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How much noise floor and other things matter in oscilloscope usability
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Fiorenzo:
As asked some photos with the avarage mode

4x average

In my opinion the avarage, even if It conserve almost the shape of the signal, destroys "the low intensity" informations
Fungus:

--- Quote from: Fiorenzo on December 29, 2021, 08:11:57 am ---The spikes you can clearly see in the Siglent i think are switching noise  coming from the next stage of this psu. I am going to do some test about It to check if the front end noise of the Rigol is covering such interference

--- End quote ---

Thanks for the photos! This is all very useful information.

The one remaining test is to see the effect of turning up the display intensity on the Rigol to see if it reveals those spikes better (without averaging).
2N3055:
I 'm reading some of these posts and  :-//

It is obvious MSO5000 has much more noise, and that it is a problem, unless you only look at digital signals and just want to look at general shape and some timing information.
It is shame, really, because new Rigol scopes are much more powerful processing wise than the old ones, and generally held great promise but analog front end/ADC noise performance is not very good.

Scope with low noise is always going to be better instrument than the one with high noise. Why is that even a discussion?
Is this some audiofool discussion how this huge noise is pleasant to look at because it's pretty?  |O

I don't use bandwidth limiting, averaging or any "signal cleanup" features when I'm looking into a signal I want to understand. You would want to look at this switcher signal with a full 1GHz bandwidth and with as low noise scope you can.
To really see what is there... Switching ripple is most of the time least interesting part of switching PSU. We expect it to be there, and most of the time it will be roughly what we calculated. Other, higher frequency stuff (those little hairs on top) is much more problematic and most of the time those will give you headaches.. Nanovolts of those will already be seen on any EMI test...

You filter, limit and "cleanup" signal in circumstances where you understand your signal and you want to ignore noise and other parts of signal on purpose. If your signal is buried inside the noise, you average.
But is that noise part of signal you're measuring or your scope is not irrelevant. If it comes from DUT I want to know that. I want to see it..
Only way to do that is to have low noise scope.

Of course, like OP correctly asked, there is a point of diminishing returns..
Is scope with 5 uV of RMS noise so much better than one with 50uV RMS noise for measuring this switcher signal from this example? Probably not.
It would be definitely better but probably not usefully so in this case. But one with 50uV of RMS noise is definitely better than one which has trace that is whooping 20 mV wide... On a signal that is 60mV P-P...
On this test I would call MSO5000 from Rigol useless for this measurement. And averaging this not autocorrelated signal ( it doesn't repeat cleanly and doesn't retrace it's waveform exactly but varies slightly all the time) will not extract more detail but will hide even more information about signal..

OTOH Siglent shows pretty much perfect representation of the signal, big peaks, ripple AND little hairs. That is your switcher output. That is useful information..

Little Micsig STO1104C/E, or Siglent SDS1104X-E could do equally good job here.

Sad part is that little Rigol DS1054Z would be much better for this signal than MSO5000.. DS2000A had excellent low noise front end .. But new series of Rigol scopes is very powerful in processing power but analog performance is worse than older series. Shame really, otherwise they are very nice scopes.



 
Fiorenzo:

--- Quote from: Fungus on December 29, 2021, 10:22:10 am ---
--- Quote from: Fiorenzo on December 29, 2021, 08:11:57 am ---The spikes you can clearly see in the Siglent i think are switching noise  coming from the next stage of this psu. I am going to do some test about It to check if the front end noise of the Rigol is covering such interference

--- End quote ---

Thanks for the photos! This is all very useful information.

The one remaining test is to see the effect of turning up the display intensity on the Rigol to see if it reveals those spikes better (without averaging).

--- End quote ---

Sorry fungus i have been very busy. I have more photos. Check in the next messages
Fiorenzo:
16x average
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