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Pocket-Sized 6 GHz 1 TS/s ET Scope

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joeqsmith:
Consider that my math skills are about the level of Jethro Bodine's (Beverly Hillbillies, sixth grader dropout),  it will take a lot of effort on my part to work through it. 

I don't like that you are not seeing a problem with linear interpolation.  That tells me we are missing something.  Let's minimize the variables.  The attached were created using your latest software/firmware/FPGA.  Same Marconi RF generator, Pasternak splitter and cables.  Using different settings than before.  Note how it glitches positive on the rise and negative on the fall.  Also note, all four glitch synchronously. 

Your software works a little different than mine and the settings appear to make a difference.  Or, maybe something else is going on. 

SJL-Instruments:

--- Quote from: joeqsmith on January 29, 2024, 06:12:37 pm ---I don't like that you are not seeing a problem with linear interpolation.  That tells me we are missing something.  Let's minimize the variables.  The attached were created using your latest software/firmware/FPGA.  Same Marconi RF generator, Pasternak splitter and cables.  Using different settings than before.  Note how it glitches positive on the rise and negative on the fall.  Also note, all four glitch synchronously. 

--- End quote ---
Can you send us raw CDF data from when this occurs? Choose the "Raw CDF Data" option in the stream or export dialog (v2.5.7 preview 2). The file you attached only contains CSV with the extracted voltages.

***

The fact that all four glitch synchronously looks like a timing issue (i.e. it's returning correct CDF data at an incorrect time). The four small spikes in your data are consistent with the timing being late by either 25 ps or 12 ps.

We've never seen this happen before, so there's no check for this in firmware. It's easy to add one - we just didn't think it would be necessary.
We have a few ideas about the root cause, but more data would be very helpful - particularly if you phase-shift one of the channels. This would make a timing error unambiguous.

joeqsmith:
For example, while streaming I drag the screen you are expecting it to error out?   It is very possible this is what happened in this case. 

I can certainly start providing you with data using your NPZ format, however without being able to view the data, I have no way to know if I would be sending you anything useful.   It keeps getting back to the lack of some sort of min/max function. 


For the custom software, baby step 1,  showing raw CDF, Gaussian error applied and inverse Gaussian error applied.  Is this what you are expecting?





SJL-Instruments:

--- Quote from: joeqsmith on January 29, 2024, 08:19:49 pm ---For example, while streaming I drag the screen you are expecting it to error out?   It is very possible this is what happened in this case.

--- End quote ---
Yes, if you drag the screen, the timebase will get reindexed, and occasionally the newest sample will get put in the wrong place. This is known behavior.
If you see the small spikes with our software without touching the screen, then we need to investigate further.


--- Quote from: joeqsmith on January 29, 2024, 08:19:49 pm ---I can certainly start providing you with data using your NPZ format, however without being able to view the data, I have no way to know if I would be sending you anything useful.   It keeps getting back to the lack of some sort of min/max function. 

--- End quote ---
For diagnosing a timing error, the CSV voltage information is enough (especially if the channels have different phases). Based on our internal testing, and the data you provided in #168, we're confident the CDF routine has no issues. (In which case the NPZ doesn't give much additional information.)


--- Quote from: joeqsmith on January 29, 2024, 08:19:49 pm ---For the custom software, baby step 1,  showing raw CDF, Gaussian error applied and inverse Gaussian error applied.  Is this what you are expecting?

--- End quote ---
We can't tell in detail without zooming into the interesting area. But you should either:
1. Fit a Gaussian error function directly to the CDF data, or
2. Apply the inverse Gaussian error function to the CDF data and then fit a line with proper weights.
Both approaches are equivalent (to first-order).
The Gaussian error function should never be applied to the data.

It will also help the fit stability (particularly with method 2) if you discard all data where the CDF is <0.1 or >0.9.

joeqsmith:
Got it.  No dragging.   If I am able to find a glitch using your software, I will send both formats.   


--- Quote ---We can't tell in detail without zooming into the interesting area. But you should either:
1. Fit a Gaussian error function directly to the CDF data, or
2. Apply the inverse Gaussian error function to the CDF data and then fit a line with proper weights.
Both approaches are equivalent (to first-order).
...

It will also help the fit stability (particularly with method 2) if you discard all data where the CDF is <0.1 or >0.9.

--- End quote ---

From the 4.3.3 example, there are only three data points that meet that criteria.   Showing the raw plus two methods for these three points.   Using least squares for linear fit of the inverse Gaussian Error.   


--- Quote ---The Gaussian error function should never be applied to the data.
--- End quote ---
Totally lost me but I suspect based on your comment about them being the same, there is something wrong with what I have shown. 

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