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Pocket-Sized 6 GHz 1 TS/s ET Scope

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SJL-Instruments:

--- Quote from: joeqsmith on January 21, 2024, 03:05:17 am ---Showing the GigaWave with attached delayline.  LiteVNA was used for a signal source.  Shown with the delayline set to its minimum and maximum values.
--- End quote ---
Nice work with the analog delay line!  :)


--- Quote from: joeqsmith on January 21, 2024, 07:02:43 pm ---As promised, SJL has provided me with a pre-release which supports s-parameter de-embedding.   I used the LiteVNA + Solver64 to sweep my delayline from 5kHz to 8GHz to create a Touchstone file.  The LiteVNA uses harmonics above 6GHz and the data is pretty poor.   Still, importing the file into their GigaWave software, it appears to work correctly.   For the review, I'll use my Agilent PNA to properly characterize the delayline.

--- End quote ---
Glad to hear that de-embedding and s-parameter import are working. As promised, we've now publicly released v2.5.5 of the software which contains this feature:
https://www.sjl-instruments.com/software/

The accompanying manual has also been significantly expanded (revision H4, refresh if not updating for you):
https://www.sjl-instruments.com/user-manual.pdf


joeqsmith:

--- Quote from: hpw on January 09, 2024, 06:03:15 pm ---... as I like to trigger a LVCMOS edge and analyze the variations of like 20%..80% rise time over time as also some Chatter.

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Looking at 5ps resolution of LiteVNA output using their supplied cable.  The min/max are shown to provide you with some idea on the variance.  This is roughly 1 hour of data.  Also shown is the 3D graph of all of the sweeps, along with the baseline subtracted. 

My software does not make use of the glitch detection mentioned in the latest manual, although it was my collecting over long periods like this that raised the question about the glitches. 

SJL-Instruments:

--- Quote from: joeqsmith on January 23, 2024, 03:10:01 am ---My software does not make use of the glitch detection mentioned in the latest manual, although it was my collecting over long periods like this that raised the question about the glitches. 

--- End quote ---
For transparency, the relevant manual section is 4.3.3 ("single-point upsets") - a small fraction of returned CDFs may have an error in one point. These errors can be caught by looking for non-monotonic CDFs (which is the workaround mentioned in the manual).

The official software implements this workaround, so this primarily affects users who directly query the serial interface. We are tracking down the root cause of the glitches, and will issue a firmware update when it is resolved.

joeqsmith:
This was one of the plots showing the glitch problem using my software.  The Gigawave software did not allow for min/max detection and I had not noticed the problem until I started writing my own.  I assumed it was a bug in my code, but I was eventually able to capture a few glitches using the released software.    SJL was then able to replicate the problem with one of their units.   

As it stands, glitches appear more often towards the start of the sweep and are negative going.  I have seen positive glitches throughout the sweep but these seem less prevalent.     

While I have tried their latest software, there is no min/max function and I have to watch the screen looking for a glitch.   It appears to correct it but until we get some way to track these kinds of problems, I am not certain.

I had thought about implementing their error checking/recovery but I wasn't sure how to interpret the manual.   Using their example in 4.3.2, where they show 15 pairs, I would assume they run through all four conditions for 14 sets.   This assume "either of" meant to "OR" the two "ANDed" checks.  An example would have helped remove any ambiguity. 


--- Quote ---the issue can be circumvented by discarding and retaking CDF data that meets either of the following two criteria:
• Two neighboring voltages V1, V2 satisfy V2−V1 >5 mV and F(V2;Δt)−F(V1;Δt) < −0.1.
• Two neighboring voltages V1, V2 satisfy V2 > V1 and F(V2;Δt) − F(V1;Δt) > 0.9.

--- End quote ---

For the review, I plan to use their software and decided to wait for them to solve it.   While they seem confident the problem is firmware, it seems the have not yet found the root cause and I would not rule out hardware.  It will be interesting to hear what they find. 

There are a few other minor problems I ran into.  High offset voltage for example.  The plan is to add a way to correct for this in the software.  The one concern I have raised was how they plan to de-skew the channels.  While they have made a lot of progress, it's a new product.  Based on how responsive they've been, I'm confident any concerns I have will be addressed as the product matures.   

SJL-Instruments:

--- Quote from: joeqsmith on January 23, 2024, 02:05:31 pm ---I had thought about implementing their error checking/recovery but I wasn't sure how to interpret the manual.   Using their example in 4.3.2, where they show 15 pairs, I would assume they run through all four conditions for 14 sets.   This assume "either of" meant to "OR" the two "ANDed" checks.  An example would have helped remove any ambiguity. 


--- Quote ---the issue can be circumvented by discarding and retaking CDF data that meets either of the following two criteria:
• Two neighboring voltages V1, V2 satisfy V2−V1 >5 mV and F(V2;Δt)−F(V1;Δt) < −0.1.
• Two neighboring voltages V1, V2 satisfy V2 > V1 and F(V2;Δt) − F(V1;Δt) > 0.9.

--- End quote ---

--- End quote ---
We've provided an example (attached) in the next manual revision. Let us know if this is clear. It should eliminate the glitches you're seeing.


--- Quote from: joeqsmith on January 23, 2024, 02:05:31 pm ---The one concern I have raised was how they plan to de-skew the channels.
--- End quote ---
Just to clarify: We could make a test fixture that outputs two synchronized fast rising edges. You'd then connect CH1 to one output, CH2 to the other, and click a button. Repeat with CH3,CH4,etc in place of CH2. This would compensate for any probe length mismatches. Would this fit the bill?

Note that the inherent channel-to-channel skew is 15 ps max without any deskew. If a deskew offset is used, then data acquisition will be slower (and depend on the number of active channels), as data can no longer be acquired in parallel for all channels.

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