<Stephie>
seems to go back to a more classic "hand probe + holder" design, just with a slimmer probe
<azonenberg>
idgaf
<azonenberg>
without a spring ground on that ring
<azonenberg>
on that barrel*
<azonenberg>
there is no chance they are getting 500 MHz bw
<Stephie>
yeah, I assume they had that planned
<Stephie>
they just used a shitty ground for the show
<azonenberg>
except the fundamental problem with spring grounds and positioners
<azonenberg>
they're stiff and provide horizontal force when loaded
<azonenberg>
while the positioner only applies vertical force
<azonenberg>
so unless you have an exposed ground plane at *exactly* the right distance from your test point, they're useless
<Stephie>
yeah, i do wonder how it'll turn out
<Stephie>
but seems to be where they're headed
<azonenberg>
i consider the spring ground on the classic passive scope probe to be the worst grounding solution, except all the others
<Stephie>
i tend to design my boards around them, with dedicated groumnd test points at about the right spacing
<Stephie>
i shouldnt have to but it works
<Stephie>
and well, it only works if you thought about putting a test point there beforehand
<azonenberg>
They're also extremely prone to shorting
<azonenberg>
*especially* if under any lateral pressure
<azonenberg>
one slip of the finger and the spring pops out and touches something else
<azonenberg>
very often the tallest thing in close proximity is a power bypass cap
<azonenberg>
boom you're dumping vcc into your scope ground
<azonenberg>
And my experience is also that test points are handy but i very often find myself probing stuff i didn't anticipate when I designed the system
<Stephie>
yeah, definitely
<Stephie>
options for good grounding are fairly limited outside of solder-ins
<electronic_eel>
yey for solder in probes
<Stephie>
they really are great, though i wish they weren't as neccesary
<electronic_eel>
try probing a 0.5mm pitch qfn with something else than a solder in probe...
<azonenberg>
electronic_eel: funny you say that because i am right now looking for a handheld multimeter probe to do exactly that :p
<azonenberg>
but yeah there is a reason i am working on this whole line of solder in probes
<azonenberg>
there is no good alternative
<electronic_eel>
i have multimeter probes from probemaster. they have very sharp pins. they work well for what they are. but holding them on a bump of a 0.5 pitch qfn is not what they are made for
<azonenberg>
yeah i just ordered a set of fine pitch probemaster probes to see if they're at least better than my current fluke leads
<azonenberg>
but i want something suitable for things like continuity or voltage measurements on 0.5mm pitch qfn parts
<electronic_eel>
what i often do in this case is solder a small wire to the pins or bumps i'm interested in and then probe them with a small grabber probe. this allows me to quickly change between different test points without resoldering
<electronic_eel>
quick continuity testing, when you are sure that touching or shorting the pins next to it doesn't damage anything, works quite well
<electronic_eel>
i have an idea for a quick continuity tester that doesn't output more than 0.2v in the back of my brain. that would not be able to damage all but the most sensitive circuits
<Stephie>
does anyone know who manufactures replacable pogo pins like the ones pcbite uses?
<Stephie>
ah, found the right keywords right after asking :P
<azonenberg>
Hmmmm
<azonenberg>
So the CL mode loop does not correct my DC offset on the BUF802
<azonenberg>
but i think i may have found a root cause
<azonenberg>
the negative supply rail is about -4.541V while the positive is at +4.476. Which means mid supply is not actually at ground, it's at-65 mV
<azonenberg>
Positive bumps up to 4.509 when I add 1M ohms || R4 (turning it into effectively 9.9K ohms vs the original 10K)
<azonenberg>
And interestingly that made the offset problem worse by a tiny bit maybe? i now seem to have a 104 vs a 98 mV offset
<azonenberg>
actually no its 101 vs 98. so susbstantially no change
<azonenberg>
also, switching output to the multimeter to get better resolution
<azonenberg>
and the offset is dropping over time, it's 20 uV less than it was a minute ago
<azonenberg>
i wonder if it's temp related too
<azonenberg>
But that makes it hard to know if a change i made actually was helpful lol
<azonenberg>
anyway, let's say actual offset without scaling factor of the board right now, with the 1M ohm resistor added and set up on the fixture etc, is -10.036 mV
<azonenberg>
And when floating (no "0V" input provided from signal generator) the output is -10.515 mV
<azonenberg>
FLoating after removing the 1M resistor, offset is -10.183 mV and still dropping
<azonenberg>
yeah now it's -10.107 and seems to be pretty stable
<azonenberg>
now let's connect to the sig gen...
<azonenberg>
-9.725 mV or so
<azonenberg>
ok so that's substantial and measurable, the resistor made it worse
<azonenberg>
but that also suggests that the offset is indeed at least partially controlled by supply voltage
<azonenberg>
OTOH, the impact is weak
<azonenberg>
400 uV with that change, i need to correct a whole 10 mV of offset which is 25x greater
<azonenberg>
which would (assuming linear everywhere else) translate to a whopping 825 mV shift in the supply rail. which can't be right
<azonenberg>
something else is going on
<azonenberg>
The ADA4075 specifies max offset of 1 mV with typical of 200 uV
<azonenberg>
so where is this offset creeping in?
<azonenberg>
I measure -1.585V at Vaux (on R13)
<azonenberg>
The DC level on IN (on R14) is -245 mV
<azonenberg>
and OUT (before R10) is -19.65 mV
<azonenberg>
VIN measured at C8 is -2.8 mV
<azonenberg>
and voltage on the DUT thru line (nominally zero) measures about 0.225 mV
<azonenberg>
(also 100x HML 100 ohm just arrived... about time)
<d1b2>
<xabean> I don't want to know how much those cost, since that's clearly a digikey packet, and neither the model number nor digikey part number show up on digikey's website.
<azonenberg>
xabean: lol, yes
<azonenberg>
This was special order from Vishay but they wouldn't sell directly to me, i had to go through a distributor
<azonenberg>
so i got to have a chat with the friendly folks in digikey's "non catalog parts" deparmtnet
<d1b2>
<xabean> gotta make sure you're not building ICBMs!
<azonenberg>
Lol. you can buy a lot of parts on their website far more suitable for missile guidance than these
<azonenberg>
anyway, the big problem was that this part is obscure enough Vishay does not produce and stock them routinely
<azonenberg>
They're made-to-order only
<azonenberg>
as are the 450 ohm version i have coming hopefully tomorrow (alraedy have tracking)
<azonenberg>
Minimum order is 100 pieces, and the lead time is... well, i placed the order in February
<azonenberg>
and after tax they come out to something like $9 per resistor