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Pocket-Sized 6 GHz 1 TS/s ET Scope

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SJL-Instruments:

--- Quote from: joeqsmith on February 27, 2024, 01:49:59 pm ---Shown is my crappy Fibonacci PAM8 50MHz test signal, scaled to 950mV.  20,000 triggers for min/max, centered around the switch point.  I wanted to increase the spread between levels without overloading the front end.   

When using an oscilloscope, I am expecting what is being displayed represents the actual signal.   With your scope, talking about 12bits TSPS equivalent, I am expecting some decent fidelity.  Especially when the claim is the primary use is for high speed signal integrity.   

Not being a math guru,  the last thing I want to think about when trying to evaluate some high speed signals is how the scope is statistically dealing with the data.    If I saw a waveform like the one shown, I would assume the signal was bad.  I may spend time trying to determine the cause of the noise.  Eventually, I would try another scope.  (For a comparison, shown attached to my vintage LeCroy 64xi).   

I am sure some of the shortcomings could be addressed with custom software.  I wouldn't expect many of your customer's to be software developers.  If this was a direction you wanted to take, you may want to consider open sourcing the main application to allow people to build off it rather than starting from scratch.  It may actually help with sales.

Sure we can talk about the low cost compared with other scopes but IMO, if the tool can't do the basic job it was designed for, or causes the user to spend time trying to track down nonexistent hardware problems, that lower cost is a bit of a false selling point. 

Again, others may have a different view. 

--- End quote ---
These are good points. We do want to emphasize that the vertical fidelity you're seeing is entirely a software limitation.
The default settings are chosen for a good tradeoff between speed and fidelity for an eye diagram of a two-level signal. In particular, for a PAM8 signal, K needs to be set to ~100 for good resolution. The software limit is currently 30 due to OpenGL implementation.

As the number of levels increase, the required Nmin and K values increase. We think it is possible to detect these automatically and set them appropriately. As you mentioned, this is likely necessary to give a good user experience.

Later today we can send you a prerelease that increases the maximum K. This will give better vertical fidelity on your PAM8 eye.
For the next update, we will put UI features on hold, and focus on automatically determining the CDF settings. This way, the user does not need to understand the theory of operation to take more complex eye diagrams.

joeqsmith:

--- Quote from: SJL-Instruments on February 27, 2024, 03:25:32 pm ---These are good points. We do want to emphasize that the vertical fidelity you're seeing is entirely a software limitation.
The default settings are chosen for a good tradeoff between speed and fidelity for an eye diagram of a two-level signal. In particular, for a PAM8 signal, K needs to be set to ~100 for good resolution. The software limit is currently 30 due to OpenGL implementation.

As the number of levels increase, the required Nmin and K values increase. We think it is possible to detect these automatically and set them appropriately. As you mentioned, this is likely necessary to give a good user experience.

Later today we can send you a prerelease that increases the maximum K. This will give better vertical fidelity on your PAM8 eye.
For the next update, we will put UI features on hold, and focus on automatically determining the CDF settings. This way, the user does not need to understand the theory of operation to take more complex eye diagrams.

--- End quote ---

When I hear about 12-bit converters I  am thinking 4096 discrete levels, not 30.   I understand those 30 points are distributed around the input signal.  Its fine if we are looking at simple single level waveforms.  But the manual opens the gates when it talks about eye diagrams.   When we start looking at different modulation schemes things break down fast.   It makes sense that the vintage LeCroy with 8-bits is able to resolve the PAM8 test case with much higher fidelity.  It just may not be apparent to the casual follower.   It will be interesting to see what SignalPath has en-store for us. 

Guessing your proposal would support PAM16,  so it may cover the majority of cases.   I am guessing there is going to be a pretty big hit in the sweep times.    I'll post some data once I have your new software.  I'll see about changing my hardware to support another data bit.   

SJL-Instruments:

--- Quote from: joeqsmith on February 27, 2024, 10:16:30 pm ---When I hear about 12-bit converters I  am thinking 4096 discrete levels, not 30.   I understand those 30 points are distributed around the input signal.  Its fine if we are looking at simple single level waveforms.  But the manual opens the gates when it talks about eye diagrams.   When we start looking at different modulation schemes things break down fast.   It makes sense that the vintage LeCroy with 8-bits is able to resolve the PAM8 test case with much higher fidelity.  It just may not be apparent to the casual follower.   It will be interesting to see what SignalPath has en-store for us. 

Guessing your proposal would support PAM16,  so it may cover the majority of cases.   I am guessing there is going to be a pretty big hit in the sweep times.    I'll post some data once I have your new software.  I'll see about changing my hardware to support another data bit.   

--- End quote ---
For single-level waveforms and two-level eye diagrams, the scope works well. PAM4 is usable but slow. To be honest, if we got an inquiry about PAM8 or PAM16 eye diagrams, we would recommend against buying the product. The hardware is certainly capable of it, but at some point the time taken does not make commercial sense.

The time required for a good acquisition scales roughly as the square of the number of levels in the eye. A PAM-16 eye would take 64x longer than a two-level eye. We will significantly expand Section 2.4 to clarify this in the next revision, and add more information in general about the limitations of CDF sampling. This might be a good topic to put in a video on our homepage.

We are still working on the software changes and will provide a prerelease shortly. (A surprisingly large fraction of the graphics pipeline needs to be rewritten.)


--- Quote from: joeqsmith on February 27, 2024, 01:49:59 pm ---Sure we can talk about the low cost compared with other scopes but IMO, if the tool can't do the basic job it was designed for, or causes the user to spend time trying to track down nonexistent hardware problems, that lower cost is a bit of a false selling point. 

--- End quote ---
Just to hear your honest opinion: having worked with the scope for a month, do you think the price we have set is fair? Suppose we restrict the recommended use cases to single-level signals and eye diagrams for two-level protocols, and state this clearly.

Internally, one of our goals was to bring the cost of a 5+ GHz scope down far enough for hobbyist use. Bandwidth and timing precision are the two things you can't fix by averaging down - our architecture trades these for acquisition speed. But perhaps the price is still too high for this goal.

joeqsmith:

--- Quote from: SJL-Instruments on February 28, 2024, 12:31:59 am ---Just to hear your honest opinion: having worked with the scope for a month ...

--- End quote ---

I think your comment about making the limitations clear in the manual are very important, especially when you start marketing it as 12-bits 1TSPS.  IMO that  raises expectations.  Someone may read that 30 samples per CDF and think nothing of it.  Even if they take the time to read the manual, they may not understand how it relates to a multi-level signal.  Providing examples in the manual that describe the expected sweep times,  tradeoffs of performance versus various settings, why/when to change settings from the defaults, all good things to include.   As I wrote before, I think that the software is what is going to sell it. 

I appreciate trying to sell it into the hobbyist market.  It would be interesting to know why that early kickstart failed.  Or why the sampling scopes mentioned earlier failed.   That was a much lower cost unit and they still couldn't make a go of it.  Maybe they underestimated the cost of software development and support.  It could also be that there are not many hobbyist that have a use for a scope this fast.  Or, if they are, they may need features that they can't get with a sampling scope.   I fall into that category.  I can't afford new prices and my only choice is used. 

Cost wise, for me it's more a question on if the product fits a particular need I have.   This product isn't something that you would ever consider for general purpose use.  Adding ability to measure distances for fault finding and other features that expand its use may help sell it. 

****
The CDF sampling options are not saved in the setup.   It always defaults to auto. 

SJL-Instruments:

--- Quote from: joeqsmith on February 28, 2024, 01:59:16 am ---I think your comment about making the limitations very clear in the manual are very important.   Especially when you start marketing it as 12-bits 1TSPS.  IMO that  raises expectations.  Someone may read that 30 samples per CDF and think nothing of it, even if they take the time to read the manual they may not understand how it relates to a multi-level signal.  Providing examples in the manual that describe the expected sweep times,  tradeoffs of performance versus various settings, why/when to change settings from the defaults, all good things to include.   As I wrote before, I think that the software is what is going to sell it.

--- End quote ---
Thanks for the feedback. We will add at least a few pages about this in the next revision. In addition to explaining these tradeoffs in detail, we will make it clear that we only recommend the scope for eye diagrams of two-level protocols.


--- Quote from: joeqsmith on February 28, 2024, 01:59:16 am ---I appreciate trying to sell it into the hobbyist market. It would be interesting to know why that early kickstart failed.  Or why the sampling scopes mentioned earlier failed.   That was a much lower cost unit and they still couldn't make a go of it.  Maybe they underestimated the cost of software development and support.

--- End quote ---
Our guess is the lack of software support. Early on, someone mentioned:

--- Quote from: JohnG on January 09, 2024, 02:50:58 pm ---FWIW, I have the 11 GHz scope from fastsampling.com (2 actually, but one has an problem). I find it difficult to use, mainly because of the software. I am not sure if they are still in business, as the last time I tried to contact them, I got no reply. The two channel limitation and the cumbersome software has made it difficult to use for my needs.

--- End quote ---
This is part of why we are focusing so much on the software. It should never "get in the way" of making measurements. Developing without user feedback is a good way to make the UI impossible to use.
It's important for customers to feel confident that support will continue. We have baked the software development cost into the price of the product, and suspect that the earlier attempts did not.


As promised, here is a v2.5.12 pre-release that increases the max K to 200 and the max Nmin to 500k:
https://gigawave-releases.s3.us-east-2.amazonaws.com/GigaWave_v2.5.12_PREVIEW_2024-02-27_Windows.zip
Note that setting K above 100, or Nmin above 30k, will fallback to using the direct CDF read (@) command due to v13 firmware limitations. This mode incurs a lot of overhead (80% of the time is spent on communications...), and will be resolved in v14 firmware.
We've attached an example of a PAM4 signal @ Nmin = 60k, K = 200. This is of course impractically slow. But it illustrates the ultimate limits of the hardware when catching rare transitions.

***

--- Quote from: joeqsmith on February 28, 2024, 01:59:16 am ---The CDF sampling options are not saved in the setup.   It always defaults to auto. 

--- End quote ---
Thanks for catching this - will be fixed in v2.5.12.

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