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Most affordable oscilloscope capable of color graded eye diagram?

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Fungus:
My Micsig can do it for about $600:

2N3055:
That is not a proper eye diagram.
https://www.eevblog.com/forum/testgear/most-affordable-oscilloscope-capable-of-color-graded-eye-diagram/msg3498324/#msg3498324

Eye diagram has capture of each pulse that contributes to diagram, centered around center of pulse period.
So you can see both left and the  right side jitter.

Without software to perform analysis and extracting data from data-stream you cannot do it  right.

What you show will align all left sides to perfect timing with trigger, so you cannot see if that edge came late or early, you see all variations  as basicaly PWM, eg. as a variation of eye width, and only right side variable. While that is not useless (if it looks  perfect than you're probably good as far jitter and amplitude variation) it is not showing real eye opening as it should.

Berni:
Yep eye pattern with clock recovery is a whole different can of worms compared to just rainbow intensity gradation.

Triggering is indeed not used for clock recovery. Instead the scope tends to capture a long capture and then perform clock recovery on the whole thing in software. This actually requires a fair bit of processing power to do and some of the algorithms that do this can be pretty complicated. Then once clock is recovered the long waveform is chopped up into sections according to the clock and overlayed over each other to produce the image.

But what would you use an eye diagram for? Typically it is to verify the signal integrity of high speed links, be it USB3.0 over a cable or signals between a CPU and RAM. These are things that run at very high speeds and as a result not only need a very high end scope but also the appropriate low capacitance active probes that cost as much as a couple of those Siglent scopes put together. So your typical 100MHz entry level scope only really has the bandwidth to produce a usable eye diagram for data rates up to about 20Mbit at best. At these low speeds you rarely even need a eye diagram. Its easy enough to produce cables and board interconnects that support these speeds with so much headroom that the signal looks like a nice pretty square wave. So as a result it is easy to tell the signal is good just by looking at it. While at 5Gbit cables become very imperfect so these high speed serial protocols ride on the edge of still working so signals always look pretty rounded and wavey, this is where an eye diagram helps to quantitatively measure how good the signal integrity is.

Even tho i have a scope capable of generating real eye diagrams i very rarely make use of it. When im dealing with more lowish speed signals in the 10s of MHz i will just go for the "poor mans eye diagram". This is where you simply put your trigger in the middle and set the trigger on both edges. Modern scopes are very fast to capture a lot of edges, while you can crank up the waveform intensity to be able to see any lone single runt pulses going trough the middle of the eye. With nice clean sharp fast rise time signals the "clock recovery" by using a edge trigger is close enough.

nctnico:

--- Quote from: 2N3055 on March 08, 2021, 11:50:40 am ---That is not a proper eye diagram.
What you show will align all left sides to perfect timing with trigger, so you cannot see if that edge came late or early, you see all variations  as basicaly PWM, eg. as a variation of eye width, and only right side variable. While that is not useless (if it looks  perfect than you're probably good as far jitter and amplitude variation) it is not showing real eye opening as it should.

--- End quote ---
An easy solution to that is to move the trigger point off screen as far as possible. But this requires a scope with a stable enough clock source so the jitter from  oscilloscope itself is significantly smaller compared to that of the signal. In the end any clock recovery algorithm will choose a point somewhere in the signal as t=0 and goes from there (and the clock source from the oscilliscope will still be a factor).

MarcosL:
If you are probing a CAN bus you can use the PHY TX line to trigger off. According to this post:
--- Quote from: Leo Bodnar on October 25, 2021, 05:38:56 pm ---If you have access to one of the devices, trigger on the signal going into CANbus phy (TX line)
Leo

--- End quote ---

I would also like to find an affordable way to produce eye diagrams to test physical networks. I was hoping there was a device similar to NanoVNA (@joeqsmith) that could just be designed for doing eye diagrams. This would be great to probe CAN bus and RS485 if you have a wiring setup that is acting up. Does anyone know if that would be even possible with a VNA? Also is there a PC software that could do it for a cheap USB oscilloscope?

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