismatches.  I may well have misunderstood the question.

Have Fun!
Reg

mawyatt:

--- Quote from: inevitableavoidance on November 12, 2024, 10:31:11 pm ---..... I wish someone would make and standardise a miniature “kelvin” RF connector for this

--- End quote ---

You may find the Split-Kelvin Technique shown here useful for SMD components, certainly works well in the milli-Ω impedance levels with our LCR Bench Meters.

https://www.eevblog.com/forum/projects/different-type-lcr-smd-fixture/

Also, thanks for bringing up the AD2, we've been playing around with it this afternoon and it's quite good at resolving low Z components, especially if you pay attention to the DUT connections (here's where Kelvin Techniques really pay off). With the buffered output higher current drive signal, and the  additional differential low noise gain we can begin to understand the excellent results you've achieved with the AD2 low Z measurements :-+

As an interesting side note, some of the new "entry level" DSOs like the superb Siglent SDS800X HD with 500uV/Div analog scaling and true 12 bit ADCs almost beg for something along the these lines for "Impedance Measurement" augmentation with the built-in Bode Function. They have all the key ingredients already built-in for this to happen ::)

Best

mawyatt:

--- Quote from: rhb on November 13, 2024, 12:46:38 am ---I’ve reflected on this a good bit and would like to urge you as strongly as possible to attack the problem from first principles, a 4 channel DSO and a clean 50-50 square wave source.  And all that annoying algebra.  I got the crap beat out of me doing a 1st order approximation of a thermistor a few days ago.  Trivial algebra, but if you don’t practice, all skills atrophy and die.  Boy, did I ever get handed my head on a platter.  I finally sorted it, but it took hours to do what would have taken 5 minutes in HS.

It’s a significant effort, but your understanding of network analysis will expand greatly.  Based on my experience, the value of the education exceeds the price of a 4395A.

I have dozens of small bits of test gear I built when I was a grad student.  Don’t even remember what they are or how to hook them up.  Some succeeded, some failed and some succeeded but I and an EE at work failed to test it correctly and it was 30+ years before I realized I’d done it!  At that point I had a crazy high end lab and had learned a bit about impedance matching and what a *really* bad mismatch looks like.


Failure is your best friend.  It tells you what doesn’t work.

The directional bridge is the sum of a pair of sinusoids measured at different points.  If you are looking for impedance mismatch it’s handy.  As I understood the question it was directed at locating power supply impedance mismatches.  I may well have misunderstood the question.

Have Fun!
Reg

--- End quote ---

Yes us older folks (I'm even older   :-\  ) learned to appreciate fundamentals early on, and still find it fascinating how electronic things work. From that perspective it's also fun to learn how old & modern instruments work and how to adapt their use.

When working where time is $, investing significant time may be unwise when one can just buy a specific instrument for the task. However, making custom adapters or fixtures is a great means of learning and putting fundamentals at work to help the measurement tasks at hand, and can usually fit within a retiree's budget :-+

Anyway, vaguely remember when a Grad Student or Post Doc would do anything for a brew, seems it's come full circle now ???

Best

joeqsmith:

--- Quote from: nctnico on November 13, 2024, 12:30:59 am ---
--- Quote from: rhb on November 12, 2024, 11:12:51 pm ---Don’t underestimate a DSO with memory and a decent sig gen.   Suck the data into Octave for analysis.  The really hard part is a low frequency directional bridge.

--- End quote ---
Why would you want to use a directional bridge? For PDN you use a 2 port measurement AFAIK. Push AC current into the DUT from the transmitter port (generator) and measure the resulting AC voltage across the DUT.

--- End quote ---



--- Quote from: rhb on November 13, 2024, 12:46:38 am ---I’ve reflected on this a good bit and would like to urge you as strongly as possible to attack the problem from first principles, a 4 channel DSO and a clean 50-50 square wave source.  And all that annoying algebra.  I got the crap beat out of me doing a 1st order approximation of a thermistor a few days ago.  Trivial algebra, but if you don’t practice, all skills atrophy and die.  Boy, did I ever get handed my head on a platter.  I finally sorted it, but it took hours to do what would have taken 5 minutes in HS.

It’s a significant effort, but your understanding of network analysis will expand greatly.  Based on my experience, the value of the education exceeds the price of a 4395A.

I have dozens of small bits of test gear I built when I was a grad student.  Don’t even remember what they are or how to hook them up.  Some succeeded, some failed and some succeeded but I and an EE at work failed to test it correctly and it was 30+ years before I realized I’d done it!  At that point I had a crazy high end lab and had learned a bit about impedance matching and what a *really* bad mismatch looks like.

Failure is your best friend.  It tells you what doesn’t work.

The directional bridge is the sum of a pair of sinusoids measured at different points.  If you are looking for impedance mismatch it’s handy.  As I understood the question it was directed at locating power supply impedance mismatches.  I may well have misunderstood the question.

Have Fun!
Reg

--- End quote ---

He seems to be asking why you need the bridge to measure S21.  I took it that you feel you can make these measurements with S11, possible not understanding the errors that go along with it for this particular application.

joeqsmith:

--- Quote from: joeqsmith on November 12, 2024, 11:29:52 pm ---
--- Quote from: tszaboo on November 12, 2024, 10:43:45 pm ---Ah, you want to measure it while on, not like with the VNAs.

--- End quote ---

?

--- End quote ---
You seem to infer that when using a VNA to measure a PDN, you would never power it up.  Obviously this is not correct. 

Attached plots are using the original NanoVNA to look at a PDN with the populated board both unpowered and powered.  Also shown is the same bare board. 

Of course, there are risks.  The blocking caps I made for these measurements will support these low frequencies.  They could pack a punch to the VNA.  I have not had damaged my original NanoVNA when making these measurements but it certainly could happen.    I did however unknowingly damage my H4 with what appeared to be an ESD event last time I used it.  I sacrificed my original NanoVNA to bring it back to life.  These VNAs do not have a lot of protection.   

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