azonenberg changed the topic of #scopehal to: libscopehal, libscopeprotocols, and glscopeclient development and testing | | Logs:
<azonenberg> Ok so i installed the ADI ACE software
<azonenberg> It looks like the internal options for generating VCMI are 1.45, 1.6, 1.75, 1.9V
<azonenberg> and VCMO are 0.4, 0.5, 0.6, 0.7
<azonenberg> Assuming I only use a single ADL5580 (not two stage), I could set VCMI = 1.45, VCMO = 0.7
<azonenberg> then slide vdd/vss down by 700 mV from nominal
<azonenberg> At that point the output is centered at 0V, the power supply is +4.3 and -2.5V
<azonenberg> But the input is at a 750 mV common mode
<azonenberg> Which will "work" but you will also have 750 mV being back-fed into the DUT through 500 ohms of series resistance
<azonenberg> i'm not sure how big a deal that would be
<azonenberg> If I ac coupled through a nice wideband AC coupling cap, like the ATC 560L series, i'd be able to go down to ~16 kHz and have no concerns about common mode, but also lose the ability to measure DC voltages
<azonenberg> Not sure how big a deal that is for a differential probe?
<azonenberg> The other issue is, if i cascade two 5580s... actually wait a minute
<azonenberg> VCMO < VCMI. So if I shift the output side down by 700 mV
<azonenberg> now the two amps are well matched (VCMO of first = 700 mV WRT ground, VCMI of second = 700 mV WRT ground, 1400 mV wrt its shifted ground)
<azonenberg> VCMI of second = 725 / 1450 sorry
<azonenberg> But now the first stage amp is running at vdd=0V so it's got VCMI of 1.45 WRT ground
<azonenberg> gaah
<azonenberg> Really starting to feel like the best option is splitting the AC and DC paths entirely and recombining later
<azonenberg> lain: ^
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<azonenberg> So doing more testing on the AKL-PT2, it seems like the notches in the silicone overmold might not actually be necessary
<azonenberg> The tip end has about 1cm with no notches and those flex just fine
<azonenberg> i'm debating removing the notching in the next mold revision to improve durability since it doesnt seem like they actually contribute anything
<azonenberg> But i feel like having designated flex points might reduce stresses and potential cracking
<smkz> wouldnt it be the opposite, where introducing designated flex points means there's bendiness/stress concentrated there?
<azonenberg> smkz: yes but it's thinner at those points
<azonenberg> as something gets thicker the tensile stress introduced by a bend increases
<azonenberg> this is why you can bend fiber optics but not a glass window
<azonenberg> the stress is primarily located at those points but the magnitude of the stress is much smaller
<azonenberg> because the radius from the centerline of the probe to the surface is smaller
<azonenberg> miek: ping
<miek> azonenberg: pong
<azonenberg> See my recent tweet thread. Tl;dr just picked up a sma gage set
<azonenberg> either i'm misunderstanding the readings or the dielectric on 100% of the SMAs in my lab, including brand-new minicircuits attenuators that have never been mated to anything, is out of spec
<miek> i was about to reply but then saw the latest tweet, you're right about the sign being flipped
<azonenberg> So that connector is in spec?
<miek> so the dielectric position is good, but which direction was the pin position reading?
<azonenberg> Pin position read +3.5 on that connector
<azonenberg> So far both pin and dielectric have read positive on both gages (only doing female ends so far)
<miek> ah ok cool, that's all in spec then
<azonenberg> Perfect
<miek> check out the manual for the Maury set, it should apply the same to yours:
<azonenberg> I think i'm going to add this to my annual lab maintenance checklist
<azonenberg> gaging all connectors on every single cable and adapter
<azonenberg> in addition to doing frequently used ones every few months probably
<miek> yeah, it's a good idea. it's pretty quick and easy too
<azonenberg> Yeah once the covid situation stabilizes and i can have people over the house again i'll probably show Jes how to do it (my lab tech)
<azonenberg> I can just have her over quarterly or so and hit all of the frequently used stuff, then do everything at the start of the year
<azonenberg> miek: so it looks like my VNA cal standard doesn't quite meet the maury microwave standards lol
<azonenberg> FD is around 4 mils on most of the connectors
<azonenberg> FP is well within spec though
<azonenberg> And FD is still within the "industry" standard (F)
<azonenberg> Wow
<azonenberg> Several of these minicircuits attenuators measured +8 mils on MD
<azonenberg> miek: That's outside every spec in the manual lol. It's in the "safe" direction so it shouldn't damage anything
<azonenberg> So i'm not gonna RMA them but definitely something to be aware of
<azonenberg> AKL-PT2 full panel stencil ordered
<azonenberg> Planning to order the updated mold with proper cutouts for the stiffeners later today
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<azonenberg> So i just got off the phone with an ADI apps engineer, he wasn't able to answer my questions about the 5580 off the top of his head but is looking into it
<azonenberg> Also suggested i look at the ADL5566
<azonenberg> I'm really not a fan of the 5566 from looking at the s-parameters though. it has rolloff instead of peaking from 3 to 6 GHz
<azonenberg> i need that peaking to compensate for losses elsewhere in the system (most notably the probe tip)
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<azonenberg> o/ bvernoux
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<azonenberg> basically at this point i *will* be using the adl5580, the only question is a) how hard it will be to get and b) if i will be able to DC couple it or if i'll have to ac couple and make up the dc path some other way
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<azonenberg> LeoBodnar: ping
<azonenberg> I ordered one of your SMA pulse generators a little while ago
<azonenberg> Just put a SMA gage on the connector and the pulse output connector is out of spec
<azonenberg> the center contact is protruding by 0.002" past the mating plane, spec allows it to be slightly recessed but not stick out
<azonenberg> Guessing this was caused by overtightening the screws during manufacture but it might be something else?
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