Products > Test Equipment
DIY Logic Analyzer Probe and Pods for Siglent (and LeCroy) scopes
mawyatt:
Yes, we've looked into the math and the data sheets from 3M for the twisted pair. The single wire as used for the Probe lead wire and the Ground lead wire must be estimated from the self inductance of a single wire not a twisted pair tho.
Here' a simplified model we're using for the LA, later the PCB characteristics for the Base unit and the POD will be included, which will be followed up with some measurements. Note that the Scope PCIE connector and other details haven't been included yet. The model will be augmented as needed with additional components and parameters to better reflect the actual hardware envisioned as we move forward.
Also, working towards getting to a level where we can use 3D modeling and printing to create this structure, so will take some time since no prior experience with either.
Edit: Here's a controlled impedance cable "back of the envelope" concept (when you don't have the proper cables readily available) we've wanted to try but never had the time. Should show a much better signal to signal coupling and a lower intrinsic impedance approaching what a proper coaxial line would produce over a single ribbon cable. Uses a standard ribbon cable with SGSG orientation, but with another ribbon cable on top and bottom glued into the groves between the wires of the main center ribbon cable. This should approximate a coaxial cable and have an impedance of ~80 ohms as shown. Might be worth playing around with since most folks have the standard ribbon cable available and it's inexpensive, you could shroud the 3 ribbon cables with some thin heat shrink to make it more durable and look nicer.
Best,
tautech:
Mike, when I get a chance with a ~2ns pulse source and 1 GHz scope I'll scope a SPL2016 channel or 2 for you to compare against your simulations.
Should be later today after I've ticked a few other jobs off.
tautech:
--- Quote from: tautech on March 19, 2021, 08:10:47 pm ---Mike, when I get a chance with a ~2ns pulse source and 1 GHz scope I'll scope a SPL2016 channel or 2 for you to compare against your simulations.
Should be later today after I've ticked a few other jobs off.
--- End quote ---
20ns pulse with 2ns risetime ex SDG6022X.
3.3Vpp into SPL2016 grabbers.
Measurement at SPL2016 PCIe plug with SDS5104X 10x 500 MHz probes. Scope floated to use SPL2016 Gnd path for probe reference.
mawyatt:
--- Quote from: tautech on March 20, 2021, 01:06:28 am ---
--- Quote from: tautech on March 19, 2021, 08:10:47 pm ---Mike, when I get a chance with a ~2ns pulse source and 1 GHz scope I'll scope a SPL2016 channel or 2 for you to compare against your simulations.
Should be later today after I've ticked a few other jobs off.
--- End quote ---
20ns pulse with 2ns risetime ex SDG6022X.
3.3Vpp into SPL2016 grabbers.
Measurement at SPL2016 PCIe plug with SDS5104X 10x 500 MHz probes. Scope floated to use SPL2016 Gnd path for probe reference.
--- End quote ---
Thanks Rob, 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, and how long are the probe leads and ground lead? What is the tip capacitance of the scope probe used, 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? From the looks of the pulse shape it's stand alone so isn't getting the full influence of the PCIE connector in the scope and the loading effects.
All this will help get a better estimate of the SPL2016 behavior.
Edit: Also what is the DCR reading from LA probe tip to the PCIE PCB edge connector?
Cheers,
mawyatt:
[ Specified attachment is not available ]
--- Quote from: tautech on March 20, 2021, 01:06:28 am ---
--- Quote from: tautech on March 19, 2021, 08:10:47 pm ---Mike, when I get a chance with a ~2ns pulse source and 1 GHz scope I'll scope a SPL2016 channel or 2 for you to compare against your simulations.
Should be later today after I've ticked a few other jobs off.
--- End quote ---
20ns pulse with 2ns risetime ex SDG6022X.
3.3Vpp into SPL2016 grabbers.
Measurement at SPL2016 PCIe plug with SDS5104X 10x 500 MHz probes. Scope floated to use SPL2016 Gnd path for probe reference.
--- End quote ---
Rob,
After some analysis and estimating what we "think" Silgent has done with the SPL2016, here's a first cut at simulating such per your measurement.
Best,
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