Products > Test Equipment
DIY Logic Analyzer Probe and Pods for Siglent (and LeCroy) scopes
tautech:
--- Quote from: mawyatt on March 20, 2021, 01:06:13 pm ---
I'll need to try an create a model for the Siglent SPL2016.
The impedance of the coaxial lines is lower, likely around 50~60 ohms, but how long are the coaxial lines,
--- End quote ---
1150mm from PCIe plug to lead breakout connector.
--- Quote ---and how long are the probe leads and ground lead?
--- End quote ---
A further 200mm, 150mm
--- Quote ---What is the tip capacitance of the scope probe used,
--- End quote ---
Apparently 11pF
https://siglentna.com/wp-content/uploads/dlm_uploads/2020/02/SP3025A_3050A_Users_Guide.pdf
Have SAP1000 with 1.2pF if you need another measurement with that.
https://siglentna.com/product/active-probe/
--- Quote --- I'll need to include that to estimate the effects of the scope probe, and was this measured with the SPL2016 plugged into the scope or stand alone?
--- End quote ---
Stand alone.
--- Quote ---Also what is the DCR reading from LA probe tip to the PCIE PCB edge connector?
--- End quote ---
91.1k
oz2cpu:
91k1 ?? did you double check the trigger levels ? at super low speed ?
and a super high speed ?
my unit is more correctly triggering at the right spot with 120R + 86k6 // 8p2
mawyatt:
Rob,
Thanks for the data, here's what we came up with as a quick estimate model of the LA. The Digital Input pulse was manipulated to try and create what we think the actual pulse to the LA looks like, and show the offset as shown on your DSO measured trace above.
The Digital Probe wire self inductance is based upon 200 & 150mm of #26 AWG wire, the 1100mm coaxial cable (shown as twisted pair in schematic) is modeled as having a Zo of 45 ohms and delay of 6.1ns based upon a velocity factor of 60%. Later we'll need to see how the twisted pair cable (and ribbon) rather than the coaxial cable effects these simulations.
Still slowly working my way thru the 3D modeling tools, and waiting for the 3D printer to ship. Custom PCBs are being developed and hopefully at some point will be able to create a 3D printed base and POD units using connectors for the Base to POD twisted pair cable (and ribbon), maybe even a coaxial version if a low cost cable can be acquired.
BTW we had to remove the models for the connectors used for the Probe lead interface, and the POD to Base for the coaxial cable interface. They were causing convergence and simulation artifacts (problem with transmission line simulations). Rather than fiddle with the simulation parameters and integration methods, we just removed the models knowing from experience they won't have much effect on the results, later as we fine tune things we may reintroduce these connector models as a verification check.
Anyway, here's what we've got so far.
Best,
oz2cpu:
finally got a nice stack of POD pcb's today
they fit perfectly into the 3D printed shells
now i pack and ship to the first one :-)
mawyatt:
Nice :-+
Best,
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