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| How much noise floor and other things matter in oscilloscope usability |
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| 2N3055:
--- Quote from: Fungus on December 29, 2021, 11:40:23 am --- --- Quote from: Fiorenzo on December 29, 2021, 10:36:03 am ---But It has also a lot more noise.... I have an idea to show you how much the signal degrade due to this problem. --- End quote --- All 'scopes degrade the signal, none are perfect. The real problem with this Rigol vs. Siglent comparison is that you're comparing two devices side by side where one of them happens to work better at 1mV then the other one does. ie. When you turn the Siglent's vertical control to "max" then it makes the Rigol look bad at that level. If you were comparing 1V signals or 5V signals in your screenshots then you wouldn't see the same difference between them. Guess what? Electronics doesn't magically stop at the exact place where the Siglent's vertical control does. There's plenty of signals below 1mV. You'll need an amplifier to see them and the exact same same amplifier would work with a Rigol, too. Plus: You originally said you do digital stuff, so... :-// --- End quote --- Your thinking: Siglent that has 5-10X times better noise and performance and sensitivity but cannot measure properly something at 200uV levels, Rigol MSO5000 cannot measure something properly even at 10mV That makes them equal. Because they both have something they cannot measure. By the analogy: You are same as a gorilla. You both have eyes.. Let's ignore other, irrelevant, details.. Get a grip.. |
| 2N3055:
--- Quote from: Fungus on December 29, 2021, 11:51:05 am --- --- Quote from: 2N3055 on December 29, 2021, 11:46:37 am ---Also you keep repeating about some magical amplifiers. Amplifiers that have DC-100 Mhz bandwith and less noise as even a little Micsig or Siglent SDS1104X-E cost as much as a good scope from Keysight. --- End quote --- Yes, but amplifiers from DC to 1MHz are incredibly cheap (ie. a $2 OP-amp) and would be perfectly adequate for power supplies and audio work. Amplifiers from 1MHz to 2GHz are also incredibly cheap. --- End quote --- Switching power supplies are measured by convention in DC-20MHz range. And that was for old switchers switching at up to some 100ths of kilohertz. Today switchers are in MHz range, and you better be looking at them up to 300-400 MHz range because of EMI problems... Also those RF amplifiers are not replacement for a proper scope front end. |
| Fiorenzo:
--- Quote from: 2N3055 on December 29, 2021, 10:22:45 am ---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. --- End quote --- Thank you for the great explenations, I also agree with you |
| Vestom:
The lower sampling frequency of the SDS2000X+ is much less of a problem than it sounds due to the excellent ETS-like trigger implementation. There are plenty of examples showing the Leo Bodnar pulse with very good fidelity on the SDS2k+. However frame-by-frame averaging is really a kludge one should be careful about using, since it hides transients, glitches etc. Also with modern low-amplitude digital signals measured using x10 probe, low noise performance has become more important for digital signals than you might think... Of course you can add external amplifiers - but why not buy a proper scope instead? |
| Fiorenzo:
--- Quote from: Fungus on December 29, 2021, 11:48:21 am --- --- Quote from: tautech on December 29, 2021, 11:40:55 am ---With channels 1 and 3 of each scope activated a very different picture may emerge at some timebase settings. --- End quote --- Yes, because if you enable to adjacent channels the Siglent only has 1GS/sec to look at 350Mhz signals, ie. it's getting uncomfortably close to Nyquist. Turning a channel off can bump the sample rate to 2GS/sec and give a different picture. --- End quote --- No. Actually i did many experiment about It. If you set the Rigol so it has a lower sampling speed the noise doesn't become lower. I checked It in many ways. For example if you turn on all the channels together the noise stay the same. If you lower the memory buffer the sampling rate becomes lower but the noise stay again similar until you force It to work with a very very little Memory like 20k or so. I have tried all i could think to get a better sampling from the Rigol and It was not possible. In regard of me now I am doing digital stuff but i am going to work a lot with analoge signals and circuits so i preferred to switch to the Siglent. As i said i think the Rigol is a very great scope but noisy |
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