<azonenberg>
thie is zoomed in my probe S21 vs the Pico "6 GHz" probe. The big dip in mine out to 5 GHz is the response of the filter which seems to be too strong (It's supposed to be toning down peaking, not adding a dip)
<azonenberg>
but i think calling my design a 6 GHz probe is completely reasonable at this point and further improvements will just be tweaking flatness
<azonenberg>
red vs black (v1.3 vs v1.2) is better until past 5 GHz then the resonance hits
<azonenberg>
S21 measured across 50 ohm terminator, S11 across open circuit
<lain>
azonenberg: !! awesome
<azonenberg>
i'm also very optimistic for response of the solder-in probes at this point because they don't have the tip needle which is the source of the remaining resonance, or the filter needed to counteract it
<azonenberg>
I think those could very well end up being >6 GHz probes
<azonenberg>
as in, i'll spec them as 6 GHz probes because i have no way to characterize them any higher :p
<azonenberg>
lain: you can see just how atrocious the TA061 is compared to all the others lol
<azonenberg>
massive notch in S11 and huge spike in S21 right in the middle of the passband
<azonenberg>
like, i have a tip resonance but at least it's at >6 GHz and not in the middle of the operating range
<azonenberg>
but yeah, my S21 from DC to 6 GHz is already flatter than the pico probe which had been my target to beat for quite a while
<azonenberg>
And that's a $1K probe
<azonenberg>
whatever i do after this is icing on the cake
<azonenberg>
also hmmm, thinking more i don't think the dip at 2-3 GHz on mine is the filter
<azonenberg>
the filter's peak is actually closer to 5 GHz
<azonenberg>
So it might be something else. In any case this version is Good Enough (tm) for the short term
<azonenberg>
lain: also 115ps 10-90, 79ps 20-80 *including cable effects* measured by the scope
<azonenberg>
With the cable de-embedded, 74ps 20-80 through the probe. On a scope specced at 75ps 20-80
<azonenberg>
So basically i think i'm at a dead end with the design now, lol
<azonenberg>
I literally cannot make it any better. Because if i do, i'll have no way to know it's better :p
<azonenberg>
i need better instrumentation to refine it further
<azonenberg>
i might spend a little while in sonnet trying to flatten out the response around 2 GHz but other than that, i'm calling it done
<azonenberg>
The scope is specced at 100ps 10-90 but for some reason when i de-embed the cable in glscopeclient i get strange results for 10-90 rise time so i can't quote a 10-90 through the probe
<azonenberg>
i need to investigate more
<azonenberg>
but 115ps 10-90 on a scope with 100ps datasheet spec before de-embedding the cable is already really good
Degi has quit [Ping timeout: 260 seconds]
Degi has joined #scopehal
Pretzel4Life has joined #scopehal
Pretzel4Ever has quit [Ping timeout: 246 seconds]
electronic_eel_ has joined #scopehal
electronic_eel has quit [Ping timeout: 260 seconds]
_whitelogger has joined #scopehal
<Kliment>
azonenberg: how are the solderable probes meant to be used
<azonenberg>
Kliment: It's a 150 mm (for this prototype, actual length may change) flex PCB with 1mm spaced signal and ground contacts at the tip, and a SMA at the other side
<azonenberg>
and a 3d printed TPU strain relief/protective sleeve over most but not all of the length of the flex
<Kliment>
That seems quite long
<azonenberg>
The LeCroy WaveLink solder-in tips are 9 inches
<azonenberg>
i decided to try a little shorter to start
<Kliment>
is u.fl too lossy for this application?
<azonenberg>
it would be easy to make several versions, the design scales easily
<azonenberg>
You're getting ahead of me, hold on :)
<azonenberg>
Anyway, the intention is for you to secure the tip of the probe and the very end of the TPU sleeve to the DUT with kapton tape
<azonenberg>
then solder the shortest possible jumper from the tip to the test point and from the ground to the nearest ground
<azonenberg>
using 30ga wire, the circuitmedic square wire i like, etc
<Kliment>
yeah, I get how it works on the PCB end
<azonenberg>
i may also make a version with castellations on the tip, there are pros and cons. my previous version used them and i want to try without
<Kliment>
(though I'd not use it that way)
<azonenberg>
anyway, that's the AKL-PT2
<azonenberg>
The AKL-PT3 is a tiny probe about the size of a dime
<azonenberg>
with the same solderable contact area as the PT2, the same attenuator string, and a U.FL
<Kliment>
What I would do is solder it in directly - apply paste to traces, and heat it through the flex with an iron
<azonenberg>
Kliment: you mean upside down? that works if tip and ground are exactly 1mm apart
<azonenberg>
using it like an LGA
<azonenberg>
if you had a suitable test point then great
<azonenberg>
But if i intended it to be used that way i'd put a castellation on the end so you could have a solder fillet to get better contact
<azonenberg>
Long term, i will probably offer both variants
<azonenberg>
the PT2 prototype is intended to test the concept of top side contacts only
<azonenberg>
as well as be a mechanical concept for the idea of a TPU-sleeved flex board as a probe
<Kliment>
I don't see why you can't support both
<azonenberg>
The point of the top side contact is you can put it on top of components or pads
<azonenberg>
and not short
<azonenberg>
also, less capacitive loading than castellations
<Kliment>
yeah, but it's flex, you can just flip it around
<Kliment>
and you don't need castellations to solder contacts through flex
<azonenberg>
well the reason flipping it might be hard is that there are ~500um high attenuator resistors *right* next to that contact
<Kliment>
Ah
<azonenberg>
you'd need a very sharp bend in the flex and there would be lots of shear force on the joint
<Kliment>
yeah that will be a problem
<azonenberg>
minimizing distance from DUT to resistor string has significant impacts on frequency response
<Kliment>
I guess via is not an option?
<azonenberg>
there's a resonance in the AKL-PT1 i've been slowly pushing up and up in frequency by shortening the tip
<azonenberg>
now it's around 6 GHz
<Kliment>
via through flex will be like 0.12mm
<azonenberg>
If i had a full via, i might as well cut the board there and have a castellation
<azonenberg>
Which is what the very first prototypes i did back in 2017 had
<Kliment>
cutting the board makes it a pain to solder
<azonenberg>
why?
<Kliment>
because there's no flat bit to press on
<azonenberg>
you tape it down then just solder to the edge of the via like a chip resistor or something
<azonenberg>
all you have to do is get a tiny bit of solder on the PCB trace and then heat the via a tiny bit, it wicks right up
<azonenberg>
i've done it and it works great
<Kliment>
I'd honestly rather have a full via and a trace-shaped pad underneath
<azonenberg>
the other thing you can do is flux the area, tin the iron, then just tap the tip of the iron right at the castellation
<azonenberg>
and boom it's soldered
<azonenberg>
anyway AKL-PT2 v0.1 - although it wasn't called that yet - was made at pcbway and had about 30% yield due to the small via on the castellations requiring about +/- 100um tolerance on the edge cuts
<azonenberg>
v0.2 was made at multech and had very good yield due to a combination of using a nicer fab and enlarging the vias slightly
<azonenberg>
v0.3 is being done at oshpark and is top contacts only
<azonenberg>
like i said I'm PoC-ing a lot of different design concepts in this one board
<Kliment>
makes sense
<azonenberg>
I do want to trial the via-and-bottom-contact approach
<Kliment>
I think it will have better contact and better mechanical stability
<azonenberg>
v0.1 and 0.2 were both in 2017
<Kliment>
with the bottom contacts
<azonenberg>
So the other reason is, via size
<azonenberg>
at oshpark at least you need ~550um vias
<azonenberg>
how do you propose to get a probe on a single pin of a 500um pitch tqfp with that?
<azonenberg>
your tip contact has to be 250um or so in size
<azonenberg>
and you need a way to get a ground contact which could be at any unpredictable location wrt the signal if you're debugging and not probing a by-design test point
<azonenberg>
One of the things i want to do with the PT2 and PT3 prototypes is to experiment with probing random signals on real boards
<azonenberg>
and actually see how the ergonomics work if i just pick say the RGMII TX_D3 signal on a random devkit
<azonenberg>
and say i want to probe it
<azonenberg>
Right now prototypes of the PT2 and PT3 are at oshpark expected to be back from fabMonday
<azonenberg>
So based on test results we'll see how it goes. These are also my first designs on oshpark flex so my impedance calculations etc might also need some work
<azonenberg>
The other two probes in the pipeline, right now just at the concept stage, are the AKL-PT4 and AKL-AD1
<azonenberg>
the PT4 is basically the tip of a PT1 with a MMCX connector and a... M4 I think? screw stud for attaching to a sensepeek pcbite probe holder
<azonenberg>
and the AD1 is an active differential probe, details TBD
<azonenberg>
my preliminary concept for the AD1 is similar to various other active probe architectures where you have a solder-in tip containing a damping resistor and then an amplifier module that plugs into it
<azonenberg>
I think the LMH3401 might be a good starting point for it
<azonenberg>
the mating connection from the tip to the amplifier is TBD, and the proposed tip design is similar to the PT2 except with a differential pair instead of a coplanar waveguide
<azonenberg>
not sure if i'd have just a bottom side ground or anything on top too
<azonenberg>
but it would be a tightly edge coupled diffpair
<azonenberg>
I haven't done a lot of design work on it yet, the plan was to spend some time studying the lecroy probes and thinking about what i did and didn't like about them
<azonenberg>
And also get the passive probes refined to the point i was happy with them before branching out
<Kliment>
azonenberg: you can have your vias further apart than your pads
<Kliment>
azonenberg: be aware with the oshpark flex that they don't use coverlay like everyone else
<Kliment>
azonenberg: they use LPI soldermask which has different electrical properties and is much less abuse-resistant
<azonenberg>
Kliment: My prototype is maskless for that reason
<azonenberg>
and i'll just accept the ENIG losses which, on a 6 inch line, will be considerable
<azonenberg>
again it's a prototype
<azonenberg>
i expect significant changes before it's final
<Kliment>
maskless is unpleasant on a probe
<azonenberg>
that's part of what the TPU shell is for
<azonenberg>
so its less likely to short against stuff
<Kliment>
Yeah
<azonenberg>
but it has opens between the strain relief elements
<azonenberg>
The v0.3 prototype as it stands is not intended to be something i could just start deploying as is. Think of it like a concept car
<azonenberg>
The technology it demonstrates will eventually make it into the final probe
<azonenberg>
but it may look nothing like it
<azonenberg>
Key goals for this demonstrator are... Test the ergonomic aspect of top-only contacts on a solder-in probe
<azonenberg>
validate mechanical properties of oshpark flex for this application
<azonenberg>
Test the fit and snugness of 3D printed TPU as a strain relief and anti-short guard for flex PCB
<azonenberg>
Figure out a way to DIY FR4 stiffeners for oshpark flex so i can use edge launch connectors with them for prototyping
<azonenberg>
Get a feel for the mechanical properties of the LPI soldermask on the bottom side ground plane
<azonenberg>
and yes, see what kind of bandwidth is achievable on the prototype as is
<azonenberg>
v1.3 probe prototype in red vs PicoConnect 921 in blue, as well as a couple of other previous hardware revs and the Pico TA061 piece of junk
<azonenberg>
It's got a little dip around 2 GHz i'd like to eliminate eventually but it's better than -3 dB to 6 GHz which is the upper end of my VNA range :D
<azonenberg>
and that dip is nothing you can't de-embed, perfect flatness is impossible anyway
<azonenberg>
74ps 20-80% rise time after de-embedding the minicircuits cable when probing the LeoBodnar pulse generator
<azonenberg>
On a scope specced at 75ps rise time
<NeroTHz>
one second
<azonenberg>
NeroTHz: that was a very long second
<azonenberg>
:P
<NeroTHz>
oh
<NeroTHz>
right
<NeroTHz>
yeah
<NeroTHz>
:p sorry, work and distractions n shit
<NeroTHz>
but the performance seems nice. I agree, don´t spend too much time on that 2GHz dip
<NeroTHz>
rip
<NeroTHz>
my work machine that I VNC into just stopped responding
<NeroTHz>
seems like i´m gonna have to jump to a higher priority on that new-computer list at work
<azonenberg>
NeroTHz: lol fuun
<azonenberg>
i had to replaec a work machine a year or so ago due to random freezes too. some pcie device was randomly disconnecting
<azonenberg>
that was soldered to the motherboard
<azonenberg>
so the link ber was probably going bad due to a serdes failure or something
<azonenberg>
but yeah i think at this point mission accomplished on the handheld probe. I can't make it any better without higher b/w test equipment
<azonenberg>
So current plan is to send this prototype to shahriar and have him do a video on the project, order a batch of boards soon (budget is a bit tight thanks to construction on the house so a production-sized run might have to wait a little while)
<azonenberg>
and shift R&D efforts to the solder-in probes as well as probably an active differential probe at some point
<NeroTHz>
ah that will be interesting to see
<azonenberg>
The solder in probes are mostly a mechanical design problem
<azonenberg>
i can reuse my existing well tested attenuator
<azonenberg>
and the tip resonance will be way high out of band because of the much shorter "tip" which is just a solder pad
<azonenberg>
For the time being though, this probe is better than my test equipment. So i think i'm gonna make a couple more of them and actually start using them for projects
<azonenberg>
(right now i have 2 bare PCBs plus the one I'm sending to TSP
<azonenberg>
the one other little thing i might want to try is seeing if i can source where Pico gets their probe tips for the 900 series from
<azonenberg>
those tips are slightly skinnier than mine so i could use a smaller socket with less capacitance
<azonenberg>
and finer wire for solder-in applications
electronic_eel_ is now known as electronic_eel
<NeroTHz>
ffs
<NeroTHz>
people who first do a simulation of a PA, publish it
<NeroTHz>
then a year later fabricate it, then just re-write the paper (edit your sentences here and there so google/plagerism software wont catch it) and republish it
<Degi>
PA = power amplifier?
juli966 has joined #scopehal
<azonenberg>
Totally unrelated, I just found an error in the wavelink low-bandwidth probe datasheet (D4xx/D6xx)
<azonenberg>
on page 7 there's a contradiction as to the performance of the Dx10/Dx20-QC probe tip
<azonenberg>
the rise time numbers for the D410/D420 list SI, QL-SI, HiTemp, QC, and PT on the first line then QC again on the second line
<azonenberg>
based on QC being listed by itself there, and again for the D610/D620 amplifier modules at left, it appears that this is the correct number and its inclusion on the first row is an error
<azonenberg>
Already reported to them so they can fix it
<azonenberg>
Flex probe prototypes just got received by oshpark
<azonenberg>
hopefully should have them early next week
bvernoux has joined #scopehal
bvernoux has quit [Quit: Leaving]
<azonenberg>
So this is interesting
<azonenberg>
reading through more lecroy documentation
<azonenberg>
"WaveLink Medium Bandwidth probe amplifiers have no gain or attenuation control. However the WL-PLINK platform/cable assembly does provide gain and attenuation controls"
<azonenberg>
so the wavelink adapter may not be 100% passive
<azonenberg>
unsure if the ProBus version is, or if there's some intelligence there too
<azonenberg>
Also, it looks like ProLink goes up to about 20 GHz and then they switch to 2.92mm connectors
<azonenberg>
WaveLink seems to have two variants, low bandwidth is 4/6 GHz and medium bandwidth is 8/10/13 GHz. There does not appear to be a "high bandwidth" wavelink offering
<azonenberg>
instead you move to the DH series
<azonenberg>
which is a separate probe system that has 8 GHz available with probus2/prolink, then 13, 16, 20 GHz ProLink and 25, 30 with 2.92 mm
<azonenberg>
The DH probe amps are significantly larger than WaveLink ones and have a bunch of buttons on them, vs the WaveLink ones which have no physical controls
<azonenberg>
also interesting... WaveLink handheld browser tips go to the full bandwidth of the amp. But DH browser tips max out at 16 GHz, while the DH solder-in tips go to 30 GHz
<azonenberg>
I'm impressed they got 16 GHz out of a handheld browser probe considering the difficulties I had with tip resonances on mine
<azonenberg>
There are mechanical constraints that make significantly smaller tips virtually impossible, so I wonder if they're either using lossy tips to damp out the resonance or doing some kind of compensation on the probe side of the tip to damp it
<azonenberg>
also interesting, WaveLink tips appear to be entirely passive and you need to tell the scope which one you are using to get correct gain display etc
<azonenberg>
But DH tips contain some kind of identification mechanism so the probe/scope knows which one you are using
<azonenberg>
Wonder why they didn't just slap a 24C on the WaveLink tips?
<azonenberg>
they could power it up, read the idcode, then power it down and have zero contribution to noise
<azonenberg>
and it's not like a 24c will increase the cost of a $8K probe significantly