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Pocket-Sized 6 GHz 1 TS/s ET Scope

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SJL-Instruments:

--- Quote from: joeqsmith on February 01, 2024, 04:26:33 pm ---Could you provide details on what all the self test entails?   

--- End quote ---
The self-test verifies FPGA communication, checks the minimum and maximum range of the delay generator, checks the delay generator calibration is valid, checks that all channels are returning data (verify the CDF is >0.7 at 1V and <0.3 at -1V), and verifies that the internal trigger source is working.
The self-test does not verify any of the external trigger settings.


--- Quote from: joeqsmith on February 01, 2024, 04:26:33 pm ---Thinking about my comment about it not being so much related to time but rather it being the positive apex of the signal, look at the last set of plots.  Note that the highest noise for all 4 channels is in that region.  Oddly we don't see that with the negative apex.  If you think the signal's shape is exacerbating the problem with this particular hardware, should we test it with say a squarewave?  Higher frequency?   

Basically, I am looking for your thought on proving out the hardware after rework.

--- End quote ---
To be honest, we're not sure, as we can't reproduce the noise spikes you're seeing with our test units. Higher frequency will increase sensitivity to timing jitter (but as CH1 is fine, that's likely not the problem). Given that a 1 GHz sine wave is known to reveal the issue on your unit (at least sometimes), we'd recommend staying with this signal to keep things consistent. But if you find a signal that reliably causes increased noise, we'll see if we can reproduce your results.

joeqsmith:
Thanks for the added details on the self test.    Attached showing the raw data from #210. 

***
Spent a few hours today inspecting every joint (except the BGA) and reworking anything questionable (major).  Also cleaned it to remove all the loose balls and residue.   

It appears to have had some effect as the channels are not matched near as well.  Do you align the scopes for gain, offset, other...  Store in NVRAM?  Can this be performed outside of factory?  What tools are required? 

Of course, the big question is if it had any effect on the noise.  This is going to take some time to answer. 

SJL-Instruments:

--- Quote from: joeqsmith on February 01, 2024, 05:20:36 pm ---It appears to have had some effect as the channels are not matched near as well.  Do you align the scopes for gain, offset, other...  Store in NVRAM?  Can this be performed outside of factory?  What tools are required? 

--- End quote ---
We do not individually calibrate every channel - all the analog components are tightly toleranced to obtain good matching.
In what way are the channels no longer matched? (DC offset, THD, overall gain, etc.)

joeqsmith:

--- Quote from: SJL-Instruments on February 02, 2024, 01:51:57 pm ---
--- Quote from: joeqsmith on February 01, 2024, 05:20:36 pm ---It appears to have had some effect as the channels are not matched near as well.  Do you align the scopes for gain, offset, other...  Store in NVRAM?  Can this be performed outside of factory?  What tools are required? 

--- End quote ---
We do not individually calibrate every channel - all the analog components are tightly toleranced to obtain good matching.
In what way are the channels no longer matched? (DC offset, THD, overall gain, etc.)

--- End quote ---

Looking at post 197 showing all 4 channels prior to rework.  You can see, they were never really matched well.  After rework, they have spread apart even further.   I would need to run some tests to determine how much is due to gain vs offset but it sounds like it currently isn't  possible to correct for them anyway.  Are there plans to add some sort of alignment procedure to your software that could be saved?

https://www.eevblog.com/forum/testgear/pocket-sized-6-ghz-1-tss-et-scope/msg5306536/#msg5306536

The manual has a max offset with inputs shorted and a tolerance for the input impedance at 1GHz and we also now know your return loss is in the 17dBish range.   

Maybe it's not an issue for most users.  I wouldn't normally make measurements with the inputs shorted to ground or with a 1GHz signal.  It would be difficult for me to know how mismatched the channels really are when looking at them with your software.  I would wonder, how much is the scope contributing to the error compared with my signals.  Maybe there is a way to clarify this.

When you specify the maximum DC RMS (section 1.5), are you running internal trigger with all inputs shorted?   

****
In general, it appears that the gain has increased.  However, I suspect there may be more to it.  The attached data is for channel 2 only.  Yellow trace was from post 197 during the start of the collection.   The orange trace was taken the day after with the same settings.  Notice how the gain has increased.   Violet was taken after the scope had ran for about 3 hours after my rework.   

joeqsmith:
Again, looking at channel 2.  Showing the first set of data after I reworked the board.  We are looking at sweeps on the X-axis, hourish of time.  This is subtracting the mean from the signal as previously described.  Note how the noise level decreases as it warms up.

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