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A High-Performance Open Source Oscilloscope: development log & future ideas

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nctnico:

--- Quote from: tom66 on November 18, 2020, 06:59:34 pm ---Interesting idea - but it would throw out the window any option for battery operation if that heatsink size is any indication of the power dissipation.

Whether that would be a killer for people I don't know?  I think it's a nice to have especially if the device itself is otherwise portable.

--- End quote ---
Well, it would simply need a bigger battery. Laptops aren't low power either. To me portability is lowest on the list though. Personally I'd prefer a large screen.

With ultra-low power you'll also be throwing out the possibility of creating a scope with >500MHz bandwidth for example. The ADC on your prototype has a full power bandwidth of 700MHz. Use two in tandem and you can get to 2Gs/s in a single channel in order to meet Nyquist. However supporting 500MHz will probably require several chips which will get warm.

The Jetson Nano seems to need about 10W of power while running at full capacity. There is also a (I think) pin compatible Jetson Xavier NX module with vastly better specs but this also needs more power. The use of these modules would create a lot of flexibility to trade performance for money.

tom66:
It's certainly an option, but the current Zynq solution is scalable to about 2.5GSa/s for a single channel operation (625MSa/s on 4ch).  Maximum bandwidth around 300MHz per channel.

If you want 500MHz 4ch scope, the ADC requirements would be ~2.5GSa/s per channel pair (drop to 1.25GSa/s with a channel pair activated) which implies about 5GB/s data rate into RAM.  The 64-bit AXI Slave HPn bus in the Zynq clocked at 200MHz maxes out around 1.6GB/s and four channels gets you up to 6.4GB/s but that would completely saturate the AXI buses leaving no free slots for RAM accesses for readback from the RAM or for executing code/data.

The fastest RAM configuration supported would be a dual channel DDR3 configuration at 800MHz requiring the fastest speed grade, which would get the total memory bandwidth to just under 6GB/s.

Bottom line is the platform caps out around 2.5GSa/s in total with the present Zynq 7000 architecture,   and would need to move towards an UltraScale or a dedicated FPGA capture engine for faster capture rate.

So I suppose the question is -- if you were to buy an open-source oscilloscope -- what would you prefer

1. US$1200 instrument with 2.5GSa/s per channel pair (4 channels, min. 1.25GSa/s), ~500MHz bandwidth, Nvidia core, >100kwfm/s, mains only power
2. US$600 instrument with 1GSa/s multiplexed over 4 channels, ~125MHz bandwidth, RasPi core, >25kwfm/s, portable/battery powered
3. Neither/something else

tautech:

--- Quote from: tom66 on November 18, 2020, 10:50:09 pm ---
So I suppose the question is -- if you were to buy an open-source oscilloscope -- what would you prefer

1. US$1200 instrument with 2.5GSa/s per channel pair (4 channels, min. 1.25GSa/s), ~500MHz bandwidth, Nvidia core, >100kwfm/s, mains only power
2. US$600 instrument with 1GSa/s multiplexed over 4 channels, ~125MHz bandwidth, RasPi core, >25kwfm/s, portable/battery powered
3. Neither/something else

--- End quote ---
FYI Very close to the specs of a hacked SDS2104X Plus for $1400

tom66:
I suspect an instrument like this can't ever compete with a mainstream OEM on bang-per-buck - it has to compete on the uniqueness of being a FOSS product.

That is, you can customise it, you have modularity, you have upgrade routes and flexibility.  But it will always be more expensive in low volumes to produce something like this, that's just an ultimate fact of life.

tautech:

--- Quote from: tom66 on November 18, 2020, 10:56:32 pm ---I suspect an instrument like this can't ever compete with a mainstream OEM on bang-per-buck - it has to compete on the uniqueness of being a FOSS product.

That is, you can customise it, you have modularity, you have upgrade routes and flexibility.  But it will always be more expensive in low volumes to produce something like this, that's just an ultimate fact of life.

--- End quote ---
Or find a performance/features niche that's not currently being catered for.

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