Author Topic: Affordable <200MHz PDN analysis / impedance measurement hardware?  (Read 7565 times)

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Offline joeqsmith

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Re: Affordable <200MHz PDN analysis / impedance measurement hardware?
« Reply #75 on: November 17, 2024, 03:45:07 pm »
The first thing I noticed when I took their new H4 apart, the manufacture added two capacitors in series with the connectors.  It's still AC coupled at the mixers. No idea what they are thinking.

I went ahead and reworked their VNA, removing those input caps, adding the TVSs and additional caps, similar to what I had done with mine.   It's performance is no where near what I get with mine.   

They had originally purchased two of the NanoVNAs and gave one to me to get started.   I plan to steal the parts from theirs like I did with my H4 after it was damaged.   My guess is the synthesizer but maybe there is a problem with the firmware configuring the MS part.

Shown is flippers H4 after my mods with 30Hz IFBW, 401pts, 1.6-10kHz, both ports terminated, same firmware but MS.  Thru cal.  Scaled -50 to -100.  I expect yours would be similar with 30Hz.
« Last Edit: November 18, 2024, 03:18:08 pm by joeqsmith »
 

Offline joeqsmith

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Re: Affordable <200MHz PDN analysis / impedance measurement hardware?
« Reply #76 on: November 18, 2024, 01:17:50 am »
My old H4 also had a mezzanine board that was used to interface between the main PCB and the LCD.  From photo, you can see the TX input goes from the connector to R10.  Yours may have a capacitor there for what ever reason now.  The same for port 2.  Note, this was taken after swapping mixers but prior to adding caps and TVSs.   

Compared to the 75dB I previously showed with Solver, using 30Hz IFBW with this old hardware, gets us an easy 80dB below 5KHz, and 90dB above.  Of course, it takes a long time to sweep. 

I'm surprised that none of this was mentioned in the groups.io or by the manufactures, but then again....  Keeping my fingers crossed that swapping the synthesizer will get my friends new H4 to perform as well as mine.   
« Last Edit: November 18, 2024, 03:19:46 pm by joeqsmith »
 

Offline joeqsmith

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Re: Affordable <200MHz PDN analysis / impedance measurement hardware?
« Reply #77 on: November 18, 2024, 05:04:29 pm »
This was the only post I found on the change.  No mention of the low frequency performance.   

Quote
Hugen,

Hello Salva, Due to Si5351 out of stock, we started to use MS5351M to replace SI5351A-B-GT. In order to obtain the widest possible range of measurement frequencies for the NanoVNA, we have extended some usage ranges beyond those specified in the Si5351 manual. Although the performance specified in the MS5351M manual is almost identical to that of the Si5351A-B-GT, they differ slightly for the parts that go beyond the manual. Simply put the MS5351M has a slightly higher VCO frequency than the Si5351, the MS5351M has a steeper square wave edge, and the MS5351M has slightly lower phase noise than the Si5351. With targeted software adjustments, it is possible to get slightly better results with the MS5351M than with the Si5351. Since the frequency range of the VCO is slightly different, the frequency points for switching different divider are different when using Si5351 and when using MS5351, so if the software's signal generator MODE is different from the actual chip installed, it will generate some anomalies around the divider switching frequency.
You can set the measurement frequency to 50kHz-900MHz and check if some abnormal spurious is generated. If there are multiple abnormal spurious, the signal generator mode of the software is not the same as the actual installed chip. On our NanoVNA-H and NanoVNA-H4, if MS5351M is used, we add the MS suffix to the version number on the label of the backshell, such as 3.6_MS or 4.3_MS.
 

https://groups.io/g/nanovna-users/topic/88101278#msg26386

Offline inevitableavoidanceTopic starter

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Re: Affordable <200MHz PDN analysis / impedance measurement hardware?
« Reply #78 on: November 18, 2024, 10:22:24 pm »
I'm getting nowhere near that figure - 10dB per division:
...
Where do I find the revision and synthesizer?

The back of the unit should have the hardware revision and possibly an _MS.   You can also select Config, Expert Settings, More.  At the top is should show the synthesizer selected (MS5351 or Si5351).   

You can try to set the IFBW to 30Hz which should at least remove the pattern you are seeing.

That’s way better indeed:



It’s a 4.3_MS
 
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Offline joeqsmith

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Re: Affordable <200MHz PDN analysis / impedance measurement hardware?
« Reply #79 on: November 18, 2024, 10:50:31 pm »
Thanks for checking.  That's on par with my friends.   I should have his original NanoVNA in a few days.  I'll post the results once I start swapping parts. 

If it is the clock generator, it doesn't really help you other than maybe someone you know might be willing to swap you their older unit to get a brand new one.   

Offline Kean

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Re: Affordable <200MHz PDN analysis / impedance measurement hardware?
« Reply #80 on: November 19, 2024, 12:50:46 am »
Following along as I have a new Zeenko NanoVNA-H4 on the way
 

Offline inevitableavoidanceTopic starter

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Re: Affordable <200MHz PDN analysis / impedance measurement hardware?
« Reply #81 on: November 19, 2024, 10:23:08 am »
Thanks for checking.  That's on par with my friends.   I should have his original NanoVNA in a few days.  I'll post the results once I start swapping parts. 

If it is the clock generator, it doesn't really help you other than maybe someone you know might be willing to swap you their older unit to get a brand new one.

Awesome, curious to know. Would be dope to get some more low end performance out of it. I do indeed see the series capacitors on the SMA in and outputs on the PCB here. Can’t imagine that to pass a whole lot of low end.

Seeing ferrite beads without bulk capacitors also tends to worry me - they usually resonate like crazy in the lower kHz’es. Might use the AD2 to measure its PDN impedances. ;)
« Last Edit: November 19, 2024, 10:27:12 am by inevitableavoidance »
 

Offline joeqsmith

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Re: Affordable <200MHz PDN analysis / impedance measurement hardware?
« Reply #82 on: November 19, 2024, 01:18:43 pm »
Following along as I have a new Zeenko NanoVNA-H4 on the way

Once you receive it, please run the same test and post your results along with the hardware revision and type of synthesizer.   

Awesome, curious to know. Would be dope to get some more low end performance out of it. I do indeed see the series capacitors on the SMA in and outputs on the PCB here. Can’t imagine that to pass a whole lot of low end.

Seeing ferrite beads without bulk capacitors also tends to worry me - they usually resonate like crazy in the lower kHz’es. Might use the AD2 to measure its PDN impedances. ;)

My only guess is there was a fairly large group of users applying DC to their VNAs and smoking the input network and then claiming the units were defective under warranty. 

FYI, looking at my H4, I had also added another cap near the synthesizer. 

***
I had connected a step attenuator to H4 after repairs and swept from 0 to 80dB and 50k to 2GHz.  This may also give you a good comparison.  My guess is your high frequency performance is not as good as I saw some improvements by adding those caps to mine.  If you want to know values and placement, let me know and I can provide them but I would start by running a baseline.   Maybe with a working unit, the gains would be less dramatic. 

https://www.eevblog.com/forum/rf-microwave/nanovna-custom-software/msg5698991/#msg5698991


« Last Edit: November 19, 2024, 01:27:30 pm by joeqsmith »
 

Offline inevitableavoidanceTopic starter

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Re: Affordable <200MHz PDN analysis / impedance measurement hardware?
« Reply #83 on: November 19, 2024, 04:48:44 pm »
My only guess is there was a fairly large group of users applying DC to their VNAs and smoking the input network and then claiming the units were defective under warranty. 

I removed both the in- and output capacitors to see how much extra low end would get through:


More than I expected, but at a lower frequency than I thought. This is the difference in noise floor in the 1k6-50k range:


Before this I also took at look at the power delivery networks on the board - there's barely any decoupling in any of them, and the traces used are ridiculously thin. This is the difference in full range noise floor after adding a handful of 2.2uF 0603 capacitors:


Makes me feel like a first year EE student again, adding capacitors hoping it'll solve a problem, though with more knowledge about the difference it makes, and apparently it's still a valid approach.

Quite surprised to be honest that even VNA designing EE's don't seem to know how to properly apply decoupling capacitors.

The NanoVNA-H4 is specified like this:
70dB | 50kHz-300MHz
60dB | 300MHz-900MHz
40dB | 0,9GHz-1,5GHz

Before I was getting:
70dB | 10kHz-436MHz
60dB | 436MHz-740MHz
40dB | 740MHz-1,7GHz

Now I'm getting nearly getting:
70dB | 10kHz-661MHz
60dB | 661MHz-1446MHz
40dB | 1446MHz-1,85GHz

How did you improve the decoupling department over there? What did you add where?
« Last Edit: November 19, 2024, 05:15:40 pm by inevitableavoidance »
 

Offline joeqsmith

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Re: Affordable <200MHz PDN analysis / impedance measurement hardware?
« Reply #84 on: November 19, 2024, 05:21:59 pm »
Makes me feel like a first year EE student again, adding capacitors hoping it'll solve a problem, though with more knowledge about the difference it makes, and apparently it's still a valid approach.

 :-DD :-DD  I am near retirement and still feel like a first year student.   :-DD

How did you improve the decoupling department over there? What did you add where?

A couple of things.  There was no attempt what so ever to look at this from anything beyond an empirical test.  I am not suggesting these changes will help or hurt the performance.  My only goal in adding them was to see if I could detect a change in the performance of the VNA after I had damaged it.  It was part of my hunting down the root problem.   I just never backed out the changes and in my case noticed an improvement at the higher frequencies.   

Lets start with the same schematic for the H4.  See attached.  This will not match your H4.  Note the lack of the DC blocking caps.   

I placed a 4.7uF 0603 cer. across C10, C39, C41, C43.   I placed a 10uF 1206 cer across C61 & C62 (doubt these made any difference, I was shotgunning).    I placed a TVS on each port to ground, at the connector.  The parts I had on-hand are about a half puff.  While they did not effect the performance,  I would look for a better part.  Digikey has some with much lower capacitance. 

I'm still surprised I damaged mine and my only goal was not to loose it to ESD a second time.   If you go ahead and add those first four caps, I am interested in seeing if you find any difference, and what mixers were installed in your H4.   

****
When I state across, I turned the caps on-end and solder them right to the pads along side the original caps.   For the TVSs,  I scraped a bit of mask and soldered them right to the ground plane, near the SMAs. 
« Last Edit: November 19, 2024, 05:25:17 pm by joeqsmith »
 

Offline inevitableavoidanceTopic starter

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Re: Affordable <200MHz PDN analysis / impedance measurement hardware?
« Reply #85 on: November 19, 2024, 05:30:09 pm »
Quote
:-DD :-DD  I am near retirement and still feel like a first year student.   :-DD

It's nice to never stop learning. :)

Quote
I placed a 4.7uF 0603 cer. across C10, C39, C41, C43.   I placed a 10uF 1206 cer across C61 & C62 (doubt these made any difference, I was shotgunning).    I placed a TVS on each port to ground, at the connector.  The parts I had on-hand are about a half puff.  While they did not effect the performance,  I would look for a better part.  Digikey has some with much lower capacitance.

Looking at the schematic yours has more decoupling already! Two 100nF's per mixer compared to one over here. Looks like we had similar strategies, I added 3x2.2uF 0603 to each of the mixers (scratching away some solder mask from the ground plane and sliding them right up to the IC pin - aiming to minimize inductance) and 1x2.2uF to the x5351. Mixers on mine are the SA602A. So the difference in the graph in my previous post could very well be similar to the difference you've seen over there.
 

Offline joeqsmith

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Re: Affordable <200MHz PDN analysis / impedance measurement hardware?
« Reply #86 on: November 19, 2024, 05:39:57 pm »
Thanks for checking those mixers.  I had seen they had also used a different part and I wanted to make sure we didn't have yet another variable in the mix. 

With you basically replicating my finding, it's all pointing to that original synthesizer.  I'll install the latest firmware on friends original NanoVNA and run a baseline with it before I start pulling parts. 

***
Was that last data you collected using 1kHz IFBW?  I try to remember to include that when I post and have mine setup to default to 1k for now.   Wish the firmware allowed me to set it over the remote link. 
« Last Edit: November 19, 2024, 05:42:29 pm by joeqsmith »
 

Offline joeqsmith

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Re: Affordable <200MHz PDN analysis / impedance measurement hardware?
« Reply #87 on: November 19, 2024, 06:10:17 pm »
If you wanted to try adding a bit more bulk, I had also added 4.7uF on the front side of the ferrite.  Doubt it made much of a difference.   

Showing the jist of the bypass mod.  Sorry about the sloppy soldering.  I had pulled the mixer three times and was getting a bit impatient trying to hunt that problem down. 

Guessing you removed the mask where L3 silkscreen is and went right to the pin.  I was a bit concern I may damage the mask and short out the supply so I elevated them a bit when I soldered them. 

Offline Kean

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Re: Affordable <200MHz PDN analysis / impedance measurement hardware?
« Reply #88 on: November 20, 2024, 01:21:38 am »
Joe, did I understand that post from Hugen correctly that there is a special firmware needed to get the best performance from the MS clock generator?
If so, have you found that firmware posted somewhere?  I don't know if the firmware can autodetect which generator is installed and compensate...
 

Offline joeqsmith

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Re: Affordable <200MHz PDN analysis / impedance measurement hardware?
« Reply #89 on: November 20, 2024, 01:57:36 am »
Joe, did I understand that post from Hugen correctly that there is a special firmware needed to get the best performance from the MS clock generator?

Correct, there are two versions, one for the Si the other for the MS. 

If so, have you found that firmware posted somewhere? 

Yes, they are both in the release area.   I am currently testing with NanoVNA-H4-MS_20240220.dfu

I don't know if the firmware can autodetect which generator is installed and compensate...

As I understand it, they are the same firmware with different defaults for the two synthesizer but you can manually change the type using the firmware's UI.  I assume they offer two flavors in an effort to help those people who can't/won't read.   

See my prior post on how to select it:
Quote
You can also select Config, Expert Settings, More.  At the top is should show the synthesizer selected (MS5351 or Si5351).   


Offline Kean

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Re: Affordable <200MHz PDN analysis / impedance measurement hardware?
« Reply #90 on: November 20, 2024, 08:32:43 am »
Thanks.  I hadn't got around to looking into it too far, and that sounds better than I expected.

Pity about the hardware side.  I bought it to complement my existing NanoVNA V2 Plus4 and LiteVNA 64, for lower frequency measurements.
I'll try run your test once it arrives.  I ordered it a week ago and it doesn't seem to have hopped on a flight yet.
 

Offline ftg

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Re: Affordable <200MHz PDN analysis / impedance measurement hardware?
« Reply #91 on: November 20, 2024, 08:52:40 am »
All SA602/SA612/NE602/NE612 have had the same die inside since the Philips fab making 602's burned down.

I wonder how NanoVNA pricing will go in the future, now that SA612 is out of production.
https://www.nxp.com/products/no-longer-manufactured/double-balanced-mixer-and-oscillator:SA612AD


 

Offline inevitableavoidanceTopic starter

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Re: Affordable <200MHz PDN analysis / impedance measurement hardware?
« Reply #92 on: November 20, 2024, 09:25:39 am »
Guessing you removed the mask where L3 silkscreen is and went right to the pin.  I was a bit concern I may damage the mask and short out the supply so I elevated them a bit when I soldered them.

Right there indeed. I've recently had a colleague do some hyperlynx simulations of the difference a couple of millimeters of trace makes to the inductance (and thus high frequency impedance) of decoupling capacitors, which turns out to be more significant than the type of MLCC you'd pick. The fact that they have a 100pF capacitor in that board makes no sense (in general since a 100nF has the same parasitic inductance but also specifically) with the inductance that's still between the IC's power pins. High frequency operated ICs that have the power pins on different sides of the package make no sense to me!

In the same sense, more is simply better, as they all parallel to decrease the ESR and ESL. I'm curious what further high end improvement you'd be able to get adding more close by.
 

Offline inevitableavoidanceTopic starter

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Re: Affordable <200MHz PDN analysis / impedance measurement hardware?
« Reply #93 on: November 20, 2024, 12:49:19 pm »
Scored some more dynamic range by fully soldering down the circumference of the RX Shield. Blue = unmodified, green = optimized decoupling, red = soldered down RX shield:



Didn't improve it everywhere, but it is looking 'cleaner'. Curious what the rest is caused by.

Do you have any clue what repeating pattern I'm seeing here? I've zoomed in the first bit and overlayed it with the second occurrence.

« Last Edit: November 20, 2024, 01:00:47 pm by inevitableavoidance »
 

Offline joeqsmith

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Re: Affordable <200MHz PDN analysis / impedance measurement hardware?
« Reply #94 on: November 20, 2024, 02:02:55 pm »
Guessing you removed the mask where L3 silkscreen is and went right to the pin.  I was a bit concern I may damage the mask and short out the supply so I elevated them a bit when I soldered them.
Right there indeed.    .... with the inductance that's still between the IC's power pins.

I did not pay attention to the layout when I pulled the mixers.  I don't know where the optimum location is.  Looks like they may have had a ground right under the part.  It may provide a shorter loop.    We are more interested in the H4's low frequency performance for PDN work.    The port matching is better on the original NanoVNAs we have and the released firmware is also more stable now.   We were using a hacked up version of firmware on the original NanoVNA to get something stable enough to use.   Although I have had the current release lockup at least twice, requiring a power cycle.  I would like to see a flavor of firmware that provides full access to the remote interface and removes any unnecessary code that is not required to run it headless (in hopes of something rock solid), and change the protocol to match the LiteVNA...   

Beyond narrow band measurements and the improved low frequency performance the H4 offers, I use the LiteVNA. 

***
I am sure they have switch points in the firmware.  Plus harmonics, I am not surprised you could see repeating patterns.   If you average the crap out of it, you may find more detail.   
« Last Edit: November 20, 2024, 02:04:40 pm by joeqsmith »
 

Offline joeqsmith

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Re: Affordable <200MHz PDN analysis / impedance measurement hardware?
« Reply #95 on: November 21, 2024, 04:06:10 pm »
Swapping the MS for the Si synthesizer had little to no effect.   This was with the exact same firmware installed in mine with the same settings.  :palm:    I rechecked all my mods on the new H4 and can't explain why this one performs so poorly.   I had added all the same caps at this point.   There is one other potential difference...   

Guessing you removed the mask where L3 silkscreen is and went right to the pin.
Right there indeed.    .... with the inductance that's still between the IC's power pins.
I did not pay attention to the layout when I pulled the mixers.

Pulling the mixers from the new H4, the ground plane runs under them going directly to the pads of the two bypass caps.  Placing the caps to the plane where you did would add to the return path and  suspect adds a fair amount of inductance.  But again, I doubt it matters much at the frequencies I would use the H4 at.   More just an FYI.   

Remember I had swapped all of the mixers from my original NanoVNA into my H4.   Last thing to try,  swap the mixers on the new H4 with the ones from their NanoVNA.   

Oddly enough their new mixers were again marked a little different.    Sorry for the fuzzy photo but showing the new H4 with same setup after all the rework.  It is still a couple dB off, but now very close to the performance of mine.   

****
All SA602/SA612/NE602/NE612 have had the same die inside since the Philips fab making 602's burned down.

Fact or internet fiction?   Vertical marked Thailand mixers shown in the previous photo seem to be the hot ticket if you want to work close to DC. 
https://www.eevblog.com/forum/testgear/affordable-lt200mhz-pdn-analysis-hardware/msg5720009/#msg5720009
« Last Edit: November 21, 2024, 04:16:02 pm by joeqsmith »
 
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Offline joeqsmith

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Re: Affordable <200MHz PDN analysis / impedance measurement hardware?
« Reply #96 on: November 21, 2024, 06:34:57 pm »
Sanded down one of the mixers.   Sadly, a bit too much damage and not enough resolution to see much.   

***
Added photo before sanding.  This part was dead and with it marked NE vs SA, I am not sure if the die markings would be the same for what appears to be the better parts. 
« Last Edit: November 21, 2024, 06:38:22 pm by joeqsmith »
 
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Offline tszaboo

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Re: Affordable <200MHz PDN analysis / impedance measurement hardware? [Solved!]
« Reply #97 on: November 28, 2024, 12:22:37 pm »
nano/liteVNA

Over the years, I have attempted to explain that below 300MHz, the original NanoVNA can often out perform the V2Plus/4 and LiteVNA/64.  See my previous post:
https://www.eevblog.com/forum/testgear/affordable-lt200mhz-pdn-analysis-hardware/msg5670833/#msg5670833

I have seen people post about their disappointment after they purchased one of these higher frequency VNAs and attempt to use them for narrow band measurements.  Even if you crank down the IFBW, take a day per sweep rather than seconds, it will still produce artifacts that we can't address.  I've always said the fix, get the original NanoVNA.     

OP was using an H4.  The video I linked used my original NanoVNA.  These are both much better suited for PDN measurements.  You bring up the Lite though.    Using the latest 3.2 hardware and released firmware, 100Hz IFBW, 801 points, normalized.  Swept from 1.6kHz to 50kHz with ports terminated.  Note the poor dynamic range compared with my H4.  All of my LiteVNA64s are also very non-linear once you get below about 25kHz.   I never use them this low so it's not been a problem for me.   

Hopefully this clears up some of the misconceptions about these low cost VNAs.
I mention the LiteVNA because that's what I have. I only ever used a Agilent E5000 series VNA that went down to 100KHz, Megiq VNA that goes down to 400MHz (not a typo) and now this LiteVNA. The low frequency measurement didn't really interest me up until now. I'm starting to understand the issues with the shunt trough method, and the applicability to other low cost VNAs.  Indeed if they go down to 1.6KHz they sound useful. I watched your video about measuring PDNs again, where you use the transformer to overcome the ground loop problem. I was thinking that active amplifiers can be used to make the second port of the VNA into a semi-differential input. TI suggest this in their application note:
www.ti.com/lit/an/sluaai3/sluaai3.pdf
I think it should be relatively straightforward to make:
A driver for the first port to isolate the load, DC block, and set the desired excitation currents for the DUT.
A semi-differential to single ended converter for the second port to turn the measurement into a 4 wire measurements.
And do this to cover the KHz to ~100MHz range. IMHO amplifiers should be easier to tune for a flat response than common mode transformers. Plus they can amplify, limit, and do other useful functions.
 
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Online nctnico

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Re: Affordable <200MHz PDN analysis / impedance measurement hardware?
« Reply #98 on: November 28, 2024, 01:24:51 pm »
When using a VNA or oscilloscope, just calibrate the response using a calibration fixture. Like a low inductance 0.1 Ohm resistor. Then you won't need a flat response. Just enough signal to get above the VNA's (or oscilloscope's) noise floor.

I'm contemplating turning two (Kelvin style) tweezers into PDN probes. One to inject current and one to measure the voltage across the supply. The measured impedances are too low and the components are too small to use a single tweezer reliably. I want these to be non-polarised so I can clip them at any point on a crowded (live) PCB without creating a short. I have a project where I want to measure like 15 supply rails with power applied. Soldering wires to the board is going to be too tedious & time consuming. I already got some parts (my differential probe is among them) but the tweezers need more time until delivery.
« Last Edit: November 28, 2024, 01:29:03 pm by nctnico »
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 
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Offline tszaboo

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Re: Affordable <200MHz PDN analysis / impedance measurement hardware?
« Reply #99 on: November 28, 2024, 02:13:49 pm »
When using a VNA or oscilloscope, just calibrate the response using a calibration fixture. Like a low inductance 0.1 Ohm resistor. Then you won't need a flat response. Just enough signal to get above the VNA's (or oscilloscope's) noise floor.

I'm contemplating turning two (Kelvin style) tweezers into PDN probes. One to inject current and one to measure the voltage across the supply. The measured impedances are too low and the components are too small to use a single tweezer reliably. I want these to be non-polarised so I can clip them at any point on a crowded (live) PCB without creating a short. I have a project where I want to measure like 15 supply rails with power applied. Soldering wires to the board is going to be too tedious & time consuming. I already got some parts (my differential probe is among them) but the tweezers need more time until delivery.
True, though I was thinking of the CMRR and not the actual gain. 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).
Making RF probes is difficult. I tried making Z0 probes in the past with some sucess, ones that go on 2.54mm headers. I'm guessing having two ,with 0 Ohm instead of the resistance would solve that issue. Or making it into a 2x SMA through connection on the probe. 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.
 


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