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Pocket-Sized 6 GHz 1 TS/s ET Scope

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joeqsmith:
A short article attempting to compare random and sequential sampling:

https://www.apexwaves.com/blog/random-sampling-vs-sequential-sampling/

There is really no meat on the bone.  The summarize with: 
--- Quote ---Nevertheless, the advantages of this method in practice outweigh the advantage of the random-sampling method.
--- End quote ---
, but it you take the time to read the page and a half, they never explain what these advantages are.   They do however explain the short comings.     

This 20+ year old article talks about sequential sampling and where it fits in.   
--- Quote ---This capability makes such scopes the instruments of choice in applications of rapidly growing importance-electro-optics, for example.
--- End quote ---
Of course, they are talking about 50GHz BW, not 6 like the product we are discussing. 
https://www.edn.com/50-ghz-bandwidth-sequential-sampling-dsos-test-10-gbps-network-components/

Outside the scope of this thread, but while searching for articles, I found this set of slides that mentions Teledyne LeCroy's Digital Bandwidth Interleave (DBI).  I made a video that went over this technique based on their patents.   In order to demonstrate how it works, I wrote a simulator for it (starts about 6min in). 

https://keysightevent.com/191023/handout/pdf/c/3.%20Digital%201_High-Speed%20Oscilloscope%20Fundamentals.pdf


nctnico:
I still don't see why this oscilloscope can only show the part of the signal after the trigger. The 'good old' Tektronix TDS500 series use sequential sampling as well and have no problem showing the signal before and after the trigger point. It seems Tektronix' acquisition system is free-running and timestamping the sample where the trigger occured. After that they phase-shift the sampling clock and take another acquisition.

SJL-Instruments:

--- Quote ---The 'good old' Tektronix TDS500 series use sequential sampling as well and have no problem showing the signal before and after the trigger point. It seems Tektronix' acquisition system is free-running and timestamping the sample where the trigger occured. After that they phase-shift the sampling clock and take another acquisition
--- End quote ---
We consider "sequential sampling" to refer to any technique where the sampling action is caused by the trigger.
Taking timestamped samples (independent of trigger) and later reconciling with trigger events would fall under random sampling. (See https://w140.com/tekwiki/wiki/Sampling_oscilloscope)
(Phase-shifting a periodic clock as you described is an interesting technique, in some respects a "subsampled version" of RIS.)
Some (very) early Tektronix sequential sampling scopes actually contained an analog delay line - tweaking the compensation network for these was an art.
https://groups.io/g/TekScopes/topic/tektronix_delay_line/7629123



--- Quote ---but it you take the time to read the page and a half, they never explain what these advantages are.   They do however explain the short comings.
--- End quote ---
We tend to agree. In most cases, random sampling provides more flexibility with your trigger setup - but  6 GHz random sampling scope will be 4x the price. Our hope is to provide a lower-cost alternative without compromising on bandwidth. The pretrigger requirement is really the only limitation w.r.t. random sampling (albeit a significant one).

On another note, we have released v2.5.4 of the software containing the promised features for this update. (Except for light mode - next update.)
https://www.sjl-instruments.com/software/

Coax de-embedding is working fairly well (see attached). If you're interested, the math is in "Transient Analysis of Coaxial Cables considering Skin Effect" by Wignington & Nahman.

The UI will just require you to enter cable length and type.
If the type you want isn't available, you can also enter the attenuation data at a few frequencies.
The results still need to be validated further, so it'll be rolled out next update [likely end of next week].

joeqsmith:

--- Quote from: SJL-Instruments on January 13, 2024, 12:11:47 am ---Coax de-embedding is working fairly well (see attached). If you're interested, the math is in "Transient Analysis of Coaxial Cables considering Skin Effect" by Wignington & Nahman.

The UI will just require you to enter cable length and type.
If the type you want isn't available, you can also enter the attenuation data at a few frequencies.
The results still need to be validated further, so it'll be rolled out next update [likely end of next week].

--- End quote ---

Thanks for the fast turn around on this. 

Does your software also account for the splitter or does it assume it is perfect?   Assuming a 6dB resistive splitter, any advantage to using an attenuator at the scope's trigger input to prevent reflections from perturbing the measurement signal?   If a person did have access to a VNA to fully characterize their setup, any plans to support s-parameters as well?   

SJL-Instruments:
Compensation for the splitter will come out at the same time as s-parameter import (probably not next update, but the one after implemented 2024-01-21). Coax distortion is dominated by skin effect, and so is quite well characterized by conductor material and geometry (i.e. cable type). Not so with splitters - the imperfections "are what they are," and just need to be measured.


--- Quote ---Assuming a 6dB resistive splitter, any advantage to using an attenuator at the scope's trigger input to prevent reflections from perturbing the measurement signal?
--- End quote ---
Yep, adding a (well-matched) attenuator will reduce reflections, if you can afford the loss in SNR.
This is more important on the delayed signal input (since the coax to the trigger input should be pretty short).

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