Affordable <200MHz PDN analysis / impedance measurement hardware? - Page 1
Forum section: electronics / testgear

author: inevitableavoidance
author_rank: Contributor
timestamp: October 06, 2024, 07:26:28 am
content: I’ve been stepping up my low noise game, took a deep dive into decoupling (simulations), and am feeling a lot more confident about the performance of the boards I design. The only problem - I don’t have anything to verify this / measure PDN impedances above 5MHz or below 200mOhm.The pros seem to use €30k VNAs and with €5k ground loop isolators to run S21 shunt through measurements. Is there a more affordable alternative out there? I’d be happy to get up to 200MHz / down to 5mOhm.Would the cheaper VNAs suffice for this? Or do they not have the performance for it? Do I really need the ground loop isolators? Could I spin my own with a GHz differential amplifier?I feel this is slightly out general hobby territory (but also feel people have to stop putting 100nFs everywhere like it’s the 80s, route those with way to long / thin traces compared to the capacitors ESL, and call it a day)I’d love some advice - thanks!

author: ch_scr
author_rank: Frequent Contributor
timestamp: October 07, 2024, 01:03:43 pm
content: I would say this is the realm of devices like theBode 500.While not 30k€, it' still "comfortably" into the 5 digits. It's more specialized to the task than a general purpose VNA, though, on the hard and software side.A LiteVNA64 is a lot cheaper, can be run from battery and joeqsmiths "" software might enable the kind of low impedance measurement you'd need ("shunt-through measurement") - I'm not sure of the latter, though. If you're comfortable with software you should be able to implement the needed post processing yourself (on a quick glance "shunt-through" is based on S21 so a LiteVNA should get you there)

author: nctnico
author_rank: Super Contributor
timestamp: October 07, 2024, 01:36:36 pm
content: There are various low cost network analysers. Problem is though that many don't work well below -say- 20MHz while PDN analysis is most interesting int the range from several kHz to 200MHz.

author: inevitableavoidance
author_rank: Contributor
timestamp: October 08, 2024, 07:27:23 am
content: That software looks like it makes those cheap VNAs into quite powerful tools!I just bought a NanoVNA-H4, with a dynamic range of 70dB from 50kHz-300MHz, specified with a minimum frequency of 10khz. Cheap enough to play around with as a start.Now I use my scope with its generator, a voltage + current channel, and a math channel, but it doesn't have the resolution / current capacity to measure low impedances, and doesn't have the bandwidth for the high frequencies. I might be able to wing a combination of the two to still measure DC to 50kHz it the impedance is high enough to measure on the scope.Thanks for the advice! I'll post an update on how it goes

author: Someone
author_rank: Super Contributor
timestamp: October 08, 2024, 07:39:23 am
content: Do you already have a modern oscilloscope? A signal generator and some amplification will get you into milliohms.

author: 2N3055
author_rank: Super Contributor
timestamp: October 08, 2024, 08:35:49 am
content: Look up DG8SAQ VNWA 3.

author: joeqsmith
author_rank: Super Contributor
timestamp: October 08, 2024, 12:39:53 pm
content: Quote from: inevitableavoidance on October 06, 2024, 07:26:28 amShowing the $50 VNA making PDN measurements and explaining the limitations. You can find some of these details in the software manual as well.***Looking back at my testing, looks like 1mohm was about the limit with the original NanoVNA. The LiteVNA's I have have worse performance at these lower ranges. They recently released a newer version now of the Lite hardware, but I still doubt it would out perform the original NanoVNA.QuoteIt seems that the one I procured did have slightly better noise that my NanoVNA. The firmware wasn't stable enough to use it and it sat on the shelf for about a year before I found a version that would pass my regression tests. I don't believe I tried to measure the standards I made for the PDN experiments. I also stopped developing software for the older protocol that the H4 and original NanoVNA supported. If you wanted to try it, you would need to use that last version I released, or roll your own.

author: inevitableavoidance
author_rank: Contributor
timestamp: October 08, 2024, 05:46:32 pm
content: Quote from: Someone on October 08, 2024, 07:39:23 amOur messages just crossed! As mentioned above I've indeed been using a scope for the purpose. How would you go about implementing 'some amplification'? Purchase a fancy premade preamp? Breadboarding something with a random op amp? Something in between?Quote from: 2N3055 on October 08, 2024, 08:35:49 amThat seems to have the perfect range for PDN applications, affordable too. Do you have direct experience with them? How's the software / user interface side of things?Quote from: joeqsmith on October 08, 2024, 12:39:53 pmThanks for the video link (and the software in general!) I followed along with the NanoVNA-H4 on your older software. I'm not entirely sure what, but something was quite buggy, requiring lots of restarts of both the device and the software to keep things running. While it's running it does work like a charm.Attached is a sweep of two 100nF and 10uF ceramic capacitors together to make a little resonant peak, on both the NanoVNA-H4 and an Analog Discovery 2 (which doesn't do high frequencies at all). Despite the AD2 circuit getting inductive from 200kHz onwards they agree on the sample PDN having a ~1.1Ω impedance at 10kHz and ~0.11Ω at 100kHz - bingo! That's quite usable already.What kind of probes do people typically use to probe PDNs with VNAs? Some kind of T-junction cut open coax?

author: joeqsmith
author_rank: Super Contributor
timestamp: October 08, 2024, 07:28:53 pm
content: Quote from: inevitableavoidance on October 08, 2024, 05:46:32 pmAfter wasting so much time trying to find stable firmware, mine now just sits on shelf. Good to see you at least got it to somewhat work. It's really too bad that the LiteVNA and/or V2Plus4 didn't perform as well as the original NanoVNA in all aspects. IMO, that was a big miss. Then again, sells more product.Probe wise, the video and manual show my use of coax, normally soldered directly to the PCB. If you are looking for more information, there is a lot of free videos on this subject. Search YT. If you are looking for a book, try "RIGHT THE FIRST TIME, A PRACTICAL HANDBOOK ON HIGH SPEED PCB AND SYSTEM DESIGN"As I described in that video and manual, the problem is breaking the ground loop. Assuming you are doing this for a company, I recommend just buying a commercial transformer. If you want to roll your own, I'm sure the data Brian collected for me is still available and the materials I used are documented in the manual/video.

author: 2N3055
author_rank: Super Contributor
timestamp: October 08, 2024, 07:34:35 pm
content: Quote from: inevitableavoidance on October 08, 2024, 05:46:32 pmI have it. Software is very powerful but acquired taste and needs some time to learn.There is great community support and it has decent dynamic range in it's limited BW.Software and manual can be downloaded. Take a peek.

author: joeqsmith
author_rank: Super Contributor
timestamp: October 08, 2024, 07:40:41 pm
content: Quote from: 2N3055 on October 08, 2024, 07:34:35 pmQuoteGood enough to measure the 0.005 ohms? The original NanoVNA, with homemade transformer and blocks could measure down that low but I was really pushing its limits.Do they support modes specific for PDN?

author: Someone
author_rank: Super Contributor
timestamp: October 08, 2024, 09:29:49 pm
content: Quote from: inevitableavoidance on October 08, 2024, 05:46:32 pmNo problem.Quote from: inevitableavoidance on October 08, 2024, 07:27:23 amAmplification can be on either (or both) sides of the DUT depends which is easier/cheaper for you or what you already have. You might only need a higher output signal generator or a simple LNA depending on how accurate/fast/noisy you need the measurements to be.Some other things which can help you:Use a transformer from the output of the signal generator, it breaks the ground loops and can be selected/wound with an appropriate turns ratio to better match the impedances (50ohm generator vs 0.1ohm PDN).Measure the current being fed into the PDN either with a floating/isolated shunt or a clip on current probe.

author: inevitableavoidance
author_rank: Contributor
timestamp: October 10, 2024, 08:26:36 am
content: @nctnico I've seen your DC to daylight differential amplifier on here - would it be possible to somehow spin that circuit to have a 50 ohm input impedance, and make the ground loop breaker that way?@joeqsmith I've seen the coaxes on the breadboard - how'd you do it for an actual circuit board? Solder two together, run the through calibration, and then solder both to a pin pair you'd like to measure? How'd you do the other calibrations?@Someone amplification on the current side could be done with something like this?https://www.ti.com/lit/ds/symlink/buf634a.pdfDo you have any suggestions for parts on the other side?

author: ch_scr
author_rank: Frequent Contributor
timestamp: October 10, 2024, 08:42:25 am
content: Quote from: inevitableavoidance on October 10, 2024, 08:26:36 amThe trick I've learned is to have a box of (semi-rigid) coaxes, terminated to e.g. SMA on one side, cut to precisely the same length on the other.Then you can e.g. solder two together as a cal rig, solder the other two to the circuit, have a few spare for other stuff - but still share the cal rig...

author: nctnico
author_rank: Super Contributor
timestamp: October 10, 2024, 09:08:00 am
content: Quote from: inevitableavoidance on October 10, 2024, 08:26:36 amFor PDN measurement purposes, the 26dB dampening of my DIP1400 probe is not what you want. Using a transformer is a better option.

author: inevitableavoidance
author_rank: Contributor
timestamp: October 10, 2024, 10:15:44 am
content: Quote from: nctnico on October 10, 2024, 09:08:00 amThe LMH3401 by itself has a positive gain right? Wouldn't an alternative input resistor scheme allow for 50 ohm input impedance while still offering some gain at the end?

author: nctnico
author_rank: Super Contributor
timestamp: October 10, 2024, 10:24:47 am
content: Quote from: inevitableavoidance on October 10, 2024, 10:15:44 amIf the resistors are changed, then you could turn it into a buffer or even a pre-amplifier for sure but the bandwidth will be much lower ofcourse. I'm not sure what the effect of the added noise will be.

author: inevitableavoidance
author_rank: Contributor
timestamp: October 10, 2024, 10:27:10 am
content: Quote from: nctnico on October 10, 2024, 10:24:47 amEnough for my desired 200MHz range? Do you happen to have a simulation I could play with?

author: nctnico
author_rank: Super Contributor
timestamp: October 10, 2024, 10:41:02 am
content: If you use the LMH3401 model, you should be able to get a decent idea of how it would perform. I don't expect surprises at 200MHz.

author: joeqsmith
author_rank: Super Contributor
timestamp: October 10, 2024, 01:44:13 pm
content: Quote from: ch_scr on October 10, 2024, 08:42:25 amAdd a cal standard to the board, maybe on a railSolder them together and then to the boardInsert a thru adapter and call it goodIn the case the breadboard, left the board unpopulated and called that goodI am not sure what "other calibrations" would be.Solving the ground loop could certainly be done without a transformer using a diff amp. You could easily out perform my transformers at lower frequencies going with solid state. However, the one transformer I use has 25db@10k and 37db@100k. The 3dB point is around 100Hz. Consider that these low cost VNAs can't run down this low, it may be good enough for your needs. Yes, I know they have all sorts of lower limits. I think I had seen one allowing 1Khz operation. That doesn't suggest you can measure anything useful that low.Another thing with the transformer, it's very robust. You may want to consider investing in some very low capacitance TVSs and attach them to the VNA.***Another option would be to purchase the parts you need. Maybe have a look at what Pico offers.https://www.picotest.com/solutions/pdn-measurement-forpower-integrity/

author: inevitableavoidance
author_rank: Contributor
timestamp: October 10, 2024, 04:41:54 pm
content: I've been playing with- and modifying my Analog Discovery 2 today, messing with the input attenuation and gain circuitry of the scope inputs to give me in total 26dB extra gain, giving me a great improvement in usable impedance measurement range. Here's a stack of five 10uF 0805 capacitors without any averaging:Problem however with this new milliohm range extension is... inductance. Even at 1MHz a little 10mm back-and-forth of wire has an AC impedance of around 200mΩ, severely limiting my usable frequency range now I can measure down to the milliohms. For the image above I soldered the capacitors on the AD2 PCB itself. Can't really solder an entire PDN on there...So I believe it's back to the NanoVNA-H4!

author: nctnico
author_rank: Super Contributor
timestamp: October 10, 2024, 05:23:08 pm
content: No. Your cabling is 50 Ohm so there is no wire inductance. What you can do is add some attenuation (like 6dB) at where you inject and measure the signal to improve impedance matching a bit but it should affect the measurements much. See the source's output resistor as a current source. When calculating the impedance of the board, the current from the source is used together with the measured voltage level to calculate the impedance (R = V / I).

author: inevitableavoidance
author_rank: Contributor
timestamp: October 10, 2024, 07:05:23 pm
content: @nctnico you're right! Turns out I was accidentally measuring the inductance / impedance of a shared ground path. I messed up the wiring of one of the differential inputs. Measurements are starting to make a lot more sense now I've got that sorted!Here's the impedance plot of a 3.3V LDO, both when on and off:I'm getting 60mΩ at 1MHz there - 10nH - I'd say that makes sense based on how I wired it.Here's one soldered directly over an 0805, that also has 200uF of bulk capacitance on the same net:Giving 30mΩ at 10MHz - 500pH - sounds quite appropriate for an 0805.Glad I got that sorted, thanks for the push nctnico. I can't really use it as a scope anymore with all the modifications, but am pretty happy with the little device it has become.I'm still getting back to the NanoVNA-H4, to dive more into the higher frequencies, but as an addition instead of a replacement now.

author: inevitableavoidance
author_rank: Contributor
timestamp: October 28, 2024, 02:57:41 pm
content: I ended up designing a little adapter board for the Analog Discovery series!Here's the board measuring a low impedance capacitor array:Here's a bunch of verification resistors (with varying inductances):I realized I didn't need to measure higher than ~25MHz - once I see the inductance slope at the end I'll known enough about what happens afterwards. The board has a 200mA output current buffer, and two fully differential opamps. This gives me both more current and enough resolution for all the low stuff. The bottom limit is about 100uΩ.The flat tinned bars are spaceholders for tantalum capacitors, to be able to measure with a DC Bias as well. Works great so far.Thanks for all the tips along the way!

author: axb
author_rank: Contributor
timestamp: November 11, 2024, 11:59:33 pm
content: Quote from: inevitableavoidance on October 28, 2024, 02:57:41 pmHi,Could you please share the schematic?

author: inevitableavoidance
author_rank: Contributor
timestamp: November 12, 2024, 09:01:21 am
content: Quote from: axb on November 11, 2024, 11:59:33 pmAvailable on my github page:https://github.com/remidavidkoster/Redako-PDNAnalyzer

author: axb
author_rank: Contributor
timestamp: November 12, 2024, 09:41:57 am
content: Super! Thanks!I only see one uncertainty. In my WaveForms (AD3) I don't have the selectable configuration you indicate, I only have DUT-RES-GND.

author: mawyatt
author_rank: Super Contributor
timestamp: November 12, 2024, 02:41:01 pm
content: Very impressive results with the low Z range coveredCurious why you selected Tantalums rather than Polymer or Aluminum Electrolytic Capacitors for the coupling/decoupling, size maybe?Best

author: inevitableavoidance
author_rank: Contributor
timestamp: November 12, 2024, 02:49:37 pm
content: Quote from: mawyatt on November 12, 2024, 02:41:01 pmHey Mawyatt,Thanks! Pretty stoked with it myself as well.Indeed size, and with that inductance. The shunt is 500mΩ. If I would use a capacitor with an equivalent series inductance of 10nH I'd see an additional impedance of 1.57Ω in series with the rest of the circuit at 25MHz, limiting the current I'd be able to get through with a factor of 4, and with that reducing the voltage I'd read back on the second sense channel with a similar factor of 4.Keeping the capacitor and its inductance as small as possible allows most current at high frequencies, keeping my sense voltages as high as possible there.

author: inevitableavoidance
author_rank: Contributor
timestamp: November 12, 2024, 02:50:38 pm
content: Quote from: axb on November 12, 2024, 09:41:57 amI think you should be able to select that one, and switch the scope channels around somewhere else. Then you effectively have the same configuration.

author: mawyatt
author_rank: Super Contributor
timestamp: November 12, 2024, 03:35:46 pm
content: Quote from: inevitableavoidance on November 12, 2024, 02:49:37 pmWRT to the Coupling Capacitance and ESL/ESR. Have you considered using a 0.1uF C0G/NP0 ceramic in parallel with a larger polarized cap? These have a low ESL and ESR, we've done such with our DC Bias Adapter for use with Bench LCR Meters and seems to work well.This is tempting to pull out our AD2 and put it to useBest

author: joeqsmith
author_rank: Super Contributor
timestamp: November 12, 2024, 03:44:21 pm
content: I am in the process of updating Solver's user manual and repeated the PDN measurements with my H4 using the latest firmware available. I had no lockups or glitches in the data.I had damaged my H4 (suspect ESD) and when repairing it, I had added a few additional caps which greatly improved the noise floor at higher frequencies. Still, it is not good enough to resolve 100uOhms.Link to troubleshooting, mods and performance gains of my H4.https://www.eevblog.com/forum/rf-microwave/nanovna-custom-software/msg5695349/#msg5695349I also have the newly release LiteVNA hardware. I was very much surprised that it performs slightly better then my other low cost VNAs at these lower impedance's, however it is still not able to resolve 100uOhms.That said, typically when I run into problems with emissions, they are in the several MHz on up past GHz. Assuming you are wanting to measure the PDNs stability for emissions, how do you test it at these higher frequencies? Or is it not a concern?

author: inevitableavoidance
author_rank: Contributor
timestamp: November 12, 2024, 06:09:22 pm
content: Quote from: mawyatt on November 12, 2024, 03:35:46 pmI haven't optimized that part too much - the little coaxial cables I solder to the board have quite some inductance as well, so I think the effect on the total wouldn't be too significant.I took a look at your DC Bias adapter posts - nice stuff too.

author: inevitableavoidance
author_rank: Contributor
timestamp: November 12, 2024, 06:42:32 pm
content: Quote from: joeqsmith on November 12, 2024, 03:44:21 pmNice writeup on the H4 mods!With the measurements I did so far (of single capacitors and small PCB PDNs) I've been able to measure high enough in frequency to get down to the package- / measurement setup inductances, which is more than enough for me (I mainly have audio clients at the moment), but indeed not getting to the point of plane resonances and the like. I believe because of the inductance involved the impedances here are typically a lot higher (>100mΩ), so getting out the VNA for that would probably be fine? What do you think?

author: joeqsmith
author_rank: Super Contributor
timestamp: November 12, 2024, 07:23:13 pm
content: Quote from: inevitableavoidance on November 12, 2024, 06:42:32 pmWithout knowing if you solved the ground loop problem, its hard to say. Also, our goals for making these measurements are not the same. You may be better off with what you have for now.

author: inevitableavoidance
author_rank: Contributor
timestamp: November 12, 2024, 08:25:09 pm
content: Quote from: joeqsmith on November 12, 2024, 07:23:13 pmHaving a fully differential measurement I have no shared ground path and thus no ground loops - the same as when using a for example a J2113A (Semi-Floating Differential Amplifier) with a VNA. Just like a Four-Wire Kelvin measurement, where a VNA is more like a Three-wire measurement.

author: joeqsmith
author_rank: Super Contributor
timestamp: November 12, 2024, 08:50:37 pm
content: Quote from: inevitableavoidance on November 12, 2024, 08:25:09 pmSo your plan is to use that same basic circuit you are showing with your Analog Discovery with your H4? I don't see a problem with breaking the VNA's ground this way.

author: inevitableavoidance
author_rank: Contributor
timestamp: November 12, 2024, 09:01:14 pm
content: Quote from: joeqsmith on November 12, 2024, 08:50:37 pmSorry - I completely misunderstood what you said. It’s been a long day. Disregard what I said.I haven’t solved it yet, but thought it might be accurate enough using it above 100mOhm to cover the range above 25Mhz.I do still plan to make a differential amplifier for it with the IC nctnico used in his 1.4Ghz differential probe, but haven’t gotten to it yet.

author: Smokey
author_rank: Super Contributor
timestamp: November 12, 2024, 09:10:50 pm
content: Quote from: inevitableavoidance on October 28, 2024, 02:57:41 pmwhat is that capacitor board??? I gots to know! purpose, total capacitance, how the hell did they place/solder all those caps when they are damn near touching??

author: joeqsmith
author_rank: Super Contributor
timestamp: November 12, 2024, 09:29:08 pm
content: Quote from: inevitableavoidance on November 12, 2024, 09:01:14 pmIn 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.

author: inevitableavoidance
author_rank: Contributor
timestamp: November 12, 2024, 09:32:03 pm
content: Quote from: Smokey on November 12, 2024, 09:10:50 pmHehe, I wondered when someone would scratch their head about those. I had them made a while ago for both fun (they spot weld) and for those occasions where someone says “maybe we can solve it by adding more capacitors”. There’s a total of 6960 10V 10uF 0603 capacitors on there - cheapest I could find per uF - adding up to around 70mF, with a negligible ESR (limited by the 35oz copper planes) and an ESL limited by the wires you solder on there. Works great at eradicating supply ripple if it’s within the right bandwidth. I also have some stacked together with bismuth solder.The alternating rows of capacitors are flipped in polarity, so the ends nearly contacting other ends are all the same net. Placement is done with tiny vacuum nozzles, soldering with solder paste and a reflow oven.

author: inevitableavoidance
author_rank: Contributor
timestamp: November 12, 2024, 09:36:30 pm
content: Quote from: joeqsmith on November 12, 2024, 09:29:08 pmHmm, shit, I blindly hoped it would stay the same regardless of frequency. I’ll start cooking up a board for that differential amplifier.

author: tszaboo
author_rank: Super Contributor
timestamp: November 12, 2024, 09:59:02 pm
content: Quote from: inevitableavoidance on November 12, 2024, 09:32:03 pmI think everyone had the idea of just using a lot of capacitors, but you took this to a new level.Your circuit is quite interesting. Any reason you decided to AC couple the signals instead of accepting the small DC offsets?

author: rhb
author_rank: Super Contributor
timestamp: November 12, 2024, 10:20:38 pm
content: An HPAK 4395A is reasonably priced and had a very long life, so plentiful. I’m using one to develop EMI filters to suppress conducted noise from my LED shop lighting.It will really get a workout when I start building the screen room feeds.I really can’t see how you can improve on the price - performance. I love it. Best possible tool for the frequency range of interest. It’s both a VNA and an SA with 1 Hz resolution. It covers 10 Hz to 500 MHz. For HF work it’s the king.Designing appropriate fixtures and calibration standards for testing boards won’t be easy. You’ll need machine tool access. Helps a lot if you design in test points. Low impedance fixtures are likely to be “interesting” to make. But then the challenge is the whole point for a lot of projects.Have Fun!Reg

author: inevitableavoidance
author_rank: Contributor
timestamp: November 12, 2024, 10:23:24 pm
content: Quote from: tszaboo on November 12, 2024, 09:59:02 pmThanks! When for example measuring the output impedance of a buck converter under load the DC bias will be equal to the output voltage, so for measurements like this being able to handle high DC offsets is essential

author: inevitableavoidance
author_rank: Contributor
timestamp: November 12, 2024, 10:31:11 pm
content: Quote from: rhb on November 12, 2024, 10:20:38 pmThat does look like the absolute perfect measurement range - a bit out of my initial budget but I’ll definitely keep an eye out for a good second hand deal. Test fixtures and connections are quite a world of their own I have indeed found. So far I’ve had most luck simply stripping and soldering on microcoaxial cables. I wish someone would make and standardise a miniature “kelvin” RF connector for this

author: tszaboo
author_rank: Super Contributor
timestamp: November 12, 2024, 10:43:45 pm
content: Quote from: inevitableavoidance on November 12, 2024, 10:23:24 pmAh, you want to measure it while on, not like with the VNAs. I believe a power rail probe is more suited for a measurement like that. I made a power rail probe, goes to 2GHz, no gain though. But with the small noise coming from it, you should be able to directly measure a few mv signals. And gain can be added by any 50 Ohm input/output amplifier.Now, I'm not trying to sell you my probe, just want to give you some pointers, if you are interested.

author: rhb
author_rank: Super Contributor
timestamp: November 12, 2024, 11:12:51 pm
content: 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. I suggest reading up on slotted lines and how the microwave pioneers coped. Measurements at multiple points on a delay line should handle direction separation.If time is more plentiful than money, even the 20 kPt Hanmatek DSOs made by Owon and lots of measurements will do the job. Use what you have.Most of my life I was not willing to spend money on what were “toys”. At 71 I now spend it. But I learned a lot working around no budget. So I urge doing that very strongly. It reinforces being able to work from first principles. That was ALWAYS valuable.Have Fun!RegBTW Join the T&M list on groups.io. The eBay prices are rather stiff. And be patient.

author: joeqsmith
author_rank: Super Contributor
timestamp: November 12, 2024, 11:29:52 pm
content: Quote from: tszaboo on November 12, 2024, 10:43:45 pm?

author: nctnico
author_rank: Super Contributor
timestamp: November 13, 2024, 12:30:59 am
content: Quote from: rhb on November 12, 2024, 11:12:51 pmWhy 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.

author: rhb
author_rank: Super Contributor
timestamp: November 13, 2024, 12:46:38 am
content: 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

author: mawyatt
author_rank: Super Contributor
timestamp: November 13, 2024, 12:51:44 am
content: Quote from: inevitableavoidance on November 12, 2024, 10:31:11 pmYou 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 measurementsAs 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 happenBest

author: mawyatt
author_rank: Super Contributor
timestamp: November 13, 2024, 01:08:59 am
content: Quote from: rhb on November 13, 2024, 12:46:38 amYes 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 budgetAnyway, vaguely remember when a Grad Student or Post Doc would do anything for a brew, seems it's come full circle nowBest

author: joeqsmith
author_rank: Super Contributor
timestamp: November 13, 2024, 02:14:02 am
content: Quote from: nctnico on November 13, 2024, 12:30:59 amQuote from: rhb on November 13, 2024, 12:46:38 amHe 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.

author: joeqsmith
author_rank: Super Contributor
timestamp: November 13, 2024, 02:34:53 am
content: Quote from: joeqsmith on November 12, 2024, 11:29:52 pmYou 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.

author: tszaboo
author_rank: Super Contributor
timestamp: November 13, 2024, 10:50:17 am
content: Quote from: joeqsmith on November 13, 2024, 02:34:53 amVNAs can measure PDN with it powered up. It's a measurement that I never did myself, and not sure what's the setup to do. I can also say, that with the typical low cost VNAs we have access to, it's not useful to make the measurements powered up. The loop response of a power supply is going to be in the KHz region, where these VNAs are not measuring, or the measurements are not accurate enough to measure mOhm.I quickly looked at the available info about PDN measurements.https://www.keysight.com/zz/en/assets/7018-08474/application-notes/5989-5935.pdf(might need registration to download)In this document they publish ON, OFF and modelled impedance-frequency graphs for practical PDNs. For example Figure 28. The ON and OFF state measurements only differ in any meaningful way up to 5kHz.Additionally, for the nano/liteVNA any noise present on the power supply would enter the ADC. From what I recall, mixers have frequency response that passes low frequency noise, and these VNAs don't have any bandpass filters on port 2.So yeah, I wasn't very precise when suggesting VNAs only test OFF.

author: nctnico
author_rank: Super Contributor
timestamp: November 13, 2024, 11:11:05 am
content: Quote from: rhb on November 13, 2024, 12:46:38 amPDN measurement is not for impedance matching but for measuring the impedance of a power supply to chips (like high speed processors, FPGA and memory) over a wide frequency range. From DC to tens or even hundreds of MHz. High speed logic chips typically have a specification in the design manuals for the required impedance of the power supply versus frequency. So this is something you'll want to verify.

author: joeqsmith
author_rank: Super Contributor
timestamp: November 13, 2024, 12:33:14 pm
content: Quote from: nctnico on November 13, 2024, 11:11:05 amImpedance Matching Is Critical, Steve Sandler

author: joeqsmith
author_rank: Super Contributor
timestamp: November 13, 2024, 01:00:17 pm
content: Quote from: tszaboo on November 13, 2024, 10:50:17 amOk, I think these two statements help me understand. It seems like you have one particular problem in mind, or a narrow view of what problems to look for. There are some very good presentations on-line about proper design.Quote from: tszaboo on November 13, 2024, 10:50:17 amWe are interested in impedance far beyond 5kHz.

author: tszaboo
author_rank: Super Contributor
timestamp: November 13, 2024, 01:04:20 pm
content: Quote from: joeqsmith on November 13, 2024, 01:00:17 pmI don't think you understand (with respect). Measuring a PDN with a VNA, it's going to produce the same graph whether it's ON or OFF above ~5KHz. You cannot measure with a nano/liteVNA below 5KHz. So why would you measure it when it's ON, it's just extra risk for your VNA, plus noise, without any benefits.mod: Note to others, read below, this is not correct.

author: nctnico
author_rank: Super Contributor
timestamp: November 13, 2024, 01:09:19 pm
content: Quote from: joeqsmith on November 13, 2024, 12:33:14 pmStill, using a directional bridge is not the right tool for the job as the impedances are far too low. For those interested, I think this page explains the goals of PDN design pretty well:https://www.signalintegrityjournal.com/blogs/12-fundamentals/post/2108-power-integrity-fundamentals-impedance-vs-frequencyIn real designs you won't get the curve perfectly flat. And it doesn't have to be; just as long as the impedance stays below the maximum for the circuit to work correctly.

author: tszaboo
author_rank: Super Contributor
timestamp: November 13, 2024, 01:16:03 pm
content: Let's see, this should explain it.

author: joeqsmith
author_rank: Super Contributor
timestamp: November 13, 2024, 03:21:00 pm
content: Quote from: tszaboo on November 13, 2024, 01:04:20 pmI refer you to my previous data where the on/off states converge at 400kHz.https://www.eevblog.com/forum/testgear/affordable-lt200mhz-pdn-analysis-hardware/msg5712085/#msg5712085

author: tszaboo
author_rank: Super Contributor
timestamp: November 13, 2024, 03:53:13 pm
content: Quote from: joeqsmith on November 13, 2024, 03:21:00 pmInteresting. You are right. I totally missed that.Do you know what is the DC-DC converter used on that board? It would make sense that Keysight's generic DC-DC module would have a slow control loop, and an FPGA board would have a fast transient response converter.

author: joeqsmith
author_rank: Super Contributor
timestamp: November 13, 2024, 03:55:35 pm
content: Quote from: nctnico on November 13, 2024, 01:09:19 pmYes, S21 is the better choice. Having the lowest impedance may not be the best choice. Discontinuities can cause unwanted radiation. I had posted a few video links on PDN design and testing back when I was working on the software to measure them with the low cost VNAs. You can find that here:https://www.eevblog.com/forum/rf-microwave/impedance-measurement-with-vna-using-series-shuntseries-through-methods/msg3556953/#msg3556953

author: joeqsmith
author_rank: Super Contributor
timestamp: November 14, 2024, 02:34:50 am
content: Quote from: tszaboo on November 13, 2024, 01:04:20 pmI wanted to get some data before responding to this comment. Shown is my NanoVNA H4 Rev 4.2. Again, it was damaged and repaired. During that time, I had added 5 capacitors which greatly improved the high frequency performance but not the low. I suspect it would be on par with another virgin H4.Data was taken with the current released firmware which supports a lower limit of 1.6kHz. VNA was swept from 1.6k to 10kHz, 401 points, 100Hz IFBW.Looking at S21, after normalize and terminated, H4_1 showing dynamic range. It's at least 70dB below 5kHz (not K or Kelvin BTW).I purchased a cheap 40dB attenuator for another test. With a 70dB dynamic range we should be able to measure it without any problem. Results can be seen in H4_2.Also showing the setup.

author: joeqsmith
author_rank: Super Contributor
timestamp: November 14, 2024, 02:03:46 pm
content: Quote from: tszaboo on November 13, 2024, 01:04:20 pmOver 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/#msg5670833I 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.

author: mawyatt
author_rank: Super Contributor
timestamp: November 15, 2024, 02:45:17 pm
content: Quote from: inevitableavoidance on October 28, 2024, 02:57:41 pmTook a better look at your schematic and have a question.The buffer amp U1 is powered from +-5V and the sense amps U2 and U3 are from +-2.5V. How does the current sense differential amp U3 deal with the voltage across current sense resistor R2 which is directly driven by the output from U1?Seems this might exceed the Common Mode range for the inputs to U3 which the Data Sheet shows +Vs -1.2V and -Vs -0.2V which would indicate an input range of +1.3 to -2.7V with +- 2.5V supplies?Best

author: rhb
author_rank: Super Contributor
timestamp: November 15, 2024, 06:13:10 pm
content: Quote from: joeqsmith on November 13, 2024, 02:14:02 amI was only responding to "my VNA won't go to 10 Hz and I can't afford a 4395A".I got super lucky as shown by the screen shot. The seller didn't know what it was and wanted it gone. They were in the business computer business. So far as I can tell it works flawlessly. And I've used it a lot as a scalar network analyzer evaluating combinations of EMI filters.VNAs have directional bridges in them. I was simply pointing out that you don't need a VNA. A signal generator, DSO and understanding the problem will solve it.To the frequency limits of the DSO, analog log amplifier probes and some software are capable of providing full VNA capability from DC to the limit of the DSO you currently have. Any that will write data to an SD card will do.I bought a cheap 12 bit 100 MHz Owon because it has very deep memory, 20 MPt IIRC. Sucks as a scope but is great for data capture. A perfect square wave with fast rise times will generate harmonics of very high order. Choose the fundamental based on the sample interval in frequency and use a sub ns rise time 7400 series divide by two output. Record it open circuit and then measure at various points. The processing understanding is a one time effort and valuable skill to boot.That said, my favorite tool for impedance discontinuity tests is a Tek 11801 and SD-24, but that is rather exotic and hard to come by. But it does show the precise (<0.1 mm) relative location of *every* impedance change. Just not well suited to a use case where an active device is at the other end of the line.As should be clear from the various links, this is NOT a simple problem to solve even with a large sack of money to apply as a hammer.After rereading the OP a few times I should start with a DSO and a very small DIY H field probe to isolate which segments of an actual PDN have issues as a first step. Small loop of the smallest coax you can find. Preferably semi-rigid. You'll be able to directly detect what parts of the PCB have problems.Then use an FFT to get a frequency domain view to give a sense of scale to the parasitics of concern. Build the fixtures in the Keysight App note and measure them.A differential DC log amp probe with a high input impedance should overcome the DSO dynamic range limitation. In principle, one should be able to probe two nearby points on a trace to measure the current flow changes. We all know that there is a voltage change as the current varies, but whether that's actually practical as a measurement technique for this use case is another story. I suspect that careful construction would make it viable as a punch through the solder mask probe. But someone will need to try that out to know for sure. Almost anything else has ground loop issues to be addressed.Have Fun!Reg

author: inevitableavoidance
author_rank: Contributor
timestamp: November 16, 2024, 10:07:06 am
content: Quote from: mawyatt on November 15, 2024, 02:45:17 pmThe board is developed around a maximum excitation voltage of 100mV. Besides the 10x gain on the PCB I have modified my AD2 for an additional 5x less attenuation internally, so am limited to an input voltage of ±140mV either way.

author: joeqsmith
author_rank: Super Contributor
timestamp: November 16, 2024, 05:04:11 pm
content: Quote from: inevitableavoidance on October 08, 2024, 07:27:23 amAfter my friend flipper saw the low frequency data from my repaired/modified H4, they sent me a brand new H4. It is revision 4.3_MS with the MS synthesizer where mine has the Si. The plan was to modify his H4 with the same capacitors and TVSs that I used on mine. He also wants to use that VNA for measuring PDNs. However, when I did a baseline check the low frequency performance is really poor.Please do me a favor. Provide the revision of your H4 and synthesizer type. Set it to 401 points, 1kHz IFBW, with a freq range of 1.6k to 10kHz. Short port 1&2 and normalize. Open the ports and terminate. Measure S21. I want to know if you get anywhere near that 75-80dB I measure with mine.I mentioned I doubted the caps I added had anything to do with the low frequency performance, but I never took a baseline this low. I wonder if that synthesizer is going to be a problem.They have their original NanoVNA which was purchased from the same source, same order as mine. I am wondering if I will need to swap the that old Si part to get the H4 to perform down this low.

author: mawyatt
author_rank: Super Contributor
timestamp: November 16, 2024, 06:02:01 pm
content: Quote from: inevitableavoidance on November 16, 2024, 10:07:06 amKeeping the excitation at 100mV with a 1/2 Ω current sense places the DUT current at 200mA seems reasonable for the direct USB Powered AD2 and the OPA891 Buffer Amp limitation. With an external Power Supply the AD2 specs indicates a max of 700ma, but you would need a higher current capable buffer and the later voltage limit with the 10X gain, both of which increase complexity.Reducing the AD2 attenuation by shorting the input resistor seems a good idea, but exposes the ADG612 to external signals without any series current limit resistor. Maybe a 10K parallel resistor might be better and provide some level of protection and could be compensated with the Scale Value.Anyway, are the Gerber files available? We are considered building this adapter since our AD2 doesn't get utilized for anything now.Best

author: inevitableavoidance
author_rank: Contributor
timestamp: November 17, 2024, 11:02:40 am
content: Quote from: mawyatt on November 16, 2024, 06:02:01 pmThe gerber files, BOM, and pick an place files are in the output folder in the github repository:https://github.com/remidavidkoster/Redako-PDNAnalyzer/tree/master/Project%20Outputs%20for%20PDN%20AnalyzerI'm not sure what DC bias caps are in the BOM - I ended up assembling 5 different versions of those with the best I could find for each voltage range. It doesn't show on the pictures, but I paralleled / stacked two capacitors together for the excite signal current path.I agree some current limiting with indeed be best, and simple soldering another resistor over the current 820k ones is easy enough.Please keep me posted if you end up making some - happy to see someone else get a use of the design.

author: inevitableavoidance
author_rank: Contributor
timestamp: November 17, 2024, 11:22:40 am
content: Quote from: joeqsmith on November 16, 2024, 05:04:11 pmI'm getting nowhere near that figure - 10dB per division:Where do I find the revision and synthesizer?

author: joeqsmith
author_rank: Super Contributor
timestamp: November 17, 2024, 02:59:50 pm
content: Quote from: inevitableavoidance on November 17, 2024, 11:22:40 amThe 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.

author: joeqsmith
author_rank: Super Contributor
timestamp: November 17, 2024, 03:45:07 pm
content: 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.

author: joeqsmith
author_rank: Super Contributor
timestamp: November 18, 2024, 01:17:50 am
content: 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.

author: joeqsmith
author_rank: Super Contributor
timestamp: November 18, 2024, 05:04:29 pm
content: This was the only post I found on the change. No mention of the low frequency performance.Quotehttps://groups.io/g/nanovna-users/topic/88101278#msg26386

author: inevitableavoidance
author_rank: Contributor
timestamp: November 18, 2024, 10:22:24 pm
content: Quote from: joeqsmith on November 17, 2024, 02:59:50 pmThat’s way better indeed:It’s a 4.3_MS

author: joeqsmith
author_rank: Super Contributor
timestamp: November 18, 2024, 10:50:31 pm
content: 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.

author: Kean
author_rank: Unknown
timestamp: November 19, 2024, 12:50:46 am
content: Following along as I have a new Zeenko NanoVNA-H4 on the way

author: inevitableavoidance
author_rank: Contributor
timestamp: November 19, 2024, 10:23:08 am
content: Quote from: joeqsmith on November 18, 2024, 10:50:31 pmAwesome, 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.

author: joeqsmith
author_rank: Super Contributor
timestamp: November 19, 2024, 01:18:43 pm
content: Quote from: Kean on November 19, 2024, 12:50:46 amOnce you receive it, please run the same test and post your results along with the hardware revision and type of synthesizer.Quote from: inevitableavoidance on November 19, 2024, 10:23:08 amMy 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

author: inevitableavoidance
author_rank: Contributor
timestamp: November 19, 2024, 04:48:44 pm
content: Quote from: joeqsmith on November 19, 2024, 01:18:43 pmI 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-300MHz60dB | 300MHz-900MHz40dB | 0,9GHz-1,5GHzBefore I was getting:70dB | 10kHz-436MHz60dB | 436MHz-740MHz40dB | 740MHz-1,7GHzNow I'm getting nearly getting:70dB | 10kHz-661MHz60dB | 661MHz-1446MHz40dB | 1446MHz-1,85GHzHow did you improve the decoupling department over there? What did you add where?

author: joeqsmith
author_rank: Super Contributor
timestamp: November 19, 2024, 05:21:59 pm
content: Quote from: inevitableavoidance on November 19, 2024, 04:48:44 pmI am near retirement and still feel like a first year student.Quote from: inevitableavoidance on November 19, 2024, 04:48:44 pmA 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.acrossC10, 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.

author: inevitableavoidance
author_rank: Contributor
timestamp: November 19, 2024, 05:30:09 pm
content: QuoteIt's nice to never stop learning.QuoteLooking 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.

author: joeqsmith
author_rank: Super Contributor
timestamp: November 19, 2024, 05:39:57 pm
content: 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.

author: joeqsmith
author_rank: Super Contributor
timestamp: November 19, 2024, 06:10:17 pm
content: 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.

author: Kean
author_rank: Unknown
timestamp: November 20, 2024, 01:21:38 am
content: 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...

author: joeqsmith
author_rank: Super Contributor
timestamp: November 20, 2024, 01:57:36 am
content: Quote from: Kean on November 20, 2024, 01:21:38 amCorrect, there are two versions, one for the Si the other for the MS.Quote from: Kean on November 20, 2024, 01:21:38 amYes, they are both in the release area. I am currently testing with NanoVNA-H4-MS_20240220.dfuQuote from: Kean on November 20, 2024, 01:21:38 amAs 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

author: Kean
author_rank: Unknown
timestamp: November 20, 2024, 08:32:43 am
content: 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.

author: ftg
author_rank: Frequent Contributor
timestamp: November 20, 2024, 08:52:40 am
content: 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

author: inevitableavoidance
author_rank: Contributor
timestamp: November 20, 2024, 09:25:39 am
content: Quote from: joeqsmith on November 19, 2024, 06:10:17 pmRight 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.

author: inevitableavoidance
author_rank: Contributor
timestamp: November 20, 2024, 12:49:19 pm
content: 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.

author: joeqsmith
author_rank: Super Contributor
timestamp: November 20, 2024, 02:02:55 pm
content: Quote from: inevitableavoidance on November 20, 2024, 09:25:39 amI 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.

author: joeqsmith
author_rank: Super Contributor
timestamp: November 21, 2024, 04:06:10 pm
content: 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.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...Quote from: joeqsmith on November 20, 2024, 02:02:55 pmPulling 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.****Quote from: ftg on November 20, 2024, 08:52:40 amFact 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

author: joeqsmith
author_rank: Super Contributor
timestamp: November 21, 2024, 06:34:57 pm
content: 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.

author: tszaboo
author_rank: Super Contributor
timestamp: November 28, 2024, 12:22:37 pm
content: Quote from: joeqsmith on November 14, 2024, 02:03:46 pmI 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.pdfI 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.

author: nctnico
author_rank: Super Contributor
timestamp: November 28, 2024, 01:24:51 pm
content: 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.

author: tszaboo
author_rank: Super Contributor
timestamp: November 28, 2024, 02:13:49 pm
content: Quote from: nctnico on November 28, 2024, 01:24:51 pmTrue, 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.

author: inevitableavoidance
author_rank: Contributor
timestamp: November 28, 2024, 03:19:00 pm
content: QuoteI 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.

author: tszaboo
author_rank: Super Contributor
timestamp: November 28, 2024, 03:52:16 pm
content: Quote from: inevitableavoidance on November 28, 2024, 03:19:00 pmFor 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/

author: joeqsmith
author_rank: Super Contributor
timestamp: November 28, 2024, 04:16:35 pm
content: Quote from: tszaboo on November 28, 2024, 02:13:49 pmA 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.Quotehttps://www.eevblog.com/forum/testgear/affordable-lt200mhz-pdn-analysis-hardware/msg5711731/#msg5711731We 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...So, yes, wasted time. Cost wise, I think the connectors were the highest priced components. Then the cores, box, coax, Kapton tape, hardware, labels.***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.***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...Didn't member it being that bad...

author: joeqsmith
author_rank: Super Contributor
timestamp: November 30, 2024, 05:20:04 pm
content: 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

author: joeqsmith
author_rank: Super Contributor
timestamp: December 01, 2024, 05:44:13 pm
content: A short clip from Copper Mountain Technologies presentation with Steve Sandler, after viewer asks about their common mode transformer design.Quote